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In search of novel detectors of electromagnetic radiation at terahertz frequencies, field-effect transistors (FETs) have recently gained much attention. The current literature studies them with respect to the excitation of plasma waves in the two-dimensional channel. Circuit aspects have been taken into account only to a limited degree. In this paper, we focus on embedding silicon FETs in a proper circuitry to optimize their responsivity to terahertz radiation. This includes impedance-matched antenna coupling and amplification of the rectified signal. Special attention is given to the investigation of high-frequency short-circuiting of the gate and drain contacts by a capacitive shunt, a common approach of high-frequency electronics to induce resistive mixing in transistors. We theoretically study the effect of shunting in the framework of the Dyakonov–Shur plasma-wave theory, with the following key results. In the quasistatic limit, the capacitive shunt induces the longitudinal high-frequency field needed in the FET’s channel for resistive mixing. In the non-quasi-static case, the shunt’s role is taken over by plasma waves. Rectification can then be described as distributed self-mixing in the transistor’s channel. Based on such considerations as well as other circuit-related aspects, we arrive at a rational design for FET-based detectors of terahertz radiation, and implement the first monolithically integrated 0.65 THz focal-plane array including antennas and amplifiers on a single silicon die. The measured performance data compare well with the theoretical predictions.

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Square-law power detection circuits with on-chip antennas and amplifiers are presented for the detection of 0.65-THz radiation in a low-cost 0.25-μm CMOS technology. The circuit architecture combines metal-insulator-metal (MIM) coupling capacitors with NMOS transistors to facilitate self-mixing in a resistive mixer. A low-frequency (quasi-static) and a high-frequency (non-quasi-static) analysis of the broad-band circuit is presented. Current and voltage readout techniques of nonamplified detectors are compared, and exhibit a measured responsivity of 5.3 mA/W and 150 V/W respectively. A monolithic integrated 3 × 5 pixel focal-plane array has been used for single-pixel and multi-pixel imaging of concealed objects at 0.65 THz.

A quarter-wave transversal slot in the center of a handheld terminal ground plane is proposed and evaluated as a wideband antenna for low profile mobile phones. By feeding the slot with a microstrip line, a triple-resonance response is obtained from the chassis, slot and microstrip stub interaction, providing sufficient impedance bandwidth and radiation efficiency to cover the 0.9-2.7 GHz frequency range. While the introduction of a slot in the ground plane has many advantages over e.g. PIFA or patch structures, both in terms of performance and cost, the circuit floor planning becomes more complicated. To address this problem, a possible solution in terms of module partitioning and signal line routing is suggested. In addition, simulations of parasitic antenna to signal line coupling and techniques to reduce this effect are presented.