Stacked Pixel Circuit Layout for High Dynamic Range Image Sensors
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Solution Overview
Problem
Current image sensors face challenges in increasing integration density and performance due to the limitations in forming elements within pixels, particularly in efficiently managing electric charges and achieving high dynamic range.
Innovation Solution
The image sensor design involves forming elements such as transfer transistors and floating diffusions on one substrate and other necessary transistors on a different substrate, allowing for independent control of impurity regions and improved charge accumulation, enabling enhanced performance and dynamic range through the use of multiple substrates and a logic circuit for coordinated control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If all pixel circuit elements are integrated on a single substrate with photodiodes, then device complexity is reduced, but integration density and manufacturing flexibility are limited
Solution Approach 1:
The pixel circuit elements are divided into two groups: transfer transistors (first and second transfer transistors) are formed on the first substrate with the photodiode, while other circuit elements (reset transistors, amplifier transistor, select transistor) are formed on a second substrate. This segmentation allows each substrate to be optimized independently, increasing overall integration density while managing device complexity.
Solution Approach 2:
The patent transitions from a single-substrate two-dimensional layout to a multi-substrate three-dimensional stacked architecture. By stacking the first substrate (containing photodiodes and transfer transistors) with the second substrate (containing other pixel circuit elements), the design utilizes the vertical dimension to increase integration density without increasing the planar footprint.
2Device complexity
If multiple transistors are integrated on the same substrate as photodiodes, then device complexity decreases, but manufacturing precision and performance optimization are compromised
Solution Approach 1:
By segmenting the pixel circuit into two separate substrates, each substrate can be manufactured and optimized independently with specialized processes. The first substrate can be optimized for photodiode and transfer transistor formation, while the second substrate can be optimized for other transistor types, thereby improving manufacturing precision for each element type.
Solution Approach 2:
The patent introduces intermediate connection structures (contact holes, conductive plugs) that mediate the electrical connection between elements on the first substrate and elements on the second substrate. This intermediary approach allows precise alignment and connection while maintaining independent optimization of each substrate's manufacturing process.
3Area of moving object
If charge accumulation regions are closely integrated with photodiodes, then area is reduced, but charge management and dynamic range are limited
Solution Approach 1:
The charge accumulation regions (floating diffusion regions) are moved from the planar layout on the first substrate to the second substrate in the vertical dimension. This spatial separation in three-dimensional space allows adequate isolation and management of charge accumulation while maintaining compact pixel area through vertical stacking.
Solution Approach 2:
The transfer transistors formed on the first substrate act as intermediaries that control the transfer of charges from the photodiode to the floating diffusion regions on the second substrate. This intermediary control mechanism enables precise charge management and improves dynamic range by allowing complete charge transfer while maintaining compact pixel area.
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 increases the dynamic range and improves image quality by allowing for more efficient charge handling and separate control of impurity regions, addressing the limitations of traditional image sensor designs.
Implementation Method 1
Each of the pixels may include a photodiode and a pixel circuit for converting electric charges generated by the photodiode into an electric signal
Data Source
AI summary
An image sensor including: a first layer including a plurality of photodiodes arranged in a plurality of pixel regions in a first substrate, an optical region disposed on an upper surface of the first substrate, and an element region, wherein, in at least one of the plurality of pixel regions, the element region includes a first impurity region, a first transfer gate disposed between the first impurity region and the photodiode, a second impurity region isolated from the first impurity region, and a second transfer gate disposed between the second impurity region and the photodiode: and a second layer including a second substrate stacked with the first layer, wherein the second layer includes a first transistor connected to the first impurity region by a first contact, and a second transistor connected to the second impurity region by a second contact.