902 IEEE TRANSACTIONS ON TERAHERTZ SCIENCE AND TECHNOLOGY, VOL. 5, NO. 6, NOVEMBER 2015 Antenna-Coupled MOSFET Bolometers for Uncooled THz Sensing Dan Corcos, Noam Kaminski, Evgeny Shumaker, Ofer Markish, Danny Elad, Thomas Morf, Senior Member, IEEE, Ute Drechsler, Winnie Tatiana Silatsa Saha, Lukas Kull, Member, IEEE, Ken Wood, Ullrich R. Pfeiffer, Senior Member, IEEE, and Janusz Grzyb Abstract—In this paper, we present a comprehensive study on the operation of an antenna-coupled THz bolometer based on a micro-machined SOI-CMOS thermal sensor. The pixels are designed to operate at room temperature in vacuum. We focus on a new planar skirt antenna, which combines high sensitivity within a 0.6–1.2 THz band and 30 HPBW. We present an overview of the design considerations, as well as the characterization results which were obtained with both broadband and CW THz sources. The NEP of the pixel is of the order of 25 pW/Hz , with responsivity 100 mA/W at the optimal operating point. The peak responsivity to a broadband THz signal is 600 mA/W. The ease of integration with a read-out circuit and the low power dissipation make this type of pixel a good candidate for focal plane array architecture. Index Terms—Antenna-coupled bolometers, micromachined sensors, silicon-on-insulator, terahertz (THz) imaging, uncooled sensors. I. INTRODUCTION D RIVEN by a multitude of attractive practical applica- tions, ranging from security to medical diagnostics, from the food industry to material inspection and astronomy, THz imaging is a fast developing research area [1]. The challenges involved with pushing electronic detection up to the THz frequency range are tackled today by adopting a number of complementary approaches. Cryogenic cooled detectors such as transition-edge superconductor (TES) bolometers [2], [3] and kinetic inductance detectors (KIDs) [4], [5] have demon- strated very high sensitivity. The large footprint and large power consumption of these detectors, as well as the reduced pixel count may, however, limit their exploitation potential to high-end systems only. The interest in commercial THz applications was a main driver in recent years to efforts aimed Manuscript received February 20, 2015; revised June 23, 2015; accepted July 29, 2015. Date of publication August 31, 2015; date of current version November 23, 2015. This work was supported in part by the European Union Seventh Framework Program (FP7/2007-2013) under Grant Agreement 288442. D. Corcos, N. Kaminski, E. Shumaker, O. Markish, and D. Elad are with IBM Research—Haifa, Haifa University Campus, 3498825, Israel (e-mail: dannye@il.ibm.com). T. Morf, U. Drechsler, W. T. Silatsa Saha, and L. Kull are with IBM Research—Zurich, 8803 Rueschlikon, Switzerland (e-mail: tmr@zurich.ibm. com). U. R. Pfeiffer and J. Grzyb are with the University of Wuppertal IHCT, Bergische Universität, D-42119, Wuppertal, Germany (e-mail: ull- rich.pfeiffer@uni-wuppertal.de). K. Wood is with QMC Instruments Ltd., School of Physics & Astronomy, Cardiff University, The Parade, Cardiff, CF24 3AA, U.K. (e-mail: k.wood@ter- ahertz.co.uk). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TTHZ.2015.2466470 at bridging the performance gap of THz sources and room temperature detectors. While heterostructure backward diodes (HBD) [6] and Schottky barrier diodes (SBD) [7] are the most sensitive solid-state detectors, SiGe HBTs are also becoming attractive owing to the recent advancements in process and circuit technology. The operating frequency of modern RFICs seems inexorably to approach the 1 THz target. Signal recti- fication has been demonstrated in transistor devices operating well above their cut-off frequency, exploiting the plasma wave or self-mixing effects. NEP values of 50 pW/Hz and 14 pW/Hz have been reported for HBT-based [8] and MOSFET-based [9] detectors respectively. These results prove the feasibility of solid-state uncooled detector arrays with silicon devices. Furthermore, thermal types of detectors such as bolometers and thermopiles [10], already used in mature infrared sensing technologies, were modified to operate below 10 THz, which is the conventional upper frequency edge of the THz band. These solutions perform well in terms of NEP, speed and allow high pixel counts. Micro-bolometers constructed in vanadium oxides [11], [12] and amorphous silicon [13] have been shown to exhibit NEP values of a few pW/Hz close to 1 THz. These sensors lose performance at lower frequencies due to degradation of electro-magnetic coupling efficiency. In this work, we aim to describe the development and char- acterization of a new MOSFET-based pixel design to act as the building block for an uncooled THz focal plane array (FPA) capable of passive THz imaging. Differently from previously discussed sensors, the MOSFET bolometer relies only on the layers already present in a standard SOI-CMOS process with no modification. The foundry process is followed by a MEMS bulk micro-machining process to achieve the necessary thermal insulation. There exists a trade-off between, on one hand, better penetration of radiation below 1 THz and, on the other hand, higher blackbody radiation power available above 1 THz, and we, therefore, chose our target RF band to be 0.5–1.5 THz [14]. The envisioned application is in the area of security. II. DIRECT-COUPLING APPROACH:DESIGN CONSIDERATIONS Since active silicon-based devices lack the capability of signal amplification in the envisioned frequency range, we adopted thermal sensing as the preferred approach for the de- tection of weak THz signals. With wavelengths that are several hundred of microns long, one main obstacle for the develop- ment of a bolometer sensor is the design of coupling structures (e.g., antennas or absorbers) that have adequate absorption capability and bandwidth, without adding to thermal mass and therefore slowing the device below a useful detection speed. 2156-342X © 2015 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.