Toshio Yamagishi

First study of a flat vacuum image sensor with a field-emitter array

To develop a high-definition image sensor having ultra-high sensitivity far superior to CCDs. A new compact image sensor consisting of a matrix field emitter array (FEA) and a high- gain avalanche rushing amorphous photoconductor (HARP) target is studied. Most research on devices with FEAs has so far focused on flat displays and high-frequency devices. Although the concept of a flat image sensor with FEAs has been proposed before, image sensors with FEAs have yet to be fabricated. In this paper, the fundamental driving characteristics of a new flat image sensor comprised of an X-Y matrix FEA set face to face with a HARP target have been investigated in a vacuum chamber for the first time. Experiments confirmed that the device successfully picks up images. High-sensitivity is achieved with the HARP target, and the temporal fluctuation and spatial variation of the emission currents obtained from the FEA have almost no effect on the signal output currents. Furthermore, the resolution characteristics are affected by the mesh voltage and by divergence of the emission from the field emitter tips.

128x96 pixel field emitter-array image sensor with HARP target

In pursuit of developing a next-generation pick-up device having high definition and ultrahigh sensitivity features, research continues on a new type of image sensor that combines a HARP target and a field emitter array. A new field emitter array on a small-sized substrate is designed and a unique packaging technique is proposed. The prototype device is sealed in a vacuum package with a thickness of only about 10 mm and has 128 horizontal and 96 vertical pixels. Experimental results show that images could be successfully reproduced for the first time ever in a device of this type. Highly sensitive characteristics and propr resolution were also obtained with the device. The prototype image sensor can operate stably for more than 250 hours, demonstrating its feasibility and potential as a next- generation image pickup device.

Beam characteristics of a high-gain avalanche rushing amorphous photoconductor field-emitter image sensor

A new type of image sensor that uses a field emitter array (FEA) and a high-gain avalanche rushing amorphous photoconductor (HARP) target, with a mesh electrode inserted between them, has been designed and tested. The effects of the voltage and position of the electrode were investigated in a vacuum chamber. The resolution and dynamic range were improved by applying an adequate mesh voltage. The voltage needed for the mesh electrode was decreased by reducing the distance between the FEA and the electrode. Most of the electrons emitted from the FEA are captured by the mesh electrode and therefore contribute nothing to the read-out of the signal on the target. The mesh electrode structure thus needs further study. In addition, the decelerating electric field formed between the mesh and target needs to be considered because it spreads the electron beam, thus degrading the resolution and dynamic range of the device.

Beam characteristics and a new operation method of a HARP field-emitter image sensor

A new type of image sensor featuring a unique structure is studied with the aim of achieving both super-high sensitivity and ultrahigh-definition. This image sensor combines a field emitter array (FEA) and a high-gain avalanche rushing amorphous photoconductor target. We investigated the conditions for improving resolution in a vacuum chamber by inserting a mesh electrode between the FEA and the target. The results indicate that the resolution can be improved by strengthening the accelerating electric field between the FEA gate and the mesh, and by placing the mesh closer to the FEA. We also propose a new parallel readout system that is suitable for an ultrahigh-definition image sensor. Dividing the target into multiple segments and reading out signals for each segment simultaneously enables us to decrease the drive frequency. In our first attempt, we synthesized a good 60 X 60 pixel image from two 30 X 60 pixel segments.

Development of a 18-mm-diameter all-electrostatic Super-HARP tube for HDTV Investigation of its electron optics

Abstract We have developed the 18-mm-diameter all-electrostatic Super-HARP camera tube for high-performance handheld HDTV cameras. In designing its electron optics, we focused on high resolution and a wide dynamic range. Through experiments and numerical analysis, we have optimized the beam-limiting aperture of the diode-gun to enlarge the dynamic range, and the shape and arrangement of the pattern electrodes in the focusing and deflection system to improve the resolution. A prototype tube exhibited a dynamic range of at least 800% and maximum resolution of more than 1400 TV lines. The new HDTV camera tube thus achieves a good balance of high resolution and wide dynamic range while being compact.

Super-high-sensitive camera tube for HDTV hand-held cameras

We have developed a compact HDTV camera tube that combines high sensitivity with high resolution and is compact enough for hand-held cameras. This new camera tube employs an 8-micrometers -thick HARP (High-gain Avalanche Rushing amorphous Photoconductor) target. Unlike other photoconductors, this target is unique in that its sensitivity can be increased to very high levels to cope with darker illumination. In addition, we have achieved high resolution over the entire picture through the use of a new all-electrostatic focusing and deflection system in the 18-mm-diameter tube that facilitates the use of a narrow electron beam while assuring the optimal suppression of aberration. a prototype hand-held HDTV camera equipped with three of these camera tubes has attained a maximum sensitivity of 2,000 lux at f/25 (normal gain) and a limiting resolution of more than 1,400 TV lines.