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Solid oxide fuel cells (SOFCs), which have the highest power-generation efficiency among generators, are key in achieving a low-carbon society. To reduce the cost of an SOFC system including mounting cost, thereby, expand its application, we have been developing a thin-film SOFC suitable for low-temperature operations. Since the anode, solid-electrolyte, and cathode layers are formed by sputtered thin films, the internal resistance of the cell decreases; thus, the operating temperature can be lowered [1, 2]. Figure 1 shows a cross-sectional micrograph of the developed SOFC. In this study, nanoporous anodic aluminum oxide (AAO) was used as a support substrate [3, 4, 5]. The pore diameter was 55 nm and thickness was 100 μm. On the AAO substrate, a stack of dense (70 nm) and porous-platinum (80 nm) layers was deposited for the anode. Pores were formed in the dense platinum layer because the surface of the underlying AAO support substrate has 55-nm pores. A dense yttria-stabilized zirconia (YSZ) was used for the solid electrolyte layer (290 nm). The density of the YSZ layer is significant for inhibiting both gas and electron/hole leakage between the anode and cathode sides. Reactive sputtering by using a metal Zr84-Y16 target under a DC bias condition was key to deposit the dense YSZ layer on the porous-platinum anode layer. The interfacial layer (40 nm) of gadolinia-doped ceria (GDC) was deposited on the YSZ layer. The cathode layer (20 nm) of GDC-platinum composite material was then deposited on the interfacial layer. The characteristics of our SOFC was measured at 453°C, as shown in Fig. 2. The air was flowed to the cathode, and wet 3%-hydrogen of nitrogen base was flowed to the anode. An open circuit voltage of 1.049 V and output power density of 203 mW/cm2 were achieved using 3% hydrogen. At the cathode side, the polarization resistance was reduced by forming a gadolinium-doped ceria layer at the interface [5]. In addition, the GDC-platinum cathode was found to reduce the polarization resistance compared to the porous platinum cathode. At the anode side, the hydrogen diffused through the pores of the AAO substrate and reached the anode layer of the SOFC. The triple-phase boundaries formed among gas-, porous-anode-, and solid-electrolyte phases arguably enhanced the performance of the anode. The water vapor produced at the anode side diffused through the pores of the AAO and joined the exhaust gas. The power density at 453°C is expected to increase by using high-concentration hydrogen [6], which we plan to demonstrate for future study. Apart from operation in high-concentration hydrogen, our SOFC has another application. The experimental results indicate that our SOFC can generate high power by using the low-concentration hydrogen from hydrous bioethanol even at low temperatures. References [1] A. Evans et al., "Review on microfabricated micro-solid oxide fuel cell membranes," J. Power Sources 194, pp. 119–129 (2009). [2] J. An et al., "Three-Dimensional Nanostructured Bilayer Solid Oxide Fuel Cell with 1.3 W/cm2 at 450°C," Nano Lett. 13, pp. 4551–4555 (2013). [3] S. Oh et al., "High performance low-temperature solid oxide fuel cells with atomic layer deposited-yttria stabilized zirconia embedded thin film electrolyte," J. Mater. Chem. A 6, pp. 7401–7408 (2018). [4] S. Hong et al., "Single-chamber fabrication of high-performance low-temperature solid oxide fuel cells with grain-controlled functional layers," J. Mater. Chem. A 5, pp. 2029–2036 (2017). [5] S. Hong et al., "Grain-Controlled Gadolinia-Doped Ceria (GDC) Functional Layer for Interface Reaction Enhanced Low-Temperature Solid Oxide Fuel Cells," ACS Appl. Mater. Interfaces 11, pp. 41338–41346 (2019). [6] G. DiGiuseppe and L. Sun, “On the Identification of Impedance Spectroscopy Processes of an SOFC Under Different Hydrogen Concentrations,” J. Fuel Cell Sci. Technol. 9, 051004 (2012). Figure 1

We developed a 16 x 8 quantum dot array and CMOS circuit hybrid chip (Q-CMOS). By optimizing the transistor design of Q-CMOS formed by fully depleted (FD)-SOI, it is possible to selectively control each of 16 x 8 quantum dots, and obtained characteristics of quantum dot variation for the first time. Due to the mesoscopic effect, the variation in the characteristics of the quantum dots is larger than the threshold voltage variation of the transistors. Thus, we have obtained an important finding that it is necessary to suppress the variability in order to realize a large-scale quantum computer. We have also confirmed that the characteristics of the quantum dots change depending on the applied gate voltages.

We have developed a SiC-FET-type gas sensor that enables highly sensitive NO detection in high-temperature exhaust gas. The gate of the FET is a gas detection layer consisting of yttria-stabilized zirconia, nickel oxide, and platinum, which are deposited on the SiC substrate. The threshold voltage of the FET depends on the NO concentration. Experimental results demonstrate that the FET-type sensor can detect NO concentration less than 1 ppm, thus meeting the specifications required to satisfy the strict regulations for exhaust gas in the next generation.

Low dimensional strongly correlated electron systems exhibit a variety of exotic phenomena such as fractional quantum Hall effects, high-temperature superconductivity, and topological phase transitions. However, a problem in modern condensed-matter physics is the difficulty to compare theories with experiments, because of the absence of an ideal experimental system whose properties can be controlled in a systematic way. Here we show a state-of-the-art silicon technology can provide a platform to investigate a one-dimensional quantum system, where various theoretical predictions are available on the basis of mathematically rigid models. We have found unusual transport properties in a field-effect-transistor with a wide and short hole-channel under strong electric fields at low temperatures. By gate-induced doping in the transistor, we discovered new current plateaus and negative differential conductances against drain voltages. We have also found anomalous gate leakage currents which increases upon reducing temperatures and reducing the external electric fields. This provides evidence of the broken symmetry of quantum dipoles formed at the gate interface, which increases local electric fields coming from molecular mean-fields. We obtained phase diagrams of the field-induced phase transitions, which will be correlated with a one-dimensional quantum dipole model.

Amorphous thin Ge 2 Sb 2 Te 5 films were deposited by MOCVD (metal organic chemical vapor deposition) on three-dimensional structures. Ammonium gas, used as a reactant, reduced the deposition temperature to 150 °C, which is lower than that of metal-organic precursors. Introducing nitrogen and hydrogen radicals made by decomposition of the ammonium gas further reduced the growth temperature. The lowest growth temperature producing a realistic growth rate was 100 °C. Phase-change memory cells made of MOCVD-grown films were confirmed to have operation and reliability characteristics as good as those of conventional cells made of sputter-deposited films.

We discovered anomalous transport properties in a conventional Si based Metal-Oxide-Semiconductor Field-Effect-Transistor with a wide and narrow hole-channel at low temperatures. We found the quantum dipole formed at the thin gate interface is responsible for the phase transition. We discuss its potential to use for a quantum simulator as a test bed to examine various theoretical concepts in condensed-matter physics.

The Random Telegraph Noise (RTN) in an advanced Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) is considered to be triggered by just one electron or one hole, and its importance is recognised upon the aggressive scaling. However, the detailed nature of the charge trap remains to be investigated due to the difficulty to find out the exact device, which shows the RTN feature over statistical variations. Here, we show the RTN can be observed from virtually all devices at low temperatures, and provide a methodology to enable a systematic way to identify the bias conditions to observe the RTN. We found that the RTN was observed at the verge of the Coulomb blockade in the stability diagram of a parasitic Single-Hole-Transistor (SHT), and we have successfully identified the locations of the charge traps by measuring the bias dependence of the RTN.

New methods were studied to reduce response time and threshold voltage drift of the FET-type hydrogen sensor. The advantages of the Pt-Ti-O gate over other sensor gate materials were demonstrated. Extending Langmuir's dissociative adsorption theory to non-equilibrium states enabled us to reduce the response time, and the negative gate bias operation with P-FET-type sensor reduced the drift. Thus, we successfully achieved both a response time of 0.8 s and high drift immunity.

The scaling of Silicon (Si) technology is approaching the physical limit, where various quantum effects such as direct tunnelling and quantum confinement are observed, even at room temperatures. We have measured standard Complementary Metal-Oxide-Semiconductor Field-Effect-Transistors (CMOSFETs) with wide and short channels at low temperatures to observe single electron/hole characteristics due to local structural disturbances such as roughness and defects. In fact, we observed Coulomb blockades in sub-threshold regimes of both {\it p}-type and {\it n}-type Si CMOSFETs, showing the presence of quantum dots in the channels. The stability diagrams for the Coulomb blockade were explained by the potential minima due to poly-Si grains. We have also observed sharp current peaks at narrow bias windows at the edges of the Coulomb diamonds, showing resonant tunnelling of single carriers through charge traps.

We have found a systematic way to identify the bias conditions to observe the Random-Telegraph-Noise (RTN) in advanced Metal-Oxide-Semiconductor Field-Effect-Transistors (MOSFETs). We measured a p-type MOSFET at 2K, and found narrow bias conditions to observe the RTN presumably caused by charge trapping and de-trapping, which were only observed at low temperatures. It will pave the way to address the nature of a trap, which will be useful to understand the mechanism of RTN to secure the reliability.

A resistive-switching solid-state brain-neocortex-like device for advanced non-volatile logic applications was developed. This device can be used as a reconfigurable logic device that is operated by electrically connecting and disconnecting pairs of electrodes. This paper reports for the first time the experimental evaluation results of a three-terminal test element group as the unit for a solid state brain neocortex-like device. The solid-state brain-neocortex-like device was experimentally evaluated as unit in a three-terminal test element group. The evaluation results show that the neocortex-like reconfigurable switching, in particular, fringe-electric-field-induced switching is possible in the device.

A 4-Gb AG-AND flash memory was fabricated by using a 90-nm CMOS technology. To reduce cell size, an inversion-layer-bit-line technology was developed, enabling the elimination of both shallow trench isolations and diffusion layers from the memory cells. The inversion-layer-bit-line technology combined with a multilevel cell technique achieved a bit area 2F 2 of 0.0162μm 2 , resulting in a chip size of 126mm 2 . Both an address and temperature compensation techniques control the resistance of the inversion-layer local bit line. Source-side hot-electron injection programming with self-boosted charge, accumulated in inversion-layer bit lines under assist gates, reduces the dispersal of programming characteristics and also reduces the time overhead of pre-charging the bit lines. This self-boosted charge-injection scheme achieves a programming throughput of 10MB/s.

Threshold-voltage (Vth) fluctuation due to random telegraph signal (RTS) in flash memory was observed for the first time. A large amount of data of Vth fluctuation was acquired by using a 90-nm-node memory array, and it was confirmed that a few memory cells have large RTS fluctuation exceeding 0.2 V. It was found that program-and-erase cycles increase Vth amplitude in a flash memory. It was also found by simulation and measurement that tail-bits are generated due to RTS in multilevel flash operation. The amount of Vth broadening due to the tail-bits was estimated to become larger as the scaling of memory cells advances and reaches more than 0.3 V in the 45-nm node. These results thus demonstrate that RTS will become a prominent issue in designing multilevel flash memory in the 45-nm node and beyond.

We developed a selective-capacitance constant-charge-injection programming (CCIP) scheme to achieve high programming throughput in multilevel assist-gate (AG)-AND flash memories. In the conventional CCIP scheme, only one type of capacitance for storing programming charge was used for all levels of multilevel cells. The proposed scheme utilized multiple types of capacitance to minimize the programming time of all levels by using optimized capacitance values for each V th level. In 4-Gbit AG-AND flash memories, a local bit line capacitance is utilized for mid-level programming, and the sum of local and global bit line capacitance is utilized for top-level programming. In addition, we developed a verify-less programming scheme which reduces top-level programming time because it is not necessary to verify the top-level of multilevel cells in AND flash memory architecture. A programming throughput of 10MB/s is achieved using the proposed schemes. This is 1.6 times faster than the throughput with conventional CCIP.

A high-programming-throughput three-dimensional (3D) vertical chain-cell-type phase-change memory (VCCPCM) array for a next-generation storage device was fabricated. To increase the number of write cells at one time by reducing resistance of bit and source lines, the VCCPCM array includes plate electrodes and double-gate vertical-chain-selection MOSs with 5-nm-thick poly-Si channels. In addition, CO 2 laser annealing enhances the drivability of a poly-Si cell MOS to 680 µA/µm to suppress energy loss in the cell MOS. In addition to write throughput, erase throughput is increased by erasing memory cells in a “bundle” by channel heating (called “bundle erase”). GeSbTe CVD with high uniformity is also developed.

A 1-Gb AG-AND flash memory has been fabricated using 0.13-μm CMOS technology, resulting in a cell area of 0.104 μm 2 and a chip area of 95.2 mm 2 . By applying constant-charge-injection programming and source-line-select programming, a fast page programming time of 600μs is achieved. The four-bank operation attains a fast programming throughput of 10 MB/s in multilevel flash memories. The compact SRAM write buffers reduce the chip area penalty. A rewrite throughput of 8.3 MB/s is achieved by means of the RAM-write operation during the erase mode.

Constant-charge-injection programming (CCIP) has been proposed as a way to achieve high-speed multilevel programming in flash memories. In order to achieve high programming throughput in multilevel flash memory, programming method must provide: 1) high-speed cell-programming; 2) high programming efficiency; and 3) highly uniform programming characteristics. Conventional source-side channel-hot-electron injection (SSI) programming realizes both fast cell-programming and high programming efficiency, but the large cell-to-cell variation in programming speed with SSI is a problem. CCIP reduces the characteristic variation of SSI programming and satisfies all of the above requirements. By applying CCIP to 2-bit/cell AG-AND flash memory, the high programming throughput of 10.3 MB/s is obtained with no area penalty. This is 1.8 times faster than the throughput with conventional SSI programming.

BaCuSi 2 O 6 can be regarded as an almost ideal realization of an S = 1 2 system of weakly interacting spin dimers with spin-singlet ground state and gapped excitation spectrum. We argue that the fine structure observed in low-temperature EPR spectra of BaCuSi 2 O 6 is a fingerprint of triplet excitations (excitons). Analyzing the angular dependence of the exciton modes allows us to precisely calculate the zero-field splitting within the triplet states and, correspondingly, the anisotropy parameter, D = 0.07 cm - 1 . The proposed procedure can be applied for studying anisotropy effects in a large number of S = 1 2 gapped quantum antiferromagnets with dimerized or alternating spin structure.

We have measured the magnetic susceptibilities of single crystals of ${\mathrm{Cu}}_{1\ensuremath{-}x}{\mathrm{Zn}}_{x}{\mathrm{GeO}}_{3}$ with extremely low Zn concentration $(x)$ lower than $x=5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ at very low temperatures to investigate the spin-Peierls and antiferromagnetic transitions. The results show that the undoped ${\mathrm{CuGeO}}_{3}$ has no antiferromagnetic phase down to 12 mK and there exists an antiferromagnetic long-range order with the easy axis along the $c$ axis for $x$ down to $1.12(2)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}.$ The minimum observed N\'eel temperature was 0.0285 K for the $x=1.12(2)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ sample. From the concentration dependence of the N\'eel temperature it is concluded that there is no critical concentration for the occurrence of the antiferromagnetic long-range order. This indicates that the dimerization sustains the coherence of the antiferromagnetic phase of the spin polarization in impurity-doped systems and is consistent with the theory of the impurity-doped spin-Peierls system. The temperature dependence of the susceptibilities at $Tg{T}_{N}$ of all samples indicates that the magnetic correlations between localized spins are enhanced by a relatively large interchain interaction of ${\mathrm{CuGeO}}_{3}.$

We study a spin-Peierls gap and a bound and a resonant states of two magnetic excitations in Cu 1- x Zn x GeO 3 and CuGe 1- y Si y O 3 . Breakdown of the selection rule in the doped samples enables us to observe the spin-Peierls gap excitation in the first-order Raman process. It is found that this excitation shifts to lower frequency and merges into the tail of the elastic scattering together with its line broadening with increasing dopant concentration. The bound state of a particle-hole pair is observed just below the bottom of the second-order Raman band in pure CuGeO 3 . It changes into a resonant state and disappears rapidly as the concentration of the dopant is increased, owing to the weakening of attractive interaction and the extreme increase of the dampings of the magnetic excitations. These features are demonstrated theoretically by using Green's function.

We report an observation of a commensurate-incommensurate phase transition in the Dzyaloshinskii-Moriya spiral antiferromagnet Ba${}_{2}{\mathrm{CuGe}}_{2}{\mathrm{O}}_{7}$. The transition is induced by an external magnetic field applied along the $c$ axis of the tetragonal structure, i.e., in the plane of spin rotation. Bulk magnetic measurements and neutron-diffraction experiments show that the transition occurs in a critical field ${H}_{c}\ensuremath{\approx}2.1$ T. Experimental results for the period of the magnetic structure and magnetization as functions of magnetic field are in quantitative agreement with our exact analytical solution for Dzyaloshinskii's model of commensurate-incommensurate transitions in spiral magnets.

The magnetic structure of Ba{sub 2}CuGe{sub 2}O{sub 7} is investigated by neutron diffraction in magnetic fields applied along several directions in the (a,b) plane of the crystal. In relatively weak fields, H{approx_lt}0.5 T, the propagation vector of the spin spiral rotates to form a finite angle with the field direction. This angle depends on the orientation of {bold H} itself. The rotation of the propagation vector is accompanied by a reorientation of the plane of spin rotation in the spiral. The observed behavior is well described by a continuous-limit form of a free-energy functional that includes exchange and Dzyaloshinskii-Moriya interactions, as well as the Zeeman energy and an empirical anisotropy term. {copyright} {ital 1997} {ital The American Physical Society}

Comprehensive neutron-scattering studies were carried out on a series of high-quality single crystals of Cu${}_{1\ensuremath{-}x}$Zn${}_{x}$GeO${}_{3}$. The Zn concentration $x$ was determined for each sample using electron probe microanalysis. The measured Zn concentrations were found to be 40--80 % lower than the target values. Nevertheless, the measured concentrations cover a wide range which enables a systematic study of the effects due to Zn doping. We have confirmed the coexistence of spin-Peierls (SP) and antiferromagnetic (AF) orderings at low temperatures and the measured phase diagram is presented. Most surprisingly, long-range AF ordering occurs even in the lowest available Zn concentration $x=0.42%$, which places important constraints on theoretical models of the AF-SP coexistence. Magnetic excitations are also examined in detail. The AF excitations are sharp at low energies and show no considerable broadening as $x$ increases, indicating that the AF ordering remains long ranged for $x$ up to 4.7%. On the other hand, the SP phase exhibits increasing disorder as $x$ increases, as shown from the broadening of the SP excitations as well as the dimer reflection peaks.

We report muon spin relaxation measurements of the doped spin-Peierls system $({\mathrm{Cu}}_{1\ensuremath{-}x}{\mathrm{Zn}}_{x})\ensuremath{-}({\mathrm{Ge}}_{1\ensuremath{-}y}{\mathrm{Si}}_{y}){\mathrm{O}}_{3}$. Spontaneous muon spin precession in zero applied field was observed, confirming the presence of antiferromagnetic order in this series of compounds. In contrast to usual antiferromagnets, muon spin precession is accompanied by a relaxation signal indicating a large spatial inhomogeneity of the ordered moment size. Assuming an exponential decay of the moment size away from the doping centers, we estimated a decay length of $\ensuremath{\xi}\ensuremath{\sim}10$ lattice units along the chain. We suggest that both Zn and Si doping induces the same maximum moment size around the doping center.

Bulk magnetic measurements and inelastic neutron scattering were used to investigate the magnetic properties of ${\mathrm{BaCuSi}}_{2}$${\mathrm{O}}_{6}$, a quasi-two-dimensional antiferromagnet with a square-lattice bilayer structure. The compound was shown to have a spin-singlet dimerized ground state with a gap \ensuremath{\Delta}\ensuremath{\approx}4.5 meV in the magnetic excitation spectrum. The dispersion of the gap modes was measured and found to be temperature dependent and totally suppressed at temperatures higher than the characteristic gap energy. The observed excitations are analogous to magnetoexcitons in light rare-earth compounds, but are an intrinsic property of a simple Heisenberg Hamiltonian for the S=1/2 magnetic bilayer. The behavior is discussed in comparison to that of related systems, in particular, ${\mathrm{Cs}}_{3}$${\mathrm{Cr}}_{2}$${\mathrm{Br}}_{9}$.

We have measured the temperature dependence of low-frequency Raman spectra in ${\mathrm{CuGeO}}_{3}$, and have observed quasielastic scattering in the (c,c) polarization above the spin-Peierls transition temperature. We attribute this to the fluctuations of the energy density in the spin system. The magnetic specific heat and an inverse of the magnetic correlation length can be derived from the quasielastic scattering. The inverse of the magnetic correlation length is proportional to (T-${\mathrm{T}}_{\mathrm{SP}}$${)}^{1\mathrm{/}2}$ at high temperatures. We compare the specific heat with a competing-J model. This model cannot explain quantitatively both the magnetic specific heat and the magnetic susceptibility with the same parameters. The origin of this discrepancy is discussed.

We introduce our μSR investigations of spin‐gap systems, such as, (1) a 2‐leg spin‐ladder material SrCu2O3, (2) a Haldane material (S=1 spin‐chain) Y2BaNiO5, (3) a spin‐Peierls material CuGeO3, (4) a spin‐chain# material Sr6Ca8Cu24O41. All of these antiferromagnetic spin systems are characterized by a spin‐gap between the singlet ground‐state and the triplet first excited states. In the above‐mentioned materials, we confirmed the absence of magnetic order down to milli‐Kelvin regime, supporting the non‐magnetic feature of the ground‐state. If a spin‐gap system is doped with charges and/or vacancies at the spin site, unpaired spins are induced out of the singlet ground‐state. In some materials, doping completely destroys the singlet ground‐state and induces a bulk magnetic order. We report μSR investigations of doped materials as well, which clarifies the existence/absence of a magnetic order upon doping.

The {ital S}=1/2 Heisenberg antiferromagnet CaCuGe{sub 2}O{sub 6} was studied by inelastic neutron scattering on a powder sample in the temperature range 5{endash}300 K. A sharp symmetric magnetic inelastic peak was observed around {h_bar}{omega}=6 meV, and its {ital q} and temperature dependences were investigated. The absolute values of the energy-integrated magnetic intensity were determined. Despite the fact that from the structural point of view the material has a distinct one-dimensional arrangement of magnetic sites, the experimental results are surprisingly well described by an ensemble of weakly interacting antiferromagnetic dimers, which are composed of pairs of Cu{sup 2+} ions. {copyright} {ital 1996 The American Physical Society.}

Cu 3 WO 6 has a unique structure in which Cu 2+ ( S =1/2) ions are arranged in six-spin rings. Susceptibility measurements imply a spin-singlet ground state with a spin gap. In order to elucidate magnetic excitations, we performed inelastic neutron scattering on a Cu 3 WO 6 powder sample. Two peaks are observed at 11 and 14 meV in energy spectra at low temperatures, indicating singlet-triplet excitations. The gaps are temperature independent. There is almost no dispersion in the magnetic excitations. The intensity around 11 meV decreases rapidly with increasing temperature. Constant-ω scans for the 11 meV peak exhibit an oscillating Q -dependence, which we ascribe to a structure factor of the ring. These results are in qualitative agreement with a simple model of an isolated S =1/2 six-spin ring with first, second and third nearest-neighbor antiferromagnetic exchange interactions.

Magnetizations of spin-Peierls cuprates Cu 1- x Zn x GeO 3 with x =0, 0.005, 0.010, and 0.020 were measured in order to investigate influence of impurities on a magnetic phase. A characteristic change of the magnetization related to a phase transition from dimerized to other phases was seen below a spin-Peierls-transition temperature. The magnetization above 16.0 T shows weak x and temperature dependences. A critical field associated with the phase transition decreases with increasing x . We derived a result that the effects of impurities on the magnetic phase are weaker than on the dimerized phase.

The magnetization was obtained as a function of temperature and magnetic field of a Cu 1− x Zn x GeO 3 single-crystal with x ∼ 0.04. The temperature dependence of the magnetic susceptibility in 0.1 T parallel to the c axis shows a clear cusp around 4.5 K and decreases rapidly below 4.5 K. There is no hysteresis between the data measured in zero-field-cooling and field-cooling processes. The field dependence of the magnetization parallel to the c axis at 2.0 K exhibits an apparent increase around 1.0 T, which corresponds to a spin-flop transition. The temperature and field dependences, the anisotropy, and the absence of the hysteresis undoubtedly prove the occurrence of an antiferromagnetic long-range order below 4.5 K instead of the spin-glass-like transition reported previously. Spins below the transition temperature are ordered almost parallel to the c axis. This is the first report of magnetic long-range order caused by nonmagnetic impurities.

Recently, a spin-Peierls transition was discovered in CuGeO3, which is the first inorganic compound with this type of transition [H. Hase, I. Terasaki and K. Uchinokura, Phys. Rev. Lett. 70 (1993) 3651]. As is the case for organic spin-Peierls materials, CuGeO3 has a magnetic phase in high magnetic fields. High-field magnetization was measured in pulse and steady magnetic fields. AC susceptibility measurements were also performed. The existence of the magnetic phase was confirmed. Effects of substitution of Zn for Cu were also investigated.

A three-dimensional (3-D) vertical chain-cell-type phase-change memory (VCCPCM) for next-generation large-capacity storage was developed. The VCCPCM features formation of memory holes in multi-layered stacked gates by using a single mask and a memory array without a selection transistor. As a result of this configuration, the number of process steps for fabricating the VCCPCM is reduced. The excellent scalability of the VCCPCM's new phase-change material makes it possible to reduce the cell size beyond the scaling limit of flash memory. In addition, a poly-silicon selection diode makes it possible to reduce the cell factor to 4F2. Consequently, relative cost of the VCCPCM compared to 3-D flash memory is reduced to 0.2.

Phonons and magnetic excitations were studied as a function of temperature in the spin-Peierls phase of an inorganic material ${\mathrm{CuGeO}}_{3}$ by Raman scattering. All of the phonon Raman peaks observed at room temperature can be assigned on condition that the crystal symmetry is ${\mathit{D}}_{2\mathit{h}}^{5}$(Pbmm). Five peaks intrinsic to the spin-Peierls state were observed at 30, 105, 228, 370, and 818 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ in the spin-Peierls phase. The temperature dependence of the frequency of the 30-${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ peak agrees approximately with 2\ensuremath{\Delta}(T), where \ensuremath{\Delta}(T) is the spin-Peierls gap. The Raman spectrum between 0 and 300 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ was compared with the density of states of the magnetic excitons. The 105- and 228-${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ peaks were assigned to two-magnetic-exciton Raman scattering. The peaks at 370 and 818 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ were assigned to one-phonon Raman scattering of the folded ${\mathit{A}}_{\mathit{g}}$ modes, which occurs due to the formation of a dimerization in the spin-Peierls phase.

Electron spin resonance (ESR) was investigated on the spin-Peierls system CuGeO3 and antiferromagnetic Ba2Cu3O4Cl2 at X-band and far-infrared regions (FIR). The g-values of CuGeO3 were determined to be 2.17, 2.26 and 2.11 for H∥a, H∥b and H∥c-axes, respectively. The temperature dependence of FIR and X-band ESR spectra of CuGeO3 clarified the difference of character among uniform, dimerize and high-field magnetic phases. In the Ba2Cu3O4Cl2 system, the resonance field for H∥c drastically changes around 30K, and antiferromagnetic resonance (AFMR) was observed at 5 K.

We measured the magnetic-field dependence of the magnetizations of the spin-Peierls cuprates Cu 1− x Zn x GeO 3 with the x = 0, 0.005, 0.010 and 0.020. The characteristic change of the magnetization was observed and it is associated with the phase transitions from the dimerized to the other phases. When the magnetic phase diagram is expressed by the reduced variables gH /2 T SP (0) and T / T SP (0), the phase diagrams of Cu 1− x Zn x GeO 3 qualitatively agree with those of organic spin-Peierls systems and the theoretical one.

We have observed the nuclear quadrupole resonance (NQR) of Cu in the spin-Peierls system CuGeO 3 . The NQR signals have been observed at 34.23±0.02 MHz for 63 Cu and 31.66±0.02 MHz for 65 Cu at 4.2 K under zero external field. These signals persist down to 1.3 K with neither line splitting nor broadening due to the internal magnetic field. This fact indicates there is no long-range order of Cu spins. The 63 Cu nuclear spin-lattice relaxation rate 63 (1/ T 1 ) rapidly drops below 15 K which clearly demonstrates an opening of the energy gap in the excitation spectrum. However, no anomaly was detected in the Cu NQR frequency at the transition temperature. It was also found that 63 (1/ T 1 ) above 15 K smoothly extrapolates to a finite value at 0 K. This may suggest the spin dynamics in the paramagnetic state is described in terms of the one-dimensional antiferromagnetic Heisenberg model with S =1/2.

The magnetic susceptibilities of polycrystalline ${\mathrm{Cu}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Zn}}_{\mathit{x}}$${\mathrm{GeO}}_{3}$ were measured to study the effects of nonmagnetic impurities on the spin-Peierls transition. The transition temperature drastically reduces upon Zn doping and the spin-Peierls state collapses around x=0.03. The Zn doping causes another phase transition in the samples with 0.02\ensuremath{\le}x\ensuremath{\le}0.08, which proved to be spin-glass-like. The present Letter provides the first study of the spin-Peierls system with impurities.

This paper describes for the first time the observation of the threshold voltage (Vth) fluctuation due to random telegraph signal (RTS) in flash memory. We acquired large-scale data of Vth fluctuation and confirm the existence of the tail bits generated by RTS. The amount of Vth broadening due to the tail bits becomes larger as the scaling advances, and reaches to more than 0.3 V in 45-nm node. Thus the RTS becomes prominent issue for the design of multilevel flash memory in 45-nm node and beyond

$\mathrm{Ba}\mathrm{Cu}{\mathrm{Si}}_{2}{\mathrm{O}}_{6}$, a $S=\frac{1}{2}$ quantum antiferromagnet with a double-layer structure of ${\mathrm{Cu}}^{2+}$ ions in a distorted planar-rectangular coordination and with a dimerized spin singlet ground state, has been studied by means of the electron paramagnetic resonance technique. It is argued that multiple absorptions observed at low temperatures are intimately related to a thermally activated spin-triplet exciton superstructure, which appears to be a characteristic feature of low-dimensional anisotropic spin-$\frac{1}{2}$ systems with the dimerized spin-singlet ground state. We showed that analysis of the angular dependence of exciton modes could be used for accurate estimation of anisotropy parameters in $\mathrm{Ba}\mathrm{Cu}{\mathrm{Si}}_{2}{\mathrm{O}}_{6}$; the procedure can be applied for a large number of $S=\frac{1}{2}$ quantum antiferromagnets. In addition, the temperature dependence of EPR intensity and linewidth in $\mathrm{Ba}\mathrm{Cu}{\mathrm{Si}}_{2}{\mathrm{O}}_{6}$ has been studied and discussed.

We measured and analyzed the transport properties of single-crystal ${\mathrm{NaCo}}_{2}{\mathrm{O}}_{4}$, which is a metallic transition-metal oxide consisting of a two-dimensional triangle lattice of Co. Reflecting the crystal structure, the resistivity is highly anisotropic between in- and out-of-plane directions, and the in-plane resistivity is as low as 200 $\ensuremath{\mu}\ensuremath{\Omega}$ cm at 300 K. Most strikingly, the in-plane thermoelectric power of ${\mathrm{NaCo}}_{2}{\mathrm{O}}_{4}$ is about 100 $\ensuremath{\mu}$V/K at 300 K, which is nearly ten times larger than that of typical metals. The large thermoelectric power and the low resistivity suggest that ${\mathrm{NaCo}}_{2}{\mathrm{O}}_{4}$ is a potential thermoelectric material.

The quasi-dimensional square-lattice antiferromagnet Ba2CuGe2O7 was studied by neutron scattering and bulk magnetic techniques. An incommensurate magnetic spiral structure with the propagation vector (1 + ξ,ξ,0) (ξ = 0.027) was observed below TN = 3.26 K. The spin dynamics can be adequately described by conventional spin-wave theory with two exchange constants: nearest-neighbor in-plane antiferromagnetic coupling J1 ≈ 0.48 meV and interplane ferromagnetic interaction J3 ≈ 0.013 meV. This set of exchange parameters apparently fails to explain the spiral order. The non-centrosymmetric crystal structure suggests that the incommensurate phase may be the result of a Dzyaloshinskii-Moriya instability of the Neel ground state.