Homogeneous switching mechanism in pure polyvinylidene fluoride ultrathin films

Polarization switching kinetics is one of the key issues for future development of nanoelectronic devices based on ferroelectrics. Up to now, such kinetics still remains poorly studied despite its crucial impact on the device performances. Here, the switching mechanism in 11-nm-thick ferroelectric films of pure homopolymer of polyvinylidene fluoride is investigated. While the usual mechanism involves nucleation and growth of domains, a homogeneous ferroelectric switching is evidenced in such ultrathin films. Indeed, the dependence of the switching rate on applied voltage reveals a critical behavior with the existence of a true threshold field (of $\sim 0.26\mathrm{GV}/\mathrm{m}$) which is required to overcome the energy barrier to reverse the whole polarization homogeneously as suggested by Landau-Ginzburg mean-field theory. Such finding not only supports few previous works but also raises the question on the general aspect of such homogeneous mechanism that might exist in any other nanoscale ferroelectric materials.

Figure 1

Sketch of the devices: (a) AFM topography showing three nanocapacitors. (b) Schematic of a tungsten/PVDF/gold nanodevice on a Si substrate.

Figure 2

I-V curves in the device with 11-nm-thick PVDF film at a frequency of 0.5 Hz (left) and the out-of-plane PFM phase hysteresis loop (right).

Figure 3

I-V curves in a nanodevice at frequencies of 0.01, 0.1, 0.2, and 0.5 Hz, respectively. The dashed vertical lines are a guide to the eyes showing the position of the current's jump corresponding to the coercive voltages.

Figure 4

Coercive electric field $E_C$ as a function of the frequency $f$ from three different devices. The red solid line and green dashed line are fits to Eqs. (1) and (2), respectively.