SrBi2Ta2O9 has only two polar axes – a problem for high density ferroelectric memory devices

In the microscopic polarization-switching of SrBi2Ta2O9 (SBT) thin films, a significant proportion of the crystallites have proved to remain unswitchable. From the Curie-rule and from hysteresis measurements of SBT material with uniform crystal orientation, it follows that SBT posseses only two polar axes. The switchable polarization of polycrystalline films with different numbers of polar axes is simulated numerically. It is shown that SBT capacitors with large-size electrodes may exhibit good switchability. However for high density memory applications, severe microstructural orientation requirements must be fulfilled to avoid switching failures. Materials with more than two polar axes make far reduced or no demands regarding texture quality.