ADVANCES IN LARGE-AREA NANOPATTERNING BY NANOIMPRINT LITHOGRAPHY AND APPLICATIONS IN LIGHT-EMITTING DEVICES

Abstract

The research work presented in this dissertation focused on two main areas. One part is to discuss some novel nanofabrication techniques based on nanoimprint lithography (NIL) for making dielectric and metallic nanostructures on rigid or flexible substrates. The other part is to discuss the application of the fabricated nanostructures in light-emitting devices, particularly the organic light emitting diodes (OLEDs).

In the first part, several NIL based nanofabrication techniques are discussed: (a) a compositional NIL process is developed to fabricate a 400nm-pitch 2-D nanomesh mold from 1-D grating. And by using the nanomesh mold, dielectric nanomesh structures are patterned in the glass substrate; (b) a double-imprint NIL is developed to fabricate a hexagonal-lattice moiré pattern of pillar arrays which can be used as a micro-lens array; (c) a NIL process is developed to fabricate ultrathin (15nm) metallic nanomesh with 200nm pitch and large holes (180nm); (d) a variety of NIL, termed “transfer nanoprinting” is developed to fabricate metallic nanomesh on delicate flexible substrate (e.g., PDMS) which cannot sustain the high temperature or chemical used in typical NIL process.

In the second part, firstly, by replacing the conventional planar glass substrate with the dielectric nanomesh substrate (DNM-substrate) we developed, the OLEDs can achieve a 1.33-fold light extraction efficiency enhancement and a 1.8-fold power efficiency enhancement. Then by further improving the DNM-substrate, a high-index deep-groove dielectric nanomesh substrate (HDNM-substrate) is developed. And the OLED fabricated on this substrate achieve a 1.85-fold light extraction enhancement factor. Secondly, we demonstrate the convex-lens optical behavior of the hexagonal-lattice moiré pattern of pillar arrays by optical simulations. And by applying this pattern in the OLED substrates, over 100% light extraction enhancement is achieved. Thirdly, the ITO electrode of the OLED is replaced by MESH to form a metal/dielectric/metal plasmonic-cavity OLED, termed “PlaCSH-OLED”. Optical simulations demonstrate the optical antenna effect of the PlaCSH cavity with short cavity length at the LSPR wavelength of the MESH which can be used to enhance the light extraction efficiency. Experimentally, a working PlaCSH-OLED was demonstrated and we found the fabricated device exhibited optical microcavity resonant behavior rather than plasmonic cavity resonant behavior due to the long cavity length which indicated the improvement needed for the future work.