Super-conformal Micro-lens Coating for CMOS Image Sensors
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Solution Overview
Problem
Conventional CMOS image sensors face performance degradation due to light reflection at the air-micro-lens interface and non-conformal coating issues, which reduce fill factor and can damage micro-lenses during fabrication processes.
Innovation Solution
A super-conformal micro-lens coating using a flowable oxide material like spin-on glass with a refractive index between that of air and the micro-lens material, applied in a downward orientation to form a coating that conforms closely to the micro-lens shape, reducing light reflection and enhancing image sensing performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a conventional coating is applied to the micro-lens array, then light reflection is reduced, but the coating extends non-conformally over gaps between micro-lenses, filling gaps with a U-shape profile and degrading image sensing performance
Solution Approach 1:
The substrate is inverted (flipped upside down) during the coating process. This inversion allows the coating material to be deposited in a manner that conforms to the micro-lens surface without extending into the gaps between lenses. After coating, the substrate is inverted back to its original orientation, achieving conformal coating while preventing gap filling that would otherwise occur with conventional coating approaches.
Solution Approach 2:
The substrate is inverted before the coating process begins, preparing the surface in an optimal orientation for conformal coating deposition. This preliminary action ensures that when the coating material is applied, it naturally conforms to the micro-lens geometry without requiring complex coating process adjustments or specialized equipment.
2Reliability
If micro-lenses are formed on the substrate, then light focusing capability is improved, but micro-lenses can be damaged in subsequent fabrication processes such as cleaning operations
Solution Approach 1:
A coating layer is applied to the micro-lens array before subsequent fabrication processes. This coating acts as a protective cushion that prevents damage to the micro-lenses during cleaning operations and other fabrication steps. The coating absorbs mechanical stresses and chemical exposures, protecting the fragile micro-lens structures while allowing them to maintain their optical functionality.
3Area of stationary object
If the fill factor is increased by reducing gaps between micro-lenses, then light capture area is improved, but micro-lenses tend to outgas and contaminate subsequent fabrication processes
Solution Approach 1:
A coating layer is introduced as an intermediary between the micro-lens array and the fabrication environment. This coating acts as a barrier that prevents outgassing from the micro-lenses from contaminating subsequent fabrication processes. The coating material is selected to be stable and non-outgassing, effectively isolating the micro-lens materials from the fabrication environment while allowing the micro-lenses to maintain their light-focusing function.
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 super-conformal coating effectively reduces light reflection, increases the fill factor, and prevents micro-lens damage during subsequent fabrication processes, thereby improving the overall performance and reliability of CMOS image sensors.
Implementation Method 1
Because of the refractive index difference between air and micro-lens 125, when light shines on image sensors, certain amount of the illumination is reflected at the surface of micro-lens 125. As it is hard to change the micro-lens material, reducing light reflection may be achieved by adding between the air and the micro-lens a coating layer 150 whose refractive index is between that of air and that of the micro-lens.
Data Source
AI summary
Techniques and architectures for providing a coating for one or more micro-lenses of a pixel array. In an embodiment, a pixel element includes a micro-lens and a coating portion extending over a surface of the micro-lens, where a profile of the coating portion is super-conformal to, or at least conformal to, a profile of the micro-lens. In another embodiment, the coating portion is formed at least in part by orienting the surface of the micro-lens to face generally downward with the direction of gravity, the orienting to allow a fluid coating material to flow for formation of the coating portion.