Stacked Image Sensor Layout for Per-Pixel Exposure Control
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Solution Overview
Problem
Conventional image sensors with stacked chips require two transfer pulse power supplies for each pixel to control exposure amounts individually, which can occupy a large area and reduce the fill factor of the photodiode.
Innovation Solution
The image sensor design separates the power supply units for controlling the transfer signal and reset signal between two semiconductor substrates, allowing for independent control of exposure times for each pixel without occupying space near the photodiode, thus improving the fill factor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If two transfer pulse power supplies are provided for each pixel to individually control exposure amounts, then individual exposure control is achieved, but the area occupied increases and fill factor decreases
Solution Approach 1:
The patent moves the transfer pulse power supplies from the first semiconductor substrate (where pixels are located) to a second semiconductor substrate. This spatial relocation to another dimension/layer allows individual exposure control functionality to be maintained while freeing up area on the pixel substrate, thereby improving the fill factor of photodiodes.
Solution Approach 2:
The patent divides the image sensor into two separate semiconductor substrates: one dedicated to pixel functions (photoelectric conversion, accumulation, transfer) and another dedicated to power supply functions (transfer pulse power supplies, reset power supplies). This segmentation allows each substrate to be optimized independently, with the pixel substrate having maximum area available for light-sensitive elements.
2Measurement precision
If power supply units are integrated near the photodiode for individual pixel control, then control precision is improved, but the fill factor of the photodiode is reduced
Solution Approach 1:
The patent relocates power supply units from the same plane as photodiodes to a separate second semiconductor substrate, maintaining precise control capability while eliminating area occupation on the photodiode layer, thus preserving maximum fill factor.
Solution Approach 2:
The patent introduces a second semiconductor substrate as an intermediary layer that houses the power supply units. This intermediary structure enables the power supplies to serve the pixels on the first substrate without physically occupying space near the photodiodes, resolving the conflict between control precision and fill factor.
3Adaptability or versatility
If multiple power supplies are provided on the same substrate, then control functionality is enhanced, but device complexity increases
Solution Approach 1:
The patent segments the device into two specialized substrates: one for pixel operations and another for power supply operations. This segmentation reduces the complexity of each individual substrate while maintaining enhanced control functionality through the coordinated interaction of the two substrates.
Solution Approach 2:
By moving power supply units to a second semiconductor substrate, the patent distributes complexity across multiple layers/dimensions rather than concentrating it on a single substrate. This dimensional distribution simplifies the design and manufacturing of each individual substrate while preserving the sophisticated control capabilities.
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 design enables reliable control of the transfer transistor to prevent dark current increase, improves the fill factor of the photodiode, and allows for extended dynamic range by varying exposure times for different pixels.
Implementation Method 1
a pixel, including a photodiode that photoelectrically converts incident light to generate an electric charge
Data Source
AI summary
An image sensor includes a first semiconductor substrate provided with a pixel, including a photoelectric conversion unit that photoelectrically converts incident light to generate an electric charge, an accumulation unit that accumulates the electric charge generated by the photoelectric conversion unit, and a transfer unit that transfers the electric charge generated by the photoelectric conversion unit to the accumulation unit, and a second semiconductor substrate provided with a supply unit for the pixel, the supply unit supplying the transfer unit with a transfer signal to transfer the electric charge from the photoelectric conversion unit to the accumulation unit.