Stacked Compound Semiconductor Image Sensor Without Color Filters
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Solution Overview
Problem
Conventional CMOS image sensors suffer from reduced light sensitivity due to the use of color filters that absorb approximately ⅔ of incident light, leading to inefficient light use and decreased performance.
Innovation Solution
A vertically stacked image sensor utilizing multi-layered I-III-VI-based photoelectric conversion units with specific material layers (CuGaS2, CuGa(1-x)FexS2, and CuGa(1-y)FeyS2) that absorb light across different wavelength bands, eliminating the need for color filters and enhancing light use efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Difficulty of detecting and measuring
If a color filter is used in the photodiode to select specific wavelengths, then wavelength selectivity is improved, but light absorption efficiency deteriorates because approximately 2/3 of incident light is absorbed by the filter
Solution Approach 1:
The patent transitions from a planar color filter arrangement to a vertically stacked three-dimensional structure. Multiple photodiodes with different wavelength sensitivities are stacked in the vertical dimension, allowing each layer to capture specific wavelength bands without blocking light from reaching other layers. This spatial reconfiguration eliminates the need for light-absorbing color filters while maintaining wavelength selectivity.
Solution Approach 2:
The image sensor is segmented into multiple photodiode layers, each specialized for detecting specific wavelength bands (e.g., blue, green, red). This segmentation allows each photodiode to focus on a narrow wavelength range with high efficiency, while the stacked arrangement ensures that light can be captured across all bands without the need for filtering mechanisms.
2Loss of energy
If vertically stacked photodiodes are used without color filters, then light use efficiency is improved, but manufacturing complexity increases
Solution Approach 1:
The patent varies the wavelength sensitivity parameters of photodiodes across different vertical layers. By adjusting the bandgap energy and material composition of each photodiode layer, the system achieves wavelength-selective detection without requiring additional filtering components. This parameter differentiation enables efficient light capture across the spectrum while simplifying the overall device structure compared to filter-based approaches.
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 solution allows for increased light absorption and sensitivity, enabling the capture of color images as electrical signals without color filters, resulting in higher resolution and sensitivity compared to conventional sensors.
Implementation Method 1
a first photoelectric conversion unit including a I-III-VI-based material layer which absorbs light of a first wavelength band, a second photoelectric conversion unit including a I-III-VI-based material layer which absorbs light of a second wavelength band
Data Source
AI summary
A stack-type image sensor using a compound semiconductor. The stack-type image sensor includes a stack of photoelectric conversion units which are sequentially arranged in a light incident direction and which absorb light in ascending order of a wavelength from shortest to longest.