Integrated single-crystal MEMS device
Method of manufacturing a MEMS device integrated in a silicon substrate. In parallel to the manufacturing of the MEMS device passive components as trench capacitors with a high capacitance density can be processed. The method is especially suited for MEMS resonators with resonance frequencies in the range of 10 MHz.
1. Method of manufacturing a MEMS device, which method comprises the steps of:
providing a device substrate with a top side and a bottom side;
providing at least one trench in the top side of the device substrate defining the shape of a moveable structure;
providing at least one electrically conductive area on the top side of the device substrate and at least parts of the electrically conductive area form at least one moveable electrode attached to the movable structure;
providing a dielectric layer on the top side of the device substrate at least partly covering the electrically conductive area;
providing and structuring an electrically conductive electrode layer on the top side of the device substrate;
providing at least one anchor point in the dielectric layer;
providing and structuring an electrically conductive structural layer on the top side of the device substrate and the electrically conductive structural layer anchors the moveable structure at the anchor point;
partly removing the dielectric layer through the structured structural layer;
removing the device substrate from the bottom side of the device substrate in a defined area underneath the trench defining the shape of the moveable structure at least until the trench defining the shape of the moveable structure is reached and
releasing the moveable structure.
2. Method of manufacturing a MEMS device according to claim 1 , which method comprises the additional steps of:
providing a sacrificial layer on top of the structured electrode layer;
structuring the sacrificial layer and
partly removing the sacrificial layer and the dielectric layer through the structured structural layer.
3. Method of manufacturing a MEMS device according to claim 2 , whereby the dielectric layer and the sacrificial layer can be removed with the same etchant and the etching rate of the sacrificial layer with respect to the etchant is higher than the etching rate of the dielectric layer with respect to the etchant.
4. Method of manufacturing a MEMS device according to claim 3 , whereby the device substrate is a silicon substrate, the dielectric layer is thermally grown silicon oxide and the sacrificial layer is deposited silicon oxide.
5. Method of manufacturing a MEMS device according to claim 2 , whereby the sacrificial layer can be removed with a first etchant and the first etchant essentially doesn't remove the dielectric layer and the dielectric layer can be removed with a second etchant and the second etchant essentially doesn't remove the sacrificial layer.
6. Method of manufacturing a MEMS device according to claim 5 , whereby the device substrate is a silicon substrate, the dielectric layer is thermally grown silicon oxide and the sacrificial layer is deposited silicon nitride.
7. Method of manufacturing a MEMS device according to claim 1 , which method comprises the additional steps of:
encapsulating the top side of the device substrate;
providing a vacuum;
providing a packaging substrate and
bonding the packaging substrate to the bottom side of the device substrate.
8. A MEMS device comprising a device substrate with at least one reference electrode, a moveable structure comprising the same material as the device substrate and the moveable structure having at least one moveable electrode, the moveable structure is embedded in the device substrate and indirectly attached to the device substrate via at least one anchor essentially arranged above the device substrate, and a dielectric layer being removed locally so as to allow the moveable structure attached to the moveable electrode to be movable, an electrical driving circuit is connected to the moveable electrode and the reference electrode, and a capacitive structure electrically connected to the moveable electrode and/or the reference electrode, the capacitive structure comprises a multitude of trenches in the device substrate, and the surface of the trenches is electrically conductive forming a first electrode of the capacitive structure, and the capacitive structure further comprises the dielectric layer and a second electrode comprising the same material as the reference electrode.
9. A MEMS device as claimed in claim 8 , wherein the MEMS device is a MEMS resonator.
10. A MEMS resonator as claimed in claim 9 , wherein the moveable structure comprises an essentially disk shape.