Electrical properties of BaTiO3 based ferroelectric capacitors grown on oxide sacrificial layers for micro-cantilevers applications

An investigation of all oxides ferroelectric capacitors based on $SrRuO_3/BaTiO_3/SrRuO_3$ multi-layers grown on sacrificial oxide layers of $YBa_2Cu_3O_7$\ud and MgO for Micro-Electo-Mechanical systems applications is reported. By insertion of additional MgO or $SrTiO_3$ buffer layers the orientation of the $BaTiO_3$ film can be controlled allowing the fabrication of suspended cantilevers using the 31 and the 33 piezoelectric modes. The electrical properties of $SrRuO_3/BaTiO_3/SrRuO_3$ capacitors are changed compared with those grown directly on a single crystal substrate by the introduction of sacrificial layers. Circuit modeling of the electrical characteristics of these devices shows that a reduction of the deposition pressure for $BaTiO_3$ produces a decrease of the parasitic shunting conductance (modeled with a resistor in parallel to the capacitance of the device) which reduces the resistive loss present in the $BaTiO_3$ film. However for extremely low deposition pressure the quality of the polarization hysteresis loops is compromised.\ud Particulates present on the surface of the $YBa_2Cu_3O_7$increases the parasitic conductance at low frequency in the capacitive structure grown on this sacrificial layer. Good electrical properties are obtained for the capacitive structures grown on top of the MgO sacrificial layers at pressures equal or lower than 8 Pa.\u

International Veterinary Epilepsy Task Force recommendations for a veterinary epilepsy-specific MRI protocol

Epilepsy is one of the most common chronic neurological diseases in veterinary practice. Magnetic resonance imaging (MRI) is regarded as an important diagnostic test to reach the diagnosis of idiopathic epilepsy. However, given that the diagnosis requires the exclusion of other differentials for seizures, the parameters for MRI examination should allow the detection of subtle lesions which may not be obvious with existing techniques. In addition, there are several differentials for idiopathic epilepsy in humans, for example some focal cortical dysplasias, which may only apparent with special sequences, imaging planes and/or particular techniques used in performing the MRI scan. As a result, there is a need to standardize MRI examination in veterinary patients with techniques that reliably diagnose subtle lesions, identify post-seizure changes, and which will allow for future identification of underlying causes of seizures not yet apparent in the veterinary literature. There is a need for a standardized veterinary epilepsy-specific MRI protocol which will facilitate more detailed examination of areas susceptible to generating and perpetuating seizures, is cost efficient, simple to perform and can be adapted for both low and high field scanners. Standardisation of imaging will improve clinical communication and uniformity of case definition between research studies. A 6–7 sequence epilepsy-specific MRI protocol for veterinary patients is proposed and further advanced MR and functional imaging is reviewed

New multilayer architectures for piezoelectric BaTiO₃ cantilever systems

The fabrication and characterization of released cantilevers in new multilayer thin films architectures is reported. In contrast to previous works, the cantilevers are produced without etching of the substrate and are based on lead free piezoelectric materials. The three architectures are: SrRuO3/BaTiO3/MgO/SrTiO3/YBa2Cu3O7, SrRuO3/BaTiO3/SrRuO3/YBa2Cu3O7 and SrRuO3/BaTiO3/SrRuO3/SrTiO3/YBa2Cu3O7. It is shown that the different architectures allow a choice of the orientation of the polar axis in piezoelectric layers, in plane (d33 mode) or out of plane (d31 mode). Both configurations may be utilized in piezoelectric energy harvesting devices. Released cantilevers with the above layer sequences have been produced with lengths ranging from, 100 μm to 250 μm. The residual stress after the release of the cantilevers produces an upwards bending, the distance between the cantilever tips and the substrate varying between 20 μm and 45 μm. This distance would allow the sufficient vibration amplitude to enable the cantilevers to be used as micro-generators. Measurements of Young Modulus of the cantilevers and of polarization hysteresis loop are reported

Residual stress analysis of all perovskite oxide cantilevers

We have used a method to experimentally determine the curvature of thin film multilayers in all oxide cantilevers. This method is applicable for large deflections and enables the radius of curvature of the beam, at a certain distance from the anchor, to be determined accurately. The deflections of the suspended beams are measured at different distances from the anchor point using SEM images and the expression of the deflection curve is calculated for each cantilever. With this expression it is possible to calculate the value of the radius of curvature at the free end of the cantilever. Together with measured values for the Youngs Modulus, this enabled us to determine the residual stress in each cantilever. This analysis has been applied to SrRuO3/BaTiO3/SrRuO3, BaTiO3/MgO/SrTiO3 and BaTiO3/SrTiO3 piezoelectric cantilevers and the results compared to two models in which the stresses are determined by lattice parameter mismatch or differences in thermal expansion coefficient. Our analysis shows that the bending of the beams is mainly due the thermal stress generated during the cooling down stage subsequent to the film deposition