Research On The Unconditional Stability Of GaInp/GaAs Heterojunction Device

Due to the popular using in MMIC, high-speed digitial circuit, optial communication, Wireless mobile communication Base Station Systems, mobile terminal systems, military radar systems, GaAs power transistor has becoming one of the main technology in the development of RF and microwave power amplifier.But because of big size and big feedback in input and output, the stability of GaAs HBT power transistor was low, which would cause self-excited oscillation, and the modeling, testing and application of transistor might be puzzled. Targeting at solve this problem, this paper put forward a new method could solve this problem and verification this method.The main point of this paper is that exploring the new method that modifies GaAs hetrojunction bipolar transistor (HBT) stability through the optimization of transistor structure parameters, and obtaining a unconditional stable HBT from low frequency (lower than1GHz) to high frequency, and both the high frequency power gain and output power are well considered; which could avoid the using of stabilization network.Based on experiments results, this topic uses Synopsys Sentaurus TCAD do the device simulation. Modeling and the model parameters of the device was modified, simulation results are in good agreement with the experiments.Then device physical parameters were optimized, and the influence of the main parameter on device stability was investigated. The main work can be summarized as follows:(1). Based on experimental datas, suitable physical models were adopted, and model parameters was modified by the comparation of DC Characteristics. The parameters include band gap, dielectric constant and relaxation time of GaInP and GaAs; and the SRH, Auger and Radiative recombination model parameters were improved. A set of virtual device models could represent a real device is obtained though experimental fitting.(2). The unconditional stability of GaInP/GaAs HBT was studied, and the stability factor K was obtained. Changing the physical parameters, for instance, the thickness and doping concentration of base, emitter and collector respectively, the influence of each parameter on device stability was investigated and then the optimization analysis of equivalent circuit level was carried out. (3). According to the results, a group of GaInP/GaAs HBT physical parameters which could meet the requirement of stability were selected. Then the DC and frequency characteristics were given to show the method this topic adopted is feasible.According to the results:The influence of GaInP/GaAs HBT physical parameter on device stability was very obvious; by optimizing the structure parameters of device, under the bias conditions of Vbe=1.35V and Vce=2.0V, a device with unconditional stability at the working frequency as low as100MHz is obtained; and fmax=45GHz, moreover the RF gain of the device is almost not deterated, far less than20%. So the method this topic adopted is worth being studied further and has potential application in the stability design of RF circuits.