Temperature Dependence of Switching Characteristics in Polyurea-5 Thin Films

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Abstract
In order to investigate the ferroelectric properties of polyurea-5 prepared by vapor-deposition polymerization, we used switching measurements and found that polyurea thin films showed ferroelectric polarization reversal behavior. Ferroelectric switching transients with the amount of reversed polarization P r of 20 mC/m2 were observed for the polymer thin film at room temperature. This P r is consistent with a polyurea-5 film crystallinity of 30%. We then found a two-step increase in the switching transients above 50°C. The first increase gives P r of 20 mC/m2 and the second increase gives a large P r increment of 200 mC/m2 which is much larger than the calculated value of the spontaneous polarization in the single crystal of polyurea-5. However the second increase with P r of 200 mC/m2 is almost independent of applied field E and shifts to short time regions with increasing E. These results imply that the second increase with P r of 200 mC/m2 is caused by ferroelectric switching.