Mextram Model Parameter Extraction Of SiGe HBT And Study On Its RF Avalanche Effect

Based on heterojunction energy band structure,SiGe Heterojunction Bipolar Transistor(HBT)has higher cut-off frequency,highest oscillation frequency and breakdown voltage,Compared with Si BJT.SiGe HBT is widely used in RF/microwave fields.In order to guide circuit design with SiGe HBTs and reduce production costs,more accurate models of SiGe HBTs are required to simulate and optimize performance of RF/microwave circuit.Based on the SiGe HBT Mextram505.00 model,the low current parameters and high current parameters are extracted in a wide temperature range.The avalanche mechanism of the SiGe HBT is studied.The RF avalanche effect inductive breakdown network is established and it is embedded in Mextram505.00 model.The main work of the thesis is as follows:First of all,the basic structure,working principle and device characteristics of SiGe HBT are studied and its DC characteristics and frequency characteristics are analyzed.The basic theory of the Mextram505.00 model is summarized,including the physical meaning of the model,temperature scaling rules,self-heating effects,and transistor parameter classification.Secondly,the parameter of SiGe HBT Mextram505.00 model is extracted in a wide temperature range by using the parameter extraction software ICCAP.The emitter area of SiGe HBT is 0.5×2.5 μm~2.Based on the parameter extraction strategy,the initial value of the parameter is set.The low current parameters are extracted.In the extraction process,the physical characteristics of the transistor are characterized,mainly including capacitance,Early effect,avalanche effect,Gummel effect,resistance,built-in voltage VdC,low current output characteristics and temperature scaling characteristics.The results show that there is a good agreement between the characteristic fitting curve of SiGe HBT device and the test data in a wide temperature range.Thirdly,based on the extraction of low current parameters,the high current parameters are extracted.In the process of parameter extraction,high current output characteristics,cut-off frequency and temperature scaling characteristics are considered,and the Gummel curve is verified multiple times to improve the accuracy of the model.On this basis,the epilayer parameters and time parameters are also extracted,and the temperature scaling parameters are optimized.Finally,the avalanche mechanism of SiGe HBT is studied.The RF avalanche phase delay and transit-time delay in the BC junction will cause the RF current to lag behind the collector RF voltage.The breakdown inductance and breakdown resistance are used to characterize the RF inductive delay characteristics and the contribution of the avalanche carriers in the BC junction.The RF avalanche effect inductive breakdown network is established and it is embedded in Mextram505.00 model.At the same time,the model parameters are extracted.Compared with the traditional Mextram505.00 model,the fitting accuracy of the output impedance parameter S22 and the device gain parameter S21 of the improved model is greatly improved in the range of 1～35GHz.The DC characteristics of the device will not be sacrificed.Meanwhile,the sensitive parameters Aem and Vg are extracted from the electronic breakdown inductance Ljcn,electronic breakdown resistance Rjcn,output curve,output impedance parameter S22 and device gain parameter S21 of the improved model.The results show that the improved model with RF inductive breakdown network can accurately predict the performance of SiGe HBT devices when impact ionization occurs under RF conditions.