3D MEMS resonator based on a disk

Hello everybody,

I am trying to simulate in a STATIONARY simulation a quarter of a disk which should resonate being clamped to to points which are at the end of bars couplers.

Even when I am changing the the solver (I have tried with direct, segregated and different algorithms) I still have no convergence and this error:

Failed to find a solution.
Segregated group 3

Singular matrix.
In segregated group 3:
Returned solution is not converged.

I am attaching the model in order to provide further information.

I am kind of new in COMSOL, so any help will be welcome.

Thanks in advance.