Masao Sakuraba - Academia.edu (original) (raw)

Papers by Masao Sakuraba

We present a design of a majority neuron circuit with non-volatile synaptic weights. It is based ... more We present a design of a majority neuron circuit with non-volatile synaptic weights. It is based on an analog majority circuit composed of controlled current inverters (CCIs). The proposed circuit is immune to device parameter fluctuations, and its fan-in is estimated about 1000. Synaptic weights are realized on the neuron circuit by adding variable resistors. We consider a design of a non-volatile synaptic weight by using a three-terminal magnetic domain-wall motion (DWM) device. The operation of a fully connected recurrent neural network composed of the proposed circuits has been confirmed by SPICE simulation.

Thin Solid Films, Dec 1, 2000

Doping and electrical characteristics of in-situ heavily B-doped Si,~,~,Ge,C, (0.22 < x < 0.6, 0 ... more Doping and electrical characteristics of in-situ heavily B-doped Si,~,~,Ge,C, (0.22 < x < 0.6, 0 < y < 0.02) films epitaxially grown on Si(100) were investigated. The epitaxial growth was carried out at 550°C in a SiH,-GeH,-CH,SiH,-B,H,-H, gas mixture using an ultraclean hot-wall low-pressure chemical vapor deposition (LPCVD) system. It was found that the deposition rate increased with increasing GeH, partial pressure, and only at high GeH, partial pressure did it decrease with increasing B,H, as well as CH,SiH, partial pressures. With the B,H, addition, the Ge and C fractions scarcely changed and the B concentration (C,) increased proportionally. The C fraction increased proportionally with increasing CH,SiH, partial pressures. These results can be explained by the modified Langmuir-type adsorption and reaction scheme. In B-doped Si,- ,-,Ge,Cy with y = 0.0054 or below, the carrier concentration was nearly equal to C , up to approximately 2 X 10'' cmP3 and was saturated at approximately 5 X 10'' cmP3, regardless of the Ge fraction. The B-doped Si,~,~,Ge,C, with high Ge and C fractions contained some electrically inactive B even at the lower C , region. Resistivity measurements show that the existence of C in the film enhances alloy scattering. The discrepancy between the observed lattice constant and the calculated value at the higher Ge and C fraction suggests that the B and C atoms exist at the interstitial site more preferentially.

It is widely believed that the real parallel computation achieved by quantum computers has an eno... more It is widely believed that the real parallel computation achieved by quantum computers has an enormous computing potential. In order to expand its applicable field, we have investigated the fusion of quantum and neural computations. As a first step of implementing learning function on quantum computers, we have proposed a novel quantum associative memory (QuAM) by considering an analogy between neural associative network and qubit network. The memorizing procedure of the QuAM is realized with a Hamiltonian derived from qubit-qubit interactions, and the retrieving procedure is based on the adiabatic Hamiltonian evolution. The memory capacity of the QuAM has been nominally estimated as 2N−1 where N is a number of qubits, but its retrieve property has not been discussed in our previous study. This paper proposes a retrieving process for the QuAM and evaluates its performance in detail. The results indicate that the average of the retrieving probability is over 50% even when the qubit network memorizes 2N−1 patterns and thus the QuAM is successfully implemented.

Advances in Natural Sciences: Nanoscience and Nanotechnology, Mar 9, 2012

One of the main requirements for ultra-large-scale integrations (ULSIs) is atomic-order control o... more One of the main requirements for ultra-large-scale integrations (ULSIs) is atomic-order control of process technology. Our concept of atomically controlled processing is based on atomic-order surface reaction control by CVD. By ultraclean low-pressure CVD using SiH4 and GeH4 gases, high-quality low-temperature epitaxial growth of Si1−xGex (100) (x=0–1) with atomically flat surfaces and interfaces on Si(100) is achieved. Self-limiting formation of 1–3 atomic layers of group IV or related atoms in the thermal adsorption and reaction of hydride gases on Si1-xGex (100) are generalized based on the Langmuir-type model. By the Si epitaxial growth on top of the material already-formed on Si(100), N, B and C atoms are confined within about a 1 nm thick layer. In Si cap layer growth on the P atomic layer formed on Si1−xGex (100), segregation of P atoms is suppressed by using Si2H6 instead of SiH4 at a low temperature of 450 °C. Heavy C atomic-layer doping suppresses strain relaxation as well as intermixing between Si and Ge at the Si1−xGex/Si heterointerface. It is confirmed that higher carrier concentration and higher carrier mobility are achieved by atomic-layer doping. These results open the way to atomically controlled technology for ULSIs.

Meeting abstracts, 2014

1. Introduction Low-temperature epitaxial growth process of group IV semiconductors (e.g. Si, Si1... more 1. Introduction Low-temperature epitaxial growth process of group IV semiconductors (e.g. Si, Si1-xGex and Ge) is important for quantum-effect nano heterostructures of group IV semiconductors especially with suppressed intermixing at heterointerfaces [1]. Plasma CVD process is one of the candidates for low-temperature epitaxial growth of group IV semiconductors [2-4]. Recently, epitaxial growth of Si1-xGex alloy on Si(100) by surface reaction under electron-cyclotron resonance (ECR) Ar-plasma irradiation has been found, and it has been clarified that Ge fraction of Si1-xGex thin film is in good agreement with gas mixture ratio and that the surface reaction is slightly enhanced by increase of Ge in the films [4]. In this work, in order to control the surface reaction precisely for the better film quality and to obtain a high-quality quantum well heterostructure by our ECR Ar plasma CVD, partial pressure dependence of the reaction enhancement effect by Ge and Si cap layer deposition on Si1-xGex were investigated continuously. In this paper, typical new experimental results of Si1-xGex thin film formation including crystal quality and hydrogen incorporation are reported. 2. Experimental By using ECR Ar plasma CVD without substrate heating (Fig. 1), Si, Si1-xGex alloy and Ge films were deposited directly on the dilute-HF-treated Si (100) by the reaction of GeH4 and SiH4 under ECR low-energy Ar-plasma irradiation [4]. Microwave power was 200W and Ar partial pressure was 2.1 Pa. The substrate temperature was suppressed below 50oC during plasma exposure even for a few hundred seconds [2]. Especially for evaluation of Ge fraction, crystallinity, lattice strain and hydrogen incorporation, X-ray photoelectron spectroscopy, reflection high-energy electron diffraction, high-resolution X-ray diffraction and Fourier-transform infrared spectroscopy, respectively. 3. Results and discussion Fig. 2 shows the dependence of rate coefficient [(Si1-xGex deposition rate) × (Ge or Si fraction) / (partial pressure of GeH4 or SiH4 (PGeH4 or PSiH4))] in the Si1-xGex deposition on (a) PGeH4 and (b) PSiH4. Here, it should be noted that the rate coefficient is considered to be proportional to a decomposition probability of a GeH4 or SiH4 molecule arriving at surface. It is clear that, by increasing PGeH4 or decreasing PSiH4, the rate coefficients tend to become larger (Fig. 2). Although this tendency is apparently related to increase of Ge fraction in a larger Ge fraction region above x=0.5 (as reported previously [4]), it is additionally clear that the tendency is strongly dependent on a combination of PGeH4 and PSiH4 (Fig. 3(a)). Here, it should be noted that the larger increase of rate coefficients can be observed in a condition with the smaller change of Ge. From a view point that incident Ar plasma (ions and radicals) causes surface reaction, deposition rate is considered to be another important factor in the above strong dependence, because contribution of Ar plasma to decomposition of one molecule can be varied by change of deposition rate. From dependence of the rate coefficient on deposition rate (Fig. 3(b)), it is clear that increase of rate coefficients occurs in largely different region of deposition rate. Therefore, it is suggested that the change of rate coefficients depends not only on Ge fraction at surface but also on plasma irradiation condition as well as deposition rate. Additionally, it has been also found that amount of incorporated hydrogen in the Si1-xGex films epitaxially grown on Si(100) is as small as the order of detection limit of our FT-IR measurements (about 1020 cm-3) or below. Furthermore, it has been also confirmed that, by utilizing the surface reaction of SiH4 under ECR Ar plasma irradiation, a Si cap layer can be epitaxially grown on the strained Si0.50Ge0.50films lattice-matched to Si(100) and the strain is hardly relaxed. From this result, our ECR Ar plasma CVD process is expected to be applicable to quantum well heterostructure formation with suppressed intermixing. 4. Acknowledgments This study was partially supported by a Grant-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology of Japan and the Japan Society for the Promotion of Science (JSPS) Core-to-Core Program, A. Advanced Research Networks “International Collaborative Research Center on Atomically Controlled Processing for Ultralarge Scale Integration”. References [1] K. Takahashi, M. Sakuraba and J. Murota, Solid-State Electron., 60 (2011) 112. [2] M. Sakuraba, K. Sugawara and J. Murota, Key Eng. Mat., 470 (2011) 98. [3] Y. Abe, M. Sakuraba and J. Murota, Thin Solid Films, 557 (2014) 10-13. [4] N. Ueno, M. Sakuraba, S. Sato and J. Murota, Thin Solid Films, 557 (2014) 31-35.

The Japan Society of Applied Physics, Feb 8, 2018

Lecture Notes in Computer Science, 2017

Spatial perception, in which objects’ motion and positional relationship are recognized, is neces... more Spatial perception, in which objects’ motion and positional relationship are recognized, is necessary for applications such as a walking robot and an autonomous car. One of the demanding features of spatial perception in real world applications is robustness. Neural network-based approaches, in which perception results are obtained by voting among a large number of neuronal activities, seem to be promising. We focused on a neural network model for motion stereo vision proposed by Kawakami et al. In this model, local motion in each small region of the visual field, which comprises optical flow, is detected by hierarchical neural network. Implementation of this model into a VLSI is required for real-time operation with low power consumption. In this study, we reduced the computational complexity of this model and showed cell responses of the reduced model by numerical simulation.

IEICE Technical Report; IEICE Tech. Rep., Jun 17, 2015

IEICE Transactions on Electronics, 2016

Introduction of C into Si1-xGex heteroepitaxial growth on Si has attracted considerable attention... more Introduction of C into Si1-xGex heteroepitaxial growth on Si has attracted considerable attention for fabrication of novel heterostructure devices in Si-based technology for the band engineering by strain control in group IV semiconductors (Eberl et al, 1992, Chang et al, 1998). In the previous work, carbon effect on strain compensation in Si1-x-yGexCy films epitaxially grown on Si(100) at 500 degC

2006 International SiGe Technology and Device Meeting, 2006

In this work, in order to improve the abruptness, P atomic layer formation and P atomic layer dop... more In this work, in order to improve the abruptness, P atomic layer formation and P atomic layer doping in Si epitaxial growth using Si2H6 by ultraclean low pressure CVD (LPCVD) and its electrical characteristics were investigated

The transactions of the Institute of Electrical Engineers of Japan.C, 2006

Materials Science in Semiconductor Processing, Feb 1, 2005

We propose and describe a novel method called separation by bonding Si islands (SBSI) that can be... more We propose and describe a novel method called separation by bonding Si islands (SBSI) that can be used to form silicon-on-insulator (SOI) and isolation regions simultaneously. The Si islands are formed by selectively etching the SiGe layer of Si/SiGe stacked layers grown by chemical vapor deposition (CVD). Thin oxide layers are formed at the surface of the Si islands and the Si substrate by using thermal oxidation, and the Si islands are bonded to the Si substrate with the oxide layers. We obtained a uniform SOI layer and a smooth interface between the SOI and buried oxide (BOX) layers. The thicknesses of the SOI and BOX layers observed with cross-sectional transmission electron microscopy (TEM) were 18.2 and 23.5 nm, respectively.

IEICE Technical Report; IEICE Tech. Rep., Oct 22, 2020