Method for the preparation at low temperatures of ferroelectric thin films, the ferroelectric thin films thus obtained and their applications

Abstract

A processing technology for the fabrication at low temperatures of ferroelectric crystalline oxide thin films, among others PbZrxTi1-xO3 (PZT) (<400 ºC for PZT) with ferroelectric properties appropriate for integration in devices is herein disclosed. The method is also valid for the fabrication of ferroelectric thin films of bronze tungsten (A2B2O6), perovskite (ABO3), pyrochlore (A2B2O7) and bismuth-layer (Bi4Ti3O12) structures, in which A and B are mono, bi-, tri-, tetra- and pentavalent ions. The method is based on the combination of Seeded Diphasic Sol Gel (SDSG) precursors with Photo Chemical Solution Deposition (PCSD) methodology and comprises the main following steps: i) synthesis of a modified metal-organic precursor solution of the desired metal oxide composition with a large photo-sensitivity in the UV wavelength range; ii) preparation by a sol gel process of nanoparticles of the desired composition, similar or dissimilar to the crystalline compound to be obtained from the previous precursor sol; iii) dispersion of the crystalline nanoparticles in the precursor sol to prepare a stable and homogeneous sol-gel based suspension; iv) deposition of the previous suspension onto substrates; v) UV irradiation in air or oxygen of the deposited layer and further thermal treatment in air or oxygen of the irradiated layer at temperatures below 400 ºC. This invention provides a method for the fabrication of polycrystalline ferroelectric, piezoelectric, pyroelectric and dielectric thin films, dense and without cracks with thickness above 50 nm and below 800 nm on single crystal, polycrystalline, amorphous, metallic and polymeric substrates at low temperatures and with optimised properties, being applicable in microelectronics and optics industries.

Innovative aspects & main advantages

Method of fabrication of ferroelectric crystalline metal oxide thin films with well-defined properties at crystallization temperatures lower than those referred in the literature using a chemical solution deposition approach and the combination of the two low temperature synthesis methods, previously developed separately by the inventors: the Photo Chemical Solution Deposition (PCSD) and the Seeded Diphasic Sol Gel (SDSG). The combination of the nucleation of the crystalline phase in the films at low temperatures, by the photo-activation of the precursors chemistry, in addition to the simultaneous promotion of the crystallization, by introducing nanocrystalline nucleus, allows the preparation of crystalline ferroelectric films at low temperature (<400 ºC) with well-defined dielectric and ferroelectric response.

Applications

For integration with microelectronic and micromechanical devices, e.g. MEMS, Ferroelectric Random Access Memories (FRAMs) or Dynamic Random Access Memories (DRAMs) and flexible microelectronics

Inventors

Applicant

Groups Involved

2 - multifunctional ferroic ceramics and nanostructures