Gradient Color Filter for Solid-State Image Sensor
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Solution Overview
Problem
Conventional solid-state image sensors face challenges in reducing light sensitivity degradation and color mixing between neighboring pixels due to miniaturization, which leads to issues like color density differences, flicker, and color shading, as the cross-sectional shape of color filters is not always optimized for vertical cuts and alignment with micro-lenses.
Innovation Solution
The solution involves forming color filters with a thickness that is greater at the center than at the periphery, allowing for a trapezoidal, step-like, or convex lens cross-sectional shape, and using a grey-tone mask to adjust the exposure and development of color filter resist to ensure proper alignment and reduced color mixing, even when micro-lenses and color filters are not perfectly aligned.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the color filter is made thinner to reduce the distance between the semiconductor substrate and the transparent flattening film, then the exit pupil distance is shortened and cell miniaturization is achieved, but light sensitivity degrades and color mixing occurs between neighboring pixels
Solution Approach 1:
The color filter is designed with non-uniform thickness distribution, being thicker at the center and thinner at the periphery. This local quality variation allows the center region to maintain optical density for accurate color filtering while the periphery reduces light blocking to minimize color mixing between adjacent pixels, thus resolving the contradiction between miniaturization and light sensitivity maintenance.
Solution Approach 2:
The invention changes the thickness parameter of the color filter from uniform to gradient distribution. By controlling the thickness parameter to vary spatially (thicker centrally, thinner peripherally), the filter achieves both miniaturization compatibility and maintained light sensitivity, preventing color mixing while enabling compact pixel cell design.
2Object-affected harmful factors
If the color filter is made thinner to reduce color mixing, then the distance between layers is reduced, but the trapezoidal shape causes oblique incident light to pass through the edge of neighboring color filters, increasing color mixing
Solution Approach 1:
The color filter employs local quality variation with different thicknesses in different regions. The central region has greater thickness to provide strong color filtering, while the peripheral region has reduced thickness to allow oblique light to pass through without significant color mixing, thus maintaining spectral characteristics while reducing harmful color mixing effects.
3Ease of manufacture
If conventional color filter formation methods are used with vertical cuts, then manufacturing is simplified, but alignment margin decreases with miniaturization, causing color mixing when micro-lenses and color filters are not properly aligned
Solution Approach 1:
The color filter is designed with non-uniform thickness distribution, being thicker at the center and thinner at the periphery. This local quality variation provides tolerance to alignment errors between micro-lenses and color filters, as the thicker central region ensures proper color filtering even with slight misalignment, while the thinner periphery reduces color mixing from oblique light.
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
This approach effectively reduces color mixing, improves color density uniformity, minimizes flicker, and enhances light sensitivity by ensuring that oblique light is less affected by neighboring color filters, thereby maintaining high image quality without compromising miniaturization levels.
Implementation Method 1
a color filter formed on the photoelectric conversion element... oblique incident light passes through the edge of the color filter of the neighboring pixel
Implementation Method 2
each cell including a photo-electric conversion element formed on a semiconductor substrate
Implementation Method 3
a micro-lens formed on the color filter... increase an amount of oblique light received by the photodiode
Data Source
AI summary
A solid-state image sensor having unit pixel cells arranged in a matrix form, each unit pixel cell having a photoelectric conversion element formed on a semiconductor substrate, a color filter formed on the photoelectric conversion element and a micro-lens formed on the color filter, where a thickness of the color filter is greater in the center than in the periphery. Further, the color filters adjoin in vertical and horizontal directions in the arrangement of the unit pixel cells. A cross-sectional shape of the color filter is, for example, triangular, trapezoidal, convex, lens-shaped or semielliptic.