Novel thermal shunt and thermal lens techniques have been used in the design of multiple-emitter AlGaAs/GaAs power HBTs (heterojunction bipolar transistors). Thermal stabilization was achieved by the use of a thick metal bridge connecting all emitters. The thickness of the bridge was designed to assure a virtual thermal short between emitters. The use of such a thermal shunt element redistributes temperature-dependent internal device currents to force an equalization of device junction temperature. The bridge further serves to spread heat from each emitter over a larger GaAs surface (thermal lens), thereby reducing overall device thermal resistance. Multiemitter devices with 2 mu m and 3 mu m minimum emitter feature sizes were fabricated and tested at microwave frequencies to demonstrate the thermally stable operation.
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Bayraktaroglu et al. (1993) studied this question.