Organic-Based RF Capacitors with Ceramic-Like Properties

RF capacitor applications for filtering and signal matching need stringent tolerances in Temperature Coefficient of Capacitance (TCC) and Quality factor (Q). In this paper, the temperature dependence of the dielectric properties of polymer-ceramic composites was discussed, with particular emphasis on high Q polymers and paraelectric ceramic particles. This includes the important role of ceramic paraelectric particles such as A1₂O₃, SiO₂, Ta₂O₅ etc. as ceramic fillers and high Q polymers such as benzocyclobutene (BCB) in the development of high Q and low TCC dielectrics for embedded RF capacitors. High Q polymer by itself showed a negative TCC of about -250 ppm/ degC but the composite approach with A1₂O₃, SiO₂ and Ta₂O₅ fillers improved the TCC to -190, -130, +20 ppm/ degC , respectively, between temperatures ranging from room temperature to 125degC. Liquid coatable high Q polymer-based composites with 3-4X improvement in dielectric constant and nearly-zero TCC of approximately within plusmn30 ppm/degC were developed with Ta₂O₅ as the inorganic filler. This effect can be ascribed to the TCC compensation between negative TCC of high Q polymer and the positive TCC of paraelectric ceramic particle selected. The distribution of the particles in the polymer matrix is also a crucial aspect of this application.