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

Thursday, April 29, 2010 1:30 PM in Room Royal Palm 1-3
Thursday Afternoon

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1:30 PM C2-2-1 Investigation on Post-Deposition Annealing of Amorphous Indium-Zinc-Oxide Thin-Film-Transistors
Wan-Fang Chung (National Chiao-Tung University, Taiwan); Ting-Chang Chang (National Sun Yat-Sen University, Taiwan); Hung-Wei Li (National Chiao-Tung University, Taiwan); Yu-Chun Chen (National Sun Yat-Sen University, Taiwan); Tseung-Yuen Tseng, Ya-Hsiang Tai (National Chiao Tung University, Taiwan)
In this paper, the influence of post-deposition annealing conditions on sputtered amorphous indium zinc oxide thin film transistors (a-IZO TFTs) are investigated. From literature, the portion of oxygen vacancies (Vo) in amorphous phase and the Zn-O bonding in crystalline phase directly affect the electrical characteristics of ZnO-based device. Also, the threshold voltage and the mobility were examined at increased annealing duration. In addition, X-ray Photon-emission Spectra (XPS) analysis was used to distinguish the Zn-O bonds and Vo after prolonging annealing time.
1:50 PM C2-2-3 Leakage Current and Dielectric Constant Dependencies on Single and Double Layer of Oxides in MOS Structure
Indrani Banerjee, Pinaki Laha, Atala Bihari Panda (Birla Institute of Technology, India); Biswajit Saha, P. Chakraborty (Saha Institute of Nuclear Physics, India); P.K. Barhai, S.K. Mahapatra (Birla Institute of Technology, India)

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.

2:10 PM C2-2-4 Dielectric Properties of ScxAl1-xN Thin Films Deposited by Dual Reactive DC Magnetron Sputtering
Agne Zukauskaite, Gunilla Wingqvist, Ferenc Tasnádi, Jens Birch, Lars Hultman (Linköping University, Sweden)

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-ScxAl1-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-ScxAl1-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 ScxAl1-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)/ScxAl1-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 Sc0.2Al0.8N. 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-ScxAl1-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.

[2] C. Höglund, J. Bareño, J. Birch, B. Alling, Zs. Czigany and L. Hultman, J. Appl. Phys. 105, (2009) 113517.
2:30 PM C2-2-5 Resistance Switching Mechanisms of Partial Doped SiO2 With Fe Irons in a MIM Structure
Li Feng, Chun Chang (National Chiao Tung University, Taiwan); Ting-Chang Chang (National Sun Yat-Sen University, Taiwan)

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.

2:50 PM C2-2-6 Broad Visible Photoluminescence from Two-Layer Si/C Film Deposited on Si (100) Substrate Under Rapid Thermal Annealing
Chen-Kuei Chung, Chun-Wen Lai (National Cheng Kung University, Taiwan)

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 .

From the experimental results, Raman spectra revealed that more disordered state as well as higher ID/IG ratio was obtained at higher annealing temperature. In addition, AFM and HRSEM image showed the bigger nanocluster appeared at 900°C. More Si-C bonding formation with increasing annealing temperature was identified by means of FTIR. Under 325 nm excitation, an asymmetric broad PL peak around 400~700 nm was observed in the PL spectrum. The broad visible PL spectrum can be deconvoluted by auto curve-fitting of Gaussian function into three bands of blue (~500 nm), green (~560 nm) and yellow (~600 nm yellow band () ) emission, corresponding to the formation of crystalline SiC, sp2 carbon cluster and oxygen vacancy, respectively. PL intensity of three bands distinctly enhanced at 900 °C due to the increased amount of crystalline SiC, sp2 carbon cluster and oxygen vacancy. The center of yellow band from oxygen vacancy almost fixed at same position during the thermal treatment. Redshift behavior of blue and green PL bands can be attributed to quantum confinement of nanoscale size effect .
3:10 PM C2-2-7 Low-Temperature Fabrication of Superconducting FeSe Thin Films by Pulsed Laser Deposition
Ta-Kun Chen, Jiu-Yong Luo, Chung-Ting Ke (Academia Sinica, Taiwan); Hsian-Hong Chang (National Tsing Hua University, Taiwan); Tzu-Wen Huang, Kuo-Wei Yeh, Po-Chun Hsu, Chung-Chieh Chang, Ming-Jye Wang, Mau-Kuen Wu (Academia Sinica, Taiwan)

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-SiOx, 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 (Tc) varied slightly with substrate materials. The low deposition temperature and insignificant to substrate materials make them more compatible for real applications in electronic devices.

Time Period ThA Sessions | Abstract Timeline | Topic C Sessions | Time Periods | Topics | ICMCTF2010 Schedule