SWIR detectors for night vision at AIM

Abstract

Detectors for the short-wave infrared (SWIR) spectral range are particularly suitable for observation under hazy weather conditions as well as under twilight or moon light conditions. In addition, SWIR detectors allow using the airglow for observation under moonless sky. SWIR detectors are commonly based on InGaAs or HgCdTe (MCT) and demand extremely low dark currents to ensure a high signal-to-noise ratio under low background light conditions. AIM has developed a read-out integrated circuit (ROIC) with 640×512 pixels and a 15 µm pixel pitch for low light level applications. The ROIC supports analog or digital correlated double sampling (CDS) for the reduction of reset-noise (also known as kTC-noise). Along with CDS, a rolling shutter (RS) mode has been implemented. The input stage of the ROIC is based on a capacitive transimpedance amplifier (CTIA) with two selectable gain settings. The dark current of our SWIR MCT detectors has recently been significantly reduced to allow for high operating temperatures. In contrast to InGaAs, the MCT material offers the unique possibility to adjust the cut-off wavelength according to the application while maintaining the matching of the lattice constant to the one of the CdZnTe substrate.The key electro-optical performance parameters of lately developed MCT based SWIR Focal Plane Arrays (FPA) with a 1.75 µm cut-off wavelength will be presented. In addition, AIMs SWIR detectors covering the spectral range from 0.9 µm to 2.5 µm and available in formats of 384×288 pixels -24 µm pitch and 1024×256 pixels -24×32 µm², will be introduced.

Comparative noise performance of a coded aperture spectral imager

“…The parameters used for the SWIR imager are based on AIM's 384×288 pixel CMT detector array. 12 Dark current is estimated with the aid of Tennant's Rule 07, 13 assuming an operating temperature of 150K (allowing for the rate to exceed that predicted by the rule, which is a lower limit, to a similar extent to the Teledyne detector). The grating efficiency is approximated according to equation (4) from Mouroulis et al 14 with a peak efficiency of 0.9 and a blaze wavelength of 1700nm (operating in the 1 st order); this blaze angle produces reasonable efficiency at the longwavelength end of the spectrum, at the cost of efficiency dropping below 15% at 1000nm.…”

SWIR photodetector development at Fraunhofer IAF

“…Arrays with 640 × 512 pixels at a pitch of 15 µm have been hybridized with specific read-out integrated circuits (ROICs) developed at AIM [6] in an indium-bump flip-chip process. The InP substrate has been completely removed [3] after the hybridization process and a single-layer SiON x ARC has been applied.…”

“…SWIR camera performance data for low-light-level conditions, especially for the CdHgTe detector, has been published elsewhere. [6] A sample image of a person taken with an InGaAs-pin SWIR camera is shown in Figure 2. The dimly lit indoor scene was indirectly illuminated by a small halogen lamp located in the neighboring room.…”

Design Principles for High QE HgCdTe Infrared Photodetectors for eSWIR Applications

“…23 There have been several studies in the past few years on both theoretical and experimental aspects of SWIR infrared photodetectors based on the HgCdTe alloy employing p-onn device structure. 3,10,[24][25][26][27][28][29][30][31] However, since these detectors were designed to be used as individual small-area pixels in an imaging array, they were not designed for ultra-high QE application. In this paper, we present the design rules which allow SWIR photodetectors operating in the eSWIR spectral range to achieve their maximum quantum efficiency.…”