Flat Microlenses for Solid-State Imaging Light Sensitivity
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Solution Overview
Problem
Solid-state imaging devices with small pixel sizes rely on semi-spherical microlenses to focus light, which are inefficient for larger pixel sizes, leading to reduced light sensitivity due to smaller effective photoelectric conversion areas.
Innovation Solution
The development of solid-state imaging devices with microlenses having a flat top surface, fabricated using a semiconductor substrate, color filter layer, lens material layer, and hard mask processes, allowing for increased light focus and sensitivity by aligning the flat microlens surface with the photoelectric conversion element, enhancing light gathering capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If semi-spherical microlenses are used for small pixel sizes, then light focusing is effective, but for large pixel sizes the effective photoelectric conversion area is reduced leading to reduced light sensitivity
Solution Approach 1:
The invention changes the geometric parameters of the microlens from a semi-spherical shape to a flat-top shape with specific dimensional relationships. The flat top surface has a diameter that is 0.6 to 0.8 times the outer diameter of the microlens, and the height is 0.2 to 0.4 times the outer diameter. This parameter change allows the microlens to effectively focus light onto large photoelectric conversion elements while maintaining compact dimensions, thereby improving light sensitivity for large pixel sizes.
2Area of stationary object
If the microlens focuses light to a small focal point, then small pixel sizes are accommodated, but large pixel sizes cannot utilize the full light gathering capability
Solution Approach 1:
The invention applies local quality by creating a flat top surface region on the microlens that is optically distinct from the curved outer portion. The flat top surface with diameter 0.6 to 0.8 times the outer diameter creates a specific optical zone that focuses light over a larger area matching the photoelectric conversion element, while the curved outer portion maintains the overall lens structure. This local differentiation optimizes light distribution for large pixel areas.
3Ease of manufacture
If conventional semi-spherical microlenses are used, then fabrication is straightforward, but light sensitivity for large pixels is reduced
Solution Approach 1:
The invention modifies the traditional spherical shape by introducing a flat top surface, creating a composite curvature profile. The microlens maintains a curved outer surface for structural integrity and light collection, while the flat top surface with controlled dimensions (0.6 to 0.8 times outer diameter) provides optimized light focusing. This modified spheroidality achieves both manufacturability through standard processes and improved optical performance for large pixels.
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 flat top surface microlenses effectively focus incident light onto a larger area of the photoelectric conversion element, increasing the amount of light received and thus enhancing the sensitivity of solid-state imaging devices, particularly those with large pixel sizes greater than 8 μm.
Implementation Method 1
Each microlens element of a microlens array is aligned with a corresponding photodiode in each pixel. In general, a microlens element is a condensing lens with a semi-spherical shape which is used to focus incident light upon the photodiode at a focus point.
Implementation Method 2
Through the flat top surface of the microlenses, incident light can be focused in a big focal point that is substantially equal to the area of a photoelectric conversion element in one pixel.
Data Source
AI summary
A solid-state imaging device having flat microlenses is provided. The solid-state imaging device includes a semiconductor substrate having a plurality of photoelectric conversion elements. The solid-state imaging device further includes a color filter layer disposed above the semiconductor substrate. The solid-state imaging device also includes a microlens having a flat top surface disposed on the color filter layer. The flat top surface of the microlens is directly above the photoelectric conversion element, and the area of the flat top surface of the microlens is equal to the area of the photoelectric conversion element.