Micro- and nano-soft lithography for the fabrication of photonic devices

Rights statement
Awarding institution
  • University of Strathclyde
Date of award
  • 2016
Thesis identifier
  • T14601
Person Identifier (Local)
  • 200950951
Qualification Level
Qualification Name
Department, School or Faculty
  • This thesis presents the application of two soft lithographic tools for direct patterning of (soft) photonic materials at the micro- and nano-scale. Inkjet printing and Dip-Pen Nanolithography, respectively, have been used to pattern organic molecules, photoresists, and conductive inks to create optically active structures and devices. A series of light emitting polymers (LEPs), blended with a photo-curable host system, have been integrated as colour converters with an array of matrix-addressable gallium nitride (GaN) micro LEDs to form a red-green-blue (RGB) emitting array. Surface structure and conversion efficiency have been explored in detail with peak colour conversion efficiencies of 31.6% being obtained.Inkjet printing of silver conductive inks has been used in conjunction with mask-free ultraviolet direct writing to generate an 8 x 8 GaN LED array. The smallest feature achieved with the mask-free writing set up is 1 μm and the conductive ink was used to form a contact with the n-GaN to enable wire-bonding and characterisation of the LED. This mask-free process is attractive as fabrication of conventional masks for photolithography is both costly and lengthy. Possessing the ability for define LED patterns "free form" on photoresist and subsequently producing a common n-contact with the silver ink allows for rapid prototyping for novel and experimental LED designs.Two techniques were explored for utilising the potential of Dip-Pen Nanolithography; deposition of liquid inks (positive) and removal of dried material (negative). Photoresist inks were used to generate nanoscale features (560nm) on a planar LED structure. Subsequent exposure to a CHF3 plasma treatment deactivated the Mg doped GaN which was not protected by the photoresist; LEDs with 3 μm diameter at full-width half-maximum were fabricated in this manner. Utilising dip-pen nanolithography for negative patterning allows for grating structures to be created via the displacement and removal of material. 1D and 2D structures were generated using a lasing polymer as the optically active gain medium. When optically pumped it was found that these structures lased and the grating structures acted as Distributed Bragg Reflectors (DBRs).Key advantages for the techniques used throughout this thesis are that they allow the patterning of sensitive materials that otherwise would not survive classical lithography due to aggressive chemical treatment or high UV exposure. In addition all of the techniques used are readily programmable and require no masks to be fabricated thus allowing for rapid prototype production and experimental designs to be implemented without delays or incurring extra costs.
Resource Type
Date Created
  • 2016
Former identifier
  • 9912554593402996