Enhancement of quality factor in RF-MEMS spiral inductors by etching out substrate

It is well known that substrate coupling degrades the Q value of spiral inductors. By partial or whole substrate etching out underneath the inductors, the Q of spiral inductors is improved. This paper extends the partial element equivalent circuit (PEEC) method for fast-accuracy electromagnetic analysis of such substrate coupling in RF-MEMS spiral inductors. By introducing electrical boundary conditions into PEEC, the capacitance matrix is extended to include substrate coupling. With the equivalent of charges in the interface, Green functions in uniform dielectric regions can be used in the calculations. The numerical results show good agreement with published measurement data.