MEMS device having a movable electrode

1. A microelectromechanical system (MEMS) device, comprising:

a semiconductor substrate;

a MEMS including a first fixed electrode and a movable electrode, the first fixed electrode and the movable electrode being formed on an insulating layer that is adjacent to the semiconductor substrate; and

a well formed on the semiconductor substrate below the first fixed electrode and in contact with the insulating layer, the well being one of an n-type well and a p-type well, wherein the p-type well is formed in a case of applying positive voltage to the fixed electrode while the n-type well is formed in a case of applying negative voltage to the fixed electrode,

wherein the movable electrode is formed continuously with the first fixed electrode.

2. The MEMS device according to claim 1 , wherein a voltage is applied to the well so that the well is in a depletion state.

3. The MEMS device according to claim 2 , satisfying Vp<0, Vwell≧0, and 0<|Vp−Vwell|<|Vth|, where Vp is a bias voltage of the MEMS,

Vwell is the voltage applied to the well below the MEMS, and Vth is a threshold voltage at which an inversion layer is formed in the well, wherein the semiconductor substrate is a p-type substrate while the well is the n-type well.

4. The MEMS device according to claim 2 , satisfying Vp>0, Vwell<0, and 0<|Vp−Vwell|<|Vth|, where Vp is a bias voltage of the MEMS, Vwell is the voltage applied to the well below the MEMS, Vth is a threshold voltage at which an inversion layer is formed in the well, wherein the semiconductor substrate is an n-type substrate while the well is the p-type well.

5. The MEMS device according to claim 1 , wherein the MEMS further includes a second fixed electrode formed on the insulating layer, the second fixed electrode being aligned with the movable electrode.