Balanced MSM-2DEG Varactors Based on AlGaN/GaN Heterostructure With Cutoff Frequency of 1.54 THz

AlGaN/GaN high-electron mobility transistor structures were utilized to fabricate metal-semiconductor- metal (MSM) two-dimensional electron gas (2DEG) varactors for application as a terahertz (THz) capacitive switch. By adopting an asymmetric MSM structure composed of nanoscale gates and micron-scale gates, the cutoff frequency of the MSM-2DEG varactors was dramatically improved, up to the THz range, by reducing series resistance. The balanced MSM-2DEG varactor, in which a nanoscale gate is sandwiched between two micron-scale gates exhibited a capacitance switching ratio (Cmax/Cmin) of 2.64, a cutoff frequency of 1.54 THz, and a figure of merit of 4.06 THz.