Degradation of formed metal-insulator-metal cathodes under pulsed bias

The dependence of a degradation process in formed Mo-SiO₂ -Ag cathodes operating in a pumped vacuum chamber on the pulse height, pulse width, duty cycle and device temperature ranging between 7 V and 14 V, 1 ms and 1000 ms, 5% and 50%, 300 K and 413 K respectively, was studied. It has been found that the effective rate of an increase in the diameter of emission centers, v_e, is not affected by the pulse width or duty cycle and increases with temperature. The voltage dependence of v_e has a maximum at ~12 V. It has been concluded that the same degradation mechanism, which is due to cumulative processes, is operating in both pulsed and constant voltage modes. The results of this work lend further support to the idea that the degradation of formed metal-insulator-metal cathodes is caused by the creation of new emission centers along the perimeters of the ones already present