TOF Pixel Layout With In-Pixel Ground Node for Demodulation Contrast

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Solution Overview

Problem

Conventional time-of-flight image sensors face reduced demodulation contrast due to decreased pixel pitch and photogate separation, leading to inadvertent collection of photo-electrons by the wrong photogate, and are sensitive to signal-to-noise ratio affecting distance measurement accuracy.

Innovation Solution

Incorporating an in-pixel ground node between adjacent photogates enhances the vertical electrical field, increasing the attraction of photo-electrons to the high-biased photogate and reducing collection by the low-biased photogate, while optimizing the isolation barrier and ground node for improved quantum efficiency by reflecting designated wavelength light between side-wall surfaces.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If pixel pitch is decreased to increase pixel resolution, then pixel resolution is improved, but demodulation contrast is reduced due to inadvertent collection of photo-electrons by the wrong photogate

Engineering Contradiction:

Improvepixel resolutionVSAvoiddemodulation contrast

Core Design Contradiction:

Manufacturing precisionVSMeasurement precision

Solution Approach 1:

The pixel structure is segmented into distinct regions with an isolation barrier physically separating the first and second photogates. This segmentation prevents photo-electrons generated in one region from being inadvertently collected by the wrong photogate, thereby maintaining demodulation contrast even as pixel pitch decreases.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

An in-pixel ground node is introduced as an intermediary element between the first and second photogates. This ground node acts as a mediator that establishes a defined electrical potential, enhancing the vertical electrical field and ensuring proper photo-electron collection while allowing closer photogate spacing for higher resolution.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Volume of moving object

If photogate separation is decreased to reduce sensor size, then sensor size is reduced, but signal-to-noise ratio is affected reducing distance measurement accuracy

Engineering Contradiction:

Improvesensor sizeVSAvoiddistance measurement accuracy

Core Design Contradiction:

Volume of moving objectVSMeasurement precision

Solution Approach 1:

The isolation barrier and in-pixel ground node create localized electrical field control between photogates. This local quality enhancement ensures that even with decreased photogate separation, the electrical field configuration maintains proper photo-electron collection and signal-to-noise ratio, preserving distance measurement accuracy in a compact sensor format.

Inventive Principle:

Principle #3Local quality

3Reliability

If isolation barrier is optimized for quantum efficiency by reflecting designated wavelength light, then quantum efficiency is improved, but device complexity increases

Engineering Contradiction:

Improvequantum efficiencyVSAvoidisolation barrier structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The isolation barrier is designed to serve multiple functions simultaneously: it provides electrical isolation between photogates, establishes a defined electrical potential through the in-pixel ground node, and reflects designated wavelength light to enhance quantum efficiency. This multi-functionality reduces the need for separate components, thereby limiting the increase in device complexity while achieving improved quantum efficiency.

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 enhances demodulation contrast and quantum efficiency, allowing for increased pixel resolution or reduced sensor size, and improves the accuracy of distance measurements by ensuring photo-electrons are collected by the intended photogate.

Implementation Method 1

Incorporating an in-pixel ground node between adjacent photogates enhances the vertical electrical field, increasing the attraction of photo-electrons to the high-biased photogate

Methodology Applied

Scientific EffectElectrical field: Electric Field

Implementation Method 2

optimizing the isolation barrier and ground node for improved quantum efficiency by reflecting designated wavelength light between side-wall surfaces

Methodology Applied

Scientific EffectLight reflection: Reflection

Implementation Method 3

Each pixel of the array of pixels includes a first photogate, a second photogate adjacent the first photogate... increasing the attraction of photo-electrons to the high-biased photogate

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Data Source

PatentUS11835628B2Time-of-flight image sensor

Publication Date: 2023.12.05 MICROSOFT TECHNOLOGY LICENSING LLC

AI summary

A time-of-flight image sensor is disclosed. The time-of-flight image sensor includes an array of pixels. Each pixel of the array of pixels includes a first photogate, a second photogate adjacent the first photogate, an isolation barrier intermediate the first photogate and the second photogate, and an in-pixel ground node intermediate the first photogate and the second photogate.