Robert W. Mountain

An abuttable CCD imager for visible and X-ray focal plane arrays

A frame-transfer silicon charge-coupled-device (CCD) imager has been developed that can be closely abutted to other imagers on three sides of the imaging array. It is intended for use in multichip arrays. The device has 420*420 pixels in the imaging and frame-store regions and is constructed using a three-phase triple-polysilicon process. Particular emphasis has been placed on achieving low-noise charge detection for low-light-level imaging in the visible and maximum energy resolution for X-ray spectroscopic applications. Noise levels of 6 electrons at 1-MHz and less than 3 electrons at 100-kHz data rates have been achieved. Imagers have been fabricated on 1000- Omega cm material to maximize quantum efficiency and minimize split events in the soft X-ray regime. >

CCD soft X-ray imaging spectrometer for the ASCA satellite

We describe the development of a charge-coupled device (CCD) array for use as a soft X-ray (0.4-12 keV) imaging spectrometer for the ASCA (formerly Astro-D) satellite. The CCDs are 420/spl times/420-pixel frame-transfer devices designed to be closely abutted to other chips on three sides of the imaging array. The imagers are made on 6500-/spl Omega//spl middot/cm p-type float-zone silicon for depletion depths of about 50 /spl mu/m under typical CCD bias conditions. The read noise of the CCD is typically 3-4 e/sup /spl minus// rms at data rates of 50 KHz resulting in an energy resolution E//spl delta/E/spl ap/50 at 5.9 keV. The complete focal-plane sensor consists of a 2/spl times/2 array of these devices mounted on a common substrate. Radiation damage from energetic protons is mitigated by the use of a narrow potential trough along the center of the CCD channel to confine the small X-ray event charge to a reduced volume and thereby minimize trapping effects. Charged-particle events from the non-X-ray space background are minimized by using a junction on the back of the chip to deplete most of the neutral bulk and draw background charge away from the CCD. Wafer-level device screening at low temperatures and the focal-plane packaging methods are also described. >

An integrated electronic shutter for back-illuminated charge-coupled devices

A novel electronic shutter has been integrated into the structure of a back-illuminated frame-transfer charge-coupled device (CCD) to permit short optical exposure times and to reduce the smear that occurs during the transfer of an image from the CCD detection area. The shutter consists of an n/sup +/ shutter drain placed in the vertical channel stop regions and stepped p-type buried layers formed by a high-energy implantation (1.0-1.5 MeV) located between the CCD n-type buried channel the and p substrate. These structures create electric fields that direct the photoelectrons to either the CCD detection region or the n/sup +/ shutter drain. The ratio of photons detected with the shutter open to photons detected with the shutter closed has been measured to be greater than 75000 for wavelengths below 540 nm. The corresponding shutter rise and fall times are less than 55 ns. >

A programmable CCD signal processor

A charge-coupled-device (CCD) signal processor based on a vector-matrix product-computing algorithm is described. The processor is structured to perform the generic weighted-sum operation required in a neural network, and to compute the inner product of two matrices needed for two-dimensional spatial filtering. Used as a neural net processor, the chip provides 2016 programmable interconnections between 144 input nodes and 14 output nodes, performs 2.8-billion arithmetic operations/s and dissipates less than 2 W at a 10-MHz clock rate. The CCD device consists of analog tapped delay lines as input buffers, multiplying D/A converters (MDACs), and on-chip memory for storing the digital weights.<<ETX>>

CCD soft x-ray imagers for ASCA and AXAF

We describe the development at Lincoln Laboratory of large-area CCD imager arrays for soft x-ray astronomy. One such array consists of four, closely abutted, 420 X 420-pixel CCDs for the ASCA (formerly Astro-D) satellite that was launched on February 20, 1993. The CCDs were fabricated on p-type 6500-(Omega) -cm material in order to attain the deep depletion depths needed for the higher-energy (> 4 keV) photons. The use of high- resistivity material and the effects of space-radiation are among the principal technical issues which will be discussed. We are also developing the next-generation CCD sensors for the Advanced X-ray Astrophysics Facility which is currently scheduled for launch in 1998. This mission will use two multichip focal planes comprising ten chips, each of a larger format (approximately 1000 X 1000 pixels). In addition to a new CCD, this program will require other technology developments such as an innovative packaging method for the nonplanar focal planes.

Large-Area Back-Illuminated CCD Imager Development

We describe recent work in the area of large, back-illuminated CCD imagers at M.I.T. Lincoln Laboratory as well as new technology applicable to astronomy. We completed in 1995 the development of a 2560 x 1960-pixel frame-transfer imager that filled a 100-mm wafer and several back-illuminated versions of this device were completed. More recently we have begun the development, in collaboration with the U. of Hawaii, of a three-side abuttable 2k x 4k CCD for a multi-chip focal plane. In the unused chord area of the wafer layout, we added test imagers as development vehicles for blooming control and for the demonstration of a CCD that is capable of charge transfer in all four directions. We expect the latter to find application as an electronic means of performing tip-tilt correction to compensate for atmospheric turbulence.

Fabrication of large-area CCD detectors on high-purity, float-zone silicon

Abstract One of the problems with the fabrication of radiation detectors on high-purity, float-zone silicon is that such material is more susceptible to the formation of dislocations during high-temperature processing than Czochralski-grown material. We describe here the impact of dislocations on the electrical performance of a 1024 × 1024-pixel CCD imager that we have developed as the principal detector for the Advanced X-ray Astrophysical Facility. A technique has been developed to determine both the location (to within one gate of a pixel) and the trapping parameters of a dislocation. The processes giving rise to dislocation formation and propagation will be discussed, and techniques will be described for maintaining wafers free of dislocations even after the many high-temperature steps necessary for CCD fabrication.

Advanced CCD imager technology for use from 1 to 10 000 Å

We have developed a low‐noise, high‐sensitivity charge‐coupled‐device (CCD) technology for imaging applications extending from the soft x‐ray (1 A) to the near‐infrared (10 000 A) regimes. We have also developed a fabrication technology for making back‐illuminated versions of these devices with quantum efficiencies as high as 90% from 5000 to 7000 A. Our efforts have focused on two devices, a 64×64 pixel back‐illuminated imager with two output ports that operates at 2000 frames per second with 23 electrons read noise, and a larger device, with 420×420 pixel format, designed for lower frame rates with noise as low as 1.5 electrons and used at visible, UV, and x‐ray wavelengths. Applications to plasma diagnostics include Thomson scattering and high‐frame‐rate imaging in the visible, as well as x‐ray imaging and bolometry.

Performance Characteristics Of CCD's For The Acis Experiment

The Advanced X-ray Astrophysics Facility CCD Imaging Spectrometer (ACIS) will use two arrays of CCDs to provide X-ray imaging and spectroscopy. Spectroscopy at medium resolution with the imaging array is accomplished by pulse height analysis of each X-ray interaction, while for high spectral resolution, an objective grating disperses the spectrum across a linear array of CCDs to provide a dispersed spectrum where the wavelength resolution is determined by the telescope imaging properties. Performance data for CCDs manufactured by Texas Instruments, MIT Lincoln Laboratory and Ford Aerospace Corp. will be presented. Plans for future CCD enhancements will be discussed.

A CCD matrix matrix product parallel processor

The design of a CCD matrix-matrix device operating up to 10MHz clock rates, performing the serial-in parallel-out and Fourier transform functions required in radar doppler filtering, will be reported. The chip contains 32 multipliers and 1024 accumulators.