Metasurface Nanostructures Bend NIR Light for Thin CMOS Pixels
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Solution Overview
Problem
Silicon-based CMOS image sensors have insufficient sensitivity and low quantum efficiency for Near-infrared (NIR) radiation, particularly for wavelengths greater than 900 nm, as silicon exhibits low absorption, leading to most incident power passing through the active region without being absorbed.
Innovation Solution
A metasurface with nanostructures that bend NIR radiation at high-degree opposing angles, creating standing wave patterns and increasing absorption by extending the path of NIR radiation within the sensor, utilizing deep trench isolation sidewalls and anti-reflective coatings to enhance absorption in CMOS image sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a conventional silicon-based photodetector is used, then the device structure is simple, but the absorption of NIR radiation is insufficient
Solution Approach 1:
The metasurface is segmented into multiple discrete nanostructures (pillars, holes, or particles) arranged in specific patterns. Each nanostructure acts as an independent optical element that collectively manipulates NIR radiation through interference and resonance effects, enabling enhanced absorption without requiring a complete redesign of the photodetector structure
Solution Approach 2:
The patent introduces a temporal dimension by using modulated continuous-wave illumination combined with lock-in detection. This allows the system to distinguish absorbed NIR radiation from background noise by detecting signals at the modulation frequency, effectively adding a time-based discrimination dimension to the spatial absorption enhancement provided by the metasurface
2Loss of energy
If the pixel thickness is increased to improve absorption, then the absorption of NIR radiation increases, but the device thickness increases
Solution Approach 1:
The metasurface nanostructures are designed to support optical resonances and standing wave patterns at specific NIR wavelengths. These resonant structures create localized electromagnetic field enhancements that increase absorption efficiency without requiring increased physical thickness, analogous to how mechanical resonators amplify vibrations at specific frequencies
Solution Approach 2:
The patent optimizes multiple parameters of the metasurface nanostructures including size, shape, material composition, and spatial arrangement to achieve maximum absorption at target NIR wavelengths. By tuning these geometric and material parameters, the system achieves enhanced absorption in a thin profile without relying on increased thickness
3Reliability
If a metasurface with nanostructures is added to bend NIR radiation, then the absorption of NIR radiation is significantly increased, but the device complexity increases
Solution Approach 1:
The metasurface nanostructures serve multiple functions simultaneously: they bend incident NIR radiation at high angles, create standing wave patterns for enhanced absorption, and can be integrated with existing CMOS photodetector architectures. This multi-functionality reduces the need for additional separate components, thereby limiting the increase in overall device complexity
Solution Approach 2:
The metasurface acts as an intermediary layer between the incident NIR radiation and the photodetector active region. It pre-condition the light by bending and concentrating it before it reaches the photodetector, thereby enhancing absorption without requiring fundamental changes to the photodetector structure itself
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 metasurface solution significantly increases the absorption of NIR radiation, achieving quantum efficiency greater than 50% and improving the performance of CMOS image sensors to match that of RGB sensors, particularly in low-light conditions and for NIR sensing applications.
Implementation Method 1
a metasurface on the first surface in which the metasurface may include nanostructures that bend a predetermined range of wavelengths of light at least 70 degrees from a direction that is substantially perpendicular to the first surface
Implementation Method 2
a standing wave pattern forms in an active region of the pixel
Implementation Method 3
utilizing deep trench isolation sidewalls and anti-reflective coatings to enhance absorption in CMOS image sensors
Data Source
Figure 1A~1B
Figure 2A~2C
Figure 3A~3B
AI summary
A pixel for an imaging sensor is disclosed that includes a photodetector and a metasurface. The photodetector includes a first surface and sidewalls that extend into the photodetector in a first direction from the first surface. The metasurface is formed on the first surface and includes nanostructures that bend a predetermined range of wavelengths of light at least 70 degrees in opposing angles from a direction that is substantially perpendicular to the first surface, and a standing wave pattern forms in an active region of the pixel. The predetermined range of wavelengths of light includes 700 nm to 1100 nm inclusive. In one embodiment, the pixel is a silicon-based photodetector, a thickness of the pixel in the first direction is less than or equal to 5 µm, and the pixel absorbs at least 20% of a power of the predetermined range of wavelengths of light.