Noise performance in strained Si heterojunction bipolar transistors

In this paper, a study of the noise performance of strained Si Heterojunction Bipolar Transistors (sSi HBTs) is presented. This novel device exhibits low noise levels compared with Si Bipolar Junction Transistors (Si BJTs) and SiGe Heterojunction Bipolar Transistors (SiGe HBTs) for the same collector current, which can lower the noise in circuit applications. This performance benefit originates from the high current gain in sSi HBTs. However, the latter shows a higher noise level compared with the other devices at fixed base current. This is due to the presence of defects that are caused by the integration of a strained relaxed buffer used in the fabrication of sSi HBTs. The relationship between low frequency noise and defects has also been demonstrated using material characterisation.