Thin ferroelectric

To demonstrate that this microscopy is also useful for the domain measurement of thin ferroelectric films, we measured a pzt thin film. Figure 16.3 shows the sndm (a) and afm (b) images taken from a same location of pzt thin film deposited on a SrTi03 (sto) substrate using metal organic chemical vapor deposition. 

The stability of the ferroelectric state as crystal size is reduced to typical film thicknesses (<100nm) is a shared interest between those working to reduce dielectric layer thickness in multilayer capacitors to maximize volumetric efficiency and those concerned with thin ferroelectric films for FeRAMs. There is evidence [26] for the ferroelectric state being stable to grain sizes as small as 40 nm, at least. 

One of the remarkable demonstrations of the capabilities of ultraviolet Raman spectroscopy to probe extremely thin ferroelectric oxide layers reported so far has been its application for studies of ultrathin BaTi03 films [48]. In order to investigate the size effect on the ferroelectric phase transitions, variable temperature UV Raman spectroscopy was applied to studies of a series of BaTi03 films with layer thicknesses varied from 1.6 to 10 nm (4—25 unit cells). 

Dawber M, Lichtensteiger C, Triscone J-M (2008) Phase transitions in ultra-thin ferroelectric films and fine period multilayers. Phase Transit 81 623... 

Dawber M, Stucki N, Lichtensteiger C, Gariglio S, Triscone J-M (2008) New phenomena at the interfaces of very thin ferroelectric oxides. J Phys Condens Matter 20 264015... 

In the EFM, an electric field is created at the surface of the sample by applying a voltage to a conductive AFM tip, that is in close proximity to the surface. In the case of thin ferroelectric samples, it is possible to induce extremely strong and localized electric fields and hence to produce domains of electric polarization on a (sub)micrometer scale inside the film. By means of the EFM, the evolution of such domains can be studied both in organic and inorganic ferroelectric films. The interaction between the tip and the sample as a function of the material properties and system geometry can be described within a phenomenological model, described at the end of this contribution. 

Recently, another interesting phenomenon has been revealed in thin ferroelectric films. Namely, the possibility to control the polarization orientation by varying the pressure p02 of oxidizing atmosphere [41] has been revealed for PbTiOj thin films on SrHOs substrate. More specifically, the films have a thickness from 2 to 21 nm and have been epitaxially grown on SrTiOs substrate covered by conductive... 

Glinchuk, M.D., Zaulychny, B.Y., Stephanovich, V.A. Influence of semiconducting electrodes on properties of thin ferroelectric films. Phys. Status Solid (b) 243(2), 542-554 (2006)... 

Bratkovsky, A.M., Levanuk, A.P. Abrupt appearance of the domain pattern and fatigue of thin ferroelectric films. Phys. Rev. Lett. M, 3177-3180 (2000)... 

Batra, I.P., Silverman, B.D. Thermodynamic stability of thin ferroelectric films. Solid State Commun. 11, 291-294 (1972)... 

The structural unit of the copolymer -(-CH2-CF2)n-(-CF2-CHF-)m- contains n and m corresponding monomer links. The ferroelectric properties are attributed to transverse dipole moments, formed by positive hydrogen and negative fluorine atoms. Below the temperature of the ferroelectric phase transition (about 80-100°C), the main chain of the polymer is in all-trans form and the dipole moments are parallel, at least, within ferroelectric domains separated fi-om each other by domain walls. The ferroelectric switching is due to an electric field induced, collective flip-flop of the dipoles around the backbone of the polymer. Several recent studies were devoted to a local ferroelectric switching of the domains in cast P(VDF-TrFE) films [6-8]. To this effect, a powerful technique, called Electrostatic Force Microscopy (EFM) [9] was used which was developed for studies of domains in thin ferroelectric films, see papers [10, 11] and references therein. 

Cheng W., Baudrin E., Dunn B., Zink J.I. Synthesis and electrochromic properties of mesoporons tungsten oxide. J. Mater. Chem. 2001 11 92-97 Cheng S.D., Kam C.H., Zhou Y., Lam Y.L., Chan Y.C., Sun Z., Gan W.S., Pita K. The microstructure dependence on processing temperature in sol-gel derived thin ferroelectric films of LiNbOs on Si02/Si substrate. Ferroelectrics 1999 231(1-4) 805-810... 

Thin ferroelectric films are finding applications as optical waveguides to carry light along a substrate. PLZT is particularly interesting because it is transparent and has a high electro-optical coefficient which makes it a candidate for applications for optical switching, optical memories, and display devices. 

Lo VC (2003) Simulation of thickness effect in thin ferroelectric films using Landau-Khalatkinov theory. J Appl Phys 94(5) 3353... 

The requirements of thin-film ferroelectrics are stoichiometry, phase formation, crystallization, and microstmctural development for the various device appHcations. As of this writing multimagnetron sputtering (MMS) (56), multiion beam-reactive sputter (MIBERS) deposition (57), uv-excimer laser ablation (58), and electron cyclotron resonance (ECR) plasma-assisted growth (59) are the latest ferroelectric thin-film growth processes to satisfy the requirements. 

Ferroelectric thin films have not, as of this writing, been commercialized. Demand for PTC ferroelectrics has been decreasing rapidly. Wide usage of the fuel injector in automobiles and other types of composite PTC devices is the main reason. 

PZN-PT, and YBa2Cug02 g. For the preparation of PZT thin films, the most frequently used precursors have been lead acetate and 2irconium and titanium alkoxides, especially the propoxides. Short-chain alcohols, such as methanol and propanol, have been used most often as solvents, although there have been several successful investigations of the preparation of PZT films from the methoxyethanol solvent system. The use of acetic acid as a solvent and chemical modifier has also been reported. Whereas PZT thin films with exceUent ferroelectric properties have been prepared by sol-gel deposition, there has been relatively Httle effort directed toward understanding solution chemistry effects on thin-film properties. 

Ferroelectric Thin-Film Devices. Since 1989, the study of ferroelectric thin films has been an area of increasing growth. The compositions studied most extensively are in the PZT/PLZT family, although BaTiO, KNbO, and relaxor ferroelectric materials, such as PMN and PZN, have also been investigated. Solution deposition is the most frequentiy utilized fabrication process, because of the lower initial capital investment cost, ease of film fabrication, and the excellent dielectric and ferroelectric properties that result. 

Numerous uses for PZT/PLZT thin films are under investigation. The device that, as of this writing, is closest to commercialization is a nonvolatile memory. This device, which utilizes a ferroelectric thin-film capacitor integrated onto siUcon circuitry, provides memory retention when the power is off because of the polarization retention of the ferroelectric capacitor. One and zero memory states arise from the two polarization states, — and +F, of the ferroelectric. Because PZT is radiation-hard, the devices are also of interest for military and space appHcations. 

Sheppard, L., Advances in Processing of Ferroelectric Thin Films, CeramicBull, 71(l) 85-95 (1992)... 

Yoon, S, and Kim, H, Preparation and Deposition Mechanism of Ferroelectric PbXi03 Thin Films by Chemical Vapor Deposition, J. Electrochem. Soc., 135(12) 3137-3140 (1988)... 

Xing L., Zuoqing W., Cheng J.K., Viens M., Cheeke J.D.N., Ultrasonic thin-walled tube wave structure for sensing devices, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control 1996 43 331-336. 

Schneller, T. Waser, R. 2002. Chemical solution deposition of ferroelectric thin films—state of the art and recent trends. Ferro. 267 293-301. 

Waser, R. Schneller, T. Ehrhart, P. Hoffmann-Eifert, P. 2001. Chemical deposition methods for ferroelectric thin films. Ferro. 259(l-4) 205-214. 

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