R.P. Khosla

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.

Wide-field-of-view PtSi infrared focal plane array

A 640 x 486 pixel monolithic focal plane array detector using PtSi Schottky barrier photodiodes was developed. This detector uses 1.2-micron design rules to achieve a 54-percent fill factor with 25-micron square pixels. The detector array used an interline CCD configuration with a progressive scan (noninterlaced) readout of the field, and two-phase clocking of both the vertical and horizontal registers.

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.

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.

A large area 1.3-megapixel full-frame CCD image sensor with a lateral-overflow drain and a transparent gate electrode

A large-area, 1.3 million pixel, full-frame CCD (charge coupled device) image sensor has been developed that incorporates both a lateral-overflow drain (LOD) for antiblooming control and a transparent indium-tin oxide (ITO) gate electrode for increased photosensitivity. The LOD offers high responsivity, extremely linear photoresponse, and ultrahigh optical overload protection. The replacement of one polysilicon phase with ITO increases the quantum efficiency at 400 nm to 15.8% from the 1.5% for the standard double polysilicon gate electrode process. The LOD design allows for antiblooming suppression in excess of 43000 times the saturation signal while maintaining better than 1% nonlinearity.<<ETX>>

Four-million-pixel CCD image sensor

An ultra high resolution image sensor has been developed for industrial and scientific applications. The ultra high resolution sensor is a full-frame CCD sensor, consisting of 2048 x 2048 pixels, and its image area measures 18.43 mm x 18.43 mm. The pixel size is 9 x 9 microns. The sensor has dual readout registers to increase the data rate and can be operated in the single or dual readout register mode. The architecture of this imager is suitable for accumulation mode operation, which results in a very low dark current of 10 pA/sq cm at room temperature.

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

A four-million pixel CCD image sensor

The authors have developed an ultra-high-resolution, full-frame CCD imager of 2048*2048 pixels. The pixel size is 9 mu m*9 mu m. The sensor has dual readout registers to increase the data rate. It is designed for a horizontal clock rate of 20 MHz. With the dual line readout mode, it takes 114 ms to read a frame. The experimental device has less than 0.5 nA/cm/sup 2/ dark current at room temperature, corresponding to about 25 electrons of dark shot noise at 200 ms frame time, including both integration and read time. The output amplifier, made of a two-stage source follower, has a sensitivity of 10 mV per electron. With correlated double sampling, the output amplifier contributes about 10 noise electrons at the 20 MHz data rate. Thus, the dark shot noise is the dominant noise component unless the imager is cooled. The charge capacity of the CCD is 85000 electrons, giving a dynamic range of 3000. A charge transfer efficiency of 0.99999 has been observed.<<ETX>>An ultra-high resolution image sensor was developed for industrial and scientific applications. The imager is a full-frame CCD sensor, consisting of 2048 × 2048 pixels, and its image area measures 18.43 mm × 18.43 mm. The pixel size is 9 microns × 9 microns. The sensor has dual readout registers to increase the data rate. The sensor could be operated in the single or dual readout register mode depending on the users frame rate requirements and the data capture system. The architecture of this imager is suitable for accumulation mode operation, which results in low dark current of less than 10 pA/cm2 at room temperature. The charge transfer efficiency is 0.99999 for horizontal clock rate up to 20 MHz.

1-megapixel IL-CCD image sensor with a progressive scan, antiblooming control, and lag-free operation

A 1024 x 1024 pixel, interline charge-coupled device (IL CCD) image sensor has been developed that incorporates antiblooming and electronic exposure control while eliminating lag and obtaining a high responsivity. Of the novel features of this device are its 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.