Contents I. Introduction
With recent technology advancements that push cutoff frequency and maximum oscillation frequency over 200GHz [1], [2], Si/SiGe heterojunction bipolar transistors (HBTs) have become viable candidates for most microwave applications. It is known that SiGe HBTs are suited ideally for large-volume manufacturing of RF transceiver systems at and beyond 2.4 GHz, at which the silicon homojunction technologies lack performance and where SiGe HBTs provide higher integration levels than III–V component technologies. Recently, SiGe HBTs have attracted much attention for RF power applications because of their excellent microwave power performance and thermal conductivity. By optimizing the device process, the microwave power applications of SiGe-based HBT under development have moved from L-, S-, and C-band operations to X-band operation [3], [4]. Gummel plot of a typical SiGe transistor before and after stress. For power characterization, the collector current and base current are 52 mA and 0.34 mA, respectively, before stress. After stress, changes to 0.7 mA under constant collector current measurement, while changes to 24 mA for constant base current measurement. Due to the high electric field at the base-emitter junction caused by the high doping levels of SiGe HBTs, the hot-carrier (HC) reliability has become a major concern for such advanced devices used in commercial products [5]. So it is worth investigating the effects of hot-carrier on the high-frequency and RF power performances of SiGe HBTs. However, the most literatures on HC effects deal mainly with the dc characteristics and/or the low-frequency noise behavior [6]–[8], and seldom addressed the RF characteristics [9], [10].
