TED-AJ03-420 IMPACT OF SKIN EFFECT ON THERMAL BEHAVIOR OF RF MEMS SWITCHES

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Future high-performance communications systems require increasing functionality and performance reliability at smaller size and power consumption. Microelectromechanical Systems (MEMS) have been identified as a promising enabling technology with the potential for a major impact on existing RF architectures by reducing weight, cost and size, and power dissipation. In particular, RF MEMS switches show many technological advantages over conventional switches based on a p-n diode, especially reduced power consumption. Despite this technological promise, the reliability of RF MEMS is critical to commercialize the technology for practical telecommunications applications. When the MEMS structure is operated under high RF power, heat is locally produced and selectively distributed due to metal and dielectric losses. This problem is particularly serious at frequencies above approximately 2GHz, where electron crowding becomes significant at the edge of the signal transmission metal strip of the RF MEMS switch. Localized heating due to this "skin effect" can cause switch failure. This manuscript considers the impact of the skin effect on the local temperature distribution and thermal reliability of RF MEMS switches. Prediction of temperature rise due to electrical losses requires multi-domain modeling. The current distribution in the switch is modeled using a 2-D finite element-boundary integral model of beam cross-sections. Average power dissipation in the switch is determined using the results of the electromagnetic model. The temperature in the switch is then calculated using a 2-D heat transfer finite element model. Because the current distribution depend on temperature, the electromagnetic and thermal models iterate on the current and temperature solutions until convergence is achieved. This represents the first time thermal and high-frequency electromagnetic simulations have been linked in multi-domain solutions. The model is used to predict the dominant failure mechanism in a gold beam 400μm long, 50μm wide, and 2μm thick. Two candidate mechanisms are studied : creep and buckling. Using the temperature modeling, the onset of these failure mechanisms is predicted in Fig. A-1 as a function of both frequency and RF power input. The modeling shows that failure is more likely to occur as either frequency or power increases. Frequency rise has not previously been linked to temperature increase because previous modeling efforts have not included the skin effect. Thus, for this beam geometry, buckling due to thermal stress is found to dominate, with a temperature rise of only 10℃ before buckling occurs.[figure]
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TED-AJ03-420 IMPACT OF SKIN EFFECT ON THERMAL BEHAVIOR OF RF MEMS SWITCHES

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