A charge injection material, poly(3,4-ethylene dioxythioohene)-poly(styrene sulfonic) acid, is introduced as a buffer layer between metal electrodes and a ferroelectric poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] copolymer ultrathin film. The buffer layer not only prevents the reactions between P(VDF-TrFE) layer and the top electrode during metallization process, which leads to the loss of polarization, but also supplies the amount of charges needed for compensation of the ferroelectric dipoles to stabilize the domain during switching process so that the fatigue property was improved tremendously. The sandwiched structure shows prominent ferroelectric properties in a 50 nm P(VDF/TrFE) film. A coercive electric field of 52 MV/m and a remnant polarization of 88 mC/m2 are recorded. With two additional organic interlayers, 33 nm thick in total, the coercive field decreases. After more than 1×107 cycles of switching, the polarization remains as high as 68 mC/m2. Moreover, the cell still has good ferroelectric properties at 60 °C. Even as the thickness of P(VDF/TrFE) film is down to 25 nm, a remnant polarization of 54 mC/m2 is obtained.
A ferroelectric device, making use of a flexible plastic, polyethylenterephtalate (PET), as a substrate was fabricated by all solution processes. PET was globally coated by a conducting polymer, poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) acid (PEDOT/PSSH), which is used as bottom electrode. The ferroelectric copolymer, poly(vinylidenefluoride-trifluoroethylene) (PVDF-TrFE), thin film was deposited by spin-coating process from solution. The top electrode, polyaniline, was coated by solution process as well. The ferroelectric properties were measured on this all solution processed all polymer ferroelectric thin-film devices. A square and symmetric hysteresis loop was observed with high-polarization level at 15-V drive voltage on a all polymer device with 700 Å (PVDF-TrFE) film. The relatively inexpensive conducting polyaniline electrode is functional well and therefore is a good candidate as electrode material for ferroelectric polymer thin-film device. The remnant polarization P r was 8.5 lC/cm 2 before the fatigue. The ferroelectric degradation starts after 1 Â 10 3 times of switching and decreases to 4.9 lC/cm 2 after 1 Â 10 5 times of switching. The pulse polarization test shows switching take places as fast as a few micro seconds to reach 90% of the saturated polarization. V C 2010Wiley Periodicals, Inc. J Appl Polym Sci 120: [1510][1511][1512][1513] 2011
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