Discussion Forum

Dear All,

I am attempting to model a bimorph which naturally deflects upwards due to stress in the lower layer of the beam. So far, this part has been successful. The top of the bimorph is silicon, and the bottom, stressed layer, is silicon dioxide. The idea is to apply a voltage to the top silicon, and ground an electrode underneath the deflected beam. The voltage differential creates an electrostatic force which pulls the beam down towards the electrode.
So far I've seen decent results building this in 4.1 without the MEMS module. I've used structural mechanics, ALE mesh, and electrostatics as so many other threads and discussions have suggested. The problem with my model is two fold:

1) in the deflection state, the Silicon and Oxide are supposed to be permanently attached to each other, but the plots in my results section clearly show that the Silicon layer is deflecting independently from the oxide layer. How can I express a condition that ensures the boundary that the two materials share moves in unison?

2) the bottom electrode is a slab of silicon. I've added it to the structural mechanics node, so it has solid material properties. As I ramp the voltage up, the beam does begin to deflect down towards the electrode, which is exactly what I want. However, at a certain point, it should hit the solid silicon electrode and lie flat. However, the beam continues to deflect downwards through the solid silicon electrode. This is even more strange to me, since I set the ground plane to be the top surface of the Silicon. How can a) the beam deflect through the solid, and b) the electrostatic attraction work if the beam has deflected past the ground level?

I've attached the model for anyone who is interested in helping!

Thank you!

Jason