Abstract:
This invention relates to a micro-switch assembly involving a novel magnetic latching mechanism. In one aspect of the present invention, it involves a micromachined structure that comprises an outer frame, an inner frame pivotally connected to the outer frame and rotates when an external electromagnetic force is applied, and a means for latching the inner frame at a given angle of inclination relative to the outer frame. One embodiment of the present invention involves the use of a magnetic material, such as Permalloy, and permanent magnets to achieve the latching result. A Permalloy piece is attached to the inner frame of the micro-switch assembly and a magnet layer is attached to the outer frame. The magnetic force attracting the Permalloy piece and the magnet layer allows the latching of the two frames to occur in the absence of the external applied electromagnetic force. The use of this magnetic latching mechanism allows a reduction in the use of electric current to maintain a movable frame in a micromachined structure or a micro-switch assembly in a fixed position. It provides advantages of greater mechanical and optical stability and less energy consumption. In other embodiments, additional Permalloy pieces can be added to the outer frame to increase the magnetic field, so as to further reduce the electric current necessary for latching and unlatching the frames.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a micromachined structure and to an opto-mechanical switch (micro-switch) incorporating the micromachined structure. Specifically, it relates to a latching mechanism incorporated in the opto-mechanical micromachined switch.  
           [0003]    2. Description of Related Art  
           [0004]    Micromachines are small electromechanical devices that are fabricated on wafers of silicon and other materials using semiconductor manufacturing techniques. Optical switches in micro-electromechanical systems (MEMS) employ tiny mirrors that are etched onto silicon wafers. Such optical switches are commonly used in fiber-optic networks, through which light signals/data are routed. The tiny mirrors can be positioned to intercept the incoming light signals conveyed via the individual strands of optical fiber. Or alternatively, the mirrors can be pivoted to direct the incoming light beam at a desired angle into a receiving fiber.  
           [0005]    Opto-mechanical switches typically include a light source, a light receiver, and a movable light blocking/reflecting mechanism. The light blocking/reflecting mechanism typically includes a drive motor that is selectively actuated to move a blocking/reflecting member (e.g., a mirror) between or among different positions, thereby performing the micro-switch function.  
           [0006]    Typically, an electromagnetic drive motor is used to turn on/off the micro-switch by moving the mirror. In the past, to maintain the switch in the “on” position, current must be applied continuously to maintain the electromagnetic force on the mirror. The continuously applied current inherently generates excess heat, which is dissipated to the neighboring structure, which is undesirable for a micro-electromechanical system. Among other things, this heat can cause the reflective surface and supporting structure to change shape and size, thereby increasing mechanical and optical instability. Besides, continuous application of electric current also results in high-energy consumption. This heating problem is exacerbated when a large number of micro-switches are used in a large array for switching in an optical network. It is therefore desirable to provide an opto-mechanical micromachined micro-switch that avoids the heating problems associated with the continuous application of electric current.  
         SUMMARY OF THE INVENTION  
         [0007]    To overcome the shortcomings of existing optical switches described above, the present invention relates to an opto-mechanical micro-switch assembly that is more efficient, more mechanically and optically stable, and consumes less energy. Specifically, this invention relates to a novel magnetic latching mechanism for the mirror in the micro-switch. The present invention also relates to a method of operating the opto-mechanical micro-switch assembly.  
           [0008]    According to one embodiment of the present invention, the overall assembly of a micromachined switch consists of an inner frame pivotally connected to an outer frame formed from a monocrystalline silicon substrate via torsion beams. The structure of the inner frame includes a light-reflecting (mirror) surface. A current can be applied to coils that are attached to the inner frame. Permanent magnets are attached onto the outer frame. Because of the interaction of the current and the magnetic field of the permanent magnets, an electromagnetic force causes the inner frame, and thereby the mirror, to pivot about the beams. When the mirror rotates to a certain position, the mirror surface intercepts (blocks or reflects) light transmitted via fiber optic networks. It is often required to maintain the mirror at such positions for a length of time during the operation of the micro-switch. The present invention provides a novel mechanism for latching the mirror for such purpose.  
           [0009]    According to one embodiment of the present invention, a piece of magnetic material (e.g., Permalloy) is attached to the lower portion of the moving/rotatable inner frame. The outer frame consists of layers of a silicon substrate, a permanent magnet, and a nickel/iron base. These layers are etched onto each other using prevailing art of micromachining. Upon applying an initial electromagnetic force to rotate the inner frame past a threshold, the Permalloy piece is brought closer to the permanent magnet layer. Due to the attraction between the Permalloy piece on the inner frame and the permanent magnet layer in the outer frame, the inner frame of the opto-mechanical micro-switch can be latched onto the outer frame without continuous application of electric current to maintain the electromagnetic force to keep the inner frame in the rotated position.  
           [0010]    In another embodiment of the present invention, a Permalloy piece is attached to the permanent magnet layer in the outer frame to focus the magnetic field at the Permalloy piece on the inner frame. During pivotal movements, the Permalloy piece already attached to the inner frame will be drawn to the Permalloy piece on the outer frame. The addition of the Permalloy piece on the outer frame increases the effective magnetic force, which attracts and holds the two Permalloy pieces in a latched-on position.  
           [0011]    The above, as well as additional objects, features, and advantages of the present invention will become apparent in the following detailed written description.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    For a fuller understanding of the nature and advantages of the present invention, as well as the preferred mode of use, reference should be made to the following detailed description read in conjunction with the accompanying drawings. In the following drawings, like reference numerals designate like or similar parts throughout the drawings.  
         [0013]    [0013]FIG. 1 is a perspective view showing a micromachined micro-switch structure in accordance with one embodiment of the invention.  
         [0014]    [0014]FIG. 2 is a plan view of the opto-mechanical micro-switch of FIG. 1 in relation to light source and detectors.  
         [0015]    [0015]FIG. 3 is a sectional view of the opto-mechanical micro-switch taken along line  3 - 3  in FIG. 2 at the “switch off” stage.  
         [0016]    [0016]FIG. 4 is a plan bottom view of the inner frame in FIG. 3 showing one embodiment of the present invention with Permalloys.  
         [0017]    [0017]FIG. 5 is a plan bottom view of the inner frame in FIG. 3 showing another embodiment of the present invention with Permalloys.  
         [0018]    [0018]FIG. 6 is a sectional view of the opto-mechanical micro-switch of FIG. 3 rotating towards the latched position.  
         [0019]    [0019]FIG. 7 is a graph showing the relationship of various static torques for switching on an opto-mechanical micro-switch according to one embodiment of the present invention.  
         [0020]    [0020]FIG. 8 is a sectional view of the opto-mechanical micro-switch of FIG. 3 at the “switch-on” stage.  
         [0021]    [0021]FIG. 9 is a graph showing the relationship of various static torques for latching on an opto-mechanical micro-switch according to one embodiment of the present invention.  
         [0022]    [0022]FIG. 10 is a sectional view of the opto-mechanical micro-switch of FIG. 3 at the “switch starts off” stage with latch on.  
         [0023]    [0023]FIG. 11 is a graph showing the relationship of various static torques for unlatching an opto-mechanical micro-switch according to one embodiment of the present invention.  
         [0024]    [0024]FIG. 12 is a graph showing the changes of coil actuation current during the operation of an opto-mechanical micro-switch according to one embodiment of the present invention.  
         [0025]    [0025]FIG. 13 is a sectional view of an opto-mechanical micro-switch with the Permalloy on the stop die at the latched on position in accordance with another embodiment of the present invention.  
         [0026]    [0026]FIG. 14 is a sectional view of an opto-mechanical micro-switch with the Permalloy on the stop die at the latched off position in accordance with another embodiment of the present invention.  
         [0027]    [0027]FIG. 15 is a perspective bottom view of the inner frame in FIG. 3 showing one embodiment of the present invention with Permalloy.  
         [0028]    [0028]FIG. 16 is a perspective bottom view of the inner frame in FIG. 3 showing another embodiment of the present invention with Permalloys.  
         [0029]    [0029]FIG. 17 is a perspective bottom view of the inner frame in FIG. 3, showing another embodiment of the present invention with Permalloys.  
         [0030]    [0030]FIG. 18 is a graph showing the relationship between the critical torque and the current of the coil.  
         [0031]    [0031]FIG. 19 is a cross-sectional view taken along line  19 - 19  in FIG. 5 of the inner frame with the substrate of the outer frame.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0032]    This invention is described in a preferred embodiment in the following description with reference to the drawings. While this invention is described in terms of the best mode for achieving this invention&#39;s objectives, it will be appreciated by those skilled in the art that variations may be accomplished in view of these teachings without deviating from the spirit or scope of the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims.  
         [0033]    An opto-mechanical micromachined switch is described in U.S. patent application Ser. No. 09/366,428 filed Aug. 2, 1999, assigned to Integrated Micromachines, Inc., the assignee of the present invention. That application is fully incorporated by reference herein.  
         [0034]    An opto-mechanical micro-switch, according to one embodiment of the present invention, comprises a micromachined structure that is formed from a monocrystalline silicon substrate. Referring now to FIG. 1, there is shown a perspective view of the overall assembly of such micromachined structure  100 , which is formed from a monocrystalline silicon substrate  110  having an upper surface  112  that lies in the { 100 } plane of monocrystalline silicon substrate  110 . The single crystal structure of monocrystalline silicon substrate  110  is recommended because it provides mechanical advantages, such as superior stiffness, durability, fatigue and deformation characteristics. In addition, monocrystalline silicon substrates are relatively inexpensive and readily available. Further, batch fabrication techniques using monocrystalline silicon are well established. Monocrystalline silicon substrate  110  can be economically micromachined to form relatively defect-free micromachined structure  100 . In other embodiments, substrate  110  may be formed using other materials.  
         [0035]    Micromachined structure  100  includes an outer frame  120  and an inner frame  130 . Inner frame  130  is pivotally connected to outer frame  120  by beams  40 . A controller  99  is configured to apply an external force to rotate the inner frame  130  about beams  40 . Inner frame  130  has outward-facing flat surface  138 . As described below, outward-facing flat surface  138  is utilized as a light reflecting/blocking surface that either reflects an incident light beam (i.e., when a light reflecting (mirror) material is deposited on the surface  138 ), or blocks the incident light beam (e.g., when the surface  138  is partially or fully opaque).  
         [0036]    [0036]FIG. 2 is a plan view showing an opto-mechanical micro-switch  300  incorporating the micromachined structure  100  (shown in FIG. 1) and the relationship to light source and sensors in accordance with one embodiment of the present invention. In FIG. 2 the opto-mechanical micro-switch  300  includes a light source  14 , a first light receiver  15 , a second light receiver  16 , and micromachined structure  100 , which is located adjacent to light source  14  and light receivers  15  and  16 . As indicated above, micromachined structure  100  includes an outer frame  120  and an inner frame  130  that is surrounded by and pivotally connected to the outer frame  120 . Inner frame  130  includes an outward-facing flat surface  138  that is used to selectively reflect a light beam  18  from light source  14  to first light receiver  15 . In the embodiment shown, the planar size of the inner frame  130  is on the order of 2 mm×2 mm.  
         [0037]    Although a single opto-mechanical micro-switch  300  is shown in FIG. 2, the methods and structure of the present invention may be utilized to produce a multi-switch device including an array of multiple micromachined structures  100  formed on a single substrate. Because micromachined structure  100  is formed using a batch process, multiple interacting micro-switches may be formed during the same fabrication process, thereby providing alignment of multiple mirror surfaces to produce a multi-switch arrangement. In addition, to manufacture the micromachined structure  100  and the micro-switch  300 , etch-stop diffusion, silicon nitride deposition, Permalloy formation, anisotropic etching, frame separation, metallization can be performed using the manufacturing techniques disclosed in U.S. patent application Ser. No. 09/366,428 filed Aug. 2, 1999, assigned to Integrated Micromachines, Inc., the assignee of the present invention.  
         [0038]    One aspect of the present invention is shown in FIGS.  3 - 5 . FIG. 3 is a sectional view, taken along line  3 - 3  in FIGS. 2 and 4, of opto-mechanical micro-switch incorporating an embodiment of the present invention. In FIG. 3, the micro-switch is in its “switch off” position. The { 100 } plane of monocrystalline silicon substrate  110  defines upper surface  112 . The { 111 } plane of monocrystalline silicon substrate  110  defines the outward-facing flat surface  138  of the inner frame  130 . As is characteristic of a single silicon crystal, the { 100 } plane (indicated as horizontal plane P 100 ) intersects the { 111 } plane (indicated as plane P 111 ) at an angle α equal to 54.7°.  
         [0039]    The monocrystalline silicon substrate is formed such that the upper and lower surfaces lie in { 100 } planes of the substrate. The anisotropic etchant stops at the { 111 } plane of the monocrystalline silicon substrate, thereby producing the flat wall at a known angle relative to the upper and lower surfaces of the substrate. In the KOH etching process, a notch  23  is formed by etching along the { 111 } crystal plane of the silicon substrate layer  24  so that it can be aligned with the etched { 111 } plane of the substrate  110  above it. The notch  23  is a recess that allows the layer of substrate  110  to align accurately onto the layer of substrate  24 . The angle of the KOH etched plane is about 54.7° to the { 100 } plane of the substrate  24 .  
         [0040]    When the inner frame  130  is rotated a predetermined amount relative to the outer frame  120 , the outward-facing flat surface  138  is rotated into a raised position to selectively obstruct or reflect light passing from the light source  14  to the light receiver  15 / 16  of the opto-mechanical micro-switch  300 . This is known as the “switch-on” position and is shown in FIG. 8.  
         [0041]    In accordance with one embodiment of the present invention, the method of operating the micro-switch is provided below. Actuation of micromachined structure  100  in the opto-mechanical micro-switch  300  arrangement requires the application of a force (e.g., electromagnetic) to inner frame  130  that causes pivoting or rotation of inner frame  130  relative to outer frame  120  around beam  40  (see FIGS. 4 and 5) about the axis of rotation  42 . Inner frame  130  is selectively pivoted into a position in which the plane of the light reflecting/blocking, outward facing flat surface  138  is perpendicular to upper surface  112  as shown in FIG. 8. In this manner, the opto-mechanical micro-switch  300  operates by pivoting from a first position shown in FIG. 3, in which end Y is located at or below plane P 100  defined by upper surface  112  (i.e., the “switch-off” position), to the upright (second) position shown in FIG. 8, in which the plane P 111  defining surface  138  intersects the plane P 100  of substrate  110  at an angle of approximately 90° (i.e., the “switch-on” position). As indicated in FIG. 3, when inner frame  130  is in the “switch-off” position, light beam  18  is transmitted across micromachined structure  100  from light source  14  to light receiver  16 , thereby indicating a first switch state. However, as shown in FIG. 2, when the inner frame rotates upward, light beam  18  is reflected by outward-facing flat surface  138  back to the light receiver  15  or blocked altogether (not shown in figures), thereby indicating an alternate switch state.  
         [0042]    It is noted that the terms “switch-on” and “switch-off” are referenced arbitrarily relative to two states of the switch. The “on” and “off” states of the switch may be interchanged between FIG. 3 and FIG. 8 without departing from the scope and spirit of the invention.  
         [0043]    In one embodiment, a magnetic material such as a Ni—Fe material commercially available under the trademark Permalloy is provided on the inner frame  130 , so that the inner frame can be latched onto the outer frame  120 , without continuous application of electric current through coils attached to the inner frame  130 . The electromagnetic force can be applied through an external structure, mounted in close proximity to micromachined structure  100  on a hybrid substrate, or integrated onto micromachined structure  100 .  
         [0044]    As indicated in FIG. 3, a Permalloy piece  30  on the inner frame and a permanent magnet layer  26  in the outer frame are arranged to maintain latching after pivoting/rotation. The Permalloy piece  30  is attached to the downward movable portion  32  at end X of inner frame  130 . The magnet  26  lies between the silicon substrate layer  24  and the nickel/iron layer  28 .  
         [0045]    [0045]FIG. 19 shows the cross-sectional view of the inner frame  130  along line  19 - 19  in FIG. 5 with reference to the outer frame. As seen in these two figures, the inner frame  130  has permalloys  30 b and  30 c that do not contact the substrate  24 . The width of the substrate  24  in FIG. 19 does not extend to contact the permalloys  30 b and  30 c that are suspended in the air without supports below them. The substrate  24  has minimal contact area with the inner frame  130  to reduce stiction. This configuration can also be applied to the Permalloy configuration shown in FIG. 14.  
         [0046]    As indicated above, FIG. 3 shows the initial position, or the first switch state or the “switch off” state. At this “switch-off” state, end Y remains at or below plane P 100  with upward movable portion  34  resting upon silicon substrate  24  at upper silicon surface  54 . The coils  20 , which lie on upper surface  112  of inner frame  130 , are fabricated in accordance with techniques known to those skilled in the art. Coils  20  include a plurality of electrically conductive windings, which are electrically isolated from adjacent windings by an insulating material. As current flows through coils  20 , an electromagnetic force is generated.  
         [0047]    As the inner frame  130  begins to pivot from the “switch-off” state in FIG. 3 to the “switch-on” state as shown in FIG. 8, the inner frame  130  begins to pivot in an anti-clockwise direction under the interaction of the current and the magnetic field caused by the permanent magnet layer in the outer frame. As the inner frame begins to pivot (see FIG. 6), a reactive torque, τ beam , is generated from the torsion of the beams  40  and it gradually increases. On the other hand, the torque generated by the electromagnetic force caused by a constant current in the coils, τ coil , generally decreases with rotation of the inner frame  130  in the anti-clockwise direction (the τ coil  is not constant because of the change in relative position between the coils  20  and the permanent magnet  26  and the change in the direction of the component of the magnetic force attributing to torque on the inner frame). At the same time, the torque caused by the attractive force between the Permalloy piece  30  and the magnet  26 , τ permalloy , continues to increase. In order for the inner frame  130  to be able to rotate, the following relationship must be met: |τ permalloy +τ coil |&gt;|τ beam |.  
         [0048]    When the angle of inclination (or rotation) of the inner frame reaches a critical angle (θ critical ), which is measured about the axis of rotation  42 , τ permalloy  is sufficient to counteract beam even in the absence of the current induced τ coil . Beyond θ critical , as long as τ permalloy &gt;τ beam , the inner frame will continue to rotate to an upper silicon surface  54  as shown in FIG. 8, and remain in this position (i.e., latched on) in the absence of any coil current. The magnetic force from the permanent magnet layer  26  holds the Permalloy piece  30  down, against the bias of τ beam , thus maintaining the inner frame  130  in the latched position. τ latching  is the value of τ permalloy  at the latched position. FIG. 7 shows that after θ critical , τ permalloy  is greater than τ beam , thus ensuring the switching on state. FIG. 18 further shows that the current I coil  required to ensure rotation of the inner frame lies within a range of possibilities. One can control the applied coil current to provide a changing τ coil  that just exceeds τ beam -τ permalloy  (or Δτ) along the rotation of the inner frame from θ=0 to θ=θ critical . This requires more complex control, but would minimize the applied current. θ critical  is the greatest value of τ beam -τ permalloy  during rotation to θ critical . As long as the entire I coil  curve lies on or above the Δτ curve, any of the I coil  curves will allow the necessary current for the desired rotation of the inner frame for latching. As shown in FIG. 12, in yet another embodiment of the present invention, once the threshold θ critical  is passed, a reverse current of an appropriate amount may be applied through the coils in order to generate a torque (&lt;|τ permalloy -τ beam |) in a clockwise direction to counter the τ permalloy  that is in excess of τ beam  and a torque attributed to the rotational momentum of the inner frame. The purpose of this reverse torque is to soften the impact when the Permalloy piece attached to the inner frame hits the outer frame.  
         [0049]    As indicated in FIGS. 8 and 9, in one embodiment of the present invention, when the angle of inclination, θ, reaches 35.24°, the inner frame  130  is latched onto the outer frame  120  at silicon substrate  24 . The value, 35.24°, is the difference of 90° and 54.76°, which is the angle of intersection of P 111  of the inner frame and the upper surface  112  of the outer frame  120  when the inner frame is in its “switch off” position. At this angle of inclination, the flat surface of P 111  of the inner frame  130  will form a 90° angle with the upper surface  112  of the outer frame  120 . As mentioned before, even though the power is released, the magnetic force between the magnet  26  and Permalloy piece  30  maintains the latching position. As shown in FIG. 8, in this latched on position, all light from the light source  14  is reflected to receiver  15  (see FIG. 2; receiver  15  is obscured from view by light source  14  in FIG. 8) or blocked from receiver  16 .  
         [0050]    [0050]FIGS. 10 and 11 demonstrate the process in which the latched-on switch returns to its “off” position. When the switch is to be unlatched, power is applied so that a reverse current runs through the coils  20 . As shown in FIG. 8, the latching torque in the anti-clockwise direction is the torque generated by the magnetic force between the Permalloy piece and the permanent magnet, i.e., τ latching . To unlatch the inner frame, two opposing torques to the latching torque come into play, the torque of the beam, τ beam , and the torque generated by the interaction of the reverse current through the coils  20  and the magnetic field from the permanent magnet  26 , τ coil . As shown in FIG. 11, at the point of unlatching, |τ unlatching |=|τ coil +τ beam | must be greater than |τ permalloy | to initiate rotation of the inner frame from its latched position. τ coil  must be maintained such that it is greater than |τ permalloy -τ beam | at all times to maintain rotation of the inner frame, until the inner frame reaches θ critical . If a constant reverse current is applied, τ coil  should be the maximum value of |τ permalloy -τ beam | (i.e., at the latched position τ latching -τ beam  in FIG. 11) to ensure sufficient τ coil . If a variable current is applied, τ coil  may be decreased as the inner frame rotates from the latch position. (It is noted that θ critical  for clockwise rotation (unlatching) may be slightly different from θ critical  for anti-clockwise rotation (latching) because of rotational momentum of the inner frame, a dynamic component that causes hysteresis in θ critical  and other parameters between rotations in the two directions. The reverse current may be released once the critical angle, θ critical , is passed. As indicated before and as shown in FIG. 11, after this point, τ beam  is greater than τ permalloy , and thus the inner frame will continue to tilt in the anti-clockwise direction until its end Y rests on the silicon substrate  24 . In yet another embodiment of the present invention, once the critical point is passed, a current of an appropriate amount is applied through the coils to generate a torque (less than |τ beam -τ permalloy |) in the anti-clockwise direction to counter the excessive torque of the beams and the rotational momentum of the inner frame. The purpose is to soften the impact of end Y of the inner frame when it returns to its original “off” position and rests on the silicon substrate  24  in the outer frame.  
         [0051]    [0051]FIG. 12 further illustrates the behavior (current as a function of time) of the opto-mechanical micro-switch  300  from the “switch off” to “switch on” and then back to “switch off” states under control of the controller  99 , according to one embodiment of the present invention. At time  0 , the micro-switch is at the “switch off” state as illustrated in FIG. 3. A current, I critical , is applied through the coils attached to the inner frame between t=0 and ti to rotate the inner frame from θ=0 to θ critical . The value of I critical  is chosen so that the inner frame will pivot through the critical angle of inclination, θ critical , beyond which, as indicated above, the torque generated by the magnetic force between the Permalloy piece and the permanent magnet will overcome the reactive torque of the beam, thus allowing latching to occur with the current removed. Beyond t 1  and θ critical , a reverse current is applied through the coils to reduce the impact of the Permalloy piece onto the outer frame due to the excessive torque caused by the magnetic attraction between the Permalloy piece and the permanent magnet over the reactive torque of the beam. At time t 2 , the inner frame reaches its “latched-on” position. At this point, no current needs to be applied through the coils. The excessive magnetic torque, τ permalloy , over the beam torque, τ beam , will keep the inner frame in place. When unlatching, a reverse current is applied, so that the sum of the unlatching torque and the beam torque must be higher than the latching magnetic torque, thereby causing the inner frame to tilt back to its original starting position. The time t 4  is a time where the inner frame has tilted back, slightly beyond the critical angle. Since after t 4 , the torque of the beam is higher than the magnetic torque, the inner frame will continue to tilt toward its starting position, even without any continuous current. However, again in order to reduce the impact when the inner frame hits the upper surface  54  of the silicon substrate of the outer frame, a positive current is applied to counter the excessive torque of the beam over the magnetic torque. Impact reducing is necessary during latching to prevent the end X of the inner frame  130  from making contact with the outer frame  120  that may cause structural damage; impact reducing is also necessary during “switching off” to prevent the end Y of the inner frame  130  from hitting the upper silicon surface  54  with excess force.  
         [0052]    [0052]FIG. 13 shows yet another embodiment of the present invention. An additional Permalloy piece  60  is added to the permanent magnet  26  to focus the magnetic field against the Permalloy piece  30 . In FIG. 13, the Permalloy piece  60  is incorporated within the silicon substrate  24  and placed directly on top of, or in close proximity to, the permanent magnet layer  26  to allow magnetization of the Permalloy piece  60 . This arrangement increases the magnetic force on the Permalloy piece  30  by focusing the magnetic flux of layer  26  on the Permalloy piece  30 , which attracts the Permalloy piece  30  towards lower stationary portion  64  and holds it in the latched on position.  
         [0053]    [0053]FIG. 14 shows yet another embodiment of the present invention. As shown in FIG. 14, a Permalloy piece  62  is added to the silicon substrate layer  24 . Further, the Permalloy piece  62  is placed directly on top of, or in close proximity to, the permanent magnet layer  26 , in order to allow magnetization of the Permalloy piece  62 . An additional Permalloy piece  30 b/ 30 c/ 30 d is added to the lower portion of end Y of the inner frame  130 . The magnetized Permalloy piece  62  keeps the end Y of inner frame  130  attached to the upper stationary portion  66 . This embodiment serves to securely hold the inner frame  130  in place in the non-biased state (switch-off) against external perturbations, and to reduce the force required to unlatch from the switch-on state.  
         [0054]    [0054]FIGS. 4 and 5 show two plan bottom views of inner frame  130  with different Permalloy deposit embodiments. FIG. 4 shows Permalloy  30 a with a stop edge  44 , which allows for silicon-to-silicon contact when the switch is on and the inner frame is latched onto the outer frame. The stop edge  44  avoids the Permalloy-to-silicon contact. The silicon-to-silicon contact prevents the constant impact of the Permalloy piece during the operations of the micro-switch. Not only does it prevent damage deformation but it also avoids stiction; a tremendous force is required for separation once there is contact. FIG. 15, a perspective bottom view of FIG. 4, shows one embodiment of the present invention with the Permalloy  30 a on one side of the inner frame  130 . Another embodiment of the present invention in FIG. 5 shows Permalloy  30 a and stop edge  44  with the addition of Permalloys  30 b and  30 c at the lower corners of the inner frame  130 . FIG. 16, a perspective bottom view of FIG. 5, also shows stop edge  45  in between Permalloy  30 b and  30 c. In yet another embodiment of the present invention, FIG. 17 shows an additional Permalloy  30 d with stop edges  45 a and  45 b. These additional Permalloys allow for increased latching strength in another embodiment as shown in FIG. 14.  
         [0055]    To manufacture a micromachined structure, reference is made to U.S. patent application Ser. No. 09/366,428 filed Aug. 2, 1999, assigned to Integrated Micromachines, Inc., the assignee of the present invention, which is fully incorporated by reference herein. Such patent application discloses a process that provides one skilled in the art with the steps to manufacture the following: an outer frame and an inner frame, pivotally coupled to the outer frame, which is rotatable about an axis of rotation from a first position to a second position relative to the outer frame when an external force is applied, and wherein the inner frame is biased to return to the first position in the absence of the external force, and providing a permanent magnet on the outer frame. In the present invention, the method of manufacturing a micromachined structure further includes the step of forming the Permalloy, or a magnetic material, on the inner frame.  
         [0056]    While the present invention has been particularly shown and described with reference to the preferred embodiments, it will be understood by those skilled in the art that various changes in form and detail may be made without departing from the spirit, scope, and teaching of the invention. Accordingly, the disclosed invention is to be considered merely as illustrative and limited in scope only as specified in the appended claims.