Rectangular Microlenses for SPAD Arrays
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional image sensors suffer from limited functionality, including inability to determine object distance and lower-than-desired image quality and resolution, which is addressed by incorporating single-photon avalanche diodes (SPADs) that enable single-photon detection and 3D imaging through photon time-of-flight measurement.
Innovation Solution
The implementation of SPADs in imaging systems, including passive and active quenching circuitry, readout circuitry for photon counting and time-of-flight measurement, and the use of silicon photomultipliers to enhance dynamic range and resolution by grouping SPADs in arrays, along with the design of microcells and microlenses to optimize light focusing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional photodiodes are used in image sensors, then the device structure is simple, but the sensitivity to incident light is insufficient and single-photon detection is not achieved
Solution Approach 1:
The patent changes the operating parameters of the photodiode by applying reverse bias voltage above the breakdown voltage, transforming it from a conventional photodiode operation mode to an avalanche breakdown mode. This parameter change enables single-photon detection capability while maintaining the basic photodiode structure, thus improving sensitivity without significantly increasing device complexity
Solution Approach 2:
The patent implements periodic quenching of the avalanche current through active quenching circuitry that periodically resets the photodiode after each photon detection event. This periodic action allows the SPAD to recover and be ready for the next photon detection, enabling continuous single-photon detection while managing the complexity through structured control
2Measurement precision
If SPADs with breakdown voltage operation are used, then single-photon detection capability is achieved, but the device complexity increases due to quenching circuitry and control mechanisms
Solution Approach 1:
The patent implements passive quenching where the photodiode's own avalanche current, when allowed to flow freely through a quenching resistor, naturally reduces the voltage across the photodiode below the breakdown voltage, thereby quenching itself without external control circuitry. This self-service mechanism significantly reduces device complexity while maintaining single-photon detection capability
Solution Approach 2:
Instead of using complex active circuitry to prevent avalanche breakdown and then carefully controlling it, the patent inverts the approach by allowing the avalanche breakdown to occur freely and then quenching it passively. This inversion simplifies the control mechanism while achieving the same photon detection function
3Adaptability or versatility
If conventional image sensors are used, then the manufacturing process is simple, but the functionality is limited and 3D imaging capability is not achieved
Solution Approach 1:
The patent makes the image sensor universal by enabling it to perform both conventional 2D imaging and 3D depth mapping functions using the same SPAD array. By measuring photon time-of-flight in addition to photon detection, the sensor achieves multi-functionality, allowing a single device to replace multiple specialized sensors
Solution Approach 2:
The patent adds the time dimension to conventional 2D spatial imaging by measuring the time-of-flight of photons. This transforms the imaging capability from two-dimensional (x, y coordinates) to three-dimensional (x, y, z depth) by incorporating temporal measurement of light travel time, enabling depth mapping and 3D reconstruction
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 approach enables improved sensitivity to low light levels, enhanced image quality, and 3D imaging capabilities, increasing the dynamic range and resolution of imaging systems by effectively detecting single photons and measuring photon time-of-flight.
Implementation Method 1
Each pixel typically includes a photosensitive element (such as a photodiode) that receives incident photons (light) and converts the photons into electrical signals
Implementation Method 2
3D imaging capabilities, increasing the dynamic range and resolution of imaging systems by effectively detecting single photons and measuring photon time-of-flight
Implementation Method 3
the design of microcells and microlenses to optimize light focusing
Data Source
AI summary
An imaging device may include single-photon avalanche diodes (SPADs). The single-photon avalanche diodes may be arranged in an array of microcells (such as a silicon photomultiplier). Each microcell may have an aspect ratio that is greater than 1. Each microcell may be covered by a microlens that also has an aspect ratio that is greater than 1. The microlens may have curvature in a first direction (parallel to the width of the microcell/microlens) and less curvature in a second direction that is orthogonal to the first direction (parallel to the length of the microcell/microlens). Forming non-square, rectangular microcells and microlenses in this fashion may allow for larger microcells that still have satisfactory microlens performance.