A Study Of The Mist Deposition And Patterning Of Liquid Precursor Thin Films
Open Access
- Author:
- Shanmugasundaram, Karthikeyan
- Graduate Program:
- Electrical Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- April 29, 2008
- Committee Members:
- Jerzy Ruzyllo, Committee Chair/Co-Chair
Thomas Nelson Jackson, Committee Member
Joan Marie Redwing, Committee Member
Jian Xu, Committee Member
William Kenneth Jenkins, Committee Member - Keywords:
- selective deposition
shadow mask patterning
liquid precursor thin films
solution processed thin films
mist deposition
quantum dot LED - Abstract:
- Solution processed thin films have gained much importance in recent years with new development of materials and novel electronic and photonic devices. However, technology to form solution processed thin films has not kept pace with recent demands. The focus of this thesis is to study mist deposition as an alternate thin film deposition method for a broad range of applications with emphasis the deposition and on non-relief patterning of thin films. Three different classes of materials including enhanced metal organic decomposition dielectrics, small molecule organic solutions and inorganic nanocrystal quantum dot dispersions are investigated. Deposition kinetics of all the materials was studied first. Effects of process parameters, substrate surface properties and material properties on film morphology were studied. Results obtained indicate that evolution of surface charge on the substrate can impede or enhance the growth of the film laterally and vertically. Deposition time resulted in a linear growth in thickness for all the materials and smooth films. Electrical potential applied to the substrate was found to enhance deposition of the metal organic decomposition dielectrics and small molecule organic solutions while inhibiting film growth of the colloidal dispersions. Also, thickness of the deposited film was observed to scale directly with the material concentration. Deposition of CdSe nanocrystal quantum dots on polyethylsulfone (PES) flexible substrates was also demonstrated. Electrical properties of the small molecule organic solutions and the inorganic nanocrystal quantum dots were evaluated by fabricating light emitting diodes. Organic light emitting diodes fabricated using mist deposition emitted blue light with a maximum brightness of 3000 cd/m2 and luminous efficiency of 6.7 cd/A. Light emitting diodes fabricated with the inorganic nanocrystal quantum dots emitted red light at a maximum brightness of 1000 cd/m2 and a luminous efficiency of 1.5 cd/A. Experiments on patterning dielectric films by area selective deposition were carried out. Two approaches to patterning, first by utilizing the surface energy variations of the substrate materials and second by functionalizing the surface through the growth of a self assembled monolayer were investigated. Films were successfully patterned by both approaches. Results show that the ability of the precursor to form a dipole and the moisture content of the substrate surface are the two main drivers of area selective deposition for the first approach. In the latter approach, length of exposure of the self assembled monolayer to ultra violet light was found to determine patternability. Nanocrystal quantum dot dispersions were patterned by deposition through a mechanical mask. The conductivity of the mask itself was found to be a factor for film deposition. Masks made of a polyamide insulating material allowed film deposition while conducting steel masks prevented deposition. Evaporation rate of the solvent in the liquid precursor distorts the shape of the intended pattern. A mechanism for explaining this effect is proposed. CdSe nanocrystal quantum dot arrays of square patterns of sides 500 µm and 200 µm were successfully mist deposited through a mechanical mask. Finally lines of widths 200 µm, 500 µm, 1000 µm, 1500 µm and length 0.75 mm were patterned using a polyamide mask on glass and PES flexible substrates. Finally a new mask was designed for future fabrication of nanocrystal quantum dot displays and recommendations for further studies are made.