3,026 results on '"FERROELECTRIC RAM"'
Search Results
2. Facile fabrication of highly ordered poly(vinylidene fluoride-trifluoroethylene) nanodot arrays for organic ferroelectric memory.
- Author
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Huajing Fang, Qingfeng Yan, Chong Geng, Ngai Yui Chan, Kit Au, Jianjun Yao, Sheung Mei Ng, Chi Wah Leung, Qiang Li, Dong Guo, Helen Lai Wa Chan, and Jiyan Dai
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POLYVINYLIDENE fluoride , *FABRICATION (Manufacturing) , *FERROELECTRIC RAM , *POLARIZATION (Electricity) , *POLYDIMETHYLSILOXANE - Abstract
Nano-patterned ferroelectric materials have attracted significant attention as the presence of two or more thermodynamically equivalent switchable polarization states can be employed in many applications such as non-volatile memory. In this work, a simple and effective approach for fabrication of highly ordered poly(vinylidene fluoride–trifluoroethylene) P(VDF-TrFE) nanodot arrays is demonstrated. By using a soft polydimethylsiloxane mold, we successfully transferred the 2D array pattern from the initial monolayer of colloidal polystyrene nanospheres to the imprinted P(VDF-TrFE) films via nanoimprinting. The existence of a preferred orientation of the copolymer chain after nanoimprinting was confirmed by Fourier transform infrared spectra. Local polarization switching behavior was measured by piezoresponse force microscopy, and each nanodot showed well-formed hysteresis curve and butterfly loop with a coercive field of ~62.5 MV/m. To illustrate the potential application of these ordered P(VDF-TrFE) nanodot arrays, the writing and reading process as non-volatile memory was demonstrated at a relatively low voltage. As such, our results offer a facile and promising route to produce arrays of ferroelectric polymer nanodots with improved piezoelectric functionality. [ABSTRACT FROM AUTHOR]
- Published
- 2016
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3. REDUCING THE ENERGY CONSUMPTION OF SYSTEMS WITH THE INTEGRATED CIRCUIT TI 430FR2433.
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ROTAR, DAN and ANDRIOAIA, DRAGOS-ALEXANDRU
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INTEGRATED circuits ,ENERGY consumption ,POWER resources ,ENVIRONMENTAL quality ,BUILDING performance ,MICROCONTROLLERS ,CARBON dioxide detectors - Abstract
The Texas Instruments microcontrollers in the MSP 430 series offer four ways to save power in operation in such a way as to allow for consistent reduction of the electricity consumed. Code Composer Studio programming environment also provides support in making low-power applications. In addition to these, the MSP430FR2433 microcontroller with ferroelectric RAM allows data to be stored even in the absence of power voltage. In view of these properties of the microcontroller, a data logger application has been developed to monitor the quality of the environment in a building. Given that the MSP430FR2433 microcontroller can process both analog and numerical signals, the device monitors the temperature, humidity, carbon dioxide concentration and amount of light present in the enclosure. Thanks to energy-saving mechanisms and the possibility of keeping information for an indefinite period without the need for energy consumption, the ambient quality monitoring device can operate for a long time in places without energy resources. The device has also been tested with good results for autonomous operation using solar energy and has also been used to determine the energy performance of buildings. [ABSTRACT FROM AUTHOR]
- Published
- 2021
4. Modification of energy band alignment and electric properties of Pt/Ba0.6Sr0.4TiO3/Pt thin-film ferroelectric varactors by Ag impurities at interfaces.
- Author
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Hirsch, S., Komissinskiy, P., Flege, S., Li, S., Rachut, K., Klein, A., and Alff, L.
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ENERGY bands , *SILVER , *THIN films , *FERROELECTRIC RAM , *CURRENT density (Electromagnetism) , *VARACTORS - Abstract
We report on the effects of Ag impurities at interfaces of parallel-plate Pt/Ba0.6Sr0.4TiO3/Pt thin film ferroelectric varactors. Ag impurities occur at the interfaces due to diffusion of Ag from colloidal silver paint used to attach the varactor samples with their back side to the plate heated at 600-750 °C during deposition of Ba0.6Sr0.4TiO3. X-ray photoelectron spectroscopy and secondary ion mass spectrometry suggest that amount and distribution of Ag adsorbed at the interfaces depend strongly on the adsorbent surface layer. In particular, Ag preferentially accumulates on top of the Pt bottom electrode. The presence of Ag significantly reduces the barrier height between Pt and Ba0.6Sr0.4TiO3/ leading to an increased leakage current density and, thus, to a severe degradation of the varactor performance. [ABSTRACT FROM AUTHOR]
- Published
- 2014
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5. Rate limiting step for the switching kinetics in Cu doped Ge0.3Se0.7 based memory devices with symmetrical and asymmetrical electrodes.
- Author
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Soni, R., Meuffels, P., Petraru, A., Vavra, O., and Kohlstedt, H.
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ELECTRODES , *COPPER , *FERROELECTRIC RAM , *ELECTRICAL conductors , *NANOPARTICLES - Abstract
We report on the comparison of the resistance switching properties and kinetic behavior of Cu doped Ge0.3Se0.7 solid electrolyte based dual layer memory devices integrated with asymmetrical (Pt and Cu) and symmetrical electrodes (only Cu). In spite of the fact that the observed resistance switching properties and its parameters are quite similar for both memory devices, the dependence of the SET-voltage on the voltage sweep rate suggests different microscopic rate limiting factors for the resistance switching behavior. Additionally, in order to alleviate the cross talk problem in passive crossbar arrays, a dual layer oxide stack (TiO2/Al2O3) is integrated with Ge0.3Se0.7 based dual layer memory devices to achieve a specific degree of non-linearity in the overall resistance of the low resistance state. [ABSTRACT FROM AUTHOR]
- Published
- 2013
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6. Resistive switching mechanisms relating to oxygen vacancies migration in both interfaces in Ti/HfOx/Pt memory devices.
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Lin, Y. S., Zeng, F., Tang, S. G., Liu, H. Y., Chen, C., Gao, S., Wang, Y. G., and Pan, F.
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FERROELECTRIC RAM , *X-ray photoelectron spectroscopy , *TRANSMISSION electron microscopy , *VALENCE (Chemistry) , *ELECTRIC resistance , *INTERFACES (Physical sciences) - Abstract
Resistive switching mechanism of Ti/HfOx/Pt memory devices was studied using X-ray photoelectron spectroscopy and cross-sectional transmission electron microscopy images. Spatial distributions of valence of Hf demonstrated that the fraction of Hf4+ increased from Ti/HfOx interface to HfOx/Pt interface in high resistance state (HRS), but it maintained a constant level in low resistance state (LRS). Rupture of oxygen vacancies formed conducting paths occurred near the HfOx/Pt interface. The cross sectional images of active switching region also varied with HRS and LRS. A dynamic model of interface processes was proposed to interpret interfaces migration of oxygen vacancies near both the top and bottom electrodes. [ABSTRACT FROM AUTHOR]
- Published
- 2013
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7. Optimization of resistive switching performance of metal-manganite oxide interfaces by a multipulse protocol.
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Ghenzi, N., Sánchez, M. J., Rozenberg, M. J., Stoliar, P., Marlasca, F. G., Rubi, D., and Levy, P.
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FERROELECTRIC RAM , *POLARITY (Physics) , *FERROELECTRIC crystals , *FERROELECTRIC devices , *OPTICAL polarization - Abstract
We explore different resistance states of La0.325Pr0.300Ca0.375MnO3-Ti interfaces as prototypes of non-volatile memory devices at room temperature. In addition to high and low resistance states accessible through bipolar pulsing with one pulse, higher resistance states can be obtained by repeatedly pulsing with a single polarity. The accumulative action of successive pulsing drives the resistance towards saturation, the time constant being a strong function of the pulsing amplitude. The experiments reveal that the pulsing amplitude and the number of applied pulses necessary to reach a target high resistance value appear to be in an exponential relationship, with a rate that results independent of the resistance value. Model simulations confirm these results and provide the oxygen vacancy profiles associated to the high resistance states obtained in the experiments. [ABSTRACT FROM AUTHOR]
- Published
- 2012
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8. Impact of TaOx nanolayer at the GeSex/W interface on resistive switching memory performance and investigation of Cu nanofilament.
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Rahaman, S. Z., Maikap, S., Chen, W. S., Lee, H. Y., Chen, F. T., Tien, T. C., and Tsai, M. J.
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NANOSTRUCTURED materials , *FERROELECTRIC RAM , *TRANSMISSION electron microscopy , *ELECTRONICS , *PHYSICS - Abstract
The impact of a TaOx nanolayer at the GeSex/W interface on the performance of resistive switching memory in an Al/Cu/GeSex/TaOx/W structure has been examined. All materials and the memory structure have been investigated using high-resolution transmission electron microscopy, energy dispersive x ray spectroscopy, and x ray photo-electron spectroscopy analyses. A conically shaped crystalline Cu (111) nanofilament with a diameter of around 17 nm in the TaOx nanolayer after a current compliance (CC) of 500 μA has been observed, and this has been also characterized by fast Fourier transform. The low resistance state (LRS) decreases as the current compliances (CCs) increased from 1 nA to 1 mA, since the nanofilament diameter increased from 0.04 to 23.4 nm. This is also estimated by bipolar resistive switching characteristics. The resistivity of this crystalline Cu nanofilament is approximately 2300 μΩ.cm. The nanofilament has a cylindrical shape, with CCs ranging from 1 nA to 10 μA and a conical shape with CCs ranging from 50 μA-1 mA. The resistive switching mechanism has been explained successfully under SET and RESET operations. Improved resistive switching parameters, such as SET voltage, LRS, and high resistance state with consecutive switching cycles are obtained and compared to those of pure GeSex and TaOx materials. Extrapolated, long program/erase endurance of > 106 cycles, attributed to the Al/Cu/GeSex/TaOx/W structure design, is observed. This resistive switching memory structure shows extrapolated 10 years data retention with a resistance ratio of > 10 at a low CC of 0.1 μA at 50 °C. A large memory size of ∼ 6 Pbit/sq. in. is obtained, considering the nanofilament diameter at a low CC of 0.1 μA. This study is important not only for improving the performance of low-power resistive switching memory, but also helpful for designing other nonvolatile memory devices. [ABSTRACT FROM AUTHOR]
- Published
- 2012
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9. Effect of ferroelectric parameters on ferroelectric diodes.
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Ge, Chen, Jin, Kui-juan, Wang, Can, Lu, Hui-bin, Wang, Cong, and Yang, Guo-zhen
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FERROELECTRICITY , *DENSITY , *FERROELECTRIC RAM , *THIN films , *ELECTRIC fields - Abstract
We investigate the effect of various ferroelectric parameters, such as the doping density, the permittivity, and the thickness, on ferroelectric diodes based on the proposed self-consistent numerical model. Our calculations clarify the dependence of the band diagrams, the charge density distributions, and the I-V curves on these important ferroelectric parameters in metal/ferroelectrics/metal structures. The calculated results reveal that the ON/OFF ratio of the ferroelectric diodes decreases with the increase of the doping density, the permittivity, and the thickness in the ferroelectric film, respectively. [ABSTRACT FROM AUTHOR]
- Published
- 2012
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10. Visualization of the conductive channel in a planar resistance switching device based on electrochromic materials.
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Shang, Da Shan, Shi, Lei, Sun, Ji-Rong, and Shen, Bao-Gen
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TUNGSTEN oxides , *OPTICAL images , *ELECTRIC fields , *ELECTRONIC equipment , *FERROELECTRIC RAM - Abstract
In this work, bipolar resistance switching behavior was realized in an Au/tungsten oxide/Au planar device, and the evolution of the conductive channel during resistance switching was successfully visualized by the in situ optical image technique based on the color-conductivity dependence of tungsten oxide. We found that there are two types of conductive channel, named parabolic channel and bar-like channel, exist in the planar device. The parabolic channel formed firstly near the cathode and then extended to but could not touch the anode. By applying opposite electric-field, the bar-like channel formed from the cathode (i.e., foregoing anode) and extended to the parabolic channel. With alternating the external electric-field polarity, the bar-like channel showed an indirect connection and nonmonotonic disconnection with the parabolic channel at the region near the foregoing anode, corresponding to the high-to-low and low-to-high resistance switching processes of the planar device, respectively. The instable RS behavior was caused by the change of bar-like channel occurring position under the high external field condition. The conductive channel formation was ascribed to the sodium ion immersion from the soda-lime glass substrate into the tungsten oxide film and then migration driven by the electric field to form sodium tungsten bronze. These results will give some insight into the resistance switching property improvement and mechanism elucidation as well as a possibility to develop electric/optical-coupled switch and data storage devices. [ABSTRACT FROM AUTHOR]
- Published
- 2012
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11. Nanosecond in situ transmission electron microscope studies of the reversible Ge2Sb2Te5 crystalline ⇔ amorphous phase transformation.
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Santala, M. K., Reed, B. W., Topuria, T., Raoux, S., Meister, S., Cui, Y., LaGrange, T., Campbell, G. H., and Browning, N. D.
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TRANSMISSION electron microscopy , *PHASE transitions , *CHALCOGENIDES , *FERROELECTRIC RAM , *AMORPHOUS substances , *CRYSTALLIZATION , *ATOMIC structure , *FINITE element method - Abstract
Chalcogenide-based phase-change materials have wide use in optical recording media and are growing in importance for use in non-volatile electronic memory. For both applications, rapid switching between the amorphous and crystalline phases is necessary, and understanding the changes during rapidly driven phase transitions is of scientific and technological significance. Laser-induced crystallization and amorphization occur rapidly and changes in atomic structure, microstructure, and temperature are difficult to observe experimentally and determine computationally. We have used nanosecond-scale time-resolved diffraction with intense electron pulses to study Ge2Sb2Te5 during laser crystallization. Using a unique and unconventional specimen geometry, cycling between the amorphous and crystalline phases was achieved, enabling in situ transmission electron microscope (TEM) study of both microstructural and crystallographic changes caused by repeated switching. Finite element analysis was used to simulate interactions of the laser with the nano-structured specimens and to model the rapidly changing specimen temperature. Such time-resolved experimental methods combined with simulation of experimentally inaccessible physical characteristics will be fundamental to advancing the understanding of rapidly driven phase transformations. [ABSTRACT FROM AUTHOR]
- Published
- 2012
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12. Bipolar resistive switching with self-rectifying effects in Al/ZnO/Si structure.
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Chen, C., Pan, F., Wang, Z. S., Yang, J., and Zeng, F.
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FERROELECTRIC RAM , *ALUMINUM , *ZINC oxide , *SILICON , *ARRHENIUS equation , *SUBSTRATES (Materials science) , *THIN films - Abstract
We report the electrical characteristics of room-temperature-fabricated Al/ZnO/Si memory devices. Stable and reproducible clockwise bipolar resistive switching phenomena with self-rectifying effects in the low resistance state were observed in this complementary metal oxide semiconductor compatible memory structure. The current-voltage curve in different temperatures and the corresponding Arrhenius plot confirm the semiconducting conduction behavior of both the high resistance state and the low resistance state. The conduction mechanisms are explained by the Poole-Frenkel emission and space-charge-limited conduction mechanisms for the high resistance state and the low resistance state, respectively. It is proposed that the resistive switching originates from the formation and dissolution of the AlOx barrier layer which are induced by the migration of the oxygen ions. [ABSTRACT FROM AUTHOR]
- Published
- 2012
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13. Robust unipolar resistive switching of Co nano-dots embedded ZrO2 thin film memories and their switching mechanism.
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Wu, Ming-Chi, Wu, Tsung-Han, and Tseng, Tseung-Yuen
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THIN films , *SOLID state electronics , *MOLECULAR spectroscopy , *FERROELECTRIC RAM , *MOLECULAR orbitals , *CHEMICAL reactions , *NANOELECTRONICS - Abstract
The preparation and electrical properties of Ti/Co Embedded (Co-E) ZrO2/Pt resistive switching memories are investigated. The Co nano-dots are formed in ZrO2 thin film after the memory device is annealed at 600 °C in N2 ambient for 60 s without any chemical reaction between Co and ZrO2, which is confirmed from the transmission electron microscopy, energy dispersive X-ray analyzer, and X-ray photoelectron spectroscopy observations. The devices exhibit low forming voltage of -1.5∼-2.8 V and robust negative bias unipolar resistive switching behaviors with small negative set voltage of -1.1∼-1.6 V. A physical model based on a filament mechanism is employed to explain the switching behaviors. It has a high potential for ultra high density nonvolatile memory applications . [ABSTRACT FROM AUTHOR]
- Published
- 2012
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14. Metal oxide resistive memory switching mechanism based on conductive filament properties.
- Author
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Bersuker, G., Gilmer, D. C., Veksler, D., Kirsch, P., Vandelli, L., Padovani, A., Larcher, L., McKenna, K., Shluger, A., Iglesias, V., Porti, M., and Nafría, M.
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METALLIC oxides , *STRAY currents , *DIELECTRICS , *HAFNIUM oxide , *CRYSTAL grain boundaries , *ELECTRIC breakdown , *ELECTROFORMING , *FERROELECTRIC RAM - Abstract
By combining electrical, physical, and transport/atomistic modeling results, this study identifies critical conductive filament (CF) features controlling TiN/HfO2/TiN resistive memory (RRAM) operations. The leakage current through the dielectric is found to be supported by the oxygen vacancies, which tend to segregate at hafnia grain boundaries. We simulate the evolution of a current path during the forming operation employing the multiphonon trap-assisted tunneling (TAT) electron transport model. The forming process is analyzed within the concept of dielectric breakdown, which exhibits much shorter characteristic times than the electroforming process conventionally employed to describe the formation of the conductive filament. The resulting conductive filament is calculated to produce a non-uniform temperature profile along its length during the reset operation, promoting preferential oxidation of the filament tip. A thin dielectric barrier resulting from the CF tip oxidation is found to control filament resistance in the high resistive state. Field-driven dielectric breakdown of this barrier during the set operation restores the filament to its initial low resistive state. These findings point to the critical importance of controlling the filament cross section during forming to achieve low power RRAM cell switching. [ABSTRACT FROM AUTHOR]
- Published
- 2011
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15. Multi-level phase change memory devices with Ge2Sb2Te5 layers separated by a thermal insulating Ta2O5 barrier layer.
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Gyanathan, Ashvini and Yeo, Yee-Chia
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PHASE change materials , *FERROELECTRIC RAM , *THERMAL insulation , *CRYSTALLIZATION , *THERMAL conductivity , *THERMAL analysis , *SILICA , *SUBSTRATES (Materials science) - Abstract
This work investigates multi-level phase change random access memory (PCRAM) devices comprising two Ge2Sb2Te5 (GST) layers sandwiching a thermal insulating Ta2O5 barrier layer. The PCRAM cell comprises a phase change material stack between a top and a bottom electrode. The phase change material stack comprises a nitrogen doped GST (NGST) layer on a thin Ta2O5 barrier layer on an undoped GST layer. It is demonstrated that one of the phase change layers in the GST stack can be selectively amorphized by using a voltage pulse. This enables multi-level resistance switching. The differences in resistivities, as well as the different melting and crystallization temperatures of both the NGST and GST layers, contribute to the multi-level switching dynamics of the PCRAM device. The thermal conductivity of Ta2O5 with respect to GST is also another factor influencing the multi-level switching. Extensive electrical characterization of the PCRAM devices was performed. Thermal analysis was used to examine the physics behind the multi-level switching mechanism of these devices. [ABSTRACT FROM AUTHOR]
- Published
- 2011
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16. A solution processed nonvolatile resistive memory device with Ti/CdSe quantum dot/Ti-TiOx/CdSe quantum dot/indium tin-oxide structure.
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Kannan, V. and Rhee, J. K.
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FERROELECTRIC RAM , *QUANTUM dots , *TIN compounds , *OXIDES , *TEMPERATURE - Abstract
We report a Ti-TiOx/quantum dot based bipolar nonvolatile resistive memory device. The device has ON/OFF ratio 100 and is reproducible. The memory device showed good retention characteristics under stress and excellent stability even after 100 000 cycles of switching operation. The memory devices are solution processed at room temperature in ambient atmosphere. The operating mechanism is discussed based on charge trapping in quantum dots resulting in Coulomb blockade effect with the metal-oxide layer acting as the barrier to confine the trapped charges. The mechanism is supported by negative differential resistance (NDR) observed exclusively in the ON state. [ABSTRACT FROM AUTHOR]
- Published
- 2011
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17. Resistive switching characteristics and mechanism of thermally grown WOx thin films.
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Biju, Kuyyadi P., Liu, Xinjun, Siddik, Manzar, Kim, Seonghyun, Shin, Jungho, Kim, Insung, Ignatiev, Alex, and Hwang, Hyunsang
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THIN film research , *OXIDATION , *FERROELECTRIC RAM , *SCHOTTKY barrier diodes , *PHOTOSYNTHETIC oxygen evolution - Abstract
Resistive switching characteristics of thermally oxidized tungsten thin films and their switching mechanism were investigated, modifying thickness of the active layer (WOx) by varying oxidation conditions. Two types of switching were observed in Pt/WOx/W memory devices. Thinner film (t ≤ 15 nm) exhibits clockwise switching (CWS) with filamentary characteristics, whereas thicker film (t ≥ 25 nm) exhibits counter-clockwise switching (CCWS) with more homogeneous conduction. Both switching modes are highly reliable and show good cycling endurance. The conduction phenomena in two different switching modes were examined. In the case of CWS, the conduction mechanism changes from Schottky emission to ohmic conduction due to the local bypass of Schottky barrier formed at Pt/WOx interface by oxygen vacancies. Contrary to CWS, CCWS showed a completely different conduction mechanism. The high resistance state is dominated by the Schottky emission at low electric field and by Poole-Frenkel emission at high electric field, whereas the low resistance state exhibits the Schottky emission. Different types of switching behavior might be attributed to the non-homogenous defect distribution across the active layer. A possible conduction sketch for two types switching behaviors is also discussed. [ABSTRACT FROM AUTHOR]
- Published
- 2011
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18. Charge trapping in alumina and its impact on the operation of metal-alumina-nitride-oxide-silicon memories: Experiments and simulations.
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Padovani, Andrea, Larcher, Luca, Della Marca, Vincenzo, Pavan, Paolo, Park, Hokyung, and Bersuker, Gennadi
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ALUMINUM oxide , *NITRIDES , *FERROELECTRIC RAM , *ELECTRON research , *ELECTRIC charge - Abstract
We investigate the electron/hole trapping phenomena in alumina blocking oxide and their impact on the program/erase operations and retention of TaN/Al2O3/Si3N4/SiO2/Si (TANOS) memory devices. For this purpose, we perform simulations using a physical model that reproduces the charge injection/trapping in TANOS devices, which is extended in order to account for the charge trapping phenomena in the blocking layer. We derive the electrical characteristics of both electron and hole traps in Al2O3 by reproducing the measured program, erase, and retention transients. Our results show that the amount of electron charge trapped in the alumina during a program operation strongly depends on the stack composition and program voltages and can account for up to 25% of the total threshold voltage shift, whereas hole trapping during erase is negligible. Finally, we investigate the degradation of retention caused by the electron trapping in the alumina blocking layer, which is shown to result in an accelerated charge loss. [ABSTRACT FROM AUTHOR]
- Published
- 2011
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19. Electronic and optical switching of solution-phase deposited SnSe2 phase change memory material.
- Author
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Wang, Robert Y., Caldwell, Marissa A., David Jeyasingh, Rakesh Gnana, Aloni, Shaul, Shelby, Robert M., Philip Wong, H.-S., and Milliron, Delia J.
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PHASE transitions , *LASERS , *PHASE equilibrium , *STATISTICAL physics , *FERROELECTRIC RAM - Abstract
We report the use of chalcogenidometallate clusters as a solution-processable precursor to SnSe2 for phase change memory applications. This precursor is spin-coated onto substrates and then thermally decomposed into a crystalline SnSe2 film. Laser testing of our SnSe2 films indicate very fast recrystallization times of 20 ns. We also fabricate simple planar SnSe2 electronic switching devices that demonstrate switching between ON and OFF resistance states with resistance ratios varying from 7-76. The simple cell design resulted in poor cycling endurance. To demonstrate the precursor's applicability to advanced via-geometry memory devices, we use the precursor to create void-free SnSe2 structures inside nanowells of ∼25 nm in diameter and ∼40 nm in depth. [ABSTRACT FROM AUTHOR]
- Published
- 2011
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20. Diode and photocurrent effect in ferroelectric BaTiO3-δ.
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Won, C. J., Park, Y. A., Lee, K. D., Ryu, H. Y., and Hur, N.
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FERROELECTRIC crystals , *FERROELECTRIC RAM , *DIODES , *VACUUM tubes , *GERMANIUM diodes - Abstract
The leakage current has been regarded as one of the major problems in ferroelectric memories. However, recent studies on the unidirectional electric transport through a ferroelectric single crystal and the giant tunnel electroresistance in ferroelectric tunnel junctions suggest a possibility to utilize this undesirable leakage current. Here, we present the diodelike transport and the significantly enhanced photocurrent effects in oxygen-deficient BaTiO3-δ single crystals, which are mainly dependent on the direction of ferroelectric polarization. Diode effects in the carrier doped conventional ferroelectrics may suggest an alternative way for the nondestructive readout of polarization states in common ferroelectric memories. [ABSTRACT FROM AUTHOR]
- Published
- 2011
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21. Impact of time and space evolution of ion tracks in nonvolatile memory cells approaching nanoscale.
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Cellere, G., Paccagnella, A., Murat, M., Barak, J., Akkerman, A., Harboe-Sorensen, R., Virtanen, A., Visconti, A., and Bonanomi, M.
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HEAVY ions , *IONS , *NANOSTRUCTURED materials , *FERROELECTRIC RAM , *MICROELECTRONICS research - Abstract
Swift heavy ions impacting on matter lose energy through the creation of dense tracks of charges. The study of the space and time evolution of energy exchange allows understanding the single event effects behavior in advanced microelectronic devices. In particular, the shrinking of minimum feature size of most advanced memory devices makes them very interesting test vehicles to study these effects since the device and the track dimensions are comparable; hence, measured effects are directly correlated with the time and space evolution of the energy release. In this work we are studying the time and space evolution of ion tracks by using advanced non volatile memories and Monte Carlo simulations. Experimental results are very well explained by the theoretical calculations. [ABSTRACT FROM AUTHOR]
- Published
- 2010
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22. Multilevel resistive switching in Ti/CuxO/Pt memory devices.
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Sheng-Yu Wang, Chin-Wen Huang, Dai-Ying Lee, Tseung-Yuen Tseng, and Ting-Chang Chang
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SWITCHING circuits , *ELECTRIC potential , *FERROELECTRIC RAM , *ELECTRODES , *FERROELECTRIC crystals - Abstract
The multilevel resistive switching (RS) behaviors of the Ti/CuxO/Pt device were investigated by controlling the operated parameters of current and voltage bias in this study. We demonstrated that at least five-level memory states for data storage could be determined by controlling the current compliance, the span of voltage sweeping, and the amplitude of voltage pulse imposed on the memory device. During the dc voltage sweeping mode, not only the multilevel ON-states but also the multilevel OFF-states were achieved for the multilevel storage. The RS mechanism of the Ti/CuxO/Pt device is proposed to be related to the formation/rupture of the conducting filaments, arising from the interfacial oxygen ion migration between the Ti top electrode and CuxO films. Moreover, a possible conduction scenario for the multilevel RS behaviors is also suggested. Owing to all the multilevel memory states are distinguishable and possess the nondestructive readout property, it implies that the Ti/CuxO/Pt device has the promising potential for the future multilevel-capability memory cell application. [ABSTRACT FROM AUTHOR]
- Published
- 2010
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23. Structural and electrical characteristics of high-k Tb2O3 and Tb2TiO5 charge trapping layers for nonvolatile memory applications.
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Tung-Ming Pan, Fa-Hsyang Chen, and Ji-Shing Jung
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FERROELECTRIC RAM , *PHOTOELECTRON spectroscopy , *MOLECULAR spectroscopy , *PARTICLES (Nuclear physics) , *PHOTOELECTRICITY - Abstract
In this study, we investigated the structural properties and electrical characteristics of metal/oxide/high-k material/oxide/silicon (MOHOS)-type memory devices incorporating Tb2O3 and Tb2TiO5 films as charge storage layers for nonvolatile memory applications. X-ray diffraction and x-ray photoelectron spectroscopy revealed the structural and chemical features of these films after they had been subjected to annealing at various temperatures. From capacitance-voltage measurements, we found that the MOHOS-type memory devices incorporating the Tb2TiO5 film and that had been annealed at 800 °C exhibited a larger flatband voltage shift of 2.94 V (Vg=9 V for 0.1 s) and lower charge loss of 8.5% (at room temperature), relative to those of the systems that had been subjected to other annealing conditions. This result suggests that Tb2TiO5 films featuring a thinner silicate layer and a higher dielectric constant provide a higher probability for trapping of the charge carrier and deeper electron trapping levels. [ABSTRACT FROM AUTHOR]
- Published
- 2010
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24. Conductive path formation in glasses of phase change memory.
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Simon, M., Nardone, M., Karpov, V. G., and Karpov, I. V.
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FERROELECTRIC RAM , *PHASE transitions , *CHALCOGENIDES , *INFORMATION resources management , *PERCOLATION - Abstract
We present a model of data retention for phase change memory devices in which the active medium is a thin layer of chalcogenide glass. Data retention capability is compromised when a crystalline path is spontaneously formed in the glassy host, essentially shunting the device. We determine the probability and statistics of device failure for systems in which the crystalline volume fraction is below the critical volume fraction of percolation theory. In that regime, we show that rectilinear crystalline path formation is favored and we determine the criteria for when such paths dominate over the typical percolation cluster scenario. Our analytical approach, based on modeling the formation of such paths in terms of a half-space random walk, leads to closed form expressions that relate data retention characteristics to device parameters. The model is used to examine the effects of device geometry, temperature, and external fields. The temporal statistics of device reliability are also considered for several failure mechanisms. A computer simulation is employed that supports our derived relationships between failure probability and device parameters. [ABSTRACT FROM AUTHOR]
- Published
- 2010
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25. dc and high frequency magnetic properties of nanopatterned CoFe2O4 arrays fabricated using sol-gel precursors.
- Author
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Sheet, Goutam, Cunliffe, Alexandra R., Offerman, Erik J., Folkman, Chad M., Eom, Chang-Beom, and Chandrasekhar, Venkat
- Subjects
- *
PHYSICS research , *NANOSTRUCTURED materials , *FERROMAGNETISM , *CURIE temperature , *SPINTRONICS , *FERROELECTRIC RAM , *MAGNETIC memory (Computers) , *RESONANCE ionization spectroscopy - Abstract
Nanostructures of ferromagnetic oxides having Curie temperatures above room temperature have potential for applications in memory devices and future spin-based electronic applications. In this article, we report on the dc and high frequency magnetic properties of arrays of elliptical CoFe2O4 nanopillars, covering a large area, fabricated by combined electron beam lithography, and a sol-gel based chemical route. The nanopillars were successfully fabricated on insulating oxidized silicon substrates and on epitaxial thin films of ferroelectric BiFeO3. We performed magnetic force microscopy and ferromagnetic resonance spectroscopy on the arrays to probe their magnetic properties. Due to the possible existence of dominant pinning sites, the CoFe2O4 nanopillars are not single-domain even at nanometer size scales. [ABSTRACT FROM AUTHOR]
- Published
- 2010
- Full Text
- View/download PDF
26. Atomic structure of amorphous and crystallized Ge15Sb85.
- Author
-
Zalden, Peter, Bichara, Christophe, van Eijk, Julia, Braun, Carolin, Bensch, Wolfgang, and Wuttig, Matthias
- Subjects
- *
PHYSICS research , *SEMICONDUCTOR industry , *CRYSTALLIZATION , *X-ray absorption near edge structure , *X-ray spectroscopy , *ABSORPTION spectra , *FERROELECTRIC RAM , *MAGNETIC memory (Computers) , *SEMICONDUCTOR storage device manufacturing - Abstract
Ge15Sb85 is a promising material for phase-change memory applications owing to its very short crystallization times. As deposited amorphous samples of sputter deposited Ge15Sb85 have been investigated by extended x-ray absorption fine structure (EXAFS) measurements on both, Sb and Ge K absorption edges. After crystallizing the specimen, x-ray diffraction (XRD) and EXAFS measurements have been performed to analyze the atomic structure at different annealing conditions. Thus, experimental techniques focusing on the long range order as well as on the local order have been combined. Sb atoms have on average 3.2(2) nearest neighbors, while Ge atoms have 4.0(3). The Ge–Ge and Ge–Sb bond lengths are determined to 2.46(2) and 2.66(1) Å, respectively and agree well with those observed in the amorphous phase of the common phase-change material Ge2Sb2Te5. After crystallizing the sample at 250 °C, very different EXAFS spectra with modified Ge–Sb bond lengths are observed. The higher concentration of Ge neighbors at the Ge edge as compared to the as-deposited sample is indicative for phase separation. For the corresponding sample, XRD does not show reflections of Ge, which indicates that the agglomeration of Ge is amorphous or below the coherence length of the x-radiation. The EXAFS spectrum shows a superposition of two phases: one with bond lengths which agree with sp3-hybridized Ge [2.43(1) Å] and another one with longer Ge–Ge bond lengths [2.79(8) Å]. This result can be explained by phase separation in the material. [ABSTRACT FROM AUTHOR]
- Published
- 2010
- Full Text
- View/download PDF
27. Atomic structure of amorphous and crystallized Ge15Sb85.
- Author
-
Zalden, Peter, Bichara, Christophe, van Eijk, Julia, Braun, Carolin, Bensch, Wolfgang, and Wuttig, Matthias
- Subjects
PHYSICS research ,SEMICONDUCTOR industry ,CRYSTALLIZATION ,X-ray absorption near edge structure ,X-ray spectroscopy ,ABSORPTION spectra ,FERROELECTRIC RAM ,MAGNETIC memory (Computers) ,SEMICONDUCTOR storage device manufacturing - Abstract
Ge
15 Sb85 is a promising material for phase-change memory applications owing to its very short crystallization times. As deposited amorphous samples of sputter deposited Ge15 Sb85 have been investigated by extended x-ray absorption fine structure (EXAFS) measurements on both, Sb and Ge K absorption edges. After crystallizing the specimen, x-ray diffraction (XRD) and EXAFS measurements have been performed to analyze the atomic structure at different annealing conditions. Thus, experimental techniques focusing on the long range order as well as on the local order have been combined. Sb atoms have on average 3.2(2) nearest neighbors, while Ge atoms have 4.0(3). The Ge–Ge and Ge–Sb bond lengths are determined to 2.46(2) and 2.66(1) Å, respectively and agree well with those observed in the amorphous phase of the common phase-change material Ge2 Sb2 Te5 . After crystallizing the sample at 250 °C, very different EXAFS spectra with modified Ge–Sb bond lengths are observed. The higher concentration of Ge neighbors at the Ge edge as compared to the as-deposited sample is indicative for phase separation. For the corresponding sample, XRD does not show reflections of Ge, which indicates that the agglomeration of Ge is amorphous or below the coherence length of the x-radiation. The EXAFS spectrum shows a superposition of two phases: one with bond lengths which agree with sp3 -hybridized Ge [2.43(1) Å] and another one with longer Ge–Ge bond lengths [2.79(8) Å]. This result can be explained by phase separation in the material. [ABSTRACT FROM AUTHOR]- Published
- 2010
- Full Text
- View/download PDF
28. Scandium oxide deposited by high-pressure sputtering for memory devices: Physical and interfacial properties.
- Author
-
Feijoo, P. C., del Prado, A., Toledano-Luque, M., San Andrés, E., and Lucía, M. L.
- Subjects
- *
PHYSICS research , *THIN films , *SPUTTERING (Physics) , *SCANDIUM , *SILICON oxide , *TRANSMISSION electron microscopy , *FERROELECTRIC RAM - Abstract
Scandium oxide (ScOx) thin layers are deposited by high-pressure sputtering (HPS) for physical and electrical characterization. Different substrates are used for comparison of several ScOx/Si interfaces. These substrates are chemical silicon oxide (SiOx), H-terminated silicon surface and silicon nitride (SiNx), obtained by either electron-cyclotron-resonance chemical vapor deposition or plasma enhanced nitridation of the Si surface. Transmission electron microscopy images show that a 1.7 nm thick SiOx layer grows when ScOx is deposited on H-terminated silicon surface. We demonstrate that interfacial SiNx has some advantages over SiOx used in this work: its permittivity is higher and it presents better interface quality. It also avoids Si oxidation. An improvement of one order of magnitude in the minimum of interface trap density is found for SiNx with respect to the SiOx, reaching values below 2×1011 cm-2 eV-1. HPS deposited ScOx films are polycrystalline with no preferential growth direction for the used deposition conditions and their properties do not depend on the substrate. This material could be a candidate for high-k material in flash memory applications. [ABSTRACT FROM AUTHOR]
- Published
- 2010
- Full Text
- View/download PDF
29. Role of oxygen vacancies on relaxation and conduction behavior of KNbO3 ceramic.
- Author
-
Singh, Gurvinderjit, Tiwari, V. S., and Gupta, P. K.
- Subjects
- *
DIELECTRICS , *ELECTRICAL engineering materials , *ELECTRIC conductivity , *SEMICONDUCTORS , *FERROELECTRIC crystals , *FERROELECTRIC RAM - Abstract
The temperature and frequency dependent dielectric and conductivity properties were measured on as-sintered as well as oxygen annealed KNbO3 ceramics. The results show that in addition to phase transition peaks, well defined relaxation peaks are observed in the temperature range 450–700 K. These peaks could be suppressed by annealing the samples in the oxygen atmosphere. The dc conductivity and maximum dielectric constant values decreases after oxygen annealing. Activation energy, calculated from dielectric relaxation and conductivity data on the samples, suggests that both the processes are due to doubly charged oxygen vacancies formed during sintering process. Dielectric relaxation is attributed to the hopping of oxygen vacancies in the six equivalent sites in perovskite structure. The dielectric and conductivity behaviors are influenced by the density of the samples. The results are explained on the basis of defect concentration and their dynamics. [ABSTRACT FROM AUTHOR]
- Published
- 2010
- Full Text
- View/download PDF
30. Synthetic antiferromagnet with Heusler alloy Co2FeAl ferromagnetic layers.
- Author
-
Xu, X. G., Zhang, D. L., Li, X. Q., Bao, J., Jiang, Y., and Jalil, M. B. A.
- Subjects
- *
FERROELECTRIC RAM , *METALLIC composites , *ELECTRIC resistance , *MAGNETIC fields , *MAGNETIC devices , *FERROMAGNETIC materials , *FERROMAGNETISM - Abstract
Heusler alloy Co2FeAl was employed as ferromagnetic layers in Co2FeAl (3 nm)/Ru (x nm)/Co2FeAl (5 nm) synthetic antiferromagnet structures. The experimental results show that the structure with a Ru thickness of 0.45 nm is strongly antiferromagnetic coupled, which is maintained after annealing at 150 °C for 1 h. The structure has a very low saturation magnetization Ms of 425 emu/cm3, a low switching field Hsw of 4.3 Oe, and a high saturation field Hs of 5257 Oe at room temperature, which are favorable for application in ultrahigh density magnetic read heads or other magnetic memory devices. Crystal structure study testifies that the as-deposited Co2FeAl film is in the B2 phase. Therefore, Heusler alloys can be used to fabricate synthetic antiferromagnetic and it is possible to make “all-Heusler” spin valves or magnetic tunneling junctions with better magnetic switching properties and high magnetoresistance. [ABSTRACT FROM AUTHOR]
- Published
- 2009
- Full Text
- View/download PDF
31. Degradation mechanisms of organic ferroelectric field-effect transistors used as nonvolatile memory.
- Author
-
Ng, Tse Nga, Russo, Beverly, and Arias, Ana Claudia
- Subjects
- *
ORGANIC field-effect transistors , *FERROELECTRIC RAM , *HYSTERESIS , *ELECTRIC breakdown , *DIELECTRIC devices - Abstract
Organic ferroelectric field-effect transistors were fabricated by inkjet printing for use as nonvolatile memory. Changes in device hysteresis were measured for 7 days to determine the limiting properties that restrict memory retention time. It was found that shifts in threshold voltage contributed to ∼55% of the reduction in transistor current, while decreased dielectric capacitance and reduced semiconductor mobility accounted for ∼30% and ∼15% of the current decay, respectively. The decrease in mobility and the shifts in threshold voltages are caused by remnant dipolar alignment in the ferroelectric insulator, and the reduction in gate capacitance is explained by injected charges in the ferroelectric dielectric. A method to calibrate and extract the input switching voltage is presented, and this calibration accounts for variations in device characteristics with time and allows the ferroelectric transistors to be used as analog memories. [ABSTRACT FROM AUTHOR]
- Published
- 2009
- Full Text
- View/download PDF
32. A theory of triple hysteresis in ferroelectric crystals.
- Author
-
Weng, George J.
- Subjects
- *
FORCING (Model theory) , *ELECTROMAGNETIC fields , *HYSTERESIS loop , *FERROELECTRIC crystals , *FERROELECTRIC RAM , *MICROMECHANICS , *THERMODYNAMICS , *ELECTRIC fields - Abstract
In the vicinity of the transition temperature between two ferroelectric states, a ferroelectric crystal could exhibit a triple hysteresis under an ac field. For a BaTiO3 with the “c-plate” configuration slightly below this temperature, the middle loop is caused by the 0°→180° domain switch in the orthorhombic phase, whereas the upper and lower loops are the result of orthorhombic-to-tetragonal phase transition, and vice versa. In this article we first develop a micromechanics-based thermodynamic model to determine the thermodynamic driving force for phase transition and for domain switch as a function of electric field and temperature, and in the latter case, further supplement it with a kinetic equation and a homogenization scheme. The dependence of dielectric constant of the orthorhombic and tetragonal phases on temperature and electric field are also established. The developed theory is then applied to calculate the triple hysteresis loops of BaTiO3 at several levels of temperature. The calculated results for the triple loops, and for the variation of dielectric constant, are found to be in full accord with the test data of Huibregtse and Young [Phys. Rev. 103, 1705 (1956)]. [ABSTRACT FROM AUTHOR]
- Published
- 2009
- Full Text
- View/download PDF
33. Analytical model for low-frequency noise in amorphous chalcogenide-based phase-change memory devices.
- Author
-
Betti Beneventi, G., Calderoni, A., Fantini, P., Larcher, L., and Pavan, P.
- Subjects
- *
CHALCOGENIDES , *FERROELECTRIC RAM , *PHASE transitions , *RELAXATION phenomena , *ELECTRIC noise , *SIGNAL-to-noise ratio - Abstract
Low-frequency noise has been experimentally characterized in the disordered insulating phase of chalcogenide-based phase-change memory (PCM) devices. An analytical model of noise based on the two-level systems (TLS) theory has been developed. In this framework we suggest that the origin of the 1/fγ noise in the conductivity of amorphous chalcogenides has to be ascribed to the TLS-induced fluctuations of the mean trap energy in the material. The model allows to quantitatively account for noise magnitude dependence on both voltage and temperature in the readout region of the memory device. Besides, our equations well describe the noise behavior as a function of the drift phenomenon, coherently with existing structural relaxation theories. Measurements and model results show that the noise-to-signal ratio (N/S) in the readout region of the cell is constant with respect to bias; hence there is no particular readout voltage that minimizes N/S. Furthermore, the analysis of noise data with cell scaling confirms that noise in PCMs is mainly due to the bulk properties of the chalcogenide employed rather than to interfacial effects. [ABSTRACT FROM AUTHOR]
- Published
- 2009
- Full Text
- View/download PDF
34. Mechanical flexible and electric fatigue resistant behavior of relaxor ferroelectric terpolymer.
- Author
-
Fang, Fei, Yang, Wei, and Yang, Wen
- Subjects
- *
FERROELECTRIC crystals , *ELECTRIC fields , *ELASTOMERS , *ACTUATORS , *FERROELECTRIC RAM , *ANNEALING of crystals , *POLARIZATION (Electricity) - Abstract
Uniaxial tension and polarization evolution under cyclic electric field are investigated for poly(vinylidene fluoride-trifluorethylene-chlorofluoroethylene) terpolymer films prepared by different annealing conditions. The stress-strain behavior of the terpolymer film exhibits that of polymeric elastomers, with its fracture strain reaching 680%. Structure analysis demonstrates that the polymer chains undergo reorientation, and conformational change from nonpolar to polar phase takes place during uniaxial tension. Under cyclic electric field, the terpolymer film exhibits a narrow polarization loop typical of a ferroelectric relaxor. Conformational change from nonpolar to polar phase also occurs upon the electric field, and it reverses to the nonpolar phase when the field is removed. As the cycle number accumulates, the terpolymer film demonstrates excellent resistance to electric fatigue. Compared to the film annealed at 115 °C, the terpolymer film annealed at 100 °C has a larger volume fraction of crystallite/amorphous interfaces and shows better mechanical flexibility as well as electric fatigue resistance. The mechanical flexible and electric fatigue resistant terpolymer films hold promises for many applications, ranging from embedded sensors and actuators to flexible memory devices. [ABSTRACT FROM AUTHOR]
- Published
- 2009
- Full Text
- View/download PDF
35. Direct observation of localized conduction pathways in photocross-linkable polymer memory.
- Author
-
Kwan, Wei Lek, Lei, Bao, Shao, Yue, Prikhodko, Sergey V., Bodzin, Noah, and Yang, Yang
- Subjects
- *
POLYMERS , *TRANSMISSION electron microscopes , *ELECTRIC fields , *ELECTRODES , *FERROELECTRIC RAM , *X-ray spectroscopy - Abstract
Resistive switching in photocross-linkable polymer memory devices was found to occur in localized areas of the device. In order to elucidate the reason behind the switching, we used focused ion-beam to prepare a cross-section of the device. It was found that after the device was switched to the high conductive state, in certain parts of the device, the electrodes were only about 5 nm apart. This was probably caused by a combination of high electric field and metal injection into the polymer film. Gold injection into the polymer film by locally enhanced electric field was confirmed by transmission electron microscope-energy dispersive x-ray analysis. This model was in agreement with both the temperature dependent and transient behavior of our device. We conclude that the non-uniformities at the nanoscale interface of the electrode dominated the device characteristics while the polymer played only a secondary role. [ABSTRACT FROM AUTHOR]
- Published
- 2009
- Full Text
- View/download PDF
36. Impact of floating dot distribution on memory characteristics of self-aligned dots-on-nanowire memory.
- Author
-
Nakajima, Anri, Fujiaki, Tomo, and Ezaki, Tatsuya
- Subjects
- *
NANOWIRES , *SILICON , *QUANTUM dots , *FERROELECTRIC RAM , *FLASH memory - Abstract
A nanowire memory device with self-aligned Si nanoscale floating dots has been fabricated to overcome the tradeoff between retention time and programming speed. The dependence of memory characteristics on the dot number and distribution have been systematically analyzed experimentally and numerically to provide design guidelines for optimizing device performance. Distributing multiple floating dots in series along the channel with each dot covering the whole channel width is essential for better retention characteristics, while maintaining similar programming characteristics without increasing the operating voltage. The spacing between dots is also an important factor for optimizing device performance. Taking into account the compatibility of the fabrication process with that of the conventional flash-type nonvolatile memory, the self-aligned dots-on-nanowire memory with multiple floating dots distributed in series along a nanowire channel is the best structure for high-performance memory. [ABSTRACT FROM AUTHOR]
- Published
- 2009
- Full Text
- View/download PDF
37. Physical concepts of memory device operation based on piezoacousto and pyroelectric properties of ferroelectric films.
- Author
-
Krieger, Ju. H.
- Subjects
- *
FERROELECTRIC RAM , *PYROELECTRICITY , *FERROELECTRIC thin films , *RANDOM access memory , *POLARIZATION (Electricity) - Abstract
The paper presents physical concepts of universal memory device operation based on piezoacousto and pyroelectric properties of ferroelectric materials. It is suggested to extract information about ferroelectric memory cell polarization by heating (pyroelectric approach) or mechanical deformation (piezoacousto approach) of the memory cell. The physical concepts of universal memory device operation and alternative memory array architectures are presented here, which satisfies the requirements of both a faster operation and a small effective memory cell size. For high density memory application the lowest cost can be achieved by the piezoacoustic approach, exploiting array architectures, such as cross point passive arrays and multilayer stacks. A new ferroelectric random access memory (RAM) structure, which is called acoustoferroelectric RAM, makes use of acoustic method of detecting polarization of the ferroelectric memory cells. [ABSTRACT FROM AUTHOR]
- Published
- 2009
- Full Text
- View/download PDF
38. Highly uniform resistive switching characteristics of TiN/ZrO2/Pt memory devices.
- Author
-
Sun, B., Liu, Y. X., Liu, L. F., Xu, N., Wang, Y., Liu, X. Y., Han, R. Q., and Kang, J. F.
- Subjects
- *
FERROELECTRIC RAM , *TRANSITION metal oxides , *THIN films , *ELECTRODES , *OXYGEN , *IONS , *TITANIUM nitride , *ZIRCONIUM oxide - Abstract
We fabricated the TiN/ZrO2/Pt sandwiched resistive switching memory devices. Excellent bipolar resistive switching characteristics, including a large number of switching cycles and highly uniform switching parameters, as well as long retention time were achieved. The improved switching behavior of TiN/ZrO2/Pt could be attributed to the oxygen reservoir effect of TiN electrodes on the formation and rupture of the filamentary conducting paths by modifying the concentration distributions of the oxygen ions and vacancies in ZrO2 thin films. The results demonstrate the feasibility of high performance resistive switching memory devices based on transition metal oxides by using TiN as the top electrode. [ABSTRACT FROM AUTHOR]
- Published
- 2009
- Full Text
- View/download PDF
39. An analysis of imprinted hysteresis loops for a ferroelectric Pb(Zr,Ti)O3 thin film capacitor using the switching transient current measurements.
- Author
-
Kim, Gun Hwan, Lee, Hyun Ju, Jiang, An Quan, Park, Min Hyuk, and Hwang, Cheol Seong
- Subjects
- *
FERROELECTRIC thin films , *FERROELECTRIC RAM , *CAPACITORS , *ELECTRODIFFUSION , *HYSTERESIS loop , *LEAD alloys - Abstract
This study examined the imprint mechanism of a ferroelectric Pt/Pb(Zr,Ti)O3(150-nm-thick)/Pt capacitor using pulse switching transient current measurements. The progression of the imprint was well explained by the propagation of a localized charge injection area, where there was an increase in coercive voltage and interfacial capacitance over the entire capacitor area. The as-received samples exhibited uniform interfacial capacitance over the total area. Charge injection resulted in a more rectified remanent polarization–applied voltage relationship compared with the as-received sample. Analytic functional forms for the switching charge and local switching area were also derived. [ABSTRACT FROM AUTHOR]
- Published
- 2009
- Full Text
- View/download PDF
40. Resistance switching of Au-implanted-ZrO2 film for nonvolatile memory application.
- Author
-
Liu, Qi, Guan, Weihua, Long, Shibing, Liu, Ming, Zhang, Sen, Wang, Qin, and Chen, Junning
- Subjects
- *
ZIRCONIUM oxide , *FERROELECTRIC RAM , *GOLD , *IONS , *HOPPING conduction - Abstract
The resistive switching characteristics and switching mechanisms of the Au-implanted-ZrO2 film are extensively investigated for nonvolatile memory applications. Reversible resistance-switching behavior from a high resistance to low resistance state can be traced by dc voltage and pulse voltage. After more than 200 dc switching cycles, the resistance ratio between the high and low resistance states is more than 180 times under 0.7 V readout bias. In the voltage pulse test, the “write” and “erase” speeds can be as fast as 50 and 100 ns, respectively. No data loss is observed for more than 106 s. The formation and rupture of conducting filamentary paths related to the implanted Au ions are suggested to be responsible for the resistive switching phenomenon. The dependence of resistance on temperature indicates that the variable-range hopping conduction mechanism is dominated in the low-resistance state, while the current characteristics are governed by the trap-controlled space limited conduction mechanism in the high-resistance state. [ABSTRACT FROM AUTHOR]
- Published
- 2008
- Full Text
- View/download PDF
41. Reproducible resistance switching characteristics of hafnium oxide-based nonvolatile memory devices.
- Author
-
Kim, Yong-Mu and Lee, Jang-Sik
- Subjects
- *
FERROELECTRIC RAM , *HAFNIUM oxide , *ELECTRIC fields , *THIN films , *X-ray diffraction , *ELECTRIC conductivity - Abstract
The resistance switching characteristics of HfO2 thin films deposited by reactive sputtering were examined as a function of the annealing temperature. The results showed that the Pt/HfO2/Pt devices exhibited reversible and steady bistable resistance states [high-resistance state (HRS) and low-resistance state (LRS)]. Reproducible resistance switching from one state to another state or vice versa could be achieved by applying the appropriate voltage bias. The memory performances were related to the crystal structures of the HfO2 films, as confirmed by x-ray diffraction. From current-applied voltage analysis of the devices, LRS in the low electric field regime exhibited Ohmic conduction behavior, while HRS in the high electric field was followed by Poole–Frenkel conduction behavior. The resistance ratios of the two states were maintained in the range of around two orders of magnitude during the endurance test. In addition, it was confirmed that the resistance of the on and off states can be well maintained according to the time elapsed. [ABSTRACT FROM AUTHOR]
- Published
- 2008
- Full Text
- View/download PDF
42. Magnetic polaron for a spin memory application.
- Author
-
Enaya, H., Semenov, Y. G., Zavada, J. M., and Kim, K. W.
- Subjects
- *
INTERFACES (Physical sciences) , *POLARONS , *SPINTRONICS , *QUANTUM dots , *MAGNETIC ions , *FERROELECTRIC RAM - Abstract
A memory concept based on the interfacial exchange energy between itinerant holes in a quantum dot and magnetic ions in an adjacent magnetic insulator is theoretically investigated. A model based on the free energy analysis demonstrates the existence of bistable states through the mechanism of bound collective magnetic polaron, whose formation and dissolution can be controlled electrically via a gate bias pulse. The parameter window suitable for bistability is discussed along with the conditions that support maximum nonvolatility. The analysis is extended to the influence of material choices as well as different designs. The calculation results clearly indicate the possibility of room temperature operation, given the availability of insulating ferromagnetic or antiferromagnetic materials whose Curie temperature is above room temperature. [ABSTRACT FROM AUTHOR]
- Published
- 2008
- Full Text
- View/download PDF
43. Electrical switching dynamics in circular and rectangular Ge2Sb2Te5 nanopillar phase change memory devices.
- Author
-
Ozatay, O., Stipe, B., Katine, J. A., and Terris, B. D.
- Subjects
- *
FERROELECTRIC RAM , *PHASE transitions , *ELECTRONIC pulse techniques , *ELECTRIC resistance , *INFORMATION retrieval - Abstract
We have measured the critical phase change conditions induced by electrical pulses in Ge2Sb2Te5 nanopillar phase change memory devices by constructing a comprehensive resistance map as a function of pulse parameters (width, amplitude, and trailing edge). Our measurements reveal that the heating scheme and the details of the contact geometry play the dominant role in determining the final phase composition of the device, such that a nonuniform heating scheme using rectangular contacts promotes partial amorphization/crystallization in a wide range of pulse parameters enabling multiple resistance levels for data storage applications. Furthermore we find that fluctuations in the snap-back voltage and set/reset resistances in repeated switching experiments are related to the details of the current distribution, such that a uniform current injection geometry (i.e., circular contact) favors more reproducible switching parameters. This shows that possible geometrical defects in nanoscale phase change memory devices may play an essential role in the performance of the smallest possible devices through modification of the exact current distribution in the active chalcogenide layer. We present a three-dimensional finite element model of the electrothermal physics to provide insights into the underlying physical mechanisms of the switching dynamics as well as to quantitatively account for the scaling behavior of the switching currents in both circular and rectangular contact geometries. The calculated temporal evolution of the heat distribution within the pulse duration shows distinct features in rectangular contacts providing evidence for locally hot spots at the sharp corners of the current injection site due to current crowding effects leading to the observed behavior. [ABSTRACT FROM AUTHOR]
- Published
- 2008
- Full Text
- View/download PDF
44. Memory effect near transition temperature in Sm C* phase in nonsurface stabilized ferroelectric liquid crystals.
- Author
-
Coondoo, I., Malik, A., Choudhary, A., Kumar, A., and Biradar, A. M.
- Subjects
- *
FERROELECTRIC devices , *LIQUID crystals , *FERROELECTRIC RAM , *ELECTROOPTICS , *DIELECTRICS , *HYSTERESIS - Abstract
Memory behavior in the ferroelectric liquid crystal (FLC) material, Felix 17/100, has been investigated by electro-optical, dielectric, and hysteresis methods at different temperatures ranging from room temperature to near ferro-paraelectric phase transition. Memory effect has been observed in the studied material near the transition temperature in Sm C* phase in the cells having thickness greater than the pitch value of the material. This is in contrast to the memory effect observed in conventional FLCs where thickness of the cell has to be less than the pitch value of the material. Electrical conductivity measurements elucidate that the steep increase in the conductivity near the transition temperature in Sm C* phase enhances the motion of free ions and probably weakens the depolarization field in the material, thereby showing memory effect. [ABSTRACT FROM AUTHOR]
- Published
- 2008
- Full Text
- View/download PDF
45. Electrical behavior of memory devices based on fluorene-containing organic thin films.
- Author
-
Dimitrakis, Panagiotis, Normand, Pascal, Tsoukalas, Dimitris, Pearson, Christopher, Ahn, Jin H., Mabrook, Mohammed F., Zeze, Dagou A., Petty, Michael C., Kamtekar, Kiran T., Wang, Changsheng, Bryce, Martin R., and Green, Mark
- Subjects
- *
FERROELECTRIC RAM , *FLUORENE , *ORGANIC thin films , *NANOPARTICLES , *GOLD , *THIN films , *AMINES - Abstract
We report on switching and negative differential resistance (NDR) behaviors of crossed bar electrode structures based on Al/organic layer/Al devices in which the organic layer was a spin-coated layer of 7-{4-[5-(4-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]phenyl}-9,9-dihexyl-N,N-diphenyl-fluoren-2-amine. The addition of gold nanoparticles (0.5 wt %) did not change the switching behavior of thicker film structures; however, devices incorporating the nanoparticles showed more reproducible characteristics. In most cases, a “forming” process, in which a large positive voltage was applied to the top Al electrode, was required before the NDR and conductivity switching were observed. Three different electrical conductivity mechanisms have been identified: Poole–Frenkel conductivity in unformed structures, linear current versus voltage characteristics for the ON state in formed devices, and superlinear current versus voltage behavior for the OFF state in formed devices. Models based on metallic filaments or on the injection and storage of charge do not explain all our experimental observations satisfactorily. Instead, an explanation based on the formation of nanocrystalline regions within the thin film is suggested. The devices can be used as two-terminal memory cells operating with unipolar voltage pulses. [ABSTRACT FROM AUTHOR]
- Published
- 2008
- Full Text
- View/download PDF
46. Growth atmosphere dependence of transport properties of NiO epitaxial thin films.
- Author
-
Oka, Keisuke, Yanagida, Takeshi, Nagashima, Kazuki, Tanaka, Hidekazu, and Kawai, Tomoji
- Subjects
- *
THIN films , *LOW temperatures , *CRYSTAL grain boundaries , *FERROELECTRIC RAM , *ELECTRIC conductivity - Abstract
Recent possible applications in nonvolatile resistive switching memory devices renewed the interests in the transport properties of NiO. The variation on the conductivities of NiO films was reported to strongly affect the resistive switching phenomena. The conduction mechanism of NiO has been interpreted in terms of the bulk p-type conduction mechanism via Ni deficiencies (Ni1-δO). Here we investigate the growth atmosphere dependence on the transport properties of NiO thin films epitaxially grown on MgO (001) substrate. The conductivities of NiO thin films showed completely an opposite tendency compared to the bulk p-type conduction mechanism. Microstructural analysis demonstrates that the conductivity of low temperature grown NiO thin films strongly correlates with tailing the band edge via the deterioration of entire film crystallinity rather than the grain boundaries including second phases. [ABSTRACT FROM AUTHOR]
- Published
- 2008
- Full Text
- View/download PDF
47. Effect of the intrinsic width on the piezoelectric force microscopy of a single ferroelectric domain wall.
- Author
-
Morozovska, Anna N., Eliseev, Eugene A., Svechnikov, George S., Gopalan, Venkatraman, and Kalinin, Sergei V.
- Subjects
- *
FERROELECTRIC RAM , *ANISOTROPY , *PROPERTIES of matter , *PIEZOELECTRICITY , *FERROELECTRIC devices - Abstract
Intrinsic domain wall width is a fundamental parameter that reflects bulk ferroelectric properties and governs the performance of ferroelectric memory devices. We present closed-form analytical expressions for vertical and lateral piezoelectric force microscopy (PFM) profiles of a single ferroelectric domain wall for the conical and disk models of the tip, beyond point charge and sphere approximations. The analysis takes into account the finite intrinsic width of the domain wall and dielectric anisotropy of the material. These analytical expressions provide insight into the mechanisms of PFM image formation and can be used for a quantitative analysis of the PFM domain wall profiles. The PFM profile of a realistic domain wall is shown to be the convolution of its intrinsic profile and the resolution function of PFM. [ABSTRACT FROM AUTHOR]
- Published
- 2008
- Full Text
- View/download PDF
48. The morphology control of pentacene for write-once-read-many-times memory devices.
- Author
-
Lin, Jian and Ma, Dongge
- Subjects
- *
PENTACENE , *FERROELECTRIC RAM , *THIN films , *ELECTRIC conductivity , *COMPUTER storage devices , *MAGNETIC memory (Computers) - Abstract
We realized write-once-read-many-times (WORM) memory devices based on pentacene and demonstrated that the morphology control of the vacuum deposited pentacene thin film is greatly important for achieving the unique nonvolatile memory properties. The resulted memory devices show a high ON/OFF current ratio (104), long retention time (over 12 h), and good storage stability (over 240 h). The reduction of the barrier height caused by a large interface dipole and the damage of the interface dipole under a critical bias voltage have been used to explain the transition processes. The achievement of excellent WORM memory based on pentacene opens up a new application field for organic materials. [ABSTRACT FROM AUTHOR]
- Published
- 2008
- Full Text
- View/download PDF
49. Fundamental drift of parameters in chalcogenide phase change memory.
- Author
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Karpov, I. V., Mitra, M., Kau, D., Spadini, G., Kryukov, Y. A., and Karpov, V. G.
- Subjects
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CHALCOGENIDES , *PHASE transitions , *NUCLEATION , *CRYSTALLOGRAPHY , *FERROELECTRIC RAM - Abstract
We present the data on temporal (t) drift of parameters in chalcogenide phase change memory that significantly complement the earlier published results. The threshold voltage Vth and the amorphous state resistance R are shown to drift as ΔVth∝v ln t and R∝tα in broad intervals spanning up to nine decades in time; the drift coefficient v depends on glass parameters and temperature, but does not depend on device thickness. We have demonstrated that drift saturates at long enough times that can be shorten with temperature increase. All available data on drift dynamics are fully consistent with the classical double-well-potential model, which gives simple analytical expressions for the observed temporal dependencies including numerical parameters. [ABSTRACT FROM AUTHOR]
- Published
- 2007
- Full Text
- View/download PDF
50. Modified resistive switching behavior of ZrO2 memory films based on the interface layer formed by using Ti top electrode.
- Author
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Lin, Chih-Yang, Wu, Chung-Yi, Wu, Chen-Yu, Tseng, Tseung-Yuen, and Hu, Chenming
- Subjects
- *
FERROELECTRIC RAM , *ZINC oxide thin films , *TITANIUM , *ELECTRIC resistance , *METAL-insulator transitions - Abstract
The influence of Ti top electrode material on the resistive switching properties of ZrO2-based memory film using Pt as bottom electrode was investigated in the present study. When Ti is used as top electrode, the resistive switching behavior becomes dependent on bias polarity and no current compliance is needed during switching into high conducting state. This phenomenon is attributed to the fact that a series resistance between Ti and ZrO2 film, composed of a TiOx layer, a ZrOy layer, and even the contact resistance, imposed a current compliance on the memory device. Besides, our experimental results imply that switching the device into high conducting state is a field driven process while switching back into low conducting state is a current driven process. [ABSTRACT FROM AUTHOR]
- Published
- 2007
- Full Text
- View/download PDF
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