Study On Two-dimensional Junction Temperature Measurement Technique Of LEDs Based On Microscopic Hyperspectrum

The semiconductor LED has become a widely used illumination and display source in the world due to its long life,environmental protection,high reliability,good color rendering and many other advantages.Although semiconductor LEDs are known as"cold light source",however,currently commercial LEDs on the market emit 60-70%of their energy in the form of heat energy.As a result,the junction temperature rises,which reduces the lifetime and reliability of LEDs.Therefore,the LED junction temperature problem has become the focus of the majority of scientific research workers.So far,there are many methods for detecting the junction temperature of LEDs,which are mainly divided into physical direct contact method,optical method using temperature sensitive optical parameters(TSOPs),and electrical method using temperature sensitive electrical parameters(TSEPs).The primary physical contact method,which,however,is subject to the size of detector and encapsulated LED chips has limitations.The peak wavelength method,the forward voltage method,and the blue-white ratio method in the electrical and optical methods all have certain limitations.The accuracy of the peak wavelength method is not high,the forward voltage method is limited by the current switching rate,the blue-white ratio method can only detect white LEDs made of yellow phosphors excited by the blue chip.Moreover,these methods can detect an average junction temperature.However,in fact,the junction temperature of LED devices is two-dimensional distribution.In order to detect the two-dimensional junction temperature distribution with high resolution,using the hyperspectral resolution and high spatial resolution of microscopic hyperspectral imaging technology,we have innovatively developed the microscopic hyperspectral centroid wavelength(MHCW)method.We use MHCW method to study the junction temperature of single semiconductor LED and multi-array LED.The main work and innovation of MHCW method include the following aspects:1.The hyperspectral imager is innovatively applied to the research of junction temperature detection of LED.Using the high spectral resolution and high spatial resolution of hyperspectral imaging technology,the working status of the LED is photographed.According to the linear relationship between the center of mass wavelength and the junction temperature of the LED,the two-dimensional junction temperature distribution of the chip was calculated.By comparison with thermocouple and infrared thermal imager,the junction temperature error measured by MHCW method is about 0.9?.Simultaneously,the spatial resolution of this method can reach sub-micron level.2.The effects of current intensity and duty cycle on chip temperature rise under pulse current correction mode are studied.By experiments,the following conclusions are drawn.Firstly,when the current is less than 350 mA,the temperature rise caused by 3%duty cycle of RGB LEDs is about 1?,which can ignore the effect of self-heating effect.Secondly,when the working current is about 550 mA,the duty cycle is more reasonable within 2%,the temperature rise is smaller,and the self-heating effect can be ignored.Thirdly,when the working current is about 750 mA,the duty cycle is less than 1.5%.3.The two-dimensional junction temperature and temperature interaction law of multi-array LED are analyzed by MHCW method.Through the research on array 2×2 multi-chip blue LED samples,the influence of surrounding chips on the temperature rise of a single chip is analyzed.The junction temperature distribution of a single chip in the array is derived and the reason for the uneven junction temperature is analyzed.