Light emitting diodes reliability review

Self-healing is a smart and promising way to make materials more reliable and longer lasting. In the case of structural or functional composites based on a polymer matrix, very often mechanical damage in the polymer matrix or debonding at the matrix–filler interface is responsible for the decrease in intended properties. This review describes the healing behavior in structural and functional polymer composites with a so-called intrinsically self-healing polymer as the continuous matrix. A clear similarity in the healing of structural and functional properties is demonstrated which can ultimately lead to the design of polymer composites that autonomously restore multiple properties using the same self-healing mechanism.

Self-repair of structural and functional composites with intrinsically self-healing polymer matrices: A review

Increasing the reliability of solid state lighting systems via self-healing approaches: A review

A moisture- electrical – temperature (MET) test is proposed to evaluate the outdoor reliability of high power blue LEDs, with and without phosphor, and to understand the degradation physics of LEDs under the environment of combined humidity, temperature and electrical stresses. The blue LEDs with phosphor will be the high power white LEDs. Scanning acoustic microscopy is used to examine the resulted delamination during this test for the LEDs. The degradation mechanisms of blue LEDs (LEDs without phosphor) and white LEDs (LEDs with phosphor) are found to be different, under both the power on (i.e. with 350 mA through each LED) and power off (i.e. without current supply) conditions. Difference in the coefficient of thermal expansion between the molding part and the lens material as well as the heat generated by the phosphor layer are found to account for the major differences in the degradation mechanisms observed. The findings indicate that the proposed MET test is necessary for the LED industry in evaluating the reliability of LEDs under practical outdoor usage environment.

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Degradation Physics of High Power LEDs in Outdoor Environment and the Role of Phosphor in the degradation process.

In this research work, in order to solve the unadjustability of traditional noble metal absorbers to meet the complex application requirements in the actual electromagnetic environment, we designed a simple tunable absorber based on graphene with tunable Fermi level. The performance of the proposed absorber is theoretically simulated by the finite difference time domain (FDTD) method. The proposed absorber has two perfect absorption peaks with high efficiency of 99.51% and 99.548% in its working band (90–155 μm). We have performed an in-depth analysis of the causes of perfect absorption and focused on the tunability of the absorber. The absorption frequency can be adjusted by controlling the relaxation time and Fermi level of graphene, and the same purpose can be achieved by changing the refractive index (relative dielectric constant) of the medium. In addition, we also explored the influence of the change of the top structure parameters on the absorption performance. The proposed absorber has the ability to adapt to different electromagnetic environments. In general, it can be flexibly regulated in practical applications, which will provide new possibilities for the development of many fields such as detection and communication. 

Multimode tunable terahertz absorber based on a quarter graphene disk structure

The reliability of LED is key to its application system. In this paper, the frequent failure modes and mechanisms such as chip failure and packaging failure were investigated through several failure analysis cases. Based on these analysis results, several methods to improve LED's reliability are reported in this paper.

Analysis on failure modes and mechanisms of LED

The invention discloses a short-term life test data-based quick life evaluation method, which comprises the following steps of: (1) selecting proper stress to perform life test on a device to obtain original data; (2) establishing a mathematical model based on data obtained by the life test; (3) performing linear regression analysis on the life test data; (4) determining model parameters by using a least square method principle; (5) performing calculation of test of goodness of fit to judge validity of the model; (6) calculating significance test statistic, and determining whether a regression equation has significance under a given significance level condition; and (7) statistically analyzing a reliability quantitative index of the test device by using a weibull distribution function and the established mathematical model to obtain a life index and life distribution of the device.

Short-term life test data-based quick life evaluation method

Abstract Two-dimensional (2D) materials exhibit fascinating and outstanding optoelectronic properties, laying the foundation for the development of novel optoelectronic devices. However, ultra-weak light absorption of 2D materials limits the performance of the optoelectronic devices. Here, a structure of MoS2/graphene/Au integrated onto the side-polished fiber (SPF) is proposed to achieve a high-performance fiber-integrated multifunction-in-one optoelectronic device. It is found that the device can absorb the transverse magnetic (TM) mode guided in the SPF and generate photocurrents as a polarization-sensitive photodetector, while the transverse electric (TE) mode passes with low loss through the device, making the device simultaneously a polarizer. In the device, the MoS2 film and the Au finger electrode can enhance the TM absorption by 1.75 times and 24.8 times, respectively, thus allowing to achieve high performance: a high photoresponsivity of 2.2 × 105 A/W at 1550 nm; the external quantum efficiency (EQE) of 1.76 × 107%; a high photocurrent polarization ratio of 0.686 and a polarization efficiency of 3.9 dB/mm at C-band. The integration of 2D materials on SPF paves the way to enhance the light–2D material interaction and achieve high performance multifunction-in-one fiber-integrated optoelectronic devices.

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High performance multifunction-in-one optoelectronic device by integrating graphene/MoS2 heterostructures on side-polished fiber

The invention discloses a service life test online monitoring system for a kilowatt large-power laser diode array, which comprises a current driving system, a parameter measuring system, a temperature control system, a circuit protecting system and a computer control system The current driving system is used for providing driving current for a multi-station tested device, the parameter measuring system is used for monitoring change information of a device power or wavelength along with time in the service life test process, and the temperature control system is used for controlling stable temperature of the tested device The circuit protecting system is used for detecting working conditions in service life test process of the laser diode laser array and shutting off a power output module and sending out abnormal signals to the computer control system when the laser is monitored to be in an abnormal working condition The computer control system is mainly used for achieving collection, analysis processing and control of test parameter data, safety protection of a laser diode (LD) and data storage

Service life test online monitoring system for kilowatt large-power laser diode array

Despite the superior working properties, GaN-based HEMTs and systems are still confronted with the threat of a transient ESD event, especially for the vulnerable gate structure of the p-GaN or MOS HEMTs. Therefore, there is still an urgent need for a bidirectional ESD protection diode to improve the ESD robustness of a GaN power system. In this study, an AlGaN/GaN ESD protection diode with bidirectional clamp capability was proposed and investigated. Through the combination of two floating gate electrodes and two pF-grade capacitors connected in parallel between anode or cathode electrodes and the adjacent floating gate electrodes (CGA (CGC)), the proposed diode could be triggered by a required voltage and possesses a high secondary breakdown current (IS) in both forward and reverse transient ESD events. Based on the experimental verification, it was found that the bidirectional triggering voltages (Vtrig) and IS of the proposed diode were strongly related to CGA (CGC). With CGA (CGC) increasing from 5 pF to 25 pF, Vtrig and IS decreased from ~18 V to ~7 V and from ~7 A to ~3 A, respectively. The diode’s high performance demonstrated a good reference for the ESD design of a GaN power system.

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Guoguang Lu

Papers

Analysis on failure modes and mechanisms of LED

Short-term life test data-based quick life evaluation method

High performance multifunction-in-one optoelectronic device by integrating graphene/MoS2 heterostructures on side-polished fiber

Service life test online monitoring system for kilowatt large-power laser diode array

A Novel Bidirectional AlGaN/GaN ESD Protection Diode