Improved high-frequency equivalent circuit model based on distributed effects for SiGe HBTs with CBE layout

Abstract

In this paper, we present an improved high-frequency equivalent circuit for SiGe heterojunction bipolar transistors (HBTs) with a CBE layout, where we consider the distributed effects along the base region. The actual device structure is divided into three parts: a link base region under a spacer oxide, an intrinsic transistor region under the emitter window, and an extrinsic base region. Each region is considered as a two-port network, and is composed of a distributed resistance and capacitance. We solve the admittance parameters by solving the transmission-line equation. Then, we obtain the smallsignal equivalent circuit depending on the reasonable approximations. Unlike previous compact models, in our proposed model, we introduce an additional internal base node, and the intrinsic base resistance is shifted into this internal base node, which can theoretically explain the anomalous change in the intrinsic bias-dependent collector resistance in the conventional compact model.

Thermal resistance matrix representation of thermal effects and thermal design of microwave power HBTs with two-dimensional array layout*

“…In recent years, heterojunction bipolar transistors (HBTs) array with parallel HBT cells layout has been used widely for microwave power applications [1][2][3][4] due to its high current handling capability. [5][6][7] However, the self-heating effect caused by the power dissipation of each HBT cell and the thermal coupling effect among the adjacent HBT cells result in an uneven temperature profile in the HBTs array. Because of the positive temperature coefficient of the emitter current, the central HBT cells with higher temperature will conduct more current and consequently generate more heat, which aggravates the thermal effects and leads to thermal breakdown or thermal runaway.…”