Small-scaled InGaP/GaAs HBTs with WSi/Ti base electrode and buried SiO/sub 2/

This paper describes the fabrication and characteristics of small-scaled InGaP/GaAs HBTs with high-speed as well as low-current operation. To reduce both the emitter size S/sub E/ and the base-collector capacitance C/sub BC/ simultaneously, the HBTs are fabricated by using WSi/Ti as the base electrode and by burying SiO/sub 2/ in the extrinsic base-collector region under the base electrode. WSi/Ti simplifies and facilitates processing to fabricate a small base electrode, and makes it possible to reduce the width of the base contact to less than 0.4 /spl mu/m without the large increase in the base resistance. The DC current gain of 20 is obtained for an HBT with S/sub E/ of 0.3/spl times/1.6 /spl mu/m/sup 2/ due to the suppression of emitter size effect by using InGaP as the emitter material. An HBT with SE of 0.6/spl times/4.6 /spl mu/m/sup 2/ exhibited f/sub T/ of 138 GHz and f/sub max/ of 275 GHz at I/sub C/ of 4 mA; and an HBT with SE of 0.3/spl times/1.6 /spl mu/m/sup 2/ exhibited f/sub T/ of 96 GHz and f/sub max/ of 197 GHz at I/sub C/ of 1 mA. These results indicate the great potential of these HBTs for high-speed and low-power circuit applications.