Low voltage switching of a spin cast ferroelectric polymer

Employing a conductive polymer as the bottom electrode material of a ferroelectric capacitor is shown to improve the ferroelectric properties of sub-100-nm-thick spin cast poly(vinylidene fluoride/trifluoroethylene) copolymer insulator films. It is demonstrated that a remanent polarization of 65mC/m2 is switched with only 5.2V (80MV∕m) with a switching time of 80ms. Compared to similar capacitors but with an aluminum bottom electrode the main improvement is a reduction of the switching time with 3 orders of magnitude at this field strength.
The ferroelectric poly(vinylidene fluoride/trifluoroethylene) [P(VDF∕TrFE)] copolymers have been proposed for use in low cost, large area solid state electronic memories.1 Their ease of processing through spin casting would be ideal when combined with low voltage operation. Due to the relatively high coercive field (Ec) of 50MV∕m sub-100-nm thick ferroelectric layers are required in order to attain an operation voltage below 10V. A paper regarding the thickness scaling of polymer based ferroelectrics reported an increase in both coercive field and switching time with decreasing layer thickness.2 A number of studies dealing with this issue followed.3–7 An overview of remanent polarization (Pr) values versus ferroelectric layer thickness is shown in Fig. 1. Note that the polarization also depends on the copolymer ratio of the copolymer used so only changes relative to thick film values are relevant.