Patent Publication Number: US-7714691-B2

Title: Versatile system for a locking electro-thermal actuated MEMS switch

Description:
CROSS-REFERENCE TO RELATED APPLICATION AND CLAIM OF PRIORITY 
   The present application is related to U.S. Provisional Patent No. 60/668,522, filed Apr. 5, 2005, entitled “Electro-Thermal Actuated RF-MEMS Switch with Mechanical Latch”. U.S. Provisional Patent No. 60/668,522 is assigned to the assignee of the present application and is hereby incorporated by reference into the present disclosure as if fully set forth herein. The present application hereby claims priority under 35 U.S.C. §119(e) to U.S. Provisional Patent No. 60/668,522. 

   TECHNICAL FIELD OF THE INVENTION 
   The present application relates generally to the fields of micro-electromechanical systems (MEMS) and wireless telecommunication technologies, and more particularly, to a versatile system for passively restricting the movement of certain MEMS switch structures. 
   BACKGROUND OF THE INVENTION 
   The continual demand for enhanced speed, capacity and efficiency has resulted in dramatic advances in a variety of manufacturing fields (e.g., electronics, communications, and machinery). Among many recent developments, the field of electro-mechanics has focused significant attention on the miniaturization of various devices. A micro-electromechanical system (MEMS) is a system that usually has electrically controllable micro-machines (such as a motor, actuator, optical modulating element, etc.)—most often formed monolithically on a semiconductor substrate using integrated circuit techniques. 
   Several micro-actuator technologies have been investigated for positioning individual elements in MEMS applications. Electrostatic, magneto-static, piezoelectric and thermal-expansion systems have been used in varying degrees for micro-actuator operation. From this field of technology, asymmetric electro-thermal actuators have proven particularly useful in a number of MEMS applications. 
   Generally, a MEMS polysilicon surface micromachined electro-thermal actuator uses differential heating to generate thermal expansion and movement. In one conventional asymmetric electro-thermal actuator design, a single “hot arm” is narrower than a “cold arm.” When electric current is applied, the electrical resistance of the hot arm is greater. When an electrical current passes through both the hot and cold arms, the hot arm is heated to a higher temperature than the cold arm. This temperature differential causes the hot arm to expand along its length, thus forcing the tip of the actuator to rotate about the flexure. Another variant of the asymmetric design joins together arms of similar size and shape, but having substantially different coefficients of thermal expansion. In such design, a “hot arm” has a higher coefficient of thermal expansion than that of a “cold arm.” When electric current passes through both the hot and cold arms, the hot arm expands more than the cold arm, effecting the desired actuator movement. 
   Frequently, electro-thermal actuators are deployed as bi-stable switches—i.e., as elements that switch between a first position, when no current is applied, and a second position, when current is applied. Once the current is removed, the actuator returns to its initial position. 
   Such MEMS components may be utilized in a wide variety of electrical or mechanical switching applications. Application of MEMS-scale switches may be of particular use in the wireless communications field; especially as portable wireless communication devices continue to strive for greater performance from devices of decreasing form factor. 
   There are a number of potential switching applications in wireless communication products that could benefit from MEMS-scale components. Consider, for example, a multi-mode cell phone. It would be advantageous, from a size and form factor perspective, to use a MEMS switch to shift operation between modes. In these and other small, battery-powered wireless communications devices, however, power consumption must be also minimized in order to extend time of operation on a battery charge. As such, a conventional MEMS-scale switch component may be of limited utility in such devices—since such switches often return to a default position in the absence of power. Another consideration is that a number of applications may require a multi-position switch, having more than just two positions or states. Implementing such applications using only bi-stable MEMS switches would either be cumbersome or infeasible. 
   Furthermore, even where a conventional bi-stable MEMS switch may be suitable, the direct interface between semiconductor circuitry and operational MEMS structures can still cause operational problems. For example, operation may require deployment of a conventional MEMS switch while a second, adjacent operational element is electrostatically actuated. Given the minute scale of such structures and the separations therebetween, the electrostatic signals actuating the second element could adversely affect the MEMS switch, leading to a malfunction or performance loss. Brute force solutions, such as complex routing layouts, might be employed to overcome such a problem, but they also introduce a number of inefficiencies to device manufacturing or operation. 
   As a result, there is a need for a system that provides reliable and sustainable MEMS switching, without relying on continuous electrostatic or electromagnetic force—one that is readily adaptable to a number of production or manufacturing processes, and to address a variety of specific design requirements, including the provision of multi-throw switches—while providing reliable device performance in an easy, efficient and cost-effective manner. 
   SUMMARY OF THE INVENTION 
   A versatile system, comprising various apparatus and methods, is provided for reliable passive restriction of MEMS switching structures. The system restricts MEMS switch structure movement without relying on continuous electrostatic or electromagnetic forces. The system is readily and easily adaptable to a number of device applications, design requirements, and production or manufacturing processes—efficiently providing single or multi-throw switches. The system further obviates unintended MEMS movements due to incidental forces—electrostatic and otherwise—and thus provides reliable device performance in an easy, efficient and cost-effective manner. 
   Specifically, the system provides a “lockable” MEMS switching architecture that is readily fabricated within a variety of semiconductor technologies. The locking MEMS switch is fabricated such that, once device production is completed, a clutch assembly having one or more engagement features is disposed in proximity to a switching member having one or more receiving features. Electrostatic or thermal expansion force may be applied the clutch assembly to disengage the engagement features from the receiving features, and to the switching member to move it in relation to the clutch assembly. Once the switching member is in a desired position, the electrostatic or thermal expansion force may be removed from the clutch assembly, causing the engagement features to re-engage with the switching member, thereby restricting its further movement. Electrostatic or thermal expansion force may then be removed from the switching member. 
   More specifically, a MEMS device is provided. The MEMS device comprises a switching member, and a first actuator coupled to a first portion of the switching member. A switching element is coupled to a second portion of the switching member, opposite the first actuator. An engagement feature is disposed along the switching member between the first actuator and the switching element. A first contact element is disposed along a surface of the switching element. A clutch assembly is provided, having an engagement element formed in proximity to the engagement feature. The engagement element is adapted to operably engage with the engagement feature. A second contact element is formed in proximity to the first contact element, and adapted to form contact with the first contact element when the switching member is actuated or, alternatively, when the switching member is not actuated. 
   In other embodiments, a method for lockably switching a MEMS switch device provides a switching member having a plurality of engagement features disposed along its surface. A first actuator is coupled to a first portion of the switching member. A clutch assembly is provided, having an engagement element formed in proximity to, and adapted to operably engage with, the engagement features. The clutch assembly is provided with a second actuator adapted to engage or disengage the engagement element from the engagement features. The second actuator is operated to disengage the engagement element from a first engagement feature. The first actuator is operated to move the switching element relative to the engagement element. The second actuator is de-actuated, engaging the engagement element with a second engagement feature of the switching member. 
   In still other embodiments, a wireless communications device comprises an antenna input, a plurality of antenna structures, and a switching member adapted to selectively couple the antenna input to one of the plurality of antenna structures. A first actuator is coupled to the switching member, and adapted to switch a first contact on the switching member in or out of engagement with a second contact, associated with a desired one of the plurality of antenna structures. A clutch assembly is adapted to passively engage with the switching member to prohibit movement thereof, and to actuatably disengage from the switching member, to allow switching thereof. 
   Before undertaking the DETAILED DESCRIPTION OF THE INVENTION below, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation; the term “or,” is inclusive, meaning and/or; the phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like; and the term “controller” means any device, system or part thereof that controls at least one operation, such a device may be implemented in hardware, firmware or software, or some combination of at least two of the same. It should be noted that the functionality associated with any particular controller may be centralized or distributed, whether locally or remotely. Definitions for certain words and phrases are provided throughout this patent document, those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior, as well as future uses of such defined words and phrases. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the present disclosure and its advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, in which like reference numerals represent like parts: 
       FIGS. 1   a - 1   c  illustrate various embodiments of electro-thermal actuating assemblies; 
       FIGS. 2   a - 2   d  illustrate the operation of one embodiment of a clutch assembly in accordance with the present disclosure; 
       FIGS. 3   a - 3   d  illustrate the operation of another embodiment of a clutch assembly in accordance with the present disclosure; 
       FIG. 4  illustrates one embodiment of a switching assembly in accordance with the present disclosure; 
       FIG. 5  illustrates one embodiment of a wireless communications switching component in accordance with the present disclosure; 
       FIG. 6  illustrates another embodiment of a wireless communications switching component in accordance with the present disclosure; and 
       FIG. 7  illustrates another embodiment of a wireless communications switching component in accordance with the present disclosure. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIGS. 1 through 7 , discussed below, and the various embodiments used to describe the principles of the present disclosure in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the disclosure. Those skilled in the art will understand that the principles of the present disclosure may be implemented in any suitably arranged MEMS switching structure, or any other MEMS structure in which passive physical restriction of a movable component is desired. 
   The following disclosure provides a versatile system, comprising various architectures, apparatus and methods for reliable passive restriction of MEMS switching structures. The system is operable by electrostatic, electromagnetic or thermal expansion forces, but passively restricts MEMS switch structure movement in the absence of continuous electrostatic, electromagnetic or thermal expansion forces. The system is readily and easily adaptable to a number of device applications, design requirements, and production or manufacturing processes. The system may be implemented to efficiently provide a simple bi-stable switch, or extensive multi-throw switches. The system obviates unintended MEMS movements due to incidental collateral forces—electrostatic and otherwise—that may occur near or around a switch of concern during device operation. 
   Specifically, this system provides a “lockable” MEMS switching architecture that is readily fabricated within a wide variety of semiconductor technologies. The locking MEMS switch is fabricated such that, once device production is completed, a clutch assembly having one or more engagement features is disposed in proximity to a switching member having one or more receiving features. Electrostatic or thermal expansion force may be applied the clutch assembly to disengage the engagement features from the receiving features, and to the switching member to move it in relation to the clutch assembly. Once the switching member is in a desired position, the electrostatic or thermal expansion force may be removed from the clutch assembly, causing the engagement features to re-engage with the switching member, thereby restricting its further movement. Electrostatic or thermal expansion force may then be removed from the switching member. 
   For purposes of explanation and illustration, several variations of electro-thermal actuators are depicted and described in relation to  FIGS. 1   a - 1   c . In  FIG. 1   a , a basic bent-beam type actuator assembly  100  is depicted in a top-down view. Assembly  100  comprises an electrically conductive actuating member  102  anchored between two fixed anchor members  104 . Member  102  is formed having a bend or joint feature  106  somewhere along its span. Current  108  is passed through member  102 , causing member  102  to heat and expand. Anchors  104  prohibit member  102  from expanding laterally, so member  102  is constrained to expand orthogonally. Member  102  is fabricated of a semi-rigid material (e.g., aluminum, copper) that is nonetheless flexible enough to accommodate additional bending at feature  106 . Once the expansion of member  102  is stabilized, it is left in an actuated position  110 . Current may then be removed from member  102 , allowing it to cool, condense, and return to its original position. 
   In  FIG. 1   b , a composite cantilever type actuator assembly  120  is depicted in a top-down view. Assembly  120  comprises a composite beam  122  anchored at one end to a fixed anchor member  124 . Beam  122  comprises two layers  126  and  128 . Layer  126  comprises a material having a lower coefficient of thermal expansion than the material that comprises layer  128 . A conductive or heating element  130  is disposed at anchor  124 , in contact with or proximity to layers  126  and  128 . Element  130  is heated, causing layers  126  and  128  to heat and expand. Layers  126  and  128  expand at different rates, or by different amounts, however, causing a cant or bend  132  in beam  122 . This results in beam  122  shifting to an actuated position  134 . Once heating of element  130  is discontinued, layers  126  and  128  cool, condense, and return beam  122  to its original position. 
   In  FIG. 1   c , a buckle beam type actuator assembly  140  is depicted in a top-down view. Assembly  140  comprises a composite beam  142  anchored between two fixed anchor members  144 . Beam  142  comprises two layers  146  and  148 . Layer  146  comprises a material having a higher coefficient of thermal expansion than the material that comprises layer  148 . Current  150  is passed through member  142 , causing layers  146  and  148  to heat and expand. Layers  146  and  148  expand at different rates, or by different amounts, and anchors  144  prohibit member  142  from expanding laterally. Member  142  thus expands, or buckles, orthogonally until it shifts to an actuated position  152 . Current may then be removed from member  142 , causing layers  146  and  148  to cool and condense, and return beam  142  to its original position. 
   Certain aspects and embodiments of the system of the present disclosure are now depicted and described in relation to  FIGS. 2   a - 2   d . In  FIG. 2   a , a clutch assembly  200  having tooth or pinion type engagement elements is depicted in a top-down view. Assembly  200  comprises a switching element  202  that a first set of engagement features  204 , corresponding to a first position, and a second set of engagement features  206 , corresponding to a second position. As depicted in  FIGS. 2   a - 2   d , features  204  and  206  are depicted as notches, trenches or indentations formed into a surface of member  202 . In alternative embodiments, however, features  204  or  206  may comprise any other suitable constructs—such as protuberances, teeth, or tabs extending outwardly from a surface of element  202 . Assembly  200  also comprises a clutch assembly having tooth or bearing type engagement elements  208  disposed or formed in proximity to member  202 . Elements  208  may be coupled to, formed as part of, or otherwise controlled by any suitable electro-thermal actuating assembly (not shown). Similarly, element  202  may be coupled to, formed as part of, or otherwise controlled by another suitable electro-thermal actuating assembly (not shown). 
   In some initial state, as depicted in  FIG. 2   a , assembly  200  may have elements  208  engaged with features  204 , prohibiting member  202  from moving. Elements  208  are in a passive, or non-actuated, state. Referring now to  FIG. 2   b , assembly  200  is to be switched from its initial position to a different position. Elements  208  are actuated  210 , disengaging them from features  204 . Member  202  is now free to switch. Referring now to  FIG. 2   c , member  202  is actuated  212  laterally from its initial position to a second position where features  206  are generally aligned with members  208 . In  FIG. 2   d , members  208  are de-actuated  214  and brought into engagement with features  206 , locking member  202  into the second position. Member  202  may then be de-actuated as well, since members  208  confine it to the second position. 
   Assembly  200  may be produced such that it provides an on-off or double switching as it is moved. Switch contacts (not shown) may be disposed in relation to either end of member  202  such that when in the initial position, the second position, or in both positions, element  202  opens or closes an associated switch. A conductive element (not shown), such as a metallic pad or trace, may therefore be disposed on one or both ends of element  202 , to effect the desired single or double switching. 
   Another embodiment of a clutch assembly in accordance with the present system is now depicted and described in relation to  FIGS. 3   a - 3   d . In  FIG. 3   a , a clutch assembly  300  having a plunger or stopper type architecture is depicted in a top-down view. Assembly  300  comprises a switching element  302  that a plunger or “T” shape. Along the right surface of the upper and lower branches of element  302  are disposed contact elements  304 . As depicted in  FIGS. 3   a - 3   d , elements  304  comprise metallic pad or trace type contacts, formed along a surface of member  302 . In alternative embodiments, however, elements  304  may comprise any other suitable contact structure or, depending upon the design, there may be only one contact element  304  disposed along member  302 . 
   Assembly  300  also comprises a clutch assembly having gate type engagement elements  306  disposed or formed in proximity to member  302 . Elements  306  may be coupled to, formed as part of, or otherwise controlled by any suitable electro-thermal actuating assembly (not shown). Similarly, element  302  may be coupled to, formed as part of, or otherwise controlled by another suitable electro-thermal actuating assembly (not shown). A space or aperture  310  separates elements  306 , and has a dimension sufficient to securely accommodate a lateral portion  312  of element  302 . Along the left surface of each element  306 , near aperture  310 , are disposed contact elements  318 . Elements  308  also comprise metallic pad or trace type contacts, formed along a surface of elements  306 . In alternative embodiments, however, elements  308  may comprise any other suitable contact structure or, depending upon the design, there may be only one contact element  308  disposed along one element  306 . 
   In some initial state, as depicted in  FIG. 3   a , assembly  300  may have elements  306  in a non-actuated position, prohibiting member  302  from lateral movement. Elements  304  are not in contact with elements  308 , thus assembly  300  is switched “off.” Referring now to  FIG. 3   b , assembly  300  is to be switched from its initial off position to an on position. Elements  308  are actuated  314 , opening aperture  310  to a dimension sufficient to allow passage of  302  therethrough. Member  302  is now free to move laterally. Referring now to  FIG. 3   c , member  302  is actuated  316  laterally from its initial position “off” to a second position where elements  304  have cleared aperture  310 . In  FIG. 3   d , members  306  are de-actuated  318  and returned to their non-actuated position. Element  302  now protrudes through aperture  310 , which is occupied by portion  312 . Member  302  may then be de-actuated  320  as well, bringing contacts  304  into engagement with contact  308 , and locking member  302  into an “on” position. 
   In alternative embodiments, the initial position for element  302  may be the same, but alternative provision of elements  308  and  304  may be utilized to render this position an “on” position. One or more contact elements  304  may be provided along the left surface of the upper and lower branches of element  302 , while one or more contact elements  308  are disposed along the right surface of each element  306 , near aperture  310 . 
   This configuration may be provided in substitution for the configuration depicted in  FIGS. 3   a - 3   d , or in addition to it. In embodiments where there is substitution, alternative defaults for “on” and “off” states may be provided. In embodiments where both configurations are provided, member  302  may be utilized to switch between different circuits or signals—rather that just turn on and off. 
   Having now described basic constructs and relationships, certain architectural aspects and embodiments of the system of the present disclosure are now depicted and described. Referring now to  FIG. 4 , one embodiment of a three-position switching assembly  400  is depicted. Assembly  400  comprises a switching member  402  that is, at one end or portion, operably coupled or connected to first and second actuator assemblies  404  and  406 . Assemblies  404  and  406  are disposed in relation to one another and member  402  such that they are operable to either laterally push or pull member  402  over an extended range. Disposed along member  402 , a plurality of engagement features  408  are formed and positioned, such that they respectively correspond to three desired switch positions opposing clutch assembly engagement elements  410  are disposed on opposite sides of member  402 , proximal to features  408 , and each operably coupled or connected to an actuating assembly  412 . 
   At another end or portion of member  402 , opposite assemblies  404  and  406 , a switching element  414  is disposed. A first contact element  416  is disposed or formed along one surface of element  414 . A second contact element  418  is formed along an opposite surface of element  414 . Elements  416  and  418  are provided to contact or couple to contact structures  420  and  422 , respectively, when member  402  is laterally actuated. Assembly  400  is formed such that, in addition to both of these contact positions for element  414 , a third neutral position may be provided that leaves no contact at all between elements  416  and  420  or  418  and  422  (e.g., an “off” position). 
   In accordance with the description thus far, assembly  412  may be actuated to free member  402  for lateral movement. Member  402  may be laterally actuated in either direction to establish contact between switching member  414  and either contact  420  or  422 , or to move member  414  into a neutral, non-contact position. Once member  414  is in a desired position, assembly  412  may be de-actuated to lock member  402  in place. 
   Referring now to  FIG. 5 , one embodiment of a wireless antenna switching component  500  according to the system of the present disclosure is depicted and described. Component  500  comprises two switching assemblies  502  and  504 , similar to assembly  400  in construct and operation. Component  500  comprises an input  506  through which a wireless communication device (not shown) receives and transmits communications signals via one of a plurality of antenna structures  508 . If desired, component  500  may be provided in a default “off” or disconnected state—where none of the structures  508  is operably coupled to input  506 . Once connection to a specific structure  508  is desired, either assembly  502  or  504  may be actuated to provide contact between a switching element  510  and a contact structure  512  corresponding to the desired structure  508 . Component  500  may then be selectively switched from antenna structure to antenna structure, or from a single antenna structure to multiple transceiver circuits, or cycled on and off, as desired—consuming battery power only while switching is being performed. 
     FIG. 6  depicts an alternative embodiment of a wireless antenna switching component  600  according to the system of the present disclosure. Component  600  comprises four switching assemblies  602 ,  604 ,  606  and  608 . Assemblies  602 - 608  are in similar to assembly  400  in construct, but operate to provide only two positions each—an actuated “on” position, or a non-contact “off” position. Component  600  comprises an input  610  through which a wireless communication device (not shown) receives and transmits communications signals via one of a plurality of antenna structures  612 . If desired, component  600  may be provided in a default “off” or disconnected state—where none of the structures  612  is operably coupled to input  610 . Once connection to a specific structure  612  is desired, one of the assemblies  602 - 608  may be actuated to provide contact between its respective switching element  614  and a contact structure  616  corresponding to the desired structure  612 . Component  600  may then be selectively switched from antenna structure to antenna structure, or from a single antenna structure to multiple transceiver circuits, or cycled on and off, as desired—consuming battery power only while switching is being performed. 
   Referring now to  FIG. 7 , another embodiment of a wireless antenna switching component  700  according to the system of the present disclosure is depicted and described. Component  700  comprises three-position switching assemblies  702  and  704 . Assemblies  702  and  704  are each similar, in construct and operation, to a push-pull combination of two opposing instances of assembly  300 . Component  700  comprises an input  706  through which a wireless communication device (not shown) receives and transmits communications signals via one of a plurality of antenna structures  708 . Alternately, component  700  may be utilized to switch a single antenna structure coupled to input  706  to multiple transceiver circuits. If desired, component  700  may be provided in a default “off” or disconnected state—where none of the structures  708  is operably coupled to input  706 . Once connection to a specific structure  708  is desired, either assembly  702  or  704  may be actuated to provide contact between a switching element  710  and a contact structure  712  corresponding to the desired structure  708 . Component  700  may then be selectively switched from antenna structure to antenna structure, or from a single antenna structure to multiple transceiver circuits, or cycled on and off, as desired—consuming battery power only while switching is being performed. 
   It should now be easily appreciated by one of skill in the art that the system of the present disclosure provides and comprehends a wide array of variations and combinations easily adapted to a number of MEMS applications. The relative positions and orientations of contact elements may be provided in any manner suitable for a particular application. For example, contacts may be provided along clutch engagement elements, or may be provided on separate contact structures. Various actuating assemblies may be substituted or combined to provide a particular switching configuration. For example, actuating assemblies other than electro-thermal actuators may be utilized where desired or required. Engagement features and members may be provided in a variety of different or mixed forms to accommodate specific design constraints. All such variations and modifications are hereby comprehended. 
   It should also be appreciated that the system of the present disclosure may be readily implemented in any desired fabrication processes. The constituent members or components of this system may be produced using any suitable fabrication materials, and formed by any suitable lithography or deposition techniques. This system may also be implemented in MEMS fabrication using non-semiconductor or more conventional mechanical processes. 
   The embodiments and examples set forth herein are therefore presented to best explain the present invention and its practical application, and to thereby enable those skilled in the art to make and utilize the system of the present disclosure. The description as set forth herein is therefore not intended to be exhaustive or to limit any invention to a precise form disclosed. As stated throughout, many modifications and variations are possible in light of the above teaching without departing from the spirit and scope of the following claims.