The low frequency noise performance of strained Si heterojunction bipolar transistors (sSi HBTs) is presented for the first time. Conventional SiGe HBTs and Si bipolar junction transistors (BJTs), processed with strained Si devices, were also measured as a reference. It is found that a lower noise level is obtained in sSi HBTs for a given collector current, which is important for circuit applications, compared with either SiGe HBTs or Si BJTs. However, sSi HBTs exhibit greater low frequency noise compared with other devices at fixed base current. This is due to the presence of defects that are caused by the integration of the strain-relaxed buffer in the fabrication of sSi HBTs. The relationship between low frequency noise and defects is supported by material characterization. © 2011 IEEE.

Experimental and modeling results are reported for high-performance strained-silicon heterojunction bipolar transistors (HBTs), comprising a tensile strained-Si emitter and a compressively strained Si0.7Ge0.3 base on top of a relaxed Si0.85Ge0.15 collector. By using a Si0.85Ge0.15 virtual substrate strain platform, it is possible to utilize a greater difference in energy band gaps between the base and the emitter without strain relaxation of the base layer. This leads to much higher gain, which can be traded off against lower base resistance. There is an improvement in the current gain beta of 27x over a conventional silicon bipolar transistor and 11x over a conventional SiGe HBT, which were processed as reference devices. The gain improvement is largely attributed to the difference in energy band gap between the emitter and the base, but the conduction band offset between the base and the collector is also important for the collector current level.