Barium Strontium Titanate Thick Films Research Articles

Design and Characterization of Novel Barium Strontium Titanate Thick Films for Sub-6 GHz RF Applications

In this article, a novel study of the design and characterization of barium strontium titanate (BST) thick films produced by electrophoretic deposition (EPD) on flexible platinum foils is reported. Intended for sub-6 GHz radio frequency (RF) applications, a study on film and electrode thickness is conducted. First, a comparison of tunability and quality factor between different film thicknesses regarding frequency is performed. The Ba <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.7</sub> Sr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.3</sub> TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> varactors demonstrate variable capacitance between 49% and 55% for frequencies from 500 MHz to 5 GHz. Afterward, the influence of electrode thickness on the capacitance and quality factor of the films are studied. The variable capacitance and the quality factor present a tradeoff regarding the parametric studies of film and electrode thicknesses. Lastly, a microstrip line is deposited over the BST thick film to simulate and measure the phase-shifting capabilities of the device. Using a one-tone measurement setup, the small-signal S-parameter measurements of the phase shifter are also presented, and the linearity is analyzed considering two different bias voltages, 0 and 10 V. For the first time, the BST thick films fabricated by EPD process are implemented and measured in the RF regime as a metal–insulator–metal capacitor and as a phase shifter circuit.

Design and demonstration of acoustically optimized, fully-printed, BST MIM varactors for high power matching circuits

AbstractThis work addresses the piezoelectric induced reduction of quality factor in fully-printed metal-insulator-metal (MIM) barium strontium titanate (BST) thick film varactors designed for high power operation. An acoustically optimized varactor design is presented and compared to a non-optimized high-power varactor. The design is utilized to present a narrowband acoustic suppression technique based on defined weights. The acoustically optimized varactor consists of 162 varactor cells in a capacitive matrix. The cells in the matrix are interconnectable allowing for a variable unbiased capacitance and power rating. Due to this setup, surface acoustic waves are interrupted, and the reduced size of the cells allows for a reduced BST layer thickness, shifting the acoustic resonance away from the operational frequency. Therefore, an inverted behavior in comparison to the high-power varactor is observed with an increasing quality factor with biasing voltage. Compared to the high-power varactor, the acoustically optimized varactor design shows a 40% increased quality factor in biased state. By applying the narrowband acoustic suppression technique, an increase in quality factor of 145% is achieved compared to the unsuppressed design. In comparison to the high-power varactor, the acoustical suppressed design shows an increase in quality factor of 480% at the first acoustic resonance frequency.

Ba0.6Sr0.4TiO3 thick film derived by polymer modified MOSD route for tunable microstrip antenna applications

ABSTRACTFrequency and phase agile microstrip antenna applications require relatively thick Barium Strontium Titanate (BST) films for good tunability. In this work, Polymer (PEG-200) modified MOSD process route is developed to produce cracks free (Ba0.6, Sr0.4) TiO3 Thick film on Low loss ST-X quartz substrate. Structural and electrical characteristics of the deposited films were investigated using Atomic Force Microscope, X-Ray Diffraction, C-V and C-F characterizations. XRD characterization conformed the single BST phase with polycrystalline nature of the film. AFM analysis depicted equiaxed shaped grains with average grain size and roughness of 120 nm and 4.15 nm respectively. Dielectric tunability, dielectric constant and loss tangent of the deposited films were 36.46%, 310 and 0.0213 respectively at 1 MHz frequency using MIM capacitive structure where conductive oxide LNO was used as bottom electrode. The applicability of polymer modified BST thick films over low loss substrate as composite substrate for tunable microstrip antenna applications at microwave frequency was demonstrated by design, fabrication and testing of a compact frequency tunable microstrip antenna in coplanar configuration. The tunability exhibited at X band frequency proves the suitability of developed processed route for tunable antenna applications.

Steerable Dielectric Resonator Phased-Array Antenna Based on Inkjet-Printed Tunable Phase Shifter With BST Metal-Insulator-Metal Varactors

This letter presents a steerable phased-array antenna at C/X-band. The phase shifters used in the design, are implementing inkjet-printed barium strontium titanate (BST) thick-films. This method enables low-voltage tuning and low fabrication cost. The phase shifter is tuned by integrated metal-insulator-metal varactors, whose electrodes are fabricated by photolithography and inkjet-printed dielectric layer. A tunability of 46% at 8 GHz is achieved by applying 50 V across a 1.2- μm-thick BST film. The 11-unit-cells loaded-line tunable phase shifter achieves a figure of merit above 40°/dB from 7 to 8.5 GHz. Dielectric resonator antenna, fabricated from bulk-glass ceramic, has been implemented as radiating element with a stacked architecture for wide bandwidth and high gain. A beam steering of ±30° has been measured with a 1 ×4-element phased array in the anechoic chamber.

Fully Screen‐Printed Tunable Microwave Components Based on Optimized Barium Strontium Titanate Thick Films

The composite system Ba0.6Sr0.4TiO3–ZnO–B2O3 for thick film preparation has been modified via copper–fluorine codoping of BST to make it suitable for the fabrication of co‐fired metal‐insulator‐metal (MIM) components. Based on the resulting improvement of the thick films, MIM varactors and phase shifters were produced by subsequent screen‐printing of silver and BST pastes as well as co‐firing. Microstructural investigations showed the compatibility of silver and BST with neither chemical reaction nor cracking of the layers. The microwave characterization revealed good results regarding tunability and quality factor of the varactors and high figure of merit of 70°/dB at 1.72 GHz for the phase shifter.

Microstructure and microwave properties of inkjet printed barium strontium titanate thick-films for tunable microwave devices

Abstract Barium strontium titanate (BST) is a promising material for passive tunable microwave devices such as phase shifters, tunable filters or tunable matching networks. This publication covers the preparation of BST thick-films for microwave applications through inkjet printing. A Ba 0.6 Sr 0.4 TiO 3 ink was prepared, printed on alumina substrates and sintered at temperatures between 1100 °C and 1200 °C. The microstructure of the thick-films reveals the evolution of grain growth and porosity with increasing sintering temperature. Furthermore, a reaction with the substrate was observed for T ≥ 1175 °C. A maximum tunability of 36% was observed at temperatures right below the onset of the substrate reactions. This process conditions were used for the preparation of a loaded line phase shifter, which successfully shows the capability of the inkjet printing process for future microwave device fabrication.

Preparation of Integrated Passive Microwave Devices Through Inkjet Printing

Barium strontium titanate (BST) is a promising material for passive tunable microwave devices such as phase shifters or tunable matching networks. This publication covers the preparation of BST thick-films for microwave applications through inkjet printing. Two barium strontium titanate (BST) inks were prepared, printed on alumina substrates and sintered at different temperatures. The first ink was prepared with pure BST and sintered between 1100°C and 1200°C. The second ink was prepared with a BST–ZnO–B2O3 composition and was suitable to reduce the sintering temperature down to 800°C. The microstructure of the thick-films reveals the evolution of grain growth with increasing sintering temperature in the thick-films. Furthermore, a reaction with the substrate was observed for both inks at high sintering temperatures. The microwave characterization of the thick-films shows that for the permittivity and the tunability of the films, the effect of grain growth and reaction with the substrate compete against each other. Hence, the optimal microwave properties were achieved at a transition temperature, where first additional phases could already be observed. Even though, the properties are poorer for lower sintering temperatures, the investigations show that the preparation of silver- or gold-based metal–insulator–metal (MIM) structures through inkjet printing is possible with this composition. This allows various new design concepts for partly or fully inkjet printed passive microwave devices. Furthermore, it gives the opportunity for a future integration of passive tunable microwave devices in a low temperature co-fired ceramic (LTCC) fabrication process.

Applications of electrically tunable composite right/left handed transmission lines based on barium–strontium–titanate thick films and open resonators

This paper is focused on the study and applications of tunable composite right/left handed transmission lines (CRLH TL) based on open resonators. Specifically, it will be demonstrated that CRLH TL based on open split ring resonators (OSRRs) and open complementary split ring resonators (OCSRRs) can be tuned by means of barium–strontium–titanate thick-films. These artificial lines are applied to the design of tunable band-pass filters, phase shifters, dual-band impedance inverters and dual-band power dividers, where independent or simultaneous tuning of different resonators can be considered, depending on the application. The design methodology and different proof-of-concept demonstrators are reported.

The influence of processing on the microstructure and the microwave properties of Co–F-codoped barium strontium titanate thick-films

Abstract The influence of processing on the microstructure and the dielectric properties of Co–F-codoped Ba0.6Sr0.4TiO3 (BST) thick-films has been investigated. BST powders with different particle sizes were prepared and applied on alumina substrates by screen-printing. The resulting thick-films were sintered at different holding times and characterized with respect to their microstructure and microwave properties. The microstructure of the thick-films shows a clear dependency on sintering time and initial particle size. In addition to grain growth, the formation of a secondary phase is observed at the interface between substrate and BST with increasing sintering time. The dielectric characterization at microwave frequencies shows an increase of tunability with larger grain size while the dielectric loss is even lowered. This shows the strong influence of the microstructure on the material properties and the possibility of tailoring the material through specific processing.

Influence of Tm-doping on microstructure and luminescence behavior of barium strontium titanate thick films

Tm-doped Ba0.8Sr0.2TiO3 thick films were prepared by the screen-printing technique on the alumina substrate. The microstructure of the Tm-doped BST thick films was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Raman spectroscopy, respectively. All the samples showed a typical perovskite polycrystalline structure when sintered at 1260°C. The substitution behavior of Tm3+ ion in BST was found to change with increasing the Tm3+ concentration. The observed Tm-related red emission reaches the maximum at 0.2mol% Tm3+ concentration. The effects of concentration quenching on the luminescence intensity were discussed.

Nonlinear ceramics for tunable microwave devices

The research on materials and systems for tunable microwave devices has gained attraction within the last years. The radio frequency characterization and the component design of tunable microwave components based on dielectric ceramics especially barium-strontium-titanate (BST) are presented in this second part, whereas the basic material properties are discussed in detail in the first part. After a short introduction to the processing technology used for the fabrication of tunable components based on a BST thick film, the relations between microwave properties and material properties as well as the microstructure are presented in detail. The design process for tunable microwave components based on BST thick films is described. Especially the considerations related to micro- and macrostructure and their connection are highlighted. The paper closes with two different application examples: a reconfigurable array antenna for satellite communication and varactors for high power applications.

Tunable sub-wavelength resonators based on barium–strontium–titanate thick-film technology

This study shows recent results in the implementation of electrically reconfigurable structures based on sub-wavelength resonators implemented by means of ferroelectric materials. Barium–Strontium–Titanate thick films are employed as part of the substrate to implement electrically tunable split-ring resonators and open complementary split-ring resonators. Different structures have been fabricated proving the viability of this strategy for the implementation of reconfigurable structures. The achieved frequency shift reaches 12.6%. A parameter extraction method has been applied to study the effects of the modification of the dielectric permittivity of the ferroelectric material on the structure properties and its frequency response.

Wireless Temperature Sensing with BST-Based Chipless Transponder Utilizing a Passive Phase Modulation Scheme

A passive wireless temperature sensor with identification capabilities based on a phase modulation scheme is discussed in this paper. The approach presented utilizes a pulse backscatter technique based on slow wave (metamaterial) transmission lines. The focus of the work are the material engineering for the temperature-sensitive element and the integration of this element into a passive phase modulation circuit and the entire sensor tag. The approach makes use of temperature-sensitive bariumstrontium-titanate thick film capacitances. The discussed principle has been experimentally verified with a prototype.

In-Band Frequency-Tunable Ceramic Planar Inverted-F Antenna (PIFA) Utilizing an Integrated BST-Based Variable Capacitor

The dielectric properties of low-sintering-temperature (LTCC) Barium Strontium Titanate (BST) thick film paste at high frequencies (0.8–5 GHz) are briefly presented. The utility of the BST paste was demonstrated by tuning the resonance frequency of a ceramic PIFA for mobile terminals operating at 2 GHz. The frequency tuning achieved can be used to compensate frequency detuning caused by the proximity of the user to the antenna. The impact of tuning on the antenna's total efficiency and radiation pattern was experimentally studied through a comparison with the performance of a reference antenna not incorporating the varactor.

Tunable microwave devices using low-sintering-temperature screen-printed barium strontium titanate (BST) thick films

A tunable microwave phase shifter composed of a low-sintering-temperature, screen-printable barium strontium titanate (BST) film and silver metallization was fabricated on an alumina substrate and co-fired at 900 °C for 3 h. The dielectric properties of the films were characterized in a frequency range of 0.8–8 GHz using scattering parameter measurements and a quasi-static coplanar waveguide transmission line model. The temperature dependency of the films was measured through capacitance measurements in a frequency range of 0.5–2.5 GHz. The figure of merit (phase shift/dB of insertion loss) of the phase shifter was found to be 14.6 at 3 GHz with an applied bias field strength of 2.5 V/μm. The performance of the phase shifter is briefly discussed and compared with other phase shifters fabricated by direct screen-printing of BST films.

Screen Printed ZnBO Doped BST Thick Film Interdigital Capacitors for the Microwave Applications

The microwave properties of ZnBO doped barium strontium titanate thick film interdigital capacitors with seven fingers of 200 μ m finger gap have been investigated. Thick films have been prepared by screen printing method on the alumina substrates and sintered at temperature below 1200°C. Sintering aids of ZnBO were doped into BST to confirm the sintering temperature. With increasing the amount of ZnBO dopants, the relative dielectric permittivity was decreased, while loss tangent of ZnBO doped BST was increased. 1 wt% ZnBO doped BST thick film has relative dielectric permittivity of 759 at 1 MHz, while 3 and 5 wt% of ZnBO doped BST thick films have 624 and 554, respectively. By introducing ZnBO dopants to the BST thick films, leakage current densities were decreased. The decreased leakage current with increasing ZnBO dopants can be explained by increased density and grain size of thick film on alumina substrate. From the SEM images, we observed increased grain size by introducing more ZnBO dopants in the BST thick film. We believe this decreased leakage current density probably come from the increased grain size and increased density. Also, we will discuss the microwave transmission and reflectance properties of thick film interdigital capacitors.

Characterization of metal (Fe, Co, Ni, Cu) and fluorine codoped barium strontium titanate thick-films for microwave applications

The influence of codoping of Fe, Co, Ni, Cu as acceptors and F as donor on the dielectric properties of screen-printed Ba0.6Sr0.4TiO3 ceramic thick-films has been investigated. The undoped and codoped Ba0.6Sr0.4TiO3 powders were synthesized through a sol-gel route. The thermal gravimetric analysis revealed the difference of the thermal decomposition behaviour between the undoped and codoped precursors. The ceramic powders were characterized with x-ray diffraction, scanning electron microscopy and BET measurements. Larger crystallite sizes of the codoped powders were observed. The densification behaviour of the powders was recorded by dilatometry and indicated that codoping influences the sintering mechanism. The permittivity, dielectric loss and tunability of the undoped and codoped thick-films were characterized with coplanar waveguide structures up to 30 GHz.

Dielectric properties of barium strontium titanate thick films prepared by electrophoretic deposition

Ba x Sr 1− x TiO 3 ( x = 0.5, 0.6, 0.7) thick films were prepared by electrophoretic deposition (EPD) technique on platinum metallic foils using BaTiO 3 and SrTiO 3 nanoparticles with different molar proportion of 1:1, 3:2 and 7:3, respectively. An isostatic pressure method was used to increase density of the thick films before high temperature sintering. Microstructures of the deposited films were examined with XRD and SEM techniques. Porosity of the thick films decreased after the isostatic pressure process. The Ba 0.5Sr 0.5TiO 3 thick films of 10 μm, 15 μm and 20 μm showed a tunability of 28.8%, 33.3% and 33.9%, respectively, at room temperature and at a biasing field of 2 kV/mm. The dielectric constant was from 2138 to 3446 and dielectric loss was from 0.016 to 0.011 at zero bias field at 10 kHz. The temperature dependence of dielectric constant was also measured and the effect of porosity and thickness on the electrical performance of the thick films was discussed.

Co-sintering of barium strontium titanate (BST) thick films inside a LTCC substrate with pressure-assisted sintering

Screen-printed ferroelectric BST thick films were co-fired inside a LTCC substrate by employing pressure-assisted sintering (PAS). Sintering pressure and time were varied and their effect on the microstructure and dielectric properties of the film was studied. Sintering conditions for the fabrication of buried BST thick films were experimentally defined and parallel plate capacitors were successfully fabricated inside a LTCC substrate. The relative permittivity ( ɛ r) of the films at 10 kHz varied from 188 to 220 depending on the sintering conditions, and the maximum tunability of the films was 44% (5.7 V/μm). The measured loss tangent (tan δ) at zero bias was 0.005.

Barium Strontium Titanate Thick-Films: Dependency between Dielectric Performance and their Morphology

The paper is focused on the influence of the morphology of barium strontium titanate (BST) thick-films on their effective dielectric properties. Therefore two BST thick-films are made with a minor deviation in sinter temperature, and hence their mean grain size of the films and their sintering necks. By modeling the meso-structure using a Nonlinear 3D Finite-Difference Time-Domain field solver the assumed effect of the morphology on the effective dielectric properties are confirmed. The simulation results show the potential for a further improvement of the dielectric tunability of BST thick-films.