Optical Sensor Pixel Trenches for Lower Parasitic Light Sensitivity

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Optical sensors face performance issues due to 'parasitic light sensitivity' where photons are absorbed in memory parts instead of photoactive regions, leading to increased noise levels and the need for high full-well-capacitance and quick depletion of memory parts.

Innovation Solution

The design includes a pixel with a photoactive region, first and second modulation gates, and trenches with air gaps acting as reflective structures to prevent photons from exiting, separating memory parts from the photoactive region, allowing only modulated electrons to be generated and stored.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If memory parts are placed adjacent to the photoactive region for efficient electron binning, then electron storage capacity is improved, but parasitic light sensitivity increases causing noise

Engineering Contradiction:

Improveelectron storage capacityVSAvoidparasitic light sensitivity

Core Design Contradiction:

Quantity of substanceVSObject-affected harmful factors

Solution Approach 1:

The pixel structure is segmented into distinct regions: photoactive region, memory parts, and intermediate trenches. This segmentation physically separates the memory parts from the photoactive region using trenches filled with air gaps, allowing electrons to be binned efficiently while preventing photons from reaching the memory parts and causing parasitic light sensitivity

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Air gaps are introduced as intermediary materials filling the trenches between the photoactive region and memory parts. These air gaps act as optical barriers with different refractive indices, preventing photon penetration into the memory parts while allowing electrical connectivity for electron binning operations

Inventive Principle:

Principle #24Intermediary (Mediator)

2Object-affected harmful factors

If trenches are introduced to separate memory parts from photoactive region, then parasitic light sensitivity is reduced, but device complexity increases

Engineering Contradiction:

Improveparasitic light sensitivityVSAvoidpixel structure complexity

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

Trenches are etched into the substrate to extract or remove the harmful optical path between the photoactive region and memory parts. By creating these physical voids filled with air gaps, the harmful photon transmission is eliminated while maintaining the necessary electrical connections for sensor operation

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The trench structure implements local quality changes by creating specific regions with different optical properties. The trenches are strategically positioned and dimensioned to provide optical isolation where needed while maintaining electrical connectivity, achieving parasitic light sensitivity reduction without excessive complexity

Inventive Principle:

Principle #3Local quality

3Illumination intensity

If air gaps are used as reflective structures in trenches, then photon reflection is improved, but manufacturing precision requirements increase

Engineering Contradiction:

Improvephoton reflection efficiencyVSAvoidtrench fabrication precision

Core Design Contradiction:

Illumination intensityVSManufacturing precision

Solution Approach 1:

The air gaps in the trenches are designed with specific dimensional parameters (width, depth, positioning) that optimize their reflective properties. By carefully controlling these parameters, the air gaps achieve effective photon reflection while the design tolerances are set to be compatible with standard semiconductor manufacturing capabilities

Inventive Principle:

Principle #35Parameter changes

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 reduces noise levels by preventing parasitic light sensitivity and enables efficient electron binning, improving the sensor's performance and resource usage.

Implementation Method 1

a photoactive region configured to convert photons into electrons and holes

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Implementation Method 2

the first and second trenches include air gaps configured to act as reflective structures for photons in the photoactive region

Methodology Applied

Scientific EffectReflection: Reflection

Data Source

PatentUS20230317745A1Optical sensor and method for fabricating an optical sensor

Publication Date: 2023.10.05 INFINEON TECHNOLOGIES AG

AI summary

An optical sensor includes a pixel that includes: a photoactive region configured to convert photons into electrons and holes, first and second modulation gates configured to be modulated for indirect time of flight measurement, the first and second modulation gates being arranged on a front side of the pixel, first and second trenches arranged on opposite lateral sides of the photoactive region, and a first memory part arranged laterally next to the first trench and at least partially separated from the photoactive region by the first trench and a second memory part arranged laterally next to the second trench and at least partially separated from the photoactive region by the second trench, the first and second memory parts being configured to bin electrons generated in the photoactive region, and the first and second trenches are configured as reflective structures for photons in the photoactive region.