Deposition of TiO_2/Al_2O_3 bilayer on hydrogenated diamond for electronic devices: Capacitors, field-effect transistors, and logic inverters

摘要

The wide bandgap semiconductor diamond has been studied to develop high-power and high-frequency electronic devices. Here, high dielectric constant (high-A:) TiO_2/Al_2O_3 bilayers are deposited on hydrogenated diamond (H-diamond) channel layers using sputter deposition (SD) and atomic layer deposition (ALD) techniques. Thin ALD-Al_2O_3 films are employed as buffer layers for the SD-TiO_2 and ALD-TiO_2 on H-diamond to suppress plasma discharge effect and to decrease leakage current density (J), respectively. The electrical properties of the resulting TiO_2/Al_2O_3/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-A1_2O_3 buffer layer, the ALD-TiO_2/ALD-Al_2O_3/H-diamond MOS capacitor shows a lower / and better capacitance-voltage characteristics than the SD-TiO_2/ALD-Al_2O_3/H-diamond capacitor. The maximum capacitance of the ALD-TiO_2/ALD-Al_2O_3/H-diamond capacitor and the k value of the ALD-TiO_2/ALD-AL_2O_3 bilayer are 0.83 µF cm~(-2) and 27.2, respectively. Valence band offset between ALD-TiO_2 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-TiO_2/ALD-Al_2O_3/ H-diamond and ALD-TiO_2/VALD-Al_2O_3/H-diamond MOSFETs show p-type, pinch-off, and enhancement mode characteristics with on/off current ratios around 10~9. The subthreshold swings of them are 115 and as low as 79 mV dec~(-1), respectively. The ALD-TiO_2/ALD-Al_2O_3/H-diamond MOSFET logic inverters, when coupled with load resistors, show distinct inversion characteristics with gains of 6.2-12.7.