Research On GaAs HBT Device Model

Using a material with a wider bandgap for the emitter adds a degree of freedom in the design of bipolar transistors,which enables operation at high power densities and high frequencies at the same time.Invented and patented in the 1950 s by W.Shockley and extensively theoretically investigated by H.Kroemer in the 1970 s,the technology did not become available until the 1980 s.A tremendous development has taken place since then and the heterojunction bipolar transistor(HBT)has become an indispensable microwave device.In recent years,Ga As HBT is mainly used in power amplifier of mobile phone.Due to its high cut-off frequency,it is possible to provide high breakdown voltage at medium and high frequency for components such as wireless services.For circuit design,transistor model is one of the key components.The model should accurately simulate the terminal behavior of transistors under any bias conditions,excitations and ambient temperatures,which can help designers understand the principle of transistors,so as to select appropriate devices and circuits for specific tasks.The main contents of this paper are as follows:(1)This paper introduces the basic structures and theories of PN junction and HBT,and describes the basic device testing technology.This paper introduces four common HBT models: VBIC(Vertical Bipolar Inter-Company),HIgh-CUrrent Model(HICUM),Agilent HBT and UCSD,and focuses on the equation structure and parameter significance of UCSD model.(2)An improved small-signal equivalent circuit of HBT concerning the AC current crowding effect is proposed in this paper.The AC current crowding effect is modeled as a parallel RC circuit,while the distributed base-collector junction capacitance is also taken into account.(3)Based on UCSD model equation,an improved large signal model for Ga As HBT devices is presented,with emphasis on the improvement of collector charge equation and carrier transition model.Based on a large amount of data in the laboratory,the model parameters were extracted and modeled in the frequency range from0.1?20GHz under multi-bias conditions.In addition,the nonlinear property of this improved HBT model is verified.A geometric dimension scaling model based on the improved HBT model is proposed,the scaling rules are established and verified.Finally,the output power,power gain and power additional efficiency of this proposed HBT model are verified.