Kouichi Ishida

Thin observation module by bound optics (TOMBO) : concept and experimental verification

A compact image-capturing system called TOMBO (an acronym for thin observation module by bound optics) is presented in which the compound-eye imaging system is utilized to achieve a thin optical configuration. The captured multiple images are processed to retrieve the image of the target object. For image retrieval, two kinds of processing method are considered: image sampling and backprojection. Computer simulations and preliminary experiments were executed on an evaluation system to verify the principles of the system and to clarify the issues related to its implementation.

Thin observation module by bound optics (TOMBO): an optoelectronic image capturing system

A compact image capturing system called TOMBO (thin observation module by bound optics) is presented, in which a compound-eye imaging optics is utilized for very thin system configuration. The captured multiple images are processed to retrieve the object image. An experimental system was constructed for verifying the principle and clarifying the issues related on the implementation. For the retrieve, two kinds of processing are considered: simple sampling and back projection methods. The TOMBO system is an instance of opto- electronic hybrid system providing excellent features based on opto-electronic cooperation.

Transversal-readout CMOS active pixel image sensor

This paper presents a CMOS active pixel image sensor (APS) with a transversal readout architecture that eliminates the vertically striped fixed pattern noise (FPN). There are two kinds of FPNs for CMOS APSs. One originates form the pixel- to-pixel variation in dark current and source-follower threshold voltage, and the other from the column-to-column variation in column readout structures. The former may become invisible in the future due to process improvements. However, the latter, which result sin a vertically striped FPN, is and will be conspicuous without some subtraction because of the correlation in the vertical direction. The pixel consists of a photodiode, a row- and a column-reset transistor, a source follower input transistor, and a column-select transistor instead of the row-select transistor in conventional CMOS APSs. The column-select transistor is connected to a signal line, which runs horizontally instead of vertically. Every horizontal signal line is merged into a single vertical signal line via a row- select transistor, which can be made large enough to make its on-resistence variation negligible because of its low driving frequency. Therefore, the sensor has neither a vertical nor horizontal stripe FPN.

Photo-Current Multiplication Phenomenon of Amorphous Silicon-Based Multilayer Photodiodes Fabricated on Crystalline Silicon Substrate

Recently, high-resolution and high-density solid-state imaging devices have been in high demand due to their high photogain because the smaller pixel size makes the smaller photo-current dependent on the reduced area. Multilayer photodiodes having a-SiC:H/a-Si:H/a-SiN:H structures fabricated on the crystalline silicon (c-Si) substrate were studied for their photo-multiplication effects which marked a gain of 6.6. These multiplication phenomenona arose in the wavelength region longer than 550 nm, while in the shorter-wavelength region, the photogain was less than unity. This is explained by the electron carrier process where the carriers photogenerated in the c-Si substrate are accumulated at the a-SiN:H/c-Si interface and tunneled via localized states in the a-SiN:H layer by the induced high electric field. From these results, it is considerably difficult to support the theory of avalanche effect to explain these photo-multiplication effects.

Photocurrent multiplication in amorphous Si/crystalline Si heterojunction

Abstract A photocurrent multiplication factor over 20 has been observed on a new a-Si:H c-Si heterojunction structure fabricated on a c-Si substrate under the deeply reverse biased voltage. In contrast, any marked increase in the dark current is not found on the photodiode, and the signal-to-noise ratio is achieved to be around 170. The spectral response indicates that the photocurrent multiplication factor gets smaller for illumination wavelengths. Photoconversion characteristics show that the photocurrent is proportional to the illumination intensity in the reverse bias voltage region in which multiplication occurs. A possible mechanism for the photocurrent multiplication involving the avalanche multiplication is discussed through various experiments regarding the photocurrent characteristics.