Stacked Image Sensor Pixel Isolation and Charge Transfer
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Solution Overview
Problem
Conventional stacked-structure image sensors face challenges in increasing pixel density while maintaining sensitivity and reducing optical and electrical crosstalk, as well as improving fill factor.
Innovation Solution
The implementation of a deep trench isolation method using through vias and vertical transfer gates, with insulating layers on inner side walls to block light and charge leakage between pixels, and alternative placement of these structures around the light-receiving area to enhance signal precision and fill factor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the number of pixels is increased in stacked-structure image sensors, then pixel density improves, but optical and electrical crosstalk between adjacent pixels worsens
Solution Approach 1:
The patent divides the pixel structure into multiple stacked layers (first and second light sensing elements at different depths) and introduces deep trench isolation structures that segment the pixel region into isolated units. This segmentation prevents charge carriers and light from crossing between adjacent pixels while maintaining high pixel density through the vertical stacking arrangement.
Solution Approach 2:
The patent introduces deep trench isolation structures filled with insulating material as intermediary elements between adjacent pixels. These isolation trenches act as mediators that block both optical paths and electrical charge flow between neighboring pixels, thereby eliminating crosstalk while allowing pixels to be closely packed for high density.
2Quantity of substance
If the number of pixels is increased, then pixel density improves, but sensitivity of individual pixels deteriorates
Solution Approach 1:
The patent transitions from a conventional two-dimensional pixel arrangement to a three-dimensional stacked structure with light sensing elements at multiple depths. This dimensional change allows pixels to be closely packed in the horizontal plane (increasing density) while each pixel maintains a large light-receiving area across multiple layers (preserving sensitivity).
Solution Approach 2:
The patent segments the light sensing function across multiple stacked layers, with each layer containing light sensing elements that can be independently optimized. This segmentation allows each pixel to capture light from multiple depths, maintaining high sensitivity while enabling closer horizontal spacing of pixels.
3Ease of manufacture
If through vias and vertical transfer gates are placed within the light-receiving area, then charge transfer is enabled, but the light-receiving area is reduced
Solution Approach 1:
Instead of placing the deep trench isolation structures (containing through vias and transfer gates) within the light-receiving area as in conventional designs, the patent inverts the approach by positioning these structures in the peripheral regions surrounding the light-receiving area. This inversion allows the light-receiving area to be maximized while charge transfer functionality is preserved through the peripheral trenches.
Solution Approach 2:
The patent creates multiple copies of the deep trench isolation structure arranged in peripheral patterns around each pixel's light-receiving area. These replicated peripheral trenches collectively provide comprehensive charge transfer pathways without encroaching on the central light-receiving region, thereby maintaining both transfer capability and maximum light reception.
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 allows for increased pixel density with maintained sensitivity, reduced optical and electrical crosstalk, and improved fill factor by effectively isolating adjacent pixels and optimizing the light-receiving area.
Implementation Method 1
forming an insulating layer in inner side walls of the through via to block inflow of light from adjacent pixels
Implementation Method 2
blocking leakage of light introduced into a corresponding pixel into pixels adjacent thereto
Implementation Method 3
blocking a flow of charges between pixels so as to suppress electrical crosstalk
Data Source
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AI summary
An image sensor includes a plurality of pixels, each pixel including a light sensing structure including first, second and third light sensing elements sequentially stacked on a substrate, the light sensing structure having a first surface adjacent to a readout circuit and a second surface including a light receiving portion between first and second circumferential portions, a first through via on the first circumferential portion, extending from the first surface to connect with the first light sensing element, and configured to transfer charges of the first light sensing element to the readout circuit, and a vertical transfer gate on a second circumferential portion and configured to transfer charges of the second light sensing element to the readout circuit, the first through via and the vertical transfer gate of each pixel being arranged in a 1-shaped or L-shaped pattern in the first and second circumferential portions.