Inverted Pyramids Enhance Image Sensor Quantum Efficiency
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Solution Overview
Problem
Image sensors face challenges in achieving high quantum efficiency, particularly in low-light conditions such as night vision or day-and-night surveillance, where infrared light is less efficiently converted to electrical charge, leading to reduced image brightness and efficiency.
Innovation Solution
The integration of a semiconductor substrate with an array of pixels featuring inverted pyramids and a microlens array above the top surface, optimized for alignment and configuration to enhance quantum efficiency by reducing light reflection and improving light coupling, specifically tailored for near-infrared and visible spectra.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a conventional flat surface is used on the semiconductor substrate, then the manufacturing process is simple, but the quantum efficiency is reduced due to light reflection losses
Solution Approach 1:
The patent applies curved surfaces in the form of inverted pyramids on the semiconductor substrate. These pyramidal structures replace the conventional flat surface, creating multiple reflective surfaces that redirect incident light at different angles. This curvature approach increases the probability of light coupling into the photodiode while reducing reflection losses, thereby improving quantum efficiency without requiring complex multi-layer coatings.
Solution Approach 2:
The invention transitions from a two-dimensional flat surface to a three-dimensional pyramidal structure. By adding vertical depth and angular surfaces to the substrate top layer, the patent creates multiple light interaction pathways. The inverted pyramids introduce a new dimensional aspect that enables light to be reflected and redirected through multiple bounces, increasing the effective light collection area and improving quantum efficiency.
2Loss of energy
If the microlens array is not precisely aligned with the inverted pyramids, then the manufacturing tolerance is relaxed, but the light coupling efficiency and quantum efficiency are reduced
Solution Approach 1:
The patent divides the light collection function into two separate components: inverted pyramids for light trapping and reflection, and microlenses for focal concentration. This segmentation allows each component to be optimized independently - the pyramids handle broad-angle light redirection while the microlenses provide precise focal control, improving overall system efficiency even with moderate alignment tolerances.
Solution Approach 2:
The invention applies different optical properties to different parts of the pixel structure. The inverted pyramids provide diffuse reflection and light trapping across their angled surfaces, while the microlenses provide focused convergence at their focal points. This local differentiation of optical functions allows each component to compensate for minor misalignments, reducing the strictness of alignment requirements.
3Loss of energy
If the inverted pyramids are made deeper to reduce reflection, then the light reflection is reduced and quantum efficiency is improved, but the manufacturing complexity and cost increase
Solution Approach 1:
The patent optimizes the pyramid depth parameter to achieve the best balance between quantum efficiency improvement and manufacturing feasibility. By carefully selecting the pyramid depth (typically around 0.5-2 micrometers depending on wavelength), the invention achieves sufficient light trapping effect without requiring excessively deep etching processes. This parameter optimization allows standard semiconductor fabrication techniques to be used while still achieving significant reflection reduction.
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 configuration significantly enhances the quantum efficiency of image sensors, improving their performance in low-light conditions by reducing reflection losses and optimizing light collection, thereby enhancing image brightness and quality in both near-infrared and visible light scenarios.
Implementation Method 1
enhance the quantum efficiency of image sensors, improving their performance in low-light conditions by reducing reflection losses
Implementation Method 2
a plurality of microlenses are disposed above the top surface and aligned to the plurality of inverted pyramids, respectively
Implementation Method 3
Each of the pixels is configured to convert light incident on the pixel to an electrical output signal
Data Source
AI summary
An image sensor with quantum efficiency enhanced by inverted pyramids includes a semiconductor substrate and a plurality of microlenses. The semiconductor substrate includes an array of pixels. Each of the pixels is configured to convert light incident on the pixel to an electrical output signal, the semiconductor substrate having a top surface for receiving the light. The top surface forms a plurality of inverted pyramids in each pixel. The plurality of microlenses are disposed above the top surface and aligned to the plurality of inverted pyramids, respectively.