Solid-State Imaging Event Detection With Dark Current Limiting
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Solution Overview
Problem
Asynchronous solid-state imaging elements face issues with erroneous detection due to dark current noise, particularly under low illuminance conditions, leading to noise in image data.
Innovation Solution
A solid-state imaging element is designed with a limiting circuit to set a lower limit value for electric signals generated by photoelectric conversion, using an offset current source to prevent erroneous detection, and includes differentiating and comparison circuits to accurately detect address events based on photocurrent changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a microlens is disposed above each pixel electrode in a solid-state imaging element, then light collection efficiency is improved, but manufacturing complexity increases due to the need for precise alignment and additional fabrication steps
Solution Approach 1:
The patent combines the microlens formation process with the color filter layer formation by using the same positive photoresist layer for both the color filter pattern and the microlens pattern. This integration eliminates separate fabrication steps and reduces manufacturing complexity while maintaining light collection efficiency.
Solution Approach 2:
The patent forms the microlens patterns and color filter patterns simultaneously during the same photoresist processing step before subsequent electrode formation. This preliminary action ensures precise alignment is achieved automatically through the patterning process itself, eliminating the need for separate alignment operations.
2Manufacturing precision
If multiple layers including color filters and microlenses are stacked above pixel electrodes, then imaging quality is improved, but the number of fabrication steps and device complexity increase
Solution Approach 1:
The patent merges the color filter layer and microlens layer into a single integrated structure formed from one positive photoresist layer. This combining approach maintains the optical functionality of separate layers while dramatically reducing the number of fabrication steps required.
Solution Approach 2:
The positive photoresist layer serves multiple functions simultaneously: it forms the color filter patterns, the microlens patterns, and provides the structural framework for both layers. This multi-functionality reduces material steps and process complexity while achieving the same imaging quality.
3Measurement precision
If precise alignment between microlenses and pixel electrodes is implemented, then light collection efficiency is improved, but manufacturing time and complexity increase
Solution Approach 1:
The patent establishes precise alignment between microlenses and pixel electrodes during the photoresist patterning step itself, before subsequent processing. The alignment is built into the pattern formation process, eliminating the need for time-consuming post-alignment operations.
Solution Approach 2:
By forming both color filter and microlens patterns from the same photoresist layer using the same patterning process, the patent ensures automatic alignment between corresponding features. This merged approach eliminates separate alignment steps and reduces manufacturing time.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration effectively reduces erroneous detection and noise in image data by ensuring that only significant changes in light are detected, improving the reliability of image recognition processes.
Implementation Method 1
a photorefractive crystal utilizing a photorefractive effect to modulate a phase of incident light in accordance with an image signal
Data Source
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AI summary
In a solid-state imaging element that detects a change in an amount of light on the basis of a photocurrent, erroneous detection due to a dark current or dark current shot noise is reduced. The solid-state imaging element includes a limiting circuit, a differentiating circuit, and a comparison circuit. The limiting circuit limits an electric signal generated by photoelectric conversion by a predetermined limit value and outputs the electric signal limited as an output signal. The differentiating circuit obtains an amount of change of the output signal output from the limiting circuit. The comparison circuit performs comparison between the amount of change obtained by the differentiating circuit and a predetermined threshold value to output a result of the comparison as a result of detection of an address event.