Sub-THz Sensor Array With Embedded Signal Processing in 90 nm CMOS Technology

The architecture and the operation of a sub-THz sensor array are presented, which have been implemented in standard 90 nm CMOS technology. The integrated sensor array is arranged around of 12 silicon field effect plasma wave detectors with integrated planar antennas. The received signals are further processed by pre-amplifiers, analog to digital converters, and a time shared digital domain lock-in amplifier. The system automatically locks to external modulation and provides standard digital streaming output. Instead of building a uniform array, seven different antenna types with various polarization properties (horizontal and vertical linear; left and right handed circular polarization) and spectral responsivity have been integrated. The sensors altogether provide broadband response from 0.25 to 0.75 THz. The peak amplified responsivity of the sensors is 185 kV/W at 365 GHz and at the detectivity maximum, the noise equivalent power (NEP) is near to 40 pW/√Hz. Under nonzero drain current, the peak sensitivity rises above 1.2 MV/W with a moderate NEP ~ 200 pW/ Hz at 50 nA source-drain current. Application example is provided as a multi-wavelength transmission imaging case study.

I. Introduction

The THz spectrum of electromagnetic waves is non-ionizing and has a broad application area [1]. In [2] Dyakonov and Shur predicted that the instability of electron plasma waves in short channel FETs could be used as terahertz frequency radiation detector. Several THz imaging systems and different sensor technologies appeared, among others silicon based field effect transistors [2]–[5]. It found that not only high mobility devices, but silicon based detectors with integrated planar antennas could serve as fast imagers as well [8], [9], [14]–[21]. For such detectors a different, more phenomenological, description is given as well in [15] based on resistive self-mixing. The silicon or SiGe based sensor technologies offer an advantage over other material based solutions, like bolometers [22]–[24], the on-chip integration of read-out and signal processing circuitry [14]. Related to field effect transistor (FET) detectors, we can distinguish two basic operation modes: open drain and non zero drain current cases. The former provides higher sensitivity, while the later significantly higher response [6], though with dominant flicker noise. In [4], [11] homodyne and heterodyne mixing FET detectors are presented with outstanding performance, similar to that Schottky diodes offer. These results suggest that further improvements are still expected from silicon based sensors.