Stacked Imaging Pixel Capacitor Layout for kTC Noise Reduction
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Solution Overview
Problem
Multilayer imaging devices face challenges in reducing kTC noise during reset operations due to the difficulty in completely transferring electric charges from a photoelectric conversion unit to a semiconductor substrate, limiting the effectiveness of noise reduction methods like correlated double sampling.
Innovation Solution
The imaging device incorporates a capacitor circuit with serially connected capacitors of different capacitance values between the photoelectric conversion unit and a reference voltage, along with a feedback circuit that negatively feeds back the electric signal, allowing for effective reduction of kTC noise and enabling the second transistor to function as both a reset and gain switching transistor, which helps in miniaturizing cells and reducing dark current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a photoelectric conversion unit is stacked on a semiconductor substrate to form a multilayer imaging device, then the imaging functionality is enhanced, but kTC noise generated during reset operations increases due to incomplete charge transfer
Solution Approach 1:
A transfer transistor is introduced as an intermediary component between the photoelectric conversion unit and the semiconductor substrate. This transfer transistor facilitates complete charge transfer by actively controlling the charge flow, thereby eliminating the incomplete charge transfer problem that causes kTC noise while preserving the multilayer imaging structure
Solution Approach 2:
A feedback circuit is implemented that monitors the charge transfer process and adjusts the reset operation accordingly. The feedback mechanism ensures that charge is completely transferred before reset occurs, preventing kTC noise generation while maintaining the enhanced imaging functionality of the multilayer structure
2Object-generated harmful factors
If correlated double sampling is used to reduce reset noise, then noise reduction is achieved, but the method becomes ineffective due to incomplete charge transfer from photoelectric conversion unit to substrate
Solution Approach 1:
The transfer transistor performs preliminary charge transfer action before the reset operation occurs. By ensuring complete charge transfer in advance, the conditions for effective correlated double sampling are created, making the noise reduction method reliable
Solution Approach 2:
A feedback mechanism monitors charge transfer completion and coordinates with the correlated double sampling timing. This feedback ensures that sampling occurs only after complete charge transfer, restoring the effectiveness of correlated double sampling for reset noise reduction
3Device complexity
If the pixel configuration is simplified to reduce device complexity, then manufacturing becomes easier, but dark current increases due to transistor junction leakage
Solution Approach 1:
Multiple transistor functions are merged into a single integrated transistor structure. The transfer transistor simultaneously performs charge transfer, reset, and gain switching functions, simplifying the pixel configuration while minimizing junction leakage through optimized device design
Solution Approach 2:
The transfer transistor is designed with multi-functionality to perform charge transfer, reset operation, and gain switching. This universal approach reduces the number of transistors needed while controlling dark current through careful design of the multi-functional device
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 kTC noise, allows for sensitivity switching, and minimizes transistor junction leakage, thereby enhancing the imaging device's performance by reducing dark current and noise while maintaining a dynamic range with a simple pixel configuration.
Implementation Method 1
a photoelectric converter that converts incident light into a signal charge
Data Source
AI summary
An imaging device including a semiconductor substrate; a photoelectric converter that converts incident light into a signal charge, the photoelectric converter being stacked on the semiconductor substrate; a node to which the signal charge is input; a transistor having a source and a drain, one of the source and the drain being connected to the node; and a capacitive element connected between the transistor and a voltage source or a ground. The transistor is configured to switch between a first mode and a second mode, a sensitivity in the first mode being different from a sensitivity in the second mode, and in a cross-sectional view, the capacitive element is located between the semiconductor substrate and the photoelectric converter.