Abstract:
The present invention combines electrostatic comb with parallel plate actuation in a novel design to create a robust low voltage MEMS Micromirror. Other unique advantages of the invention include the ability to close the comb fingers for additional reliability and protection during mirror snapping with over voltage.

Description:
This application claims the benefit of U.S. Provisional Application Ser. No. 60/904,697, filed on Mar. 2, 2007, under 35 USC 119(e), which is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The subject of this application generally relates to the field of Micro Electro Mechanical System (MEMS) and more particularly to MEMS with a structure rotating around a torsional hinge. 
     BACKGROUND 
     MEMS based actuators are enabling the emergence of a host of new components for use in displays, inertial measurement systems, RF and wireless systems and fiber-optic. In particular, optical components that are more compact, highly reliable, low power consumption and low cost are highly desirable. Examples of such components include switches, variable optical attenuators (VOA), tunable filters, and wavelength blockers. 
     One particularly important class of MEMS devices for such applications is the MEMS Micromirror rotating around a torsional hinge. In the early work on such devices the actuation was based on parallel plate electrostatic force usually between the minor and another electrode on one side of the axis. Some variations in this line are discussed by Miller (U.S. Pat. No. 7,010,188) and Nasiri (U.S. Pat. No. 6,533,947). More recent developments in the field include vertical comb drive actuators, which are discussed by Costello (U.S. Pat. Nos. 6,838,738; 6,628,856 and 6,782,153) and Novotny (U.S. Pat. Nos. 6,751,395; 6,914,711 and 6,914,710). 
     Combs drive actuation exhibit significant advantages over parallel plate actuation in the areas of speed, actuation voltage, and range of motion. Commercial examples include VOA products from Lightconnect (now Neophotonics), Dicon Fiberoptics and Santec. 
     Notwithstanding these advantages, there are limitations in the approaches of Costello, Novotny and others. Some of the limitations are in the actuation mechanism, the functional design space and the fabrication process of MEMS with a structure rotating around a torsional hinge. For example, the reduction of the amount of force and the throw distance are limited as in the use of fringe field in Costello&#39;s approach. In particular, the actuation mechanism of parallel plate force cannot be added. Furthermore, the comb fingers have to be like cantilevers and the fingers structure cannot be mechanically closed. Therefore, the comb fingers cannot be too long as they become susceptible to lateral snap. Similarly, in the case of Novotny, again, parallel plate force cannot be added and the stator combs can only be on one side of the structure. This will affect the air damping on the two sides of the structure axis and lead to higher susceptibility to mechanical shock. 
     MEMS with a structure rotating around a torsional hinge, such as micromirrors, are often operated close to the snapping point and the design and performance of such devices especially for low voltage and high stability applications is desired. This patent application presents a MEMS that combines both comb actuation with parallel plate force actuation to provide the maximum rotational force or torque and the design of MEMS that allows for snapping between the stator and rotor structures. Furthermore, this patent application presents a MEMS that recovers properly when the applied voltage is eliminated, or reduced below a certain operating voltage threshold thus overcoming many of the limitations of the prior art. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an exemplary MEMS that combines a rotor structure, supported by one torsional hinge, and a stator structure in accordance with one embodiment. 
         FIG. 2  shows an exemplary link structure in accordance with the embodiment of  FIG. 1 . 
         FIG. 3  shows a perspective view of exemplary MEMS that combines a rotor structure, supported by two torsional hinges, and a stator structure in accordance with another embodiment. 
         FIG. 4A  shows a plan view of an exemplary MEMS actuator that combines a rotor structure, supported by two torsional hinges, and a stator structure in accordance with yet another embodiment. 
         FIG. 4B  shows a plan view of the stator structure in accordance with the exemplary MEMS of  FIG. 4A . 
         FIG. 4C  shows a partial and expanded view of the exemplary MEMS of  FIG. 4A . 
         FIG. 4D  shows expanded view of the snapping tab and aperture structures for the exemplary MEMS of  FIG. 4A . 
         FIG. 4E  shows exemplary rotational positions for the exemplary MEMS of  FIG. 4A . 
         FIG. 5  shows exemplary manufacturing steps for the exemplary MEMS of  FIG. 4A   
     
    
    
     DETAILED DESCRIPTION 
     In general, Coulomb&#39;s law, simply stated, relates the magnitude of the electrostatic force between two point electric charges to be (a) directly proportional to the product of the magnitudes of each charge and (b) inversely proportional to the square of the distance between them. Microactuators utilize electrostatic actuation force, based on Coulomb&#39;s law, to overcome the elastic force required to deflect or deform a link that connects a movable structure to a fixed structure. The elastic force of the deformed link provides a restoring force that is needed for the movable structure to return to its initial position, i.e. in the absence of the electrostatic force. 
     An exemplary torsional hinge  100  mechanically coupling a rotor structure  110  to a substrate  120  is shown in  FIG. 1 . The torsional hinge  100  is itself composed of two portions. The first portion is a link structure  130  that can deform under twisting or flexing of the rotor structure  110 , and is normally used to suspend the rotor structure  110 . The second portion is an anchor structure  140  that is rigidly attached to the substrate  120  and the link structure  130 , and is used to provide the mechanical support to suspend the rotor structure  110  at a given distance from a stator structure  150 . The stator structure  150  comprises an electrically conductive surface area A  160 . Similarly, the rotor structure comprises an electrically conductive surface area B  170 , where it is relatively aligned to surface A  160 . The rotor structure  110  is at rest when there is no electrostatic force being generated between the rotor structure  110  and the stator structure  150 . An electrostatic force is generated whenever an electric potential is applied between surface A  160  and surface B  170 . When an electric potential is applied between surface A  160  and surface B  170 , an electrostatic force is generated and the rotor structure  110  will be tilted toward the stator structure  150  where the generated electrostatic force balances the restoring force that is due to the deformation or the twisting of the link structure  130 . 
     The electrostatic force generated between the electrically conductive surfaces A  160  and B  170  and is often referred to as a parallel plate drive, since often the surfaces A  160  and B  170  are relatively flat and parallel to each other while the rotor structure is at rest. The electrostatic force is produced when an electric potential is applied to the electrically conductive surfaces or plates. Based on Coulomb&#39;s law, the resultant electrostatic actuation force is directly proportional to the square of the voltage across the plates and inversely proportional to the square of the plate separation. The electrostatic actuation force is also directly affected by the permittivity of air. Computations of such forces will be shown further below. The movement of the rotor structure  110  is controlled with the appropriate dimensions of the link structure  130  such that the tilting of the rotor structure resembles a rotation around an axis of rotation  180 , as is shown in  FIG. 1 . 
     The dimensions of the link structure  200  usually resemble a thin long beam, as shown in  FIG. 2 . The link structure  200  is designed with its width  220  being shorter than its height  230  and much shorter than its length  210 , so that the twisting and deformation of the link structure  200  is easiest along the thinnest dimension, which is the width  220 . Therefore, the mechanical reliability of the overall hinge is directly affected by its ability to deform and then return to its original state without being damaged. In addition, please note that the dimensions of the link structure  200  directly control not only the restoring force but also the reliability of the overall MEMS. Link structures with other types of geometrical shapes, e.g. cylindrical, can also be used in place of a rectangular beam structure; and similar design criteria will be employed to appropriately dimension the link structure  130 . 
     An actuator  300  with a rotor structure  310  that is suspended by two torsional hinges is shown in  FIG. 3 . The first torsional hinge comprises a link structure  330  and an anchor structure  340  and the second torsional hinge comprises a link structure  335  and an anchor structure  345 . The rotor structure will rotates in a first direction around the axis of rotation  380  when an electric potential that is applied between surface A  360  and surface B  370  generates an electrostatic force that balances the elastic forces of the combined link structures  330  and  335 . The rotor structure will rotates in a second direction, opposite to the first direction, around the axis of rotation  380  when an electric potential that is applied between surface AA  365  and surface BB  375  generates an electrostatic force that balances the elastic forces of the combined link structures  330  and  335 . 
     A snapping of the rotor structure  310  occurs when the applied electrostatic force is large enough to rotate the rotor structure  310  all the way to the stator structure  350  and physical contact of the two structures occurs. This snapping can be catastrophic in multiple ways. One possible catastrophic failure of the MEMS occurs when an electrical short circuit of the two electrically conductive surfaces A 360  and B  370  occurs during the snapping of the rotor structure  310 . Electrically insulating the stator structure  350  or the rotor structure  310  can prevent such short circuit when snapping occurs, however at an additional cost. The insulation can be accomplished via the addition of a layer of a dielectric material to insulate the electrically conductive surfaces A  360 , AA  365 , B  370 , and BB  375 . However, the dielectric surfaces charge up with applied voltage and cause undesirable effects such as drift and other time-related effects. Another possible catastrophic MEMS failure is referred to as stiction and it occurs when the generated electrostatic force causes the rotor structure  310  to snap and becomes mechanically attached, to the stator structure  350  because of surface charges. If the stiction force is greater than the restoring force of the rotor structure  310 , then the rotor structure  310  will not be able to rotate back when the electrostatic force is removed. 
     Furthermore, the electrically conductive surfaces A  360 , AA  365 , B  370 , and BB  375 , shown in  FIG. 3  as flat surfaces, can be made up using various shapes and structures. For example, a comb structure formed by a row of long thin fingers that are designed onto surface A  360  and are interdigitated with a row of long thin fingers onto surface B  370 . The computation of the resultant electrostatic force generated from such comb structure is different from parallel plate and both are generally derived from Coulomb&#39;s law and given by equations 1 and 2 below. 
     The electrostatic force generated using a parallel plate drive structure: 
     
       
         
           
             
               
                 
                   
                     F 
                     pp 
                   
                   = 
                   
                     ɛ 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     A 
                     ⁢ 
                     
                       
                         v 
                         2 
                       
                       
                         2 
                         ⁢ 
                         
                           x 
                           2 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     1 
                   
                   ) 
                 
               
             
           
         
       
     
     Where the electrostatic force of the parallel plate drive F pp  is directly proportional to the permittivity of air (∈), the total surface area of the parallel plate (A), the square of the voltage potential across the plates (v 2 ) and inversely proportional to the square of the plates&#39; separation (x 2 ). 
     The electrostatic force generated using a comb drive structure: 
     
       
         
           
             
               
                 
                   
                     F 
                     cd 
                   
                   = 
                   
                     ɛ 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     Nl 
                     ⁢ 
                     
                       
                         v 
                         2 
                       
                       d 
                     
                   
                 
               
               
                 
                   ( 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     2 
                   
                   ) 
                 
               
             
           
         
       
     
     Where the electrostatic force of the comb drive F ed  is directly proportional to the permittivity of air (∈), number of rotor combs (N), the length of the comb drive (l), the square of the voltage potential between the rotor and stator combs (v 2 ) and inversely proportional to the comb drive separation (d). 
     One embodiment of an actuator  400  comprises an rotor structure  410  that is atop a stator structure  450 , supported by a first torsional hinge  430  and a second torsional hinge  435 . The actuator  400  is shown using a two-layer approach, one stator layer for the stator structure  450  as shown in  FIG. 4B  and one for the actuator  400  top view showing the rotor layer and only a portion of the stator layer as shown in  FIG. 4A . The rotor structure  410  uses a combination of a comb drive actuation and parallel plate actuation, thus increasing the total electrostatic force being generated and hence the total torque that is applied to the rotor structure  410 . The rotor structure  410  comprises a first comb structure  415  and a first plate structure  417  that are relatively aligned with a second comb structure  455  and a second plate structure  457 , both of which are formed on the stator structure  450 . In addition, the collinear torsional hinges  430  and  435  define an axis of rotation  480 , shown in  FIG. 4B , wherein the rotor structure  410  rotates in a plane that is orthogonal to the axis of rotation  480 . The rotor structure  410  further comprises a third comb structure  416  and a third plate structure  418  that are relatively aligned with a fourth comb structure  456  and a fourth plate structure  458 , both of which are formed on the stator structure  450 , as shown in  FIG. 4A  and  FIG. 4B . The rotor structure  410  exhibits symmetry and is balanced on either sides of the axis of rotation  480 . 
     The comb structure  415  is formed using a thin long fingers extending out of the parallel plate structure  417  on one side and are fully enclosed by the rotor structure  410  on the other side, thus it is referred to as a closed comb structure. The top view of the stator structure  450  is shown in  FIG. 4B . The stator structure  450  is relatively aligned below the rotor structure  410  using the torsional hinges  430  and  435  that are anchored to the stator structure  450 . Furthermore, the second comb structure  455  is formed using fingers that extend upward from the stator structure  450  and are interdigitated with the first comb structure  415 . Similarly, the fourth comb structure  456  is formed using fingers that extend upward from the stator structure  450  and are interdigitated with the third comb structure  416 . All comb structures fingers do not mechanically contact each other as the rotor structure  410  rotates around the rotation axis  480  and subsequently avoiding any lateral snapping between the rotor structure  410  and the stator structure  450  as shown in  FIG. 4A . The first comb structure  415  and the second comb structure  455  form a comb drive actuation mechanism for the rotor structure  410 . Similarly, the first plate structure  417  and the second plate structure  457  form a parallel plate drive actuation mechanism. The total torque generated by both actuation mechanisms causes the rotor structure  410  to rotate around the axis of rotation  480 . The computation of the total torque is discussed in the next paragraph and is simply computed by the addition of the two independently calculated torques, namely the parallel plate drive torque and comb drive torque. 
     Generally, the torque that is generated by an actuator designed to use both the parallel plate drive and the comb drive can be theoretically computed by adding the two independently calculated torques and is governed by equation 3, as listed below.
 
 T=T   cd   +T   pp =ƒ( F   cd   +F   pp ) x.dA=k   T θ  (Equation 3)
 
θ= T/k   T   (Equation 4)
 
Where T is the total torque, T cd  is the torque component from the comb drive actuation, T pp  is the torque from the parallel plate actuation. F cd  and F pp  are the electrostatic forces generated by the comb drive structure and the parallel plate structure respectively and x is the lever arm distance from the axis of rotation as defined by two collinear torsional hinges. The torque T is applied against two torsional hinges that pushback with a restoring torque, k T θ where k T  is the torsional stiffness of the two hinges and θ is the rotational angle of the rotor structure  410 . The rotational angle θ can be controlled by the balance of the total torque T and the torsional stiffness k T , as shown in equation 4 above. In the next few paragraphs, the electrical configuration of the comb drive and parallel plates drive and the resultant rotation of the rotor structure  410  will be discussed.
 
     An isolation trench  485  electrically isolates the stator structure  450  from the second comb structure  455 , the second plate structure  457 , the fourth comb structure  456  and the fourth plate structure  458 , as shown in  FIG. 4B . Furthermore, the second comb structure  455  and the second plate structure  457  are electrically coupled to a first bondpad  490 . Similarly, the fourth comb structure  456  and the fourth plate structure  458  are electrically coupled to a second bondpad  495  that is electrically isolated from the first bondpad  490  by the isolation trench  485 , as shown in  FIG. 4B . Both the first and second bondpads are isolated from the rest of the stator structure  450 . In addition, the rotor structure  410  is electrically coupled to a rotor structure bondpad  498 , and the stator structure  450  is electrically coupled to a stator structure bondpad  499 , wherein both bondpads  498  and  499  are electrically coupled and together are referred to as the third bondpad. 
     A partial and expanded view of the actuator  400  is shown in  FIG. 4C , where the isolation trench  485 , the first comb structure  415 , the second comb structure  455 , a snapping tab  460  and a snapping tab aperture  470  are shown. The snapping tab  460 , which extends out of the rotor structure  410 , is electrically coupled to the third bondpad through the rotor structure  410 . The snapping tab aperture  470  is shaped as a narrow opening in the stator structure  450  and is electrically coupled to the third bondpad. The snapping tab aperture  470  is dimensioned slightly larger than the snapping tab  460  such as to limit the lateral movement of the rotor structure  410  as it rotates around the axis of rotation  480 . An expanded view of the snapping tab  460  and snapping tab aperture  470  is shown in  FIG. 4D . According to a preferred embodiment, the rotor structure comprises two snapping tabs  460  on one side of the rotor structure  410  and another two snapping tabs  465  on the opposite side of the rotor structure  410 , as shown in  FIG. 4A . The snapping tabs  460  and  465  comprise electrically conductive surfaces and are electrically coupled to the rotor structure  410 . In addition, when snapping occurs, the snapping tabs apertures  470  and  475  guide the snapping tabs  460  and  465  to make mechanical and electrical contact with the stator structure  450 . Therefore, two major benefits are derived, the first is avoiding catastrophic failures due to electrical short circuit since both the snapping tabs apertures  470  and  475  and the snapping tabs  460  and  465  are at the same electrical potential, namely the third bondpad potential. The second major benefit is reducing to a great extent the stiction forces since the snapping tabs  460  and  465  have very small surface area that can make mechanical contact at the corresponding snapping tab apertures  470  and  475 , thus the ability for the rotor structure  410  to quickly recover when snapping occurs. Further benefits are also achieved, for example, the likelihood that a lateral snapping can occur between the comb drive structures  415 ,  455 ,  416  and  456  is greatly reduced because the snapping tabs apertures  470  and  475  limit the lateral movement of the rotor structure  410  and thus avoiding a possibility for catastrophic failure. Therefore, the actuator  400  possesses an enhanced operational stability and reliability. Next, we will discuss the rotation of Rotor structure  410  due to the application of electrical potential to the comb drive and parallel plate drive. 
     Exemplary rotational positions of the actuator  400  according to one embodiment are presented in  FIG. 4E . In the absence of any electrical potential between the first and third bondpads or between the second and third bondpads, the rotor structure  410  is normally at rest, namely at a first position, suspended over the stator structure  450  by the torsional hinges  430  and  435 . Let us start by applying a first electrical potential between the first and third bondpads. The comb drive formed by the first and second comb structures  415  and  455  and the parallel plate drive formed by the first and second plate structures  417  and  457  will generate an electrostatic force and in turn a torque T. If the first electrical potential is sufficient to generate a torque T 1  that is greater than the torsional stiffness k T  of the torsional hinges  430  and  435 , then the rotor structure will rotate from a first position to a second position, as shown in  FIG. 4E , until T 1  balances the torsional stiffness k T  at the second position. Furthermore, a snapping of the rotor structure  410  occurs when a second relatively large electrical potential, is applied between the first and third bond pads, generates a large torque T max  that is greater than the torsional stiffness k T  exerted by the torsional hinges. The large torque T max  rotates the rotor structure  410  to a maximum rotational angle θ max , whereat the rotor structure  410  mechanically contact the stator structure  450  at a third position, as shown in  FIG. 4E . 
     Similarly, applying a third electrical potential between the second and third bondpads will generate an electrostatic force in the comb drive formed by the third and fourth comb structures  416  and  456  and the parallel plate drive formed by the third and fourth plate structures  418  and  458  and in turn a torque T 2 . If the third electrical potential is sufficient to generate a torque T 2  that is greater than the torsional stiffness k T  of the torsional hinges  430  and  435 , then the rotor structure will rotate from the first position to a fourth position, as shown in  FIG. 4E , until T 2  balances the torsional stiffness k r  at the fourth position. Furthermore, a snapping of the rotor structure  410  occurs when a fourth relatively large electrical potential is applied between the second and third bond pads and thus generates a large torque T 2max , that is greater than the torsional stiffness k T  exerted by the torsional hinges. The large torque T 2max  rotates the rotor structure  410  to a maximum rotational angle θ 2max , whereat the rotor structure  410  mechanically contact the stator structure  450  at a fifth position, as shown in  FIG. 4E . It is important to note that at either the third or the fifth positions the snapping tabs  460  and  465  will be the first to contact the stator structure  450  mechanically and electrically at the snapping tab apertures  470  and  475 . Furthermore, because both the rotor structure  410  and the snapping tab aperture  470  are both coupled to the third bondpad, then they are at the same electrical potential and there is no likelihood that a short circuit will occur when electrical contact is made between the rotor structure  410  and the stator structure  450 . Therefore, according to this embodiment the snapping of the rotor structure  410  is not catastrophic and can easily recover by reducing or eliminating the applied electrical potential. This is not the case for many MEMS devices where snapping creates a catastrophic damage. Furthermore, many MEMS devices with dielectric surfaces, between their rotor and stator structures to avoid short circuit, charged up and that causes their rotor structure to recover slowly as well. Hence, the stability and reliability of the actuator  400  is further increased. Next, we will discuss exemplary manufacturing steps for a MEMS actuator, where the rotor structure is used as a mirror that can reflect incoming light at different angles in accordance with another embodiment. Yet in another embodiment, the rotor structure can be made to support other types of structure, for example, used to send and receive radio waves. 
     Exemplary manufacturing steps  500  are presented using the cross-sectional views of  FIGS. 5   a - 5   f  and are accomplished with a straightforward fabrication process. We start with a first SOI wafer  510 , shown in  FIG. 5   a , with a silicon handle  511 , buried oxide  512  and SOI layer  513 . The buried oxide is typically 0.5-1.0 um thick and the SOI layer is typically 10-30 um. A thermal oxide  524  is grown and the wafer is patterned with a “Cavity” mask that is then etched first with an oxide etcher followed by a silicon deep reactive ion etcher (DRIE), such as the STS silicon etcher, a cross-sectional view is shown in  FIG. 5   b  and the plan view is shown in  FIG. 4B . The etching step opens up a cavity in which a micromirror will rotate and at the same time defines the stator combs  526 . The width of the stator combs  526  is typically a few microns and there are 10s to low 100s that provide the comb drive actuation force to the micromirror. The etching step goes through half to two thirds the depth of the SOI layer  513 . The remaining SOI is used to define the stator plate  528  that provides the parallel plate actuation force to the micromirror. In the next step, the Electrode Trench  534  that will electrically separates the stator combs  526  and stator plate  528  from the rest of the SOI layer  513  is defined. The SOI layer  513  is normally connected to ground. A thick photo resist covers the stator combs  526  which is then patterned with the Electrode Trench  534  mask. Again, the STS silicon etcher is used to etch the silicon down to the buried oxide  512 , as shown in  FIG. 5   c  and the corresponding trench  485  as shown in  FIG. 4B . This electrode trench  534  electrically isolates the stator combs  526  drive and the plate drive  528  from the ground. 
     In the next step, a second SOI wafer  540  is bonded to the first SOI wafer  510  at the thermal oxide  524  interface, and its handle is removed by grind and polish followed by chemical etching thus defining a micromirror layer  543 , as shown in  FIG. 5   d . Further processing steps of the micromirror layer will define a closed rotor combs  555 , rotor plate  557  and bondpad structures  558 , as shown  FIGS. 5   d  and  5   e . In the following step, the rotor combs  555  are defined and etched, as shown in  FIG. 5   e , thus exposing the thermal oxide  524  layer atop the stator combs  526  and the bondpad  558 . The alignment requirement on lithography for this step is very stringent because the rotor and stator comb alignment is very critical for proper function. This can be accomplished by a good back to front alignment scheme or by opening up windows in the micromirror layer  543  to alignment marks in the SOI layer  513 . The micromirror layer  543  alignment marks are then aligned to the SOI layer  513  marks. After lithography, the STS silicon etcher etches the micromirror and rotor combs. 
     The next processing step is an oxide etcher to remove the thermal oxide  524  from the top of the stator combs  526  and the bondpad  558 , as shown in  FIG. 5   f . The bondpad structure  558  corresponds to the stator structure bondpad  499 , as shown in  FIG. 4A  and  FIG. 4B . Finally the photoresist is removed in a plasma asher and then a bondpad metal is deposited through a shadow mask and is nominally Aluminum or Gold with some adhesion layer such as Ti or Cr. The bondpad metal is alloyed at an elevated temperature (350-400 C) to activate the ohmic contact. This is followed by depositing the micromirror metal through another shadow mask onto the octagonal shaped silicon micromirror. For IR (infrared) application in the Telecom wavelength, this is usually a thin layer of Gold with an adhesion layer of Ti. This completes the fabrication of the wafer. Various industry standard methods are available to dice the wafer and create individual chips. 
     According to one embodiment, the approach allows for closing of the comb fingers as shown in  FIG. 4A  and  FIG. 4C . This leads to a more robust design. Another unique feature is the snapping tabs  460  and  465 , and the corresponding aperture  470  and  475 , as shown in  FIG. 4A . When the micromirror snaps because of over voltage in the vertical or the transverse direction, the snapping tabs  460  and  465 , hit the bottom or side of snapping tabs aperture  470  and  475 . Both of the snapping tabs  460  and  465  and snapping tabs apertures  470  and  475  are at the same ground potential. In addition, the snapping tabs  460  and  465  provide the micromirror with limited contact area and thus enhancing its performance and reliability. 
     The bondpad  558  metal contact allows the electrical ground connection to the SOI layer  513  that is defined outside the Electrode Trench  534 , as shown in  FIG. 5   e , including the snapping tabs apertures  470  and  475  and thus grounds the bottom SOI layer  513  (cavity layer) everywhere except the drive region, i.e. the combs  526  and plate  528  regions. The bondpad  558  corresponds to the bondpad  499  as shown in the plan view of  FIG. 4A  and  FIG. 4B . The bondpad  498 , shown in  FIG. 4A , electrically grounds the micromirror, rotor combs and the rest of the micromirror layer including the snapping tabs  460  and  465 . The drive bondpad  490 , as shown in  FIG. 4B  carries a positive voltage to the stator combs  526  and the plate region  528 . Since the micromirror plate  557  and the rotor combs  555  are grounded, then a corresponding, electrostatic force is created and in turn, torque is generated that cause the micromirror to rotate. 
     A Micro Electro Mechanical System (MEMS) actuator operation and manufacturing are described to enable the use in applications where a micro movement of the rotor structure corresponds to a desired operation. The rotor structure can be made for optical or radio frequency applications, e.g. the actuator can be made to act as a mirror to reflect light at different angles thus can be used in optical applications. Furthermore, it can be used as directional antenna where the micro movement of the antenna can be made to optimize reception or emission of radio frequency. Snapping tabs and snapping tabs apertures structures are described to greatly enhance performance, stability and reliability of MEMS actuator. Application utilizing some of the described techniques can avoid MEMS device catastrophic failures and improve overall system performance. In addition, actuator quick recovery and simple manufacturing steps by avoiding the dielectric layer between stator and rotor structure allows cost reduction with increase in performance.