Toshimasa Matsuoka

A study on a palladium-titanium oxide Schottky diode as a detector for gaseous components

Abstract It has been found that the current through a Schottky barrier formed at the interface between palladium film and n-type titanium oxide (TiO 2 ) single crystal is sensitive to hydrogen or other reducing gases in the ambient. This effect is explained by taking account of the diminished barrier height at the Pd and TiO 2 interface caused by the action of gases, changing the work function of Pd metal. The change in the Pd work function estimated from the result is confirmed by the direct measurements of the metal surface potentials by use of a vibrating capacitor method. Similar electrical properties have been studied for junctions of TiO 2 with Pt, Au, Ni, Al, Cu, Mg and Zn, and of ZnO, CdS, GaP and Si w ith Pd.

DS-CDMA wired bus with simple interconnection topology for parallel processing system LSIs

A new bus architecture is described which is suitable for a parallel processing system without complexity of interconnection, and also drastically reduces the I/O pin count, which is highly desirable for future gigascale integrated systems. The architecture is based on the direct sequence code division multiple access (DS-CDMA) technique.

Temperature Dependence of Electron Mobility in InGaAs/InAlAs Heterostructures

Temperature dependence of the electron mobility in modulation-doped InGaAs/InAlAs single heterostructures has been investigated by Hall effect measurements in the temperature range from 15 K to 300 K in order to clarify the scattering mechanisms of the electrons. Two kinds of samples are used with doping densities in the InAlAs barrier layer, ND=3×1017 cm-3 and 1×1018 cm-3. The measured electron mobility is compared with the calculated values by taking into account the scattering by InAs-like and GaAs-like LO phonons in the InGaAs channel layer, in addition to the acoustic deformation potential, piezoelectric, ionized impurity, alloy disorder and interface roughness scatterings. The calculated electron mobility shows a good agreement with the experimental data when the alloy disorder potential is assumed to be about 0.7 eV.

Hot-carrier-induced degradation of N/sub 2/O-oxynitrided gate oxide NMOSFETs

Measurement of long term electrical characteristics of N/sub 2/O-oxynitrided gate oxide NMOSFETs revealed that the role of the nitrogen-rich layer as a blocking barrier for molecular hydrogen diffusion is dominant in the reduced device degradation. A two-step model was proposed, in which the release of hydrogen species and their reaction with the trivalent silicon atoms are the main factors for hot-carrier-induced-degradation. Hot carrier immunity of the NMOSFETs was also found to originate partially from the small increase of both the effective barrier height for electron injection and the interface trap creation energy due to the negatively charged nitrogen-rich layer.

Effect of various substrates on the hydrogen sensitivity of palladium‐semiconductor diodes

The effect of hydrogen at various partial pressures in air on the current‐potential (I‐U) curves for various palladium‐semiconductor diodes were studied. The diodes were prepared by depositing Pd on TiO2, ZnO, CdS, GaP, or Si. The onset potentials of the I‐U curves in the forward bias region were very sensitive to hydrogen for the TiO2 and ZnO diodes, but those of other semiconductors were insensitive. The substrates in the hydrogen‐sensitive diodes are ionic semiconductors and those in the hydrogen‐insensitive diodes are covalent semiconductors. The large variation in the hydrogen sensitivity of various diodes is explained by the degree of change in their barrier heights which are produced by the change in the palladium work function caused by hydrogen.

Degradation of inversion layer electron mobility due to interface traps in metal‐oxide‐semiconductor transistors

Degradation of inversion layer electron mobility during Fowler–Nordheim electron injection has been investigated using n‐channel metal‐oxide‐semiconductor transistors. The change of the reciprocal effective mobility, Δ(1/μEFF), has been found to be linearly related to the generated interface trap density, ΔNit, at a given effective electric field normal to the Si/SiO2 interface. The effect of trapped charges in the oxide on the mobility degradation is rather insignificant, which is attributed to the location of trapped charges from the Si/SiO2 interface. The dependence of mobility degradation on inversion layer electron density has also been explained using a transport theory based on two‐dimensional electron gas.

A 0.5 V feedforward delta-sigma modulator with inverter-based integrator

This paper presents an inverter-based switched-capacitor integrator for 0.5 V low-voltage applications. The proposed integrator utilizing floating voltage source and forward body bias obtains high performance as well as good independence of variations in process and temperature. It is applied to a 0.5 V feedforward AD modulator. The test results indicate that the designed AD modulator achieves a peak SNDR of 71 dB in a 78 kHz bandwidth, and the core power consumption is only 860 µW. This work is designed in a standard 0.18 µm CMOS process.

Monte Carlo study of hot-electron transport in an InGaAs/InAlAs single heterostructure

Monte Carlo simulation of two-dimensional hot-electron gas in an InGaAs/InAlAs single heterostructure was carried out in order to clarify high-field drift velocity and drift velocity overshoot at 77 K. The electronic states of the two-dimensional electron gas are calculated self-consistently and are used to calculate the scattering probabilities. The importance of the conduction band nonparabolicity is shown by using the energy-band structures calculated by the k*p perturbation method for In/sub 0.53/Ga/sub 0.47/As and In/sub 0.52/Al/sub 0.48/As. In the present calculations alloy disorder scattering and two modes of LO phonons in InGaAs layers are taken into account in addition to acoustic deformation potential scattering, screened ionized impurity scattering, nonpolar optical phonon scattering, and intervalley phonon scattering. It is found that alloy disorder scattering reduces the drift velocity and that the maximum drift velocity and negative differential mobility depend on the energy separation between the Gamma and L valleys, indicating that the intervalley scattering plays an important role in hot-carrier transport in InGaAs/InAlAs single heterostructures. >

Ultralow-Power Current Reference Circuit with Low Temperature Dependence

SUMMARY An ultralow power constant reference current circuit with low temperature dependence for micropower electronic applications is proposed in this paper. This circuit consists of a constant-current subcircuit and a bias-voltage subcircuits, and it compensates for the temperature characteristics of mobility µ, thermal voltage VT , and threshold voltage VTH in such a way that the reference current has small temperature dependence. A SPICE simulation demonstrated that reference current and total power dissipation is 97.7 nA, 1.1 µW, respectively, and the variation in the reference current can be kept very small within ±4% in a temperature range from −20 to 100 ◦ C.

Analytical design of a 0.5V 5GHz CMOS LC-VCO

A low-voltage complementary cross-coupled differential LC-VCO was investigated using simple modeling. The bias-controllability of the VCO provides a simple design for low-voltage operation. An analytical design approach realized a 5GHz VCO under a 0.5V supply voltage using a 90-nm digital CMOS process.