ICMCTF2010 Session C2-2: Thin Films for Active Devices and Microstystems

Metal/Oxide layers of Al/Al₂O₃, Al/TiO₂ and Al/Al₂O₃/TiO₂ were deposited on silicon substrate to make Metal/Oxide/Semiconductor (MOS) structures using RF Magnetron Sputtering system. The thickness (40+5 nm) of the oxide layer was kept constant. Performance of MOS structure depends on leakage current & dielectric constant of the oxide layer. The leakage current of these Metal/Oxide/Semiconductor (MOS) structure was investigated using I-V characteristic. It was observed that the leakage current density was maximum for Al/TiO₂/Si (~ 7.4 X 10^-8 amp/cm²₎ and minimum for Al/Al₂O₃/Si (~ 1.02 X 10^-8 amp/cm²), whereas for Al/Al₂O₃/TiO₂/Si compensated to ~1.12 X 10^-8 amp/cm² at 1 Volt. The dielectric constant of the multilayers was measured by C-V analyzer. The dielectric constant increased from 10 for Al/TiO₂/Si and 4 for Al/Al₂O₃/Si to 40 for Al/Al₂O₃/TiO₂/Si at 1 Volt bias voltage. Variations of the leakage current density were due to band gap variation of the deposited layers and pinning of the Fermi level of the multilayer. The interdiffusion of the two layers at the interface (heterojunction) was responsible for this pinning of Fermi level. Secondary Ion Mass Spectrometry (SIMS) was employed to probe in-depth elemental distributions in the individual layers and intermixing of the layers across the interfaces. The interface broadening in SIMS depth profiles gave a measure of the intermixed layer thickness. The chemical composition and band gap of the deposited oxide layers were characterized by X-ray photoelectron spectroscopy (XPS) and UV-Visible spectroscopy, respectively. It was observed that Al/Al₂O₃/TiO₂/Si is a promising grown hetero-structure with high dielectric constant and less leakage current for fabrication of MOS devices.

Wurtzite-structure (w) AlN is commonly used in the fabrication of high-frequency electro-acoustic devices. Its main advantages are high acoustic velocity and low acoustic and dielectric losses. Recently, an increased piezoelectric effect in w-Sc_xAl_1-xN with increased Sc content (0<x<0.5) was reported [1] and for x>0.5, a non-piezoelectric cubic phase was found favorable [2]. To reveal the true potential of this material, the dielectric and elastic properties as well as the piezoelectric properties of high quality crystalline material need to be investigated. In this work we present an experimental, as well as theoretical investigation of the dielectric constants of w-Sc_xAl_1-xN(0001). Thin films with 0<x<0.5 have been grown as single crystal epitaxial layers onto TiN(111)/Al₂O₃(0001) substrates by dual reactive magnetron sputtering epitaxy using Sc and Al targets in an N₂/Ar discharge. XRD and HRTEM confirmed the epitaxial nature of the layers and were used to quantify the lattice parameter ratio c/a of the as-deposited layers. RBS and ERDA measurements have confirmed Sc_xAl_1-xN film growth with negligible oxygen content or other contaminants. A strong non-linear increase of the dielectric constant e₃₃ was observed with increased x, as determined by electrical measurements of the (Au/Cr)/Sc_xAl_1-xN/TiN capacitor structures in the microwave frequency range. For x=0, e₃₃= 10 and dielectric losses <0.02 were measured, corresponding well to published values of pure AlN. Preliminary analyses show a ten-fold increase of e₃₃ for Sc_0.2Al_0.8N. However, the dielectric losses also increased with Sc content which ultimately could limit the electromechanical coupling of the material. First-principles calculations showed a monotonous, non-linear enhancement of the piezoelectric constant e₃₃ with increasing x. For x=0.5, e₃₃ approaches 3.02 C/m², a value twice as large as for pure w-AlN (1.55 C/m²). Furthermore, the stiffness constant C₃₃ shows a monotonous linear decrease with Sc content, from 367 GPa down to 131 GPa. In conclusion, the observed increased piezoelectric constant and decreased elastic constant of w-Sc_xAl_1-xN epitaxial layers work in favor of an improved electromechanical coupling, but an associated observed increase in the dielectric constant, may limit the effect.

[1] M. Akiyama, T. Kamohara, K. Kano, A. Teshigahara, Y. Takeuchi, N. Kawahara, Adv. Mater. 21 (2009), 593.

In this study, large and stable resistive switching characteristics were observed on a novel structure of Ti/TiN/SiO₂/PtFe . This structure would form a thin Fe-O constituent examined by X-ray photoelectron spectroscopy between SiO₂ and bottom PtFe electrode . The metal-insulator-metal structure with alloy PtFe bottom electrode was also studied and current transport characteristics after forming process. In addition, a physical mechanism was proposed to explain the role of oxygen vacancies in the resistive witching process.

In order to investigate the effect of annealing temperature on the photoluminescence property of two layer Si/C film for potential optoelectronic devices, the Si/C film was deposited on the crystalline Si(100) substrate by using ultra high vacuum ion beam sputtering (UHV IBS) at room temperature and annealed at 750°C and 900°C for 2 min . Raman spectra, Fourier transform infrared spectroscopy (FTIR), high resolution scanning electron microscopy ( HRSEM ), atomic force microscopy (AFM) and photoluminescence (PL) spectrometry were used to characterize the evolution of bonding, optoelectronic behavior and microstructure of two-layer C/Si films, respectively .

Superconducting FeSe thin films were prepared at a substrate temperature of 320°C by pulsed laser deposition. X-ray diffraction and transmission electron microscopy showed that highly orientated and high quality films could be grown at various substrate materials, including STO, LAO, MgO, Si, a-SiO_x, and SiN, at such low temperature. A film thickness of at least 400 nm is required to overcome the substrate-to-film strain for a low temperature (~ –173°C) structural distortion, which is indispensible for the occurrence of superconductivity. The superconducting transition temperature (T_c) varied slightly with substrate materials. The low deposition temperature and insignificant to substrate materials make them more compatible for real applications in electronic devices.