The effect of excess Mg content on the crystal structure, microstructure and microwave dielectric properties of MTO ceramics is discussed. The effect of OMP on the growth, morphology, optical and physical properties of thin films is discussed.
Introduction to High ε r and Low Loss Bulk and Thin Films 1-28
Preparation Methods and Characterization Techniques 29-70
Mechanochemical and Solid State Synthesis of MgTiO 3
- Effect of Additives on Microwave Dielectric Properties of MgTiO 3 Ceramics
- Influence of Co Substitution on Microwave and Magnetic Properties of MgTiO 3 Ceramics
- Studies on Pure and Co Doped MgTiO 3 Thin Films 147-190
- Introduction to High ε r and Low Loss Bulk
76 3.3 (a) The variation in relative density as a function of meal time, . b) Variation in relative density of MTO ceramics as a function of sintering temperature. 6.8 (a) Variation in bandgap as a function of OMP for as-deposited and annealed MTO thin films deposited on quartz substrates.
Introduction to Dielectric Resonators 1.1 Introduction to dielectric resonators
History of dielectric resonators
The dielectric air boundary will be a perfect reflector of microwaves if the angle of incidence is greater than the critical angle θc= sin-1 (1/εr). As the dielectric constant increases, the electric and magnetic fields become confined in and near the resonator, resulting in small radiation losses.
Modes in a dielectric resonator
- Material requirements of a DR
- Well known dielectric resonator materials
- Current state of materials developed for dielectric resonator applications
- Future requirements of the DR materials
Mode map graphically represents the variation of the factor εr (D/λ0)2 as a function of (D/L)2 for all the resonant modes. The dielectric constant of the dielectric resonator material is important because it will ultimately determine the size of the DR.
Physics of DR materials
- Polarization mechanisms in dielectrics
- Dielectric losses
- Temperature coefficients
Dielectric losses associated with phonon damping are usually described in terms of the classical dielectric function. It is important to note from equation 1.11 that polarizability α is equal to the sum of polarizabilities of all atoms in a unit cell with volume υ only if all atoms in the structure have a cubic environment.
Electronic applications of high ( εεεε r ) materials in thin film form
The incorporation of interfacial layers between the silicon substance and the high εr material effectively reduces the overall dielectric constant of the material. Equation 1.15 shows that when an interfacial SiO2 layer is present, the minimum achievable EOT is that of the material with the lower dielectric constant.
Furthermore, the dielectric exhibits small amounts of stress-induced leakage currents (SILC) due to stress strain, high surface mobility at the interface, and is significantly reliable after years of high field stress (~10 years). SiO2 is thermally, chemically and mechanically compatible with Si and heavily doped poly-Si doping and anneals at 950 - 1050oC, without appreciable loss of the intrinsic properties mentioned above.
Efforts to replace SiO 2
It is well understood that transition metal oxides can offer higher dielectric constants due to their higher polarizability. The use of mixed transition metal oxides had been explored as an approach to achieve higher dielectric constants while achieving other required properties such as low leakage current and high stability.
Magnesium Titanate (MTO): An interesting system in both bulk and thin film forms
- Bulk MTO for microwave applications
- MTO thin film as a possible gate oxide in electronic applications
- Crystal Structure of MTO
The crystal structure of MgTiO3 is an ilmenite type structure and belongs to 3 space groups, is shown in Figure 1.4(a). The crystal structure and schematic representation of MgTiO3 unit cell are shown in Figure 1.4(a) and (b) respectively.
Motivation of this study
As an ongoing effort in our microwave materials laboratory, we have chosen to investigate MTO in the bulk form produced by solid-state reaction, mechanochemical method, and semi-alkoxide precursor methods. We have prepared MTO films from a ceramic target that was fabricated using MTO's optimized processing parameters.
Preparation Methods and Characterization
Preparation and Characterization Techniques Used for Bulk and Thin Films of MgTiO 3
Preparation techniques used for bulk MgTiO 3
- Solid-state reaction method
- Mechanochemical processing
- Sol - gel method (Semi Alkoxide Precursor Method)
- Stoichiometric weighing of reagents
- Uniform mixing of reagents
- Calcination stage
- Particle size reduction
- Uniaxial Pressing
- a Solid - State Sintering
- b Recrystallization and grain growth
- Liquid phase sintering
MgO+ → (2.1) The required ratios of reagents according to the above chemical equation are weighed. In this study, a planetary ball mill was used to achieve initial stoichiometric mixing before firing and to reduce the particle size of the fired ceramic powders. In the initial phase, surface smoothing of particles, growth of necks and rounding of interconnected open pores occur.
Characterization techniques used for the bulk MTO ceramics
- X - ray diffraction
- Surface area analyzer
- Particle size analyzer
- Density Measurement
The surface area of the prepared nanopluders was measured using Brunauer, Emmett and Teller (BET) theory by gas adsorption [14]. The specific surface area of a powder is determined by the physical adsorption of a gas on the surface of the solid. The brightness of the signal depends on the number of secondary electrons reaching the detector.
Microwave measurements
- Measurement of quality factor (Q)
Here βl corresponds to αn, which can be obtained from the mode graph given in [20] one of the characteristic equations. By identifying the TE01δ mode, the resonant frequency can be obtained and -3 dB width of the spectrum to calculate the loaded Q factor (Ql). Further rigorous electromagnetic analyzes should be performed to evaluate the dielectric constant of the sample under test.
Electrical conductivity measurements
- General theory
The temperature is varied from room temperature to 80oC to obtain the temperature coefficient of resonant frequency using equation (2.14). For example, in Figure 2.7(a), in addition to a semicircle, a straight line is observed at low frequencies, which is a characteristic of the double layer capacitance. The indentation in the semicircle is explained by introducing a constant phase element (CPE) connected in parallel with the bulk resistor [25].
Raman Spectroscopy
An integrated Raman system (HR 800) used for all our samples to acquire the Raman spectra. If the particular sample used is fluorescence that has occurred up to a certain wavelength, the next higher wavelength is used to observe the Raman spectra. The notch filter allows only the Raman scattered wavelength while blocking the incident wavelength.
Vibrating Sample Magnetometer
Vibrating sample magnetometer (VSM) is an important piece of equipment for fast and reliable measurement of the magnetic moment of a wide range of magnetic materials. Using a vibrating sample magnetometer, the DC magnetic moment can be measured as a function of temperature, magnetic field and time. Calibration of the vibrating sample magnetometer was performed by measuring the magnetic moment of a standard pure Ni sample.
Preparation and characterization techniques for thin films 2.7 Thin film preparation techniques
- Chemical vapor deposition technique
- Physical vapor deposition technique
- a Thermal Evaporation
- Thin film characterization
The Ar+ ions produced by the glow discharge are accelerated as the cathode falls and knock atoms out of the target, causing a thin film to be deposited on the substrate. In the direct current sputtering technique, the target is made of metal because the glow discharge is maintained between metal electrodes. In this study, we chose reactive RF magnetron sputtering (Advanced Process Technologies, India) to deposit films in the MgTiO3 system.
Optical properties
When light is incident on a film of refractive index n, applied to a substrate of refractive index s, some of the incident light is reflected at the air-film, film-substrate and substrate-air interfaces and some of it is transmitted. 2e = mλ (2.25) where n is the refractive index of the film at a wavelength λ and m is the order of interference, d is the thickness of the film which can be calculated from the derivative values of refractive indices. Knowing α from the expression for the so-called “Tauc gap”, the fundamental absorption edge of the material can be determined.
Surface profilometer
Since d is known from previous calculations and I is a measured quantity (i.e. transmission at a wavelength λ), the absorption coefficient α can be calculated.
Microwave dielectric properties of thin films using post split dielectric resonator method
The armature air gap and the active area dimension of the armature depend on the operating frequency of the resonator. After the film deposition, the resonance frequency and quality factor of the (fs, Qs) substrate covered with the film must be measured again. Here, h is the sample thickness, f0 is the resonance frequency of the SPDR with the substrate, and fs is the resonance frequency of the SPDR with the film-coated substrate.
Electrical measurements
Since Ks is a slowly varying function of εr and h, the iterations using formula (2.40) converge quickly. Qc is the Q factor dependent on the metal losses of the SPDR containing the dielectric sample, and QDr is the Q factor dependent on the dielectric losses in the dielectric resonators.
Atomic force microscope
In the dynamic mode, the cantilever is externally oscillated at or near its resonance frequency. These changes in oscillation with respect to the external reference oscillation provide information about the sample's properties. In the present study, the AFM images were acquired using Agilent atomic force microscope (Agilent technologies, Model 5500 series) and analyzed using WSXM software [ 37 ].
Laegreid “Production of Thin Films by Controlled Deposition of Sputtered Material, in: Sputtering by Particle Bombardment III, Topics in Applied Physics, Springer Verlag, Berlin (1991).
Mechanochemical and Solid State Synthesis of
- Literature review
- Experimental details
- Mechanochemical method
- Solid state reaction method (non-stoichiometric compositions)
- Mechanochemical method
- Effect of milling time on the phase formation of MTO ceramics
- Effect of sintering temperature on crystal structure
- Microstructure
- Relative density
- Raman spectra
- Low frequency dielectric properties
- Microwave dielectric properties
- Preparation of non - stoichiometric Mg 1+ δ TiO 3+ δ composition and Mg 1.07 TiO 3.07 with the addition of V 2 O 5 by solid state reaction method
- Crystal structure
- Microstructure
- Microwave dielectric properties
- Conclusions
- References
The SEM image of the MTO ceramic sintered at different sintering temperatures for 3 hours is shown in Figure 3.2(b - d). The improvement in relative density is due to the excess MgO, which promotes uniform grain growth, and the formation of the single-phase MgTiO3 with an increase in grain size (see Figure 3.10(c)). In the present case, the secondary phase and grain size significantly affected the microwave dielectric properties of the MTO ceramics.
Effect of Additives on Microwave Dielectric Properties
- Brief literature review of MgTiO 3 processing
- Low temperature sintering of MTO ceramics by chemical processing
- Low temperature sintering with liquid - phase sintering aids
- Experimental Details
- Effects of CeO 2 nanoparticles and annealing temperature on MTO ceramics
- Crystal structure
11] reported the sintering temperature of MTO ceramics as 950oC with the addition of Li-based salts. Furthermore, the same group reported that with the addition of 6 wt% CuO - Bi2O3 - V2O5 the sintering temperature of MTO ceramics was lowered to 900oC. Furthermore, the values of relative density of MTO ceramics are found to decrease with an increase in x wt% beyond x = 0.5 wt%.
In addition, the sintering rate is increased when the diffusion across the grain boundary increases. Therefore, during the sintering process, surface defect atoms of powders tend to become normal atoms with lower energy inside the crystalline grains.
- Microstructural analysis
- Microwave dielectric properties To comprehend the influence of CeO
- Effects of Bi 2 O 3 and La
- Crystal structure
In addition, pure MTO ceramics have the highest value of dielectric constant only after sintering at 1400 oC. It was found that the Q×f0 values of pure MTO ceramics increase with increasing sintering temperature, and the maximum value is reached at 1400 oC. Nevertheless, upon annealing, pure MTO ceramics showed the best microwave dielectric properties compared to MTO with x wt.
- Microstructure of MTO ceramics added with Bi 2 O 3 and La 2 O 3
- Effect of Bi 2 O 3 or La 2 O
- Microwave dielectric properties
- Conclusions
- References
- Influence of Co Substitution on Dielectric and
- Brief literature survey
- Experimental Details
- Phase analysis and crystal structure of gel powders
- Crystal structure of sintered pellets
Moreover, in the case of MTO ceramics added with y = 1.5 wt%, smaller grains were observed at the grain boundaries of the large grains. Moreover, the obtained comparable average grain size of the MTO ceramics added with x = 0.5 wt% is due to the identical grain growth. Furthermore, the microstructures of the MTO ceramics were improved with the concentration of these additives.
Crystal structure of sintered pellets
Microstructure and Relative density
At lower sintering temperature, most sintering mechanisms will therefore be active as a result of the increased sintering rate, leading to a maximum relative density and larger uniform grain size [30]. This can be attributed to the use of finer starting particles (see Figure 5.2(b)) and understood as follows: Nanoparticles have larger surface area, resulting in higher surface energy. Furthermore, it is well known that the sintering rate depends on the nature of powder, particle size and sintering. Nanoparticles exhibit characteristic contact necks in the powder and form different , most of the sintering mechanisms would be active as a result of the increased sintering rate, leading to a It is also observed that relative x = 0.05.
Microwave dielectric properties
Microwave dielectric properties
Low frequency dielectric properties
The decrease in dielectric constant with increase in frequency is a typical feature of the. The obtained dielectric constant and loss tangent values are in the range of 15.35 and for the measured temperatures, respectively. The variation in dielectric constant with frequency can be explained on the basis of Maxwell. The decrease in dielectric constant with increase in frequency is a typical feature of the. The obtained dielectric constant and loss tangent values are in the range of 0.0011 for the measured temperatures, respectively.
Magnetic properties
A bifurcation was observed between the ZFC and FC data, which shifts to a lower temperature from 170 to 150 K with increasing applied field. This could be a substitution that was not seen by XRD due to the secondary phase. It is observed that (i) with decreasing temperature, the 28 K sample reveals a magnetic phase transition from a paramagnetic (PM) to a ferromagnetic (FM) state. ii) As the temperature further decreases, both ZFC and FC increase up to a certain temperature sensitive to the data between ZFC and FC, which shifts to a lower temperature from 170 to 150 K with increasing applied field.
Broadband dielectric properties
Conclusions
Due to the small initial particle size, the maximum relative density was reached at 1200oC. Interestingly, all sintered samples exhibit paramagnetic nature at room temperature and a maximum sensitivity of emu/g-Oe) was obtained for x = 0.03 sample. The observed anomalies were similar to the transitions observed in the magnetic properties and were correlated with the magnetic properties.
Studies on Pure and Co Doped MgTiO 3
- A short literature review
- Experimental Details
- Pure MgTiO 3 thin films
- MgTiO 3 thin films
- Structural Characterization of sputtering target
- Structure and microstructure of MTO thin films
- Optical Characterization
- Dielectric studies
It is found that the composition of the target is almost achieved in the deposited thin films. With an increase in OMP, the deposition rate and thickness of thin films decreased. It was observed that the refractive index of MTO thin films decreased with an increase in OMP concentration in both as-deposited and annealed films.
Structural Characterization of sputtering target and thin films
The results obtained for both bulk and thin films of MTO ceramics are almost comparable. From this study, it is clear that the obtained optical and dielectric properties of MTO thin films show that these films are one of the potential candidates for applications in integrated circuits and optical devices. However, after annealing at 700oC for 1 hour in air, all the thin films exhibit rhombohedral crystal structure, which is consistent with the previous reports [28].
