High Resolution Micro-LED Arrays Using Au–Sn Flip-Chip Bonding

Abstract

In this article, a 0.39-in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$512\times384$ </tex-math></inline-formula> monochrome micro-light-emitting diode (Micro-LED) array was demonstrated using GaN epi-wafers on sapphire. The array, with a pixel size of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$13~\mu \text{m}$ </tex-math></inline-formula> and a pixel pitch of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$15~\mu \text{m}$ </tex-math></inline-formula> , is connected to the sapphire substrate by Au–Sn flip-chip bonding. A single pixel of Micro-LED shows an extremely low leakage current of 0.2 pA at −5 V and a low threshold voltage of 2.5 V. In the optical aspect, it has a maximum brightness of 10591.8 cd/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{m}^{{2}}$ </tex-math></inline-formula> (50.79%) at 700 mA, uniformity of 52.88% (4213.185 cd/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{m}^{{2}}{)}$ </tex-math></inline-formula> at small current 180 mA and 54.43% (10225.35 cd/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{m}^{{2}}{)}$ </tex-math></inline-formula> at high current 550 mA. The full width at half maxima (FWHM) of the array ranges from 14.5 to 18.4 nm and the peak wavelength variation is 2.1 nm. And it shows a deep-blue emission with CIE coordinates of (0.1506, 0.0289) at 100 mA. The use of high density Au–Sn flip-chip bonding in this work demonstrates a promising solution for the future bonding technology of Micro-LEDs with CMOS, as well as a new direction for the study of high resolution microdisplays.