Study On Microwave Power SiGe HBT Key Technology

In the military electronic system, the microwave power transistor plays an important role in promoting and underpinning the performance and application of solid transmitters. The Si BJT (Bipolar Junction Transistor), applied in transmitters below L band, is the first choice, but the RF power, gain and efficiency of Si BJT are acutely decreasing with the increasing of work frequency, which limits its application on high frequency. The GaAs HBT's frequency characteristics is good, its gain and efficiency are high, and is adopted in S-band and beyond. But its power density is low, in addition to its high cost, which limits its applications.SiGe HBT (Heterojunction Bipolar Transistor) holds a similar power characteristic to Si BJT and also has a much superior frequency characteristic than Si BJT does. SiGe HBT could not only replace the Si BJT in S-band and under, and could also replace GaAs HBT up to S-band, since it holds good characteristics of power, gain and efficiency, in which condition Si BJT could not work. SiGe HBT could be sued to improve the performances of the solid transmitters, and the could help radar system to get more flexible design and application. The difficulty of development and fabrication of S-band power transistor is widely acknowledged in the domestic and overseas. At the present time, the technology of S-band 100W Si BJT have been commercialized and technology of SiGe HBT is still in the coures of exploration developing. While in domestic, technology of S-band 100W of Si BJT is developing, and the technology of SiGe HBT has not yet steped in.In this disseration, technologies and theories of S-band power SiGe HBT are thoroughly developed. The research work holds exploration, and is a novel research field. The S-band 100W SiGe HBT is developed. The main area and contents of this disseration are as follows.1) Models of physical parameterBased on the design of SiGe HBT structure and study of electrical characteristics, the models of physical parameters of SiGe material are established, which character DC and AC characteristics of SiGe HBT, and they includ the model of forbidden band width, the model of availability state density, the model of intrinsic carrier concentration, the model of mobility, the model of forbidden band becoming narrow by heavy doping, the model of Ge and impurity profile in the base of SiGe material, and so on.2) Model of DC parameter on microwave power SiGe HBTBased on the hetero-emitter-junction of Si/SiGe, the model of emitter junction current injection ratio is established. Based on the structure characteristic and physical parameter of SiGe HBT, the models of the hole reversed injection current, the neutral base region recombination current, the space-charge region Augre recombination current and the space-charge region SRH (Shockley-Read-Hall) recombination current are established, on the basis of which the model of current gain is established. And combining all models, the model of the base extending critical current density of SiGe HBT is setup. And the models of current gain, the hole reversed injection current, the collector current density and base extending critical current density of SiGe HBT are simulated and analyzed.3) Model of AC parameter of microwave power SiGe HBTThe model of frequency characteristic and the model power gain are established. The frequency characteristic is dominated by the sum of emitter delay time, the base transit time, the collector depletion-layer transit time and the collector transit time. Based on study and analyse of influence of mobil charge on capacitance, the model of the emitter junction barrier capacitance and the model the collector junction barrier capacitance are established. And on the basis of these, the model of the emitter delay time is established, including base extending effect. The model of the base transit time is established. Various physical effects caused by doping and Ge fraction in base and current density are considered in the model. The model is suitable for uniform and exponential base doping with different Ge profiles in the base, and different current densities. An analytical model for the base transit time in SiGe HBT with an arbitrary base Ge profile is developed and the optimum base Ge composition profile function for minimizing the base transit time is also obtained by simulation and analysis. The models of collector depletion-layer transit time, considering the collector current densities and base extension effect, are established. Based on stuctural characteristic of SiGe HBT, the model of collector transit time is established. And these models are simulated and analyzed.4) Model of large signal equivalent circuit of microwave power SiGe HBTThe model of large signal equivalent circuit of SiGe HBT could indicate the influence of micro-structure on electricity characteristic. Based on physical conceptions, microscopic structure, work mechanism, carryers distribution and transport of SiGe HBT, the model of large signal equivalent circuit for SiGe HBT and relevant model parameters are established. The Early effect, the velocity saturation, the base extending effect and the self-heating effect are taken into account in this equivalent circuit model.The model holds the features of definite physical meaning and simple topology. And these models are embedded in the Pspice by its DEVEQ. The model is simulated and analyzed in DC and AC by the Pspice, and the simulation results accord with that of other literatures.5) Optimization of microwave power SiGe HBT structureAccording to design requirement of electrical parameters of S-band 100W SiGe HBT chip, based on the SiGe material physical parameters, the hetero-emitter-junction and the achievable technology of SiGe HBT, the vertical structure parameters are optimized, including the thickness of emitter, base and collector region, the doping concentration, the Ge profiles in the base of SiGe HBT. And the planar structure parameters are optimized, including the length and the width of emitter and base, the space between emitter and base, the ballast resistor of the emitter and the multi-layer metal electrode structure of SiGe HBT. The ratio of the emitter region area and the base region area is optimized.6) Technology design and realization of microwave power SiGe HBTBased on design requirement of frequency and power of microwave power SiGe HBT and specific fabrication technology of strained SiGe material, the process flow of SiGe HBT fabrication is optimized. The estimated models of depth and concentration of ion-implant is established. Based on the geometric structure of SiGe HBT, the technology of ion-implant and short annealing are optimized. Based on the work condition of SiGe HBT, the layer structure of multi-layer metal electrode and achievement process of sputter and electroplating are optimized.The chip of HBT is firstly fabricated in domestic, and the chip is tested, and meets follows:BVEBO=6.5V, BVCBO=75V, BVCEO=35V,β~25.7) Internal matching and power combination of microwave power SiGe HBTThe models of input and output resistance of S-band power SiGe HBT chip are established, and input and output resistance are estimated. The input and output internal matching networks are optimized. The influence of element of internal matching networks on performance of HBT is studied. And the models of inductance introducted by metal leading wire and mutual-inductance between two metal leading wires are established. The reason leading non-uniform distribution of power in power combination is studied, and the estimated model of power deviation is established. And the power combination technology is studied. Based on preview research, the S-band 100W SiGe HBT are firstly developed in domestic, which are tested, and meet follows: Working voltage 30 V Working frequency 2.7GHz—3.1GHz Impulse duyt ratio 1%--5% Input power>100W Power gain≥5dB.