Center-Shift Method for the Characterization of Dielectric Charging in RF MEMS Capacitive Switches

Radio frequency (RF) micro-electro-mechanical systems (MEMS) capacitive switches show great promise for use in wireless communication devices such as mobile phones, but for the successful application of these switches their reliability needs to be demonstrated. One of the main factors that limits the reliability is charge injection in the dielectric layer (SiN) which can cause irreversible stiction of the moving part of the switch. We present a way to characterize charge injection. By stressing the dielectric with electric fields on the order of 1 MV/cm, we inject charge in the dielectric and measure the effects it has on the curve. Instead of conventionally measuring the change of the pull-in voltage, the presented center shift method measures the change of the voltage at which the capacitance is minimal. This way, the measurement method does not influence the charge injected by the stress voltage. Another advantage is that the measurement of the amount of injected charge is not influenced by changes in the width of the curve. These two advantages make it possible to test RF-MEMS capacitive switches in a more accurate way.