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This paper is dedicated to preparation and analysis of metal insulator semiconductor (MIS) photoanode with a metal organic chemical vapor deposited RuO2 layer and TiO2 protection layer for photoelectrochemical water splitting. It is shown that utilization of TiO2 layers of 2, 4, and 6 nm thickness preserve the catalytic activity of underlying RuO2. The origin of increased overpotential and decreased photovoltage of the photoanode upon the increase of TiO2 layer thickness is discussed in the paper. Results revealed that utilization of TiO2 layer in the MIS concept is suitable for photoelectrochemical water oxidation applications.

We compared the morphology and Raman response of nanoscale shaped surfaces of Si substrates versus monocrystalline Si. Samples were structured by reactive ion etching, and four of them were covered by a RuO2-IrO2 layer. Raman bands, centred at approx. 520 cm–1, belonging to samples processed by etching the Si surface have intensities higher by approximately one order of magnitude than those of reference non-etched samples. For nanostructured samples, the rise in the Raman signal was 12–14 ×, which is in agreement with the model of the electric field at the tips of Si due to their geometry. This phenomenon is related to the high absorption of excitation radiation. Nanostructured surfaces of samples containing a layer of RuO2-IrO2 give rise to the phenomenon of surface enhancement of the Raman response most likely due to the charge transfer at the interface between silicon and conductive oxides. The nanostructured surface of Si without a metal layer behaves as a SERS substrate and detects the analytes at a low concentration.

Lithiated thin films are necessary for the fabrication of novel solid-state batteries, including the electrodes and solid electrolytes. Physical vapour deposition and chemical vapour deposition can be used to deposit lithiated films. However, the issue of conformality on non-planar substrates with large surface area makes them impractical for nanobatteries the capacity of which scales with surface area. Atomic layer deposition (ALD) avoids these issues and is able to deposit conformal films on 3D substrates. However, ALD is limited in the range of chemical reactions, due to the required volatility of the precursors. Moreover, relatively high temperatures are necessary (above 100 °C), which can be detrimental to electrode layers and substrates, for example to silicon into which the lithium can easily diffuse. In addition, several highly reactive precursors, such as Grignard reagents or n-butyllithium (BuLi) are only usable in solution. In theory, it is possible to use BuLi and water in solution to produce thin films of LiH. This theoretical reaction is self-saturating and, therefore, follows the principles of solution atomic layer deposition (sALD). Therefore, in this work the sALD technique and principles have been employed to experimentally prove the possibility of LiH deposition. The formation of homogeneous air-sensitive thin films, characterized by using ellipsometry, grazing incidence X-ray diffraction (GIXRD), in situ quartz crystal microbalance, and scanning electron microscopy, was observed. Lithium hydride diffraction peaks have been observed in as-deposited films by GIXRD. X-ray photoelectron spectroscopy and Auger spectroscopy analysis show the chemical identity of the decomposing air-sensitive films. Despite the air sensitivity of BuLi and LiH, making many standard measurements difficult, this work establishes the use of sALD to deposit LiH, a material inaccessible to conventional ALD, from precursors and at temperatures not suitable for conventional ALD.

In spite of the apparent simplicity of the system under study, compact modeling of complementary resistive switching (CRS) devices, i.e., two antiserially connected memristive structures, is by no means straightforward. This requires a deep understanding of the voltage drops occurring across the circuit elements and correct treatment of the so-called snapback (SB) effect typical of the breakdown process of a thin dielectric film in an MIS or a MIM structure. The SB effect fundamentally consists in a sudden reduction of the device resistance caused by the formation of a filamentary path spanning the insulator. Beyond this point, the filament widens keeping the voltage drop across its extremes constant. The consequence of disregarding this effect is clearly distinguishable in the simulated curves: progressive openings of the on-state windows for both positive and negative voltages instead of abrupt ones. In this paper, a modification is introduced in the original memdiode model for memristive devices in order to account for this remarkable feature. Ta2O5-based CRS devices are considered to demonstrate the suitability of our approach.

This paper presents an electrical and photoelectrochemical comparison of MIS photoanodes with a metal organic chemical vapor deposited RuO2 layer and evaporated Ni layer to provide a deeper insight into the interface properties of such structures. The unique properties of RuO2 such as high transparency, high conductance, high catalytic activity, and high work function make this material an excellent candidate for a Schottky contact of MIS photoanodes for water splitting. In contrast to the Ni-based MIS structure, no Fermi level pinning was observed when RuO2 was used. This allowed achieving a high measured photovoltage of 0.46 V compared to 0.3 V for a Ni based structure. The ability to achieve the high photovoltage by utilization of RuO2 catalyst is an important achievement for fabrication of high performing MIS structures.

The impact of oxidation agent and post-metallization annealing (PMA) on the quality of oxide-semiconductor interface in AlGaN/GaN metal-oxide semiconductor heterostructure field-effect transistors (MOS-HFETs) with HfO2 grown by atomic layer deposition (ALD) was investigated. About six orders of magnitude lower gate leakage current (∼10−7 mA/mm at −10 V) was observed for MOS-HFETs with HfO2 gate oxide grown by ALD using ozone oxidation agent (O-HfO2), compared with grown using water oxidation agent (T-HfO2). In addition, the output current frequency dispersion was effectively reduced for O-HfO2 by applying PMA performed at 400 °C in N2 ambient, where the current frequency dispersion measured using 100 ns-long pulses was reduced from 40% for as-deposited gate oxide to only 10% for devices after applied PMA. Frequency dispersion was found to be consistent with density of oxide/semiconductor interface states (Dit) determined near the semiconductor conduction and valence band edge using the capacitance-voltage curves measured at different temperatures (CV-T) and photo-assisted capacitance transient (photo-C-t) technique, respectively. MOS-HFET structures with O-HfO2 showed about one order of magnitude lower Dit near the semiconductor valence band compared with structures with T-HfO2 (2 × 1011 compared with 1012 eV−1 cm−2 at EC-E = 2.5 eV, respectively). Moreover, for devices with O-HfO2, Dit was further reduced in entire energy gap as a result of PMA performed at 400 °C. The increased Dit for T-HfO2 oxides was attributed to Hf-Hf bonds at the HfO2/GaN interface, as deduced X-ray photoelectron spectroscopy (XPS) analysis. In contrast, formation of Hf Hf bonds was negligible in as-deposited O-HfO2 oxide films, while PMA at 400 °C led to reduction of the hydroxyl group observed by XPS.

In our contribution we present and analyze implementation of the resistive switching structures for logic application based on Zadeh fuzzy logic. Resistive switching structures based on HfOx and TaOx were connected in an anti-serial configuration (complementary resistive switch). The complementary resistive switches integrated into logic circuit for Min-Max function implementation were analyzed using quasi-static voltage sweeps. We have shown that the accuracy of the Min/Max function determination depends on the ratio of the high and low resistivity states of the single switches. Determination of the Min/Max values is relevant only above the threshold voltage of the resistive structures. Reproducibility of the Min/Max function constructed from the resistive switching structures is demonstrated.

We report the use of H3PO4 as a reactant in atomic layer deposition (ALD) of lithium metaphosphate. The ALD growth cycle starts by injection of the lithium tetramethyl heptadionate ( LiTMHD) precursor followed by injection of the H3PO4 reactant. Both the reactant and the precursor are injected into the ALD chamber via direct liquid injection, which allows us to achieve ALD without plasma or high temperatures. The liquid H3PO4 solution, injected 10 s after the precursor, evaporates and decomposes into the gaseous mixture of H3PO4, P4O10, and H2O. The H3PO4 and P4O10 molecules finally react with the LiTMHD molecules adsorbed at the sample substrate, which results in the film growth. The obtained films are amorphous, and the x-ray photoelectron spectroscopy measurements reveal the LiPO3 composition. The growth process exhibits the features of the ALD, namely, the saturation of the growth rate with cycle duration and the maximum growth rate when the number of the injected precursor/reactant molecules reaches a critical value. We show theoretically that the growth rate is governed by the gas-phase equilibrium between H3PO4 and P4O10, both of which are reactive but to different degrees. Depending on the temperature and other conditions, we obtain a reactive gas adjustable at will between pure H3PO4 and pure P4O10. Our theory explains essential features of the observed ALD growth. It determines which of the two reactants ( H3PO4 or P4O10) causes the growth and which of them provides a faster growth.

Transparent conducting Al-doped ZnO films were grown by atomic layer deposition (ALD). Al-doping was introduced by inserting 1 A l 2 O 3 cycle per 28 ZnO cycles. The x-ray photoelectron spectroscopy showed that the density of the Al donors is 2 × 10 21– 3 × 10 21 cm − 3, while the Hall-effect measurements showed a ten times lower electron density. This low doping efficiency is a well-known inherent problem of the ALD method, and we wanted to explain its origin. We have found that the electron density is reduced by electron traps at the grain surface; however, the effect was too weak to explain the low doping efficiency. Therefore, the mechanism of the A l 2 O 3 doping was analyzed. We have proposed that each A l 2 O 3 molecule ideally provides two single-electron Al donors accompanied by one Zn vacancy, which acts as a two-electron acceptor. This would cause a perfect compensation; however, the compensation is in reality not perfect, which results in weakly efficient doping. Calculations also showed that each Zn vacancy creates a bound pair with an Al donor. To verify our doping model experimentally, it was inserted into the metallic transport theory and compared with the electron transport measurements. A good agreement was found for a broad range of experimental conditions. In the regime of weak localization, the conductivity showed the temperature dependence σ ( T ) = a + b T 3 / 4, which is a signature of weak localization and electron–electron scattering in a 3D dirty metal.

Materials Research Letters 7(3), 117 - 123 (2019). doi:10.1080/21663831.2018.1561535, The HfO2-based resistive random access memory (RRAM) is one of the most promising candidatesfor non-volatile memory applications. The detection and examination of the dynamic behavior ofoxygen ions/vacancies are crucial to deeply understand the microscopic physical nature of theresistive switching (RS) behavior. By using synchrotron radiation based, non-destructive and bulksensitivehard X-ray photoelectron spectroscopy (HAXPES), we demonstrate an operando diagnosticdetection of the oxygen ‘breathing’ behavior at the oxide/metal interface, namely, oxygen migrationbetween HfO2 and TiN during different RS periods. The results highlight the significance ofoxide/metal interfaces in RRAM, even in filament-type devices., Published by Taylor & Francis, London [u.a.]

The results of capacitive and current voltage measurements on metal-insulator-semiconductor (MIS) photoanode structures with n-type silicon substrate are presented in this paper. The best photo-voltage and photo-current results were obtained on MIS structures with SiO2 grown by Atomic Layer Deposition (ALD). High ideality factor observed in the voltage range 0.1-0.3 V indicates the tunnelling as a dominant transport mechanism through the ALD grown SiO2 layer. Low Flat band voltages confirmed good passivation properties of the prepared ALD grown SiO2. High saturation current and low overpotential of MIS photo-electrochemical structure with ALD SiO2 and RuO2 catalytic layer predict good applicability of ALD prepared passivation layer for light assisted water splitting.

Ubiquitous carbon nanomaterials have great potential for emerging technologies, but they also pose a threat to human health at the end of their lifecycle, especially when they are introduced into waste or ground waters. Graphene field-effect transistors (GFET) and real time in situ confocal Raman microscopy (CRM) were employed to detect a submonolayer of carbon quantum dots (CQDs) in water. An effective GFET channel was formed on exfoliated and chemical vapor deposited (CVD) graphene. The adsorption of CQDs was monitored by measuring conductance changes in GFETs. The graphene channel was functionalized with (3-aminopropyl) triethoxysilane (APTES), which allowed for easy observation of a shift in the charge neutrality point (CNP) when the graphene channel was exposed to CQDs. The affinity of the CQD's carboxyl terminal groups to the aminofunctionalized channel enabled a highly sensitive CQD detection based on changes in the GFET conductivity. The adsorption of the CQDs induced a positive shift of the CNP with a limit of detection at concentrations of 239 ppm and 62 ppm for the exfoliated and CVD graphene, respectively. A supporting study of graphene functionalization and CQD adsorption was performed by real time in situ CRM, ellipsometry, and ex situ X-ray photoelectron spectroscopy. © 2019 Author(s).

Ga2O3, a wide-bandgap semiconductor material, offers a great potential for power and high-voltage electronic devices. We report on the growth of undoped α- and β-phase Ga2O3 using liquid-injection metal-organic chemical vapor deposition (LI-MOCVD) on sapphire substrates. Using the same precursor (gallium acetylacetonate) and deposition temperature of 700 °C, the phase selection was controlled by the sapphire substrate orientation, where the growth of α- and β-phase Ga2O3 was achieved on m- and c-plane surface, respectively. As deduced from x-ray diffraction, α-Ga2O3 films show epitaxial character, while β- Ga2O3 films exhibit highly textured structure. Oxygen flow was also found to have a strong impact on the phase purity of α-Ga2O3 for the flow rates examined. Optical and electrical properties of the layers grown at different oxygen flow rates were also studied systematically. LI-MOCVD growth of α-phase Ga2O3 layers at relatively high deposition temperature widens the high-temperature processing of the Ga2O3-based electronic and optoelectronic devices.

This paper describes fabrication and characterisation of Ruo2 based metal-insulator-semiconductor (MIS) structure for photoelectrochemical water splitting. The expected high catalytic activity, transparency, stability and conductivity of Ruo2 make this material highly appealing for preparation of a photoanode with high performance. Optical, electrical and photoelectrochemical properties of Ruo2based MIS structures are compared with MIS structures with a Ni catalytic layer. The lower overpotential $V_{\text{op}}=0.12\mathrm{V}$ of Ruo2structure compared to $V_{\text{op}}=0.3\mathrm{V}$ obtained for Ni structure as well as higher saturation photocurrent indicates promising application of the developed Ruo2 structures for solar water splitting.

Storage-class memory, non-volatile, ultra-dense and lightning fast, may enable memory-driven computing to revolutionize the current architectures leading to an on-chip processing of vast amount of data. 3D vertical resistive random access memory (ReRAM) is a hot candidate for storage-class memory. In this talk we review current state-of-the-art works which offer promising solutions, utilizing either filamentary or non-filamentary ReRAM designs, including our own. We will discuss the pros and cons of different approaches and summarize the open problems, drawing possible solutions.

We present a new way to passively implement permutation circuits, a concept of importance in bit-oriented or line-oriented designs, used in communications, cryptography, field-programmable gate arrays or next-generation pulsed neural networks. We argue that the proposed implementation is more reliable and efficient than previous designs when the number of permuted signals is at least 16. It uses complementary resistive gates, which are natural extensions of the concept of a complementary resistive switch. When Ir/TaO $_x$ /Ta stack is used for switching, the devices show abrupt transitions among a discrete number of states resulting in a complex input–output characteristic. This deviates significantly from the fuzzy logic model of such gates previously proposed on the basis of theoretical models.

Self-aligned normally-off n(++)GaN/InAlN/AlN/GaN MOS HEMTs with a recessed gate show scalable threshold voltage between 1.3 to 3.7V, which increases with the gate oxide thickness. Al2O3 or HfO2 gate insulators were grown by ALD at 100 degrees C so that one photoresist mask could be used for the gate recessing, ALD and metal lift-off. A low density of the barrier surface donors approximate to 1x10(13)cm(-2) stems from the low thermal budged during the HEMT processing and explains the threshold voltage behaviour. Maximal I-DS reaches approximate to 0.4 A/mm despite 2-m gate length and 8-m source-to-gate distance invariant to the threshold voltage. It is shown that for the present device Al2O3 provides better gate insulation than HfO2, however, the latter may be more appropriate for highly scaled short gate-length HEMTs. Schematic picture of the self-aligned InAlN/GaN MOS HEMT.

Thin solid films consisting of ZrO2 and Ta2O5 were grown by atomic layer deposition at 300 °C. Ta2O5 films doped with ZrO2, TaZr2.75O8 ternary phase, or ZrO2 doped with Ta2O5 were grown to thickness and composition depending on the number and ratio of alternating ZrO2 and Ta2O5 deposition cycles. All the films grown exhibited resistive switching characteristics between TiN and Pt electrodes, expressed by repetitive current-voltage loops. The most reliable windows between high and low resistive states were observed in Ta2O5 films mixed with relatively low amounts of ZrO2, providing Zr to Ta cation ratio of 0.2.

We prepared Pt/HfO 2 /TiN metal–insulator–metal structures for resistive switching experiments. The HfO 2 films were prepared by thermal, ozone and plasma assisted atomic layer deposition. The deposition techniques yielded HfO 2 films that were conducive to stable and reproducible bipolar resistive switching. We observed that the forming voltage scaled with the HfO 2 film thickness. The structures did not show degradation after 10 4 consecutive resistive switching operations in a millisecond pulsed regime.

Possibilities for atomic layer deposition of Al2O3 films from chloride and ozone were studied in order to avoid application of precursors that could leave hydrogen impurities in the films. Growth of Al2O3 was obtained at substrate temperatures of 300–450 °C. At these temperatures, the growth rate was close to the values reported for corresponding H2O-based processes. Studies of thin-film composition revealed that reactivity of O3 was sufficient to ensure deposition of films with chlorine concentration below 0.05 at.% at 350–450 °C. Application of the AlCl3–O3 atomic layer deposition process for in situ Al-doping of TiO2 thin films demonstrated that the amount of Al incorporated into the films during a single deposition cycle depended on the doping level. A reason for this effect was the influence of Al-doping on the phase composition of the film material. Al-doping of the TiO2 films significantly reduced the surface roughness allowing deposition of high-density films with very flat surfaces. In capacitor structures with capacitance equivalent oxide thicknesses below 0.4 nm, the Al-doped TiO2 films deposited from TiCl4, AlCl3 and O3 demonstrated markedly lower leakage current densities than the films with similar capacitance densities grown from TiCl4, Al(CH3)3 and H2O and from TiCl4, Al(CH3)3 and O3 did.

In this work we systematically study the effect of the Al 2 O 3 barrier layer thickness on the resistive switching properties of Al 2 O 3 /TiO 2 bilayer grown by atomic layer deposition in the Pt/Al 2 O 3 /TiO 2 /TiN stacks. It was found that an Al 2 O 3 layer of a certain thickness is essential to stabilize the resistive switching parameters while these can be further tuned by current compliance during SET. A two-step forming process was required to achieve stable repetitive bipolar switching loops. The endurance of 10 4 readings of alternating resistance states was obtained for structures with 3 and 4 nm of Al 2 O 3 during pulsed measurements. Forming was performed also at elevated temperatures using constant voltage stress. It was found that the switching is filamentary and happens in the Al 2 O 3 layer while TiO 2 is acting as an oxygen vacancy reservoir.

Resistive switching (RS) effects in Pt/HfO2/TiN metal-insulator-metal (MIM) capacitors have been investigated in dependence on the TiN bottom electrode engineering, deposition process, switching conditions and dielectric thickness. It is found that RS ratio depends strongly on the amount of oxygen introduced on TiN surface during interface engineering. In some structures a full recovery of conductive filament is observed within more than 100 switching cycles. RS effects are discussed in terms of different energy needed to dissociate O ions in structures with different TiN electrode treatment.

Under certain conditions, the current-voltage (I-V) characteristic of transition metal oxide (TMO)-based resistive switching (RS) devices exhibits the so-called snapback effect. This effect is not always observable and is a feature associated with the abrupt reduction of the voltage drop across the device caused by the formation of a filamentary pathway spanning the insulating layer. Since the device electrical behavior must always comply with the load line constraint, the current increases following a trajectory dictated by the circuit series resistance. When the voltage drop across the device reaches the minimum value required to induce the ion movement, the filament starts to expand laterally with the consequent current increase. Remarkably, this phase develops at a fixed voltage drop between the device terminals. In this work, a simplified SPICE model for the intrinsic I-V curve of RS devices based on the memdiode concept (diode + memory) which includes the snapback effect is proposed. A thorough analysis of the role played by the model parameters related to that aspect is presented. Simulations are compared with experimental data obtained from Ta2O5-based RS devices.

HighlightsThe metal-oxide gate stack was realized by a single photolitographic step.Low temperature ALD Al2O3 layer was used for MOS gate stack.Plasma enhancement and thermal modes were compared.MOS devices were evaluated by DC, pulse and C-V measurements. We present the technology and performance of AlGaN/GaN MOS HEMTs with Al2O3 gate insulation. Definition of the Ni/Au gate metallization and underlying Al2O3 into a gate stack was realized by a single photolithographic step and lifted-off. 10nm thick Al2O3 layers were deposited by the low-temperature (100?C) atomic layer deposition (ALD), using ALD processes with (PA) and without (T) remote plasma enhancement. A dielectric constant of as deposited Al2O3 er~7.5 was determined from C-V measurements. The MOS HEMTs properties were evaluated from I-V, and C-V measurements, and the PA and T modes for the ALD deposition of Al2O3 in the gate stacks were compared also after consecutive annealing/passivation steps.

The switching current–voltage ( $I$ – $V$ ) characteristics of high-permittivity (high- $\kappa )$ Al2O3/TiO2 stacks are modeled using the double diode equation in combination with a recursive hysteresis operator that represents the memory state of the device. The model uses the outer experimental $I$ – $V$ loop corresponding to the maximum excursion of the input signal and current compliance as the calibration curve. It is shown that an asymmetric logistic-type dynamics for the system state variable is able to account for the abrupt set and progressive reset transitions. Additional recovery effects occurring close to the input signal turning points are also modeled by considering a proper extension of the original operator.

Crystallization of TiO2 thin films grown by atomic layer deposition from TiCl4 and O3 on RuO2 layers was investigated with the aim to develop alternative methods for preparation of high-permittivity dielectrics with low leakage current density for capacitor structures of memory devices. The lowest substrate temperature allowing reproducible growth of TiO2 with a rate exceeding 0.01 nm per cycle was determined to be around 225 °C. The highest deposition temperature used was limited to 450 °C because of RuO2 decomposition at higher temperatures. The TiO2 films deposited on RuO2 electrodes at substrate temperatures of 225–450 °C contained rutile phase. Reference films deposited on Si substrates were amorphous when deposited at 225 °C and contained anatase when deposited at 250 °C and higher temperatures. At temperatures 250–450 °C, the growth rate values of 10–25 nm thick films ranged from 0.04 to 0.07 nm per cycle being somewhat higher on RuO2 than on Si substrates. The dependence of the mean growth rate on the substrate material was mainly due to differences in nucleation and became weaker with increasing film thickness. Relative permittivity measured for TiO2 in the Pt/TiO2/RuO2 structures at a frequency of 10 kHz ranged from 106 to 126. The TiO2 films with the lowest leakage current densities were grown at 300–350 °C. Leakage current densities as low as (5–7)×10–8 A/cm2 at an applied voltage of 0.8 V were recorded for capacitor structures with capacitance–equivalent dielectric thicknesses of 0.41–0.45 nm.

The influence of the growth temperature on structure and the electrical properties of TiO2 thin films deposited from TiCl4 and H2O and from TiCl4 and O3 was investigated in the temperature range of 150–500 °C. The high-permittivity rutile phase of TiO2 was obtained on RuO2 in both processes at 225 °C and higher substrate temperatures. The films deposited on Si contained rutile only when were deposited from TiCl4 and H2O at temperatures above 425 °C. Comparison of the films grown on RuO2 revealed superior electrical performance of those deposited from TiCl4 and O3. Although the k values ranging from 100 to 130 in the Pt/TiO2/RuO2 structures were somewhat lower for these films than for the films deposited from TiCl4 and H2O, the former process resulted in lower leakage current densities at similar capacitance effective thicknesses (CET). The leakage current density as low as 6.6 × 10−8 A cm−2 at 0.8 V and CET = 0.41 nm was obtained for films deposited from TiCl4 and O3 at 350 °C.

Capacitors with TiO2 and Al-doped TiO2 dielectric films grown by atomic layer deposition exhibit promising properties for application in DRAM technology for 20 nm node and beyond. For stabilization of the high dielectric constant rutile TiO2 phase RuO2 thin films were employed as a bottom electrode. The capacitors with the equivalent oxide thickness below 0.5 nm show leakage current below 10-7 A/cm2 at voltage 0.8 and 0.6 V, respectively. Current distribution study using Conductive AFM studies revealed preferential leakage current flow through grains. Low equivalent oxide thickness and low leakage currents of TiO2-based capacitors confirm that they can be considered as an alternative to the SrTiO3 DRAM capacitors.

Suppression of surface donors (SDs) in AlGaN/GaN MOS-HEMTs represents a promising approach towards realization of normally-off switching devices with high threshold voltage. In this work, density of oxide/barrier interface traps (D it ) was determined in AlGaN/GaN MOS-HEMT structures with different SDs density (Nds), resulted from HCl pre-treatment variation. The results suggest deteriorated interface quality for sample without HCl cleaning. D it was found to increase from ∼1012 to ∼1013 eV−1 cm−2 in the energy range of 0.8 to 1.1 eV below the conduction band edge for structures with and without HCl cleaning step, respectively. On the other hand, our analysis indicates negligible contribution of interface traps to observed threshold voltage in thermal equilibrium. This indicates the nature of SDs to be different from that of interface traps.

The impact of post-deposition annealing of silicon based metal-insulator-semiconductor structures with SiO 2 /TiO 2 dielectric layers is inspected by means of electrical characterisation. It is shown that annealing at 400 °C in the forming gas results into the photovoltaic response of MIS structure. Such behaviour is facilitated by the tunnelling of holes through SiO 2 . Annealing at higher temperature or in the air ambient exhibit negligible photovoltaic response due to grown of additional SiO 2 at the interface and/or low interface quality.

The sub-threshold slope (SS) of AlGaN/GaN MOSHFETs with HfO 2 gate oxide prepared by Atomic Layer Deposition (ALD) were investigated. The different SS values, like as 290 mV/dec and 100 mV/dec for MOSHFETs with and w/o oxygen-plasma pre-treatment (PHf- and Hf-MOS) respectively, were estimated. The analysis were realized in temperature range from RT to 300°C. From SS, the average Dit, like as 8.4×1012 eV1 cm−2 and 1.5×1012 eV−1 cm−2 for Hf-and PHf-MOS, respectively, were evaluated. The gate leakage current has a strong effect on the SS. The gate leakage were reduced about two orders of magnitude for PHf-MOS (∼10−8A/mm at −10V) with oxygen-plasma pre-treatment. The improved SS obviously is also due to the large I ON /I OFF ratio (108). An increase of SS values with temperature, were found. However, the PHf-MOS have exhibited an approximately half angle of slope of SS with temperature (0,37mV/°C) than Hf-MOS (0,63mV/°C). As a result from SS the D it for PHf-MOS were reduced approximately five times.

Metal-oxide-semiconductor (MOS) structure represents an important gate technology in GaN HEMTs. As oxide/semiconductor interface quality is remaining reliability concern, several techniques for determination of interface state density (D it ) has been proposed. In the literature, the hysteresis in C-V sweeps (or V th shift, ΔV th ) is often interpreted as D it in particular energy range in the semiconductor band-gap. In this work, we critically assessed a relevancy of relation between ΔV th (measured at 25 and 125 °C) and experimentally determined D it distribution, to point out possible pitfalls in the data interpretation. D it distributions were measured by combination of complementary techniques and ID simulations applied to state-of-the-art MOS-HEMTstructures with Al 2 O 3 films grown by ALD on AlGaN/GaN heterostructures. It is demonstrated that, apart from interface traps, also other parasitic effects related to border traps and oxide bulk traps can have dominant impact on ΔV th -This means that ΔV th could not be solely related to D it , unless negligibility of other relevant effects is confirmed.

The paper examines the influence of ozone pre-treatment of the bottom TiN electrode in a HfO 2 -based resistive switching metal-insulator-metal structure. The HfO 2 layers with thicknesses 5.7, 4 and 3 nm were prepared by ozone assisted atomic layer deposition. Selected samples were pre-treated by ozone-only cycles prior to HfO 2 deposition. Stable and reproducible bipolar resistive switching was obtained with all structures. The resistivity ratio at a read-out voltage of +0.2 V was above 100 for Pt/HfO 2 (5.7 nm)/TiN structure with ozone pre-treatment, Pt/HfO 2 (4 nm)/TiN and Pt/HfO 2 (3 nm)/TiN without ozone pre-treatment. Moreover, ozone pre-treated structures exhibited a lower value of the forming voltage.

AlGaN/GaN metal-oxide-semiconductor high electron mobility transistors (MOS-HEMTs) represent an important technology for future high-efficient power and RF electronics. Due to oxide/semiconductor interface issues, fabrication of reliable MOS gate stack is still challenging, however. In this work we investigated the influence of gate oxide preparation technique to static and pulsed-mode operation of Al 2 O 3 /GaN/AlGaN/GaN MOS-HEMTs. Devices with gate oxide prepared by high-temperature MOCVD and low-temperature ALD using water vapour or ozone as oxidants are compared in terms of dynamic on-state resistance (R DSon ), threshold voltage shift (ΔV th ), and Al 2 O 3 /GaN interface charge density (N it )·

In this article, we comprehensively review recent progress in the ReRAM cell technology for 3D integration focusing on a material/device level. First we briefly mention pioneering work on high-density crossbar ReRAM arrays which paved the way to 3D integration. We discuss the two main proposed 3D integration schemes---3D horizontally stacked ReRAM vs 3D Vertical ReRAM and their respective advantages and disadvantages. We follow with the detailed memory cell design on important work in both areas, utilizing either filamentary or interface-limited switching mechanisms. We also discuss our own contributions on HfO$_{2}$-based filamentary 3D Vertical ReRAM as well as TaO$_{x}$/TiO$_{2 }$ bilayer-based self-rectifying 3D Vertical ReRAM. Finally, we summarize the present status and provide an outlook for the nearterm future.

We report on preparation and electrical characterization of InAlN/AlN/GaN metal–oxide–semiconductor high electron mobility transistors (MOS HEMTs) with Al2O3 gate insulation and surface passivation. About 12 nm thin high-κ dielectric film was deposited by MOCVD. Before and after the dielectric deposition, the samples were treated by different processing steps. We monitored and analyzed the steps by sequential device testing. It was found that both intentional (ex situ) and unintentional (in situ before Al2O3 growth) InAlN surface oxidation increases the channel sheet resistance and causes a current collapse. Post deposition annealing decreases the sheet resistance of the MOS HEMT devices and effectively suppresses the current collapse. Transistors dimensions were source-to-drain distance 8 μm and gate width 2 μm. A maximum transconductance of 110 mS/mm, a drain current of ∼0.6 A/mm (VGS = 1 V) and a gate leakage current reduction from 4 to 6 orders of magnitude compared to Schottky barrier (SB) HEMTs was achieved for MOS HEMT with 1 h annealing at 700 °C in forming gas ambient. Moreover, InAlN/GaN MOS HEMTs with deposited Al2O3 dielectric film were found highly thermally stable by resisting 5 h 700 °C annealing.

Properties of TiO2 based DRAM capacitors with equivalent oxide thickness of 0.5 nm are described. It is shown, that dielectric constant values more than 100 can be obtained in these structures for the TiO2 films with the thickness down to 10 nm. Leakage current density below 10-7 A/cm2 at 0.8 V can be obtained after post-deposition processing for the films with the thickness of 16 nm (EOT ≈ 0.5 nm). Al doping of the TiO2 films decreases dielectric constant, but improves leakage current density. Al-doped TiO2 films with the thickness of 10 nm (EOT = 0.46 nm) exhibit leakage current density below 10-7 A/cm at 0.8 V.

Properties of TiO"2-based capacitors with RuO"2 bottom electrode were examined. It is shown that post-deposition room temperature plasma treatment and oxygen annealing at 300^oC significantly reduces amount of impurities in the TiO"2 layer. Leakage current density of the capacitors is suppressed due to improvement of oxygen stoichiometry and increase of Schottky barrier height at the TiO"2-dielectric/metal electrode interface after post-deposition processing. Leakage current density below 10^-^7A/cm^2 was achieved for capacitor with equivalent oxide thickness of 0.58nm.

Hf-doped Ta 2 O 5 thin films are studied with respect to their composition, dielectric and electrical properties. The incorporation of Hf is performed by sputtering of a 0.7 nm thick Hf layer on top of Ta 2 O 5 and subsequent annealing to stimulate diffusion of Hf into Ta 2 O 5 and their intermixing. The elemental in-depth distribution of the films is investigated by the time of flight secondary ion mass spectroscopy (ToF-SIMS), which has revealed that Hf and Ta 2 O 5 are intermixed throughout the whole thickness. Two sub-layers exist in all the samples – an upper homogeneous Hf-doped Ta 2 O 5 sub-layer and a near interfacial region which is a mixture of Ta- and Si-oxides. The X-ray reflectivity (XRR) analysis shows existence of interfacial layer with a thickness of about 1.9–2 nm, irrespectively of the total thickness of the stacks. Metal–oxide–Si structures with Ru and RuO 2 metal electrodes have been prepared and investigated in terms of dielectric constant, effective work function (EWF) and interfacial layer parameters. The influence of post-metallization annealing steps on these parameters was also studied.

While the main application of resistive switching structures currently targets non-volatile memories, increasing interest is being focused on their logic applications. Resistive switches are suitable for Boolean logic, neuromorphic computing and for implementation of Zadeh fuzzy logic. In this work, we analyzed implementation of the resistive switching structures for logic application based on Zadeh fuzzy logic. Resistive switching structures based on hafnium oxide and tantalum oxide were connected in an anti-serial configuration (complementary resistive switch). The complementary resistive switches integrated into logic circuit for Min-Max function implementation were analyzed using quasi-static voltage sweeps. We have shown that the accuracy of the Min/Max function determination depends on the ratio of the high and low resistivity states of the single switches. Determination of the Min/Max values is relevant only above the threshold voltage of the resistive structures. Reproducibility of the Min/Max function constructed from the resistive switching structures was evaluated. In addition, pulsed reconfiguration of complementary resistive switch using 100 ns long pulses was demonstrated.

We have grown RuO2 films by pulsed liquid injection atomic layer deposition using (Ru(thd)2(cod)) dissolved in pyridine. The deposition process took place at 290 °C and consisted of four steps. The films exhibited smooth surface. Analysis of the films using secondary ion mass spectroscopy (SIMS) revealed low content of carbon in the films. Resistivity of the RuO2 film at room temperature was about 160 µΩ cm.

In this article, we optimized the ohmic contact processing in InAlN/GaN high electron mobility transistors for the lower temperature of annealing by recessing of metalliza-tion to approach the 2DEG at the InAlN/GaN interface. The ohmic contacts which were recessed down to 5 nm depth and annealed at 700 °C 2 min. exhibited the contact resistance of 0,39 Ωmm while the channel sheet resistance was 210 Ω/square. These values are comparative to values of contacts processed at more conventional an-nealing conditions (800 °C, 2 min). Moreover we applied the recessed ohmic contact technology to fabricate Schottky barrier (SB) HEMTs and MOSHEMTs with Al2O3 dielectric film. For MOSHEMTs, we measured the maximal reduction of the gate leakage current by about 6 orders of magnitude if compared with SB HEMTs. The maximal drain current of MOSHEMTs was about 750 mA/mm at VGS = 0 V and the maximal extrinsic transconductance (gme) reached 101 mS/mm. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We have studied thermal stability of GdScO3 and LaLuO3 films prepared by liquid injection metal-organic chemical vapour deposition (MOCVD). In the present work, we report on the characterization of LaLuO3 and GdScO3 thin dielectric films by SIMS and capacitance–voltage (C–V) measurements. In both GdScO3 and LaLuO3 films, SIMS analysis revealed the presence of a silicate interfacial layer. The C–V characteristics were found to be shifted after thermal treatment to negative and positive voltages for GdScO3 and LaLuO3 films, respectively. Furthermore we have observed that LaLuO3 films exhibit C–V characteristics more stable to annealing conditions compared with GdScO3 films.

The Ti-doped Ta 2 O 5 thin films ( 2 O 5 and a bulk doping where the Ti layer is sandwiched between two layers of Ta 2 O 5 . The effect of the process parameters (the method and level of doping) on the elemental distribution in-depth of the films is investigated by the time of flight secondary ion mass spectroscopy (ToF-SIMS). The Ti and Ta 2 O 5 are intermixed throughout the whole thickness but the layers are very inhomogeneous. Two sub-layers exist in all the samples — a near interfacial region which is a mixture of Ta-, Ti-, Si-oxides as well as TaSiO, and an upper Ti-doped Ta 2 O 5 sub-layer. For both methods of doping, Ti tends to pile-up at the Si interface. The electrical characterisation is performed on capacitors with Al- and Ru-gate electrodes. The two types of MIS structures exhibit distinctly different electrical behavior: the Ru gate provides higher dielectric permittivity while the stacks with Al electrode are better in terms of leakage currents. The specific metal-dielectric reactions and metal-induced electrically active defects for each metal electrode/high- k dielectric stack define its particular electrical behavior. It is demonstrated that the Ti doping of Ta 2 O 5 is a way of remarkable improvement of leakage characteristics (the current reduction with more than four orders of magnitude as compared with undoped Ta 2 O 5 ) of Ru-gated capacitors which originates from Ti induced suppression of the oxygen vacancy related defects.