Pixels in both hybridized and monolithic complementary metal-oxide semiconductor (CMOS) detector arrays may couple capacitively to their neighboring pixels. This "interpixel capacitance" can significantly distort the characterization of conversion efficiency and modulation transfer function (MTF) in CMOS devices. These effects have been largely unaccounted for in measurements to date. In this work, the effects of this coupling are investigated. Compensation methods for these errors are described and applied to silicon P-I-N array measurements. The measurement of Poisson noise, traditionally done by finding the mean square difference in a pair of images, needs to be modified to include the mean square correlation of differences with neighboring pixels.
With the introduction of the Raytheon 2.5 micron HgCdTe VIRGO detector array, some astronomy programs, such as the VISTA Program, are turning to Raytheon for near infrared detector arrays. We characterize one VIRGO detector array and provide results of measurements at low backgrounds including dark current, read noise, total noise, quantum efficiency, and operability. The Raytheon VIRGO HgCdTe detector arrays are excellent candidates for many low background astronomical programs, including space-borne telescope missions.
Inter-pixel capacitive coupling can exist in a non-destructive detector array if the detector nodes change voltage as they integrate charge and the design of the device allows for an electric field to exist between adjacent collection nodes. Small amounts of inter-pixel capacitance can cause large errors in the measurement of poissonian noise versus signal, and all subsequently derived measurements such as nodal capacitance and quantum efficiency. Crosstalk and MTF can also be significantly influenced by interpixel capacitance. Two 1k by 1k Raytheon SB226-based hybridized silicon PIN arrays were tested for nodal capacitance and MTF. Initial results indicated unexpected and unexplainably large nodal capacitance, poor MTF, and odd edge spread. It was hypothesized that inter-pixel capacitive coupling was responsible for these discrepancies. A stochastic method of measuring the coupling using 2D autocorrelation and Fourier Transform techniques was devised and implemented. Autocorrelation of the shot noise in the images revealed a correlation consistent with 3.2% interpixel capacitive coupling. When the effects of the measured interpixel capacitance were taken into account, the initially measured nodal capacitance of 56 fF was found to be 31% higher than the corrected nodal capacitance measurement of 43 fF. Large discrepancies between the theoretical and observed edge spread response were also greatly reduced. A simulation of the electric field in the PIN detector intrinsic region predicted an interpixel coupling very close to the observed coupling. Interpixel capacitance was also observed in a 2k by 2k Raytheon SB304-based InSb detector array, but was not strongly evident in a bare Raytheon SB226 multiplexer.
The James Webb Space Telescope (JWST), the successor to the Hubble Space Telescope, will draw on recent improvements in infrared array technologies to achieve its goals and mission. In order to best meet the goals of JWST, NASA is funding a competition between two near infrared detector technologies: InSb detector arrays from Raytheon Vision Systems and HgCdTe detector arrays from Rockwell Scientific. The University of Rochester, in collaboration with Raytheon, is testing near infrared InSb detectors in a 2048 x 2048 array format
to meet the stringent requirements for JWST. Results from characterization under top level requirements, such as noise, quantum efficiency, well capacity, pixel operability, etc., are discussed. Dark current and its contribution to the total noise are analyzed.
A system for controlling and testing high-resolution non-destructive astronomical imagers was constructed using open-source components, both hardware and software. The open-source electronics design, originated by Carnegie Observatories (OCIW) for CCD cameras, was modified, assembled, and augmented with new circuitry which facilitates monitoring of voltages and currents. The electronics was run from Python user interface software based on a design from the University of Rochester. This new software utilized the Numarray and pyFITS modules developed at the Space Telescope Science Institute (STScI). Interfacing to the "dv" FITS image analysis package from the NASA IRTF was also implemented. Python (the STScI language of choice) was used as the primary language for systems integration, scripts for data acquisition, and scripts for data analysis. The DSP clocking software was a mixture of C and Motorola 56303 assembly. An interrupt-driven kernel-mode PCI device driver for Red Hat Linux was written in C, and used the PC processor and memory for image processing and acquisition. Two 1Κ × 1Κ Raytheon SB226-based hybridized silicon p-i-n arrays were operated and tested with the new system at temperatures as low as 10K. Signal path gain, node capacitance, well depth, dark current, and MTF measurements were made and are presented here.
The astronomical community has benefited from the scientific advances in photo-detection over the last few decades, from optical CCDs to infrared array detectors, for both large ground-based telescopes and space-borne telescopes. NGST, the successor to the Hubble Space Telescope, will draw on the improvements in infrared array technologies to achieve its goals and mission. The University of Rochester, in collaboration with Raytheon and NASA Ames Research Center, is developing and testing near infrared InSb array detectors to meet the stringent requirements for NGST. The latest development involves a suitable multiplexer in a 2048 x 2048 format that will be bump-bonded to an InSb array. Twenty of these arrays will be required for NGST imaging and spectroscopy. We present results for pathfinder 1024 x 1024 arrays. This is a companion work to the paper in these SPIE proceedings by Ken Ando, Peter Love, Nancy Lum, Alan Hoffman, Roger Holcombe, John Durkee, Joseph Rosbeck, and Elizabeth Corrales (Raytheon Infrared Operations).