Investigating the Performance and Reliability of Au-Sn Bonded Flip-Chip Micro-LEDs

In this article, a flip-chip
$15\times30$
blue micro-LED array with a pixel size of
$20\times 22\,\,\mu \text{m}$
and a pixel pitch of
$84.6~\mu \text{m}$
was prepared. The micro-LEDs connected with Si substrate containing Sn bumps by flip-chip bonding and sapphire substrate was removed by wet etching. Prior to bonding, the single micro-LED exhibits a leakage current of 2.91 pA at −5 V and a threshold voltage of 2.5 V. After bonding, the leakage current slightly rises to 3.97 pA while the threshold voltage stays constant. The micro-LED array has a high brightness of
$2.9\times 10^{{6}}$
cd/m2 at 1 mA, as well as the peak wavelength exhibits a blue shift of 6.3 nm. The FWHM increased from 14.5 to 23.2 nm within the range of
$10~\mu \text{A}$
to 1 mA. Moreover, the electrical, optical, shear force, and Au- Sn intermetallic compound (IMC) composition of the fracture surfaces of the micro-LEDs under different bonding conditions were also analyzed. At 280 °C, it presents a uniformly high luminance (
$1.51\times 10^{{5}}$
cd/m2) and a large shear force (2.83 g). With the further increase in temperature (320 °C), despite the increase in shear force (3.36 g), the luminous efficiency of micro-LED decreases significantly (
$5.7\times 10^{{4}}$
cd/m2). The essential steps and bonding parameters for preparing high-performance micro-LED arrays are discussed in this study, which provides useful guidance for the application of micro-LEDs in the field of display technology.