D. Remiens

Lamb wave and plate mode in ZnO/silicon and AlN/silicon membrane: Application to sensors able to operate in contact with liquid

Abstract Lamb waves, especially the A 0 mode, can be used to build sensors able to operate in contact with liquid. Nevertheless, some difficulties remain for practical devices. First, we discuss the relevance of the electromechanical coefficient. We present the element of choice of the device characteristics and the piezoelectric material. We compare two kinds of devices, the first is a classical delay line device and the second a resonant device. The behavior of these devices has been controlled using optical visualization of vibration modes. Furthermore, the performance of the devices is experimentally tested and advantages of the resonant device are shown.

Piezoelectric properties of PZT films for microcantilever

The investigation of piezoelectric properties of materials in the thin layer form has become an important task because of the increased range of their applications as actuators and sensors. The sensor magnitude, is a direct function of the e31 piezoelectric constant. Pb(Zr,Ti)O3 thin films and the modified compositions have attracted great attention in recent years as promising for use in microelectromechanical systems. To determine this constant we use an unusual experimental method. A remanent piezoelectric constant of −4.7 C/m2 was obtained. The parameters as, coercive field, saturation field, curve of first polarization, and self polarization of the remanent piezoelectric hysteresis loop are presented for 1.6 μm thick PZT thin film. We will associate also dielectric results. To show the possible integration of the piezoelectric films in microelectromechanical systems, we have deposited PZT thin film on a 100 μm long, 20 μm wide, 1 μm thick silicon oxide beam to control the z actuation.

Laser Doppler vibrometry for evaluating the piezoelectric coefficient d33 on thin film

The problem of electromechanical film characterization, and, in particular, the determination of the piezoelectric activities of thin films deposited on substrates, is of fundamental importance in the development of structures for microelectromechanical system (MEMS) applications. The design and the architecture of the piezoelectric MEMS are directly related to the mechanical and the piezoelectric performances of the material. In this article, we present and compare some results obtained on different experimental setup for the determination of the d33 coefficient. We have optimized the experimental conditions using a laser Doppler vibrometer. The main problem is the contribution of the bending effect of the substrates on the d33 coefficient, which is an intrinsic property of the film. We show that the d33 values are directly related to parameters such as the top electrode diameter and the substrate holder. The results are in agreement with those obtained with the conventional double beam interferometer us...

Ferroelectric properties of PZT thin films prepared by sputtering with stoichiometric single oxide target: Comparison between conventional and rapid thermal annealing

The influence of growth conditions and post-annealing treatments on radio frequency (r.f.) magnetron sputtered lead zirconate titanate (PZT) thin films have been investigated. By adjusting the plasma discharge parameters, it is possible to control, with stoichiometric single oxide target, the film composition precisely. No excess lead was used either during sputtering (in the target) or during post-deposition annealing. The structural, microstructural and electrical properties have been systematically examined as a function of the annealing treatments. Perovskite structure was obtained by conventional annealing as well as by rapid thermal annealing. The films were dense and crack-free; the film orientation, the microstructure and the surface morphology are directly related to the thermal processes. The ferro-electric properties in terms of coercive field and remanent polarization are also very sensitive to the annealing treatments.

Structure control of Pb(Zr,Ti)O3 films using PbTiO3 buffer layers produced by magnetron sputtering

The orientation of Pb(Zr,Ti)O3 (PZT) thin films grown by sputtering on a Si/SiO2/Ti/Pt substrate using a PbTiO3 (PT) buffer layer was controlled by changing the thickness of the buffer layer. The x-ray diffraction of PT as a function of the thickness, in the range of 20–400 A, showed modification of the PT orientation. That suggests a gradual evolution of the lattice parameters in the nucleation stage of PT films. The main growth mechanism was certainly due to the passing from an island growth to a continuous layer. The (111) oriented and (100) oriented PZT films were grown on 50 and 200 A PT buffer layers, respectively.

Ion beam etching of lead–zirconate–titanate thin films: Correlation between etching parameters and electrical properties evolution

Ion beam etching of sputtered Pb(Zrx,Ti1−x)O3 (PZT) with x equal to 0.54 thin films grown on Pt/Ti/SiO2/Si substrates has been performed using pure Ar gas. The etch rate dependence on the process parameters (current density, acceleration voltage, gas pressure) has been investigated. The PZT etch rate can reach 600 A/min with acceleration voltage of 1000 V and current density of 1 mA/cm2. Selectivity ratios between PZT and masks of various natures (photoresist, Pt, Ti) have been evaluated to determine a pertinent material for etching mask. According to our etching conditions, titanium seems to be the best candidate. We evaluated the PZT surface damage by contact mode atomic force microscopy. It appears that the roughness increases after ion bombardment, and that the grain boundary zone is preferentially etched. For some etching parameters, we also observed electrical damage. Carrying out C(V) and hysteresis loops P(E) measurements before and after etching have provided evidence of degradation. We noted a l...

LiNbO3 thick films grown on sapphire by using a multistep sputtering process

We present the results of investigations of lithium niobate (LiNbO3) films grown on (0001) sapphire substrate by radio-frequency magnetron sputtering. With the aim of producing thick films we have developed a multistep process. To assess the structural quality of our films, we performed x-ray diffraction, transmission electron microscopy, and atomic force microscopy of the films. The results revealed that the epitaxial structure is verified on sapphire whatever the film thickness. Based on our studies we concluded that the proposed multistep process leads to a good controlled epitaxy of thick LiNbO3 samples on sapphire. Using the prism coupling technique we have characterized the optical properties of the deposited layers. The ordinary (no) and extraordinary (ne) refractive indices are, respectively, 2.289±0.001 and 2.206±0.001 at 632.8 nm, and waveguide losses of 1.2 dB/cm have been demonstrated. In addition, we have qualified the film properties between each growth step and between the substrate to laye...

Microwave properties of epitaxial (111)-oriented Ba0.6Sr0.4TiO3 thin films on Al2O3(0001) up to 40 GHz

Perovskite Ba0.6Sr0.4TiO3 (BST) thin films have been grown on Al2O3(0001) substrates without/with inserting an ultrathin TiOx seeding layer by rf magnetron sputtering. X-ray diffraction and pole figure studies reveal that the film with the TiOx layer (12-A-thick) is highly oriented along the (111) direction and exhibits a good in-plane relationship of BST(111)∥Al2O3(0001). The high frequency dielectric measurements demonstrate that the complex permittivity (e=e′−je″) is well described by a Curie–von Scheidler dispersion with an exponent of 0.40. The resulting epitaxial BST films show high permittivity (∼428) and tunability (∼41%, at 300 kV/cm and 40 GHz) and their microwave properties (1–40 GHz) potentially could be made suitable for tunable devices.

True Young modulus of Pb(Zr,Ti)O3 films measured by nanoindentation

In order to assess transverse elastic modulus of lead zirconate titanate (PZT) thin films, we used a nanoindenter with constant monitoring of the force. It is shown that the true elastic modulus, i.e., the low pressure elastic modulus, can be measured by this method. This permitted a determination that sputter deposited PZT (54∕46) films display a Young modulus close to a ferroelectric hard type PZT bulk ceramic. Moreover, this low pressure modulus is independent of grain size and thickness of the film, but this is no more true for high pressure modulus. This provides a step toward a better understanding of the properties of these PZT films and the possibility to better use them in microsystems.

Enhancement of energy storage in epitaxial PbZrO3 antiferroelectric films using strain engineering

We demonstrate an approach to enhance the energy storage density W of antiferroelectric film through simple altering a crystallographic orientation of the substrate. We reveal that the antiferroelectric phase stability of PbZrO3 can be enhanced for the (110) or (111) SrTiO3 substrate orientation, thus suppresses the antiferroelectric-ferroelectric phase transition to higher electric field with ∼120 kV/cm increment. In addition, the polarization values of these films are also favorably increased hence increases W by 5.3 J/cm3 at 700 kV/cm. The observed enhancement is found to originate from a high sensitivity of phase transition to mechanical confinements due to the volume expansion at the transition.