高阻Si衬底对SiGe HBT高频性能的改善研究

Research on Improvement of the High Frequency Performances of SiGe HBT by the High Resistivity Si Substrate

选用电阻率高达1 000Ω·cm的硅衬底结构改善SiGe HBTs频率性能。介绍了器件的结构设计,根据衬底寄生参数模型分析了衬底阻抗影响器件高频性能的原理,计算出器件f_T和f_(max)随衬底电阻率变化的规律。测试结果表明,高电阻率衬底器件比n^+衬底器件的特征频率f_T提高了28%,而最高振荡频率f_(max)提高了47.7%;表明高电阻率衬底基本消除了SiGe HBT中大多数容性寄生网络;通过对器件的最小噪声系数的计算与测试分析,发现高阻Si衬底的引入使器件的噪声系数在低频时几乎不变,在高频时轻微增加。

The high resistivity substrate of 1000Ω·cm was employed to improve the high frequency performances of SiGe HBT. After the structure of device was introduced, the principle of how the substrate affects the high frequency performances of the device was analyzed based on the equivalent two-port network model, The characteristics of fT and fmax versus the resistivity of the substrate were analyzed. Tested results indicate that the fT and the fmax of the device based on the high resistivity substrate are 28% and 47.7% larger than that of the one based on the conventional N^＋substrate respectively. This shows that the parasitic capacitor network made by the substrate can be reduced greatly when the high resistivity substrate is employed. More ever, the minimum noise figures were deduced and measured. The results show that the minimum noise figure of SiGe HBT based on the high resistivity substrate has almost not been deteriorated at low frequency, but slightly higher at high frequency than that of one based on the n^＋ substrate.