Semiconductor Image Sensor Pixel With Light Trapping for IR Quantum Efficiency
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Solution Overview
Problem
Modern CMOS image sensors suffer from low quantum efficiency in the infrared band due to light escaping without detection and high noise contributions from unwanted background signals, especially when maintaining small pixel dimensions for compact, high-resolution imaging.
Innovation Solution
The solution involves a pixel design with a structured interface and isolation layers to trap light within the pixel volume, combined with a filter element that acts as an effective one-way mirror, ensuring narrowband sensitivity at a target wavelength and preventing noise from unwanted background light. This design includes a light-scattering layer and isolation layers on perpendicular surfaces, along with a filter element positioned near the entrance surface to manage light incidence and reflection effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the thickness of the detector material is increased to increase the active region, then quantum efficiency is improved, but pixel dimensions increase which prevents compact high resolution imaging
Solution Approach 1:
The patent transitions from a planar light detection approach to a three-dimensional light trapping architecture using pyramidal structures and side surfaces. By utilizing the vertical dimension and lateral surfaces within the constrained pixel volume, the patent achieves extended light interaction paths without increasing the overall pixel footprint, thereby resolving the contradiction between quantum efficiency and compact dimensions
Solution Approach 2:
The patent implements nested light-trapping structures where pyramidal formations are positioned within the pixel volume, and additional light-trapping elements are arranged on side surfaces. These nested structures maximize the use of available space within the pixel, allowing enhanced light absorption without increasing external dimensions
2Volume of moving object
If the pixel dimensions are reduced to achieve compact high resolution imaging, then device compactness is improved, but quantum efficiency deteriorates due to light escaping
Solution Approach 1:
The patent employs three-dimensional light trapping structures including pyramidal formations and side surface elements that create multiple reflection paths. This dimensional approach allows light to interact with the detector material multiple times within the reduced pixel volume, compensating for the smaller detection area and maintaining high quantum efficiency in compact pixels
Solution Approach 2:
The patent creates continuous light-trapping pathways using pyramidal structures and side surface arrangements that guide light through multiple interactions with the detector material. This continuous action ensures that light escaping tendency is counteracted by repeated absorption opportunities, maintaining high quantum efficiency even in reduced pixel volumes
3Adaptability or versatility
If the detector is designed to be sensitive to a broad wavelength range, then coverage of electromagnetic spectrum is improved, but noise contributions from unwanted background signals increase
Solution Approach 1:
The patent implements wavelength-selective filtering at specific locations within the pixel structure. Filter elements are positioned at particular depths and locations to selectively transmit target wavelengths while blocking unwanted background radiation. This local application of filtering properties allows the detector to maintain broad spectral adaptability while reducing noise from specific wavelength ranges
Solution Approach 2:
The patent introduces filter elements as intermediary components between the light entry path and the detector material. These intermediaries selectively transmit desired wavelengths while blocking unwanted background signals, enabling the detector to maintain wavelength versatility while being protected from harmful background radiation
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 approach enhances quantum efficiency by trapping light within the pixel until it is absorbed, reducing noise and maintaining high sensitivity at the target wavelength, particularly beneficial for infrared imaging applications like 3D imaging and facial recognition.
Implementation Method 1
The structured interface is configured to scatter incident light by realizing a light-scattering interface which is formed by a light scattering layer on a surface of the semiconductor body
Implementation Method 2
Light within the pixel volume that impinges on the interface created by the isolation layer with an incident angle larger than a cut-off angle is totally reflected and therefore trapped within the pixel volume
Implementation Method 3
The filter element is configured to transmit incident light such that the latter can impinge on the first surface and hence enter the pixel volume and to reflect light that impinges on the filter element after leaving, i.e. escaping from, the pixel volume
Implementation Method 4
the working principle of the pixels is the conversion of optical intensity into a photocurrent using a photodiode
Data Source
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AI summary
A pixel (1) with enhanced quantum efficiency comprises a semiconductor body (2) that has a first surface (3) configured as an entrance surface and a light capturing region (4a) configured for capturing light that is incident on the first surface (3). The pixel further comprises a structured interface (5), isolation layers (6) on at least two surfaces (7) of the semiconductor body that are perpendicular to the first surface (3), and a filter element (8) that is arranged at a distance from the first surface (3) such that light that is incident on the first surface (3) at an angle of incidence (a) smaller than a critical angle (αc) impinges on the filter element (8).