3D Stacked Image Sensor Crosstalk Reduction
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Solution Overview
Problem
As CMOS image sensors become more highly integrated, the reduction in photodiode size leads to decreased charge generation and increased crosstalk between pixels, causing errors in image data due to reduced horizontal area and interference.
Innovation Solution
The solution involves a multi-layered structure with a first substrate containing driving elements and a second substrate with a photoelectric conversion element, connected by a conductive connector that penetrates through oxide layers, allowing for shared floating diffusion regions and reduced crosstalk, and includes a method of manufacturing where sacrificial layers are used to form contact holes and deposit conductive material.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the photodiode horizontal area is reduced to increase integration density, then more pixels can be included in the sensor, but the number of charges generated decreases and crosstalk between pixels increases
Solution Approach 1:
The patent transitions from a planar pixel structure to a three-dimensional stacked structure with multiple substrates. The photodiode is placed on a first substrate while driving elements are placed on a second substrate, vertically stacking functional components to increase integration density without reducing photodiode area, thereby maintaining charge generation capability while reducing crosstalk.
Solution Approach 2:
The pixel structure is segmented into multiple independent substrates: the first substrate contains the photodiode for charge generation, while the second substrate contains driving elements. This segmentation allows each substrate to be optimized independently and connected through vertical connections, resolving the trade-off between integration density and image quality.
2Productivity
If the photodiode horizontal area is reduced, then integration density increases, but crosstalk between neighboring pixels increases
Solution Approach 1:
By moving driving elements to a separate second substrate and connecting them vertically to the photodiode on the first substrate, the patent eliminates lateral interference between pixels. The vertical connection path isolates each pixel's signal path, preventing crosstalk while maintaining high integration density through the stacked architecture.
3Reliability
If conductive materials are exposed on substrate surfaces for connection, then electrical connectivity is achieved, but adhesion between substrates is weakened
Solution Approach 1:
The patent introduces oxide layers as intermediary materials between the substrate surfaces. These oxide layers serve dual functions: providing adequate electrical connectivity through the connector structures while simultaneously acting as adhesion promoters that strengthen the bond between substrates, eliminating the trade-off between connectivity and adhesion.
Solution Approach 2:
The connection structure uses composite material layers including oxide layers and conductive materials in specific configurations. The oxide layers provide both electrical properties and adhesive properties, while conductive materials provide electrical connectivity, creating a composite structure that achieves both adhesion and electrical connectivity simultaneously.
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 configuration enhances image sensor performance by reducing crosstalk and increasing charge transfer efficiency, enabling higher integration density without errors, and allows for a more robust adhesion process using oxide layers without exposing conductive materials.
Implementation Method 1
a surface of the second oxide layer is adhered to an upper surface of the first oxide layer
Data Source
AI summary
An image sensor includes a first substrate including a driving element, a first insulation layer on the first substrate and on the driving element, a second substrate including a photoelectric conversion element, and a second insulation layer on the second substrate and on the photoelectric conversion element. A surface of the second insulation layer is on an upper surface of the first insulation layer. The image sensor includes a conductive connector penetrating the second insulation layer and a portion of the first insulation layer. Methods of forming image sensors are also disclosed.