VLIWR HgCdTe staring focal plane array development

Abstract

Atmospheric remote-sensing have been one of the primary drivers toward longer wavelength infrared sensors beyond the 8 to 12 um atmospheric window typically used for terrestrial imaging systems. This paper presents the recent performance improvement attained with very long wavelength infrared (VLWIR) focal plane arrays, by the stringent control of the small bandgap HgCdTe material quality. Array operability is further enhanced by design using a 2:1 super-pixel detector format scheme with programmable bad element de-select and our new detector input offset optimization circuitry within each unit cell. Focal plane arrays with peak quantum efficiencies in excess of 80 percent, and cutoff wavelengths out to 15 µm have NEI operabilities around 95 percent for mid 10 14 ph/s-cm 2 fluxes operating near 50 K. Average NEI of 3.5 x 10 10 ph/s-cm 2 was demonstrated for a 14 µm cutoff wavelength focal plane array, consisting of over 55,000 elements, operating with an effective sample time of 87.5 ms. IntroductionRecent strides in very long wavelength infrared (VLWIR) HgCdTe focal planes have reinvigorated their use in VLWIR atmospheric remote sensing applications. These VLWIR focal plane arrays, comprised of HgCdTe photovoltaic diodes, have demonstrated unprecedented operability for large area arrays with detector cutoffs beyond 14 µm. Significant improvement in array yield have occurred over the last 10 years due to all aspects of the array fabrication, including larger and more uniform substrates with tighter process controls, and better understanding of defects which have led to successful mitigation strategies [1-3]. The readouts for these arrays have also improved and several features have been added specifically to address yield issues to achieve producible high operability performance above 95 percent [4]. The two main features are SuperPixels, where each pixel is sub-divided into several sub-elements that can be individually deselected if found defective, and through input bias optimization on a pixel by pixel basis to remove CMOS threshold variations across the chip. This latter feature allows the reverse bias of each detector to be optimized. The data also clearly shows the operability benefit of using smaller pixel higher density FPAs to cover the same focal plane area, demonstrating that the majority of the defects are randomly distributed defects that are much smaller than a pixel.In this paper we discuss the VLWIR detector technology at BAE Systems in section 2, followed by the excellent photodiode array performance presented in section 3. The operability performance of two staring VLWIR FPA systems using these detector arrays are discussed in section 4. The first FPA is a 256 x 256 array on 40 µm pitch specifically designed for low background applications with a frame rate of 100 Hz and a charge capacity of 11 million electrons. Each pixel is divided into a 2 x 2 array of sub-elements for SuperPixel de-selection. The baseline operation of this device uses the best 3 of every 4 sub-elements per pixel for optimal...

Study of LWIR and VLWIR Focal Plane Array Developments: Comparison Between p-on-n and Different n-on-p Technologies on LPE HgCdTe

“…The situation appears rather different in the p-on-n configuration. In this case, the typical diffusion length is clearly larger (up to 30 lm to 50 lm for low doping levels such as 10 15 cm À3 typically reached with indium doping 1,8,13 ) and the dark carrier generation volume is then limited by the absorbing layer volume itself. Therefore the resultant dark current becomes thickness dependent.…”

“…Some applications such as spectrometer retina may ask for nearly 100% operability (one dead pixel meaning one missing spectral line), suggesting the use of superpixels. 1 In imaging applications, defective pixel rate remains also an important issue as cluster defects are usually not tolerated.…”

Meteosat Third Generation (MTG) critical technology pre-development activities

“…BAe (US) detector supplier has already published achievements in manufacturing flight hardware involving VLWIR detectors [6,7] for GIFTS. MTG relies on the results of the on-going pre-development activities and preliminary results of the VLWIR pre-development have been widely published by all 3 major Europeans (AIM, Selex-GA and SOFRADIR) MCT detector manufacturers [8][9][10] .…”

Development of Low Dark Current SiGe Near-Infrared PIN Photodetectors on 300 mm Silicon Wafers

“…Group III-V compound semiconductor and HgCdTe based infrared photodetectors offer certain advantages including high absorption efficiency, high carrier drift velocity, and mature design and fabrication technology. HgCdTe infrared photodetectors have been developed for 1 -3, 3 -5, and 8 -14 µm applications, InSb for 3 -5 µm applications, and InGaAs for ~1.1 -1.7 µm applications [1]- [3]. However, III-V detectors commonly require cooling (typically down to 77 K), and integrating them into the Si complementary metal-oxide semiconductor (CMOS) process is likewise at the expense of high cost and greater complexity and can introduce doping contaminants into the devices since III-V materials can act as dopants for group IV materials [4].…”