Active Guard Ring Buffer for Electron Imaging Pixel Leakage
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Solution Overview
Problem
Conventional imaging circuits face challenges in reducing electron leakage due to differential voltage between pixels and guard rings, which often require increased surface leakage resistance through costly and yield-reducing post-processing techniques.
Innovation Solution
An active guard ring is implemented surrounding each pixel, with a buffer that maintains a charge potential equal to the pixel's potential, minimizing differential voltage and leakage current, and an optional ground guard ring further isolates pixels to redirect residual leakage to a ground node.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a fixed voltage guard ring is used to block charge leakage, then charge leakage between pixels is reduced, but leakage current increases due to differential voltage between pixel and guard ring
Solution Approach 1:
The guard ring voltage is changed from a fixed value to a dynamic value that tracks the pixel potential. A buffer amplifier is used to dynamically adjust the guard ring voltage to match the pixel potential, eliminating the differential voltage that causes leakage current while maintaining the charge leakage barrier function.
Solution Approach 2:
The voltage parameter of the guard ring is changed from a constant fixed voltage to a variable voltage that follows the pixel potential. This parameter change allows the guard ring to maintain both its charge blocking function and minimize leakage current by eliminating the voltage difference.
2Loss of energy
If surface leakage resistance is increased through super cleaning to reduce leakage current, then leakage current is reduced, but manufacturing complexity and cost increase
Solution Approach 1:
The mechanical/chemical approach of super cleaning the surface is replaced with an electrical approach using a buffer amplifier to actively control the guard ring voltage. This substitution eliminates the need for complex post-processing manufacturing steps while achieving the same goal of reducing leakage current.
3Loss of energy
If post processing is applied to form lengthy leakage paths to increase surface leakage resistance, then leakage current is reduced, but chip yield and cost decrease
Solution Approach 1:
The post-processing manufacturing step that creates lengthy leakage paths is replaced with an electrical solution using a buffer amplifier. This eliminates the need for additional manufacturing steps that reduce chip yield, while still achieving effective leakage current reduction through active voltage control.
4Device complexity
If a fixed voltage guard ring is used, then device complexity is low, but leakage current cannot be sufficiently reduced
Solution Approach 1:
A buffer amplifier is introduced as an intermediary device between the pixel and the guard ring. This intermediary actively controls the guard ring voltage to match the pixel potential, providing an effective solution to reduce leakage current while adding only moderate complexity through a single buffer stage.
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 effectively reduces or eliminates electron leakage between pixels, potentially eliminating the need for costly post-processing and enhancing chip yield by maintaining a zero differential voltage between pixels and guard rings.
Implementation Method 1
a buffer having an input terminal coupled to the pixel and an output terminal coupled to the active guard ring. The buffer places a charge potential on the active guard ring that is substantially equal to a charge potential on the pixel
Implementation Method 2
The ground guard ring conducts pixel leakage current to a ground node
Data Source
AI summary
A pixel accumulates charge and an active guard ring surrounds the pixel. A buffer has an input terminal coupled to the pixel and an output terminal coupled to the active guard ring. The buffer places a charge potential on the active guard ring that is substantially equal to a charge potential on the pixel. The charge leakage from the pixel is effectively reduced.