So far, a few chemical solution routes for the fabrication of ferroelectric HfO2 films have been reported. Most of them employ precursors, solvents or additives that are considered difficult to...

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Polyvinylidene fluoride (PVDF) has been attracting a lot of interest among researchers for the fabrication of biocompatible flexible piezoelectric sensors. However, low piezoelectric properties and lack of a simple large-scale fabrication method has prevented commercialization of such sensors. In this research, a nozzle-less ultrasonic spray coating (USC) method is introduced and used for the development of pure PVDF sensors with high performance and sensitivity. PVDF films with thickness of ~9 µm are fabricated by USC, and their morphology, crystalline structure, piezoelectric properties, and sensing performance are studied and compared to sensors made by casting method. The obtained piezoelectric coefficients of the USC fabricated sensors (d33=38 pm/V) are higher than PVDF sensors available in the literature fabricated by other common methods. By applying various testing forces at controlled low frequencies, the output voltage, linearity, and sensitivity of the sensor is found to be higher than the similar sensor made by drop casting method. Therefore, this study presents a simple and cheap process for large-scale fabrication of high-efficiency biocompatible sensors.

So far, a few chemical solution routes for the fabrication of ferroelectric HfO2 films have been reported. Most of them employ precursors, solvents or additives that are considered difficult to handle, unstable, toxic, generally unfriendly with the environment and/or unsuitable for large scale industrial processes. In this work, we present a new effective chemical route for preparation of ferroelectric doped-HfO2 films. The solution is prepared from simple, stable, and available precursors, handled in an open atmosphere and requires no restrictive processing conditions. We used 5 at.% Ca as dopant of HfO2 to induce a maximum remnant polarization of 9.3 and 11.1 µC/cm2 for 54 and 90 nm thick Ca:HfO2 films, respectively. The current-electric field loops show intense and distinctive ferroelectric switching peaks and the corresponding ferroelectric loops show excellent saturation, which speaks of good device quality with low leakage. Crystallization and the wake-up of ferroelectricity in Ca:HfO2 films was attained by means of rapid thermal annealing at different temperatures and times in Ar:O2 atmosphere. In comparison to the thin films, thicker ones exhibited the highest remnant polarization at shorter annealing times, thus evidencing the need for precise control of thermal processing. The Ca:HfO2 films with thickness of 50 nm displayed a good balance between leakage and retention, maintaining the ferroelectric response above 105 cycles at 1 kHz. The developed precursor solution is promising for its use in spray-coating and ink-jet printing techniques.

So far, a few chemical solution routes for the fabrication of ferroelectric HfO2 films have been reported. Most of them employ precursors, solvents or additives that are considered difficult to handle, unstable, toxic, generally unfriendly with the environment and/or unsuitable for large scale industrial processes. In this work, we present a new effective chemical route for preparation of ferroelectric doped-HfO2 films. The solution is prepared from simple, stable, and available precursors, handled in an open atmosphere and requires no restrictive processing conditions. We used 5 at.% Ca as dopant of HfO2 to induce a maximum remnant polarization of 9.3 and 11.1 µC/cm2 for 54 and 90 nm thick Ca:HfO2 films, respectively. The current-electric field loops show intense and distinctive ferroelectric switching peaks and the corresponding ferroelectric loops show excellent saturation, which speaks of good device quality with low leakage. Crystallization and the wake-up of ferroelectricity in Ca:HfO2 films was attained by means of rapid thermal annealing at different temperatures and times in Ar:O2 atmosphere. In comparison to the thin films, thicker ones exhibited the highest remnant polarization at shorter annealing times, thus evidencing the need for precise control of thermal processing. The Ca:HfO2 films with thickness of 50 nm displayed a good balance between leakage and retention, maintaining the ferroelectric response above 105 cycles at 1 kHz. The developed precursor solution is promising for its use in spray-coating and ink-jet printing techniques.