| Summary: | 碩士 === 國立清華大學 === 電子工程研究所 === 90 === N-channel metal-oxide-semiconductor field-effect-transistors (MOSFETs) using barium strontium titanate (Ba0.5,Sr0.5)TiO3 (BST) gate dielectric were successfully fabricated. The BST films are deposited by RF magnetron sputtering. The IDS-VDS and IDS-VGS characteristics are measured. The threshold voltage, the electron mobility, and the subthreshold slope are about 0.34 V, 295.4 cm2/V-s, and 106.9 mV/dec., respectively.
A two-capacitor model was used to extract the thickness of the native SiO2 layer between the BST and the Si substrate and the thickness is about 0.9 nm.
The leakage current conduction mechanism of BST thin films at room temperature is studied. For MIS structure, Schottky emission is dominant when the device is negatively biased. The barrier height of Al/BST extracted is 0.53 eV. Thermionic emission is dominant when the device is positively biased. The barrier height of BST/Silicon extracted is 0.56 eV. An Al/BST/Si energy band diagram based on these barrier heights is proposed.
The interface trap density, surface recombination velocity and the minority carrier lifetime in the field-induced region measured from gated diodes are 5.13×1014 cm-2eV-1, 4.17×104 cm/s and 1.9×10-10 s, respectively. Comparison with conventional MOSFETs with SiO2 gate oxide was made. It shows that the surface properties of BST transistors are worse than SiO2 transistors. For BST transistors, there are still many places for improvement in the future.
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