REPOSITORY > RESULTS

Abstract

The miniaturization of electronic devices requires the fabrication of functional components
in the form of μm-sized thick films. Some of the most promising functional materials are
relaxor-ferroelectric (1-x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 (PMN–100xPT), as they exhibit
versatile dielectric, piezoelectric and relaxor-ferroelectric properties. However, the
integration of functional ceramic thick films with non-conventional substrates such as
metals and polymers remains challenging due to the thermally activated processes and
incompatibilities that arise during the high-temperature sintering process of ceramics. To
overcome the integration barrier, an aerosol deposition (AD), spray-coating method based
on room-temperature deposition is used.
In this work, PMN–100xPT thick films were deposited on low-cost substrates using the
AD method. We deposited PMN–10PT and PMN–35PT on stainless-steel (SS) and PMN–
10PT on flexible polyimide (PI) substrates. The focus of this thesis is on the optimization
of the deposition process of thick films and on the effect of thermal annealing the samples
on their structural, microstructural and functional properties.
First, the main material parameters for successful AD of the powder were identified
and used in the process. It was found that after the mechanochemically assisted synthesis
of PMN–10PT powder, additional powder treatments such as heating and subsequent
milling are crucial for efficient film deposition, as the treatment yields highly crystalline
powder particles in the range of several hundred nm. The optimized PMN–10PT and PMN–
35PT powders resulted in high-density and few-μm-thick films with very low porosity (1.5–
3.0%) and good adhesion. These are also the properties that contribute to the very high
dielectric breakdown strength of the films (above 900 kV·cm–1).
The as-deposited thick films were thermally annealed at temperatures of 400 °C (for PI
substrates) and 500 °C (for SS substrates), which are far below the temperatures for
sintering ceramics. Thermal annealing at such moderate temperatures does not change the
microstructure of the ceramic thick films, i.e., crystallite and grain growth is insignificant,
and the density remains the same. However, thermal annealing leads to compressive stress
relaxation in PMN–10PT and PMN–35PT thick films, which is evident from structural
analysis by X-ray diffraction and Raman spectroscopy. The as-deposited films show
promising room-temperature electrical energy-storage properties, which improve after
thermal annealing due to stress relaxation. After thermal annealing, the recoverable energystorage
density (Urec) and energy-storage efficiency (η) reach 8.8–9.8 J·cm–3 and 61–79%
at 900 kV·cm–1, respectively. In particular, the PMN–10PT thick films on SS exhibit
excellent temperature stability up to 200 °C and electric field cycling stability up to 16·106
cycles. The PMN–10PT thick films on PI were subjected to flexural bending tests, which
showed high flexibility (1.1% bending strain) and high durability (105 bending cycles). The
piezoelectric activity of the AD thick films was also confirmed for the PMN–35PT thick
films on SS. The as-deposited and annealed thick films achieve a piezoelectric coefficient
of 25 and 41 pm·V–1, respectively. We demonstrate that the integration of PMN–100xPT
on low-cost substrates such as SS and PI is feasible, which can significantly impact the
diversity and affordability of future electro-energy systems and devices.