| Summary: | 碩士 === 國立成功大學 === 電機工程學系 === 89 === Recent advances in communication, radar and computational systems demand very high performance electronic circuit. Heterojunction bipolar transistors (HBTs) have potential of providing a more efficient solution to many key system requirements through intrinsic device advantages than competing technologies. HBTs have also shown great potential both for microwave power and low-voltage applications.
Many applications will require HBTs transistor to operate above ambient temperature due to high power density and poor thermal conductivity of GaAs substrate. In this thesis, the temperature dependence of current gain is investigated for GaAs-base HBT. The thermionic- emission current plays an important role for the hole current, which results in a negative temperature coefficient for current gain.
The dependence of the collector-emitter offset voltage (Voffset) on the base current, substrate temperature. We found that Voffset decreases at moderate base current, and begins to increase at very high IB. Moreover, Voffset increases linearly with the temperature.
Under high self-heating operating conditions, a technique is presented that can directly extract the mean device junction and thermal impedance. The method uses three trivial dc measurements of the device where the junction temperature is known to be the same. Result show that the thermal impedance varied with both ambient temperature and power dissipation at high junction temperature.
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