Patent Document

CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a division of U.S. patent application Ser. No. 11/077,099, filed on Mar. 9, 2005, and incorporated herein by reference. 
     
    
     FIELD OF INVENTION  
       [0002]     This invention relates to scanning mirror devices, and more particularly to micro-electro-mechanical system (MEMS) scanning mirrors  
       DESCRIPTION OF RELATED ART  
       [0003]     Various electrostatic comb actuator designs for MEMS scanning mirrors have been proposed. The extensive applications of these devices include barcode readers, laser printers, confocal microscopes, projection displays, rear projection TVs, and wearable displays.  
         [0004]     A MEMS scanning mirror is typically driven at its main natural frequency to achieve a high scanning angle. Invariably the manufacturing processes produce MEMS scanning mirrors with dimensional inconsistencies that vary the natural frequencies of the individual devices. If the main natural frequency of a MEMS scanning mirror is too low or too high, the device will not produce the proper scan speed and the proper scan angle under an alternating current (AC) drive voltage selected for a majority of the MEMS scanning mirrors.  
         [0005]     Thus, an apparatus and a method are needed to tune the main natural frequency of the MEMS scanning mirrors to improve the manufacturing yield of these devices. Furthermore, such an apparatus and a method allow a single design of a scanning mirror to be modified to make various devices with different natural frequencies.  
       SUMMARY  
       [0006]     In one embodiment of the invention, a mirror device includes a mirror, an anchor, and a spring coupling the mirror to the anchor. The anchor can define one or more rows of holes adjacent to the location where the anchor is coupled to the spring. Alternatively or in addition to the anchor defining one or more rows of holes, the mirror can define one or more rows of holes adjacent to the location where the mirror is coupled to the spring. The natural frequency of the device can be adjusted by removing material between the perimeter of the anchor/mirror and the outermost holes, and between adjacent holes in the same row.  
         [0007]     The mirror can further include one or more sacrificial portions. The natural frequency of the device can also be adjusted by trimming the sacrificial portions.  
         [0008]     In another embodiment of the invention, a MEMS mirror device includes a mirror, anchors, and springs coupling the mirror to the anchors. The natural frequency of the device can be adjusted by decoupling one or more springs coupling the mirror to the anchors.  
         [0009]     The mirror can further include one or more sacrificial portions. The natural frequency of the device can also be adjusted by trimming the sacrificial portions. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  illustrates a MEMS mirror prior to trimming in one embodiment of the invention.  
         [0011]      FIGS. 2 and 3  illustrate the MEMS mirror of  FIG. 1  after trimming to fine tune the natural frequency of the mirror in one embodiment of the invention.  
         [0012]      FIG. 4  illustrates a MEMS mirror prior to trimming in one embodiment of the invention.  
         [0013]      FIGS. 5 and 6  illustrate the MEMS mirror of  FIG. 4  after trimming to fine tune the natural frequency of the mirror in one embodiment of the invention.  
         [0014]      FIG. 7  illustrates a MEMS mirror prior to trimming in one embodiment of the invention.  
         [0015]      FIG. 8  illustrates the MEMS mirror of  FIG. 7  after trimming to fine tune the natural frequency of the mirror in one embodiment of the invention. 
     
    
       [0016]     Use of the same reference numbers in different figures indicates similar or identical elements.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0017]      FIG. 1  illustrates a micro-electro-mechanical system (MEMS) mirror device  100  in one embodiment of the invention. Device  100  includes a mirror  102 , anchors  104  and  106 , a serpentine spring  108  coupling mirror  102  to anchor  104 , and a serpentine spring  110  coupling mirror  102  to anchor  106 . Typically anchors  104  and  106  suspend mirror  102  to allow mirror  102  to rotate along the rotational axis of springs  108  and  110 . Mirror  102  can include rotational fingers  111 A that are interdigitated with in-plane or out-of-plane stationary fingers  111 B. Rotational fingers  111 A and stationary fingers  111 B can be driven in a variety of fashion to oscillate mirror  102 .  
         [0018]     On the left side of device  100 , anchor  104  has a row  112  of holes  114  (only one is labeled for clarity) located adjacent to the attachment location of anchor  104  to spring  108 . Row  112  is parallel to the rotational axis of spring  108 . Mirror  102  also has a row  116  of holes  118  (only one is labeled for clarity) located adjacent to the attachment location of mirror  102  to spring  108 . Row  116  is also parallel to the rotational axis of spring  108 .  
         [0019]     On the right side of device  100 , anchor  106  has a row  122  of holes  124  (only one is labeled for clarity) located adjacent to the attachment location of anchor  106  to spring  110 . Row  122  is parallel to the rotational axis of spring  110 . Mirror  102  also has a row  126  of holes  128  (only one is labeled for clarity) located adjacent to the attachment location of mirror  102  to spring  110 . Row  126  is also parallel to the rotational axis of spring  110 .  
         [0020]     Mirror  102  has a slot  130  near its upper perimeter and a slot  132  near its bottom perimeter. Slots  130  and  132  divide mirror  102  into a reflective region  134  and sacrificial portions  136  and  138 . Each sacrificial portion can include alignment marks for the trimming process. When the material between two neighboring alignment marks is removed, then the natural frequency of the device changes by a known amount.  
         [0021]     The natural frequency of device  100  can be reduced by increasing the lengths of springs  108  and  110 . The natural frequency of device  100  can be increased by reducing the inertia of mirror  102 . Thus, any combination of mirror  102 , anchor  104 , and anchor  106  can be trimmed to physically adjust the natural frequency of device  100 .  
         [0022]     Referring to  FIGS. 1 and 2 , the lengths of springs  108  and  110  can be increased in multiple ways. Material  140  between the perimeter of anchor  104  and the outermost hole  114  in row  112  can be removed to lengthen spring  108 . Material  142  between adjacent holes  114  in row  112  can be removed to further lengthen spring  108 . Material  144  between the perimeter of mirror  102  and the outermost hole  118  in row  116  can be removed to length spring  108 . Material  146  between adjacent holes  118  in row  116  can be removed to further lengthen spring  108 .  
         [0023]     Similarly, material  150  between the perimeter of anchor  106  and the outermost hole  124  in row  122  can be removed to lengthen spring  110 . Material  152  between adjacent holes  124  in row  122  can be removed to further lengthen spring  110 . Material  154  between the perimeter of mirror  102  and the outermost hole  128  in row  126  can be removed to length spring  110 . Material  156  between adjacent holes  128  in row  126  can be removed to further lengthen spring  110 . Materials from mirror  102  and anchors  104  and  106  can be removed by a laser beam or an ion beam.  
         [0024]     Referring to  FIG. 3 , the inertia of mirror  102  can be reduced by trimming sacrificial portions  136  and  138  of mirror  102 . Sacrificial portions  136  and  138  can be trimmed by a laser beam or an ion beam. In one embodiment, each sacrificial portion can consist of two smaller individual pieces when a large range of adjustment is not necessary.  
         [0025]      FIG. 4  illustrates a MEMS mirror device  400  in one embodiment of the invention. Device  400  includes a mirror  402 , anchors  404  and  406 , a linear spring  408  coupling mirror  402  to anchor  404 , and a linear spring  410  coupling mirror  402  to anchor  406 . Typically anchors  404  and  406  suspend mirror  402  to allow mirror  402  to rotate along the rotational axis of springs  408  and  410 . Mirror  402  include rotational fingers  411 A that are interdigitated with in-plane or out-of-plane stationary fingers  411 B. Rotational fingers  411 A and stationary fingers  411 B can be driven in a variety of fashion to oscillate mirror  102 .  
         [0026]     On the left side of device  400 , anchor  404  has two rows  412 A and  412 B of holes  414  (only one is labeled for clarity) located adjacent to the attachment location of anchor  404  to spring  408 . Rows  412 A and  412 B are parallel to the rotational axis of spring  408 . Mirror  402  also has two rows  416 A and  416 B of holes  418  (only one is labeled for clarity) located adjacent to the attachment location of mirror  402  to spring  408 . Rows  416 A and  416 B are also parallel to the rotational axis of spring  408 .  
         [0027]     On the right side of device  400 , anchor  406  has two rows  422 A and  422 B of holes  424  (only one is labeled for clarity) located adjacent to the attachment location of anchor  406  to spring  410 . Rows  422 A and  422 B are parallel to the rotational axis of spring  410 . Mirror  402  also has two rows  426 A and  426 B of holes  428  (only one is labeled for clarity) located adjacent to the attachment location of mirror  402  to spring  410 . Rows  426 A and  426 B are also parallel to the rotational axis of spring  410 .  
         [0028]     Mirror  402  has a slot  430  near its upper perimeter and a slot  432  near its bottom perimeter. Slots  430  and  432  divide mirror  402  into a reflective region  434  and sacrificial portions  436  and  438 . Alternatively, each sacrificial portion can consist of two smaller individual pieces. Each sacrificial portion can include alignment marks  439  for the trimming process.  
         [0029]     The natural frequency of device  400  can be reduced by increasing the lengths of springs  408  and  410 . The natural frequency of device  400  can be increased by reducing the inertia of mirror  402 . Thus, any combination of mirror  402 , anchor  404 , and anchor  406  can be trimmed to physically adjust the natural frequency of device  400 .  
         [0030]     Referring to  FIGS. 4 and 5 , the lengths of springs  408  and  410  can be increased in multiple ways. Materials  440  between the perimeter of anchor  404  and the outermost holes  414  in rows  412 A and  412 B can be removed to lengthen spring  408 . Materials  442  between adjacent holes  414  in each row can be removed to further lengthen spring  408 . Materials  444  between the perimeter of mirror  402  and the outermost holes  418  in rows  416 A and  416 B can be removed to length spring  408 . Materials  446  between adjacent holes  418  in each row can be removed to further lengthen spring  408 .  
         [0031]     Similarly, materials  450  between the perimeter of anchor  406  and the outermost holes  424  in rows  422 A and  422 B can be removed to lengthen spring  410 . Materials  452  between adjacent holes  424  in each row can be removed to further lengthen spring  410 . Materials  454  between the perimeter of mirror  402  and the outermost holes  428  in rows  426 A and  426 B can be removed to length spring  410 . Materials  456  between adjacent holes  428  in each row can be removed to further lengthen spring  410 . Material from mirror  402  and anchors  404  and  406  can be removed by a laser beam or an ion beam.  
         [0032]     Referring to  FIG. 6 , the inertia of mirror  402  can be reduced by trimming sacrificial portions  436  and  438  of mirror  402 . Sacrificial portions  436  and  438  can be trimmed by a laser beam or an ion beam. As described before, each sacrificial portion can consist of two smaller individual pieces when a large range of adjustment is not necessary. As described before, the natural frequency of the device changes by a known amount when the material between two neighboring alignment marks  439  is removed.  
         [0033]      FIG. 7  illustrates a MEMS mirror device  700  in one embodiment of the invention. A mirror  702  has beam structures  703  and  705  with rotational fingers  709 . Rotational fingers  709 A are interdigitated with in-plane or out-of-plane stationary fingers  709 B. The rotational and stationary fingers can be driven in a variety of fashion to oscillate mirror  702 .  
         [0034]     Anchors  704 A and  704 B are located within openings in beam structure  703 . An anchor  704 C is located at the end of beam structure  703 . Serpentine springs  708  couple beam structure  703  to anchors  704 A,  704 B, and  704 C. Anchors  706 A and  706 B are located within openings in beam structure  705 . An anchor  706 C is located at the end of beam structure  705 . Serpentine springs  710  couple beam structure  705  to anchors  706 A,  706 B, and  706 C. Typically anchors  704 A,  704 B,  704 C,  706 A,  706 B, and  706 C suspend mirror  702  to allow mirror  702  to rotate along the rotational axis of springs  708  and  710 .  
         [0035]     Mirror  702  has a slot  730  near its upper perimeter and a slot  732  near its bottom perimeter. Slots  730  and  732  divide mirror  702  into a reflective region  734  and sacrificial portions  736  and  738 . Alternatively, each sacrificial portion can consist of two individual pieces extending from reflective region  734 . Each sacrificial portion can include alignment marks for the trimming process.  
         [0036]     The natural frequency of device  700  can be reduced by decoupling one or more of springs  708  and  710 . The natural frequency of device  700  can be increased by reducing the inertia of mirror  702 . Thus, any combination of mirror  702  and springs  708  and  710  can be trimmed to physically adjust the natural frequency of device  700 .  
         [0037]     Referring to  FIG. 8 , any of springs  708  and  710  can be decoupled. Springs  708  and  710  can be decoupled by severing the spring. Springs  708  and  710  can be severed by a laser beam or an ion beam. In addition, the previously described rows of holes can be placed adjacent to the mounting locations of springs  708  and  710  so that they can be connected to lengthen springs  708  and  710 . The inertia of mirror  702  can be reduced by trimming sacrificial portions  736  and  738  of mirror  702 . Sacrificial portions  736  and  738  can be trimmed by a laser beam or an ion beam. As described before, each sacrificial portion can consist of two smaller individual pieces when a large range of adjustment is not necessary. As described before, the natural frequency of the device changes by a known amount when the material between two neighboring alignment marks  439  is removed.  
         [0038]     Various other adaptations and combinations of features of the embodiments disclosed are within the scope of the invention. For example, the design of the mirrors and the trimming/tuning method can be applied to electromagnetic scanning mirror, parallel plate electrostatic scanning mirror, thermally actuated scanning mirror, and piezoelectric scanning mirror. Numerous embodiments are encompassed by the following claims.

Technology Category: g