Exotic semiconductor technologies are often associated with devices functioning at terahertz frequencies (above 300 GHz). But researchers working at the State Key Laboratory of Superlattices and Microstructures of the Institute of Semiconductors of the Chinese Academy of Sciences have developed an 860-GHz sensor based on a 180-nm standard silicon CMOS process. The sensor integrates an NMOS terahertz detector, a low-noise chopper instrumentation amplifier, and a high-resolution delta-sigma analog-to-digital converter (ADC). The detector consists of an on-chip grounded patch antenna and a source-feeding NMOS field-effect transistor (FET), with microstrip transmission line to improve the power transfer efficiency between the antenna and the FET.
The researchers performed theoretical analysis through modeling to better understand the operation and possible optimization of the CMOS sensor. Optimum impedance matching between the antenna and the FET was achieved through careful design of the interconnecting microstrip transmission lines. The detector is actually a 3 × 5 array of different detectors, with an optimum reading taken from one detector in the array at a time.
The device relies on a readout circuit to translate signals from the individual detector elements. The readout circuit consists of a low-noise chopper instrumentation amplifier and a high-resolution delta-sigma ADC. When used as part of an imaging system—whether used at oversampling rates of 8,192 or 1,024—the terahertz detector captured clear images of much different materials, such as pieces of metal and tree leaves illuminated by terahertz energy. The sensor shows the capability to detect continuous terahertz waves reflecting off such images and offers great potential in highly integrated raster-scanning imaging systems.
See “CMOS Fully Integrated 860-GHz Terahertz Sensor,” IEEE Transactions on Terahertz Science and Technology, Vol. 7, No. 4, July 2017, p. 455.