Self-sealing membrane for MEMS devices
Embodiments of the present disclosure are related to MEMS devices having a suspended membrane that are secured to and spaced apart from a substrate with a sealed cavity therebetween. The membrane includes openings with sidewalls that are closed by a dielectric material. In various embodiments, the cavity between the membrane and the substrate is formed by removing a sacrificial layer through the openings. In one or more embodiments, the openings in the membrane are closed by depositing the dielectric material on the sidewalls of the openings and the upper surface of the membrane.
1. A method of forming a flexible membrane, comprising:
forming a sacrificial layer over a surface of a substrate;
forming a conductive electrode over the sacrificial layer, the conductive electrode including a plurality of openings with sidewalls;
forming a cavity between the conductive electrode and the substrate by removing the sacrificial layer through the plurality of openings in the conductive electrode; and
closing the openings by depositing a dielectric material on the sidewalls of the openings and on an upper surface of the portion of the conductive electrode, and continuing to deposit the dielectric material for a time period after the openings are closed to seal the cavity from atmosphere, wherein depositing the dielectric material includes alternatingly directing the dielectric material between a first angle of incidence and a second angle of incidence, the second angle of incidence being different from the first angle of incidence, the deposited dielectric material and the conductive electrode together forming the flexible membrane.
2. The method of claim 1 wherein the first angle of incidence is between about positive 30° and 60° and the second angle of incidence is between about negative 30° and 60°.
3. The method of claim 1 wherein depositing the dielectric material comprises depositing the dielectric material by chemical vapor deposition.
4. The method of claim 1 wherein depositing the dielectric material further includes depositing dielectric material on the outer surface of the released conductive electrode.
5. The method of claim 1 wherein depositing the dielectric material further includes providing portions of the dielectric material through the plurality of openings and depositing the portions of the dielectric material on the surface of the substrate below the released portion of the structural layer.
6. The method of claim 1 wherein forming the plurality of openings in the structural layer having a width or a diameter equal to or less than a thickness of the conductive electrode.
7. The method of claim 1 wherein the dielectric material has a thickness that is 1.5 times greater than a thickness of the structural layer.
8. A method of forming a flexible membrane, the method comprising:
forming a conductive electrode over a surface of a substrate, the conductive electrode being spaced apart from the surface of the substrate and defining a cavity therebetween, the conductive electrode having a plurality of openings with sidewalls; and
depositing a dielectric material on the sidewalls of each opening and an outer surface of the conductive electrode to a sufficient depth to seal the cavity thereby forming the flexible membrane, wherein depositing the dielectric material includes alternatingly directing the dielectric material between a first angle of incidence and a second angle of incidence, the second angle of incidence being different from the first angle of incidence.
9. The method of claim 8 wherein the pressure in the cavity is lower than atmosphere.
10. The method of claim 8 wherein forming the conductive electrode over the surface of the substrate comprises removing a sacrificial layer through the plurality openings to define the cavity.
11. The method of claim 8 wherein each opening has a width or diameter that is equal to or less than a thickness of the conductive electrode.
12. The method of claim 8 wherein the cavity has a depth that is at least 5 times greater than a thickness of the conductive electrode.
13. The method of claim 8 wherein the first angle of incident is positive and the second angle of incident is negative.