MEMS-based structure for pico speaker

1. A microelectromechanical system (MEMS) device, the device comprising:

a first movable element that is positioned in a first plane, formed from a first layer of a semiconductor substrate, and configured to oscillate along a first directional path substantially orthogonal to the first plane; and

a second movable element that is formed from a second layer of the semiconductor substrate that is a different layer than the first layer of the semiconductor substrate, wherein the second movable element is configured to oscillate along a second directional path that is substantially parallel to the first directional path.

2. The MEMS device of claim 1 , wherein the second movable element is positioned in a second plane that is substantially parallel to the first plane.

3. The MEMS device of claim 1 , wherein the second movable element comprises a shutter portion configured to linearly translate along the second directional path.

4. The MEMS device of claim 1 , wherein the second movable element comprises a comb drive configured to actuate along the second directional path.

5. The MEMS device of claim 1 , wherein the first movable element comprises a membrane that is configured to generate an ultrasonic acoustic signal along the first directional path.

6. The MEMS device of claim 5 , wherein the first movable element is electrically coupled to a voltage source.

7. The MEMS device of claim 5 , wherein the second movable element comprises a shutter portion configured to modulate the ultrasonic acoustic signal such that an audio signal is generated.

8. The MEMS device of claim 7 , wherein the shutter portion is configured to linearly translate along the second directional path.

9. The MEMS device of claim 8 , wherein the second movable element further comprises a comb drive configured to actuate along the second directional path.

10. The MEMS device of claim 7 , wherein the shutter portion is configured to translate in a direction substantially parallel to the first directional path.

11. The MEMS device of claim 10 , wherein the second movable element is configured without an external mechanical actuator.

12. The MEMS device of claim 5 , further comprising a blind element that is disposed between the first movable element and the second movable element, defines one or more apertures, is formed from a third layer of the semiconductor substrate that is a different layer than the first layer or the second layer, and is substantially separated from the first movable element and the second movable element, wherein the second movable element is configured to modulate the first ultrasonic acoustic signal by at least partially obscuring the one or more apertures.

13. The MEMS device of claim 1 , wherein at least a portion of the second movable element is electrically coupled to a first voltage source.

14. The MEMS device of claim 13 , wherein the first movable element is electrically coupled to a second voltage source and is electrically isolated from the portion of the second movable element that is electrically coupled to the first voltage source by at least one electrical insulation layer of the semiconductor substrate.

15. The MEMS device claim 14 , further comprising a free volume adjacent to the second movable element that is configured to allow movement of the second movable element, wherein the free volume is formed by removal of a portion of an electrical insulation layer that is adjacent to the second layer of the semiconductor substrate.

16. The MEMS device of claim 15 , wherein the second movable element comprises a shutter portion configured to linearly translate along the second directional path that is substantially parallel to the first directional path and wherein the electrical insulation layer that is adjacent to the second layer of the semiconductor substrate has a thickness that is no greater than about 10 microns.

17. The MEMS device of claim 1 , further comprising a first free volume adjacent to a first side of the first movable element that is configured to allow movement of the first movable element along the first directional path, wherein the first free volume is formed by removal of a portion of a first electrical insulation layer of the semiconductor substrate.

18. The MEMS device of claim 17 , further comprising a second free volume adjacent to a second side of the first movable element that is configured to allow movement of the first movable element along the first directional path, wherein the second free volume is formed by removal of a portion of a second electrical insulation layer of the semiconductor substrate.

19. The MEMS device of claim 18 , wherein the first electrical insulation layer of the semiconductor substrate has a thickness that is no greater than about 20 microns and the second electrical insulation layer of the semiconductor substrate has a thickness that is no greater than about 20 microns.

20. A microelectromechanical system (MEMS) device, the device comprising:

an acoustic pipe configured to conduct an ultrasonic acoustic signal along a first directional path;

a first movable element that is positioned at a first end of the acoustic pipe, formed from a first layer of a semiconductor substrate, and configured to direct the ultrasonic signal into the acoustic pipe;

a blind element that is formed from a second layer of the semiconductor substrate, includes one or more apertures, and is positioned at a second end of the acoustic pipe, wherein the second layer is a different layer than the first layer and the second end is opposite to the first end; and

a second movable element that is disposed outside the acoustic pipe and is formed from a third layer of the semiconductor substrate, wherein the third layer of the semiconductor substrate is a different layer than the first layer or the second layer, wherein the second movable element is configured to oscillate along a second directional path that is substantially parallel to the first directional path.

21. The MEMS device of claim 20 , wherein the second movable element comprises a shutter portion configured to linearly translate along the second directional path that is substantially orthogonal to the first directional path.

22. The MEMS device of claim 20 , wherein the second movable element comprises a shutter portion configured to linearly translate along the second directional path.

23. The MEMS device of claim 21 , wherein the second movable element is configured to modulate the ultrasonic acoustic signal such that an audio signal is generated.

24. The MEMS device of claim 20 , wherein the first movable element is configured to generate the ultrasonic signal at a fixed frequency and the acoustic pipe is configured to have a maximum acoustic impedance at the fixed frequency.

25. The MEMS device of claim 20 , wherein the first movable element is configured to generate the ultrasonic signal at a fixed frequency and the acoustic pipe is configured to be a resonant cavity at the fixed frequency.

26. The MEMS device of claim 25 , wherein the acoustic pipe has a length from the first end to the second end that is an integral multiple of one half of a wavelength of a sound wave at the fixed frequency.

27. A method to operate a microelectromechanical system (MEMS) device, the method comprising:

oscillating a first movable element along a first directional path to generate an ultrasonic acoustic signal;

conducting the ultrasonic acoustic signal along the first directional path via an acoustic pipe to a second movable element; and

oscillating the second movable element along a second directional path that is substantially orthogonal or substantially parallel to the first directional path to modulate the ultrasonic acoustic signal and generate an audio signal.

28. The method of claim 27 , wherein the ultrasonic acoustic signal has a wavelength that is two times a wavelength of the acoustic pipe divided by an integer value.