Image Sensor Metal Shield for Parasitic Light Sensitivity
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Solution Overview
Problem
Global shutter image sensors suffer from parasitic light sensitivity due to leakage charge introduced to the floating diffusion region, which affects image quality as the readout time increases, caused by diffraction and diffuse reflection of incident light.
Innovation Solution
An image sensor design incorporating a metal shield above the electrical charge storage element, with vertically extending side walls and a horizontally extending overlying layer, configured to block incident light and prevent leakage charge from reaching the floating diffusion region, thereby reducing parasitic light sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a global shutter method is used to transmit entire signal photoelectrically converted by all optical elements in one frame simultaneously, then the image signal output speed is improved, but leakage charge is introduced to the floating diffusion region due to diffraction and diffuse reflection of incident light, worsening parasitic light sensitivity
Solution Approach 1:
The harmful light paths (diffraction and diffuse reflection) are separated from the main optical path by introducing a shield structure. The shield extracts and blocks the stray light that would otherwise reach the floating diffusion region, allowing the global shutter method to maintain high output speed without the harmful side effects.
Solution Approach 2:
A shield structure is introduced as an intermediary element between the optical elements and the floating diffusion region. This shield mediates the interaction by blocking stray light paths while allowing the desired optical signals to pass through, thus preventing parasitic light sensitivity without affecting the global shutter operation.
2Reliability
If the readout time is increased to transmit charge signals, then the image signal transmission completeness is improved, but the amount of leakage charge introduced to the floating diffusion region increases proportionally, worsening the parasitic light sensitivity characteristic
Solution Approach 1:
The shield structure extracts and removes the harmful leakage charge paths from the system. By blocking the diffraction and diffuse reflection paths, the shield prevents leakage charge from being introduced during the extended readout time, allowing complete signal transmission without accumulating parasitic light effects.
Solution Approach 2:
The shield structure is positioned to preemptively block stray light paths before the light can reach the floating diffusion region. This preliminary anti-action prevents the formation of leakage charge during the readout process, allowing extended readout times to be used for complete signal transmission without the harmful side effects accumulating.
3Ease of manufacture
If no shield structure is used above the electrical charge storage element, then the manufacturing process is simpler, but light incident on the electrical charge storage element causes leakage charge that adversely affects image results
Solution Approach 1:
The shield structure uses a simple, inexpensive material ( aluminum) that can be easily deposited and patterned. Although it adds a manufacturing step, the simplicity of the material and structure makes the additional process cost-effective and manageable, while providing essential protection against leakage charge.
Solution Approach 2:
The shield structure changes the optical parameters (light blocking) in the region above the electrical charge storage element. By introducing this metallic layer, the optical properties are modified to prevent light incidence, thereby eliminating leakage charge without fundamentally changing the overall device architecture or 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 shield effectively prevents leakage charge from affecting the image sensor, improving parasitic light sensitivity and reducing dark current by ensuring reliable light blocking and insulation, while simplifying the manufacturing process.
Implementation Method 1
a shield above an electrical charge storage element in a pixel region to block light incident toward the electrical charge storage element
Data Source
AI summary
An image sensor having a shield including, for example, a metal, is above an electrical charge storage element in a pixel region to block light incident toward the electrical charge storage element, thereby making it possible to reduce or prevent reading a charge value including leakage charge introduced to the electrical charge storage element, and thus adversely affecting an image result.