COLD ATMOSPHERIC PLASMA (CAP) ASSISTED DEPOSITION OF FUNCTIONAL SiO<sub>x</sub>/SiN<sub>x</sub> COATINGS FOR FLEXIBLE ELECTRONIC AND BIOMEDICAL APPLICATIONS
Creators: name: Kasisomayajula, Venkat
Publisher: name: Purdue University Graduate School
Year: 2024
Subjects: classificationCode: 401601
subject: Ceramics
classificationCode: 401605
subject: Functional materials
classificationCode: 401602
subject: Composite and hybrid materials
classificationCode: 401606
subject: Glass
classificationCode: 400906
subject: Electronic sensors
classificationCode: 400902
subject: Digital electronic devices

description: Thin films of ceramic materials are of significant importance in various industries due to their unique properties, versatility, and abundance. These materials are applied as thin layers on different types of substrates, providing a wide range of benefits and applications in industries such as automotive, aerospace, electronics, energy, and environmental monitoring. Historically, ceramic thin films have been used to enhance the properties and performance of metallic substrates by providing corrosion resistance, wear resistance, and thermal stability in harsh environmental and extreme conditions. Among various ceramic materials, thin films of silicon oxide (SiO<sub>x</sub>) and silicon nitride (SiN<sub>x</sub>) are the most widely used in the semiconductor and biomedical industries due to their excellent barrier properties, biocompatibility, and environmental stability. Traditionally, thin ceramic films or coatings of SiO<sub>x</sub> and SiN<sub>x</sub> are deposited using various methods including sol-gel, physical vapor deposition (PVD), chemical vapor deposition (CVD), atomic layer deposition (ALD), and thermal spraying. Despite the widespread use of traditional vapor deposition methods, their limitations such as the requirement of vacuum systems, high processing temperatures, slow deposition rates, and limited substrate capabilities render them unfitting for large scale manufacturing. To address the challenges associated with these traditional methods, this dissertation focuses on exploring the potential use of the cold atmospheric plasma (CAP) technology as an effective, scalable, and low-temperature approach for depositing SiO<sub>x</sub> and SiN<sub>x</sub> thin films under atmospheric conditions and demonstrating its applicability in sensing and packaging applications. In the first part of this dissertation, the CAP deposited silica coating is used as a key sensing element in flexible sensors. For the first time in literature, the demonstration of a low-cost and flexible glass-based pH sensor (sensitivity ~ 48mV/pH) consisting of CAP deposited silica coating as a sensing membrane is reported. In the second part, to realize the reliability and durability of these flexible electronic devices, robust encapsulation is achieved through a systematic study optimizing the conditions of plasma deposition while utilizing the CAP-deposited silica coating as an adhesion promoter to enhance the barrier properties of traditional polymeric encapsulants on flexible electronics devices. The third part aims to provide corrosion protection to electronic devices by applying ultrathin films of silica coatings with various thicknesses ranging from 75 nm to 1110 nm and varying degree of crosslink density and barrier properties. The final part demonstrates the effectiveness of CAP-deposited silica coating with enhanced antibacterial properties by integrating quaternary ammonium functionality to the coating for biomedical applications. In summary, these contributions in the CAP deposition technology can open up a new platform with tremendous opportunities toward scalable manufacturing of cost-effective and reliable devices for a broad range of applications.