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.     

LARGE AREA PIEZOELECTRIC ACTUATORS USING METAL FOIL SUBSTRATES WITH Pb(Zrx,Ti1 - x)O3 THIN FILMS

ABSTRACT

We report on the deposition of Pb(Zr_x,Ti_{1 - x})O₃ (PZT) thin films by chemical solution deposition (CSD) on stainless steel foils. The electrical characterization proves good ferroelectric properties with a remnant polarization of 38 μ C/cm². Since PZT is also piezoelectric the 35 μ m and 50 μ m thick metal foils are used to make piezoelectric actuated cantilever beams of several millimeter lengths. Actuated with 10–30 V a displacement up to 32 μ m was measured in quasi-static mode. In resonance mode the displacement increases several times at the same driving voltage.     

Preparation and characterization of PZT ferroelectric thin films by plasma enhanced metalorganic chemical vapor deposition

Abstract

PZT thin films with a uniform distribution of components were prepared by plasma enhanced chemical vapor deposition (PECVD) using Pb(C₂H₅)₄, Z (O-i-C₄H₉)₄, Ti(O-i-C₃H₇)₄, and oxygen. The crystallization of films was occure after annealing in the temperature range between 450 and 550°C under O₂ ambient for 1 hr. The significant change of Pb concentration in PECVD PZT thin films was not observed in the relation to annealing temperature and time. The dielectric constant PECVD PZT thin films increased with the Ti content, showed the maximum value in the vicinity of morphotropic phase boundary (MPB) composition of PZT material, and decreased with the Ti content. The leakage current density of PZT (65/35) thin film of 180 nm in thickness was 3·37 × 10^?7 A/cm² at the applied voltage of 3 V. Remanent polarization increased with increasing of Zr content in the film and coercive field was nearly independent of the composition. The typical values of electrical properties were ε_r = 570, E_c = 90 kV/cm, and P_r = 19 μC/cm² in the PECVD PZT (54/46) thin film of 220 nm in thickness.     

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.     

Characteristics of PMW-PNN-PT-PZ thick films on various bottom electrodes

Characteristics of piezoelectric thick films on various bottom electrodes prepared by screen printing method were investigated. The composition of the ceramics used in this study was 0.01Pb(Mg_1/2W_1/2)O₃–0.41Pb(Ni_1/3Nb_2/3)O₃–0.35PbTiO₃–0.23PbZrO₃ + 0.1wt% Y₂O₃ +2.0 wt.%ZnO(PMW-PNN-PT-PZ). The Ag and the Ag-Pd electrodes were coated on SiO₂/Si substrate by screen printing method and Pt electrode was deposited on Ti/ SiO₂/Si substrate by DC sputtering system. The piezoelectric PMW-PNN-PT-PZ thick films were fabricated on each electrode and annealed by rapid thermal annealing (RTA). The PMW-PNN-PT-PZ piezoelectric thick films on Ag/SiO₂/Si has higher remanent polarization (P _r) of 22.4 μC/cm².     

Effect of excess-PB and prenucleation layer on properties of Pb(ZryTi1-y)O3 thin films prepared by mod process

Abstract

A modified metal-organic decomposition process, MOD has been successfully utilized to improve the ferroelectric properties of Pb(Zr_0.52Ti_0.48)O₃, PZT, thin films. Multilayer PZT/Pt(Si) films, which contain 0.12 μm layer of spin coated PbO-excess (10 mol%) precursors on top of 0.12 μm layer of stoichiometric PZT precursors, exhibit superior ferroelectric properties (P_r=14.2 μC/cm²; E_c=62 kV/cm) to the single layer PZT/Pt(Si) films of the same thickness (0.24 μm), which are either stoichiometric or 10 mol% Pb-enriched. The ferroelectric properties are further improved when the PZT films were synthesized using a thin pulsed laser deposited (PLD) prenucleation layer (0.06 μm). The subsequently MOD-prepared PZT films posses high remanent polarization (P_r=23.2–26.6 μC/cm²) and low coercive field (E_c=62.9–69.0 kV/cm).     

Pulsed excimer laser deposition of ferroelectric thin films

Abstract

Pulsed UV excimer laser ablation was employed to deposit multi-axial, bi-axial and uni-axial ferroelectric compositions of PZT, bismuth titanate and lead germanate respectively. In general, a fluence lower than 2 J/cm² caused a preferential evaporation of volatile components, resulting in stoichiometric imbalance. However, the fluences beyond 2 J/cm² enabled the deposition of stoichiometric thin films of multi-component oxide systems. The intrinsic bombardment due to the energetic ablated species during the thin film deposition seemed to influence the composition, structure, orientation and the electrical properties. The electrical characterization of ferroelectric films indicated a dielectric constant of 800–1000, a P_r of 32μC/cm² and E_c of 130KV/cm for polycrystalline PZT films and the corresponding quantities were measured to be 150, 7 μC/cm² and 20 KV/cm for in-situ crystallized c-axis preferred oriented bismuth titanate films. Lead germanate thin films oriented along c-axis (003) showed a dielectric constant of 30, a P_r of 2.5 μC/cm² and E_c of 55 KV/cm.     

Piezoelectric and dielectric properties of low temperature sintering Pb(Mn1/3Nb2/3)O3–Pb(Zn1/3Nb2/3)O3–Pb(Zr0.48Ti0.52)O3 ceramics with variation of sintering time

Pb(Mn_1/3Nb_2/3)O₃–Pb(Zn_1/3Nb_2/3)O₃–Pb(Zr_0.48Ti_0.52)O₃ (abbreviated as PMN–PZN–PZT) ceramics containing Li₂CO₃, Bi₂O₃ and CuO as sintering aids were fabricated using two-stage calcinations method in order to develop low temperature sintering ceramics for multilayer piezoelectric actuators. Their dielectric and piezoelectric properties were investigated according to the variation of sintering time. All the specimens sintered at 930°C for 60~150 min showed tetragonal phases without secondary phases. Electromechanical coupling factor (kp), dielectric constant (ε _r) and piezoelectric constant (d ₃₃) increased with the increase of the sintering time. The mechanical quality factor (Qm) exhibited maximum of 1,815 with the increase of sintering time for 120 min and then slightly decreased. At the sintering temperature of 930°C and the sintering time of 120 min, the optimal values such as the density of 7.69 g/cm³, kp of 0.516, ε _r of 1158, Qm of 1815, and d ₃₃ of 287 pC/N were found for multilayer piezoelectric actuators.     

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.     

Pyroelectric Properties of PZT/PMNZTU Composite Thick Films

Lead zirconate titanate/uranium doped lead magnesium niobate—lead zirconate titanate (PZT/PMNZTU) composite thick films have been fabricated on silicon substrates at 710°C using a composite sol gel technique. A slurry, made up of PMNZTU powder and PZT sol, was spun onto a silicon substrate and fired to yield a porous skeletal ceramic structure. Subsequent sol infiltration and pyrolysis was used to modify the density of the films prior to final sintering at 710°C.Pyroelectric and dielectric properties have been measured as a function of sol infiltration. The pyroelectric coefficients (p _max = 2.41 × 10^–4 Cm^–2 K^–1) of the composite thick films were found to be comparable to the tape cast and monolithic ceramics of similar composition (2.8 and 3.0 × 10^–4 Cm^–2 K^–1 respectively).Maximum figures of merit (F _V = 2.23 × 10^–2 m² C^–1, F _D = 0.89 × 10^–5 Pa^–1/2), calculated using the electrical properties of the thick films, can be compared with those of screen printed thick films (F _V = 2.7–3.9 × 10^–2 m² C^–1, F _D = 0.8–1.1 × 10^–5 Pa^–1/2) processed at temperatures of ca 1100°C. The ability to directly integrate thick pyroelectric films onto substrates at temperatures as low as 710°C, while maintaining competitive figures-of-merit is of considerable interest for future device applications.     

Single-grained PZT thin films for high level FRAM integration—fabrication and characterization

Abstract

A new method for formation of large single grains as large as 40 μm in length of the sputter-deposited PZT(65/35) thin films has been developed in this research group. Crystallized PZT dots were used as a seed and the grains were laterally grown to form a square pattern on the Pt substrate. It turned out that the electrical characteristics of the single grained PZT thin films were much superior to those of the poly-grained PZT thin films. The leakage current was measured to be less than 8x10^?8 A/cm², the breakdown field more than 1,240 kV/cm, the value of saturation polarization and remanent polarization as high as 42 μC/cm², 30 μC/cm², respectively. No degradation of the polarization properties was observed even after the 2×10¹¹ cycles at 1 MHz using a ± 10 V wave form in Pt/PZT/Pt structure. The accelerated retention test revealed that it takes more than 6×10⁷ years for the remanent polarization to be reduced down to 80% of the original value.     

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.     

Low Temperature Process for Synthesis of (100) Textured Pb(Zr0.48Ti0.52)O3 Thin Films on Si Substrate by Laser Lift-Off Transferring Technique

(100) textured Pb(Zr_0.48Ti_0.52)O₃ (PZT) films were prepared on silicon substrates by MOD process and laser lift-off technique. Textured PZT films were first grown on (001) Sapphire substrate, using Ba(Mg_1/3Ta_2/3)O₃ (BMT) materials as buffer layer. The (100) textured PZT/BMT/Sapphire films were attached to Si substrate using a transient-liquid-phase Pd-In bonding process, and then were separated from Sapphire substrates by a laser lift-off process, in which, a 38 ns pulse from excimer laser (248 nm) at 600 mJ/cm² fluence melted BMT buffer layer, expelling the Sapphire. The crystallinity of the surface of films was further improved by laser annealing. X-ray diffraction analysis of the PZT films showed that the crystallographic structure of films is maintained during laser lift-off process. Electrical testing of the films after laser lift-off process followed by laser annealing demonstrated that the ferroelectric properties are retained for the transferred films (P_r = 9μ C/cm² and E_c = 74 kV/cm).     

PZT thick films by diol chemical solution deposition

Process optimization and properties of lead zirconate titanate (PZT) films for piezoelectric micromachined ultrasonic transducers (pMUTs) for scanning probe devices will be presented. The goal of the work was a replacement of the tetragenic and mutagenic solvent and a decrease of time-consuming PZT 2–methoxy ethanol (2MOE) route. An alternative diol-based solution synthesis process was developed and “Design Of Experiment” (DOE) was used to achieve processing optimization for thick and crack free films. Tight parameter control allowed to develop a highly reproducible PZT diol process. The crystallization behaviour of crack-free PbZr_0.53Ti_0.47O₃ films (1–5 μm) with oriented perovskite structure was examined by X-ray diffraction and surface analysis using scanning electron microscopy. Piezoelectric and dielectric properties were examined. The effective transverse piezoelectric coefficient e _31,f of sol–gel processed films was investigated for 4 μm thick layers. Best properties were achieved with {1 0 0}-textured films, where a remanent e _31,f value of −7.3 C/m² was measured for 4.1 μm thick films.     

Advances in processing and properties of perovskite thin-films for FRAMs,DRAMs, and decoupling capacitors

Abstract

Highly oriented, dense, and crack-free ferroelectric and paraelectric thin-films on three inch diameter Pt/Ti/Si₃N₄/Si (100) substrates were obtained by polymeric sol-gel processing. Ferroelectric PZT thin-films were fabricated at temperatures as low as 550°C within 15 minutes by rapid thermal annealing. The films heat treated at 700°C for 5 minutes were single grain thick and exhibited P_r, P_sp, and E_c in the ranges of 29–32 μC/cm², 44–53 μC/cm², and 50–60 kV/cm, respectively, and high speed switching times below 5 ns on 30×30 μm² electrodes. A switching time of 2.7 ns was observed on 19×19 μm² area electrodes at a field of 200 kV/cm. Results of low and high field characterization on paraelectric PLT thin-films which were conventionally heat treated indicated that it has an excellent potential for use in ULSI DRAMs and as decoupling capacitors. These films showed a high charge storage density (15 μC/cm²) and a low leakage current (0.5 μA/cm²) at a field of 200 kV/cm. Also, the charging time for a capacitor area of 1 μm² at 200 kV/cm was estimated to be 0.10 ns.     

Study of 1–3 PZT Fibre/Epoxy Composites with Low Volume Fraction of Ceramics

Lead zirconate titanate (PZT) fibres were prepared by the viscous suspension spinning process (VSSP). Pre-sintered PZT powder mixed with poly (acrylic acid) was spun in a spinnerette to form fibres. The diameter of the fibre was 0.4 mm. The piezoelectric and ferroelectric properties of the single fibre were studied. The piezoelectric coefficient (d₃₃) and the remnant polarization P_r for a single fibre were found to be 490 pC/N and 26 μC/cm², respectively, which are comparable with that in the bulk sample. The fibres were used to fabricate 1–3 PZT fibre/epoxy composites with low volume fraction of PZT (<0.2). Different theoretical models were used to calculate the piezoelectric coefficient (d₃₃) of the composites and compared with experimental results.     

Sol-gel PZT and Mn-doped PZT thin films for pyroelectric applications

Abstract

Thin films of ferroelectric lead zirconate titanate (PbZr_0.3Ti_0.7O₃ PZT30/70) and manganese doped lead zirconate titanate ((Pb(Zr_0.3Ti_0.7)_1?xMn_x)O_{3 ? x} = 0.01, PM01ZT30/70 and x = 0.03, PM03ZT30/70) have been prepared using sol-gei processing techniques. These materials can be used as the pyroelectric thin films in uncooled infrared (IR) detectors. Films deposited on Pt/Ti/SiO₂/Si substrates and annealed on a hot plate at 530°C for 5 min were seen to fully crystallize into the required perovskite phase and showed excellent ferroelectric behavior, demonstrated by reproducible hysteresis loops (P_r = 33 to 37 μC/cm², Ec(+) = 70 to 100 kV/cm, E_c(-) = -170 to -140 kV/cm). The pyroelectric coefficients (p) were measured using the Byer-Roundy method. At 20°C, p was 2.11×10^?4 Cm^?2K^?1 for PZT30/70, 3.00×10^?4 Cm^?2K^?1 for PM01ZT30/70 and 2.40×10^?4 Cm^?2K^?1 for PM03ZT30/70 thin films. The detectivity figures-of-merit (F_D) were 1.07×10^?5 Pa^?0.5 for PZT30/70, 3.07×10^?5 Pa^?0.5 for PM01ZT30/70 and 1.07×10^?5 Pa^?0.5 for PM03ZT30/70. These figures compare well with values reported previously.     

Preparation and electrical properties of 0.4Pb(Zn1/3Nb2/3)O3-0.6Pb(Zr0.4Ti0.6)O3 thin films by 2-step annealing method

Films of (1−x)Pb(Zn_1/3Nb_2/3)O₃-xPb(Zr_0.4Ti_0.6) O₃ (x = 0.6, 40PZN-60PZT) were deposited on Pt/TiO₂/ SiO₂/Si substrate through spin coating. Using a combination of homogeneous precursor solution preparation and two-step pyrolysis process, we were able to obtain the 40PZN-60PZT thin films of perovskite phase virtually without pyrochlore phase precipitation after annealing above 650^∘C. But since annealing done at the high temperatures for extended time can cause diffusion of Pt, TiO₂ and Si, and precipitation of nonstoichiometric PbO, we adopted 2-step annealing method to circumvent these problems. The 2-step annealed films show dense microstructure than the 1-step films annealed at higher temperature. Furthermore, the root-mean-square surface roughness of 220 nm thick films which are annealed at 720^∘C for 1 min and then annealed at 650^∘C for 5 min was found to be 3.9 nm by atomic force microscopy as compared to the 12 nm surface roughness of the film annealed only at 720^∘C for 5 min. The electrical properties of 2-step annealed films are virtually same and those of the 1-step annealed films annealed at high temperature. The film 2-step annealed at 720^∘C for brief 1 min and with subsequent annealing at 650^∘C for 5 min showed a saturated hysteresis loop at an applied voltage of 5 V with remanent polarization (P _r) and coercive voltage (V _c) of 25.3 μC/cm² and 0.66 V respectively. The leakage current density was lower than 10⁻⁵A/cm² at an applied voltage of 5 V.     

Microstructures and Piezoelectric Properties of Microwave-Sintered Pb(Mn1/3Nb2/3)0.1Zr0.52Ti0.38O3 Ceramics

In this work, we study the microstructural modifications and the electrical properties of Pb(Mn_1/3Nb_2/3)_0.1Zr_0.52Ti_0.38O₃ + 1.5 wt% PbO (PMNZT) ceramics processed using microwave sintering (MS) and conventional sintering (CS) techniques. Dielectric and piezoelectric properties were evaluated via an impedance/gain phase analyzer and the corresponding microstructures were examined using transmission electron microscopy (TEM). The experimental results imply that smaller grain size and less loss of PbO obtained for specimens using MS process. The MS specimens (1200°C-15 min) show the remanent polarization (P_r) of 24.1 μC/cm², coercive field (E_c) of 15.2 kV/cm, dielectric constants (?_r) of 432 and electromechanical coupling coefficient (k_p) of 0.47, which are superior to CS specimens (1200°C-2 h) with P_r = 19.5 μC/cm², E_c = 16.1 kV/cm, ?_r = 395 and k_p = 0.45. The results revealed that the MS process shows capability of fabrication of good quality PMNZT ceramics with advantages of lowing process temperature and shorten process time. TEM investigations of MS specimens show that smaller grain size and simpler domain arrangements exist inside the specimens. From the energy aspect, the domain structure in piezoelectric ceramics below the temperature of a ferroelectric structural phase transformation is a result of energy minimization. Homogeneous elastic strain energy is reduced at the expense of domain boundary energy during the phase transformation. Density of domain boundaries, 71° (109°) domains in particular, depends on and increases with the grain size. Base on the above argument, therefore, CS specimens exhibit more complicated domain arrangements because they possess larger grain size than MS specimens do. The microstructural investigations suggest that the electrical property difference is intimately related to different sintering methods since the complicated domain arrangements could hinder domain moving and deteriorate electrical performance. In addition, the microstructural characteristics in both MS and CS specimens will be discussed further in the context.