Motoji Yagura

Thermal stabilization of AlGaAsGaAs power HBTs using n-AlxGa1−xAs emitter ballast resistors with high thermal coefficient of resistance

Abstract The use of n -Al x Ga 1− x As an emitter ballast layer material for AlGaAs GaAs heterojunction bipolar transistors (HBTs) is proposed and demonstrated. A high thermal coefficient of resistance can be obtained owing to the temperature dependence of the relative populations of the conduction band Γ, L and X valleys if the Al mole fraction x of the n -Al x Ga 1 − x As ballast layer is adjusted to give the appropriate intervalley energy separation. Al 0.3 Ga 0.7 As and Al 0.35 Ga 0.65 As emitter ballast layers incorporated in HBT structures have an average thermal coefficient of resistance of about 8 × 10 −3 °C −1 , which is significantly higher than that of GaAs ballast resistances. The temperature stabilizing effect of n -Al x Ga 1− x As ballast layer is assessed by measuring the d.c. current-voltage characteristics of single-emitter finger and multi-emitter finger HBTs. Large power HBTs with integrated n -Al x Ga 1− x As ballast resistors have been fabricated and an output power of up to 10 W at 0.9 GHz has been obtained.

Analytical model for electrical and thermal transients of self-heating semiconductor devices

Transients of self-heating semiconductor devices are theoretically investigated based on a feedback circuit model, which is composed of three sub-circuits describing the isothermal electrical characteristics, thermal impedance, and temperature dependence of the electrical characteristics of the devices, respectively. Analytical expressions of the frequency and transient responses have been derived for both the electrical and thermal characteristics of self-heating devices, yielding accurate methods to extract the thermal time constant in both the time and frequency domains. The model is verified by the transient electrical-response measurement of a GaInP/GaAs heterojunction bipolar transistor.

60GHz-band low noise amplifier and power amplifier using InGaP/GaAs HBT technology

In this paper, we present a 60 GHz-band low noise amplifier (LNA) and a 60 GHz-band power amplifier (PA) utilizing high performance InGaP/GaAs HBTs. The InGaP/GaAs HBTs feature a highly doped base layer, a self-aligned base contact and an undercut collector mesa structure in order to achieved low noise and high gain in the millimete-wave band. By adjusting the collector current of each HBT in the LNA to the optimum value a noise figure as low as 5.8 dB with a gain of more than 25 dB was obtained. The PA exhibited a linear gain of more than 15 dB with P1dB of 13 dBm in the 60 GHz-band.

Monolithically Fabricated Hybrid Head for Near-Field Assisted Magnetic Recording

In this paper, we show a monolithically fabricated hybrid head with a GaAs-based laser diode capable of near-field-assisted magnetic recording. A bottlenecked conductor was placed beside the laser cavity formed on the trailing side of the head. The bottlenecked structure is used as a generator of magnetic and near fields. The structure consists of a couple of opposite electrodes with a 200-nm gap and a bridge connection between the electrodes. The magnetic field is mainly generated around the bottleneck by feeding current through the conductor. The near field is produced along edges of the bottleneck by irradiating a laser beam. We confirmed the 3-D localization of near field in the nanometer size around the bottleneck by means of a near-field scanning optical microscope. We attained the nanosized overlap between magnetic filed and near-field distributions on the hybrid head with the laser diode.

Huge magnetoresistive effects using space charge limited current in ZnO/SiO2 system

Huge magnetoresistive effects were observed in a metal/insulator current-in-plane (CIP) diode feeding space charge limited (SCL) current. The insulator laterally toward opposite gold (Au) electrodes was fabricated on a SiO2 substrate by the standard photolithography method using dry etching. The insulator consisted of a SiO2∕ZnO∕SiO2∕ZnO multilayer sputtered on the substrate. Current-voltage curves showed Ohmic property and SCL current characteristics accompanied by Child-Langmuir and Mott-Gurney laws derived from first order differential calculus. Current-magnetic field curves indicated the huge magnetoresistive effects up to 1010% under the magnetic field of 0.3T at room temperature. The current-magnetic field curves have even symmetry for the applied magnetic field. The Au/insulator CIP diode is abruptly switched between a conducting state and an insulating state by the applied magnetic field.

Simulation of Self-heating HBTs Based on Isothermal Gummel-Poon Model

Based on the correlation between the electron and hole injection currents at the emitter junction, a simple dc model of self-heating HBTs has been developed by introducing three physically-based parameters into the isothermal Gummel-Poon model, which is easy to construct and implant to circuit simulators. Both the self-heating and the anbient temperature effects can be simulated accurately. The electrical and thermal parameters of HBTs can be evaluated from the extracted model parameters, and a novel method for separating the base current components has also be developed.