| dc.description.abstract | This thesis focuses on the establishment of VBIC model and the characteristics analysis, including the thermal influence, of power HBTs. It contains three parts: (1) the simplification and the optimization for the elementary cell HBT model, which is applied to large-size power HBTs, (2) investigating the characteristics with thermal effect, (3) obtaining thermal resistance and junction temperature by means of two measured methods.
After the simplification and the optimization procedure of the VBIC model, the characteristics of HBT for elementary cell could be derived efficiently and exactly. However, when the model was applied to the HBTs which operate in parallel, the model would not perform correctly. Therefore, the developed model is necessary to be used to improve the accuracy. Adding the lumped equivalent circuit into the elementary cell, the proposed approach could reduce error ratio when applying to the large-size device.
Furthermore the power HBT’s characteristics, including the thermal effect, is also investigated. Since such HBTs are operated at high power levels, the device temperature will significantly rise, which results in the self-heating effect and degrade the device performance and reliability. Thermal resistance is the key parameter of thermal effect. Two different methods would be applied to measure the thermal resistance. Firstly, a CW mode method to accurately obtain the thermal resistance of HBT’s is presented. The key advantage of the method is its simplicity, because it requires only the measurement of the device DC output characteristics at two different temperatures. In addition, the other method is the measurement of IR thermograph, which could derive the highest temperature of device surface, following to obtain the thermal resistance. The thermal resistance obtained with two methods would be in comparison finally. | en_US |