Microwave Power Heterojunction Bipolar Transistors Research Articles

Failure Model Research of Power HBTs

Heterojunction bipolar transistors (HBTs) are playing an important role in microwave and power applications. When HBTs operated at high power, the power dissipation and self-heating effects will enable the generation of electrical properties in the transistor failure. The failure experiment system of microwave power HBTs was established. Based on this system, the changes of electrical parameters of HBTs in deferent stress, such as Gummel plots, base current various different base-emitter voltage and base-collector voltage, were measured and analyzed. At the same time, the failure of base current of SiGe HBTs under the condition of FC, SC and thermal stress are studied respectively. It was found that ΔIBis the sensitive parameter of electrical and thermal stress. Based on this reason, we presented the failure model of IB. This model could explain the experiment phenomenon successfully, which is very important and useful for applications of microwave power analog IC’s.

Waveform-based modeling and characterization of microwave power heterojunction bipolar transistors

A waveform measurement technique has been successfully used to extract the large-signal nonlinear characteristics of microwave power heterojunction bipolar transistors. The extracted model parameters were compared to those extracted from dc and small-signal parameters in a conventional manner. It was found that, for high input drive conditions, the present model predicts a much longer collector transit time than the conventional model. Therefore, the present model is more consistent with the physical structure of the transistors and more suitable for evaluating future design improvement.

Fabrication of self-aligned GaAs/AlGaAs and GaAs/InGaP microwave power heterojunction bipolar transistors

Self-aligned processing of high efficiency power heterojunction bipolar transistors (HBTs) using implant isolation, selective wet and dry etching for mesa formation, plasma-enhanced chemical vapor deposited SiNx for sidewall spacers and through-wafer via connections is reported. GaAs/AlGaAs and GaAs/InGaP HBTs grown by metalorganic molecular beam epitaxy utilizing carbon for high, well-confined base doping produced power-added efficiencies of 63%, power gain of 10 dB and output power of 1.7 W at 4 GHz for twelve 2×15 μm2 double-emitter finger devices (GaAs/AlGaAs) and 57% power-added efficiency, power gain of 11.3 dB and output power of 0.6 W at 4 GHz (GaAs/InGaP), respectively.

Emitter-length design for microwave power heterojunction bipolar transistors

Area consideration in large microwave power heterojunction bipolar transistors requires maximizing the emitter length per emitter finger. In this investigation, typical device geometry in which the emitter length is the same as the base contact length is analyzed. The limitations on the base contact length (and hence the emitter length) placed by the resistance in base contact metal and the base utilization factor of the base contact are discussed. The critical base contact length is determined as a function of the deposited base contact metal thickness and the device current gain.

Thermally stable AlGaAs/GaAs microwave power HBT's

Novel thermal shunt and thermal lens techniques have been used in the design of multiple-emitter AlGaAs/GaAs power HBTs (heterojunction bipolar transistors). Thermal stabilization was achieved by the use of a thick metal bridge connecting all emitters. The thickness of the bridge was designed to assure a virtual thermal short between emitters. The use of such a thermal shunt element redistributes temperature-dependent internal device currents to force an equalization of device junction temperature. The bridge further serves to spread heat from each emitter over a larger GaAs surface (thermal lens), thereby reducing overall device thermal resistance. Multiemitter devices with 2 mu m and 3 mu m minimum emitter feature sizes were fabricated and tested at microwave frequencies to demonstrate the thermally stable operation.