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It is well known that the high-k interpoly dielectric (IPD) layer is important for further scaling down of floating gate (FG) type flash memory to improve the gate coupling ratio [1, 2]. Therefore, the high-k Al2O3 layer has already been used as a blocking layer in the charge trapping (CT) type planar and bulk FinFET flash memories [3-5]. However, the high-k Al2O3 has not been used as an IPD layer in the FG type SOI-FinFET flash memories, to our knowledge. In this work, we introduce the high-k Al2O3 into the FG type triangular-fin (TF) and rectangular-fin (RF) channel SOI-FinFET flash memories, and investigate the effects of fin shape and IPD layer material on the electrical characteristics of the fabricated FG type SOI-FinFET flash memories. In the device fabrication, we used (100) and (110) oriented SOI wafers to fabricate TF and RF channels by using the orientation dependent wet etching [6]. A 30-nm-thick n+ poly-Si layer was used as the FG material. Figure 1 shows the cross-sectional STEM images of the fabricated FG-type SOI-FinFET flash memories with different channel shapes and different IPD layers. Figure 2 shows the P/E characteristics of the fabricated 3 kinds of SOI-FinFET flash memories at the same P/E condition. It is clear that a higher P/E speed, a larger memory window and a lower-voltage operation are achieved in the TF-ONA device as compared to the TF-ONO and RF-ONA ones. This result indicates that a high-k Al2O3 layer is very useful for enhancing memory window due to the improved gate coupling, and the TF channel is very suitable for the low-voltage operation thanks to the high-k of Al2O3 and the electric field enhancement at the sharp foot edges of a TF. [1] B. Govoreanu et al., IEDM 2006, p. 479. [2] H.-T. Lue et al., IEDM 2011, p. 203. [3] C. H. Lee et al., IEDM 2003, p. 613. [4] S.-K. Sung et al., VLSI 2006, p.106. [5] B. J. Tang et al., IEDM 2011, p. 219. [6] Y. X. Liu et al., VLSI 2010, p.101. Figure 1

Ruthenium doped indium oxide (In1 − xRuxOy) films fabricated using DC magnetron co-sputtering with In2O3 and Ru targets were investigated for use as transparent conductive oxides. The In1 − xRuxOy films had an amorphous structure in the wide compositional range of x = 0.3–0.8 and had an extremely smooth surface. The transmittance and resistivity of the In1 − xRuxOy films increased as the Ru content increased. The transmittance of the In0.38Ru0.62Oy film improved to over 80% when the film thickness was less than 5 nm, while the specific resistivity (ρ) was kept to a low value of 1.6 × 10− 4 Ω cm. Based on these experimental data, we demonstrated that thick indium tin oxide (In0.9Sn0.1Oy, ITO) (150 nm)/ultrathin In0.38Ru0.62Oy (3 nm) bilayers have a high effective work function of 5.3 eV, transmittance of 86%, and low ρ of 9.2 × 10− 5 Ω cm. This ITO/In0.38Ru0.62Oy bilayer is a candidate for use as an anode for organic electroluminescent devices.

To clarify the Fermi level pinning observed in Hf based gate structures, we employed two types of Hf based gate structures and investigated their bias-dependent potential distribution in the structures using operando hard x-ray photoelectron spectroscopy. In the case of the Pt/HfSiO2/SiO2/p-Si(100) structure, the Si substrate and SiO2 peaks in Si 1 s were shifted when a bias voltage was applied to the structure, indicating that Si substrate was mostly biased. Thus the Pt/HfSiO2/SiO2/p-Si(100) structure had an ideal metal oxide semiconductor structure. On the other hand, applying a bias voltage in the case of the Pt/HfO2/SiO2/p-Si(100) structure shifted HfO2 in Hf 3d, SiO2, and the substrate in Si 1 s, suggesting that a potential drop occurred at the Pt/HfO2 interface. Thus the Fermi level pinning was occurred at the Pt/HfO2 interface. In order to clarify the Fermi level pinning, angle-resolve O1 s photoelectron spectroscopy (PES) was performed at the Pt/HfO2 interface. Analysis of the O1 s PES revealed the formation of a SiO2 layer at the Pt/HfO2 interface, which could be the origin of the Fermi level pinning observed in Hf based gate structures.

Multivalued logic circuits, which can handle more information than conventional binary logic circuits, have attracted much attention as a promising way to improve the data-processing capabilities of integrated circuits. In this study, we developed a ternary inverter based on organic field-effect transistors (OFET) as a potential component of high-performance and flexible integrated circuits. Key elements are anti-ambipolar and n-type OFETs connected in series. First, we demonstrate an organic ternary inverter that exhibits three distinct logic states. Second, the operating voltage was greatly reduced by taking advantage of an Al2O3 gate dielectric. Finally, the operating voltage was finely tuned by the designing of the device geometry. These results are achievable owing to the flexible controllability of the device configuration, suggesting that the organic ternary inverter plays an important role with regard to high-performance organic integrated circuits.

Orthorhombic rare-earth trivalent manganites RMnO

Composite of metal and conducting polymer is expected for electrical application by the use of their advantages. For improvement of the composite’s characteristics, it is important to control formation rate and structure of the composites obtained by simultaneous metal deposition and polymerization under photo irradiation. The purpose of this research was to reveal the effects of UV irradiation and dopant type for conducting polymer on photo-electrochemical deposition of metal. Cathodic polarization curves for silver deposition on polypyrrole doped with different types of anion at different intensity of the UV light were compared. Deposited particles were evaluated by the statistical analysis. The experimental results showed that silver deposition on polypyrrole was enhanced by UV introduction and depended on the dopant type.

The thin film growth of (110) rutile TiO 2 on a (100) Ge substrate at a substrate temperature of 450 °C, which is generally the growth temperature of anatase TiO 2 , was demonstrated by using pulsed laser deposition. X-ray diffraction and X-ray photoelectron spectroscopy revealed that the incorporation of Ge into TiO 2 enhances the rutile phase formation, and the ambient oxygen condition enhances the Ge oxide diffusion. Photoelectron spectroscopy also revealed that the valence band offset of rutile TiO 2 and p-type Ge is approximately 2.5 ± 0.1 eV with a type II band alignment.

This work investigates the spectroscopic properties of (Co1-xZnx)Al2O4 with a range of x of 0 ≤ x ≤ 1. Spectroscopic and crystallographic evaluations using XRD, Raman, FT-IR and UV-Vis spectroscopy reveal that Zn(2+) substitution systematically changes the lattice constant, which mainly depends on the Co-O bonds, and the related optical characteristics of this material. The x dependence of these properties shows two trends, and the mutation point seems to be at x ≈ 0.5. This implies that the electronic structure of (Co1-xZnx)Al2O4 is not changed monotonically by Zn(2+) substitution. Interestingly, some of the optical phenomena observed in this study become prominent for samples with x ≥ 0.5. That is, we observed sideband peaks near the main peaks in the Raman spectra, and their relative intensities systematically and significantly increased with increasing Zn(2+) substitution. The rates of increase are not constant, and are fast for samples with x ≥ 0.5. The sideband peaks are considered to reflect the unique changes in the local electronic structure of (Co1-xZnx)Al2O4, and they are useful for evaluating the substitution level without the influence of the site change phenomenon. Thus, clarifying them is expected to be important for understanding and controlling the electronic structure of the spinel oxide. On the other hand, investigation of the visible light absorption due to the d-d transition of Co(2+) reveals that the efficiency is also high for samples with high Zn(2+) substitution (x ≥ 0.5). This is also considered to be valuable information for investigation of the optical properties and/or the catalytic function of the spinel oxide. Moreover, the fluorescence of the (Co1-xZnx)Al2O4 samples is also identified as a novel functional property of this material. The intensity of the fluorescence peak also dramatically increases for samples with x ≥ 0.7. The effect of Zn(2+) substitution on the local electronic structure of (Co1-xZnx)Al2O4 has not been clarified yet. However, some of the interesting characteristics reviewed in this study are worth investigating from the viewpoint of materials science and applications.

The interconnect of flexible electronics requires to be electronically conductive as well as mechanically flexible, adhesive to plastic substrate and productively efficient while conventional technologies to form the interconnect are difficult to attain all of these requirements. The conductive polymer/metal composite material synthesized by solution chemistry was developed to meet these requirements. This composite material is promising as the interconnect of flexible electronics.

A NaF/KF postdeposition treatment (PDT) has recently been employed to achieve new record efficiencies of Cu(In,Ga)Se

A NaF/KF postdeposition treatment (PDT) has recently been employed to achieve new record efficiencies of Cu(In,Ga)Se2 (CIGSe) thin film solar cells. We have used a combination of depth-dependent soft and hard X-ray photoelectron spectroscopy as well as soft X-ray absorption and emission spectroscopy to gain detailed insight into the chemical structure of the CIGSe surface and how it is changed by different PDTs. Alkali-free CIGSe, NaF-PDT CIGSe, and NaF/KF-PDT CIGSe absorbers grown by low-temperature coevaporation have been interrogated. We find that the alkali-free and NaF-PDT CIGSe surfaces both display the well-known Cu-poor CIGSe chemical surface structure. The NaF/KF-PDT, however, leads to the formation of bilayer structure in which a K—In—Se species covers the CIGSe compound that in composition is identical to the chalcopyrite structure of the alkali-free and NaF-PDT absorber.

Thermally induced structural change in photoisomerization molecules is a serious obstacle to the development of optically controllable organic field-effect transistors (OFETs). This is because the thermal relaxation of molecular structures degrades photo-induced change in drain current and removes the memory function. To deal with this issue, a naphthopyran (NP) derivative, namely 3,13-dihydro-3-(4-triphenylaminyl)-3,13-diphenylbenzopyrano[5,6-a]carbazole (NP-TPAC) was tested that displays pseudo p-type photochromism at room temperature. The NP-TPAC-doped poly(triarylamine) (PTAA) film exhibited a reversible change in transistor properties; the drain current was reduced by ultraviolet (UV) and returned to its original value by visible (VIS) light irradiation. Importantly, no change in the drain current was observed at room temperature for more than 30 h under dark conditions. This was because the open-ring trans–trans (TT) isomer of NP-TPAC is thermally stable owing to the CH-π interaction and the steric force exerted by the phenyl ring of the carbazole unit onto the double bond responsible for the thermal back reaction. In other words, the thermal stability of photochromism-based optical devices can be greatly improved by adopting an appropriate molecular design.

We produced an optically controllable dual-gate organic field-effect transistor by a simple one-step spin-coating of a mixed solution of photochromic spiropyran (SP) and poly(3-hexylthiophene) (P3HT). Postannealing enhanced polymer chain ordering of P3HT to induce phase separation into an SP-rich lower layer and an SP-free upper layer. These layers worked independently as transistor channels with distinct optical responsivity. The top channel was optically inactive, but the bottom channel was optically active, because of the photoisomerization of SP. These results demonstrate the potential of our technique to produce a multifunctional photoactive organic transistor by a simple process.

This paper describes the interface reactions and diffusion between silver/polypyrrole (Ag/PPy) composite and silicon substrate. This composite material can be used as a novel technique for 3D-LSI (large-scale integration) by the fast infilling of through-silicon vias (TSV). By immersion of the silicon wafer with via holes into the dispersed solution of Ag/PPy composite, the holes are filled with the composite. It is important to develop a layer between the composite and the Si substrate with good diffusion barrier and adhesion characteristics. In this paper, SiOx and two types of SiOxNy barrier layers with various thicknesses were investigated. The interface structure between the Si substrate, the barrier, and the Ag/PPy composite was characterized by transmission electron microscopy. The adhesion and diffusion properties of the layers were established for Ag/PPy composite. Increasing thickness of SiOx proved to permit less Ag to transport into the Si substrate. SiOxNy barrier layers showed very good diffusion barrier characteristics; however, their adhesion depended strongly on their composition. A barrier layer composition with good adhesion and Ag barrier properties has been identified in this paper. These results are useful for filling conductive metal/polymer composites into TSV.

The scaled charge trapping (CT) type silicon on insulator (SOI) FinFET flash memories with different blocking layer materials of Al2O3 and SiO2 have successfully been fabricated, and their electrical characteristics including short-channel effect (SCE) immunity, threshold voltage (Vt) variability, and the memory characteristics have been comparatively investigated. It was experimentally found that the better SCE immunity and a larger memory window are obtained by introducing a high-k Al2O3 blocking layer instead of a SiO2 blocking layer. It was also confirmed that the variability of Vt before and after one program/erase (P/E) cycle is almost independent of the blocking layer materials.

Y. X. Liu, T. Matsukawa, K. Endo, S. O’uchi, J. Tsukada, H. Yamauchi, Y. Ishikawa, W. Mizubayashi, Y. Morita, S. Migita, H. Ota, and M. Masahara National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 2, 1-1-1 Umezono, Tsukuba-shi, Ibaraki 305-8568, Japan. Tel: +81-29-861-3417, Fax: +81-29-861-5170, E-mail: yx-liu@aist.go.jp Three-dimensional (3D) fin-channel devices provide excellent short-channel effect (SCE) immunity thanks to the strong controllability of channel potential by the multiple gates. Therefore, the scaled charge trapping (CT) type FinFET flash memories have actively been developed in the past few years (1-3). Very recently, we have also developed floating gate (FG) type SOI-FinFET flash memories with different gate structures (4, 5), and experimentally confirmed that tri-gate (TG) structure shows the better SCE immunity and a larger memory window than double-gate (DG) structure. As a further study, in this work, we fabricate CT type TG-structured SOI-FinFET flash memories with different gate materials and different blocking layer materials, and comparatively investigate their electrical characteristics. 1. Device Fabrication In the device fabrication, we used (110)-oriented SOI wafers, and the Si-fin channels were fabricated by using orientation dependent wet etching (6). To fabricate TG structure, the SiO2 fin hard-mask layer was removed by RIE. Then, a 4.3-nm-thick tunnel oxide was formed by thermal oxidation, followed by the deposition of a 10-nm-thick nitride (Si3N4) layer by LPCVD. As the blocking layer, a 10-nm-thick Al2O3 layer or a 9-nm-thick SiO2 layer was deposited on the different sample wafers. As the different gate materials, we used n+-poly-Si and PVD-TiN metal. Figure 1(a) shows the SEM image of the fabricated FinFET flash memory with a scaled gate length (Lg) of 26 nm. The cross-sectional STEM images of the fabricated n+-poly-Si gate SONOS, PVD-TiN metal gate MONOS and MANOS with a high-k Al2O3blocking layer are shown in Figs. 1(b), 1(c) and 1(d), respectively. It is clear that uniform and ultrathin Si-fin channels are successfully fabricated thanks to the orientation dependent wet etching. 2. Gate Material Dependent of Memory Property At first, we measured the initial Id-Vg characteristics of the fabricated SONOS and MONOS type FinFET flash memories, and the threshold voltage (Vt) values were evaluated at a constant drain current of Id = 1 mA. It was experimentally found that almost the same sVt is obtained in the SONOS and MONOS devices. This result indicates that Vt variation is independent of gate material. Then, we measured P/E characteristics of the fabricated SONOS and MONOS devices. It was found that a larger memory window is obtained in the MONOS devices than the SONOS ones due to the higher work function of PVD-TiN gate than the n+-poly-Si gate as shown in Fig. 2. The higher gate work function is effective to the suppression of electron back tunneling during erase operation [7]. 3. Blocking Layer Dependent of Memory Property To investigate blocking layer material dependence on the electrical characteristics of the CT type FinFET flash memories, we fabricated MONOS and MANOS type devices with different blocking layers of SiO2 and Al2O3 as mentioned before. The initial Id-Vg characteristics of the fabricated MONOS and MANOS type FinFET flash memories with different Lg values from 26 to 103 nm were measured and the SCE immunity was systematically evaluated. It was found that the smaller Vt roll-off and the better subthreshold slope (S-slope) are observed in the MANOS devices as compared to the MONOS ones due to the high-k effect of Al2O3 in MANOS devices. The P/E characteristics of the fabricated MONOS and MANOS devices were also comparatively investigated. It was found that a significant memory window increment is obtained by introducing an Al2O3 blocking layer instead of the SiO2 one as shown in Fig. 3. This result is reasonable because a high-k Al2O3blocking layer is effective to enhance the electric field across the tunnel oxide layer and to reduce the electric field across itself. Therefore, electron back tunneling from the gate to nitride layer is effectively suppressed during erase operation. As a result, a deep erase and a large memory window are obtained in the MANOS devices than the MONOS ones. It was also confirmed that the fabricated MONOS and MANOS devices can operate over 100 k cycles, and can maintain a reasonable memory window after 10 years. In summary, we have investigated the gate material and blocking layer material dependences on the electrical characteristics of the fabricated CT type FinFET flash memories. It was experimentally found that a high work function metal gate and a high-k blocking layer are very useful to the enhancement of memory window. Acknowledgment: This work was supported in part by the Nanotechnology Project of NEDO, Japan. [1] P. Xuan et al., IEDM Tech. Dig., 609 (2003). [2] M. Spechi et al., IEDM Tech. Dig., 1083 (2004). [3] S-K. Sung et al., Symp. VLSI Tech. Dig., 106 (2006). [4] Y. X. Liu et al., Ext. Abstract, SSDM, 985 (2011). [5] T. Kamei et al., IEEE EDL 33345 (2012). [6] Y. X. Liu et al., IEEE EDL 24484 (2003). [7] C. H. Lee et al., IEDM Tech. Dig., 613 (2003).

Resistive random access memory (ReRAM) has been proposed as a new application for oxide materials. An oxide sandwiched between two metal electrodes shows reversible electric field–induced resistance switching behaviors. Hafnium oxide (HfO2), which is used as a high-k gate insulator, has also shown resistance switching phenomena and been increased interest in the use of HfO2 and related oxides as potential ReRAM materials [1]. For the oxide based ReRAM with the conductive filament formation model, two mechanisms of resistance switching have been proposed. One is the nanoionics model, which comprises the generation and rupture of a metal filament using a metal such as Cu acting as a fast mobile ion in oxides. The other model is that of oxygen vacancy nucleation at the metal/oxide interface. To put the oxide based ReRAM on practical applications, understanding on controls of metal/oxide interface is essentially important. Here, we employed hard x-ray photoelectron spectroscopy (HX-PES) under bias operation to examine the electronic structure of Pt or Cu/HfO2 ReRAM structures in an operating device. HX-PES is a powerful tool for investigating the electronic structure and chemical state of the surface/interface of stacking structures for nanoelectronics devices without any degradation because it has a longer photoelectron mean free path than conventional x-ray photoelectron spectroscopy using Al Kα radiation (hν= 1486.6 eV). The detection depth of HX-PES with an energy of 6 keV is approximately three times deeper than that of conventional XPS, so the photoelectron from a metal/oxide interface, which works as an electrical device, can be detected by HX-PES. With this method, bias-induced compositional changes around the metal/oxide interface during device operation have been directly observed. The interface electronic states of 10-nm-thick Pt or Cu top electrodes/HfO2/Pt structures were measured with HX-PES in the SPring-8 BL15XU undulator beamline. The incident X-ray energy was 5.95 keV. In the case of the Pt/HfO2 interface, applying a forward bias increased the Pt–O bonding peak as shown in Fig 1, indicating evidence of Pt electrode oxidization and oxygen vacancy formation around the interface [2]. In contrast, the application of a bias to the Cu/HfO2 interface reduced the copper oxide bonding state, providing evidence of oxygen reduction and Cu diffusion into the HfO2 layer [3,4]. We achieved direct observation of oxygen migration at the metal/HfO2 interface under device operation, which is the key to controlling the electrical properties of oxide based ReRAM. Based on these results, we demonstrated the control of the switching voltage and the initial conductive filament formation process of the Ta−Nb binary oxide ((TaxNb1−x)2O5) ReRAM structure using a combinatorial method [5]. The relationship between the interface structure and the electrical properties also will be discussed in detail at the presentation.

We attained multilevel manipulation of resonant tunneling in a metal–insulator–semiconductor (MIS) structure, in which heterogeneous molecules of copper hexadecafluorophthalocyanine (F16CuPc) and copper phthalocyanine (CuPc) were embedded in an insulating layer to form a double-tunneling junction. Resonant tunneling was observed in samples with either molecule, revealing that the molecules worked as intermediate electrodes for the tunneling current. The carrier transport was ascribed to resonant tunneling through the energy levels of individual molecules. That is, the threshold voltage of resonant tunneling can be controlled according to the energy levels of the molecules. We achieved multilevel resonant tunneling operation with binary molecules of F16CuPc and CuPc, in which the carriers were injected into the respective molecules at corresponding threshold voltages. Our findings point to a new multilevel operation of resonant tunneling through organic molecules in a practical MIS device structure.

We used hard X-ray photoelectron spectroscopy (HX-PES) to investigate the polarity effect of ZnO, which has Zn terminated (+ polar) and O terminated (− polar) surfaces, on poly(3-hexylthiophene-2,5-diyl) (P3HT)/ZnO photovoltaic structures. HX-PES, which has a longer inelastic mean free path than conventional X-ray photoelectron spectroscopy, revealed that the open circuit voltage (V OC ), estimated from the gap between the highest occupied molecular orbital of P3HT and the conduction band minimum of Zn-polar ZnO, was larger than that of the O-polar ZnO. Although polarity dependence was observed for the electrical structure at the P3HT/ZnO interface, the V OC of the photovoltaic property of Zn-polar ZnO was almost the same as that of O-polar ZnO (~ 0.4 V) due to electron–hole recombination, which degrades the photovoltaic properties at the interface. The HX-PES results also suggested that the recombination could be attributed to the short depletion length of the ZnO surface.

Formation of a polycrystalline thin film from a Prussian blue analogue (PBA) on insulating substrates through a chemical method is reported here. One of the typical PBAs, Ni-Co PBA, K0.4Ni2.8[Co(CN)6]2·nH2O, was selected to demonstrate the growth process. Silicon substrate surface is functionalized through a typical self-assembled monolayer process using aminopropyltrimethoxysilane (APTMS) to form relatively robust interface with PBAs through the coordination bonds with the terminal amino-groups of APTMS. Then, these amino-functionalized silicon wafers are used as anchors for the controlled assembly of homogeneous Ni-Co PBA thin films which shows several kinds of pyramidal structures on the surface. The obtained thin films exhibit paramagnetic properties at room temperature without a negative magnetization.

Electronic states and band bending behavior of SnO2 single crystals grown by physical vapor transport were investigated by combining surface-sensitive soft- and bulk-sensitive hard X-ray photoelectron spectroscopy (PES). The as-grown SnO2 crystals had a higher density of in-gap states relating to oxygen vacancies in comparison with the SnO2 crystal annealed at 1100 °C under oxygen atmosphere. Both samples have similar Fermi level pinning at 0.26 eV below the conduction band minimum at the surface and no surface accumulation layer. The estimated carrier density by PES at the surface of the as-grown and annealed SnO2 crystals were 3.2 × 1017 and 3.2 × 1015 cm−3, respectively.

The effects of the N2 gas flow ratio and the substrate self-bias of reactive sputtering on the polarity of AlN film on various planar sapphire substrates were investigated to obtain a non-polar oriented AlN film. On a c-plane sapphire substrate, substrate self-bias enhanced c-plane AlN growth and Al termination at the surface, as confirmed by X-ray diffraction (XRD) and time-of-flight low-energy atom scattering spectroscopy. In addition, the AlN film deposited at an N2 gas:Ar sputtering gas ratio of 14% with substrate self-bias had high crystallinity with an XRD ω-rocking curve of 17 arcsec for the 0002 diffraction. In contrast, the AlN films on a- and r-plane sapphire substrates had semi-polar and non-polar plane orientations, respectively. However, on the a-plane sapphire substrate, the c-plane-orientated AlN phase was also observed, which was increased under substrate self-bias condition and an N2 flow rate below 30%. Preferable conditions for non-polar AlN growth by reactive sputtering were non-substrate self-bias and a high N2 flow rate of 30% or more.

Surface electronic states and band-bending behavior of a melt-grown (111)-plane In2O3 single crystal were investigated using X-ray photoelectron spectroscopy (XPES). The In2O3 single crystal was cleaved under vacuum conditions below 5 × 10−5 Pa, and loaded to a measurement chamber with a vacuum level of approximately 5 × 10−7 Pa. After cleaving, density reduction of in-gap states relating to oxygen vacancies was confirmed. Nevertheless, the cleaved surface had a surface electron accumulation layer with the surface Fermi level pinned at approximately 0.76 eV above the conduction band minimum. The bulk and surface carrier density were estimated as 3.9 × 1017 and 6.0 × 1019 cm−3 respectively by combining the XPES result and the Poisson–Schrodinger solutions. Scanning nonlinear dielectric microscopy indicated a higher carrier density at the (100) surface than that at the (111) surface, suggesting a crystallographic plane dependence which may originate in defects relating to the dipole and surface instability of the In2O3 surface.

The reaction mechanism of ZrO-based metal resists by extreme ultraviolet (EUV) exposure was investigated using hard X-ray photoelectron spectroscopy, near edge X-ray absorption fine structure spectroscopy, and X-ray diffraction. EUV exposure did not affect the amorphous structure of the metal resist. After EUV exposure, the π* states of the C atom and the σ* states of the O atom of the cell molecules were reacted. Moreover, EUV exposure decomposed the carbonyl species of the cell molecules and forms the high oxidation states of ZrO x . Thus, the metal resist reaction occurred with the decomposition of cell molecules and the formation of ZrO2 by EUV exposure.

We demonstrated optical manipulation of single-electron tunneling (SET) by photoisomerization of diarylethene molecules in a metal-insulator-semiconductor (MIS) structure. Stress is placed on the fact that device operation is realized in the practical device configuration of MIS structure and that it is not achieved in structures based on nanogap electrodes and scanning probe techniques. Namely, this is a basic memory device configuration that has the potential for large-scale integration. In our device, the threshold voltage of SET was clearly modulated as a reversible change in the molecular orbital induced by photoisomerization, indicating that diarylethene molecules worked as optically controllable quantum dots. These findings will allow the integration of photonic functionality into current Si-based memory devices, which is a unique feature of organic molecules that is unobtainable with inorganic materials. Our proposed device therefore has enormous potential for providing a breakthrough in Si technology.

A thin epitaxial CeO2 film was grown on a Cu(111) single crystal in order to investigate the mechanism of resistive memory/switching devices with an ultimately thin high-k dielectric film. A small amount of Pt was deposited on the CeO2 film and the Pt/CeO2/Cu structure was characterized by conductive atomic force microscopy and X-ray photoelectron spectroscopy. It was found that the grown epitaxial CeO2 film was fully oxidized, i.e., the valence of Ce atoms in the film was completely Ce4+. However, after the deposition of a small amount of Pt, it was revealed that Ce atoms were partially reduced to Ce3+ in full thickness of the film. The Pt/CeO2/Cu structure did not show switching behavior in resistance. The observed reduction of CeO2 film is considered to be responsible to the non-switching behavior. The thermodynamics of the reduction of the CeO2 film and the kinetics of oxygen diffusion in the reduced CeO2 film are discussed.

Resistive random access memory (ReRAM) has been proposed as a new application for oxide materials. We have proposed a Cu electrode/dielectric oxide/bottom electrode stack structure as a potential ReRAM material that is compatible with the LSI process. Control of the switching voltage and the initial conductive filament formation process is beneficial for actual applications. To control the switching property by controlling the valence state of metals, we investigated the Ta-Nb binary oxide ((TaxNb1-x)2O5) system as a dielectric oxide layer using a combinatorial method. A combinatorial pulsed laser deposition method was used to fabricate the (TaxNb1-x)2O5 system systematically on a Pt/Si substrate. X-ray photoelectron spectroscopy revealed defect formation relating to Ta and the compensation of oxygen vacancies caused by a change in the valence number of Nb. As the Ta content decreased, there were a decrease in the threshold voltage of the low resistive state and an enhancement of the leakage current, meaning that the switching properties can be controlled by controlling the (TaxNb1-x)2O5 system.

Composite of metal and conducting polymer is expected for the electrical application by the use of their advantages. The purpose of this research was to reveal photo-electrochemical deposition behavior of metal, which is important to control the formation rate and the composite’s structure obtained by simultaneous metal deposition and polymerization under the photo-irradiation. Cathodic polarization curves for silver deposition on polypyrrole film with different substrates under UV irradiation were compared in addition to the electrical resistance of the polypyrrole and the substrate. Morphology of silver deposition on polypyrrole was characterized by microscopic observation. The experimental results showed that photo introduction to polypyrrole upon silver deposition enhanced the deposition rate to 24 times at maximum.

GaN films with single-crystalline and polycrystalline structures were deposited by metalorganic chemical vapor deposition (MOCVD) on (111) and (100) MgAl2O4 substrates modified by chemical etching and thermal passivation. The oriented GaN films on the as-processed (111) MgAl2O4 substrate revealed broad visible emission band bands at 3.2 eV and a sharp luminescence peak centered at 1.8 eV in room temperature cathodoluminescence measurements, which can be attributed to the recombination of donor–acceptor pairs and GaN-related emission, respectively. Field emission (FE) measurements demonstrated that the oriented nanostructured 150 nm-thick GaN film on the as-processed (111) MgAl2O4 substrate has an ultralow turn-on-field of 4.29 V μm−1 at 10 nA cm−2 and a stable emission of 0.028 mA cm−2 with 5% current density fluctuation for 22 h without any degradation. Compared to GaN films on as-processed (100) MgAl2O4 substrate, the mechanism for the improved performance in optical and FE properties of the GaN film on as-processed (111) MgAl2O4 substrate has been investigated in detail.

For a computing process such as making a decision, a software controlled chip of several transistors is necessary. Inspired by how a single cell amoeba decides its movements, the theoretical 'tug of war' computing model was proposed but not yet implemented in an analogue device suitable for integrated circuits. Based on this model, we now developed a new electronic element for decision making processes, which will have no need for prior programming. The devices are based on the growth and shrinkage of Ag filaments in α-Ag2+δS gap-type atomic switches. Here we present the adapted device design and the new materials. We demonstrate the basic 'tug of war' operation by IV-measurements and Scanning Electron Microscopy (SEM) observation. These devices could be the base for a CMOS-free new computer architecture.

With progressive downsizing of semiconductor devices, conducting polymers are a promising candidate for Ohmic contacts because of their variable size and work function. In order to optimize the polymer structure, it is important to evaluate the Fermi level of the polymer joined with semiconductor because that depends on the polymer structure and surface state of semiconductor. In this study, polypyrrole as a conducting polymer was formed through photo-electrochemical reaction on single crystal TiO 2 as the n-type semiconductor with a well-defined surface. Surface potential of the polypyrrole was measured by Kelvin probe force microscopy. The Fermi level estimated from the surface potential was homogeneous and independent on the morphology of polypyrrole, determined by the balance of the charge density between the polypyrrole layer and the TiO 2 substrate. The Fermi level was changed 0.25 eV with the amount of polypyrrole formed on TiO 2 .

We investigated the new materials applicable for the field effect passivation layer in crystalline Si solar cells, ZrO2-Al2O3 and ZrO2-Y2O3 binary systems, by using combinatorial synthesis method. As-deposited samples indicated hysteresis curves and flat band-voltage (VFB) shifts at capacitance-voltage (C-V) measurements. After oxygen gas annealing (OGA) at 700 oC for 5min, an improvement of the hysteresis and a positive shift of VFB were observed. OGA process influenced defects density related to decreasing oxygen vacancy. OGA processed ZrO2 incorporated with 20 % Al2O3 and 15 % Y2O3 structures showed the maximized negative fixed charge of -5.8 × 1012 cm-2 and -7.8 × 1012 cm-2 in each system, respectively, suggesting that the ZrO2 based alloy systems were revealed to be the promising material for the passivation in the solar cell application.

We investigate Vfb behavior of (TaC)1-xAlx gated HfO2 MOS capacitors as a function of post metal annealing (PMA) temperature. The positive Vfb shift appears in PMA temperature at above 700 °C, while the negative Vfb shift occurs at below 600 °C. At below 600 °C, the effective work function (φm,eff) of gate electrode becomes lower by increasing Al atoms with a low work function. We found that the positive Vfb shift occurs dominantly due to the φm,eff change induced by Al diffusion from gate electrode at 700 and 800 °C. At above 900 °C, Al atoms reach to the HfO2/SiO2 interface and form the AlOx layers, and results in positive Vfb shift due to the bottom interface dipole. We can divide into two components of φm,eff change of gate electrode and the bottom interface dipole due to AlOx layer as a function of PMA temperature.

We investigated flatband voltage (Vfb) behavior for several Hf-based high-k dielectrics, including HfO 2 , Mg-, and La-incorporated HfO 2 , HfSiO x , and Mg-, La-, and N-incorporated HfSiO x , during the reduction (forming gas annealing: FGA) and oxidation annealing (ODA) processes. A negative Vfb shift appeared in all high-k dielectrics as the FGA temperature increased. In contrast, a positive Vfb shift was observed after the introduction of additional oxygen into the high-k layer during ODA. The oxygen diffusion coefficient (D) values of all samples were estimated using Fick's law. The results showed that the D value of the HfO 2 dielectric was five times as large as that of the HfSiO x dielectric in ODA at 400 °C. Furthermore, the Mg-, La-, and N- incorporated high-k dielectrics exhibited a larger D value compared with the pure high-k dielectrics. These results strongly suggest that the ionicity of high-k dielectrics, which we attribute to a large positive Vfb shift, enhances oxygen diffusion in the high-k layer.

We have demonstrated resistance switching using polycrystalline HfO2 film with a Cu top electrode for nonvolatile memory applications and revealed the Cu diffusion into the HfO2 layer during the filament formation process. Resistive switching was clearly observed in the Cu/HfO2/Pt structure by performing a current–voltage measurement. The current step from a high-resistive state to a low-resistive state was of the order of 103–104 Ω, which provided a sufficient on/off ratio for use as a switching device. The filament formation process was investigated by employing hard x-ray photoelectron spectroscopy under bias operation. The application of a bias to the structure reduced the Cu2O state at the interface and the intensity ratio of Cu 2p3/2/Hf 3d5/2, providing evidence of Cu2O reduction and Cu diffusion into the HfO2 layer. These results also provide evidence that the resistance switching of the Cu/HfO2/Pt structure originates in a solid electrolyte (nanoionics model) containing Cu ions.

Thiols and carboxylic acids are important molecules for the anchor of Self-Assemble Monolayer (SAM) on metal surface in organic devices. In order to consider whether carboxylate or thiolate adsorbs on various metals, adsorption energies of methanthiolate and acetate on various metals were thermodynamically calculated using basic quantities of formation enthalpies of metal oxides (Hf(MxOy)) and metal sulfide (Hf(MxSy)). The calculations were carried out for the adsorption on clean, O adsorbed, and OH adsorbed surface. The results suggested that methanethiolate adsorbs on all clean metals, and on O and OH adsorbed metals except Ti and Al (the high Hf(MxOy) metals). On the other hand, acetate adsorbed on all O and OH covered metals, and the clean metals except Au, Ag and Pt (the low Hf(MxOy) metals). As the modification of electrodes using SAM is carried out under atmospheric and liquid conditions, it is considered that thiols prefer the adsorption on the low Hf(MxOy) metals to the high Hf(MxOy) metals, on the contrary, carboxylic acids prefer the adsorption on the high Hf(MxOy) metals to the low Hf(MxOy) metals.

An elemental species that bonds oxide and metal at the interface of electronic devices is crucial to the electric properties of the devices. In this study, interface between alumina and metal in general is discussed from a viewpoint of thermodynamics. By introducing a concept of chemical equilibrium and developing a new way of estimating bonding energy at the interface, a novel numerical formula to predict a stable interface bonding species at a metal/alumina interface is proposed. The effectiveness of the formula was examined by experimental results in references. It was revealed that the prediction by the formula agreed quite well with the results reported in the references. The formula uses only basic quantities of pure elements and the formation enthalpy of oxides. Therefore it can be applied for most of metals in the periodic table and is useful for material screening in developing interfaces with particular functions.