Motonori Ishii

A MOS Image Sensor With a Digital-Microlens

We have developed a MOS image sensor with digital-microlenses (DMLs), each of which has an effective refractive index realized by variation of the subwavelength separations between the concentric SiO2 ring walls. The effective refractive index profiles are optimized for the location of each pixel. The light-collection efficiency of the image sensor is twice as high as that of a conventional image sensor because of the enhanced light acceptance in the periphery. A 2.2-mum pitch 3-megapixel MOS image sensor based on the DML technology exhibited excellent uniformity of the light-collection efficiency across the image area, even for light with a very large incident angle, i.e., over 45deg. The DML promises new levels of performance of image sensors.

A 2.2/3-inch 4K2K CMOS image sensor based on dual resolution and exposure technique

The recent trend in ultra-high-density cameras is running from HD to 4K2K, which will further extend to 8K4K / portable 4K2K. With advancements in device fabrication process technologies, there has been a pressing need for the miniaturization as well as high resolution and high sensitivity in image sensors [1].

Experimental and theoretical examination of orientation effect on piezoelectric charge at gate periphery in AlGaN/GaN HFETs

Orientation effect on AlGaN/GaN heterojunction field-effect transistors (HFETs) has been experimentally and theoretically examined in detail. The drain-currents of the fabricated AlGaN/GaN HFETs with various gate directions do not depend on the gate orientation, whereas those of GaAs-based HFETs strongly depend on the gate direction due to the piezoelectric charges induced around the gate electrode. The piezoelectric charges induced in the vicinity of the gate electrode are simulated by using a finite-element method. This simulation solves the piezoelectric equations with piezoelectric and elastic stiffness constants, assuming that stress is applied to the gate edges in the HFET. The detailed simulation reveals that the piezoelectric charge distribution does not depend on the gate direction, although a large amount of piezoelectric charges is induced in the vicinity of the gate edges, which is consistent with the experimental result. Moreover, it is mathematically clarified that these experimental and simulated results are due to the symmetry characteristic of the piezoelectric and elastic stiffness constants for nitride semiconductor materials

A MOS Image Sensor with Microlenses Built by Sub-Wavelength Patterning

A MOS image sensor has digital-microlenses implemented by sub-wavelength patterning of concentric SiO2 ring walls. The sensitivity at the periphery of the imager is 3000e-/1x-s. In comparison, the sensitivity at the periphery of a conventional imager is 1300e/1x-s. Thus, extremely uniform brightness throughout the reproduced image is demonstrated even with an angle of incidence > 45deg.

Compressive sensing reconstruction using collaborative sparsity among color channels

This study describes a reconstruction method for compressive sensing using collaborative sparsity among multi-frame images and color channels. The proposed method reduces the artifact for compressive sensing and obtains better image quality. Experimental results reveal that the proposed method reconstructs 6.1 dB higher quality images than the conventional one for complex texture at occlusion boundaries.