Masanori Inada

Grain growth control in ZnO varistors using seed grains

A method for making low‐voltage ZnO varistors having extraordinarily large grain size without necessity of sintering at much higher temperatures or for much longer times is reported. The device is made by sintering a mixture of ZnO fine powder, additives, and ZnO seed grains having grain sizes of 63–105 μm obtained by washing a ZnO sintered body containing BaO in boiling water. The device has a grain size around 500 μm and low threshold voltage of 6 V/mm. Such anomalous grain growth is caused by the difference between the radii of curvature of ZnO fine powder and ZnO seed grains.

Advanced technologies of low-power GaAs ICs and power modules for cellular telephones

Low-power GaAs ICs and power modules have been developed for 150-cc-type cellular telephones. The front-end IC and power splitter IC can operate under 3 V, and the dissipation current is only half that of Si bipolar ICs. The front-end IC, consisting of a low-noise amplifier, local amplifier, and downconverter, shows a conversion gain of 22 dB at a local power of -15 dBm. The power splitter IC, used in dividing the output power of the voltage-controlled oscillator and supplying the local power to two mixers, shows an output power of 0 dBm and internal isolation of over 25 dB. The power module as a transmitter, composed of a two-stage hybrid amplifier using GaAs MESFETs, can operate at 4.7 V and deliver an output power of 1.5 W at f=950 MHz.<<ETX>>

AlGaAs/GaAs heterojunction bipolar transistors with small size fabricated by a multiple self-alignment process using one mask

A multiple self-alignment process for HBTs using one mask is developed to form emitters, emitter contacts, emitter contact leads, buried small collectors, base contacts, and base contact leads. This process makes it possible to produce HBTs of very small size and to reduce parasitic elements. An AlGaAs/GaAs HBT fabricated by the process, with an emitter 1 × 20/µm2in size and a buried collector by O+implantation gives a good performance of ft= 54 GHz and fmax= 42 GHz. The performance may be explained by the reduction of parasitic elements, base transit time, and collector depletion layer transit time.

Photoluminescence in AlGaAs/GaAs heterojunction bipolar transistors

Photoluminescence in AlGaAs/GaAs heterojunction bipolar transistors (HBTs) with heavily doped GaAs layers and a p+‐GaAs/n‐AlGaAs heterojunction grown by molecular beam epitaxy at a low temperature of 600 °C is discussed. Each photoluminescence signal in the HBT is identified, and the relationship between performance as a transistor and photoluminescence discussed. A novel photoluminescence signal related to the p+‐GaAs/n‐AlGaAs heterojunction in the HBT was identified. This signal is thought to originate in the transition of the two‐dimensional electrons in the notch formed at the heterojunction to the acceptor and acceptor‐related defect levels.

Properties of molecular‐beam‐epitaxy‐grown and O+‐implanted GaAs and their application to the formation of a buried collector of an AlGaAs/GaAs heterojunction bipolar transistor

Changes in properties of molecular‐beam‐epitaxy‐grown GaAs by oxygen‐ion (O+) implantation and annealing, such as crystallinity, carrier concentration, and sheet resistance, are investigated. Using these results, we developed a method of O+ implantation through an external base area to form a small buried collector and to minimize the product, RbCbc, of the base‐collector capacitance Cbc and the base resistance Rb in an AlGaAs/GaAs heterojunction bipolar resistance Rb in an AlGaAs/GaAs heterojunction bipolar transistor (HBT) fabricated by a multiple self‐alignment process with one mask. High‐frequency properties of HBT’s are improved by this method remarkably.

Emitter&#8212;Base&#8212;Collector self-aligned heterojunction bipolar transistors using wet etching process

The first emitter-base-collector (EBC) self-aligned (SA) heterojunction bipolar transistors (HBTs) using wet etching process are described. This self-alignment fabrication technique is extremely simple but can get excellent high-frequency performance. An HBT with a 4-µm-wide emitter mesa showed 18 GHz of Ftand 13 GHz ofF_{\max}. By optimizing this process, high-frequency operation above 40 GHz can be expected.

A Small Collector-Up AlGaAs/GaAs Heterojunction Bipolar Transistor Fabricated Using H+ Implantation

A small collector-up AlGaAs/GaAs heterojunction bipolar transistor with a collector size of 1×10 µm2 is developed by making the entire emitter layer under the external base highly resistive by oblique H+ implantation from both sides along the elongated direction of the collector mesa, and by forming the collector electrode and base electrodes by self-alignment method. The transistor shows high-frequency properties of fT=31 GHz and fmax=50 GHz. The relationship between the process used and the properties of the transistor is analyzed.

An Npn AlGaAs/GaAs Collector-up HBT with an H + -Implanted High Resistivity Layer under the External p + -GaAs Base

The npn AlGaAs/GaAs collector-up (C-up) heterojunction bipolar transistor (HBT) with an H+-implanted high resistivity layer (HRL) under the external p+-GaAs base layer has been successfully fabricated for the first time. For suppressing parasitic current from the emitter to external base when operating foward bias voltages, the H+-implanted HRL is superior to the O+-implanted and annealed HRL or the pn junction of wide band gap under the external base.

Photoluminescence study of AlGaAs/GaAs heterojunction bipolar transistors fabricated by molecular beam epitaxy

Abstract Photoluminescence (PL) in AlGaAs/GaAs heterojunction bipolar transistors (HBTs) fabricated by molecular beam epitaxy (MBE) is discussed. Each PL signal is identified. A novel PL signal related to the N-AlGaAs/p+-GaAs heterojunction in the HBT was identified. Thi signal is thought to originate in the two dimensional electrons at the heterojunction.