Abstract:
A micro-machined actuator for use in, among other things, sensors and data storage devices. The actuator includes a stator wafer and a micro-mover positioned adjacent to the stator wafer. Between the stator wafer and the micro-mover are electrodes that are set to specified voltages and that emanate electric fields that position the micro-mover relative to the stator wafer. Also between stator wafer and the micro-mover are bumpers that prevent the electrodes from coming into contact with each other.

Description:
BACKGROUND OF THE INVENTION: 
     1. Field of the Invention 
     The present invention relates generally to micro-machined actuators. The present invention also generally relates to methods for manufacturing and operating micro-machined actuators. 
     2. Description of the Related Art 
     FIG. 1 illustrates a micro-machined actuator  10  according to the related art. The actuator  10  illustrated includes a stator wafer  20  at the bottom thereof and a rotor wafer  40  above the stator wafer  20 . The rotor wafer  40  includes a section, called a micro-mover  50 , that is separated from the rest of the rotor wafer  40 . The micro-mover  50  is connected to the rest of the rotor wafer  40  via suspensions  60 . The wafers  20 , 40  are bonded together by a bond material  70  that both holds the wafers  20 , 40  together and separates them a specified distance. 
     On the surface of the stator wafer  20  closest to the rotor wafer  40  is a series of stator electrodes  80 . On the surface of the micro-mover  50  closest to the stator wafer  20  are formed a series of actuator electrodes  90 . Although, for the purposes of clarity, only five stator electrodes  80  and four actuator electrodes  90  are illustrated in FIG. 1, typical micro-machined actuators  10  according to the related art include many more electrodes  80 , 90  than those illustrated. 
     The stator wafer  20  typical contains the electronics of the actuator  10  and makes up half of the motor that moves the micro-mover  50 , as will be discussed below. The stator wafer  20  is typically made from materials that can be micro-machined (e.g., silicon). 
     The rotor wafer  40  is typically on the order of 100 microns thick. The rotor wafer  40  must also be micro-machinable, hence it too is often made from silicon. As stated above, the micro-mover  50  generally consists of a portion of the rotor wafer  40  that has been separated from the remainder of the rotor wafer  40  but that remains attached by suspensions  60 . Hence, the micro-mover  50  is also typically on the order of 100 microns thick and made from a micro-machinable material. 
     The suspensions  60  are designed to allow the micro-mover  50  to have in-plane motion while restricting the micro-mover  50  out-of-plane motion. In other words, the suspensions  60  are designed to allow the micro-mover  50  to move horizontally relative to the stator wafer  20  and to restrict the micro-mover  50  from moving vertically. A variety of suspensions  60  are known in the art and are designed with different amounts of in-plane compliance and out-of-plane stiffness. However, none of these suspensions  60  can prevent out-of-plane motion completely. 
     The bond material  70  typically is a metallic, thin-film material. The type of bond material  70  used depends upon several factors. Commonly, the bond material  70  is chosen so as to provide electrical conductivity between the various wafers  20 ,  40 . The bond material  70  is also chosen on its ability to hermetically seal the chamber in which the micro-mover  50  resides. 
     The stator electrodes  80  consist of inter-digitated metal lines formed on the surface of the stator wafer  20  closest to the micro-mover  50 . The actuator electrodes  90  are another set of inter-digitated metal lines formed on the micro-mover  50 . Each metal line that makes up an electrode  80 , 90  is approximately one to two microns wide and can have a length of up to one or two millimeters. A one to two micron gap typically exists between any two electrodes  80 , 90 . 
     The actuator electrodes  90  typically cover a substantial portion of the micro-mover  50 , which itself can have a total area of between one and two square millimeters. The electrodes  80 , 90  can be made up of various metals that are generally compatible with semiconductors. Such metals include, but are not limited to, molybdenum, aluminum and titanium. 
     FIG. 2 illustrates a cross-sectional view of a micro-machined actuator  10  taken across the plane A—A defined in FIG.  1 . In operation, the actuator  10  operates by moving the micro-mover  50  relative to the stator wafer  20 . In order to move the micro-mover  50  relative to the stator wafer  20 , the voltages of selected stator electrodes  80  and actuator electrodes  90  are raised and lowered in a specific pattern in order to alter the electric fields emanating from the electrodes  80 , 90 . 
     For example, the actuators electrodes  90  can have their voltages set in a pattern where a first electrode  90  would be placed at an operating voltage such as 40 volts, the electrode  90  adjacent to it would be grounded, the next electrode  90  would be at 40 volts, and the remaining electrodes would have their voltages set in a similar manner. The stator  80 , on the other hand, could have their voltages set in a pattern that is not quite alternating. For example, a first stator electrode  80  could be set to a high voltage, a second stator electrode  80  immediately adjacent to the first could be set to a low voltage, a third stator electrode  80  adjacent to the second could be set to a high voltage, a fourth stator electrode  80  adjacent to the third could be set to a low voltage, adjacent fifth and sixth stator electrodes  80  could be set to high voltages and a seventh adjacent stator electrode  80  could be set to a low voltage. This seven-electrode  80  voltage pattern could then be repeated for all of the stator electrodes  80  in the actuator  10 . 
     In order to move the micro-mover  50 , the pattern of the voltages in the stator electrodes  80  is changed by increasing or decreasing the voltage on one or more of the stator electrodes  80 . Such voltages changes alter the distribution of the electric fields present between the stator electrodes  80  and actuator electrodes  90 . Therefore, the attractive and repulsive forces between the stator electrodes  80  and actuator electrodes  90  are also altered and the position of the micro-mover  50  is changed until these forces are balanced. 
     In other words, as the stator electrode  80  voltages are changed, new, low-energy potential regions are created where the forces generated by the electric fields balance the mechanical forces exerted on the micro-mover  50  by the suspensions  60 . Hence, once the voltages of the stator electrodes  80  have been changed to a new pattern, the micro-mover  50  repositions itself. 
     An unwanted side effect of the electric fields is the out-of-plane component of the attractive forces between the stator electrodes  80  and the actuator electrodes  90 . These attractive forces pull the micro-mover  50  towards the stator wafer  20  and, if too great, allow the actuator electrodes  90  and stator electrodes  80  to come into close enough contact that they electrically “short out” and fuse together. Such an event causes catastrophic failure of the actuator  10 . 
     Although the suspension  60  is designed to be sufficiently stiff to restrict the out-of-plane movement of the micro-mover  50 , it is difficult to design a suspension  60  that simultaneously provides the required in-plane mobility of the micro-mover  50  and restricts out-of-plane motion. Hence, to date, micro-machined actuators  10  have been susceptible to catastrophic failure. 
     Fusing of the stator electrodes  80  and the actuators electrodes  90  can also occur if an external jolt is applied to the system. For example, if the micro-chip that contains the micro-machined actuator  10  is tapped or jolted, enough additional physical force in the out-of-plane direction could be transferred to the micro-mover  50  and stator wafer  20  configuration to sufficiently overcome the suspension  60  stiffness and to fuse together the stator electrodes  80  and actuator electrodes  90 . 
     Hence, what is needed is a micro-actuator that prevents out-of-plane motion of the micro-mover relative to the stator wafer. 
     What is also needed is a micro-actuator capable of being tapped or jolted, for example, without having the outside force cause catastrophic failure of the device. 
     BRIEF SUMMARY OF THE INVENTION 
     According to one embodiment, an actuator that includes a stator wafer, a first stator electrode protruding from a first surface of the stator wafer, a micro-mover above the first surface of the stator wafer, a first actuator electrode protruding from a first surface of the micro mover, wherein the first surface of the micro-mover and the first surface of the stator face each other, and a first bumper positioned between the stator wafer and the micro-mover. 
     According to another embodiment, a method of operating a micro-mover that includes providing a stator wafer and a micro-mover over the stator wafer, forming stator electrodes on the stator wafer and actuator electrodes on the micro-mover, moving the micro-mover relative to the actuator electrode by altering the voltages of selected stator electrodes over time, and preventing physical contact between the stator electrodes and actuator electrodes. 
     According to yet another embodiment, a method of manufacturing an actuator that includes providing a stator with stator electrodes on a first surface of the stator, providing a micro-mover with actuator electrodes on a first surface of the micro-mover, positioning the first surface of the micro-mover facing the first surface of the stator, and providing a bumper between the stator and the micro-mover. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The invention will be described by way of example, in the description of exemplary embodiments, with particular reference to the accompanying drawings in which: 
     FIG. 1 illustrates a perspective view of a micro-machined actuator according to the related art; 
     FIG. 2 illustrates a cross-sectional view of a micro-machined actuator illustrated in FIG. 1 as seen from line A—A; 
     FIG. 3 illustrates a cross-sectional view of a micro-machined actuator wherein a bumper is positioned next to a set of stator electrodes; 
     FIG. 4 illustrates a cross-sectional view of a micro-machined actuator wherein a bumper is positioned in between a set of stator electrodes; 
     FIG. 5 illustrates a cross-sectional view of a micro-machined actuator wherein a first bumper is positioned next to a set of stator electrodes and a second bumper is positioned next to a set of actuator electrodes; 
     FIG. 6A illustrates a top perspective view of a micro-machined actuator wherein three bumpers are included; 
     FIG. 6B illustrates a top perspective view of a micro-machined actuator wherein four bumpers are included; and 
     FIGS. 7A-7B illustrate a cross-sectional and top perspective view, respectively, of bumpers that overlap one or more electrodes. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 3 illustrates one embodiment of the present invention wherein the stator wafer  20  surface closest to the micro-mover  50  has upon it not only stator electrodes  80  but also a bumper  120 . Although the bumper  120  is positioned adjacent to only one stator electrodes  80 , this configuration is not restrictive of the present invention. In fact, as shown in FIG. 4, the bumper  120  can easily be position between any two of the stator electrodes  80 . 
     FIG. 5 illustrates another embodiment of the present invention with two bumpers, a first bumper  120  on the surface of the stator wafer  20  closest to the micro-mover  50 , and a second bumper  121  on the surface of the micro-mover  50  closest to the stator wafer  20 . Although both bumpers  120 , 121  illustrated in FIG. 5 are positioned to the outside of the electrodes  80 , 90 , either or both of the bumpers can be positioned between two electrodes  80 , 90 , as shown in FIG.  4 . 
     FIGS. 6A and 6B illustrate yet other embodiments of the present invention wherein three and four bumpers  120  are present in a micro-machined actuator  10 . In FIG. 6A, the three bumpers  120  are arranged in a triangular configuration. Dependent upon the particular embodiment of the present invention, each of the three bumpers  120  can be positioned either on the stator wafer  20  or on the micro-mover  50 . For example, a first and second bumper can be positioned on the stator wafer  20  while a third bumper can be positioned on the micro-mover  50 . Also, each of the bumpers  120  can be positioned either adjacent to one electrode  80 , 90  or between two electrodes  80 , 90 . 
     In FIG. 6B, four bumpers  120  are positioned in a square or rectangular configuration wherein each bumper  120  can be either on the stator wafer  20  or the micro-mover  50 . Each of the bumpers  120  can be adjacent to one electrode  80 , 90  or positioned between two electrodes  80 , 90 . 
     In addition to the configurations illustrated in FIGS. 6A and 6B, more than four bumpers  120  can also be positioned between the stator wafer  20  and micro-mover  50 . Regardless of how many bumpers  120  are present, no limitations are made regarding the geometric arrangement of the bumpers  120 . For example, although FIG. 6A shows the bumpers  120  to be in a triangular configuration, the three bumpers  120  can be in a linear, random, or other geometrical configuration. The same is true for the four bumpers  120  illustrated in FIG.  6 B and for higher-bumper number embodiments of the present invention. 
     According to the embodiments illustrated in FIGS. 3-6B, each of the bumpers  120  protrude a greater distance from the surfaces to which they are attached than the electrodes  80 , 90  protruding from those same surfaces. Although no particular restrictions are placed on how far the bumpers  120  and electrodes  80 , 90  protrude from their respective surfaces, certain embodiments of the present invention provide for the electrodes  80 , 90  to protrude 75% as far as the bumpers  120 . Other embodiment of the present invention have electrodes  80 , 90  that protrude from the surfaces to which they are attached 90%, 50%, 10%, 5% and 1% as far as the bumpers  120  attached to the same surfaces. 
     The bumpers  120  can be made from many different materials and are not restricted in its geometry. Hence, the bumpers  120  can be circular protrusions, square protrusions, or protrusions of other geometrical shapes. Also, although the bumpers  120  discussed above have been either adjacent to one electrode  80 , 90  or positioned between two electrodes  80 , 90 , certain embodiments of the present invention include bumpers  123  that overlap at least portions of one or more electrodes  80 , 90 . Such a configuration is shown in FIGS. 7A and 7B, where FIG. 7A illustrates a cross-sectional view of an actuator  10  and FIG. 7B illustrates a top perspective view of the surface of the stator wafer  20  that contains stator electrodes  80 . The bumper  122  is shown in FIG. 7B as overlapping two stator electrodes  80  partially. 
     For the purposes of simplicity, the bumpers described above are preferably made from the same material as the surface from which they protrude. However, this is in no way restrictive of the present invention and the bumpers, according to certain embodiments, can be made from materials different from those of the surfaces from which they protrude. For example, metal, insulator, dielectric, semiconductor or polymer bumpers could be formed on the surface of a semiconductor stator wafer  20 . According to certain embodiments of the present invention, electrically grounded metal bumpers are used. 
     The overall dimensions of the bumper  120  are typically on the order of microns, though these dimensions are in no way limiting of the present invention. In fact, if the electrodes  80 , 90  were made from nanowires, the bumper  120  could have nanometer dimensions. 
     Although it was mentioned above that, without the bumper  120  positioned between the micro-mover  50  and the stator wafer  20 , the actuator electrodes  90  and stator electrodes  80  could fuse, the actual method of fusion was not described. For the sake of completeness, the fusion occurs as, when the electrodes  80 , 90  come in close enough contact to each other, a current path forms between the electrodes  80 , 90  and the electrodes  80 , 90  melt together. 
     The actuator described above can be included in many types of devices. For example, any micro-machine or nano-machine having a suspended platform above a surface is within the scope of the present invention. This includes, but is not limited to, all sorts of sensors, data storage devices, and other devices that require micro-actuators. 
     The distance separating the micro-mover  50  and stator wafer  20  is generally on the order of 1-10 microns. However, this is in no way limiting of the present invention and any actuator wherein the electrodes  80 , 90  can exert enough force on each other to move the micro-mover  50  without coming into such close contact that they fuse together are also within the scope of the present invention. 
     One method of manufacturing some of the actuators within the scope of the present invention includes forming stator electrodes  80  on a first surface of a stator wafer  20 . Then, a micro-mover  50  is formed and positioned adjacent to the first surface of the stator wafer  20 . On the surface of the micro-mover  50  closest to the stator wafer are formed actuator electrodes  90 . At least one bumper  120  is formed on either the first surface of the stator wafer  20  or of the micro-mover  50 . This bumper  120  can be formed by selective etching, deposition, or another method of forming a protrusion from a surface. 
     The foregoing detailed description has been given for understanding exemplary implementations of the invention only and no unnecessary limitations should be understood therefrom as modifications will be obvious to those skilled in the art without departing from the scope of the appended claims and their equivalents.