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.     

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.     

Comparing macroscopic and microscopic properties of seeded ferroelectric thin films

The comparison of macroscopic and microscopic properties of ferroelectric thin films in the systems of lead zirconate titanate (PZT) and strontium bismuth tantalate (SBT) with and without seeds is carried out. Microscopic properties were studied by piezo-response force microscopy (PFM). The local piezoelectric properties with and without seeds are compared with their macroscopic electric properties measured by conventional techniques. Previous microstructure analysis of PZT thin films showed that an intermetallic Pt _x Pb layer between PZT and Pt, formed during the annealing process, was reduced and even eliminated in seeded PZT films. In SBT films, the addition of SBT seeds suppressed the interdiffusion of Pt and film components. Hence, the interfaces of PZT/substrate and SBT/substrate are modified by the presence of seeds, and their electrical properties are improved. In both PZT and SBT films, the remanent polarization values are higher in seeded films than in unseeded ones. Similarly, local piezo-response signal of single grain showed higher longitudinal piezoelectric coefficient d ₃₃ in seeded films than in unseeded ones. The critical voltage in which the ferroelectric domain starts to switch is lower in seeded films than in unseeded ones. The analysis of nanoscale switching in PZT and SBT films by PFM is presented and related to the corresponding macroscopic electric properties.     

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.     

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.     

Investigation of top electrode for PZT thick films based MEMS sensors

In this work processing of screen printed piezoelectric PZT thick films on silicon substrates is investigated for use in future MEMS devices. E-beam evaporated Al and Pt are patterned on PZT as a top electrode using a lift-off process with a line width down to 3 μm. Three test structures are used to investigate the optimal thickness of the top electrode, the degradation of the piezoelectric properties of the PZT film in absence of a diffusion barrier layer and finally how to fabricate electrical interconnects down the edge of the PZT thick film. The roughness of the PZT is found to have a strong influence on the conductance of the top electrode influencing the optimal top electrode thickness. A 100 nm thick top electrode on the PZT thick film with a surface roughness of 273 nm has a 4.5 times higher resistance compared to a similar wire on a planar SiO₂ surface which has a surface roughness of less than 10 nm. It is found that the piezoelectric properties of the PZT thick film are degraded up to 1,000 μm away from a region of the PZT thick film that is exposed directly to the silicon substrate without a diffusion barrier layer. Finally, ferroelectric hysteresis loops are used to verify that the piezoelectric properties of the PZT thick film are unchanged after the processing of the top electrode.     

Structural and improved electrical properties of rare earth (Sm, Tb and Ho) doped BiFe0.975Mn0.025O3 thin films

Pure BiFeO₃ (BFO) and rare earth (RE) ion co-doped (Bi_0.9RE_0.1)(Fe_0.975Mn_0.025)O₃ (RE?=?Sm, Tb and Ho, denoted by BSFM, BTFM and BHFM) thin films were prepared on Pt(111)/Ti/SiO₂/Si(100) substrates by using a chemical solution deposition method. Formations of distorted rhombohedral perovskite structure for the thin films were confirmed by using an X-ray diffraction and a Raman scattering analysis. Microstructural features for the thin films were examined by using a scanning electron microscopic analysis. Among the thin films, the lowest leakage current density of 1.22?×?10^?6 A/cm² (at 100 kV/cm), large remnant polarization (2Pr) of 72.4 μC/cm² and low coercive field (2E _c ) of 689 kV/cm (at 980 kV/cm) were measured for the BTFM thin film.     

Effects of transition metal (Ni, Mn, Cu) doping on ferroelectric properties of Bi0.9Nd0.1FeO3 thin films prepared by chemical solution deposition method

Transition metal (Ni, Mn, Cu) doped Bi_0.9Nd_0.1FeO₃ thin films were prepared on Pt(111)/Ti/SiO₂/Si(100) substrates by using a chemical solution deposition method. Compared to pure BiFeO₃ (BFO) thin film, improved ferroelectric and leakage current properties were observed in the transition metal doped thin films. The values of remnant polarization (2P _r ) and coercive electric field (2E _c ) of the transition metal doped thin films were 59 μC/cm² and 690 kV/cm at 700 kV/cm for the Ni-doped Bi_0.9Nd_0.1FeO₃ thin film, 57 μC/cm² and 523 kV/cm at 670 kV/cm for the Mn-doped thin film, and 85 μC/cm² and 729 kV/cm at 700 kV/cm for the Cu-doped thin film, respectively. The 2P _r values observed in the transition metal doped thin films were much larger than that of the BFO thin film, 21 μC/cm² at 660 kV/cm. Also the 2E _c values of in the transition metal doped thin films were lower than that of the BFO thin film, 749 kV/cm at 660 kV/cm. The reduced leakage current density was observed in the transition metal doped thin films, which is approximately two orders of magnitude lower than the BFO thin film, 2.6?×?10^?3 A/cm² at 100 kV/cm.     

DC conduction behavior of Bi3.15Nd0.85Ti3O12 thin films grown by RF-magnetron sputtering

The Bi_3.15Nd_0.85Ti₃O₁₂ (BNT) thin films were deposited on Pt(111)/Ti/SiO₂/Si substrates by using RF-magnetron sputtering method and studied the ferroelectric and leakage current charateristics. The polarization – electric field (P-E) hysteresis loops of BNT film was well saturated with the remnant polarization (2P _r ) of 29.8 μC/cm² and a coercive field (2E _c ) of 121 kV/cm. The leakage current density – electric field (J-E) characteristics of the Pt/BNT/Pt capacitor reveals the presence of two conduction region, having Ohmic behavior at low electric field (below 50 kV/cm) and Schottky-emission or Poole-Frenkel emission at high electric field (above 60 kV/cm). The barrier height and trapped level of BNT films are estimated to be 1.11 eV and 0.90 eV, respectively.     

Piezoelectric PZT films for MEMS and their characterization by interferometry

Piezoelectric films can be used in micro-electro-mechanical system (MEMS) devices because the piezoelectric effect can provide high forces with relatively low energy losses. The energy output by a piezoelectric film per unit area is proportional to the film thickness, so it is desirable to have relatively thick films. Chemical solution deposition (CSD) techniques were used to prepare lead zirconate titanate (PZT) thin films with Zr/Ti ratios of 30/70 and 52/48. Usually CSD processing is restricted to making crack-free single layer films of ca 70 nm thick, but modifications to the sol-gel process have permitted the fabrication of dense, crack-free single layers up to 200–300 nm thick, which can be built-up into layers up to 3 μm thick. Thicker PZT films (> 2 μm single layer) can be produced by using a composite sol-gel/ceramic process. Knowledge of the electro-active properties of these materials is essential for modeling and design of novel MEMS devices and accurate measurement of these properties is by no means straightforward. A novel double beam common path laser interferometer has been developed to measure the piezoelectric coefficient in films and the results were compared with the values obtained by Berlincourt method. A laser scanning vibrometer was also used to measuring the longitudinal (d ₃₃) and transverse (d ₃₁) piezoelectric coefficients for PZT films and ceramics and the results were compared to those obtained by the other methods. It was found that for thin film samples, the d _33,f values obtained from the Belincourt method is usually larger than those obtained from the interferometer method but smaller than those from the vibrometer method and the reasons for this are discussed.     

Flat-band voltage and breakdown in single-grained ferroelectric thin film capacitors

Abstract

Single-grained ferroelectric Pb(Zr, Ti)O₃(PZT) thin films, with thickness varying from 0.1 to 0.7μm, were prepared on Pt-coated silicon substrates by pulsed laser deposition combined with rapid thermal annealing method. The current-voltage characteristics of the Pt/PZT/Pt capacitors, with various thickness of PZT, were measured. Two important turning points in J-V curves, namely flat-band voltage and breakdoiwn voltage according to the totaly minority-carrier injection model, were discussed. The electrical strength of the film was also studied by applying the square test pulses with different pulser duration.     

Fabrication of dome-shaped PZT-epoxy actuator using modified solvent and spin coating technique

Thick film two phase, 0–3 composite PZT-epoxy dome-shaped structures have been fabricated for the first time using a modified solvent and spin coating technique, where a PZT and ethanol solution was dispersed in an epoxy matrix, combined with a hardener, spin coated onto stainless steel sheets, and poled at ~2.2 kV/mm. The electro-mechanical performances of the films were investigated as a function of volume fraction of PZT. The volume fraction of PZT was varied from 0.1 to 0.7 and the piezoelectric coefficients d ₃₁ and d ₃₃ , and the capacitance, C, were measured, and used to calculate the effective dielectric constants. The values for d₃₃, d₃₁, C and dielectric constant were 1.06 pC/N, 0.74 pC/N, 6.0 pF and 76.1 respectively, at 70 % volume fraction of PZT. The surface topography and morphology were examined via AFM and SEM. The piezoelectric strain coefficients, capacitance and effective dielectric constant increased with increasing PZT content, in addition to the surface roughness. Agglomeration of PZT particles and surface crevices were observed on sample surfaces, which are most likely due to surface tension and air bubbles formed during the mixing process.     

Triaxial MEMS accelerometer with screen printed PZT thick film

Piezoelectric thick films have increasing interest due to the potential high sensitivity and actuation force for MEMS sensors and actuators. The screen printing technique is a promising deposition technique for realizing piezoelectric thick films in the thickness range from 10–100 μm. In this work integration of a screen printed piezoelectric PZT thick film with silicon MEMS technology is shown. A high bandwidth triaxial accelerometer has been designed, fabricated and characterized. The voltage sensitivity is 0.31 mV/g in the vertical direction, 0.062 mV/g in the horizontal direction and the first mode resonance frequency is 11 kHz. A Finite Element Method (FEM) model is used to validate the measured sensitivity and resonance frequency. Good agreement between the model and the measurements is seen.     

Preparation of Zr-rich PZT and La-doped PbTiO3 thin films by RF magnetron sputtering and their properties for pyroelectric applications

Abstract

Zr-rich PZT and La-doped PT films were fabricated on a PLT/Pt/Ti/SiO₂/Si or Pt/Ti/SiO₂/Si substrate by an RF planar magnetron sputtering equipment using powder targets with compositions of PbZr_{0 94}Ti_0.06O₃, PbZr_0.92Ti_0.08O₃ and Pb_0.85La_0.15 Ti_0.96O₃ with excess PbO of 20 mol%. The dielectric constants of PZT and PLT films showed anomalies at the transition temperatures of around 246 and 300°C, and their dielectric constants at room temperature were 350 and 1070, respectively. Significant pytroelectric currents were observed in both as-grown PZT and PLT films even without a poling treatment. The pyroelectric coefficients of those films were 10 and 30 nC/cm²K, respectively. Therefore, Zr-rich PZT and [111]-oriented PLT films sputtered on Pt/Ti/SiO₂/Si substrates possess desirable properties for potential applications to pyroelectric devices.     

Ferroelectric properties of Ba1−x Sr x TiO3 thin films synthesized by using novel sol–gel technique through carbonates

Ba_1?x Sr _x TiO₃ (BST) thin films were prepared on the substrate of Pt/Ti/SiO₂/Si by using novel sol–gel process through carbonates. The surface morphology and domain contrast of the films were investigated by atomic force microscopy (AFM), and the domain structures of the BST film were observed when AFM were operated in piezoelectric force microscopic (PFM) analysis and in the friction mode (FFM). The ferroelectric properties of the films were also investigated. It is shown that BST films obtained by the new sol–gel process through carbonates exhibit good properties.     

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.     

Preparation of BaPbO3 Electrode Thin Films by RF Magnetron Sputtering

For electrode materials of Pb(Zr,Ti)O₃ (PZT) thin films in ferroelectric random access memory (FeRAM), various materials have been studied. As new electrode material with which the polarization and fatigue properties are improved, we take notice of barium metaplumbate BaPbO₃ (BPO). Because the BPO contained lead (Pb) and oxygen is conductor that adopted same perovskite structure as PZT. BPO thin films were prepared by rf magnetron sputtering on various substrates. (SiO₂/Si, MgO, Al₂O₃ and Pt-coated substrates), and influence of growth conditions (sputtering gas, rf power, the substrate-heating temperature and post anneals) on crystallization and conductivity were investigated. In case of post anneal after sputtering at room temperature, perovskite single phase was obtained above 400°C. In case of substrate heating while sputtering, without post anneal, perovskite single phase was obtained at 350–500°C on SiO₂/Si substrates (110) preferred orientation BPO films obtained at low temperature, and resistivity of the films decreased at decreasing sputtering temperature. Resistivity of the film at substrate temperature 350°C was 3 × 10^?3 Ω cm. In the case of single crystal substrate, the BPO films were epitaxially grown. Orientation of the films was varied with the sputtering condition. The epitaxial PZT thin films were also grown on the BPO, revealing that PZT(111)[011] //BPO(111)[011] //Pt(100)[011] //MgO(100)[011] and PZT(111)[011] //BPO(111)[011] //Pt(111)[011] //Al₂O₃(001)[100] structures were obtained, and their ferroelectric properties were also evaluated.     

Low-temperature sintering of ferroelectric Pb(Zr,Ti)O3 thick films derived from stable sol-gel solutions

Abstract

We have studied sintering and densification of PbZr_0.52Ti_0.48O₃ (PZT) films derived from diol-based sol-gel solutions. We found that densification by sintering began at below 750°C and completed at 850°C in 5 min. Initially, 0.83- μm-thick PZT single-coated films were prepared on Pt/Ti/SiO₂/Si substrates from stable propylene-glycol (l,2-propanediol)-based solutions by crystallization at 700°C. The crystallized films consisted of fine perovskite grains and voids. We studied the firing temperature dependence of various properties such as microstructure, crystallinity, and ferroelectric properties for the single-coated films. Finally, 0.54- μm-thick PZT single-coated dense films were prepared by firing at 850°C for 5 min. In order to prepare thicker PZT dense films, we studied low-temperature sintering of PZT multicoated thick films. Using this approach, 1.7- μm-thick PZT dense films were prepared by firing at 850°C for 5 min.     

Fundamental characteristics of DRAM capacitor application of PLZT ultrathin films prepared by MOCVD

Lanthanum-modified lead zirconate titanate (PLZT) thin films (50 nm to 200 nm) were deposited on Pt/SiO₂/Si substrate by metal-organic chemical vapor deposition (MOCVD). The electrical properties of the films were investigated as a function of the La content or the substrate temperature. Ferroelectric PZT(0/50/50) films were obtained at substrate temperatures as low as 500 °C; their electrical characteristics improved with increasing substrate temperature. La exhibited adequate solid solution in the PZT above 650 °C. PLZT(15/45/55) films with a thickness of 100 nm were found to have good properties for application to the capacitors of dynamic random access memory (DRAM), namely, an effective charge density of 80 fF/μm², a permittivity of 1000, an SiO₂ equivalent thickness of 0.4 nm, and a leakage current density of 5 × 10⁻⁸ A/cm. Addition of La to PZT was effective in reducing the leakage current with an increase in the registration rate. RuO₂ and/or IrO₂ bottom electrodes for ferroelectric PLZT films were also investigated. The RuO₂ films were found effective as diffusion barriers for PLZT and MgO. Significant interdiffusion at RuO₂/Si and RuO₂/SiO₂ interfaces occurred during the deposition of PLZT films. Annealing of the RuO₂ film considerably depressed interface reactions. © 1998 Scripta Technica. Electr Eng Jpn, 122(1): 25–36, 1998     

Influence of Post-Annealing on the Characteristics of Pb(Zr,Ti)O3 Thin Films Deposited by Liquid Delivery MOCVD Using a Cocktail Solution

Ferroelectric PZT thin films were deposited by liquid delivery MOCVD using a cocktail solution. The cocktail solution consisted of Pb(METHD)₂, Zr(METHD)₄ and Ti(MPD)(METHD)₂ diluted with ethylcyclohexane. The films deposited on Pt/Ti/SiO₂/Si at a substrate temperature of 500°C consisted of PZT, PbO and PbPt_x, and showed poor properties. However, after annealing at 450°C in air for thirty minutes, the PbPt_x phase disappeared while the volume of the PbO phase increased. The hysteresis properties were also improved by annealing at 450°C. After annealing at 600°C in air for thirty minutes, the PbPt_x and the PbO phases disappeared perfectly and the PZT thin films showed good hysteresis properties with the remanent polarization of 30 μC/cm² and the coercive field of 88 kV/cm.