JP4635023B2 - MEMS - Google Patents

Description

  The present invention relates to a micro electro mechanical system (MEMS) using an actuator, for example.

  Conventionally, a variable capacitor using an actuator as a MEMS has an upper electrode and a lower electrode, and can function as a variable capacitor by moving the upper electrode or the lower electrode up and down by the actuator. For example, it is assumed that the lower electrode is disposed on the substrate, the upper electrode is attached to the actuator, and moves up and down by the actuator. In the variable capacitor having such a structure, the upper electrode attached to the actuator has a direction opposite to the lower electrode (hereinafter referred to as an upward direction) or a lower portion due to the residual stress of the film constituting the upper electrode itself. It will bend in the electrode direction (hereinafter referred to as the downward direction). For this reason, in the initial state where the actuator is not driven, there is a problem that the upper electrode is disposed at an inappropriate position or the position of the upper electrode varies.

As this type of related technology, various variable capacitors using actuators as MEMS have been proposed (see, for example, Patent Document 1).
JP 2006-281418 A

  According to the present invention, in the initial state where the actuator is not driven, the electrode can be arranged at a desired position even when the electrode attached to the actuator bends upward or downward due to residual stress. An object is to provide a MEMS that can be used.

The MEMS of one embodiment of the present invention is provided on a substrate, has an end and an other end, the one end fixed to the substrate, a first electrode disposed on the substrate, and one end The other end of the actuator is fixed to the other end of the actuator, the other end is a free end, and is provided between the one end and the other end of the second electrode. A fixed shaft having a linear axis extending in a direction perpendicular to the longitudinal direction of the second electrode and parallel to the substrate surface, and an end of the linear axis being fixed on the substrate The first electrode is opposed to the second electrode on the other end side of the second electrode with respect to the fixed shaft, and the fixed shaft is integrally formed of the same material as the second electrode, The length of the second electrode closer to the first electrode than the fixed shaft is determined by the actuator and the fixed shaft. Longer than the length of the second electrode between said depending second residual stresses electrode has the vicinity of the fixed shaft is a direction opposite to the direction of the substrate or substrate in the second electrode between the fixed shaft and the actuator The portion near the fixed shaft in the second electrode on the first electrode side from the fixed shaft is displaced in the opposite direction to the one, and the actuator moves, The second electrode between the actuator and the fixed shaft is displaced in the same direction as the actuator, and the second electrode on the first electrode side from the fixed shaft is displaced in the opposite direction to the actuator. To do.

The MEMS according to another embodiment of the present invention is provided above the substrate, and includes an actuator having a movable part, a first electrode formed on the substrate, the fixed part to the movable part of the actuator, and the first A second electrode disposed at a position facing the electrode and having a fixed shaft fixed to the substrate between the movable portion of the actuator and the first electrode, and displaced by the actuator And the fixed shaft has a linear shaft extending in a direction perpendicular to the longitudinal direction of the second electrode and parallel to the substrate surface, and an end portion of the linear shaft is Fixed on the substrate, the fixed shaft is integrally formed of the same material as the second electrode;
The length of the second electrode on the first electrode side with respect to the fixed shaft is longer than the length of the second electrode between the actuator and the fixed shaft, and the actuator has a residual stress caused by the second electrode. The portion near the fixed axis of the second electrode between the fixed axis and the fixed axis is displaced in either the substrate direction or the direction opposite to the substrate, and in the second electrode on the first electrode side from the fixed axis . The vicinity of the fixed shaft is displaced in the opposite direction to the one,
As the actuator moves, the second electrode between the actuator and the fixed shaft is displaced in the same direction as the actuator, and the second electrode closer to the first electrode than the fixed shaft is opposite to the actuator. It is displaced in the direction.

  According to the present invention, in the initial state in which the actuator is not driven, the electrode is disposed at a desired position even when the electrode attached to the actuator is bent upward or downward due to residual stress. MEMS that can be provided can be provided.

  Embodiments of the present invention will be described below with reference to the drawings. In the MEMS using the actuator of each embodiment, a variable capacitor using a piezoelectric actuator will be described as an example.

[Example 1]
FIG. 1 is a plan view showing the structure of a variable capacitor using a piezoelectric actuator according to Embodiment 1 of the present invention. 2A is a cross-sectional view taken along line 2A-2A of the variable capacitor of the first embodiment shown in FIG. FIG. 2B is a cross-sectional view of the variable capacitor along line 2B-2B.

As shown in FIGS. 1, 2 (a), and 2 (b), an insulating layer 2 is formed on the semiconductor substrate 1. Here, as the semiconductor substrate 1, for example, an intrinsic semiconductor such as Si or Ge, a compound semiconductor such as GaAs or ZnSe, a highly conductive semiconductor doped with impurities in these semiconductors, or the like can be used. Further, an SOI (Silicon On Insulator) substrate or a glass substrate can be used instead of the semiconductor substrate. The insulating layer 2 is composed of, for example, a silicon oxide film (SiO ₂ ).

  The insulating layer 2 is partially provided with a groove 3. A lower electrode 4 of a variable capacitor is formed on the semiconductor substrate 1 in the groove 3. The surface of the lower electrode 4 is covered with an insulating layer 5 made of, for example, a silicon nitride film (SiN). The insulating layer 5 serves as a dielectric material between the upper electrode 16 and the lower electrode 4 of the variable capacitor. Here, examples of the material for forming the lower electrode 4 include Al, Cu, and W.

An insulating layer 6 is provided on the insulating layer 2 and the groove 3. Specifically, one end of the insulating layer 6 is formed on the insulating layer 2, and the other end of the insulating layer 6 is formed so as to protrude from the insulating layer 2 to the upper portion of the groove 3. Here, the insulating material used for the insulating layer 6 is preferably a material that can be easily moved in conjunction with the movement of the piezoelectric actuator 7, for example, Si ₃ N ₄ , SiO ₂ , AlN, Ta ₂ O ₅ , Al _2. O ₃ etc. are mentioned. This insulating layer 6 may be a single layer of the above insulating material or may have a laminated structure in which a plurality of these are combined.

  A piezoelectric actuator 7 is provided on the insulating layer 6. In this piezoelectric actuator 7, a lower electrode 8, a piezoelectric layer 9, and an upper electrode 10 are sequentially stacked on an insulating layer 6. Here, as shown in FIG. 2A, the area of the lower electrode 8 is formed larger than the areas of the piezoelectric layer 9 and the upper electrode 10. By making the area of the lower electrode 8 larger than the areas of the piezoelectric layer 9 and the upper electrode 10, there is an advantage that the contact plug 11 connected to the lower electrode 8 can be easily formed. The area of the lower electrode 8 and the piezoelectric layer 9 and the upper electrode 10 may be the same, or the area of the piezoelectric layer 9 and the upper electrode 10 may be larger than that of the lower electrode 8.

  Further, the area of the piezoelectric layer 9 may be larger or smaller than the area of the lower electrode 8 and the upper electrode 10 as in the case of the lower electrode 8, or the same area. Furthermore, the planar shape of the piezoelectric layer 9 is often rectangular. However, the planar shape of the piezoelectric layer 9 can be various shapes such as a meander shape such as a square or a polygon.

  The material of the lower electrode 8 and the upper electrode 10 of the piezoelectric actuator 7 is, for example, Au, an alloy containing Co or Ni in Au, Pt, Sr, Ru, Cr, Mo, W, Ti, Al, Cu, Materials containing any one of Ni and the like, nitrides containing any one of these materials, conductive oxides, compounds composed of the above materials, or these materials, nitrides, conductive oxides There is a laminate of materials selected from materials and compounds.

Moreover, as a material of the piezoelectric layer 9, for example, a piezoelectric ceramic material such as PZT (Pb (Zr, Ti) O ₃ ), AlN, ZnO, PbTiO, BTO (BaTiO ₃ ), or a high material such as PVDF (polyvinylidene fluoride) is used. There are molecular piezoelectric materials.

An insulating layer 12 is formed on the piezoelectric actuator 7 and the insulating layer 2 so as to cover the piezoelectric actuator 7. Here, as a material of the insulating layer 12, there is SiO ₂ or the like. A contact plug 11 is formed through the insulating layer 12 at the end of the lower electrode 8 of the piezoelectric actuator 7. The contact plug 11 is connected to a contact layer 13 formed on the insulating layer 12. Thereby, a voltage can be applied from the contact layer 13 to the lower electrode 8. A contact plug 14 is also formed on the upper electrode 10 of the piezoelectric actuator 7. The contact plug 14 is connected to a contact layer 15 formed on the insulating layer 12. Thereby, a voltage can be applied from the contact layer 15 to the upper electrode 10. Here, materials used for the contact plugs 11 and 14 and the contact layers 13 and 15 include Al, Cu, and W.

  The upper electrode 16 of the variable capacitor is formed so as to protrude from the insulating layer 6 to a position located above the lower electrode 4. A fixed shaft 17 is provided in a direction orthogonal to the longitudinal direction of the upper electrode 16. The fixed shaft 17 is connected to the upper electrode 16 or is integrally formed of the same material as the upper electrode 16 and is disposed between the lower electrode 4 of the variable capacitor and the piezoelectric actuator 7. Further, as shown in FIG. 2B, the upper electrode 16 is provided on the semiconductor substrate 1 through a cavity. The fixed shaft 17 on the groove 3 is disposed on the semiconductor substrate 1 through a cavity, and the fixed shaft 17 on the insulating layer 2 is fixed to the insulating layer 2. Further, the fixed shaft 17 connected to the upper electrode 16 is connected to a contact (not shown) to which a potential is applied in order to operate the upper electrode 16 as a variable capacitor. Here, examples of the material used for the upper electrode 16 and the fixed shaft 17 of the variable capacitor include Si, Au, Cu, and Al, and alloys including Au and Co or Ni. In the following description, the upper electrode 16 is divided into a first portion 16A located between the piezoelectric actuator 7 and the fixed shaft 17 and a second portion 16B located closer to the lower electrode 4 than the fixed shaft 17. .

  In the MEMS variable capacitor having such a structure, in the initial state where the piezoelectric actuator 7 is not driven, the first portion 16A of the upper electrode 16 between the actuator 7 and the fixed shaft 17 and the lower electrode 4 from the fixed shaft 17 are provided. The second portion 16B of the upper electrode 16 on the side bends upward or downward depending on the residual stress of the upper electrode itself. Here, as shown in FIG. 2C, it is assumed that the first portion 16A and the second portion 16B of the upper electrode 16 bend upward. At this time, the first portion 16A side of the upper electrode 16 is fixed to one end of the actuator 7, and the other end of the actuator 7 is fixed to the insulating layer 2 on the semiconductor substrate 1, so that the displacement of the first portion 16A The degree of freedom is small. On the other hand, since the tip of the second portion 16B of the upper electrode 16 is a free end, the vicinity of the fixed shaft 17 in the second portion 16B is displaced downward by bending the first portion 16A upward. can do. Due to the downward displacement of the second portion 16B, the upward displacement amount of the second portion 16B is reduced. Thereby, the 2nd part 16B of the upper electrode 16 can be arrange | positioned in a desired position.

  For example, when the fixed shaft 17 is not provided, the upper electrode 16 including the first portion 16A and the second portion 16B in the initial state bends upward due to residual stress, and thus the upper electrode 16 is greatly displaced upward. In some cases, the desired position may deviate.

  When the fixed shaft 17 is formed between the first portion 16A and the second portion 16B as in the present embodiment, the first portion 16A and the second portion 16B bend upward due to residual stress. . Then, when the first portion 16A is bent upward, a portion near the fixed shaft 17 in the first portion 16A is displaced upward. In the vicinity of the fixed shaft 17 in the second portion 16B, a force that tends to be displaced in the upward direction is generated. However, unlike the first portion 16A, the other end of the second portion 16B is a free end. Due to the upward displacement of the first portion 16A, a force that tends to rotate downward about the fixed shaft 17 easily acts on the second portion 16B. As a result, the fixed shaft 17 of the second portion 16B The neighboring part is displaced downward. For this reason, as described above, the second portion 16B bends upward due to the residual stress, but due to the downward displacement of the portion near the fixed shaft 17, the upward displacement amount of the second portion 16B is reduced. The Thereby, the 2nd part 16B of the upper electrode 16 facing the lower electrode 4 can be arrange | positioned in a desired position.

  In order to make the upper electrode 16 closer to the lower electrode 4 in order to make the capacitance of the MEMS variable capacitor variable, the first portion 16A of the upper electrode 16 is moved upward by driving the piezoelectric actuator 7 upward. Displace in the direction. Thereby, based on the rotation of the upper electrode 16 around the fixed shaft 17, the second portion 16B is displaced downward from the initial position, and the capacitance of the variable capacitor can be made variable. In this embodiment, the case where the upper electrode 16 bends upward (in the direction opposite to the substrate) due to the residual stress has been described. it can.

  The variable capacitor using the piezoelectric actuator according to the first embodiment can be manufactured by the following procedure. FIG. 3A, FIG. 3B, and FIG. 3C are cross-sectional views illustrating the method for manufacturing the variable capacitor according to the first embodiment.

  As shown in FIG. 3A, the insulating layer 2 is formed on the semiconductor substrate 1 by using, for example, a CVD (Chemical Vapor Deposition) method. Further, for example, the groove 3 is formed in a part of the insulating layer 2 by using lithography and RIE (Reactive Ion Etching) method. Next, the lower electrode 4 of the variable capacitor and the insulating layer 5 are formed on the semiconductor substrate 1 in the groove 3 so as to cover the lower electrode 4. Then, a polycrystalline silicon film (sacrificial film) 18 is buried in the groove 3 formed in a part of the insulating layer 2 by using, for example, a CVD method.

  Next, as shown in FIG. 3B, the piezoelectric actuator 7 having the above-described configuration and the upper electrode 16 of the variable capacitor are formed on the insulating layer 2 and the polycrystalline silicon film 18. At this time, the fixed shaft 17 connected to the upper electrode 16 or the fixed shaft 17 integrally formed of the same material as the upper electrode 16 is processed by a well-known patterning technique simultaneously with the formation of the upper electrode 16 of the variable capacitor. That's fine.

  Next, the insulating layer 12 is formed on the piezoelectric actuator 7 and the insulating layer 2. Then, contact plugs 11 and 14 and contact layers 13 and 15 connected to the upper electrode 10 and the lower electrode 8 of the piezoelectric actuator 7 are formed. Further, contacts (not shown) connected to the upper electrode 16 and the lower electrode 4 of the variable capacitor are formed.

Next, as shown in FIG. 3C, a polycrystalline silicon film (sacrificial film) 18 in the trench 3 is formed using a CDE (Chemical Dry Etching) method using a fluorine gas, for example, XeF _2. Remove. Here, when the polycrystalline silicon film (sacrificial film) 18 is removed, as described above, the fixed shaft 17 is formed between the first portion 16A and the second portion 16B of the upper electrode 16, The upward bending due to the residual stress of the upper electrode 16 can be suppressed. Still, the first portion 16A and the second portion 16B bend upward due to residual stress, but when the first portion 16A bends upward, the vicinity of the fixed shaft 17 in the second portion 16B is displaced downward. . Due to the downward displacement of the second portion 16B, the upward displacement amount of the second portion 16B is reduced. As a result, the second portion 16B of the upper electrode 16 can be arranged at a desired position. As described above, the variable capacitor using the piezoelectric actuator according to the first embodiment of the present invention can be manufactured.

  The above-described variable capacitor according to the first embodiment of the present invention can be operated by the following operation.

  When a voltage is applied to the upper electrode 10 and the lower electrode 8 of the actuator 7, for example, a ground potential of 0 V is applied to the lower electrode 8 and a voltage of 3 V is applied to the upper electrode 10, the piezoelectric layer 9 of the actuator 7 contracts in the lateral direction. . Then, the actuator 7 moves upward or downward. Here, the actuator 7 is configured to move upward.

  Then, due to the upward displacement of the actuator 7, the first portion 16A of the upper electrode 16 connected to the movable portion of the actuator 7 is displaced upward. At this time, in this embodiment, since the fixed shaft 17 is provided on the upper electrode 16, the lower electrode 4 from the fixed shaft 17 is displaced by the upward displacement of the first portion 16 </ b> A closer to the actuator 7 than the fixed shaft 17. The second portion 16B on the side is displaced downward (in the direction of the lower electrode 4). Then, the distance between the upper electrode 16 and the lower electrode 4 of the variable capacitor is reduced, and the capacitance of the variable capacitor is increased. When the upper electrode 16 and the insulating layer 5 on the lower electrode 4 come into contact with each other, the capacity of the variable capacitor is maximized. In this manner, by controlling the upward displacement amount of the actuator 7, the capacitance of the variable capacitor can be made variable.

  As described above, in the variable capacitor using the piezoelectric actuator according to the first embodiment, the fixed shaft 17 is provided on the upper electrode 16 of the variable capacitor, so that the actuator is attached to the actuator in the initial state where the actuator is not driven. Even when the upper electrode is bent in either the upper direction or the lower direction due to residual stress, the upper electrode can be disposed at a desired position.

[Example 2]
FIG. 4 is a plan view showing the structure of the variable capacitor using the piezoelectric actuator according to the second embodiment of the present invention.

  Differences between the second embodiment and the first embodiment will be described below. In the first embodiment, the elongated fixed shaft 17 connected to the upper electrode 16 is provided in the direction orthogonal to the longitudinal direction of the upper electrode 16 of the variable capacitor. In the second embodiment, as shown in FIG. 4, a wide region 19 is provided in a part of the fixed shaft 17 in order to increase the strength for fixing the upper electrode 16 by the fixed shaft 17. In addition, about the structure same as the other Example 1, the same code | symbol is attached | subjected and description is abbreviate | omitted.

  In the variable capacitor having such a configuration, when the upper electrode 16 and the fixed shaft 17 are formed in the manufacturing method shown in the first embodiment, a wide region 19 is formed in a part of the fixed shaft 17. It can be manufactured by patterning. Since the manufacturing method of other parts of the variable capacitor is the same as that of the first embodiment, the description thereof is omitted. The operation of the variable capacitor using the piezoelectric actuator according to the second embodiment is also the same as that of the first embodiment, and the description thereof is omitted.

  In the variable capacitor using the piezoelectric actuator according to the second embodiment, the fixed electrode 17 is provided on the upper electrode 16 of the variable capacitor so that the upper electrode attached to the actuator is not driven in the initial state. Even when the upper electrode is bent in the upward direction or the downward direction due to the residual stress, the upper electrode can be disposed at a desired position.

  Furthermore, in Example 1, the strength of the fixed shaft 17 for fixing the upper electrode 16 can be increased by providing a wide region 19 in a part of the fixed shaft 17 made of a thin material. Thereby, the variation in the arrangement position of the upper electrode in the initial state of the variable capacitor can be reduced, and the position of the upper electrode in the initial state can be stabilized.

  Here, as a method for further strengthening the fixed shaft 17 connected to the upper electrode 16 of the variable capacitor, the fixed shaft 17 can be formed thick. In addition, the strength of the fixed shaft 17 can be improved by increasing the width of the fixed shaft 17. Further, another metal material can be deposited on the fixed shaft 17 to improve the strength of the fixed shaft 17. As this other metal material, the same material as that used for the upper electrode 16 and the lower electrode 4 of the variable capacitor may be used.

[Example 3]
FIG. 5 is a plan view showing the structure of a variable capacitor using a piezoelectric actuator according to Embodiment 3 of the present invention. FIG. 6 is a cross-sectional view taken along line 6-6 of the variable capacitor shown in FIG.

  The difference between the third embodiment and the first embodiment is that the distance in the longitudinal direction of the upper electrode 16 in the first embodiment is longer in the longitudinal direction of the upper electrode 16 in the third embodiment as shown in FIGS. The distance is significantly longer. In addition, about the structure same as the other Example 1, the same code | symbol is attached | subjected and description is abbreviate | omitted.

  Here, for example, the distance between the end of the upper electrode 16 and the insulating layer 5 when the actuator 7 is not operating is A, and the end of the insulating layer 6 below the actuator 7 when the actuator 7 is operating. Let B be the displacement of. In this case, the distance C between the end of the insulating layer 6 constituting the actuator 7 and the fixed shaft 17 and the distance D between the fixed shaft 17 and the end of the upper electrode 16 have a relationship of D × B / C> A. Arrange so that it holds. Specifically, when the distance A between the end portion of the upper electrode 16 and the insulating layer 5 is 2 μm and the end portion of the insulating layer 6 under the actuator 7 is displaced by 1 μm by the operation of the actuator 7, the fixed axis The distance C between 17 and the end of the insulating layer 6 constituting the actuator 7 is 1 μm, and the distance D between the fixed shaft 17 and the end of the upper electrode 16 is 3 μm.

  In the variable capacitor using the piezoelectric actuator constructed as described above, when the groove 3 is formed in the insulating layer 2, the groove 3 is formed in the upper electrode so that the upper electrode 16 of the variable capacitor can be formed long in the longitudinal direction. 16 wide in the longitudinal direction. In the formation of the upper electrode 16, patterning is performed so that the longitudinal direction of the upper electrode 16 becomes significantly longer when the upper electrode 16 and the fixed shaft 17 are formed. Thereby, a variable capacitor using the piezoelectric actuator of the third embodiment can be formed. Since the manufacturing method of other parts of the variable capacitor is the same as that of the first embodiment, the description thereof is omitted. The operation of the variable capacitor using the piezoelectric actuator of the third embodiment is also the same as that of the first embodiment, so that the description thereof is omitted.

  In the variable capacitor using the piezoelectric actuator according to the third embodiment, by providing the fixed shaft 17 on the upper electrode 16 of the variable capacitor, the upper electrode attached to the actuator can be moved in the initial state where the actuator is not driven. Even when the upper electrode is bent in the upward direction or the downward direction due to the residual stress, the upper electrode can be disposed at a desired position.

  Further, by adjusting the position of the fixed shaft 17 connected to the upper electrode 16, the upper electrode 16 can be largely displaced by a small displacement of the actuator 7. Therefore, by making the longitudinal direction of the upper electrode 16 of the variable capacitor significantly longer than that of the first embodiment, the upper electrode 16 can be largely displaced downward with a small displacement amount of the piezoelectric actuator 7.

[Example 4]
FIG. 7 is a plan view showing the structure of a variable capacitor using a piezoelectric actuator according to Embodiment 4 of the present invention. 8 is a cross-sectional view taken along line 8-8 of the variable capacitor shown in FIG.

The difference between the fourth embodiment and the third embodiment is that a film 20 having a tensile stress is formed on the upper electrode 16 in the fourth embodiment, as shown in FIGS. Here, examples of the film 20 having tensile stress include SiN, TiN, Pt, Ti, PZT, and SrTiO ₃ . In addition, about the structure same as the other Example 3, the same code | symbol is attached | subjected and description is abbreviate | omitted.

  In the variable capacitor according to the fourth embodiment, when the upper electrode 16 and the fixed shaft 17 are formed, after forming a metal film as a material for the upper electrode 16 and the fixed shaft 17, the film 20 having a tensile stress is formed on the film. A film is formed on the metal film. Then, by patterning the upper electrode 16 and the fixed shaft 17 on the metal film and the film 20 having a tensile stress, a variable capacitance capacitor in which the film 20 having a tensile stress is laminated on the upper electrode 16 is formed. Is done. Since the manufacturing method of other parts of the variable capacitor is the same as that of the first embodiment, the description thereof is omitted. The operation of the variable capacitor according to the fourth embodiment is also the same as that of the first embodiment, and the description thereof is omitted.

  In the variable capacitor according to the fourth embodiment, the upper electrode 16 protruding from the insulating layer 6 can be prevented from sagging by forming the film 20 having a tensile stress on the upper electrode 16 of the variable capacitor. Further, by providing the fixed shaft 17 on the upper electrode 16 of the variable capacitor, in the initial state where the actuator is not driven, the upper electrode attached to the actuator is moved upward or downward by residual stress. Even when bent, the upper electrode can be disposed at a desired position.

  In the fourth embodiment, the upper electrode 16 of the variable capacitor is formed in the longitudinal direction as in the third embodiment. However, as in the first embodiment, the upper electrode 16 is formed in the longitudinal direction. It can also be applied to the case where it is not formed for a long time.

[Example 5]
FIG. 9 is a plan view showing the structure of a variable capacitor using a piezoelectric actuator according to Embodiment 5 of the present invention. FIG. 10 is a cross-sectional view of the variable capacitor shown in FIG. 9 taken along line 10-10.

  Differences between this embodiment and the above embodiments will be described below. In each of the above embodiments, the fixed shaft 17 is provided at one location of the upper electrode 16. In the fifth embodiment, as shown in FIGS. 9 and 10, fixed shafts 17 and 21 are provided at two locations of the lower electrode 22.

  In the variable capacitor according to the fifth embodiment, as shown in FIG. 10, the lower electrode 4 is not formed on the semiconductor substrate 1 in the groove 3, and the electrode connected to the actuator 7 is the lower electrode 22. An upper electrode 23 is formed above the lower electrode 22. The upper electrode 23 is formed below the insulating layer 24, and the insulating layer 25 is formed so as to cover the upper electrode 23. The insulating layer 24 is supported by a support layer 26 provided on the insulating layer 12 and the insulating layer 2 so that a space is formed between the lower electrode 22 and the upper electrode 23.

  In the MEMS variable capacitor having such a structure, in the initial state where the piezoelectric actuator 7 is not driven, the first portion 22A between the actuator 7 and the fixed shaft 17, which forms the lower electrode 22, the fixed shaft 17, The second portion 22B between the fixed shafts 21 and the third portion 22C closer to the upper electrode 23 than the fixed shaft 21 bend upward due to the residual stress of the lower electrode itself. Here, when the first portion 22A bends upward, the vicinity of the fixed shaft 17 in the second portion 22B is displaced downward. Due to the downward displacement of the second portion 22B, the upward displacement amount of the second portion 22B is reduced. Here, when the second portion 22B is displaced upward, the portion near the fixed shaft 21 in the third portion 22C is displaced downward. Due to the downward displacement of the third portion 22C, the amount of upward displacement of the third portion 22C is reduced. As a result, the third portion 22C of the lower electrode 22 can be disposed at a desired position.

  The above-described variable capacitor according to the fifth embodiment of the present invention can be operated by the following operation.

  When a voltage is applied to the upper electrode 10 and the lower electrode 8 of the actuator 7, for example, a ground potential of 0 V is applied to the lower electrode 8 and a voltage of 3 V is applied to the upper electrode 10, the piezoelectric layer 9 of the actuator 7 contracts in the lateral direction. . Then, the actuator 7 moves upward or downward. Here, the actuator 7 is configured to move upward.

  Then, due to the upward displacement of the actuator 7, the first portion 22 </ b> A of the lower electrode 22 connected to the movable portion of the actuator 7 is displaced upward. Due to the upward displacement, the second portion 22B of the lower electrode 22 is displaced downward. Further, due to the downward displacement, the third portion 22C of the lower electrode 22 is displaced upward. As a result, the distance between the lower electrode 22 and the upper electrode 23 is reduced, and the capacitance of the variable capacitor is increased. When the lower electrode 22 and the insulating layer 25 on the upper electrode 23 come into contact with each other, the capacitance of the variable capacitor is maximized. In this manner, by controlling the upward displacement amount of the actuator 7, the capacitance of the variable capacitor can be made variable.

  As described above, in the variable capacitor using the piezoelectric actuator according to the fifth embodiment, the fixed shafts 17 and 21 are provided at the two positions of the lower electrode 22 of the variable capacitor so that the actuator 7 is not driven at the initial stage. In the state, even when the lower electrode 22 attached to the actuator 7 bends in the upward direction or the downward direction due to residual stress, the lower electrode 22 can be disposed at a desired position. Although the number of fixed shafts provided on the electrodes of the variable capacitor is two here, the number of fixed shafts may be further increased to three or more.

  In the variable capacitor using the piezoelectric actuator according to the embodiment of the present invention, the electrode attached to the actuator remains in the initial state where the actuator is not driven by providing a fixed shaft on the electrode attached to the actuator. It is possible to provide a MEMS in which an electrode can be arranged at a desired position even when it is bent in either an upward direction or a downward direction due to stress.

  The present invention is not limited to the embodiments described above, and various modifications can be made without departing from the spirit of the present invention. For example, in each of the above embodiments, the variable capacitance capacitor is configured using a piezoelectric actuator, but other actuators such as electrostatic, thermal, and magnetic actuators are also used in each of the above embodiments. be able to. In each of the above embodiments, a variable capacitor using MEMS technology has been described as an example. However, it can also be used for a switch by eliminating the dielectric material between the electrodes.

It is a top view which shows the structure of the variable capacitor using the piezoelectric actuator which concerns on Example 1 of this invention. (A), (b) is sectional drawing which shows the structure of the variable capacitor shown in FIG. 1, (c) is sectional drawing to which the vicinity of the fixed axis | shaft in (a) was expanded. (A), (b), (c) is sectional drawing which shows the manufacturing method of the variable capacitor using the piezoelectric actuator which concerns on Example 1. FIG. It is a top view which shows the structure of the variable capacitor using the piezoelectric actuator which concerns on Example 2 of this invention. It is a top view which shows the structure of the variable capacitor using the piezoelectric actuator which concerns on Example 3 of this invention. FIG. 6 is a cross-sectional view of the variable capacitor shown in FIG. 5 taken along line 6-6. It is a top view which shows the structure of the variable capacitor using the piezoelectric actuator which concerns on Example 4 of this invention. FIG. 8 is a sectional view taken along line 8-8 of the variable capacitor shown in FIG. It is a top view which shows the structure of the variable capacitor using the piezoelectric actuator which concerns on Example 5 of this invention. FIG. 10 is a cross-sectional view of the variable capacitor shown in FIG. 9 taken along line 10-10.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Semiconductor substrate, 2 ... Insulating layer, 3 ... Groove, 4 ... Lower electrode (variable capacitor), 5 ... Insulating layer (variable capacitor), 6 ... Insulating layer, 7 ... Piezoelectric actuator, 8 ... Lower electrode, DESCRIPTION OF SYMBOLS 9 ... Piezoelectric layer, 10 ... Upper electrode, 11 ... Contact plug, 12 ... Insulating layer, 13 ... Contact layer, 14 ... Contact plug, 15 ... Contact layer, 16 ... Upper electrode (variable capacitor), 16A ... Upper electrode 16 First part 16B ... Second part of the upper electrode 16, 17 ... Fixed axis, 18 ... Polycrystalline silicon film (sacrificial film), 19 ... Wide region of the fixed axis 17, 20 ... Film having tensile stress, 21 ... Fixed shaft, 22 ... lower electrode (variable capacitance capacitor), 22A ... first portion of lower electrode 22, 22B ... second portion of lower electrode 22, 22C ... third portion of lower electrode 22, 23 ... upper electrode (variable capacitance) Ki Pashita), 24: insulating layer, 25: insulating layer (variable capacitor), 26 ... support layer.

Claims (2)

An actuator provided on a substrate, having one end and the other end, the one end fixed to the substrate;
A first electrode disposed on the substrate;
A second electrode having one end and the other end, the one end being fixed to the other end of the actuator, and the other end being a free end;
A linear axis provided between the one end and the other end of the second electrode and extending in a direction perpendicular to the longitudinal direction of the second electrode and parallel to the substrate surface; A linear shaft having an end portion fixed on the substrate;
The first electrode is opposed to the second electrode on the other end side of the second electrode with respect to the fixed axis,
The fixed shaft is integrally formed of the same material as the second electrode,
The length of the second electrode closer to the first electrode than the fixed shaft is longer than the length of the second electrode between the actuator and the fixed shaft,
Due to the residual stress of the second electrode , the vicinity of the fixed shaft in the second electrode between the actuator and the fixed shaft is displaced in either the substrate direction or the direction opposite to the substrate, and the fixed shaft More, the vicinity of the fixed shaft in the second electrode on the first electrode side is displaced in the opposite direction to the one,
As the actuator moves, the second electrode between the actuator and the fixed shaft is displaced in the same direction as the actuator, and the second electrode closer to the first electrode than the fixed shaft is opposite to the actuator. A MEMS characterized by being displaced in a direction. An actuator provided above the substrate and having a movable part;
A first electrode formed on the substrate;
A fixed shaft fixed to the substrate between the movable part of the actuator and the first electrode, and is fixed to the movable part of the actuator and disposed at a position facing the first electrode. And a second electrode displaced by the actuator,
The fixed shaft has a straight shaft extending in a direction perpendicular to the longitudinal direction of the second electrode and parallel to the substrate surface, and an end portion of the straight shaft is fixed on the substrate. And
The fixed shaft is integrally formed of the same material as the second electrode,
The length of the second electrode closer to the first electrode than the fixed shaft is longer than the length of the second electrode between the actuator and the fixed shaft,
Due to the residual stress of the second electrode , the vicinity of the fixed shaft in the second electrode between the actuator and the fixed shaft is displaced in either the substrate direction or the direction opposite to the substrate, and the fixed shaft More, the vicinity of the fixed shaft in the second electrode on the first electrode side is displaced in the opposite direction to the one,
As the actuator moves, the second electrode between the actuator and the fixed shaft is displaced in the same direction as the actuator, and the second electrode closer to the first electrode than the fixed shaft is opposite to the actuator. A MEMS characterized by being displaced in a direction.

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