Apparatus and method for anchoring electrodes in MEMS devices

One or more electrodes that interact with a movable mass in a MEMS device are anchored or otherwise supported from both the top and bottom and optionally also from one or more of the lateral sides other than the transduction side (i.e., the side of the electrode facing the mass) in order to severely restrict movement of the electrodes such as from interaction with the mass and/or external forces.

TECHNICAL FIELD

The invention generally relates to MEMS devices and, more particularly, the invention relates to anchoring of electrodes in MEMS devices.

BACKGROUND ART

In many MEMS device (e.g., MEMS gyroscopes, accelerometers, resonators, switches, and other types of devices), movement of a mass may be driven, adjusted, and/or sensed using one or more electrodes placed at least partially adjacent to the mass. Such interaction between the electrode and the mass may be electrostatic, although other types of configurations may be used (e.g., piezoelectric). For example, as shown schematically inFIG. 1, an electrode604may be placed adjacent to a mass602in substantially the same plane as the mass602.FIG. 1Ashows a side view andFIG. 1Bshows a top view of an exemplary mass/electrode system. Typically, the electrode604is formed on or otherwise anchored to an underlying substrate or support structure (not shown). The electrode604also may be attached or otherwise anchored laterally to a side structure. The electrode604may be constructed in whole or in part from the same material as the mass602(e.g., the mass602and electrode604may be formed from the top silicon layer of a silicon-on-insulator wafer) and/or may include other materials/layers (e.g., formed by deposition of one or more materials on the silicon wafer).

Ideally, the electrode604is perfectly stationary, with a precise gap between the electrode604and the stationary mass602. In practice, however, any of a number of factors can cause the electrode604to move, even slightly, and such movements can introduce errors into the system. For example, the electrode604may deflect due to movement of the device (e.g., an acceleration) and/or electrostatic interaction of the electrode604with the mass602. Among other things, the electrode may move or pivot out-of-plane as depicted by arrows605and606, may move toward or away from the mass603in-plane as depicted by arrows607, may pivot in-plane as depicted by arrows608and609, and/or may translate sideways within the plane as depicted by arrows612.

Of course, other mass/electrode configurations are often used in MEMS devices, such as electrodes placed entirely or partially above or below the mass, or electrode “fingers” interdigitated with corresponding structures on the mass. Furthermore, other types of electrodes are often used in MEMS devices, such as piezoelectrically coupled electrodes. Such electrodes are similarly subject to movements that can cause erroneous behavior, such as increased sensitivity to external forces (i.e., unwanted forces such as unwanted acceleration), erroneous signals, and reduced performance in MEMS devices such as gyroscopes, accelerometers, and other types of MEMS devices.

U.S. Pat. No. 7,134,340, which is hereby incorporated herein by reference in its entirety, discloses elongated finger structures (e.g., drive and/or sense electrodes) including elongated or multiple anchors to mitigate certain types of electrode movements, particularly pivoting/twisting movements in-plane about the anchor point.

Bulk acoustic wave (“BAW”) gyroscope use has increased in recent years. This trend is driven by their many benefits including, among other things, their high gain factor, which causes them to use less power than conventional gyroscopes. In addition, such gyroscopes generally cost less to manufacture.

To those ends, many bulk acoustic wave gyroscopes known to the inventors have a proof mass (with any polygon shape, e.g., circular or rectangular) with a crystal lattice that, during either or both an actuation or detection phase, vibrates/resonates at a very high frequency, typically in the megahertz range. This is in contrast to gyroscopes having a mass mechanically moving back and forth about a substrate in both phases. When the crystal lattice of the mass vibrates, the mass is considered to be operating in a “bulk” mode.

Some exemplary BAW gyroscope configurations are discussed in Johari, H., Micromachined Capacitive Silicon Bulk Acoustic Wave Gyroscopes, Georgia Institute of Technology, December 2008 and in the following U.S. patents and published patent applications: U.S. Pat. No. 7,895,892, U.S. Pat. No. 7,874,209, U.S. Pat. No. 7,543,496, U.S. Pat. No. 7,427,819, US 2009/0266162, US 2008/0180890, US 2008/0054759, US 2007/0284971, and US 2006/0238078, each of which is hereby incorporated herein by reference in its entirety.

In addition to being subject to external forces, the drive and sense electrodes in shell-type MEMS gyroscopes (e.g., flexure mode and BAW mode gyroscopes) may be subject to very high forces due in part to the high frequencies of operation of such devices, and such forces can deflect the electrodes which in turn can distort the angular rate sensitivity of the gyroscope, causing errors in the system.

SUMMARY OF EXEMPLARY EMBODIMENTS

In embodiments of the present invention, one or more electrodes that interact with a movable mass in a MEMS device are anchored or otherwise supported from both the top and bottom and optionally also from one or more of the lateral sides other than the transduction side (i.e., the side of the electrode facing the mass) in order to severely restrict movement of the electrodes such as from interaction with the mass and/or external forces. Constraint of the electrodes using top and bottom anchoring with optional side anchoring may be useful in MEMS devices generally but may be particularly useful in devices where the electrodes are subject to very high forces, such as for drive and/or sense electrodes in shell-type gyroscopes (e.g., BAW gyroscopes) that operate at very high frequencies (e.g., in the megahertz range) with very small gaps between the electrodes and the mass (e.g., in the nanometer range, particularly 100 nm-200 nm) or flexure gyroscopes that operate in the kilohertz range, where such constraint generally reduces deflection of electrodes from external forces (e.g., movement of the MEMS device) and/or internal forces (e.g., interaction of the electrodes with the movable mass) and there generally improves sensitivity and overall performance and also may allow for smaller gaps between the electrodes and surrounding structures such as the movable mass, adjacent electrodes, etc. Constraint of the electrodes using top and bottom anchoring with optional side anchoring may be used in combination with top and bottom anchoring of the mass to further mitigate erroneous behavior.

In accordance with aspect of the invention, a MEMS device includes a movable mass and at least one electrode configured to interact with the mass, the electrode having a top surface substantially parallel with a top surface of the movable mass and a bottom surface substantially parallel with a bottom surface of the movable mass, wherein the top surface of the electrode is anchored to a overlying support structure and wherein the bottom surface of the electrode is anchored to an underlying support structure in order to constrain movement of the electrode.

In various alternative embodiments of such a MEMS device, the at least one electrode may be configured to interact with the mass electrostatically. The electrode may be anchored to the top support structure via a plurality of top anchors and may be anchored to the bottom support structure via a plurality of bottom anchors. The electrode may be further anchored by at least one surface other than the top surface and bottom surface to at least one side support structure. The electrode may be formed on an electrode support structure, in which case the electrode may include at least one side anchor through at least a portion of the electrode support structure. The electrode support structure and the mass may be fabricated from a common layer of material, such as from the top silicon layer of an SOI wafer or from a common deposited layer of material, or may be made from different materials/layers. Electrodes may be configured for driving and/or sensing movement of the mass. The top support structure may be a device cap. The bottom support structure may be a device substrate or cap.

Embodiments of the above-described invention may include virtually any type of MEMS device, including MEMS gyroscopes, accelerometers, resonators, and switches, to name but a few.

In certain embodiments, a MEMS gyroscope includes a resonant mass and at least one electrode configured to interact with the mass, the electrode having a top surface substantially parallel with a top surface of the movable mass and a bottom surface substantially parallel with a bottom surface of the movable mass, wherein the top surface of the electrode is anchored to a overlying support structure and wherein the bottom surface of the electrode is anchored to an underlying support structure in order to constrain movement of the electrode.

In various alternative embodiments of such a MEMS gyroscope, the at least one electrode may be configured to interact with the mass electrostatically. The electrode may be anchored to the top support structure via a plurality of top anchors and may be anchored to the bottom support structure via a plurality of bottom anchors. The electrode may be further anchored by at least one surface other than the top surface and bottom surface to at least one side support structure. The electrode may be formed on an electrode support structure, in which case the electrode may include at least one anchor through at least a portion of the electrode support structure. The anchor through at least a portion of the electrode support structure may be formed by trench refilling with a conductive or non-conductive material. The electrode support structure and the mass may be fabricated from a common layer of material, such as from the top silicon layer of an SOI wafer or from a common deposited layer of material. Electrodes may be configured for driving and/or sensing movement of the mass. The top support structure may be a device cap. The bottom support structure may be a device substrate or cap.

The MEMS gyroscope may be a shell-type gyroscope in which the resonant mass is configured to resonate in a flexure mode or bulk mode in response to receipt of an electrostatic signal, and the at least one electrode may be configured for at least one of driving and sensing movement of the resonant mass. The top surface of the resonant mass may be anchored to an overlying support structure and the bottom surface of the resonant mass may be anchored to an underlying support structure in order to constrain movement of the resonant mass, in which case the top surface of the electrode and the top surface of the resonant mass may be anchored to the same overlying support structure or to different overlying support structures, and, similarly, the bottom surface of the electrode and the bottom surface of the resonant mass may be anchored to the same underlying support structure or to different underlying support structures.

Embodiments also may include a method for forming a MEMS device having a movable mass and at least one electrode configured to interact with the mass, the electrode having a top surface substantially parallel with a top surface of the movable mass and a bottom surface substantially parallel with a bottom surface of the movable mass the method including anchoring the top surface of the electrode to a overlying support structure and anchoring the bottom surface of the electrode to an underlying support structure in order to constrain movement of the electrode.

In alternative embodiments, the method may further include anchoring the electrode by at least one surface other than the top surface and bottom surface to at least one side support structure.

Additional embodiments may be disclosed and claimed.

It should be noted that the foregoing figures and the elements depicted therein are not necessarily drawn to consistent scale or to any scale. Unless the context otherwise suggests, like elements are indicated by like numerals.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

In embodiments of the present invention, one or more electrodes that interact with a movable mass in a MEMS device are anchored or otherwise supported from both the top and bottom and optionally also from one or more of the lateral sides other than the transduction side (i.e., the side of the electrode facing the mass) in order to severely restrict movement of the electrodes such as from interaction with the mass and/or external forces. Constraint of the electrodes using top and bottom anchoring with optional side anchoring may be useful in MEMS devices generally but may be particularly useful in devices where the electrodes are subject to very high forces, such as for drive and/or sense electrodes in shell-type gyroscopes (e.g., BAW gyroscopes) that operate at very high frequencies (e.g., in the megahertz range) with very small gaps between the electrodes and the mass (e.g., in the nanometer range, particularly 100 nm-200 nm) or flexure gyroscopes that operate in the kilohertz range, where such constraint generally reduces deflection of electrodes from external forces (e.g., movement of the MEMS device) and/or internal forces (e.g., interaction of the electrodes with the movable mass) and there generally improves sensitivity and overall performance and also may allow for smaller gaps between the electrodes and surrounding structures such as the movable mass, adjacent electrodes, etc. Constraint of the electrodes using top and bottom anchoring with optional side anchoring may be used in combination with top and bottom anchoring of the mass to further mitigate erroneous behavior.

FIG. 2schematically shows the electrode604anchored to an underlying (bottom) structure705by one or more bottom anchors704and anchored to an overlying (top) structure703by one or more top anchors702. Various embodiments may include multiple top and/or bottom anchors in order to further constrain the electrode604. Additionally or alternatively, various embodiments may use specially-shaped anchors (e.g., elongated or otherwise non-round anchors) to further constrain the electrode604.

It should be noted that one or both of the support structures703and705may support the mass602or may be separate from a mass support structure. In some embodiments, the bottom support705may be the substrate on which the remaining MEMS device structures are formed (e.g., the bottom silicon layer or oxide layer of an SOI wafer), while in other embodiments, the bottom support705may be a structure above the base substrate. Similarly, in some embodiments, the top support703may be a device cap or other top structure, while in other embodiments, the top support703may be a structure below the device cap or other top structure.

FIG. 2also shows the electrode604optionally anchored to a lateral (side) structure707by one or more side anchors706. Thus, certain embodiments include just top and bottom anchors while other embodiments include top, bottom, and side anchors, and a particular MEMS device may include one or more anchors with just top and bottom anchors and one or more anchors with top, bottom, and side anchors.

It should be noted that the anchors and other structures shown inFIG. 2are represented schematically, and no limitation is placed on the types of anchors and other structures including the materials from which they are made, the manner in which they are fabricated, and the manner in which they are interconnected or otherwise attached. Thus, any of a variety of techniques may be used to form an electrode anchored to top and bottom structures and optionally anchored to a side structure, such as, for example, micromachining techniques (e.g., material deposition, patterning, and etching processes), wafer bonding processes, conductive and non-conductive bonding techniques, and other fabrication techniques.

For example, anchors may be an integral part of the electrode604and/or the support structure(s). For example, as depicted schematically inFIG. 3, the electrode604may be an elongated electrode that couples with the top and bottom structures703and705. Alternatively, anchors may be formed on the electrode and coupled with the support structures, or anchors may be formed on the support structures and coupled with the electrode. Some or all of the anchors may be formed in-situ as part of the MEMS fabrication process onto, into, through, or partially through the electrode and/or support structure, in which case such anchors are generally considered to be self-aligning.

Some or all of the anchors may protrude at least partially into the electrode and/or support structure. For example,FIG. 4Ashows a top perspective view andFIG. 4Bshows a side cross-sectional view of an electrode604with the top anchors702protruding partially into the top structure703and the electrode604and with the bottom anchors704protruding partially into the bottom structure705and the electrode604.

Additionally or alternatively, some or all of the anchors may extend completely through the electrode, and some or all of the anchors may attach to the surface of the electrode and/or support structure. For example,FIG. 5Ashows a top perspective view andFIG. 5Bshows a side cross-sectional view of an electrode604with the top anchors702attached at the surface of the electrode and/or the surface of the top support structure703and with the bottom anchors704extending through the electrode604to or into the bottom support structure705.

In some embodiments, the electrode604may be formed on a structure at least partially in the same plane as the mass602. For example, as depicted schematically inFIGS. 6 and 7, the electrode604may be formed on structure606, which at least partially supports the electrode604to provide added constraint. InFIG. 6, the bottom anchor704extends through the structure606to the bottom support705, and an extended portion706provides additional side anchoring by virtue of being coupled to the structure606. InFIG. 7, the top and bottom anchors702and704are coupled directly to the top and bottom supports703and705, and an extended portion706provides additional side anchoring by virtue of being coupled to the structure606and also including an anchor708at least partially into or through the structure606, which also may be anchored to top and/or bottom structures. In certain embodiments, the structure606is formed from the same material layer as the mass602, such as, for example, the top silicon layer of an SOI wafer, although the structure606may be made from different materials/layers than that of the mass602. Anchors that extend through the silicon structure606(e.g., the bottom anchor704shown inFIG. 6or the anchor708shown inFIG. 7) may be referred to as through-silicon anchors and generally are formed at least in part by etching a trench through the structure606and refilling the trench with the anchor material, which may be conductive or not conductive (e.g., polysilicon or oxide).

Some or all of the anchors may be electrically isolated from the electrode604, the support structure703, the support structure705, and/or the structure606, e.g., using an insulating material (e.g., an oxide material), spacing, or other electrical or mechanical separation.

Illustrative embodiments are described below with reference to a shell-type gyroscope that is specially configured to mitigate the impact of linear acceleration on the determination of angular rotation. To that end, the gyroscope may have a side electrode that is anchored at up to all of its surfaces other than the transduction side. In addition, or alternatively, the gyroscope has a vibrating mass mechanically secured on both its top and bottom sides. Either or both of those sides may be secured with an anchor extending partly or fully through the vibrating mass. Details of illustrative embodiments are discussed below.

FIG. 8schematically shows a perspective view of a packaged inertial sensor10having a shell-type MEMS gyroscope12, such as a flexure based and/or bulk acoustic wave based gyroscope12(FIG. 9and others, discussed below), configured in accordance with illustrative embodiments of the invention. This package protects its interior gyroscope12from the environment. As shown, the package has a top portion14that connects with a bottom portion16to form an interior (not shown) for containing the gyroscope12. Although not necessary, some embodiments of the invention hermetically seal the package interior. Other embodiments of the package, however, do not provide a hermetic seal.

The package can be any of a variety of different types, such as, among other things, a pre-molded leadframe package, a substrate package, or a ceramic package (cavity or non-cavity packages). The top portion14and/or the bottom portion16can be planar or form a cavity. In either case, the top and bottom portions14and16should appropriately couple to protect the gyroscope12. For example, if the top portion14is flat, then the bottom portion16should have a cavity, or there should be some spacing apparatus to form the interior with an appropriate volume for containing the gyroscope12.

In alternative embodiments, the package is a conventional post-molded, plastic leadframe package. Specifically, as known by those skilled in the art, this relatively inexpensive package type molds plastic, in liquid form, directly around the gyroscope die12. This packaging process therefore can damage the gyroscope12if it is not properly sealed. In that case, the sensitive microstructure within the gyroscope12preferably is hermetically sealed or otherwise protected from the molding process.

The packaged inertial sensor10may be used in any number of different applications. For example, it could be part of a larger guidance system in an aircraft, or part of a satellite sensor in an automobile that cooperates with a stabilization system to maintain a smooth ride. To those ends, the packaged inertial sensor10has a plurality of interfaces (not shown) for communicating with exterior components.

To those ends, the packaged inertial sensor10may have a plurality of pins (not shown) on its bottom, top, and/or side surfaces for making a mechanical and electrical connection with an underlying system, such as a printed circuit board. Alternatively, the package may have a plurality of pads (not shown) for surface mounting the package to an underlying printed circuit board. Conventional soldering techniques should suffice to make this connection. The printed circuit board may have additional components that interact with the device to both control the gyroscope die12, and receive output signals indicating rotational acceleration of the overall system. For example, the printed circuit board also may have one or more application-specific integrated circuits (ASICs) and other circuit devices for controlling operation.

FIG. 9schematically shows a perspective view of a bulk acoustic wave gyroscope12configured in accordance with illustrative embodiments of the invention. The use of a bulk acoustic wave gyroscope for this illustrative embodiment is for convenience only with respect to electrode anchoring, and the present invention is not limited a bulk acoustic wave gyroscope or to specific concepts of operation described below for this illustrative embodiment, many of which are known generally in the art. This figure also has a partial cutaway view to show its vibrating proof mass18, and an outline of a member stabilizing a portion of that proof mass18(shown in dashed lines). The proof mass may be any polygon shape, e.g., circular or rectangular, and for convenience, may be referred to herein merely as a “mass,” “movable mass,” “vibrating mass,” “resonating body,” or the like. To further illustrate this embodiment,FIG. 10schematically shows a rotated, cross-sectional view of the bulk acoustic wave gyroscope ofFIG. 9along line3-3.

Specifically, this description uses the terms “top,” “bottom,” and the like for descriptive purposes only. Those terms are used with respect to the frame of reference ofFIG. 10.FIG. 9, however, is rotated 180 degrees (i.e., the top is down and the bottom is up) to better show the components. Accordingly, elements identified as “top” elements inFIG. 10, the correct orientation, are on the bottom side ofFIG. 9. For example,FIG. 9shows a top substrate40near the top of the structure, whileFIG. 10shows that same top substrate40near the bottom of the structure—becauseFIG. 10is rotated 180 degrees from the frame of reference figure.

Although the gyroscope12may be any type of gyroscope, the gyroscope12as depicted is a two dimensional gyroscope that measures rotational movement about the X-axis and Y-axis shown inFIG. 9. Accordingly, those skilled in the art refer to this type of gyroscope as an X/Y gyroscope, or a two dimensional gyroscope. It nevertheless should be reiterated that illustrative embodiments apply to gyroscopes that measure rotation about its other axes, such as the Z-axis alone, about the X-axis and Z-axis, or about all three axes, among other things. Accordingly, discussion of this specific two-dimensional bulk acoustic wave gyroscope12should not limit various embodiments of the invention.

The bulk acoustic wave gyroscope12has a generally planar mass18(noted above) that resonates in a flexure mode upon receipt of an electrostatic actuation signal. In particular, during the flexure mode, a bottom electrode22(discussed below) produces an electrostatic force that causes portions of the mass18to vibrate in out of the plane modes of the mass18. As a bulk acoustic wave gyroscope, however, the crystal lattice of the mass18itself vibrates in response to both a rotation and the continued actuation by the noted electrostatic signal. This is in contrast to other types of gyroscopes that have a shuttle/mass vibrating back and forth above a substrate during both actuation and detection phases. To that end, the embodiment shown inFIGS. 9 and 10has the above noted bottom electrode22for actuating/vibrating the mass18in a flexure mode at a preselected frequency. As known by those skilled in the art, this frequency can be quite high, such as on the order of about 100 Kilohertz to 100 Megahertz. This bottom electrode22also could be used for sensing.

The mass18is configured to vibrate in a predetermined manner at the known vibration frequency. For example, the vibration frequency may be the resonant frequency of the mass18itself. As such, the mass18vibrates in and out of plane in a non-uniform manner. Specifically, parts of the mass18may vibrate, while other parts of the mass18may remain substantially stable; i.e., the stable portions will vibrate at approximately zero Hertz. In other words, the stable portions substantially do not vibrate at all. The stable portions are known as “nodes24” and preferably are located generally symmetrically about the top and bottom faces of the mass18. For example, when vibrating at the resonant frequency, the bottom face of a 200 micron radius mass18may have a node24that forms a general ellipse about the center of the mass18. This elliptical node24may have a donut-shape, with a radius of between about ten and forty microns.

Rotation about the X-axis or Y-axis causes the shape of the mass18to change into a bulk mode or flexural mode shape, depending on the configuration of the gyroscope12. For example, if a 2-axis gyroscope12(i.e., X-Y gyroscope) is driven in flexural out of plane mode, then the sense mode may be in-plane bulk mode. As another example, if the gyroscope12is driven in bulk mode, then the sense mode may be a flexural out-of plane mode.

To detect any of these changes in shape, the gyroscope12has a plurality of side electrodes604generally circumscribing the mass18. For example, the cutaway ofFIG. 9shows four side electrodes604that can detect this change. More specifically, the side electrodes604form a variable capacitor with the side wall of the mass18. A change in the shape of the mass18, in the bulk mode, causes at least a portion of its side wall to change its position, thus changing the distance between it and the side electrode604. This changes the variable capacitance measured by the side electrode604. It is this capacitance change that provides the necessary movement information.

As known by those skilled in the art, the gyroscope12can operate in a flexural mode for actuation, and a bulk mode for sense. In yet other embodiments, the gyroscope can operate in a bulk mode for both actuation and sense.

A plurality of pads28formed on the same layer or different layer as the bottom electrode22electrically connect the bottom and top electrodes22and604to other circuitry. The bottom electrodes22can be independent of the top electrodes604, or have some connection or relationship, depending on the application. Off-chip circuitry or on-chip circuitry (not shown) thus detects the noted capacitance change as a changing signal, which includes the necessary information for identifying the degree and type of rotation. The larger system then can take appropriate action, such as controlling the rotation of tires in an automobile for stabilization control, or changing the trajectory of a guided missile.

Naturally, the mass18(i.e., the primary member, which can take on other forms, such as a spoke or ring) should be supported to function most effectively. To that end, the gyroscope12has a bottom substrate30mechanically bonded to the bottom of the mass18, and a top substrate40mechanically bonded to the top of the mass18. These and other bonds can be conductive or non-conductive, depending on the anticipated application. In illustrative embodiments, the bottom substrate30is formed from a single crystal silicon wafer and hermetically bonded to the layer having the bottom electrode22and pads28, which also is bonded to the top substrate40. For example, a ring of seal glass32, or glass frit or metal-metal bonding, can hermetically seal this bottom substrate30to the mass/electrode structure.

The bottom substrate30shown inFIGS. 9 and 10also has a bottom support portion34that mechanically connects to the bottom face of the mass18. In illustrative embodiments, the bottom support portion34is connected directly to the node24on the bottom face of the mass18. As noted above, this node24substantially does not vibrate, or has a very small vibration, when the mass18as actuated at its resonant frequency. The bottom support portion34can be formed from any number of materials. For example, this structure can be a solid piece of polysilicon, or a part of the layer forming the bottom electrode22and seal glass32. Alternatively, the bottom support can be formed from the same material as the bottom substrate30—e.g., one or more pedestals formed from a timed etch of the bottom substrate30. In that case, the bottom support is integral with the bottom substrate30, and formed from the same material as the bottom substrate30(e.g., single crystal silicon).

The substrates30and40can be connected to the mass18by a conductive or non-conductive bond. Alternatively, they could be connected to the mass18by a method of deposition that can create top or bottom anchors, or both top and bottom anchors. The anchors can have conductors that electrically connect with any or all of the electrodes22/604and/or the mass18. Moreover, in some embodiments, the bottom electrodes22are both mechanically and electrically isolated from the side electrodes604.

Conventional micromachining processes may form the mass18and layer immediately beneath the mass18in any number of known ways. For example, that portion of the gyroscope12may be formed from a micromachined silicon-on-insulator wafer (also known as an “SOT” wafer). In that case, the mass18may be formed from the top, single crystal silicon layer of the SOT wafer. Moreover, the side electrodes604may be formed from deposited polysilicon and electrically connected with the bond pads28, which may be formed from deposited metal.

As known by those skilled in the art, the top SOT layer is typically much thinner than the bottom layer36of the SOT wafer, which also is formed from single crystal silicon. The layer having the bottom electrode22(referred to as the “bottom layer36”), however, is thinner than the layer having the mass18(referred to as the “top layer38”). Although not necessary, illustrative embodiments thin this bottom layer36to reduce the profile of the overall sensor, and improve the performance of the bottom electrode22. For example, the mass18may have a thickness of about 50 microns, while the bottom electrode22may have a thickness of about the same thickness of the mass or less, e.g., about 40 microns.

AsFIGS. 10 and 11show, preferred embodiments form an anchor that extends from the side electrode in the Z-direction. Specifically, the side electrodes604shown inFIGS. 10 and 11have one or more anchors extending integrally from their bottom surfaces and onto or into the bottom substrate30or structures secured by the bottom substrate30. The side electrodes604also have similar anchors extending from their top surfaces to the top substrate40. InFIGS. 10 and 11, the portion of the electrode that is anchored to the top and bottom structures is highlighted. The top and bottom anchors are in addition to other anchors that can anchor from the side surface of the side electrodes604. Thus, the side electrodes604can be anchored from its top, bottom, and side surfaces, or some subset of those sides—and can be generally polygon shaped, e.g., donut shaped or rectangular shaped or round. Despite all these anchors, the sides of the side electrodes604facing the mass18(the “transduction side”) should have no anchors.

Illustrative embodiments form the electrodes604, mass18, and spaces between the mass18and electrodes604, among other things, to be self-aligning. To that end, as known by those skilled in the art, those features are formed from the same mask during fabrication.

The mass18can be secured to the top or bottom substrate40,30in any number of manners. For example, polysilicon anchors can extend from the bottom substrate30and through the mass18(e.g., seeFIGS. 12A and 12B, which show two different types of proof mass anchoring). These anchors can extend all the way up to the top surface of the mass18, or only partially through the profile of the mass18. In a similar manner, the anchors can extend from the top substrate40and through the mass18. These anchors, in either of the noted embodiments, can ensure rigidity of the support mechanism. They can be polygon shaped, e.g., donut shaped or rectangular shaped or round.FIGS. 12A and 12Balso show the side electrodes604anchored to the top substrate40and to an intermediate support structure705that is below the plane of the proof mass and above the plane of the bottom substrate30. One consequence of anchoring the electrode604to the intermediate support structure705rather than to the bottom substrate30is that the electrode604can be shortened and therefore will be stiffer and less prone to bending, thus further constraining the electrode.

FIG. 13shows the device ofFIG. 12Bin greater detail, with components labeled as inFIG. 7. Specifically, the top and bottom anchors702and704of each electrode604are coupled directly to the top and bottom supports703and705, and an extended portion706provides additional side anchoring by virtue of being coupled to the structure606(which in this example is formed from the same material layer as the mass602) and also including two through-silicon anchors708through the structure606, one of which connects to a base structure730and may in electrical connectivity with a bond pad for providing electrical connection to the electrode604. In this example, each electrode604is mechanically and/or electrically isolated from the structure606via a material720.

It should be noted that principals of illustrative embodiments also apply to other devices. For example, they can apply to resonators, and resonator based sensors, such as biosensors, chemical sensors, etc.

It should be noted that, where reference is made to anchoring of a surface, the entire surface or just a portion of the surface may be anchored.

Accordingly, illustrative embodiments mitigate the impact of linear acceleration on a shell-type gyroscope (i.e., a gyroscope that operates in one or both the flexure mode and bulk mode) by implementing one or more of the following:mechanically constraining the mass18from both its top and bottom sides,mechanically anchoring the side electrodes604from their top and/or bottom surfaces,extending an anchor through the mass18, andself-aligning the mass18, electrodes, and the space between the mass and electrodes.

Various embodiments of the present invention may be characterized by the potential claims listed in the paragraphs following this paragraph (and before the actual claims provided at the end of this application). These potential claims form a part of the written description of this application. Accordingly, subject matter of the following potential claims may be presented as actual claims in later proceedings involving this application or any application claiming priority based on this application.

Potential claims (prefaced with the letter “P” so as to avoid confusion with the actual claims presented below):

a primary member configured to resonate in a flexure mode or bulk mode in response to receipt of an electrostatic signal, the primary member having a bottom side, the primary member being configured to operate in a bulk mode or flexure mode when rotated;

a bottom substrate supporting the primary member;

a side electrode for electrostatically interacting with the primary member, at least a portion of the side electrode being in the same plane as the primary member, the side electrode having at least one surface that is generally parallel with the bottom side of the primary member; and

an anchor stabilizing the at least one surface of the side electrode.

P2. The gyroscope as defined by claim P1 wherein the anchor secures the at least one surface of the side electrode to the bottom substrate.

P3. The gyroscope as defined by claim P1 further comprising an anchor through the primary member.

P4. The gyroscope as defined by claim P3 wherein the anchor secures the primary member to the bottom substrate.

P5. The gyroscope as defined by claim P1 wherein the side electrode has a first side surface generally facing a side surface of the primary member, the side electrode having a second side surface that is generally opposite the first side surface, the second side surface being secured with a second anchor to a stationary portion.
P6. The gyroscope as defined by claim P5 wherein the first side surface is generally free of anchors.
P7. The gyroscope as defined by claim P1 further comprising a top substrate secured to the primary member, the anchor securing the at least one surface of the side electrode to the top substrate.
P8. The gyroscope as defined by claim P1 further comprising a bottom electrode between the primary member and the bottom substrate, the bottom electrode being for electrostatically interacting with the primary member.
P9. The gyroscope as defined by claim P1 wherein the primary member and side electrode are self-aligned.
P10. A shell-type gyroscope comprising:

a primary member configured to resonate in a flexure mode or bulk mode in response to receipt of an electrostatic signal, the primary member having a bottom side, the primary member being configured to operate in a bulk mode or flexure mode when rotated;

a substrate supporting the primary member; and

an anchor extending into the primary member and securing the primary member to the substrate.

P11. The gyroscope as defined by claim P10 wherein the substrate is one of a bottom and top substrate.

P12. The gyroscope as defined by claim P10 wherein the substrate comprises at least one of a bottom substrate and a top substrate.

P13. The gyroscope as defined by claim P12 wherein the primary member is secured by both the bottom and top substrate.

P14. The gyroscope as defined by claim P12 wherein the primary member is secured by both the bottom and top substrates and an anchor through primary member.

P15. The gyroscope as defined by claim P14 wherein the anchor comprises trenches filled with conductive material.

P16. The gyroscope as defined by claim P12 wherein the side electrodes are secured by both the bottom and top substrates.

P17. The gyroscope as defined by claim P12 wherein the primary member is secured by both the bottom and top substrates with an ultra-low g×g sensitivity.

P18. The gyroscope as defined by claim P17 wherein the gxg sensitivity is between about 10−2to 10−5deg/sec/g2.

These potential claims are directed generally to a shell-type gyroscope (i.e., a gyroscope that operates in one or both of bulk and flexure modes) that has a primary member configured to resonate in a flexure mode or bulk mode in response to receipt of an electrostatic signal. The primary member has a bottom side and is configured to operate in a bulk mode when rotated. In addition, the gyroscope has a bottom substrate supporting the primary member, and a side electrode for electrostatically interacting with the primary member. At least a portion of the side electrode is in the same plane as the primary member and has at least one surface that is generally parallel with the bottom side of the primary member. An anchor stabilizes the at least one surface of the side electrode.

In accordance with one embodiment of such invention, a shell-type gyroscope (i.e., a gyroscope that operates in one or both of bulk and flexure modes) has a primary member configured to resonate in a flexure mode or bulk mode in response to receipt of an electrostatic signal. The primary member has a bottom side and is configured to operate in a bulk mode (or flexural mode) when rotated. In addition, the gyroscope has a bottom substrate supporting the primary member, and a side electrode for electrostatically interacting with the primary member. At least a portion of the side electrode is in the same plane as the primary member and has at least one surface that is generally parallel with the bottom side of the primary member. An anchor stabilizes the at least one surface of the side electrode.

For example, the anchor can secure the at least one surface of the side electrode to the bottom substrate (or a top substrate, if one is included). Moreover, the gyroscope also may have an anchor that extends through the primary member. Among other things, the anchor may secure the primary member to the bottom substrate.

The side electrode has a first side surface generally facing a side surface of the primary member, and a second side surface that is generally opposite the first side surface. In some embodiments, the second side surface is secured to a stationary portion of the substrate. The first side surface may be generally free of anchors. Various embodiments also have a top substrate secured to the primary member. Moreover, the gyroscope also may have a bottom electrode.

In accordance with another embodiment of such invention, a shell-type gyroscope has a primary member configured to resonate in a flexure mode or bulk mode in response to receipt of an electrostatic signal. The primary member has a bottom side and is configured to operate in a bulk mode or flexure mode when rotated. In addition, the gyroscope has a substrate supporting the primary member, and an anchor extending into the primary member (either completely through its profile or partly through its profile) and securing the primary member to the substrate.

The primary member may be secured by both the bottom and top substrates with to improve and achieve ultra-low gxg sensitivity as well as g sensitivity (e.g., linear acceleration in gyroscopes). For example, the gxg sensitivity may be between about 10−2to 10−5deg/sec/g2. Some embodiments may have a range for linear acceleration sensitivity of between about 10−4to 10−8deg/sec/g.

It should be noted that, although specific features are shown in some drawings and not in others, this is for convenience only, as various features generally may be combined with any or all other features to produce various alternative embodiments of the invention.