3D Stacked Pixel Circuit With FD Capacitance Switching for Low-Light Imaging
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Solution Overview
Problem
Solid-state imaging devices with three-dimensional structures face challenges in miniaturization and pixel density due to the addition of capacitance switching configurations, which can lead to device enlargement and deterioration in low-light characteristics.
Innovation Solution
A solid-state imaging device comprising three substrates: a first substrate with photoelectric converters, a second substrate with a pixel circuit for generating pixel signals, and a third substrate with a peripheral circuit for signal processing, including a charge accumulation unit, amplification transistor, and switching transistor to manage capacitance, allowing for improved low-light characteristics without enlarging the device.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a configuration for connecting or disconnecting additional capacitance is added to the floating diffusion, then low-light characteristics are improved, but device size enlarges and pixel density deteriorates
Solution Approach 1:
The patent transitions from a two-dimensional planar structure to a three-dimensional stacked structure with multiple substrates. The photoelectric converter substrate, pixel circuit substrate, and peripheral circuit substrate are stacked vertically, allowing capacitance switching functionality to be added in the vertical dimension without increasing the horizontal device footprint, thus improving low-light characteristics while maintaining compact size and high pixel density
Solution Approach 2:
The patent divides the solid-state imaging device into three separate functional substrates: a photoelectric converter substrate, a pixel circuit substrate, and a peripheral circuit substrate. This segmentation allows the capacitance switching configuration to be integrated into the pixel circuit substrate without affecting the photoelectric converter area, enabling improved low-light characteristics while maintaining device compactness through vertical stacking
2Reliability
If a configuration for connecting or disconnecting additional capacitance is added to the floating diffusion, then low-light characteristics are improved, but pixel density deteriorates
Solution Approach 1:
By moving the capacitance switching configuration to the vertical dimension through substrate stacking, the horizontal area available for each pixel is preserved. The pixel circuit substrate contains the switching transistors and capacitance control circuitry, allowing full pixel density to be maintained while still providing the functionality needed for improved low-light characteristics
3Measurement precision
If capacitance switching configuration is added to the floating diffusion, then saturation charge amount can be acquired, but device complexity increases
Solution Approach 1:
The patent segments the device into three substrates, placing the capacitance switching configuration specifically in the pixel circuit substrate. This separation consolidates the additional complexity into a dedicated functional layer rather than distributing it throughout the entire device, making the complexity manageable and the saturation charge measurement capability achievable without overwhelming system 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
The solution enables the acquisition of saturation charge amount and improved low-light characteristics while maintaining compact device size and high pixel density, effectively addressing the limitations of existing technologies.
Implementation Method 1
a photodiode PD that generates a charge in accordance with an amount of received light L
Data Source
AI summary
Provided is a technology capable of acquiring a saturation charge amount and improving low-light characteristics while suppressing an enlargement of a device and deterioration in pixel density. A solid-state imaging device according to an embodiment includes: a first substrate (100) including a plurality of photoelectric converters (PD) arranged in a matrix; a second substrate (200) that is bonded to a first surface of the first substrate and includes a pixel circuit (120) that generates a pixel signal based on a charge generated in each of the photoelectric converters; and a third substrate (300) bonded to a third surface of the second substrate opposite to a second surface to which the first substrate is bonded, the third substrate including a peripheral circuit that executes predetermined processing on the pixel signal generated by the pixel circuit, in which the pixel circuit includes: a charge accumulation unit (FD) that accumulates a charge generated in the photoelectric converter; an amplification transistor (AMP) that generates the pixel signal having a voltage value corresponding to a charge amount regarding the charge accumulated in the charge accumulation unit; and a switching transistor (FDG) that switches capacitance of the charge accumulation unit.