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In the last few years Rockwell has developed a novel simultaneous unipolar multispectral integrated HgCdTe detector and focal plane array technology that is a natural and relatively straightforward derivative of our baseline double layer planar heterostructure (DLPH) molecular beam epitaxial (MBE) technology. Recently this technology was awarded a U.S. patent. This simultaneous unipolar multispectral integrated technology (SUMIT) shares the high performance characteristics of its DLPH antecedent. Two color focal plane arrays with low-1013 cm−2s−1 background limited detectivity performance (BLIP D*) have been obtained for mid-wave infrared (MWIR, 3–5 m) devices at T>130 K and for long-wave infrared (LWIR, 8–10 m) devices at T∼80 K.

Short wave infrared (SWIR) devices have been fabricated using Rockwell’s double layer planar heterostructure (DLPH) architecture with arsenic-ion implanted junctions. Molecular beam epitaxially grown HgCdTe/CdZnTe multilayer structures allowed the thin, tailored device geometries (typical active layer thickness was ∼3.5 µm and cap layer thickness was ∼0.4 µm) to be grown. A planar-mesa geometry that preserved the passivation advantages of the DLPH structure with enhanced optical collection improved the performance. Test detectors showed Band 7 detectors performing near the radiative limit (∼3-5X below theory). Band 5 detector performance was ∼4-50X lower than radiative limited performance, apparently due to Shockley-Hall-Read recombination. We have fabricated SWIR HgCdTe 256 × 12 × 2 arrays of 45 um × 45 µm detector on 45 µm × 60 µm centers and with cutoff wavelength which allows coverage of the Landsat Band 5 (1.5−1.75 µm) and Landsat Band 7 (2.08−2.35 µm) spectral regions. The hybridizable arrays have four subarrays, each having a different detector architecture. One of the Band 7 hybrids has demonstrated performance approaching the radiative theoretical limit for temperatures from 250 to 295K, consistent with test results. D* performance at 250K of the best subarray was high, with an operability of ∼99% at 1012 cm Hz1/2/W at a few mV bias. We have observed 1/f noise below 8E-17 AHz 1/2 at 1 Hz. Also for Band 7 test structures, Ge thin film diffractive microlenses fabricated directly on the back side of the CdZnTe substrate showed the ability to increase the effective collection area of small (nominally

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

This paper describes recent advances in MBE HgCdTe technology. A new 3 inch production molecular beam epitaxy (MBE) system, Riber Model 32P, was installed at Rockwell in 1994. The growth technology developed over the years at Rockwell using the Riber 2300 R&D system was transferred to the 32P system in less than six months. This short period of technology transfer attests to our understanding of the MBE HgCdTe growth dynamics and the key growth parameters. Device quality material is being grown routinely in this new system. Further advances have been made to achieve better growth control. One of the biggest challenges in the growth of MBE HgCdTe is the day-to-day control of the substrate surface temperature at nucleation and during growth. This paper describes techniques that have led to growth temperature reproducibility within + - 1°C, and a variation in temperature during substrate rotation within 0.5°C. The rotation of the substrate during growth has improved the uniformity of the grown layers. The measured uniformity data on composition for a typical 3 cm × 3 cm MBE HgCdTe/CdZnTe shows the average and standard deviation values of 0.229 and 0.0006, respectively. Similarly, the average and standard deviation for the layer thickness are 7.5 and 0.06 µm, respectively. P-on-n LWIR test structure photodiodes fabricated using material grown by the new system and using rotation during growth have resulted in high-performance (R0)A, quantum efficiency) devices at 77 and 40K. In addition, 128 × 28 focal plane arrays with excellent performance and operability have been demonstrated.

Extensive material, device, and focal plane array (FPA) reproducibility data are presented to demonstrate significant advances made in the molecular beam epitaxial (MBE) HgCdTe technology. Excellent control of the composition, growth rate, layer thickness, doping concentration, dislocation density, and transport characteristics has been demonstrated. A change in the bandgap is readily achieved by adjusting the beam fluxes, demonstrating the flexibility of MBE in responding to the needs of infrared detection applications in various spectral bands. High performance of photodiodes fabricated on MBE HgCdTe layers reflects on the overall quality of the grown material. The photodiodes were planar p-on-n junctions fabricated by As ion-implantation into indium doped, n-type, in situ grown double layer heterostructures. At 77K, diodes fabricated on MBE Hg1−xCdxTe with x ≈ 0.30 (λco ≈ 5.6 μm), x ≈ 0.26 (λco ≈ 7 μm), x ≈ 0.23 (λco ≈ 10 μm) show R0A products in excess of 1 x 106 ohm-cm2, 7 x 105 ohm-cm2, and 3 x 102 ohm-cm2, respectively. These devices also show high quantum efficiency. As a means to assess the uniformity of the MBE HgCdTe material, two-dimensional 64 x 64 and 128 x 128 mosaic detector arrays were hybridized to Si multiplexers. These focal plane arrays show an operability as high as 97% at 77K for the x ≈ 0.23 spectral band and 93% at 77K for the x ≈ 0.26 spectral band. The operability is limited partly by the density of void-type defects that are present in the MBE grown layers and are easily identified under an optical microscope.

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. >

Infrared sensor designers have long maximized S/N ratio by employing pixel-based amplification in conjunction with supplemental noise suppression. Instead, we suppress photodiode noise using novel SoC implementation with simple three transistor pixel; supporting SoC components include a feedback amplifier having elements distributed amongst the pixel and column buffer, a tapered reset clock waveform, and reset timing generator. The tapered reset method does not swell pixel area, compel processing of the correlated reset and signal values, or require additional memory. Integrated in a 2.1 M pixel imager developed for generating high definition television, random noise is ∼8e-at video rates to 225 MHz. Random noise of ∼30e-would otherwise he predicted for the 5 μm 5 μm pixels having 5.5 fF detector capacitance with negligible image lag. Minimum sensor S/N ratio is 52 dB with 1920 by 1080 progressive readout at 60 Hz, 72 Hz and 90 Hz. Fixed pattern noise is

Deep sub-micron (≤0.25 μm) CMOS enables the existence of imaging sensors with lower noise at higher video frequencies and lower power dissipation than previously possible. This CMOS-based imaging System-on-Chip (i-SoC) technology hence produces large monolithic and hybrid Focal Plane Arrays (FPAs) that outperform competing CCD-based imaging sensors. The hybrid approach produces visible 20482 FPAs and 40962 mosaics with ∼ 5e− read noise at 1 MHz and quantum efficiency >80% from 390 nm to 930 nm. The monolithic approach produces visible 12-bit imaging system-on-chips such as a 1936 by 1088 with higher quantum efficiency than mainstream CCDs

We have developed a three-dimensional (3D) imaging ladar focal plane array (FPA) for military and commercial applications. The FPA provides snap-shot, direct detection, high-resolution range and range-sampled intensity imaging capability on a single chip. The FPA is made of a 64x64 element, 100-μm pixel pitch detector array that is directly bump bonded to a matched CMOS based silicon readout integrated circuit (ROIC) with parallel ladar signal processing at each pixel. A room temperature, SWIR InGaAs detector variant for imaging near 1.5-μm wavelengths and a cooled MWIR HgCdTe detector variant for imaging near 3-μm to 5-μm wavelengths have been fabricated. We have built a prototype SWIR FPA, integrated it to a compact, transportable SWIR flash ladar transceiver, and collected initial range images outdoors. We present the measured performances of the detector, the readout, and the image data collected with the focal plane array.

Large two-dimensional imaging arrays, spanning infrared focal plane arrays through visible CCDs, usually require extensive support electronics. We present an application specific integrated circuit (ASIC) that combines, on a single chip, all necessary functions to operate CMOS-based focal plane arrays and provide digital data from 12 to 16 bits. The interface to the external world is completely digital, thus eliminating the complexity of dealing with sensitive analog voltages. The ASIC's first application is for use with the HAWAII-2RG (a 2048 x 2048 multiplexer specifically optimized for the Next Generation Space Telescope). Due to its flexibility, it can control other FPAs and SCAs not requiring clocks or biases higher than 3.3 V. The low-power, system-on-chip controller comprises a 16-bit microcontroller, program and data memory, clock generator, bias generator, 36 programmable gain amplifiers (0 to 27 dB), thirty-six 12-bit 10 MHz A/D converters, thirty-six 16-bit 500 kHz A/D converters, glue logic and programmable I/O pads. When configured for NGST, we estimate ≤ 8.4 mW continuous power for the 2k x 2k FPA and ASIC. The programmable ASIC, dubbed SIDECAR, for System for Image Digitization, Enhancement, Control And Retrieval, is likely an optimum "back-end" solution for other high-performance instruments.

The HAWAII-2RG is a major upgrade of our prior 2048 x 2048 CMOS readout for astronomy (HAWAII-2) to support the requirements of the Next Generation Space Telescope and enable breakthrough capability for ground-based astronomy. By migrating to 0.25μm CMOS, for the first time guide mode readout is simultaneously supported in combination with various programmable science modes on a frame-by-frame basis. Consequently, the readout simultaneously supports programmable guide mode window and full-field science using the rest of the 4.2 million pixels at read noise 60 Hz. As with the HAWAII-2, the readout can be mated to our infrared and visible detector arrays including low dark current MBE HgCdTe at cutoff wavelengths from 1.5μm to 14μm, 2.5μm PACE HgCdTe, and silicon p-i-n detectors with superior quantum efficiency to backside-illuminated CCDs.

Rockwell Scientific's 3rd generation FPAs and sensor chip assemblies (SCA) are complete imaging systems-on-chip for IR and visible cameras. They provide 12-bit to 16-bit digital video at very low power consumption in hybrid and monolithic configurations. A 1936 by 1088 i-SoC with 5μm pixel pitch performs stand-alone visible imaging and a related application-specific integrated circuit supports SCAs. The former generates high-definition video at 30 Hz with

CMOS-based imaging system-on-chip (i-SoC) technology is successfully producing large monolithic and hybrid FPAs that are superior in many respects to competing CCD-based imaging sensors. The hybrid approach produces visible 2048 by 2048 FPAs with

The past 2 to 3 years has been a period of explosive growth in technology development for imaging sensors at Rockwell Scientific Co. (RSC). The state of the art has been advanced significantly, resulting in a number of unique advanced imaging sensor products. A few key examples are: 2048 x 2048 sensor chip assemblies (SCA) for ground and space-based applications, 4096 x 4096 mosaic close-butted mosaic FPA assemblies, a very high performance 10 x 1024 hybridized linear SCA for optical network monitoring and other applications, the revolutionary CMOS ProCam-HD imaging system-on-a-chip for high definition television (HDTV), and RSC's near-infrared emission microscope camera for VLSI defect detection/analysis. This paper provides selected updates of these products and thereby provides an overview of the ongoing highly fertile period of technology and product development at Rockwell Scientific. A view into future directions for advanced imaging sensors is also provided.

We are developing a novel 2D focal plane array (FPA) with read-out integrated circuit (ROIC) on a single chip for 3D laser radar imaging. The ladar will provide high-resolution range and range-resolved intensity images for detection and identification of difficult targets. The initial full imaging-camera-on-a-chip system will be a 64 by 64 element, 100-micrometers pixel-size detector array that is directly bump bonded to a low-noise 64 by 64 array silicon CMOS-based ROIC. The architecture is scalable to 256 by 256 or higher arrays depending on the system application. The system will provide all the required electronic processing at pixel level and the smart FPA enables directly producing the 3D or 4D format data to be captured with a single laser pulse. The detector arrays are made of uncooled InGaAs PIN device for SWIR imaging at 1.5 micrometers wavelength and cooled HgCdTe PIN device for MWIR imaging at 3.8 micrometers wavelength. We are also investigating concepts using multi-color detector arrays for simultaneous imaging at multiple wavelengths that would provide additional spectral dimension capability for enhanced detection and identification of deep-hide targets. The system is suited for flash ladar imaging, for combat identification of ground targets from airborne platforms, flash-ladar imaging seekers, and autonomous robotic/automotive vehicle navigation and collision avoidance applications.

Continuing advances in CMOS technology including finer lithography, the addition of dense planarized interconnect layers, concomitant improvements in transistor performance, and the availability of design tools that facilitate large- scale circuit integration, are now enabling the development of systems on a chip. While the first such imaging systems- on-a-chip supported detection of radiation at visible wavelengths, recent imaging systems-on-a-chip extend into the infrared. The result is high-performance infrared FPAs with high functionality. We report our progress at Rockwell Science Center in exploiting submicron CMOS to produce such infrared imaging systems-on-a-chip while overcoming accompanying challenges such as lower operating voltage. Our goal is to develop third-generation infrared imagers with compelling performance and functionality advantages that not only provide high sensitivity and resolution, but also facilitate on-demand sensor selection to adeptly match each mission without need for extensive support logistics including extensive cooling and elaborate camera electronics.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Hg:Cd:Te grown by Molecular Beam Epitaxy onto a lattice matched Cd:Zn:Te substrate with Double Layer Planar Heterostructure architecture holds promise of extremely low, near theoretical dark current out to wavelengths beyond 5 micrometers while eliminating the persistent images and reduced short-wave quantum efficiency disadvantages of the liquid phase epitaxial (LPE) material now in widespread astronomical use. We report on the characterization of two Rockwell FPAs consisting of (lambda) c approximately 4.75 micrometers MBE material hybridized to 1K by 1K HAWAII multiplexers within the context of establishing their performance relative to the stringent focal plane goals for the Next Generation Space Telescope (NGST). The effort has concentrated primarily on characterizing total FPA noise at selected temperatures from 30 to 90 K although short wave quantum efficiency and image persistence have also been measured. The test procedures are based on the use of both DC and variance nosie techniques and, at T approximately 60K, have allowed characterization of the total noise as the sum of separate contributions due to dark current, read noise and read charge. The test facility and characterization techniques are described and results, which verify the remarkable potential of this material to exceed the NGST performance goals at temperatures both at, and also significantly higher than, the approximate 30K now anticipated for the NGST NIR focal pane, are presented.

Rockwell Space Center is developing low-noise visible and IR imaging sensors and systems for astronomy, high-end commercial, NASA, and advanced military applications. The first science grade 2048 by 2048 HAWAII-2 focal plane array (FPA) for astronomy was recently demonstrated for the SWIR waveband. Science-grade deliveries to the University of Hawaii's Institute for Astronomy, the European Southern Observatory and the Subaru Telescope, among others, will soon start. MWIR/visible 2048 by 2048 HAWAII-2 arrays are also being developed for the NGST program using our process for removing the CdZnTe substrate from the back-side illuminated HgCdTe FPAs to detect visible radiation in addition to IR. Previously, more than 25 science grade 2.5micrometers 1024 by 1024 HAWAII FPAs were delivered for use in many observatories; these typically exhibit 90 percent with near-100 percent fill factor, and the dark current is negligible with minimum cooling. Our near-term plan to develop 4096 by 4096 visible and IR FPAs will also be discussed.

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 instrument's IR channels is another attractive feature for integrators of sensor sites such as for hyperspectral spectrometers. In this paper, the technical merits of Rockwell's 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.

Sub-micron CMOS has already enabled the development of IR focal plane array with ultra-low read noise and high sensitivity for many demanding applications. The successful monolithic integration of silicon photo detector with low- noise pixel-based amplifiers in fine pixel pitch via modern CMOS technology now suggests the imminent obsolescence of CCDs and photographic film for consumer uses. Specifically, we report the achievement of < 20 e- read noise at high data rates and video frame rate,s the confirmation of the fundamental superiority of the CMOS imager for visible imaging, and approximately 2X reduction in kTC noise without invoking classical correlated double sampling techniques. These suggest a strong likelihood reduction in kTC noise without invoking classical correlated double sampling techniques. These suggest a strong likelihood that the CCDs long reign is coming to an end.

Short wavelength, middle wavelength, mid-long wavelength, long wavelength, and very long wavelength focal plane arrays (FPAs) are required for remote sensing applications. Advances in the Molecular Beam Epitaxy (MBE) growth of Mercury Cadmium Telluride (HgCdTe) and detector architectures utilized, have resulted in high performance detectors being fabricated in the 1 micrometers to 16 micrometers spectral range Custom Read Out Integrated Circuits (ROICs) are designed and fabricated to interface the HgCdTe detector arrays. The hybrid focal pane array is made up of the HgCdTe detector array and the CMOS-based ROIC. Hybrid FPAs performance parameters are presented. The HgCdTe detector material is used are grown by MBE on lattice matched CdZnTe substrates. Custom ROICs are fabricated in a commercial CMOS foundry. FPA D* performance values have been obtained for a multitude of spectral ranges and configurations that include; (i) (lambda) c equals 1.8 micrometers , 12 X 256 arrays operating at 295 K with median D* approximately 1.4 X 1012 cm Hz1/2/W, (ii) (lambda) c equals 10.5 micrometers , 256 X 256 arrays operating at 85 K with medina D* equals 3.9 X 1011 cm Hz1/2/W at a background flux (phi) b equals 7.82 X 1015 ph/cm2-2 and (iii) (lambda) c equals 15.8 micrometers at 65K, 128 X 128 array operating at 40K with peak D* of 2.76 X 1011 cm Hz1/2/W at a background flux (phi) b equals 8.0 X 1015 ph/cm2- s. The performance of these FPAs will be presented.

Rockwell is developing the world's 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 75 percent across the spectral band, and noise levels of 40K for the MWIR band. The status of the 2048 X 2048 detector arrays and FPAs are discussed.

Infrared (IR) remote sensing imaging applications require high-performance Focal Plane Arrays (FPAs) operating in all ranges of the IR spectrum. Short wavelength (SWIR; 1 to 3 micrometer), middle wavelength (MWIR; 3 to 5 micrometer), mid- long wavelength (MLWIR; 6 to 8 micrometer), long wavelength (LWIR; 8 to 14 micrometer), and very long wavelength (VLWIR; greater than 14 micrometer). These diverse spectral bands require high performance detectors and Read Out Integrated Circuits (ROICs) to perform the multi-spectral mission requirements. Significant progress in the design and fabrication of HgCdTe detector arrays and Read Out Integrated Circuits (ROICs) over the past few years has led to the demonstration of high resolution, low noise and large format reliable FPAs. Hybrid FPAs have been measured and their performance parameters are presented. Focal Plane Array D* performance values have been obtained for a multitude of spectral ranges and configurations that include; (1) (lambda) c equals 1.8 micrometer, 12 X 256 arrays operating at 295 K with median D* approximately 1.4 X 1012 cm Hz1/2/W, (2) (lambda) c equals 2.4 micrometer, 12 X 256 arrays operating at 250 K with median D* equals 1.6 X 1012 cm Hz1/2/W, detectors used are grown by MBE on lattice matched CdZnTe, (3) PACE-1 detectors with (lambda) c equals 2.5 micrometer, 1024 X 1024 arrays operating at 115 K with peak D* of 2.3 X 1013 cm Hz1/2/W at a background flux (phi) b equals 1.2 X 1011 ph/cm2- s, (4) MBE HgCdTe on Silicon MWIR detectors have been fabricated and the detector RoA performance for (lambda) co approximately 5.0 micrometer is in the 106 to 107 ohm-cm2 range at 78 K. (5) MBE HgCdTe on CdZnTe detectors, ((lambda) c equals 15.8 micrometer at 65 K), 128 X 128 array operating at 40 K with peak D* of 2.76 X 1011 cm Hz1/2/W at a background flux (phi) b equals 8.0 X 1015 ph/cm2-s. High performance 640 X 480 arrays imaging in the MWIR band have been fabricated on CdZnTe and PACE-1 substrates. The performance of these and additional FPAs will be presented.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Low-noise pixel-based amplification via sub-micron CMOS is enabling advanced focal plane arrays offering ultra-low read noise for infrared astronomy, wave-front sensing, IR spectroscopy, spaceborne sensors and other discriminating uses. Specifically, we report the achievement of less than 30 e- read noise at video frame rates using capacitive transimpedance amplification and less than 1 e- using an enhanced form of gate modulation. We also compare several low- noise IR FPAs at various cutoff wavelengths from 1.1 micrometer to nearly 17 micrometer.

The availability of submicron CMOS has enabled the development of shingle-chip IR cameras having performance capabilities and on-chip functions which were previously impossible. Sensor designers are, however, encoutering and overcoming several challanges including steadily decreasing operating voltage.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

An active pixel sensor (APS) integrated in standard CMOS process technology is shown to be superior to an alternative passive pixel sensor (PPS). Further, the CMOS APS provides video sensitivity and SNR comparable to CCDs. Though the CMOS PPS has lower performance, it offers >50% optical fill factor without microlenses and can be produced at lower cost for applications not requiring broadcast quality SNR (>35 dB) under low light conditions (

The HAWAII-2 is an IR 2048 2 focal plane array (FPA) that is being developed for next-generation IR astronomy. It will supplant our HAWAII 1024 2 as the largest high- performance imaging array available for IR astronomy. As with our prior IR sensor, the flip-chip hybrid will consist of a low-capacitance HgCdTe detector array mated to a low- noise CMOS silicon multiplexer via indium interconnects. In order to accommodate reasonable telescope optics and fabrication of the large sophisticated readout using world- class submicron CMOS, the FPA has 18 micrometers pixel pitch. We anticipate > 5 percent yield of defect-free multiplexers using 0.8 micrometers CMOS. The HgCdTe detector arrays will be fabricated on large wafers including sapphire and silicon. Though the first FPAs will have 2.5 micrometers cut-off, the readout will be able to support longer wavelengths. Also reported are the latest 1024 X 1024 FPA results with 2.5 micrometers HgCdTe detectors.

Rockwell Science Center has developed a double layer planar heterostructure (DLPH) detector array fabrication process with significant advantages over the PACE-1 process now being used to produce 256 X 256 and 1024 X 1024 FPAs for low background IR astronomy. The DLPH detectors are p- on-n photodiodes fabricated in a double layer of wide and narrow bandgap HgCdTe grown by molecular beam epitaxy on CdZnTe substrates. The double layer structure provides superior surface passivation while the lattice matched CdZnTe substrate reduces the defect density. DLPH FPAs have been fabricated in array sizes up to 640 X 480 and with cutoff wavelengths as long as 15 micrometers . Quantum efficiencies are typically in the 0.5 to 0.8 range. For a 256 X 256 array DLPH detectors with 5.3 micrometers cutoff wavelength at 50K, the median dark current was 0.39 e-/sec at 0.5V reverse bias. For 7 of 17 individual DLPH detector with 10.6 micrometers cutoff at 30K, the dark current was less than 10 4 e-/sec at 20 mV bias. For long cutoff wavelengths, the detector breakdown voltage is too low to permit signal integration directly on the reverse biased detector capacitance. Such detectors require a readout circuit that maintains the detector near zero bias and provides a separate capacitor to store the integrated signal.

We have developed 1024 X 1024 HAWAII (HgCdTe Arrays for Wide-field Astronomical Infrared Imaging) focal plane arrays (FPAs) for use in astronomical applications. These devices have been delivered to various astronomy organizations around the world and have resulted in increased sensitivities and decreased observation times for deep space imaging. The detector material is PACE-I for SWIR and Molecular Beam Epitaxy (MBE) HgCdTe on CdZnTe for MWIR. The 1024 X 1024 multiplexer has a 18.5 micrometer unit cell pitch, source follower per detector (SFD) input, and it was fabricated at or internal commercial CMOS process line with excellent yield. Mean dark currents as low as 0.02 e-/s have been measured at 77 K for 2.5 micrometer devices (1024 X 1024 format, 18.5 micrometer pitch) and 0.39 e-/s for 5.3 micrometer devices at 50 K (256 X 256 format, 40 micrometer pitch). Quantum efficiencies are greater than 50% for both SWIR and MWIR detectors; with AR coatings, these are expected to be above 75%. Noise levels of 3 e- have been measured by multiple sampling techniques for the SWIR and 75 e- for the MWIR. All of these devices are simple to operate and are readily available. We are presently developing 2048 X 2048 FPAs with 18 micrometer unit cell pitch for both SWIR and MWIR applications.

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.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Significant advances have been made in growing high quality HgCdTe detector arrays, designing and fabricating multiplexing readouts in submicron CMOS, and in subsequently fabricating large hybrid FPAs having excellent reliability. Consequently, high performance IR cameras are now being routinely developed for diverse applications. For example, FPAs as large as 1024 X 1024 with mean dark current 1 X 1014 Jones are being supplied for IR astronomy. Affordable high performance IR imaging cameras, however, require cost-effective staring focal plane arrays (FPA) that operate at temperatures compatible with long-life, low-power coolers. We thus report a 5 micrometers 256 X 256 FPAs having mean D > 8.8 X 1011 cm-(root)Hz/W with > 99.5 percent pixel operability at 90K operating temperature. The device's large charge capacity enables full coverage of the 3 to 5 micrometers atmospheric window to provide many of the advantages promised by competing staring LWIR sensors including enhanced S/N under stringent operating conditions and reduced background clutter. The staring Hg1-xCdxTe FPAs offer not only high sensitivity, operability and reliability at elevated operating temperatures, but also stable, temporal noise-limited imaging over the 3.4 to 4.8 micrometers passband. We report temporal sensitivity < mK with comparable spatial noise at 95K operating temperature. We also quantify the operating temperature stability required to maintain high sensitivity. Finally, we briefly status our HgCdTe FPA technology by focusing on key off-the-shelf CMOS readouts.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We have developed two high performance 1024 multiplied by 1024 focal plane arrays for astronomy, spectroscopy, surveillance and conventional imaging. Each hybrid consists of a photovoltaic HgCdTe detector array, fabricated on Al 2 O 3 substrate and having photoresponse cutoff wavelength optimized for each specific application, mated to a CMOS silicon readout via indium column interconnects. In addition to updating the performance of our 1024 multiplied by 1024 FPA for astronomy developed in 1994, we introduce a second 1024 multiplied by 1024 having capability for operation at TV-type frame rates. The latter device also has low read noise but at much higher bandwidth by virtue of its capacitive transimpedance amplifier input and pipelined readout architecture. Both devices have been shown capable of consistently achieving background-limited sensitivity at very low infrared backgrounds (less than or equal to 10 9 photons/cm2-sec) by their low read noise, low dark current including negligible MOSFET self-emission, and high quantum efficiency. FPA pixel operability as high as 99.94% with mean peak D* of 10 14 cm-Hz 1/2 /W has been demonstrated. Proprietary hybridization and mounting techniques are being used to insure hybrid reliability after many thermal cycles. The hybrid methodology has been modeled using finite element modeling to understand the limiting mechanisms; very good agreement has been achieved with the measured reliability.

To achieve the DoD objective of low cost high performance infrared focal plane arrays a manufacturing technique is required which is intrinsically flexible with respect to device configuration and cutoff wavelength and easily scaleable with respect to volume requirements. The approach adopted is to fully develop the technology of molecular beam epitaxy (MBE) to a level where detector array wafers with a variety of configurations can be fabricated with first pass success at a reduced cost. As a vapor phase process, MBE lends itself directly to: (1) the inclusion of real-time monitoring and process control, (2) a single or multiple wafer growth mode, (3) nearly instantaneous changes in growth parameters. A team has been assembled to carry out the program. It is composed of four industrial organizations -- Rockwell International, Hughes Aircraft Company, Texas Instruments, and Lockheed-Martin, and a university -- Georgia Tech Research Institute. Since team members are committed suppliers and users of IRFPAs, technology transfer among team members is accomplished in real-time. The technical approach has been focused on optimizing the processes necessary to fabricate p-on-n HgCdTe double layer heterostructure focal plane arrays, reducing process variance, and on documenting flexibility with respect to cutoff wavelength. Two device structures have been investigated and fabricated -- a 480 by 4 and a 128 by 128.

Attainment of high D* at room temperature via gate-modulated detector interfaceL.J. Kozlowski and K. VuralRockwell Science Center1049 Camino Dos RiosThousand Oaks, CA 91360(805)-373-4267FAX: (805) 373-4687W.E. Kleinhans and T. LiuValley Oak Semiconductor3 1255 Cedar Valley Drive Suite 314Westlake Village, CA 91362G.M. Olson and M. CohenSensors Unlimited, Inc.3490 US Route 1Princeton, New Jersey 08540(609) 520-0610FAX: (609) 520-0638ABSTRACTWe report the performance oflnGaAs and HgCdTe FPAs using multiplexing readouts having gate modulated interface to theinfrared detectors. Gate modulation enables extremely high sensitivity via self-adjusting current gain and concomitant hightransimpedance. At operating temperatures where the detector current was dominated by photocurrent, gate modulationcurrent gain is >40,000 and yields input-referred read noise of

We compare the capacitive transimpedance amplifier (CTIA) to two other IR detector interface circuits using data compiled from hybrid FPAs in various formats from 8 X 8 to 1024 X 1024. The CTIA generally offers the best overall performance characteristics including read noise as low as 27 e- at signal bandwidths compatible with TV-type frame rates, low power dissipation (in some cases significantly less than 200 nW per pixel), and sufficiently low MOSFET self-emission for background-limited sensitivity at scene backgrounds significantly less than 109 photons/cm2- s. The alternative schemes should, however, be considered especially when very high transimpedance is needed at moderate bandwidths or when radiometric linearity is not required.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We report significant improvements in the performance of short wavelength infrared 128 X 128 focal plane arrays at room temperature. Using InGaAs and HgCdTe detector materials coupled to readout multiplexers having gate modulated detector interface, sensitivity that is near the theoretical detector-limited levels has been achieved via both low detector dark current and self-adjusting readout current gain. Extrapolating to nocturnal imaging conditions, the uncooled FPA-level sensitivities of 1.68 micrometers InGaAs and 1.86 micrometers HgCdTe arrays are shown to be within 35% and 80% of theoretical, respectively.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We compare several key infrared 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 equal to 1017 photons/cm2-sec. The detector materials include photovoltaic (PV) HgCdTe/Al2O3, PV HgCdTe/CdZnTe, photoconductive (PC) GaAs/AlGaAs quantum well infrared photodetector (QWIP) and PV InGaAs/InP; the device sizes range from 64 multiplied by 64 to 1024 multiplied by 1024.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The first prototype of a HgCdTe infrared detector array with 1024 X 1024 pixels developed by the Rockwell International Science Center has been tested in a new infrared camera at the UH 2.2 m telescope, the 0.6 m telescope, and the CFHT. At the 2.2 m tests were conducted both at f/31, where images of very high resolution were obtained using tip-tilt correction, and at f/10 for a wide field of view. At the CFHT both wide field imaging (f/8) and adaptive optics work was done. The HAWAII (HgCdTe astronomical wide area infrared imager) prototype device achieved very good performance. In the camera system, a double correlated readnoise of 15 e - rms was achieved. The dark current at 1 V bias could be confirmed to be below 1 e - , even though the device was operated above 77 K. The quantum efficiency is slightly below 50% and shows the wavy pattern characteristic of LPE-grown HgCdTe. The full well capacity is above 10 5 e - at 1 V bias, limited in our system by the dynamic range of the A/D converter. Data reduction is practically identical to what is used for NICMOS3 256 X 256 devices. Combined integration times of more than 1 hour have been used and demonstrate that the HAWAII devices are suitable for very deep imaging. The residual excess dark current problem known from NICMOS3 devices is not fully resolved. However, it appears less serious in our first HAWAII prototype device.

Extensive material and device statistics of performance and reproducibility are presented to show the maturity of this technology. The demonstration vehicles to monitor yields during this demonstration were long-wavelength infrared (LWIR) HgCdTe multilayer wafers with 128 X 128 detector arrays. The heterostructure photodetectors were of the p-on-n planar configuration. Device data show that MBE LWIR diode test structures have performance that equals that of p-on-n double heterostructure photodiodes made by LPE. Due to the special attention given to understanding and reducing epilayer growth-induced defects, we have achieved improvements in FPA operability values from 92% to 98%. These improvements have resulted in the demonstration of a 128 X 128 FPA hybrid that had detectivity (D*) background limited performance when operating at 80 K in a tactical background environment. Mean D* was 1.28 X 1011 cmHz1/2/W. The corresponding mean NE(Delta) T was an excellent 5.9 mK.

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.

Rockwell Science Center and the University of Hawaii have developed a short wavelength infrared (SWIR) 1024 x 1024 focalplane array (EPA). The continuing project is funded by the U.S. Air Force Phillips Laboratory in connection with their AdvancedElectro Optical System (AEOS) 3.67 m telescope project on Haleakala, Maui. We have achieved our objective of developing a 1024 x 1024 EPA with a cut-off wavelength of 2.5 im. The device is named the HgCdTe Astronomical Wide Area InfraredImager (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 ofprior astronomical 256 x 256 FPAs), total FPA dark current 99%,quantum efficiency > 50%, BLIP-limited sensitivity at Iow-109 photons/cm2-sec background and operating temperatures to 120K, and read noise < 10 e-. Keywords: Infrared, Focal Plane Array, Astronomy, HgCdTe, 1024 x 1024, Low Noise

In this paper we present p-on-n heterostructure HgCdTe photovoltaic device data that illustrates the high performance and flexibility in band gap control of the molecular beam epitaxy (MBE) technology. This flexibility demonstration was carried out by growing material for operation in the following cut-off wavelength ((lambda) co) ranges of interest: LWIR [(lambda) co(77 K) equals 9-11 micrometers ], MLWIR [(lambda) co(77 K) equals 6-7 micrometers ], and VLWIR [(lambda) co(40 K) equals 20 micrometers ]. Detailed analyses of the current-voltage characteristics of these diodes as a function of temperature show that their dark currents are diffusion-limited down to 80 K, 50 K, and 30 K for the MLWIR, LWIR, and VLWIR photodiodes, respectively. In general, the RoA device values were uniform for the three band gap ranges when operating under diffusion limited conditions. The planar MBE HgCdTe technology has been further validated with the successful fabrication and operation of 64 X 64 hybrid FPAs.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

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.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A high performance 640 X 480 focal plane array has been developed for the 1 - 5 micron band with excellent sensitivity at temperatures below 120 K. The detectors are processed on 2' or 3' diameter PACE-I (producible alternative to CdTe for epitaxy) HgCdTe material. The multiplexer is a direct injection input, switched-FET device with four independent quadrants. The detector is hybridized to the multiplexer through indium columns and is characterized. A mean camera NE(Delta) T (noise equivalent temperature difference) of 13 mK has been achieved for temperatures

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 10 10 photons/cm 2 -s background and 35 K operating temperature. The mean D* of 4.5 X 10 13 Jones at 8.3 micrometers peak wavelength is 75% of BLIP. A maximum peak D* of 5.7 X 10 14 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.

Rockwell's 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 Hubble's Near Infrared Camera Multi-Object Spectrometer. Typical NICMOS3 FPAs have read noise 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.

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-.

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