Publication Date
8-2025
Date of Final Oral Examination (Defense)
3-7-2025
Type of Culminating Activity
Dissertation
Degree Title
Doctor of Philosophy in Electrical and Computer Engineering
Department
Electrical and Computer Engineering
Supervisory Committee Chair
Jim Browning, Ph.D.
Supervisory Committee Co-Chair
Nirmala Kandadai, Ph.D.
Supervisory Committee Member
Marcus Pearlman, Ph.D.
Supervisory Committee Member
Kris Campbell, Ph.D.
Supervisory Committee Member
David Estrada, Ph.D.
Abstract
Advanced additive manufacturing techniques such as Inkjet Printing (IJP) and Aerosol Jet Printing (AJP) are used to fabricate printed electronics. These printed electronics require an additional sintering step to form conductive and functional traces. Traditionally, the prints are sintered thermally, under high temperatures, and for extended periods which disqualifies heat-sensitive substrates such as paper, textiles, and other polymer substrates. Plasma based sintering methods such as in situ sintering using a Plasma Jet Printer (PJP) and post-deposition sintering using Cold Atmospheric Pressure Plasma (CAP) have been developed to overcome this limitation. This research explores the mechanisms behind sintering in the in situ and post-deposition atmospheric pressure plasma sintering. These are explored in three different aspects: electron temperature, reactive and excited species in the plasma, and energy/dose of the plasma.
Electron temperature and excited and reactive species are explored in PJP using Optical Emission Spectroscopy (OES). The PJP using helium was operated with and without ink from 5 kV to 23 kV of applied AC voltage (28 kHz). Electron temperature was calculated to be around 0.1 – 0.3 eV across the 5 kV to 23 kV variation. This shows that electron temperature was not a major driving factor in sintering of ink depositions.
Presence of excited and reactive species in the plasma was determined by identifying the species through emission line peaks present in the emission spectrum of the plasma. Excited helium lines dominate the emission spectrum at lower voltages while excited molecular nitrogen second positive system (N2 SPS) emission lines dominate the spectrum at higher voltages. Presence of highly reactive hydroxyl (OH) radicals at higher voltages can also be observed from the emission spectra. It can be concluded that these species play a major role in in-situ plasma sintering. Highly energetic species like N2 SPS provides energy for the nanoparticles to diffuse and form conductive pathways with each other. OH radicals can degrade and break down organic compounds used as stabilizers in the ink. This allows for the metal nanoparticles in the ink to establish contact and facilitate grain formation.
Dose is a metric introduced in this research for analysis of post deposition plasma sintering. This parameter incorporates plasma power and treatment time to provide a normalized measure that allows for a direct comparison between different setups. It is defined as the total energy incident on the substrate per unit area. For this dissertation, a Boise State University (BSU) Low Temperature Co-Fired Ceramic (LTCC) Cold Atmospheric Pressure (CAP) plasma array was used for post-deposition sintering experiments (20 – 30 W). These experiments show that increased dose generally resulted in a decrease in resistivity of the print. Addition of water vapor to the plasma gas is also seen to increase the effectiveness of plasma treatment. This provides further evidence that OH radicals play a vital role in sintering as addition of water vapor increases the presence of OH radicals in plasma.
DOI
10.18122/td.2401.boisestate
Recommended Citation
Dhamala, Anupama Shree, "Understanding the Role of Atmospheric Pressure Plasma in Sintering of Metal Nanoparticle Ink" (2025). Boise State University Theses and Dissertations. 2401.
10.18122/td.2401.boisestate