Abstract:Single micro-light emitting diodes(LEDs) with different sizes and array micro-LED are designed and prepared, where the sizes of the single micro-LEDs are in a range of 40?100 μm, their electrodes are all co-N electrodes, P electrode is drawn out alone; the number of array pixels is $ 8\times8 $, which is a passively driving structure with a pixel size of 60 μm. In the process of device preparation, N electrode and P electrode are fabricated by the sputtering & stripping method. The electrode thickness is 2.4 μm. Thick photoresist 5120 is used as a mask, and N GaN is etched to the substrate by using the ICP dry etching to form an isolation trench. The PECVD technique is used to deposit an SiO2 insulating layer with a thickness of 10000 ?. By optimizing the electrode structure and thickness, the reliability of the P electrode at the slope of the isolation trench is improved, and the SiO2 insulating layer has good encapsulation; field programmable gate array (FPGA) is used to drive and display the micro-LED passive array. The single micro-LEDs of different sizes are tested and analyzed in the aspects of electrics, photics and thermotics and the results of which show that the current density corresponding to the peak radiation flux of 80 μm micro-LED is 1869.2 A/cm2, which is 57.1% higher than that of 100 μm micro-LED, indicating that the current density corresponding to the peak radiation flux of micro-LED increases as the size decreases; compared with the ordinary blue LED, the micro-LED has a large k factor, and with the size decreases, the value of the k factor increases, indicating that the micro-LED series resistance is larger, and the thermal stability is not so good as the traditional blue LED. Finally, the field programmable gate array (FPGA) can achieve a good drive for the micro-LED passive array. The driving principle is passive scanning driving, which is carried out in a row-by-row lighting mode. The FPGA clock is 50 MHz, and 320 ns is required for the circuit to scan all rows. Keywords:micro-light-emitting diode/ size effect/ k-factor/ passive
图 3 Micro-LED的尺寸与光通量和辐射通量的关系 (a) 光通量与电流密度的关系; (b) 辐射通量与电流密度的关系 Figure3. Size-dependent characteristics of luminous flux and radiant flux: (a) Current density versus luminous flux; (b) current density versus radiant flux.
23.2.热学特性 -->
3.2.热学特性
本实验对40—100 μm尺寸的Micro-LED进行不同温度下电压进行测量, 并拟合出在不同驱动电流下Micro-LED尺寸和k系数关系曲线, 如图4所示; 并且测量出环境温度与Micro-LED辐射通量的关系曲线, 如图5所示. 其中图4(a)—(c)分别是在测试电流0.5, 2.0和5 mA下测得的不同尺寸Micro-LED电压随温度变化, 图4(d)是由图4(a)—(c)拟合后得到的k系数曲线. 图 4 不同测试电流下温度与电压的关系, 以及k系数与Micro-LED尺寸的关系 (a) 0.5 mA下温度与电压关系图; (b) 2 mA下温度与电压关系图; (c) 5 mA下温度与电压关系图; (d) 使用最小二乘法拟合图(a)—(c)得到的k系数与尺寸的关系曲线 Figure4. Temperature versus voltage curves with various test current, and Micro-LED size versus k coefficient: (a) Temperature versus voltage curves at 0.5 mA; (b) temperature versus voltage curves at 2 mA; (c) temperature versus voltage curves at 5 mA; (d) size and drive current versus k coefficient.
图 5 不同温度和测试电流下尺寸和辐射通量的关系 Figure5. Micro-LED pixel size versus radiant flux with different temperature and test current.