Capacitive LED Testing via Field Plate Current Injection
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Solution Overview
Problem
The challenge in manufacturing LED devices lies in functional testing of millions of micro-LEDs without direct electrical contact, which is essential for quality control and yield evaluation, especially on large substrates where individual contact is impractical due to the sheer volume of devices.
Innovation Solution
The method employs a non-direct electrical contact approach using a capacitive current injection (C2I) technique, where a dielectric-coated field plate drives current through a capacitor to inject current into LED devices, allowing functional testing with as few as two electrical contacts, and uses an integrating camera to measure light emission, enabling parallel testing of large numbers of devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If individual contact probes are used to test each LED device, then measurement precision is improved, but device complexity and ease of operation deteriorate due to the need for millions of contacts
Solution Approach 1:
The substrate is divided into multiple regions, each region containing multiple LED devices that share common anode or cathode contacts. This segmentation allows the test structure to be broken down into manageable units, reducing the overall complexity of individual contacts required.
Solution Approach 2:
Multiple LED devices are electrically combined by sharing common contact structures. Instead of providing individual contacts to each device, the invention merges the contact requirements by using common anode and cathode lines that serve multiple devices simultaneously, dramatically reducing the total number of contacts needed.
2Measurement precision
If individual contact probes are used for each LED device, then measurement precision is improved, but productivity deteriorates due to the time required to contact and test millions of devices
Solution Approach 1:
The common contact structures are pre-configured during substrate fabrication before the testing phase. This preliminary action of establishing shared electrical pathways eliminates the need for time-consuming individual contact establishment during testing, thereby improving productivity while maintaining measurement precision.
3Measurement precision
If direct electrical contact is made with each LED device, then measurement precision is improved, but reliability deteriorates due to the risk of device damage from probing
Solution Approach 1:
Common contact structures serve as intermediary elements between the test equipment and the LED devices. These intermediaries distribute the electrical contact load and reduce the mechanical stress on individual device contacts, thereby protecting device integrity while enabling precise functional testing through the shared contact pathways.
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 approach eliminates the need for high-pin count probe cards, reduces the risk of device damage, and allows for efficient, scalable testing of both small and large LED devices, including micro-LEDs, by avoiding direct electrical contact, thereby improving yield and reliability while reducing testing costs.
Implementation Method 1
a non-direct electrical contact approach where the current is injected through a capacitor formed using a dielectric-coated field plate
Implementation Method 2
a voltage ramp drives the electrodes to forward bias the LEDs situated between these electrodes, developing a displacement current that flows current into each of the large plurality of LED devices
Implementation Method 3
Light emitting diodes (LEDs) have been used as a replacement technology for conventional light sources
Data Source
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.