Research on SiGe heterojunction bipolar transistor with a trench-type emitter

A novel SiGe heterojunction bipolar transistor (HBT) with a trench-type emitter is presented. Effects of the trench-type emitter on device performance are analyzed in detail, and current transport mechanism of the novel device is studied. The emitter resistances are parallel partitions by changing current path. Under the precondition without increasing the junction capacitance, the resistances of the new emitter are reduced effectively, and the frequency characteristics of the device are improved. Results show that the cutoff frequency and the maximum oscillation frequency of the new device are increased to 100.2 GHz and 134.4 GHz, respectively. More important is that the frequency characteristics are improved by the introduction of the trench-type emitter, while the current gain is not reduced and the junction capacitance is also not increased. A good trade-off is achieved among frequency, current gain, and junction capacitance. The trench-type emitter is designed to be optimal. With the change in sidewall height, no effects are found on the emitter resistances, and the frequency characteristics do not change, while the frequency characteristics are reduced when the sidewall width is increased.