AC LED with Diagonally Opposed Electrodes for Uniform Current
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Solution Overview
Problem
GaN-based LEDs face issues with non-uniform current distribution and light emission efficiency due to high specific resistivity of P-type semiconductor layers and light blocking by electrodes, especially when connected to AC power sources.
Innovation Solution
The design features a substrate with light emitting cells having a transparent upper electrode layer and diagonally opposed upper and lower electrodes, which are symmetrically arranged to minimize light blocking and enhance current distribution, allowing for efficient operation with AC power.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the P-type electrode is formed on the P-type semiconductor layer to enable current injection, then the LED can be electrically driven, but the current becomes concentrated on a specific portion rather than uniformly distributed due to high specific resistivity of the P-type layer
Solution Approach 1:
A transparent electrode layer with low specific resistivity is introduced as an intermediary between the P-type electrode and the P-type semiconductor layer. This intermediate layer receives current from the P-type electrode and distributes it uniformly across the P-type semiconductor layer, solving both the electrical drive requirement and the current concentration problem.
Solution Approach 2:
The transparent electrode layer is designed with specific local properties (low specific resistivity and optical transparency) that are tailored to its function of current distribution. This localized functional design allows the layer to effectively spread current while maintaining light emission efficiency.
2Manufacturing precision
If a transparent electrode layer is used to distribute current uniformly, then the light emitting area can be expanded, but the thickness of the transparent electrode is restricted because it absorbs light
Solution Approach 1:
The thickness parameter of the transparent electrode layer is optimized to balance two competing requirements: sufficient thickness to achieve low specific resistivity for current distribution, and limited thickness to minimize light absorption. By precisely controlling this parameter, both current uniformity and light emission efficiency are maintained.
3Reliability
If the upper electrode pad and lower electrode are formed to enable electrical connection, then the LED can be driven, but they block light emitted from the LED, reducing light emission efficiency
Solution Approach 1:
The upper electrode pad and lower electrode are extracted from the central light emitting region and repositioned to the periphery of the LED structure. This spatial extraction allows the electrodes to maintain their electrical connection function while minimizing their interference with light emission, as they are located at the edges rather than blocking the central emission area.
4Adaptability or versatility
If the LED is connected directly to an AC power source, then the device can operate with AC input, but the LED is repeatedly turned on/off and is easily broken by reverse current
Solution Approach 1:
Multiple LED elements are connected in series to form an LED array that can withstand AC voltage. By combining multiple LEDs in a series configuration, the total voltage rating matches AC power supply voltage, and the series connection ensures that current flows in one direction through each LED, preventing reverse current damage while enabling AC operation.
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 improves light emission efficiency by reducing the area occupied by electrodes, allowing for uniform current distribution and increased light output, as demonstrated by higher optical power output compared to traditional designs.
Implementation Method 1
An active layer, which emits light, is interposed between the lower and upper semiconductor layers
Data Source
AI summary
AC LED according to the present invention comprises a substrate, and at least one serial array having a plurality of light emitting cells connected in series on the substrate. Each of the light emitting cells comprises a lower semiconductor layer consisting of a first conductive compound semiconductor layer formed on top of the substrate, an upper semiconductor layer consisting of a second conductive compound semiconductor layer formed on top of the lower semiconductor layer, an active layer interposed between the lower and upper semiconductor layers, a lower electrode formed on the lower semiconductor layer exposed at a first corner of the substrate, an upper electrode layer formed on the upper semiconductor layer, and an upper electrode pad formed on the upper electrode layer exposed at a second corner of the substrate. The upper electrode pad and the lower electrode are respectively disposed at the corners diagonally opposite to each other, and the respective light emitting cells are arranged so that the upper electrode pad and the lower electrode of one of the light emitting cells are symmetric with respect to those of adjacent another of the light emitting cells.