TEM Cross-Section Investigations of Epitaxial Ba 2. Thin Films on LaNiO 3. Bottom Electrodes on CeO 2

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1 Cryst. Res. Technol D. HESSE, N. D. ZAKHAROV, A. PIGNOLET, A. R. JAMES, S. SENZ Max-Planck-Institut für Mikrostrukturphysik, Halle, Germany TEM Cross-Section Investigations of Epitaxial Thin Films on LaNiO 3 Bottom Electrodes on Ce /YSZ-Buffered Si(100) Dedicated to Professor Heydenreich on the occasion of his 70 th birthday. Epitaxial, ferroelectric films grown on LaNiO 3 /Ce /Zr :Y 2 O 3 epitaxial layers on Si(100) are investigated by plan-view and cross-section transmission electron microscopy. The films consist of well-developed grains of rectangular shape, in the following called tiles. The boundaries between the tiles are strained and contain many defects. A new, specific type of lattice defect is found in the tile boundaries. This defect is described as a staircase formed by repeated lattice shifts of c t / Å in the [001] direction, which result in seemingly bent ribbons of stacked Bi 2 planes. The individual Bi 2 planes remain, however, strongly parallel to the (001) plane. Each step of the staircase being formed by short sections of two or more Bi 2 layers in direct contact, the defects carry a bismuth excess. Accordingly, the tile boundaries are bismuth-rich. A model to explain this bismuth excess of the tile boundaries is proposed. Keywords: lattice defects, Aurivillius-type structures, ferroelectric films, epitaxy,, transmission electron microscopy. (Received April 17, 2000; Accepted July 1, 2000) 1. Introduction Ferroelectric thin films gain more and more importance in microelectronics and microsystem technology owing to their ferroelectric, piezoelectric and optical properties, cf. DAMJANOVIC, 1998, and SCOTT, Among the most promising applications of ferroelectric thin films are non-volatile ferroelectric random access memories (FeRAMs) integrated into the silicon-based microelectronics technology (AUCIELLO, SCOTT, and RAMESH 1998). For this type of applications, bismuth-layer ferroelectric materials, like SrBi 2 Ta 2 O 9 (SBT) - having a perovskite-derived crystal structure involving extended Bi 2 layers - are particularly promising. They are advantageous over usual perovskite materials, like Pb(Zr 1-x Ti x )O 3 (PZT), in that they do not suffer from fatigue, even if used together with metal electrodes (SYMETRIX CORPORATION 1992, PAZ DE ARAUJO et al., 1995). Although polycrystalline SBT thin films are already in use in some FeRAMs, the integration of bismuth-layer type ferroelectric thin films into the silicon technology remains a challenge, because many important physical, chemical and structural aspects remain unclear and need still to be further investigated. A particularly challenging task is the growth of epitaxial bismuth-layer ferroelectric thin films on single crystalline silicon substrates, allowing fundamental and applied studies to be performed in order to probe the properties of these rather unconventional materials. In a series of investigations we have studied epitaxial thin films of various bismuth-layer type ferroelectrics, like Ti 3 O 12, SrBi 2 Ta 2 O 9, Ba Ti 4 O 15 and, grown onto

2 642 D. HESSE et al.: Epitaxial Films epitaxial perovskite electrodes, like SrRuO 3 and LaNiO 3 (ALEXE et al., 1998, PIGNOLET et al., 1999; SATYALAKSHMI et al., 1999; HARNAGEA et al., 2000, JAMES et al., 2000a, PIGNOLET et al., 2000). These investigations are carried out in order to optimize the growth conditions and to understand the influence of crystal anisotropy, film orientation, and lattice defects on the structure-property relationships. Here we report on transmission electron microscopy (TEM) investigations of epitaxial thin films grown onto LaNiO 3 (LNO) electrode layers on Ce /YSZ-buffered Si(100), YSZ being the yttria-stabilized cubic modification of Zr. is one of several bismuth-layer compounds of the so called Aurivillius-type structure, the general formula of which is (Bi 2 ) 2+ (A n-1 B n O 3n+1 ) 2- (AURIVILLIUS, 1950; FANG, ROBBINS, AURIVILLIUS, 1962; SUBBA RAO 1962). For, n = 5, A = (Ba,Bi), and B = Ti. Figure n is called the Aurivillius parameter, indicating the number of oxygen octahedra between two consecutive Bi 2 layers. n-1 is the number of perovskite blocks between two consecutive Bi 2 layers. Ferroelectricity in the compound had been reported by AURIVILLIUS and FANG as early as in According to these authors, the compound crystallizes in the tetragonal space group I4/mmm with the lattice parameters a t = 3.88 Å and c t = 50.3 Å. The following correspondence between the electric properties and the crystal structure holds for most Aurivillius-type compounds: In the paraelectric high-temperature phase, the structure is tetragonal (class 4/mmm), whereas in the ferroelectric low-temperature phase, it is orthorhombic (class mm2). In the ferroelectric phase, compounds with even n (like SrBi 2 Ta 2 O 9 ) crystallize in the orthorhombic space group A2 1 am, whereas compounds with odd n crystallize in the orthorhombic space group B2cb. Accordingly, one may expect that instead of a tetragonal structure has an orthorhombic structure in the ferroelectric phase, with the lattice parameters a orth 5,49 Å; b orth 5,49 Å (with b orth a orth ); c orth = 50,3 Å. For the purpose of the present paper, we will, however, keep to the tetragonal unit cell with the lattice parameters a t = 3.88 Å and c t = 50.3 Å. To our knowledge, there are no reports on the structure of epitaxial thin films, except preliminary information given in our two recent papers (JAMES et al., 2000a, JAMES et al., 2000b). Epitaxial thin films of bismuth-layer ferroelectrics other than have been grown by several groups. In particular, epitaxial SrBi 2 Ta 2 O 9 (SBT) thin films were successfully grown by pulsed laser deposition (PLD), metal organic chemical vapour deposition (MOCVD), and r.f. magnetron sputtering, see, e.g., LETTIERI et al., 1998, ISHIKAWA and FUNAKUBO, 1999, MOON et al., 1999, NAGAHAMA et al., 1999, PARK et al., 1999, LETTIERI et al., 2000, PIGNOLET et al., There are only very few reports on lattice defects in bismuth-layer type perovskites. HRTEM investigations of epitaxial SBT films revealed the presence of twin domain boundaries in (116)-oriented, and so called wavy c/6 translational boundaries in (001)- and (116)-oriented SBT films grown on SrTiO 3 single crystal substrates (SUZUKI et al., 1999a and 1999b). c/6 translational boundaries can be considered a special case of a more general defect occurring in bismuth-layer compounds, characterized by a parallel shift of the lattice along [001] by an irrational (only approximately rational) fraction of the lattice parameter c. A related type of defect involving shifts by c t /12 along [001] is present in our films as described below. A similar type of defect occurs in SBT and has recently been called out-of-phase boundary (LETTIERI et al., 2000). Recently, ferroelectric domain and antiphase boundaries have also been visualized in SBT ceramics by diffractioncontrast transmission electron microscopy (DING, LIU and WANG, 2000). It is the aim of the present paper to contribute to a better knowledge and understanding of the structure of epitaxial bismuth-layer type perovskite thin films and of lattice defects in Aurivillius-type materials.

3 Cryst. Res. Technol. 35 (2000) Experimental The depositions of the buffer layers, the electrode layer, and the film were all performed by pulsed laser deposition in an ultra-high vacuum (UHV) system that allows large-area deposition of wafers having a diameter of 3 inch. Computer-controlled movements of the targets and of the substrate holder, taking the actual pulse repetition rate of the laser into account, permitted the deposition of large-area buffer layers, electrode layers, and ferroelectric films, in this case epitaxial films, of homogeneous composition, crystallography, and film thickness over the entire 3 -diameter wafer area. Details of this large-area process and of the used system have been described elsewhere (PIGNOLET et al., 1998). Briefly, a KrF excimer laser (λ = 248 nm) was used at a repetition rate of 5 or 10 Hz, at a pulse energy of 450 mj (YSZ and Ce ) and 300 mj (LNO and ), respectively. The radiating-type substrate heater permitted a substrate temperature up to 750 C during deposition. The latter was computer-controlled via a thermocouple located inside the heater. Silicon (100) wafers with a diameter of 3 were used as substrates. Before depositing the epitaxial film (d = 280 nm; d film thickness), two buffer layers, viz. one of YSZ (d = 110 nm) and one of Ce (d = 70 m), and an electrode layer of LaNiO 3 (LNO; d = 170 nm) were deposited onto the wafer. All layers were deposited in one single run not breaking the vacuum. Commercial targets of nominally stoichiometric composition were used. The depositions were performed in an oxygen atmosphere of 10-2 mtorr (YSZ), 300 mtorr (LNO) and 100 mtorr (Ce and ), respectively. The substrate temperature was fixed to 700 C (YSZ) and 675 C (Ce, LNO, and ), respectively. Details of the deposition procedure have been described elsewhere (JAMES et al., 2000a, JAMES et al., 2000b). After deposition, the samples were cut into pieces of one to several cm 2 in area. Part of the pieces were used for the electrical measurements (see JAMES et al., 2000a), and part for the X-ray diffraction (XRD), scanning electron microscopy (SEM), and scanning force microscopy (SFM) analyses (see JAMES et al., 2000b). Yet another part of the pieces were used for transmission electron microscopy (TEM) in plan-view and cross-section geometry, including high-resolution TEM investigations (HRTEM). TEM samples were thinned down by usual mechanical and ion-beam techniques (see, e.g., WILLIAMS and CARTER, 1996). Samples for cross-sectional TEM investigations were prepared using the method of TRAEHOLT et al. (1993). Plan-view TEM investigations were carried out in a Philips CM20T transmission electron microscope at a primary beam voltage of 200 kv and a point resolution of 2.7 nm, while cross-sectional HRTEM investigations were performed in a Jeol 4000 EX high-resolution TEM at a primary beam voltage of 400 kv and a point resolution of 1.8 nm. Structure models were constructed, and HRTEM image simulations performed (not shown here), by the CrystalKit/MacTempas software package (Total Resolution Inc.). 3. Results Fig.1 is a schematic of the crystal structure of, seen along the [100] t direction. This schematic has been calculated using the atom positions given by AURIVILLIUS and FANG (1962). The structure consists of four perovskite units with the overall composition ([ Bi 2 ] O 16 ) --, stacked between two (Bi 2 ) ++ double layers. The latter extend along the (001) planes of the crystal structure, separated by a distance of ½ c t = Å. Quite a similar structure is known from the high-t C superconductor Bi 2 Sr 2 CaCu 2 O z, where it has been shown that in epitaxial thin films the Bi 2 layers are running parallel to the film plane and are easily recognized as dark lines in HRTEM micrographs, cf., e.g., ZAKHAROV et al. (1996).

4 644 D. HESSE et al.: Epitaxial Films Fig. 1: Schematic of the crystal structure of, seen along the [100] t direction. Fig. 2: XRD Φ Ψ pole figure of a film performed with the (0 1 11) peak at 2Θ = Ψ ranges from 0 (midpoint) to 90 (rim). The crystallographic orientations of the YSZ, Ce, LNO, and layers were determined from X-ray diffraction analyses, which comprised Θ 2Θ scans and Φ Ψ pole figures recorded at different 2Θ angles. The Θ 2Θ scans revealed the very good out-of-plane orientation of all the four layers, including the (100) orientations of YSZ, Ce, and LNO and the (001) orientation of. The Φ Ψ pole figures showed that the in-plane orientations of all the four layers were perfect, too. From these investigations, Fig. 2 shows a Φ Ψ pole figure recorded at 2Θ = 30.2, i.e. for the (0 1 11) reflection of. Four well-resolved peaks of high intensity are seen, which are due to the good in-plane orientation of the (001)-oriented epitaxial film. The smaller shoulders close to the peaks

5 Cryst. Res. Technol. 35 (2000) stem from the YSZ (111) reflection, the 2Θ angle of which is very close to the angle of 30.2 used. The four positions of these shoulders demonstrate both the good in-plane orientation of the (100)-oriented YSZ layer and the good in-plane orientation of the film with respect to the YSZ layer. From these investigations, the following orientation relationships were deduced (index pc indicates the pseudo-cubic indexing of LNO) : (001) LNO (100) pc Ce (100) YSZ (100) Si(100); [100] t LNO [100] pc Ce [110] YSZ [110] Si[110]. Fig. 3 shows a SEM image of the film surface. The film consists of tiles of mostly rectangular shape, the edges of which have a definite in-plane oriention. The lateral tile size amounts to about 0.2 to 0.5 µm. The film is uniform over the imaged area and has a rather flat surface. Long cracks have formed along the two directions parallel to the edges of the tiles, and a few particles having diameters between 0.5 and 1 µm show up in white. Fig. 3: SEM image showing the surface of a film. Fig. 4: Plan-view, diffraction-contrast bright-field TEM micrograph showing the rectangularly shaped grains (tiles) of a film. The tile boundaries are strained and contain many defects. Beam direction is [001]. Low-resolution, plan-view TEM micrographs (Fig.4) confirm the rectangular shape of the tiles and reveal that the boundaries between the tiles are highly strained and contain many lattice defects. Although not free from defects, the tiles show much less of them. A cross-section sample was prepared to reveal the film structure along the viewing direction [100] t of. The overview micrograph (Fig.5) shows the entire Si/YSZ/Ce /LNO/ film system, revealing that all the interfaces are plane and that the individual films of the system have homogeneous thicknesses and morphologies.

6 646 D. HESSE et al.: Epitaxial Films A very thin amorphous interlayer, visible as a white line, is present at the Si/YSZ interface. This amorphous interlayer has most probably formed after the epitaxial YSZ layer was grown, cf. SARINANTO et al. (1999). Strain contrast indicates that the silicon substrate is somewhat strained near its surface. While the LNO film consists of very narrow columns, the film reveals the large tiles already known from the SEM and plan-view TEM images. The tile boundaries are rather flat, extend from the bottom to the top of the film and most of them are approximately perpendicular to the film plane. Fig. 5: Overview micrograph showing the entire Si/YSZ/Ce /LNO/ film system. Beam direction is [100] t. Fig. 6: Cross-section HRTEM overview micrograph of one tile. Horizontal lines represent the Bi 2 layers of the structure. Arrows point to tile boundaries. Beam direction is [100] t. Fig. 6 shows an enlarged cross-section view of the tile boundaries shown in Fig. 5. In the tiles, a pattern of almost horizontal dark and bright lines is visible, the lines having a separation of 2.5 nm. This separation corresponds to the distance of ½ c t = Å between two Bi 2 layers in the unit cell. Thus these lines represent the Bi 2 layers of the crystal structure. Due to the overall epitaxial (001) orientation of the film, the Bi 2 layers are parallel to the (001) plane and thus extend horizontally in the tile interior. Near the tile boundary, however, the Bi 2 layers seem to be bent upwards, as indicated by a pair of curved black ink lines on each side of the left tile boundary. This apparent bending of the Bi 2 planes near a tile boundary is easily seen in the magnified HRTEM image of Fig. 7. Here, the Bi 2 layers manifest themselves as sharp black lines running parallel to the horizontal edges of the image and being embedded in a bright surrounding, which results in a broad bright ribbon with a white/black/white/black/white fine structure. Near the left rim of the image, these bright ribbons run parallel to the horizontal edges of the image. But near the tile boundary they are

7 Cryst. Res. Technol. 35 (2000) clearly bent upwards, as emphasized by a pair of drawn-in black ink lines near the center of the micrograph. A similar bending of these ribbons occurs near the sites marked A and B, where the bright ribbons form dislocation-like patterns. It turns out that by this bending, the ribbons are able to accommodate differences in the atomic-scale stacking of the crystal lattice of the two tiles. However, instead of just ending at the tile boundary, the bending enables the bright ribbons of both tiles to meet in the boundary region and thus allows the structure to remain coherent over the tile boundary. Fig. 7: Cross-section HRTEM micrograph of a tile boundary. Near the boundary, the bright ribbons containing the Bi 2 layers are seemingly bent upwards. A and B point to dislocation-like details formed by the ribbons. Beam direction is [100] t. Fig. 8: Detail of Fig.7. The Bi 2 planes, visualized as sharp black lines, indeed remain parallel to the (001) plane, even in the seemingly bent regions of the bright ribbons. An important modification of this overall picture is, however, required after having a closer look to Fig. 7. It reveals that the sharp black lines do not follow the bending of the bright

8 648 D. HESSE et al.: Epitaxial Films ribbons. While the ribbon bends, the sharp black lines keep running horizontally. This is more clearly shown in the magnified image of Fig. 8. Obviously, the sharp black lines representing the Bi 2 layers remain parallel to the overall (001) crystal plane even in those regions, where the bright ribbons bend. This (apparent) bending of the ribbons is caused by a repeatedly occurring small upward shift of the Bi 2 layers in the [001] direction, forming an overall staircase-like pattern. The magnitude of the shift seems to be irrational, but is close to 4.2 Å = c t /12. As a consequence of the shift of the Bi 2 layers, the perovskite blocks are also shifted in the [001] direction. The bright ribbons are indeed the loci of the Bi 2 layers, but in spite of the bending of the ribbons on a coarser scale, the Bi 2 layers remain strongly parallel to the (001) plane on the atomic scale. Strictly speaking it is not correct to use the term shift in the above discussion, because no discrete shift along a well-defined crystallographic plane occurs. Rather the horizontally extending sections of two or three adjacent levels ( steps ) of the staircase are overlapping. A model of this staircase-like overlapping structure was derived from the structure model of Fig. 1 and is shown in Fig. 9. Initial observations revealed that this type of overlapping of two (or more) Bi 2 layers also happens in conjunction with other, more rarely occurring defects located inside the tile, i.e. far from a tile boundary. Further investigations of these defects are under way. Fig. 9: Structure model of the staircasetype defect, seen along [100] t. See Fig.1 for the designation of the symbols. 4. Discussion A locally occurring overlap of two or more adjacent Bi 2 layers is equivalent to a local bismuth excess. This is obvious from the schematic of Fig.9. Consequently, the observed bending of the ribbons near the tile boundaries indicates a local deviation of the composition from the overall stoichiometry of the film. Hence, the tile boundaries are bismuth-rich. What can be the origin of this bismuth excess? And in which way is it connected with the different stacking sequences on the two sides of the tile boundary? It is known that an (accidental or adjusted at-will) excess of bismuth during the growth of a bismuth-containing complex oxide thin film is either desorbing from the growing film surface, or if the temperature is not high enough for excessive desorbing to occur this excess is being driven towards the final film surface by the moving free surface of the film. This behaviour of excess bismuth is a consequence of its high volatility, and is known from the growth of high-t C superconducting Bi-Sr-Ca-Cu-O thin films. Recently it has also been found during the growth of Ti 3 O 12 and SrBi 2 Ta 2 O 9 thin films, where an excess of bismuth results in the formation of bismuth particles or bismuth-rich oxide particles, respectively, on the film surface (ZAFAR et al., 1997; ALEXE et al., 1998; MIGITA et al., 1999). This effect occurred even with a nominally stoichiometric target used during pulsed laser deposition (ALEXE et al., 1998).

9 Cryst. Res. Technol. 35 (2000) In depositing our films we indeed used a nominally stoichiometric ceramic target. Though pulsed laser deposition (PLD) is generally considered to provide a stoichioimetric transfer of the target to the growing thin film, this is not necessarily true for all deposition conditions. Deviations of the film composition from that of the target are not unusual in PLD, especially in case of a complex target composition. A bismuth excess may therefore indeed have occurred in our process, owing to the specific deposition parameters chosen, viz. target-to-substrate-distance, pulse energy, energy density on the target, oxygen pressure, repetition rate and substrate temperature. Whether the bismuth excess is only local, resulting in Bi-poor regions of the film, or rather global requires further investigation. Considering the facts that our films consist of individual rectangular-shaped, epitaxial grains (tiles) and that these grains are in fact columns extending from the bottom to the top of the film, it is reasonable to assume that during an early stage of film growth these grains were separated islands, i.e. islands that were not in contact with each other. Each of these islands was growing independently of the neighbouring islands, which means that nucleation and further epitaxial growth proceeded on a strongly local scale, under the influence of the local structure of the underlying LNO electrode layer. As a consequence, the Bi 2 O 3 /perovskite/bi 2 O 3 /perovskite atomic-scale layer sequence need not be identical in all the growing islands, but is certainly influenced by local defects of the LNO surface, e.g. by steps. It is thus reasonable to expect the formation of defects, e.g., out-of-phase boundaries or stacking faults, along the tile boundaries that form during the coalescence of the formerly separated islands. If, in addition, the island growth indeed proceeds under bismuth-rich plasma conditions, the bismuth excess is certainly driven to the surface of the separated islands, i.e. both to its upper surface and to their side walls. Consequently, under these bismuth-rich conditions, the defects forming at the tile boundaries have not only to accommodate different stacking sequences, but also to comply with the bismuth excess. The staircase-like defects of Figs. 7 and 8 are obviously an answer to these very different two requirements: They are able to accommodate differences in the layer stacking between the two former islands, and simultaneously they bind the excess bismuth by incorporating it into the defect structure. The rather surprising fact that the bismuth-containing ribbons are continuously running over the tile boundary and do not bluntly end there, is, however, not understood so far. This and other observed structure details require further investigation. 5. Conclusions Epitaxial, ferroelectric films grown on LNO/Ce /YSZ epitaxial layers on Si(100) consist of well-developed grains of rectangular shape ( tiles ). The tile boundaries are rather flat and extend from the bottom to the top of the film. These boundaries are strained and contain many defects. Most of these defects are of a new specific type. The latter can be described as a staircase formed by repeated lattice shifts of c t / Å in the [001] direction, which result in seemingly bent ribbons of stacked Bi 2 planes near the tile boundaries. In spite of the overall bent morphology of these ribbons the Bi 2 planes remain strongly parallel to the (001) plane. Each step of the staircase is formed by short straight sections, where two or more Bi 2 layers are in direct contact, which is equivalent to a local bismuth excess. Accordingly, the tile boundaries are bismuth-rich. A possible mechanism to explain the bismuth excess of the tile boundaries is a bismuth enrichment of the side walls of the separately growing film islands before coalescence occurs. The staircase-like defects obviously are able to accommodate both this bismuth excess by incorporating it, as well as the stacking mismatches between the different tiles, which originate from the independent nucleation and growth of the initially separated

10 650 D. HESSE et al.: Epitaxial Films islands. The coherence of the bismuth-rich ribbons over the tile boundaries is not understood so far. More investigations of the lattice defects are thus required. Acknowledgements The authors are indebted to Prof. J.F. Scott and Dr. M. Alexe for many fruitful discussions, and to Prof. U. Gösele for his invaluable support. References ALEXE, A., SCOTT, J.F., CURRAN, C., ZAKHAROV, N.D., HESSE, D., and PIGNOLET, A.: Appl.Phys.Lett. 73 (1998) 1592 AUCIELLO, O., SCOTT, J.F., and RAMESH, R.: Phys. Today 51 (1998) 22 AURIVILLIUS, B.: Arkiv Kemi 2/37 (1950) 519 AURIVILLIUS, B., FANG, P.H.: Phys.Rev. 126 (1962) 893 DAMJANOVIC, D.: Rep. Prog. Phys. 61 (1998) 1267 DING, Y., LIU, J.S., AND WANG Y.N., Appl.Phys.Lett. 76 (2000) 103 FANG, P.H., ROBBINS, C.R., and AURIVILLIUS, B.: Phys.Rev. 126 (1962) 892 HARNAGEA, C., PIGNOLET, A., ALEXE, M., HESSE, D., and GÖSELE, U.: Appl.Phys.A 70 (2000) 261 ISHIKAWA, K., FUNAKUBO, H.: Appl.Phys.Lett. 75 (1999) 1970 JAMES, A.R., PIGNOLET, A., HESSE, D., and GÖSELE, U.: J.Appl.Phys. 87 (2000a) 2825 JAMES, A.R., PIGNOLET, A., SENZ, S., ZAKHAROV, N.D., and HESSE, D.: Solid State Commun. 114 (2000b) 249 LETTIERI, J., JIA, Y., URBANIK, M., WEBER, C.I., MARIA, J.-P., SCHLOM, D.G., LI, H., RAMESH, R., UECKER, R., and REICHE P.: Appl.Phys.Lett. 73 (1998) 2923 LETTIERI, J., ZURBUCHEN, M.A., JIA, Y., SCHLOM, D.G., STREIFFER, S.K., AND HAWLEY, M.E.: Appl.Phys.Lett., 76 (2000) 2937 MIGITA, S, UESUGI, T., KISHI, H., HIRAI, T., SAKAI, S., and TARUI, Y.: Jpn.J.Appl.Phys. 38 (1999) 5411 MOON, S.E., SONG, T.K., BACK, S.B., KWUN, S.-I., YOON, J.-G., and LEE, J.S.: Appl.Phys.Lett. 75 (1999) 2827 NAGAHAMA, T., MANABE, T., YAMAGUCHI, I., KUMAGAI, T., TSUCHIYA, T., and MIZUTA, S.: Thin Solid Films 353 (1999) 52 PARK, B.H., HUYN, S.J., BU, S.D., NOH, T.W., LEE, J., KIM, H.-D., KIM, T.H., AND JO, W.: Appl.Phys.Lett. 74 (1999) 1907 PAZ DE ARAUJO, C.A., CUCHIARO, J.D., MCMILLAN, L.D., SCOTT, M.C., and SCOTT, J.F.: Nature 374 (1995) 627 PIGNOLET, A., WELKE, S., CURRAN, C., SENZ, S., and HESSE, D., J.Korean Phys.Soc. 32 (1998) S1476 PIGNOLET, A., ALEXE, M., SATYALAKSHMI, K.M., SENZ, ST., HESSE, D., and GÖSELE, U.: Ferroelectrics 225 (1999) 201 PIGNOLET, A., SCHÄFER, C., SATYALAKSHMI, K.M., HARNAGEA, C., HESSE, D., and GÖSELE, U.: Appl.Phys.A 70 (2000) 283 SARINANTO, M.M., IMADA, S., SHORIKI, S., PARK, P.E., TOKUMITSU, E., and ISHIWARA, H.: Integrated Ferroelectrics 27 (1999) 1125 SATYALAKSHMI, K.M., ALEXE, M., PIGNOLET, A., ZAKHAROV, N.D., HARNAGEA, C., SENZ, S., and HESSE, D.: Appl.Phys.Lett. 74 (1999) 603 SCOTT, J.F.: Ferroelectric Memories, Springer-Verlag, Heidelberg 2000 SUBBA RAO E.C.: J.Am.Ceram.Soc. 45 (1962) 166 SUZUKI, T., NISHI, Y., FUJIMOTO, M., ISHIKAWA, K., and FUNAKUBO, H.: Jpn.J.Appl.Phys. 38 (1999a) L1261 SUZUKI, T., NISHI, Y., FUJIMOTO, M., ISHIKAWA, K., and FUNAKUBO, H.: Jpn.J.Appl.Phys. 38 (1999b) L1265 SYMETRIX CORPORATION: International Patent H01L27/115, 21/320529/92 (1992) TRAEHOLT, C., WEN, J.G., SVETCHNIKOV, V., DELSING, A., ZANDBERGEN, H.W.: Physica C 206 (1993) 318

11 Cryst. Res. Technol. 35 (2000) WILLIAMS, D.B. and CARTER, C.B.: Transmission electron microscopy, Plenum, New York 1996 ZAFAR S., KAUSHIK, V., LABERGE, P., CHU, P., JONES, R.E., HANCE, R.L., ZURCHER, P., WHITE, B.E., TAYLOR, D., MELNICK, B., and GILLESPIE, S.: J.Appl.Phys. 82 (1997) 4469 ZAKHAROV, N.D., HESSE, D., AUGE, J., ROSKOS, H.-G., KURZ, H., HOFFSCHULZ, H., DREßEN, J., STAHL, H., and GÜNTHERODT, G.: J.Mater.Res. 11 (1996) 2416 Contact information: Priv.-Doz. Dr. Dietrich HESSE Max-Planck-Institut für Mikrostrukturphysik Weinberg Halle (Saale) Germany hesse@mpi-halle.de