FET-based THz Research Articles

Sensitivity of Field-Effect Transistor-Based Terahertz Detectors.

This paper presents an overview of the different methods used for sensitivity (i.e., responsivity and noise equivalent power) determination of state-of-the-art field-effect transistor-based THz detectors/sensors. We point out that the reported result may depend very much on the method used to determine the effective area of the sensor, often leading to discrepancies of up to orders of magnitude. The challenges that arise when selecting a proper method for characterisation are demonstrated using the example of a detector array. This array utilises field-effect transistors and monolithically integrated patch antennas at 620 GHz. The directivities of the individual antennas were simulated and determined from the measured angle dependence of the rectified voltage, as a function of tilting in the E- and H-planes. Furthermore, this study shows that the experimentally determined directivity and simulations imply that the part of radiation might still propagate in the substrate, resulting in modification of the sensor effective area. Our work summarises the methods for determining sensitivity which are paving the way towards the unified scientific metrology of FET-based THz sensors, which is important for both researchers competing for records, potential users, and system designers.

A Readout Channel Optimized for Minimum NEP of a FET-Based THz Pixel

This paper presents a high-gain, noise-efficient readout interface for a FET-based direct THz detector fabricated in 0.15 μm standard CMOS technology. The pixel, conceived to be used in array configuration for an imaging application, consists of an on-chip antenna, a FET device for THz signal detection and a chopper-stabilized readout interface performing in-pixel filtering and amplification. The switched-capacitor multistage design achieves a closed-loop gain of 70 dB and a system bandwidth of 1 kHz, thereby improving the SNR and limiting the total integrated input referred noise of the channel to less than the minimum detectable signal limit defined by the FET detector. The measurement results show that the pixel is able to achieve a maximum voltage responsivity of 470 kV/W and a minimum NEP value of 480 pW/√Hz at the antenna frequency of 370 GHz. The pixel consumes 200 μW power, and it occupies an area of 0.375mm2.

Integrated, Multichannel Readout Circuit Based on Chopper Amplifier Concept for FET-Based THz Detectors

This work presents the integrated, multichannel readout circuit dedicated to FET-based THz detectors. Described solution provides an unique approach to FET detectors readout, able to replace the measurement equipment deploying the lock-in technique and to eliminate the necessity of modulating the THz wave. The IC proposed by the authors is based on the chopper amplifier architecture, enhanced and adapted for multichannel signal processing. It also ensures significant 1/f noise minimisation, which is the key requirement for the FET-based detectors readout. The circuit prototypes were manufactured in standard 350 nm CMOS process (AMS A.G.) and then measured in the dedicated test set-up.