Improved Performance of CMOS Terahertz Detectors by Reducing MOSFET Parasitic Capacitance

The parasitic circuit elements significantly affect rectification performance of metal-oxide-semiconductor field-effect transistor devices. In this paper, we develop a gate-source parasitic capacitance reduction technique by shifting the source lightly doped drain region and analyze the effectiveness on the improved performance of complementary metal-oxide-semiconductor (CMOS) terahertz (THz) detectors. It is experimentally found that for a 0.65-THz integrated CMOS detector, the maximum improvement of voltage responsivity and noise-equivalent power can be 155% and 70%, respectively, by suppressing the gate-source parasitic capacitance. The device simulation further quantitatively evaluates the gate-source parasitic capacitance under different gate-source overlap areas in the novel fabricated transistor structure. It reveals that a smaller gate-source overlap area can result in a lower gate-source parasitic capacitance, which is more favorable for reducing input THz signal leakage and therefore for increasing the THz responsivity. The works open a wide range of possibilities for the ease of design and fabrication of the high-performance THz detectors in standard CMOS technology.