ELECTROMECHANICAL RESONATOR AND METHOD OF OPERATING SAME
An electromechanical resonator includes a substrate (150, 450), an anchor (110, 510, 810) coupled to the substrate, a beam (120, 620, 1020, 1120, 1220, 1420) coupled to the anchor and suspended over the substrate, and a drive electrode (130, 435, 630, 930, 933, 935, 1030, 1035, 1130, 1135, 1435) coupled to the substrate and separated from the beam by a gap (140, 445, 640, 1040, 1045, 1140, 1145, 1445). The beam has a first surface (321, 621, 1021, 1121), a second surface (322, 622), and a third surface (323, 623, 1023, 1123, 1223, 1423). The first surface defines a width and a height, the second surface defines the height and a length, and the third surface defines the length and the width. The width, height, and length are substantially mutually perpendicular, and the beam resonates substantially only in compression mode and substantially only along an axis defined by the length.
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This invention relates generally to resonators, and relates more particularly to electromechanical resonators in semiconductor components.
BACKGROUND OF THE INVENTIONMicro-Electro-Mechanical Systems (MEMS) is the integration of mechanical elements and electronics on a common substrate, allowing the realization of a complete system on a single chip. MEMS resonators are passive elements that possess a high quality factor (Q) and that can be used to integrate filtering, oscillator, and other functions on a single chip for applications such as wireless communications systems. As an example, MEMS resonators can advantageously be used at intermediate frequency (IF) and radio frequency (RF) in communications systems based on superheterodyne, quasi-direct conversion, and direct conversion architectures. A MEMS resonator can replace discrete elements, active circuitry, and/or inductor-capacitor (LC) resonators and provide the same functionality with a higher Q, lower power consumption, lower noise, and lower parts count, thus enabling systems with higher performance at lower cost. In existing MEMS resonators, however, the electromechanical coupling decreases as the frequency of the resonator increases, meaning such resonators are increasingly harder to drive at higher frequencies. Accordingly, a need exists for a resonator in which the electromechanical coupling is independent of the resonator frequency.
BRIEF DESCRIPTION OF THE DRAWINGSThe invention will be better understood from a reading of the following detailed description, taken in conjunction with the accompanying figures in the drawings in which:
For simplicity and clarity of illustration, the drawing figures illustrate the general manner of construction, and descriptions and details of well-known features and techniques may be omitted to avoid unnecessarily obscuring the invention. Additionally, elements in the drawing figures are not necessarily drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve understanding of embodiments of the present invention. The same reference numerals in different figures denote the same elements.
The terms “first,” “second,” “third,” “fourth,” and the like in the description and in the claims, if any, are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, capable of operation in sequences other than those illustrated or otherwise described herein. Furthermore, the terms “comprise,” “include,” “have,” and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements is not necessarily limited to those elements, but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.
The terms “left,” “right,” “front,” “back,” “top,” “bottom,” “over,” “under,” and the like in the description and in the claims, if any, are used for descriptive purposes and not necessarily for describing permanent relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, capable of operation in other orientations than those illustrated or otherwise described herein. The term “coupled,” as used herein, is defined as directly or indirectly connected in an electrical or non-electrical manner.
DETAILED DESCRIPTION OF THE DRAWINGS Referring now to the figures,
The electromechanical coupling and the frequency of electromechanical resonator 100 are independent of each other, and the same is true of each of the other electromechanical resonators described herein. This independence of electromechanical coupling and frequency allows each electromechanical resonator according to embodiments of the invention to be driven at higher frequencies than are possible with existing resonators. More specifically, in at least one embodiment, the frequency of the resonance is inversely proportional to the dimension of the beam in which the beam resonates (the resonance dimension), but does not depend on any other dimension of the beam. On the other hand, the electromechanical coupling of the electromechanical resonator depends on a dimension of the beam other than the resonance dimension and does not depend on the resonance dimension. Accordingly, for each of the electromechanical resonators described herein, the frequency of the resonance can be increased without decreasing the electromechanical coupling. As an example, in the embodiment illustrated in
The biasing of drive electrode 130 (
Substrate 150 can comprise silicon, and anchor 110, beam 120, and drive electrode 130 can comprise doped polysilicon. Alternatively, substrate 150 can comprise another material, such as ceramic, glass, a semiconductor material, or the like, and beam 120 and drive electrode 130 can comprise another electrically conductive material, such as silicon, metal, or the like, or any combination of an electrically conductive and an electrically non-conductive material such as silicon oxide, silicon nitride, or the like. In one embodiment, anchor 110 also comprises an electrically conductive material.
The biasing of drive electrodes 430 and 435 and of beam 420, e.g., via anchor 510, will force surfaces 421 and 426 of beam 420 to contract toward and expand away from drive electrodes 430 and 435, respectively, along an axis substantially parallel to surface 423 and substantially perpendicular to surfaces 421 and 426, and to resonate substantially only in compression mode. In one embodiment, the biasing of drive electrodes 430 and 435 and of beam 420 can be superimposed with an RF signal in order to bring about the contraction-mode resonance.
The biasing of drive electrodes 430 and 435 in a polarity that is the same as the polarity of the bias applied to beam 420, e.g., via anchor 510, causes surfaces 421 and 426 of beam 420 to contract toward each other along an axis substantially parallel to surface 423 and substantially perpendicular to surfaces 421 and 4256. Surfaces 421 and 426 of beam 420 expand, along the same axis, toward drive electrodes 430 and 435, respectively, to the original length of beam 420 as soon as the contraction caused by drive electrodes 430 and 435 is complete.
For simplicity of illustration, additional features of electromechanical resonator 600, such as a substrate, an anchor, and optional indentations, are not shown in
It will be understood that the difference between length 673 and length 674 is very small. As an example, the difference in length may represent twenty percent or less of length 673 or of length 674. Accordingly, electromechanical resonator 600 may exhibit a resonance peak in frequency space that is broader than the resonance peak in frequency space of electromechanical resonator 100, first shown in
Some alternate configurations of beams, drive electrodes, and anchors that may also affect resonance peaks in frequency space are shown in
Electromechanical resonator 700 further comprises an anchor 711, an anchor 712, and an anchor 713. Beam 720 is coupled to anchor 711 at the surface opposite surface 723, and is coupled to anchors 712 and 713 at surface 723. In other embodiments, electromechanical resonator 700 can comprise more or fewer anchors than the number of anchors shown in
Electromechanical resonator 800 further comprises an anchor 811, an anchor 812, and an anchor 813. Beam 820 is coupled to anchor 811 at surface 822, and is coupled to anchors 812 and 813 at the surface opposite surface 822. Free ends 860 of anchors 810, 811, 812, and 813 may be coupled to non-illustrated support blocks, which support blocks may be located above and/or rest on substrate 850. Anchors 810, 811, 812, and 813 are sized such that they do not bend or flex in a direction perpendicular to surface 823 of beam 820. The non-illustrated support blocks may provide an electrical connection to beam 820 through anchors 810, 811, 812, and 813.
In other embodiments, electromechanical resonator 800 can comprise more or fewer anchors than the number of anchors shown in
It will be understood by one of ordinary skill in the art that the characteristic of multiple drive electrodes adjacent to at least one single surface of a beam of an electromechanical resonator, which characteristic is first shown in
A length of beam 1020 is measured between surface 1021 and surface 1026, and a width of beam 1020 is measured between surface 1022 and surface 1027. As illustrated in
A length of beam 1120 is measured between surface 1121 and surface 1126, and a width of beam 1120 is measured between surface 1122 and surface 1127. As illustrated in
Electromechanical resonator 1500 further comprises an anchor 1511, an anchor 1512, and an anchor 1513. Beam 1520 is coupled to anchor 1511 at the surface opposite surface 1523, and is coupled to anchors 1512 and 1513 at surface 1523. In other embodiments, electromechanical resonator 1500 can comprise more or fewer anchors than the number of anchors shown in
Anchor 1512 comprises a plurality of anchor segments 1518, and anchor 1513 comprises a plurality of anchor segments 1519. Electromechanical resonator 1500 further comprises a plurality of anchor gaps 1528 and 1529. Adjacent ones of anchor segments 1518 are separated by one of the plurality of anchor gaps 1528, and adjacent ones of anchor segments 1519 are separated by one of the plurality of anchor gaps 1529. Anchors 1512 and 1513, being segmented as shown and described, serve to reduce the amount of energy lost to absorption within anchor 110 in a manner similar to indentations 125 and/or indentations 126, first shown in
A step 1620 of method 1600 is to provide an anchor coupled to the substrate. As an example, the anchor can be similar to anchor 110, first shown in
A step 1630 of method 1600 is to provide a beam coupled to the anchor and suspended over the substrate by the anchor, the beam comprising a first surface, a second surface, and a third surface, wherein the first surface defines a width and a height, the second surface defines the height and a length, and the third surface defines the length and the width. As an example, the beam can be similar to beam 120, first shown in
A step 1640 of method 1600 is to provide a drive electrode coupled to the substrate and separated from the beam by a gap. As an example, the drive electrode can be similar to drive electrode 130, first shown in
A step 1650 of method 1600 is to cause the beam to resonate substantially only in a compression mode and substantially only along an axis defined by the length. As an example, the beam may be caused to so resonate by biasing the drive electrode and the beam, e.g., via the anchor. Such biasing forces the beam to move toward or away from the drive electrode(s), and facilitates the resonance substantially only in compression mode. In one embodiment, the biasing of the drive electrode and the beam can be superimposed with an RF signal in order to bring about the contraction-mode resonance.
Although the invention has been described with reference to specific embodiments, it will be understood by those skilled in the art that various changes may be made without departing from the spirit or scope of the invention. Various examples of such changes have been given in the foregoing description. Accordingly, the disclosure of embodiments of the invention is intended to be illustrative of the scope of the invention and is not intended to be limiting. It is intended that the scope of the invention shall be limited only to the extent required by the appended claims. For example, to one of ordinary skill in the art, it will be readily apparent that the electromechanical resonator discussed herein may be implemented in a variety of embodiments, and that the foregoing discussion of certain of these embodiments does not necessarily represent a complete description of all possible embodiments.
Additionally, benefits, other advantages, and solutions to problems have been described with regard to specific embodiments. The benefits, advantages, solutions to problems, and any element or elements that may cause any benefit, advantage, or solution to occur or become more pronounced, however, are not to be construed as critical, required, or essential features or elements of any or all of the claims.
Moreover, embodiments and limitations disclosed herein are not dedicated to the public under the doctrine of dedication if the embodiments and/or limitations: (1) are not expressly claimed in the claims; and (2) are or are potentially equivalents of express elements and/or limitations in the claims under the doctrine of equivalents.
Claims
1. An electromechanical resonator comprising:
- a substrate;
- an anchor coupled to the substrate;
- a beam coupled to the anchor and suspended over the substrate by the anchor, the beam comprising a first surface, a second surface, and a third surface; and
- a drive electrode coupled to the substrate and separated from the beam by a gap,
- wherein: the first surface defines a width and a height, the second surface defines the height and a length, and the third surface defines the length and the width; and the beam resonates substantially only in a compression mode and substantially only along an axis defined by the length.
2. The electromechanical resonator of claim 1 wherein:
- the width, height, and length are substantially mutually perpendicular to each other.
3. The electromechanical resonator of claim 1 wherein:
- the drive electrode is adjacent to the first surface; and
- the beam is coupled to the anchor at a surface of the beam opposite the first surface.
4. The electromechanical resonator of claim 3 wherein:
- the beam comprises at least one indentation in the surface opposite the first surface.
5. The electromechanical resonator of claim 3 wherein:
- the anchor comprises at least one indentation adjacent to the surface opposite the first surface.
6. The electromechanical resonator of claim 1 wherein:
- the drive electrode comprises a first drive electrode;
- the electromechanical resonator further comprises a second drive electrode;
- the first drive electrode is adjacent to the first surface;
- the second drive electrode is adjacent to a surface of the beam opposite the first surface;
- the anchor is located between the substrate and the beam; and
- the beam is coupled to the anchor at a surface of the beam opposite the third surface.
7. The electromechanical resonator of claim 6 wherein:
- the electromechanical resonator further comprises: a second anchor coupled to the beam at the third surface.
8. The electromechanical resonator of claim 1 wherein:
- the drive electrode comprises a first drive electrode;
- the electromechanical resonator further comprises a second drive electrode;
- the first drive electrode is adjacent to the first surface;
- the second drive electrode is adjacent to a surface of the beam opposite the first surface; and
- the beam is coupled to the anchor at the third surface.
9. The electromechanical resonator of claim 7 wherein:
- a line perpendicular to the third surface defines a vertical direction; and
- the anchor and the second anchor are aligned in the vertical direction.
10. The electromechanical resonator of claim 7 wherein:
- the anchor comprises a plurality of anchor segments and a plurality of anchor gaps; and
- adjacent ones of the anchor segments are spaced apart by one of the plurality of anchor gaps.
11. The electromechanical resonator of claim 6 wherein:
- the length of the third surface varies across the width of the third surface.
12. The electromechanical resonator of claim 11 wherein:
- the anchor comprises a plurality of anchor segments and a plurality of anchor gaps; and
- adjacent ones of the anchor segments are spaced apart by one of the plurality of anchor gaps.
13. The electromechanical resonator of claim 1 wherein:
- the drive electrode comprises a first drive electrode;
- the electromechanical resonator further comprises a second drive electrode;
- the first drive electrode is adjacent to the first surface;
- the second drive electrode is adjacent to a surface of the beam opposite the first surface; and
- the beam is coupled to the anchor at the second surface.
14. The electromechanical resonator of claim 13 wherein:
- the electromechanical resonator further comprises: a second anchor coupled to the beam at a surface of the beam opposite the second surface.
15. The electromechanical resonator of claim 14 wherein:
- a line perpendicular to the second surface defines a horizontal direction; and
- the anchor and the second anchor are aligned in the horizontal direction.
16. The electromechanical resonator of claim 1 wherein:
- the drive electrode comprises a first drive electrode;
- the electromechanical resonator further comprises a second drive electrode;
- the first drive electrode is adjacent to the first surface;
- the second drive electrode is adjacent to a surface of the beam opposite the first surface; and
- the beam is coupled to the anchor at a surface of the beam opposite the second surface.
17. The electromechanical resonator of claim 13 wherein:
- the length of the third surface varies across the width of the third surface.
18. The electromechanical resonator of claim 1 wherein:
- the length of the third surface varies across the width of the third surface; and
- the beam is coupled to the anchor at a surface opposite the first surface.
19. The electromechanical resonator of claim 18 wherein:
- the beam comprises at least one indentation in the surface opposite the first surface.
20. The electromechanical resonator of claim 18 wherein:
- the anchor comprises at least one indentation adjacent to the surface opposite the first surface.
21. A MEMS resonator comprising:
- a semiconductor substrate having a substrate surface;
- an anchor coupled to the substrate;
- a beam coupled to the anchor and suspended over the substrate surface by the anchor, the beam comprising a first surface substantially perpendicular to the substrate surface, a second surface substantially perpendicular to the substrate surface, and a third surface substantially parallel to the substrate surface;
- a first drive electrode coupled to the substrate and separated from the beam by a first gap; and
- a second drive electrode coupled to the substrate and separated from the beam by a second gap,
- wherein: the first drive electrode is adjacent to the first surface; the second drive electrode is adjacent to a surface of the beam opposite the first surface; the first surface defines a width and a height, the second surface defines the height and a length, and the third surface defines the length and the width; the width, height, and length are substantially mutually perpendicular to each other; and the beam resonates substantially only in a compression mode and substantially only along an axis defined by the length.
22. The MEMS resonator of claim 21 wherein:
- the anchor is located between the substrate and the beam; and
- the beam is coupled to the anchor at a surface of the beam opposite the third surface.
23. The MEMS resonator of claim 22 wherein:
- the anchor comprises a plurality of anchor segments and a plurality of anchor gaps; and
- adjacent ones of the anchor segments are spaced apart by one of the plurality of anchor gaps.
24. The MEMS resonator of claim 22 wherein:
- the MEMS resonator further comprises: a second anchor coupled to the beam at the third surface.
25. The MEMS resonator of claim 24 wherein:
- a line perpendicular to the third surface defines a vertical direction; and
- the anchor and the second anchor are aligned in the vertical direction.
26. The MEMS resonator of claim 24 wherein:
- at least one of the first anchor and the second anchor comprises a plurality of anchor segments and a plurality of anchor gaps; and
- adjacent ones of the anchor segments are spaced apart by one of the plurality of anchor gaps.
27. The MEMS resonator of claim 21 wherein:
- the length of the third surface varies across the width of the third surface.
28. The MEMS resonator of claim 21 wherein:
- the beam is coupled to the anchor at the second surface.
29. The MEMS resonator of claim 28 wherein:
- the MEMS resonator further comprises: a second anchor coupled to the beam at a surface of the beam opposite the second surface.
30. The MEMS resonator of claim 29 wherein:
- a line perpendicular to the second surface defines a horizontal direction; and
- the anchor and the second anchor are aligned in the horizontal direction.
31. A method of operating an electromechanical resonator, the method comprising:
- providing a substrate;
- providing an anchor coupled to the substrate;
- providing a beam coupled to the anchor and suspended over the substrate by the anchor, the beam comprising a first surface, a second surface, and a third surface, wherein the first surface defines a width and a height, the second surface defines the height and a length, and the third surface defines the length and the width;
- providing a drive electrode coupled to the substrate and separated from the beam by a gap; and
- causing the beam to resonate substantially only in a compression mode and substantially only along an axis defined by the length.
Type: Application
Filed: Aug 28, 2003
Publication Date: Mar 3, 2005
Applicant:
Inventors: Peter Zurcher (Phoenix, AZ), Rashaunda Henderson (Chandler, AZ), Sergio Pacheco (Chandler, AZ)
Application Number: 10/652,406