Date of Award


Document Type


Degree Name

Master of Science


Department of Electrical and Computer Engineering

First Advisor

Tod V. Laurvik, PhD


This research utilizes plasma treatments as a method to decrease the contact resistance on zinc oxide (ZnO) thin film transistors (TFT). In recent years, researchers have achieved gigahertz RF switch cutoff frequency with ZnO TFTs. To further increase the cutoff frequency, the total resistance of this device must be minimized. Modern ZnO TFTs are fabricated with submicron channel lengths, which contains minimal resistance due to the TFT channel, making contact resistance significant to the total resistance of the device. This research developed a method to integrate plasma treatments into the fabrication of ZnO TFT to decrease the contact resistance, thus increasing the cutoff frequency of the device. Three plasma treatment methods were used, including Ar plasma generated in an inductively coupled reactive-ion etch (ICP-RIE) chamber, Ar plasma applied in-situ in a metal-sputter chamber before sputtering tungsten (W) contacts, and by remotely generated hydrogen plasma. The plasma treatments were implemented after the deposition of ZnO and prior to the deposition of sputtered tungsten (W) contacts. The plasma treatments increased the conductivity of the ZnO, which allowed for the formation of ohmic contacts on the ZnO TFT. The contact resistance of the untreated ZnO TFT sample was 1.9 ohm-mm, while the ICP-RIE Ar plasma treatment, in-situ Ar plasma treatment, and H plasma treatment demonstrated minimum contact resistances of 1.2, 1.0, and 1.5 ohm-mm respectively. The in-situ Ar plasma treatment demonstrated the best results, with a decrease in contact resistance of 47%.

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