Patent Publication Number: US-8991253-B2

Title: Microelectromechanical system

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to German Patent Application Serial No. 10 2010 046 798.7, which was filed Sep. 28, 2010, and is incorporated herein by reference in its entirety. 
     TECHNICAL FIELD 
     Various embodiments relate to a microelectromechanical system, which may be based on a semiconductor chip and a chip carrier. 
     BACKGROUND 
     In so-called MicroElectroMechanical Systems MEMS, a movable part can be realized on a chip. Membranes used for static and/or dynamic pressure measurements, for example, are known here. In this case, the electrical measurement is usually effected capacitively or piezoresistively. So-called structures anchored on one side, also known as “micro-springboards”, are also known, which are often used as acceleration sensors. Other conventional movable or oscillating systems are disclosed in US 2010/0072626. 
     In a conventional “wafer-level packaged” integrated circuit, an MEMS is integrated in a first semiconductor layer. A thin-film layer is applied on the first semiconductor layer and arranged in such a way that it seals the cutout of the first semiconductor layer. At least one further layer is applied on the sealing thin-film layer and a so-called “under bump metallization” is arranged on the sealing thin film for the purpose of contact-connection. Such microstructures are very small since they are usually realized by etching processes on small semiconductor chips. Resulting from this, the correspondingly moved masses or volumes are very small. This fact may restrict the deflection amplitudes and frequency ranges obtainable therewith such as natural oscillation properties and hence the spreading of such technologies in corresponding applications. 
     One possibility for solving this issue consists in using small membrane and tongue structures, typically having thicknesses in the sub-μm range and up to 10 μm. The resulting lateral extents are thus in the range of &lt;0.5 mm. The technologies used are usually etching and sacrificial technologies from microsystems engineering, also known as surface or bulk micromachining. Disadvantages here include, for example, the small mass and the small lateral extent of the movable parts of the corresponding structures. 
     SUMMARY 
     In various embodiments, a microelectromechanical system may include a chip, a substrate, a signal generator, and a fixing structure configured to fix the chip to the substrate. The chip may be fixed in such a way that, upon an acceleration of the microelectromechanical system, the chip is moved relative to the substrate. Furthermore, a signal may be generated by the movement of the chip by means of the signal generator. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings, like reference characters generally refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention. In the following description, various embodiments of the invention are described with reference to the following drawings, in which: 
         FIGS. 1A to 1C  show various embodiments of an MEMS including “Spring Bumps”; 
         FIG. 2  shows various embodiments of an MEMS including spring-like contacts; 
         FIGS. 3A to 3B  show various embodiments of an MEMS including spring-like contacts; and 
         FIGS. 4A to 4B  show various embodiments of an MEMS including elastic material. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description refers to the accompanying drawings that show, by way of illustration, specific details and embodiments in which the invention may be practiced. 
     The word “exemplary” is used herein to mean “serving as an example, instance, or illustration”. Any embodiment or design described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments or designs. 
     The word “over” used with regards to a deposited material formed “over” a side or surface, may be used herein to mean that the deposited material may be formed “directly on”, e.g. in direct contact with, the implied side or surface. The word “over” used with regards to a deposited material formed “over” a side or surface, may be used herein to mean that the deposited material may be formed “indirectly on” the implied side or surface with one or more additional layers being arranged between the implied side or surface and the deposited material. 
     Various embodiments provide an MEMS which is cost-effective to produce and nevertheless measurement-sensitive. 
     A microelectromechanical system according to various embodiments may include a chip, a substrate, a signal generator and a fixing structure configured to fix the mass element to the substrate. In various embodiments, the chip may be fixed in such a way that, upon an acceleration of the microelectromechanical component, the chip is moved relative to the substrate, and a signal is generated by the movement of the mass element by means of the signal generator. 
     In various embodiments, the chip may be embodied as a signal detection and evaluation circuit. An advantage of various embodiments may consist in the fact that the signal detector and evaluator itself may serve as a mass element, as a result of the movement of which a signal may be generated. A corresponding signal may be generated in a simple manner by means of the mass of the chip. 
     In various embodiments, the substrate of the MEMS may form a hollow body, and the chip may be arranged within the hollow body. An advantage of various embodiments may consist in the fact that the chip may be fixed in the hollow body, and accelerations can be measured. 
     In various embodiments of the MEMS, the signal generator may include coils for generating magnetic signals. By means of coils, signals may be generated by the movement of the chip in a very simple manner by induction and may be forwarded to the corresponding evaluation device or evaluator and may be processed. 
     In various embodiments of the MEMS, the signal generator may include electrodes configured to generate or provide capacitive effects. By means of electrodes, signals may be generated capacitively and may be forwarded to the corresponding evaluation device and may be processed. 
     In various embodiments of the MEMS, the signal generator may include flexible and/or elastic connecting elements or structures configured to generate piezoresistive signals. As a result of the movement of the mass element fixed to the substrate by means of the connecting elements or connecting structures, given the use of piezoresistive materials, e.g. crystalline silicon, of the connecting elements or structures, a piezoresistive signal may be generated and, in various embodiments, too, the generated signals may be forwarded to the corresponding evaluation device and may be processed. 
     In various embodiments of the MEMS, the fixing structure configured to fix the chip may include flexible and/or elastic contacts. The latter may e.g. be embodied as a helical spring, bent leadframe lamina or else a piezoresistive element. The use of such contacts makes it possible to realize a simple and cost-effective connection of the mass element to the substrate body. The mass element may oscillate upon acceleration and generate a signal. 
     In various embodiments of the MEMS, the fixing structure configured to fix the mass element may include elastic adhesive. Elastic adhesive is easy to process and suitable for producing flexible and/or elastic connections. 
     In various embodiments of the MEMS, the elastic adhesive at least partly fills the hollow body. The mass element may be movable in the adhesive, which is suitable as an elastic connecting element, and thus generate a signal. The mass element may perform as it were a damped movement in the elastic adhesive. 
     In various embodiments of the MEMS, the fixing structure configured to fix the chip may include spring-like contacts, wherein the spring-like contacts may furthermore have a bent shape. Contacts shaped in this way are simple and cost-effective to produce. 
       FIG. 1   a  shows an MEMS  100  including a chip  10  and a substrate  20 . The substrate  20  may be embodied in such a way that it forms a completely or else partly closed hollow body or a cavity housing. The chip  10  is connected to the substrate  20  by means of flexible flip-chip contacts  30 , also designated as “Spring-Bumps”. The chip  10  is movable relative to the substrate  20 . Consequently, the chip  10  also has a movable mass. Upon a movement, acceleration or else vibration of the MEMS  100 , the chip  10  is moved relative to the substrate  20 . As a result of the movement of the chip  10 , shown in  FIG. 1   b , an electrical signal is generated by means of the provided signal generator  30 . The electrical signal may be generated capacitively, inductively or else piezoresistively. A piezoresistive signal may in various embodiments be generated by a change in a resistance of the spring-like contacts  30 . 
       FIG. 1   c  likewise shows an MEMS  100  including a chip  10  and a substrate  20 . In various embodiments, too, the substrate  20  may be embodied in such a way that it forms a completely or else partly closed hollow body. The MEMS may include electrodes  40 , wherein electrical signals may be generated by the movement of the chip  10  by means of capacitive effects. Moreover, the MEMS may include magnetic coil pairs  40 , wherein here, too, electrical signals may be generated by the movement of the chip  10  by means of inductive effects. The MEMS may furthermore include flexible connecting structures  40 , which may in various embodiments generate piezoresistive signals upon movement of the chip  10 . The MEMS likewise includes electrical conductor tracks  50  suitable to provide the generated electrical signal at suitable locations of the MEMS. 
       FIG. 2  shows an MEMS  200  including a chip  10  and a substrate  20 . The chip  10  is arranged on a chip carrier  30 , e.g. a leadframe. As a result of the movement of the chip  10  e.g. in the arrow direction, an electrical signal may be generated by means of inductive or capacitive effects. In this exemplary application, too, the electrical signal may be provided by means of electrical conductor tracks  50  at suitable locations of the MEMS. 
       FIG. 3   a  shows an MEMS  300  including a chip  10  and a substrate  20 . The chip  10  may be connected to the substrate  20  by means of spring-like contacts  30 . In various embodiments, the spring-like contacts  30  may be embodied as a bent leadframe lamina. In this embodiment, too, the chip  10  is movable relative to the substrate  20 . Consequently, the chip  10  has a movable mass here, too. Upon a movement, acceleration or vibration of the MEMS  100 , the chip  10  is moved relative to the substrate  20 . As a result of the movement of the chip  10 , shown in  FIG. 3   b , an electrical signal is generated by means of the provided signal generator. The signal generator may have a configuration composed of electrodes or magnetic coils. The electrical signal may be generated capacitively or inductively. In this embodiment, too, the electrical signal may be provided by means of electrical conductor tracks  50  at suitable locations of the MEMS. 
       FIG. 4   a  shows an MEMS  400  including a chip  10  and a substrate  20 . The chip  10  may be connected to the substrate by means of bonding wires  30 . In various embodiments, the substrate  20  may be embodied in such a way that it forms a hollow body  400 . The chip  10  may be arranged in the substrate hollow body  20 . In addition, the substrate hollow body  20  is at least partly filled with an elastic material  60 . The chip  10  is arranged and movable within the substrate hollow body in the elastic material. The elastic material may include an adhesive having different adhesive thicknesses, elastic and soft material properties. In this embodiment, too, upon a movement, acceleration or else vibration of the MEMS  400 , the chip  10  is movable relative to the substrate  20 , wherein the movement is damped by means of the elastic material,  FIG. 4   b . In this embodiment, too, electrical signals may be generated capacitively, inductively or piezoresistively and the electrical signal may be provided by means of electrical conductor tracks  50  at suitable locations of the MEMS. Generally, all the embodiments mentioned may e.g. be used in a wide variety of types of sensors. Thus, by way of example, an electrical signal generated capacitively between a chip metallization and a substrate metallization can be tapped off. Inductive variants are conceivable if the sides of the chip and of the substrate which are moved relative to one another may include a permanent-magnetic material or a coil. Systems for “Energy Harvesting”, that is to say systems for obtaining energy, can thus also be realized. These systems convert, for example, the vibrations of the surroundings into electrical energy by way of movement of the chip  10 . For example such “Energy Harvesting” applications, by means of the MEMS mentioned, may distinctly be superior to the previously known traditional MEMS technologies in terms of their efficiency, on account of the higher masses. 
     While the invention has been particularly shown and described with reference to specific embodiments, it should be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. The scope of the invention is thus indicated by the appended claims and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced.