CMOS Image Sensor Auxiliary Lens Refraction
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Solution Overview
Problem
Current CMOS image devices face limitations in light collection efficiency due to the precise control challenges in forming inner lenses, which can result in suboptimal curvature and size, affecting their ability to collect light from oblique angles.
Innovation Solution
A CMOS image device design that includes an auxiliary lens with the same refractive index as the inner lens, positioned on the surface of the inner lens, to compensate for its size and curvature, along with a micro-lens offset from the inner lens to enhance light collection efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an inner lens is formed by dry-etching a passivation layer, then the light collection efficiency is improved, but the manufacturing precision deteriorates due to time-dependent etching processes
Solution Approach 1:
A curvature control layer is introduced as an intermediary between the passivation layer and the photosensitive pattern. This layer acts as a mediator that defines the curvature radius of the inner lens through its thickness, decoupling the etching time from the final lens geometry. The etching process etches through the passivation layer to expose the curvature control layer, which then serves as a template for the inner lens curvature, eliminating the need for precise time control.
Solution Approach 2:
The invention changes the controlling parameter for inner lens curvature from etching time to layer thickness. By controlling the thickness of the curvature control layer during deposition rather than during etching, the curvature radius becomes a function of deposited material quantity rather than etching duration, significantly improving manufacturing precision and reducing process variability.
2Ease of manufacture
If the passivation layer is underetched, then the manufacturing process is simpler, but the inner lens cannot have the desired curvature radius
Solution Approach 1:
The curvature control layer is formed in advance with a predetermined thickness that corresponds to the desired inner lens curvature radius. This preliminary action sets the geometric template before the etching process begins, allowing the etching to proceed without precise time control while still achieving the correct curvature. The layer thickness is pre-calculated and deposited to match the target lens specifications.
3Productivity
If the passivation layer is overetched, then the etching process is more aggressive, but the inner lens is reduced in size and cannot function properly
Solution Approach 1:
The curvature control layer serves as a cushioning layer that protects against overetching. By designing the layer thickness to be greater than the minimum required for the desired curvature, a margin of safety is built in. The etching process can proceed more aggressively without risking lens size reduction, as the extra thickness compensates for variability in the etching process, ensuring the inner lens maintains its functional dimensions.
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 auxiliary lens improves the light collection efficiency by reducing the area where light is not collected, thereby enhancing the overall performance of the CMOS image device.
Implementation Method 1
an auxiliary lens formed on the inner lens, wherein the auxiliary lens has a same index of refraction as the inner lens
Data Source
AI summary
A CMOS image device comprises a semiconductor substrate having a photo diode region formed therein, an inner lens formed at a position corresponding to the photo diode region on the semiconductor substrate, and an auxiliary lens formed on the inner lens along a surface of the inner lens, wherein the auxiliary lens has a same index of refraction as the inner lens.