Tohru Sugiyama

A 40-GHz D-type flip-flop using AlGaAs/GaAs HBT's

We report master-slave D-type flip-flop (D-FF) circuit implemented with AlGaAs/GaAs HBTs. The fabricated HBTs had an f/sub T/ of 107 GHz and an f/sub max/ of 110 GHz. To maximize the speed, the logic swing and transistor size in the IC were optimized. In the D-FF, to facilitate the high-speed testing, a selector circuit was integrated on the same chip. As a result, the operation of this IC was confirmed up to 40 GHz, which is the highest speed in D-FF. >

Ultra-low resistance base ohmic contact with Pt/Ti/Pt/Au for high-fmax AlGaAs/GaAs heterojunction bipolar transistors

Ohmic contacts to 500-A-thick p-Al0.1Ga0.9As layer formed with a Pt/Ti/Pt/Au metal system were investigated. An extremely low contact resistivity of 4.2×10-7 Ω cm2 was obtained. The contact resistance increased with the increment of the Pt thickness, because the thicker the intermetallic layer becomes the thinner the AlGaAs layer beneath it, which leads to a higher contact resistance. The optimum Pt thickness was around 50 A. Moreover, this metal scheme was thermally stable at 350° C. A high f max of 160 GHz was obtained for AlGaAs/GaAs HBTs using Pt/Ti/Pt/Au base electrodes. A multiplexer (MUX) lC implemented with these high-f max HBTs operated properly up to 40 Gbps, the highest speed ever reported. This value was restricted by the measuring instrument capability.

DC to 40-GHz broad-band amplifiers using AlGaAs/GaAs HBT's

In this paper, we report two types of broad-band amplifiers implemented with AlGaAs/GaAs HBTs. One is a Darlington feedback amplifier and the other is a transimpedance amplifier. In the former circuit, a dc gain of 9.5 dB and a -3-dB bandwidth of 40 GHz were achieved. In the latter circuit, a transimpedance gain of 50 dB/spl Omega/ and a -3-dB bandwidth of 27 GHz were achieved. To our best knowledge, they are the highest speed in each circuit configuration. >

Five AlGaAs/GaAs HBT ICs for a 20 Gb/s optical repeater

The development of future ultra high bit rate optical transmission systems is now under way to meet the need for a rapid increase in transmission capacity. The capability of AlGaAs/GaAs heterojunction bipolar transistors (HBTs) is already demonstrated by a 10 Gb/s optical transmission unit This paper describes a complete 5-chip set of AlGaAs/GaAs HBT ICs for a 20Gb/s direct detection optical repeater.<<ETX>>

Highly reproducible fabrication technology for passivated AlGaAs/GaAs heterojunction bipolar transistors with Pt/Ti/Pt/Au base electrodes

A highly reproducible fabrication technology for passivated heterojunction bipolar transistors (HBTs) has been developed. A thermally stable Pt/Ti/Pt/Au base electrode metal penetrates through the Al 0.3 Ga 0.7 As emitter layer to contact the base layer. This feature leads to the formation of the base passivation layer. A citric-acid-based selective etchant eliminates the ambiguity of etching and thus confirms the reproducibility of passivation layer thickness. The excess base leakage current density was reduced to about 1 μA/μm

Molecular beam epitaxy growth for a heavily-doped thin base layer of heterojunction bipolar transistors used for high-speed integrated circuits

The technique of molecular beam epitaxy (MBE) growth has been developed for high-speed AlGaAs/GaAs heterojunction bipolar transistors (HBTs) with a heavily beryllium-doped base layer. Doping limit, DC current gain and reliability were examined under various growth conditions. By the growth under the conditions that substrate temperature was 580°C and V/III flux ratio was 27, the authors have developed HBTs in which the base doping concentration was set to as heavy as 8×10 19 cm -3 and the base thickness was set to 45 nm or 90 nm. Using these HBTs, they have fabricated ICs which can operate at 40 GHz

CHANGES IN COLLECTOR AND BASE CURRENTS FOR ALGAAS/GAAS HETEROJUNCTION BIPOLAR TRANSISTORS

The changes in the collector and base currents after a 5-min operation with a collector current density of more than 2.5×104 A/cm2 has been investigated for AlGaAs/GaAs heterojunction bipolar transistors (HBTs) with a Be doped base layer. Their dependence on the V/III flux ratio during molecular beam epitaxy (MBE) growth and on ion implantation conditions for emitter isolation were examined. A larger change in the collector current was observed for HBTs which were grown under a lower V/III ratio or fabricated under a heavier implantation condition. A change in the base current has also been found even when the change in the collector current was small. The change has been attributed to a decrease in the non-radiative recombination rate. A high V/III flux ratio growth and a low damage implantation are needed to suppress the changes.