A Study of Room Temperature Deposition Techniques on Insulator Substrates.

A Study of Electrophoretic Deposition (EPD) of Carbon Nanotubes on Insulator SubstratesJared DeSoto, Anirban Sarkar, and Theda Daniels-RaceApplied Hybrid Electronics Materials & Structures (AHEMS) LaboratoryDivision of Electrical and Computer Engineering School of Electrical Engineering and Computer ScienceLouisiana State University and A&M College, Baton Rouge, LA 70803SESAPS, 2013

Bottom right corner: SESAPS 20131Table of Contents

Carbon Nanotubes: Introduction and SynthesisSolution-Based Deposition TechniquesElectrophoretic DepositionFundamentalsBenefitsResearch MotivationExperimental ProcedureProcess RecipesExperimental ResultsConclusions and Future Work

Carbon Nanotubes (CNTs): Introduction and Synthesis

http://www.futuretimeline.net/21stcentury/images/carbon-nanotube-2040.jpghttp://jnm.snmjournals.org/content/48/7/1039/F1.large.jpgSingle-walled carbon nanotubes (SWCNTs)Multi-walled carbon nanotubes (MWCNTs)Single sheet of graphene rolled as a cylinderMultiple sheets of graphene rolled into concentric cylinders

Synthesis: Direct Growth

Arc Discharge (Prof. Ijima,1991)

2. Laser Ablation(Prof. Smalley, Rice University)

3. Chemical Vapor Deposition (CVD)Solution-Based Deposition TechniquesBenefits:Economical set-upRoom temperature processingLow cost Simple apparatus Solution based depositionChoice of solvents for dispersionDeposition of purified materialsControl of deposition parametersFast processing timeNo vacuumPotential to scale-up for mass productionPlastic and low temperature printing technologieshttp://spie.org/Images/Graphics/Newsroom/Imported/0969/0969_fig1.jpgUsed with Permission

State-of-the-art techniques:Spray Coating

Inkjet Printing

Drop CastingSpin CoatingDip/Rod CoatingAdd pictures for maybe spray coating and inkjet printing4Electrophoretic Deposition (EPD):Fundamentals and Benefits

Benefits of EPD:Simple experimental set up/ no vacuumFast processing, high yieldApplicable to any powdered solid that forms a stable suspensionBetter surface coverageControl of deposition thicknessSingle-step processingPossibility to scale up for large-scale applicationsTwo step process:Electrophoresis:Particle migration under electric field Deposition:Particle coagulation on the depositing electrode

Schematic of EPDChallenge and Research Motivation

EPD of CNTsPredominantly performed on conducting substrates e.g. Al, Cu, ITO and conducting polymersCNT-based thin film transistorsDeposition necessary on gate dielectric films (SiO2, polyimide, Al2O3) Research Objective:Study of Electrophoretic Deposition of CNTs on insulator (glass) substrates

Gate DielectricSource metalDrain metalSemiconducting CNT networks6Experimental Procedure

Pre-cleaning of glass substrates by piranha treatmentSurface functionalization by organosilane 20% APTES*Acid treatment of CNTs ( H2SO4:HNO3=3:1)Ultrasonic dispersion of CNTs in water (H2O): EtOH=1:1 Controlled drop casting of CNTs 2nd round of APTES treatment on the drop casted CNTsDispersion of acid-refluxed CNTs in IPA (EPD Solution)Electrophoretic Deposition Applied voltage: 100-150 V for 3 minutesAPTES*- 3-Amino propyl tri ethoxy silaneProcess Recipes:

Recipe ARecipe BRecipe CPiranha treatment 1 hr.Piranha treatment 1 hr.

Piranha treatment 1 hr.20% APTES- 1 hr.20% APTES- 1 hr.

20% APTES- 1 hr.

Drop castingSolvent: H2O: EtOH=1:1Drop castingSolvent: H2O: EtOH=1:1

Drop castingSolvent: H2O: EtOH=1:1

20% APTES- 1 hr.20% APTES- 1 hr.2% APTES- 1 hr.EPD voltage: 150 VDep. Time: 3 minEPD voltage: 30-40 VDep. Time: 3 min

EPD voltage: 150 VDep. Time: 3 min

Film Thickness: ~2.0mFilm Thickness: ~1.8mFilm Thickness: ~3.4mExperimental Results

EPD coated CNTsDrop casted CNTsOptical images of the EPD coated CNTs on drop casted layer of CNTs1 cmAppreciable surface coverageNo microscopic voids in the film morphologySEM image of the EPD coated filmsExperimental ResultsKLA Tencor Alpha Step results:

Average film thickness: ~2-2.5 m

Average surface Roughness: ~500-600 nm

Raman SpectroscopyAbsence of radial breathing modes (RBM)Disordered induced D-band (~1300 cm-1)Tangential G-band (~1600 cm-1)

Thickness and Surface RoughnessConclusion and Future WorkFuture work:Use of semiconducting CNTsUse of competing deposition techniques e.g. spray coating, inkjet printing to obtain the initial CNT coating CNT EPD on sputter coated silicon dioxide (SiO2), silicon nitride (SiN) filmsDevice Fabrication

First time study of EPD of CNTs on glass (insulator) substrates

Use of CNTs (drop casted) to deposit thick CNT films by EPD

Characterization of the deposited films ( SEM, Raman, Alfa Step data)

AcknowledgementsThis work was funded in part by the Louisiana Board of Regents (LEQSF(2011-14) -RD-A-07), NASA (2011)-DART-44, the generous support of Dr. Kristina Johnson, and the AES Corporation. We are also grateful for the use of the Electronic Material and Device Laboratory within the Division of Electrical & Computer Engineering (LSU).