Nondestructive Evaluation Of Junction Temperature Of LED With Optical Coherence Tonography

A light-emitting diode(LED)is a two-lead semiconductor light source,and a p-n junction diode,which emits light when activated.When a suitable voltage is applied to the leads,electrons are able to recombine with electron holes,releasing energy in the form of photons.However,junction temperature is an important issue for LED lifetime and performance.However,it is difficult to directly measure the junction temperature in the LED package.In this study,we use optical coherence tomography(OCT)for direct measurement of LED junction temperature.OCT,which is based on an interferometer configuration by receiving the backscattered signal from the sample,can reconstruct the depth-resolved microstructures of a sample in a depth range of 3 mm.The work of this paper mainly that are listed as follows:1.The development situation of LED and the importance of LED junction temperature are described.2.This paper describes the principle of optical coherence tomography and systematically elaborates the optical coherence tomography's development course that from time domain to frequency domain from the view of the definition of the interference theory.On this basis,this paper focuses on the two kinds of interferometer and understands the two different structures of the interferometer in the system of the difference between the imaging.3.For the research of the design of Lab VIEW software system,this paper focuses on the four components of the framework of the Lab VIEW system,which are sequential control,image acquisition,image processing and image reconstruction.4.When the LED operates normally,the author breakover bipolar voltage at 3 V by using the voltage method and compares the difference between the thermal conductive adhesive and the non-thermal conductive adhesive's LED,and the variation of the signal intensity of the phase of the chip.5.On the situation that a pulse current whose injection period of 7.5 mircoseconds to the LED is given and the influence of transient temperature effect is removed,the LED is going on between the light and the light,but the LED varies the on and off,however,it is on as we can see.In this way,the LED junction temperature is the same as the external temperature.By controlling the change of LED junction temperature,the relationship between the signal intensity and the interference signal intensity is observed.From the results,one can see that OCT could be a useful tool for nondestructive measurement of junction temperature of LED to evaluate the lifetime and performance.