Ryohei Miyagawa

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. >

Effects of Oxygen on the Properties of Sputtered Molybdenum Thin Films

The effects of oxygen on film structures and film stresses of sputtered Mo thin films have been investigated. Mo films (8000 A) were deposited on Si(111) wafers in 0.4 Pa using Ar or Ar+O2 (O2 partial pressure: 0.01 Pa) working gases at 423 K. The major impurity was oxygen, and argon content was below the detection limit (0.05 at.%) of the fluorescence X-ray analysis. Microstructure and film stresses were affected by oxygen. The fibrous grain width in the films was decreased from 40-130 nm with 2.4 at.% oxygen to 40-70 nm with 14.4 at.% oxygen. The high tensile stress, 1×1010 (dyn/cm2) with 2.4 at.% oxygen, changed to the low compressive stress, 1.0×109 (dyn/cm2) with 30.1 at.% oxygen. This paper discusses the relationships between oxygen content and the film structures, and between oxygen content and the film stresses.

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

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>>

A 2/3-in 2 million pixel STACK-CCD HDTV 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. >

Photodegradation for a hydrogenated amorphous silicon photoconversion layer in a solid-state image sensor

Photodegradation for a hydrogenated amorphous silicon photoconversion layer in a two-level solid-state imaging device was studied. The residual current after a light pulse, which causes image lag for the imaging device, was most sensitive to light exposure among several properties, so that the residual current determines the lifetime for the photoconversion layer. The space charge was also increased with increasing residual current by light exposure, because both properties reflected light-induced defect states. The space charge was found to be a good monitor for the photodegradation. The space-charge density had light intensity and exposure-time dependency, which is similar to that for dangling bond density. The lifetime for the photoconversion layer, which was evaluated through the space-charge density change, was 1.5*10/sup 7/ h under standard illumination for the imager. This lifetime is sufficiently long for practical imager use. >

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

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>>

A-Si:H photoconversion layer thermal degradation for a two level image sensor

Thermal degradation under reverse-bias for an a-Si:H photoconversion layer was investigated. Residual current, which causes image lag, and space charge density increased by thermal degradation. The deep states in a-Si:H, which were evaluated by electron μ τ product and subband-gap light photoconductivity, did not increase. The increase in residual current is due to an electric field distortion which is caused by the induced space charge.

A Predischarge Doping Method for Hydrogenated Amorphous Silicon Films

A new slight boron doping method, predischarge doping, for a-Si:H films was investigated. Highly resistive borondoped a-Si:H films with 1011~1012 (Ωcm) orders of magnitude have been realized without mobility-lifetime product decrease. The mobility-lifetime product value was nearly the same as that for undoped films.

Light-annealing effect on a-Si:H photodiode with the Ar laser-irradiation

Abstract The light stability of a-Si:H photodiode is much improved by light-annealing treatment, which is produced by the Hg-sensitized photochemical vapor deposition method. The dark-current density of the photodiode with light-annealing (2 h, 180 °C) is about seven times smaller than that without light-annealing after Ar laser irradiation ( λ=514 nm , ∼6 W/cm2, 7 min). On the other hand, the photodegradation property of the photocurrent is not improved by light-annealing for a-Si:H single layer. Although the defects are produced by light-annealing around the mid-gap level of a-Si:H(i) film, the a-Si:H(i)/a-SiC:H(p) boundary of the photodiode is considered to be improved in the case. The electric field of a-Si:H(i) is considered to become strong, which decreases the dark-current density of the photodiode after Ar laser exposure.

A 2/3 inch 400 k pixel sticking-free stack-CCD image sensor

A 2/3-in 400-k pixel-stack-CCD (charge coupled device) image sensor that has bias charge injection into the a-Si layer is described. Because the bias charges fill the deep level traps in advance, image sticking is reduced to imperceptible levels 0.3 s after 10000*standard incident light is turned off. This device has the frame interline transfer architecture; the V-CCD (vertical-CCD) registers are used not only as signal charge transfer paths in the vertical-blanking period, but also as blooming drains in the signal-charge-integration period. The equivalent circuit of the stack-CCD sensor is shown along with a cross-section view of the unit pixel in the stack-CCD sensor. >