We review the failure modes and mechanisms of gallium nitride (GaN)-based light-emitting diodes (LEDs). A number of reliability tests are presented, and specific degradation mechanisms of state-of-the-art LED structures are analyzed. In particular, we report recent results concerning the following issues: 1) the degradation of the active layer induced by direct current stress due to the increase in nonradiative recombination; 2) the degradation of LEDs submitted to reverse-bias stress tests; 3) the catastrophic failure of advanced LED structures related to electrostatic discharge events; 4) the degradation of the ohmic contacts of GaN-based LEDs; and 5) the degradation of the optical properties of the package/phosphors system of white LEDs. The presented results provide important information on the weaknesses of LED technology and on the design of procedures for reliability evaluation. Results are compared with literature data throughout the text.

A Review on the Physical Mechanisms That Limit the Reliability of GaN-Based LEDs

GaN based high electron mobility transistors (HEMTs) have demonstrated extraordinary features in the applications of high power and high frequency devices. In this paper, we review recent progress in AlGaN/GaN HEMTs, including the following sections. First, challenges in device fabrication and optimizations will be discussed. Then, the latest progress in device fabrication technologies will be presented. Finally, some promising device structures from simulation studies will be discussed.

https://www.mdpi.com/2079-9292/7/12/377/pdf

A Comprehensive Review of Recent Progress on GaN High Electron Mobility Transistors: Devices, Fabrication and Reliability

Over the last years, GaN-based light-emitting diodes (LEDs) have been shown to be excellent candidates for the realization of high-efficiency light sources. White LEDs based on phosphor conversion can reach record efficiencies in excess of 150?lm?W?1, as demonstrated by several manufacturers and research groups. However, the reliability of white LEDs is still limited by a number of issues that must be addressed before these devices can find wide application in the market. This paper gives an overview on the most important physical mechanisms that limit the reliability of GaN-based LEDs for application in solid-state lighting. Starting from general considerations on the reliability of state-of-the-art white LEDs, the following degradation mechanisms are described in detail: (i) the degradation of the active layer of LEDs due to increased non-radiative recombination and reverse-bias stress; (ii) the degradation of the package/phosphor system, with subsequent worsening in the chromatic properties of the LEDs; (iii) the failure of GaN-based LEDs submitted to electrostatic discharge events. The data presented in this paper are critically compared with those reported in the literature.

/pdf/recent-results-on-the-degradation-of-white-leds-for-lighting-53pqxmkhrw.pdf

Recent results on the degradation of white LEDs for lighting

High-power white light-emitting diodes (LEDs) have attracted much attention due to their versatility in a variety of applications and growing demand in markets such as general lighting, automotive lamps, communications devices, and medical devices. In particular, the need for high reliability and long lifetime poses new challenges for the research and development, production, and application of LED lighting. Accurate and effective prediction of the lifetime or reliability of LED lighting has emerged as one of the key issues in the solid-state lighting field. Prognostic is an engineering technology that predicts the future reliability or determines the remaining useful lifetime of a product by assessing the extent of deviation or degradation of a product from its expected normal operating conditions. Prognostics bring benefits to both LED developers and users, such as optimizing system design, shortening qualification test times, enabling condition-based maintenance for LED-based systems, and providing information for return-on-investment analysis. This paper provides an overview of the prognostic methods and models that have been applied to both LED devices and LED systems, especially for use in long-term operational conditions. These methods include statistical regression, static Bayesian network, Kalman filtering, particle filtering, artificial neural network, and physics-based methods. The general concepts and main features of these methods, the advantages and disadvantages of applying these methods, as well as LED application case studies, are discussed. The fundamental issues of prognostics and photoelectrothermal theory for LED systems are also discussed for clear understanding of the reliability and lifetime concepts for LEDs. Finally, the challenges and opportunities in developing effective prognostic techniques are addressed.

A Review of Prognostic Techniques for High-Power White LEDs

A near-field scanning is usually time-consuming to map the electromagnetic field along the surface of a device. In this communication, a dual probe is proposed with a U-shaped loop to sense radio frequency (RF) magnetic and electric fields simultaneously, so that the one-time scanning by the dual probe can replace the two-time scanning by single-detector probes. Different from the traditional near-field scanning by using a single-detector probe and spectrum analyzer, the proposed scanning can be achieved by the two-output probe and a two-port vector network analyzer connecting to the probe. The efficient near-field scanning measurements of the electric and magnetic field on a conductor-backed coplanar waveguide transmission line and an RF power divider by using the dual probe are in agreement with those by using two single-detector probes.

Simultaneous Measurement of Electric and Magnetic Fields With a Dual Probe for Efficient Near-Field Scanning

The invention relates to a magnetic field detection module and a magnetic field probe. The magnetic field detection module comprises a strip line, a first coplanar waveguide transmission line, a second coplanar waveguide transmission line and a printed circuit board (PCB) for detecting an aperture, wherein a conductor belt of the strip line comprises a sensing part, a first connection part and a second connection part; the first coplanar waveguide transmission line comprises a first central conduction band and a second grounding conduction band; the second coplanar waveguide transmission linecomprises a second central conduction band and a second grounding conduction band; an orthographic projection of the sensing part on the PCB halfly surrounds the orthographic projection of a detectionaperture on the PCB; a first end of the sensing part is connected with a first end of the first connection part; a second end of the sensing part is connected with a first end of the second connection part; a first end of the first central conduction band is connected with a second end of the first connection part; a second end of the first central conduction band is used for connecting externalsignal analyzing equipment; a first end of the second central conduction band is connected with a second end of the second connection part; and a second end of the second central conduction band is used for connecting the external signal analyzing equipment.

Magnetic field detection module and magnetic field probe

The invention relates to a method, a device and a system for measuring a mechanical beam rigidity of a capacitive MEMS (Micro-Electro-Mechanical System) accelerometer. The method comprises: applying apreload voltage to the accelerometer, wherein the preload voltage comprises a first preload voltage and a second preload voltage; acquiring a first voltage change amount output by the accelerometer at the first preload voltage when the acceleration experienced by the accelerometer changes, and acquiring a second voltage change amount output by the accelerometer at the second preload voltage whenthe acceleration experienced by the accelerometer changes; and obtaining the mechanical beam rigidity of the accelerometer according to a first electrostatic negative rigidity of the first preload voltage, a second electrostatic negative rigidity of the second preload voltage, the first voltage change amount and the second voltage change amount. According to the method, the device and the system for measuring the mechanical beam rigidity of the capacitive MEMS accelerometer, the influence of the parameters, of the traditional measuring technology, such as displacement capacitance conversion coefficient, inertial mass block quality, etc., on the measurement precision when measuring the mechanical beam rigidity can be avoided, so that the measurement precision of the mechanical beam rigidityof the accelerometer is improved.

Method, device and system for measuring mechanical beam rigidity of capacitive MEMS accelerometer

The invention relates to a hydrogen effect testing device and system. The hydrogen effect testing device comprises a control module, an atmosphere regulation and control module, a sample testing module, a data acquisition module and a server electrically connected with the control module, wherein the sample testing module includes a sealed box body, a heater and a testing circuit board electrically connected with a device under test; the heater and the testing circuit board are arranged in the sealed box body; the heater is electrically connected with the control module; and the testing circuit board is electrically connected with the control module through the data acquisition module. The testing environment, namely, the atmosphere and temperature of the box body, of the device under testcan be conveniently regulated at any time by using the hydrogen effect testing device, so that influences imposed on the device under test by a hydrogen effect under different conditions can be tested, and thus the influences imposed on the device by the hydrogen effect can be tested comprehensively, accurately and quickly.

Hydrogen effect testing device and system

The application relates to a differential magnetic field probe, comprising an intermediate dielectric plate, a first magnetic field detection portion and a second magnetic field detection portion. Theintermediate dielectric plate is arranged between the first magnetic field detection portion and the second magnetic field detection portion; the end of a magnetic field detection wire in the first magnetic field detection portion and the end of a magnetic field detection wire in the second magnetic field detection portion are mechanically connected with the intermediate dielectric plate, whereinthe first magnetic field detection portion is used for sensing an external magnetic field to generate a first electrical signal and outputting the first electrical signal, the second magnetic field detection portion is used for sensing the external magnetic field to generate a second electrical signal and outputting the second electrical signal, and the first electrical signal and the second electrical signal form a differential signal. The differential common-mode rejection design is utilized to correspondingly generate and output first and second signals which form the differential signal;the differential signal is utilized to filter interference signals in the magnetic field detection process, so that electric field rejection ratio of the differential magnetic field probe is increased.

Differential magnetic field probe

The invention discloses a system for detecting the transmitting rate of an electronic assembly. The system comprises a temperature regulating system and a thermal imager, wherein the temperature regulating system comprises a thermostat and a temperature control unit, the electronic assembly is isolated from an external environment by the thermostat, the temperature of the electronic assembly is regulated by the temperature control unit based on the heat convection of air, an infrared detection window is formed in the thermostat, and the thermal imager is used for detecting the infrared irradiation energy of the electronic assembly through the infrared detection window. Through the application of the system provided by the invention, the electronic assembly is isolated from the external environment by the thermostat, the temperature of the electronic assembly which consists of elements made from various materials is regulated by the temperature control unit based on the heat convection of the air, and the infrared detection window is formed in the thermostat, so that the accurate regulation of the temperatures of all parts of the electronic assembly is realized; meanwhile, various materials are synchronously measured, and the accuracy of the obtained transmitting rate can be improved.

System for detecting transmitting rate of electronic assembly

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