Abstract

The work deals with the experimental study of ferroelectric (FE) performance scaling for nanometer-sized devices. In the emerging and advanced devices, it is desirable to couple FE performance with other functions. This requires integration of nanoscale FEs with other materials, which is especially promising in epitaxial heterostructures. Such heterostructures inevitably possess a large lattice mismatch, the effect of which on FE properties is unknown and is in the focus of the present work.

In the study, heteroepitaxial thin and ultrathin films and superlattices of ABO₃-type perovskite structure FEs were used, with A = Pb, Ba, Sr, K, and N, and B = Ti, Zr, Nb, and Ta.

FE domains and local polarization switching were explored on the nanometer scale using piezoresponse force microscopy. The experiment was modified that allowed achieving images with high contrast and lateral resolution, and also allowed analysis of nanodomains in lateral capacitor configuration. Local properties were related to a macroscopic response. For this, the method of simultaneous on-wafer low-frequency impedance measurements was optimized allowing studies of thin and ultrathin (to 5 nm) films in a broad range of conditions and regimes.

Experimental studies have reveled phenomena which cannot be explained in the frame of the existing theories. The observed new effects are important for applications such as multistate memory devices, storage capacitors, and FE tunnel junction devices.