Silicon ALED-PD Optical Link Module for Galvanic Isolation

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Solution Overview

Problem

The indirect band gap nature of silicon materials makes it impractical to develop light-emitting diodes (LEDs) due to slow radiative recombination rates, limiting their application in optical galvanic isolation (OGI) systems, as they rely on non-radiative recombination processes and require phonon involvement.

Innovation Solution

A practical avalanche LED (ALED) and photodiode (PD) pair is developed using silicon, with avalanche breakdown junctions configured in close proximity and varying spacings to enhance electron-hole pair creation and recombination, integrated as a single integrated circuit in a CMOS or BiCMOS SOI process, utilizing deep trench isolation to promote local avalanche breakdown and efficient light generation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If silicon material is used for LED, then cost and integration are improved, but light emission efficiency deteriorates due to indirect band gap

Engineering Contradiction:

Improveintegration costVSAvoidradiative recombination efficiency

Core Design Contradiction:

Ease of manufactureVSLoss of energy

Solution Approach 1:

The patent changes the operational parameters of silicon by inducing avalanche breakdown conditions (high electric field) to enable radiative recombination. By applying reverse bias voltage to create impact ionization, the system transforms silicon from a non-radiative material under normal conditions to a light-emitting material under avalanche conditions, resolving the contradiction between using silicon for cost/integration and achieving light emission.

Inventive Principle:

Principle #35Parameter changes

2Productivity

If avalanche breakdown junctions are placed in close proximity, then light generation efficiency is improved, but device complexity increases

Engineering Contradiction:

Improvelight pulse generation efficiencyVSAvoidjunction configuration complexity

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The patent merges the avalanche breakdown junctions into a single integrated structure where multiple junctions are combined in close proximity within one device. This combining approach improves light generation efficiency by reducing spacing while managing complexity through unified design and integration, rather than treating each junction as a separate component.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent transitions from planar junction arrangement to three-dimensional configuration with junctions at different depths and spatial positions. By utilizing vertical stacking and depth variations, the design achieves close proximity for efficient light generation while organizing complexity in the third dimension rather than spreading components across a large planar area.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

3Adaptability or versatility

If varying spacings between avalanche breakdown junctions are used, then wavelength energy accommodation is improved, but manufacturing precision requirements increase

Engineering Contradiction:

Improvewavelength accommodation rangeVSAvoidjunction spacing tolerance

Core Design Contradiction:

Adaptability or versatilityVSManufacturing precision

Solution Approach 1:

The patent applies local quality by creating different spacing configurations at different locations within the device. Each region has optimized spacing tailored to specific wavelength requirements, allowing the device to handle multiple wavelengths. This localized optimization accommodates wavelength diversity while concentrating precision requirements to specific critical regions rather than requiring uniform high precision throughout the entire device.

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 enables efficient light pulse generation in the 1-25 GHz range, overcoming the limitations of indirect band gap materials by increasing carrier density and promoting radiative recombination, making silicon-based OGI systems viable and cost-effective with reduced parasitic capacitance.

Implementation Method 1

an anode and a cathode defining an avalanche breakdown junction between buried layers of the anode and cathode

Methodology Applied

Scientific EffectAvalanche breakdown: Avalanche Breakdown

Implementation Method 2

increasing carrier density and promoting radiative recombination

Methodology Applied

Scientific EffectImpact ionization:

Implementation Method 3

the receiver takes the form of a photo diode (PD)

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Implementation Method 4

utilizing deep trench isolation to promote local avalanche breakdown

Methodology Applied

Scientific EffectElectric field concentration: Electric Field

Data Source

PatentUS8237177B2Fully silicon ALED-photodiode optical data link module

Publication Date: 2012.08.07 NAT SEMICON CORP

AI summary

In a silicon-based light emitting diode-photodiode (LED-PD) arrangement, the LED is implemented as an avalanche LED (ALED) and the ALED and PD are integrated into a common integrated circuit. The ALED is formed around a cross-shaped PD and is separated from the PD by a deep trench region. In order to create current crowding close to the deep trench the ALED includes an NBL or PBL having a narrowing at its end.