Thin films ferroelectric/piezoelectric

Synthesized ferroelectric niobate thin films with preferred orientation along the polar and optic axis can satisfy several requirements for various appUcations in piezoelectric or elecroacoustic transducers, high-frequency surface-acoustic-wave (SAW) devices, pyroelectric infrared detectors, ferroelectric memory cells, ferroelectric photoconductive displays, two dimensional special light modulators or optical waveguide devices, etc. 

Blattner H., Kanzig W.J., Merz W.J., Sutter H. Helv. Phys. Acta 1948 21 207 Boulton J.M., Teowee G., Bommersbach W.M., Uhlmann D.R. Second harmonic generation from sol-gel derived ferroelectric and piezoelectric thin films. In Sol-Gel Optics, vol. II, J.D. Mackenzie, ed. Proc. SPIE 1992 1758 292-303... 

As with piezoelectric materials, ferroelectric materials have a variety of applications and have been intensively investigated. Again, textured crystalline thin films are likely to be needed, which implies that microstructure control is again an issue. Screening and measurement approaches are straightforward. 

Figure 13.1 Examples of the field dependence of piezoelectric coefficients (a) direct effect in ferroelectric ceramics, measured with a dynamic press (b) converse effect in rhombohedral 60/40 pzt thin films with different orientations, measured with an optical interferometer [1], correspond to pseudocubic axes.

Piezoelectric characterization at nano scale of ferroelectric thin films... 

There are two main approaches or configurations for the AFM-assisted detection of the local piezoelectric activity (pfm) in ferroelectric thin films for ferroelectric memory applications (FeRAM). The most used one was introduced in the early 90s and uses a conductive afm-tip as both top electrode and sensor for the induced vibration [2-4]. The second and more recent one [15,16], uses a normal metallic thin top electrode to apply the electric field and the vibration signal is detected by the AFM-tip above the top electrode. Both approaches present numerous advantages and disadvantages, as widely discussed in the literature, and are quite complementary. 

Chemical and physical processing techniques for ferroelectric thin films have undergone explosive advancement in the past few years (see Ref. 1, for example). The use of PZT (PbZri- cTi c03) family ferroelectrics in the nonvolatile and dynamic random access memory applications present potentially large markets [2]. Other thin-film devices based on a wide variety of ferroelectrics have also been explored. These include multilayer thin-film capacitors [3], piezoelectric or electroacoustic transducer and piezoelectric actuators [4-6], piezoelectric ultrasonic micromotors [7], high-frequency surface acoustic devices [8,9], pyroelectric intrared (IR) detectors [10-12], ferroelectric/photoconduc-tive displays [13], electrooptic waveguide devices or optical modulators [14], and ferroelectric gate and metal/insulator/semiconductor transistor (MIST) devices [15,16]. 

Hattori, X, Takahashi, Y, lijima, M., Fukada, E., 1996. Piezoelectric and ferroelectric properties of polyurea-5 thin films prepared by vapor deposition polymerization. J. Appl. Phys. 79,1713-1721. 

He, X. Yao, K, (2006), Crystallization mechanism and piezoelectric properties of solution-derived ferroelectric poly(vinylidene fluoride) thin films. Applied Physics letter. Vol. 89, No. 11, pp. 112909-1 -112902-3, ISSN 0003-6951. 

An understanding of hardening-softening properties can be achieved through the analysis of the domain wall contribution to the polarization response of ferroelectrics. It should be noted here that this is not the only contribution to the polarization response rather, the intrinsic polarization response as well as surface, boundary, and interface effects may also contribute significantly to the total polarization of a ferroelectric material, especially in thin films. However, the dominant contribution to the dielectric, elastic, and piezoelectric properties in ferroelectric materials is extrinsic, and typically originates from displacement of the domain walls [59]. 

Kingon, A.I. and Srinivasan, S. (2005) Lead zirconate titanate thin films directly on copper electrodes for ferroelectric, dielectric and piezoelectric applications. Nat. Mater., 4 (3), 233-237. 

Pertsev, N.A., Zembilgotov, A.G., and Waser, R. 1998. Aggregate linear properties of ferroelectric ceramics and polycrystalline thin films calculation by the method of effective piezoelectric medium. Journal of Applied Physics 84 [3] 1524-1529. 

Bolten, D., Bdttger, U., Waser, R. 2004. Reversible and irreversible piezoelectric and ferroelectric response in ferroelectric ceramics and thin films. Journal of the European Ceramic Society 24,725-732. 

Ferroelectric crystals (especially oxides in the form of ceramics) are important basic materials for technological applications in capacitors and in piezoelectric, pyroelectric, and optical devices. In many cases their nonlinear characteristics turn out to be very useful, for example in optical second-harmonic generators and other nonlinear optical devices. In recent decades, ceramic thin-film ferroelectrics have been utilized intensively as parts of memory devices. Liquid crystal and polymer ferroelectrics are utilized in the broad field of fast displays in electronic equipment. 

D. Damjanovic Ferroelectric, dielectric and piezoelectric properties of ferroelectric thin films and ceramics. Rep. Prog. Phys. 62,1267 (1998)... 

An AC field with a period of 100 s and an amplitude of 100 V, applied to polyurea films 1 tm thick, was capable of aligning the urea dipoles. A ferroelectric hysteresis loop as observed in Fig. 3 was observed for the poly urea thin films [47,48]. A remanent polarization of 1 /aC/cm and a coercive field strength ( ,.) of 100 MV/m were observed for such polyurea films [9]. The tensile piezoelectric... 

J. T. Dawley, G. Teowee, B. J. J. Zelinski, and D. R. Uhlmann, Piezoelectric Characterization of Bulk and Thin Film Ferroelectric Materials Using Fiber Optics, MTI Instruments Inc., Application Note. 

Some of the piezoeleetric materials are being used in applieations in the form of thin films of various thieknesses. The physieal situation is somewhat different from bulk materials. For example the electrode layer thickness is of comparable size with the thickness of piezoelectrically active film. If the film is deposited on the substrate the mechanical clamping is significant. Clamping could influence the film effective properties and the domain stracture for ferroelectric substances. Material coefficients are not usually completely available in the hterature because of the specific geometry and they depend on film thickness. Material properties of thin films are different from the bulk properties of the same material. Especially the size effect could result in loss of ferroelectricity below certain film thickness. Lower limit for the ferroelectricity is not generally known for all materials. 

AIN non-ferroelectric thin films are studied for their potential use as pressure transducers, speakers and SAW devices (Turner et al. 1994). Polyciystalhne AIN is an important substrate ceramic material due to its high thermal conductivity and dielectric breakdown strength however it does not exhibit piezoelectric activity in the bulk form. When properly oriented, AIN film shows piezoelectric activity up to the high temperatures. For some of the material coefficients of AIN (and also ZnO) films see Gualtieri et al. (1994). 

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