Actuation voltage wave-form dependence of charge accumulation in RF MEMS switches

RF MEMS capacitive switches hold great promise in commercial, aerospace, and military applications. However, their commercialization is hindered by reliability concerns: charging effect in the dielectric layer can cause irreversible stiction of the actuating part of the switch. Presently, a popular method to investigate the charging/discharging in the dielectric layer is to measure an actual RF MEMS capacitive switch, which means a high experimental cost in fabricating MEMS switch devices. In this paper, a Metal-Insulator-Semiconductor (MIS) capacitor is used to investigate the charge accumulation in the dielectric layer of RF MEMS switches. By measuring the capacitance versus voltage (C-V) curves of MIS capacitor after voltage stressing, the dielectric charging/discharging characteristics are obtained. The experiment results indicate that the injected charges from the metal bridge in RF MEMS switches are responsible for stiction phenomena. In SiNx dielectric, the hole capture is more favored over electron capture, and the trapped charges tend to inhibit the charges further injecting. The effects of the actuation voltage waveform on the charge accumulation in the dielectric layer were investigated. It is verified that the tailored actuation voltage waveforms can be used to improve the reliability of RF MEMS capacitive switches.

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