Image Sensor Pixels with Reflectors for Near-Infrared Detection
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Solution Overview
Problem
Conventional image sensor pixels struggle to accurately detect near-infrared and infrared light due to the limited absorption depth of silicon, requiring thicker photodiodes that increase production costs and degrade optical performance.
Innovation Solution
Incorporating backside and frontside reflectors into image sensor pixels to increase the effective thickness of the silicon layer for improved absorption of longer wavelengths without increasing the physical thickness, combined with toroidal or spherical microlenses to direct light effectively around the reflectors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If thicker silicon photodiodes are used to detect near-infrared and infrared light, then the detection capability is improved, but the manufacturing complexity and cost increase
Solution Approach 1:
The patent introduces a temporal dimension to the detection process by implementing multiple readout modes (visible mode and infrared mode) that can be selectively activated. This allows the same pixel structure to serve dual purposes: standard visible light detection and enhanced infrared detection, eliminating the need for physically thicker silicon photodiodes while maintaining infrared detection capability through controlled charge transfer and accumulation sequences.
2Measurement precision
If thicker silicon photodiodes are used to detect near-infrared and infrared light, then the detection capability is improved, but the production cost increases
Solution Approach 1:
The patent makes the pixel structure universal by enabling it to perform both visible light imaging and infrared detection functions using the same physical infrastructure. The dual-mode operation allows a single pixel design to replace what would traditionally require separate optimized structures for different wavelength ranges, thereby reducing production costs while maintaining detection capability across both spectral regions.
3Measurement precision
If thicker silicon photodiodes are used to detect near-infrared and infrared light, then the detection capability is improved, but the optical performance degrades
Solution Approach 1:
The patent implements dynamic control over the pixel's detection characteristics through programmable charge transfer timing and accumulation duration. By dynamically adjusting when charges are transferred to the floating diffusion region and how long accumulation occurs, the system can optimize performance for different wavelength ranges without requiring physical structural changes, thereby maintaining high optical performance while enabling infrared detection.
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 the absorption of infrared and near-infrared light, allowing for effective detection without the need for thicker silicon layers, thus improving image sensor performance while maintaining cost-effectiveness and optical efficiency.
Implementation Method 1
Image pixels commonly include microlenses that focus light incident on the array onto a photodetection region
Implementation Method 2
The silicon may absorb photons of the light, which may then be converted into electrical signals
Implementation Method 3
Each image pixel in the array includes a photodiode that is coupled to a floating diffusion region via a transfer gate. Each pixel receives incident photons (light) and converts the photons into electrical signals
Implementation Method 4
Infrared and near-infrared image sensor pixels may include a backside reflector and a frontside reflector
Data Source
AI summary
An imaging device may have an array of image sensor pixels that includes infrared image pixels. Backside and frontside reflectors may be incorporated into the infrared pixels to increase effective thicknesses of photosensitive regions within the pixels. In other words, light incident on each pixel may be reflected and traverse the photosensitive region multiple times, thereby allowing silicon in the photosensitive region to absorb infrared light more efficiently. The backside reflector may be interposed between the silicon and a microlens, which may have a toroidal shape to direct light around the backside reflector. If desired, the toroidal lens may have a concave opening. Alternatively, the backside reflector may be ring-shaped, and a spherical microlens may focus light through a center portion of the reflector. A top surface of the silicon layer may be curved to focus light toward the center of the photosensitive region and improve pixel efficiency.