Investigation of Charge Injection and Relaxation in Multilayer Dielectric Stacks for Capacitive RF MEMS Switch Application

摘要

This paper proposes a new approach to the problem of irreversible stiction of capacitive radio frequency (RF) microelectromechanical (MEMS) switch attributed to the dielectric charging. We investigate how charge accumulates in multi- and single-layer dielectric structures for a capacitive RF MEMS switch using metal–insulator–semiconductor (MIS) capacitor structure. Two multidielectric-layers are structured, which are ${rm SiO}_{2}+{rm Si}_{3}{rm N}_{4}$ and ${rm SiO}_{2}+{rm Si}_{3}{rm N}_{4}+{rm SiO}_{2}$ stack films. Meanwhile, ${rm Si}_{3}{rm N}_{4}$ single-layer dielectric structure is also fabricated for comparison. In the experiments, the space charges are first injected into the dielectric layers by stressing MIS devices with a dc bias; then the injected charge kinetics are monitored by capacitance–voltage measurement before and after charge injection. We found that the polarity of charge accumulated in the dielectric is strongly influenced by the dielectric structure. When the metal electrode is positively biased, a negative charge accumulates in the single and triple-layer devices, while a positive charge accumulates in the double-layer devices. Furthermore, the experiment results also show that the lowest charge accumulation can be achieved using double-layer dielectric structure even though the fastest relaxation process takes place in triple-layer dielectric structure.