A CMOS Fully Integrated 860-GHz Terahertz Sensor

This paper proposes a CMOS fully integrated 860-GHz terahertz (THz) sensor. The sensor integrates a single-NMOS THz detector, a low-noise chopper instrumentation amplifier and a high-resolution ΔΣ-ADC. The detector consists of a novel on-chip grounded patch antenna and a source-feeding NMOS field-effect transistor (FET) of the minimum size. A microstrip transmission line is designed to improve the power transfer efficiency between the antenna and the NMOS transistor. A notch filter is proposed to improve detector performance. To enable the theoretical analysis of the operation of the THz detector and the formulation of design guidelines, we propose a THz-FET device model in which a source-coupled FET for THz detection is modeled as a dc voltage source with a resistor. The model indicates that an FET with the minimum physical dimensions for a given CMOS process can produce the maximum output signal. The sensor is implemented in a 180-nm standard CMOS process. The detector achieves a voltage responsivity of 3.3 kV/W and an NEP of 106 pW/Hz
^1/2
at 860 GHz. The sensor noise and the readout circuit noise are 10.81 and 2.03 
μ
Vrms, respectively. The sensor obtains clear raster-scanning transmission images under continuous THz illumination.