Characterization And Research On The Electrostatic Failure Of GaN Based LED Thin Film Chips With Vertical Structure

In recent years,semiconductor lighting technology represented by GaN based LED has made great progress.LED products are widely used in various fields,such as backlight,commercial lighting,landscape lighting,outdoor lighting and display,have gradually enter the indoor lighting market.With the expansion of the application,higher requirements are put forward for the reliability of LED devices.During the manufacturing,packaging,installing and using,it will be hurt by electrostatic discharge(ESD),which will lead to the degradation of device performance even electrostatic failure.At present,the research on LED electrostatic failure is mostly based on the same side structure of sapphire substrate,while the research on GaN based LED chip with vertical structure integrated with Ag based reflector is less.Therefore,we studied the electrostatic failure of GaN based LEDs with vertical structure,and the results are following:(1)The basic properties of ESD black spots on GaN based LED chips integrated with Ag based mirrors after electrostatic test are characterized and studied.The results show that ESD black spot is one of the initial forms of electrostatic failure of GaN based LED with vertical structure,and its distribution position is random.With the increase of voltage,ESD black spot will eventually evolve into electrostatic hole.Through EDS component analysis of electrostatic breakdown spillage,the reason of ESD black spot may be due to the damage of Ag based reflector by electrostatic discharge,which leads to the decrease of Ag mirror reflectivity.(2)The influence of electrostatic breakdown on SiO2 passivation film and coarsening surface was studied.The results show that in the early stage of breakdown,there are series of changes in the morphology of passive film,such as rupture,loss,bulge,particle size becoming smaller and density increasing.It is found that the coarsening surface around the ESD black spot appears the phenomenon of particle becoming smaller and density increasing.The possible causes of the phenomenon are analyzed,the relationship between the phenomenon and electrostatic breakdown is explored.(3)The high temperature generated by electrostatic breakdown not only causes the coarsening surface to melt due to Gan melting,but also melts the local Ag based mirror,which results in the generation of ESD black spots.At the same time,under the joint action of high temperature and residual stress inside the chip,Cr/Pt protective layer and Pt/Ti/Ag barrier layer deform towards the position of electrostatic holes,showing an inverted V-shape.