射频功率HBT热稳定性分析及镇流电阻优化

Thermal Stability Analysis of RF Power HBT and Ballasting Resistor Optimum for the Self-heating Effect Compensation

为了有效改善射频功率HBT的热不稳定性、消除自加热效应对功率器件电学特性的影响,从热电反馈网络出发,阐述了晶体管热稳定因子S的物理意义.在考虑发射极电流正温度系数、器件能带连续性(△E_v)、重掺杂效应(△E_g)、基极和发射极加入镇流电阻(R_B和R_E)等因素的情况下。给出了功率HBT自热完全补偿(S= 0)所需最小镇流电阻(R_c)表达式.结果表明,在△E_v+△E_g>2κT时,HBT工作温度丁越大,R_c反而越小.由于R_c的减小,功率HBT将能提供更大的输出功率、功率增益和功率附加效率.

In order to improve the thermal stability of RF power HBT and eliminate the self-heating effect which degenerates the transistor＇s electrical characteristics, the physical significance of thermal stability factor S is presented in detail based on the thermal-electric feedback network analysis. Furthermore, the expression of the minimum ballasting resistance R c of HBT to compensate the self-heating effect （S = 0） is presented by taking into account of the temperature dependence of emitter current, the valence-band discontinuity at emitter junction （△EV）, the bandgap narrowing due to heavy doping （△Eg）, additional ballasting resistance in emitter and base. It is found that the higher the temperature T is, the smaller the minimum ballasting resistance Rc to compensate the self-heating effect is under the condition that （△EV ＋△Eg） 〉2KT. Owing to the reducing of ballasting resistance, RF power HBT will provide higher output power, power gain, and power-added efficiency （PAE） in an amplifier block.