James D. Garnett

HAWAII-2RG: a 2k x 2k CMOS multiplexer for low and high background astronomy applications

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 <5 e-. Also for the first time with any imaging sensor, low and high background astronomy is supported using from 1 to 32 low-noise outputs via low-speed and high-speed signal paths. The latter supports throughput rate of up 320 MHz for real time imaging at >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.

Detectors for the James Webb Space Telescope Near‐Infrared Spectrograph. I. Readout Mode, Noise Model, and Calibration Considerations

We describe how the James Webb Space Telescope (JWST) Near-Infrared Spectrographs (NIRSpec) detectors will be read out, and present a model of how noise scales with the number of multiple nondestructive reads sampling up the ramp. We believe that this noise model, which is validated using real and simulated test data, is applicable to most astronomical near-infrared instruments. We describe some nonideal behaviors that have been observed in engineering-grade NIRSpec detectors, and demonstrate that they are unlikely to affect NIRSpec sensitivity, operations, or calibration. These include a HAWAII-2RG reset anomaly and random telegraph noise (RTN). Using real test data, we show that the reset anomaly is (1) very nearly noiseless and (2) can be easily calibrated out. Likewise, we show that large-amplitude RTN affects only a small and fixed population of pixels. It can therefore be tracked using standard pixel operability maps.

SIDECAR low-power control ASIC for focal plane arrays including A/D conversion and bias generation

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 ASICs 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.

2Kx2K molecular beam epitaxy HgCdTe detectors for the James Webb Space Telescope NIRCam instrument

The NIRCam instrument will fly ten of Rockwell Scientific’s infrared molecular beam epitaxy HgCdTe 2048x2048 element detector arrays, each the largest available with current technology, for a total of 40 Megapixels. The instrument will have two varieties of MBE HgCdTe, a SWIR detector with λco = 2.5 μm, for the shortwave channel of NIRCam (0.6-2.3 μm); and a MWIR detector with λco = 5.3 μm, for the longwave channel of NIRCam (2.4-5.0 μm). Demonstrated mean detector dark currents less than 0.01 electrons per second per pixel at operating temperatures below 42 K for the MWIR and below 80 K for the SWIR, combined with quantum efficiency in excess of 80 percent and read noise below 6 electrons rms, make these detector arrays by far the most sensitive SWIR and MWIR devices in the world today. The unique advantages of molecular beam epitaxy as well as FPA data on noise, dark current, quantum efficiency, and other performance metrics will be discussed. In addition, the focal plane assembly package designs will be presented and discussed.

Detector arrays for the James Webb Space Telescope near-infrared spectrograph

The James Webb Space Telescopes (JWST) Near Infrared Spectrograph (NIRSpec) incorporates two 5 μm cutoff (λco =5 μm) 2048×2048 pixel Teledyne HgCdTe HAWAII-2RG sensor chip assemblies. These detector arrays, and the two Teledyne SIDECAR application specific integrated circuits that control them, are operated in space at T ~ 37 K. In this article, we provide a brief introduction to NIRSpec, its detector subsystem (DS), detector readout in the space radiation environment, and present a snapshot of the developmental status of the NIRSpec DS as integration and testing of the engineering test unit begins.

Large-area visible arrays: performance of hybrid and monolithic alternatives

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 <6 e- read noise and quantum efficiency above 80% from 400 nm to 920 nm; 4096 by 4096 mosaics are now being developed. The monolithic approach produces visible 12-bit imaging system-on-chips such as a 1936 by 1088 with higher quantum efficiency than mainstream CCDs, <25 e- read noise, <0.02% fixed pattern noise, automatic identification and replacement of defective pixels, black-level clamping, total power dissipation of only 180 mW, and various programmable features. Several successors having ≥12 Mpixels are in development. In both cases low-light-level performance is boosted by coupling the sensors to image intensifiers.

Burst noise in the HAWAII-1RG multiplexer

Burst noise (also known as popcorn noise and random telegraph signal/noise) is a phenomenon that is understood to be a result of defects in the vicinity of a p-n junction. It is characterized by rapid level shifts in both positive and negative directions and can have varying magnitudes. This noise has been seen in both HAWAII-1RG and HAWAII-2RG multiplexers and is under investigation. We have done extensive burst noise testing on a HAWAII-1RG multiplexer, where we have determined a significant percentage of pixels exhibit the phenomenon. In addition, the prevalence of small magnitude transitions make sensitivity of detection the main limiting factor. Since this is a noise source for the HAWAII-1RG multiplexer, its elimination would make the HAWAII-1RG and the HAWAII-2RG even lower noise multiplexers.

Space qualification and performance results of the SIDECAR ASIC

The SIDECAR ASIC is a fully integrated FPA controller system-on-a-chip. Compared to conventional control electronics, it requires significantly less power, less space and less weight. The SIDECAR ASIC, which can operate at ambient and cryogenic temperatures, is currently being space-qualified for integration in the science instruments of the James Webb Space Telescope (JWST). This paper gives an overview of the SIDECAR architecture and its supporting drive electronics. It describes the JWST flight configuration including the custom packaging approach. Test results obtained as part of the space qualification effort are presented. CDS noise of the ASIC itself amounts to less than 25 μV for full 2K x 2K data frames. The noise reduces to less than 6 μV for up-the-ramp-sampling with 88 frames. Based on the existing qualification results and a number of additional tests in the next few months, NASA Technology Readiness Level 6 (TRL6) will be demonstrated by August 2006.

A 4Kx4K HgCdTe astronomical camera enabled by the James Webb Space Telescope NIR detector development program

The ambitious science goals of the James Webb Space Telescope (JWST) have driven spectacular advances in λco ~ 5um detector technology over the past five years. This paper reviews both the UH/RSC team’s Phase A development and evaluation of 2Kx2K arrays exceeding the detector requirements for JWST’s near infrared instruments and also the hardware integration of these into a 4Kx4K (16Mpxl) close packed mosaic focal plane array housed in an Ultra Low Background test facility. Both individual first generation 2Kx2K SCA’s and 4Kx4K mosaic focal planes have been extensively characterized in the laboratory and, since September 2003, a NIR camera utilizing the 4Kx4K mosaic focal plane has been in use for nearly 100 nights at the UH 2.2 m telescope on Mauna Kea. Typical test results for the first generation 2Kx2K arrays and their integration into 4Kx4K mosaic focal planes are reported. Demonstration of the design concepts and both array and mosaic focal plane performance in actual hardware, as described here, has provided the foundation for design iterations leading to later generations of 2Kx2K arrays and 4Kx4K mosaic focal planes. Four major technology developments leading to first generation hardware demonstrations of both 2Kx2K SCA’s and a 4Kx4K mosaic FPA are reviewed. These are: 1) improvement in test equipment and procedures to characterize the detectors against JWST requirements and goals, primarily at 37K but with the capability to test from 30K to 100K; 2) optimization of λc ~ 5 um MBE HgCdTe material on a CZT substrate for low dark current (goal of 0.003 e-/sec at 37K) with high quantum efficiency, low cross-talk and greatly reduced image persistence; 3) development of the 2Kx2K HAWAII-2RG multiplexer designed specifically to take full advantage of these detector characteristics for a wide range of astronomical applications (and fully compatible with an ASIC controller developed under the JWST Instrument Technology Development initiative) and 4) development of molybdenum SCA carriers allowing modules to be close-butted on three sides and easily installed onto a molybdenum plate to form a 4Kx4K mosaic focal plane. We describe both the improvements in the KSPEC test facility and in test procedures for individual 2Kx2K arrays and the Ultra Low Background (ULB) test facility developed specifically to evaluate 4Kx4K mosaic focal plane assemblies required for the NIRCam instrument. The laboratory test configuration of the ULB facility utilizes multiple shields and internal light sources to achieve background fluxes <1 photon/hour per pixel for λc ~ 5um while providing temperature stability <1mK over periods of weeks. An alternate configuration utilizes fore optics to allow the mosaic FPA module of the ULB facility to be mounted at the Cassegrain focus of the UH 2.2 meter telescope, providing an image scale of 0.25”/pixel over a 17’x17’ field. A cold PK 50 lens cuts off around 1.7 um, limiting the background at wavelengths below 1.65 um (where the array can be used with normal filters and where narrow band filters reduce the background to levels comparable to NIRCam on JWST). Observations at the telescope, which provide the best way of verifying certain JWST requirements and allow direct astronomical characterization of the detectors, are reported.

Advanced technology trends for astronomy at Rockwell Scientific

This paper discusses the latest technologies for space and ground-based astronomy being pursued by Rockwell Scientific. The discussion covers the latest demonstrated performance of large format NIR (~1.7um cutoff) detectors mated to the HAWAII-2RG readout integrated circuit, our proven readout for large-format arrays for astronomy. Developmental work is presented on the HAWAII-4RG family (consisting of 4k x 4k, 4k x 8k, and 8k x 8k formats), RSC’s newest additions planned to the HAWAII series of astronomy readout integrated circuits. We also present the status of our multifunctional command-and-control ASIC for FPAs, which was first reported at the August 2002 SPIE.