MEMS die and MEMS-based sensor
A micro-electro-mechanical systems (MEMS) die includes a piston; an electrode facing the piston, wherein a capacitance between the piston and the electrode changes as the distance between the piston and the electrode changes; and a resilient structure (e.g., a gasket or a pleated wall) disposed between the piston and the electrode, wherein the resilient structure supports the piston and resists the movement of the piston with respect to the electrode. A back volume is bounded by the piston and the resilient structure and the resilient structure blocks air from leaving the back volume. The piston may be a rigid body made of a conductive material, such as metal or a doped semiconductor. The MEMS die may also include a second resilient structure, which provides further support to the piston and is disposed within the back volume.
1. A micro-electro-mechanical systems (MEMS) die comprising:
an enclosure;
a diaphragm disposed across an opening of the enclosure, the diaphragm comprising a first electrode,
wherein the enclosure and the diaphragm define a back volume and every point within the back volume is less than a thermal boundary layer thickness from a nearest surface; and
a second electrode disposed outside of the back volume and facing the diaphragm.
2. The MEMS die of claim 1 ,
wherein the thermal boundary layer thickness is defined by the expression,
2
κ
ω
ρ
0
C
p
where k is the thermal conductivity of gas within the back volume, ρ 0 is the density of the gas, C p is the specific heat at constant pressure of the gas, and ω is the radian frequency.
3. The MEMS die of claim 1 , further comprising a back plate, wherein the second electrode is disposed on the back plate.
4. The MEMS die of claim 2 , further comprising a second back plate disposed between the diaphragm and the opening.
5. The MEMS die of claim 1 , wherein the diaphragm comprises a first diaphragm, wherein the MEMS die further comprises a second diaphragm facing the second electrode, the second diaphragm comprising a third electrode, wherein the second electrode is disposed between the first diaphragm and the second diaphragm.
6. The MEMS die of claim 5 , further comprising a plurality of posts that extend through the second electrode and connect the first diaphragm to the second diaphragm.
7. The MEMS die of claim 5 , wherein the first diaphragm and the second diaphragm define a sealed region in which the pressure is lower than an atmospheric pressure.
8. The MEMS die of claim 1 , wherein the enclosure comprises a plurality of pillars, a plurality of channels is defined between the pillars.
9. The MEMS die of claim 1 , wherein ring-shaped channels are formed into the enclosure.
10. A sensor comprising:
micro-electro-mechanical systems (MEMS) die comprising:
an enclosure;
a diaphragm disposed across an opening of the enclosure, the diaphragm comprising a first electrode, wherein the enclosure and the diaphragm enclose a back volume;
a second electrode disposed outside of the back volume and facing the diaphragm;
wherein:
every point within the back volume is less than a thermal boundary layer thickness from a nearest surface, and
during operation of the sensor, the MEMS die outputs a signal that is based on a capacitance between the first electrode and the second electrode changing due to a change in a distance between the first electrode and the second electrode.
11. The sensor of claim 10 , wherein the diaphragm comprises a first diaphragm, wherein the sensor further comprises a second diaphragm facing the second electrode, the second diaphragm comprising a third electrode, wherein
the second electrode is disposed between the first diaphragm and the second diaphragm,
during operation, the MEMS die outputs a second signal that is based on a capacitance between the third electrode and the second electrode changing due to a change in a distance between the third electrode and the second electrode.
12. The sensor of claim 11 , further comprising a plurality of posts that extend through the second electrode and connect the first diaphragm to the second diaphragm.
13. The sensor of claim 11 , wherein the first diaphragm and the second diaphragm define a sealed region in which the pressure is lower than an atmospheric pressure.
14. The sensor of claim 10 , wherein the enclosure comprises a plurality of pillars, a plurality of channels is defined between the pillars.
15. The sensor of claim 10 , wherein ring-shaped channels are formed into the enclosure.
16. The sensor of claim 10 , further comprising:
a base having a port;
a can attached to the base, wherein the MEMS die is disposed within the can and wherein sound enters through the port and causes the diaphragm to move during operation of the sensor.
17. A micro-electro-mechanical systems (MEMS) die comprising:
an enclosure;
a first diaphragm disposed across an opening of the enclosure, wherein the enclosure and the first diaphragm define a back volume and every point within the back volume is less than a thermal boundary layer thickness from a nearest surface;
a second diaphragm disposed outside of the back volume and facing the first diaphragm;
a solid dielectric disposed between the first diaphragm and the second diaphragm, the solid dielectric having a plurality of apertures;
a first electrode having a first end coupled to the first diaphragm and a second end coupled to the second diaphragm, the first electrode extending through an aperture of the plurality of apertures;
a second electrode oriented lengthwise and parallel to the first electrode, the second electrode having a first end attached to the second diaphragm and a second end disposed within an aperture of the plurality of apertures; and
a third electrode oriented lengthwise and parallel to the first electrode and the second electrode, the third electrode having a first end attached to the first diaphragm and a second end disposed within an aperture of the plurality of apertures.
18. The MEMS die of claim 17 , wherein the second end of the second electrode and the second end of the third electrode are disposed within the same aperture of the plurality of apertures.
19. The MEMS die of claim 17 , wherein
the first electrode is one of a first plurality of electrodes, each of which has a first end coupled to the first diaphragm, a second end coupled to the second diaphragm, and which extends through an aperture of the plurality of apertures,
the second electrode is one of a second plurality of electrodes, each of which has a first end attached to the second diaphragm and a second end disposed within an aperture of the plurality of apertures, and
the third electrode is one of a third plurality of electrodes, each of which has a first end attached to the first diaphragm and a second end disposed within an aperture of the plurality of apertures.