MEMS microphone with spring suspended backplate
View Patent ↗A MEMS microphone has a base, a backplate, and a backplate spring suspending the backplate from the base. The microphone also has a diaphragm forming a variable capacitor with the backplate.
1. A MEMS microphone comprising:
a base;
a backplate having a plurality of apertures;
a backplate spring suspending the backplate from the base;
a diaphragm forming a variable capacitor with the backplate; and
a diaphragm spring suspending the diaphragm from the base.
2. The MEMS microphone as defined by claim 1 wherein the backplate spring comprises a serpentine shape.
3. The MEMS microphone as defined by claim 1 wherein the backplate spring is substantially solid and circumscribes the backplate.
4. The MEMS microphone as defined by claim 3 wherein the backplate has a thickness, the backplate spring having a thickness that is less than the thickness of the backplate.
5. The MEMS microphone as defined by claim 1 wherein the backplate spring comprises at least one tether.
6. The MEMS microphone as defined by claim 5 wherein the tether is solid.
7. The MEMS microphone as defined by claim 1 wherein the diaphragm spring has a diaphragm spring constant, the backplate spring having a backplate spring constant, the backplate spring constant being at least ten times larger than the diaphragm spring constant.
8. The MEMS microphone as defined by claim 1 wherein when the microphone is stationary, the backplate spring has a spring constant that is high enough to cause the backplate to remain substantially stationary upon receipt of audio signals having amplitudes on the order of magnitude of the human speaking voice.
9. A MEMS microphone comprising:
a base;
a backplate having a backplate edge and a plurality of apertures, the backplate edge forming a trench with the base, the trench being radially outward of the plurality of apertures to form a active sensing area of the backplate;
a backplate spring suspending the backplate from the base and at least in part forming the trench; and
a diaphragm forming a variable capacitor with the active sensing area of the backplate.
10. The MEMS microphone as defined by claim 9 wherein the diaphragm extends radially beyond the trench.
11. The MEMS microphone as defined by claim 9 further comprising:
a plurality of backplate springs suspending the backplate from the base and at least in part forming the trench; and
a plurality of diaphragm springs suspending the diaphragm substantially parallel to the backplate, the plurality of diaphragm springs being aligned with the plurality of backplate springs.
12. The MEMS microphone as defined by claim 11 wherein the backplate spring is serpentine shaped.
13. The MEMS microphone as defined by claim 9 wherein the backplate spring comprises at least one tether.
14. The MEMS microphone as defined by claim 13 wherein the backplate has a thickness, the backplate spring having a thickness that is less than the thickness of the backplate.
15. The MEMS microphone as defined by claim 9 wherein the diaphragm has a diaphragm spring with a diaphragm spring constant, the backplate spring having a backplate spring constant, the backplate spring constant being at least ten times larger than the diaphragm spring constant, the backplate spring causing the backplate to remain substantially stationary upon receipt of only an incident audio signal of the spoken human voice.
16. The MEMS microphone as defined by claim 9 wherein the backplate spring permits movement of the backplate relative to the base upon application of torsional force sufficient to overcome the force of the backplate spring.
17. A method of reducing stress on a MEMS microphone backplate, the method comprising:
providing a base;
supporting a diaphragm on the base;
forming a variable capacitor by spacing a backplate from the diaphragm, the backplate being connected to the base with at least one spring configured to reduce stress on the backplate; and
forming a trench between the base and the backplate.
18. The method as defined by claim 17 further comprising applying an incident audio signal of a spoken human voice against the backplate and diaphragm while the base remains substantially immovable, the backplate remaining substantially immovable upon receipt of the audio signal.
19. The method as defined by claim 17 wherein the backplate is connected to the base with no more than one spring, further comprising forming a trench around at least a portion of the diaphragm.
20. The method as defined by claim 17 wherein the base is formed from a first material, at least one of the springs being formed from a second material, the first and second materials being different.