Annealing effect upon chain orientation, crystalline morphology, and polarizability of ultra-thin P(VDF-TrFE) film for nonvolatile polymer memory device

The ferroelectric behavior of spin-cast ultra-thin P(VDF-TrFE) (72-28) film is highly influenced by sample preparation methods including thermal annealing. The effect of sample preparation methods on the surface morphology, chain and dipole orientation, ferroelectric properties, and nonvolatile memory characteristics were studied using FTIR-grazing incident reflection absorption spectroscopy (GIRAS), grazing incident wide angle X-ray diffraction (GIWAXD), atomic force microscope (AFM), dynamic contact electrostatic force microscope (DC-EFM), and polarization-electric field (P-E) hysteresis measurements to find the feasibility of applying the ultra-thin P(VDF-TrFE) film to scanning probe microscopy (SPM)-based storage device or low-cost nonvolatile ferroelectric polymer random access memory (NvFePoRAM) device. From the collective analysis of GIRAS, GIWAXD, and AFM data, annealing the as-cast sample at temperature (ca. 120 °C) above Curie transition, but below its melting transition temperature was found to be the most suitable condition to fabricate the NvFePoRAM and/or SPM-based storage device with a memory density of about 30 GB/in2. DC-EFM technique was successfully used to characterize the nonvolatile memory properties by 'writing and erasing' the data bit through applying a dc bias voltage much larger than coercive voltage with different polarities and then reading the data bit by applying a high frequency ac voltage of only 2 V to the 'written or erased' area.