Point-Symmetric Transfer Gates for ToF Sensor Parasitic Light Reduction

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Solution Overview

Problem

The existing gate type indirect Time of Flight (ToF) sensor technology fails to uniformly reduce parasitic light sensitivity due to line-symmetric arrangement of transfer gates with respect to the optical center.

Innovation Solution

The light receiving element incorporates plural transfer gates that distribute and transfer signal charge from a photodiode, with at least two gates arranged point-symmetrically with respect to the optical center, and includes overflow gates for charge discharge, ensuring even distribution and robustness against misalignment.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If transfer gates are arranged line-symmetrically with respect to the optical center, then the structure is simple and easy to manufacture, but parasitic light sensitivity is not uniformly reduced

Engineering Contradiction:

Improvemanufacturing simplicityVSAvoiduniformity of parasitic light sensitivity reduction

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

The patent applies asymmetry by changing from line-symmetric arrangement to point-symmetric arrangement of transfer gates with respect to the optical center. This point-symmetric configuration ensures that parasitic light sensitivity is uniformly reduced in all directions, while still maintaining structural regularity that facilitates manufacturing. The asymmetric correction specifically targets the symmetry type to resolve the uniformity issue without significantly complicating the manufacturing process.

Inventive Principle:

Principle #4Asymmetry

2Productivity

If multiple transfer gates are used to distribute signal charge, then charge distribution capability is improved, but the risk of transfer failure increases

Engineering Contradiction:

Improvecharge distribution capabilityVSAvoidtransfer failure risk

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent introduces overflow gates that are activated before the transfer gates to preliminarily discharge accumulated signal charge. This preliminary action prevents excessive charge accumulation that could lead to transfer failures, thereby improving reliability while maintaining the charge distribution capability of multiple transfer gates. The overflow gates act as a safety mechanism that prepares the system in advance to avoid potential failures.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The overflow gates provide beforehand cushioning by creating a safety buffer that discharges excess charge before it can cause transfer failures. This cushioning mechanism protects the transfer gates from operating under excessive load conditions, thereby reducing the risk of transfer failure while preserving the overall charge distribution functionality of the multiple transfer gate system.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

3Speed

If transfer gates are positioned closer to the photodiode to improve charge transfer efficiency, then transfer speed increases, but parasitic light sensitivity increases

Engineering Contradiction:

Improvecharge transfer speedVSAvoidparasitic light sensitivity

Core Design Contradiction:

SpeedVSObject-affected harmful factors

Solution Approach 1:

The patent applies local quality by positioning transfer gates at specific locations that are optimized for each function: some transfer gates are positioned closer to the photodiode to achieve fast charge transfer, while overflow gates are positioned to specifically address parasitic light sensitivity. This localized optimization allows different parts of the transfer gate system to have different functional qualities, resolving the contradiction between transfer speed and parasitic light sensitivity.

Inventive Principle:

Principle #3Local quality

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 uniformly reduces parasitic light sensitivity and enhances robustness against transfer failures, maintaining in-plane uniformity and charge separation efficiency while simplifying manufacturing complexity.

Implementation Method 1

signal charge accumulated in a photodiode that performs photoelectrical conversion of incident light

Methodology Applied

Scientific EffectPhotoelectrical conversion: Photoelectric Effect

Data Source

PatentUS20220397651A1Light receiving element and ranging module

Publication Date: 2022.12.15 SONY SEMICON SOLUTIONS CORP

AI summary

Disclosed herein is a ranging module including a light receiving element, a light emitting unit, and a light-emission control unit. The light receiving element has plural transfer gates which distribute and transfer, to plural floating diffusions, signal charge accumulated in a photodiode that photoelectrically converts incident light, and at least two of the plural transfer gates are disposed point-symmetrically with respect to an optical center as seen from a direction of incidence of the light. The light emitting unit emits irradiation light having a periodically varying brightness. The light-emission control unit controls irradiation timing of the irradiation light.