Fig. 1. The measured emitter-base junction voltage V_BE as a function of T under different emitter currents of 3 mA， 1 mA， 100 µA and 10 µA respectively

Fig. 2. The schematic diagram of an N-finger HBT， where R_Ei is the emitter ballasting resistor of the ith emitter finger^［8-9］

Fig. 3. The schematic-cross section of a cell in multi-finger HBTs

Fig. 4. Micrographs of the fabricated multi-fingers SiGe HBTs with emitter ballasting resistor.（Note： polysilicon emitter ballasting resistors locate at root terminal of each emitter finger， see the enlarged image）

Fig. 5. Micrograph of the fabricated multi-fingers SiGe HBTs with non-uniform finger spacing

Fig. 6. Measured surface temperature distribution by US QFI Infrared TMS for (a) a multi-finger power HBT with emitter ballasting resistor, and (b)for a multi-finger power HBT with non-uniform finger spacing under I_C＝800 mA, V_CE＝5 V and case temperature of T_C=80 ℃

Fig. 7. The block diagram of RF power measurement system

Fig. 8. RF Output power p_outversus RF input power p_in for two types of multi-fingers power HBTs with emitter ballasting resistor and with non-uniform emitter finger spacing respectively

Fig. 9. Collector efficiency η_Cversus RF input power p_in for two types of multi-fingers power HBTs with emitter ballasting resistor and with non-uniform emitter finger spacing respectively.

Fig. 10. Power-added-efficiency（PAE） versus RF input power p_in for two types of multi-fingers power HBTs with emitter ballasting resistor and with non-uniform emitter finger spacing respectively