Analysis of thermal instability in multi-finger power AlGaAs/GaAsHBT's |
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Authors: | Lu K Snowden CM |
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Institution: | Dept. of Electron. & Electr. Eng., Leeds Univ. ; |
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Abstract: | A new theory is developed in this paper to explain the collapse of current gain in multi-finger power AlGaAs/GaAs Heterojunction Bipolar Transistors (HBT's). The reasons behind this unwanted phenomenon are fully clarified using a simple model to investigate the thermo-electrical interaction between the fingers. The existence of multi-value equilibrium points in model's constitutive equations is shown to be the necessary condition for the collapse of current gain to appear. For a N-finger device, N different patterns of collapse exist. The criterion to select the global stable pattern is given. The method has been used to predict the collapse in AlGaAs/GaAs HBT's and the agreement is excellent. The method also predicts that the collapse can happen far earlier than is normally expected in multi-finger high-power devices. The influence of ballasting resistance and thermal resistance is also investigated |
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