The phase velocity of the propagating waves can be changed by changing the dielectric permittivity of a ferroelectric strip using an applied bias voltage. The idea is that by changing the composition, x, in the growth direction, the heterogeneous structure would result in a diffuse phase transition and a high dielectric constant over a wide temperature range, corresponding to different Curie temperatures for the different 'layers'. The diffuse phase transition would restore temperature sensitivity, while the high dielectric response would reduce the necessary size of the microwave components (Vanderah, 2002), since the length of the electromagnetic waves in the dielectric medium is inversely proportional to the square root. of the dielectric constant.
The Phenomenon of Ferroelectricity
Due to the symmetry of the material, there are now six equivalent directions along which the polarization can be aligned. The observed spontaneous polarization is related to the deformation of the BO6 octahedra relative to the A cations, in the tetragonal phase under Tc.
Chemical Vapor Deposition
Nevertheless, CVD is considered one of the most cost-effective ways for high-throughput, high-throughput thin-film deposition of semiconductor and oxide layers in device manufacturing. The solid precursors sublimate in the temperature-controlled “bubblers” under reduced pressure and are then passed through optical cells held at 250 ◦C, where the UV absorption spectra are collected and used for feedback control of the gas-phase relative stoichiometry of Pb. , Ba and Ti.
Coherent Gradient Sensing
The approaches used are mostly variants of the Devonshire-Ginzburg-Landau (DGL) formalism that predicts the domain structure in terms of energy-minimizing domain volume fractions (Speck and Pompe, 1994; Koukhar et al., 2001; Alpay and Roytburd, 1998). It can be shown (Rosakis et al.,1998) that the condition for constructive interference of the wavefront with its displaced version is. Furthermore, Rosakis et al. (1998) that this result can be related to the sample surface f(x1, x2), for small surface deflections, at.
Pulsed Laser Deposition
High frequency response and work output per unit volume are two important figures of merit for microactuator materials (Krulevitch et al., 1996). Results available in the literature for MOCVD PBT on Pt/Si (Schafer et al., 2000) indicated only ferroelectric behavior for x >0.8 and strongly distorted c/aratios (<1 forx <0.8), where the distortions were attributed to film stress. There is evidence that the ferroelectric and fatigue properties of thin films depend on crystal orientation (Chateigner et al., 1998; Kim et al., 1994; Mansour and Vest, 1992).
Experimental
Deposition
UV-based precursor control has been demonstrated in the literature for YBCO superconducting thin films (Tripathi, 2001; Desisto and Rappoli, 1998). The solid precursors sublime in the temperature-controlled bubblers under the reduced pressure and are then passed through separate optical cells maintained at 250. Active control in the feedback loop is accomplished by varying the carrier gas flow rate (3 SLM argon total) through the individual bubbles.
Diagnostics and Characterization
This technique involves moving one of the gratings in the shearing direction in small increments and measuring the corresponding edge movements. The microstructure, surface morphology and chemical composition of PBT thin films were studied using a line electron microscope (LEO 1550 VP Field Emission SEM) equipped with an energy dispersive spectrometer (EDS). In this study, we used EBSD to study the texture of ferroelectric thin films.
Results and Discussion
Orientation
Only samples with high Pb content (x ≥ 0.8) were analyzed using this technique, as the addition of tetragonal distortion makes it easier to distinguish between c and a domains during automated indexing. The film grown on a MgO crystal is mainly oriented along the c-axis (out-of-plane), while the PBT on the biaxially textured MgO/Si3N4/Si substrate is mainly oriented along the a-axis. As the film cools below the Curie temperature, PBT transforms into the tetragonal ferroelectric phase and experiences compressive stress in a MgO crystal (promoting c-axis orientation), while PBT in biaxially textured MgO/Si3N4/Si experiences tensile stress (promoting a formation).
Imaging
PBT films of various compositions were deposited on MgO and the change in lattice parameters, determined from normal θ -2θ scans, with Pb(x) content is consistent with published results (Burns, 1974) in bulk powder as shown in Fig. - urea 3.6. The small PBT grain size in the biaxially textured templates is most likely due to the reduced MgO grain size, which is characteristic of the IBAD process.
Domain Characterization
A sample (100) pole figure (Figure 3.10) for PT in a MgO crystal is divided four times, indicating the presence of these four variants. Quadruple splitting is observed for PT in single-crystal MgO (a), indicating the presence of 90◦ domain walls. The TEM plane view showed that the grain size for PBT on biaxially textured MgO (average 60 nm) was indeed smaller than that for PBT on single crystal MgO.
Microtexture
We suggest that this reduced grain size is the primary reason for the absence of 90◦ domain walls. This is consistent with the absence of domain boundaries (from pole figures and XTEM) for the films on biaxially textured substrates where the grain size is well below this boundary. The EBSD data were also consistent with the observation of the tetragonal tilt angle, whereas domains (for PBT on single crystal MgO) were tilted from the surface normal by δ (see Figure 3.9).
Phase Transition
The known bulk Tc of both BaTiO3 and PbTiO3 is included in the graph to indicate that Tc varies almost linearly between the final compositions.
Domain Switching
Figure 3.16 shows a series of θ−2θ scans of the first-order diffraction peaks of a 240 nm PT thin film on single-crystal MgO. The spectra are consistent with work predicting and experimentally verifying the change of domain fractions for PT on MgO (Pertsev and Zembilgotov and we here extend the range of compositions for which domain switching with temperature is verified. Such coherent domain switching was not observed for the PT thin films deposited on IBAD MgO/Si3N4/Si.
We begin by examining the raw successive curvature measurements during growth and subsequent cooling of the x = 1 film, shown in Figure 3.18. The result is Figure 3.19, which allows us to examine the stress behavior with temperature to look for evidence of stress relaxation. Significant domain switching has been observed for all PbxBa1−xTiO3 films grown here (Figure 3.17), and the curvature results (Figure 3.19) indicate that the rate of strain accumulation decreases below Tc(x), as expected, but the relaxation is not complete.
Conclusion
For example, being a suitable epitaxial template for many perovskite materials, it has been used as a buffer for highly oriented superconducting YBCO thin films and as a normal metal layer in high-temperature superconducting Josephson junctions (Antognazza et al., 1993). . Fewer results are reported on inexpensive MgO substrates (a = 4.213˚A) as reported in Singh et al. 2002) due to greater network misalignment. Previous detailed microstructural studies of SrRuO3 on MgO stem from the work of Jia et al, who demonstrated that YBCO/SrRuO3/IBAD MgO heterostructures produce the superior superconducting properties of YBCO.
Pulsed Laser Deposition System
The target is on a motorized rotating holder and faces the substrate heater on the opposite side of the chamber. The rotating SrRuO3 target faces the substrate heater in the chamber, as shown in Figure 4.4, which is an internal view of the vacuum chamber, so the plume ejected from the target surface is directly transferred to the substrate mounted on the heater. The schematic design is shown in Figure 4.5, while Figure 4.6 is a view of the final assembly on the mounting flange prior to use in the vacuum chamber.
Experimental
The program associated with these DAQ cards (Figure 4.8) allows direct monitoring of chamber pressure, sample temperature and heater power, in addition to direct control of power supply, ramp speed and heater cooling. Two types of substrates were used: commercially obtained monocrystalline MgO substrates (used as received) and amorphous Si3N4/Si using 20 nm IBAD (ion beam-assisted deposition) MgO followed by 20 nm homoepitaxial MgO as a template layer. Figure 4.9 is an image of the plume ejected from the SrRuO3 target during deposition under these conditions.
Results and Discussion
Orientation
The final indexing of these peaks as 002 (004 for the second order), 112 and 024 in Figure 4.12 is the result of a more careful analysis that took into account the intensity of the different diffraction orders and the texture distribution of the deposited films using x-ray pole figures, in section 4.4.2 below, which enable analysis of the angular relationship between these crystallites in the pole figure. This is an important step in the characterization of SrRuO3 electrodes since the texture of this layer affects the structure and, consequently, the properties of the ferroelectric active layer. The end result is that the SRRUO3 film in Figure 4.12 is predominantly oriented out of the planes, and the accompanying RHEED image confirms the crystalline nature of the film.
Texture
Therefore, this pool figure represents the non-(00l) grains; the film is mainly (00l) oriented out of plane and has a strong in-plane structure. The out-of-plane texture is examined via a ω-wobble curve and the in-plane texture via a φ-scan at ψ of 45◦, which is equivalent to a circumferential slice of the pole. These results and the obtained full-width at half-maximum (FWHM) values are presented in Figure 4.15 as quantitative indicators of out-of-plane and in-plane textures.
PbTiO3, SrRuO3, and MgO deposited by MOCVD, PLD, and IBAD, respectively, on a Si3N4/Si wafer, demonstrating the ability to directly integrate highly oriented ferroelectric materials with silicon, complete with oxide electrodes, for fatigue-free behavior. The PbTiO3 functional layer, SrRuO3 electrode, and biaxial MgO template in this sample are deposited onto a Si3N4/Si wafer by MOCVD, PLD (courtesy of Dan Potrepka, Army Research Lab), and IBAD, respectively.
Conclusion
Ferroelectric thin films, especially those of BaxSr1−xTiO3 (BST), have recently emerged as candidate materials for tunable components in frequency-tunable RF and microwave devices, benefiting from their high dielectric constants and associated high tunability (Potrepka et al., 2006). ; Cole et al., 2003; Acikel et al., 2002; Serraiocco et al. Xu et al., 2005). For tunable filters, for example, this would be unacceptable, as the resonant frequency changes directly with changes in the dielectric constant (Zhu et al., 2002b). In short, ferroelectrics are highly tunable and have high dielectric constants, but an equally important challenge arises: instead, a low temperature dependence of the dielectric constant in the operating temperature range is required (Tagantsev et al., 2003). sharp peaks at the phase transition.
Model
The first is a film graded along the entire film thickness and fully protected by two parallel plate electrodes (PE). The heterogeneity of the ferroelectric is taken into account by making a1,a2, anda4 space dependent in the above equations. Capacitance is calculated similarly for the IDE geometry, at the specific locations of the coplanar electrodes.
Results and Discussion
These results have a direct influence on the dielectric properties of the film, causing it to behave as a homogeneous ferroelectric material, as shown in Figure 5.1 above. The behavior of the graded BST film in the IDE geometry is in stark contrast to the PE case, Figure 5.2(b). In the case of IDE parallel capacitances, a large part of the applied field is located over the layers of different compositions, as shown by the potential contours in Figure 5.3.
Conclusion
Ultraviolet absorption sensors for precursor delivery rate control for metalorganic chemical vapor deposition of multiple component oxide thin films. Substrate effects on the structure of epitaxial pbtio3 thin films prepared on mgo, laalo3 and srtio3 by metalorganic chemical vapor deposition. High tunability in compositionally graded epitaxial barium strontium titanate thin films by pulsed laser deposition.