The Research Of The Thermal Stability Of Multi-fingers Heterojunction Bipolar Transistor

Since multi-finger heterojunction bipolar transistors(HBTs) have better output power than one-finger HBTs, they often be used as power devices. But the self-heating and heat coupling between fingers of multi-finger HBTs lead to the uniform distribution of temperature and current, and the thermal instability problem such as collapse of current gain happen, it degrades the device performance. According to this problem, this paper present a new design method to improve the thermal stability of mutli-finger InGaP/GaAs HBT.At first, in this paper the effect of different epitaxial layer designs on the thermal stability of multi-finger InGaP/GaAs HBT was researched. Taking critical power density at collapse loci as the criteria of the thermal instability, the theoretical formulas of thermal-electrical feedback coefficient Φ, collector current ideality factor η and thermal resistance Rth were derived with the longitudinal structure parameters of epitaxial layer, such as the base doping concentration and base thickness. And then the influence machanism of these paramters on thermal stability of mutli-finger InGaP/GaAs HBT was obtained.Then, we ascertained the simulation method of thermal characteristics of InGaP/GaAs HBT, after filtering and correcting the simulation models by fitting the simulation results with measurement data. The project completed device structure design with Sentaurus Structure Editor and device physical properties simulation with Sentaurus Device. Finally, the simulation of the effect of structure parameters on the thermal characteristics of InGaP/GaAs HBT was finished in Sentaurus Workbench integration platform. We obtained the commom-emitter Ⅰ-Ⅴ characteristics and collapse curves with different epitaxial layer designs through the simulation method above. Based on the simulation results, the thermal stability of multi-finger InGaP/GaAs HBT with different epitaxial layer designs was discussed, compared with the results derived by theoretical formulas and confirmed them in turn. Then a new method to improve the thermal stability of multifinger InGaP/GaAs HBT was provided. The centre work of this article is that we theoretically analysed the relation between epitaxial layer structure of multi-finger InGaP/GaAs HBT and its thermal stability, simulated InGaP/GaAs HBT thermal characteristics in TCAD simulation platform, and optimized the device structure for improving the thermal stability of device.The main contribution of this article is that, based on the derived theoretical formulas and simulation by TCAD, we achieved optimization design for improving thermal stability of multi-finger InGaP/GaAs HBT, proposed and proved the feasibility of improving the thermal stability by the epitaxial layer optimization design, and then presented a new method in improving the thermal stability of multi-finger InGaP/GaAs HBT.The new method presented in this article improves the combination property of multi-finger InGaP/GaAs HBT without the ballasting resistance, and has the potential application value in solving the thermal instability problem exist in HBT device when it operates in the microwave millimeter wave scope.