CMOS Image Sensor Overflow Path for Saturation Signal Stability
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Solution Overview
Problem
Conventional solid-state image sensors with integrated planar and vertical gate electrodes fail to maintain a sufficient saturation characteristic when a mechanical shutter is operated, leading to a decrease in saturation signal amount over time.
Innovation Solution
A solid-state imaging device is designed with a photo diode, a floating diffusion, multiple vertical gate electrodes formed in a depth direction between the photo diode and floating diffusion, and an overflow path formed in a shallower region between the vertical gate electrodes, along with a planar gate electrode that strides across the photo diode and floating diffusion, and a driving circuit that applies a negative voltage greater than previously applied at the shutter closure.
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 is insufficient
Solution Approach 1:
The overflow path is formed in advance in the semiconductor substrate between the photo diode and floating diffusion. This preliminary structural preparation enables the system to handle saturation conditions effectively when the mechanical shutter operates, preventing signal amount decrease by providing a pre-established charge overflow pathway.
Solution Approach 2:
The overflow path acts as an intermediary structure between the photo diode and floating diffusion. It mediates the charge flow during saturation conditions by providing an alternative path for excess charge, thereby maintaining the saturation characteristic while preventing signal amount degradation.
2Reliability
If vertical gate electrodes are formed to control overflow path, then the saturation characteristic improves, but the device complexity increases
Solution Approach 1:
The vertical gate electrodes are integrated with the planar gate electrode to form a unified transfer gate structure. This merging approach controls the overflow path using a combined gate system rather than separate independent components, improving saturation characteristic while managing device complexity through structural integration.
Solution Approach 2:
The transfer gate electrode structure serves multiple functions: it controls charge transfer between photo diode and floating diffusion, and simultaneously controls the overflow path potential. This multi-functionality improves saturation characteristic without proportionally increasing device complexity.
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 improves the saturation characteristic by dynamically controlling the overflow path, preventing a decrease in saturation signal amount and enhancing the dynamic range of the image sensor.
Implementation Method 1
a photo diode formed on a substrate
Implementation Method 2
a plurality of vertical gate electrodes formed from a surface of the substrate in a depth direction in a region between the photo diode and the floating diffusion
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.