In this paper we use Scanning Kelvin Probe Microscopy (SKPM) to detect charge in the dielectric of RF MEMS capacitive switches. We observe a laterally inhomogeneous distribution. Laterally inhomogeneous dielectric charging leads to a narrowing of the -curve [1], and can lead to stiction of the membrane. The measurements show that trapped charges slowly diffuse, which reduces the inhomogeneity and shows that charge is vertically confined. From these measurements we estimate the lateral diffusion coefficient of trapped charges.
A major issue in the reliability of RF MEMS capacitive switches is charge injection in the dielectric. In this study we try to establish the time and voltage dependence of dielectric charging in RF MEMS with silicon nitride as a dielectric. It is shown that the voltage shift of the CV-curve due to injected charge shows a √ t dependence over a large time range. By doing measurements on a large number of devices (early development material made at NXP Semiconductors in Nijmegen) we further show that the charging rate increases exponentially with the applied stress voltage.
In this paper we demonstrate how different degradation mechanisms of RF MEMS capacitive switches can be identified by carefully examining changes in key aspects of the measured C-V curves. We show that C-V curve narrowing can occur either due to mechanical deformation or to laterally inhomogeneous dielectric charging. We also show how these two degradation mechanisms can be distinguished by monitoring the change in the pull-in and pull-out voltages. Our measurements indicate that both degradation mechanisms do indeed occur in practice, depending on the stress conditions.
One of the major limitations in the speed of the atomic force microscope (AFM) is the bandwidth of the mechanical scanning stage, especially in the vertical (z) direction. According to the design principles of "light and stiff" and "static determinacy," the bandwidth of the mechanical scanner is limited by the first eigenfrequency of the AFM head in case of tip scanning and by the sample stage in terms of sample scanning. Due to stringent requirements of the system, simply pushing the first eigenfrequency to an ever higher value has reached its limitation. We have developed a miniaturized, high speed AFM scanner in which the dynamics of the z-scanning stage are made insensitive to its surrounding dynamics via suspension of it on specific dynamically determined points. This resulted in a mechanical bandwidth as high as that of the z-actuator (50 kHz) while remaining insensitive to the dynamics of its base and surroundings. The scanner allows a practical z scan range of 2.1 μm. We have demonstrated the applicability of the scanner to the high speed scanning of nanostructures.
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