280GHz and 860GHz image sensors using Schottky-barrier diodes in 0.13μm digital CMOS

Millimeter and sub-millimeter-wave imaging using solid-state circuits is gaining attention for security and medical applications. To lower cost and increase integration, MOSFETs in CMOS are being investigated for implementing broadband detectors [1-3]. However, neither measured noise-equivalent power (NEP) nor noise floor of the imager was given in [1]. Although NEP of 17pW/Hz^1/2 was achieved at 650GHz in [2], an external lens was attached to the 65nm SOI CMOS chip. In [3], an NEP of 66pW/Hz^1/2 was measured at 1.05THz using 65nm CMOS without a lens attached to the chip. Additionally, although the efforts reported in [1-3] realized an array, none demonstrated the image-array function. As an alternative, polysilicon-gate-separation (PGS) Schottky-barrier diodes (SBD) with cut-off frequency of ~2THz were fabricated in CMOS without process modifications [4] and were used to demonstrate a 280GHz detector with NEP of 30pW/Hz^1/2 [5,6]. To significantly enhance the scanning speed, a 16-pixel 280GHz SBD imager is fabricated and its array function is reported in this paper. The imager including baseband amplifiers achieves responsivity of 5.1kV/W and NEP of 29pW/Hz^1/2. More importantly, its operation was demonstrated in a setup that requires no mirror or lens that is bulky and costly. Next, an 860GHz SBD detector is demonstrated with a measured non-amplified responsivity of 355V/W and NEP of 32pW/Hz^1/2. This NEP is ~2X lower than the best reported work in CMOS [3]. Both chips are fabricated in a 0.13μm logic CMOS. The results suggest a path for high performance, compact and affordable sub-millimeter-wave and terahertz CMOS imagers using SBDs.