能带工程对射频功率SiGe异质结双极晶体管热性能的改善

Effect of bandgap engineering on thermal characteristic of radio frequency power SiGe heterojunction bipolar transistor

众所周知,基区"能带工程"可以改善Si1-xGex基区异质结双极晶体管(HBT)的直流、频率和噪声等特性,但"能带工程"对HBT热学特性的影响的研究还很少。本文基于三维热电反馈模型,分析了"能带工程"对射频功率SiGeHBT热性能的影响。考虑到电流增益随温度的变化以及发射结电压负温度系数,给出了器件热稳定所需最小镇流电阻(REmin)的表达式,在此基础上给出了非均匀镇流电阻的设计,进一步提高了SiGe HBT的热稳定性。研究发现,随基区Ge组分的增加,芯片表面温度降低,这是SiGeHBT内部产生了热电负反馈效应的结果。在相同的耗散功率下,随着基区Ge组分的增加,器件热稳定所需的镇流电阻减小。这些结果对器件的热学设计具有重要的参考意义,也有利于改善器件的饱和压降、功率增益、频率特性等整体性能。

As is well known,direct-current（DC） characteristic,frequency characteristic and noise characteristic of SiGe heterojunction bipolar transistor（HBT） can be improved by＂bandgap engineering＂（by Ge composition）.However,the effect of＂bandgap engineering＂on the thermal characteristic of HBT has not been reported.In this paper,the effect of ＂bandgap engineering＂is analyzed by the use of 3D thermal-electric feedback model.Considering the temperature dependence of emitter junction voltage and current gain,the expression of the minimum emitter ballasting resistance（REmin）,which is necessary for SiGe HBT thermal stability,is presented.Furthermore,non-uniform ballasting resistance design is given so as to further enhance the thermal stability of device.It is found that the surface temperature of the device decreases with the increase of Ge composition in SiGe base.This is because SiGe HBT internally possesses the thermal-electrical negative feedback.For the same dissipated power,the REmin decreases as Ge composition increases,which is beneficial to the improvment of the performance of radio frequancy（RF） power SiGe HBT.These results provide a good guide to further optimization of RF power SiGe HBT performance,especially thermal design.