Study of an Atmospheric Pressure, Pulsed Arc Plasma Jet: Downstream Characterization and its Application to ZnO Thin Film Deposition
Date Issued
2010
Date
2010
Author(s)
Hsu, Yao-Wen
Abstract
An atmospheric pressure nitrogen plasma jet sustained by a repetitive pulsed DC power source is studied. The afterglow characteristics of this plasma jet are studied by an optical emission spectrometer and thermocouples. The effects of the process parameters, namely the applied voltage and the gas flow rate, on the plasma characteristics are investigated. It is shown that the plasma reactivity is controlled by the power deposition to the plasma as well as the decay process of the reactive species upon formation. The reactivity increases with the increase in the applied voltage and with the decrease in the gas flow rate. The jet temperature is primarily controlled by the power density, and it increases with the increase in the applied voltage and with the decrease in the gas flow rate. These observations suggest that the plasma reactivity and the jet temperature of this plasma jet can be nearly independently controlled.
The ZnO thin film deposition process by using an AP plasma jet is studied. In this process, nebulized solution is sprayed into the downstream of the nitrogen plasma jet to perform thin film deposition. XRD analysis confirms that this AP jet has the capability to convert zinc-salt containing solution to well-crystallized ZnO thin films with a hexagonal wurtzite structure in a short time. A 1.3 nm/s deposition rate is obtained using this process. Given the fast deposition rate of this process, we believe that both the temperature and the reactivity of the plasma play important roles. Conductive AFM reveals that there are clear grain boundaries, which leads high resisitivity of the films.
The effects of the plasma operating parameters, namely applied volitage and the gas flow rate, on the film quality are investigated. It is shown that the film quality is controlled by the gas temperature, the reactivity, and the resident time of precursor in the downstream. The film shows a better quality with a moderate distance between the jet nozzle and the substrate. Better quality films can be obtained with low gas flow rate. It is shown that the resident time appears to be the major factor that controls the film quality in this process. The grain size increases with an increase of gas temperature, which means high temperature is helpful for grain growth. By properly adjusting the operating parameters, the optimal deposition condition can be achieved.
Subjects
atmospheric pressure plasma jets
large-area deposition
thin films
ultrasonic spray
zinc oxide
Type
thesis
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