Performance comparison of flip-chip blue-light microLEDs with various passivation

Abstract

In this study, arrays of μLEDs in four different sizes (5 × 5 μm², 10 × 10 μm², 25 × 25 μm², 50 × 50 μm²) were fabricated using a flip-chip bonding process. Two passivation processes were investigated with one involving a single layer of SiO₂ deposited using plasma-enhanced chemical vapor deposition (PECVD) and the other incorporating Al₂O₃ deposited by atomic layer deposition (ALD) beneath the SiO₂ layer. Owing to superior coverage and protection, the double-layers passivation process resulted in a three-order lower leakage current of μLEDs in the 5 μm chip-sized μLED arrays. Furthermore, higher light output power of μLEDs was observed in each chip-sized μLED array with double layers passivation. Particularly, the highest EQE value 21.9% of μLEDs array with 5 μm × 5 μm chip size was achieved with the double-layers passivation. The EQE value of μLEDs array was improved by 4.4 times by introducing the double-layers passivation as compared with that of μLEDs array with single layer passivation. Finally, more uniform light emission patterns were observed in the μLEDs with 5 μm × 5 μm chip size fabricated by double-layer passivation process using ImageJ software.