Microelectromechanical microphone with differential capacitive sensing
Microelectromechanical microphones include structures that permit differential capacitive sensing. In certain structures, a movable plate is disposed between a rigid plate and a substrate. A first capacitor is formed between the movable plate and the substrate and a second capacitor is formed between the movable plate and the rigid plate. Respective bias voltages can be applied to the rigid plate and the substrate, and a differential capacitive signal can be probed in response to displacement of the movable plate caused by a pressure wave. The movable plate and the rigid plate are mechanically coupled to first and second portions of the substrate, respectively. A dielectric member mechanically couples the movable plate and the rigid plate, thus providing mechanical stability.
1. A microelectromechanical microphone system, comprising:
a substrate that defines an opening configured to receive an acoustic wave;
a movable diaphragm having a first portion mechanically coupled to the substrate and a second portion that is flexibly coupled to the first portion, wherein the movable diaphragm and the substrate form a first capacitor having a first capacitance based on a displacement of the movable diaphragm caused by the acoustic wave; and
a backplate mechanically coupled to the movable diaphragm via one or more dielectric members, each of the one or more dielectric members extends between a surface of the backplate and a surface of the movable diaphragm, wherein the backplate and the movable diaphragm form a second capacitor having a second capacitance based on the displacement of the movable diaphragm, and wherein the first capacitor is measured on a first side of the movable diaphragm and the second capacitor is measured on a second side of the movable diaphragm, the first side being opposite the second side.
2. The microelectromechanical microphone system of claim 1 , wherein the movable diaphragm defines openings.
3. The microelectromechanical microphone system of claim 1 , wherein a surface of the first portion is in contact with a dielectric layer overlaying the substrate.
4. The microelectromechanical microphone system of claim 1 , wherein each of the one or more dielectric members comprises a semiconductor oxide.
5. The microelectromechanical microphone system of claim 1 , wherein the substrate comprises a semiconductor.
6. The microelectromechanical microphone system of claim 1 , wherein the diaphragm comprises polycrystalline silicon or a doped semiconductor.
7. The microelectromechanical microphone system of claim 1 , wherein the backplate comprises silicon, germanium, a semiconductor from group III, a semiconductor from group V, a semiconductor from group II, a semiconductor from group VI, silicon oxide, polycrystalline silicon, or a combination thereof.
8. A device, comprising:
a microelectromechanical microphone including:
a substrate that defines an opening configured to receive an acoustic wave;
a movable diaphragm having a first portion mechanically coupled to the substrate and a second portion that is flexibly coupled to the first portion, wherein the movable diaphragm and the substrate form a first capacitor having a first capacitance based on a displacement of the movable diaphragm caused by the acoustic wave; and
a backplate mechanically coupled to the movable diaphragm via one or more dielectric members, each of the one or more dielectric members extends between a surface of the backplate to a surface of the movable diaphragm, wherein the backplate and the movable diaphragm form a second capacitor having a second capacitance based on the displacement of the movable diaphragm, and wherein the first capacitor is measured on a first side of the movable diaphragm and the second capacitor is measured on a second side of the movable diaphragm, the first side being opposite the second side; and
a circuit coupled to the microelectromechanical microphone and configured to receive a first signal indicative of the first capacitance and a second signal indicative of the second capacitance, the circuit is further configured to generate a third signal indicative of a difference between the first capacitance and the second capacitance, the third signal is representative of an amplitude of the acoustic wave.
9. The device of claim 8 , wherein the movable diaphragm defines openings, and wherein a surface of the first portion is in contact with a dielectric layer overlaying the substrate.
10. The device of claim 8 , wherein the circuit is further configured to apply a first bias voltage to the backplate and a second bias voltage to the substrate, and wherein the circuit is further configured to apply a ground reference voltage to the movable diaphragm.
11. The device of claim 8 , further comprising a housing comprising the microelectromechanical microphone and the circuit.
12. The device of claim 11 , wherein the microelectromechanical microphone and the circuit are formed on a single die.
13. The device of claim 11 , wherein the microelectromechanical microphone is formed on a first die and the circuit is formed on a second die, and wherein the first die and the second are electrically coupled.