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Theses Doctoral

MicroLED and Microdevices for Next-Generation Display Systems

Behrman, Keith

Micro light-emitting diode (microLED) technologies have been rapidly developing in the past decade and stand to be the prominent display technology for high-brightness applications. MicroLED microdisplays are particularly well-suited for systems that compete with high ambient light, such as augmented reality headsets and smartwatches that reflect light from the sun. However, there are several technological issues to overcome before microLED cost can be driven to a point that enables widespread commercial use.

This dissertation covers the current microLED technological landscape, key issues to overcome, and an in-depth discussion on microLED performance and applications using modeled and experimentally fabricated microLEDs. The first experiment focuses on microLED fabrication fidelity and methods to overcome the challenge of defect-free displays. Current ultra-high definition display resolution standards require approximately 25 million individual microLED emitters with an expected zero dead pixels. To better identify defect states at early stages of fabrication, this dissertation presents methods using photoluminescence and cathodoluminescence that can identify dry-etching related damage to GaN/InGaN microLEDs that result in dead pixels.

Expanding on fabrication fidelity, the second study in this dissertation examines surface recombination losses in etched GaN/InGaN microLEDs from nitrogen vacancy trap states. As microLED emitter size decreases, the ratio of etched surface area to emitter area size increases and injected current recombining at surface trap states increases causing large efficiency losses. To combat this, this study examines pGaN contact geometry selections and the influence on surface recombination losses. In particular, the results show that there is a strong dependence on efficiency for a desired output power in relation to current density.

Utilizing the fabrication knowledge from the first two studies, applications and implementations of microLED microdisplays as a structured illumination microscopy light source within miniaturized microscopes are presented. There is discussion on future miniaturization strategies and next steps to improve device performance.

Finally, this dissertation includes a short discussion on a display-adjacent technology, organic field-effect transistors (OFETs). An investigation on the electrostatic discharge resilience of parylene in OFETs is presented for applications in flexible high-voltage thin-film transistors.

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More About This Work

Academic Units
Electrical Engineering
Thesis Advisors
Kymissis, Ioannis
Degree
Ph.D., Columbia University
Published Here
June 14, 2021