Kadri Vural

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

256*256 hybrid HgCdTe infrared focal plane arrays

Hybrid HgCdTe 256*256 focal plane arrays have been developed to meet the sensitivity, resolution, and field-of-view requirements of high-performance medium-wavelength infrared (MWIR) imaging systems. The detector arrays for these hybrids are fabricated on substrates that reduce or eliminate the thermal expansion mismatch to the silicon readout circuit. The readouts are foundry-processed CMOS switched-FET circuits that have charge capacities greater than 10/sup 7/ electrons and a single video output capable of 20-MHz data rates. The high quantum efficiency, tunable absorption wavelength, and broad operating temperature range of these large HgCdTe staring focal plane arrays give them significant advantages over competing sensors. The mature Producible Alternative to CdTe for Epitaxy-1 (PACE-1) technology, using sapphire detector substrates, has demonstrated 256*256 MWIR arrays with mean laboratory noise equivalent temperature difference (NETD) of 9 mK for a 4.9- mu m cutoff wavelength, 40- mu m pixel size, and 80-K operating temperature. RMS detector response nonuniformities are less than 4%, and pixel yields are greater than 99%. The newly developed PACE-3 process uses silicon for the detector substrate to eliminate completely the thermal mismatch with the silicon readout circuit. It has the potential for similar performance in even larger array sizes. A 640*480 hybrid array is under development. >

Performance of HgCdTe, InGaAs and quantum well GaAs/AlGaAs staring infrared focal plane arrays

The ability to hybridize various detector arrays in disparate technologies to an assortment of state-of-the-art silicon readouts has enabled direct comparison of key IR detector technologies including photovoltaic (PV) HgCdTe/Al2O3, PV HgCdTe/CdZnTe, PV InGaAs/InP, and the photoconductive (PC) GaAs/AlGaAs quantum well IR photodetector (QWIP). The staring focal plane arrays range in size from 64 X 64 to 1024 X 1024; we compare these IR detector technologies versus operating temperature and background flux via hybrid FPA test at operating temperatures from 32.5 K to room temperature and photon backgrounds from mid-105 to approximately equals 1017 photons/cm2-s. Several state-of-the-art IR FPAs are included: a 1.7 micrometers 128 X 128 InGaAs hybrid FPA with room temperature D of 1.5 X 1013 cm-Hz1/2/W and 195K D of 1.1 X 1015 cm-Hz1/2/W; a 3.2 micrometers 1024 X 1024 FPA for surveillance; a 4.6 micrometers 256 X 256 HgCdTe/Al2O3 FPA for imaging with BLIP NE(Delta) T of 2.8 mK at 95K; and a 9 micrometers 128 X 128 GaAs QWIP with 32.5 K D > 1014 cm-Hz1/2/W at 32.5K and 8 X 1010 cm-Hz1/2W at 62K.

Low-background infrared hybrid focal plane array characterization

Exploiting hybrid focal plane array methodology and a flexible multiplexing readout, 128 X 128 FPAs were made and directly compared using several short wavelength infrared (SWIR) and long wavelength (LWIR) detector technologies. The detector types include two GaAs/AlGaAs quantum well infrared photodetectors (QWIP), 1.7 micrometers InGaAs/InP, and 2.5 micrometers PV HgCdTe. The tests were performed at operating temperatures ranging from 35 K for the LWIR devices to as high as 175 K for the SWIR FPAs. Highlights include the first FPA demonstrations (to the best of our knowledge) of BLIP-limited detectivity (D*) for both LWIR GaAs/AlGaAs QWIP and 1.7 micrometers PV InGaAs/Inp. The 9 micrometers QWIP peak detectivity is near the theoretical background limit at 1.2 X 1010 photons/cm2-s background and 35 K operating temperature. The mean D* of 4.5 X 1013 Jones at 8.3 micrometers peak wavelength is 75% of BLIP. A maximum peak D* of 5.7 X 1014 Jones was achieved with the PV InGaAs/InP device at 200 K. This is also believed to be the highest reported FPA-level D* for a staring mosaic array operated at TV-type frame rate and integration time.

Attainment of high sensitivity at elevated operating temperatures with staring hybrid HgCdTe-on-sapphire focal plane arrays

Cost-effective high-performance IR imaging cameras need affordable staring focal plane arrays (FPAs) that can operate effectively at temperatures compatible with inexpensive long-life coolers. We report on staring hybrid 128 x 128 and 256 x 256 Hg1-xCdxTe FPAs that have requisite yield, sensitivity, operability, and reliability at a medium-wavelength IR (MWIR) cutoff wavelength (λc ~4.6 μm at 180 K) and elevated operating temperatures. Mean 256 x 256 FPA noise-equivalent temperature differences (NEΔT) using broadband f/1.7 optics were 4.3, 7.7, and 55 mK at 120, 140, and 180 K, respectively. We extrapolate that camera NEΔT ≤ 0.02 K can be achieved at 190 K using optimized (λc of ~4.4 μm (180 K), a 3.4- to 4.2-μm bandpass filter, and f/1 optics. Because the CMOS multiplexers have a low-power dissipation and need little ancillary circuitry in the dewar, a viable thermoelectrically-cooled FPA technology is thus implied once the λc is optimized for MWIR imaging.

Mercury cadmium telluride short- and medium-wavelength infrared staring focal plane arrays

Abstract. Short-wavelength (1 to 2.5 µm) and medium-wavelength (1 to 4.0 µm and 1 to 4.8 µm) 64 x 64 hybrid focal plane arrays (FPAs) have been developed. The short-wavelength (SWIR) arrays were developed for use in a prototype Airborne Imaging Spectrometer system. The medium-wavelength (MWIR) arrays are suitable for tactical missile seekers and strategic surveillance systems. The detector material is HgCdTe LPE grown on a sapphire substrate. The unit cell size is 52 µm x 52 µm, and the detectors are ion-implanted planar structures. The multiplexer is a surface- or buried-channel, four-phase charge-coupled device. The unit cell has a direct-injection FET and a storage capacitor. The current-voltage characteristics of the 64 x 64 detector arrays were measured at near-zero background using Si fan-out chips. For the detector arrays with a 2.5 µm cutoff, the mean RoA for 29 random elements was 2.7 x 106 cm2 at T = 150 K. The mean RoA was 3 x 104 cm2 at 120 K for detector arrays with a 4.6 µm cutoff. Both results were adequate for specific system applications. The arrays were also characterized at different temperatures, and the results are presented herein. The 64 x 64 SWIR and MWIR detector arrays were mated to a multiplexer, and the resulting FPAs were characterized under different operating conditions. Detailed characterization results are presented.

Development of hybrid CMOS visible focal plane arrays at Rockwell

Silicon-based hybrid CMOS visible focal plane array (FPA) technology is emerging as a strong contender for scientific applications that require broad spectral response with low noise, highly integrated functionality and radiation hardness. CMOS-based FPAs offer many advantages in high speed, low-noise detection and signal processing. As a high performance alternative to advanced CCD imaging arrays, the hybrid design enables independent optimization of the silicon detector array and silicon readout electronics. Multiplexer commonality with the instruments IR channels is another attractive feature for integrators of sensor sites such as for hyperspectral spectrometers. In this paper, the technical merits of Rockwells CMOS-based hybrid visible FPAs are described including key detector performance aspects, interface electronics requirements, radiation hardness and concomitant implications for diverse imaging applications. At this time we have developed 640 X 480 and 1024 X 1024 hybrid imagers with approximately equals 100% optical fill factor, high broadband QE spanning ultraviolet (UV) through near infrared (NIR), wide dynamic range, and high pixel operability. Dark current of approximately equals 0.01e-/sec and read noise approximately equals 6e- have been measured on one prototype 1024 X 1024 FPA that uses Hawaii readout integrated circuit (ROIC). Initial radiation data indicate a total ionization dose (TID) tolerance greater than 35 Krad for our standard CMOS process.

2048x2048 HgCdTe focal plane arrays for astronomy applications

Rockwell is developing the worlds largest HgCdTe IR focal plane array (FPA) for astronomy and low background applications. The format of the device is a hybrid 2048 X 2048 with a unit cell size of 18 micrometers X 18 micrometers . SWIR detectors with a spectral response of 0.85 micrometers to 2.5 micrometers have been processed on liquid phase epitaxy (LPE) HgCdTe on sapphire substrates. The MWIR detectors with a spectral response of 0.4 micrometers to 5 micrometers will be processed on molecular beam epitaxy HgCdTe on CdZnTe substrates. The multiplexer has been designed and fabricated at Conexant. Room temperature probing shows that the device is functional with excellent yield. Novel hybrid fabrication techniques will be used to demonstrate the FPA. This HAWAII-2 device is based on the highly successful HAWAII 1024 X 1024 device and the performance will be similar. The ultimate performance expected from the array is: dark currents of < 0.01 3-/s, quantum efficiency of > 75 percent across the spectral band, and noise levels of < 3 e- for the SWIR and < 10 e- for the MWIR band using Fowler sampling. We expected to achieve these performance levels at 77K for the SWIR and > 40K for the MWIR band. The status of the 2048 X 2048 detector arrays and FPAs are discussed.

Recent advances in staring hybrid focal plane arrays: comparison of HgCdTe, InGaAs and GaAs/AlGaAs detector technologies

A comparison of photovoltaic HgCdTe/Al2O3, HgCdTe/CdZnTe, InGaAs/InP and photoconductive GaAs/AlGaAs quantum well infrared photodetector detector technologies has been conducted at Rockwell by exploiting the ability to selectively hybridize disparate mosaic detector arrays to an assortment of silicon multiplexers. Hybrid FPA characteristics are reported as functions of operating temperature from 32.5 K to room temperature and at photon backgrounds from approximately equals 106 to mid-1016 photons/cm2-sec. The staring arrays range in size from about sixteen thousand to over a million pixels. Background-limited detectivities significantly exceeding 1014 cm-(root)Hz/W were achieved.

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.