3D Stacked Photodiode Array Eliminates Color Filters
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Solution Overview
Problem
Conventional image sensor technologies face challenges in achieving optimal color accuracy and image resolution due to limitations in color filter arrays, sensitivity, and manufacturing yield, particularly with three-color filters and the need for optical losses, which also affect dynamic range and photon availability.
Innovation Solution
A three-dimensional array of 1-bit light receptors is used, where the depth within a silicon substrate determines the wavelength absorption, allowing for wavelength-dependent detection without color filters, enabling improved sensitivity and dynamic range by optimizing receptor size and placement based on absorption properties and chief ray angle considerations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If color filter arrays are used for multi-color detection, then color separation is achieved, but optical losses occur and sensitivity is reduced
Solution Approach 1:
The patent transitions from two-dimensional color filter arrays to a three-dimensional stacked photodiode structure. Multiple photodiodes are stacked vertically at the same pixel location, with each photodiode having different thickness to detect different wavelengths. This vertical stacking approach eliminates the need for color filters while achieving multi-color detection through depth-based wavelength separation.
Solution Approach 2:
The patent removes color filter arrays and micro lenses from the optical path. By using wavelength-dependent absorption in silicon substrates of varying thickness, the system extracts color information directly through the substrate depth without requiring additional optical filtering components, thereby eliminating optical losses.
2Ease of manufacture
If conventional pixel structures are used, then manufacturing is simplified, but manufacturing yield and sensitivity are limited
Solution Approach 1:
The pixel structure is segmented into multiple independent photodiodes stacked vertically, with each photodiode having optimized thickness for specific wavelength detection. This segmentation allows independent optimization of each photodiode's absorption characteristics while maintaining compatibility with standard semiconductor manufacturing processes.
3Measurement precision
If color filter arrays are implemented, then multi-color imaging is achieved, but image resolution and dynamic range are compromised
Solution Approach 1:
The patent uses the vertical dimension (depth) to encode wavelength information, allowing all color channels to be detected at the same spatial location simultaneously. This eliminates the need for color filter arrays that reduce spatial resolution and enables full dynamic range utilization for each wavelength channel.
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 enhances sensitivity, yield, and color accuracy while allowing for dynamic resolution adjustments, eliminating the need for color filters and micro lenses, and improving image quality by capturing different wavelengths in various layers.
Implementation Method 1
the detection of color is based on the depth of the light sensitive areas or pixels within a semiconductor substrate. These types of sensors may rely on the wavelength-dependent absorption coefficient of silicon (Si)
Implementation Method 2
The absorption of the photon energy in each diode creates electron-hole pairs therein which produce in each diode a change in conductivity that is proportional to the absorbed energy
Data Source
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Figure 3
Figure 4A~4B
AI summary
An apparatus includes a three dimensional array of light receptors disposed within a substrate having a light receiving surface, where light receptors disposed closer to the light receiving surface are responsive to light having shorter wavelengths than light receptors disposed further from the light receiving surface, and where each light receptor is configured to output a binary value and to change state between an off-state and an on- state by the absorption of at least one photon.