We have developed organic photoconductive film (OPF) CMOS image sensors with pixel structures different from those of a conventional silicon image sensors, in which, the organic thin film for photoelectric conversion and the charge storage part for signal charge accumulation are completely independent. In this paper, we focus on two unique features of the OPF image sensor: (1) technology that realizes over 120 dB simultaneous-capture wide dynamic range, (2) global shutter technology achieving high saturation signals per unit square that is 10 dB higher than that of silicon image sensors with the global shutter function, without sacrificing pixel area. In addition, we have developed a test chip that realizes a high resolution of 8K4K, a high frame rate of 60 fps, a high saturation signals of 450 ke−, and the global shutter function simultaneously. These features of the OPF image sensor will contribute to significant progress in imaging and sensing fields.
A rewritable phase-change optical disk providing a large capacity of 100 Gbyte on a 120 mm disk was first demonstrated using the multilayer Bluray Discä (BD-XL) format. The doubled capacity of this optical disk compared with that of a conventional dual-layer disk was achieved firstly by stacking triple recording layers and secondly by increasing the recording capacity per layer from 25 to 33.4 Gbyte at 33.6%. The high transmittances of 50% (middle layer) and 60% (front layer) were achieved by thinning a Ge-Sb-Te phase-change film to 7.5 and 6 nm and also by thinning a Ag-alloy film to 9 and 7 nm, respectively. An additional TiO 2 -based film formed on the Ag-alloy film was effective in improving the transmittance at 3%, compared with the structure using a conventional TiO 2 film. Furthermore, a transmittance-balanced structure was adopted for these layers in order to stabilize the recording-reading properties. To improve cyclability, ZrO 2 -Cr 2 O 3 -based interface films were provided on both sides of the phase-change film for the middle and front layers. The increase in recording capacity per layer was achieved by reducing the minimum mark length from 0.149 to 0.112 m. Since the optical changes degrade with the reductions in the mark lengths and thicknesses of the Ge-Sb-Te and Ag-alloy films, a phase-change material with a GeTe-rich composition on a GeTe-Sb 2 Te 3 pseudo-binary line was adopted for every layer to compensate it. It was confirmed that the sample disk successfully satisfies all the requirements of the BD-XL format.
The excellent performance of a 100-GB-capacity write-once disk was demonstrated. The disk has quadruple recording layers, i.e., Layer 3, 2, 1, and 0 (from the laser-incident side of the disk) based on the 4Â Blu-ray disc (BD) format. Each layer is provided with a phase-change type memory film of Te-O-Pd, whose thickness was 20 nm for Layer 0, and only 6 nm for Layers 1, 2, and 3 in order to obtain high transmissivity. Additionally, for Layers 2 and 3, a metallic reflection layer was not needed and an AlN film with high thermal conductivity was formed next to each recording film. The AlN film suppressed the heat-induced damage of thin recording films. Consequently, the high transmissivities of 64% (Layer 1), 75% (Layer 2), and 81% (Layer 3) were achieved so that a quadruple layer disk with high quality was realized. The experimental disk showed tolerance to a wide range of writing speeds from 1Â (36 Mbps) to 4Â (144 Mbps). Good jitter values for each layer within an available maximum laser power of 27 mW on the disk were demonstrated. The acceleration test for lifetime using the Arrhenius plots showed that this write-once disk has an estimated lifetime of more than 100 years at 30 C and 85% relative humidity (RH).
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