Monolithic 28.3 THz thermal image sensor incorporating 0.18-µm CMOS foundry

This paper presents a fully monolithic approach to the design and fabrication of THz CMOS image sensor operating at 28.3 THz using the mass-producible 0.18-μm 1P6M CMOS foundry. The CMOS sensor consists of antenna-coupled transducer, linearly transforming the intercepted THz (terahertz) electromagnetic energy into voltage representation in the region of interest. The THz image sensor adopts PTAT (Proportional To Absolute Temperature) sensing circuit configuration. The THz thermal sensor occupies 68 μm × 42 μm chip area. A 500 μm-thick CMOS test chip of chip size 700 μm × 700 μm was scanned by a THz laser beam of 26 μm diameter with built-in THz thermal sensors. The scanned THz thermal image of the test chip was compared with the die photo, clearly demonstrating the validity of the design concept of the proposed THz image sensor. The responsivity measured by considering the entire test chip is 6 V/W.

I. Introduction

Recently more and more terahertz (THz) technology development and applications had been reported [1]–[2]. To date the state-of-art CMOS foundry-based RF components, however, had rarely been studied for terahertz electronics except in few literatures [3]–[4]. CMOS technology has the following advantages: various levels of circuit components from RF building blocks to the signal processing units can be integrated in a single chip; the photolithography accuracy is high enough for implementing the electromagnetic passive devices at micron wavelength level ; CMOS technology is mass-production ready. To overcome the limit of (maximum oscillation frequency) of CMOS devices [3], we present a thermal sensor approach to the detection of THz electromagnetic signals impinging on the CMOS chip, thus extending the typical 1P6M CMOS technology, with at 65GHz typically, to the detection of 28.3 THz electromagnetic radiation using on-chip PTAT (Proportional- To-Absolute-Temperature) thermal sensing circuit [5] properly incorporated into the receiving antenna/resonator design.