Stacked Image Sensor Wiring for Wider Dynamic Range
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Solution Overview
Problem
Imaging devices with three-dimensional structures face challenges in extending their dynamic range due to reduced pixel size, which limits their ability to handle high saturation signals and maintain high conversion efficiency, especially in high illuminance conditions.
Innovation Solution
The implementation of a capacitance addition wiring line that is electrically coupled to the conversion efficiency switching transistor, increasing the capacitance of the floating diffusion and allowing for variable FD capacitance, thereby enhancing the dynamic range without increasing the number of wiring lines or steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the pixel size is reduced to increase packaging density, then the pixel density increases, but the dynamic range decreases due to limited capacitance
Solution Approach 1:
The patent extends the wiring line from the first substrate through the bonding interface to the second substrate, utilizing the vertical dimension created by the stacked configuration. This three-dimensional wiring approach increases the effective capacitance area without increasing the two-dimensional pixel area, thereby extending dynamic range while maintaining high pixel density
Solution Approach 2:
The patent introduces an intermediate wiring structure that spans across the bonding interface between substrates. This intermediary wiring line acts as a bridge, connecting the floating diffusion region on the first substrate to additional capacitance elements on the second substrate, enabling extended dynamic range in miniaturized pixels
2Adaptability or versatility
If the capacitance of the floating diffusion is increased to extend dynamic range, then the dynamic range extends, but the number of wiring lines and manufacturing steps increases
Solution Approach 1:
The patent merges the capacitance function with the inter-substrate wiring structure. The wiring line that naturally connects the first and second substrates is extended to also provide the capacitance function, combining two functions into a single structure and avoiding additional dedicated capacitance wiring lines
Solution Approach 2:
The wiring line structure serves multiple functions: it provides electrical connection between substrates, acts as a capacitance element for extending dynamic range, and maintains compatibility with existing bonding processes. This multi-functional design avoids increasing device complexity while achieving extended dynamic range
3Volume of moving object
If the pixel size is reduced to increase packaging density, then the imaging device becomes more compact, but the ability to handle high saturation signals decreases
Solution Approach 1:
The patent utilizes the vertical dimension in the stacked substrate configuration to increase the effective capacitance area. By extending the wiring line into the third dimension (across substrates), the signal handling capability is enhanced without increasing the horizontal pixel area, maintaining compact imaging device size while improving reliability for high saturation signals
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 solution enables the imaging device to handle larger signal amounts and extend its dynamic range, improving conversion efficiency and reducing noise, especially in high illuminance conditions, while maintaining a compact design.
Implementation Method 1
a sensor pixel that performs photoelectric conversion
Data Source
AI summary
An imaging device including: a first semiconductor substrate; a second semiconductor substrate; and a wiring layer. The first semiconductor substrate has a first surface and a second surface and includes a sensor pixel. The second semiconductor substrate has a third surface and a fourth surface and includes a readout circuit that outputs a pixel signal based on an output from the sensor pixel. The second semiconductor substrate is stacked on the first semiconductor substrate with the first surface and the fourth surface opposed to each other. The wiring layer is between the first semiconductor substrate and the second semiconductor substrate and includes a first wiring line and a second wiring line that are electrically coupled to each other. One of the first wiring line and the second wiring line is in an electrically floating state while the other is electrically coupled to a transistor.