H. S. Sharma

Anisotropic Etching of GaAs Using CCl2 F 2 / CCl4 Gases to Fabricate 200 μm Deep Via Holes for Grounding MMICs

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 CCl 2 F 2 and CCl 4 gases for fabrication of through substrate via holes for grounding in monolithic microwave integrated circuits (MMICs). The effect of process parameters viz. pressure, CCl 4 /CCl 2 F 2 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 diam = 60 ′ 10 μm and bottom diam = 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 A) 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%.

Advances in Gunn Diode Technology

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.

Light-induced effect in GaAs MESFETs

Abstract In this paper the possibility of using GaAs MESFETs under Schottky gate illumination for photodetection and switching has been experimentally demonstrated. Semitransparent Au metallization is used for Schottky gate formation. The results discussed here provide experimental support to the behaviour predicted for such configurations.

(n)GaAs/Ti/Pt/Au Schottky contacts and their effect on MESFET's dc parameters

Abstract Rf sputtered Ti/Pt/Au Schottky contacts with varying titanium thickness have been made on (n)GaAs by the lift-off process under actual device processing conditions. The ideality factor of the Schottky barrier is dose to unity (∼ 1.07) with a barrier height of 0.80 ± 0.02 eV. The contacts with Ti films as thin as 100 A remain thermally stable with annealing up to 400°C. These contacts have been next used to fabricate submicron gate length GaAs MESFETs. The MESFETs gm increases with improved gate diode ideality but is not a strong function of it. The effect of Schottky gate annealing on the MESFETs dc characteristics shows that IDSS, gm, Vp and VR(GS) remain stable with annealing upto 350°C and degrade with 400° anneal.

Fabrication of millimetre-wave Gunn and IMPATT devices with integral heat sink and integral bonding ribbon: a new approach

Abstract Discrete millimetre-wave devices, i.e. Gunn and IMPATT diodes, dissipate a large amount of power in the form of heat. Devices fabricated with an integral heat sink (IHS) are known to show superior performance compared with conventional devices. A novel process was developed for the fabrication of IHS integral bonding ribbon (IBR) millimetre-wave devices. The method employs “through holes” generated on the wafer as marks for “front to back” alignment of the IHS and IBR. The process is found to be highly reproducible and versatile. Devices have shown several advantages in terms of ease of processing and yield. The process can thus be used to fabricate devices different semiconductor materials and possibly for all devices requiring the IHS-IBR configuration.