Piezoelectric Lead Zirconate Titanate Thin Films Research Articles

A Novel Three-Axial Magnetic-Piezoelectric MEMS AC Magnetic Field Sensor.

We report a novel three-axial magnetic-piezoelectric microelectromechanical systems (MEMS) magnetic field sensor. The sensor mainly consists of two sensing elements. Each of the sensing elements consists of a magnetic Ni thick film, a Pt/Ti top electrode, a piezoelectric lead zirconate titanate (PZT) thin film, a Pt/Ti bottom electrode, a SiO2 insulation layer, and a moveable Si MEMS diaphragm. When the sensor is subjected to an AC magnetic field oscillating at 7.5 kHz, a magnetic force interaction between the magnetic field and Ni thick film is produced. Subsequently, the force deforms and deflects the diaphragms as well as the PZT thin film deposited on the diaphragms. The deformation and deflection produce corresponding voltage outputs due to the piezoelectric effect. By analyzing the voltage outputs through our criterion, we can obtain details of the unknown magnetic fields to which the sensor is subjected. This achieves sensing of three-axial magnetic fields. The experimental results show that the sensor is able to sense three-axial magnetic fields ranging from 1 to 20 Oe, with X-axial, Y-axial, and Z-axial sensitivities of 0.156 mVrms/Oe, 0.156 mVrms/Oe, and 0.035 mVrms/Oe, respectively, for sensing element A and 0.033 mVrms/Oe, 0.044 mVrms/Oe, and 0.130 mVrms/Oe, respectively, for sensing element B.

Wafer-scale growth of highly textured piezoelectric thin films by pulsed laser deposition for micro-scale sensors and actuators

Piezoelectric lead-zirconate-titanate (PZT) thin films were deposited on 4-inch (111)Pt/Ti/SiO2/Si(001) wafers using large-area pulsed laser deposition (PLD). This study was focused on the homogeneity in film thickness, microstructure, ferroelectric and piezoelectric properties of PZT thin films. The results indicated that the highly textured (001)-oriented PZT thin films with wafer-scale thickness homogeneity (990 nm ± 0.8%) were obtained. The films were fabricated into piezoelectric cantilevers through a MEMS microfabrication process. The measured longitudinal piezoelectric coefficient (d33f = 210 pm/V ± 1.6%) and piezoelectric transverse coefficient (e31f = -18.8 C/m2 ± 2.8%) were high and homogeneity across wafers. The high piezoelectric properties on Si wafers will extend industrial application of PZT thin films and further development of piezoMEMS.

Development of Au-Pt Buffer Layer Substrate to Improve PZT Piezoelectric Property

In this study, high piezoelectric lead zirconate titanate (PZT) thin film was prepared with MPB (Morphotoropic Phase Boundary) composition and buffer layer. From our previous study, high piezoelectricity of PZT thin film was confirmed through MPB (Morphotoropic Phase Boundary) composition and also noted that the piezoelectricity becomes maximum when PZT (111) and PZT (110) thin films stacked evenly. MPB composition and buffer layer significantly reduces the lattice mismatch to attain maximum piezoelectricity. It has been already reported that Au (111) and Pt (111) take high priority to orient PZT thin film in (111) and (110) crystal planes respectively. Therefore, the purpose of this study is to create alternately oriented buffer layer of Au (111) and Pt (111) and its influence on crystal quality.Sputtering technique was used to deposit Au-Pt buffer layer on Si substrate. Due to natural oxidation of Si in air atmosphere, the growth orientation of the thin film may be affected. Hence, prior to deposition, Si substrate was washed with hydrofluoric acid to remove the natural oxidation film. Further using Au-Pt composite target, buffer later was deposited on Si substrate and consequently the film was annealed. As a result of Au-Pt buffer layer 127 % of increase in crystal quality was observed as compared with the film deposited without buffer layer.

Development of a lead-zirconate-titanate (PZT) thin-film microactuator probe for intracochlear applications

In this paper, we present design, fabrication, and testing results of a small-scale piezoelectric lead-zirconate-titanate (PZT) thin-film microactuator probe that could be implanted in the inner ear for hearing rehabilitation. The PZT probe would generate a pressure wave directly stimulating perilymph in the cochlea to provide acoustic stimulation. Specifically, the PZT probe is 1-mm wide, 10-mm long, and 0.4-mm thick with a PZT thin-film diaphragm at the tip of the probe serving as an acoustic actuator. The diaphragm size is 0.8mm×0.8mm and the probe is packaged with parylene of 0.25-μm thickness. The design effort includes finite element simulations to determine thickness of the parylene package as well as back-of-the-envelope calculations of implantation depth of the PZT probe. The fabrication work includes deposition of a PZT thin film via sol–gel processes, deep reaction ion etching to form an array of vibrating PZT diaphragms, dicing the wafer to release the PZT probes, and application of parylene layer to package the PZT probes. The testing effort includes measurements of actuator velocity (via a laser Doppler vibrometer) and impedance (via an impedance analyzer) in air and in water. After the PZT probe is submerged in water, its displacement gradually increases and saturates at around 2h. Impedance measurements also show a similar trend. To explain these phenomena, we hypothesize that water infiltrates into the PZT thin film via diffusion, thus increasing the dielectric constant of the PZT film. SEM images reveal numerous nano-pores on PZT and probe surfaces, indirectly supporting the hypothesis. The PZT probe functions in water for 55h without breaking down.

Lift‐off process of piezoelectric lead–zirconate–titanate thin film using self‐assembled monolayer as sacrificial layer

In this work, a hydrophobic self-assembled monolayer, perfluorodecyltrichlorosilane (FDTS) (CF3(CF2)7(CH2)2SiCl3), was proposed as a sacrificial layer for a lift-off process of a piezoelectric lead–zirconate–titanate (PZT) thin film on a Pt/Ti/SiO2/Si substrate. A FDTS fine pattern was firstly vapour deposited on a Pt/Ti/SiO2/Si substrate by a lift-off process, and then the PZT precursor was spin-coated on the Pt/Ti/SiO2/Si substrate, post-baked so the solvent decomposed and evaporated and annealed for crystallisation. The experimental results demonstrated that the super-hydrophobic FDTS with a contact angle of >120° is effective in preventing PZT crystallisation because of its thermal stability during PZT post-baking, and its barrier-effects between the spin-coated PZT precursor and the Pt/Ti substrate. After removing the FDTS and the PZT which is on top of the FDTS by a second lift-off process using ultrasonic agitation, a PZT fine pattern was successfully obtained on the Pt/Ti/SiO2/Si substrate with a thickness of 200–300 nm and feature size of a few tens of microns. In this Letter, the hydrophobic properties and surface morphology of different types of FDTS were studied and its barrier-effect on PZT crystallisation were analysed. The effects of PZT thickness in each spin-coating to lift-off the and PZT properties were investigated. The obtained PZT pattern was evaluated by an X-ray diffraction measurement.

Piezoelectric PZT MEMS technologies for small-scale robotics and RF applications

Abstract

Inductively Coupled Plasma Reactive Ion Etching of Lead Zirconate Titanate Thin Films for MEMS Application

Piezoelectric lead zirconate titanate (PZT) thin film has been widely studied in microelectromechanical systems (MEMS) as an electromechanical conversion material. However, the application of the piezoelectric MEMS devices is still delayed by PZT integration difficulties, especially in PZT etching process. In this study, PZT thin film was etched using Ar/SF6 mixed gas in a conventional ICP-RIE system. The etch rate, etch selectivity and profile of the PZT film as well as platinum bottom electrode and photoresist were investigated as a function of the Ar concentration (Ar %) in Ar/SF6 mixture. The surface roughness, ferroelectric properties and dielectric properties of the PZT film were evaluated to indentify the effects of various etching receipts. It was found that high Ar % resulted in better PZT surface morphology. The largest PZT etch rate was achieved at 66.7 % of Ar. Reactive-physical mixed etching was preferred for great efficiency, but at the cost of bad surface roughness and low etch selectivity. Moreover, the ferroelectric properties and the dielectric properties of the PZT film were found not degraded by the proposed process. Fine PZT-electrode stack with the feature size of 15 μm and the PZT thickness of 1 μm was successfully obtained in this paper for piezoelectric MEMS application.

M5-3 サーフェスマイクロマシン技術を用いたPZT薄膜アクチュエータの作製に関する研究(M5 アクチュエータ/フィジカルセンサ)

Micro-cantilevers with piezoelectric lead zirconate titanate (PZT) thin film have been widely investigated for various MEMS applications. However, most of them are fabricated by bulk micromachine techniques in silicon on insulator substrate. On the other hand, if micro-cantilevers could be fabricated by surface micromachine techniques, it is advantageous to arrange them in the high density array. In this study, we suggested a new simple process for fabricating PZT unimorph cantilevers by surface micromachining process. Through this process, we fabricated micro actuators with PZT thin films deposited using rf magnetron sputtering. Dielectric loss of PZT thin films are 0.02-0.06, and piezoelectric constant d_<31> calculated from measured displacement of cantilevers was -72.6 pm/V The proposed piezoelectric actuator fabrication process can be applied to various MEMS devices.

Subpicoliter droplet generation based on a nozzle-free acoustic transducer

This letter reports picoliter liquid droplet generation using an orifice-free acoustic ejector operating at its harmonic frequencies. For an acoustic ejector working at the thickness-mode resonance, the droplet size is primarily determined by the acoustic wavelength, which is proportional to the piezoelectric substrate thickness. In our design, we do not need to lap the bulk piezoelectric lead zirconate titanate (PZT) substrate or deposit high temperature processing PZT thin film, but we use harmonic frequencies of the bulk form to reduce the wavelength. The fabricated acoustic ejector with a size of 1200×1200μm2 has been shown to be very effective up to the ninth harmonic (180MHz), continuously ejecting ∼10μm diameter droplets, corresponding to droplet volumes as small as 0.5pl.

Quality factor of micro cantilevers transduced by piezoelectric lead zirconate titanate film

The quality factors (Q-factor) of micro cantilevers transduced by piezoelectric lead zirconate titanate (PZT) film under atmospheric pressure conditions were investigated and discussed. It was found that Q-factors increased with thicker PZT film. Due to air damping, shorter cantilevers resulted in preferred larger Q-factors. The Q-factor was found to be as high as 450 for a 150-μm long PZT cantilever when using 1.04-μm thick PZT film as the electromechanical conversion medium. Differences in the measured Q-factors when using integrated PZT film self-excitation and external PZT vibrator actuation indicate that energy dissipation induced by the electromechanical coupling in PZT thin films was noteworthy even under atmospheric pressure conditions. Moreover, the mechanical properties of the PZT film were found contribute significantly to decreases of the Q-factor.

Transformation process of laser ablated PZT thin films

Transformation behavior of piezoelectric lead zirconate titanate (PZT) thin films prepared by laser ablation on unheated Al2O3 substrates was investigated within a broad temperature region. As-deposited films were mainly amorphous containing some microcrystalline perovskite and pyrochlore phases. The rhombohedral perovskite was the main phase in the films annealed between 500 and 800°C. These films also contained some pyrochIore, PbTiO3, PbO, and ZrO2. The PbO and ZrO2 disappeared in the optimal annealing temperature interval of 700 to 800°C. Decomposition reactions took place above 800°C due to evaporation of lead and diffusion reactions occurred between substrate and film so that the films annealed at 1100°C consisted of ZrO2, TiO2, and PbO.

Preparation of PZT Thin Films by Sol-Gel Process and Properties

Thin films of piezoelectric lead zirconate titanate (PZT) were prepared by the dip-coating method in the sol-gel process. Lead acetate, zirconylnitrate and titanium tetra-n-butoxide were used as raw materials. Water, acetic acid and tri-ethylene glycol were used as solvents. A thin film was prepared by dipping a substrate having a thin layer of ITO electrode on a silica glass plate. Thin films having single-phased PZT were obtained by heat-treatment at 600°C for 2h in air. The film thickness was 0.155μm per dipping, and PZT films 1-3μm thick were prepared by multiple deposition technique. Au thin layer by PVD method was used as upper electrodes. The dielectric constants and losses for the composition ratio (PZ/PT) of 53/47 were 1380 and 0.03, respectively by heat-treatment at 750°C for 2h. The spontaneous polarization, the remanent polarization and the coercive field were 21μC/cm2, 11μC/cm2 and 34kV/cm, respectively. These films prepared by the sol-gel process were shown to have more excellent dielectric properties and transparency than the conventional powder method.

Acoustic lenses employing PZT thin film transducers

Acoustic lenses made of thin piezoelectric lead zirconate titanate (PZT) films fabricated by a chemical sol-gel process are presented. A frequency range between 50 and 250 MHz has been achieved. PZT films have been successfully coated on substrates such as fused quartz and metals, flat and cylindrical surfaces, and substrates with a large coating area or length. The piezoelectricity of the film is achieved by electric poling. The comparison between PZT and ZnO films for ultrasonic high frequency transducers is outlined.