LWIR Polarization Sensor Pixels With Floating Grid Structures
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional image sensors are limited in detecting the polarization of long infrared wavelength light and require complex and costly fabrication processes, leading to reduced sensitivity and reliability.
Innovation Solution
The development of a sensor device with pixels comprising sub-pixels and grid structures on a light incident surface, allowing for the detection of infrared light polarization by comparing signals from sub-pixels with differently oriented grid structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional silicon-based photodiodes are used, then manufacturing is simple and reliable, but detection of long wavelength infrared light (>1000 nm) is not possible
Solution Approach 1:
The patent introduces an intermediary mechanism: metal diffraction gratings are placed over the silicon photodiodes to enable long wavelength infrared detection. The gratings act as mediators that convert long wavelength infrared light into diffracted patterns that the silicon photodiodes can detect, bridging the gap between the limited silicon detection range and the desired long wavelength capability without requiring alternative sensor materials
Solution Approach 2:
The patent changes the operational parameters by using diffraction grating structures with specific line orientations and spacing designed for long wavelength infrared light. By adjusting the grating parameters (line orientation, spacing, and geometry) to match the longer wavelengths, the system enables detection beyond the natural silicon bandgap limitation while maintaining silicon-based photodiodes
2Measurement precision
If metal diffraction gratings are used for polarization detection, then polarization sensitivity is improved, but overall light sensitivity is reduced due to light blocking
Solution Approach 1:
The patent segments the pixel array into multiple pixels, each equipped with diffraction gratings of different line orientations (e.g., horizontal, vertical, diagonal). This segmentation allows polarization detection through comparison of signals from differently oriented gratings while maintaining high light sensitivity in each individual pixel, as each grating only blocks light for its specific polarization direction rather than all polarizations
3Adaptability or versatility
If non-CMOS materials like polymers are used for filters and micro lenses, then infrared wavelength detection is enabled, but fabrication complexity and cost increase
Solution Approach 1:
The patent extracts and eliminates the need for complex non-CMOS materials by using only standard CMOS-compatible silicon photodiodes combined with metal diffraction gratings. The grating structures can be fabricated using conventional CMOS metal layers, removing the need for polymer-based filters and micro lenses while maintaining infrared detection capability through the grating diffraction mechanism
Solution Approach 2:
The patent makes the silicon photodiode system universal by enabling it to detect both visible and long wavelength infrared light through the addition of diffraction gratings. The same CMOS fabrication process produces both the photodiodes and the grating structures, allowing a single device to perform multiple detection functions without requiring separate material systems
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
Enables the accurate determination of infrared light polarization and intensity without the need for micro lenses or wavelength selective filters, providing high sensitivity across a wide infrared wavelength range.
Implementation Method 1
Incident light having a polarization that is perpendicular to the grating lines is diffracted through the grating and reaches the pixel with little loss
Implementation Method 2
Incident light having a polarization that is parallel to lines of the grating is absorbed and does not reach the pixel
Implementation Method 3
Each pixel can include a photodiode that generates charge in an amount that is generally proportional to the amount of light (i.e. the number of photons) incident on the pixel
Data Source
AI summary
Long wavelength polarization sensitive image sensor devices and methods are provided. The image sensor includes pixels that each include a plurality of sub-pixels. At least some of the sub-pixels within each pixel are associated with a grid structure. Each grid structure includes two or more linear grid elements that are parallel to one another. The grid elements are disposed directly on a light incident surface of a sensor substrate in which the sub-pixels are formed, and are electrically floating. The sub-pixels can be formed as photodiodes in a silicon or other semiconductor substrate. Infrared light incident on the pixels results in the heating of the grid elements, and in particular of grid elements oriented in a direction that is parallel to a polarization of the incident light, which in turn generates a current in associated a sub-pixels. A polarization state and intensity of the incident light can be determined.