CMOS Image Sensor Light Shield ESD Current Shunting
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional ESD buses in image sensor arrays have high resistance, leading to increased die size and cost, which can result in damage to the image sensor and other devices due to excessive ESD current shunting through sensitive areas.
Innovation Solution
A light shield with a large surface area is integrated to direct ESD current away from the image sensor device, connected to the ESD ground bus and bond pads, reducing the overall resistance of the ESD bus without increasing the die size, by using a parallel connection with the ESD ground bus.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a wide metal bus is used to achieve low ESD bus resistance, then the ESD protection capability is improved, but the die size increases leading to higher per die cost
Solution Approach 1:
The patent combines the light shield structure with the ESD bus function, merging two separate components (light shielding and ESD protection) into a single integrated structure. The light shield is configured to serve dual purposes: blocking stray light from reaching the image sensor and providing a low-resistance ESD current path to ground, thereby achieving both light shielding and ESD protection without increasing die size
Solution Approach 2:
The light shield is designed to perform multiple functions simultaneously: it acts as both a light-blocking element and an ESD bus. By making the light shield electrically conductive and connecting it to ground, it provides ESD protection while maintaining its primary light shielding function, thus achieving multi-functionality without requiring additional dedicated ESD bus structures
2Reliability
If a wide metal bus is used to achieve low ESD bus resistance, then the ESD current shunting capability is improved, but the number of die per wafer decreases
Solution Approach 1:
The patent merges the ESD bus function with the light shield structure, eliminating the need for separate wide metal bus structures. The light shield itself serves as the ESD current path, allowing effective ESD protection while maintaining a compact layout that maximizes the number of die that can be produced per wafer
3Reliability
If the ESD bus resistance is reduced, then the ESD protection effectiveness is improved, but the manufacturing complexity increases
Solution Approach 1:
The patent combines ESD protection functionality with the existing light shield structure, eliminating the need for separate ESD bus manufacturing steps. The light shield is formed using the same fabrication processes as the light shielding layer, and electrical connections are established through standard connection methods, thereby achieving low ESD resistance without adding significant manufacturing complexity
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
The solution effectively reduces ESD bus resistance to less than 1Ω, preventing damage to the image sensor device by shunting ESD current safely to ground, while maintaining the die size and reducing manufacturing costs.
Implementation Method 1
the light shield being configured to block light from being detected by the image sensor device
Implementation Method 2
the light shield having an electrical connection to the bond pad... directing ESD current away from the image sensor device
Data Source
AI summary
Techniques of drawing ESD current away from an image sensor device of a CMOS image sensor die include using a light shield configured to block light from an image sensor device. The light shield may be used to draw the ESD current away when it has an electrical connection to an ESD ground bus and/or to a bond pad of the CMOS image sensor die. Advantageously, the light shield has a low resistance due to its large surface area. Accordingly, parallel connections to the bond pads and/or ESD bus have a resistance close to the low resistance of the light shield without altering the size of the die.