High efficiency AlGaAs/GaAs power HBTs at a low supply voltage for digital cellular phones

We present a high performance AlGaAs/GaAs power HBT with very low thermal resistance for digital cellular phones. Device structure with emitter air-bridge is utilized and device layout is optimized to reduce thermal resistance by three-dimensional thermal flow analysis, and in spite of a rather thick substrate (100 /spl mu/m), a low thermal resistance of 23/spl deg/C/W is achieved for a multi-finger (4/spl times/40 /spl mu/m/sup 2//spl times/40 fingers) HBT. This 40 finger HBT achieved power added efficiency (PAE) of over 53%, 29.1 dBm output power (Pout) and high associated gain (Ga) of 13.5 dB with 50 KHz adjacent channel leakage power (Padj) of less than 48 dBc under a 948 MHz /spl pi//4-shifted QPSK modulation with 3.4 V emitter-collector voltage.