Effects of interface charges on imprint of epitaxial Bi4Ti3O12 thin films

Abstract

Growth, structure, and properties of all-epitaxial ferroelectric ( Bi , La ) 4 Ti 3 O 12 ∕ Pb ( Zr 0.4 Ti 0.6 ) O 3 ∕ ( Bi , La ) 4 Ti 3 O 12 trilayered thin films on Sr Ru O 3 -covered Sr Ti O 3 ( 011 ) substrates Appl. Phys. Lett. 86, 082906 (2005); 10.1063/1.1864248 ( Bi , La ) 4 Ti 3 O 12 (BLT) thin films grown from nanocrystalline perovskite nuclei for ferroelectric memory devices Appl. Phys. Lett. 85, 4118 (2004); 10.1063/1.1812840 Effect of oxygen stoichiometry on the ferroelectric property of epitaxial all-oxide La 0.7 Sr 0.3 MnO 3 /Pb(Zr 0.52 Ti 0.48 )O 3 /La 0.7 Sr 0.3 MnO 3 thin-film capacitors CoO 3 ͑LSCO͒ or Pt film as a bottom electrode layer, epitaxial Bi 4 Ti 3 O 12 ͑BTO͒ thinfilms were grown on MgO͑001͒ substrates by pulsed laser deposition. A symmetric Pt/BTO/Pt capacitor structure shows a surprisingly large asymmetric polarization switching behavior, but a Pt/BTO/LSCO structure has a nearly symmetric P -V hysteresis. The strong asymmetric behavior in the Pt/BTO/Pt was attributed to positive charges resulting from interdiffusion at the bottom BTO/Pt interface. P -V hysteresis studies using numerous top electrode materials and Auger electron spectroscopy depth profile measurement also support formation of interfacial charges. Imprint pulse test shows that such an imprint failure cannot be recovered by applying a dc bias field.

Modeling the role of oxygen vacancy on ferroelectric properties in thin films

“…Several authors have also suggested the space charge developed by the trapping of carriers in these oxygen vacancies is responsible for the imprint effect. 18,25,26 . The presence of an oxygen vacancy, therefore, impedes the displacement of Ti 4ϩ .…”

“…18,26,32,33 The oxygen vacancy itself bears a positive charge by releasing electrons. Experimental results also reveal that holes are injected across the electrode film interface, 34 and that oxygen vacancies or their related defect complexes are hole traps.…”

Effect of lattice-misfit strain on the process-induced imprint behavior in epitaxial Pb(Zr0.52Ti0.48)O3 thin films

“…Since the PZT capacitors with noble metal electrodes like Pt exhibit a significant polarization loss when subject to bipolar switching pulses, in the past decade, for the growth of fatigue-free PZT capacitors and especially in the epitaxial form, various oxide electrodes such as La 0.5 Sr 0.5 CoO 3 (LSCO), SrRuO 3 (SRO), La 0.7 Sr 0.3 MnO 3 (LSMO), and LaNiO 3 (LNO) have been employed. [3][4][5][6][7][8]11,12 For epitaxial LSCO/PZT/LSCO capacitors, however, when exposed to reducing atmosphere for device fabrication, a large voltage offset was observed. [3][4][5] This process-induced imprint behavior was greatly complicated by the instability of the LSCO layer at reduced oxygen pressures, 5,13 and rarely examined for the other oxide electrodes.…”

“…However, there is a lack of understanding on the formation of the internal field. Different models, such as the aligned dipolar defect complexes and asymmetric distribution of charged defects through a bulk thin film, 2-5 and a built-in electric field or a nonswitching layer at the ferroelectric-electrode interface, [6][7][8][9] have been proposed to explain the asymmetric behavior of ferroelectric capacitors.…”

“…However, it is often observed that ferroelectric films exhibit significant imprint, or asymmetry of switching parameters, such as the coercive field ͑E c ͒ and the remnant polarization ͑P r ͒. [2][3][4][5][6][7][8][9][10] The cause of the imprint is generally attributed to the presence of an internal electric field in the capacitor which supports the given polarization state while opposing the antiparallel one. However, there is a lack of understanding on the formation of the internal field.…”