2008 NSTI Nanotechnology Conference and Trade Show - Nanotech 2008 - 11th Annual

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Clean Technology 2008

High-Frequency Characteristic Optimization of Heterojunction Bipolar Transistors

Y. Li, C-H Hwang, Y-C Chen
National Chiao Tung University, TW

bipolar transistors, impurity doping, SiGe, HBT, high frequency, GP optimization

In this paper, an optimization technique (so-called the geometric programming) is employed to optimize the base doping and Ge-dose for SiGe HBTs with high cut-off frequency and base-collector current gain. This work first formulates Kroemer’s double integration base transit time model as a function of base doping and Ge dose. By transforming this model, approximating the gradient of doping profile, and considering background doping, the solution of GP model quantitatively finds that the effects of Ge profile on high frequency and current gain property for the explored SiGe HBT. Our GP’s results show that a 23% Ge fraction maximizes the current gain, where a factor of 1100 is attained, and a 12.5% Ge can maximize the cut-off frequency which could be 253.98 GHz. TCAD simulation is further performed to verify the result of the GP optimized doping profile of Ge HBTs. The cut-off frequency optimized by GP is 70.55 GHz, which is closed to the result of TCAD simulation (it is about 69.52 GHz). Experimental calibration for the fabricated samples is currently under examination.

Nanotech 2008 Conference Program Abstract