具有高频高压大电流优值的超结集电区SiGe HBT

为了在兼顾特征频率( fT )和电流增益(β)的情况下有效提高器件的击穿电压( BVCBO/BVCEO ),利用SILVACO TCAD建立了npn型超结集电区SiGe异质结双极晶体管( heterojunction bipolar transistor,HBT)的器件模型.研究表明：通过在集电结空间电荷区( collector-base space charge region,CB SCR)内引入p型超结层可有效降低“死区”内的电场强度,使较高的电场强度转移至“死区”外较深的CB SCR内,进而在几乎不增加CB SCR宽度的情况下抑制碰撞电离,达到提高击穿电压、改善fT和β的目的.随着p型超结层厚度( dp )的增加,击穿电压BVCBO和BVCEO的改善也越明显.但dp值需优化,较大的dp值将引发Kirk效应,大幅降低器件的fT和β.进一步通过优化p型超结层的dp值,设计出一款dp为0.2μm且具有高频高压大电流优值( fT ×BVCEO ×β)的新型超结集电区SiGe HBT.结果表明：与传统SiGe HBT相比,新器件的fT ×BVCEO ×β优值改善高达35.5%,有效拓展了功率SiGe HBT的高压大电流工作范围.

Superjunction Collector SiGe HBT With Figure of Merit of High Frequency High Voltage and High Current

To enhance the breakdown voltages ( BVCBO/BVCEO ) at a fixed cutoff frequency ( fT ) and current gain (β) , a model of npn SiGe heterojunction bipolar transistor ( HBT ) with superjunction collector was established by SILVACO TCAD. The research shows that the p-type superjunction layer inside the collector-base ( CB) space charge region ( SCR) lowers the electric field in the “dead space region”, and shifts the part of the high electric field somehow deep into the CB SCR which is located at the outside of the “dead space region”. As a result, impact ionization is suppressed, whereas the width of the CB SCR is slightly increased, and hence the breakdown voltages are improved at a minor expense of fT and β. As the increase of the thickness of p-type superjunction layer (dp), the breakdown voltages including BVCBO and BVCEO are improved more obviously. However, dp also needs to be optimized, considering that larger dp would lead to Kirk effect and give rise to a dramatic decrease of fT and β. Furthermore, the value of dp in p-type superjunction layer is optimized as 0. 2μm for a novel superjuction
collector SiGe HBT with figure of merit of high frequency high voltage and high current ( fTíBVCEOíβ) . Compared with the conventional SiGe HBT, the figure of merit of fT íBVCEO íβ for the novel device is markedly improved by 35. 5%, which effectively develops the high voltage and high current application of power SiGe HBT.