In this study we have investigated the reactive ion etching of 60 μm diam, 200 μm deep holes in 3 in. diam semi-insulating GaAs wafer using a combination of CCl2F2 and CCl4 gases for fabrication of through substrate via holes for grounding in monolithic microwave integrated circuits (MMICs). The effect of process parameters viz. pressure, CCl4/CCl2F2 ratio, and power on GaAs etch rate and resultant etch profile was investigated. Two kind of masks, photoresist and Ni, were used to etch GaAs and their performance was compared by investigating effect on etch rate, etch depth, etch profile, and surface morphology. The etch profile, etch depth, and surface morphology of as-etched samples were characterized by scanning electron microscopy. The desired 200 μm deep strawberry profile, with a top normaldiam=60±10 μm and bottom normaldiam=180±10 μm, was obtained at 40 mTorr process pressure with an average etch rate ∼1.3 μm/min using Ni mask. The vias were then metallized by depositing a thin seed layer of Ti/Au (1000 Å) using radio frequency sputtering and Au (5 μm) electroplated to connect the front side pad and back side ground plane. The parasitic inductance offered by these vias was ∼76 pH. The developed process was then integrated into the MMIC process line and a 16-18 GHz amplifier was fabricated using grounding vias with yield >90%. © 2003 The Electrochemical Society. All rights reserved.

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A Gunn diode is a simple two terminal source of low-noise, high frequency microwave power. It is most commonly used as local oscillator in critical microwave and mm-wave systems. The system requirement of frequency agility and temperature stability impose stringent demands on the device performance and hence on its material and fabrication technology. The present paper discusses some of the technological innovations attempted in this direction along with results obtained. Some of the issues addressed are carrier concentration ramping to check velocity degradation in the active layer, power optimisation by in-situ etching, minimisation of dead zone and thermal management. Physics, design and fabrication technology and testing of Gunn diodes is also briefly described in this article.

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