In this presentation, we discuss the integration of amorphous GaOx into back-gated transistors. The a-GaOx films (22 -100 nm) were grown by plasma-enhanced atomic layer deposition (PE-ALD). The conductivity of the films was tuned by changing the O2 plasma exposure time during the ALD cycles, which determines the content in oxygen vacancies. Back-gated transistors were fabricated with Al2O3 gate oxide on highly-doped Si substrate, with or without encapsulation of the top surface. The electrical properties of the devices will be discussed. Low sub-threshold swing (~150 mV/dec), on/off ratio >105 and operating drain voltage below 5V were obtained.
Mircea Modreanu, P. Hurley, B. O'Sullivan, Breda O'Looney, Jean-Pierre Senateur, H. Rousell, F. Rousell, M. Audier, C. Dubourdieu, Ian Boyd, Q. Fang, T. Leedham, S. Rushworth, A. Jones, Hywel Davies, C. Jimenez
The optical properties of a set of high-k dielectrics HfO2 thin films obtained by two different modified metal organic chemical vapour deposition (MOCVD) techniques were studied using spectroscopic ellipsometry (SE). HfO2 thin films with thickness varying from 10-40 nm were formed over a range of temperatures (300-425°C). After deposition the sample were annealed by Rapid Thermal Annealing (RTP) at 800°C in an oxygen/argon ambient and UV annealing at 400°C in oxygen. The films were analysed physically using XRD and FTIR. The XRD results show that as-deposited HfO2 films microstructure strongly depends on deposition temperature. Both polycrystalline (T>365°C) and amorphous films (T<320oC) were formed. The polycrystalline structure is identified as monoclinic. The SE results demonstrate that as-deposited amorphous HfO2 thin films have a high degree of porosity. After annealing at 800oC in oxygen and in nitrogen ambient, due to the solid phase crystallisation, as-deposited amorphous HfO2 thin films become crystalline and the film porosities are strongly reduced. In addition, an increase of the refractive index and a decrease of the film thickness are also obtained. Optical properties of the as-deposited polycrystalline HfO2 are also improved after annealing and an increase of the refractive index and a decrease of the film thickness is also obtained.
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