The Study On The Reflective Layer And The Preparation Of LED Flip Chip

With the continuous development of the global economy,the demand for energy is increasing accordingly.Meanwhile,human beings all around the world are unprecedentedly concerned energy conservation and emission reduction.As a result,light-emitting diode?LED?becomes the focus of the world since its significant advantages of low energy consumption and high brightness.In recent years,LED flip chip is becoming a hot area of research not only for its good heat dissipation,but also for its long lifetime.However,the reflective layer adopted in current technology generally brings about the issues such as large contact resistance with P-GaN layer and uneven current distribution,resulting in a higher LED voltage and a poor luminous efficiency,which restrict the further development of the LED industry to some extent.Therefore,it is very important to carry out the research on reflective layer materials of the LED flip chip and related processing techniques.In this paper,vapor deposition and sputtering methods were conducted in the preparation of Ni/Ag/Au and ITO/Ag/TiW reflective layers.The surface topography of the reflective layers were characterized by atomic force microscopy?AFM?,and the annealing processes were optimized by the specific contact resistance?SCR?,square resistance and the optical characteristics at 455 nm wavelength.Then the prepared layers were applied in254?m×559?m GaN flip-chip independently,followed by electrical testing.The forward voltage and the light output efficiency of the prepared GaN flip-chip with ITO/TiW thin film measured by 60 mA driving current was 3.24 V and 89.6 mW,respectively.Compared with Ni/Ag/Au reflector,the forward voltage was decreased about 0.03V and efficiency of light output was increased about 0.7mW.The following conclusions can be drawn in the paper:?1?The optimum annealing conditions of Ni/Ag/Au coupon were as follows:N₂ flow rate:10 L/min;annealing temperature:400?;annealing time:10minutes.Under these conditions,the coupon's reflectivity for 455 nm wavelength was up to 96.3%;the SCR between the coupon and the P-GaN was 1.1×10^-2?·cm²;the RMS was just 7.06 nm.?2?The optimum annealing conditions of ITO film were as follows:Total N₂ amount:9L;annealing temperature ramp up at 25?/s and keeping the temperature at 550?for250 seconds.Under these conditions,the film's transmittance for 455 nm wavelength was up to 97.4%.In addition,due to annealing treatment,the square resistance declined from 311?/?to 89.3?/?,about 71.3%.