Abstract:
Ferroelectrics are multifunctional materials (piezoelectric, pyroelectric, tunable dielectric constant, non-linear optical properties) that are in use for many high-technology applications (non-volatile memories, thermal imaging, optical shutters, etc.). Among the most used are those ferroelectrics with perovskite structure, such as BaTiO3 or PZT solid solutions. For many years, these materials were used in applications in the bulk form, single crystals or ceramics. The growing demand on integrating the devices based on ferroelectrics with semiconductor technology has shifted the interest towards thin films. The rapid development of the deposition techniques allows, nowadays, the growth of high quality epitaxial structures based on ferroelectric layers with oxide structure. However, all these heterostructures are including interfaces, and the quality of the interfaces can have a considerable impact on the macroscopic properties of the structure or on the physical characteristics of the device including the irrespective structure. Therefore, the study of interface properties in correlation with the macroscopic physical properties such as polarization, dielectric constant or leakage current is very important. Here we report on some recent results obtained on the role of interfaces in some epitaxial structures based on ferroelectric perovskites. The investigations involved several techniques, such as structural investigations by XRD and (HR)TEM, investigation of domain structure by PFM and macroscopic electrical measurements. The main conclusion was that the interfaces may dominate the macroscopic properties. Other important conclusion, referring specifically to the electrode-ferroelectric interface, is that the polarization charges are controlling the band-bending and the height of the potential barrier. Furthermore, it was found that interfaces can enhance the dielectric constant, the stress at the interfaces can induce thickness driven phase transitions, or that the memory window in MFS structures can be affected by the quality of the interfaces. The above results open new perspectives in designing ferroelectric based structures interface engineering.
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