A Strained Si/SiGe Heterojunction Bipolar Transistor with Thin Si3N4 Film Fabricated on SOI Substrate

In this paper, a layer of Si
₃
N
₄
deposited on the top layer of the device structure introduces uniaxial compressive stress in the base to enhance the carrier mobility and improve the cutoff frequency and the maximum oscillation frequency. First, the current gain of the SOI SiGe HBT and the Early voltage are introduced. Next, the influence of the thickness of the buried oxide layer on the frequency characteristics is studied. The increase of T
_BOX
can improve frequency characteristics. However, the increase of T
_BOX
will affect the stability of the device. Finally, the influence of the uniaxial compression stress on the frequency characteristics of the device is studied. When T
_BOX
is 190nm, the Ge composition of the base region is 17% to 30% in a stepped distribution and a layer of Si
₃
N
₄
is deposited to introduce stress, the current gain is about 2342, and the Early voltage is about 105.6V, the product of the Early voltage and the current gain is about 2.473×10
⁵
V, the cutoff frequency is about 587GHz, and the maximum oscillation frequency is about 849GHz. Compared with the traditional SOI SiGe HBT, it has a 4 % improvement in the cutoff frequency and a 13% improvement in the maximum oscillation frequency.