Candidate: Mohsen Asad
Title: GaN-based micro-LED integration with thin-film transistor devices for flexible displays
Date: March 11, 2019
Time: 10:30 AM
Place: EIT 3142
Supervisor(s): Wong, William S.
Abstract:
Micron-sized inorganic light-emitting diodes (μ-iLEDs) have been extensively investigated as the core-technology for the next generation flat-panel and flexible display. In comparison with organic LEDs (OLEDs), μ-iLEDs provide higher efficiency, longer lifetime, and stronger luminescence. Recently, several technologies such as transfer-printing, epitaxial lift-off, and laser-induced transfer have been developed to remove μ-iLEDs from its rigid growth substrate onto a heterogenous substrate to fabricate bendable displays. In most flexible demonstrations, passive matrix (PM) is the dominant method to drive the μ-iLEDs despite the disadvantages of low-resolution and high power-consumption. Unlike the PM operation, active-matrix (AM) driving can provide benefits such as lower power consumption, uniform brightness over a large area, and easier grey-scale control of individual pixels. In addition, the efficiency of the flexible μ-iLEDs depends on the electrical and thermal properties of the bonding structures. Due to the absence of the precise conductive adhesive, fabrication of high-resolution vertically driven μ-iLEDs on flexible substrates has not been demonstrated yet. In this research, we propose a novel approach for low-cost mass-transfer of the μ-iLEDs from a growth substrate onto flexible substrates. This approach enables us to reliably integrate the μ-iLEDs with active matrix driving circuits for making flexible displays. All the electrical and optical characterization showed an improvement in μ-iLEDs’ performance after the transfer process. In addition, we have performed process and characterization development to understand the effect of down-scaling onto electro-optical performance of the μ-iLEDs. As preliminary results, we demonstrate that fine-size μ-iLEDs benefit from a better heat dissipation that consequent better emission stability at higher current densities. However, they are suffering from the larger defect densities at the sidewall that increases the value of ideality factor. Finally, the preliminary results for fabrication of high-resolution μ-iLEDs display will be presented. This work will pave the technology developments required for mass-transfer of μ-iLEDs from the growth substrate onto a heterogenous one with a high-yield and a low-cost.