Series Photodiode Light Detection for 1.5 μm Sensitivity

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Distance image sensors using silicon substrates lack sensitivity to light with a wavelength of approximately 1.5 μm, and forming photogate electrodes on compound semiconductor substrates is difficult, while CMOS signal control is insufficient for high-speed indirect TOF schemes.

Innovation Solution

A light detection device comprising a first photodiode and a second photodiode connected in series, with a first light source emitting pulsed light sensitive to the first photodiode and a signal output unit generating a detection signal current from the second photodiode, allowing for high-speed signal control with a simple configuration.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If a silicon substrate is used for the distance image sensor, then the device complexity is low and manufacturing is easy, but the sensitivity to light with a wavelength of approximately 1.5 μm is insufficient

Engineering Contradiction:

Improveease of manufactureVSAvoidsensitivity to 1.5 μm light

Core Design Contradiction:

Ease of manufactureVSMeasurement precision

Solution Approach 1:

The device is divided into two separate photodiode units: a first photodiode made of silicon substrate for detecting visible light, and a second photodiode made of compound semiconductor for detecting 1.5 μm infrared light. This segmentation allows each photodiode to be optimized for its specific wavelength range while maintaining overall manufacturing feasibility.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention uses a composite structure combining silicon substrate and compound semiconductor materials. The silicon-based first photodiode and compound semiconductor-based second photodiode are integrated in a single device, leveraging the complementary properties of different materials to achieve both ease of manufacture and high sensitivity to 1.5 μm light.

Inventive Principle:

Principle #40Composite materials

2Measurement precision

If a compound semiconductor substrate is used for the distance image sensor, then the sensitivity to light with a wavelength of approximately 1.5 μm is improved, but it becomes difficult to form photogate electrodes and transfer electrodes

Engineering Contradiction:

Improvesensitivity to 1.5 μm lightVSAvoidease of manufacture

Core Design Contradiction:

Measurement precisionVSEase of manufacture

Solution Approach 1:

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The silicon-based first photodiode acts as an intermediary that can be easily manufactured with standard photogate and transfer electrodes, while the compound semiconductor second photodiode provides the necessary 1.5 μm sensitivity. The two are integrated through a shared control circuit and signal processing unit.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Device complexity

If CMOS control is used for signal output, then the device complexity is low, but the control speed is insufficient for indirect TOF schemes requiring nanosecond-level response

Engineering Contradiction:

Improvedevice complexityVSAvoidcontrol speed

Core Design Contradiction:

Device complexityVSSpeed

Solution Approach 1:

The invention replaces the CMOS-based electronic control system with a direct hardware-level control mechanism using transfer electrodes and floating diffusion regions. This substitution of control methodology enables nanosecond-level response times by utilizing direct charge transfer and voltage switching at the pixel level, bypassing the slower CMOS processing pipeline.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The transfer electrodes and floating diffusion regions are pre-configured to enable rapid charge transfer and signal output. By preparing the charge transfer path in advance and using voltage-driven control, the system achieves high-speed operation without requiring complex real-time processing.

Inventive Principle:

Principle #10Preliminary action

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

Enables high-speed detection signal output and sensitivity to 1.5 μm light, facilitating the acquisition of distance images in challenging conditions like fog or smoke, while maintaining a straightforward device configuration.

Implementation Method 1

a first photodiode 21 and a first light source 24... the first light source is configured to output first pulsed light to which the first photodiode is sensitive

Methodology Applied

Scientific EffectPhotoelectric conversion: Photoelectric Effect

Implementation Method 2

a second photodiode 22... sensitivity to 1.5 μm light... a signal output unit configured to output a current as a detection signal, the current that flow through the second photodiode

Methodology Applied

Scientific EffectPhotoelectric conversion: Photoelectric Effect

Data Source

PatentUS11194026B2Light detection device

Publication Date: 2021.12.07 HAMAMATSU PHOTONICS KK

AI summary

A light detection device includes a first photodiode, a second photodiode connected in series to the first photodiode, a first light source configured to output first pulsed light to which the first photodiode is sensitive, and a signal output unit configured to output a current as a detection signal, the current that flow through the second photodiode.