LED Epitaxial Structure for Low Side Light in Optical Encoders
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Solution Overview
Problem
In optical encoders, LEDs used as optical signal generators suffer from sideway light emission, which interferes with the accuracy of measurement due to their proximity to photodetectors, leading to noise and erroneous detection.
Innovation Solution
A light-emitting diode (LED) design featuring a substrate with a light-tight reflective layer, epitaxial layers separated by a space to block current and reduce sideway light, and a non-conducting layer with a light-transmitting material to redirect light emissions effectively, minimizing sideway light emission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the LED is used in a reflective encoder with the photodetector on the same side, then the optical signal generation is achieved, but the sideway light emission is received by the photodetector causing measurement noise
Solution Approach 1:
The epitaxial layer is segmented into an inner epitaxial layer and an outer epitaxial layer that are separated by a separation space. This segmentation confines the light emission region to the inner epitaxial layer, preventing sideway light from reaching the photodetector while maintaining the optical signal generation function.
Solution Approach 2:
The harmful sideway light emission is extracted and isolated by creating a separation space between the inner and outer epitaxial layers. The outer epitaxial layer acts as a barrier that takes out the sideway light path from the system, preventing it from reaching the photodetector.
2Measurement precision
If the separation space is created between epitaxial layers to block current and reduce sideway light, then measurement accuracy is improved, but the device structure becomes more complex
Solution Approach 1:
The epitaxial layer is divided into inner and outer segments with a separation space between them. This segmentation achieves current blocking and sideway light reduction while maintaining a relatively simple overall structure that can be integrated into existing LED designs.
Solution Approach 2:
The separation space between the inner and outer epitaxial layers serves multiple functions simultaneously: it blocks electrical current to define the active emission region, prevents sideway light from reaching the photodetector, and maintains structural integrity. This multi-functionality reduces the need for additional components.
3Object-generated harmful factors
If the inner epitaxial layer is surrounded by the outer epitaxial layer with a separation space, then the light emission is confined to reduce noise, but the manufacturing process becomes more difficult
Solution Approach 1:
The epitaxial layer is grown in two sequential steps: first the inner epitaxial layer, then the outer epitaxial layer with a separation space between them. This segmented growth process allows for precise control of each layer's properties and simplifies the overall manufacturing compared to attempting to create the complex structure in a single step.
Solution Approach 2:
The inner epitaxial layer is grown first as a preliminary structure before growing the outer epitaxial layer. This preliminary action establishes the active emission region and separation space configuration early in the manufacturing process, making subsequent steps more straightforward and improving overall ease of manufacture.
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 LED design significantly reduces sideway light emission, enhancing measurement accuracy and reducing noise in optical sensors, thereby improving the reliability of optical encoders.
Implementation Method 1
a light-tight reflective layer, which is formed on the top surface of the substrate
Implementation Method 2
a non-conducting layer, which covers a top surface and the outside wall of the inner epitaxial layer and a top surface and the inside wall of the outer epitaxial layer, and covers a portion of the top surface of the light-tight reflective layer between the inner epitaxial layer and the outer epitaxial layer, the non-conducting layer comprising a light-transmitting material
Implementation Method 3
a first electrode, which is in electrical connection with the ohmic metallic body, the first electrode comprising a light-reflecting material
Data Source
AI summary
A light-emitting diode (LED) and a manufacturing method thereof are disclosed. The LED includes: a substrate, a light-tight reflective layer, an inner epitaxial layer, an outer epitaxial layer, a non-conducting layer, an ohmic metallic body, a first electrode, and a second electrode. The inner epitaxial layer and the outer epitaxial layer are separated from each other by a separation space. In a view made from a top side of the LED, the separation space forms a closed path and surrounds the light exit hole. The separation space provides an effect of blocking an electrical current and a light emission area in the inner epitaxial layer. By redirecting light emitting from a lateral side of the inner epitaxial layer toward a top side of the LED, the LED shows a low side light ratio.