【作者】 刘亮；

【导师】 亢宝位；

【作者基本信息】 北京工业大学 ， 微电子学与固体电子学， 2004， 硕士

【摘要】 锗硅技术因其良好的集成功能以及优越的高频性能而在微波功率器件领域和射频集成电路领域中得到了广泛的应用，而制造高线性度的微波功率锗硅异质结晶体管（SiGe HBT）也成为一个非常有实际意义的课题。已有实验通过研究SiGe HBTs中锗的分布和建立器件模型来分析应用于射频集成电路或微波功率器件中的SiGe HBTs的线性问题，使现有SiGe HBTs的三阶截取点（IP3）能达到25dBm左右。但是还缺少全面的从器件设计角度来进一步提高微波功率SiGeHBT线性度的方法。论文通过建立非线性模型分析SiGe HBT的高频线性特性，并利用该模型推导出各种非线性因素（如非线性基区电阻RB、非线性基区-集电区电容CBC、非线性跨导gm）产生的各次谐波电流的计算公式。结合Volterra级数以及复合改进节点法（CMNA）法来求解模型端点处的各次谐波电压的大小，利用计算结果解释SiGe HBT的非线性相消现象并总结出可以提高微波功率SiGeHBT线性度的方法。 根据现有的SiGe HBT制造工艺设计出合理的仿真结构，结合交流小信号仿真和瞬态仿真来计算器件的高频性能参数：器件工作在VCE为 2.5 伏的低压下其? ，? T max分别超过 20Ghz和 100Ghz；工作在 1Ghz的高频信号下，器件的IP3能达到 28dBm。通过大量的计算机仿真和对不同尺寸和杂质掺杂浓度的SiGe HBTs的IP3进行比较发现：①、增大发射区电阻RE能增加电路的负反馈从而降低跨导gm的非线性，并因此改善器件的线性度（RE为 0.7?比RE为 0.2?的器件IP3提高1~1.5dBm）。②、基区电阻RB产生的三次谐波电流与RB的高次项成反比，因此减小基区的掺杂浓度或基区宽度会提高IP3。③、当注入到集电区中的电子浓度和集电区的掺杂浓度相比不可忽略时， CBC成为器件主要的非线性因素，这时空间电荷区的分布会随电流密度变化而改变，而且空间电荷区边界变化越明显线性度越差，仿真结果表明集电区掺杂浓度为 5×1016cm-3的 SiGe HBT其IP3要比掺杂浓度为 4×1016cm-3的SiGe HBT高 2~3dBm。④、增加集电区宽度会使电流横向扩展现象更加明显，从而延长空间电荷区，并使器件的线性性能下降。⑤、用挖槽减小外基区-集电区电容（Cbcx）的方法在小电流密度工作时能改善器件的线性度，但是当电流密度增加时，因集电区中的电流无法横向扩展而使器件的线性性能明显下降。 论文中的仿真始终与理论分析相结合，这些仿真数据和分析结果将有助于今后设计应用于现代无线通信中的高线性度的微波功率 SiGe HBTs。更多还原

【Abstract】 The SiGe (silicon-germanium) technology is used widely in the fields ofmicrowave power devices and RF integrated circuits because of its easily integratedfunction and excellent high frequency characteristics. And making high linearitymicrowave power SiGe HBTs (heterojunction bipolar transistors) has been a projectwith high practical meaning. The linearity problem of SiGe HBTs used on RFintegrated circuits or microwave power devices have been analyzed by someexperiments through studying the Ge-Profile of SiGe HBTs and building devicesmodel, and the IP3 of existing SiGe HBTs has reached about 25dBm. Butcomprehensive methods that can improve the linearity of SiGe HBTs from the anglesof devices design are still to be researched. To analyze the high frequency linearitycharacteristics of SiGe HBTs, a nonlinear model is built. And this model is also usedto deduce the formulae of harmonic currents which are induced by several kinds ofnonlinear factors, such as nonlinear base resistor RB, nonlinear base-collectorcapacitor CBC and nonlinear transconductance gm. Combing the Volterra series andCMNA (compacted modified nodal analysis) method to calculate the harmonicvoltages of the nodes of the model, and use the result to explain the nonlinearitycancellation phenomenon and to find the ways that can improve the linearity of themicrowave power SiGe HBTs. Designing reasonable simulation structures accords existing SiGe fabricationtechnologies. Calculate parameters of high frequency characteristics of the devicesthrough small signal AC simulation and transient simulation: the ? and ? T maxreachhigher than 20Ghz and 100Ghz respectively when the VCE of the device is 2.5V; thehighest IP3 (third-order intercept point) can reach 28dBm when the working frequencyis 1Ghz. Through a great deal of simulations and comparisons of IP3 among SiGeHBTs with different size or different doping concentration the followings can befound. 1) Augmenting emitter resistance RE can increase the minus feedback of thecircuit and reduce the nonlinearity of transcondutance gm, and then improve thelinearity of the device (the IP3 of the device whose RE is 0.7? is 1~1.5dBm higherthan the device whose RE is 0.2?). 2) The third-order harmonic current induced bybase resistance RB is in proportion to the high-order value of RB, so the IP3 isincreased by decreasing the doping concentration or by decreasing the base width. 3)When the electron density injecting into collector could not be ignored compared with - II -<WP=6>摘要the doping concentration, the CBC becomes the main factor of the nonlinearity of thedevice. At this time the space charge region will change with the change of currentdensity, the more the boundary of space charge region changes the worse the linearity.Through the outcome of simulations it is found that the IP3 of SiGe HBT whosecollector doping concentration is 5×1016cm-3 is 2~3dBm higher than the SiGe HBTwhose collector doping concentration is 4×1016cm-3. 4) Increasing the width ofcollector will make the current spreading effect more obvious, and then extend thespace charge region and make the linearity characteristic of the devices worse. 5) Theway that can decrease the Cbcx (extrinsic base-collector collector) by making trenchcan improve the linearity of the device when the current density is small. But whenthe current density increases, the linearity characteristic will decline because thecurrent in collector could not spread transversely. The simulations in this paper are combined with theory analysis all the time. Thedata of simulations and the analysis result will be helpful in designing microwavepower SiGe HBTs with high linearity used in modern wireless communication.更多还原