Donald E. Cooper

H2RG focal plane array and camera performance update

Teledyne’s H2RG focal plane arrays have been widely used in scientific infrared and visible instruments for ground-based and space-based telescopes. The majority of applications use the H2RG with 2.5 micron cutoff HgCdTe detector pixel at an operating temperature of ~77 K (LN2). The exceptionally low dark current of the 2.5 micron H2RG allows for operation at higher temperatures which facilitates simplified instrument designs and therefore lower instrument cost. Performance data of 2.5 micron H2RG arrays at 77K, 100 K, and 120 K are presented and are discussed as a function of detector bias and pixel readout rate. This paper also presents performance data of 1.75 micron and 5.3 micron H2RG focal plane arrays and discusses some of the inherent performance differences compared to 2.5 micron cutoff arrays. A complete infrared camera system that uses the H2RG focal plane array and SIDECAR ASIC focal plane electronics is introduced.

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.

Latest results on HgCdTe 2048x2048 and silicon focal plane arrays

The worlds first 2048 X 2048 HgCdTe infrared focal plane array (FPA) has been developed by Rockwell Science Center for infrared astronomy. The Hawaii-2 is the largest CMOS multiplexer designed to date, developed to interface with both infrared and visible detector arrays. The 18 micrometer pixel pitch was selected to accommodate both reasonable telescope optics and maximize yield in the fabrication of such a large readout. The fabrication uses world-class submicron photolithography to maximize yield of high quality devices. We will report on the characterization of FPAs using the Hawaii-2 multiplexer mated to SWIR detector arrays with a spectral response of 0.9 micrometer to 2.5 micrometer. These detector arrays have been processed on Liquid Phase Epitaxy (LPE) HgCdTe on sapphire substrates, also known as PACE-1. We also report on characterization of Silicon detectors in terms of their quantum efficiency, spectral response, and dark current.

LPE HgCdTe on sapphire status and advancements

With the evolution of infrared arrays to over four million pixels, larger formats have demanded higher quality mercury cadmium telluride (MCT) wafers. Since single defects can easily degrade multiple diodes, high operability requires very homogeneous and nearly flawless epitaxial surfaces. Subsequent photolithography and hybridization also demand unprecedented levels of substrate flatness and low imperfections. To consistently and reliably produce large area arrays, Insaco Inc., The Boeing Company, and Rockwell International Corporation have developed major quality improvement procedures which address all three components of the infrared material wafer architecture. Centered on the producible alternative to cadmium telluride for epitaxy (PACE) process, technological advancements encompassed sapphire substrates, organometallic vapor phase epitaxy (OMVPE), cadmium telluride (CdTe) buffer layer growth, and liquid phase epitaxial (LPE) mercury cadmium telluride growth. Processed material from these runs mated to Conexant™ fabricated multiplexers have successfully produced 1024 1024 and the first 2048 2048 IR short-wave (2.5 m at 80 K) hybrid focal plane arrays. Operabilities in these implanted n-on-p junction devices reach 99.98% with near 70% quantum efficiency in the astronomy ‘K’ band (2.2–2.4 microns).

Visible and infrared detectors at Rockwell Science Center

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 Hawaiis 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 < 0.1 e-/s dark current and < 10 e- read noise after correlated double sampling at temperatures above 60K. 1024 by 1024 FPAs development is also continuing; dark current < 1 e-/s has been measured at 140K for a NIR 1024 by 1024 HAWAII array. In a related effort, development of high frame rate, low noise FPAs has begun for wavefront sensing including adaptive optical systems for both visible and NIR/SWIR bands. Hybrid Visible Silicon Imager development is also continuing, expanding the success achieved with prior 640 by 480 FPAs. We are now demonstrating 1024 by 1024 arrays with 0.3-1.05 micrometers response. The silicon detectors in HyViSI FPAs are independently processed on silicon wafers and mated to the same multiplexers fabricated originally for interface to HgCdTe detectors. HyViSI FPA quantum efficiency is > 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.

HgCdTe 20482 FPA for infrared astronomy: development status

The HAWAII-2 is an IR 20482 focal plane array (FPA) that is being developed for next-generation IR astronomy. It will supplant our HAWAII 10242 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.

4K×4K format 10μm pixel pitch H4RG-10 hybrid CMOS silicon visible focal plane array for space astronomy

Teledyne’s silicon hybrid CMOS focal plane array technology has matured into a viable, high performance and high- TRL alternative to scientific CCD sensors for space-based applications in the UV-visible-NIR wavelengths. This paper presents the latest results from Teledyne’s low noise silicon hybrid CMOS visible focal place array produced in 4K×4K format with 10 μm pixel pitch. The H4RG-10 readout circuit retains all of the CMOS functionality (windowing, guide mode, reference pixels) and heritage of its highly successful predecessor (H2RG) developed for JWST, with additional features for improved performance. Combined with a silicon PIN detector layer, this technology is termed HyViSI™ (Hybrid Visible Silicon Imager). H4RG-10 HyViSI™ arrays achieve high pixel interconnectivity (<99.99%), low readout noise (<10 e- rms single CDS), low dark current (<0.5 e-/pixel/s at 193K), high quantum efficiency (<90% broadband), and large dynamic range (<13 bits). Pixel crosstalk and interpixel capacitance (IPC) have been predicted using detailed models of the hybrid structure and these predictions have been confirmed by measurements with Fe-55 Xray events and the single pixel reset technique. For a 100-micron thick detector, IPC of less than 3% and total pixel crosstalk of less than 7% have been achieved for the HyViSI™ H4RG-10. The H4RG-10 array is mounted on a lightweight silicon carbide (SiC) package and has been qualified to Technology Readiness Level 6 (TRL-6). As part of space qualification, the HyViSI™ H4RG-10 array passed radiation testing for low earth orbit (LEO) environment.

Advanced imaging sensors at Rockwell Scientific Company

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 RSCs 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.

Development and production of the H4RG-15 focal plane array

In preparation for the large number of infrared pixels required in the era of Extremely Large Telescopes, Teledyne, in partnership with the University of Hawaii and GL Scientific, has been funded to develop the next generation of largeformat infrared focal plane array for ground-based astronomy; the 4096 × 4096 pixel (15 micron pitch) H4RG-15. Teledyne has successfully designed, produced, and tested the first generation H4RG-15 prototype arrays. This paper reports on the functionality and performance test results of the H4RG-15 prototypes and provides status of the 2012 pilot production effort.

MEMS-based tunable filters for compact IR spectral imaging

Arrays of independently tunable MEMS Fabry-Perot filters have been developed that enable spectral tuning over the range of 11 - 8 microns with a filter bandwidth of ~ 120 nm. Actuation is provided using a MEMS driver IC that is hybridized to the MEMS chip. Combining the filter array with an IR FPA enables spatially-resolved spectral tuning in a compact architecture. Tunable spectral response data from the first integrated tunable filter / FPA device are presented.