Terahertz detection with CMOS: Simulation Studies

Abstract

‘Terahertz gap’ refers to the still widely un-utilised part of electromagnetic spectrum. EM waves in THz frequency range have great uses in areas like security and inspection, spectroscopy and material dentification, medical diagnosis and high-speed communication. These applications can be efficiently realized only if inexpensive sources and detectors operating at such frequencies are developed. Silicon MOSFETs have a cut-off frequency in range of few tens of GHz. However, active research in recent years has established that Si MOS transistors can be used as power detectors for electromagnetic waves up to frequencies in the THz range, i. e. far beyond their cut-off frequencies. The detection is based on self-mixing of THz signals in the transistor channel resulting in a photoresponse in the form of a DC voltage proportional to the power of incident radiation. Based on this principle, a 1k pixel video camera for 0.7- 1.1 THz imaging application has been recently realised using 65 nm CMOS technology. The transistor operation in THz power detectors differs fundamentally from the operation in typical digital and analog circuits. herefore, it should be expected that the optimum transistor design for THz detectors is different from that of the standard CMOS transistors. Device simulations to study the impact of transistor geometries and doping profiles on the performance of THz detectors can be very useful and such analysis can be used to suggestfor improvements in transistor design. In this work, detailed TCAD simulations to study of the impact of NMOS device design and doping distribution on detector performance are presented. Extensive time-domain simulations are used to obtain the THz response and the impact of different device parasitics and design parameters on this response is analyzed. Improvements in the device design are suggested to enhance the performance of Silicon MOSFET THz detectors.