Capacitance-Switched Image Sensor Pixel for Stable S/N Ratio
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Solution Overview
Problem
The existing solid-state image sensing devices face a deterioration in photoelectric conversion characteristics due to varying voltage of the photoelectric conversion unit, leading to reduced sensitivity and S/N ratio, especially when the capacitance of the charge holding unit is increased or decreased depending on illuminance levels.
Innovation Solution
A solid-state image sensing device is designed with a photoelectric conversion unit outside the semiconductor substrate, incorporating a charge holding unit, a reset transistor, a capacitance switching transistor, and an additional capacitance device to control the capacitance of the charge holding unit, allowing for adaptive capacitance switching based on signal charges, thereby maintaining optimal voltage and reducing leak currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the capacitance of the charge holding unit is increased to reduce voltage variation, then sensitivity deterioration is restricted, but the signal amplification rate decreases and S/N ratio is lowered
Solution Approach 1:
The charge holding unit dynamically switches between two capacitance values (first capacitance and second capacitance) based on illuminance conditions. At low illuminance, the first capacitance value is used to prioritize S/N ratio, while at high illuminance, the second capacitance value is used to handle larger signal charges, thereby adaptively optimizing performance across different lighting conditions
Solution Approach 2:
The capacitance value of the charge holding unit is changed based on illuminance levels. A capacitance switching transistor controls the connection of different capacitance values to the charge holding unit, allowing the system to adjust the capacitance parameter according to lighting conditions to balance sensitivity and S/N ratio requirements
2Measurement precision
If the capacitance of the charge holding unit is decreased to increase signal amplification rate, then S/N ratio is improved, but the ability to hold large amounts of signal charges is reduced
Solution Approach 1:
The system dynamically adjusts capacitance based on illuminance: using first capacitance at low illuminance for high S/N ratio, and switching to second capacitance at high illuminance to accommodate larger signal charge amounts, thereby adaptively optimizing both S/N ratio and charge holding capacity
Solution Approach 2:
The capacitance parameter is changed according to illuminance conditions through the capacitance switching transistor, allowing the charge holding unit to switch between different capacitance values to optimize both signal amplification and charge holding capability under varying lighting conditions
3Measurement precision
If a depleted region is connected to the charge holding unit to decrease capacitance at low illuminance, then S/N ratio is improved, but leak characteristic is deteriorated
Solution Approach 1:
A capacitance switching transistor is introduced as an intermediary component between the charge holding unit and the depleted region. This transistor controls the connection to the depleted region based on illuminance conditions, enabling capacitance reduction at low illuminance while preventing direct connection that would cause leak current through the depleted region
4Adaptability or versatility
If the photoelectric conversion unit is arranged outside the semiconductor substrate, then photoelectric conversion characteristic can be changed, but voltage variation deteriorates photoelectric conversion efficiency
Solution Approach 1:
The capacitance value of the charge holding unit is changed based on illuminance conditions to maintain stable voltage for the photoelectric conversion unit. By switching between different capacitance values, the system compensates for voltage variation and maintains optimal photoelectric conversion efficiency while allowing flexibility in photoelectric conversion characteristics
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 restricts the deterioration of photoelectric conversion efficiency and image quality by controlling the capacitance of the charge holding unit, maintaining optimal voltage and reducing leak currents, thus enhancing the S/N ratio and image quality across varying illuminance conditions.
Implementation Method 1
a photoelectric conversion unit (11) formed outside a semiconductor substrate (21)
Data Source
AI summary
The present technology relates to a solid-state image sensing device capable of restricting a deterioration in photoelectric conversion characteristic of a photoelectric conversion unit, and an electronic device. A solid-state image sensing device includes: a photoelectric conversion unit formed outside a semiconductor substrate; a charge holding unit for holding signal charges generated by the photoelectric conversion unit; a reset transistor for resetting the potential of the charge holding unit; a capacitance switching transistor connected to the charge holding unit and directed for switching the capacitance of the charge holding unit; and an additional capacitance device connected to the capacitance switching transistor. The present technology is applicable to solid-state image sensing devices and the like, for example.