A study of material stoichiometry on charging properties of SiNx films for potential application in RF MEMS capacitive switches

This work presents an in depth investigation regarding the effect of PECVD silicon nitride (SiNx) stoichiometry on its charging mechanisms. The investigation took place in SiNx dielectric films with different Si-content (x = 0.47-1.04) with the aid of Metal-Insulator-Metal capacitors. The experimental assessment involved a single-point Kelvin probe System, the monitoring of Current - Voltage characteristics and the employment of Thermally Stimulated Depolarization Currents technique. The results indicate that when Si-content increases the injected charge distribution is expected to extend deeper in the dielectric films and charges are displaced faster through the bulk material and towards the bottom electrode. The effective temperature is used in order to investigate hopping conduction that dominates charge transport in the bulk material and thus a more realistic approach of the discharging process is presented. Finally, the increase of Si-content seems to introduce defect states in SiNx, which are probably associated to Si-dangling bonds, and the presence of discrete depolarization mechanisms are investigated, the characteristics of which are analytically described taking into consideration the effect of stoichiometry. These results that can be useful in material engineering in order to improve the lifetime of RF MEMS capacitive switches.