Graduate Thesis Or Dissertation
 

Application of Self-Assembled Monolayers to InGaZnO Thin Film Transistors

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/1831cn61k

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  • Investigations on the application of self-assembled monolayers (SAM) to indium gallium zinc oxide (IGZO) thin film transistors (TFT) for fabrication and channel modification are presented. The back channel of IGZO thin film transistors can be modified by the absorption of self-assembled monolayers. The electrical properties of the IGZO exposed back channel are sensitive to surface chemistries and can be tailored using SAMs. Chemistry at the back channel interface alters device performance. The back channel surface sensitivities can be used in applications for chemical sensing TFTs. IGZO TFTs with and without octadecyl phosphonic acid applied to the back channel with varied channel thicknesses (10-50 nm) were examined. TFT parameters, such as, turn-on voltage, hysteresis, mobility, subthreshold swing, and current on/off ratio were evaluated by current-voltage electrical measurements. The use of electrohydrodynamic ink jet (EHDP) printing as non-contact method for patterning etch resists with sub-10 μm features was demonstrated for fabrication of IGZO TFTs. EHDP uses an electric field to generate ink droplets that can be smaller than the nozzle diameter. EHDP was used for depositing a self-assembled monolayer, n-hexyl phosphonic acid (HPA), and photoresist, SU8, as etch resists for patterning the IGZO TFT channel. Drop on demand printing is accomplished by overlapping of discrete droplets to form the desired feature. The optimal ink formulations and EHDP parameters were determined for each ink. Parameters were optimized for producing the smallest, uniform printed features. Bottom gate IGZO TFTs were fabricated by plasma sputtering IGZO onto a SiO₂/Si substrate. The IGZO TFT channels were patterned by printing HPA or SU8 ink as the etch resist, and using HCl as the etch solution. Indium tin oxide source and drain were deposited over the patterned channel using plasma sputtering. The electrical performance of IGZO TFTs patterned using HPA and SU8 were compared and evaluated using I-V electrical measurements. Drop on demand printing offers a high-speed, low cost route to TFT fabrication and manufacturing. The long narrow channels produced have applications for TFT sensor technologies. EHDP was shown to be capable of printing etch resists for the patterning and fabrication of IGZO TFTs on the scales relevant for digital displays.
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