Research ArticleMATERIALS SCIENCE

Flexible ferroelectric element based on van der Waals heteroepitaxy

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Science Advances  09 Jun 2017:
Vol. 3, no. 6, e1700121
DOI: 10.1126/sciadv.1700121
  • Fig. 1 Flexible memory design.

    Growth scheme (A) and photograph (B) of a flexible NVM element on mica. RHEED, reflection high-energy electron diffraction. (C) Atomic force micrograph. (D) Schematic illustration of PZT/mica heterostructure via vdW heteroepitaxy.

  • Fig. 2 Structural information.

    (A) Typical 2θ-θ scan of the heterostructure. (B) Φ scans at PZT{002}, SRO{002}, CFO{004}, and mica{202} diffraction peaks. a.u., arbitrary units. (C) The reciprocal space mapping of the heterostructure. r.l.u., relative light units. (D) The cross-sectional TEM image depicting the PZT/SRO and SRO/CFO/mica interfaces along with the selected area diffraction patterns of PZT, SRO, and mica.

  • Fig. 3 Piezoresponse force microscopy.

    The surface topography (A) with out-of-plane (B) and in-plane phase (C) images. (D) Representative local PFM amplitude and phase hysteresis loops. (E) The local coercive voltage variation as a function of bending radius.

  • Fig. 4 Ferroelectric properties.

    P-E (A) and C-E (B) hysteresis loops at various temperatures. (C) Remnant, saturation polarizations, and coercive field as functions of temperature. (D) PUND switching polarization as a function of pulse width at different voltages. The inset shows the measurement sequence. Retention (E) and fatigue (F) measurements at two typical temperatures.

  • Fig. 5 Flexibility and durability.

    P-E (A) and C-E (B) hysteresis loops under various tensile and compressive bending radii. (C) Psat, Pr, and Ec variation as a function of bending radius. (D) ΔP as a function of pulse width at 4 V under mechanical flexing. Polarization switching speed variation is shown in the inset. Retention (E) and fatigue (F) for the samples in unbent and compressively and tensilely bent for 1000 cycle conditions.

  • Table 1 Flexible memory elements.

    Summary of the flexible NVM elements. PZTx, PbZrxTi1−xO3; P(VDF-TrFE), poly[(vinylidenefluoride)-co-trifluoroethylene]; BTO, barium titanate; PET, polyethylene terephthalate; PI, polyimide; PEN, polyethylene naphthalate.

    Ferroelectric materialPZT20*PZT20*PZT52PZT52PZT53PZT30PZT52PZTBTOP(VDF-TrFE)
    Flexible substrateMicaSiNi superalloy
    ribbons
    SiPt foilPICu foilPlasticPETAl foilOrganicPENPI
    Transfer requiredNoYesNoNoYesNoNoYesNoYesNoNoNo
    Pr (μC/cm2)6075401825.51520~20117.48.52
    Ec (kV/cm)100400916054.9~500~251.1 V830500650
    Capacitance
    (F/cm2)
    2.85~1.642.70.062
    Dielectric constant460
    @ 1 MHz
    541
    @ 1 kHz
    80
    @ 1 kHz
    ~1150250
    @ 0.1 MHz
    Switching time (ns)2000500165
    Fatigue (cycles)>1010
    (unbent)
    >1010 (bent)
    >109
    (unbent)
    >1010
    (bent)
    10715% loss
    @ 107
    1010102
    Retention (years)>10
    (unbent)
    >10 (bent)
    >1020% loss
    @ 105 s
    >7000 s
    Cell size (mm2)0.00785–
    0.0314
    0.04840.00785–
    0.0471
    0.01–
    0.0625
    0.0080.030.01160.0250.03–
    0.25
    Minimum bending
    radius (mm)
    2.558670.5
    Bending cycles @
    radius
    >1000
    @ 5 mm
    1000
    @ 5 mm
    500
    @ 11 mm
    >1000
    @ 4 mm
    ReferenceThis work(26)(16)(12, 13)(14)(18)(15)(17)(39)(19)(20)(21)(22)

    *Single-crystalline.

    †Highly oriented.

    Supplementary Materials

    • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/6/e1700121/DC1

      Supplementary Text

      fig. S1. RHEED pattern.

      fig. S2. Piezoresponse force microscopy.

      fig. S3. Dielectric constant and capacitance at different temperatures.

      fig. S4. Dielectric constant and capacitance under bending.

      fig. S5. P-E hysteresis loops under tensile and compressive bending of 5 mm before and after 10 to 1000 bending cycles.

      fig. S6. ΔP as a function of pulse width at various voltage pulses under compressive and tensile strains.

      fig. S7. Raman spectra under bending.

      References (4043)

    • Supplementary Materials

      This PDF file includes:

      • Supplementary Text
      • fig. S1. RHEED pattern.
      • fig. S2. Piezoresponse force microscopy.
      • fig. S3. Dielectric constant and capacitance at different temperatures.
      • fig. S4. Dielectric constant and capacitance under bending.
      • fig. S5. P-E hysteresis loops under tensile and compressive bending of 5 mm before and after 10 to 1000 bending cycles.
      • fig. S6. ΔP as a function of pulse width at various voltage pulses under compressive and tensile strains.
      • fig. S7. Raman spectra under bending.
      • References (40–43)

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