JP2007125626A - Mems element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an MEMS element including an actuator capable of controlling the displacement amount with good productivity and with high accuracy. <P>SOLUTION: This MEMS element includes: a substrate 10 having a fixed electrode 14; and a beam 40 having a movable electrode 22 disposed opposite to the fixed electrode 14 and fixed to the substrate 10 by a fixing part 42 away from a working part 44 where the movable electrode 22 and the fixed electrode 14 are disposed opposite to each other through a void at least in part of the space up to the substrate 10. In this case, in the initial state before the beam 40 is driven, the substrate 10 and the working part 44 of the beam 40 come into contact with each other. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a MEMS element having an actuator.

  In recent years, micro parts (MEMS elements) having electrical and mechanical functions have been actively developed by using a semiconductor device manufacturing process such as an integrated circuit. In the MEMS element, there is a problem that the movable part is deformed due to variations in film thickness, size, material characteristics, or the like, and cannot satisfy a desired specification.

  For example, a microswitch having a cantilever actuator as a MEMS element has been proposed (see, for example, Patent Document 1). It is also possible to apply a cantilever actuator to a MEMS variable capacitor. A metal electrode for driving is provided on the beam which is a movable part of the actuator. The actuator is supported in the air and has a long and thin beam structure. For this reason, there is a problem that the beam is warped up and down by a slight stress generated in the beam.

  For example, stress is generated in the beam due to the residual stress of the material of the beam or the metal electrode. In addition, the stress generated in the beam changes due to manufacturing variations in the thickness and dimensions of the beam and the metal electrode. Controlling and managing the manufacturing variation has an upper limit of the manufacturing process. Therefore, it becomes difficult to control the warp of the beam of the actuator and control the drive displacement amount with high reproducibility and high accuracy. As a result, it is difficult to adjust the capacitance value of the variable capacitor before and after voltage application as designed, and to set the driving voltage of the microswitch to a constant value.

As means for solving the above problem, there is a structure in which a movable part is sandwiched between a substrate and an upper substrate (for example, see Patent Document 2). The movable part is provided with a signal upper electrode and connected to a beam supported by the upper substrate. The movable part moves up and down by the drive electrode on the upper substrate. In this case, it is necessary to form a gap for the vertical movement of the movable part. In addition, the substrate having the lower electrode for signal must be connected to the upper substrate through the fixing portion. Thus, there is a problem that the manufacturing process becomes complicated and the cost increases. Also, since the beam has residual stress, it is difficult to control and manage the warp of the beam.
US Pat. No. 5,578,976 JP 2003-258502 A

  The present invention provides a MEMS device including an actuator that can control a warp caused by a residual stress and control a drive displacement amount with high reproducibility and high accuracy.

  According to the aspects of the present invention, (a) a substrate having a fixed electrode, and (b) a movable electrode disposed opposite to the fixed electrode, and fixed to the movable electrode through a gap at least at a part between the substrate and the substrate. A MEMS element comprising a beam fixed to a substrate with a fixed portion spaced apart from a working portion opposed to an electrode, and (c) in an initial state before driving the beam, A MEMS device is provided in which the working parts are in contact with each other.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the MEMS element provided with the actuator which controls the curvature resulting from a residual stress and can control a drive displacement amount with high reproducibility and high precision.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. However, it should be noted that the drawings are schematic, and the relationship between the thickness and the planar dimensions, the ratio of the thickness of each layer, and the like are different from the actual ones. Therefore, specific thicknesses and dimensions should be determined in consideration of the following description. Moreover, it is a matter of course that portions having different dimensional relationships and ratios are included between the drawings.

(First embodiment)
As shown in FIGS. 1 and 2, the variable capacitor actuator, which is a MEMS element according to the first embodiment of the present invention, has a beam extending from a fixed portion 42 fixed on a substrate 10 to an action portion 44. 40. As electrodes of the variable capacitor, there are provided a movable electrode 22 disposed on the action portion 44 and a fixed electrode 14 disposed on the substrate 10 so as to face the movable electrode 22. The beam 40 includes a first insulating film 18, a driving layer 24 on the first insulating film 18, a second insulating film 26 provided so as to cover the driving layer 24, and the like. A base layer 12 is provided on the surface of the substrate 10. The fixing portion 42 is fixed on the anchor 16 disposed on the surface of the foundation layer 12.

  The fixed electrode 14 is embedded in the surface of the foundation layer 12. The movable electrode 22 is embedded in the first insulating film 18. The movable electrode 22 may be disposed on the first insulating film 18 so as to be covered with the second insulating film 26.

  The drive layer 24 includes a lower electrode 30 on the first insulating film 18, a piezoelectric film 32 on the lower electrode 30, and an upper electrode 34 that faces the lower electrode 30 with the piezoelectric film 32 interposed therebetween. The action portion 44 of the beam 40 is in contact with the fixed electrode 14 and the base layer 12. The beam 40 is separated from the foundation layer 12 by the gap 28 on the anchor 16 side.

For example, the substrate 10 is a semiconductor substrate such as silicon (Si). An insulating film such as silicon oxide (SiO ₂ ) is used for the base layer 12 and the anchor 16. As the first insulating film 18, an insulating film such as silicon nitride (Si ₃ N ₄ ) by low pressure chemical vapor deposition (LPCVD) is used. As the second insulating film 26, an insulating film such as SiO ₂ or Si ₃ N ₄ by plasma CVD using tetraethoxysilane (TEOS) is used.

  Further, the fixed electrode 14, the movable electrode 22, the lower and upper electrodes 30, 34, and the like are made of platinum (Pt), strontium (Sr), ruthenium (Ru), chromium (Cr), molybdenum (Mo), tungsten (W). , Titanium (Ti), tantalum (Ta), aluminum (Al), copper (Cu), nickel (Ni) and other metals, nitrides of these metals, compounds of materials selected from these metals, strontium ruthenium oxide A laminated structure of a material selected from conductive oxides such as (SRO) or these metals and conductive oxides is used. The piezoelectric film 32 is made of a piezoelectric material such as lead zirconate titanate (PZT), barium titanate (BTO), aluminum nitride (AlN), zinc oxide (ZnO), or polyvinylidene fluoride (PVDF). A polymeric piezoelectric material is used.

  In the variable capacitor according to the first embodiment, the drive voltage Vdr is applied from the drive power supply between the lower and upper electrodes 30 and 34 of the drive layer 24, and the fixed electrode 14 and the movable electrode 22 are applied as shown in FIG. Control the capacity Cvar between. When the drive voltage Vdr is applied, the piezoelectric film 32 is distorted and expands and contracts due to the piezoelectric effect. The second insulating film 26 and the first insulating film 18 provided above and below the drive layer 24 do not exhibit a piezoelectric effect.

  Further, the thickness of the lower electrode 30 and the first insulating film 18 which are layers below the piezoelectric film 32 is larger than the sum of the thicknesses of the upper electrode 34 and the second insulating film 26 which are layers above the piezoelectric film 32. The sum is thickened. For example, when the drive voltage Vdr is applied so that the piezoelectric film 32 is contracted between the lower electrode and the upper electrodes 30 and 34 of the drive layer 24, the beam 40 is bent toward the contracting film thickness direction, that is, toward the second insulating film 26. . As a result, the movable electrode 22 is displaced in a direction away from the fixed electrode 14, and the capacitance Cvar changes.

  In general, the deflection of the beam structure represented by FIG. 2 is described by the following basic equation of deflection.

d ² y / dx ² = (1 / ρ) (= − M / (EI)) (1)

Here, the fixed point of the beam is the origin, the longitudinal direction of the beam is (+ x), and the substrate direction is (+ y). Further, ρ represents a radius of curvature, M represents a bending moment, E represents a Young's modulus, and I represents a cross-sectional secondary moment. The fact that the beam warps down towards the substrate means that the bending moment has a negative sign. The bending moment is a function of the stress and film thickness of the material making up the beam.

  The beam 40 is a composite material composed of a plurality of films. Usually, an internal stress resulting from the film forming conditions is generated in each of the plurality of films included in the beam 40. Therefore, the beam 40 is warped due to residual strain after the formation of a plurality of films. Further, the residual strain varies within the range of control of the manufacturing process. Furthermore, the film thickness of each of the plurality of films also varies within the range of control of the manufacturing process. Therefore, it is difficult to control the bending moment generated in the beam 40 to be constant, for example, zero. As described above, in the current actuator, it is difficult to control the distance between the fixed electrode 14 and the movable electrode 22 with high reproducibility and high accuracy in an initial state where no drive voltage is applied. As a result, it becomes difficult to adjust the capacitance value of the variable capacitor before application of the driving voltage as designed.

In the first embodiment, an LPCVD Si ₃ N ₄ film and a plasma CVD SiO ₂ film are used as the first and second insulating films 18 and 26, respectively. For example, in the LPCVD Si ₃ N ₄ film, a tensile stress of about 1 GPa (that is, a stress in a direction in which the film tends to shrink) is generated as an internal stress. In the plasma CVD SiO ₂ film, an internal stress of about 100 MPa compressive stress (that is, stress in the direction in which the film is desired to stretch) is generated. As a result, since the bending moment of the beam 40 becomes negative, the acting portion 44 can be brought into contact with the fixed electrode 14 by bending the beam 40 toward the substrate 10 as shown in FIG. Therefore, the distance between the fixed electrode 14 and the movable electrode 22 can always be minimized in the initial state where the drive voltage Vdr is not applied. As described above, it is possible to suppress the influence of the warp of the beam 40 due to the residual strain, and to adjust the capacitance value of the variable capacitor before applying the driving voltage as designed.

  In this structure, it is sufficient that the beam 40 is bent toward the substrate 10 in the initial state and the working portion 44 is designed to come into contact with the fixed electrode 14, and it is assumed that manufacturing distortion and film thickness variation occur. However, there is no problem in the performance of the variable capacitor. Further, as the material constituting the beam 40, in the first embodiment, the first insulating film 18, the driving layer 24 (the driving layer 24 is composed of the lower electrode 30, the piezoelectric film 32, and the upper electrode 34), the second A total of five layers of the insulating film 26 is used as the composite material, but a plurality of films may be formed by further laminating the layers constituting each of them. As a whole, the film structure may be such that the bending moment becomes negative in the initial state where the driving voltage Vdr is not applied and the beam 40 is bent toward the substrate 10 side. It may be designed so that the bending moment is positive. For example, by increasing the film thickness of the first insulating film 18 with respect to the second insulating film 26 to about 1.5 times or more, the beam 40 curved so as to bring the action portion 44 into contact with the fixed electrode 14 in the initial state. The drive voltage Vdr can be applied and displaced in a direction away from the substrate 10.

  Next, a variable capacitor manufacturing method according to the first embodiment of the present invention will be described with reference to the cross-sectional views shown in FIGS. Here, the cross section corresponding to the AA line shown in FIG. 1 is shown in the cross sectional view used for the description.

(A) For example, a base layer 12 such as a SiO ₂ film is formed on the surface of the substrate 10 such as a Si semiconductor by thermal oxidation or the like. As shown in FIG. 4, a fixed electrode 14 is formed by selectively depositing a metal film such as W in the underlayer 12 by photolithography, etching, sputtering, or the like.

(B) As shown in FIG. 5, an anchor 16 such as SiO ₂ is formed on the surface of the underlayer 12 by plasma CVD, photolithography, reactive ion etching (RIE), or the like. A polycrystalline Si (poly-Si) film is deposited on the surface of the underlayer 12 so as to cover the anchor 16 and the like by LPCVD or the like. The sacrificial layer 128 is formed by planarizing the poly-Si film by chemical mechanical polishing (CMP) so that the surface of the anchor 16 is exposed.

(C) As shown in FIG. 6, a first insulating film 18 such as Si ₃ N ₄ is deposited on the surface of the anchor 16 and the sacrificial layer 128 to a thickness of, for example, about 200 nm by LPCVD or the like. The first insulating film 18 is selectively removed by photolithography, RIE, sputtering, or the like to form the movable electrode 22 such as Al.

  (D) As shown in FIG. 7, a lower electrode 30 such as Pt, a piezoelectric film 32 such as PZT, and an upper electrode 34 such as Pt are sequentially deposited by sputtering or the like. The drive electrode 24 is formed by selectively removing the upper electrode 34, the piezoelectric film 32, and the lower electrode 30 by photolithography, RIE, or the like.

(E) As shown in FIG. 8, a second insulating film 26 such as SiO ₂ is deposited on the first insulating film 18 to a thickness of about 100 nm so as to cover the drive layer 24 by plasma CVD or the like. To do. The second insulating film 26 and the first insulating film 18 are selectively removed so that the surface of the sacrificial layer 128 is exposed by photolithography, RIE, or the like. The sacrificial layer 128 is selectively removed by chemical dry etching (CDE) or the like, and the beam 40 is fixed so that the fixed portion 42 is fixed on the anchor 16 and the action portion 44 is in contact with the fixed electrode 14 as shown in FIG. Is formed. The beam 40 between the fixed portion 42 and the action portion 44 is held above the foundation layer 12 through the gap 28.

In the variable capacitor according to the first embodiment, Si ₃ N ₄ of the first insulating film 18 and SiO _{2 of} the second insulating film 26 of the beam 40 are formed by LPCVD and plasma CVD, respectively. The internal stresses of the LPCVD Si ₃ N ₄ film and the plasma CVD SiO ₂ film are a tensile stress of about 1 GPa and a compressive stress of about 100 MPa, respectively. The internal stress of each of the lower electrode 30, the piezoelectric film 32, and the upper electrode 34 of the driving layer 24 is about 100 MPa. As a result, in the beam 40, the tensile stress of the first insulating film 18 wins, and the beam 40 can be bent toward the substrate 10 so that the action portion 44 can be brought into contact with the fixed electrode 14. Thus, for example, the beam 40 is included so that a bending moment is generated in the beam 40 so that the tensile stress of the first insulating film 18 becomes dominant and the action portion 44 of the beam 40 comes into contact with the fixed electrode 14. What is necessary is just to control the internal stress and film thickness of each film | membrane. In the variable capacitor according to the first embodiment, the beam 40 can be bent and the distance between the fixed electrode 14 and the movable electrode 22 can be controlled to a minimum in the initial state where the drive voltage of the actuator is not applied. It is possible to adjust the capacitance value before applying the driving voltage as designed.

  In the first embodiment, a film having compressive stress is used as the second insulating film 26. However, a film having a tensile stress can be used as the second insulating film 26 if the internal stress is, for example, about one tenth of the tensile stress of the first insulating film 18. Needless to say, a film with negligible internal stress can be used as the second insulating film 26. On the other hand, in the beam 40, the internal stress and film thickness of each film included in the beam 40 may be controlled so that the compressive stress of the second insulating film 26 wins and the beam 40 is bent toward the substrate 10 side. Any of the included films may be a film having an internal stress that is dominant in the beam 40.

  In the first embodiment, the actuator is driven by the piezoelectric effect of the piezoelectric film 32. However, the driving of the actuator is not limited to the piezoelectric effect. For example, a bimetal effect using materials having different thermal expansion coefficients may be used. For example, as shown in FIG. 10, the drive layer 24 a of the beam 40 a is a bimetallic structure film including a high expansion material film 35 and a low expansion material film 36 deposited on the first insulating film 18. The thermal expansion coefficient of the high expansion material film 35 is larger than that of the low expansion material film 36. When a drive current is applied to the drive layer 24a from the drive power source to generate heat in the drive layer 24a, the drive layer 24a is bent toward the low expansion material film 36 side. As a result, the beam 40 a can be displaced so that the movable electrode 22 is separated from the fixed electrode 14.

  An electromagnetic force can also be used as the actuator. For example, as shown in FIGS. 11 and 12, the drive layer 24 b of the beam 40 b is a magnetic body deposited on the first insulating film 18. An electromagnetic coil 37 is disposed on the surface of the base layer 12 facing the drive layer 24b. By applying a drive current from the drive power source to the electromagnetic coil 37, an electromagnetic force that causes the drive layer 24b to separate from the substrate 10 is generated. In this way, the beam 40b can be displaced so that the movable electrode 22 is separated from the fixed electrode 14.

  In the first embodiment, the movable electrode 22 is disposed independently on the action portion 44. For example, the lower electrode 30 of the drive layer 24 can be used as the movable electrode. In this case, the lower electrode 30 may be extended so as to face the fixed electrode 14 at the action portion 44.

  In addition, an example in which a variable capacitor is used as the MEMS element according to the first embodiment is described. The MEMS element can be applied to, for example, a microswitch in addition to the variable capacitor. For example, with the same structure as shown in FIG. 1, the movable electrode 22 of the action portion 44 is formed so as to penetrate the first insulating film 18 and is used as a normally-on type switch by contacting with the fixed electrode 14. You can also.

(Second Embodiment)
As shown in FIG. 13, the variable capacitor, which is a MEMS element according to the second embodiment of the present invention, includes an actuator including a first beam 40c and a second beam 40d. The first and second beams 40c and 40d are arranged in the region of the gap 28 from the fixing portions 42a and 42b on the anchor 16, respectively, and are connected to the action portion 44a. In the first beam 40c, the lower electrode wiring 56a and the upper electrode wiring 58a are arranged so as to extend on the anchor 16 from the fixing portion 42a. Pads 64a and 66a are disposed on the lower and upper electrode wirings 56a and 58a, respectively. In the second beam 40d, the lower electrode wiring 56b and the upper electrode wiring 58b are arranged so as to extend on the anchor 16 from the fixed portion 42b. Pads 64b and 66b are disposed on the lower and upper electrode wirings 56b and 58b, respectively.

  Further, the variable capacitor according to the second embodiment includes a third beam 40e. The third beam 40e is arranged in a region from the fixing portion 42c on the anchor 16 to the gap 28, and is connected to the actuator operating portion 44a. The first signal wiring 60 is disposed so as to face the third beam 40e with the action portion 44a interposed therebetween. Pads 68a and 68b are disposed on the first signal wiring 60 and the fixing portion 42c of the third beam 40e.

  As shown in FIG. 14, the first and second beams 40 c and 40 d are suspended on the gap 28 with fixing portions 42 a and 42 b being fixed on the anchor 16, respectively. The fixed electrode 14 covered with the protective film 13 is disposed on the surface of the base layer 12 on the substrate 10 so as to face the movable electrode 22 of the action portion 44a. The action part 44 a is in contact with the protective film 13 on the fixed electrode 14.

  In the first and second beams 40c and 40d, driving layers 24a and 24b are disposed on the surface of the first insulating film 18, respectively. The drive layers 24 a and 24 b are covered with the insulating film 20. A second insulating film 26 is provided on the insulating film 20. The movable electrode 22 provided on the surface of the insulating film 20 is covered with a second insulating film 26.

  The drive layer 24a includes a lower electrode 30a on the first insulating film 18, a piezoelectric film 32a on the lower electrode 30a, and an upper electrode 34a facing the lower electrode 30a across the piezoelectric film 32a. The lower and upper electrodes 30a and 34a are connected to the lower and upper electrode wirings 56a and 58a through the insulating film 20.

  The drive layer 24b includes a lower electrode 30b on the first insulating film 18, a piezoelectric film 32b on the lower electrode 30b, and an upper electrode 34b facing the lower electrode 30b across the piezoelectric film 32b. The lower and upper electrodes 30b and 34b are connected to lower and upper electrode wirings 56b and 58b provided through the insulating film 20.

  As shown in FIG. 15, the third beam 40e includes the first insulating film 18, the insulating film 20 on the first insulating film 18, the second signal wiring 62 on the insulating film 20, and the second signal. A second insulating film 26 is provided so as to cover the wiring 62. The second signal wiring 62 extends so as to connect the movable electrode 22 of the action portion 44a and the pad 68b of the fixed portion 42c. Opposing to the third beam 40e, the first signal wiring 60 is provided so as to be connected to the fixed electrode 14 through the insulating film 20, the first insulating film 18, the anchor 16, and the protective film 13.

  The variable capacitor according to the second embodiment includes first and second beams 40c and 40d as actuators, and a third beam 40e connected to the first and second beams 40c and 40d by the action portion 44a. The point provided with is different from the first embodiment. Other configurations are the same as those of the first embodiment, and thus redundant description is omitted.

  In the second embodiment, the first insulating film 18 having a tensile stress is provided on the first to third beams 40c to 40e as in the first embodiment. In the initial state in which the drive voltage Vdr is not applied, the first to third beams 40c to 40e can be curved toward the substrate 10 to always minimize the distance between the fixed electrode 14 and the movable electrode 22. As described above, it is possible to suppress the influence of the warp of the first to third beams 40c to 40e due to the residual strain, and to adjust the capacitance value of the variable capacitor before application of the driving voltage as designed.

  Next, a variable capacitor manufacturing method according to the second embodiment will be described with reference to plan views and cross-sectional views shown in FIGS. Here, in the cross-sectional view used for the description, a cross-section corresponding to the line CC shown in FIG. 13 is shown.

(A) For example, a base layer 12 such as a SiO ₂ film is formed on the surface of the substrate 10 such as a Si semiconductor by thermal oxidation or the like. As shown in FIG. 16, a fixed electrode 14 is formed by selectively depositing a metal film such as W on the surface of the underlayer 12 with a thickness of about 100 nm by sputtering, photolithography, etching, or the like. A protective film 13 such as Si ₃ N _{4 is} deposited on the underlayer 12 by CVD or the like so as to cover the fixed electrode 14 with a thickness of about 200 nm. The fixed electrode 14 is rectangular and has a size of about 25 μm × about 70 μm.

(B) An anchor 16 such as SiO ₂ is formed with a thickness of about 1 μm on the surface of the protective film 13 by plasma CVD, photolithography, reactive ion etching (RIE), or the like. A polycrystalline Si (poly-Si) film is deposited on the surface of the protective film 13 so as to cover the anchor 16 and the like by LPCVD or the like. As shown in FIG. 17, the poly-Si film is planarized by chemical mechanical polishing (CMP) so that the surface of the anchor 16 is exposed, and a T-shaped sacrificial layer 128 surrounded by the anchor 16 is formed. Is done. The sacrificial layer 128 has a width of about 40 μm, the length of the region extending in the horizontal direction in the figure is about 200 μm, and the length of the region extending in the vertical direction is about 100 μm. The sacrificial layer 128 is opposed to the fixed electrode 14 with a width of about 70 μm in the horizontal direction and about 20 μm in the vertical direction at the center of the region extending in the horizontal direction.

(C) As shown in FIG. 18, a first insulating film 18 such as Si ₃ N ₄ is deposited on the surface of the anchor 16 and the sacrificial layer 128 to a thickness of about 200 nm by LPCVD or the like.

  (D) A lower metal film such as Ti / SRO / Pt / Ti having a thickness of about 2.5 nm / about 10 nm / about 100 nm / about 10 nm on the surface of the first insulating film 18 by sputtering or the like; A piezoelectric material such as PZT and an upper metal film such as Pt / SRO having a thickness of about 70 nm / about 10 nm are sequentially deposited. As shown in FIGS. 19A and 19B, the upper metal film, the piezoelectric body, and the lower metal film are selectively removed by photolithography, RIE, or the like, so that the lower electrodes 30a and 30b, the piezoelectric film are removed. Drive layers 24a and 24b having 32a and 32b and upper electrodes 34a and 34b are formed. The drive layers 24a and 24b are respectively arranged above the region extending in the lateral direction of the sacrificial layer 128 and above both ends of the sacrificial layer 128 and above the anchor 16 side.

(E) An insulating film 20 such as SiO _{2 is} deposited on the surface of the first insulating film 18 by plasma CVD or the like so as to cover the drive layers 24a and 24b, for example, with a thickness of about 50 nm. As shown in FIGS. 20A and 20B, via holes 50a, 52a, 50b, 52b, and 54 are formed by selectively removing the insulating film 20 by photolithography, RIE, or the like. The lower portions of the drive layer 24a and the surfaces of the upper electrodes 30a and 34a are exposed in the via holes 50a and 52a, respectively. The lower portions of the drive layer 24b and the surfaces of the upper electrodes 30b and 34b are exposed in the via holes 50b and 52b, respectively. The surface of the fixed electrode 14 is exposed in the via hole 54.

  (F) A metal film such as TiN / Ti / AlCu / Ti / TiN is deposited on the surface of the insulating film 20 by sputtering or the like. As shown in FIGS. 21A and 21B, the lower electrode wirings 56a and 56b, the upper electrode wirings 58a and 58b, the first signal wiring 60, and the second signal wiring 62 are formed by photolithography and RIE. And the movable electrode 22 are formed. The lower and upper electrode wirings 56a and 58a are connected to the lower and upper electrodes 30a and 34a by filling the via holes 50a and 52a shown in FIGS. 20A and 20B, respectively. The lower and upper electrode wirings 56b and 58b are connected to the lower and upper electrodes 30b and 34b by filling the via holes 50b and 52b, respectively. The first signal wiring 60 is connected to the fixed electrode 14 by filling the via hole 54. The second signal wiring 62 is connected to the movable electrode 22. The movable electrode 22 faces the fixed electrode 14 above the sacrificial layer 128. The movable electrode 22 is rectangular and has a size of about 20 μm × about 70 μm.

(G) The second insulating film 26 such as SiO ₂ is formed by plasma CVD or the like, and the lower and upper electrode wirings 56a, 56b, 58a, 58b, the first and second signal wirings 60, 62, and the movable electrode 22 are formed. A thickness of about 100 nm is deposited on the insulating film 20 so as to cover it. As shown in FIGS. 22A and 22B, the second insulating film 26 is selectively removed by photolithography, RIE, etc., and pads 64a, 64b, 66a, 66b, 68a, 68b are formed. Is done. Further, the second insulating film 26, the insulating film 20, and the first insulating film 18 are selectively removed by photolithography, RIE, or the like so that the surface of the sacrificial layer 128 is exposed. The sacrificial layer 128 is selectively removed by chemical dry etching (CDE) or the like, the fixing portions 42 a, 42 b, 42 c are fixed on the anchor 16, and the action portion 44 a is in contact with the protective film 13 on the fixed electrode 14. First to third beams 40c, 40d, and 40e are formed. The first to third beams 40 c to 40 e between the fixing portions 42 a, 42 b and 42 c and the action portion 44 are held above the protective film 13 through the gap 28.

In the variable capacitor according to the second embodiment, the Si ₃ N ₄ of the first insulating film 18 and the SiO _{2 of} the second insulating film 26 of the first to third beams 40c to 40e are LPCVD and plasma, respectively. The film is formed by CVD. The internal stresses of the LPCVD Si ₃ N ₄ film and the plasma CVD SiO ₂ film are a tensile stress of about 1 GPa and a compressive stress of about 100 MPa, respectively. The internal stresses of the lower electrodes 30a and 30b, the piezoelectric films 32a and 32b, the upper electrodes 34a and 34b, the insulating film 20, and the second signal wiring 62 of the drive layers 24a and 24b are about 100 MPa. As a result, in the first to third beams 40c to 40e, the tensile stress of the first insulating film 18 is won, and the action portion 44a is bent toward the substrate 10 to be brought into contact with the protective film 13 on the fixed electrode 14. It becomes possible. As described above, in the variable capacitor according to the second embodiment, the first to third beams 40c to 40e are bent and the fixed electrode 14 and the movable electrode 22 are bent in the initial state in which the driving voltage of the actuator is not applied. The distance can be controlled to the minimum, and the capacitance value of the variable capacitor before and after applying the driving voltage can be adjusted as designed.

  In the variable capacitor actuator according to the second embodiment, as shown in FIG. 13, the first and second beams 40c and 40d are arranged on a straight line with the action portion 44a interposed therebetween. The third beam 40e is disposed so as to be orthogonal to the first and second beams 40c, 40d at the action portion 44a. However, the arrangement of the first to third beams 40c to 40e is not limited. For example, as shown in FIG. 23, each of the first to third beams 40c to 40e may be arranged so as to be connected at an angle of 120 degrees in the action portion 44a. By arranging the first to third beams 40c to 40e at substantially equal angular intervals, it is possible to alleviate warpage or distortion of the region of the movable electrode 22a, and to make the interval between the fixed electrode 14a uniform. It becomes possible.

  Further, the actuator beam may be two or more. For example, as shown in FIG. 24, the first beams 40c and 40f and the second beams 40d and 40g are arranged symmetrically with respect to the first and second signal wirings 60 and 62. The actuator beam becomes four, and the driving force increases. Further, since the movable electrode 22a is held from four directions, it is possible to suppress the influence of external vibration and noise.

  In the second embodiment, the third beam 40e on which the second signal wiring 62 is disposed is rectangular, but the shape is not limited. For example, as shown in FIG. 25, a meandering third beam 40h may be used. With respect to the first and second beams 40c and 40d of the actuator, the mechanical spring constant of the third beam 40h in which the second signal wiring 62 is arranged can be reduced, and the drive voltage of the actuator can be lowered. Become. Note that a bonding wire can also be used as the second signal wiring 62. In this case, the third beam is not necessary.

(Application examples)
As shown in FIG. 26, a MEMS device 100 according to an application example of the first and second embodiments of the present invention includes a microprocessor (MPU) 82, a memory 84, a reference fixed capacitor 86, a drive power supply 88, and A MEMS element 90 is provided. An input terminal 80 is connected to the MPU 82. An output terminal 92 is connected to the MEMS element 90.

  For example, the variable capacitor according to the first and second embodiments is used for the MEMS element 90. The drive power supply 88 applies a drive voltage to the MEMS element 90. The MPU 82 sets the capacitance value of the MEMS element 90 by controlling the drive power supply 88 based on the relationship between the drive voltage and the capacitance value stored in the memory 84. Further, the MPU 82 refers to the reference fixed capacitor 86 and acquires the relationship between the drive voltage applied from the drive power supply 88 and the capacitance value of the MEMS element 90. The relationship between the drive voltage and the capacitance value is stored in the memory 84.

  For example, when an initialization signal is input to the input terminal 80, the MPU 82 transmits a drive voltage supply signal to the drive power supply 88. The drive power supply 88 outputs a drive voltage corresponding to the drive voltage supply signal to the MEMS element 90. The MPU 82 acquires the capacitance value signal of the MEMS element 90 and determines the capacitance value with reference to the reference fixed capacitance 86. The acquired relationship between the drive voltage and the capacitance value is stored in the memory 84.

  When the capacitance value request signal is input to the input terminal 80, the MPU 82 determines the drive voltage supply signal of the target drive voltage corresponding to the target capacitance value based on the relationship between the drive voltage and the capacitance value stored in the memory 84. And transmitted to the drive power supply 88. The target drive voltage output from the drive power supply 88 is applied to the MEMS element 90. As a result, the target capacitance value is output from the MEMS element 90 to the output terminal 92.

  As described above, in the MEMS device 100 according to the application example, the relationship between the driving voltage and the capacitance value of the MEMS element 90 is acquired in advance by the initialization signal. Also, the drive voltage corresponding to the required capacitance value is determined based on the calibrated drive voltage versus capacitance value relationship. Therefore, the deviation of the capacitance value from the design value due to manufacturing variations of the MEMS element 90 can be calibrated, and the requested capacitance value can be controlled with high reproducibility and high accuracy.

(Other embodiments)
Although the embodiments of the present invention have been described as described above, it should not be understood that the descriptions and drawings constituting a part of this disclosure limit the present invention. From this disclosure, various alternative embodiments, examples and operational techniques will be apparent to those skilled in the art.

  In the first and second embodiments of the present invention, a unimorph piezoelectric actuator is used. However, a bimorph structure may be used as the piezoelectric actuator. In a piezoelectric actuator having a bimorph structure, a first piezoelectric film, an intermediate electrode, and a second piezoelectric film are provided between a lower electrode and an upper electrode. A driving voltage is applied between the lower electrode and the upper electrode in common with the intermediate electrode.

  As described above, the present invention naturally includes various embodiments that are not described herein. Accordingly, the technical scope of the present invention is defined only by the invention specifying matters according to the scope of claims reasonable from the above description.

1 is a schematic plan view showing an example of a MEMS element according to a first embodiment of the present invention. It is the schematic which shows an example of the AA cross section of the MEMS element of FIG. It is the schematic which shows an example of the drive of the MEMS element which concerns on the 1st Embodiment of this invention. It is sectional drawing (the 1) which shows an example of the manufacturing method of the MEMS element which concerns on the 1st Embodiment of this invention. It is sectional drawing (the 2) which shows an example of the manufacturing method of the MEMS element which concerns on the 1st Embodiment of this invention. It is sectional drawing (the 3) which shows an example of the manufacturing method of the MEMS element which concerns on the 1st Embodiment of this invention. It is sectional drawing (the 4) which shows an example of the manufacturing method of the MEMS element which concerns on the 1st Embodiment of this invention. It is sectional drawing (the 5) which shows an example of the manufacturing method of the MEMS element which concerns on the 1st Embodiment of this invention. It is sectional drawing (the 6) which shows an example of the manufacturing method of the MEMS element which concerns on the 1st Embodiment of this invention. It is a cross-sectional schematic diagram which shows the other example of the MEMS element which concerns on the 1st Embodiment of this invention. It is a plane schematic diagram showing other examples of a MEMS element concerning a 1st embodiment of the present invention. It is the schematic which shows an example of the BB cross section of the MEMS element of FIG. It is the plane schematic which shows an example of the MEMS element which concerns on the 2nd Embodiment of this invention. It is the schematic which shows an example of CC cross section of the MEMS element of FIG. It is the schematic which shows an example of the DD cross section of the MEMS element of FIG. It is sectional drawing which shows an example of the process (the 1) of the manufacturing method of the MEMS element which concerns on the 2nd Embodiment of this invention. It is a top view which shows an example of the process (the 2) of the manufacturing method of the MEMS element which concerns on the 2nd Embodiment of this invention. It is sectional drawing which shows an example of the process (the 3) of the manufacturing method of the MEMS element which concerns on the 2nd Embodiment of this invention. It is (a) top view and (b) sectional drawing which show an example of the process (the 4) of the manufacturing method of the MEMS element which concerns on the 2nd Embodiment of this invention. It is (a) top view and (b) sectional drawing which show an example of the process (the 5) of the manufacturing method of the MEMS element which concerns on the 2nd Embodiment of this invention. It is (a) top view and (b) sectional drawing which show an example of the process (the 6) of the manufacturing method of the MEMS element which concerns on the 2nd Embodiment of this invention. It is (a) top view and (b) sectional drawing which show an example of the process (the 7) of the manufacturing method of the MEMS element which concerns on the 2nd Embodiment of this invention. It is a plane schematic diagram which shows the other example of the MEMS element which concerns on the 2nd Embodiment of this invention. It is a plane schematic diagram which shows the other example of the MEMS element which concerns on the 2nd Embodiment of this invention. It is a plane schematic diagram which shows the other example of the MEMS element which concerns on the 2nd Embodiment of this invention. It is the schematic which shows an example of the MEMS apparatus which concerns on the application example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Substrate 12 Underlayer 13 Protective film 14 Fixed electrode 16 Anchor 18 First insulating film 22 Movable electrode 24 Drive layer 26 Second insulating film 28 Void 30 Lower electrode 32 Piezoelectric film 34 Upper electrode 40, 40a, 40b Beam 40c First 1 beam 40d 2nd beam 40e 3rd beam 42 fixed part 44 action part 128 sacrificial layer

Claims (5)

A substrate having fixed electrodes;
The movable electrode disposed opposite to the fixed electrode, and a fixed portion spaced apart from the working portion disposed opposite to the movable electrode and the fixed electrode through a gap in at least a portion between the substrate and the substrate. A MEMS device comprising a beam fixed to a substrate,
The MEMS device according to claim 1, wherein the substrate and the action portion of the beam are in contact with each other in an initial state before the beam is driven.   The MEMS element according to claim 1, wherein the beam has a drive layer that displaces the beam so that the substrate and the action portion of the beam are separated from each other.   The MEMS element according to claim 2, wherein the driving layer includes any one of a piezoelectric film, a bimetal effect film, and a magnetic film.   The said beam contains the 1st insulating film which has a tensile stress under the said drive layer, and the 2nd insulating film which has a compressive stress on the said drive layer, The Claim 2 or 3 characterized by the above-mentioned. MEMS element.   5. The drive layer is driven based on a relationship between a drive voltage of the drive layer acquired in advance and a capacitance value between the fixed electrode and the movable electrode. 6. The MEMS device according to 1.

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