Dielectric ceramics and substrates are electrical insulators with dielectric strength, dielectric constant and loss tangent values tailored for specific device or circuit applications. In capacitor applications, ceramics with a high dielectric constant are used to increase the charge that can be stored. In microelectronic circuits, low dielectric constant or low-k materials are sought to reduce inductive crosstalk and noise generation in the circuit. In high voltage insulator applications, high electrical resistivity (ohm-cm) and high dielectric strength (KV per meter) is required.
Dielectric Ceramic Parameters
Parameters that are important to consider when specifying dielectric ceramics and substrates include dielectric strength, dielectric constant (relative permittivity), loss tangent (tan ), electrical resistivity, and operating frequency. Dielectric strength is the maximum voltage field that the ceramic or material can withstand before electrical breakdown occurs. The dielectric constant is the relative permittivity of a material compared to a vacuum or free space. In dielectric materials, the loss tangent or loss coefficient is the ratio of the imaginary or loss permittivity to the real permittivity of a material. Resistivity is the longitudinal electrical resistance (ohm-cm) of a uniform rod of unit length and unit cross-sectional area. Operating frequency is the frequency range that the material is capable of operating within while providing acceptable performance and/or without excessive power losses.
Dielectric Ceramic Materials
Dielectric ceramics and substrates have a wide range of selection for materials. These include alumina, aluminum nitride, aluminum silicate or sillimanite, barium neodymium titanate, barium strontium titanate (BST), barium tantalate, barium titanate (BT), beryllia, boron nitride, calcium titanate, calcium magnesium titanate (CMT), glass ceramic, cordierite / magnesium aluminum silicate, forsterite / magnesium silicate, lead magnesium niobate (PMN), lead zinc niobate (PZN), lithium niobate (LN), magnesium silicate, magnesium titanate, niobate or niobium oxide, porcelain, quartz, sapphire, strontium titanate, silica or silicate, steatite, tantalate or tantalum oxide, titania or titanate, zircon, zirconia or zirconate, and zirconium tin titanate. The dielectric ceramic can be provided as a piezoelectric or relaxor ceramic, which is a dielectric ceramic with piezoelectric or electrostrictive characteristics.
Dielectric ceramics and substrates can be supplied in many forms. These include bar, disc, plate or slab, powder or grain, precursor, ring, rod, tube or cylinder, sputtering target, wafer or substrate and custom or application specific forms. Features of dielectric ceramics and substrates include stack or multilayer composite, electrical or high voltage, glaze or protective coating, metallized or electrode, modified or doped, microwave or high frequency, and single crystal construction.
Dielectric ceramics and substrates can have one of several different metal layers. These include, silver, gold, gold-tin alloy, copper, nickel, tantalum nitride, and titanium-tungsten. The metallization method for dielectric ceramics and substrates can be electroplated, fired on or thick film, patterned circuits or vias, evaporated thin film, or sputtered thin film.