Fabrication and Electromechanical Properties of Pb(Zr0.52,Ti0.48)O3 Micro-Diaphragm

ABSTRACT

Multilayered piezoelectric micro-diaphragms have been successfully fabricated by micro-electro-mechanical-system (MEMS) processing. The micro-diaphragms consisted of diol based sol-gel derived Pb(Zr_0.52Ti_0.48)O₃ (PZT) capacitor, sputtered Pt electrode, and low temperature oxide(LTO)/SiN_x/Si substrate. The PZT film exhibited (111) oriented structure. The dielectric constant and loss of the PZT thin films were 800 and 3% at 100～ 100 kHz, respectively. The remanent polarization was 20 μ C/cm². The lateral dimension of the PZT film was varied relative to the square-shaped supporting membrane with 300 or 400 μ m length. The relative size (ratio of lateral dimensions) of the PZT film to the supporting membrane was varied from 0.7 to 1.1 to investigate its influence on the system performance. The micro-diaphragm exhibited mechanical displacement from 0.067 to 0.135 μ m at 15 V and had a maximum displacement at a ratio of relative size of 0.8, regardless of the lateral size of the supporting membrane. The fundamental resonant frequency of the micro-diaphragm which has 300 μ m length supporting membrane was in the range of 348 kHz to 365 kHz, depending on the relative size. As the PZT size increased relative to the supporting membrane, the resonant frequency decreased and reached a minimum at the relative size of 0.8. The micro-diaphragm with the supporting membrane (400 μ m length) had a lower resonant frequency, i.e., 251～270 kHz, but showed a similar behavior to the micro-diaphragm with the supporting membrane (300 μ m length) in relation to the resonant frequencies with the relative size.     

Thick piezoelectric coatings via modified sol-gel technique

Abstract

A hybrid sol-gel approach is reported for the deposition of high-quality composite PZT films of the thickness  1 μm. In this approach, the metallo-organic sol-gel precursor solution is mixed with fine piezoelectric powders and dip-coated onto Pt/Ti/SiO₂/Si substrates. Different organic viscous additives and deposition strategies were tried in order to deposit dense films with the properties approaching to those of bulk PZT. Using commercial PZT powder (TRS600FG) and ultrasonic mixing during deposition process, composite films having dielectric permittivity of ～2500 and saturation polarization ～35 μC/cm² were obtained. These values are intermediate between bulk ceramics and conventional sol-gel PZT films and therefore are indicative of good piezoelectric properties.     

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 PbZr_1?xTi_xO₃. 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.     

Fabrication and characteristics of PZT thick films on Pt/Ti foil substrates for piezoelectric vibrators

Crack free perovskite PbZr_0.53Ti_0.47O₃ (PZT (53/47)) thick films up to 30 μm were prepared on flexible platinum-coated titanium foil substrates (Pt/Ti) by a metal organic decomposition (MOD) process. The dielectric, ferroelectric and piezoelectric properties of the films were examined and discussed. A well-saturated hysteresis loop of the thick film was present in almost rectangular shape (Pr?=?35 μC/cm²; Ec?=?32 kV/cm). The efficient piezoelectric coefficient d _{33, f} of the thick film is about 448 (1 kHz). PZT piezoelectric vibrators were made in bimorph mode. The displacements of the vibrators were investigated as the functions of the applied electric field and the substrate thickness. Under the same condition, the vibrator made from the thinnest Pt/Ti substrate gives the largest displacement.     

Properties of reactively sputtered IrOx for PZT electrode applications

Abstract

The use of IrO_x for electrodes in PbZr_xTi_1?xO₃ (PZT) capacitors for ferroelectric memory applications has proven to be advantageous in several respects. In comparison with Pt, IrO_x often exhibits improved fatigue and provides resistance to hydrogen induced degradation at elevated temperatures. Since IrO_x is often produced by sputtering in an oxygen containing environment, several forms of IrO_x can be produced depending on the process conditions. This work concentrates on an analysis of the DC reactive sputtering of IrO_x from an Ir metal target. As with other oxidizable metals, Ir exhibits a transition between metal and oxide mode sputtering when sputtered in oxygen containing atmospheres. Variations in the Ar/O₂ gas flow ratio were used to produce Ir and IrO_xfilms on both sides of the metal-to-oxide mode reactive sputtering transition. Changes in the IrO_x film properties were quantified by using a combination of metrics including X-ray diffraction, sheet resistance, and stress. It was found that the, IrO_x crystalline structure and other IrO_x properties could be directly related to the ferroelectric switching performance of PZT capacitors with IrO_xtop electrodes. A relationship between IrO_x deposition processes and resistance to etch induced damage of the ferroelectric properties was also observed.     

Laser ablation-deposited PZT thin films for piezoelectric microsensors and microactuators

Abstract

We report on growth and deposition process optimization of laser ablation-deposited Pb(Zr_0.53Ti_0.47)O₃ thin films for application in piezoelectric microdevices. Films were grown on three different substrates: (100) cut LaAlO₃ single crystals, Pt/Ti/SiO₂/Si, and Pt/Ti/Si_3+xN₄/Si. On all three substrates, a deposition temperature of 620°C yielded perovskite films with good ferroelectric hysteresis properties. La_0.5Sr_0.5CoO₃ bottom and top electrodes were used for all films. PZT films on Pt/Ti/SiO₂/Si showed a variation of texture with film thickness. Thin membranes of PZT on Si_3+xN₄ were also fabricated.     

Effect of seed layer on electrical properties of Pb(Zr,Ti)O3 films grown by metalorganic chemical vapor deposition

Abstract

Pb(Zr_xTi_1?x)O₃ (PZT) ferroelectric thin films were prepared by metalorganic chemical vapor deposition (MOCVD) on Pt/Ti/SiO₂/Si substrate. Very thin PZT films, which were deposited at a lower temperature and post-annealed at higher temperature for crystallization, were used as a seed layer. PZT films grown on the seed layer exhibited superior characteristics in the crystalline structure and electrical properties, compared to those deposited without seed layer. Depending on the deposition conditions of PZT seed layer, a wide variation of surface morphology and stoichiometry was found between samples, whereas chemical composition was found to be very similar.     

Nanoscale characterization of polycrystalline ferroelectric materials for piezoelectric applications

In this work, the nanoscale electromechanical properties of several important piezoelectric materials [as exemplified by PbZr _x Ti_1−x O₃ (PZT)] suitable for both bulk actuator and microelectromechanical system (MEMS) applications are reported. The investigations are performed by the piezoresponse force microscopy (PFM) that is currently the most suitable tool for both ferroelectric domain imaging and local piezoelectric studies. The local piezoresponse of individual grains is measured in PZT films and compared with average piezoelectric behavior. Frequency dependencies of local piezoelectric coefficients are presented and analyzed. The results on local piezoelectric nonlinearity, as well as on nanoscale fatigue and aging are briefly discussed. These measurements demonstrate that PFM is promising for studying local piezoelectric phenomena in polycrystalline ferroelectrics where defects and other inhomogeneities are essential for the interpretation of macroscopic piezoelectric properties. Finally, local electromechanical properties of polycrystalline relaxors (PMN-PT, PLZT, doped BaTiO₃) are briefly outlined.     

Effect of Buffer Layer on the Properties of Laser Ablated PZT Thin Films

Lead zirconate titanate (PbZr _x Ti_1?x O₃) or PZT ceramics are a class of piezoelectric materials that are currently experiencing widespread use in industry as electromechanical devices. PtSi/ZnO/PZT thin films were deposited by pulsed laser deposition at relatively low substrate temperature. The PZT thin films on PtSi substrates and on ZnO buffer layer were deposited at substrate temperature 300°C. The composition analysis shows that the film deposited at low temperature is stoichiometric. The films exhibit ferroelectric nature with coercive field of 19.6 kV/cm for 800 nm thick film. The leakage current density of the films shows a good insulating behavior.     

High-rate sputtering of thick PZT thin films for MEMS

Crack and void free polycrystalline Lead Zirconate Titanate (PZT) thin films in the range of 5 µm to 10 µm have been successfully deposited on silicon substrates using a novel high rate sputtering process. The sputtered PZT layers show a high dielectric constant ε_r between 1,000 and 1,800 with a moderate dissipation factor tan (δ) = 0,002???0,01 measured at f = 1 kHz, a distinct ferroelectric hysteresis loop with a remanent polarisation of 17 µC/cm² and coercive field strength of 5.4 kV/mm. The piezoelectric coefficients d_33,f = 80 pm/V are measured by using a Double Beam Laser Interferometer (DBLI). Based on this deposition process a membrane actuator mainly consisting of a SOI layer and a sputtered PZT thin film was prepared. The deflection of this membrane actuator depending on the driving voltage was measured with a white light interferometer and compared to the results of finite element analysis (FEA). With this approach a transverse piezoelectric coefficient of about e₃₁?=??11.2 C/m² was calculated, whereas all the other material parameters in the model were lent from PZT-5A.     

Filament-assisted pulsed laser deposition of epitaxial PbZrxTi1−xO3 films: Morphological and electrical characterization

Abstract

A modification of the conventional pulsed laser deposition technique was employed, whereby a low energy electron emitting filament was placed between the target and the substrate (-20 V filament/substrate bias) in order to produce reactive species (O_2- and O_?) during deposition. Using this modification, epitaxial thin films of PbZr_xTi_1?xO3 (PZT, 0 ≤ × ≤ 0.6) were prepared in situ on virgin (100) MgO and (100) Pt/(100) MgO substrates at a substrate temperature of 550°C and in an oxygen ambient (0.3 Torr). The topography of films prepared without a filament on virgin MgO were porous and composed of grains of about 1000 Å in diameter. As the emission current was increased from 0 to 400 μA, the grain size decreased to less than 100 Å with a concomitant decrease in the porosity. The nucleation of crystallites of other orientations was observed at emission currents greater than about 500 μA. Trilayer structures (Pt/PZT/Pt/<100>MgO) were fabricated for electrical measurements. Non-filament-assisted PZT cells usually failed because of a high probability of conductive paths through the PZT layer. Filament-assisted films were much less prone to this problem. Typical remanent polarizations and coercive fields were 15–20 μC/cm² and 30–50 kV/cm, respectively.     

Basic investigations on a piezoelectric bending actuator for micro-electro-mechanical applications

Abstract

This article deals with basic investigations into the development and manufacturing process of a piezoelectric animated micro actuator. The concept of the fabrication of a piezoelectric microactuator will be introduced and first fundamental investigations on materials characterization and process technology for the Pt bottom electrode and piezoelectric PZT layer will be presented. PZT thin film have been deposited with the chemical solution deposition (CSD) technique and have been characterized with dielectric and ferroelectric measurements. For optimization of actuator properties an analytical approach and a simulation with finite element method was carried out. This shows that the cantilever must have a length above 300 μm to reach a tip deflection higher than 10 μm at voltages comparable to those used in integrated circuits (IC). Additionally, stress measurements of each layer have been used to characterize the films mechanically.     

Electrical properties of 3-component piezoelectric thick films by screen printing method

Abstract

PZT(52/48) thick films with Pb-based complex oxide (PCW) additive were prepared on Pt/TiO₂/YSZ/SiO₂/Si substrate by screen printing method. PCW addition and PZT sol application are performed to fabricate high density PZT thick film and to lower sintering temperature. With the increase of sintering temperature, electrical properties of screen-printed films were improved. Further, for the sol-gel treated thick films, the electrical properties were improved as compared to only screen-printed films. For the PZT-0.12PCW thick films with sol-treated and sintered at 900°C, the remanent polarization (P_r) was about 23.8 μC/cm² at the applied filed of 150 kV/cm², the dielectric permittivity (Ω_r) was 1024 at the frequency of 100 kHz, and the piezoelectric coefficient (d₃₃) was 339 pC/N at the applied pressure of 1 atm. Finally, the application of these PZT thick films to piezoelectric actuator is described.     

Fabrication and Electromechanical Properties of Piezoelectric Micro-Transducers for Smart Device

We have fabricated piezoelectrically driven micro-transducer for the application to smart device. Two types of micro-transducers, i.e., micro-cantilever and micro-bridge, have been designed and fabricated. Finite element method (FEM) simulation was performed on the micro-transducer with various length and shapes. Lead zirconate titanate thin film as a piezoelectric layer was incorporated into the micro-transducer. The transducer structure consists of PZT thin layer capacitor, low temperature oxide (LTO) and low stress SiN_x layer. Pb(Zr_0.52Ti_0.48)O₃ (PZT) films were prepared by diol-based sol-gel process. The PZT films were not damaged by fabrication process and thus maintained their electrical properties in the transducer structure after all the fabrication steps. The dielectric constant and loss of the PZT film in the transducer structure were 870 and 2% respectively. The remanent polarization was 20 μC/cm². The micro-cantilever had a fundamental resonant frequency in the range of 16 to 25 kHz when its length was in the range of 320 μm to 380 μm. Meanwhile, the resonant frequency of the micro-bridge was higher by a factor of 7 than that of the micro-cantilever with a similar dimension.     

Low temperature sintering of screen-printed Pb(ZrTi)O3 thick films

Abstract

There has been increasing interest in ferroelectric lead zirconate titanate (PZT) films for the applications in piezoelectric and pyroelectric devices. Many potential applications require a film thickness of above 10 μm for higher force, better sensitivity and stability. But it is very difficult to fabricate the PZT thick film on the silicon substrate because of the volatility of PbO and the interdiffusion of the Pb and Si through the bottom electrode during the sintering at normal temperatures (such as above 1200°C). We speculated densification and reaction mechanism of the PZT thick films fabricated at relatively low temperature (under 1000°C) without sintering aids. The PZT thick films were screen-printed on Pt / Al₂O₃ substrate using a paste of PbO, ZrO₂ and TiO₂ powder mixture. Highly densified PZT thick films could be fabricated on Pt / Al₂O₃ substrate at 1000°C, and we achieved the density, remanent polarization, coercive field, dielectric permittivity, dissipation factor and breakdown field of 98%, 10 μC/cm² and 20 kV/cm, 540, 0.009 and 15 MV/m, respectively. The results show the possibility of densification of the PZT thick film at relatively low temperature without sintering aids, and the results are promising for the use of PZT thick films in various applications.     

Properties of PbZrxTi1−xO3/CeO2/SiO2/Si structure

Abstract

We report the crystalline quality and electrical properties of PbZr_xTi_1?xO₃ (PZT) films on n-type Si(100) substrates with CeO₂/SiO₂ dual buffer layers. PZT films and CeO₂ buffer layers were prepared by pulsed laser deposition technique, and SiO₂ buffer layers were formed by thermal dry oxidation. It was found that CeO₂/SiO₂ dual buffer layers effectively prevented Si and Pb interdiffusion between PZT and Si substrates. Furthermore, the capacitance-voltage (C-V) characteristics of the PZT/CeO₂/SiO₂/Si heterostructures demonstrated ferroelectric switching properties, showing a memory window as large as 2.7 V at 1 MHz.     

Novel 3D PZT thin film structure for micromechanics

In this work, fabrication and properties of 3-dimensional structures coated with piezoelectric Pb(Zr,Ti)O₃ (PZT) thin films have been studied in order to improve the piezoelectric coupling into the third dimension. Calotte layers have been chosen as demonstration devices. The base diameters range from 40 to 120 μm, the height varies between 10 to 40 μm. A dynamic, in-situ co-sputtering process allowing for in-situ growth was applied. Micromoulds were formed by wet etching in silicon. The etchant was a HNA solution (HF, HNO₃, CH₃COOH) on a silicon dioxide mask. Calottes were obtained with the desired geometry and smooth surface state after few minutes etching time, and the use of chemical mechanical polishing (CMP). After deposition of the PZT membrane, deep silicon dry etching was then used to liberate the calotte layer. The dielectric constant and loss tangent of the calotte capacitors amounted to 830 and 5%, respectively (10 kHz). The fundamental resonance frequencies varied between 2.5 and 16.5 MHz, and were found to be inversely proportional to the base area of the calotte, the proportionality factor being 0.08 Hz m².     

Excellent properties of 0.15 micrometer ferroelectric PZT capacitor with SRO electrodes for future Gbit-scale ferams

Abstract

Excellent ferroelectric properties of PZT capacitors with 0.15μ m lateral dimension were obtained for the first time using SrRuO₃ electrode technology. The switching charge of the capacitor was not degraded even for the 0.15 μ m capacitor. The ferroelectric properties such as saturation, fatigue, and imprint characteristics were similar for the capacitors with 12 μ m to 0.15 μ m dimensions. We demonstrated that the SrRuO₃ electrode technology could be used for the future Gbit-scale FeRAMs. An apparent increase in switching charge was also observed with decrease in capacitor size. The ferro-film around the top electrode may contribute to the increase of switching charge.     

PIEZOELECTRIC RESPONSE OF PZT NANOSTRUCTURES OBTAINED BY FOCUSED ION BEAM

ABSTRACT

Pb(Zr_x,Ti_{1 - x})O₃ (PZT) microscale island (1μ m～ 100 nm) was fabricated by Focused Ion Beam (FIB) before and after its crystallization. In the first case the FIB etching is realized on amorphous films and a post annealing treatment, at the crystallization temperature of the PZT films, is necessary to cristallize the film in the perovskite phase. In the second case the etching are made on crystallized films. Local electrical properties were evaluated by piezoresponse force microscopy (PFM) technique and the degradations induce in the films are studies by Raman spectroscopy. Compared to the PZT island fabricated after crystallization, the result shows that there is noticeable enhancement in nanoscale electrical properties of PZT island fabricated before crystallization, especially when the island size decreases.     

Energy harvesting MEMS device based on thin film piezoelectric cantilevers

A thin film lead zirconate titanate Pb(Zr,Ti)O₃ (PZT), energy harvesting MEMS device is developed to enable self-supportive sensors for in-service integrity monitoring of large social and environmental infrastructures at remote locations. It is designed to resonate at specific frequencies of an external vibrational energy source, thereby creating electrical energy via the piezoelectric effect. Our cantilever device has a PZT/SiN_x bimorph structure with a proof mass added to the end. The Pt/Ti top electrode is patterned into an interdigitated shape on top of the sol-gel-spin coated PZT thin film in order to employ the d ₃₃ mode. The base-shaking experiment at the first resonant frequency of the cantilever (170 × 260 μm) generates 1 μW of continuous electrical power to a 5.2 MΩ resistive load at 2.4 V DC. The effect of proof mass, beam shape and damping on the power generating performance are modeled to provide a design guideline for maximum power harvesting from environmentally available low frequency vibrations. A spiral cantilever is designed to achieve compactness, low resonant frequency and minimum damping coefficient, simultaneously.