Microstructure, optical properties, and optical resonators of Hf1-xTixO2 amorphous thin films

We report Hf1-xTixO2 (0< = x< = 1) thin films (HTO) as index tunable and highly transparent materials for ultraviolet to near infrared integrated photonic devices. By varying the Ti concentration, reactive cosputtered HTO thin films on thermal oxidized SiO2 on Si substrates show continuously tunable optical band gaps from 3.9 eV to larger than 5 eV. The film refractive index monotonically increases with Ti concentration, varying from 1.8 to 2.4 in the visible to near infrared wavelength range. Micro-disk amorphous HfO2 resonators on SiO2/Si substrates are fabricated using sputtering and lift-off method. A loaded quality factor of ~15800 at around 1580 nm wavelength is achieved in HfO2 disk resonators with diameters of 100 μm. The propagation loss of the HfO2 ridge waveguide is estimated to be 2.5 cm. The wide optical transparency range, variable index of refraction, low temperature, CMOS-compatible fabrication capability, and high optical transparency make amorphous HTO thin films promising candicates for integrated photonic applications. ©2016 Optical Society of America OCIS codes: (310.0310) Thin films; (310.6860) Thin films, optical properties; (230.0230) Optical devices; (230.5750) Resonators. References and links 1. B. Jalali and S. Fathpour, “Silicon photonics,” J. Lightwave Technol. 24(12), 1400–1415 (2006). 2. J. T. Choy, J. D. B. Bradley, P. B. Deotare, I. B. Burgess, C. C. Evans, E. Mazur, and M. Lončar, “Integrated TiO2 resonators for visible photonics,” Opt. Lett. 37(4), 539–541 (2012). 3. C. C. Evans, K. Shtyrkova, J. D. B. Bradley, O. Reshef, E. Ippen, and E. Mazur, “Spectral broadening in anatase titanium dioxide waveguides at telecommunication and near-visible wavelengths,” Opt. Express 21(15), 18582– 18591 (2013). 4. T. H. Loh, Q. Wang, K. T. Ng, Y. C. Lai, and S. T. Ho, “CMOS compatible integration of Si/SiO2 multilayer GRIN lens optical mode size converter to Si wire waveguide,” Opt. Express 20(14), 14769–14778 (2012). 5. L. Bi, J. Hu, P. Jiang, D. H. Kim, G. F. Dionne, L. C. Kimerling, and C. A. Ross, “On-chip optical isolation in monolithically integrated non-reciprocal optical resonators,” Nat. Photonics 5(12), 758–762 (2011). 6. B. Guha, J. Cardenas, and M. Lipson, “Athermal silicon microring resonators with titanium oxide cladding,” Opt. Express 21(22), 26557–26563 (2013). 7. C. Xiong, W. H. P. Pernice, J. H. Ngai, J. W. Reiner, D. Kumah, F. J. Walker, C. H. Ahn, and H. X. Tang, “Active silicon integrated nanophotonics: ferroelectric BaTiO3.devices,” Nano Lett. 14(3), 1419–1425 (2014). 8. J. P. Coutures and J. Coutures, “The system HfO2-TiO2,” J. Am. Ceram. Soc. 70(6), 383–387 (1987). 9. P. Rabiei, J. Ma, S. Khan, J. Chiles, and S. Fathpour, “Submicron optical waveguides and microring resonators fabricated by selective oxidation of tantalum,” Opt. Express 21(6), 6967–6972 (2013). 10. J. D. B. Bradley, C. C. Evans, J. T. Choy, O. Reshef, P. B. Deotare, F. Parsy, K. C. Phillips, M. Lončar, and E. Mazur, “Submicrometer-wide amorphous and polycrystalline anatase TiO2 waveguides for microphotonic devices,” Opt. Express 20(21), 23821–23831 (2012). 11. C. Ting, S. Chen, and D.-M. Liu, “Structural evolution and optical properties of TiO2 thin films prepared by thermal oxidation of sputtered Ti films,” J. Appl. Phys. 88(8), 4628–4633 (2000). #260645 Received 7 Mar 2016; revised 26 Apr 2016; accepted 27 Apr 2016; published 12 May 2016 © 2016 OSA 1 Jun 2016 | Vol. 6, No. 6 | DOI:10.1364/OME.6.001871 | OPTICAL MATERIALS EXPRESS 1871 12. G. E. Jellison, Jr., L. A. Boatner, J. D. Budai, B.-S. Jeong, and D. P. Norton, “Spectroscopic ellipsometry of thin film and bulk anatase (TiO2),” J. Appl. Phys. 93(12), 9537 (2003). 13. O. Reshef, K. Shtyrkova, M. G. Moebius, S. Griesse-Nascimento, S. Spector, C. C. Evans, E. Ippen, and E. Mazur, “Polycrystalline anatase titanium dioxide microring resonators with negative thermo-optic coefficient,” J. Opt. Soc. Am. B 32(11), 2288–2293 (2015). 14. T. Guang-Lei, H. Hong-Bo and S. Jian-Da, “Effect of Microstructure of TiO2 Thin Films on Optical Band Gap Energy,” Chi. Phys. Lett. 22(7), 1787–1789 (2005). 15. C. Jia, E. Xie, A. Peng, R. Jiang, F. Ye, H. Lin, and T. Xu, “Photoluminescence and energy transfer of terbium doped titania film,” Thin Solid Films 496(2), 555–559 (2006). 16. Q. G. Zeng, Z. J. Ding, and Z. M. Zhang, “Synthesis, structure and optical properties of Eu3+/TiO2 nanocrystals at room temperature,” J. Lumin. 118(2), 301–307 (2006). 17. J. Domaradzki, A. Borkowska, D. Kaczmarek, and E. Prociow, “Transparent oxide semiconductors based on TiO2 doped with V, Co and Pd elements,” J. Non-Crystall. Solids 352(23–25), 2324–2327 (2006). 18. G. Ayguna, A. Cantasa, Y. Simseka, and R. Turan, “Effects of physical growth conditions on the structural and optical properties of sputtered grown thin HfO2 films,” Thin Solid Films 519(17), 5820–5825 (2011). 19. C. L. Wu, B. T. Chen, Y. Y. Lin, W. C. Tien, G. R. Lin, Y. J. Chiu, Y. J. Hung, A. K. Chu, and C. K. Lee, “Lowloss and high-Q Ta2O5 based micro-ring resonator with inverse taper structure,” Opt. Express 23(20), 26268– 26275 (2015). 20. M. Balog, M. Schieber, M. Michman, and S. Patai, “Chemical vapor deposition and characterization of HfO2 films from organo-hafnium compounds,” Thin Solid Films 41(3), 247–259 (1977). 21. H. Padma Kumar, S. Vidya, S. Saravana Kumar, C. Vijayakumar, S. Solomon, and J. K. Thomas, “Optical properties of nanocrystalline HfO2 synthesized by an auto-igniting combustion synthesis,” Journal of Asian Ceramic Societies 3(1), 64–69 (2015). 22. M. F. Al-Kuhaili, “Optical properties of hafnium oxide thin films and their application in energy-efficient windows,” Opt. Mater. 27(3), 383–387 (2004). 23. F. Chen, X. Bin, C. Hella, X. Shi, W. L. Gladfelter, and S. A. Campbell, “A study of mixtures of HfO2 and TiO2 as high-k gate dielectrics,” Microelectron. Eng. 72(1–4), 263–266 (2004). 24. Q. Tao, A. Kueltzo, M. Singh, and G. Jursich, “Atomic Layer Deposition of HfO2, TiO2, and HfxTi1−xO2 Using Metal (Diethylamino) Precursors and H2O,” J. Electrochem. Soc. 158(2), G27–G33 (2011). 25. G. Ayguna, A. Cantasa, Y. Simseka, and R. Turan, “Effects of physical growth conditions on the structural and optical properties of sputtered grown thin HfO2 films,” Thin Solid Films 519(17), 5820–5825 (2011). 26. F. L. Martinez, M. Toledano-Luque, J. J. Gandía, J. Cárabe, W. Bohne, J. Röhrich, E. Strub, and I. Mártil, “Optical properties and structure of HfO2 thin films grown by high pressure reactive sputtering,” J. Phys. D Appl. Phys. 40(17), 5256–5265 (2007). 27. F. Chen, X. Bin, C. Hella, X. Shi, W. L. Gladfelter, and S. A. Campbell, “A study of mixtures of HfO2 and TiO2 as high-k gate dielectrics,” Microelectron. Eng. 72(1–4), 263–266 (2004). 28. J. W. Zhang, G. He, L. Zhou, H. S. Chen, X. S. Chen, X. F. Chen, B. Deng, J. G. Lv, and Z. Q. Sun, “Microstructure optimization and optical and interfacial properties modulation of sputtering-derived HfO2 thin films by TiO2 incorporation,” J. Alloys Compd. 611, 253–259 (2014). 29. M. Vargas, N. R. Murphy, and C. V. Ramana, “Structure and optical properties of nanocrystalline hafnium oxide thin films,” Opt. Mater. 37, 621–628 (2014). 30. C. Y. Ma, W. J. Wang, J. Wang, C. Y. Miao, S. L. Li, and Q. Y. Zhang, “Structural, morphological, optical and photoluminescence properties of HfO2 thin films,” Thin Solid Films 545, 279–284 (2013). 31. R. M. A. Azzam and N. M. Bashara, Ellipsometry and Polarized Light (North Holland Publishing Company, 1977). 32. J. M. Khoshman and M. E. Kordesch, “Optical properties of a-HfO2 thin films,” Surface amd Coatings Tech. 201, 3530–3535 (2006). 33. F. Jiang, N. Duan, H. Lin, L. Li, J. Hu, L. Bi, H. Lu, X. Weng, J. Xie, and L. Deng, “ZrO2-TiO2 thin films and resonators for mid-infrared integrated photonics,” SPIE 8988, 89880S (2014).