K. Orihara

A 2/3-inch 2 M-pixel IT-CCD image sensor with individual p-wells for separate V-CCD and H-CCD formation

This 2/3-inch optical-lens-format, 2 M-pixel interline-transfer (IT) CCD image sensor achieves large charge handling capability in the vertical CCD (V-CCD), and at the same time ensures sufficient transfer efficiency in the horizontal CCD (H-CCD). A V-CCD/H-CCD connection eliminates the potential barrier caused by separate V-CCD/H-CCD formation. Image sensor performance includes a 40 k-electron charge-handling capability in the V-CCD, leading to a 71 dB dynamic range, and sufficient transfer efficiency in the H-CCD, with no deterioration in V-CCD to H-CCD transfer efficiency. The power consumption is 0.49 W, just 22% of that previously achieved in a 1-inch 2 M pixel frame interline transfer (FIT) CCD. This is possible because the p-well reduces the driving pulse amplitude in the V-CCD and the IT scheme decreases electrode capacitance and driving frequency.<<ETX>>

A novel tungsten light-shield structure for high-density CCD image sensors

A novel tungsten light-shield structure has been developed. Tungsten film properties, the device configuration with the tungsten light-shield structure, and experimentally achieved results regarding device characteristics are described. Optical measurement clarified that tungsten film has a sufficiently low transmittance value for practical use for more than 200-nm-thick film and is stable up to 1000 degrees C. The good step coverage and low reflectance, such as 20-40% for aluminum, required for light-shield film were also obtained. A tungsten light-shield structure was applied to a 1/2-in format 668(H)-pixel*575(V)-pixel charge coupled-device (CCD) image sensor. An extremely low smear value, less than 0.001%, was obtained for a 300-nm film thickness. >

A 1920(H)*1035(V) pixel high-definition CCD image sensor

A 1920(H) × 1035(V) pixel high definition CCD image sensor has been developed. In order to follow up 74.25 MHz high sampling frequency, as well as to avoid the necessity for ultra fine patterning work for horizontal CCD register electrode formation, the device adopts a dual channel configuration for the horizontal CCD register. To accomplish both vertical signal charge transfer in the V-CCD register and signal charge distribution from the V-CCD registers into the dual channel horizontal CCD registers simultaneously within a 3.77 ¿s short horizontal blanking period, the 1H memory electrode between the V-CCD and H-CCD is introduced. The device operates successfully and a 1000 TV line limiting resolution has been obtained.

A 1/4 inch 380 k pixel IT-CCD image sensor employing gate-assisted punchthrough read-out mode

A newly developed 1/4-inch 380 k pixel IT-CCD image sensor features a novel cell structure in which signal charges are read out from a photodiode (PD) to a vertical-CCD (V-CCD) in a gate-assisted punchthrough mode. The cell structure, fabricated through the use of high energy ion implantation technology, enables both deep PD formation and transfer-gate (TG)/channel-stop (CS) length reduction. Deep PD formation helps increase sensitivity per PD unit area, and TG/CS length reduction widens both PD and V-CCD areas. Although the cell size is small (4.8 /spl mu/m (H)/spl times/5.6 /spl mu/m (V)), the sensor achieves both high sensitivity (35 mV/lx) and a high saturation signal (600 mV). >

Optical limitations to cell size reduction in IT-CCD image sensors

We have determined the practical limits of cell size reduction in interline-transfer CCD image sensors, limits resulting from diffraction occurring at the aperture above the photodiode. We have found that image cell size cannot be reduced to a level for which aperture width would fall below about 0.2 /spl mu/m. We have also found, however, that image cells with greater than 0.2 /spl mu/m aperture size are sensitive over the entire wavelength range of visible light, and that sensitivity can be increased by thinning the photoshield film.

A 1/2-in 1.3 M-pixel progressive-scan IT-CCD for digital still camera applications

A 1/2-in 1.3 M-pixel progressive-scan interline-transfer charge-coupled-device (IT-CCD) image sensor has been developed for small, low-power mega-pixel digital still cameras (DSCs). The pixel size as small as 5 /spl mu/m square makes small-size progressive-scan IT-CCD (8.3/spl times/7.1 mm/sup 2/) for the SXGA format. A two-phase-drive horizontal-CCD with phosphorus-implanted storage regions helps reduce the driving voltage to 2.5 V, resulting in the power consumption of the device being as low as 146 mW. A new source-follower amplifier with separate p-well driver transistors achieves 12% higher gain than that obtained using a conventional amplifier. An overflow drain with a self-adjusting potential barrier can instantly remove superfluous charges in vertical-CCDs just before an exposure period, which enables DSCs to perform such functions as quick auto-focusing and dark-current removal. New dual operation modes for still and motion pictures can provide not only high-resolution color signals in a 15-frame/s 1050-line progressive mode but also wide-dynamic-range color signals in a 30-frame/s 525-line progressive mode. The latter mode employs a pixel-exchange-and-mix readout operation that helps halve the number of scanning lines with no loss in sensitivity and color information.

A 1-inch 2-M pixel HDTV CCD image sensor with tungsten photo-shield and H-CCD shunt wiring

A 1-inch 2-million pixel FIT-CCD image sensor for HDTV has been developed, which features a tungsten photo-shield and horizontal CCD (H-CCD) shunt wiring. Tungsten photo-shield, which has low reflectance and good step coverage characteristics, reduces smear level to -110 dB, combined with a frame-interline-transfer (FIT) scheme. The tungsten photo-shield also acts as a shunt busline, supplying transfer pulses to vertical CCD (V-CCD) electrodes, so that a 1.2/spl times/10/spl circ/5 electron charge handling capability is obtained at a frame transfer frequency of 1 MHz. Newly developed H-CCD shunt wiring suppresses vertical line pair FPN, even with smaller transfer pulse amplitudes. H-CCD shunt wiring also helps reduce power consumption in the H-CCD by 2/3 as compared to that achieved with conventional wiring. >

Driving voltage reduction in a two-phase CCD by suppression of potential pockets in inter-electrode gaps

This study reports an optimum design for a two-phase charge-coupled device (CCD) and limitations on its driving voltage reduction. The two-phase CCD to be used as a horizontal-CCD (H-CCD) in a CCD image sensor requires low-voltage and high-speed operation. Reducing the driving voltage, however, may induce potential pockets in the channel under the inter-electrode gaps which results in a fatal decrease in charge-transfer efficiency. In this case it is necessary to optimize the CCD design to be free of pocket generation. For this requirement, we conducted two-dimensional (2-D) device simulations for the two-phase CCD, whose potential barriers are formed by boron ion-implantation. Our simulations indicated that the edge position of the potential barrier region and the dose of boron-ion implantation would be important parameters for controlling the size of potential pockets. At an optimum edge position and a boron dose, the minimum driving voltage appears to be reducible to 1.1 V. Characteristics of potential pockets and methods of their suppression are also discussed.

1/2-in 768(H)*492(V) pixel CCD image sensor

A sensor with unit cell dimensions as small as 8.4(H)*9.8(V) mu has been developed. In order to realize such a high-density device, the following technologies have been developed: (1) dual-channel horizontal CCD registers, (2) single p-well vertical overflow drain, (3) high-capacitance p-well structure, and (4) inverted-LOCOS channel isolation process. A horizontal resolution of more than 500 TV lines has been obtained. Maximum signal charge for the vertical CCD register is as much as 1.5*10/sup 5/ electrons, corresponding to 270-nA output current, in spite of a narrow-channel vertical CCD register with a mask width of only 1.8 mu m. The total random noise is less than 20 electrons after correlated double sampling. The dynamic range reaches 77 dB, and the photosensitivity is 0.092 mu A/ mu W. Experimental results also show that the technologies used here are effective for realizing a high-definition CCD image sensor for future use. >

A 30 frames/s 2/3-in 1.3 M-pixel progressive scan IT-CCD image sensor

A 30 frames/s 2/3-in 1.3 M-pixel progressive scan interline-transfer charge-coupled device (IT-CCD) image sensor has been developed for video and digital still-camera applications. To obtain high frame-rate images, a 49-MHz driving horizontal CCD (H-CCD) was developed. An 8-phase drive for vertical CCDs (V-CCDs) makes it possible to operate in a variety of modes, such as 1050 line progressive scan mode and 1049 line wide dynamic range interlaced scan mode. For digital still camera use, removing residual charges stored in the V-CCDs before exposure is essential, therefore new narrow-channel barrier over-flow drain (NCB-OFD) attached under the H-CCD was developed. The NCB-OFD automatically drains out extra charges and has the advantages of requiring neither an over-flow control gate nor any additional masks.