Method and system for measuring service life distribution of current carriers of electroluminescent micro LED (light-emitting diode)

Abstract

The invention discloses a method and a system for measuring the service life distribution of a carrier of an electroluminescent micro LED (Light Emitting Diode). The method comprises the following steps of: mounting the micro LED to be measured on a temperature control platform; configuring double output channels of a pulse delay generator, so that the trigger time of camera exposure is synchronized with the falling edge time of an electric pulse signal for driving the micro LED to emit light; sequentially delaying a triggering moment of camera exposure relative to a moment of an electric pulse signal falling edge based on a preset time delay step, and collecting a light-emitting grayscale image of the micro LED in an electric pulse falling edge stage; and based on a gray level image set arranged according to a time sequence, through fitting an attenuation curve of light intensity of each pixel point along with time change, carrier lifetime distribution information of the micro LED is extracted. According to the measurement method provided by the invention, the miniature LED carrier lifetime distribution measurement which is low in cost, high in time resolution and capable of deeply analyzing the carrier recombination mechanism is realized.

Description

Technical Field

[0001] This invention belongs to the field of chip testing technology, and in particular relates to a method and system for measuring the carrier lifetime distribution of electroluminescent micro-LEDs. Background Technology

[0002] Mini-LEDs are considered by the industry as the next-generation core technology for XR (including VR, AR, and MR) near-eye display systems due to their advantages such as self-illumination, ultra-high resolution, high brightness, and low power consumption. However, chip miniaturization leads to sidewall defects, distortion of material band structure, and degradation of metal electrode contacts, causing non-radiative recombination and reducing electro-optical conversion efficiency and reliability. To ensure the quality of miniature LEDs, optoelectronic characterization technology is particularly important, among which carrier lifetime measurement is key to locating defects and evaluating performance.

[0003] In existing technologies, time-resolved photoluminescence (TRPL) focuses on measuring the conditional charge carrier lifetime of photoluminescence, but the results are affected by the laser focal zone and structural layers, making it difficult to reflect the real electroluminescence scenario. Time-resolved electroluminescence (TREL) is more in line with practical LED applications, providing a two-dimensional mapping of the electroluminescence charge carrier lifetime. However, traditional TREL systems rely on expensive equipment such as high-speed cameras, image intensifiers, and precision retarders, resulting in high costs and system complexity, which limits their widespread application.

[0004] Therefore, there is an urgent need in this field for a low-cost, low-complexity solution that can achieve nanosecond-level carrier lifetime distribution measurement. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a method and system for measuring the carrier lifetime distribution of electroluminescent micro-LEDs, which solves the problems of high equipment cost and complex operation of existing TREL systems, and achieves high-precision, low-cost nanosecond-level lifetime distribution measurement.

[0006] This invention provides a method for measuring the carrier lifetime distribution of electroluminescent micro-LEDs, comprising the following steps: The micro LED under test is mounted on a temperature control platform and controlled to reach the target temperature. At the same time, the position of the micro LED is adjusted so that its light-emitting area is imaged onto the camera sensor. Configure a dual-output channel for the pulse delay generator to synchronize the trigger time of camera exposure with the falling edge time of the electrical pulse signal that drives the micro LED to emit light; Based on a preset time delay step, the trigger time of the camera exposure is delayed sequentially relative to the falling edge of the electrical pulse signal, and the camera is triggered to acquire the grayscale image of the micro LED during the falling edge stage of the electrical pulse after each delay, thereby obtaining a set of grayscale images arranged in time sequence. Based on the set of grayscale images arranged in a time series, the carrier lifetime distribution information of the microLED is extracted by fitting the decay curve of light intensity of each pixel over time.

[0007] Optionally, the process of mounting the micro-LED under test on a temperature-controlled platform and controlling it to reach the target temperature, while adjusting the position of the micro-LED so that its emitting area is imaged onto the camera sensor, includes: The micro LED is fixed to the heat sink of the temperature control platform, and the temperature of the heat sink is controlled at a preset target value; The spatial position of the micro-LED is adjusted by a displacement stage so that its light-emitting area is imaged onto the center of the sensor target surface of the camera via a microscope objective.

[0008] Optionally, configuring a dual-output channel of the pulse delay generator to synchronize the trigger time of the camera exposure with the falling edge time of the electrical pulse signal driving the micro-LED to emit light includes: The pulse delay generator is configured to generate a pulse electrical signal for driving the micro LED through its first output channel, and a pulse signal for triggering the camera exposure through its second output channel. The width and relative phase of the pulse signals generated by the first output channel and the second output channel are adjusted so that the rising edge of the pulse of the second output channel is aligned with the falling edge of the pulse of the first output channel to achieve synchronization.

[0009] Optionally, the pulse repetition frequency of the first output channel and the pulse repetition frequency of the second output channel of the pulse delay generator are the same, and its pulse period is greater than twice the single exposure time of the camera.

[0010] Optionally, the process of sequentially delaying the trigger time of the camera exposure relative to the falling edge of the electrical pulse signal based on a preset time delay step, and triggering the camera to acquire the grayscale image of the micro-LED during the falling edge phase of the electrical pulse after each delay, includes: The time delay step is on the order of nanoseconds or picoseconds; The single exposure time of the camera is at least one thousand times the typical carrier lifetime of the microLED; The acquired set of grayscale images covers the complete time process from the maximum light intensity to its 1 / e value.

[0011] Optionally, the process of extracting the carrier lifetime distribution information of the microLED by fitting the decay curve of light intensity over time for each pixel based on the set of grayscale images arranged in a time series includes: A double exponential decay model was used to fit the light intensity decay curve of each pixel; Based on the fitting results, the spatial distribution of the fast lifetime component characterizing defect recombination, the slow lifetime component characterizing radiative recombination, and the average carrier lifetime in the light-emitting region of the micro-LED is calculated and output.

[0012] Optionally, the double exponential decay model is a double exponential transient decay model or an integral average double exponential decay model.

[0013] This invention also proposes a carrier lifetime distribution measurement system for electroluminescent micro-LEDs, used to implement the method, comprising: A pulse delay generator with at least two output channels and a relative delay resolution between channels reaching the nanosecond level; The driver module, whose input terminal is connected to the first output channel of the pulse delay generator, is used to amplify the pulse signal to drive the micro LED; The camera, with its exposure trigger terminal connected to the second output channel of the pulse delay generator, is used to acquire the luminous image of the micro LED; The displacement stage and temperature control stage are used to support and adjust the position of the micro LED and control its operating temperature. The data storage and processing terminal is used to store the image data acquired by the camera and execute a carrier lifetime distribution fitting algorithm to extract the carrier lifetime distribution information of the microLED.

[0014] Optionally, the relative delay resolution between the two output channels of the pulse delay generator is no greater than 1 nanosecond.

[0015] Optionally, the driving signal output by the driving module is a pulse current or a pulse voltage.

[0016] Compared with the prior art, the present invention has the following advantages and technical effects: This invention replaces the high-speed camera and image intensifier required by traditional solutions with a conventional camera, and uses a pulse delay generator to achieve high-precision time control, eliminating the need for expensive precision delay devices, thus significantly reducing the hardware cost of the entire measurement system and making the system structure simpler, easier to operate and maintain.

[0017] This invention achieves high time resolution capture of the electroluminescence decay process of micro LEDs by configuring a pulse delay generator with nanosecond-level or shorter delay resolution and precisely controlling the delay step of the camera exposure trigger relative to the falling edge of the electric drive pulse, thus meeting the requirement for accurate measurement of micro LED carrier lifetime.

[0018] This invention employs a double exponential decay model to perform pixel-level fitting on the acquired light intensity decay image sequence, which can effectively distinguish and extract the fast lifetime component related to nonradiative recombination of defects and the slow lifetime component related to radiative recombination, thereby obtaining a two-dimensional distribution mapping of carrier lifetime, providing richer information for chip defect localization and performance evaluation.

[0019] The core of the system of this invention consists of a general-purpose pulse generator, a conventional camera, a drive module, etc. It has a simple structure, strong compatibility, and can be easily integrated into existing photoelectric testing or microscopic observation platforms, thereby improving the practicality and feasibility of the solution. Attached Figure Description

[0020] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings: Figure 1 This is a schematic diagram of the method flow according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the system structure according to an embodiment of the present invention; Figure 3 This is a schematic diagram of the test point sequence according to an embodiment of the present invention; Figure 4 This is a graph showing the double exponential fitting results of an embodiment of the present invention. Detailed Implementation

[0021] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0022] It should be noted that the steps shown in the flowchart in the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and although a logical order is shown in the flowchart, in some cases the steps shown or described may be executed in a different order than that shown here.

[0023] Example 1 like Figure 1 As shown, this embodiment provides a method for measuring the carrier lifetime distribution of an electroluminescent micro-LED, including the following steps: The micro LED under test is mounted on a temperature control platform and controlled to reach the target temperature. At the same time, the position of the micro LED is adjusted so that its light-emitting area is imaged onto the camera sensor. Configure the pulse width and phase of the dual output channels (CH1, CH2) of the pulse delay generator so that the trigger time of the camera exposure (CH2 trigger) is synchronized with the falling edge of the electrical pulse signal that drives the micro LED to emit light (CH1 control). Based on a preset time delay step, the trigger time of the camera exposure is delayed sequentially relative to the falling edge of the electrical pulse signal, and the camera is triggered to acquire the grayscale image of the micro LED during the falling edge stage of the electrical pulse after each delay, thereby obtaining a set of grayscale images arranged in time sequence. Based on the set of grayscale images arranged in a time series, the carrier lifetime distribution information of the microLED is extracted by fitting the decay curve of light intensity of each pixel over time.

[0024] The feasible process of mounting the micro-LED under test on a temperature-controlled platform and controlling it to reach the target temperature, while adjusting the position of the micro-LED so that its emitting area is imaged onto the camera sensor, includes: The microLED is fixed on the heat sink of the temperature control stage, and the temperature of the heat sink is controlled at a preset target value; the spatial position of the microLED is adjusted by the displacement stage so that its light-emitting area is imaged onto the center of the sensor target surface of the camera through the microscope objective.

[0025] In one specific implementation, a micro-LED is mounted on a temperature control stage, and the heat sink temperature is set to 25°C. The displacement stage is adjusted so that the LED emitting area is clearly imaged onto the camera sensor through a microscope (50× objective lens).

[0026] The feasible process of configuring a dual-output channel of the pulse delay generator to synchronize the trigger moment of the camera exposure with the falling edge moment of the electrical pulse signal driving the micro-LED to emit light includes: The pulse delay generator is configured to generate a pulse signal for driving the micro LED through a first output channel and a pulse signal for triggering the camera exposure through a second output channel. The width and relative phase of the pulse signals generated by the first and second output channels are adjusted so that the rising edge of the pulse from the second output channel is aligned with the falling edge of the pulse from the first output channel to achieve synchronization.

[0027] In one specific implementation, the pulse delay generator has the following characteristics: both CH1 and CH2 have a frequency of 1 kHz, CH1 has a pulse width of 1 μs, and CH2 has a pulse width of 500 μs. (Camera exposure time) T e =500μs, delay step T shift =1ns. The exposure trigger of CH2 was verified to be synchronized with the falling edge of CH1 using an oscilloscope.

[0028] Furthermore, the pulse repetition frequency of the first output channel and the second output channel of the pulse delay generator are the same, and its pulse period is greater than twice the single exposure time of the camera.

[0029] The feasible process of sequentially delaying the trigger time of the camera exposure relative to the falling edge of the electrical pulse signal based on a preset time delay step, and triggering the camera to acquire the luminous grayscale image of the micro-LED during the falling edge phase of the electrical pulse after each delay, includes: The time delay step is on the order of nanoseconds or picoseconds; The single exposure time of the camera is at least one thousand times the typical carrier lifetime of the microLED; The acquired set of grayscale images covers the complete time process from the maximum light intensity decay to its 1 / e value, and T shift It is negatively correlated with the number of images.

[0030] As a specific implementation method, with T shift =1ns increments, performing 200 delay offsets to cover the entire falling edge (200ns). 15 images are captured at each delay point, and the average is taken to reduce noise. Images are named and stored according to their time sequence, such as... Figure 3 The image shows a sequence of test points, displayed 200 times. T shift Delayed timing.

[0031] An feasible process for extracting carrier lifetime distribution information of the microLED by fitting the decay curve of light intensity over time for each pixel based on the time-series grayscale image set includes: A double exponential decay model was used to fit the light intensity decay curve of each pixel; based on the fitting results, the fast lifetime component characterizing defect recombination was calculated and output. τ 1) Characterizing the slow lifetime component of radiative recombination ( τ 2) and mean carrier lifetime ( τ avg ( ) Spatial distribution diagram of the light-emitting area of ​​the micro LED.

[0032] Furthermore, the double exponential decay model can be either a double exponential transient decay model or an integral average double exponential decay model, with the integral average double exponential decay model being preferred to reduce the impact of noise.

[0033] As a specific implementation method, the double exponential transient decay model is as follows: ; The integral-average double-exponential decay model is as follows: ; in, I ( t () represents light intensity. A1. A 2 represents the amplitude. τ 1. τ 2 represents the lifespan, whether fast or slow.

[0034] Camera exposure time T e Selection: Typical carrier lifetime is 40 ns. T e =500μs meets the requirement of ≥1000 times, ensuring the effectiveness of light intensity integration.

[0035] Preset fixed time interval T shift Option: 1ns stepping ensures nanosecond-level time resolution, covering the entire lifespan decay process.

[0036] The average lifespan is calculated as follows: ; Generate lifetime distribution maps, such as Figure 4 ,include τ 1. τ 2. τ avg Spatial distribution and goodness of fit R 2 .

[0037] On the other hand, such as Figure 2 As shown, this embodiment also proposes an electroluminescent micro-LED carrier lifetime distribution measurement system for implementing the method, including: A pulse delay generator with at least two output channels and a relative delay resolution between channels reaching the nanosecond level; The driver module, whose input terminal is connected to the first output channel of the pulse delay generator, is used to amplify the pulse signal to drive the micro LED; The camera, with its exposure trigger terminal connected to the second output channel of the pulse delay generator, is used to acquire the luminous image of the micro LED; The displacement stage and temperature control stage are used to support and adjust the position of the micro LED and control its operating temperature. The data storage and processing terminal is used to store the image data acquired by the camera and execute a carrier lifetime distribution fitting algorithm to extract the carrier lifetime distribution information of the microLED.

[0038] A feasible pulse delay generator: using the DG535 model, dual-channel output, with a relative delay resolution of 1ns.

[0039] Drive module: Integrated current amplifier, outputting pulse current (80mA) or voltage (5V).

[0040] Camera: Ordinary CMOS camera (such as Hikvision industrial camera), with adjustable exposure time.

[0041] Displacement stage: Three-dimensional precision displacement stage with positioning accuracy of ±1μm.

[0042] Temperature control table: thermoelectric refrigeration temperature control, range from 0℃ to 100℃, stability ±0.1℃.

[0043] Data storage and processing terminal: computer and custom MATLAB / Python processing scripts.

[0044] This embodiment achieves the following technical effects by employing a conventional area scan camera in conjunction with high-precision pulse delay triggering and image sequence analysis: Significantly reduces system cost and complexity: By using a conventional camera instead of the high-speed camera and image intensifier required by traditional solutions, and by using a pulse delay generator to achieve high-precision time control, expensive precision delay devices and other equipment are eliminated, resulting in a significant reduction in the hardware cost of the entire measurement system, and a simpler system structure that is easier to operate and maintain.

[0045] Achieving high-resolution lifetime measurement at the nanosecond level: By configuring a pulse delay generator with nanosecond-level or shorter delay resolution, the delay step of the camera exposure trigger relative to the falling edge of the electric drive pulse is precisely controlled, achieving high time resolution (up to 1 nanosecond or less) capture of the electroluminescence decay process of micro LEDs, meeting the requirements for accurate measurement of carrier lifetime of micro LEDs.

[0046] Provides in-depth carrier recombination mechanism analysis: By using a double exponential decay model to perform pixel-level fitting on the acquired light intensity decay image sequence, it is possible to effectively distinguish and extract the fast lifetime component related to nonradiative recombination of defects and the slow lifetime component related to radiative recombination, thereby obtaining a two-dimensional distribution mapping of carrier lifetime, providing richer information for chip defect localization and performance evaluation.

[0047] Enhanced system practicality and integration convenience: Since the core of the system consists of a general-purpose pulse generator, a conventional camera, and a drive module, the structure is simple and highly compatible. It can be easily integrated into existing optoelectronic testing or microscopic observation platforms, thus improving the practicality and feasibility of the solution.

[0048] In the implementation methods and claims, unless otherwise specified in the text, "a" and "described" can refer to a single or multiple features. Furthermore, if the embodiments of the present invention involve descriptions such as "first," "second," etc., these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features.

[0049] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for measuring the carrier lifetime distribution of electroluminescent micro-LEDs, characterized in that, Includes the following steps: The micro LED under test is mounted on a temperature control platform and controlled to reach the target temperature. At the same time, the position of the micro LED is adjusted so that its light-emitting area is imaged onto the camera sensor. Configure a dual-output channel for the pulse delay generator to synchronize the trigger time of camera exposure with the falling edge time of the electrical pulse signal that drives the micro LED to emit light; Based on a preset time delay step, the trigger time of the camera exposure is delayed sequentially relative to the falling edge of the electrical pulse signal, and the camera is triggered to acquire the grayscale image of the micro LED during the falling edge stage of the electrical pulse after each delay, thereby obtaining a set of grayscale images arranged in time sequence. Based on the set of grayscale images arranged in a time series, the carrier lifetime distribution information of the microLED is extracted by fitting the decay curve of light intensity of each pixel over time.

2. The method according to claim 1, characterized in that, The process of mounting the micro-LED under test on a temperature-controlled platform and controlling it to reach the target temperature, while adjusting the position of the micro-LED so that its emitting area is imaged onto the camera sensor, includes: The micro LED is fixed to the heat sink of the temperature control platform, and the temperature of the heat sink is controlled at a preset target value; The spatial position of the micro-LED is adjusted by a displacement stage so that its light-emitting area is imaged onto the center of the sensor target surface of the camera via a microscope objective.

3. The method according to claim 1, characterized in that, The process of configuring the dual output channels of the pulse delay generator to synchronize the trigger time of the camera exposure with the falling edge time of the electrical pulse signal driving the micro LED to emit light includes: The pulse delay generator is configured to generate a pulse electrical signal for driving the micro LED through its first output channel, and a pulse signal for triggering the camera exposure through its second output channel. The width and relative phase of the pulse signals generated by the first output channel and the second output channel are adjusted so that the rising edge of the pulse of the second output channel is aligned with the falling edge of the pulse of the first output channel to achieve synchronization.

4. The method according to claim 3, characterized in that, The pulse repetition frequency of the first output channel and the second output channel of the pulse delay generator are the same, and its pulse period is greater than twice the single exposure time of the camera.

5. The method according to claim 1, characterized in that, The process of sequentially delaying the camera exposure trigger time relative to the falling edge of the electrical pulse signal based on a preset time delay step, and triggering the camera to acquire the luminous grayscale image of the micro-LED during the falling edge phase of the electrical pulse after each delay, includes: The time delay step is on the order of nanoseconds or picoseconds; The single exposure time of the camera is at least one thousand times the typical carrier lifetime of the microLED; The acquired set of grayscale images covers the complete time process from the maximum light intensity to its 1 / e value.

6. The method according to claim 1, characterized in that, Based on the set of grayscale images arranged in a time series, the process of extracting the carrier lifetime distribution information of the micro-LED by fitting the decay curve of light intensity over time for each pixel includes: A double exponential decay model was used to fit the light intensity decay curve of each pixel; Based on the fitting results, the spatial distribution of the fast lifetime component characterizing defect recombination, the slow lifetime component characterizing radiative recombination, and the average carrier lifetime in the light-emitting region of the micro-LED is calculated and output.

7. The method according to claim 6, characterized in that, The double exponential decay model is either a double exponential transient decay model or an integral average double exponential decay model.

8. A system for measuring the carrier lifetime distribution of an electroluminescent micro-LED, used to implement the method according to any one of claims 1-7, characterized in that, include: A pulse delay generator with at least two output channels and a relative delay resolution between channels reaching the nanosecond level; The driver module, whose input terminal is connected to the first output channel of the pulse delay generator, is used to amplify the pulse signal to drive the micro LED; The camera, with its exposure trigger terminal connected to the second output channel of the pulse delay generator, is used to acquire the luminous image of the micro LED; The displacement stage and temperature control stage are used to support and adjust the position of the micro LED and control its operating temperature. The data storage and processing terminal is used to store the image data acquired by the camera and execute a carrier lifetime distribution fitting algorithm to extract the carrier lifetime distribution information of the microLED.

9. The system according to claim 8, characterized in that, The relative delay resolution between the two output channels of the pulse delay generator is no greater than 1 nanosecond.

10. The system according to claim 8, characterized in that, The driving signal output by the driving module is a pulse current or a pulse voltage.

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