Bernard B. Kosicki

Soft-X-ray CCD imagers for AXAF

We describe the key features and performance data of a 1024/spl times/1026-pixel frame-transfer imager for use as a soft-X-ray detector on the NASA X-ray observatory Advanced X-ray Astrophysics Facility (AXAF). The four-port device features a floating-diffusion output circuit with a responsivity of 20 /spl mu/V/e/sup -/ and noise of about 2 e/sup -/ at a 100-kHz data rate. Techniques for achieving the low sense-node capacitance of 5 fF are described. The CCD is fabricated on high-resistivity p-type silicon for deep depletion and includes narrow potential troughs for transfer inefficiencies of around 10/sup -7/. To achieve good sensitivity at energies below 1 keV, we have developed a back-illumination process that features low recombination losses at the back surface and has produced quantum efficiencies of about 0.7 at 277 eV (carbon K/spl alpha/).

Multifocal multiphoton microscopy (MMM) at a frame rate beyond 600 Hz

We introduce a multiphoton microscope for high-speed three-dimensional (3D) fluorescence imaging. The system combines parallel illumination by a multifocal multiphoton microscope (MMM) with parallel detection via a segmented high-sensitivity charge-couple device (CCD) camera. The instrument consists of a Ti-sapphire laser illuminating a microlens array that projects 36 foci onto the focal plane. The foci are scanned using a resonance scanner and imaged with a custom-made CCD camera. The MMM increases the imaging speed by parallelizing the illumination; the CCD camera can operate at a frame rate of 1428 Hz while maintaining a low read noise of 11 electrons per pixel by dividing its chip into 16 independent segments for parallelized readout. We image fluorescent specimens at a frame rate of 640 Hz. The calcium wave of fluo3 labeled cardiac myocytes is measured by imaging the spontaneous contraction of the cells in a 0.625 second sequence movie, consisting of 400 single images.

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. >

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.

Genosensors: microfabricated devices for automated DNA sequence analysis

A new technology is introduced for developing potentially low cost, high throughput DNA sequence analysis. This approach utilizes novel bioelectronic genosensor devices to rapidly detect hybridization events across a DNA probe array. Detection of DNA probe/target hybridization has been achieved by two electronic methods. The first method utilizes a permittivity chip which interrogates the miniature test fixtures with a low voltage alternating electric field. The second method, which is the emphasis of this paper, utilizes a charge- coupled device (CCD) to detect the hybridization of appropriately tagged (radioisotope, fluorescent, or chemiluminescent labels) target DNA to an array of DNA probes immobilized above the pixels. Such direct electronic-biologic coupling is shown to provide a tenfold sensitivity improvement over conventional lens-based detection systems.

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.

High-speed, electronically shuttered solid-state imager technology (invited)

Electronically shuttered solid-state imagers are being developed for high-speed imaging applications. A 5 cm×5 cm, 512×512-element, multiframe charge-coupled device (CCD) imager has been fabricated for the Los Alamos National Laboratory DARHT facility that collects four sequential image frames at megahertz rates. To operate at fast frame rates with high sensitivity, the imager uses an electronic shutter technology designed for back-illuminated CCDs. The design concept and test results are described for the burst-frame-rate imager. Also discussed is an evolving solid-state imager technology that has interesting characteristics for creating large-format x-ray detectors with short integration times (100 ps to 1 ns). Proposed device architectures use CMOS technology for high speed sampling (tens of picoseconds transistor switching times). Techniques for parallel clock distribution, that triggers the sampling of x-ray photoelectrons, will be described that exploit features of CMOS technology.

640/spl times/480 back-illuminated CCD imager with improved blooming control for night vision

We describe a back-illuminated 640/spl times/480 CCD imager which operates at 30-Hz frame rates with 5 e/sup -/ noise and which is capable of high resolution down to near starlight illumination levels. A new process for fabricating a compact blooming control is also described.

Quantum efficiency model for p+-doped back-illuminated CCD imager

An analytical model has been developed for predicting the spectral response of thinned, p+-doped back-illuminated charge-coupled device (CCD) imagers. The device is divided into two regions: a thin, uniformly doped p+ layer used to passivate the illuminated back surface from external electrical effects, and a p- region that extends from the p+ region across the approximately 10-micrometers thickness of the device to the potential well in the buried channel. The one-dimensional steady-state continuity equation for low-injection conditions has been solved analytically for the surface p+ region, which is characterized by electron diffusion length and coefficients appropriate for the doping level and a surface recombination velocity Sn that represents the loss of photoelectrons at the surface. All photoelectrons generated in the p- region are assumed to be collected in the buried channel because of the long diffusion length and the presence of a field sweeping the carriers into the CCD channel. The effect of multiple internal reflections on photoabsorption at long wavelengths is included. The quantum efficiency of this device is calculated as a function of the depth and recombination velocity of the p+ surface layer, using Sn as the only independent fitting parameter, and matches experimental results well over the wavelength range from 360 to 1100 nm.

CCD For Two-Dimensional Transform

With the ever increasing demand for image transmission and image storage, various algorithms for image data compression have been developed. 1 To transmit pictures at lower bandwidth or to minimize the memory size for storage, the image must be compressed by the removal of redundant information. Transform image coding has been proven to be an efficient method for image compression.2,3 In the basic transform image coding concept, an image is divided into small blocks of pixels and each block undergoes a two-dimensional transformation to produce an equal-sized array of transform coefficients. The coding process is then performed on the transformed block image. It has been shown that the compression factor of the discrete cosine transform (DCT) compares closely with that of the Karhunen-Loeve transform, which is considered to be the optima1.4 But, comparatively, using the fast cosine transform (FCT) algorithm, the implementation of DCT is much simpler. Therefore, in many transform coding systems a large amount of digital hardware is dedicated to perform the 2-D FCT, because it is believed to be the only practical approach to get close to optimal performance. This consideration leads the recent research efforts on the transform image coding concentrated on the improvement of the coding process only.