Yoshinori Iida

A 2-million-pixel CCD image sensor overlaid with an amorphous silicon photoconversion layer

A highly sensitive 2-million-pixel high-definition charge-coupled device (CCD) image sensor was developed that features an overlaid amorphous silicon photoconversion layer on an interline transfer-type CCD scanner. The device is adapted to the 16:9 aspect ratio. 1125 scanning lines and 2:1 interlace high-definition TV system. A dual-channel horizontal CCD register is used to reduce the operating frequency to one half of the 74.25-MHz readout frequency. A horizontal period signal storage memory (1H line memory) is provided between the vertical CCD register and the horizontal CCD register to provide the signal distribution from the vertical CCD to the horizontal CCD register during the 3.77- mu s short horizontal blanking interval. This device realized a 1000 TV line horizontal limiting resolution 210 nA/1x high sensitivity. Total random noise was found to be 52 electrons RMS and a 72-dB dynamic range was achieved. >

A Color CMOS Imager With 4

A color CMOS image sensor with the 4 times 4 White-RGB color filter array (CFA) including 50% white pixels has been developed. A transparent layer has been fabricated on the white pixel to realize over 95% transmission for visible light with wavelengths of 400-700 nm. Pixel pitch and number of the pixels were 3.3 mum and 2 million, respectively. With the simple and low-noise color separation process, low-illumination signal-to-noise ratios of luminance signal have been increased by 6 dB, compared with those of the Bayer pattern. Moreover, by locating the pixels so that every color components can be detected in every column and line, color artifacts at the edge were suppressed. The edge detection process became unnecessary and the process time was reduced by 70%. The new CFA has the potential to significantly increase the sensitivity of CMOS/CCD image sensors.

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Shrinking pixel size in conventional CCD imagers degrades device performance. Unsatisfactory smear noise of -90 dB is attained in a 2/3-inch 2M pixel CCD imager. The STACK-CCD imager has a great advantage regarding this problem. A 100% aperture ratio and low smear noise are maintained regardless of future pixel shrinking, because CCD scanning circuits are overlaid with an amorphous silicon (a-Si) photoconversion layer.<<ETX>>

4 White-RGB Color Filter Array for Increased Low-Illumination Signal-to-Noise Ratio

We have developed a CMOS image sensor with a novel color filter array(CFA) where one of the green pixels of the Bayer pattern was replaced with a white pixel. A transparent layer has been fabricated on the white pixel instead of a color filter to realize over 95% transmission for visible light with wavelengths of 400-700 nm. Pixel pitch of the device was 3.3 um and the number of pixels was 2 million (1600H x 1200V). The novel Bayer-like WRGB (White-Red-Green-Blue) CFA realized higher signal-to-noise ratios of interpolated R, G, and B values in low illumination (3lux) by 6dB, 1dB, and 6dB, respectively, compared with those of the Bayer pattern, with the low-noise pre-digital signal process. Furthermore, there was no degradation of either resolution or color representation for the interpolated image. This new CFA has a great potential to significantly increase the sensitivity of CMOS/CCD image sensors with digital signal processing technology.

A 2/3-inch 2M-pixel STACK-CCD imager

A 2/3-in optical format 2 M pixel STACK-CCD imager has been developed. The STACK-CCD imager, overlaid with an amorphous silicon photoconversion layer, realizes a large signal charge handling capability of 1.0/spl times/10/sup 5/ electrons, a -140 dB smear noise and a 90 dB dynamic range with a newly introduced device configuration and its unique operation. The 5.0 /spl mu/m(H)/spl times/5.2 /spl mu/m(V) unit pixel imager with sufficiently low image lag has been realized by a novel bias charge injection scheme These device performances are the best ever achieved by a CCD HDTV imager. This is the first such imager satisfying the device performances required for a practical use 2/3-in 2 M pixel HDTV imager. >

A novel Bayer-like WRGB color filter array for CMOS image sensors

E-beam recrystallization has been applied to the fabrication of a three-layer processor. The seed structure and the E-beam conditions were successfully optimized so that a large-area SOI as wide as 1 mm was recrystallized without void generation with no damage to underlying devices. The actual SOI area in the device, 850*1100 mu m, was recrystallized with one E-beam scan by aligning its position. The three-layer image processor was capable of visual image sensing with a feature outline extraction in a parallel processing manner. Normal operations of the fundamental functions have been confirmed, demonstrating the feasibility of E-beam recrystallization for three-dimensional IC application. >

A 2/3-in 2 million pixel STACK-CCD HDTV imager

A 2 Mpixel two-level CCD (charge-coupled device) image sensor which has no capacitive image lag is discussed. Image lag is reduced to 0.4% and the dynamic range expanded from 72 dB to 110 dB. A schematic diagram of this device is shown. The pixel structure adopts an additional storage-diode-resetting gate (SRG) and bias-charge-injecting diode (CID) formed adjacent to a vertical CCD. A single CID is shared by two horizontally adjacent pixels, allowing the charge to be injected into two storage diodes simultaneously.<<ETX>>

Application of E-beam recrystallization to three-layer image processor fabrication

An Hg-sensitized photochemical vapor deposition method has been developed which has enabled a hydrogenated amorphous silicon photoconversion layer to be overlaid on a charge coupled device (CCD) imager, without a pixel separation structure. This chemical vapor deposition (CVD) method has been used to realize imaging devices with high sensitivity and high resolution for high-definition TV.

A 2 M-pixel two-level vertically integrated HDTV image sensor

Abstract The influence of gas flow and H 2 dilution ratio on the bulk and surface properties of a-SiC:H films is discussed. Infrared and electron spin resonance studies reveal that structural relaxation is achieved through control of surface reactions. On the other hand, the surface morphology as observed by atomic force microscopy is shown to be determined by growth rate under supply-limited conditions. This evidence implies that an improvement in bulk properties does not always lead to surface smoothening. Both surface reaction control and growth rate control are found to be crucial if films with excellent bulk and surface properties are to be obtained.

Hg-Sensitized Photochemical Vapor Deposition Application to Hydrogenated Amorphous Silicon Photoconversion Layer Overlaid on Charge Coupled Device

A new, laminar flow type photochemical vapor deposition method has been applied to prepare a-Si:H films. The main feature of this method is introduction of Ar gas as a flow down gas through the lower part of the quartz window into the reaction chamber to keep the window highly transparent. The high deposition rate (150 A/min) of the a-Si:H film has been stably maintained by optimizing the flow rate for each gas into the chamber. Utilizing this new method, we have been able to realize high quality films with low impurity content, high resistivity (>10 11 Ω cm), low dangling bond density (5×10 15 cm -3 ), etc