Metal oxides and oxynitrides exhibit optical and electrical properties that can be tailored by the introduction of defects and impurities. Hafnium-based oxides and oxynitrides possess a dielectric constant between 16 and 30, band-offsets with Si above 1.4 eV and higher thermodynamic stability (when in contact with Si) compared with other high-kmaterials making them a viable replacement for SiO2 as the gate insulator in complementary metal-oxide-semiconductor (CMOS) transistors. We report on HfO2-xNx films deposited by high power impulse magnetron sputtering in an Ar-O2-N2 atmosphere with a series of nitrogen partial pressures. X-ray absorption spectroscopy has revealed effective passivation of O vacancies with nitrogen in energetically deposited HfO2-xNx films. Furthermore, atomic force microscopy and electron microscopy have shown that low-mobility interstitial species prevent crystallisation in nitrogen-incorporated films. These effects combine to remove leakage paths, resulting in superior breakdown strengths compared to films deposited without nitrogen.
In amorphous form, zinc tin oxide (ZTO) exhibits high transparency and higher n-type carrier mobility than amorphous Si. The structural and electronic properties of ZTO thin films deposited from a filtered cathodic vacuum arc have been studied using energy filtered electron diffraction and electron energy loss spectroscopy. Their conductivity is systematically dependent on growth temperature and post-deposition annealing temperature. Devices which exhibit both memristive switching and current-controlled negative differential resistance above room temperature have been formed on these ZTO films, suggesting suitability for electronic emulation of synapses and axons in neuromorphic circuits.