Search

The performance of liquid crystal displays (LCDs) is expected to be improved further with the emergence of their new applications. Numerical simulations such as the finite differential method (FDM) and the finite element method are useful in optimum design. However, they take a long time because dynamical systems in LCDs are nonlinear multiphysics composed of electromagnetism, fluid dynamics, and elastic mechanics. A machine learning method is one of the solutions to reduce computational cost. In this paper, we have extended the parallel reservoir computing framework and applied it to LCD simulation. We have discussed how to implement each natural feature of liquid crystal cells, namely, non-autonomy, multiphysics and long-range orientational order, into the framework of parallel reservoir computing. Sufficient higher accuracy was obtained with several display patterns and driving frequencies at computational speeds more than 100 times higher than FDM.

We demonstrated high-electron-mobility transistors (HEMTs) with enhanced two-dimensional electron gas (2DEG) mobility using a low-strain AlGaN barrier grown by metalorganic vapor phase epitaxy under a nitrogen atmosphere. We investigated the effects of the growth temperature under a nitrogen atmosphere on the electrical properties of AlGaN-HEMT structures, focusing on 2DEG mobility. At growth temperatures below 855 °C, the 2DEG mobility decreased with decreasing growth temperature owing to an increase in the threading dislocation density. However, at growth temperatures above 855 °C, the 2DEG mobility decreased with increasing growth temperature. This finding was attributed to the compressive strain in the GaN channel, which increased with increasing growth temperature owing to the increased tensile strain in the AlGaN barriers. We concluded that temperatures around 855 °C are suitable for AlGaN barrier growth under nitrogen atmosphere. Finally, we achieved the highest 2DEG mobility of 2182 cm2 V−1 s−1 with a low sheet resistance of 406 Ω sq−1. using an Al0.41Ga0.59N barrier.

GaN-based high electron mobility transistors (HEMTs) are expected to have high performance in base station applications. Recently, it was reported that the combination of the Poisson–Schrödinger method and cellular automaton method is effective for predicting the mobility of channel two-dimensional electron gas of GaN HEMTs. In the operation condition of HEMT, the surface electron density of the channel is on the order of 1013 cm−2, and the effect of degeneracy cannot be ignored in calculating the mobility. Since the electron distribution function is always stably obtained by the cellular automaton method, the degeneracy effect can be considered stably. In this paper, through the comparison of different degeneracy evaluation methods, the anisotropy of the electron distribution function under the electric field acceleration is clarified to affect the HEMT mobility prediction significantly.

In this study, a differential-drive CMOS RF rectifier equipped with photovoltaic assistance and self-Vth-cancellation (SVC) mechanism has been developed for efficient energy harvesting from ambient radio waves. In addition to the differential-drive dynamic biasing, in which by dynamically biasing the MOSFET gates with differential input signal, both on-resistance and reverse leakage current of the MOSFET are reduced and high power conversion efficiency (PCE) can be achieved, the combination of SVC technology and photovoltaic assist technology allows further improvement of the PCE under low input power conditions. As a result, the PCE of 38.5% was achieved at an input power level of −22 dBm, a frequency of 1 GHz, an output load resistance of 10 kΩ, and a light irradiance of 1 W m−2.

We report hollow-cone imaging and small-angle electron diffraction of nanoscale magnetic textures such as magnetic-striped domains and magnetic bubbles of M-type hexagonal ferrite BaFe$_{10.35}$Sc$_{1.6}$Mg$_{0.05}$O$_{19}$. The advantage of the hollow-cone Foucault method is that magnetic domains with various directions of magnetization can be visualized under an infocus condition. Moreover, the contrast of magnetic domain walls in magnetic bubbles depends on the inclination angle of the illumination beam. The combination of small-angle electron diffraction and hollow-cone Foucault imaging proves that magnetization at domain walls exhibits in-plane directions in the magnetic-striped domains and magnetic bubbles.

We investigated the magnetization dynamics of Co/Pt multilayer dots with diameters in the micron scale by X-ray magnetic circular dichroism (XMCD) with a focused beam with submicron dimensions. XMCD measurement with soft and hard X-rays revealed that the magnetic moments of Co and Pt strongly couple and precess with the same cone angle in ferromagnetic resonance conditions. The transient magnetization behavior of Co/Pt multilayer dots was investigated by pump–probe XMCD measurement with a scanning focused X-ray beam. A non-uniform magnetization distribution with concentric geometry including the phase of magnetization precession was visualized with excitation frequencies up to 3.05 GHz.

We investigated magnetic textures in a Sc-doped hexaferrite film by means of phase microscopy (PM) with a hole-free phase plate in a transmission electron microscope. In a zero magnetic field, the stripe-shaped magnetic domains coexist with magnetic bubbles. The magnetization in both magnetic domains was oriented perpendicular to the film and the domain walls have an in-plane magnetization. In the remnant state at 9.2 mT, several magnetic bubbles were formed with the formation of stripe-shaped magnetic domains, and the out-of-plane component in the stripe-shaped domains gradually appeared as the film thickness increased. As the film thickness increases further, the magnetic bubbles with clockwise or counter-clockwise spin helicities formed a triangular lattice. These results in the remnant state suggest that the domain wall energy in the magnetic bubble domains is lower in the thicker region.

Observation of magnetic domains is important in understanding the magnetic properties of magnetic materials and devices. In this study, we report that the magnetic domains of M-type hexaferrites with uniaxial anisotropy can be visualized via small-angle electron diffraction and Foucault imaging. The position of the diffraction pattern spots has the same period as that of magnetic domains in a Sc-substituted hexaferrite (BaFe$_{12-x-\delta}$Sc$_x$Mg$_\delta$O$_{19}$). Conversely, the spots were observed four times longer than the period of magnetic domains in hexaferrite without substitution (BaFe$_{12}$O$_{19}$), demonstrating the long-range order of the Bloch walls. When the specimen was tilted, the magnetic deflection effect, as well as the periodic spots of magnetic domains, occurred. Thus, we were able to visualize the magnetic domains with different magnetization directions and domain orientations by selecting deflection spots. The results indicate that the technique utilized in this study is useful in observing the magnetic materials with uniaxial anisotropy., Comment: 17 pages, 6 figures

In accordance with the detailed balance limit model of single-intermediate-band solar cells (IBSCs), the optimum matrix bandgap and IB–conduction band (CB) energy gap are ~1.9 and 0.7 eV, respectively. We present the room-temperature polarized infrared absorption of 20 stacked InAs quantum dot (QD) structures in the Al0.32Ga0.68As matrix with a bandgap of ~1.9 eV for the design of high-efficiency IBSCs by using a multipass waveguide geometry. We find that the IB–CB absorption is almost independent of the light polarization, and estimate the magnitude of the absorption per QD layer to be ~0.01%. We also find that the IB–CB absorption edge of QD structures with a wide-gap matrix is ~0.41 eV. These results indicate that both the significant increase in the magnitude of IB–CB absorption and the lower energy of the IB state for the higher IB–CB energy gap are necessary toward the realization of high-efficiency IBSCs.

Langmuir–Blodgett (LB) deposition was employed to fabricate high-κ dielectric nanofilms of titania nanosheets. The LB-based layer-by-layer approach using an atomically flat SrRuO3 substrate is effective for the fabrication of atomically uniform and highly dense nanofilms. These films exhibited both high dielectric constant (κ~123) and low leakage current density (J< 10-7 A cm-2) for thicknesses down to 5 nm, while eliminating the size-effect problems encountered in current high-κ films. From analyses of interfacial structures by transmission electron microscopy and hard X-ray photoelectron spectroscopy, we have clarified that the films are composed of a well-ordered lamellar structure without an interfacial dead layer. According to first-principles calculations, a highly polarizable nature of titania nanosheets can bring improved dielectric properties, yielding high-κ values even in an ultrathin geometry (

The enhancement factors of a new structure called the nanograting metal–oxide–semiconductor field-effect transistor (MOSFET), which was proposed to achieve higher current drivability, were analyzed. From the measurement of the transconductance, the drivability enhancements of both n- and p-type MOSFETs were confirmed. This was mainly ascribed to the increased effective channel width. However, the enhancement ratios in nMOS and pMOS were different. In the nanograting MOSFETs, the existence of the current flowing in the direction on the (110) surface caused the effective electron mobility to be lower and the effective hole mobility to be higher than that in the conventional devices on the (100) surface. The stress from the polycrystalline silicon (poly-Si) gate also resulted in the change of the mobility. Because of the reasons above, the mobility difference between the nanograting nMOSFET and pMOSFET became slighter, thus, the area balance of the nanograting complementary MOS (CMOS) circuit could be improved. Combining this with the increased drivability could give the area advantage of the nanograting CMOSFETs.

Randomly oriented polycrystalline silicon (poly-Si) thin films with a typical grain size of 20×2 µm2 grown by continuous-wave laser lateral crystallization (CLC) were obtained. It was found that CLC poly-Si thin films have a large tensile strain corresponding to 0.6% of single-crystalline Si lattice in the in-plane direction. These results suggest that there is a possibility that not only grain size but also the large tensile strain in in-plane direction can affect thin film transistor (TFT) performance.

The cw laser recrystallization of amorphous silicon (a-Si) thin films deposited on SiO2 films with Si(100) substrates was investigated by controlling irradiation conditions. The effects of the laser spot shape and laser-irradiated region overlap were found important resulting in two dimensional crystal growth different from conventional lateral crystallization. A laser beam spot was designed to realize a gradual temperature slope in the laser-irradiated region. The crystal grain growth of the Si thin films was effectively enhanced. Raster scanning was performed to make the crystal growth direction regular and effectively enhanced the crystallization of the recrystallized Si thin films. The laser-irradiated region overlap also effectively enhanced the crystallization of the recrystallized Si thin films. Consequently, (100) well-oriented polycrystalline Si thin films with an average grain size of 1.60 µm, which is about 5 times larger than that obtained by conventional excimer laser recrystallization, were obtained.

We investigated the deposition phenomena of diamond-like carbon (DLC) film on a microstructured Al2O3 surface using an ion-beam technique. In the case of an acceleration voltage of 300 V, the microstructured Al2O3 surface was smoothly coated to have an unevenness of about 200 nm height with DLC film. The hardness of the DLC film indicated maximum values at acceleration voltages of 100–200 V and gradually decreased for acceleration voltages of 300–400 V. By using Raman spectroscopy and Fourier transform infrared spectroscopy, it was shown that the numbers of sp3 bonds in films deposited at acceleration voltages of 100 and 200 V was larger than that of films deposited at acceleration voltages of 300 and 400 V.

Optical proximity correction (OPC) features are frequently used in photolithography. It is necessary to measure the shape characteristics such as height, width, area, position of center of gravity, and corner-rounding with nm-order accuracy. For this purpose, critical-dimension scanning electron microscope (CD-SEM) images are utilized. However, it is difficult to extract the shape characteristics mentioned above from a corrected pattern with conventional CD-SEM measurement. The authors developed a method to extract the shape characteristics automatically from a corrected reticle pattern with high accuracy, with combination of discriminant analysis and nonlinear regression.

One-dimensional ZnO nanodot arrays have been realized by metalorganic chemical vapor deposition on SiO2 substrates patterned by focused ion beam (FIB). Especially for the lines with the depth of 5 nm and the length of 0.7, 1.3 or 1.7 µm, one, two or three nanodots, respectively, of fairly uniform size 6-nm height and 80-nm width are symmetrically accommodated in a line. These phenomena are translated as "self-tailoring" of ZnO nanodots, i.e., where the nanodots will be is predetermined before the growth and is arbitrarily controlled by the nanopatterns. This can be a promising technique to build nanostructure blocks for nanoscale device applications.

Dynamically customizable and reconfigurable hardware architecture for a specific task on demand is one of the most important issues to bring out a novel-computing paradigm in the era of system LSIs. Our target is to realize a flexible processor which is a kind of dynamically reconfigurable field-programmable gate array (FPGA) and is able to execute signal processing while reading the next configuration data (CD) simultaneously. In order to realize the flexible processor, since the amount of CD is enormous in conventional FPGAs, it is necessary to reduce the amount of CD as much as possible. In this paper, we propose a newly developed programmable logic module that can reduce the amount of CD to no less than 86% of that for the conventional Look Up Table (LUT)-based programmable logic module.

Corrosion of W plugs in LSI interconnects during chemical solvent stripping was investigated by scanning Maxwell-stress microscopy (SMM). The surface potential of TiN, Al and W, of which the interconnects are composed, was measured by SMM, and the changes in electrostatic charging and work functions through the processes were estimated. After immersion in aqueous amine stripper, which actually caused the W plug corrosion, the work functions of the Al and W films were comparable. Due to the similarity of the work function to the electrochemical reduction potential, we consider that the corrosion protection of the Al/W contact becomes inactive in the aqueous amine stripper. This is also supported by the electrode potential measurement in the aqueous amine stripper, for which the Al potential exhibited a higher value than that of W only for the films after O2 ashing. We consider that the W plug corrosion is caused by the electrochemical interaction between the aqueous amine stripper and the material deposited on the Al by O2 ashing.

The magnetic moments of a Pt|Fe(0.5 nm)|MgO film at an external electric field of in a 0.35 V/nm were characterized by analyzing the X-ray magnetic circular dichroism (XMCD) at the L-edges of Fe using a partial fluorescence yield method with a precision 40 times greater than that in our previous study. The XMCD induced by the electric field was negligible (