Method of making a suspended membrane device
The present disclosure is directed to a device that includes a substrate and a sensor formed on the substrate. The sensor includes a chamber formed from a plurality of integrated cavities, a membrane above the substrate, the membrane having a plurality of openings, each opening positioned above one of the cavities, and a plurality of diamond shaped anchors positioned between the membrane and the substrate, the anchors positioned between each of the cavities. A center of each opening is also a center of one of the cavities.
1. A method, comprising:
forming a support layer on a substrate;
forming a membrane layer on the support layer;
forming a plurality of openings in the membrane layer;
forming a single, contiguous chamber having a plurality of integrated cavities, each of the plurality of openings positioned above and aligned with one of the plurality of integrated cavities; and
forming a plurality of anchors in the single, contiguous chamber by removing portions of the support layer below the openings in the membrane layer.
2. The method of claim 1 , further comprising:
forming a first electrode on the substrate between the support layer and the substrate;
forming a second electrode on the membrane layer, the membrane layer being between the first electrode and the second electrode.
3. The method of claim 2 wherein the contiguous chamber and the membrane layer separate the first electrode and the second electrode.
4. The method of claim 2 , further comprising forming the second electrode as a conductive mesh having intersecting rows and columns.
5. The method of claim 4 , further comprising forming an intersection between the rows and columns above each anchor.
6. The method of claim 1 wherein each integrated cavity is centered around one of the openings and having a square shape with rounded corners, as seen from a top down view.
7. The method of claim 1 wherein the anchors are diamond shaped.
8. A method, comprising:
forming a bottom electrode on a substrate;
forming a support layer on the bottom electrode;
forming a sensor layer overlying the support layer, the sensor layer including a thin film membrane;
forming a top electrode as a conductive mesh having openings therein, the openings exposing areas of the thin film membrane; and
forming a contiguous chamber having a plurality of integrated cavities by etching the support layer through the openings for a selected time, each of the openings positioned above and aligned with one of the plurality of integrated cavities, the etching continuing until the support layer is removed sufficient to form an array of supporting anchors that suspend the thin film membrane.
9. The method of claim 8 wherein the thin film membrane is made of silicon nitride.
10. The method of claim 8 wherein forming the support layer further includes
covering the bottom electrode with a photo-patternable material;
exposing the photo-patternable material to light; and
curing the photo-patternable material.
11. The method of claim 8 wherein the support layer is made of polyimide.
12. The method of claim 8 wherein the etching entails etching the support layer in a low-temperature process, below 200 C.
13. The method of claim 8 wherein the support layer has a height within the range of 2.0-8.0 μm.
14. The method of claim 8 wherein the substrate includes an integrated circuit.
15. The method of claim 8 wherein the anchors contact a total surface area of the thin film membrane that is within the range of 5-15%.
16. The method of claim 8 wherein the etching uses an isotropic plasma etching process that produces anchors having curved sidewalls.
17. The method of claim 16 wherein the plasma etching process accesses the support layer through the openings in the exposed areas of the thin film membrane.
18. The method of claim 8 , further comprising:
forming a passivation layer covering the top electrode; and
forming openings in the passivation layer.
19. The method of claim 18 wherein the openings in the exposed areas of the thin film membrane are aligned with the openings in the passivation layer.
20. The method of claim 8 wherein the suspended thin film membrane is a flexible membrane suitable for use as a pressure sensor.