Low noise microwave bipolar transistors fabricated by electron and photon lithography

A low noise microwave bipolar transistor was designed and fabricated with the aid of the BTL electron beam exposure system (EBES) (1). The transistors have nominal 1 µm emitter stripes and were processed on 2-inch silicon wafers. The alignment of the critical levels which were written on the wafers directly by EBES were within 0.25 µm. A self-aligned submicron buffer base region is inserted between the heavily doped inactive base region and the active base region. This buffer base region alleviated the problem of emitter-base shorts without having to lower the inactive base doping. At 1.7 GHz the noise figure ranges from 1.8 - 1.9 dB and the available gain ranges from 11 - 12 dB. The current gain-bandwidth frequency, fT, is 7 GHz at the optimum collector current.