Robert B. Bailey

The HAWAII Infrared Detector Arrays: testing and astronomical characterization of prototype and science-grade devices

Abstract Two generations of prototypes of a HgCdTe infrared detector array with 1024 × 1024 pixels developed by the Rockwell International Science Center have been tested in the new Quick Infrared Camera (QUIRC) and an upgraded version of KSPEC a cross-dispersed near-infrared spectrograph, on the University of Hawaii 2.2 m telescope. The HAWAII (HgCdTe Astronomical Wide Area Infrared Imager) prototype devices achieved very good performance. The read-noise in correlated double sampling (CDS) is between 10 and 15 e − rms, depending on the conditions of the operations and the way read-noise is computed. The quantum efficiency in H and K is above 50%. The full-well capacity is above 10 5 e − at 0.5 V applied detector bias and is, in our system, limited by the dynamic range of the A/D converter. The residual excess dark-current problem known from NICMOS-3 devices (Hodapp et al., 1992) [PASP, 104, 441] is not fully resolved. However, it appears less serious in our first HAWAII prototype devices. Using KSPEC, operation under low background conditions has been tested. At an operating temperature of 65 K, and using up to 128 samples of multi-sampling, a read-noise of − and a dark current −1 /min has been demonstrated. Tests of fast sub-array reads for wavefront sensing were conducted using QUIRC. For a sub-array frame repeat time of 11 ms, a read-noise of 6 e − has been demonstrated. An engineering-grade second-generation HAWAII device with reliable hybridization is now in routine operation in KSPEC. The first science-grade HAWAII device has now been installed in the QUIRC camera and is in routine operation. Steven Beckwith

High-performance 5-um 640 x 480 HgCdTe-on-sapphire focal plane arrays

A high-performance 5-μm 640 X 480 HgCdTe/CdTe/Al2O3 infrared focal plane array (FPA) that offers full TV-compatible resolution with excellent sensitivity at temperatures below 120 K has been developed. Mean FPA D* at 95 K and background of 1014 photons/cm2 s is background-limited at ~1 x 1012 cm Hz1/2/W for the typical mean quantum efficiency of 60 to 70%. The key technology making this large, high-sensitivity device producible is the epitaxial growth of HgCdTe on a rugged CdTe-buffered sapphire substrate. Mean camera noise-equivalent temperature difference NEΔT of 13 mK has been achieved at ≤ 120 K operating temperature and 3.4- to 4.2-μm passband; this is about an order of magnitude better than similar currently available cameras, which use PtSi FPAs and require cooling to ≤ 77 K to maintain performance at low scene temperatures.

Low-noise performance and dark-current measurements on the 256 x 256 NICMOS3 FPA

The NICMOS3 infrared focal plane array (FPA), which was designed as a Hubble Telescope upgrade device, provides excellent low-noise images in the 1 - 2.5 micrometers (SWIR) band. Both the detector array and the readout multiplexer of this hybrid FPA are optimized for low- noise operation. The NICMOS detector array is fabricated in HgCdTe grown on a sapphire substrate (PACE-I material). The sapphire substrate is very rugged and provides a good thermal contraction match to the silicon multiplexer, producing excellent reliability. The composition of the HgCdTe is adjusted to yield a response cutoff at 2.5 micrometers which limits the detector response to thermal background from the atmosphere and telescope. The quantum efficiency of the detectors is %GRT 50% over the 1 - 2.4 micrometers range. The dark current of the NICMOS detector is < 1 eMIN/s at 77 K, which is unprecedented for an IR detector. The multiplexer is a switched-FET CMOS design with a single source-follower per unit cell. The photocurrent is integrated on each detector diode, and the diode voltage level can be read nondestructively, or reset after each readout. This flexibility in the FPA operation makes it possible to generate images at a 12 Hz data frame rate or to optimize for low-noise exposures of many thousands of seconds. With a readout before and after each reset, off-chip correlated double sampling can be implemented to reduce the read noise to < 30 e-.

Status and direction of PACE-I HgCdTe FPAs for astronomy

Rockwells short wavelength infrared (SWIR) focal plane arrays (FPA) were originally designed for use in Orbital Replacement Instrument for the Hubble Space Telescope, but the 256 X 256 FPA version subsequently has found a home in many observatories. Developed for the University of Arizona under a NASA-Goddard prime contract to the University, the device is designated NICMOS3 due to its original relationship with the Hubbles Near Infrared Camera Multi-Object Spectrometer. Typical NICMOS3 FPAs have read noise < 35 e- with < 1 e-/sec detector dark current at 77 K and broadband quantum efficiency > 50% from 0.8 to 2.5 micrometers . These devices are in use all over the world by many researchers for SWIR astronomy. Based on long-term interaction with these scientists and on our own tests, the consensus is that the NICMOS3 is an extremely useful device. We are working to facilitate several paths for the subsequent low risk development of significantly upgraded astronomical FPAs. These include an even higher performance 256 X 256 FPA consisting of an upgraded readout mated to either standard or improved PACE-1 HgCdTe detector arrays, the near-term development of a 512 X 512 FPA via a proposed astronomical research consortium, and the longer term development of a 1024 X 1024 via several possible paths.

2.5-μm PACE-I HgCdTe 1024x1024 FPA for infrared astronomy

Rockwell Science Center and the University of Hawaii have developed a short wavelength infrared (SWIR) 1024 X 1024 focal plane array (FPA). The continuing project is funded by the U.S. Air Force Phillips Laboratory in connection with their Advanced Electro Optical System (AEOS) 3.67 m telescope project on Haleakala, Maui. We have achieved our objective of developing a 1024 X 1024 FPA with a cut-off wavelength of 2.5 micrometers . The device is named the HgCdTe Astronomical Wide Area Infrared Imager (HAWAII). The first hybrids have been characterized, delivered and first light achieved two days ahead of schedule; performance highlights include successful elimination of the reset anomaly (whose presence limited the noise performance of prior astronomical 256 X 256 FPAs), total FPA dark current < 0.1 e-/sec at 77 K, pixel yield > 99%, quantum efficiency > 50%, BLIP-limited sensitivity at low-109 photons/cm2-sec background and operating temperatures to 120 K, and read noise < 10 e-.

640 x 480 PACE HgCdTe FPA

A hybrid HgCdTe 640 X 480 infrared (IR) focal plane array (FPA) that meets the sensitivity, resolution, and field-of-view requirements of high-performance medium wavelength infrared (MWIR) imaging systems has been developed. The key technology making this large, high sensitivity device producible is the epitaxial growth of HgCdTe on a CdTe-buffered, sapphire substrate (referred to as PACE, for Producible Alternative to CdTe for Epitaxy; PACE-I refers to sapphire). The device offers TV resolution with excellent sensitivity at temperatures below 120 K. Mean NE(Delta) T as low as 13 mK has been achieved at operating temperatures < 130 K, which is about an order of magnitude better than has been achieved with PtSi 640 X 480 FPAs. In addition, the latter require cooling to <EQ 77 K. Mean PACE-I FPA D* at 78 K and background of 1014 photons/cm2-sec is BLIP-limited at 1 X 1012 cm-Hz1/2/W for the typical mean quantum efficiency of 60 - 70%. Imagery having excellent quality has been obtained using simple two-point nonuniformity compensation.

The CHROMA focal plane array: a large-format, low-noise detector optimized for imaging spectroscopy

The CHROMA (Configurable Hyperspectral Readout for Multiple Applications) is an advanced Focal Plane Array (FPA) designed for visible-infrared imaging spectroscopy. Using Teledyne’s latest substrateremoved HgCdTe detector, the CHROMA FPA has very low dark current, low readout noise and high, stable quantum efficiency from the deep blue (390nm) to the cutoff wavelength. CHROMA has a pixel pitch of 30 microns and is available in array formats ranging from 320×480 to 1600×480 pixels. Users generally disperse spectra over the 480 pixel-length columns and image spatially over the n×160 pixellength rows, where n=2, 4, 8, 10. The CHROMA Readout Integrated Circuit (ROIC) has Correlated Double Sampling (CDS) in pixel and generates its own internal bias signals and clocks. This paper presents the measured performance of the CHROMA FPA with 2.5 micron cutoff wavelength including the characterization of noise versus pixel gain, power dissipation and quantum efficiency.

256 x 256 PACE-1 PV HgCdTe focal plane arrays for medium and short wavelength IR applications

The development of two 256 by 256 hybrid HgCdTe focal plane array (FPA) families is described, and their performance is discussed. The hybrid FPAs employ a PV HgCdTe detector array and custom Si CMOS readouts. The PACE-1 process was used to fabricate the detectors, whereby the liquid phase epitaxial growth of HgCdTe occurs on sapphire substrates buffered by a layer of CdTe. The performance characteristics of the detector arrays are given. A tactical 256 by 256 CMOS readout is tested, in which a high functional yield was achieved. Updated test results are given for a 256 by 256 readout circuit developed for use in an orbital replacement instrument for the Hubble Space Telescope. The characterizations of several MWIR and SWIR FPAs were thorough and shown to be reliable. The pixel yield, maximum FPA responsivity nonuniformity, and SWIR FPA read noise for the tests are given. The high contrast and insignificant fixed pattern noise of the imagery from the MWIR 256 by 256 FPA are emphasized. These qualities were obtained when the device was operating at 80 k and utilizing f/2 optics with an 8-in. focal length and a 4.4 micron high pass filter.

Large staring IRFPAs of HgCdTe on alternative substrates

PACE-I HgCdTe, an industry-leading intrinsic detector technology for developing large, high performance IR focal plane arrays (IRFPAs) in the MWIR (3-5 microns) spectral band, is reviewed. Emphasis is placed on hybrid HgCdTe 256 x 256 IRFPAs and the status of 640 x 480 hybrid HgCdTe FPA.

Status report on 1024x1024 HgCdTe detector arrays for low-background operation in the 1.0- to 2.5-um range

The University of Hawaii and the Rockwell International Science Center are developing a large format SWIR detector array optimized for low background astronomical imaging and spectroscopic observations. This so called HgCdTe astronomical wide area IR imager (HAWAII) device will be based on the technology developed for the NICMOS project, but will incorporate several modifications of this design to improve the performance.