Polarization retention dependence of imprint time within LiNbO3 single-crystal domain wall devices

Abstract

Ferroelectric LiNbO3 single crystals have wide applications in surface acoustic wave filters, pyroelectric sensors, and electro-optic modulators. Large-area LiNbO3 single-crystal thin films integrated on silicon are promising for high density integration of ferroelectric domain-wall resistance switching memories and transistors. However, the short-time operation of the memory often suffers from poor polarization retention due to the built-in imprint voltage. Here, we observed the strong polarization orientation-dependent imprint effect within either out-of-plane or in-plane LiNbO3 thin-film capacitors. The imprint effect can shift domain switching hysteresis loops toward positive/negative voltages seriously with written negative/positive polarizations that occur within a characteristic imprint time of 5.1 ms–360 s. Once the write time of the memory is shorter than the imprint time, the inverted domain is unstable and switches back into its previous orientation automatically after the termination of a write operation. However, the write failure can be avoided if the write time is longer than the imprint time, and the written domain can be deeply protected by the imprint field. A model of polarization-dependent charge injection at the interface is developed to explain the time-dependent imprint effect. For a mesa-like LiNbO3 memory cell in contact with two side electrodes fabricated at the film surface, the imprint time can be greatly shortened below 30 ns with the extension of one side electrode over the cell surface to screen the tail of the switched domain, enabling ferroelectric domain-wall resistance switching devices in excellent retention and high operation speeds.