Abstract:
Described herein are ruggedized wafer level MEMS force dies composed of a platform and a silicon sensor. The silicon sensor employs multiple flexible sensing elements containing Piezoresistive strain gages and wire bonds.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. Provisional Patent Application No. 61/690,161, filed on Jun. 21, 2012, entitled “RUGEDIZED MEMS FORCE DIE,” the disclosure of which is expressly incorporated herein by reference in its entirety. 
     
    
     FIELD 
       [0002]    The present disclosure describes piezoresistive force sensing dies that are used for converting force into strain, which is sensed by strain gages. 
       BACKGROUND 
       [0003]    Current OEM force sensors, joysticks, touch-controls, etc generally employ older low performance technologies. The purpose of the present disclosure is to provide MEMS force dies, which are compact, mass producible and cost effective for OEM force sensors, joysticks, etc. 
       SUMMARY 
       [0004]    Described herein are ruggedized wafer level MEMS force dies composed of a platform and a silicon sensor. The silicon sensor employs multiple flexible sensing elements containing Piezoresistive strain gages and wire bonds. 
         [0005]    The platform protects the die and is employed to link the force to the flexible sensing elements. Apertures in the platform provide access for wire bonding and protect the wire bonds from the applied force. 
         [0006]    The platform is joined to the sensing element at the outer periphery. An interior gap, which is formed by sculpturing the silicon sensor and/or the platform, allows the sensing element to deflect. It can be designed to limit the deflection in order to provide overload protection. 
         [0007]    Bonding the thick platform to the outer periphery of the thin flexible sensing elements ruggedizes the die and prevents damage during dicing. 
         [0008]    The force applied to the platform is linked to the flexible sensing elements. The gap allows the flexible sensing elements to bend and to stress the piezoresistive strain gages, which provide an output signal proportional to the applied force. 
         [0009]    Other systems, methods, features and/or advantages will be or may become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features and/or advantages be included within this description and be protected by the accompanying claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The components in the drawings are not necessarily to scale relative to each other. Like reference numerals designate corresponding parts throughout the several views. 
           [0011]      FIG. 1  shows a top view of the force die. 
           [0012]      FIG. 2  shows a side view of the force die. 
           [0013]      FIG. 3  shows a top view of a section of composite silicon and Pyrex wafer. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. Methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present disclosure. As used in the specification, and in the appended claims, the singular forms “a,” “an,” “the” include plural referents unless the context clearly dictates otherwise. The term “comprising” and variations thereof as used herein is used synonymously with the term “including” and variations thereof and are open, non-limiting terms. While implementations will be described for with respect to a ruggedized MEMS force die, it will become evident to those skilled in the art that the implementations are not limited thereto. 
         [0015]    Referring to  FIG. 1  the side view of the sensing die  10  is shown. The die is comprised of Pyrex platform  11  and silicon sensor  12 . The bottom side of silicon sensor  12  is etched to predetermined depth to form four flexible sensing elements  14  supported by a cross-shaped structure  18 . The top side of silicon sensor  12  is etched to a predetermined depth to form gap  25 . Platform  11 , has four apertures  17 , is attached to flexible sensing elements  14  by anodic bonding  19 . The geometry of gap  25  in combination of apertures  17 , form four linking areas  15  at the corners of the die. 
         [0016]    Referring to  FIG. 2  the top view of the sensing die  10  is shown. Piezoresistive strain gages  20 A and  20 B are diffused or deposited on flexible sensing elements  14 . Wire bonding pads  21  are placed on structure  18 . Apertures  17  of platform  11  provide access to the wire bonding pads. The thick platform  11  prevents damage to the flexible sensing elements and shields the wire bonds  23  from the force applied to platform  11 . Force “F” is linked via outer edges (e.g., linking areas  15 ) to flexible sensing elements  14 . Gap  25  allows the force to bend the flexible sensing elements  14  and to stress strain gages  20  A &amp; B, which provide an output signal proportional to the applied force. 
         [0017]    Referring to  FIG. 3  the top view of a section of composite silicon and Pyrex wafer is shown. The bottom side of the silicon wafer is etched to predetermined depth to form diaphragms  31 . The top side of the silicon wafer is etched to predetermined depth to form gaps  25 . The Pyrex wafer has round holes  33 . The Pyrex wafer and the silicon wafer are anodic bonded, which produces bonded areas  34  comprised of thin silicon ruggedized by being bonded to thick Pyrex. When the wafer is diced along lines  32 A&amp;B, the saw cuts through ruggedized areas. Furthermore, since areas  34  are sawed into four linking areas  15 , no bending or torsion moments can be produced in the dies by the saw. The dies are completely protected from being damaged during the dicing. 
         [0018]    Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.