Abstract:
A piezoelectric driving type MEMS apparatus includes: a supporting portion provided on a substrate; and a piezoelectric actuator, which is supported on the supporting portion, including a piezoelectric film and a driving electrode configured to drive the piezoelectric film, the piezoelectric film in the piezoelectric actuator having at least one slit extending along a longitudinal direction of the piezoelectric actuator.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2004-355240 filed on Dec. 8, 2004, the entire contents of which are incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a piezoelectric driving type MEMS apparatus that is manufactured utilizing a MEMS (Micro-Electro-Mechanical Systems) technique. 
   2. Related Art 
   In recent years, attention is paid to a technique for manufacturing such a high frequency element as a variable capacitor or a switch utilizing a MEMS. A variable capacitor obtained by the MEMS has such an advantage that a Q value thereof is higher than that of a variable capacitance diode. On the other hand, the MEMS switch has such merits that an insertion loss thereof is low and isolation property thereof is excellent compared to PIN diode and GaAsFET based-switch (for example, see U.S. Pat. No. 4,670,682). The merits come from a feature of the MEMS that can manufacture a mechanically movable portion. 
   In order to manufacture the mechanically movable portion, it is necessary to provide an actuator for converting an electrical signal to a mechanical behavior. Actuators can be classified to some types according to their driving systems. As well-known driving systems, there are ones of an electrostatic type, a thermal type, an electromagnetic type and a piezoelectric type. The piezoelectric type driving system is constituted to realize a movable structure utilizing a piezoelectric effect of piezoelectric material. The piezoelectric type actuator has such an advantage that both a low voltage operation and a low power consumption can be realized. Therefore, an MEMS variable capacitor or a MEMS switch utilizing a piezoelectric type actuator is suitable for a high frequency part for a portable device or equipment. 
   A conventional MEMS variable capacitor employs such a structure that a lower electrode for the variable capacitor is provided at a central portion of a substrate, supporting portions are provided at both ends of the substrate, and a beam which is supported by the supporting portions to displace toward the substrate is provided. The beam is provided with a first insulating film, a first electrode film that is provided on the first insulating film to extend from one end of the beam to the other end thereof, piezoelectric films which are provided on both end portions of the first electrode film except for a central portion thereof, second electrode films which are provided on the piezoelectric films, and a second insulating film which covers the first and second electrode films. As material for the piezoelectric film, PZT, AlN, ZnO, or the like is used. Incidentally, the first electrode film serves as an upper electrode for the variable capacitor. 
   When different voltages, V 1  and V 2 , are respectively applied to the first electrode film and the second electrode film the piezoelectric films strain so that the length of the beam in its extending direction (hereinafter, “X-axis direction”) varies. When it is assumed that a length L x  of the piezoelectric film in the X-axis direction has changed to L x +ΔL x  due to voltage application, a strain ε x =ΔL x /L x  can be expressed by the following equation (1).
 
ε x   =d   31 ( V 1 −V 2)/ t   (1)
 
Here, t represents a thickness of a piezoelectric film, and d 31  represents a piezoelectric constant. The piezoelectric constant d 31  is a parameter which represents amounts of strain occurring in the X-axis direction and in a direction (hereinafter, “Y-axis direction) orthogonal to the X and Z axes and a film thickness direction of the piezoelectric film (hereinafter, “Z-axis direction”) when electric field is applied in the Z-axis direction, whose value varies according to piezoelectric material. The beam including the piezoelectric films flexes in the direction of the substrate due to strain in the piezoelectric film so that a distance between the first electrode (film) and the lower electrode changes. A change δ z  of the distance between the electrodes meets the following relationship or equation (2).
 
δ z ∝ d 31 (V1−V2) L   x   2   (2)
 
   Accordingly, according to increase of a length of the piezoelectric film in the X-axis direction, namely, a length of the beam, a variable range of the capacitor is increased. 
   Since a cavity is formed under the upper electrode in an MEMS variable capacitor with such a structure, there is such a drawback that, when an acceleration is applied to the MEMS variable capacitor, the upper electrode may move, which results in change in capacitance value. In order to make it harder for the upper electrode to move even when acceleration is applied to the MEMS variable capacitor, such a constitution can be employed that the beam and the upper electrode are reduced in weight and a width L y  of the beam which supports the upper electrode is increased. When the MEMS variable capacitor is mounted to a portable device, there is a high possibility that the portable device is used under an environment where acceleration is applied to the portable device. Therefore, such a countermeasure as widening of the beam becomes important among others. 
   However, when the width L y  of the beams is increased, the piezoelectric film also strains in the Y-axis direction at a time of application of voltage to the first and second electrodes. A strain ε y  (=ΔL y /L y ) in the Y-axis direction can be expressed as follows:
 
ε y   =d   32 ( V 1 −V 2)/ t   (3)
 
Here, d 32  represents a piezoelectric constant. The beam flexes in the Y-axis direction toward the substrate due to the strain. As a result, such a problem occurs that the upper electrode and the lower electrode do not become parallel to each other so that a desired capacitance value can not be obtained. Incidentally, a displacement amount due to flexion, namely, δ y  is proportional to square of the beam width L y .
 
   The flexion of the beam also causes a problem in a piezoelectric type MEMS switch. In order to prevent the isolation property during turning-off of the MEMS switch from depending on acceleration, it is necessary to increase the width of the beam in the MEMS switch. As a result, however, the flexion of the beam also occurs in the Y-axis direction during voltage application. Therefore, when the switch turns on, the electrodes at a contact portion do not become parallel to each other, and they come in contact with each other at only one point. As a result, a resistance occurring when the switch turns on increases and an insertion loss increases so that a desired property can not be obtained. Further, the increase in resistance tends to cause malfunction in the switch due to melting of the electrodes at the contacting portion. 
   SUMMARY OF THE INVENTION 
   A piezoelectric driving type MEMS apparatus according to an aspect of the present invention includes: a supporting portion provided on a substrate; and a piezoelectric actuator, which is supported on the supporting portion, including a piezoelectric film and a driving electrode configured to drive the piezoelectric film, the piezoelectric film in the piezoelectric actuator having at least one slit extending along a longitudinal direction of the piezoelectric actuator. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a plan view showing a piezoelectric driving type MEMS apparatus according to a first embodiment of the present invention; 
       FIG. 2  is a sectional view showing the piezoelectric driving type MEMS apparatus taken along line A-A shown in  FIG. 1 ; 
       FIG. 3  is a sectional view showing the piezoelectric driving type MEMS apparatus taken along line B-B shown in  FIG. 1 ; 
       FIG. 4  is a plan view showing a piezoelectric driving type MEMS apparatus according to modification of the first embodiment of the present invention; 
       FIG. 5  is a plan view showing a piezoelectric driving type MEMS apparatus according to a second embodiment of the present invention; 
       FIG. 6  is a sectional view showing the piezoelectric driving type MEMS apparatus taken along line A-A shown in  FIG. 5 ; 
       FIG. 7  is a plan view showing a piezoelectric driving type MEMS apparatus according to a third embodiment of the present invention; 
       FIG. 8  is a sectional view showing the piezoelectric driving type MEMS apparatus taken along line A-A shown in  FIG. 7 ; 
       FIG. 9  is a sectional view showing the piezoelectric driving type MEMS apparatus taken along line B-B shown in  FIG. 7 ; 
       FIG. 10  is a plan view showing a piezoelectric driving type MEMS apparatus according to a fourth embodiment of the present invention; 
       FIG. 11  is a sectional view showing the piezoelectric driving type MEMS apparatus taken along line A-A shown in  FIG. 10 ; 
       FIG. 12  is a sectional view showing the piezoelectric driving type MEMS apparatus taken along line B-B shown in  FIG. 10 ; 
       FIG. 13  is a plan view showing a piezoelectric driving type MEMS apparatus according to a fifth embodiment of the present invention; 
       FIG. 14  is a sectional view showing the piezoelectric driving type MEMS apparatus taken along line A-A shown in  FIG. 13 ; 
       FIG. 15  is a sectional view showing the piezoelectric driving type MEMS apparatus taken along line B-B shown in  FIG. 13 ; 
       FIG. 16  is a plan view showing a piezoelectric driving type MEMS apparatus according to a sixth embodiment of the present invention; 
       FIG. 17  is a sectional view showing the piezoelectric driving type MEMS apparatus taken along line A-A shown in  FIG. 16 ; 
       FIG. 18  is a sectional view showing the piezoelectric driving type MEMS apparatus taken along line B-B shown in  FIG. 16 ; 
       FIG. 19  is a plan view showing a piezoelectric driving type MEMS apparatus according to a seventh embodiment of the present invention; 
       FIG. 20  is a sectional view showing the piezoelectric driving type MEMS apparatus taken along line A-A shown in  FIG. 19 ; 
       FIG. 21  is a sectional view showing the piezoelectric driving type MEMS apparatus taken along line B-B shown in  FIG. 19 ; 
       FIG. 22  is a plan view showing a piezoelectric driving type MEMS apparatus according to a eighth embodiment of the present invention; 
       FIG. 23  is a sectional view showing the piezoelectric driving type MEMS apparatus taken along line A-A shown in  FIG. 22 ; 
       FIG. 24  is a sectional view showing the piezoelectric driving type MEMS apparatus taken along line B-B shown in  FIG. 22 ; 
       FIG. 25  is a plan view showing a piezoelectric driving type MEMS apparatus according to a first modification of the eighth embodiment of the present invention; 
       FIG. 26  is a plan view showing a piezoelectric driving type MEMS apparatus according to a second modification of the eighth embodiment of the present invention; 
       FIG. 27  is a plan view showing a piezoelectric driving type MEMS apparatus according to a third modification of the eighth embodiment of the present invention; 
       FIG. 28  is a plan view showing a piezoelectric driving type MEMS apparatus according to a fourth modification of the eighth embodiment of the present invention; 
       FIG. 29  is a plan view showing a piezoelectric driving type MEMS apparatus according to a ninth embodiment of the present invention; 
       FIG. 30  is a sectional view showing the piezoelectric driving type MEMS apparatus taken along line A-A shown in  FIG. 29 ; and 
       FIG. 31  is a sectional view showing the piezoelectric driving type MEMS apparatus taken along line B-B shown in  FIG. 29 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Embodiments of the present invention will be explained below with reference to the drawings. 
   First Embodiment 
   A piezoelectric driving type MEMS apparatus according to a first embodiment of the invention will be explained with reference to  FIGS. 1 to 3 .  FIG. 1  is a plan view of the piezoelectric driving type MEMS apparatus according to the embodiment,  FIG. 2  is a sectional view of the piezoelectric driving type MEMS apparatus according to the embodiment taken along line A-A shown in  FIG. 1 , and  FIG. 3  is a sectional view of the piezoelectric driving type MEMS apparatus according to the embodiment taken along line B-B shown in  FIG. 1 . 
   The piezoelectric driving type MEMS apparatus according to the embodiment is a variable capacitor which has such a constitution that a lower electrode  4  is provided on a central portion of a substrate  2  made from silicon or glass, and a plurality of (for example, three) supporting portions  6  are provided at each of both end portions of the substrate  2  so as to be opposed to corresponding supporting portions  6  at the other end portion thereof. Further, the variable capacitor has a constitution that a beams  10  is spanned between the opposed supporting portions  6  over the lower electrode  4 . 
   The beams  10  is provided with an insulating film  11  made from, for example, SiO 2 , a first electrode  12  provided on the insulating film  11 , a piezoelectric film  13  provided on a region of the first electrode  12  except for a central portion of the first electrode  12 , a second electrode  14  provided on the piezoelectric film  13 , and a protective film  15  provided so as to cover the second electrodes  14  and the central portion of the first electrode  12  and made from, for example, SiO 2 . The beam  10  is formed such that a central portion thereof is wider than each end portions thereof (a vertical size or length in  FIG. 1 ), and two slits  20  are provided at the end portion so as to extend along a longitudinal direction of the beam  10  so that three branched beams are formed on the each end portion by the slits  20 . Each slit  20  is formed such that a length thereof (a horizontal size or length in  FIG. 1 ) is equal to or longer than that of each piezoelectric film  13 . Incidentally, such a constitution is employed that the three branched beams are respectively supported by the supporting portions  6 . Such a constitution is adopted that a height of each supporting portion  6  is larger than a film thickness of the lower electrode  4 , so that a clearance  7  is formed between the lower electrode  4  and the beam  10  (see  FIG. 2 ). 
   In the embodiment, when a driving voltage V 1  and a driving voltage V 2  are respectively applied to the first electrode  12  and the second electrode  14 , the piezoelectric film  13  strains and a length thereof in its longitudinal direction (the horizontal direction in  FIG. 1 ) changes so that the beam  10  flexes toward the lower electrode  4 . A distance between the lower electrode  4  and the first electrode  12  changes due to the flexion so that a capacitance also changes. That is, the beam  10  constitutes a piezoelectric actuator. The first electrode  12  doubles with an upper electrode for the variable capacitor. 
   A magnitude relationship between the driving voltages V 1  and V 2  changes according to such a factor as the kind of the piezoelectric film, orientation of polarization, film thickness sizes of films positioned above and below the piezoelectric film, or Young&#39;s modulus. For example, a case that an AlN film whose orientation ( FIG. 2 ) of polarization is directed upwardly is used as the piezoelectric film will be explained. A total film thickness of films positioned under the piezoelectric film, namely, the sum of film thicknesses of the insulating film  11  and the first electrode  12  is represented as t 1 , and a total film thickness of films positioned above the piezoelectric film, namely, the sum of film thicknesses of the second electrode  14  and the protective film  15  is represented as t 2 . For simplification, it is assumed that the insulating film  11 , the first electrode  12 , the second electrode  14 , and the protective film  15  are equal in Young&#39;s modulus. Since d 31  of AlN is negative, under the condition of t 2 &gt;t 1 , when the driving voltage V 1  is larger than the driving voltage V 2 , the piezoelectric film shrinks so that the actuator moves downwardly and when the driving voltage V 1  is smaller than the driving voltage V 2 , the piezoelectric film stretches so that the actuator moves upwardly. The actuator moves in directions reversed to the above directions under the condition of t 2 &lt;t 1 . Even when PZT is adopted as the piezoelectric film, moving directions of the actuator are similar to those in the above case. However, it is desirable that PZT is used under such a voltage condition that polarization reversal does not occur. This is because the piezoelectric performance of the piezoelectric film degrades due to polarization fatigue caused by repetition of polarization reversal. 
   As explained above, in the embodiment, the branched beams are formed by providing the slits  20  on the both ends of the beam  10 . Therefore, since a total sum of widths of the piezoelectric films  13  on the branched beams is smaller than a width of a piezoelectric film of a beam  10  which is not provided with the slits  20 , it is made possible to reduce flexion of the piezoelectric film  13  due to strain in the widthwise direction. For example, when n branched beams are formed by providing (n−1) slits  20  on each of both ends of the beam  10  and a total sum of transverse widths of the n branched beams is set to be equal to a width of a beam where no slit is formed, a displacement amount δ due to strain of a piezoelectric film on one branched beam in a widthwise direction thereof can be reduced to 1/n 2  that in the case that the slits  20  are not provided. Accordingly, as shown in  FIG. 3 , a section of the beam  10  takes an approximately flat shape without being deformed substantially. Thereby, the lower electrode  4  and the upper electrode  12  constituting the capacitor become substantially parallel to each other, so that a desired capacitance can be obtained. 
   When the total sum of the widths of the branched beams is set to be equal to the width of the beam where the slits are not provided, acceleration tolerance can be prevented from deteriorating. 
   As shown in  FIG. 4 , the slits may be formed in such a manner that adjacent branched beams are connected to each other by a bridge portion(s)  18 . In that case, each bridge portion  18  may be constituted of a dielectric or insulating film, a first electrode, a piezoelectric film, a second electrode, and a protective film. When the shape shown in  FIG. 4  is employed, acceleration tolerance can be further improved. 
   By forming slit(s) in the piezoelectric actuator, the following advantages can be achieved. (1) By removing a sacrifice layer from the slit portion at a time of removal of a sacrifice layer from a lower portion of the actuator, an etching depth may be made shallow, so that an etching time can be reduced as compared with that in case that no slit is formed. (2) Since air passes through the slit(s) during operation of the actuator, a damping effect (squeezed film damping effect) due to air resistance can be suppressed, so that operation of the actuator at a higher speed can be made possible. 
   As explained above, according to the embodiment, a desired capacitance can be obtained even during application of acceleration. 
   Second Embodiment 
   Next, a piezoelectric driving type MEMS apparatus according to a second embodiment of the invention will be explained with reference to  FIGS. 5 and 6 .  FIG. 5  is a plan view showing a constitution of a piezoelectric driving type MEMS apparatus according to the embodiment and  FIG. 6  is a sectional view of the piezoelectric driving type MEMS apparatus taken along line A-A shown in  FIG. 5 . 
   The MEMS apparatus according to the embodiment is an MEMS switch, which has such a constitution that a supporting portion  6  is provided at one end of a silicon substrate  2 , a pair of lower electrodes  37  and leading electrodes  38  are provided at the other end thereof, and a cantilever beam  30  is fixed on the supporting portion  6 . The cantilever beam  30  is provided with an insulating film  31 , a first electrode  32  provided on the insulating film  31 , a piezoelectric film  33  provided on the first electrode  32 , a second electrode  34  provided on the piezoelectric film  33 , a protective film  35  provided on the second electrode  34 , and an upper electrode  36  provided on a face of the insulating film  31  which is opposed from the first electrode. A slit  20  is formed at a central portion of the cantilever beam  30  so as to extend along a longitudinal direction thereof. 
   A height of the supporting portion  6  is set to be larger than a film thickness of the lower electrode  37 , so that a clearance  7  is formed between the lower electrode  37  and the upper electrode  36 . 
   In the embodiment, when a voltage V 1  and a voltage V 2  (&lt;V 1 ) are respectively applied to the first electrode  32  and the second electrode  34 , the piezoelectric film  33  strains in the longitudinal direction of the cantilever beam  30 , the cantilever beam  30  flexes toward the substrate  2  due to the strain, and the upper electrode  36  comes in contact with the lower electrodes  37 , so that the switch turns on. 
   According to the embodiment, since the slit  20  is formed in the cantilever beam  30 , flexing in a widthwise direction of the beam  30  is reduced, so that when the switch is turned on, the upper electrode  36  comes in surface-contact with the lower electrodes  37  without substantially deforming in the widthwise direction of the beam  30 . Therefore, insertion loss can be reduced, as compared with a case that an upper electrode and a lower electrode come in point-contact with each other. Since the total sum of the width of the beam  30  is large, sufficient acceleration tolerance can be achieved. Thereby, a high frequency switch with reduced insertion loss and high acceleration tolerance can be realized. 
   Third Embodiment 
   Next, a piezoelectric driving type MEMS apparatus according to a third embodiment of the invention will be explained with reference to  FIGS. 7 to 9 .  FIG. 7  is a plan view of the piezoelectric driving type MEMS apparatus according to the embodiment,  FIG. 8  is a sectional view of the piezoelectric driving type MEMS apparatus taken along line A-A shown in  FIG. 7 , and  FIG. 9  is a sectional view of the piezoelectric driving type MEMS apparatus taken along line B-B shown in  FIG. 7 . Incidentally,  FIG. 7  is a plan view where a protective film described later has been removed. 
   The piezoelectric driving type MEMS apparatus according to the embodiment is a T-shaped type unimorph variable capacitor, which is provided with a lower electrode  4  and a beam  10 . The lower electrode  4  is provided at a central portion of a substrate  2  made from silicon and formed thereon with an insulating layer  3  made from, for example, SiO 2 , and an insulating layer  5  made from, for example, SiN is formed on the lower electrode  4 . A plurality of supporting portions  6  are provided on both ends of the substrate  2 . The beam  10  is arranged so as to be spanned between the supporting portions  6  on the both ends of the substrate over the lower electrode  4 . 
   The beam  10  is provided with an insulating film  16  made from, for example, SiO 2 , an upper electrode  17  provided at a central portion of the insulating film  16 , an insulating film  11  made from, for example, SiO 2  and provided on a region of the insulating film  16  except for the central portion thereof, a first electrode  12  provided on the insulating film  11 , piezoelectric films  13  provided on the first electrodes  12 , second electrodes  14  provided on the piezoelectric films  13 , and a protective film  15  made from, for example, SiO 2 . Two slits  20   a  are provided on each of both end portions of the beam  10  so as to extend along a longitudinal direction of the beam  10 , so that the beam is formed at each end portion with three branched beams by the slits  20 . The three branched beams are respectively supported by the supporting portions  6  (see  FIG. 8 ). 
   The upper electrode  17  is electrically connected to a leading electrode  17   a  extending in a direction orthogonal to the longitudinal direction of the beam  10 . The leading electrode  17   a  is provided with a plurality of slits  18  such that its rigidity is reduced and the beam  10  is flexed easily. The leading electrode  17   a  is supported by a supporting portion  6  (see  FIG. 9 ). Incidentally, such a constitution is employed that a height of the supporting portion  6  is larger than a film thickness of the lower electrode  4 , so that a clearance  7  is formed between the lower electrode  4  and the beam  10  (see  FIG. 8 ). 
   The first electrode  12  is electrically connected to a wire  12   b  for applying a voltage to the first electrode  12  via a contact  12   a,  and the second electrode  14  is electrically connected to a wire  14   b  for applying a voltage to the second electrode  14  via a contact  14   a  (see  FIG. 7 ). The lower electrode  4  is also electrically connected to a leading electrode  4   b  for applying a voltage to the lower electrode  4  via a contact  4   a  (see  FIG. 9 ). The leading electrode  4   b  is also supported by a supporting portion  6 , as shown in  FIG. 9 . 
   In the embodiment, when a driving voltage V 1  and a driving voltage V 2  are respectively applied to the first electrode  12  and the second electrode  14 , the piezoelectric film  13  strain and a length thereof in its longitudinal direction (the horizontal direction of the beam  10  in  FIG. 7 ) changes so that the beam  10  flexes toward the lower electrode  4 . As a result, a distance between the lower electrode  4  and the first electrode  12  changes so that a capacitance changes. 
   In the embodiment, the branched beams are formed by providing the slits  20  on the both end portions of the beam  10  like the first embodiment. Therefore, a section of the beam  10  in a widthwise direction takes an approximately flat shape without being deformed substantially, and the lower electrode  4  and the upper electrode  12  constituting the capacitance become substantially parallel to each other, so that a desired capacitance can be obtained like the first embodiment. When the total sum of the widths of the branched beams is set to be equal to the width of the beam where the slits  20  are not provided, acceleration tolerance can be prevented from deteriorating. 
   As explained above, according to the embodiment, a desired capacitance can be obtained even during application of acceleration. 
   Fourth Embodiment 
   Next, a piezoelectric driving type MEMS apparatus according to a fourth embodiment of the invention will be explained with reference to  FIGS. 10 to 12 .  FIG. 10  is a plan view of the piezoelectric driving type MEMS apparatus according to the embodiment,  FIG. 11  is a sectional view of the piezoelectric driving type MEMS apparatus taken along line A-A shown in  FIG. 10 , and  FIG. 12  is a sectional view of the piezoelectric driving type MEMS apparatus taken along line B-B shown in  FIG. 10 . Incidentally,  FIG. 10  is a plan view where a protective film has been removed. 
   The piezoelectric driving type MEMS apparatus according to the embodiment is an I-shaped type unimorph variable capacitor, which has such a constitution that the upper electrode  17  is put in an electrically floating state by removing the leading electrode  17   a  for the upper electrode  17  and two lower electrodes  4  are arranged in the T-shaped type unimorph variable capacitor according to the third embodiment shown in  FIGS. 7 to 9 . 
   In the embodiment, terminals  4   b  and  4   d  are capacitance-coupled via the floating electrode  17 . Therefore, a capacitance between the terminals  4   b  and  4   b  can be changed by moving the electrode  17  in a vertical direction. In the embodiment, since a leading wire such as the leading wire for the upper electrode  17  in the third embodiment is not provided, the upper electrode is difficult to flex. 
   In the piezoelectric driving type MEMS apparatus according to the embodiment, since the branched beams are formed by providing slits  20  on the both end portions of the beam  10 , a desired capacitance can be obtained even during application of acceleration like the third embodiment. 
   Fifth Embodiment 
   Next, a piezoelectric driving type MEMS apparatus according to a fifth embodiment of the invention will be explained with reference to  FIGS. 13 to 15 .  FIG. 13  is a plan view of the piezoelectric driving type MEMS apparatus according to the embodiment,  FIG. 14  is a sectional view of the piezoelectric driving type MEMS apparatus taken along line A-A shown in  FIG. 13 , and  FIG. 15  is a sectional view of the piezoelectric driving type MEMS apparatus taken along line B-B shown in  FIG. 13 . Incidentally,  FIG. 13  is a plan view where a protective film has been removed. 
   The piezoelectric driving type MEMS apparatus according to the embodiment is an I-shaped type bimorph variable capacitor, which has such a constitution that a piezoelectric film  13   1  and an electrode  14   1  are provided on the electrode  14  of the beam  10  in the piezoelectric driving type MEMS apparatus according to the embodiment shown in  FIGS. 10 to 12 . The electrode  14   1  is connected to a wire  14   b   1  via a contact  14   a   1 . 
   In the embodiment, according to application of voltages to the electrodes  12 ,  14 , and  14   1  of the beam  10 , the beam  10  flexes, and a distance between the upper electrode  17  and the lower electrode  4  changes, so that a capacitance can be made variable. 
   In the embodiment, a large capacitance can be obtained and a desired capacitance can be obtained during application of acceleration like the fourth embodiment. 
   Sixth Embodiment 
   Next, a piezoelectric driving type MEMS apparatus according to a sixth embodiment of the invention will be explained with reference to  FIGS. 16 to 18 .  FIG. 16  is a plan view of the piezoelectric driving type MEMS apparatus according to the embodiment,  FIG. 17  is a sectional view of the piezoelectric driving type MEMS apparatus taken along line A-A shown in  FIG. 16 , and  FIG. 18  is a sectional view of the piezoelectric driving type MEMS apparatus taken along line B-B shown in  FIG. 16 . Incidentally,  FIG. 16  is a plan view where a protective film  15  has been removed. 
   The piezoelectric driving type MEMS apparatus according to the embodiment is an I-shaped type unimorph variable capacitor, which has such a constitution that a beam  10  is constituted as a cantilever beam in the I-shaped unimorph variable capacitor according to the fourth embodiment shown in  FIGS. 10 to 12 . 
   In the embodiment, a large capacitance can be obtained and a desired capacitance can be obtained during application of acceleration like the fourth embodiment. 
   Seventh Embodiment 
   Next, a piezoelectric driving type MEMS apparatus according to a seventh embodiment of the invention will be explained with reference to  FIGS. 19 to 21 .  FIG. 19  is a plan view of the piezoelectric driving type MEMS apparatus according to the embodiment,  FIG. 20  is a sectional view of the piezoelectric driving type MEMS apparatus taken along line A-A shown in  FIG. 19 , and  FIG. 21  is a sectional view of the piezoelectric driving type MEMS apparatus taken along line B-B shown in  FIG. 19 . Incidentally,  FIG. 19  is a plan view where a protective film  15  has been removed. 
   The piezoelectric driving type MEMS apparatus according to the embodiment is an I-shaped type unimorph switch, which has such a constitution that a lower face of the insulating film  16  and a lower face of the upper electrode  17  are made flush with each other by removing the insulating layer  5  on the upper face of the lower electrode  4  to expose an upper face of the lower electrode  4  and removing the insulating film  16  on the lower face of the upper electrode  17  in the I-shaped unimorph variable capacitor according to the fourth embodiment shown in  FIGS. 10 to 12 . 
   In the embodiment, since the slits  20  are formed in the beam  10 , flexing in a widthwise direction of the beam  10  is reduced, so that when the switch is turned on, the upper electrode  17  comes in surface-contact with the lower electrodes  4  without substantially deforming in the widthwise direction of the beam  10 . Therefore, insertion loss can be reduced, as compared with a case that an upper electrode and a lower electrode come in point-contact with each other. Since the total sum of the widths of the beam  10  is large, sufficient acceleration tolerance can be achieved. Thereby, a high frequency switch with reduced insertion loss and high acceleration tolerance can be realized. 
   Eighth Embodiment 
   Next, a piezoelectric driving type MEMS apparatus according to an eighth embodiment of the invention will be explained with reference to  FIGS. 22 to 24 .  FIG. 22  is a plan view of the piezoelectric driving type MEMS apparatus according to the embodiment,  FIG. 23  is a sectional view of the piezoelectric driving type MEMS apparatus taken along line A-A shown in  FIG. 22 , and  FIG. 24  is a sectional view of the piezoelectric driving type MEMS apparatus taken along line B-B shown in  FIG. 22 . Incidentally,  FIG. 22  is a plan view where a protective film  15  has been removed. 
   The piezoelectric driving type MEMS apparatus according to the embodiment is an I-shaped type unimorph switch, which has such a constitution that the beam  10  is constituted as a cantilever beam in the I-shaped type unimorph switch according to the seventh embodiment shown in  FIGS. 19 to 21 . 
   In the embodiment, since the slits  20  are formed in the beam  10  like the seventh embodiment, flexing in a widthwise direction of the beam  10  is reduced, so that when the switch is turned on, the upper electrode  17  comes in surface-contact with the lower electrodes  4  without substantially deforming in the widthwise direction of the beam  10 . Therefore, insertion loss can be reduced, as compared with the case that the upper electrode and the lower electrode come in point-contact with each other. Since the total sum of the widths of the beam  10  is large, sufficient acceleration tolerance can be achieved. 
   In the eighth embodiment, two slits  20  are provided in the beam  10  for each side thereof. Three or more slits may be formed in the beam, as shown in  FIG. 25 . Such the number of slits can be applied to not only the eighth embodiment but also the first to seventh embodiments. 
   As shown in  FIG. 26 , the slits  20  may be formed in such a manner that adjacent branched beams are connected to each other by a bridge portion(s)  18 . As shown in  FIG. 27 , the slits  20  may be formed in a mesh manner. These shapes of the slits can be applied to not only the eighth embodiment but also the first to seventh embodiments. 
   As shown in  FIG. 28 , the beam  10  may be formed in a spreading shape toward the end portion thereof. Such a shape can be applied to not only the eighth embodiment but also the first to seventh embodiments. 
   Ninth Embodiment 
   Next, a piezoelectric driving type MEMS apparatus according to a ninth embodiment of the invention will be explained with reference to  FIGS. 29 to 31 .  FIG. 29  is a plan view of the piezoelectric driving type MEMS apparatus according to the embodiment,  FIG. 30  is a sectional view of the piezoelectric driving type MEMS apparatus taken along line A-A shown in  FIG. 29 , and  FIG. 31  is a sectional view of the piezoelectric driving type MEMS apparatus taken along line B-B shown in  FIG. 29 . Incidentally,  FIG. 29  is a plan view where a protective film  15  has been removed. 
   The piezoelectric driving type MEMS apparatus according to the embodiment is an I-shaped type unimorph variable capacitor, which has such a constitution that the supporting layer or portion  16  for the upper electrode  17  is provided above the upper electrode  17  of the beam  10  in the I-shaped type unimorph variable capacitor according to the fourth embodiment shown in  FIGS. 10 to 12 . Such a constitution is employed that the supporting portion  16  for the upper electrode  17  is provided above the upper electrode  17  and the electrode  14  via an interlayer insulating film  19 . 
   In the embodiment, a large capacitance can be obtained and a desired capacitance can be obtained during application of acceleration like the fourth embodiment. 
   In the above embodiments, the MEMS variable capacitors or the MEMS switches have been explained, but the structure of a beam having a piezoelectric actuator, namely a piezoelectric film can be applied to devices except for these capacitors and the switches. 
   As explained above, according to the respective embodiments of the invention, a piezoelectric driving type MEMS apparatus which can obtain desired characteristics even during application of acceleration can be provided.