CMOS Image Sensor Overflow Path for Stable Saturation Signal
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Solution Overview
Problem
Conventional solid-state image sensors with integrated planar and vertical gate electrodes face a decrease in saturation signal amount over time when a mechanical shutter operates, leading to insufficient saturation characteristics and deteriorated dynamic range.
Innovation Solution
A solid-state imaging device with a photo diode, floating diffusion, and vertical gate electrodes, featuring an overflow path between the electrodes, where a planar gate electrode is integrated with the vertical electrodes, and a driving circuit applies a negative voltage to the vertical gate electrodes at the shutter closure, modulating the overflow path to maintain signal balance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a mechanical shutter is operated, then the saturation signal amount decreases with time, but the saturation characteristic becomes insufficient
Solution Approach 1:
The overflow path is formed in advance between the photo diode and floating diffusion region, positioned shallower than the vertical gate electrodes. This preliminary structure enables charge to overflow through the predetermined path before saturation occurs, preventing signal loss when the mechanical shutter operates and maintaining stable saturation characteristics over time.
Solution Approach 2:
The overflow path acts as an intermediary charge transfer path between the photo diode and floating diffusion region. It provides a controlled overflow mechanism that mediates the charge accumulation process, allowing excess charge to be diverted through the shallower region between vertical gate electrodes, thereby maintaining signal balance during mechanical shutter operation.
2Reliability
If vertical gate electrodes are formed to control overflow path potential, then blooming characteristic is improved, but saturation signal stability deteriorates
Solution Approach 1:
The overflow path is positioned in a specific shallow region between the vertical gate electrodes, creating a localized charge overflow channel. This local quality differentiation allows the overflow path to operate independently at a shallower depth, controlling overflow locally without affecting the overall vertical gate electrode structure and maintaining saturation signal stability.
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 prevents the decrease in saturation signal amount over time, improving the saturation characteristic and dynamic range by dynamically controlling the overflow barrier potential.
Implementation Method 1
a driving circuit which applies predetermined voltage to the plurality of vertical gate electrodes, and the driving circuit applies negative voltage larger than the negative voltage applied until then to the plurality of vertical gate electrodes at timing at which an opening mechanical shutter closes
Data Source
AI summary
The present technology relates to a solid-state imaging device and an electronic device capable of improving a saturation characteristic. A photo diode is formed on a substrate, and a floating diffusion accumulates a signal charge read from the photo diode. A plurality of vertical gate electrodes is formed from a surface of the substrate in a depth direction in a region between the photo diode and the floating diffusion, and an overflow path is formed in a region interposed between a plurality of vertical gate electrodes. The present technology may be applied to a CMOS image sensor.