Reversed Tapered Light-Emitting Device for Planar Light Source

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Solution Overview

Problem

Conventional planar light sources combining a light guide plate and a light-emitting apparatus suffer from insufficient light output due to inefficient light incidence and diffusion, particularly when using Group III nitride semiconductor devices.

Innovation Solution

A planar light source design featuring a light-emitting apparatus with a reversed tapered long-side lateral surface and a perpendicular short-side lateral surface, where the light-emitting apparatus is oriented to suppress light diffusion perpendicular to the light guide plate, enhancing light incidence and output. The method involves forming long-side grooves in a rectangular lattice pattern and wet etching the semiconductor layer to achieve the desired surface orientation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Illumination intensity

If conventional light-emitting devices with perpendicular lateral surfaces are used, then the device structure is simple, but the light output from the planar light source is insufficient

Engineering Contradiction:

Improvelight outputVSAvoiddevice structure

Core Design Contradiction:

Illumination intensityVSDevice complexity

Solution Approach 1:

The light-emitting device employs asymmetric lateral surface configurations where long-side lateral surfaces are reversed tapered (inclined) while short-side lateral surfaces remain perpendicular. This asymmetric design optimizes light extraction characteristics by directing light toward the light guide plate while maintaining structural simplicity, thereby resolving the contradiction between light output and device complexity.

Inventive Principle:

Principle #4Asymmetry

Solution Approach 2:

Different lateral surfaces of the light-emitting device are given different geometric properties: long-side surfaces have reversed tapering to enhance light extraction efficiency, while short-side surfaces maintain perpendicular orientation. This local differentiation of surface quality optimizes overall light output without requiring complex structures throughout the entire device.

Inventive Principle:

Principle #3Local quality

2Productivity

If light diffusion is allowed in all directions, then light distribution is uniform, but light incidence into the light guide plate is inefficient

Engineering Contradiction:

Improvelight incidence efficiencyVSAvoidlight distribution uniformity

Core Design Contradiction:

ProductivityVSEase of operation

Solution Approach 1:

The reversed tapering of long-side lateral surfaces creates asymmetric light emission patterns that preferentially direct light toward the light guide plate. This asymmetric light distribution optimizes incidence efficiency while the perpendicular short-side surfaces maintain adequate uniformity by allowing lateral light spread.

Inventive Principle:

Principle #4Asymmetry

3Volume of moving object

If the planar light source size is reduced, then the device becomes more compact, but the light output decreases

Engineering Contradiction:

Improvelight source sizeVSAvoidlight output

Core Design Contradiction:

Volume of moving objectVSIllumination intensity

Solution Approach 1:

By changing the geometric parameters of the light-emitting device, specifically implementing reversed tapering on long-side lateral surfaces, the light extraction efficiency is enhanced. This parameter modification allows the light source to maintain high output in a more compact form factor, as the optimized geometry extracts more light from the same semiconductor material volume.

Inventive Principle:

Principle #35Parameter changes

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 design improves light output by efficiently directing light into the light guide plate, allowing for a reduced size and thickness of the planar light source while maintaining equivalent output to conventional designs without reversed tapering.

Implementation Method 1

a long-side lateral surface of the semiconductor layer is reversed tapered having an inclination such that a cross section area increases in a plane parallel to the main surface of the substrate as a distance from the main surface increases

Methodology Applied

Scientific EffectLight emission and orientation control:

Implementation Method 2

a sealing resin filling the concave portion to seal the light-emitting device and being mixed with yellow fluorescent material

Methodology Applied

Scientific EffectFluorescence: Fluorescence

Data Source

PatentUS10101522B2Planar light source and method for producing light-emitting device

Publication Date: 2018.10.16 TOYODA GOSEI CO LTD

AI summary

A planar light source comprises a light guide plate and a light-emitting apparatus disposed on a lateral surface of the light guide plate. The light-emitting apparatus comprises a light-emitting device, a case, and a sealing resin. The light-emitting device has a rectangular shape in a plan view, a long-side lateral surface of a semiconductor layer is reversed tapered having an inclination such that a cross section area increases in a direction parallel to a main surface of a sapphire substrate as a distance from the sapphire substrate increases, and a short-side lateral surface is perpendicular to the main surface of the sapphire substrate. A short-side and a long-side direction of the light-emitting device are perpendicular and parallel to the planar main surface of the light guide plate, respectively. The main surface of the light-emitting device is parallel to the lateral surface of the light guide plate.