Nano-Photonic Microlens Array for Low-Light Image Sensor Pixels
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Solution Overview
Problem
As image sensor resolution increases, the degradation of image quality in low-light environments and the inefficiency of light utilization become significant challenges, particularly with the use of pixels composed of multiple photosensitive cells.
Innovation Solution
Incorporation of a nano-photonic microlens array with a two-dimensional arrangement of nano-structures that condense light and provide improved light utilization efficiency and auto-focusing capabilities by isolating photosensitive cells electrically, utilizing a convex phase profile and specific nano-structure arrangements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the resolution of the image sensor is increased by decreasing the size of unit pixels, then the resolution is improved, but the light utilization efficiency deteriorates and image quality in low-light environments degrades
Solution Approach 1:
Each pixel is divided into multiple photosensitive cells (e.g., four cells in a 2x2 arrangement) that independently sense light. This segmentation allows the pixel to capture more total light while maintaining resolution, as each cell contributes to the overall signal. The isolation structures electrically separate these cells while the microlens optically combines their inputs.
Solution Approach 2:
The microlens is positioned above and covers multiple photosensitive cells, creating a nested structure where a single optical element serves multiple sensing elements below. This allows the microlens to effectively gather and distribute light to multiple cells, improving light utilization efficiency without increasing pixel size.
2Loss of energy
If multiple photosensitive cells are bound to form one pixel, then light utilization efficiency is improved, but the device complexity increases due to the need for isolation structures and complex arrangements
Solution Approach 1:
Multiple photosensitive cells are merged into a single pixel unit that functions as one sensing element. The microlens above each pixel combines the light from multiple cells, and the isolation structures electrically connect them while maintaining optical coherence. This merging approach simplifies the overall system by treating multiple cells as a unified sensing unit.
Solution Approach 2:
The microlens structure serves multiple functions simultaneously: it focuses light onto the photosensitive cells, distributes light evenly across multiple cells within a pixel, and provides structural support for the pixel array. This multi-functionality reduces the need for additional specialized components, thereby reducing overall device complexity.
3Loss of energy
If a conventional microlens is used, then light condensation is achieved, but the auto-focusing function is lost due to the fixed focal length
Solution Approach 1:
The patent employs multiple microlenses with different focal lengths arranged in an array above each pixel. By selectively activating or weighting signals from different microlens elements, the system can dynamically adjust its effective focal length to achieve auto-focusing. This dynamic configuration allows the pixel to adapt to different object distances while maintaining efficient light condensation.
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
Enhances light utilization and auto-focusing performance, improving image quality in low-light conditions and maintaining efficient light condensation across different wavelength bands.
Implementation Method 1
a nano-photonic microlens array arranged to face a light incident surface of the sensor substrate, the nano-photonic microlens array including a plurality of nano-photonic microlenses configured to condense the incident light
Implementation Method 2
nano-photonic microlenses configured to condense the incident light
Implementation Method 3
each nano-photonic microlens of the plurality of nano-photonic microlenses includes a plurality of nano-structures that are configured to output light having a convex phase profile
Implementation Method 4
a plurality of pixels configured to sense incident light; and each pixel of the plurality of pixels includes: a plurality of photosensitive cells that are two-dimensionally arranged
Data Source
AI summary
An image sensor includes a sensor substrate including a plurality of pixels for sensing incident light, and a nano-photonic microlens array arranged to face a light incident surface of the sensor substrate, and including a plurality of nano-photonic microlenses for condensing incident light. Each of the plurality of pixels includes a plurality of photosensitive cells that are two-dimensionally arranged in a first direction and a second direction perpendicular to the first direction and are configured to independently sense the incident light, and an isolation for electrically isolating the plurality of photosensitive cells, each of the nano-photonic microlenses includes a plurality of nano-structures that are arranged such that the light transmitting each of the nano-photonic microlenses has a convex phase profile, and the plurality of nano-structures are arranged in the form of a two-dimensional array in a diagonal direction between the first direction and the second direction.