340-GHz Heterogeneously-Integrated THz Imager With 4°-Beamwidth 16×16 IPD Antenna Array for Lensless Terahertz Imaging Applications

Abstract

A low-cost and planar heterogeneously-integrated 340-GHz THz imager is proposed for lensless THz imaging applications. The proposed THz imager is composed of a 16 × 16 antenna array realized in an integrated-passive-device (IPD) technology, an IPD-to-CMOS THz interconnect, and a power detector implemented in a 0.18-µm CMOS technology. The 16×16 IPD antenna array can provide simulated antenna gain of 23.9 dBi, antenna directivity of 30 dB, and half-power beamwidth (HPBW) of 5.6 • at 340 GHz. The proposed THz interconnect utilizes a transmission line coupling technique to provide low-loss and broadband signal transition from a CMOS chip to an IPD one while occupying a small chip area. The simulated insertion loss of the THz interconnect is only 1.8 dB at 340 GHz while providing 3-dB bandwidth from 230 to 446 GHz. The power detector exploits the transistor's inherent even-order nonlinearity to rectify the input signal for power detection. The power detector can give simulated voltage responsivity R V and noise equivalent power (NEP) of 190.2 kV/W and 1.9 nW/Hz 0.5 at 340 GHz, respectively, as the chopping frequency f mod is 1 kHz. A nonlinear curve fit technique is proposed to tackle the undesired fluctuation of the measured output voltage due to a standing-wave effect. Experimental results show that the proposed heterogeneously-integrated THz imager can provide measured effective R V and NEP of 0.967 MV/W and 0.18 nW/Hz 0.5 at 328 GHz, respectively, as f mod is 1 kHz. The measured antenna directivity and HPBW can be 30 dB and 4 • at 340 GHz, respectively. Such a THz imager with advantages of high antenna directivity and narrow HPBW can be employed to realize a simple, low-cost, and lensless THz imaging system. To the best of the authors' knowledge, the proposed THz imager integrates the highest number of antennas and exhibits the highest antenna directivity and the narrowest HPBW at THz frequencies reported thus far.