Uncooled Infrared Imaging Using a Substrate-Free Focal-Plane Array

Abstract

A substrate-free 160 × 160 focal-plane array (FPA) with a 60-µm × 60-µm pitch has been developed and used for an optical readout uncooled infrared (IR) detector. The supporting frame of the FPA is a temperature-variable one due to its large decreases in both heat capacity and thermal conductance. This thermal characteristic significantly increases the temperature change of the microcantilever, which depends on both the temperature change induced by its absorption of IR radiation and the linear superposition of the temperature prechange induced by other microcantilevers, and therefore improves the performance of the substrate-free FPA. In the proposed IR detector, the fabricated FPA had an average noise equivalent temperature difference (NETD) and a response time of 330 mK and 16 ms, respectively. Its performance increased by about 4.3 times compared with that of the substrate FPA that consists of the same microcantilevers.Index Terms-Focal-plane array (FPA), infrared (IR) detectors, substrate-free, uncooled.

Microthermomechanical infrared sensors

“…However, the image quality of FPAs operating in air is poor, mainly due to the decreased microstructures' Q−factor. In 2009 the USTC/CAS group has published their final paper [111] with achievements of a 60 μm pitch 160×160 pixel substrate−free FPA, read out with a 4f optical configuration using a knife−edge filter, with a performance of 330 mK NETD, 16 ms time constant and 30 Hz 12−bit imaging (CCD) [112]. Since 2009 numerous articles were published by BIT and the Peking University addressing THz detection [113], signal processing impro− vement techniques [114] and tri−band detection [107].…”

An Uncooled Infrared Microbolometer Array for Low-Cost Applications

“…A second design implements focal plane arrays using a microcantilever sensor as the thermally sensitive element. This architecture requires additional optical readout devices, such as charge coupled devices (CCDs) or CMOS cameras [7], [8]. The optical readout device introduces vibration, thermomechanical noise and shot noise, which can impair the microbolometer performance.…”

Research of Infrared Imaging at Atmospheric Pressure Using a Substrate-Free Focal Plane Array

“…[3−10] One of the most significant achievements is the strategy of the substrate-free FPA. [8] Its architecture is substantially different from the conventional design, there are no electrical connections or onboard electronics, and the substrate material underneath the effective absorbing area is completely removed. Early experiments have shown that the substrate-free FPA not only provides an unobstructed optical path for IR radiation, but also greatly improves the performance of IR detection to several times higher than the conventional substrate FPA.…”

“…Using the finite element analysis (FEA), the substratefree FPA has been discussed rigorously, and it was found that the thermal response of the substrate-free FPA would be estimated by comprehensive analysis of the heat affected zone better than a single pixel. [8,9] However the FEA has the disadvantages of being both complex and time consuming, especially when the array size of the FPA is larger and larger. In this Letter, an equivalent circuit model to the substrate-free FPA is presented and applied to identify the performance of IR imaging at atmospheric pressure.…”

“…The most significant difference from the substrate FPA is the temperature-variable supporting frame. [8,9] It not only absorbs the IR radiation, but also participates in all the heat exchange mechanisms. Note that because of the heat conduction of the supporting frame, the heat will be transported from one pixel to the others, so that the thermal response must be evaluated by comprehensive analysis of the heat affected zone.…”