Capacitive Field-Plate Testing for High-Throughput Micro-LED Arrays
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Solution Overview
Problem
The challenge in the manufacturing process of light emitting diode (LED) devices is the difficulty in functional testing of millions of micro-LED devices without direct electrical contact, which is essential for quality control and yield evaluation, especially on substrates where individual contact is impractical due to the sheer volume of devices.
Innovation Solution
A non-direct electrical contact method using a capacitive current injection (C2I) approach, where a dielectric-coated field plate injects current through a capacitor driven by a suitable voltage waveform, allowing functional testing of LED devices without individual contact, utilizing a camera to measure light emission and enabling scalable testing from small to large devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If direct electrical contact testing is used for LED devices, then individual device functionality can be tested, but the complexity and cost increase significantly when testing millions of micro-LED devices
Solution Approach 1:
The patent segments the testing approach by dividing the substrate into regions with common contacts, allowing groups of LED devices to be tested simultaneously through shared electrical contacts rather than requiring individual contacts for each device
Solution Approach 2:
The patent makes the common contact structure serve multiple functions: it acts as both the electrical contact for current injection and as a reference electrode for capacitive sensing, eliminating the need for separate contact structures
2Reliability
If high-pin count probe cards are used for functional testing, then comprehensive device testing is achieved, but the risk of contact damage and manufacturing cost increase
Solution Approach 1:
The patent introduces a dielectric layer as an intermediary between the electrical contact and the LED devices, enabling capacitive coupling for current injection without direct physical contact, thereby eliminating mechanical damage risks
Solution Approach 2:
The patent replaces the mechanical probe card contact system with a field-based capacitive coupling system, where electrical signals are transmitted through electric fields across a dielectric barrier rather than through direct mechanical contact
3Measurement precision
If individual electrical contact is made for each LED device, then precise functional measurement is possible, but the manufacturing efficiency decreases due to the sheer volume of devices
Solution Approach 1:
The patent merges multiple testing operations into a single capacitive coupling step, where one field plate structure can simultaneously excite and sense multiple LED devices through their common contacts, dramatically increasing throughput
Solution Approach 2:
The patent adds a spatial dimension to the testing approach by using field plates positioned above or below the substrate plane, enabling parallel testing of multiple devices through the third dimension rather than requiring linear sequential contact
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 method eliminates the need for high-pin count probe cards, reduces the risk of contact damage, and allows for efficient, scratch-free testing of LED devices, significantly improving yield and reliability while enabling the testing of millions of devices with minimal contacts, thus enhancing manufacturing efficiency.
Implementation Method 1
a field plate comprising an electrode and a dielectric layer, the open face of the dielectric layer being in sufficient proximity to the open face of the LED device contact surface to capacitively couple a displacement current
Implementation Method 2
capacitively couple a displacement current through the LED device
Implementation Method 3
a camera...to capture the light emission response of the plurality of LED devices
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
Embodiments relate to functional test methods useful for fabricating products containing Light Emitting Diode (LED) structures. In particular, LED arrays are functionally tested by injecting current via a displacement current coupling device using a field plate comprising of an electrode and insulator placed in close proximity to the LED array. A controlled voltage waveform is then applied to the field plate electrode to excite the LED devices in parallel for high-throughput. A camera records the individual light emission resulting from the electrical excitation to yield a function test of a plurality of LED devices. Changing the voltage conditions can excite the LEDs at differing current density levels to functionally measure external quantum efficiency and other important device functional parameters. Spectral filtering is used to improve measurement contrast and LED defect detection. External light irradiation is used to excite the LED array and improve onset of charge injection light emission and throughput.