Deposition of TiO2/Al2O3 bilayer on hydrogenated diamond for electronic devices: Capacitors, field-effect transistors, and logic inverters

• Published in: Journal of applied physics Vol. 121; no. 22
• Main Authors: Liu, J. W., Liao, M. Y., Imura, M., Banal, R. G., Koide, Y.
• Format: Journal Article
• Language: English
• Published: Melville American Institute of Physics 14.06.2017
• Subjects: Aluminum oxide; Applied physics; Atomic layer epitaxy; Bilayers; Buffer layers; Capacitance-voltage characteristics; Capacitors; Diamonds; Electrical properties; Electronic devices; Field effect transistors; Hydrogenation; Inverters; Leakage current; Logic; Metal oxides; MOSFETs; Plasma jets; Resistors; Semiconductor devices; Thin films; Titanium dioxide; Transistors; Valence band; Wide bandgap semiconductors
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/1.4985066

The wide bandgap semiconductor diamond has been studied to develop high-power and high-frequency electronic devices. Here, high dielectric constant (high-k) TiO2/Al2O3 bilayers are deposited on hydrogenated diamond (H-diamond) channel layers using sputter deposition (SD) and atomic layer deposition (ALD) techniques. Thin ALD-Al2O3 films are employed as buffer layers for the SD-TiO2 and ALD-TiO2 on H-diamond to suppress plasma discharge effect and to decrease leakage current density (J), respectively. The electrical properties of the resulting TiO2/Al2O3/H-diamond metal-oxide-semiconductor (MOS) capacitors, MOS field-effect transistors (MOSFETs), and MOSFET logic inverters are investigated. With the same thickness (4.0 nm) for ALD-Al2O3 buffer layer, the ALD-TiO2/ALD-Al2O3/H-diamond MOS capacitor shows a lower J and better capacitance-voltage characteristics than the SD-TiO2/ALD-Al2O3/H-diamond capacitor. The maximum capacitance of the ALD-TiO2/ALD-Al2O3/H-diamond capacitor and the k value of the ALD-TiO2/ALD-Al2O3 bilayer are 0.83 μF cm−2 and 27.2, respectively. Valence band offset between ALD-TiO2 and H-diamond is calculated to be 2.3 ± 0.2 eV based on the element binding energies measured using an X-ray photoelectron spectroscopy technique. Both the SD-TiO2/ALD-Al2O3/H-diamond and ALD-TiO2/ALD-Al2O3/H-diamond MOSFETs show p-type, pinch-off, and enhancement mode characteristics with on/off current ratios around 109. The subthreshold swings of them are 115 and as low as 79 mV dec−1, respectively. The ALD-TiO2/ALD-Al2O3/H-diamond MOSFET logic inverters, when coupled with load resistors, show distinct inversion characteristics with gains of 6.2–12.7.