David L. Losee

Persistent photoconductivity in donor‐doped Cd1−xZnxTe

Phototransport measurements on chlorine‐doped Cd1−xZnxTe crystals with 0⩽x⩽0.35 show a persistent impurity photoconductivity below 140 °K. The thermal activation energy of the defect center responsible for both the dark carriers and photocarriers increases from −0.045 eV for x=0 to +0.27 eV for x=0.25 (negative implies above the conduction‐band edge), resulting in a decrease of the dark free‐carrier density with increasing Zn content. This permits an increasing light‐to‐dark‐conductivity ratio with increasing Zn content, reaching 2.5×105 for x=0.25. The increase of the mobility under photoexcitation indicates the center to be a double acceptor. Thermal emission rate, photoconductivity decay, and optical cross‐section measurements are also reported.

A 1-Megapixel, progressive-scan image sensor with antiblooming control and lag-free operation

A 1024-pixel*1024-pixel interline charge-coupled device (IL CCD) image sensor has been developed. It incorporates antiblooming and electronic exposure control while eliminating lag and obtaining a high responsivity. The novel features of this device include a noninterlaced, or progressive-scan, architecture and dual-horizontal registers that can be used to clock out the image area by one or two lines at a time. These features make it well suited for applications demanding high-resolution-image capture from a single, high-speed scan. The progressive-scan architecture of this device covers the same resolution in an electronic-camera application as that of a 2-million-element, interlaced device. >

Phosphorus diffusion in polycrystalline silicon

The diffusion of phosphorus in crystallized amorphous Si layers was studied with secondary‐ion mass spectroscopy. A two‐dimensional diffusion model is used to find effective grain (Dg) and grain‐boundary (Dgb) diffusion coefficients. This simplified model leads to Dgb ≤ 10Dg, which is significantly lower than what has been deduced from conventional, larger grained polysilicon. Our result is consistent with specific‐gravity measurements, which found a significantly lower ‘‘mass defect’’ for layers deposited amorphous and subsequently crystallized as compared to initially polycrystalline layers.

A 1/3" format image sensor with refractory metal light shield for color video applications

The authors report results obtained on a full-color interline transfer CCD (charged-coupled device) image sensor with pixel dimensions of 8.6 mu m(H)*6.8 mu m(V) using 1.2- mu m design rules and a two-phase, single-polysilicon-per-phase technology. In order to reduce image smear and to provide suitable topography for integral color filters, a refractory light shield with a flowed glass overlayer was incorporated. The basic sensor and pixel architecture is shown. Image smear as a percent of full well, measured with 10% vertical illumination at saturated intensity, is shown as a function of wavelength. Smear is lowest at short wavelengths but is at an acceptable level for applications with controlled illumination.<<ETX>>

A 1.4 million element, full frame CCD image sensor with vertical overflow drain for anti-blooming and low color crosstalk

Blooming and color crosstalk must be greatly suppressed in solid-state image sensors for nearly all imaging applications. A vertical overflow drain has been developed for a 1.4 megapixel image sensor for blooming suppression and low color crosstalk. The overflow drain is formed using a uniform flat p-well. This paper describes the modeling, fabrication, and experimental data associated with implementing vertical overflow in this device.

Monte Carlo treatment of impurity diffusion in polycrystalline films

A Monte Carlo method for a random walk on a lattice is used to model impurity diffusion in a polycrystalline thin film. This approach permits the modeling of diffusion in films with more than one grain vertically. Numerical results illustrate the effects on the diffused impurity profile of a multiple‐grain structure that resembles a brick wall.

A 360,000 pixel color image sensor for imaging photographic negatives

We describe a740(H) \times 242(V) × 2 charge-coupled color image sensor for imaging photographic negatives. The sensor achieves charge capacity of1 \times 10^{6}electrons per pixel, random noise of 300 rms electrons per pixel, and dynamic range of 70 dB. Sensor design, spectral sensitivity, charge capacity, and noise are discussed.

Large-area interline CCD with low-dark current

When interline CCD image sensors increase in size beyond 4 million pixels, CCD dark current begins to degrade the signal. Some scientific and photographic applications use very slow readout rates (less than 1 MHz) to reduce the noise level. At a 1-MHz readout rate, a 4-megapixel imager will take at least 4 s to read out. This extended time period allows a significant amount of dark current to build up and frustrate efforts to reduce noise. Often this situation leads to the additional expense of a low-temperature operation. The accumulation-mode readout method for interline CCD image sensors is being developed at Eastman Kodak Company. Previously, accumulation mode could only be applied to the full-frame architecture because the p-type substrate acted as a source for holes. Interline CCD image sensors with n-type substrates have no ready source of holes to accumulate the surface of the CCD under all phases. This problem has been overcome, allowing room-temperature operation without significant dark current generation.

A novel solid-state image sensor for image recording at 2,000 frames per second

A very high-speed image sensor for image recording at up to 2,000 full or 12,000 partial frames per second consists of a 192 V × 248 H array of photocapacitors. For high-speed operation, the image-sensing area is divided into six blocks, each block having 32 parallel outputs. The blocks are addressed sequentially, and the 32 outputs are sensed simultaneously. The sensor dynamic range is 46 dB at 2,000 fps. Spectral sensitivity, noise, and spatial resolution are discussed.

High‐resolution interline image sensors using two‐phase CCD technology

Two interline, 30 frames/second, high‐resolution image sensors are described that use two‐phase charge coupled device (CCD) technology. One is a two‐megapixel, interlaced high‐definition television, sensor, and the other is a 1‐megapixel, progressive‐scan sensor for machine vision applications. These sensors include features such as dual‐horizontal CCD readout, antiblooming protection, electronic shutter capability, low smear, and no lag.©1994 John Wiley & Sons Inc