Stacked Pixel Accumulation Layout for High-Capacitance Image Sensors
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Solution Overview
Problem
Existing image sensors face challenges in reducing chip area while maintaining high capacitance values, often resulting in increased chip size due to the need for numerous capacitances in the pixel region and surrounding areas.
Innovation Solution
The image sensor design incorporates accumulation units stacked on the semiconductor substrate within the pixel region, providing capacitances corresponding to each pixel column, which reduces the chip area and allows for efficient signal and noise signal accumulation without increasing the chip size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a large number of capacitances are provided in the pixel region and surrounding areas to achieve high capacitance values, then the capacitance value is improved, but the chip area increases
Solution Approach 1:
The patent introduces a time dimension by implementing sequential signal transfer across multiple rows. While one row is being read out, signal charges from other rows are transferred to the accumulation unit, enabling time-multiplexed accumulation that achieves high capacitance values without requiring parallel capacitance structures that would increase chip area
Solution Approach 2:
The accumulation unit is designed to sequentially accumulate signal charges from multiple pixel rows within its single capacitance structure. The unit nestedly accumulates charges row by row, effectively multiplying its capacitance value by the number of rows it can accumulate, thereby achieving high total capacitance without proportionally increasing chip area
2Area of stationary object
If signals are read out sequentially from each pixel row, then the chip area is reduced, but the readout time increases and frame rate decreases
Solution Approach 1:
The patent implements periodic action by alternating between signal transfer operations and readout operations in a cyclic manner. While odd rows transfer signals to the accumulation unit, even rows perform readout, and this pattern continues sequentially. This periodic alternation enables continuous utilization of the accumulation unit and maintains high frame rates despite sequential processing
Solution Approach 2:
The accumulation unit continuously accumulates signal charges from different rows without idle periods. While one row's signal is being read out, another row's signal is simultaneously being transferred to the accumulation unit, ensuring that the accumulation function operates continuously and efficiently, thereby reducing overall readout time
3Quantity of substance
If multiple capacitances are provided for each pixel column to accumulate signals and noise signals, then the accumulation capability is improved, but the device complexity increases
Solution Approach 1:
The patent merges the accumulation of signal charges and noise charges into a single accumulation unit with one capacitance per pixel column. Instead of providing separate capacitances for signal and noise accumulation, the system uses time-multiplexed accumulation where the same capacitance accumulates signal charges from one row and noise charges from another row, thereby reducing device complexity while maintaining accumulation capability
Solution Approach 2:
The accumulation unit is designed as a multi-functional component that can accumulate both signal charges and noise charges using the same capacitance structure. By making the accumulation unit universal and capable of handling different types of charges sequentially, the patent reduces the number of dedicated components needed, thereby simplifying the overall device structure
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 approach enables a large capacitance value without expanding the chip area, facilitating high frame rates by parallel horizontal signal transfer during readout, thereby improving image sensor performance.
Implementation Method 1
a photoelectric conversion unit 12 that converts incident light into an electric charge
Data Source
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AI summary
An image sensor includes: a plurality of pixels each having a photoelectric conversion unit that converts incident light into an electric charge, the incident light being incident from one side of a substrate, and an output unit that outputs a signal caused by the electric charge, the plurality of pixels being arranged in a first direction and a second direction intersecting the first direction; and an accumulation unit provided to be stacked on the photoelectric conversion unit on a side opposite to the one side of the substrate, the accumulation unit accumulating the signal.