Growth of nanostructured thin films for enhancing surface and barrier properties using Roll-to-Roll chemical and atomic layer deposition techniques

Abstract

In recent days flexible devices have begun to be regularly used in our daily lives for communications, renewable energy resources, and information technology. Conventional glass substrates can provide excellent protection from permeation species, but the glass substrate is rigid due to which it cannot be used for the application of flexible electronics. On the other hand, electronic devices made on flexible plastic substrates such as, organic thin film transistors (OTFTs), solar cells , and organic light emitting diodes (OLEDs) enable low cost, flexible, mass production and weight reduction in these devices. However, flexible polymer substrates can be easily damaged by the atmospheric gas molecules oxygen (O_2) and water (H_2O) and therefore these substrates must be protected with some additional encapsulating nanolayer. Several deposition techniques have been reported for the successful development of encapsulating thin films in order to protect electronic devices. These fabrication techniques include sputtering, thermal evaporation with good surface and barrier properties. However, these methods are only suitable for vacuum coating and rigid device coatings and cannot meet the requirements of atmospheric condition fabrication. Hence the researcher moved to the under atmospheric condition high quality thin film fabrication for flexible electronics applications.Among the variety of thin film process atmospheric roll to roll chemical and atomic layer deposition process have highly contributed thin film industry for mass production. This thesis report to the inoroganic TiO_2 and Al_2O_3 thin film deposited on a flexible PET substrate by using atmospheric roll-to-roll chemical and atomic layer deposition. The R2R-ACVD deposited (100° C) TiO_2 thin film expressed excellent surface,chemical,optical and electrical properties. The optical transmittance of the film displayed more than 91% in the visible region. The R2R-AALD developed single layer Al_2O_3 thin film also exhibited excellent surface,chemical and better barrier properties. Finally, a multilayer barrier thin film based on polyvinylidene difluoride (PVDF) – silicon dioxide (SiO_2) has been fabricated on the PET substrate through a novel method of joint fabrication techniques. The Inorganic SiO_2 thin film was deposited using a roll to roll atmospheric atomic layerdeposition system (R2R-AALD) while the organic PVDF layer was deposited on the surface of SiO2 through Electro hydrodynamic atomization (EHDA) techniques. The multilayer barrier thin films exhibited very good surface morphology, chemical composition and optical properties. The total thickness of the multilayer barrier thin film was 520 nm with a high optical transmittance value (85-90%). The obtained value of water vapor transmission rate (WVTR) of the barrier thin film was ~ 0.9 × 10^-2 g m^-2 day^-1. This combination of dual fabrication techniques R2R-AALD and EHDA for the development of multilayer barrier thin films are promising for gas barrier application.