Image Sensor Absorbing Layer for Parasitic Infrared Reduction
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Solution Overview
Problem
Conventional image sensors face challenges in reducing the detection of parasitic infrared radiations, which degrade the quality of visible and depth images due to the sensitivity of pixels to wavelengths outside their intended band, leading to decreased image quality.
Innovation Solution
The implementation of a semiconductor image sensor pixel design that incorporates a band-pass or band elimination interference filter, combined with an absorbing layer made of a material like germanium or carbon, which absorbs more than 30% of incident radiation at the central wavelength, reducing the detection of parasitic infrared radiations and improving image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If pixels are designed to be sensitive to radiations in a specific waveband, then the sensor can capture images in the intended wavelength range, but the pixels also detect parasitic radiations outside the targeted waveband, decreasing image quality
Solution Approach 1:
An absorbing layer made of germanium or carbon is introduced between the pixel and the interference filter. This intermediary layer selectively absorbs parasitic infrared radiations at specific wavelengths (more than 30% absorption at the central wavelength of the stop band) while allowing the desired waveband to pass through, thereby resolving the contradiction between maintaining waveband sensitivity and eliminating parasitic detection
Solution Approach 2:
The patent combines multiple materials with different optical properties: the semiconductor photodetection region (silicon), the absorbing layer (germanium or carbon), and the interference filter (multi-layer dielectric structure). This composite structure enables selective wavelength filtering by leveraging the complementary absorption characteristics of each material layer
2Object-affected harmful factors
If an interference filter is used to block parasitic radiations, then the quality of visible and depth images is improved, but the filter may also block some desired wavelengths, reducing the overall light transmission
Solution Approach 1:
The radiation filtering function is segmented into two distinct components: the absorbing layer that handles parasitic infrared wavelengths through selective absorption, and the interference filter that manages the desired waveband through constructive and destructive interference. This segmentation allows each component to operate optimally without compromising the other, maintaining high transmission in the desired band while effectively blocking parasitic radiations
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 design significantly decreases the detection of parasitic infrared radiations, enhancing the quality of both visible and depth images by limiting the detection of unwanted wavelengths, thereby improving the overall image capture efficiency.
Implementation Method 1
the absorbing layer being capable of absorbing, in a single passage, more than 30% of an incident radiation at the central wavelength of the pass band or of the stop band of the interference filter
Implementation Method 2
a band-pass or band elimination interference filter arranged on a second surface of the semiconductor region
Data Source
AI summary
An image sensor including a plurality of pixels, each including: a semiconductor photodetection region; a metal region arranged on a first surface of the semiconductor region; a band-pass or band elimination interference filter arranged on a second surface of the semiconductor region opposite to the first surface; and between the semiconductor region and the metal region, a portion of the absorbing layer made of a material different from that of the semiconductor region, the absorbing layer being capable of absorbing, in a single passage, more than 30% of an incident radiation at the central wavelength of the pass band or of the stop band of the interference filter.