Solid-State Imaging Device Well Potential Control for Dark Electron Suppression
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Solution Overview
Problem
Conventional solid-state imaging devices face issues with dark electrons generated at the surface of the well under the gate electrode, leading to increased dark output, variation in dark signal among pixels, and after-image or kTC noise, especially during long exposure times or in low-light environments, due to surface defects and depletion layer expansion.
Innovation Solution
A solid-state imaging device with a semiconductor substrate well that receives a second reference voltage, larger in absolute value than a first reference voltage, to suppress dark electrons by setting the potential near the gate electrode to nearly zero, thereby reducing dark output and after-image noise without complicating the control method or circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a conventional reference voltage is applied to the well, then the circuit configuration remains simple, but dark electrons accumulate at the surface of the well under the gate electrode, increasing dark output and causing after-image noise
Solution Approach 1:
The patent applies a second reference voltage to the well that has a different potential level from the first reference voltage. This parameter change in the well's potential suppresses the accumulation of dark electrons at the surface of the well under the gate electrode, thereby reducing dark output and after-image noise without complicating the circuit configuration
2Object-affected harmful factors
If the depletion layer expands to cover surface defects, then manufacturing remains straightforward, but dark electrons are generated and accumulated in the photoelectric converter section
Solution Approach 1:
By changing the potential of the well through application of a second reference voltage, the patent suppresses the generation and accumulation of dark electrons caused by surface defects, thereby reducing dark output without requiring additional manufacturing precision or complex processes
3Object-affected harmful factors
If a negative voltage is applied to the gate electrode to pin the back gate region potential, then dark electron generation is suppressed, but the control method becomes complicated
Solution Approach 1:
Instead of applying a negative voltage to the gate electrode, the patent applies a second reference voltage to the well, achieving the same effect of suppressing dark electron generation while maintaining a simple control method and circuit configuration
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
The solution effectively suppresses dark electrons and associated noise, improving image quality by reducing dark output variations and after-image issues, while maintaining a simpler circuit configuration and reducing power consumption.
Implementation Method 1
a photoelectric converter section which is a region of a second conductivity type formed from a surface to an inside of the well and accumulates a signal charge obtained through a photoelectric conversion of an incident light
Data Source
AI summary
During an exposure time period (long accumulation time period) of a low shutter speed shooting mode, a second reference voltage Vss2, which is different from a first reference voltage Vss1 (a ground voltage) corresponding to a reference voltage of a peripheral circuit, is applied to a well (5) where a photoelectric converter section (2) and a drain region (4) are formed, whereby generation of dark electrons at a portion of a surface of the well (5) below a gate electrode (6) is suppressed. A polarity of the second reference voltage Vss2 is positive in the case where a conductivity type of the well (5) is a P-type, and is negative in the case of an N-type.