The maximum and minimum capacitances of the MSM-2DEG varactor were 137 and 1.5 pF, respectively, which resulted in a capacitance ratio (C max/C min) of 91.33.Īn Agilent B1500A analyzer and an HP-8510C network analyzer system were used for the DC and RF characteristics measurements for the HEMT devices with and without the FC submount (referred to as FC HEMT and FC-free HEMT), respectively. 8 The capacitance–voltage (C–V) characteristics were measured using an HP 4285A precision LCR meter. More details can be found in our previous report. The Ni/Au Schottky contact areas were fabricated on a 153 600 μm 2 area. 7 The fabrication of MSM-2DEG varactors on the same layer system using identical technology confirms its absolute compatibility with HEMT technology and the potential for monolithic integration.
The MSM-2DEG varactors were processed simultaneously using HEMT transistors and standard HEMT fabrication process steps. The gate width was designed as 1 mm and the gate length was 1 μm. The HEMT devices were passivated by a 120 nm-thick SiNx layer that enhanced the electrical performance of the device and reduced the dispersion effects. This was followed by the deposition of an Ni/Au Schottky contact and contact pad formation. After chlorine-based reactive ion-etch mesa etching, a Ti/Al/Ni/Au ohmic contact was deposited by lift off and consecutively annealed at 800 ☌. The room temperature Hall measurements yielded a 2DEG carrier concentration of 9.70 × 10 12 cm –2 and a mobility of 1541 cm 2/V s. The variable impedance characteristics of the varactor cause it to be either within the high-impedance region (to block the surge energy) or within the low-impedance region (to transmit the signal normally). 9 The impedance of the varactor can be varied by varying its maximum or minimum capacitance when the incoming voltage is less than or greater than the varactor capacitance transition voltage (V th), respectively. Compared to the above-mentioned protection components, the AlGaN/GaN varactor has been shown to have a good capacitance swing 7,8 and can be used for low-loss high-power RF switching. These waveforms combine to produce an instantaneous power profile that tends to heat the device and may induce thermal failure under certain conditions. 4–6 Each of these surge stresses subjects the device to different current and voltage wave profiles. To protect electronic devices against natural and man-made surge threats, which include lightning, electromagnetic pulses, and electrostatic discharges (ESDs), nonlinear protection components such as gas discharge arresters, metal oxide varistors, and transient voltage suppressor diodes are among the state-of-the-art countermeasures that have been developed.
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