Abstract:
A highly reliable semiconductor device less susceptible to external noise is provided. The semiconductor device has a signal output chip and a substrate. The signal output chip has one or more semiconductors and outputs a predetermined signal. The substrate has a circuit formed thereon and is electrically connected to the signal output chip. A potential of the substrate is fixed to a certain level.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a semiconductor microdevice used for an acceleration sensor, an angular acceleration sensor, an electrostatic actuator or the like.  
           [0003]    2. Description of the Background Art  
           [0004]    [0004]FIG. 7 is a cross-sectional view which shows a structure of a conventional semiconductor microdevice  70 . Semiconductor microdevice  70  is packaged so as to realize predetermined functions and operations. Semiconductor microdevice  70  is provided with two types of chips on a die pad  13  in a package. To be specific, the chips are a microstructure chip  71  provided on a chip substrate  74  and an application specific IC chip (to be referred to as “ASIC” (Application Specific Integrated Circuit) hereinafter)  72 . These chips are appropriately selected according to the purpose of semiconductor microdevice  70 . Microstructure chip  71  is electrically connected to chip substrate  74 . Chip substrate  74  is connected to ASIC  72  by a bonding wire  75 . ASIC  72  is also connected to a lead  17  a bonding wire  76 . By connecting lead  17  to a circuit or the like outside of the package, power is supplied to microstructure chip  71  and ASIC  72  to enable these chips  71  and  72  to operate. It is noted that die pad  13  and chip substrate  74  are fixed to each other and die pad  13  and ASIC  72  are fixed to each other through resin layers  78 , respectively.  
           [0005]    There has been known hitherto a capacitive type inertial sensor made by a semiconductor micromachining technique as a sensor for detecting acceleration or the like. FIGS. 8A and 8B show a microstructure chip  80  used in the capacitive type inertial sensor. To be specific, FIG. 8A is a top view of microstructure chip  80  and FIG. 8B is a cross-sectional view of microstructure chip  80 .  
           [0006]    Microstructure chip  80  detects the capacitance of a capacitor formed by electrodes  82  and  83  suspended on a silicon substrate  81 . Electrode  82  is a fixed electrode which is fixed to substrate  81 . Electrode  83  is a movable electrode which can be moved relative to substrate  81  according to an inertial force. Movable electrode  83  is formed as one structure and supported by the silicon substrate  81  by beams  84 . Since electrode  83  is movable relative to electrode  82 , the position of electrode  83  is changed according to acceleration and the distance between electrodes  82  and  83 , i.e., the capacitance of the capacitor is, therefore, changed. By detecting the change of the capacitance of the capacitor, it is possible to obtain the acceleration of an object, to which the capacitor is attached.  
           [0007]    Since the change of the capacitance is very small (e.g., 1 pF), microstructure chip  80  is susceptible to external noise such as static electricity or radio wave. For that reason, a semiconductor microdevice (an acceleration sensor) employing conventional microstructure  80  is low in reliability.  
         SUMMARY OF THE INVENTION  
         [0008]    It is an object of the present invention to provide a highly reliable semiconductor microdevice less susceptible to external noise.  
           [0009]    A semiconductor device includes: a signal output chip which has one or more semiconductors and which outputs a predetermined signal; and a substrate which has a circuit formed thereon, said circuit electrically connected to the signal output chip. A potential of the substrate is fixed to a certain level, for example, a ground level. The signal output chip may be formed on a substrate of the signal output chip. A rear surface of the substrate of the signal output chip may have a metal layer.  
           [0010]    According to this aspect of the present invention, it is possible to realize a high performance, highly reliable product capable of preventing the substrate and the signal output chip from being charged and avoiding the influence of disturbance such as static electricity and radio interference.  
           [0011]    A semiconductor device includes: a signal output chip which has one or more semiconductors and which outputs a predetermined signal; a substrate which has a circuit formed thereon, said circuit electrically connected to the signal output chip; and a die pad, to which the substrate fixedly attached by a conductive material. A potential of the die pad is fixed to a certain level. The conductive material may be a conductive resin. The conductive material may be a conductive metal. The signal output chip may be formed on a substrate of the signal output chip. A rear surface of the substrate of the signal output chip may have a metal layer.  
           [0012]    According to this aspect of the present invention, it is possible to realize a high performance, highly reliable product capable of preventing the substrate and the signal output chip from being charged through the conductive material and avoiding the influence of disturbance such as static electricity and radio interference.  
           [0013]    The semiconductor device further includes a signal processing chip fixedly attached to the die pad by a conductive material. The signal processing chip processing the signal outputted from the signal output chip. By applying a ground potential level to the signal processing chip, potentials of the die pad and the substrate are fixed to the certain ground potential level. The conductive material may be a conductive resin. The conductive material may be a conductive metal.  
           [0014]    According to this aspect of the present invention, it is possible to realize a high performance, highly reliable product capable of preventing the substrate and the signal output chip from being charged through the conductive material and avoiding the influence of disturbance such as static electricity and radio interference.  
           [0015]    The die pad may be arranged at a position farther from a side of the substrate, on which the semiconductor device is mounted, than the signal output chip, the substrate and the signal processing chip.  
           [0016]    According to the present invention, the semiconductor device can exhibit a shielding effect for shielding the die pad from disturbance such as radio interference.  
           [0017]    A semiconductor device includes: a signal output chip which has one or more semiconductors and which outputs a predetermined signal; a substrate which has a circuit formed thereon, said circuit electrically connected to the signal output chip; a signal processing chip which processes the signal outputted from the signal output chip; and a conductive layer formed on a surface of the signal processing chip, and having a conductive property, said conductive layer fixedly attached to the substrate by a conductive material. By fixing a potential of the conductive layer to a certain level, a potential of a surface, which the signal output chip and the substrate contacts, is fixed to the certain level. The signal output chip may be formed on a substrate of the signal output chip. A rear surface of the substrate of the signal output chip may have a metal layer.  
           [0018]    According to this aspect of the present invention, the potential of the surface on which the signal processing chip contacts with the substrate is fixed to the certain value. It is, therefore, possible to realize a high performance, highly reliable product capable of preventing the substrate and the signal output chip from being charged and avoiding the influence of disturbance such as static electricity and radio interference. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]    This and other objects and features of the present invention will become clear from the subsequent description of a preferred embodiment thereof made with reference to the accompanying drawings, in which like parts are designated by like reference numerals and in which:  
         [0020]    [0020]FIGS. 1A and 1B are cross-sectional views of a configuration of a semiconductor microdevice in the first embodiment according to the present invention;  
         [0021]    [0021]FIG. 2 is a top view of a semiconductor microdevice having a die pad and an internal lead connected to each other by a bonding wire;  
         [0022]    [0022]FIG. 3 is a top view of a semiconductor microdevice having an internal lead connected to a die pad;  
         [0023]    [0023]FIG. 4 is a cross-sectional view of a configuration of a semiconductor microdevice in the second embodiment according to the present invention;  
         [0024]    [0024]FIG. 5 is a cross-sectional view of a configuration of another semiconductor microdevice in the second embodiment;  
         [0025]    [0025]FIG. 6 is a cross-sectional view of a configuration of a semiconductor microdevice in the third embodiment according to the present invention;  
         [0026]    [0026]FIG. 7 is a cross-sectional view of a configuration of a conventional semiconductor microdevice; and  
         [0027]    [0027]FIGS. 8A and 8B show a configuration of a microstructure chip used for a capacitive type inertial sensor, where FIG. 8A is a top view of the microstructure chip and FIG. 8B is a cross-sectional view of the microstructure chip. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0028]    The embodiments of the present invention will be described hereinafter with reference to the accompanying drawings.  
         [0029]    (First Embodiment)  
         [0030]    [0030]FIGS. 1A and 1B are cross-sectional views which show a configuration of a semiconductor microdevice  10  in the first embodiment according to the present invention. Semiconductor microdevice  10  is packaged so as to realize predetermined functions and operations. Semiconductor microdevice  10  functions as, for example, an acceleration sensor.  
         [0031]    Referring to FIG. 1A, semiconductor microdevice  10  has two types of chips provided on a die pad  13  in a package. More specificaly, these chips are a microstructure chip  11  having a microstructure and mounted on a chip substrate  14  and an application specific IC chip  12  for signal processing (to be referred to as “ASIC” (Application Specific IC) hereinafter). If semiconductor microdevice  10  is, for example, an acceleration sensor, microstructure chip  11  is an acceleration sensor chip, which outputs a detected signal. On the other hand, ASIC  12  processes the signal outputted from microstructure chip  11  and outputs a detection signal representing acceleration to the outside of the package of semiconductor microdevice  10 . It is noted that semiconductor microdevice  10  is not limited to the acceleration sensor and the internal chips thereof are appropriately selected according to the purpose of semiconductor chip  10 . The present invention provides semiconductor microdevice  10  made by surface micro machining, by which microstructure chip  11  is formed on the silicon substrate.  
         [0032]    A predetermined one or more electric circuits are formed on chip substrate  14 . At least one electric circuit is electrically connected to microstructure chip  11 . Chip substrate  14  is made of silicon. Microstructure chip  11  has a movable section (movable electrode  83 ) and a fixed section (fixed detection electrode  82 ), as shown in FIG. 8A, provided on chip substrate  14 . Referring again to FIGS. 1A and 1B, chip substrate  14  is connected to ASIC  12  by a bonding wire  15 . Further, ASIC  12  is connected to a lead  17  by a bonding wire  16 . More precisely, lead  17  in the package is referred to as an internal lead and lead  17  outside of the package as an external lead. By connecting lead  17  to a power source circuit outside of the package, power is supplied to microstructure chip  11  and to ASIC  12 , to enable these chips to operate.  
         [0033]    One feature of first embodiment is to fix one or more constituent elements in a predetermined potential (e.g., ground potential). Constituent elements are susceptible to external noise to be removed. By fixing the potential, disturbance such as static electricity and radio interference can be removed, which will be described hereinafter with reference to concrete examples.  
         [0034]    Die pad  13  is fixedly attached to chip substrate  14  and to ASIC  12  by bonding materials  18 , respectively. Each of bonding materials  18  is a conductive resin such as silver epoxy resin or a conductive metal such as an Au—Si eutectic. By employing the conductive material as bonding material  18 , it is possible to maintain ASIC  12 , chip substrate  14  and die pad  13  to have the same potential.  
         [0035]    Now, consideration will be given to a case where the potential of chip substrate  14  is fixed to a certain level. For example, chip  14  is connected to a terminal (a GND terminal for a reference ground potential or a terminal for a constant voltage source, which are not shown) applying a fixed potential to chip  14 . For example, the terminal is on a substrate on which semiconductor microdevice  10  is provided. Normally, the internal circuit of ASIC  12  is connected to an external circuit by bonding wire  16  and lead  17 . This external circuit includes the above-stated GND terminal provided on the substrate. As a result, the rear surface of ASIC  12  conductive to the internal circuit of ASIC  12  has a ground potential level. Further, since chip substrate  14  is electrically connected to the rear surface of ASIC  12 , chip substrate  14  has also the ground potential level. As already stated above, since ASIC  12 , chip substrate  14  and die pad  13  are maintained to have the same potential level, it is possible to prevent ASIC  12 , chip substrate  14  and die pad  13  from being charged. This means that disturbance such as static electricity and radio interference can be eliminated from entire semiconductor microdevice  10  as well as chip substrate  14  and microstructure chip  11 . Accordingly, by fixing the potential of chip substrate  14  to a certain level, it is possible to realize a product having high reliability and high performance without the influence of disturbance such as static electricity and radio interference.  
         [0036]    Needless to say, in the above description, while the potential of chip substrate  14  is fixed to a certain level, the potential of die pad  13  or ASIC  12  can be fixed. When the potential of die pad  13  is fixed to a certain level, die pad  13  is connected to the external lead applying the certain potential, i.e., the package external portion of lead  17  through ASIC  12  and bonding wire  16  as shown in FIGS. 1A and 1B. Alternatively, die pad  13  is directly connected to inner lead  17  and then to the external lead. FIGS. 2 and 3 show examples of the direct connection. To be specific, FIG. 2 is a top view which shows semiconductor microdevice  20  wherein die pad  13  is connected inner leads  17  by bonding wires  26 . FIG. 3 is a top view which shows semiconductor device  30  having an internal lead  36  connected to die pad  13 . By such direct connection, the semiconductor microdevice can exhibit the same advantage as that described above.  
         [0037]    Now, as shown in FIG. 1B, a metal layer  19  may be provided on the rear surface of the chip substrate and/or the substrate on which the ASIC is formed. By providing metal layer  19 , it is possible to further ensure fixing the potential of the substrate. This metal layer can be formed by, for example, the sputtering method or deposition method using Au or Ti—Ni—Au. When the potential of the chip substrate is fixed to a certain level, the metal layer is preferably provided on the rear surface of the chip substrate. On the other hand, when the potential of the rear surface of the ASIC is fixed to a certain level, the metal layer is preferably provided on the rear surface of the ASIC.  
         [0038]    (Second Embodiment)  
         [0039]    In the second embodiment, description will be given to a semiconductor microdevice wherein microstructure chip  11  and ASIC  12  are arranged differently from those in the first embodiment.  
         [0040]    [0040]FIG. 4 is a cross-sectional view which shows a configuration of a semiconductor microdevice  40  in the second embodiment. Semiconductor microdevice  40  is a device of a stack structure in which one or more chips having a microstructure are arranged on a signal processing circuit ASIC. More specifically, a bonding material  41 , an ASIC  12 , a conductive layer  42 , a bonding material  41 , a chip substrate  44  and a microstructure chip  11  are stacked on a lowermost die pad  43  in this order. Each of bonding materials  41  is a conductive resin such as a silver epoxy resin or a conductive metal such as an Au—Si eutectic as in the case of bonding materials  18  in the first embodiment. The connection between ASIC  12  and chip substrate  44  and that between ASIC  12  and a lead  17  are established by bonding wires  15  and  16 , respectively.  
         [0041]    In the first embodiment, consideration has been given to a case where the potential of chip substrate  14  is fixed to a certain level. In the second embodiment, by contrast, consideration will be given to a case where the potential of conductive layer  42  provided on the surface region of ASIC  12  is fixed to a certain level. In this case, since bonding materials  41  are conductive and chip substrate  44  is electrically connected to one of bonding materials  41  and microstructure chip  11 , the potential of the rear surface of microstructure chip  11  is also fixed to the level. Consequently, the second embodiment can obtain the same advantage as that of the first embodiment, i.e., the second embodiment can realize a product having high performance and high reliability without the influence of disturbance such as static electricity and radio interference.  
         [0042]    It is noted that the positional relationship among ASIC  12 , chip substrate  44  and microstructure chip  11  should not be limited to that described above. FIG. 5 is a cross-sectional view which shows a configuration of another semiconductor device  50  in the second embodiment. The differences of semiconductor microdevice  50  from semiconductor microdevice  40  (FIG. 4) are that the positions of an ASIC  12 , a chip substrate  54  and a microstructure chip  11  are changed and that conductive layer  42  (FIG. 4) is not provided.  
         [0043]    In semiconductor microdevice  50 , if the potential of the surface of microstructure chip  11  is set to be equal to that of chip substrate  54  (e.g., GND level) and the potential of ASIC  12  is also set to be equal to that of chip substrate  54 , then the same advantage as that described above can be obtained.  
         [0044]    As described above in the first embodiment with reference to FIG. 1B, a metal layer may be provided on the rear surface of the chip substrate and/or the substrate on which the ASIC is formed. By providing the metal layer, it is possible to further ensure fixing the potential of the substrate.  
         [0045]    (Third Embodiment)  
         [0046]    In the third embodiment, description will be given to a semiconductor microdevice wherein a microstructure chip  11  and an ASIC  12  are arranged differently from the first and second embodiments.  
         [0047]    [0047]FIG. 6 is a cross-sectional view which shows a configuration of a semiconductor microdevice  60  in the third embodiment. Semiconductor microdevice  60  is configured by vertically inverting the package of semiconductor microdevice  10  (FIG. 1). Consequently, an external lead  17  is bent oppositely to external lead  17  of semiconductor microdevice  10  (FIG. 1). As a result, a die pad  63  is arranged at a position farther from a side on which semiconductor microdevice  60  is mounted on a mounting substrate than a microstructure chip  11 , a chip substrate  64  and an ASIC  12 . To be specific, in semiconductor microdevice  60 , die pad  63  is arranged on the uppermost portion and a bonding material  61 , chip substrate  64  and microstructure chip  11  are provided below die pad  63  in this order. Connection between ASIC  12  and chip substrate  64  and that between ASIC  12  and internal lead  17  are established by bonding wires  15  and  16 , respectively.  
         [0048]    By arranging die pad  63  on the uppermost portion of semiconductor microdevice  60 , microdevice  60  can exhibit a shielding effect for shielding die pad  63  from disturbance such as radio interference. In addition, by providing a conductive pattern (GND pattern  69 ) on the surface facing semiconductor chip  11  of chip substrate  53  and setting the potential of chip substrate  64  at a certain level (e.g., GND level), it is possible to obtain a high performance product capable of shielding the influence of disturbance.  
         [0049]    As described above in the first embodiment with reference to FIG. 1B, a metal layer may be provided on the rear surface of the chip substrate and/or the substrate on which the ASIC is formed. By providing the metal layer, it is possible to further ensure fixing the potential of the substrate.