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

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.