MEMS device including a mobile element and a resistive sensor, and method for generating a signal indicating the position of the mobile element

• US 9,255,782 B2
• Filed: 08/26/2013
• Issued: 02/09/2016
• Est. Priority Date: 08/31/2012
• Status: Active Grant

• Current Assignee: STMicroelectronics International N.V. (STMicroelectronics NV)
• Original Assignee: STMicroelectronics SRL (STMicroelectronics NV)
• Inventors: Defazio, Marco, Murari, Bruno
• Primary Examiner(s): NGUYEN, HOAI AN D
• Application Number:
  US13/975,565
• Publication Number:
  US 20140062506A1
• Time in Patent Office: 897 Days
• Field of Search: 324/516, 324/519, 324/600, 324/649, 324/658, 324/661, 324/686, 345/173, 345/174, 340/545.4, 340/562, 733/04.C, 737/18, 737/24, 737/80, 733/350.4, 735/143.2, 738/623.37, 738/626.26, 702/47, 702/52
• US Class Current: 1/1
• CPC Class Codes: G01B 7/14 for measuring distance or clearance between spaced objects or spaced apertures G01B7/30 takes precedence
• CPC Class Codes: G01D 5/24 by varying capacitance
• CPC Class Codes: G01R 27/2605 Measuring capacitance capacitive sensors G01D5/24
• CPC Class Codes: G02B 26/0841 the reflecting element being moved or deformed by electrostatic means
• CPC Class Codes: H04N 9/3129 scanning a light beam on the display screen scanning a light beam on a screen in displays other than projection devices G09G3/02; scanning systems in general G02B26/10; projectors using laser light sources in general H04N9/3161

Abstract

A MEMS device includes a supporting body, a first deformable element and a second deformable element, and a mobile element set between the first and second deformable elements and rotatable with respect to the fixed supporting body. A generator causes a current to flow through at least one of the first and second deformable elements, which function as resistors, so as to generate an electrical position signal proportional to deformation of the first and second deformable elements and indicative of angular position of the mobile element. The electrical signal is processed to determine mobile element angular position. A drive signal is generated in response to the electrical signal for the purpose of driving oscillation of the mobile element.

Claims

1. A MEMS device, comprising:

a fixed supporting body;

a first deformable element and a second deformable element constrained to the fixed supporting body;

a mobile element interposed between, and connected to, said first and second deformable elements, the mobile element being rotatable with respect to the fixed supporting body, with consequent deformation of the first and second deformable elements; and

a generator configured to cause a current to flow through the first deformable element, the mobile element and the second deformable element, so as to generate an electrical position signal proportional to a sum of a first resistance of the first deformable element and a second resistance of the second deformable element, said first and second resistances being, respectively, proportional to deformations of the first and second deformable elements and indicative of an angular position of the mobile element.

2. The MEMS device according to claim 1, further comprising a processing circuit configured to process said electrical position signal to determine the angular position of the mobile element.

3. The MEMS device according to claim 1, wherein the fixed supporting body forms a first rotor subregion and a second rotor subregion, to which the first and second deformable elements are constrained, respectively, in such a way that the mobile element and the first and second deformable elements are electrically interposed between the first and second rotor subregions.

4. The MEMS device according to claim 1, wherein the first and second rotor subregions, the mobile element and the first and second deformable elements are made of semiconductor material and form a single piece.

5. The MEMS device according claim 1, further comprising an electrical actuation circuit configured to exert a torque on the mobile element as a function of the electrical position signal.

6. The MEMS device according to claim 5, wherein the fixed supporting body moreover forms a first stator subregion, and wherein the electrical actuation circuit is configured to generate an electrical driving signal based on the electrical position signal and to apply to the first stator subregion said electrical driving signal.

7. The MEMS device according to claim 6, wherein the fixed supporting body moreover forms a second stator subregion, and wherein the electrical actuation circuit is moreover configured to apply the electrical driving signal also to the second stator subregion.

8. The MEMS device according to claim 7, wherein each of the first and second deformable elements has a first dimension, a second dimension and a third dimension, measured, respectively, in a first direction, a second direction and a third direction that are mutually orthogonal, said first dimension being greater than said second and third dimensions, said first and second stator subregions being arranged in such a way that, when they receive the electrical driving signal, the mobile element rotates about an axis of rotation parallel to the first direction.

9. The MEMS device according to claim 1, wherein the electrical actuation circuit comprises:

a phase-shifter circuit configured to generate a shifted electrical signal, which is shifted by 90°

with respect to the electrical position signal; and

a comparator circuit configured to compare the shifted electrical signal with an electrical threshold and to generate, at each crossing of the electrical threshold by the shifted electrical signal, a corresponding edge of the electrical driving signal.

10. The MEMS device according to claim 1, further including a reflecting element, which is designed to reflect electromagnetic radiation and is constrained to the mobile element.

11. The MEMS device according to claim 7, wherein the first and the second stators further comprise fingers forming a variable capacitor with fingers of the mobile element.

12. The MEMS device according to claim 11, wherein the fingers of the first and the second stators are attracted to the fingers of the mobile element with an electrostatic force in response to a control voltage applied to the variable capacitor, the electrostatic force actuating the mobile element.

13. The MEMS device according to claim 12, wherein the electrostatic force actuates the mobile element to oscillate about the first and the second deformable element at about a resonant frequency.

14. The MEMS device according to claim 12, wherein the control voltage is generated in a closed loop control circuit in response to a first variable resistance of the first deformable element and a second variable resistance of the second deformable element, wherein the first variable resistance is proportional to a mechanical stress in the first deformable element and the second variable resistance is proportional to a mechanical stress in the second deformable element.

15. A method for generating an electrical signal indicating the angular position of a mobile element of a MEMS device including a fixed supporting body, a first deformable element and a second deformable element constrained to the fixed supporting body, the mobile element being interposed between, and connected to, said first and second deformable elements, and being rotatable with respect to the fixed supporting body, with consequent deformation of the first and second deformable elements, said method comprising:

causing a current to flow through the first deformable element, the mobile element, and the second deformable element to generate said electrical signal having a value proportional to a sum of a first resistance of the first deformable element and a second resistance of the second deformable element, said first and second resistances being, respectively, proportional to the deformations of the first and second deformable elements.

16. The method according to claim 15, wherein the fixed supporting body forms a first rotor subregion and a second rotor subregion, to which the first and second deformable elements are, respectively, constrained in such a way that the mobile element and the first and second deformable elements are electrically interposed between the first and second rotor subregions.

17. An apparatus, comprising:

a rotatable MEMS structure supported for oscillation by a first torsional member formed of a semiconductor material that defines a first resistor having a first resistance that varies as a function of deformation of the first torsional member; and

a generator configured to cause a current to flow through the first torsional member and the rotatable MEMS structure so as to generate an electrical position signal having a value proportional to said first resistance and indicative of an angular position of the rotatable MEMS structure.

18. The apparatus of claim 17, wherein the rotatable MEMS structure is further supported by a second torsional member formed of a semiconductor material that defines a second resistor have a second resistance that varies as a function of deformation of the second torsional member.

19. The apparatus of claim 18, wherein said current flows through the first torsional member, the rotatable MEMS structure and the second torsional member and the value of the electrical position signal is proportional to a sum of said first and second resistances and indicative of the angular position of the rotatable MEMS structure.

20. The apparatus of claim 19, wherein said first and second torsional members are positioned on opposite sides of the rotatable MEMS structure.

21. The MEMS device according to claim 17, further comprising a processing circuit configured to process said electrical position signal to determine the angular position of the rotatable MEMS structure.

22. The MEMS device according to claim 21, wherein the processing circuit is further operable to generate a drive signal, in response to said electrical position signal, for the purpose of driving oscillation of the rotatable MEMS structure.

23. The MEMS device according to claim 17, further comprising a stator structure positioned adjacent to the rotatable MEMS structure, the stator structure and rotatable MEMS structure defining a capacitor having a capacitance that varies as a function of the rotatable MEMS structure.

24. The MEMS device according to claim 23, wherein a first plate of the capacitor is coupled to a terminal of said first resistor.

25. A MEMS device, comprising:

a fixed supporting body;

a first deformable element and a second deformable element constrained to the fixed supporting body;

a mobile element interposed between, and connected to, said first and second deformable elements, the mobile element being rotatable with respect to the fixed supporting body, with consequent deformation of the first and second deformable elements;

a generator configured to cause a current to flow through at least one of the first and second deformable elements, so as to generate an electrical position signal proportional to at least one of a first resistance, of the first deformable element, and a second resistance, of the second deformable element, said first and second resistances being, respectively, proportional to deformations of the first and second deformable elements and indicative of an angular position of the mobile element;

an electrical actuation circuit configured to exert a torque on the mobile element as a function of the electrical position signal;

wherein the fixed supporting body moreover forms a second stator subregion, and wherein the electrical actuation circuit is moreover configured to apply the electrical driving signal also to the second stator subregion; and

wherein each of the first and second deformable elements has a first dimension, a second dimension and a third dimension, measured, respectively, in a first direction, a second direction and a third direction that are mutually orthogonal, said first dimension being greater than said second and third dimensions, said first and second stator subregions being arranged in such a way that, when they receive the electrical driving signal, the mobile element rotates about an axis of rotation parallel to the first direction.

26. A MEMS device, comprising:

a fixed supporting body;

a first deformable element and a second deformable element constrained to the fixed supporting body;

a mobile element interposed between, and connected to, said first and second deformable elements, the mobile element being rotatable with respect to the fixed supporting body, with consequent deformation of the first and second deformable elements;

a generator configured to cause a current to flow through at least one of the first and second deformable elements, so as to generate an electrical position signal proportional to at least one of a first resistance, of the first deformable element, and a second resistance, of the second deformable element, said first and second resistances being, respectively, proportional to deformations of the first and second deformable elements and indicative of an angular position of the mobile element;

an electrical actuation circuit configured to exert a torque on the mobile element as a function of the electrical position signal; and

wherein the electrical actuation circuit comprises;

a phase-shifter circuit configured to generate a shifted electrical signal, which is shifted by 90°

with respect to the electrical position signal; and

a comparator circuit configured to compare the shifted electrical signal with an electrical threshold and to generate, at each crossing of the electrical threshold by the shifted electrical signal, a corresponding edge of the electrical driving signal.