Optical Sensor Pixel Guard Ring for Crosstalk-Accurate Light Sensing
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Solution Overview
Problem
Optical sensors with pixels of different spectral properties suffer from crosstalk, leading to erroneous color data due to photon interference between adjacent pixels, which reduces the accuracy of output data.
Innovation Solution
Incorporating a semiconductor guard ring around each photodetector with a fill factor of less than or equal to 50% to prevent carrier collection by adjacent pixels, combined with a readout circuit that determines ambient light levels by resetting and incrementing voltage across the photodetector, and using band pass filters and optically reflective coatings to enhance accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the photodetector size is increased to improve light sensitivity, then the fill factor increases, but crosstalk between adjacent pixels increases
Solution Approach 1:
The pixel structure is segmented into distinct functional zones: an active photodetector region for light detection and a semiconductor guard ring region for isolation. This segmentation allows the photodetector to maintain a larger area for improved sensitivity while the guard ring creates electrical isolation barriers that prevent carrier diffusion to adjacent pixels, thus reducing crosstalk.
Solution Approach 2:
The semiconductor guard ring acts as an intermediary element positioned between adjacent photodetectors. It serves as a buffer zone that intercepts and recombines minority carriers before they can diffuse into neighboring pixels. The guard ring is doped to create a high recombination rate, effectively blocking carrier migration while allowing the photodetectors to maintain larger active areas.
2Measurement precision
If the semiconductor guard ring width is increased to reduce crosstalk, then measurement accuracy improves, but the fill factor decreases
Solution Approach 1:
The doping concentration parameter of the semiconductor guard ring is optimized to achieve effective crosstalk reduction with minimal width. By increasing the doping concentration in the guard ring, the recombination rate of minority carriers is enhanced, allowing the guard ring to be narrower while still maintaining effective isolation. This parameter optimization enables better utilization of the pixel area.
Solution Approach 2:
The semiconductor guard ring employs localized high doping concentration specifically at the interfaces with photodetectors where carrier diffusion is most problematic. This localized quality enhancement creates strong electric fields and recombination zones exactly where needed for crosstalk prevention, while the central region of the guard ring can be less heavily doped, optimizing the balance between isolation effectiveness and area utilization.
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 solution effectively reduces crosstalk between pixels, improving the accuracy of ambient light sensing while maintaining a high fill factor, thus enhancing the sensitivity and responsivity of the optical sensor without significant cost or space penalties.
Implementation Method 1
a photodetector configured to absorb at least one photon and collect at least one carrier generated thereby
Data Source
AI summary
An optical sensor includes pixels. Each pixel has a photodetector. A readout circuit performs a process over an exposure time where the photodetector is connected to a reverse bias voltage supply to reset a voltage across the photodetector, and the photodetector is disconnected from the reverse bias voltage supply until that the voltage across the photodetector decreases in response to received ambient light. An ambient light level is then determine an based on a number of times the voltage across the photodetector is reset over the exposure time.