Comparison Study of (001)-/(100)-Oriented Epitaxial and Fiber-Textured Pb(Zr,Ti)O3 Thick Films Prepared by MOCVD

(001)-/(100)-oriented epitaxial PZT films and fiber-textured PZT films with a thickness of 2 μ m were deposited on (100) _c SrRuO₃//(100)SrTiO₃ and (111)Pt/TiO₂/SiO₂/(100)Si substrates, respectively, by metalorganic chemical vapor deposition (MOCVD). Crystal structure and the electrical properties were compared for epitaxial PZT films with those of fiber-textured ones, which had the same out-of-plane orientation but different in-plane orientation. The constituent phase change from the single phase of tetragonal PZT, mixture phases of tetragonal and rhombohedral ones and the single phase of rhombohedral one for both films when the Zr/(Zr + Ti) ratio increased. The out-of-plane lattice parameter of (001)- and (100)-axes of PZT films were almost the same value for both films. This indicates the residual strain in the PZT films was almost the same. Dielectric constant (? _r) took the maximum value around the MPB composition for (001)-/(100)-oriented fiber-textured films but was almost independent of the Zr/(Zr + Ti) ratio for epitaxial ones. Moreover, there was no significantly dependence of remanent polarization (P _r) value on the Zr/(Zr + Ti) ratio for (001)-/(100)-oriented fiber-textured films, while it took minimum value near the morphotropic phase boundary (MPB) for epitaxial ones.     

Low-Leakage Epitaxial PZT Thin Films Grown on Ir/MgO Substrates by Metalorganic Chemical Vapor Deposition

250 nm-thick PZT films were grown on (001)lr/(001)MgO substrates by metalorganic chemical vapor deposition (MOCVD). It was ascertained that PZT films on lr substrates are epitaxially grown without the formation of large amount of lrO 2 phase. Crystal structure and the electrical properties of Pt/PZT/(001)lr/(001)MgO structure was compared with Pt/PZT/ (001)c SrRuO 3 /(001)SrTiO 3 structure with the same Zr/(Zr+Ti) ratio of 0.50. X-ray diffraction pattern was almost the same to be identified as (001)- and (100)-oriented tetragonal PZT phase. P-E hysteresis loops and saturation properties of the remanent polarization ( P r ) and the coercive field ( E c ) were also the same, because of the same volume fraction of (001)-oriented grains that contributed to polarization. On the other hand, the leakage current density of Pt/PZT/lr/MgO structure was superior to that of Pt/PZT/SrRuO 3 /SrTiO 3 structure. As a result, lr/MgO substrate is suitable for epitaxial PZT film with low-leakage and good ferroelectricity.     

Growth and characterization of non-c-axis-oriented SrBi2Ta2O9 epitaxial thin films on Si(100) substrates with SrRuO3 bottom electrodes

Abstract

We have successfully grown non-c-axis-oriented epitaxial ferroelectric SrBi₂Ta₂O₉ (SBT) films with (116) and (103) orientations on Si(100) substrates using epitaxial (110)- and (111)-oriented SrRuO₃ (SRO) bottom electrodes, respectively. The SRO orientations have been induced by coating the Si(100) substrates with epitaxial YSZ(100) and MgO(111)/ YSZ(100) buffer layers, respectively. All films were sequentially grown by pulsed laser deposition. Specific in-plane orientations of the epitaxial SBT films were found, which are in turn determined by specific in-plane orientations of the epitaxial SRO bottom electrodes. These include a diagonal rectangle-on-cube epitaxy of SRO(110) on YSZ(100) and a triangle-on-triangle epitaxy of SRO(111) on MgO(111).     

Film Thickness Dependence of Electrical Properties for Pb(Zr,Ti)O3 Thin Films Prepared on (111)Ir/TiO2/SiO2/Si and (111)Pt/TiO2/SiO2/Si Substrates by Pulsed-Metalorganic Chemical Vapor Deposition

Polycrystalline Pb(Zr,Ti)O₃ (PZT) films with various film thicknesses were deposited on (111)Ir/TiO₂/SiO₂/Si and (111)Pt/TiO₂/SiO₂/Si substrates at 540°C by source-gas-pulsed metalorganic chemical vapor deposition (pulsed-MOCVD). PZT films deposited on (111)Ir/TiO₂/SiO₂/Si substrates showed good surface flatness and lower leakage current density. The rate of the decrease of remanent polarization (P _r ) and the rate of increase of coercive field (E _c ) for the films with decreasing the film thickness smaller on (111)Ir/TiO₂/SiO₂/Si substrates than those of (111)Pt/TiO₂/SiO₂/Si substrates. In addition, P _r and E _c values saturated at low voltage when the film thickness was the same. As a result, good ferroelectricity with P _r and E _c values of 40 μC/cm² and 140 kV/cm were obtained for 35 nm-thick films prepared on (111)Ir/TiO₂/SiO₂/Si substrates by pulsed-MOCVD.     

Preparation of BaPbO3 Electrode Thin Films by RF Magnetron Sputtering

For electrode materials of Pb(Zr,Ti)O₃ (PZT) thin films in ferroelectric random access memory (FeRAM), various materials have been studied. As new electrode material with which the polarization and fatigue properties are improved, we take notice of barium metaplumbate BaPbO₃ (BPO). Because the BPO contained lead (Pb) and oxygen is conductor that adopted same perovskite structure as PZT. BPO thin films were prepared by rf magnetron sputtering on various substrates. (SiO₂/Si, MgO, Al₂O₃ and Pt-coated substrates), and influence of growth conditions (sputtering gas, rf power, the substrate-heating temperature and post anneals) on crystallization and conductivity were investigated. In case of post anneal after sputtering at room temperature, perovskite single phase was obtained above 400°C. In case of substrate heating while sputtering, without post anneal, perovskite single phase was obtained at 350–500°C on SiO₂/Si substrates (110) preferred orientation BPO films obtained at low temperature, and resistivity of the films decreased at decreasing sputtering temperature. Resistivity of the film at substrate temperature 350°C was 3 × 10^?3 Ω cm. In the case of single crystal substrate, the BPO films were epitaxially grown. Orientation of the films was varied with the sputtering condition. The epitaxial PZT thin films were also grown on the BPO, revealing that PZT(111)[011] //BPO(111)[011] //Pt(100)[011] //MgO(100)[011] and PZT(111)[011] //BPO(111)[011] //Pt(111)[011] //Al₂O₃(001)[100] structures were obtained, and their ferroelectric properties were also evaluated.     

Epitaxial growth of multilayered (Bi,La)4Ti3O12/Pb(Zr,Ti)O3 ferroelectric thin films with different orientations

Epitaxial (Bi,La)₄Ti₃O₁₂ (BLT) thin films, epitaxial Pb(Zr,Ti)O₃ (PZT) thin films, and epitaxial multilayered BLT/PZT ferroelectric thin films with different orientations were prepared on SrTiO₃ (STO) single crystal substrates by pulsed laser deposition. From X-ray pole-figures and electron diffraction patterns, the epitaxial orientation relationships between BLT layers, PZT layers, and STO substrates were identified to be (1) BLT(001)//PZT(001)//STO(001), and BLT[110]//PZT[100]//STO[100] for the multilayered thin films on (001)-oriented STO substrates, and (2) BLT(118)//PZT(011)//STO(011), and $ {\text{BLT}}{\left[ {\overline{1} \overline{1} 0} \right]}//{\text{PZT}}{\left[ {100} \right]}//{\text{SrTiO}}_{3} {\left[ {100} \right]} $ for the multilayered films on (011)-oriented STO substrates. Tri-layered films of the same compositions showed well-defined hysteresis loops as well as a high fatigue resistance up to 1?×?10¹⁰ switching cycles.     

Polarization Switching in (100)/(001) Oriented Epitaxial Pb(Zr, Ti)O3 Thin Films

Thin films made of (100)/(001)-oriented Pb(Zr, Ti)O₃ (PZT) were deposited by liquid-delivery metal-organic chemical vapor deposition on Ir/MgAl₂O₄/SiO₂/Si(100) substrates. For comparison, PZT thin films were also deposited on Ir/MgO(100) substrates. The X-ray scan spectra for the (202) reflections revealed that the PZT films have four-fold symmetry. It indicates that the PZT films were epitaxially grown as a cube-on-cube structure on both substrates. The switchable polarization (Q_sw) of the PZT capacitors on the silicon substrate was only 23 C/cm² at 1.8 V; however, Q_sw of PZT capacitors on MgO was 99 C/cm². In the case of PZT films deposited on silicon, the volume fraction of (001)-oriented domains (which contribute to polarization switching) was 15.1% (calculated from an XRD pattern). This result is due to the lower Q_sw of PZT capacitors on silicon. By piezoresponse-force microscopy, switchable and unswitchable domains could be identified by imaging color contrast, namely, (001) and (100) domains, respectively. Consequently, domain distribution of the PZT film on a silicon substrate indicates that the (001) domain exists in the (100) domain matrix.     

Microstructures and pyroelectric properties of (Pb,La)TiO3 thin films grown on MgO and ON Pt/MgO

Abstract

Comparison has been made between the microstructures and electrical properties of Pb_0·95La_0·05TiO₃ (PLT) thin films deposited on bare (100)MgO and on Pt/(100)MgO. Nearly perfect epitaxial PLT was grown on (100)MgO. (100)-oriented Pt film was obtained via coalescence of Pt islands formed on MgO. Highly c-axis oriented PLT thin film was successfully grown on the Pt bottom electrode with an electrically conductive network structure. High detectivity of 3·5 × 10⁸ and 2·6 × 10⁸ cm√Hz/W was obtained at 30 Hz without any poling treatments from the PLT/MgO- and PLT/Pt/MgO-based infrared detectors, respectively.     

Preparation of Zr-rich PZT and La-doped PbTiO3 thin films by RF magnetron sputtering and their properties for pyroelectric applications

Abstract

Zr-rich PZT and La-doped PT films were fabricated on a PLT/Pt/Ti/SiO₂/Si or Pt/Ti/SiO₂/Si substrate by an RF planar magnetron sputtering equipment using powder targets with compositions of PbZr_{0 94}Ti_0.06O₃, PbZr_0.92Ti_0.08O₃ and Pb_0.85La_0.15 Ti_0.96O₃ with excess PbO of 20 mol%. The dielectric constants of PZT and PLT films showed anomalies at the transition temperatures of around 246 and 300°C, and their dielectric constants at room temperature were 350 and 1070, respectively. Significant pytroelectric currents were observed in both as-grown PZT and PLT films even without a poling treatment. The pyroelectric coefficients of those films were 10 and 30 nC/cm²K, respectively. Therefore, Zr-rich PZT and [111]-oriented PLT films sputtered on Pt/Ti/SiO₂/Si substrates possess desirable properties for potential applications to pyroelectric devices.     

Enhancement of Ferroelectric Properties of Pb(Zr,Ti)O3 Films Grown by Metal-Organic Chemical Vapor Deposition on Noble-Alloy Bottom Electrodes

Pb(Zr,Ti)O₃ (PZT) films grown on Ir electrodes by a metal-organic chemical vapor deposition (MOCVD) have suffered from high leakage and rough surface. We sputtered Pt and Ir simultaneously onto Ti/SiO₂/Si substrates and formed Ir-Pt alloy bottom electrodes with various compositions. With an optimal composition of Ir and Pt, PZT films grown by MOCVD on this substrate showed smoother surface and suppressed leakage via the bottom interface. At the specific composition of Ir and Pt, two different phases seemed to be acquired. They constituted the electrodes and affected the PZT grain nucleation independently so that the grains with different origins grew and restrained the vicinal grains, and finally soothed the faceted-grain-formation. No fatigue was observed even in PZT on Ir-Pt alloy with much Pt content.     

Low-temperature synthesis in vacuum of c-axis oriented ferroelectric YMnO3 thin films using alkoxy-derived precursors

Abstract

Hexagonal YMnO₃ thin films were prepared on Pt(111)/TiO_x/SiO₂/Si and Pt(111)/Al₂O₃(0001) substrates using alkoxy-derived precursor solutions. The films were prepared by spin coating the YMnO₃ precursor solutions and then, the films were calcined and crystallized via rapid thermal annealing in oxygen or vacuum ambient. The annealing conditions and substrates were critical for crystallization of ferroelectric YMnO₃ films. When annealed in vacuum, the films both on Pt(111)/TiO_x/SiO₂/Si and Pt(111)/Al₂O₃(0001) substrates crystallized to hexagonal YMnO₃ and the orientation depended on the substrates. The film on Pt(111)/Al₂O₃(0001) had c-axis orientation and the film on Pt(111)/TiO_x/SiO₂/Si had no preferred orientation. In addition, it was found that crystallization behavior, orientation and morphology of YMnO₃ films on Pt(111)/TiO_x/SiO₂/Si substrates depended on the annealing condition. The heat-treatment in vacuum at initial stage for crystallization affected the restraint of perovskite phase and formation of hexagonal phase. The following heat-treatment in oxygen promoted the c-axis orientation and grain growth. The optimum annealing procedure for crystallization of the c-axis oriented YMnO₃ films on Pt(111)/TiO_x/SiO₂/Si was addressed.     

Preparation and evaluation of sub-100 nm Pb(Zr,Ti)O3 films derived from modified sol-gel solutions for low-voltage operation of feram

Abstract

Sub-100 nm PbZr_0.3Ti_0.7O₃ (PZT) films were prepared on Pt/SiO₂/Si substrates from modified sol-gel solutions without using any seeding layers. Firstly, we studied Pb content [Pb/(Zr+Ti)] dependence of 90-nm-thick films. In the wide Pb content region of 108 – 125%, the films had perovskite-single-phase fine columnar grains with (111)-orientation and no voids. Electric properties were dependent on Pb content. The film with good microstructure, rectangular hysteresis, high remanent polarization (P_r), and low leakage current was gained for Pb content of 116%. Secondly, we studied film thickness dependence of PZT(116/30/70) films. Films from 90 down to 61 nm in thickness were prepared. We found that the sub-100 nm films with good microstructures could be prepared from the modified solutions. The sub-100 nm films had saturation voltage of 1.25 V and high P_r even at 1 V or less. In particular, a 61-nm-thick film had high.P_r of 17 μC/cm2 at 0.75 V.     

Fatigue and retention of Pb(Zr0.53Ti0.47)O3 thin film capacitors with Pt and RuO2 electrodes

Abstract

Pb(Zr_0.53Ti_0.47)O₃ (PZT) thin films were deposited on Pt and RuO₂ coated Si and MgO substrates using the sol-gel process. Fatigue and retention tests were performed on these samples. The films grown on RuO₂ electrodes are fatigue-free up to nearly 10¹¹ cycles. Their retention life-time extrapolates to more than 10¹⁰ seconds. The fatigue behavior of films grown on Pt electrodes depends on the PZT film orientation. Highly oriented (001) PZT films maintain 50% of their initial P?r-P?r value after 10¹¹ cycles. The randomly oriented films maintain less than 3% of the initial P?r-P?r value after 10¹¹ cycles. However, the retention life-time of both highly oriented and randomly oriented PZT films grown on Pt electrodes extrapolates to higher than 10¹¹ seconds. It appears that fatigue of films grown on RuO₂ is mainly controlled by the film/electrode interface. On the other hand, fatigue of films grown on Pt appears to depend on both the film/electrode interface as well as on bulk effects.     

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.     

Filament-assisted pulsed laser deposition of epitaxial PbZrxTi1−xO3 films: Morphological and electrical characterization

Abstract

A modification of the conventional pulsed laser deposition technique was employed, whereby a low energy electron emitting filament was placed between the target and the substrate (-20 V filament/substrate bias) in order to produce reactive species (O_2- and O_?) during deposition. Using this modification, epitaxial thin films of PbZr_xTi_1?xO3 (PZT, 0 ≤ × ≤ 0.6) were prepared in situ on virgin (100) MgO and (100) Pt/(100) MgO substrates at a substrate temperature of 550°C and in an oxygen ambient (0.3 Torr). The topography of films prepared without a filament on virgin MgO were porous and composed of grains of about 1000 Å in diameter. As the emission current was increased from 0 to 400 μA, the grain size decreased to less than 100 Å with a concomitant decrease in the porosity. The nucleation of crystallites of other orientations was observed at emission currents greater than about 500 μA. Trilayer structures (Pt/PZT/Pt/<100>MgO) were fabricated for electrical measurements. Non-filament-assisted PZT cells usually failed because of a high probability of conductive paths through the PZT layer. Filament-assisted films were much less prone to this problem. Typical remanent polarizations and coercive fields were 15–20 μC/cm² and 30–50 kV/cm, respectively.     

Determination of Cross Sectional Variation of Ferroelectric Properties for Thin Film (Ca. 500 nm) PZT (30/70) via PFM

There is much speculation about the origin of fatigue in ferroelectric thin films that have been grown by sol-gel on various substrates. One of the most important substrates for growing thin film ferroelectric materials is native SiO₂. After the deposition of suitable electrode, most common are Ti-Pt, a thin film of a ferroelectric material can be grown on the substrate. Procedures to grow thin film lead zirconate titanate (PZT 30-70) have been well publicized and it is now routine that almost 100% [111] orientated PZT with a columnar structure of ca. 100 nm is grown on SiO₂ substrates. Recent studies using PFM have shown that it is possible to determine a variation in hysteresis loops with a spatial accuracy of 50 nm on the surface of a ferroelectric material. This study was to determine the variation in d₃₃ for a thin film sample of ferroelectric in terms of a depth profile. It was not suitable to just turn the sample on it's side and analyze the d₃₃ in terms of depth as the continuous back electrode would mean that the resulting vibration of the ferroelectric surface would be a combination of d₃₃ and d₃₁. The de-convolution of this signal was outside the scope of the current investigation. In order to determine the d₃₃ of the material in terms of depth the sample was machined (with an accuracy of 10 nm) to release the ferroelectric from the underlying electrode and electroded in the correct orientation for d₃₃ to be investigated in cross section. Samples of perovskite PZT(30/70) have been produced via sol-gel using a spin coating technique that are ca. 500 nm in cross sectional thickness on Pt/Ti/SiO₂ back electrodes. The PZT is shown to be highly [111] orientated and has in the past been well characterized both at the macro and nanoscale using a variety of techniques. Using focused ion beam (FIB) milling the PZT layer has been released from the SiO₂/Ti/Pt substrate and electroded in such a way as to determine the δ₃₃ properties of the film in terms of thickness of the as-deposited film. Figure 1 indicates the machining process used to generate the free standing PZT block. In Fig. 2, the results of the FIB machining process are shown. The ‘bridge’ structure has the dimensions of 500 nm in cross section and is long enough to ensure that electrode cross talk between the d₃₃ and d₃₁ modes is reduced. Hysteresis loops have been generated using the technique of piezo force microscopy (PFM) at discrete locations across the surface of the film corresponding to a depth profile of the as-deposited PZT. Variations in the shape of the hysteresis loops, calculated δ₃₃ and coercive field for the film have been related to the variation in oxygen defect density in the film. This study shows that the PZT thin film has a variety of fundamental piezoelectric constants that are associated with the variation in local crystal chemistry.     

The Effect of La-Doped Bi4Ti3O12 Buffer Layer on Crystallinity and Ferroelectric Properties of PbZr0.58Ti0.42O3/Bi3.25La0.75Ti3O12 Multilayered Thin Films

PbZr_0.58Ti_0.42O₃ (PZT) ferroelectric thin films with Bi_3.25La_0.75Ti₃O₁₂ (BLT) buffer layer of various thickness were fabricated on Pt/TiO₂/SiO₂/p-Si(100) substrates by rf-magnetron sputtering method. The pure PZT film showed (111) preferential orientation in the XRD patterns, and the PZT/BLT films showed (110) preferential orientation with increasing thickness of the BLT layer. There were no obvious diffraction peaks for the BLT buffer layer, for its thin thickness in PZT/BLT multilayered films. There were the maximum number of largest-size grains in PZT/BLT(30 nm) film among all the samples from the surface images of FESEM. The growth direction and grain size had significant effects on ferroelectric properties of the multilayered films. The fatigue characteristics suggested that 30-nm-thick BLT was just an effective buffer layer enough to alleviate the accumulation of oxygen vacancies near the PZT/BLT interface. The comparison of these results suggests that the buffer layer with an appropriate thickness can improve the ferroelectric properties of multilayered films greatly.     

Structure and properties of sol-gel processed (Pb,La)TiO3 ferroelectric thin films

Abstract

The influence of heat treatment and substrate materials on PLT thin films by sol-gel processing has been researched. Epitaxial growth PLT thin films with perovskite-type structure on sapphire, SrTiO₃ and MgO single crystal substrates have been prepared. The epitaxial relations are (100)PLT28/(100)SrTiO₃, (111)PLT28//(0001)sapphire and (100)PLT14//(100)MgO. The PLT polycrystal thin films with perovskite-type structure on Si single crystal and quartz glass substrates have been prepared. The remanent polarization Pr and the coercive field Ec of PLT15 ceramic thin films are 7.7 μc/cm² and 34 kv/cm at 4 KHz respectively. The optical transmittance of PLT28 ceramic thin films within the wavelength range of λ = 500–1000 nm is approximately 80%.     

Phase Development and Electrical Properties of Pb(Yb 1/2 Nb 1/2 )O 3 -PbTiO 3 Epitaxial Films

The growth and electrical properties of Pb(Yb 1/2 Nb 1/2 )O 3 -PbTiO 3 (PYbN-PT) epitaxial films were investigated. PYbN-PT epitaxial films with SrRuO 3 bottom electrodes were grown by pulsed laser deposition. Optimization of the growth conditions for the PYbN-PT epitaxial films was carried out on (100) SrRuO 3 /(100) LaAlO 3 substrates using the (50/50) composition target. It was found that formation of pyrochlore phase could be caused not only by low growth temperatures or lead deficiency, but also by poor surface condition of the SrRuO 3 bottom electrodes. (001) PYbN-PT epitaxial films with good crystalline quality were obtained for a range of deposition rates (60-100 nm/min) and temperatures (620-680 °C) after vacuum annealing the SrRuO 3 bottom electrodes. The ferroelectric and piezoelectric properties of 1 w m-thick PYbN-PT epitaxial films with (50/50) and (60/40) compositions and with (001) and (111) orientations were investigated using (100) LaAlO 3 , (100) SrTiO 3 , and (111) SrTiO 3 substrates with SrRuO 3 bottom electrodes. The highest remanent polarization (29 w C/cm 2 ) and effective piezoelectric coefficient e 31.f ( m 14 C/m 2 ) were observed in the (001) PYbN-PT (50/50) film. The transition temperature of the (001) PYbN-PT (50/50) film was about 380 °C. Because of the degradation of the target during the deposition, a 3 w m-thick film was prepared by three depositions (1 w m each layer). The 3 w m-thick film exhibited a higher e 31.f coefficient of m 19 C/m 2.     

Microstructural Properties of Ba0.6Sr0.4TiO3/RuO2 Multi-Layers Grown on MgO and YSZ by Pulsed-Laser Deposition

The microstructure of Ba_0.6Sr_0.4TiO₃ (BST)/RuO₂ multi-layers grown on (100) MgO and (100) YSZ substrates, respectively, by pulsed-laser deposition (PLD) has been studied by transmission electron microscopy (TEM) and high-resolution electron microscopy (HREM). The RuO₂ films deposited at 700°C adopt epitaxial relationships with both substrates. The epitaxial films on (100) MgO consist of two variants with an orientation relationship given by (110) RuO₂//(100) MgO and [001] RuO₂//[011] MgO. The epitaxial films on (100) YSZ contain four variants with an orientation relationship given by (200) RuO₂//(100) YSZ and [011] RuO₂//[001] YSZ. The BST films deposited on the RuO₂ electrode are epitaxial on the (200) RuO₂ films deposited on YSZ, and non-epitaxial on the (110) RuO₂ films deposited on MgO. The epitaxial relationship between the BST and (200) RuO₂ films can be described as (111) BST//(200) RuO₂ and [1&1macr;0] BST//[011] RuO₂. The BST films contain at least four variants. The growth and microstructural properties of the multi-layer structures can be understood based on geometrical consideration of the crystal structures.