MSM Varactor Diodes Based on ${\rm In}_{0.7}{\rm Ga}_{0.3}{\rm As}$ HEMTs With Cut-Off Frequency of 908 GHz

Metal-semiconductor-metal varactor diodes were realized on the 2-D electron gas (2DEG) of an In0.7Ga0.3As HEMT structure. The electrical performances, such as capacitance switching ratio (Cmax/Cmin) and cutoff frequency (fo), were determined by using S-parameters measurements up to 40 GHz. Devices with 130-nm gate length and a gate distance of 2 μm exhibited a cutoff frequency (fo) of 908 GHz and a capacitance switching ratio of 1.4. The corresponding figure of merit, which is defined as fo·Cmax/Cmin, was 1.29 THz.