Patent Abstract:
The purpose of the present invention is to improve the pressure resistance of a cavity in a semiconductor sensor device employing a resin package, and to do so without adversely affecting the embeddability of an electrically conductive member. The semiconductor sensor device has a gap  1   a  sealed in an airtight manner inside a laminate structure of a plurality of laminated substrates  1, 4,  and  5,  and has a structure in which the outside of the laminate structure is covered by a resin, wherein a platy component  2  having at least one side that is greater in length than the length of one side of the gap  1   a  along this side is arranged to the outside of an upper wall  1   b  of the gap  1,  the upper wall  1   b  of the gap being mechanically suspended by the platy component  2.

Full Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a semiconductor sensor device and more specifically relates to a MEMS (Micro Electro Mechanical Systems) device into which structures are sealed in an airtight manner such as an inertial sensor such as an acceleration or angular velocity sensor measuring a motion state of a moving body such as a vehicle, an airplane, a robot, a mobile phone, and a video camera, and a vibrator for generating filters and clocks. 
       BACKGROUND ART 
       [0002]    In recent years, for the purpose of prevention of hand shake of a digital camera, posture control for an automobile and a robot, and the like, a sensor including a vibrator using a MEMS technique has widely been used. 
         [0003]    In general, the vibrator of this kind is formed by processing a semiconductor substrate such as a silicon substrate with use of the MEMS technique such as etching and is sealed in an airtight manner by attaching another substrate to the semiconductor substrate under a preset atmosphere and pressure environment. For example, JP 5298047 B2 (PTL 1) describes an angular velocity sensor chip and an acceleration sensor chip sealed in an airtight manner. 
         [0004]    Also, as a package structure for the sensor chip, a plastic package attracts attention. The plastic package has higher mass productivity than a conventional ceramic package and is an efficient package structure to decrease manufacturing cost of the sensor. For example, JP 10-148642 A (PTL 2) describes an acceleration sensor using a plastic package. 
       CITATION LIST 
     Patent Literature 
       [0005]    PTL 1: JP 5298047 B2 
         [0006]    PTL 1: JP 10-148642 A 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0007]    According to the aforementioned conventional technique, the vibrator in the sensor chip is sealed in an airtight manner in a cavity formed between the attached substrates. Also, the inside of the cavity is in an atmospheric pressure or vacuum state. In a case of plastic-packaging such a sensor chip by means of a transfer mold process, high pressure is applied to the sensor chip when plastic is filled in the mold with as high pressure as 5 to 20 MPa or so. At this time, since a pressure difference between the inside and the outside of the sensor chip increases, the cavity of the sensor chip is deformed. In a case in which stress that is equal to or higher than breaking stress of a material constituting the cavity is applied to the cavity, the cavity will break, and airtightness in the cavity will be lost. Also, in a case in which the entire cavity is depressed in a direction toward the vibrator, the vibrator may break together. 
         [0008]    The relationship between stress o and pressure P is expressed by Equation  1 . To improve withstanding pressure of a cavity upper part, it is apparent that the substrate at the cavity upper part needs to be thickened. The maximum stress at this time is applied to an end portion of a cavity longer side, and the cavity breaks at the portion against the withstanding pressure. 
         [0000]        h   2   =αPa   2 /σ  (Equation 1)
 
         [0000]    In the equation, h is a thickness of the substrate at the cavity upper part, a is a length of a cavity shorter side, and α is a coefficient. 
         [0009]    However, in a case in which an electric signal is to be input/output between the vibrator and an outside of the sensor chip, the electric connection with the outside of the sensor chip is sometimes established by means of wire bonding by forming a through interconnection in a vertical direction of a substrate forming the cavity and providing the cavity upper part with a pad for the wire bonding. At this time, to form the through interconnection, the substrate is etched in the vertical direction, the etched sidewall is electrically isolated by an isolator, and a conductive member is buried. In a case in which the substrate at the cavity upper part is thickened to improve withstanding pressure of the cavity upper part, the burying performance of the conductive member will be degraded, and the airtightness will be degraded. Also, resistance Rv of the through interconnection expressed in Equation 2 will increase. Consequently, a thermal noise Vn expressed in Equation 3 will increase, and the sensor performance will be lowered. In consideration of these problems, it is not easy to thicken the substrate at the cavity upper part. 
         [0000]        Rv=μt/A    (Equation 2)
 
         [0000]    In the equation, t is a length of the through interconnection, A is a cross-sectional area of the through interconnection, and ρ is resistivity of the conductive member. 
         [0000]        Vn =√(4 kt ( Rv+Rs ) B )   (Equation 3)
 
         [0000]    In the equation, k is a Boltzmann coefficient, B is a bandwidth of a signal, T is an absolute temperature, and Rs is interconnection resistance in a horizontal direction of the cavity substrate. 
         [0010]    An object of the present invention is to improve withstanding pressure of a cavity without degrading burying performance of a conductive member in a semiconductor sensor device using a plastic package. 
       Solution to Problem 
       [0011]    To solve the above problem, in a semiconductor sensor device according to the present invention, a suspension substrate is attached directly on a cavity substrate into a structure in which a cavity upper part is suspended by the suspension substrate. Thus, the thickness h of the cavity upper part expressed in Equation 1 appears to increase as much as the thickness of the suspension substrate. Also, a substrate at the cavity upper part does not need to be thickened, and a length of a through interconnection does not need to increase. As a result, withstanding pressure P of the cavity upper part can be improved. 
       Advantageous Effects of Invention 
       [0012]    According to the present invention, by suspending a cavity upper part with use of a suspension substrate, withstanding pressure of the cavity can be improved without degrading burying performance of a conductive member. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0013]      FIG. 1  is a plan view of an acceleration sensor chip according to a first embodiment of the present invention. 
           [0014]      FIG. 2  is a cross-sectional view along II-II in  FIG. 1 . 
           [0015]      FIG. 3  is a cross-sectional view along III-III in  FIG. 1 . 
           [0016]      FIG. 4  is a plan view illustrating the IV-IV cross-section in  FIG. 2 . 
           [0017]      FIG. 5  is a plan view illustrating the V-V cross-section in  FIG. 2 . 
           [0018]      FIG. 6  is a cross-sectional view of a chip package of the acceleration sensor chip according to the first embodiment of the present invention. 
           [0019]      FIG. 7  is a plan view of the acceleration sensor chip according to a second embodiment of the present invention. 
           [0020]      FIG. 8  is a plan view of the acceleration sensor chip according to a third embodiment of the present invention. 
           [0021]      FIG. 9  is a plan view of an angular velocity sensor chip according to a fourth embodiment of the present invention. 
           [0022]      FIG. 10  is a cross-sectional view along X-X in  FIG. 9 . 
           [0023]      FIG. 11  is a cross-sectional view along XI-XI in  FIG. 9 . 
           [0024]      FIG. 12  is a plan view illustrating the XII-XII cross-section in  FIG. 10 . 
           [0025]      FIG. 13  is a plan view illustrating the XIII-XIII cross-section in  FIG. 10 . 
           [0026]      FIG. 14  is a plan view of the acceleration sensor chip according to a fifth embodiment of the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0027]    In the following embodiments, description will be provided by dividing the content into plural sections or embodiments as needed for convenience. However, these are not irrelevant to each other but have a relationship in which one is partially or entirely a modification example, a detail, a supplemental explanation, or the like of another unless otherwise stated. 
         [0028]    Also, in the following embodiments, in a case in which the number (such as number, value, amount, and range) or the like of elements is stated, the number is not limited to the specified number but may be equal to, more than, or less than the specified number unless otherwise stated and unless it is apparent that the number is limited to the specified number in principle. 
         [0029]    Further, in the following embodiments, it is to be understood that components (including component steps) thereof are not necessarily essential unless otherwise stated and unless it is apparent that the components are essential in principle. 
         [0030]    Similarly, in the following embodiments, in a case in which a shape, a positional relationship, and the like of components are stated, the shape and the like shall include those approximate or similar to these unless otherwise stated and unless the shape and the like do not seem to include those approximate or similar to these in principle. The same is true of the aforementioned number and range. 
         [0031]    Also, in the figures for describing the embodiments, similar components are shown with the same reference numerals, and description of the duplicate components is omitted. Also, to facilitate understanding of the figures, even a plan view may be hatched. 
       First Embodiment 
       [0032]    In the present embodiment, the present invention will be described using a MEMS-type acceleration sensor. In particular, an example of using a capacitive sensing acceleration sensor as the MEMS-type acceleration sensor will be described. 
         [0033]      FIG. 1  is a plan view (upper view) of an acceleration sensor chip according to a first embodiment of the present invention.  FIG. 2  is a cross-sectional view along II-II in  FIG. 1 .  FIG. 3  is a cross-sectional view along III-III in  FIG. 1 .  FIG. 4  is a plan view illustrating the IV-IV cross-section in FIG. 2 .  FIG. 5  is a plan view illustrating the V-V cross-section in  FIG. 2 .  FIG. 6  is a cross-sectional view of a chip package  19  of an acceleration sensor chip  11  according to the first embodiment of the present invention. 
         [0034]    The acceleration sensor according to the present embodiment includes a cavity substrate  1  forming a cavity  1   a  therein, a device substrate  4  forming a vibrator (weight)  4   a  therein, a support substrate  5  supporting the vibrator, and a suspension substrate  2  suspending a cavity upper part  1   b  of the cavity substrate  1 . 
         [0035]    In forming the vibrator, the device substrate  4  made of monocrystalline silicon and the support substrate  5  made of monocrystalline silicon or glass are first attached to each other via an insulating film  6 . At this time, the support substrate  5  may or may not be provided with a cavity  5   a  in advance. Subsequently, the substrate assembly into which the device substrate  4  and the support substrate  5  are attached is subject to photolithography and DRIE (Deep Reactive Ion Etching) to process the device substrate  4  and the insulating film  6 , to form the vibrator  4   a.    
         [0036]    As illustrated in  FIG. 4 , to the weight  4   a,  serving as the vibrator, formed on the device substrate  4 , support beams  4   b  are connected in a direction perpendicular to a vibrating direction of the weight  4   a.  The other ends of these support beams  4   b  are respectively connected to anchors  4   c  provided in the direction perpendicular to the vibrating direction. At this time, since the anchors  4 c are fixed to the support substrate  5  via the insulating film  6 , the weight  4   a  can vibrate in a Y-axial direction. Also, some of the anchors  4   c  can electrically be connected to a below-mentioned through interconnection  7  similarly to an anchor  4   d  and are used to electrically connect the weight  4   a  to an external circuit. 
         [0037]    Comb-like detection electrodes  4   e  formed on the device substrate  4  are formed outside the weight  4   a.  Comb-like fixed electrodes  4   f  are formed on the device substrate  4  and the insulating film  6  to face the comb-like detection electrodes  4   e  and are fixed to the support substrate  5 . That is, the detection electrodes  4   e  are provided to project from an outer circumference of the weight  4   a  in an extending direction of the support beams  4   b.  Although only one detection electrode  4   e  is drawn in  FIG. 4 , the plurality of detection electrodes  4   e  are provided in a comb-like shape. Also, the fixed electrodes  4   f  receiving the comb-like detection electrodes  4   e  are provided in a comb-like shape to correspond to the number of the detection electrodes  4   e.    
         [0038]    As expressed in Equation 4, capacitance C is derived by a distance d between the detection electrode  4   e  and the fixed electrode  4   f,  a facing area A, dielectric constant E, and a facing number n between the electrodes  4   e  and  4   f.    
         [0000]        C=εAn/d    (Equation 4)
 
         [0000]    When acceleration is applied to the vibrator in the y direction, the weight  4   a  serving as a movable body is displaced in the y direction, and a displacement amount Δy between the electrodes at this time is a capacitance change ΔC. 
         [0039]    Next, the cavity substrate  1  will be described. The cavity substrate  1  is made of monocrystalline silicon and is provided with a plurality of through holes for the cavity and the through interconnection  7  with use of photolithography and DRIE. The through interconnection  7  is formed by covering a sidewall of the through hole with an insulating film  8  and burying low-resistance silicon or a metal material therein. On an opposite surface of the surface provided with the cavity  1   a , a planar interconnection  9  is formed as illustrated in  FIG. 5 . The planar interconnection  9  electrically connects a pad  9   a  arranged further outside than an outer circumference of the cavity  1   a  to the through interconnection  7  and is covered with an insulating film  10  except a pad opening portion  10   a  for protection against corrosion caused by damage and moisture. 
         [0040]    By attaching the cavity substrate  1  configured as above to the device substrate  4 , the detection electrode  4   e  and the fixed electrode  4   f  formed on the device substrate are electrically connected to the pad  9   a  on the upper surface of the cavity substrate  1  via the through interconnection  7  and the planar interconnection  9 . At the time of attachment, the substrates are sealed in an airtight manner in atmospheric pressure or in a vacuum to obtain an effect of damping. 
         [0041]    Subsequently, the suspension substrate  2  is mounted on the cavity upper part (cavity upper wall)  1   b  of the cavity substrate  1 . At this time, the suspension substrate  2  is provided to cover a range from a position directly on the cavity  1   a  to an outside of an outer circumference of the cavity upper part  1   b  ( 1   ba ,  1   bb ). At this time, the suspension substrate  2  is provided to cover an upper side of the through interconnection  7  as illustrated in  FIG. 2 . Also, the thickness of the suspension substrate  2  is set so that withstanding pressure of the cavity upper part  1   b  may be higher than pressure at the time of below-mentioned plastic sealing as expressed in Equation 1 shown above. In mounting the suspension substrate  2 , the suspension substrate  2  is attached via adhesive  3  such as DAF (Die Attach Film), epoxy, and silicon since a material for the suspension substrate  2  is assumed to be silicon or glass in  FIGS. 2 and 3 . In a case in which the material for the suspension substrate  2  is plastic, the plastic itself functions as adhesive, and the adhesive  3  can be dispensed with. In other words, the suspension substrate  2  is connected to the cavity substrate  1  by the adhesive or the plastic. Meanwhile, as described above, the insulating films  8  and  10  or the like are provided between the suspension substrate  2  and the cavity substrate  1  as needed. 
         [0042]    The acceleration sensor chip  11  configured as above is assembled into the chip package  19  as illustrated in  FIG. 6 . The acceleration sensor chip  11  is implemented on a circuit board  12  via adhesive  13  and is electrically connected to the circuit board  13  by wire bonding  14 . The circuit board  13  is implemented on a lead frame  15  via adhesive  16  and is electrically connected to the lead frame  15  by wire bonding  17 . These are then sealed in plastic  18  into the chip package  19 . At this time, the plastic  18  seals the entirety of the acceleration sensor chip  11  to cover the upper part of the suspension substrate  2  as illustrated in  FIG. 6 . In the plastic packaging by means of a transfer mold process, the sensor chip  11  is under a high-pressure environment as described above. However, since the cavity upper part  1   b  is suspended by the suspension substrate  2 , withstanding pressure of the cavity upper part is higher than pressure at the time of the plastic sealing, and breakage of the cavity can be prevented. 
         [0043]    A semiconductor sensor device according to the present embodiment includes the airtight cavity  1   a  in a laminated structure into which the plurality of substrates  1 ,  4 , and  5  are laminated and has a structure in which an outside of the laminated structure is covered with the plastic  18 . At an outside of the upper wall  1   b  of the cavity  1   a  is arranged the suspension substrate (plate-like member)  2  in which a length of at least one side thereof is longer than a length of a side of the cavity  1   a  residing along the side, and the plate-like member  2  mechanically suspends the upper wall  1   b  of the cavity  1   a.    
         [0044]    In the plate-like member  2 , an opposite surface thereof of a surface thereof suspending the cavity upper wall  1   b  is covered with the plastic  18 . Higher pressure than atmospheric pressure is applied to an outside of a part suspended by the plate-like member  2  on a surface suspended by the plate-like member  2 . 
         [0045]    In the present embodiment, the substrate (cavity substrate)  1  suspended by the plate-like member  2  includes the through electrode  7  provided at the part suspended by the plate-like member  2  and passing through the substrate  1  in a thickness direction, the pad  9 a for wire bonding provided outside the part suspended by the plate-like member  2 , and the interconnection (planar interconnection)  9  electrically connected to the through electrode  7 , extracted outside the part suspended by the plate-like member  2 , and electrically connected to the pad  9   a.  The planar interconnection  9  is made of metal or silicon. 
         [0046]    In the present embodiment, the through interconnection  7  is provided to pass through the cavity substrate  1 , and the suspension substrate  2  is provided to cover an upper side of the through interconnection  7 . Thus, the through length of the through interconnection  7  will not be long, which can prevent burying performance of a conductive member for the through interconnection  7  from being degraded. The through interconnection  7  is electrically connected to the pad  9   a  arranged outside the suspension substrate  2  by the planar interconnection  9 . 
       Second Embodiment 
       [0047]    Next, a modification example of  FIG. 1  will be described with reference to  FIG. 7 .  FIG. 7  is a plan view of the acceleration sensor chip  11  according to a second embodiment of the present invention. It is to be noted that detailed description of similar components to those in  FIG. 1  will be omitted, and different points will mainly be described below. 
         [0048]    In the present embodiment, in a suspension substrate  2   a  suspending the cavity upper part  1   b  illustrated in  FIG. 7 , a length of a shorter side  2   aa  of the suspension substrate  2   a  is a length generating in the cavity substrate upper part  1   b  an area  1   c  not suspended by the suspension substrate  2   a.  That is, in the present embodiment, the cavity  1   a  is formed in a rectangular shape in which one side (two opposed sides) is a longer side while a side perpendicular to this longer side is a shorter side. Also, the suspension substrate (plate-like member)  2  is formed in a rectangular shape in which one side (two opposed sides) is a longer side while a side perpendicular to this longer side is a shorter side. The length of the shorter side of the suspension substrate  2  is a length that is shorter than the shorter side of the cavity and that causes a part of the cavity in the shorter-side direction not to be suspended. Meanwhile, although two areas  1   c  in the cavity substrate upper part  1   b  not suspended by the suspension substrate  2   a  are provided in  FIG. 7 , one area  1   c  may be provided on either side of the suspension substrate  2   a.    
         [0049]    Accordingly, as expressed in Equation 1 shown above, the length a of the shorter side  1   ba  of the cavity upper part  1   b  decreases, which brings about an effect of an increase in the withstanding pressure P of the cavity upper part. Also, since the longer side  1   bb  in the cavity upper part  1   b  of the cavity substrate  1 , to which the maximum stress is applied, is included in the area  1   c,  one can easily determine whether or not the cavity upper part  1   b  breaks against the withstanding pressure by observing the area  1   c.    
         [0050]    In the present embodiment, the through interconnection  7  may be arranged in the area  1   c  not suspended by the suspension substrate  2 . In this case, the through interconnection  7  can be configured not to be covered with the suspension substrate  2 . 
       Third Embodiment 
       [0051]    Next, a modification example of  FIG. 1  will be described with reference to  FIG. 8 .  FIG. 8  is a plan view of the acceleration sensor chip  11  according to a third embodiment of the present invention. It is to be noted that detailed description of similar components to those in  FIG. 1  will be omitted, and different points will mainly be described below. 
         [0052]    In the present embodiment, a plurality of suspension substrates  2   c  suspending the cavity upper part  1   b  are provided as illustrated in  FIG. 8 . Meanwhile, although the number of the suspension substrates  2   c  illustrated in  FIG. 4  is two, the number may be two or more. Also, although one area  1   c  in the cavity upper part  1   b  not suspended by the suspension substrate  2   c  is provided in  FIG. 8 , two or more areas  1   c  maybe provided. 
         [0053]    Accordingly, as expressed in Equation 1 shown above, the length a of the shorter side  1   ba  of the cavity upper part  1   b  decreases, which brings about an effect of an increase in the withstanding pressure P of the cavity upper part. 
         [0054]    In the present embodiment, the through interconnection  7  maybe arranged in the area  1   c  not suspended by the suspension substrate  2 . In this case, the through interconnection  7  can be configured not to be covered with the suspension substrate  2 . 
       Fourth Embodiment 
       [0055]    Hereinbelow, a MEMS-type angular velocity sensor will be described as a fourth embodiment of the present invention. In particular, an example of using a capacitive sensing angular velocity sensor as the MEMS-type angular velocity sensor will be described. 
         [0056]      FIG. 9  is a plan view (upper view) of an angular velocity sensor chip  11   a  according to the fourth embodiment of the present invention.  FIG. 10  is a cross-sectional view along X-X in  FIG. 9 .  FIG. 11  is a cross-sectional view along XI-XI in  FIG. 9 .  FIG. 12  is a plan view illustrating the XII-XII cross-section in  FIG. 10 .  FIG. 13  is a plan view illustrating the XIII-XIII cross-section in  FIG. 10 . 
         [0057]    The present structure can be prepared by a similar method to that of the structure illustrated in  FIGS. 1, 2, 3, 4, 5 , and  6  but differs in a structure of a vibrator prepared in the device substrate  4 . In describing  FIGS. 9, 10, 11, 12, and 13  below, detailed description of similar components to those in  FIGS. 1, 2, 3, 4, 5, and 6  will be omitted, and different points will mainly be described. 
         [0058]    In the present embodiment, the angular velocity sensor chip  11   a  has a configuration in which the cavity substrate  1  and the support substrate  5  are attached to the device substrate  4  forming a below-mentioned vibrator therein and are sealed in an airtight manner in a vacuum or in atmospheric pressure, and in which the cavity substrate upper part  1   b  is suspended by the suspension substrate  2 . 
         [0059]    Meanwhile, in the suspension substrate  2 , as described in the second embodiment, the length of the shorter side  2   aa  of the suspension substrate  2   a  may be a length generating in the cavity substrate upper part  1   b  the area  1   c  not suspended by the suspension substrate  2   a.  Also, as described in the third embodiment, the plurality of suspension substrates  2  may be provided. 
         [0060]    The angular velocity sensor chip  11   a  is assembled into the chip package  19  in a similar manner to  FIG. 6 . 
         [0061]    In the angular velocity sensor chip  11   a,  a left-side vibrating unit  4   q   1  and a right-side vibrating unit  4   q   2  are arranged to be symmetrical and opposed to each other and are connected via a link beam  4   p.  That is, the vibrating unit  4   q   1  and the vibrating unit  4   q   2  are line-symmetrical across a center line  100  as illustrated in  FIG. 12 . As for a part formed only by the device substrate  4 , both of the vibrating units are movable with respect to the support substrate  5  via the anchors  4   c  and the insulating film  6 , and the vibrating units  4   q   1  and  4   q   2  are designed to have equal natural vibration frequency. 
         [0062]    On the device substrate  4 , a weight  4   h,  serving as a first vibrator, is formed, and to the weight  4   h,  support beams  4   i  are connected in a direction perpendicular to a driving direction of the vibrator. The other ends of these support beams  4   i  are respectively connected to the anchors  4   c  provided in the direction perpendicular to the driving direction. The weight  4   h  serving as the first vibrator can vibrate in an X-axial direction due to the support beams  4   i.  Also, some of the anchors  4   c  can electrically be connected to the aforementioned through interconnection  7  similarly to the anchor  4   d  and are used to electrically connect the vibrator side to an external circuit. 
         [0063]    Comb-like driving electrodes  41  formed in the device substrate  4  are formed outside the weight  4   h  serving as the first vibrator. Comb-like driving electrodes  4   m  are formed on the device substrate  4  and the insulating film  6  to face the comb-like driving electrodes  4   l  and are fixed to the support substrate  5 . 
         [0064]    The driving electrode  4   m  is electrically connected to the pad  9   a  via the through interconnection  8  and the planar interconnection  9  on the cavity substrate and is connected to an external oscillating circuit. When a predetermined frequency signal is applied to the driving electrode  4   m,  an electrostatic force is generated between the electrodes  4   l  and  4   m,  and the weight  4   h  serving as the first vibrator vibrates in the X-axial direction. 
         [0065]    On the device substrate  4 , a weight  4   j , serving as a second vibrator, is formed inside the weight  4   h  serving as the first vibrator. On the upper and lower sides of the weight  4   j,  detection beams  4   k  extending in an equal direction to the vibrating direction of the weight  4   h  are provided. That is, one end of the beam  4   k  is connected to the weight  4   j.  The other end of the beam  4   k  is connected to the weight  4   h  serving as the first vibrator. The weight  4   j  serving as the second vibrator is movable against the support substrate  5  and can vibrate in association with the weight  4   h  serving as the first vibrator due to the support beams  4   k  and also vibrate in the Y-axial direction perpendicular to the X-axial direction. 
         [0066]    As a means to detect displacement of the weight  4   j  serving as the second vibrator in the Y-axial direction, comb-like detection electrodes  4   n  are provided on the device substrate  4  to be adjacent to the weight  4   j . Comb-like detections  4   o  are provided at positions facing the detection electrodes  4   n.  The detection electrodes  4   o  are formed on the device substrate  4  and the insulating film  6  and are fixed to the support substrate  5 . The detection electrode  4   o  is electrically connected to the pad  9   a  via the through interconnection  8  and the planar interconnection  9  on the cavity substrate  1  and is connected to an external signal processing circuit. 
         [0067]    When the weight  4   j  serving as the second vibrator is displaced in the Y-axial direction, capacitance between the electrodes  4   n  and  4   o  changes, and the electrode  4   o  outputs a signal corresponding to the capacitance. 
         [0068]    By arbitrarily setting the mass of the weight  4   h  serving as the first vibrator and the weight  4   j  serving as the second vibrator and the shapes of the support beams  4   i,  the weight  4   h  and the weight  4   j  vibrate in the X-axial direction with natural vibration frequency of fx. 
         [0069]    Also, by arbitrarily setting the mass of the weight  4   j  serving as the second vibrator and the shapes of the detection beams  4   k,  the weight  4   j  vibrates in the Y-axial direction as well with natural vibration frequency of fy. 
         [0070]    The angular velocity sensor according to the present embodiment is operated in the following manner. 
         [0071]    First, alternating voltage with frequency of f is applied to the driving electrode  4 m in  FIG. 12  so that the left-side vibrating unit  4   q   1  and the right-side vibrating unit  4   q   2  may vibrate in opposite phase to cause an electrostatic force to be generated between the electrodes  4   m  and  4   l  and cause the weight  4   h  serving as the first vibrator to vibrate in the X-axial direction. At this time, the weight  4   j  serving as the second vibrator vibrates in the X-axial direction in association with the weight  4   h.  At this time, the relationship between displacement x of the weight  4   h  in the X-axial direction and speed v thereof is expressed by Equation 5. 
         [0000]        x=Xe sin (2πft)
 
         [0000]        v= 2 πfXe cos (2πft)   (Equation 5)
 
         [0000]    In Equation 5, f is frequency, Xe is amplitude, and t is time. 
         [0072]    When angular velocity Ω is applied to the angular velocity sensor in a direction of an axis (Z) perpendicular to the drawing sheet of  FIG. 12  in a state in which the weight  4 h and the weight  4   j  vibrate in the X-axial direction, a Coriolis force Fc (Equation 6) is generated in the Y-axial direction. The weight  4   j  is displaced in the Y-axial direction by the Coriolis force Fc. 
         [0000]      Fc=2mΩv   (Equation 6)
 
         [0000]    In Equation 6, m is mass of the weight  4   j.    
         [0073]    The weight  4   j  serving as the second vibrator vibrates in the Y-axial direction by the Coriolis force Fc expressed in Equation 6, and capacitance between the detection electrodes  4   n  and  4   o  changes. By detecting the capacitance change, the angular velocity Ω around the Z axis can be detected. 
         [0074]    Meanwhile, as a method for measuring the displacement amount of the weight  4   j  serving as the second vibrator, voltage to be applied between the electrodes  4   n  and  4   o  may be servo-controlled so that the capacitance change between the detect ion electrodes  4   n  and  4   o,  that is, the displacement amount of the weight  4   j  in the Y-axial direction, maybe zero, and the Coriolis force Fc may be derived from the applied voltage. 
         [0075]    Also, since the left-side vibrating unit  4   q   1  and the right-side vibrating unit  4   q   2  arranged to be symmetrical and opposed to each other are provided, both of the vibrating units vibrate in opposite phase. Accordingly, while external acceleration is cancelled, a detection signal of angular velocity can be detected with high sensitivity as the sum of the two vibrating units. As another advantage, leakage of vibration of the vibrating units to an outside can be restricted. 
         [0076]    Further, the present invention can be applied to a MEMS device having a cavity as well as the acceleration sensor and the angular velocity sensor. By suspending a cavity upper part by means of a suspension substrate, an effect of improvement in withstanding pressure of the cavity upper part can be obtained without thickening the cavity substrate. 
       Fifth Embodiment 
       [0077]    Hereinbelow, a fifth embodiment of the present invention will be described with reference to  FIG. 14 .  FIG. 14  is a plan view of the acceleration sensor chip according to the fifth embodiment of the present invention. In the present embodiment, an example of using a capacitive sensing acceleration sensor as a MEMS-type acceleration sensor will be described. However, a capacitive sensing angular velocity sensor or another sensor may be used as the MEMS-type sensor. 
         [0078]    In the present embodiment, a first acceleration sensor  20 A detecting acceleration in the y direction and a second acceleration sensor  20 B detecting acceleration in the x direction are provided. To include the first acceleration sensor  20 A and the second acceleration sensor  20 B in one sensor chip  11 , two cavities  1   a A and  1   a B are provided in one sensor chip  11 . The number of sensors included in the sensor chip  11  is not limited to one or two, and more sensors can be included. Also, the number of sensor kinds is not limited to one, and plural kinds of sensors may be combined. In this manner, by providing a plurality of cavities in accordance with the number of sensors included in the sensor chip  11 , the function of the sensor chip  11  can be enhanced. 
         [0079]    Effects obtained by the aforementioned respective embodiments are summarized in the following manner. 
         [0080]    In the semiconductor sensor device including the cavity substrate, the configuration in which the cavity upper part of the cavity substrate is provided with the wider suspension substrate than the outer circumference of the cavity upper part, and in which the cavity upper part is thus suspended, provides the following effect. As described in Equation 1 shown above, the withstanding pressure P of the cavity upper part is a function for the thickness h of the cavity upper part and the stress σ. At this time, since the cavity upper part is thicker due to the suspension substrate, the withstanding pressure P is improved. At this time, by making the suspension substrate larger than the outer circumference of the cavity, an increase of the stress σ to the end of the cavity upper part can be restricted by the suspension substrate, and the withstanding pressure P of the cavity upper part can be improved. Accordingly, by using such a configuration, a structure in which the withstanding pressure of the cavity upper part is improved can be achieved without thickening the cavity substrate itself. 
         [0081]    Also, the configuration in which the length of the shorter side of the suspension substrate is a length that is shorter than the shorter side of the cavity upper part and that generates in a part of the cavity upper part the area not suspended by the suspension substrate provides the following effect. That is, as described in Equation 1 shown above, the length a of the cavity shorter side is short, and the withstanding pressure P can be improved. Also, since the end portion on the cavity longer side, to which the maximum stress is applied, is exposed, one can observe the area and can easily determine whether or not the cavity breaks against the withstanding pressure. 
         [0082]    Further, the configuration in which the plurality of suspension substrates are provided provides the following effect. That is, as described in Equation 1 shown above, the length a of the cavity shorter side is short, and the withstanding pressure P can be improved. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           1  cavity substrate 
           1     1   cavity 
           1   b  cavity upper part 
           1   ba  shorter side of cavity upper part 
           1   bb  longer side of cavity upper part 
           1   c  area of cavity upper part not suspended 
           2  suspension substrate 
           2   a  suspension substrate 
           2   aa  shorter side of suspension substrate  2 a 
           2   ab  longer side of suspension substrate  2 a 
           2   b  suspension substrate 
           3  adhesive 
           4  device substrate 
           4   a  weight 
           4   b  support beam 
           4   c  anchor 
           4   d  anchor (connected to through interconnection) 
           4   e  detection electrode 
           4   f  fixed electrode 
           4   g  cavity 
           4   h  weight (first vibrator) 
           4   i  support beam 
           4   j  weight (second vibrator) 
           4   k  beam (for detection) 
           4   l  driving electrode (side of weight  4   h ) 
           4   m  driving electrode (fixed to support substrate) 
           4   n  detection electrode (side of weight  4   j ) 
           4   o  detection electrode (fixed to support substrate) 
           4   p  link beam 
           4   q   1  vibrating unit 
           4   q   2  vibrating unit 
           5  support substrate 
           5   a  cavity 
           6  insulating film 
           7  through interconnection 
           8  insulating film 
           9  planar interconnection 
           9   a  pad 
           9   b  through interconnection upper part 
           10  insulating film 
           10   a  pad opening portion 
           11  acceleration sensor chip 
           11   a  angular velocity sensor chip 
           12  circuit board 
           13  adhesive 
           14  wire bonding 
           15  lead frame 
           16  adhesive 
           17  wire bonding 
           18  plastic 
           19  chip package

Technology Classification (CPC): 6