Diamond field effect transistors have operated in electrolyte solution for the first time. Since the hydrogen-terminated diamond surfaces are stable enough for the use as an electrochemical electrode, the diamond surface channels are exposed to the electrolyte in the transistor structure. A perfect pinch-off and saturated current-voltage characteristics have been obtained for bias voltages within the potential window. The threshold voltages are almost constant in electrolytes with different pH values of 7-13, indicating pH insensitiveness of the hydrogen-terminated diamond surface. Based on this pH insensitive surface, ion selective regions can be fabricated to form transistor-based biosensors.

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In this paper, we describe a three-layer-stacked color image sensor comprising two organic photoconductive films (OPFs) with thin-film transistor-based readout circuits and a complementary metal–oxide–semiconductor (CMOS) image sensor. In this three-layer-stacked sensor, a blue-sensitive OPF selectively absorbs blue light, a green-sensitive OPF selectively absorbs green light, and a CMOS image sensor (CIS) receives red light. Color video imaging operation at 60 frames per second was confirmed for a prototype sensor having 320 × 240 pixels with a pixel pitch of 20 μm without a color filter array, and good color separation and a linear response of the sensor were achieved owing to the combination of the CIS and color-selective OPFs.

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A color image was produced by a vertically stacked image sensor with blue (B)-, green (G)-, and red (R)-sensitive organic photoconductive films, each having a thin-film transistor (TFT) array that uses a zinc oxide (ZnO) channel to read out the signal generated in each organic film. The number of the pixels of the fabricated image sensor is 128 Â 96 for each color, and the pixel size is 100 Â 100 m 2 . The current on/off ratio of the ZnO TFT is over 10 6 , and the B-, G-, and R-sensitive organic photoconductive films show excellent wavelength selectivity. The stacked image sensor can produce a color image at 10 frames per second with a resolution corresponding to the pixel number. This result clearly shows that color separation is achieved without using any conventional color separation optical system such as a color filter array or a prism.

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