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

3D finite element electrical model of larval zebrafish ECG signals

Assessment of heart function in zebrafish larvae using electrocardiography (ECG) is a potentially useful tool in developing cardiac treatments and the assessment of drug therapies. In order to better understand how a measured ECG waveform is related to the structure of the heart, its position within the larva and the position of the electrodes, a 3D model of a 3 days post fertilisation (dpf) larval zebrafish was developed to simulate cardiac electrical activity and investigate the voltage distribution throughout the body. The geometry consisted of two main components; the zebrafish body was modelled as a homogeneous volume, while the heart was split into five distinct regions (sinoatrial region, atrial wall, atrioventricular band, ventricular wall and heart chambers). Similarly, the electrical model consisted of two parts with the body described by Laplace’s equation and the heart using a bidomain ionic model based upon the Fitzhugh-Nagumo equations. Each region of the heart was differentiated by action potential (AP) parameters and activation wave conduction velocities, which were fitted and scaled based on previously published experimental results. ECG measurements in vivo at different electrode recording positions were then compared to the model results. The model was able to simulate action potentials, wave propagation and all the major features (P wave, R wave, T wave) of the ECG, as well as polarity of the peaks observed at each position. This model was based upon our current understanding of the structure of the normal zebrafish larval heart. Further development would enable us to incorporate features associated with the diseased heart and hence assist in the interpretation of larval zebrafish ECGs in these conditions

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