Pixel Array Layout With Optical Waveguides for Higher Image Sensor Sensitivity
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Solution Overview
Problem
In solid-state imaging devices, the reduction in pixel size leads to difficulties in efficiently transmitting incident light to photoelectric converting units, resulting in lowered sensitivity due to increased light propagation loss and non-effective regions caused by overlapping color filters.
Innovation Solution
A solid-state imaging device is designed with photodiodes formed separately for each pixel on a semiconductor substrate, along with a signal reading unit, an insulating film with optical waveguides, color filters, and on-chip lenses. The color filters are arranged in specific combinations to minimize overlapping and maximize light collection efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If pixel size is reduced to increase pixel density, then productivity is improved, but light transmission efficiency deteriorates due to increased light propagation loss
Solution Approach 1:
An optical waveguide is introduced as an intermediary structure between the color filter and the photodiode. This waveguide acts as a light-guiding medium that efficiently transmits incident light to the photodiode, overcoming the light propagation loss that occurs when pixel size is reduced. The waveguide serves as a mediator that maintains light transmission efficiency despite the reduced pixel dimensions.
Solution Approach 2:
The optical waveguide extends the light transmission path in the vertical dimension (depth) rather than relying solely on horizontal/planar transmission. By utilizing the vertical dimension through the insulating film layer, the system achieves efficient light guidance to the photodiode even when pixel area is reduced, effectively adding a dimensional solution to the light transmission problem.
2Device complexity
If conventional Bayer arrangement is used with overlapping color filters, then device complexity is reduced, but sensitivity deteriorates due to non-effective regions caused by filter overlap
Solution Approach 1:
The patent introduces asymmetry in the color filter arrangement by creating a green pixel cluster (2x2 green pixels) adjacent to a single red pixel and a single blue pixel. This asymmetric layout prevents the overlapping issues inherent in symmetric Bayer arrangements while maintaining manufacturing simplicity. The asymmetric design ensures that color filters for adjacent pixels of different colors do not overlap, eliminating non-effective regions.
Solution Approach 2:
The pixel array is segmented into distinct clusters: green pixel clusters (2x2 arrangements) and single red/blue pixels. This segmentation allows for optimized color filter placement within each segment, preventing overlap between different color filters while maintaining overall array functionality. The segmentation strategy resolves the contradiction by organizing pixels into functional groups with specific filter arrangements.
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 proposed solution reduces the area of non-effective regions and enhances sensitivity by minimizing color filter overlap and optimizing light transmission through larger optical waveguide openings, particularly improving the sensitivity of green pixels which have high sensitivity for human vision.
Implementation Method 1
an optical waveguide was provided above a light sensing unit and below an on-chip lens (OCL) in one pixel in order to reduce a light propagation loss
Implementation Method 2
pixels having photodiodes on the light sensing surfaces thereof
Data Source
AI summary
A solid-state imaging device includes a semiconductor substrate; and a pixel unit having a plurality of pixels on the semiconductor substrate, wherein the pixel unit includes first pixel groups having two or more pixels and second pixel groups being different from the first pixel groups, wherein a portion of the pixels in the first pixel groups and a portion of the pixels in the second pixel groups share a floating diffusion element.