Simulations and measurements of the electromagnetic response of broadband THz uncooled antenna-coupled microbolometer array

Bolometer sensors are good candidates for room-temperature THz imaging thanks to their maturity and capability to sense THz waves on the whole spectrum. Starting with infrared microbolometer technology, uncooled antenna-coupled microbolometer focal plane array are being developed at CEA-LETI with the objective of offering low-cost, real-time 2D terahertz imaging sensors. These detectors, which are 320×240 pixels monolithically processed above CMOS read-out circuits, show very good performances, potentially better than other uncooled direct detectors, such as FET transistor or Schottky diode: at the measured detection threshold power is 30 pW at 2.4 THz with a responsivity of 14 MV/W, resulting in a NEP close to 1 pW/√Hz. Unlike the two other above-cited uncooled detectors for which sensitivity is frequency dependent and strongly affected by parasitic elements as shunt capacitances and resistances in series, thermal detectors sensitivity can be maintained constant over the whole spectrum, as long as the optical coupling is efficient. Therefore, studying the optical coupling mechanism of the detector in THz frequency range is a critical stage. In this paper, we present results of the electromagnetic simulation and characterization process of these focal plane arrays, concentrating on the spectral absorption.