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CN-121986269-A - Micro-LED array for detection using non-contact field effect electroluminescence

CN121986269ACN 121986269 ACN121986269 ACN 121986269ACN-121986269-A

Abstract

Systems and methods for detecting micro LED arrays using non-contact field effect electroluminescence are disclosed.

Inventors

  • Z. Dulco
  • A. Verowitz
  • S - Jaber
  • A. Fourkosh
  • A. J. Fidler
  • P. Horvat
  • L. Asterebsky
  • G. Naduwori
  • P. Titten
  • SABB ANNMARIE LOUISE

Assignees

  • 塞米拉布半导体物理实验室有限公司

Dates

Publication Date
20260505
Application Date
20241004
Priority Date
20231004

Claims (20)

  1. 1. A method, comprising: Positioning an array of Light Emitting Diodes (LEDs) on a chuck; Positioning a transparent electrode relative to a surface of the LED array when the LED array is placed on the chuck such that the transparent electrode is separated from the surface of the LED array by a gap having a thickness of 0.1 micrometers to 100 micrometers, the gap containing a gas at ambient pressure or higher; applying a voltage to the transparent electrode sufficient to induce a current flow in at least some of the light emitting diodes of the LED array, the current flow causing electroluminescent emission in the light emitting diodes of the LED array; Obtaining an image of the LED array using the electroluminescent emission, and An emission characteristic of at least some of the light emitting diodes in the LED array is evaluated based on the obtained image.
  2. 2. The method of claim 1, further comprising venting gas into the gap while the transparent electrode is positioned relative to the surface of the LED array.
  3. 3. A method according to claim 1 or 2, wherein the gas is nitrogen.
  4. 4. A method according to any one of claims 1 to 3, wherein the chuck is a grounded chuck when the voltage is applied.
  5. 5. A method according to any one of claims 1 to 3, wherein the potential of the chuck is offset relative to ground potential upon application of the voltage.
  6. 6. The method of any preceding claim, wherein applying the voltage comprises varying the voltage between a minimum voltage to a maximum voltage.
  7. 7. The method of claim 5, wherein the maximum voltage during the change is below a breakdown field of the gas in the gap.
  8. 8. The method of claim 5, wherein varying the voltage comprises ramping the voltage at a plurality of different ramp rates sufficient to induce different current values through at least some of the light emitting diodes.
  9. 9. The method of claim 7, wherein evaluating the emission characteristic comprises: determining a functional dependence between the emission from the at least some of the light emitting diodes and a characteristic of an applied voltage, and Based on the functional dependence, an emission intensity of the at least some of the light emitting diodes for a preset current value is determined.
  10. 10. The method of any preceding claim, wherein positioning the transparent electrode relative to a surface of the LED array comprises measuring a thickness of the gap at least one measurement location and adjusting a relative position of the electrode relative to the surface of the LED array based on the thickness measurement.
  11. 11. The method of claim 9, wherein the thickness is measured at a plurality of measurement locations.
  12. 12. The method of claim 9, wherein the relative position is adjusted using one or more piezoelectric actuators.
  13. 13. The method of claim 9, wherein the relative position is adjusted by changing the pressure of the gas or the flow rate of the gas.
  14. 14. The method of claim 9, wherein adjusting the relative position improves uniformity of the thickness across the gap of the LED array.
  15. 15. The method of claim 9, wherein the thickness is measured at three different measurement locations outside an edge of the electrode and the relative position is adjusted at one or more of three different adjustment locations outside the edge of the electrode.
  16. 16. The method of claim 14, wherein the electrode has a central axis corresponding to an optical axis of an optical measurement system that acquires the image of the LED array, each of the three measurement locations is along a different radial direction from the central axis, and each of the three adjustment locations is along a respective one of the radial directions and at a different radial distance from the central axis than the respective measurement location.
  17. 17. The method of claim 9, further comprising calculating a gap thickness at one or more of the light emitting diodes based on the thickness measurements, and evaluating the emission characteristics comprises considering the gap thickness at each of the at least some of the light emitting diodes.
  18. 18. The method of claim 9, wherein the gap thickness is measured based on a capacitance between the transparent conductive electrode and the LED array.
  19. 19. A method according to any preceding claim, wherein the image is obtained through the transparent conductive electrode.
  20. 20. A method according to any preceding claim, wherein the light emitting diode is a micro LED.

Description

Micro-LED array for detection using non-contact field effect electroluminescence Background Micro LED (micro LED) arrays are a flat panel display technology employing micro LED arrays. Potential applications of the technology include wearable displays, such as displays used in Augmented Reality (AR) and/or Virtual Reality (VR) applications. To scale this technology to commercial levels, efficient, non-destructive inspection of micro LED arrays during fabrication is required. For example, it is desirable to identify defective individual Light Emitting Diodes (LEDs) or clusters of LEDs based on Electroluminescence (EL) intensity, emission wavelength, and emission peak half-width. There is also a need to identify systematic changes in emission characteristics, such as systematic intensity changes across the array (e.g., from shadowing effects). Disclosure of Invention Field Effect Electroluminescence (FEEL) refers to the excitation of light emission by application of a sufficiently high electric field to a material or device. Systems and methods for detecting and characterizing light emitting diode arrays (e.g., micro LED arrays) using FEELs are described herein. Specifically, the application of "air-bearing technology (air couchant technology)" (also referred to as "air-bearing method") can position the probe near but not in contact with the micro-LED array to be tested, thereby achieving repeatable and well-controlled capacitive coupling during the FEEL detection of the LED array. Among other advantages, the disclosed technique is non-contact, i.e., the probe does not contact the wafer under test during measurement. In High Volume Manufacturing (HVM) processes, non-contact measurement is an ideal choice for inspection and/or characterization because non-contact measurement generally causes less mechanical damage and/or contamination to the part being tested than measurement methods employing probes to contact the wafer, which can reduce yield. The disclosed techniques may be performed under ambient conditions, such as at ambient temperature and in the atmosphere. For example, the disclosed techniques may be implemented without the need to heat or cool the wafer under test and/or without the need to pump or purge air from the test environment. The detection at ambient conditions is faster and improves manufacturing throughput compared to processes involving temperature and/or atmospheric environmental changes. Other features and advantages will be apparent from the drawings, the following description, and the claims. Drawings FIG. 1 is a schematic diagram of an exemplary system for detecting micro-LED arrays using field effect electroluminescence; FIGS. 2A and 2B are schematic and top views of an exemplary probe of the system of FIG. 1, where FIG. 2A is a cross-sectional view of the exemplary probe (the probe may be rotationally symmetrical), and FIG. 2B is a top view of the bottom of the probe; FIG. 3A is a schematic diagram of an exemplary optical measurement system for use in the system shown in FIG. 1; FIG. 3B is a schematic diagram of another exemplary optical measurement system for use with the system shown in FIG. 1; Fig. 4 is a schematic diagram of another exemplary system for detecting micro LED arrays using field effect electroluminescence. In the drawings, like numbering represents like elements. Detailed Description Systems and methods for detecting and characterizing a Light Emitting Diode (LED) array using Field Effect Electroluminescence (FEEL) are described in which a transparent electrode is placed over and separated from a tested LED array supported by a chuck to form a capacitive coupling with the LED array. A time-varying voltage is applied to the transparent electrode to induce a forward current (J) to flow through at least some of the LEDs, causing them to produce Electroluminescence (EL). The value of this current is proportional to the value of the capacitance (C) and the rate of change of voltage (dV/dt) according to the following formula: In general, the maximum applied voltage should not exceed the breakdown field strength of the LED structure, e.g. of the dielectric material in the LED structure and between the terminals forming the capacitor. The capacitance C of the capacitive coupling depends on the distance between the LED array and the transparent electrode, and the dielectric constant epsilon of the medium between the transparent electrode and the LED array, calculated according to the following formula: Wherein A is the area of the capacitor, and T is the thickness of the dielectric layer between the transparent electrode and the LED array. As can be seen from this, to increase the current flowing through the LED, the capacitance C should be increased as much as possible. One way to increase the capacitance C is to reduce the thickness T of the dielectric layer between the transparent electrode and the LED array. Thus, in the exemplary systems described below, the gap betwee