High Q factor MEMS resonators

• US 6,624,726 B2
• Filed: 08/31/2001
• Issued: 09/23/2003
• Est. Priority Date: 08/31/2001
• Status: Active Grant

• Current Assignee: Google Technology Holdings LLC (Alphabet Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Niu, Feng, Cornett, Kenneth D.
• Primary Examiner(s): Tokar, Michael
• Assistant Examiner(s): NGUYEN, LINH V
• Application Number:
  US09/944,568
• Publication Number:
  US 20030052742A1
• Time in Patent Office: 753 Days
• Field of Search: 333/186, 333/197, 333/198, 333/200, 333/187, 310/9.6
• US Class Current: 333/197
• CPC Class Codes: H03H 2009/02496 Horizontal, i.e. parallel to the substrate plane
• CPC Class Codes: H03H 9/02433 Means for compensation or elimination of undesired effects
• CPC Class Codes: H03H 9/2405 of microelectro-mechanical resonators

Abstract

Microelectromechanical resonators that can be fabricated on a semiconductor die by processes normally used in fabricating microelectronics (e.g., CMOS) circuits are provided. The resonators comprises at least two vibratable members that are closely spaced relative to a wavelength associated with their vibrating frequency, and driven to vibrate one-half a vibration period out of phase with each other, i.e. to mirror each others motion. Driving the vibratable members as stated leads to destructive interference effects that suppress leakage of acoustic energy from the vibratable members into the die, and improve the Q-factor of the resonator. Vibratable members in the form of vibratable plates that are formed by deep anisotropic etching one or more trenches in the die are disclosed. Embodiments in which two sets of vibratable plates are spaced by ½ the aforementioned wavelength to further suppress acoustic energy leakage, and improve the Q-factor of the resonator are disclosed.

Claims

1. An electromechanical resonator comprising:

a semiconductor die including;

a first vibratable plate that is capable of resonant vibration at a frequency that corresponds to a wavelength of acoustic waves in the die; and

a second vibratable plate that is capable of resonant vibration at the frequency, and is spaced from the first vibratable plate by less than about one-half the wavelength.

2. The electromechanical resonator according to claim 1 wherein:

the first vibratable plate is spaced from the second vibratable plate by less than about one-quarter the wavelength.

3. The electromechanical resonator according to claim 1 wherein:

the second vibratable plate is spaced from the first vibratable plate by less than about one-tenth of the wavelength.

4. The electromechanical resonator according to claim 1 wherein:

the first vibratable plate includes a first electrode that is adapted for coupling to an electrical circuit for establishing an electric field that emanates from the first vibratable plate whereby an electric force associated with the electric field drives the resonant vibration of the first vibratable plate.

5. The electromechanical resonator according to claim 4 wherein:

the second vibratable plate comprises a second electrode for terminating the electric field;

whereby, the electric force drives the resonant vibration of the first vibratable and the second vibratable plate in phase synchronism.

6. The electromechanical resonator according to claim 5 wherein:

the second vibratable electrode is adapted for coupling to a biasing circuit.

7. The electromechanical resonator according to claim 1 wherein:

the semiconductor die has a die major surface characterized by a die surface normal; and

the first vibratable plate comprises;

a first vibratable plate major surface characterized by a first vibratable plate major surface normal that is substantially perpendicular to the die surface normal;

a first side edge;

a second side edge;

a bottom edge; and

a top edge.

8. The electromechanical resonator according to claim 7 comprising:

a number N, where N is a multiple of four, of vibratable plates arranged in an array, the vibratable plates each including;

one of a sequence of N electrodes;

wherein

the sequence of N electrodes is adapted for coupling to a sequence of signals that includes a repeating sequence of four driving signals.

9. The electromechanical resonator according to claim 7 further comprising:

a number N, where N is a multiple of two, of vibratable plates arranged in an array, the vibratable plates each including one of a sequence of N electrodes;

a first fixed electrode on a first side of the array;

a second fixed electrode on a second side of the array;

wherein the sequence of N electrodes, the first fixed electrode, and the second fixed electrode are adopted for coupling to a sequence of N+2 signals that includes a subsequence of N signals in which signals appear repeated twice consecutively.

10. The electromechanical resonator according to claim 7 wherein:

the second vibratable plate comprises;

a second vibratable plate major surface characterized by a second vibratable plate major surface normal that is substantially perpendicular to the die surface normal;

a first side edge;

a second side edge;

a bottom edge; and

a top edge.

11. The electromechanical resonator according to claim 10 wherein:

the first vibratable plate major surface normal is substantially parallel to the second vibratable plate major surface normal.

12. The electromechanical resonator according to claim 10 wherein:

the first side edge, second side edge, and bottom edge of the first vibratable plate are connected to the die;

the top edge of the first vibratable plate is free;

the first side edge, second side edge, and bottom edge of the second vibratable plate are connected to the die;

the top edge of the second vibratable plate is free;

the first vibratable plate is characterized by a length L measured along the top edge of the first vibratable plate, and a height H measured along the first side edge of the first vibratable plate;

the second vibratable plate is characterized by the length L, and the height H; and

the first and second vibratable plates vibrate in a mode characterized by;

a first number N of nodal lines that are substantially aligned with the height of the first and second vibratable plates; and

a second number M of nodal lines that are substantially aligned with the length of the first and second vibratable plates; and

the quantity;

$\frac{N·<br><br>H}{\left(2·<br><br>M-1\right)·<br><br>L}$

is at least about three.

13. The electromechanical resonator according to claim 10 wherein:

the first side edge, and bottom edge of the first vibratable plate are connected to the die;

the top edge and the second side edge of the first vibratable plate are free;

the first side edge, and bottom edge of the second vibratable plate are connected to the die;

the top edge and second side edge of the second vibratable plate are free;

the first vibratable plate is characterized by a length L measured along the top edge of the first vibratable plate, and a height H measured along the first side edge of the first vibratable plate;

the second vibratable plate is characterized by the length L, and the height H; and

the first and second vibratable plates vibrate in a mode characterized by;

a first number N of nodal lines that are substantially aligned with the height of the first and second vibratable plates; and

a second number M of nodal lines that are substantially aligned with the length of the first and second vibratable plates; and

the quantity;

$\frac{\left(2·<br><br>N-1\right)·<br><br>H}{\left(2·<br><br>M-1\right)·<br><br>L}$

is at least about three.

14. The electromechanical resonator according to claim 10 further comprising:

a first conductive pathway from the die major surface onto the first vibratable plate; and

a second conductive pathway from the die major surface onto the second vibratable plate.

15. The electromechanical resonator according to claim 14 wherein:

the first and second vibratable plates are characterized by a height; and

the first conductive pathways comprises a doped region that extends from the top edge of the first vibratable plate down through at least about ⅓

of the height of the first vibratable plate; and

the second conductive pathway comprises a doped region that extends from the top edge of the second vibratable plate down through at least about ⅓

of the height of the second vibratable plate.

16. The electromechanical resonator according to claim 14 further comprising:

a third conductive pathway from the die major surface onto the first vibratable plate, wherein the first conductive pathway is isolated from the third conductive pathway.

17. The electromechanical resonator according to claim 14 further comprising:

a first fixed electrode located proximate the first vibratable plate.

18. The electromechanical resonator according to claim 17 wherein:

the first and second vibratable plates are characterized by a height;

the first fixed electrode comprises a doped region that extends down within the die from the die major surface by a distance equal to at least ⅓

of the height.

19. The electromechanical resonator according to claim 17 further comprising:

a trench that is located between the first fixed electrode and the first vibratable plate and includes;

a first isolation leg extending away from the first vibratable plate on a first side of the first fixed electrode; and

a second isolation leg extending away from the first vibratable plate on a second side of the first fixed electrode.

20. The electromechanical resonator according to claim 17 wherein:

the first fixed electrode is located between the first vibratable plate and the second vibratable plate.

21. The electromechanical resonator according to claim 17 further comprising:

a second fixed electrode located proximate the second vibratable plate.

22. The electromechanical resonator according to claim 21 wherein:

the first vibratable plate and the second vibratable plate are located between first fixed electrode and the second fixed electrode.

23. The electromechanical resonator according to claim 17 wherein:

the first fixed electrode is located on a first side of the first vibratable plate; and

a second fixed electrode is located proximate the first vibratable plate.

24. The electromechanical resonator according to claim 23 wherein:

the second fixed electrode is located on the first side of the first vibratable plate adjacent to the first fixed electrode.

25. The electromechanical resonator according to claim 24 further comprising:

a trench that is located between the first vibratable plate and the first and second fixed electrodes, and includes a first isolation leg that extends away from the first vibratable plate between the first and second fixed electrodes.

26. The electromechanical resonator according to claim 25 further comprising:

a second isolation leg proximate the first fixed electrode opposite the first isolation leg.

27. The electromechanical resonator according to claim 24 further comprising:

a third fixed electrode located on a first side of the second vibratable plate; and

a fourth fixed electrode located on the first side of the second fixed electrode.

28. The electromechanical resonator according to claim 27 wherein:

the first vibratable plate and the second vibratable plate are located between the first fixed electrode and the third fixed electrode.

29. The electromechanical resonator according to claim 10 wherein:

the bottom edge of the first vibratable plate is connected to the semiconductor die; and

the top edge of the first vibratable plate is free;

the bottom edge of the second vibratable plate is connected to the semiconductor die; and

the top edge of the second vibratable plate is free.

30. The electromechanical resonator according to claim 29 wherein:

the first side edge of the first vibratable plate is connected to the semiconductor die;

the first side edge of the second vibratable plate is connected to the semiconductor die;

the second side edge of the first vibratable plate is free; and

the second side edge of the second vibratable plate is free.

31. The electromechanical resonator according to claim 30 further comprising:

a fixed electrode located between the first vibratable plate and the second vibratable plate.

32. The electromechanical resonator according to claim 30 further comprising:

a first fixed electrode located on a first side of the first and second vibratable plates; and

a second fixed electrode located on a second side of the first and second vibratable plates.

33. The electromechanical resonator according to claim 31 further comprising:

a third fixed electrode adjacent to the first fixed electrode on the first side of the first and second vibratable plates; and

a fourth fixed electrode adjacent to the second fixed electrode on the second side of the first and second vibratable plates.

34. The electromechanical resonator according to claim 29 further comprising:

a first coupling member for coupling to the first and second vibratable plates, and destructively combining acoustic energy emitted by the first and second vibrational plates.

35. The electromechanical resonator according to claim 34 wherein:

the first coupling member is coupled to the first side edge of the first vibratable plate and the first side edge of the second vibratable plate.

36. The electromechanical resonator according to claim 35 wherein:

the bottom edge of the first vibratable plate is connected to the die;

the top edge and the second side edge of the first vibratable plate are free;

the bottom edge of the second vibratable plate is connected to the die;

the top edge and second side edge of the second vibratable plate are free;

the first vibratable plate is characterized by a length L measured along the top edge of the first vibratable plate, and a height H measured along the first side edge of the first vibratable plate;

the second vibratable plate is characterized by the length L, and the height H; and

the first and second vibratable plates vibrate in a mode characterized by;

a first number N of nodal lines that are substantially aligned with the height of the first and second vibratable plates; and

a second number M of nodal lines that are substantially aligned with the length of the first and second vibratable plates; and

the quantity;

$\frac{\left(2·<br><br>N-1\right)·<br><br>H}{\left(2·<br><br>M-1\right)·<br><br>L}$

is at least about three.

37. The electromechanical resonator according to claim 35 wherein the first coupling member comprises:

a coupling plate.

38. The electromechanical resonator according to claim 35 further comprising:

a second coupling member that is coupled to the second side edge of the first vibratable plate and the second side edge of the second vibratable plate, for coupling the first and second vibratable plates and destructively combining acoustic energy emitted by the first and second vibrational plates.

39. The electromechanical resonator according to claim 38 wherein:

the bottom edge of the first vibratable plate is connected to the die;

the top edge of the first vibratable plate is free;

the bottom edge of the second vibratable plate is connected to the die;

the top edge of the second vibratable plate is free;

the first vibratable plate is characterized by a length L measured along the top edge of the first vibratable plate, and a height H measured along the first side edge of the first vibratable plate;

the second vibratable plate is characterized by the length L, and the height H; and

the first and second vibratable plates vibrate in a mode characterized by;

a first number N of nodal lines that are substantially aligned with the height of the first and second vibratable plates; and

a second number M of nodal lines that are substantially aligned with the length of the first and second vibratable plates; and

the quantity;

$\frac{N·<br><br>H}{\left(2·<br><br>M-1\right)·<br><br>L}$

is at least about three.

40. The electromechanical resonator according to claim 35 further comprising:

a recess in the semiconductor die that has a peripheral wall;

wherein, the first vibratable plate, the second vibratable plate, and the first coupling member are located in the recess.

41. The electromechanical resonator according to claim 40 further comprising:

a first electrical crossover coupled between the peripheral wall and the first coupling member for coupling one or more electrical signals from the die major surface to the first coupling member.

42. The electromechanical resonator according to claim 41 further comprising:

a second coupling member that is coupled to the second side edge of the first vibratable plate and the second side edge of the second vibratable plate, for coupling the first and second vibratable plates and destructively combining acoustic energy emitted by the first and second vibrational plates; and

a second electrical crossover coupled between the peripheral wall and the second coupling member for coupling one or more electrical signals from the die major surface to the second coupling member.

43. The electromechanical resonator according to claim 42 wherein:

the first conductive pathway runs from the die major surface, over the first electrical crossover, over the first coupling member and onto the first vibratable plate; and

the second conductive pathway runs over the second electrical crossover, over the second coupling member and onto the second vibratable plate.

44. The electromechanical resonator according to claim 40 further comprising:

a third vibratable plate having;

a third vibratable plate major surface characterized by a third vibratable plate major surface normal that is substantially perpendicular to the die surface normal;

a first side edge;

a second side edge;

a bottom edge; and

a top edge; and

a fourth vibratable plate having;

a fourth vibratable plate major surface characterized by a fourth vibratable plate major surface normal that is substantially perpendicular to the die surface normal;

a first side edge;

a second side edge;

a bottom edge; and

a top edge; and

a second coupling member;

wherein,

the first side edge of the third vibratable plate and the first side edge of the fourth vibratable plate are coupled to the first coupling member;

the second side edge of the third vibratable plate and the second side edge of the fourth vibratable plate are coupled to the second coupling member;

the first, second, third and fourth vibratable plates are capable of vibrating at the first frequency;

a first distance between the first side edge of the first vibratable plate, and the first side edge of the third vibratable plate is about ½

the wavelength;

a second distance between the first side edge of the second vibratable plate, and the first side edge of the fourth vibratable plate is about ½

the wavelength;

whereby, acoustic energy emitted by the first, second, third, and fourth vibratable plates is destructively combined by the first and second coupling members.

45. The electromechanical resonator according to claim 44 further comprising:

a first electrical crossover for coupling signals from the die major surface to the first coupling member.

46. The electromechanical resonator according to claim 44 wherein the second conductive pathway includes:

a first branch that runs from the die major surface over the first electrical crossover to the first coupling member;

a second branch that runs from first electrical crossover over the first coupling member and onto the second vibratable plate; and

a third branch that runs from the first electrical crossover over the first coupling member and onto the third vibratable plate.

47. The electromechanical resonator according to claim 46 further comprising:

a second electrical crossover;

wherein the first conductive pathway includes;

a first branch that extends from the die major surface over the second electrical crossover, to the second coupling member;

a second branch that extends from the second electrical crossover, over the second coupling member and onto the first vibratable plate; and

a third branch that extends from the second electrical crossover over the second coupling member and onto the fourth vibratable plate.

48. The electromechanical resonator according to claim 46 further comprising:

a second electrical crossover over which the first conductive pathway runs;

a third electrical crossover that extends from the peripheral wall to the second coupling member;

a third conductive pathway that runs over the third electrical crossover, along the second coupling member, and onto the fourth vibratable plate;

a fourth electrical cross over that extends from the peripheral wall to the second coupling member; and

a fourth conductive pathway that includes;

a first branch that runs from the die major surface over the fourth electrical crossover to the second coupling member;

a second branch that runs from fourth electrical crossover over the second coupling member and onto the second vibratable plate; and

a third branch that runs from the fourth electrical crossover over the second coupling member and onto the third vibratable plate.

49. An electromechanical system comprising:

a semiconductor die including;

a first vibratable plate including;

a first vibratable plate electrode;

a second vibratable plate that is located proximate the first vibratable plate and includes;

a second vibratable plate electrode;

a first fixed electrode located on a first side of the first and second vibratable plates;

a second fixed electrode located on a second side of the first and second vibratable plates opposite the first side;

one or more biasing circuits for applying a first bias to the first vibratable plate electrode, applying a second bias to the second vibratable plate electrode, applying a third bias to the first fixed electrode, and applying a fourth bias to the second fixed electrode, wherein the first bias, second bias, third bias, and fourth bias are selected so that electrostatic forces on the first and second vibratable plates that are due to the first bias, second bias, third bias, and fourth bias are balanced.

50. The electromechanical system according to claim 49 wherein:

the first vibratable plate and the second vibratable plate are dimensioned to vibrate at a predetermined frequency that corresponds to a wavelength of acoustic waves in the die; and

the first and second vibratable plates are spaced apart by less than one-tenth of the wavelength.

51. A method of signal processing comprising the steps of:

biasing an electrode of a first vibratable plate to a first voltage;

applying a signal that includes a periodic signal component to an electrode of a second vibratable plate that is proximate to the first vibratable plate;

whereby, the signal establishes an attractive electric force between the first vibratable plate and the second vibratable plate that causes the first and second vibratable plates to vibrate in such a manner as to mirror each other, such that acoustic energy radiation from the first and second vibratable plates is cancelled by destructive interference.

52. The method according to claim 51 further comprising the step of:

biasing the electrode of the second vibratable plate to a second voltage.

53. The method according to claim 51 wherein:

the first vibratable plate comprises a first vibratable plate that is mechanically coupled to a die through a coupling member; and

the second vibratable plate comprises a second vibratable plate that is mechanically coupled to the die through the coupling member;

whereby, acoustic energy radiation from the first and second vibratable is cancelled by destructive interference in the coupling member.

54. A method of signal processing comprising the steps of:

biasing an electrode of a first vibratable plate to a first voltage;

biasing an electrode of a second vibratable plate to a second voltage;

biasing a fixed electrode that is located between the first vibratable plate and the second vibratable plate to a third voltage;

applying a signal that includes a periodic signal component to the fixed electrode;

whereby, the signal establishes a first attractive electric force between the first vibratable plate and the fixed electrode, and a second attractive force between the second vibratable plate and the fixed electrode, that cause the first and second vibratable plates to vibrate in such a manner as to mirror each other such that acoustic radiation from the first and second vibratable plates is cancelled by destructive interference.

55. The method according to claim 54 wherein:

the first voltage is substantially equal to the second voltage.