As the ionic conductivity of solid-state lithium ion conductors rises, knowledge of the detailed conductivity mechanisms is harder to obtain due to the limited frequency resolution of the traditional ...impedance spectrometers. Moreover, the data is easily affected by the local microstructure (i.e. pores, grain-boundaries) and the preparation conditions. The aim of this work is to demonstrate the feasibility of the coaxial reflection technique as a reliable tool to study fast ionic conductors (i.e. > 10−4 S cm−1). Especially the relative permittivity can be determined more accurately at room temperature. For the first time the electrical performance of LATP and LLZO manufactured via a scalable top-down glass-ceramic route is evaluated. The density turns out to be a key parameter influencing both relative permittivity and resulting conductivities. For a 100% dense LATP sample the coaxial reflection technique reveals a high grain-core conductivity of 6 × 10−3 S cm−1 similar to the conductivity of ideal single crystals.
Modern communication platforms require a huge amount of switched RF component banks especially made of different filters and antennas to cover all operating frequencies and bandwidth for the targeted ...services and application scenarios. In contrast, reconfigurable devices made of tunable components lead to a considerable reduction in complexity, size, weight, power consumption, and cost. This paper gives an overview of suitable technologies for tunable microwave components. Special attention is given to tunable components based on functional materials such as barium strontium titanate (BST) and liquid crystal (LC).
This paper aims to propose new approaches based on fully screen printing technology for realization of tunable components with frequency extension based on BST paste composite optimization. The ...tunable phase shifters are fabricated to demonstrate the capabilities of these simple, flexible and low-cost methods. The proposed phase shifters contain tunable ferroelectric varactors in metal-insulator-metal (MIM) configuration, which are fully printed on top of an alumina carrier substrate with metallic and dielectric pastes, subsequently dried and cofired. The printed phase shifters work in different frequency ranges by using different ferroelectric composites. The BST pastes are optimized for low sintering temperature performance. Using BST composite with MgBO, the frequency range is extended to 7.6GHz.
The design of a BaSrTi 3 (BST) thin film varactor in metal-insulator-metal configuration is presented, prepared for surface mount device (SMD) package integration. Instead of metal, the oxide ...conductor SrMoO 3 (SMO) is used as bottom electrode. This material shows not only metal-like conductivity (comparable to platinum), but additionally structural similarity to BST. This allows the growth of very thin, high quality epitaxial ferroelectric layers, which provide a higher quality and full tuning at low voltage levels. The fabrication, on-wafer characterization and modeling of the integrable varactor design is explained. The measured varactor performance with Q = 38 and tunability τ = 28.6% at 1GHz and bias voltage 3.7 V is degraded with respect to material performance. The reasons for this degradation are analyzed in detail, as Q = 75 and τ > 70 % were expected from material characterization. De-embedded results and the model for improved metal thicknesses predict a device Q = 95 and indicate the general suitability of this varactor concept for the application in mobile communication.
Ferroelectrics for Tunable High-Power Applications Maune, H.; Kienemund, D.; Wiens, A. ...
2018 IEEE MTT-S International Microwave Workshop Series on Advanced Materials and Processes for RF and THz Applications (IMWS-AMP),
2018-July
Conference Proceeding
This paper presents recent development of ferroelectric varactors for tuning applications. While Barium-StrontiumTitanate (BST) based thick-film components have formerly been realized in planar ...interdigital (IDC) topology, low-sintering BST composites offer the possibility of metal-insulator-metal (MIM) structures. The possibilities and limits of this technology are discussed in respect to high-power applications, especially the power handling capability and linearity are considered. Thickfilm components with very high power rating of 1kW show acoustic effects, which have to be carefully considered in the design.
This work presents a characterization technique and an EM-model for a thin film BST50 varactor grown on the oxide electrode material SMO, describing the benefits and limits of this characterization ...technique. Effective capacitance, Q factor, ESR and leakage current are evaluated and analyzed to understand the dominating mechanisms for the overall characteristic. The Q factor for this 13.3 pF varactor is 20.5 at 1 GHz. The extracted permittivity is 365, indicating a good BST crystal quality despite only 80 nm film thickness. The tunability at battery voltage level 3.7 V bias voltage (\pmb{46} \ \mathbf{V}/\mu \mathbf{m}) is 67.8 %. The EM model shows very high Q factors up to 6 GHz, revealing outstandingly high potential for this oxide varactor with Q factors of up to 70 at 1 GHz, while still maintaining its large tunability. Hence, the ability to epitaxially grow BST on structurally similar SMO allows for very thin BST thicknesses with very low defect density, and thus, very high tunability at very low voltage below 3.7 volts.
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