C. Soyer

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...

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.

Determination of the d31 piezoelectric coefficient of PbZrxTi1−xO3 thin films using multilayer buckled micromembranes

The aim of this paper consists in the determination of the piezoelectric transverse coefficient d31 of PbZrxTi1−xO3 (PZT) thin films integrated in dedicated multilayer silicon-based micromembranes exhibiting an initial buckled profile. An analytical model specific to this configuration was built and used for the calculation of d31 starting with the static profiles of the microfabricated devices determined by means of a double-beam interferometer. The influence of dc voltage and buckling effects on the d31 piezoelectric coefficient at the microscale were investigated, and high values were obtained, from 30to75pm∕V, within a hysteresyslike cycle. These results demonstrated the good electrical behavior of PZT thin films at the microscale with a low influence of buckling effects and determined optimal operation conditions for high values of d31.

Micromachining of an SU-8 flapping-wing flying micro-electro-mechanical system

This paper presents a feasibility step in the development of an ultra-small biomimetic flying machine. Advanced engineering technologies available for applications such as the micro-electro-mechanical system (MEMS) technologies are used. To achieve this goal, a flapping-wing flying MEMS concept and design inspired from insects is first described. Actuators and an actuation way for the control over the wing kinematics are proposed. The initial concepts are subsequently analyzed and presented using multi-body and finite element models. An overview of SU-8 photoresist structures and their functions in the future micro-robot insect is then presented. Consequently, micromachining enables the implementation of a flying MEMS. It is also demonstrated that the structure can be made at insect sizes and actuated at low power inputs. Moreover, the flapping frequency obtained is within the flapping frequency range of wings of many common insects of millimetric dimensions. Such prototypes are of interest as tools to artificially recreate and study insect flight with characteristics, similar to those of insects, that are able to produce lift and hover. Finally, if a micro-battery, wireless receivers, microcontrollers, sensors and actuators can all be fitted onto chips only a few millimeters square, with a mass in the order of milligrams, then we believe that an insect-size flying MEMS can be realized. All these requirements can now be achieved due to advanced engineering methods.

Ferroelectric (116) SrBi2Nb2O9 thin films epitaxially grown by pulsed laser deposition on epitaxial (110) Pt/(110) SrTiO3 electrode

Epitaxial SrBi2Nb2O9 thin films have been grown by pulsed-laser deposition on (110)Pt bottom electrode epitaxially grown on (110) SrTiO3 by dc sputtering. X-ray φ-scans and electron channeling patterns reveal the epitaxial growth of the (116) SrBi2Nb2O9/(110)Pt bilayers. The hysteresis loop, dielectric response, and capacitance–voltage characteristics of this bilayer are presented. The remnant polarization was measured to be close to 5 μC/cm2, and the coercive field was calculated to be ∼120 kV/cm. The zero field permittivity was about 150 and the dielectric loss was ∼2%.

Dielectric microwave characterizations of (Ba,Sr)TiO3 film deposited on high resistivity silicon substrate: Analysis by two-dimensional tangential finite element method

(Ba,Sr)TiO3 (BST) thin films were deposited on high resistivity silicon substrates by in situ rf magnetron sputtering. A buffer layer was used to improve the cristallinity of the films, the composition was fixed to Ba/Sr=30/70. The relative permittivity and the losses were measured up to 60 GHz using coplanar strip lines. The dispersion of the permittivity and the losses has been determined with a home made numerical code based on finite elements: ELFI. We show that, with the measurements of the scattering parameters coupled with ELFI, it is possible to know the BST complex permittivity over a very broad frequency band. The BST films deposited by in situ (700 °C) present excellent properties between 1 to 60 GHz. The relative permittivity is in the order of 270 and the losses are very small 0.09 at 60 GHz. These structures BST/silicon high resistivity show good potentialities for devices microwaves applications which need future integration in a silicon environment.

Analysis of size effects in Pb(Zr0.54Ti0.46)O3 thin film capacitors with platinum and LaNiO3 conducting oxide electrodes

The problem of thickness dependence of dielectric and ferroelectric properties of Pb(Zr0.54Ti0.46)O3 (PZT) thin film capacitors is addressed. Experimental data collected on PZT capacitors with different thicknesses and different electrode configurations, using platinum and LaNiO3 conducting oxide, are examined within the prism of existing models. Available literature data, abounding but contradictory, led us to conclude that in the range of thickness investigated, size effect under all its aspects, i.e., increase in coercive field (Ec) as well as decrease in both dielectric permittivity and remnant polarization (Pr), result basically from existence of a depolarization field. It is shown however that the latter arises from interface chemistry, mostly related to the upper surface of the films, instead of finite screening length in the electrodes unlike commonly accepted. Moreover it is established that increase in Ec and decrease in Pr are not concomitant, and significant degradation of one or the other of ...

Rigorous extraction tunability of Si-integrated Ba0.3Sr0.7TiO3 thin film up to 60 GHz

400-nm-thick Ba0.3Sr0.7TiO3 thin films are deposited on high resistivity silicon by in situ radio frequency magnetron sputtering. Coplanar waveguides with 1 μm slot width are designed, with accurate knowledge frequency losses behavior, to determine ferroelectric thin-films properties up to 60 GHz. Permittivity, loss tangent, and tunability are extracted through measurements and home made finite element analysis. Tunability of 33% and 29%, with 30 V maximum applied voltage (electric field of 300 kV/cm), are measured at 5 GHz and 60 GHz, respectively, while the dielectric losses evolve from 0.5% to 5%. A brief highlight is proposed about tunable silicon integrated quarter wavelength transformer potentialities for impedance matching.

Electrical damage induced by reactive ion-beam etching of lead-zirconate-titanate thin films

Ion-beam etching of sputtered Pb(Zrx,Ti1−x)O3 (PZT) thin films with x equal to 0.54 grown on Pt∕TiOx∕SiO2∕Si substrates has been performed using pure Ar gas and a varying CHF3∕Ar gas mixing ratio. The etch rate dependence on the process parameters (gas composition, current density, and acceleration voltage) has been investigated. PZT etch rate under 40% CHF3 in Ar can reach 100nm∕min with an acceleration voltage of 900 V and a current density of 0.7mA∕cm2 (in comparison to 35nm∕min in pure Ar). A selectivity ratio of 8 has been obtained between PZT and photoresist (1.3 in pure Ar). We have evaluated the PZT surface damage by contact mode atomic force microscopy. It appears that the roughness increases less under a gas mixture than under a pure argon beam, and that the preferential etching observed at the grain boundaries under a pure argon beam disappears when we increase the proportion of CHF3 in the gas mixture. For some etching parameters (current density, acceleration voltage, and gas mixing ratio), w...

Interface depolarization field as common denominator of fatigue and size effect in Pb(Zr0.54Ti0.46)O3 ferroelectric thin film capacitors

Dielectric, hysteresis and fatigue measurements are performed on Pb(Zr0.54Ti0.46)O3 (PZT) thin film capacitors with different thicknesses and different electrode configurations, using platinum and LaNiO3 conducting oxide. The data are compared with those collected in a previous work devoted to study of size effect by R. Bouregba et al., [J. Appl. Phys. 106, 044101 (2009)]. Deterioration of the ferroelectric properties, consecutive to fatigue cycling and thickness downscaling, presents very similar characteristics and allows drawing up a direct correlation between the two phenomena. Namely, interface depolarization field (Edep) resulting from interface chemistry is found to be the common denominator, fatigue phenomena is manifestation of strengthen of Edep in the course of time. Change in dielectric permittivity, in remnant and coercive values as well as in the shape of hysteresis loops are mediated by competition between degradation of dielectric properties of the interfaces and possible accumulation of i...