Tunable Thin Film Integrated Material Characterizations for Microwave Applications
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1075-J02-07
Tunable Thin Film Integrated Material Characterizations for Microwave Applications Mahmoud Al Ahmad1, Sandrine Payan2, Dominique Michau2, Mario Maglione2, and Robert Plana1 1 LAAS CNRS, 7 avenue du Colonel Roche, Toulouse Cedex 4, France 2 Université de Bordeaux, ICMCB CNRS, 87 Av Dr Schweitzer, Pessac Cedex, 33608, France Abstract In this work, a simple, fast and repeatable technique is proposed for tunable integrated thin film material characterizations. The technique does not depend on the type of material development method or special thin film processing. Moreover, additional structures or calibrations are not required. The proposed method can be used to determine the loss of a thin film material using radio frequency capacitance measurements in both parallel plate and interdigital topologies. An analytical formulation is given for the computation of the film loss based on its measured input impedance which is extracted from the measured scattering parameters. This technique is used for barium strontium titanate (BST) thin film material characterizations. Introduction The change of dielectric parameters under a DC electrical field (tunability) opens the way for a number of very interesting enabling technologies. One type of the materials that is gaining more and more importance are thin film where there is a strong interaction between the dc applied field and the materials electrical properties that could be translated into innovative components and circuits architectures. Among the different thin film materials that exist today, barium strontium titanate (BST) is employed due to its tunability at room temperature which finds great potential applications to assist microwave tunability. Integrated barium strontium titanate voltage-controlled capacitors are core components in tunable RF and microwave devices such as voltage controlled oscillators (VCOs) [1,3], tunable filters [4,5], phase shifters [6,7], and tunable matching networks [8]-[9]. A varactor with high quality factor and large tuning range is a mandatory prerequisite to meet the requirements of high tunable components specifications [10]. The quality of the BST thin film depends on its processing conditions such as temperature, thickness and substrate [11]. However, the development of BST growth conditions for optimizing its film losses demands a standard characterization method. The losses in BST thin films are due to: • Lattice oscillations of ions in the crystalline network. • BST growth conditions (oxygen vacancies, grain boundaries, extended defects). • Type of the deposition method (grain size and shape). • Thickness of the film. • The dielectric constant. Whereas the full stack losses in BST based components are due to: • BST film losses. • Substrate coated dielectrics losses. • Metallization loss. • Films defected interface. • The inherent crystallographic incompatibility of two materials. Interdigitated capacitor structures were achieved by lift-off process [12]. The structure has 16 fingers of width 3.5μm, length of 100μm and spa
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