Sakhno M. Limiting parameters and properties of uncooled multielement sub-THz/THz detectors.

Model of THz/sub-THz radiation detection in silicon FET was created with account of some parasitic effects. Detector is divided into three parts: intrinsic part of FET, extrinsic part of FET, antenna. Each part is analyzed independently and than results were combined to describe the whole system. Peculiarities of determining responsivity connected to antenna presents are discussed. Previous models of THz detection in FET such as Dyakonov-Shur one and that of resistive selfmixing were discussed and compared with models for static characteristics. From this comparison, the importance of diffusion current in weak inversion region for detection becomes clear. Intrinsic part of FET is modeled using transmission line approximation. It was shown from transmission line approach that detection occurs only on small distance near source. Detection in channel is described by dividing channel into two parts. Each part can be modeled by equations for static mode. Connection between static characteristic and detected signal was explained for all inversion regions. Models for high and low intensities were developed from this approximation. For the low intensity case input impedance and responsivity were determined. Saturation of response at high irradiation levels were obtained. Frequency dependence of signal were obtained. Extrinsic part of transistor is discussed. Simplified equivalent circuit of FET is proposed similar to those of Shottky diode. It is shown that parasitic effects play crucial role in operation as large part of power is dissipated in them. Thus, they limit very large intrinsic responsivity. Frequency dependency of responsivity for whole transistor is determined. The way of using parameters of industrial model BSIM3 to estimate NEP is proposed. In the framework of developed model several FET types and Schottky diodes were compared and analogy between FET and Schottky diode was shown. Comparison of optical NEP shows that SBD and FET have similar performance with NEP~10-11 W/Hz1/2. Main factors limiting detector NEP were found: parasitic effects and antenna-detector matching. Limits for performance of these detectors have been estimated. NEP was estimated for several technologies. It has been shown that with advanced FET technology the performance of FET mm-wave/THz detectors can be made similar to that of SBD ones or in high frequency range can surpass it. It has been ascertained that FETs can be preferable in some applications due to smaller parasitic effects. Energy input in detection element was investigated. Methods of modelling antennas for THz range is discussed. Several antenna types were modeled in assumptions of finite and infinite substrate. Connection wires influence on antenna pattern is shown. It is shown that infinite substrate approximation is valid only for electrically thin substrate. Importance of substrate parameters was shown from consideration of printed antennas on thick substrate. It was shown that properties of antenna depend on its position on electrically thick substrate. Antenna pattern depends strongly on frequency. Several ways to decrease issues with substrate thickness is discussed such as usage of substrate lens, hybrid structure.