Event Imaging Pixel Structure for Low Dark Current Detection

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Solution Overview

Problem

Conventional Event-Based Vision Sensors (EVS) face challenges in completely depleting photodiodes, leading to reduced quantum efficiency and increased dark current due to contact connections, which complicates device structure and hampers performance in dark conditions.

Innovation Solution

An imaging apparatus with a photoelectric converter, a charge transfer region inside the substrate, and a charge accumulation region, utilizing transistors to control charge transfer and a detector to output signals based on charge changes, without direct contact to the substrate, thereby improving sensitivity and reducing dark current.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If a contact is connected to the N region of the photodiode to transfer electrons efficiently, then electron transfer efficiency is improved, but dark current increases and quantum efficiency is reduced

Engineering Contradiction:

Improveelectron transfer efficiencyVSAvoiddark current

Core Design Contradiction:

ProductivityVSObject-generated harmful factors

Solution Approach 1:

The patent extracts the harmful contact interface from the photodiode structure by introducing an intermediate charge transfer region. The N region is no longer directly contacted but transfers charge through this intermediate region, removing the dark current generation source while maintaining electron transfer functionality.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The charge transfer region acts as an intermediary between the photodiode's N region and the pixel circuit. This intermediate structure enables charge transfer without direct contact, solving the contradiction between transfer efficiency and dark current reduction.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Productivity

If a contact is connected to the N region of the photodiode, then electron transfer is enabled, but the photodiode cannot be completely depleted leading to reduced quantum efficiency

Engineering Contradiction:

Improveelectron transfer capabilityVSAvoidquantum efficiency

Core Design Contradiction:

ProductivityVSMeasurement precision

Solution Approach 1:

The contact is extracted from direct connection to the N region, allowing the photodiode to be completely depleted. The charge transfer region mediates the connection, enabling full depletion for high quantum efficiency while maintaining electron transfer capability.

Inventive Principle:

Principle #2Taking out (Extraction)

3Ease of manufacture

If the N region is exposed to an interface to provide contact, then charge transfer connection is established, but dark current generation increases

Engineering Contradiction:

Improvecontact connectionVSAvoiddark current

Core Design Contradiction:

Ease of manufactureVSObject-generated harmful factors

Solution Approach 1:

The charge transfer region serves as an intermediary that eliminates the harmful interface exposure. Instead of exposing the N region to a contact interface, the charge transfer region provides the connection path, preventing dark current generation while maintaining manufacturability.

Inventive Principle:

Principle #24Intermediary (Mediator)

4Productivity

If electrons remain in the undepleted photodiode, then charge transfer connection is maintained, but quantum efficiency is reduced

Engineering Contradiction:

Improvecharge transfer connectionVSAvoidquantum efficiency

Core Design Contradiction:

ProductivityVSMeasurement precision

Solution Approach 1:

The contact connection is extracted and replaced with the charge transfer region mechanism. This allows complete depletion of the photodiode to improve quantum efficiency, while the charge transfer region maintains the necessary charge transfer connection functionality.

Inventive Principle:

Principle #2Taking out (Extraction)

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 enhances the sensitivity of the imaging apparatus by completely depleting photodiodes and reducing dark current, leading to improved performance in low-light conditions and more accurate event detection.

Implementation Method 1

a photoelectric converter that generates a charge according to a received light amount

Methodology Applied

Scientific EffectPhotoelectric conversion: Photoelectric Effect

Data Source

PatentUS12256166B2Imaging apparatus and imaging method to surpresss dark current and improve quantum efficiency

Publication Date: 2025.03.18 SONY SEMICON SOLUTIONS CORP

AI summary

Provided is an imaging apparatus that includes a photoelectric converter that generates a charge according to a received light amount, and a charge transfer region that is disposed at a place inside a substrate not exposed to a substrate surface and in contact with the photoelectric converter, and to which the charge generated by the photoelectric converter is transferred. The imaging apparatus further includes a charge accumulation region that is disposed apart from the charge transfer region in a substrate surface direction and accumulates the charge transferred from the charge transfer region, a transistor that performs control to transfer the charge from the charge transfer region to the charge accumulation region, and a detector that outputs a detection signal indicating whether or not an absolute value of a change amount of an electrical signal according to an amount of the charge transferred by the transistor exceeds a predetermined threshold value.