Semiconductor Image Sensor Pixel Structure for Light Trapping
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Solution Overview
Problem
CMOS image sensors, particularly in infrared applications, suffer from low quantum efficiency 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 implementation of 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.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the thickness of the detector material is increased to improve quantum efficiency, then light absorption is enhanced, but pixel dimensions increase reducing compactness and resolution
Solution Approach 1:
The patent applies curved/structured interfaces (pyramidal structures, textured surfaces) instead of flat surfaces to trap light within the pixel volume. The curved geometry increases the optical path length and promotes total internal reflection, enhancing light absorption without increasing physical pixel thickness.
Solution Approach 2:
The patent introduces vertical structuring (pyramidal layers, textured interfaces) within the pixel volume to create additional optical paths. This dimensional complexity allows light to be trapped and redirected multiple times through the detector material, effectively increasing absorption probability without increasing the horizontal pixel footprint.
2Manufacturing precision
If the pixel dimensions are reduced to achieve compact high-resolution imaging, then resolution is improved, but quantum efficiency decreases due to reduced light capture volume
Solution Approach 1:
Curved interfaces and pyramidal structures are implemented within small pixel dimensions to trap light effectively. The geometric complexity compensates for the reduced pixel size by increasing the optical interaction length and promoting multiple internal reflections, maintaining high quantum efficiency in compact pixels.
Solution Approach 2:
The patent modifies optical parameters (refractive index matching, surface geometry, layer thicknesses) to optimize light trapping in small pixels. By carefully tuning these parameters, the design achieves high quantum efficiency despite reduced pixel dimensions, enabling compact high-resolution imaging.
3Adaptability or versatility
If the detector is made sensitive to a broad wavelength range, then detection capability is improved, but noise from unwanted background light increases
Solution Approach 1:
The patent implements wavelength-selective filtering at specific locations within the pixel structure (filter elements positioned at predetermined distances). This allows the detector to maintain broad spectral sensitivity while locally rejecting unwanted wavelengths that contribute to noise, achieving both versatility and low noise performance.
Solution Approach 2:
Filter elements are introduced as intermediary components between the light entry path and the detector active region. These filters selectively transmit desired wavelengths while blocking unwanted background light, acting as a mediator that preserves detection capability while reducing noise contributions.
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 enhances quantum efficiency by trapping light until it is absorbed and reduces noise, achieving high sensitivity and low noise imaging at specific wavelengths, particularly beneficial for infrared 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
isolation layers on at least two surfaces of the semiconductor body that are perpendicular to the first surface
Implementation Method 3
a filter element that is arranged at a distance from the first surface such that light that is incident on the first surface at an angle of incident smaller than a critical angle impinges on the filter element
Implementation Method 4
the working principle of the pixels is the conversion of optical intensity into a photocurrent using a photodiode
Data Source
AI summary
A pixel with enhanced quantum efficiency comprises a semiconductor body that has a first surface configured as an entrance surface and a light capturing region configured for capturing light that is incident on the first surface. The pixel further comprises a structured interface, isolation layers on at least two surfaces of the semiconductor body that are perpendicular to the first surface, and a filter element that is arranged at a distance from the first surface such that light that is incident on the first surface at an angle of incidence smaller than a critical angle impinges on the filter element.