TEMPERATURE MEASUREMENT SYSTEM COMPRISING A RESONANT MEMS DEVICE

• US 20110210801A1
• Filed: 02/24/2011
• Published: 09/01/2011
• Est. Priority Date: 02/26/2010
• Status: Abandoned Application

• Current Assignee: IMEC International
• Original Assignee: IMEC International
• Inventors: Jansen, Roelof, Tilmans, Hendrikus, Rottenberg, Xavier
• Application Number:
  US13/033,932
• Publication Number:
  US 20110210801A1
• Time in Patent Office: Days
• US Class Current: 331/156
• CPC Class Codes: G01K 7/32 using change of resonant frequency of a crystal
• CPC Class Codes: H03H 2009/02496 Horizontal, i.e. parallel to the substrate plane
• CPC Class Codes: H03H 9/02377 Symmetric folded-flexure
• CPC Class Codes: H03H 9/2463 Clamped-clamped beam resonators

Abstract

A micromechanical resonator device and a method for measuring a temperature are disclosed. In one aspect, the device has a resonator body, an excitation module, a control module, and a frequency detection module. The resonator body is adapted to resonate separately in at least a first and a second predetermined resonance state, selected by applying a different bias, the states being of the same eigenmode but having a different resonance frequency, each resonance frequency having a different temperature dependence. The micromechanical resonator device may have a passive temperature compensated resonance frequency.

Claims

1. A micromechanical resonator device for measuring a temperature, the device comprising:

a resonator body;

an excitation element associated with the resonator body and configured to excite the resonator body; and

a control element connected to the excitation element and configured to control the excitation element to excite the resonator body,

wherein the resonator body is configured to resonate in a first and a second predetermined resonance state, the first and second resonance states being of the same eigenmode but having different resonance frequencies, the resonance frequencies having a different temperature dependency,

wherein the control element is configured to supply to the excitation element separately a first bias to excite the resonator body into the first resonance state, and a second bias to excite the resonator body into the second resonance state,

wherein the micromechanical device further comprises;

a frequency detection element associated with the resonator body and configured to detect a frequency at which the resonator body resonates, and

a temperature determination element connected to the frequency detection element and configured to determine a temperature of the micromechanical resonator device from a first frequency, detected while the resonator body is in the first resonance state, and a second frequency, detected while the resonator body is in the second resonance state.

2. The micromechanical resonator device according to claim 1, wherein the temperature determination element comprises circuitry for determining a frequency difference and/or a frequency ratio using a look-up table and/or a mathematical relationship for determining the operation temperature.

3. The micromechanical resonator device according to claim 1, wherein the control element is configured to excite the resonator body in the first resonance state and the second resonance state alternately.

4. The micromechanical resonator device according to claim 1, wherein the temperature dependency of the resonance frequency of the first resonance state is inverse to the temperature dependence of the resonance frequency of the second resonance state.

5. The micromechanical resonator device according to claim 1, wherein the resonator body comprises a material selected from the group of silicon, polysilicon, diamond, ruby, sapphire, quartz, alumina, nickel, and SiGe.

6. The micromechanical resonator device according to claim 1, wherein the resonator body comprises a bar resonator suspended above a substrate.

7. The micromechanical resonator device according to claim 6, wherein the substrate comprises a material selected from the group of silicon, diamond, ruby, sapphire, glass, quartz, alumina, and LCP.

8. The micromechanical resonator device according to claim 1, wherein the first bias comprises a first DC voltage and the second bias comprises a second DC voltage.

9. The micromechanical resonator device according to claim 1, wherein the first bias comprises a first DC current and the second bias comprises a second DC current.

10. A method of determining a temperature of a micromechanical resonator device, the device comprising a resonator body configured to resonate in a first and a second predetermined resonance state, the first and second resonance states being of the same eigenmode but having different resonance frequencies, the resonance frequencies having a different temperature dependency, the method comprising:

applying a first bias to excite the resonator body into the first resonance state and measuring a first frequency while the resonator body is in the first resonance state;

applying the second bias to excite the resonator body into the second resonance state and measuring a second frequency while the resonator body is in the second resonance state; and

determining a temperature of the micromechanical resonator device using the measured first and second frequency.

11. The method according to claim 10, wherein the determination of the temperature using the measured first and second frequency comprises determining a frequency difference and/or a frequency ratio, and using a look-up table and/or a mathematical relationship.

12. The method according to claim 10, wherein the first bias and the second bias are applied alternately.

13. A micromechanical resonator device having a predetermined resonance frequency (f_res), the device comprising:

a resonator body suspended above and anchored to a substrate and configured to resonate in a predetermined resonance state at the predetermined resonance frequency (f_res);

an excitation element configured to excite the resonator body, the excitation element and the resonator body being separated from each other and together forming a transconductive structure;

a control element connected to the excitation element and configured to apply a predetermined bias (V, NI) to the excitation element to excite the resonator body into the predetermined resonance state;

wherein the resonance state is a mechanical vibration mode parallel to the plane of the substrate, the material of the resonator body and the material of the substrate are selected such that the ratio of the coefficient of thermal expansion of the substrate material (CTE_sub) and the coefficient of thermal expansion of the resonator body material (CTE_bar) is larger than 1.0,

wherein the transconductive structure has a transconductance with a predetermined temperature dependency which is defined by a set of parameters, the set of parameters comprising the material of the resonator body, the material of the substrate, the geometry of the resonator device (W₀, d₀), and the predetermined bias (V, NI), wherein the set of parameters being selected such that at a predetermined temperature (T₀), the predetermined temperature dependency of the transconductance compensates the intrinsic temperature dependence of the resonance frequency (f_res).

14. The micromechanical resonator device according to claim 13, wherein the resonator body is a free-standing bar resonator configured to resonate in a longitudinal vibration mode above and parallel to the plane of the substrate substantially at the predetermined resonance frequency (fres).

15. The micromechanical resonator device according to claim 14, wherein the bias is a bias voltage (V), and the bar resonator has a predetermined width (W₀), and the excitation element comprises electrodes located at a predetermined gap distance (d₀) from the bar resonator, and wherein the width (W₀), the gap distance (d₀), and the bias voltage (V) satisfy the following formula:

16. The micromechanical resonator device according to claim 13, wherein the resonator body is a free-standing bar resonator configured to resonate in a flexural vibration mode above and parallel to the plane of the substrate substantially at the predetermined resonance frequency (f_res).

17. The micromechanical resonator device according to claim 13, wherein the transconductive structure comprises an interdigitated structure with a first set of fingers connected to the excitation element and a second set of fingers connected to the resonator body, wherein the set of parameters further comprises an overlap between the first and second set of fingers.

18. The micromechanical resonator device according to claim 13, wherein the resonator body comprises a material selected from the group of silicon, polysilicon, diamond, ruby, sapphire, quartz, alumina, nickel, and SiGe.

19. The micromechanical resonator device according to claim 13, wherein the substrate comprises a material selected from the group of silicon, diamond, ruby, sapphire, glass, quartz, alumina, and LCP.