Monolithic Device with Dual Capacitor and Varistor Functions

Protective devices are needed in electronic systems to protect against voltage surges. In this paper, a monolithic device incorporating both the functions of a capacitor and a varistor is described. The device has a capacitance of 1 μF and a dissipation factor less than 0.05 between 1 and 100 kHz. At voltages greater than the threshold voltage, V₀, of about 15 volts, the device conducts a current, I, according to the power-law relation of varistors, I=AV^α. The nonlinearity index, α, is 11.4. In this device, the capacitor function protects against the lowamplitude and high-frequency transients while the varistor function protects against the high-amplitude voltage surges. Appropriate capacitor and varistor composition can be found to have similar sintering temperatures, allowing the fabrication of monolithic devices with a range of sintering temperatures between 900° and 1350°C.