Stephane Hiboux

Self-polarization effect in Pb(Zr,Ti)O3 thin films

Abstract The self-polarization effect is investigated in Pb(Zr,Ti)O3 (PZT) thin films deposited by sol-gel and magnetron sputtering techniques. The effective piezoelectric coefficient of as-grown films, which is proportional to their initial polarization (self-polarization), is measured by a sensitive interferometric technique as a function of the annealing temperature, PZT composition, film thickness and bottom electrode material. The results indicate that the films are self-polarized by an internal bias field upon cooling through the phase transition temperature. It is suggested that a built-in field of a Schottky barrier between the PZT film and the bottom electrode is responsible for the observed effect. Self-polarization of the films is found to be very stable and in some cases to be as high as 90% of that produced by the subsequent room temperature poling. This property is very useful for piezoelectric and pyroelectric applications of PZT films since the poling procedure can be avoided. The properti...

Domain and lattice contributions to dielectric and piezoelectric properties of PZT thin films as a function of composition

In situ reactively sputter deposited, 300-nm-thick Pb(Zrx,Ti1-x)O3 thin films were investigated as a function of composition, texture, and different electrodes (Pt,RuO2). X-ray diffraction analysis, ferroelectric, dielectric, and piezoelectric measurements were carried out. While for dielectric properties bulklike contributions from lattice as well as from domains are observed, domain wall contributions to piezoelectric properties are very much reduced in the morphotropic phase boundary (MPB) region. Permittivity and d33 do not peak at the same composition; the MPB region is broadened up and generally shifted to the tetragonal side.

Mixed titania-lead oxide seed layers for PZT growth on Pt(111): a study on nucleation, texture and properties

Growth and properties of sputter in situ sputter deposited Pb(Z,Ti)O-3 (PZT) thin films have been studied on (111)-textured Pt electrodes as a function of seed layers of the type (TiO2)(x)(PbO)(y). The PZT process was run with a limited lead excess resulting in pyrochlore nucleation on bare Pt electrodes. When the electrode was covered with a dense seed layer, perovskite was obtained everywhere. Ti rich seed layers yielded (111)-textured PZT even for very thin seed layers. Pb rich seed layers nucleated as PbTiO3{100} and gave rise to (100)-textured PZT. In an intermediate zone, the major perovskite orientations (100), (110) and (111) have been found together With pyrochlore for a small seed layer thickness. In this zone, the seed layer nucleates in islands leaving bare Pt spots. The intermediate region is a transition region between (111) seeds and (100) seeds. The latter exhibit diverging critical sizes at a given critical flux ratio, leading to large nuclei and bare Pt

Downscaling of Pb(Zr,Ti)O3 film thickness for low-voltage ferroelectric capacitors: Effect of charge relaxation at the interfaces

In this communication we address two issues essential for low-voltage memory applications of ferroelectric thin films: the size effect on polarization switching, and polarization fatigue. According to the proposed concept, both of these phenomena are controlled by local injection of charge into the interfacial layers of the ferroelectric film. In the experimental part of this work, we show that the entrapped charge relaxation can be enhanced by introducing a thin RuO2 layer into the top interface of the Pt/PZT/Pt ferroelectric capacitor. Capacitors prepared in this way using PZT with a 45/55 Zr/Ti ratio show a substantial improvement of fatigue performance and withstand relatively well the thickness downscaling. As a result, these capacitors exhibited good ferroelectric properties for driving voltage amplitudes as low as 0.6–0.8 V. Our results suggest that control of charge relaxation at the interface is a key issue for development of low-voltage ferroelectric capacitors.

Which PZT thin films for piezoelectric microactuator applications

Abstract The effective piezoelectric coefficient e31 has been measured on sol-gel processed Pb(ZrxTi1−x)O3 thin films with Zr concentrations ranging from 45 to 60%. The largest value was observed at 45% Zr, although dielectric constant and effective d33 peak at 53% Zr. The findings suggest that the optimal composition for microactuators and sensors is less than 45% Zr, i.e., in the tetragonal part of the phase diagram.

Orientation and Composition Dependence of Piezoelectric-Dielectric Properties of Sputtered Pb(Zr x ,Ti 1-x )O 3 Thin Films

In-situ, reactively sputter deposited 300 nm thick Pb(Zr x ,Ti 1-x )O 3 films on Pt/Si based substrates are investigated as a function of composition and texture. (111) PZT is grown on a (111) oriented Pt bottom electrode covered with a very thin TiO 2 film. Highly {100} oriented PZT is grown on Pt (111) by means of a 10 nm thick PbTiO 3 seed layer. Pronounced deviations from known bulk PZT behavior are observed for the (111) texture. Maximum of d 33 and e are shifted to 40/60 and 45/55 compositions, respectively. (100) textured films exhibit a higher d 33 . 1.3 μm (100) thick films attain the predicted d 33 value of clamped bulk ceramics. Coercive fields and voltage offsets increase strongly with increasing Ti content. In parallel, the as-grown polarization increases. Polarization switching is not possible for x ≤ 0.1. Post-anneals in O 2 and hot poling show that oxygen vacancies play an important role in this phenomenon. Ti-rich (100) oriented films exhibit very high and stable pyroelectric and piezoelectric coefficients whithout poling treatments.

Piezoelectric and dielectric properties of sputter deposited (111), (100) and random-textured Pb(ZrxTi1-x)O3 (PZT) thin films

Abstract Highly textured PZT(111), PZT(001/100) and random PZT films have been grown on Pt and RuO2 bottom electrodes by means of an in-situ, multimagnetron reactive sputtering process with three metal targets (Pb, Zr, Ti). The orientation was varied with the bottom electrode/PZT initial interlayer deposition conditions. Series of 300 nm thick films with varying composition x have been prepared. The Ti and Zr ratio was changed by adjusting the powers of the corresponding targets. The lead content was self stabilized by the process at the deposition temperature of 570°C. Polarization, dielectric and piezoelectric properties were studied. Coercive field, built-in electric field and unswitchable polarization for Ti-rich compositions have been determined by polarisation hysteresis loops.

Processing optimization of solution derived PbZr1−xTixO3 thin films for piezoelectric applications

Abstract Processing optimization allowed the sol-gel fabrication of 1 μm thick, phase pure perovskite thin films with identical grain size and controlled texture. This made it possible to fabricate stress compensated beams to measure the transverse piezoelectric coefficient over the whole composition range of PbZr1−xTixO3. The highest value of -12.1 C/m2 was measured for (100)/(001) textured PZT53/47. For (111) textured films the maximum value of -8.7 C/m2 was found to be in the tetragonal phase field at 55% Ti.

Piezoelectric cantilever microphone for photoacoustic GAS detector

Abstract New micromachined pressure sensors based on PZT coated silicon cantilevers have been fabricated and integrated in a photoacoustic gas detector. PZT Sol-gel thin films texture and composition were optimized with respect to the transverse piezoelectric coefficient e31,f. A best value of -12 C/m2 was obtained with (100)/(001) textured thin films at the MPB composition. Optimum stress compensation between the different layers composing the cantilever has been studied in order to yield flat cantilevers. A high response of 150 mV/Pa with a S/N of 700 at 1 Pa and 1 Hz bandwidth has been measured. The influence of the damping chamber under the cantilever is also reported.

Excess lead in the perovskite lattice of PZT thin films made by in-situ reactive sputtering

Abstract The incorporation of up to 40 % lead excess into the perovskite lattice of Pb(Zr,Ti)O3 (PZT) has been investigated. Three independent chemical composition analysis methods confirmed the correct determination of the lead excess, present as Pb2O3. High resolution TEM excludes any second phases and restricts the occurrence of lead excess to the perovskite lattice, suggesting a lead oxide perovskite of the form Pb2+Pb4+O3 with a 4-valent ion on the B-site. PZT containing such lead excess is thus a solid solution of PbZrO3, PbTiO3 and PbPbO3. The measured volume increase of the lattice due to a larger average B-ion matches very well with the calculated behavior based on standard ion radii and the B-ion radius dependence of the unit cell dimensions of PZT crystals. Structure factors as determined from Synchrotron X-ray diffraction are much better compatible with the B-site lead model than with the standard PZT ion lattice.