Abstract:
Anchor systems and methods anchor components of a Micro-Electro-Mechanical Systems (MEMS) device to a substrate. An exemplary embodiment has a trace anchor bonded to a substrate, a device anchor bonded to the substrate, and an anchor flexure configured flexibly couple the trace anchor and the device anchor to substantially prevent transmission of a stress induced in the trace anchor from being transmitted to the device anchor.

Description:
BACKGROUND OF THE INVENTION 
     Various silicon-based devices, such as a Micro-Electro-Mechanical Systems (MEMS) gyroscope, are mechanically coupled to a substrate. Coupling of the MEMS device to the substrate occurs at one or more anchor points (anchors) bonded to the substrate, referred to herein as mesas. 
     Portions of the MEMS device may be suspended from the substrate using one or more silicon flexures. A number of recesses etched into the substrate allow the portions of the MEMS device, referred to herein as a MEMS mechanism, to move freely within an interior portion of the MEMS device. 
       FIG. 1  is a top view  100  of a prior art anchor  102  bonded to a portion of a substrate  104 .  FIG. 2  is a side cut-away view  200  of the prior art anchor  102  bonded to the portion of a substrate  104 . The anchor  102  is bonded to the substrate  104  on a mesa  106  along the contact region  108  where the anchor  102  and the substrate  104  are in contact. 
     The anchor  102  fixes and supports a MEMS mechanism  118  via an interconnecting flexure  110  or the like. Flexure  110  allows for movement of the MEMS mechanism  118  in selected directions and limits movement in other directions. 
     Prior to bonding the anchor  102  to the substrate  104 , a trace  112  is formed from an external location to a location on the mesa  106 . The trace  112  may be made of a metal and formed by a suitable process, such as metal sputtering over a mask oriented above the substrate  104 . 
     An optional bump  114  (or bumple) is located at or near the end of the trace  112  to facilitate electrical coupling between the anchor  102  and the trace  112 . If the trace  112  is made of metal, the bump  114  may be the same metal or another metal that is relatively soft and deformable under pressure and/or temperature. 
     Often, the process of bonding the anchor  102  to the substrate mesa  106  uses a pressure which deforms the trace  112  and/or the bump  114 . Deformation of the trace  112  and/or the bump  114  improves the electrical connectivity between the anchor  102  and the trace  112 . 
     During the process of bonding, stresses occur in the anchor  102 . The stress is caused by forces exerted by the trace  112  and/or the bump  114  onto the material of the anchor  102 . Such stresses (conceptually illustrated by a plurality of stress lines  116 ) exerted by the bump  114  to the anchor  102  may cause damage or otherwise stress the material of the anchor  102 . Further, temperature fluctuations during use of the MEMS device may change the relative size of the trace  112  and/or the bump  114 , inducing a time-varying change in the stress of the material of the anchor  102 . Additional stress may be induced by a coefficient of thermal expansion mismatch between silicon and substrate material. 
     The stresses induced in the material of the anchor  102  are undesirable in that such stresses, in addition to forces transmitted from the flexure  110  to the anchor  102  during MEMS device use, may result in the formation of microcracks. Such microcracks may lead to structure failure of the MEMS device at the anchor  102 . 
     Additionally, the movement of the MEMS mechanism  118  generates forces that are transmitted to the anchor  102  via the flexure  110 . The stresses and/or microcracks may sufficiently weaken the anchor  102  such that the anchor  102  may structurally fail when the forces generated by movement of the MEMS mechanism  118  are transmitted to the anchor  102 . 
     Accordingly, the anchor  102  is designed with sufficient size and mass to accommodate the stresses induced in the material of the anchor  102  from the trace  112  and/or the bump  114 , and to accommodate forces generated by the MEMS mechanism  118 . However, the prior art process has several disadvantages. The minimum size of the anchor  102  is limited since the anchor  102  must have sufficient material to accommodate the induced stresses. As MEMS devices become increasingly smaller, it is very desirable to reduce the size of anchors used in a MEMS device. Further, it is desirable to reduce fabrication process costs. 
     SUMMARY OF THE INVENTION 
     Systems and methods that anchor components of a Micro-Electro-Mechanical Systems (MEMS) device to a substrate are disclosed. An exemplary embodiment has a trace anchor bonded to a substrate, a device anchor bonded to the substrate, and an anchor flexure configured to flexibly couple the trace anchor and the device anchor to substantially prevent transmission of a stress induced in the trace anchor from being transmitted to the device anchor. 
     In accordance with further aspects, an exemplary embodiment bonds a trace anchor of the MEMS device to a trace anchor mesa of the substrate, wherein at least one of a trace and a bump induce a stress into the trace anchor; and bonds the device anchor to the device anchor mesa of the substrate. The device anchor is flexibly coupled to the trace anchor by an anchor flexure that substantially prevents transmission of the stresses induced in the trace anchor to the device anchor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred and alternative embodiments are described in detail below with reference to the following drawings: 
         FIG. 1  is a top view of a prior art anchor bonded to a portion of a substrate; 
         FIG. 2  is a side cut-away view of the prior art anchor bonded to the portion of the substrate of  FIG. 1 ; 
         FIG. 3  is a top view of an embodiment of a dual anchor system bonded to a portion of a substrate embodiment; 
         FIG. 4  is a side cut-away view of the dual anchor system bonded to the portion of the substrate of  FIG. 3 ; and 
         FIG. 5  is a side cut-away view of an alternative embodiment of the dual anchor system. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 3  is a top view  300  of an embodiment of a dual anchor system  302  bonded to a portion of a substrate  304 .  FIG. 4  is a side cut-away view  400  of the dual anchor system  302  bonded to the portion of the substrate  304 . Embodiments of the dual anchor system  302  include a trace anchor  306 , a device anchor  308 , and an anchor flexure  310 . In one embodiment, the substrate  304  includes a trace anchor mesa  312  and a device anchor mesa  314 . The dual anchor system  302  corresponds to a portion of a Micro-Electro-Mechanical Systems (MEMS) device that is bonded to the substrate  304 . 
     The trace anchor  306  is bonded to the trace anchor mesa  312  at a contact region  402 . The device anchor  308  is bonded to the substrate  304  at a contact region  404 . The anchor flexure  310  physically couples and electrically couples the trace anchor  306  and the device anchor  308 . The anchor flexure  310  is flexible, and is not bonded to the substrate  304 . 
     As noted above, the bonding process may apply a pressure which would deform the bump  114  to improve the electrical connectivity between the device anchor  308  and the trace  112 . However, forces exerted by the trace  112  and/or the bump  114  to the trace anchor  306  cause stresses in the material of the trace anchor  306  (conceptually illustrated by the stress lines  116 ). Further, temperature fluctuations during use may change the relative size of the bump  114 , further inducing time-varying changes in the stress in the trace anchor  306 . 
     Since the anchor flexure  310  is not bonded in the location of the trace  112  and/or the bump  114 , and since the anchor flexure  310  is flexible, stresses induced into the device anchor  308  are not significantly transmitted from the trace anchor  306 , through the anchor flexure  310 , into the device anchor  308 . Accordingly, the device anchor  308  will be substantially free of the microcracks that might be otherwise formed by the stress from the bump  114 . The anchor flexure  310  may have any suitable shape and/or amount of flexibility. 
     The device anchor  308  fixes and supports the MEMS mechanism  118  via the interconnecting flexure  110  or the like. The flexure  110  allows for movement of the MEMS mechanism  118  in selected directions and may prevent movement in other directions. Since stresses from the trace anchor  306  are not transmitted to the device anchor  308 , the structural integrity of the device anchor  308  is maintained. That is, the absence of the stresses substantially reduces the presence, if any, of microcracks that would otherwise weaken the device anchor  308 . Accordingly, stresses generated by the flexure  110  will not cause failure at the device anchor  308 . 
     Furthermore, stresses transmitted from the flexure  110  onto the device anchor  308  are not transmitted to the trace anchor  306  in view of the flexible anchor flexure  310 . Accordingly, even if the stresses and/or microcracks in the trace anchor  306  exist, the stresses generated by the anchor flexure  110  from movement of the MEMS mechanism  118  will not cause failure at the trace anchor  306  (since they are not substantially transmitted past the anchor flexure  110 ). 
     Prior to the bonding process wherein the trace anchor  306  is bonded to the trace anchor mesa  312 , and the device anchor  308  is bonded to the device anchor mesa  314 , the trace anchor mesa  312  and the device anchor mesa  314  are formed on the substrate  304 . The mesas  312  and  314  may be formed using any suitable process, such as, but not limited to, etching or micromachining. Accordingly, a void region  406  is formed between the mesas  312  and  314  such that during bonding, the anchor flexure  310  is not bonded to the substrate  304 . Accordingly, the anchor flexure  310  is free to flex as needed to prevent transmission of stresses from the trace anchor  306  to the device anchor  308 , and vice versa. 
       FIG. 5  is a side cut-away view  500  of an alternative embodiment of the dual anchor system  302 . In this alternative embodiment, a lower portion of the anchor flexure  310  has been removed so that a void region  502  is formed between the substrate  304  and the anchor flexure  310 . Accordingly, the anchor flexure  310  is not bonded to the substrate  304  and the anchor flexure  310  is free to flex as needed to prevent transmission of stresses from the trace anchor  306  to the device anchor  308 , and vice versa. The region  502  may be formed using any suitable etching or micromachining process. 
     In the embodiment illustrated in  FIG. 5 , the trace anchor mesa  312  and the device anchor mesa  314  are formed as a single mesa. Alternatively, the trace anchor mesa  312  and the device anchor mesa  314  may not be raised above the surface of the substrate  304 . Rather, components of the MEMS device are under etched or machined so that they are free to move. These regions  312  and  314  where the bonding occurs, corresponding to the trace anchor mesa  312  and the device anchor mesa  314 , are defined as mesas for convenience. 
     While the preferred embodiment of the invention has been illustrated and described, as noted above, many changes can be made without departing from the spirit and scope of the invention. Accordingly, the scope of the invention is not limited by the disclosure of the preferred embodiment. Instead, the invention should be determined entirely by reference to the claims that follow.