Noncontact probing method for estimation of ferroelectric properties of PbTiO 3 -based films for microelectromechanical
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Tomoaki Yamada Department of Materials, Physics and Energy Engineering, Nagoya University, Nagoya 464-8603, Japan; and PRESTO, Japan Science and Technology Agency, Tokyo 102-0075, Japan
Takashi Iijima Research Center for Hydrogen Industrial Use and Storage, National Institute of Advanced Industrial Science and Technology, Ibaraki 305-8568, Japan
Ken Nishida and Takashi Yamamoto Department of Communications Engineering, National Defense Academy, Kanagawa 239-8686, Japan
Hiroshi Funakuboa) Department of Innovative and Engineered Materials, Tokyo Institute of Technology, Kanagawa 226-8503, Japan (Received 24 November 2011; accepted 14 March 2012)
Raman scattering spectra and ferroelectric properties of epitaxial tetragonal Pb(Zr, Ti)O3 were investigated for polar axis-oriented thin films with various Zr/(Zr 1 Ti) ratios and by changing the ratios from 0 to 0.50 at different measurement temperatures. The chosen films in the thickness range of 1–2 lm present the advantage of showing small residual strain. The E (TO) modes were successfully isolated using cross-polarization configurations, while A1 (TO) and B1 modes were activated using parallel polarization configurations. Systematic changes in Raman peak positions were observed with changes in the Zr/(Zr 1 Ti) ratios at different measurement temperatures. It was found in both cases that the tetragonal distortion (c/a-1) and the value of square of spontaneous polarization (Ps2) linearly increased with increasing x2[A1(1TO)], where a and c are the lattice parameters of a and c-axes. This indicates that monitoring A1(1TO) mode is efficient as a characterization method of ferroelectricity. It can also be used as a novel nondestructive process check or reliability assessment technique during fabrication of microelectromechanical systems (MEMS) using piezoelectric materials.
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2012.100
[(c/a) -1] is proportional to the square of Ps, Ps2.5 In addition, the square of A1(1TO) soft mode frequency, x2 [A1(1TO)], is expected to be almost proportional to Ps2.6 The relationship between Ps and x[A1(1TO)] is very useful from a practical viewpoint such as checking MEMS characteristics during production because the Ps value can be estimated using simple Raman spectroscopy. However, literature is still lacking in some fundamental experimental data on Pb(Zr, Ti)O3, such as the equation that correlated between Ps and Raman spectra data. Because, as far as we know, there are no reports on the measurements of both the Ps and Raman spectra (against the above parameters) using same Pb(Zr, Ti)O3 samples having a single polar-axis orientation. In the previous reports, we reported on the equations between Ps2 – [(c/a) -1] and Ps2 –x2[A1(1TO)].7 In the present study, we characterized polar-axis oriented tetragonal PZT thin films using polarized and unpolarized Raman spectroscopy, as function of Zr/(Zr 1 Ti) ratio and measurement temperature. The use of polarized and unpolarized Raman spectroscopy aims to get
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