Class I dielectrics include negative positive zero (NPO) ceramics, which are designated COG and BY. These ceramics are made by combining magnesium titanate (with a positive coefficient) and calcium titanate (with a negative coefficient) to form a dielectric with excellent temperature stability. Their properties are essentially independent of frequency, and they have ultrastable temperature coefficients of 0 +- 30 ppm°C over the range of −55 to 125°C. These dielectrics show a flat response to both AC and DC voltage changes. Low-k multilayer ceramic capacitors (MLCs) are used in resonant circuits and filters.
Class II dielectrics are high-k ceramics called ferroelectrics made from barium titanate. The addition of barium stannate, barium zirconate, or magnesium titanate lowers the dielectric constant from values as high as 8000. These compounds stabilize the capacitor over a wider temperature range. Class II dielectrics include the general-purpose X7R (BX) and Z5U (BZ). X7R is stable but its capacitance can vary +-15 percent over the temperature range of −55 to 125°C. Its capacitance value decreases with DC voltage but increases with AC voltage. Z5U compositions exhibit maximum temperature-capacity changes of +22 and −56 percent over the range of 10 to 85°C.
Class III dielectrics, developed for ceramic-disk capacitors, give high volumetric efficiency but with the tradeoff of high leakage resistance and dissipation factor. Capacitors made with Class III dielectrics have low working voltages. Ceramic dielectric capacitors are constructed in three styles: (1) single-layer disk, (2) tubular, and (3) monolithic multilayer
