新型宽温区高热稳定性微波功率SiGe 异质结双极晶体管

宽温区大电流下的热不稳定性严重制约着功率SiGe 异质结双极晶体管 (HBT) 在射频和微波电路中的应用.为改善器件的热不稳定性, 本文利用SILVACO TCAD建立的多指功率SiGe HBT模型, 分析了器件纵向结构中基区Ge组分分布对微波功率SiGe HBT电学特性和热学特性的影响. 研究表明, 对于基区Ge组分为阶梯分布的HBT, 由于Ge组分缓变引入了少子加速电场, 使它与均匀基区Ge组分HBT相比, 具有更高的特征频率f_T, 且电流增益β和f_T随温度变化变弱, 这有利于防止器件在宽温区工作时电学特性的漂移.同时, 器件整体温度有所降低, 但器件各指温度分布均匀性较差.考虑多指HBT各发射极指散热能力存在差异, 在器件纵向结构设计为基区Ge组分阶梯分布的同时, 对其横向版图进行发射极指间距渐变结构设计, 用于改善器件各指温度分布的均匀性, 进而提高HBT的热稳定性.结果表明, 与基区Ge组分为均匀分布的等发射极指间距结构HBT相比, 新器件各指温度分布均匀性明显改善, f_T保持了较高的值, 且β和f_T 随温度变化不敏感, 热不稳定性得到显著改善, 显示了新器件在宽温区大电流下工作的优越性. 关键词： SiGe 异质结双极晶体管 Ge组分分布 发射极指间距渐变技术 热稳定性

Novel microwave power sige heterojunction bipolar transistor with high thermal stability over a wide temperature range

Thermal instability of power SiGe heterojunction bipolar transistor (HBT) at high current over a wide temperature range restricts the applications of the device in RF and microwave circuits. In order to improve the thermal instability, the influences of Ge profile in a base region on the electrical and thermal characteristics of microwave power SiGe HBT are studied with the aid of the model of multi-finger power SiGe HBT established by SILVACO TCAD. It is shown that for the HBT with graded step Ge profile, a higher cut-off frequency f_T can be achieved due to the accelerating electric field caused by the graded step Ge concentration in the base region when compared with the device with uniform Ge profile. The influences of temperature on current gain β and f_T are weakened, which avoids the drift of electrical characteristics over a wide temperature range. Although the temperature of device is lowered, the temperature of each emitter finger is still non-uniform. Considering the difference in heat dissipation among emitter fingers, a new device with non-uniform emitter finger spacing in layout and a graded step Ge profile in base region is designed. For the new device, the uniformity of temperature among emitter fingers is achieved, higher f_T is kept, β and f_T are less sensitive to temperature variation. Hence the thermal instability is obviously improved compared with the device with uniform emitter finger spacing and uniform Ge profile in base region, indicating the superiority of the new device at high current over a wide temperature range.
Keywords： SiGe heterojunction bipolar transistor Ge-profile non-uniform emitter finger spacing thermal stability