System and Method for a Capacitive Thermometer

• US 20150338285A1
• Filed: 05/21/2014
• Published: 11/26/2015
• Est. Priority Date: 05/21/2014
• Status: Active Grant

• Current Assignee: Infineon Technologies AG
• Original Assignee: Infineon Technologies AG
• Inventors: Irsigler, Peter, Schmid, Ulrich, Grille, Thomas, Hedenig, Ursula, Silvano de Sousa, Jonathan, Frischmuth, Tobias, Figueira da Silva, Sylvicley
• Granted Patent: US 9,939,331 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: B81B 3/0021 Transducers for transforming electrical into mechanical energy or vice versa dynamo-electric machines H02K99/00; electrostatic machines H02N1/00; piezoelectric devices H10N30/00
• CPC Class Codes: G01K 1/024 for remote indication
• CPC Class Codes: G01K 13/20 Clinical contact thermometers for use with humans or animals
• CPC Class Codes: G01K 7/34 using capacitative elements capacitors per se H01G

Abstract

Various embodiments disclosed herein include a capacitive thermometer including a deflectable membrane and a sense electrode. The deflectable membrane is configured to adjust a capacitive value based on a temperature of the deflectable membrane.

Claims

1. A circuit comprising:

a capacitive microelectromechanical system (MEMS) thermometer comprising a deflectable membrane and a sense electrode, wherein the deflectable membrane is configured to adjust a capacitive value based on a temperature of the deflectable membrane.

2. The circuit of claim 1, wherein:

the sense electrode comprises a rigid sense electrode;

the deflectable membrane forms a parallel plate capacitor with the rigid sense electrode; and

the capacitive MEMS thermometer further comprises;

a first thermal material with a first coefficient of thermal expansion, and

a second thermal material with a second coefficient of thermal expansion different from the first coefficient of thermal expansion, wherein the first and second thermal materials are configured to cause the deflectable membrane to deflect based on the temperature of the capacitive MEMS thermometer.

3. The circuit of claim 2, wherein the deflectable membrane comprises the first and second thermal materials.

4. The circuit of claim 3, further comprising a radio frequency (RF) antenna and an inductive element coupled to the capacitive MEMS thermometer, wherein the thermometer is configured to transmit RF signals based on an inductance of the inductive element and on the capacitive value.

5. The circuit of claim 4, wherein the thermometer comprises no internal power supply.

6. The circuit of claim 2, wherein the deflectable membrane separates a first cavity from a second cavity, and wherein the first thermal material is in the first cavity and the second thermal material is in the second cavity.

7. The circuit of claim 1, wherein the capacitive MEMS thermometer further comprises:

a first cavity containing a first fluid with a first coefficient of thermal expansion;

an overpressure cavity formed adjacent to the first cavity and separated from the first cavity;

the sense electrode formed as a rigid sense electrode overlying the first cavity and the overpressure cavity, wherein the sense electrode is configured to seal a top opening of the first cavity and the overpressure cavity;

a second cavity containing a second fluid with a second coefficient of thermal expansion different from the first coefficient of thermal expansion, wherein the second cavity is in fluid communication with the overpressure cavity; and

the deflectable membrane separating the first cavity from the second cavity.

8. The circuit of claim 7, wherein the capacitive MEMS thermometer is formed on a same substrate with an inductive element and coupled thereto.

9. The circuit of claim 8, wherein the capacitive MEMS thermometer and the inductive element are configured to transmit a signal related to temperature when excited by a radio frequency (RF) signal.

10. A wireless device comprising:

a radio frequency (RF) circuit, the RF circuit comprising;

an inductive element; and

a capacitor coupled to the inductive element, wherein the capacitor comprises a capacitive thermometer with a mechanically deflectable membrane configured to adjust a capacitive value proportionally to a change in temperature.

11. The wireless device of claim 10, wherein the wireless device is configured to receive all power and communication signals wirelessly.

12. The wireless device of claim 10, wherein the wireless device comprises no internal power supply.

13. The wireless device of claim 10, further comprising a package encasing the capacitive thermometer and the RF circuit.

14. The wireless device of claim 13, wherein the package comprises a biocompatible material and the wireless device is implantable in human or animal bodies.

15. The wireless device of claim 10, wherein the radio frequency (RF) circuit is coupled to a ground plane on the wireless device.

16. The wireless device of claim 10, wherein the wireless device has a maximum length of 1 cm and a maximum width of 4 mm.

17. The wireless device of claim 10, wherein the capacitive thermometer comprises a microelectromechanical system (MEMS) thermometer.

18. The wireless device of claim 17, wherein the MEMS thermometer comprises:

a rigid sensing electrode;

the deflectable membrane forming a parallel plate capacitor with the rigid sensing electrode;

a first thermal material with a first coefficient of thermal expansion; and

a second thermal material with a second coefficient of thermal expansion different from the first coefficient of thermal expansion, wherein the first and second thermal materials are configured to cause the deflectable membrane to deflect based on the temperature of the MEMS thermometer.

19. The wireless device of claim 10, wherein the RF circuit is disposed on a single semiconductor substrate.

20. A capacitive thermometer comprising:

a first cavity;

a second cavity formed beneath the first cavity;

a third cavity formed beneath the second cavity;

a deflectable membrane separating the first cavity from the second cavity, the deflectable membrane comprising a first material having a first coefficient of thermal expansion and a second material having a second coefficient of thermal expansion different from the first coefficient of thermal expansion, wherein the deflectable membrane comprises a ventilation hole;

a first perforated sense electrode separating the second cavity from the third cavity, wherein the electrode is separated from the membrane by a separation distance and is capacitively coupled to the membrane;

a first protective layer formed over the first cavity and sealing the first cavity; and

a second protective layer formed beneath the third cavity and sealing the third cavity.

21. The capacitive thermometer of claim 20, wherein the capacitive thermometer is formed on a same substrate with an inductive element and coupled thereto.

22. The capacitive thermometer of claim 21, wherein the capacitive thermometer and the inductive element are configured to transmit a signal related to temperature when excited by a radio frequency (RF) signal.

23. The capacitive thermometer of claim 20, wherein the perforated sense electrode is configured to deflect based on a change in temperature.

24. The capacitive thermometer of claim 20, further comprising a second perforated sense electrode separated from the membrane in a direction opposite the first perforated sense electrode.

25. The capacitive thermometer of claim 20, wherein the capacitive thermometer comprises a capacitive microelectromechanical system (MEMS) thermometer.

26. The capacitive thermometer of claim 20, further comprising additional cavities formed below or above the first, second, and third cavity.

27. A method of wirelessly determining temperature, the method comprising:

thermally coupling a capacitive thermometer to a target medium;

wirelessly exciting an RLC circuit, wherein the capacitive thermometer comprises the major capacitance of the RLC circuit;

wirelessly transmitting a signal from the RLC circuit in response to the wireless exciting; and

detecting the wirelessly transmitted signal from the RLC circuit.

28. The method of claim 27, further comprising determining a temperature of the medium based on the detecting.

29. The method of claim 27, wherein the capacitive thermometer comprises a deflectable membrane, the deflectable membrane configured to deflect based on temperature.

30. The method of claim 27, wherein the target medium is an internal location of a human or animal body.