MEMS device with isolation sub-frame structure

1. A method of fabricating a microelectromechanical systems (MEMS) device, the method comprising:

depositing a sacrificial layer over a substrate;

patterning and etching the sacrificial layer to form a plurality of openings in the sacrificial layer;

depositing a structural layer over the substrate, including into the plurality of openings;

patterning and etching the structural layer to form a plurality of structures comprising: a proof mass, an anchor structure comprising two or more separated anchors, and an isolation sub-frame; and

removing the sacrificial layer to release the plurality of structures, wherein

the isolation sub-frame structure surrounds the anchor structure and is flexibly connected to each of the two or more separated anchors, and

the proof mass is flexibly connected to the isolation sub-frame structure.

2. The method of claim 1 , wherein

the isolation sub-frame structure is located interior to the proof mass, and

the isolation sub-frame structure is separated from the proof mass by one or more openings.

3. The method of claim 1 , wherein

a portion of each of the two or more anchors are located interior to the isolation sub-frame structure, and

the portion of each of the two or more anchors is separated from the isolation sub-frame structure by one or more openings.

4. The method of claim 1 , further comprising:

prior to the depositing the sacrificial layer:

depositing a conductive layer over the substrate, and

patterning and etching the conductive layer to form electrodes and circuitry on the substrate, wherein the depositing the sacrificial layer over the substrate includes depositing the sacrificial layer over the electrodes and circuitry.

5. The method of claim 4 , wherein

the circuitry comprises connective pads for the anchor structure, and

the openings in the sacrificial layer are aligned with the connective pads.

6. The method of claim 4 , further comprising:

prior to the depositing the sacrificial layer:

depositing a nitride layer over the substrate, including over the electrodes and circuitry, and

patterning and etching the nitride layer to form a remaining nitride layer, wherein

the electrodes and circuitry are exposed through the remaining nitride layer, and

the depositing the sacrificial layer over the substrate includes depositing the sacrificial layer over the remaining nitride layer.

7. The method of claim 1 , further comprising:

prior to the depositing the sacrificial layer:

depositing a dielectric layer over the substrate, wherein the depositing the sacrificial layer over the substrate includes depositing the sacrificial layer over the dielectric layer.

8. The method of claim 1 , wherein

the proof mass is configured to pivot on a rotational axis parallel to the substrate, and

the anchor structure is aligned with the rotational axis.

9. The method of claim 8 , wherein

the plurality of structures further comprises torsion springs that flexibly connect the proof mass to the isolation sub-frame structure, and

the torsion springs are centered through the rotational axis.

10. The method of claim 1 , wherein

the plurality of structures further comprises compliant structures that flexibly connect each anchor to the isolation sub-frame structure, wherein the compliant structures are separated from the isolation sub-frame structure by a plurality of openings.

11. The method of claim 10 , wherein

each anchor of the anchor structure is flexibly connected to a pair of compliant structures.

12. The method of claim 8 , wherein

each of the two or more separated anchors is aligned with the rotational axis.

13. The method of claim 8 , wherein

the two or more separated anchors comprise at least two rows of separated anchors, and

each row of the two or more separated anchors is aligned with a line parallel to and offset from the rotational axis.

14. The method of claim 8 , further comprising:

a pair of electrodes mounted on the surface of the substrate, wherein the electrodes underlie the proof mass on either side of the rotational axis.