The Study of HfZnO Thin Film and Thin Film Transistor
Date Issued
2015
Date
2015
Author(s)
Lee, Chih-Hung
Abstract
This thesis reports the properties of the HfxZn1-xO thin films deposited by rf-sputtering and sol-gel method. The sputter-deposited HfxZn1-xO thin films were then used as the active layers of thin film transistors (TFTs) on the glass substrates. The sputtering HfxZn1-xO thin films with various Hf contents are sputter-deposited on glass substrates from HfxZn1-xO (x = 0, 2.5, 5, 7.5 and 10 at%) targets at room temperature. The incorporation of Hf in the ZnO film leads to the amorphization of the materials. As the annealing temperature increases, the built-in stresses in the thin films are relaxed. The optical bandgap increases with the Hf content, yet it decreases with the annealing temperature. This can be attributed to the alteration of strain (stress) status in the films and the slight grain growth. Hf doping increases the resistivity of ZnO owing to the disorder of the material structure and the higher bandgap. The electrical properties of the rf-sputtered HfxZn1-xO/ZnO heterostructures were also investigated. A highly conductive interface is formed at the interface between HfxZn1-xO and ZnO thin films as the ZnO annealing temperature exceeds 500°C, leading to the apparent decrease of the electrical resistance. The resistance decreases with an increase of either thickness or Hf content of the HfxZn1-xO capping layer. The second part of thesis reports the characterization of sol-gel derived HfxZn1-xO thin films deposited on glass substrates. The incorporation of Hf in the films increases the crystallinity of the as-deposited films. The bandgap increases with the Hf content but reduces after thermal annealing because of the relaxation of built-in stress, atomic rearrangement, and precipitation of HfO2. The resistivity of ZnO decreases as the annealing temperature increases owing to the improvement of crystallinity and reduction of defect densities. On the contrary, the resistivity of HfxZn1-xO thin films increases with the annealing temperature owing to the precipitation of HfO2 and reduction of oxygen vacancies. The electrical properties of sol-gel derived Hf0.1Zn0.9O/ZnO and ZnO/HfxZn1-xO heterostructures were also investigated. The amount of resistance reduction increases as the bottom layer annealing temperature increases. According to the XPS result, the incorporation of Hf in the films improves the Zn-O bonding state, and thermal annealing enhances metal-oxygen bonding. Sputtered HfxZn1-xO (x=0.005, 0.01 and 0.025) is used as the channel layer of the bottom-gate TFT with MgO dielectric layer deposited by e-beam evaporation. The Hf0.005Zn0.995O shows the better device performance. The Vth, S.S., μlin and on-off ratio values for the Hf0.005Zn0.995O TFT were 4.1 V, 1.66 V/dec, 9.0 cm2/Vs and >107. In the top gate TFTs, Hf0.1Zn0.9O/ZnO hetertstructure is used as the channel of TFTs. The multilayer enhances the electrical properties of TFTs. The Vth, S.S., and μlin, values for the Hf0.1Zn0.9O/ZnO TFT were 0.38 V, 1.79 V/dec, and 158 cm2/Vs.
Subjects
ZnO
HfZnO
Thin Film
Thin Film Transistor
Type
thesis
File(s)![Thumbnail Image]()
Loading...
Name
ntu-104-D99543012-1.pdf
Size
23.54 KB
Format
Adobe PDF
Checksum
(MD5):016c44e85614aabd87a32179e44b96ab