Controlled thin-film ferroelectric polymer corona polarizing system and process

Abstract

A corona polarization (also denoted 'poling') process and associated apparatus polarizes a ferroelectric polymer thin film while monitoring and evaluating a substrate current whose magnitude, slope and noise profile (Barkhausen noise) varies in accordance with phase transformation processes of crystallites within the film and, thereby, provides an indication of the polarization status. The electric current flowing through the microstructures of the thin film can be modeled by an equivalent circuit, within which electrical charges stored in the respective microstructures are denoted by a plurality of discrete components (e.g., capacitors). Alternatively, the process can be modeled in terms of a hysteresis loop of polarization vs. electric field, corresponding to the availability of recombination sites on the thin-film surface. By comparing the measured substrate current to the result derived from the equivalent circuit, the major processing parameters such as poling current and voltage can be adjusted via an in-situ manner throughout the corona poling process and an accurate process endpoint can be established. As a consequence, a ferroelectric thin film is fabricated that has an enhanced piezoelectric effect yet minimized aging problems.