System and Method for a MEMS Transducer

• US 20160377569A1
• Filed: 06/24/2015
• Published: 12/29/2016
• Est. Priority Date: 06/24/2015
• Status: Active Grant

• Current Assignee: Infineon Technologies AG
• Original Assignee: Infineon Technologies AG
• Inventors: Arnanthigo, Yonsuang, Rajaraman, Vijaye Kumar, Dehe, Alfons, Kolb, Stefan
• Granted Patent: US 9,658,179 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: B81B 2201/0214 Biosensors; Chemical sensors
• CPC Class Codes: B81B 2201/0257 Microphones or microspeakers
• CPC Class Codes: B81B 2201/0278 Temperature sensors
• CPC Class Codes: B81B 3/0018 Structures acting upon the moving or flexible element for transforming energy into mechanical movement or vice versa, i.e. actuators, sensors, generators
• CPC Class Codes: B81B 7/02 containing distinct electrical or optical devices of particular relevance for their function, e.g. microelectro-mechanical systems [MEMS] B81B7/04 takes precedence
• CPC Class Codes: B81C 1/00166 Electrodes
• CPC Class Codes: B81C 1/00182 Arrangements of deformable or non-deformable structures, e.g. membrane and cavity for use in a transducer
• CPC Class Codes: B81C 1/00206 Processes for functionalising a surface, e.g. provide the surface with specific mechanical, chemical or biological properties
• CPC Class Codes: G01N 27/223 for determining moisture content, e.g. humidity rain detectors on vehicle windows B60S1/0825
• CPC Class Codes: H04R 19/005 using semiconductor materials
• CPC Class Codes: H04R 19/04 Microphones H04R19/01 takes precedence
• CPC Class Codes: H04R 2201/003 Mems transducers or their use
• CPC Class Codes: H04R 31/003 for diaphragms or their outer suspension

Abstract

According to an embodiment, a microelectromechanical systems (MEMS) transducer includes a substrate with a first cavity that passes through the substrate from a backside of the substrate. The MEMS transducer also includes a perforated first electrode plate overlying the first cavity on a topside of the substrate, a second electrode plate overlying the first cavity on the topside of the substrate and spaced apart from the perforated first electrode plate by a spacing region, and a gas sensitive material in the spacing region between the perforated first electrode plate and the second electrode plate. The gas sensitive material has an electrical property that is dependent on a concentration of a target gas.

Claims

1. A microelectromechanical systems (MEMS) transducer comprising:

a substrate comprising a first cavity that passes through the substrate from a backside of the substrate;

a perforated first electrode plate overlying the first cavity on a topside of the substrate;

a second electrode plate overlying the first cavity on the topside of the substrate and spaced apart from the perforated first electrode plate by a spacing region; and

a gas sensitive material in the spacing region between the perforated first electrode plate and the second electrode plate, wherein the gas sensitive material has an electrical property that is dependent on a concentration of a target gas.

2. The MEMS transducer of claim 1, further comprising a MEMS acoustic transducer integrated on the substrate, wherein the MEMS acoustic transducer comprises:

a perforated backplate overlying a second cavity in the substrate; and

a deflectable membrane overlying the second cavity and spaced apart from the perforated backplate.

3. The MEMS transducer of claim 2, wherein

the perforated backplate is formed of a same semiconductor layer as the perforated first electrode plate;

and

the deflectable membrane is formed of a same semiconductor layer as the second electrode plate.

4. The MEMS transducer of claim 3, wherein the first cavity and the second cavity are a same cavity that passes through the substrate from a backside of the substrate.

5. The MEMS transducer of claim 4, wherein the perforated first electrode plate comprises a central portion of the perforated backplate and the second electrode plate comprises a central portion of the deflectable membrane.

6. The MEMS transducer of claim 4, wherein the perforated first electrode plate comprises a peripheral portion of the perforated backplate and the second electrode plate comprises a peripheral portion of the deflectable membrane.

7. The MEMS transducer of claim 1, wherein the target gas is water vapor and the gas sensitive material is a humidity sensitive material.

8. The MEMS transducer of claim 7, wherein the humidity sensitive material is polyimide.

9. The MEMS transducer of claim 1, wherein the target gas is carbon dioxide.

10. The MEMS transducer of claim 1, further comprising:

a perforated third electrode plate overlying the first cavity on the topside of the substrate and spaced apart from the second electrode plate by an additional spacing region; and

the gas sensitive material in the additional spacing region between the perforated third electrode plate and the second electrode plate.

11. The MEMS transducer of claim 1, wherein the perforated first electrode plate is coupled to an ambient environment through the first cavity and a port in a package containing the MEMS transducer.

12. The MEMS transducer of claim 1, wherein the perforated first electrode plate overlies the second electrode plate and is coupled to an ambient environment through a top port in a package containing the MEMS transducer.

13. The MEMS transducer of claim 1, further comprising a temperature sensing element integrated on the substrate.

14. The MEMS transducer of claim 1, further comprising a heating element in physical contact with the gas sensitive material.

15. The MEMS transducer of claim 1, further comprising a ventilation opening that bypasses the perforated first electrode plate and the second electrode plate and provides a ventilation path between the first cavity and the topside of the substrate.

16. The MEMS transducer of claim 1, wherein the gas sensitive material comprises a gas sensitive dielectric material that has a dielectric constant that is dependent on the concentration of the target gas.

17. A method of fabricating a microelectromechanical systems (MEMS) sensor, the method comprising:

forming a first electrode plate on a substrate;

forming a second electrode plate spaced apart from the first electrode plate;

exposing a bottom surface of the first electrode plate by etching a cavity in a backside of the substrate;

releasing the first electrode plate and the second electrode plate; and

forming a gas sensitive material between the first electrode plate and the second electrode plate.

18. The method of claim 17, wherein forming the gas sensitive material comprises dispensing the gas sensitive material as a liquid into a region between the first electrode plate and the second electrode plate after releasing the first electrode plate and the second electrode plate.

19. The method of claim 18, wherein dispensing the gas sensitive material as a liquid comprises dispensing polyimide as a liquid.

20. The method of claim 17, wherein forming the gas sensitive material comprises depositing the gas sensitive material on the first electrode plate before forming the second electrode plate.

21. The method of claim 17, wherein the gas sensitive material comprises a gas sensitive dielectric material with a dielectric constant that is proportional to a concentration of a target gas.

22. The method of claim 17, wherein forming the first electrode plate comprises forming a perforated first electrode plate.

23. The method of claim 22, wherein

forming the perforated first electrode plate on the substrate comprises forming a perforated backplate;

forming the gas sensitive material comprises forming the gas sensitive material in a first region over the perforated backplate and forming an air gap in a second region over the perforated backplate; and

forming the second electrode plate on the gas sensitive material further comprises forming a deflectable membrane over the air gap in the second region.

24. The method of claim 23, wherein the first region is a peripheral region and the second region is a central region.

25. The method of claim 23, wherein the second region is a peripheral region and the first region is a central region.

26. The method of claim 22, further comprising:

forming a perforated backplate simultaneous to forming the perforated first electrode plate, wherein the perforated backplate and the perforated first electrode plate are formed of a same semiconductor layer; and

forming a deflectable membrane simultaneous to forming the second electrode plate, wherein

the deflectable membrane and the second electrode plate are formed of a same semiconductor layer, and

the deflectable membrane is spaced apart from the perforated backplate.

27. The method of claim 17, further comprising forming a heating element thermally coupled to the gas sensitive material.

28. The method of claim 17, further comprising forming a temperature sensing element on the substrate.

29. A microelectromechanical systems (MEMS) transducer comprising:

a MEMS acoustic transducer comprising;

a perforated backplate overlying a substrate, and

a membrane overlying the substrate and spaced apart from the perforated backplate by a first spacing; and

a MEMS gas sensor comprising;

a perforated first electrode overlying the substrate,

a second electrode overlying the substrate and spaced apart from the perforated first electrode by a second spacing, and

a gas sensitive dielectric between and in contact with the perforated first electrode and the second electrode.

30. The MEMS transducer of claim 29, wherein the perforated backplate and the perforated first electrode are formed of a same semiconductor layer.

31. The MEMS transducer of claim 29, wherein the substrate comprises a cavity and the perforated first electrode, the second electrode, and the gas sensitive dielectric overly the cavity.

32. The MEMS transducer of claim 29, further comprising a temperature sensing element integrated on the substrate.

33. The MEMS transducer of claim 29, further comprising a heating element in physical contact with the gas sensitive dielectric.

34. The MEMS transducer of claim 29, wherein

the perforated first electrode is formed in a central region of the perforated backplate;

and

the second electrode is formed in a central region of the membrane.

35. The MEMS transducer of claim 29, wherein

the perforated first electrode is formed in a peripheral region of the perforated backplate;

and

the second electrode is formed in a peripheral region of the membrane.