Vertical membranes for pressure sensing applications
Pressure sensors having vertical diaphragms or membranes. A vertical diaphragm may be located in a first silicon wafer between a first and second cavity, where the first and second cavities are covered by a second silicon wafer. One or more active or passive devices or components may be located on a top of the vertical diaphragm.
1. A pressure sensor comprising:
a first wafer having a first recess and a second recess etched in a top side such that a vertical membrane is formed between the first recess and the second recess, wherein the vertical membrane has a first lateral portion between the first recess and the second recess and a second lateral portion between the first recess and the second recess, the first lateral portion thicker than the second lateral portion; and
a second wafer having a bottom side attached to the top side of first wafer such that a first cavity is formed by the first recess and the bottom of the second wafer and a second cavity is formed by the second recess and the bottom of the second wafer.
2. The pressure sensor of claim 1 further comprising a first passage through the second wafer from a top of the second wafer to the first cavity.
3. The pressure sensor of claim 2 wherein the first lateral portion is separate from the second lateral portion.
4. The pressure sensor of claim 2 further comprising a second passage through the first wafer from a bottom of the first wafer to the second cavity such that the pressure sensor forms a differential pressure sensor.
5. The pressure sensor of claim 2 further comprising a second passage through the first wafer from a bottom of the first wafer to the second cavity.
6. The pressure sensor of claim 1 further comprising a first device over the first lateral portion and a second device over the second lateral portion.
7. The pressure sensor of claim 6 wherein the first device and the second device comprise resistors.
8. The pressure sensor of claim 7 wherein the resistors each include a p-type region extending through the second wafer into the vertical membrane in the first wafer.
9. The pressure sensor of claim 1 further comprising a stop in the first cavity extending from a wall of the first cavity opposing the vertical membrane towards the vertical membrane.
10. The pressure sensor of claim 9 wherein the stop is positioned such that a deflection of the vertical membrane may be limited.