Nanostructured PDMS Antireflective Layer for Wider Image Sensor Incidence
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Solution Overview
Problem
Complementary metal-oxide-semiconductor (CMOS) image sensors face limitations in light transmission due to a small angle of incidence and antireflective properties, which restrict their sensitivity and quantum efficiency.
Innovation Solution
A subwavelength, hydrophobic polydimethylsiloxane (PDMS) layer with nanostructures, such as arrays of convex protuberances or concave recesses, is applied to increase the angle of incidence for light collection, formed using a porous anodic aluminum oxide (AAO) template, enhancing light absorption and reducing reflections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a conventional antireflective layer is used on the image sensor, then reflections are reduced, but the angle of incidence for light collection remains small, limiting sensitivity and quantum efficiency
Solution Approach 1:
The antireflective layer is segmented into multiple layers with different refractive indices. The first antireflective layer has a refractive index of 1.3-1.6 and the second antireflective layer has a refractive index of 1.7-2.0, creating a gradient that progressively reduces reflections while maintaining broadband antireflective properties across a wide angle of incidence range.
Solution Approach 2:
The patent changes the refractive index parameter across different layers of the antireflective coating. By using materials with progressively higher refractive indices from the first to the second layer, the optical impedance matching is improved, reducing reflections at each interface and enabling effective light collection at higher angles of incidence.
2Adaptability or versatility
If the image sensor is exposed to humid environments, then operational flexibility is improved, but moisture buildup occurs on the sensor surface, degrading performance
Solution Approach 1:
The hydrophobic coating applied to the microlens array and/or color filter layer self-actively repels moisture through its inherent hydrophobic properties. This coating continuously prevents water condensation and moisture buildup on the sensor surface without requiring external intervention, maintaining optical performance in humid environments.
Solution Approach 2:
The hydrophobic coating creates an inert, water-repelling environment on the sensor surface. By making the surface hydrophobic, the patent effectively excludes moisture from contacting the optical surfaces, preventing condensation and maintaining optimal operating conditions even in humid environments.
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 PDMS layer increases the sensitivity and quantum efficiency of the image sensor by allowing greater light collection at higher angles of incidence, while also being antireflective and hydrophobic to prevent moisture buildup.
Implementation Method 1
The nanostructures may each have a respective width that is less than a wavelength of incident light that is to be collected by the image sensor to increase light absorption by increasing the angle of incidence for which the image sensor is capable of collecting incident light
Implementation Method 2
A CIS for a smartphone camera may be embedded with phase detection autofocus (PDAF) pixels to provide an auto focusing function for the camera. Some CISs include on-chip polarization filters and multi-band spectral filters that enable extraction of special information from a scene.
Implementation Method 3
A subwavelength, hydrophobic polydimethylsiloxane (PDMS) layer with nanostructures, such as arrays of convex protuberances or concave recesses, is applied to increase the angle of incidence for light collection
Data Source
AI summary
An image sensor may include a polydimethylsiloxane (PDMS) layer that is subwavelength, hydrophobic, and/or antireflective. The PDMS layer may be fabricated to include a surface having a plurality of nanostructures (e.g., an array of convex protuberances and/or an array of concave recesses). The nanostructures may be formed through the use of a porous anodic aluminum oxide (AAO) template that uses a plurality of nanopores to form the array of convex protuberances and/or the array of concave recesses. The nanostructures may each have a respective width that is less than the wavelength of incident light that is to be collected by the image sensor to increase light absorption by increasing the angle of incidence for which the image sensor is capable of collecting incident light. This may increase the quantum efficiency of the image sensor and may increase the sensitivity of the image sensor.