Global Shutter Image Sensor Light Guide and Shield Structures
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Solution Overview
Problem
Conventional image sensors, especially those operating in global shutter mode, suffer from reduced quantum efficiency and image artifacts due to parasitic light scattering and diffraction into storage nodes, which limits their performance, particularly in low-light conditions.
Innovation Solution
Incorporating light guide structures and light shield structures in image sensors to funnel light away from storage nodes and block stray light, with light guide structures formed from materials with a higher refractive index than the dielectric material and light shields having anti-reflective coatings to prevent light from entering storage nodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional frontside or backside illuminated image pixels are used, then the device can operate with a simple single-pass light path, but quantum efficiency is reduced and image artifacts occur due to parasitic light scattering into storage nodes
Solution Approach 1:
The light path is segmented into distinct regions: a light guide structure that directs light to the photodiode, a light shield structure that blocks light from storage nodes, and a color filter structure. This segmentation prevents parasitic light from reaching storage nodes while maintaining efficient light collection, resolving the contradiction between quantum efficiency and preventing image artifacts
Solution Approach 2:
Light guide and light shield structures are introduced as intermediary elements between the lens and the photodiode/storage nodes. These intermediaries actively manage light distribution, guiding useful light to photodiodes while blocking parasitic light from storage nodes, thereby improving quantum efficiency without causing image artifacts
2Productivity
If light guide structures with higher refractive index materials are implemented, then light funneling efficiency improves, but manufacturing complexity increases
Solution Approach 1:
The refractive index parameter of the light guide material is changed to be higher than the surrounding dielectric material. This parameter change enables effective light funneling through total internal reflection at the interfaces, improving light collection efficiency. The fabrication process incorporates this parameter change by selecting appropriate materials during manufacturing
3Object-affected harmful factors
If light shields with anti-reflective coatings are added, then parasitic light blocking improves, but device complexity and manufacturing steps increase
Solution Approach 1:
Anti-reflective coatings are applied to light shield structures to change their optical properties. These coatings reduce reflection and absorption of parasitic light, enhancing the light blocking effectiveness. The coatings are integrated into the manufacturing process as additional fabrication steps, improving parasitic light rejection while maintaining manufacturability
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
Enhances the efficiency of global shutter image pixels by reducing parasitic light, minimizing image artifacts such as vertical shading and moving object smear, and improving overall low-light imaging performance.
Implementation Method 1
light guide structures formed from materials with a higher refractive index than the dielectric material
Implementation Method 2
light shields having anti-reflective coatings to prevent light from entering storage nodes
Data Source
AI summary
An image sensor operable in global shutter mode may include an array of image pixels. Each image pixel may include a photodiode for detecting incoming light and a separate storage diode for temporarily storing charge. To maximize the efficiency of the image pixel array, image pixels may include light guide structures and light shield structures. The light guide structures may be used to funnel light away from the storage node and into the photodiode, while the light shield structures may be formed over storage nodes to block light from entering the storage nodes. The light guide structures may fill cone-shaped cavities in a dielectric layer, or the light guide structures may form sidewalls having a ring-shaped horizontal cross section. Metal interconnect structures in the dielectric layer may be arranged in concentric annular structures to form a near-field diffractive element that funnels light towards the appropriate photodiode.