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NASA NTRS1981

Single photon X-ray imaging with charge-coupled devices /CCDs/

The paper describes a CCD camera facility designed and built for testing and characterization of CCDs in response to single X-ray photons in the 1-10 keV energy range. Results from the frontside-illuminated Fairchild 211 and 221 area imagers are presented; high quantum efficiency over the 3-6 keV range was verified. In order to avoid the problem of charge spreading at the higher energies, deep-depleted CCDs for soft X-ray imaging have been constructed, and good response was obtained at 6 keV. The present results are a first step toward the demonstration of the CCD as an appropriate device for at least the central part of the focal plane of a large X-ray telescope, e.g., the proposed Advanced X-ray Astrophysics Facility.

Griffiths, R. E.↗
NASA NTRS1981

Echelle spectroscopy with a charge-coupled device /CCD/

The recent availability of large format CCD's with high quantum efficiency makes it possible to achieve significant advances in high dispersion astronomical spectroscopy. An echelle CCD combination excels or equals other techniques presently available, and offers the advantage of complete spectral coverage of several thousand Angstroms in a single exposure. Attention is given to experiments which were conducted with a CCD camera head and an echelle spectrograph on a 4-meter telescope. It was found possible to achieve a signal-to-noise ratio of 150/1 on a 13th magnitude star at 6000 A in a two-hour exposure at 0.16 A/pixel, limited primarily by photon statistics. For fainter objects, readout noise is the limiting factor in precision. For 20 electron rms readout noise, an S/N = 15/1 at 18th magnitude is expected, all other things being equal.

York, D. G.↗
NASA NTRS1981

Low and moderate resolution spectroscopy with an RCA charge-coupled device /CCD/

An RCA buried channel thinned 320 x 512 CCD has recently been put into operation as the detector on the blue side of a new double spectrograph used at the Cassegrain focus of the Hale 5.08 m telescope. The chip is used in a vacuum dewer at a temperature of -132 C. The readout noise over most of the chip is 46 electrons per pixel, but on one side of the device there are columns with readout noise three times as high as this. When used in a spectroscopic mode with an f/1.5 beam, the CCD shows interference pattterns with an amplitude of 5 to 20%. This pattern occurs most clearly above 5000 A. It appears to be stable and can be removed by using standard flat-field exposures. At signal levels of a few hundred electrons there are some charge transfer problems. The quantum efficiency between 4000 and 6500 is very high, and the efficiency at 3260 A is about 20% of that at 4200 A. Above 6500 A the sensitivity begins to drop steadily.

Oke, J. B.↗
NASA NTRS1981

Texas Instruments /TI/ 800 x 800 charge-coupled device /CCD/ image sensor

Very-large area high-performance CCD image sensors with 800 x 800 pixel format have been successfully fabricated and operated on the basis of a three-level polysilicon gate technology. They are thinned to 8 microns over the entire 12.2 x 12.2 mm active area, and are used in the rear illumination mode. The light transfer characteristic has a gamma value of 1.000 + or - 0.002 over most of the dynamic range. Analysis of the noise behavior shows that the device SNR is shot-noise-limited over most of the dynamic range. Simple on-chip signal processing can be performed using an integration well to noiselessly collect signal charge from multiple pixels prior to reading out the charge. A UV-sensitive phosphor has been applied to the chip, yielding a device capable of imaging at wavelengths from the vacuum UV to the near IR.

Blouke, M. M.↗
NASA NTRS1977

Design, fabrication, and evaluation of charge-coupled devices with aluminum-anodized-aluminum gates

A 4-phase, 49 1/2 bit CCD shift register was designed and fabricated using two levels of aluminum metallization with anodic Al2O3 insulation separating the layers. Test circuitry was also designed and constructed. A numerical analysis of an MOS-RC transmission line was made and results are given to characterize performance for various conductivities. The electrical design of the CCD included a low-noise dual-gate input and a balanced floating diffusion output circuit. Metallization was accomplished both by low voltage DC sputtering and thermal evaporation. The audization was according to published procedures using a buffered tartaric acid bath. Approximately 20 wafers were processed with 50 complete chips per wafer. All devices failed by shorting between the metal levels at some point. Experimental procedures eliminated temperature effects from sintering and drying, anodic oxide thickness, edge effects, photoresist stripping procedures, and metallization techniques as the primary causes of failure. It was believed from a study of SEM images that protuberances (hillocks) grow up from the first level metal through the oxide either causing a direct short or producing a weak, highly stressed insulation point which fails at low voltage. The cause of these hillocks is unknown; however, they have been observed to grow during temperature excursions to 470 C.

Gassaway, J. D.↗
NASA NTRS1978

Indium antimonide infrared CCD linear imaging arrays with on-chip preprocessing

A description is presented of the fabrication of a new InSb CCD chip based on an improved process which eliminates the limitations inherent with the earlier techniques. This process includes planar junction formation and an aluminum and SiO2 material system which is amenable to state-of-the-art chemical and plasma delineation techniques. Further, the new chip integrates for the first time in monolithic format InSb IR detectors with an InSb CCD. The reported experiments represent the first operation of an InSb infrared CCD array. In addition to fuller characterization of the 20-element charge-coupled infrared imaging device, several factors which influence device performance are currently being addressed. These include surface state density, the CCD output circuit, and storage time (dark current).

Thom, R. D.↗
NASA NTRS1981

Wideband comet camera lens design

A quarter-meter diameter, modified Ritchey-Chretien camera is described for spacecraft-based observation of Halley's Comet. The system will operate over an unusually broad spectral region, from 0.1216 micron (the hydrogen Lyman-alpha line) to 1.1 microns using reflective primary and secondary mirror optics and a thin UV-grade lithium fluoride refractive element as a field corrector near the image plane. The f/12, 3000 mm focal length camera has a 0.4 deg full field of view for operation with a 15 x 15 mm charge-coupled device detector array. The UV-enhanced silicon CCD detector is a 1000 x 1000 array of 15 micron pixels which establishes the system resolution requirement. The optical design and performance are discussed, with an emphasis on the image analysis with respect to pixel resolution elements used for viewing extended objects such as comets.

Huber, E. D.↗
NASA NTRS1981

Evaluation of RCA thinned buried channel charge-coupled devices /CCDs/ for scientific applications

An experimental version of a thinned illuminated buried-channel 512 x 320 pixel CCD with reduced amplifier input capacitance has been produced which is characterized by lower readout noise. Changes made to the amplifier are discussed, and readout noise measurements obtained by several different techniques are presented. The single energetic electron response of the CCD in the electron-bombarded mode and the single 5.9 keV X-ray pulse height distribution are reported. Results are also given on the dark current versus temperature and the spatial frequency response as a function of signal level.

Zucchino, P.↗
NASA NTRS1978

Time-delay-and-integration charge-coupled devices using tin oxide gate technology

Doped tin oxide gates are used in a time-delay-and-integration (TDI) CCD scheme in an effort to develop a stable transparent gate technology. Design characteristics of the system are discussed, including 2 sections of 10 by 9 integration stages, four-phase buried channel construction, and 10 input parallel-in/serial-out output shift register at a video rate of 1.25 MHz. A quantum efficiency of 65% with smooth spectral response is attained by front surface imaging. The suitability of the system for the Landsat program is discussed in terms of TDI-CCD operating parameters.

Thompson, L. L.↗
NASA NTRS1981

Soft X-ray and XUV imaging with a charge-coupled device /CCD/-based detector

A soft X-ray/XUV imaging camera which uses a thinned, back-illuminated, all-buried channel RCA CCD for radiation sensing has been built and tested. The camera is a slow-scan device which makes possible frame integration if necessary. The detection characteristics of the device have been tested over the 15-1500 eV range. The response was linear with exposure up to 0.2-0.4 erg/sq cm; saturation occurred at greater exposures. Attention is given to attempts to resolve single photons with energies of 1.5 keV.

Loter, N. G.↗
NASA NTRS1977

Charge-coupled differential amplifier

Device solves problem of differential voltage gain in sampled-data metal-oxide semiconductor, producing gain at any frequency compatible with CCD operation, with low noise, low power, good linearity, and high stability.

Hewes, C. R.↗
NASA NTRS1980

A dual charge-coupled device /CCD/, astronomical spectrometer and direct imaging camera. I - Optical and detector systems

The MASCOT (MIT Astronomical Spectrometer/Camera for Optical Telescopes), an instrument capable of simultaneously performing both direct imaging and spectrometry of faint objects, is examined. An optical layout is given of the instrument which uses two CCD's mounted on the same temperature regulated detector block. Two sources of noise on the signal are discussed: (1) the CCD readout noise, which results in a constant uncertainty in the number of electrons collected from each pixel; and (2) the photon counting noise. The sensitivity of the device is limited by the sky brightness, the overall quantum efficiency, the resolution, and the readout noise of the CCD. Therefore, total system efficiency is calculated at about 15%.

Meyer, S. S.↗
NASA NTRS1977

Programmable convolution via the chirp Z-transform with CCD's

Technique filtering by convolution in frequency domain rather than in time domain presents possible solution to problem of programmable transversal filters. Process is accomplished through utilization of chip z-transform (CZT) with charge-coupled devices

Buss, D. D.↗
NASA NTRS1976

Spectral analysis using CCDs

Charge-coupled devices (CCDs) are ideally suited for performing sampled-data transversal filtering operations in the analog domain. Two algorithms have been identified for performing spectral analysis in which the bulk of the computation can be performed in a CCD transversal filter; the chirp z-transform and the prime transform. CCD implementation of both these transform algorithms is presented together with performance data and applications.

Hewes, C. R.↗
NASA NTRS1973

Two-phase charge-coupled device

A charge-transfer efficiency of 99.99% per stage was achieved in the fat-zero mode of operation of 64- and 128-stage two-phase charge-coupled shift registers at 1.0-MHz clock frequency. The experimental two-phase charge-coupled shift registers were constructed in the form of polysilicon gates overlapped by aluminum gates. The unidirectional signal flow was accomplished by using n-type substrates with 0.5 to 1.0 ohm-cm resistivity in conjunction with a channel oxide thickness of 1000 A for the polysilicon gates and 3000 A for the aluminum gates. The operation of the tested shift registers with fat zero is in good agreement with the free-charge transfer characteristics expected for the tested structures. The charge-transfer losses observed when operating the experimental shift registers without the fat zero are attributed to fast interface state trapping. The analytical part of the report contains a review backed up by an extensive appendix of the free-charge transfer characteristics of CCD's in terms of thermal diffusion, self-induced drift, and fringing field drift. Also, a model was developed for the charge-transfer losses resulting from charge trapping by fast interface states. The proposed model was verified by the operation of the experimental two-phase charge-coupled shift registers.

Kosonocky, W. F.↗
NASA NTRS1976

Development of InSb charge-coupled infrared imaging devices: Linear imager

The following results were accomplished in the development of charge coupled infrared imaging devices: (1) a four-phase overlapping gate with 9 transfers (2-bits) and 1.0-mil gate lengths was successfully operated, (2) the measured transfer efficiency of 0.975 for this device is in excellent agreement with predictions for the reduced gate length device, (3) mask revisions of the channel stop metal on the 8582 mask have been carried out with the result being a large increase in the dc yield of the tested devices, (4) partial optical sensitivity to chopped blackbody radiation was observed for an 8582 9-bit imager, (5) analytical consideration of the modulation transfer function degradation caused by transfer inefficiency in the CCD registers was presented, and (6) for larger array lengths or for the insertion of isolated bits between sensors, improvements in InSb fabrication technology with corresponding decrease in the interface state density are required.

Phillips, J. D.↗
NASA NTRS1975

Applications of charge-coupled device transversal filters to communication

The paper discusses the computational power of state-of-the-art charged-coupled device (CCD) transversal filters in communications applications. Some of the performance limitations of CCD transversal filters are discussed, with attention given to time delay and bandwidth, imperfect charge transfer efficiency, weighting coefficient error, noise, and linearity. The application of CCD transversal filters to matched filtering, spectral filtering, and Fourier analysis is examined. Techniques for making programmable transversal filters are briefly outlined.

Buss, D. D.↗
NASA NTRS1979

Programmable charge-coupled device /CCD/ correlator for pattern classification

The potential use of charge coupled device (CCD) programmable digital/analog correlators for multispectral data classification is discussed. CCD digital/analog correlator technology and the experimental evaluation of a 32-stage 4-bit test device are presented. The design of an IC for use in a multispectral classification system for 16 sensors and 8 bit accuracy is reviewed.

Mayer, D. J.↗