Blooming Suppression Research Articles

A small pixel CMD image sensor

A charge modulation device (CMD) imager with pixel dimensions of 7.3 mu m(H)*7.6 mu m(V) was designed, fabricated, and examined. These pixel dimensions are suitable for an HDTV imager with a 1-in image format. The optical aperture ratio is 34%. The effective number of pixels in the imager is 660 horizontal and 492 vertical. The saturation signal current is 17 mu A/pixel at an exposure of 1 lx-s with good linearity of photoconversion characteristics. The peak of its spectral response occurs at a wavelength of 575 nm. The blooming suppression ratio of the CMD was measured to be -122 dB. The sensor produces a high-quality image with no degradation in spatial resolution and no image lag. These features show that the CMD imager is eminently suitable for a further high-resolution imager sensor.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A 1/3-in 510(H)*492(V) CCD image sensor with mirror image function

A 1/3-in optical format 510(H)*492(V) interline charge-coupled-device (CCD) image sensor with a mirror-image function has been developed. To realize both a normal image and a mirror image, the horizontal shift register (H-CCD) is transferred forward and backward by a four-electrode, quasi-two-phase clock drive. The unit cell size is 9.6(H)*7.5(V) mu m/sup 2/. An on-chip microlens has been developed to achieve a sensitivity of 28 mV/lx, which is higher than that of the conventional 1/2-in device. The hole accumulation diode (HAD) sensor used has the advantage of low dark current, negligibly small lag, high blooming suppression, and a variable-speed electronic shutter. The smear reduction level is -83 dB. Horizontal resolution of 330 TV lines is obtained.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Junction CCD optical line sensor

An optical line sensor based on a junction CCD is presented. The expected good quantum efficiency of a junction CCD appears to be better than 0.8. In addition, this type of CCD has excellent blooming suppression. The resolution is 49.5 μm and the sensor is driven by a 3-phase clock.

Analysis of n-p-n photodiode in p-well CPD image sensors

A CPD image sensor with the p-well structure having two kinds of impurity profiles has been developed. The potential along the depth of the n-p-n photodiode in the p-well is calculated for a linearly graded junction. Based on this calculation, the capability of the blooming suppression and the dynamic range of the photodiode are discussed. The blooming suppression efficiency is found to increase with V sub (the voltage applied to the n-substrate with respect to the p-well) up to a certain value, beyond which the dynamic range of the photodiode decreases. It is shown that the lightly doped p-well is strikingly effective for the blooming suppression.

A CCD imager overlaid with a thin-film photodetector of a heterojunction ZnSe-Zn1-xCdxTe

A CCD imager which is composed of an interline transfer type scanner in the imaging area and a thin-film photodetector of a heterojunctjon ZnSe-Zn 1-x Cd x Te has been developed. The array consists of 506^{V} \times 404^{H} picture elements. The imaging area is about 6.7^{V} \times 9.0^{H} mm2in size which corresponds to that of a 2/3-in vidicon. For the device to achieve high performance, necessary conditions between the parameters of the overlaid thin-film photoconductor and the scanner have been analyzed. Blooming phenomenon is deeply related to the sensitivity. The blooming has been suppressed without sacrificing the sensitivity by applying the pulse operation of the heterojunction. As a result, excellent performances such as high sensitivity and large blooming suppression have been realized. The scene illumination if F 1.4 100 1x (S/N ratio is 46 dB for luminance signal) in a single-chip color camera. The blooming control capability is 250 times of the saturation exposure.

Solid-State Color Image Sensor Using Hydrogenated Amorphous Silicon

The device structure, fabrication and performance of a solid-state color image sensor using hydrogenated amorphous silicon as a photoconductive materal are reported in this paper. The number of photodiodes made of nitrogen doped amorphous silicon is 485 (V) × 384 (H), and they are scanned by n-MOS switches. An RGB color filter array is put on the chip to make a 2/3'' size single chip color sensor. This device features high spectral sensitivity, high blooming suppression, low lag and little burning.

A CCD Imager Using ZnSe-Zn1-xCdxTe Heterojunction Photoconductor

A new CCD imager, having ZnSe-ZnCdTe heterojunction photoconductor as a photosensor which is vacuum-deposited on the CCD scanner, has been fabricated. The device has 404 (H) × 506 (V) scanning elements, each element measures 24 µm(H) by 14 µm(V), and the imaging area is 9.0 mm(H) × 6.7 mm(V) in size which is applicable to 2/3 inch camera format. The CCD scanner is fabricated with denuded zone which defines the defect-free device. A glass-reflow process is introduced to obtain the high breakdown of the heterojunction diode. The experimental result are as follows,; The sensitivity is 0. 16 µA/lx (3200 K). The horizontal and the vertical resolution are 280 and 450 TV lines, respectively. Dark current is 2 nA/cm2 for the photosensor (27°C). The signal to noise ratio is above 60 dB. The smearing suppression is effective for reducing the blooming phenomenon under the intense light illumination. The successful blooming suppression is achieved by this PLOSS structure device with metal screen grid. The high light exposure is allowable up to 1000 times as intense as the saturation exposure.

Quantum efficiency and blooming suppression in junction charged-coupled devices

The quantum efficiency and blooming suppression in a buried channel three phase junction CCD, used as a line sensor, have been measured. A quantum efficiency of approximately 65 percent, relatively uniform throughout the visible spectrum, has been measured with front illumination. Channel blooming suppression up to about 500 times saturation has been obtained.

Measurements on a charge-coupled area image sensor with blooming suppression

Blooming, the lateral spreading of charge from an intensely illuminated area of an image sensor, can be present in an especially objectionable form in charge-coupled devices. Bright lines are formed in the display, owing to a charge propagation along the transfer channels. The introduction of overflow drains, i.e., stripes of a reverse-biased p-n junction placed between the transfer channels, provides a well-defined leakage path for excess carriers from saturated potential wells. An implanted threshold barrier between these drains and the integrating potential wells determines the saturation potential of the integration sites and prevents the total collapse of the associated depletion region. Therefore, the lateral diffusion of minority carriers is also greatly reduced. An existing design of a charge-coupled area image sensor with 64 × 106 resolution elements and frame transfer organization has been modified to study these methods of blooming suppression. The lateral distance of charge spreading has been reduced by a factor of seven at overload conditions of 20 dB. For stronger overloads the booming suppression becomes even more striking, but the performance of the device iS limited by frame transfer smearing. Furthermore, lens flare limits most optical systems at overloads above 30 dB. However, by using an optical fiber, well-localized overloads of 50 dB could be generated. Although, in our particular test device, the addition of blooming suppression reduced the light sensitivity by a factor of four, other geometries for overflow drain structures that should result in only a negligible loss in sensitivity are discussed.