Coventor's MEMS Design Blog

Modeling and Simulation of an RF MEMS Switch Bouncing

  

  

  

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Written by: Shantanu Kedar

Introduction

This example shows an ohmic RF switch with gold dimples, which make contact with transmission lines upon electrostatic actuation. The voltage waveform used for electrostatic actuation should be designed very carefully so as to prevent the switch from bouncing after impact. The switch bouncing will lead to electrical discontinuities and increased wear. Figure 1 shows the 3D model of the RF switch.The RF switch consists of a center plate suspended by four folded beams. The plate has four tabs, namely NE, NW, SE and SW. The dimples at the bottom of the tabs make contact with waveguide once the switch closes.

Figure 1 : 3D model of the RF switch 

Modeling:
Architect is used to build a fully parametric 3D model of the RF switch using L-beams, rigid plates and electrodes from the Parameterized Electromechanical Parts Library.Figure 2 shows the schematic of the RF switch. 

Figure 2: RF switch schematic in Architect

The center plate of the switch behaves as a rigid body and is modeled using ‘Rigid Plate' component from Architect Parts library. Rectangular and quadrilateral plates have been used to define the geometry of the plate and the tabs. The four dimples are also modeled using rigid plates and are labeled as ‘Dimple TL', ‘Dimple TR', ‘Dimple BL' and ‘Dimple BR'. The electrode beneath the center plate is modeled using ‘Electrode' component from the library. The folded beams are modeled using a combination of ‘L-Beam' and ‘Beam' components. A ‘Rigid Plate Damper' is used to model the effect of squeezed film damping.

Simulation:
Figure 3 shows the result of a transient simulation in Architect. The figure plots the soft landing waveform (a pulse with a magnitude of 190 volts and 500 nanoseconds rise and fall time) and the Z displacement of the plate center versus time. You can see the plate makes contact at around 30 microseconds. The plate remains in the displaced position till 150 microseconds. As the voltage is reduced to 0 Volts, the plate is released and bounces back. You can see that the plate bounce dies out over the next 450 microseconds due to damping. A fully coupled electro-mechanical transient simulation with contact and damping effects takes just 1 minuteto run on a 2GHz laptop. 

Figure 3: Transient simulation in Architect 

Figure 4 shows an animation of the transient analysis. This animation has been created using Scene3D. For clarity, the electrodes are transparent and the displacement in Z is scaled by a factor of 2. 

Figure 4: Animation of Transient simulation

Download instructions Customers who have an active CoventorWare license can access this example using their download account. Please contact your application engineering support for access. You will need CoventorWare 2008 to run this example
Reference: David A. Czaplewski, Christopher W. Dyck, Member, IEEE, Hartono Sumali, Member, ASME, Jordan E. Massad, Member, ASME, Jaron D. Kuppers, Student Member, ASME, Isak Reines, William D. Cowan, Senior Member, IEEE, and Christopher P. Tigges "A Soft-Landing Waveform for Actuation of a Single-Pole Single-Throw Ohmic RF MEMS Switch".