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.     

Pyroelectric properties and X-ray photoelectron spectroscopic study of R.F. magnetron-sputtering-derived PZT thin films deposited on various interlayers

PZT thin films and interlayers were fabricated by the radio frequency (r.f.) Magnetron-sputtering from the Pb_1.1Zr_0.53Ti_0.47O₃, PbO and TiO₂ target. As a result of the XPS depth profile analysis, we can confirm that the substrate temperature affects the oxidation condition of each element of interlayers and the PZT film. Compared to the PZT/Pt structure, the dielectric and pyroelectric properties of PZT thin films inserted by interlayers were measured to a relatively high value. In particular, the PZT/PbO structure had the highest pyroelectric properties (P = 189.4 μC/cm²K; F _D = 12.7×10⁻⁶ Pa^−1/2; F _V = 0.018 m²/C).     

Optimized PZT Thin Films for Pyroelectric IR Detector Arrays

A planar multi target sputtering technology was used to deposit highly (111) oriented Pb(Zr _x Ti_1–x )O₃ (PZT) thin films with x ranging from 0–0.6. The preparation of a stable Pt/ZrO₂ electrode is described and analyzed in terms of stress and stress-temperature behavior. The PZT films with low Zr content are under compressive stress after deposition. The dielectric constant and loss peaks occur at a composition close to the morphotropic phase boundary. Films on the tetragonal side of the phase diagram with a Zr content up to about 25% exhibited a strong self polarization and strong voltage shifts in the C(V) curves. High pyroelectric coefficients of >2×10^–4 C/(m²K) have been measured on these films without additional poling. The self polarization fades out with increasing Zr content. The low values of the pyroelectric coefficient for the PZT film with 60% Zr is discussed in terms of the possible crystallographic variants after distortion and the tensile stress state during the phase transition. Based on the systematic study of stress and electrical properties of PZT films with a wide range of composition presented in this paper, films with a Zr content up to about 25% turned out to give the best properties for the use in pyroelectric detector arrays.     

A 11×6 element pyroelectric detector array utilizing self-polarized pzt thin films grown by sputtering

Abstract

A planar multi target sputtering approach was used to deposit PbTiO₃ (PT) and Pb(Zr, Ti)O₃ (PZT) films on TiO₂/Pt bottom electrodes for the use in thin film pyroelectric IR detector arrays. PZT films with a Zr content of 28 at% (PZ28T) exhibited the best pyroelectric coefficient of typically 2×10^?4 Cm^?2K^?1. The PZ28T films have been used for fabricating a two dimensional 11×6 pixel pyroelectric detector array on Si wafers. The array pixels with a sensitive area of 280 ×280 μm² have a noise lequivalent power NEP of less than 0.7 nW at 1 Hz. It is planned to use the detector array in systems for motion detection.     

Pyroelectric properties of sol-gel derived PZT thin films with various Zr/Ti ratios

Abstract

Integrated pyroelectric arrays are receiving serious attention for the next generation of room temperature uncooled IR cameras. Such pyroelectric arrays are based on monolithic ferroelectric(FE) thin films. FE films with large values of reported pyroelectric coefficients include PbTiO₃, Ca-doped PbTiO₃, La-doped PbTiO₃, PZT 53/47 and Pb(Sc_0.5Ta_0.5)O₃. The present paper reports a systematic study of the compositional dependence of PZT thin films on their pyroelectric properties. A series of sol-gel derived PZT (lead zirconate titanate) thin films with various Zr/Ti ratios, namely, PbTiO₃, PZT 20/80, PZT 35/65, PZT 53/47, PZT 65/35, PZT 92/8 and PbZrO₃, were prepared on platinized Si substrates. The films were fired to 650 – 700°C to crystallize them into single-phase perovskite. The degree of preferred orientation, grain size and firing temperature affect the pyroelectric responses. Pyroelectric coefficients as large as 2.5 × 10^?8 C/cm²-K were obtained, making such PZT thin films attractive in pyroelectric arrays.     

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.     

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.     

Piezo- and pyroelectric properties of lead scandium tantalate thin films

Abstract

This paper discusses the piezo- and pyroelectric properties of lead scandium tantalate thin films prepared by modified sol-gel technology. Films were deposited on Pt/Ti/SiO₂/Si-sub-strates at 530–630 °C. The quality of the thin films was optimized by design of both the deposition conditions and the solution chemistry. These approaches include spin coating speed, drying plus crystallization temperature and time, drying atmosphere, the use of rapid thermal annealing, PST sol composition, Pb-excess concentration and mixing method. The finished thin films were characterized by optical microscopy, X-ray diffraction, atomic force microscopy, and pyroelectric measurements at 30°C under a DC-bias. Piezo-response AFM was conducted on PST to monitor various piezoelectric responses, which depend on the micro-structure of the film. The maximum pyroelectric figure-of-merit F_D was 3.85×10^?5 Pa^?1/2 at 30°C and 1 kHz under a 35 V DC-bias.     

Screen Printed PZT Thick Films Using Composite Film Technology

A spin coating composite sol gel technique for producing lead zirconate titanate (PZT) thick films has been modified for use with screen printing techniques. The resulting screen printing technique can be used to produce 10 μm thick films in a single print. The resultant films are porous but the density can be increased through the use of repeated sol infiltration/pyrolysis treatments to yield a high density film. When fired at 710°C the composite screen printed films have dielectric and piezoelectric properties comparable to, or exceeding, those of films produced using a ‘conventional’ powder/glass frit/oil ink and fired at 890°C.     

Ca Substituted PbTiO3 Thin Films for Infrared Detectors

Crack free Ca substituted PT thin films have been deposited on ITO coated 7059 glass substrates by sol gel technique and crystallized at 650C. Characterization of these films by X-ray diffraction show that the films exhibit tetragonal structure with perovskite phase. AFM, hysteresis, dielectric relaxation and pyroelectric studies have been carried out. The pyroelectric figures of merit of the films have been calculated. Our investigations show that these films are expected to give high infrared detector performance due to its high pyroelectric coefficient (43 nC/cm²K), high voltage responsivity (2340 Vcm²/J) and detectivity(3 × 10^{– 5} Pa^{– 1/2}) along with small value of dielectric constant (83) and loss tangent (0.04).     

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.     

Pyroelectric Arrays: Ceramics and Thin Films

Pyroelectric infra-red detectors have been of-interest for many years because of their wide wavelength response, good sensitivity and lack of need for cooling. They have achieved a wide market acceptance for such applications as people sensing, IR spectrometry (especially for environmental protection) and flame/fire protection. Arrays of such detectors, comprising a pyroelectric material interfaced to an application specific integrated circuit for signal amplification and read out, provide an attractive solution to the problem of collecting spatial information on the IR distribution in a scene and a range of new applications are appearing for such devices, from thermal imaging to people sensing and counting. The selection of the best material to use for such a device is very important. Because all polar dielectrics are pyroelectric, there is a very wide range of such materials to choose. The performance of a pyroelectric IR sensor array can be derived from the physics of their operation and figures-of-merit (FoM) defined that will describe the performance of a material in a device, in terms of its basic pyroelectric, dielectric and thermal properties. These FoM and their appropriateness for the array application are reviewed. Large arrays of small detectors are best served by the use of pyroelectric materials with permittivities between 200 and 1000, depending upon the element size and the element thermal conductance, and a maximised FoM F_D = p{c ( _otan )^1/2}. Such properties are found in ferroelectric perovskite ceramics and a wide range have been explored for their use in pyroelectric arrays. These include materials based on compositions in the PbZr_xTi_{1 – x}O₃ (PZT) system, for example close to PbZrO₃, with Curie temperatures well above ambient. Examples of the ways in which these materials can be modified by doping to optimise their FoM and other important properties such as electrical resistivity are given and the physics operating behind this discussed. The performances and costs of uncooled pyroelectric arrays are ultimately driven by the materials used. For this reason, continuous improvements in materials technology are important. In the area of bulk ceramics, it is possible to obtain significant improvements in both production costs and performance though the use of tape-cast, functionally-gradient materials. Finally, the use of directly-deposited ferroelectric thin films on silicon ASICs is offering considerable potential for low cost high performance pyroelectric arrays. The challenges involved in developing such materials will be discussed, especially from the aspect of low temperature deposition and other fabrication issues, such as patterning. Sol gel deposition provides an excellent technique for thin film growth and Mn-doped PZT films can be grown at 560C with a FoM F_D exceeding those of many bulk materials.     

Ferroelectric ceramics and thin films for pyroelectric applications

Abstract

The extensive work carried out at Caswell in recent years on ferroelectric ceramics for pyroelectric applications is reviewed briefly. With the ultimate aim of fully CMOS compatible integrated thermal detectors and imagers, pure and lanthanum doped lead titanate thin films have been deposited using the emerging PVD technique of dual ion beam sputtering (DIBS). The DIBS process produces high quality orientated perovskite films. Films have been formed at 500–600°C onto sapphire, MgO and silicon substrates by sputtering from an adjustable composite PLZT ceramic/Ti and Pb metallic target. Some substrates were coated with platinum/titanium prior to deposition to allow longitudinal electrical measurements to be made on the films. On silicon, the platinum/titanium electrodes were found to blister during the PLZT thin film deposition process. Pure and 7% lanthanum doped lead titanate films have shown pyroelectric effects with coefficients in the range 0.5–4.0 × 10^?4 Cm^?2 K^?1 and a figure of merit of 2.6 × 10^?5 Pa^?0.5 These results are encouraging with respect to the goal of integrated pyroelectric IR detector arrays on silicon. Further improvements should be possible since the process and substrate/electrode preparation have not yet been fully optimised.     

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.     

Dielectric and Pyroelectric Properties of Lead Zirconate Titanate Composite Films

A new sol-gel approach has been established to prepare dense and crack-free lead zirconate titanate (PZT)/PZT composite films. This new process combines the modified sol-gel method for preparing ceramic/ceramic composite films and the infiltration technique. In the modified sol-gel method, sintered PZT powder is dispersed in a PZT precursor solution to form a slurry which is then spin-coated on a substrate. However, the resulting composite film usually contains a considerable amount of pores, and thus resulting in serious degradation of the mechanical, ferroelectric and piezoelectric properties of the films. In the present work, an additional step, infiltration, has been included in the method. A diluted PZT precursor solution is deposited on the composite film to infiltrate and fill-up the pores, and hence a dense composite film is obtained. The dielectric, ferroelectric and pyroelectric properties of the resulting PZT/PZT composite film are comparable to those of a sol-gel derived PZT film; showing the values of 1200, 0.04, 21 μC/cm² and 180 μC/m² K for relative permittivity, dielectric loss, remanent polarization and pyroelectric coefficient, respectively.     

Fabrication of PZT Thick Films on Silicon Substrates for Piezoelectric Actuator

In recent years, there has been an increased interest in ferroelectric lead zirconate titanate (PZT) films for applications in piezoelectric devices. Many potential applications require a film thickness of about 10 μm for higher force, better sensitivity and stability. In this study we fabricate lead zirconate titanate (PZT) thick films by screen printing on silicon substrates with a platinum bottom electrode. Various substrates were studied. The longitudinal piezoelectric coefficient, d₃₃, was measured by the normal load testing method. Breakdown voltage, tan δ, P-E hysteresis loop and permittivity were measured on the PZT thick films. The results are promising for the use of PZT thick films in various applications, for example, in silicon micromachined micro-pump.     

Fabrication of sub 50-nm direct-patterned Pb(Zr,Ti)O<Subscript>3</Subscript> films by electron beam-induced metal-organic deposition

Direct-patterned lead zirconate titanate (PZT) films prepared from an electron beam sensitive stock solution were investigated for advanced stage applications in sub 50-nm patterned systems. The required electron beam dose for the direct-patterning of PZT precursor films was 4.5 mC/cm². The PZT precursor films with pattern size of 500 × 500 μm² were exposed to an electron beam for 2 h and annealed at 400°C for 30 min under an O₂ ambient. After exposure and annealing, values of the remnant polarization and coercive field were 7.0 μC/cm² and 97 kV/cm at 10 V, respectively. These results suggest a possible application of PZT films in micro- or nano-electromechanical systems.     

Measurement of Microwave Dielectric Properties of Pb(Zr1−x Tr x )O3 Thin Films

Ferroelectric Pb(Zr_1–xTi_x)O₃ (PZT) thin films were prepared by sol-gel deposition method. The structural and surface morphologies were investigated using X-ray diffractometer and atomic force microscope. Microwave dielectric properties were obtained using co-circle electrode patterns, which were made by photolithography and etching process. The dielectric constant of PZT films was about 450 from 0.05–1 GHz range.     

Fabrication of PZT Thick Films on Silicon Substrates for Piezoelectric Actuator

In recent years, there has been an increased interest in ferroelectric lead zirconate titanate (PZT) films for applications in piezoelectric devices. Many potential applications require a film thickness of about 10 m for higher force, better sensitivity and stability. In this study we fabricate lead zirconate titanate (PZT) thick films by screen printing on silicon substrates with a platinum bottom electrode. Various substrates were studied. The longitudinal piezoelectric coefficient, d₃₃, was measured by the normal load testing method. Breakdown voltage, tan , P-E hysteresis loop and permittivity were measured on the PZT thick films. The results are promising for the use of PZT thick films in various applications, for example, in silicon micromachined micro-pump.     

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.