Emitter-ballasting-resistor-free SiGe microwave power heterojunction bipolar transistor

The emitter ballasting resistor is used to equalize the current distribution between the emitter stripes in pou er transistor, but it will degrade the output power, power gain, and power added efficiency. Experimental result indicates that the current gain of uniform-base SiGe heterojunction bipolar transistors (HBT's) decreases with the increase of the temperature above temperature of 160 K, so the current distribution is equalized by itself to some extent. Therefore, the microwave pow er SiGe HBT's without emitter ballasting resistor were fabricated for the first time, and the continuous output power of 5 W and power added efficiency of 63% were obtained under Class C operation at frequency of 900 MHz. Hence, the emitter current density of the SiGe HBT's with emitter width of 6 mu m is 0.79 A/cm.