CMOS Image Sensor Protection Structure for Plasma Charge Damage
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Solution Overview
Problem
CMOS image sensing devices face challenges during plasma processes, where electric charges accumulate at transistor gates, leading to altered electrical characteristics and potential damage, and existing protection devices may restrict operating voltages and affect sensing operations due to insufficient breakdown voltage.
Innovation Solution
The implementation of a protection device with a specific doping structure, including regions doped with P-type and N-type impurities, and a shallow trench isolation structure, which effectively directs excess electric charges away from the transistor gates during plasma processes without affecting the device's operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a protection device is added to remove electric charges from transistor gates during plasma processes, then transistor reliability is improved, but device complexity increases
Solution Approach 1:
The protection device is nested within the existing transistor structure by forming P-type and N-type doped regions that surround and integrate with the transistor gate, allowing charge removal functionality to be embedded without adding separate external components
Solution Approach 2:
The protection device merges the charge removal function with the transistor structure by combining P-type doped regions (for charge extraction) and N-type doped regions (for electrical connection) into a unified structure that works alongside the transistor gate
2Ease of operation
If the protection device has high breakdown voltage to avoid affecting transistor operation, then transistor operation is preserved, but manufacturing precision requirements increase
Solution Approach 1:
Different regions of the protection device have different doping densities optimized for their specific functions: the P-type region has high doping density for effective charge extraction, while the N-type region has lower doping density to achieve high breakdown voltage and prevent affecting transistor operation
Solution Approach 2:
The doping density parameter is varied across different regions of the protection device, with the P-type region using higher doping density for charge removal and the N-type region using lower doping density for high breakdown voltage, allowing both functions to coexist
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 solution effectively protects transistors from plasma-induced damage while maintaining the device's operational integrity by ensuring high breakdown voltage and preventing leakage currents, thus ensuring reliable image sensing performance.
Implementation Method 1
the protection device has a high breakdown voltage, such that the protection device does not affect the operation of the protected transistor
Data Source
AI summary
An image sensing device comprising a plurality of unit photosensing pixels to convert light into electrical signals, each unit photosensing pixel including a photosensor and a plurality of transistors to perform operations associated with the photosensor and a plurality of protection devices, each of which is coupled to any one of the plurality of transistors, wherein each of the plurality of protection devices includes a first region doped with a first type of conductive impurities, a second region doped with a second type of conductive impurities and surrounding the first region, and a third region doped with the first type of conductive impurities and surrounding the second region, wherein the first region includes a contact portion and a first well located below the contact portion, and wherein the contact portion has a higher doping density than the first well, and is coupled to any one of the plurality of transistors.