JP2008210640A - Electrostatically-driven element, and electrostatically-driven device equipped with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrostatically-driven element high in reliability for operation. <P>SOLUTION: Fixed conductor patterns 3a and 3b are formed on a surface of a board 2, and a movable part 4 is arranged on the upper of the fixed conductor patterns 3a and 3b. A movable conductor pattern 7 is formed on the movable part 4. The movable part 4 is brought into such a state that it is supported and fixed to a fixation part 5 fixed to the board 2 by beams 6a and 6b. Material parts 18 each having an expansion coefficient different from that of the beams 6a and 6b are formed on the beams 6a and 6b, and bent parts 17 each having a shape projecting upward with respect to the board 2 are formed. Top parts of the bent parts 17 abut on a driving fixed electrode 8 in a pressing state; and the bent parts 17 press the movable part 4 toward the board 2 by coming into such a state that the bent parts 17 are elastically deforming toward the board 2. When electrostatic attraction is generated between the movable part 4 and the driving fixed electrode 8, the movable part 4 is displaced toward the driving fixed electrode 8 by using the top parts of the bent parts 17 as support points, and distances between the fixed conductor patterns 3a and 3b and the movable conductor pattern 7 are increased. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electrostatic driving element that drives using electrostatic attraction and an electrostatic driving device including the same.

  FIG. 12A is a schematic plan view showing an example of main components of a variable capacitance element that is one of electrostatic drive elements, and FIG. 12B shows an A- of FIG. 12A. A schematic cross-sectional view of the variable capacitance element of portion A is shown. A variable capacitance element 40 shown in FIGS. 12A and 12B has a glass substrate 41, a fixed electrode 42 is formed on the surface of the glass substrate 41, and an insulating material is formed on the surface of the fixed electrode 42. A protective film 46 is formed. A fixed portion 43 is fixed on the surface of the glass substrate 41 so as to surround the formation region of the fixed electrode 42 with a space therebetween. A movable portion 44 is disposed above the fixed electrode 42 in a floating state, and the movable portion 44 is supported and fixed to the fixed portion 43 in the form of a cantilever beam by beams 45A and 45B. The beams 45 </ b> A and 45 </ b> B can be bent and deformed in the vertical direction of FIG. 12 (b), so that the movable portion 44 can be displaced in the perspective direction with respect to the fixed electrode 42.

  In the example of the variable capacitance element 40, the fixed portion 43, the movable portion 44, and the beams 45A and 45B are manufactured by etching a semiconductor substrate (for example, a silicon substrate). The movable portion 44 has an electrical resistance value lowered by doping impurities, and functions as a movable electrode. The movable part (movable electrode) 44 and the fixed electrode 42 constitute a capacitor.

  The variable capacitance element 40 is configured as described above, and a voltage applying unit 48 is connected to the variable capacitance element 40. The voltage application means 48 applies a voltage between the movable portion 44 and the fixed electrode 42, and includes a voltage source 49 and a switch means 50. When the switch means 50 is turned on, the voltage of the voltage source 49 is applied between the movable portion 44 and the fixed electrode 42, and an electrostatic attractive force F is generated between the movable portion 44 and the fixed electrode 42. Due to the electrostatic attractive force F, as shown by the solid line in FIG. 12C, the movable portion 44 is displaced to the fixed electrode 42 side by elastic deformation (deflection deformation) of the beams 45A and 45B. As a result, the interval between the movable portion 44 and the fixed electrode 42 is narrowed, and the capacitance between the movable portion (movable electrode) 44 and the fixed electrode 42 increases.

  When the switch means 50 is turned off and the voltage application between the movable part 44 and the fixed electrode 42 is stopped, the generation of the electrostatic attractive force F between the movable part 44 and the fixed electrode 42 is stopped. For this reason, the movable portion 44 is displaced in the direction away from the fixed electrode 42 as indicated by the chain line in FIG. 12C due to the elastic force of the beams 45A and 45B. As a result, the interval between the movable portion 44 and the fixed electrode 42 is widened, and the capacitance between the movable portion (movable electrode) 44 and the fixed electrode 42 is changed in a decreasing direction. Thus, by displacing the movable portion 44 by the electrostatic attractive force F, the distance between the movable portion 44 and the fixed electrode 42 changes widely, and the capacitance of the capacitor formed by the movable portion 44 and the fixed electrode 42 is reduced. The size changes.

Japanese Patent Laid-Open No. 11-274805

  By the way, the position indicated by the chain line in FIG. 12 (c) and the position shown in FIG. 12 (c) by the electrostatic attractive force (driving force) F between the movable portion 44 and the fixed electrode 42 and the elastic force of the beams 45A and 45B. ), The electrostatic attractive force F is desirably a magnitude determined by the following equation (1) associated with the elastic force of the beams 45A and 45B. .

  F = k · x (1)

  Here, k is a spring constant of the beams 45A and 45B, and x is a displacement amount of the movable portion 44 due to the change in generation and stop of the electrostatic attractive force F (see FIG. 12C).

  If the electrostatic attractive force F is a magnitude determined by the mathematical formula (1), it is possible to prevent the problem that the electrostatic attractive force F is small, the force is insufficient, and the movable portion 44 cannot be displaced to the fixed electrode 42 side. In addition, the sticking failure that the electrostatic attractive force F is too large and the beams 45A and 45B are abnormally deformed toward the substrate 41 and the movable portion 44 remains displaced toward the fixed electrode 42 and the movable portion 44 cannot be driven. Can also be prevented.

  However, since the displacement amount x of the movable portion 44 varies due to the accuracy in the etching process of the semiconductor substrate for manufacturing the movable portion 44 and the like, the magnitude of the electrostatic attractive force F suitable for driving the movable portion 44 is large. In addition, the following problems occur. In other words, the movable portion 44 is actually driven by the electrostatic attractive force F based on the preset design value of the displacement amount x of the movable portion 44 even though the magnitude of the appropriate electrostatic attractive force F varies. Therefore, the sticking failure may occur due to the electrostatic attractive force F being too large, or the movable portion 44 may not be displaced to a predetermined position on the fixed electrode 42 side due to the small electrostatic attractive force F. In particular, in recent years, there is a tendency to reduce the displacement amount x of the movable portion 44 in order to reduce the electrostatic attractive force F in order to save the power of the variable capacitance element 40, thereby causing variation in the displacement amount x of the movable portion 44. Is getting bigger. For this reason, the problem of the occurrence of the sticking failure is likely to occur. In addition, if the electrostatic attractive force F is reduced in order to prevent the sticking failure, there occurs a situation in which the movable portion 44 cannot be displaced to a predetermined position on the fixed electrode 42 side. The magnitude of the electric capacity deviates from a predetermined set value, thereby reducing the reliability of the variable capacitance element 40 with respect to the performance.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an electrostatic drive element capable of stably driving a movable part as designed and improving reliability of performance. An object is to provide an electrostatic drive device including the same.

In order to achieve the above object, the present invention has the following configuration as means for solving the above-mentioned problems. That is, the electrostatic drive element of the present invention is
A substrate,
A fixed conductor pattern formed on the surface of the substrate;
A fixed portion fixed to the surface of the substrate;
A beam having one end connected to the fixed portion;
A movable part connected to the other end of the beam and arranged to face the substrate;
A movable conductor pattern formed on the substrate-side surface of the movable portion and facing the fixed conductor pattern;
A material part having an expansion coefficient different from that of the beam in order to make the shape of the beam formed on the beam convex upward with respect to the substrate;
A driving fixed electrode that presses the convex top of the beam;
Have
Due to the generation of electrostatic attraction by applying a voltage between the driving fixed electrode and the movable part, the movable part is displaced in a direction approaching the driving fixed electrode with the convex top of the beam as a fulcrum. It is characterized in that the distance between the conductor pattern and the fixed conductor pattern changes in the direction of increasing.

In addition, the electrostatic drive element of the present invention is
A substrate,
A fixed conductor pattern formed on the surface of the substrate;
A fixed portion fixed to the surface of the substrate;
A beam having one end connected to the fixed portion;
A movable part connected to the other end of the beam and arranged to face the substrate;
A movable conductor pattern formed on the substrate-side surface of the movable portion and facing the fixed conductor pattern;
A material part having an expansion coefficient different from that of the beam in order to make the shape of the beam formed on the beam convex downward with respect to the substrate;
Have
The convex top of the beam is configured to be in contact with the substrate in a pressed state,
Due to the generation of electrostatic attraction by applying a voltage between the movable conductor pattern and the fixed conductor pattern, the movable portion is displaced in a direction approaching the substrate with the convex top of the beam as a fulcrum, and the movable conductor pattern and It is also characterized in that the distance from the fixed conductor pattern changes in the direction of narrowing.

  Furthermore, the electrostatic drive device of the present invention is characterized by having an electrostatic drive element having a configuration unique to the present invention.

  According to the present invention, the beam has a convex shape upward or downward with respect to the substrate, and the beam has an electrostatic attraction force for displacing the movable part by pressing the top of the convex shape. It is in an elastically deformed state both when it occurs and when it does not occur. In this configuration, the appropriate magnitude of the electrostatic attractive force (driving force) for displacing the movable part is mainly related to the stress of the elastically deformed beam when the electrostatic attractive force is not generated. To be determined. For this reason, even if the thickness of the beam, the distance between the fixed electrode for driving and the movable part, or the distance between the movable conductor pattern and the movable part varies from the design value due to problems in etching processing accuracy, It is possible to prevent the appropriate magnitude of the attractive force from greatly varying. As a result, it is possible to suppress the occurrence of problems due to excessive electrostatic attraction and the occurrence of problems due to insufficient electrostatic attraction, and it is easy to drive the movable part stably as designed. .

  In the configuration in which the beam has a convex shape with respect to the substrate, the movable portion is pressed against the substrate side by the elastic force of the beam when the electrostatic attraction is not generated. For this reason, not only when the electrostatic attractive force is generated, but also when the electrostatic attractive force is not generated, the movable portion can be stably disposed at a preset position, and the movable conductor The interval between the pattern and the fixed conductor pattern can be set to a predetermined set value almost accurately. As a result, the reliability of the performance of the electrostatic driving element and the electrostatic driving device including the electrostatic driving element can be increased.

  Also, in the case where the beam has a convex shape downward with respect to the substrate, the arrangement position of the movable part can be stabilized by the elastic force of the beam as described above when the electrostatic attractive force is not generated. Thus, the interval between the movable conductor pattern and the fixed conductor pattern can be set to a set value. For this reason, the reliability of the performance in an electrostatic drive element and an electrostatic drive device provided with the same can be improved.

  Furthermore, in this invention, when the movable part is displaced by electrostatic attraction, the movable part is displaced using the convex top of the beam as a fulcrum. With this configuration, the distance between the movable part and the fulcrum is shorter than the structure in which the movable part is displaced with the joint between the beam and the fixed part as a fulcrum. can do. This is also an important factor that enables the movable part to be driven stably and satisfactorily.

  Furthermore, in the present invention, the beam is deformed into a convex shape by providing a material portion having an expansion coefficient different from that of the beam. For this reason, compared with the case where a beam is deformed into a convex shape by machining, the beam can be deformed into a convex shape with certainty while suppressing deterioration in yield.

  Embodiments according to the present invention will be described below with reference to the drawings. Note that FIGS. 1 to 11 used in the description of the embodiment described below are drawn in a deformed manner for easy understanding, and each configuration of the electrostatic drive element shown in FIGS. The dimensional ratio of the part is different from the actual dimensional ratio.

  FIG. 1A is a schematic plan view showing main components of a variable capacitance element which is an example of an electrostatic drive element according to the first embodiment, and FIG. FIG. 1C is a schematic side view when the variable capacitance element is projected from the upper side to the lower side of FIG. 1, and FIG. 1C is a schematic cross-sectional view of the variable capacitance element in the AA portion of FIG. The figure is shown. The variable capacitance element 1 according to the first embodiment includes a substrate 2, fixed conductor patterns 3a and 3b, a movable portion 4, a fixed portion 5, beams 6a and 6b, a movable conductor pattern 7, and a fixed driving device. And an electrode 8.

That is, the substrate 2 is formed using a glass substrate and has a thickness of about 100 μm. Each of the fixed conductor patterns 3a and 3b is formed on the surface of the substrate 2 by a conductor layer such as copper (Cu) and has a thickness of about 5 μm and is used as a high-frequency electrode. An insulating film 11 made of SiO ₂ or the like having a function as an insulating and protective film is formed on the entire surface of the substrate 2 on which the fixed conductor patterns 3a and 3b are formed. The substrate 2 has holes 19a and 19b that reach the fixed conductor patterns 3a and 3b from the bottom surface shown in FIG. 1C, respectively, and a conductor material is formed inside the holes 19a and 19b. ing. Each of the fixed conductor patterns 3a and 3b can be electrically connected to the outside through the conductor material of the holes 19a and 19b.

  The movable portion 4 is in a state of floating above the substrate 2, and the size and arrangement position of the movable portion 4 are set so as to face both the fixed conductor patterns 3 a and 3 b. The movable portion 4 can be displaced in the perspective direction with respect to the fixed conductor patterns 3a and 3b. The movable portion 4 is made of Si, and by implanting impurities such as boron into the Si, the one having an electric resistance value of, for example, 200 Ωm becomes lower than that and can function as an electrode. ing. An oxide layer 9 is formed on the upper surface side of the movable portion 4, and an oxide layer (not shown for simplicity of illustration) is also formed on the lower surface side of the movable portion 4. The thickness of the oxide layer 9 on the upper surface side is very thin such as 50 nm or less, and the thickness of the oxide layer on the lower surface side is about 2 μm.

  A movable conductor pattern 7 is embedded in the lower surface side of the movable portion 4. The movable conductor pattern 7 is formed of a conductor layer such as copper (Cu) and is used as a high frequency electrode. The thickness of the movable conductor pattern 7 is about 0.2 μm, which is thinner than the oxide layer on the lower surface side of the movable portion 4, and the movable conductor pattern 7 is insulated from the movable portion 4 by the oxide layer. The movable conductor pattern 7 has a size facing both the solid conductor patterns 3a and 3b, and constitutes the circuit shown in FIG. 4 together with the solid conductor patterns 3a and 3b. That is, the variable capacitor C1 is formed by the fixed conductor pattern 3a and the movable conductor pattern 7, and the variable capacitor C2 is formed by the fixed conductor pattern 3b and the movable conductor pattern 7. The variable capacitors C1 and C2 are connected to the series resistance component Rc1, A series connection circuit is formed together with Rc2.

  The surface of the movable conductor pattern 7 is exposed to the outside of the movable portion 4, and the insulating film 10 is formed on the surface of the movable conductor pattern 7. By the way, the surface of the movable conductor pattern 7 is preferably flat. However, when the movable conductor pattern 7 having a larger expansion coefficient than Si is formed on the movable portion 4 made of Si, the movable portion 4 and the movable conductor pattern 7 are formed. Will warp. From this, the insulating film 10 is formed with a constituent material and a film thickness in consideration of an expansion coefficient so that the warp of the movable portion 4 and the movable conductor pattern 7 can be corrected. The surface of the pattern 7 is flat. The insulating film 10 also functions as a buffer member when the movable part 4 is displaced toward the fixed conductor patterns 3a and 3b.

  The fixed portion 5 has a frame shape surrounding the arrangement region of the movable portion 4 with a space therebetween, and is fixed to the substrate 2 by an anodic bonding method. Each of the beams 6a and 6b is connected to the movable part 4 at one end and is connected to the fixed part 5 at the other end, and the two beams 6a and 6b support the movable part 4 from both sides to the fixed part 5. It is fixed. In this example, the connecting portion of the beam 6a and the movable portion 4 and the connecting portion of the beam 6b and the movable portion 4 are in a positional relationship that is a diagonal of the rectangular movable portion 4. Further, the beams 6a and 6b have portions that are parallel to each other with the movable portion 4 therebetween. The beam portions 6 a and 6 b are formed in a thin plate shape and a narrow width, and can be bent and deformed in the perspective direction with respect to the substrate 2.

  The beams 6a and 6b are made of Si, and a metal layer such as copper (Cu) is embedded on the lower surface side of the M region (see FIG. 1A) in each of the beams 6a and 6b. (Material part) 18 is formed. That is, the M region of the beams 6a and 6b has a laminated structure in which the metal layer 18 having a larger expansion coefficient than Si and the Si layer are laminated in order from the substrate 2 side to the upper side. Therefore, due to the stress of the metal layer 18 due to the difference in thermal expansion coefficient, the M region of the beam portions 6a and 6b is curved upwardly with respect to the surface of the substrate 2 (a shape that swells away from the substrate 2). It is part 17. The amount of bulging deformation of the curved portion 17 can be adjusted by the metal layer 18 so as to increase as the formation area and thickness of the metal layer 18 increase. Therefore, in the first embodiment, the metal layer 18 has a bulging deformation amount x1 (see the exploded view of FIG. 2) of the curved portion 17 of each beam 6a, 6b, and the beam 6a, 6b and the driving fixing. It is formed with a layer thickness and a formation area in consideration of an expansion coefficient of the constituent material of the metal layer 18 so as to be larger than the distance x2 between the electrode 8 and the electrode 8.

  The beams 6a and 6b, like the movable portion 4, are made low in electrical resistance by diffusion of impurities such as boron, so that a current easily flows. Further, the variable capacitance element 1 is provided with an external connection terminal (not shown) for electrically connecting the movable portion 4 to the outside via the beam 6a (6b). Further, an oxide layer is formed on both the upper and lower surfaces of the beams 6a and 6b in the same manner as the movable portion 4, the thickness of the oxide layer on the lower surface side is about 2 μm, and the thickness of the upper oxide layer is 50 nm or less. It is a thin layer. These oxide layers do not prevent the curved deformation of the beams 6a and 6b by the metal layer 18. Further, the metal layer 18 and the beams 6a and 6b are insulated from each other by an oxide layer on the lower surface side.

The driving fixed electrode 8 is disposed in common above the movable part 4, the fixed part 5, and the beam 6, and is joined to the fixed part 5 via the insulating layer 13, and together with the substrate 2 and the fixed part 5, the movable part 4. A closed space is formed to accommodate the. In addition, since the fixed electrode 8 for driving has an interval (thickness of the insulating layer 13) x2 between the beams 6a and 6b that is smaller than the bulging deformation amount x1 of the curved portion 17 of the beams 6a and 6b, the beams 6a and 6b. The top of the curved portion 17 is pressed to elastically deform the curved portion 17 toward the substrate 2 side. Further, the driving fixed electrode 8 is made of Si, and has a low electrical resistance by impurity diffusion treatment, like the movable portion 4 and the beam 6. An insulating layer 16 such as SiO ₂ is formed on the surface side of the driving fixed electrode 8 on the substrate 2 side. The insulating layer 16 insulates the movable portion 4 and the beams 6a and 6b from the driving fixed electrode 8 together with the oxide layer on the upper surface side of the movable portion 4 and the beams 6a and 6b. The variable capacitance element 1 is provided with an external connection terminal (not shown) for connecting the driving fixed electrode 8 to the outside.

  The variable capacitance element 1 of the first embodiment is configured as described above. The variable capacitance element 1 constitutes an electrostatic drive device by being packaged as one package with the voltage application means 20 as shown in FIGS. 1B, 3A, and 3B connected thereto. To do. The voltage application means 20 applies a DC voltage (for example, 3 V) between the movable portion 4 of the variable capacitance element 1 and the driving fixed electrode 8, and includes a voltage source 21 and a switch means 22. It is configured.

  When the switch means 22 of the voltage application means 20 is turned on and a voltage based on the voltage source 21 is applied between the driving fixed electrode 8 and the movable part 4, the driving fixed electrode 8 and the movable part 4 In between, electrostatic attraction occurs. 3 (b) from the state shown in FIG. 3 (a), with the movable portion 4 acting as a fulcrum by the contact portion between the top of the curved portion 17 of the beams 6a and 6b and the driving fixed electrode 8 by this electrostatic attraction. As a result, the distance between the movable conductor pattern 7 and the fixed conductor patterns 3a and 3b increases. For this reason, the electrostatic capacitances of the variable capacitors C1 and C2 including the movable conductor pattern 7 and the fixed conductor patterns 3a and 3b are reduced.

  Further, when the switch means 22 of the voltage application means 20 is turned off, voltage application between the driving fixed electrode 8 and the movable part 4 is eliminated, and electrostatic attraction between the driving fixed electrode 8 and the movable part 4 is eliminated. For this purpose, the movable portion 4 is supported by the elastic force in the elastic return direction of the curved portions 17 of the beams 6a and 6b with the contact portion between the top of the curved portion 17 and the driving fixed electrode 8 as a fulcrum. As shown in FIG. 4, the substrate is displaced toward the substrate 2 and is locked to the fixed conductor patterns 3a and 3b through the insulating layer 10 in an elastically pressed state. Thereby, the space | interval between the movable conductor pattern 7 and the fixed conductor patterns 3a and 3b becomes narrow, and the electrostatic capacitance of the variable capacitors C1 and C2 becomes large.

  In the first embodiment, the curved portions 17 of the beams 6a and 6b are elastically deformed even when no electrostatic attractive force is generated between the movable portion 4 and the driving fixed electrode 8. The movable portion 4 is locked to the substrate 2 by the elastic force. The force Foff that the movable part 4 presses the substrate 2 in this state is based on the elastic force of the curved portion 17 of the beams 6a and 6b, and can be expressed by the equation Foff = k · x1. . However, the symbol k in the equation is the spring constant of the curved portion 17 of the beams 6a and 6b, and x1 is the bulge deformation amount of the curved portion 17 (see FIG. 2).

  Further, the electrostatic attractive force Fs generated between the movable part 4 and the driving fixed electrode 8 in order to draw the movable part 4 to the driving fixed electrode 8 and displace it to the state shown in FIG. The beam 6 is caused by displacing the movable portion 4 by the thickness x2 of the insulating layer 13 (see FIG. 2) against the elastic force of the curved portions 17 of 6a and 6b, and by the excessive magnitude of the electrostatic attractive force Fs. In view of preventing abnormal deformation of the force, it is preferable that the force is slightly stronger than the force Fon represented by the formula Fon = k · (x1 + x2). As a result, the electrostatic attractive force Fs generated between the movable part 4 and the driving fixed electrode 8 is set to an appropriate magnitude based on the force Fon.

  In the first embodiment, since the bulging deformation amount x1 of the curved portions 17 of the beams 6a and 6b is larger than the displacement amount x2 of the movable portion 4, the displacement amount x2 of the movable portion 4 is a force Fon (Fon = k · The influence on the appropriate magnitude of the electrostatic attractive force Fs based on (x1 + x2)) is small. For this reason, even if the displacement amount x2 of the movable portion 4 varies depending on the etching processing accuracy or the like, the appropriate magnitude of the electrostatic attractive force Fs is substantially the same, and the appropriate magnitude of the electrostatic attractive force Fs is stabilized. be able to. As a result, the movable part 4 can be stably driven without being adversely affected by variations in the displacement amount x2 of the movable part 4.

  Next, an example of the manufacturing process of the variable capacitance element 1 of the first embodiment will be described based on the model diagrams of FIGS. 5 to 7 are schematic side views projected from the upper side to the lower side shown in FIG.

An SOI substrate 15 as shown in FIG. 5A is prepared. The SOI substrate 15 is a substrate in which a support layer 12, an insulating layer (BOX layer) 13, and an active layer 14 are sequentially stacked and integrated. For example, the support layer 12 is composed of n + Si that is an n-type semiconductor, The thickness is about 400 μm. The insulating layer 13 is made of SiO ₂ and has a thickness of about 0.3 μm. Further, the active layer 14 is made of p-type Si and has a thickness of about 5 μm.

First, an impurity such as boron is thermally diffused into the active layer 14 of the SOI substrate 15 to reduce the electrical resistance of the active layer 14. Similarly, the support layer 12 of the SOI substrate 15 has a low electrical resistance. Next, an SiO ₂ oxide layer having a thickness of about 2 μm, for example, is formed over the entire region on the surface side of the active layer 14 by thermal oxidation. Thereafter, on the surface side of the active layer 14, as shown in FIG. 5B, a recess 23a is formed in a portion where the movable conductor pattern 7 is formed, and the metal layer 18 of the curved portion 17 of each beam 6a, 6b. Recesses 23b are respectively formed in the portions where the film is formed by etching. The depths of the recesses 23a and 23b are in accordance with the thicknesses of the movable conductor pattern 7 and the metal layer 18, respectively. Then, after the formation of the recesses 23a and 23b, as shown in FIG. 5C, the conductor material (for example, copper) 24 constituting the movable conductor pattern 7 and the metal layer 18 is applied to the entire surface of the active layer 14, for example. It is formed by plating. Thereafter, the surface of the active layer 14 is planarized by, for example, a CMP (Chemical-Mechanical-Plenarization) technique, and as shown in FIG. 5D, a conductor material 24 other than the conductor material 24 in the recesses 23a and 23b. Remove. As a result, the movable conductor pattern 7 having the form of an embedded electrode (embedded conductor pattern) and the metal layer 18 are formed. Thereafter, as shown in FIG. 5E, an insulating layer 10 of SiO ₂ is formed on the surface of the movable conductor pattern 7.

  Thereafter, the portion of the active layer 14 other than the portions to be the movable portion 4, the fixed portion 5, and the beams 6a and 6b is removed by etching processing (RIE processing), and the movable portion 4 having a shape as shown in FIG. And the fixed part 5 and the beams 6a and 6b are formed. Then, only the portion of the insulating layer 13 bonded to the fixed portion 5 is left, and the other portions of the insulating layer 13 are removed by sacrificial layer etching using, for example, an HF aqueous solution. By removing the insulating layer 13, the movable portion 4 and the beams 6a and 6b are formed in a thin flat plate shape. Thereby, the beams 6a and 6b are easily bent and deformed. Further, as shown in FIG. 5 (f), the portions where the metal layer 18 is formed in the beams 6a and 6b are raised by the stress of the metal layer 18 having a larger expansion coefficient than Si forming the beams 6a and 6b. The curved portion 17 is formed by being curved and deformed into a convex shape. Further, the movable portion 4 is maintained in a flat state by being prevented from bending deformation by the insulating film 10 on the surface of the movable conductor pattern 7.

After the sacrificial layer etching process of the insulating layer 13, the surfaces of the movable portion 4, the beams 6a and 6b, and the driving fixed electrode 8 are oxidized using an oxidizing agent made of, for example, acid and hydrogen peroxide, to form SiO ₂ . Oxide layers 16 and 9 are formed. Then, it is dried by a hydrophobizing treatment using a silane coupling agent.

  On the other hand, fixed conductor patterns 3a and 3b are formed on the surface of a glass substrate 2 having a thickness of 400 μm, for example, as shown in FIG. The fixed conductor patterns 3a and 3b can be formed in the same manner as the movable conductor pattern 7 and the like. That is, as shown in FIG. 6B, the recesses 25 are formed in the respective portions to be the fixed conductor patterns 3a and 3b on the surface of the substrate 2 by, for example, etching, and thereafter, as shown in FIG. 6C. Then, a conductor material 26 such as copper, which is a constituent material of the fixed conductor patterns 3a and 3b, is formed on the entire surface of the substrate 2 by, for example, plating. Then, as shown in FIG. 6D, the surface of the substrate 2 is subjected to a surface flattening process by, for example, a CMP technique to remove the conductor material 26 other than the conductor material 26 in the recess 25. In this way, the fixed conductor patterns 3a and 3b having the form of embedded electrodes (embedded conductor patterns) are formed.

Thereafter, as shown in FIG. 6E, at least a portion of the surface of the substrate 2 to be joined to the fixing portion 5 and a portion where the fixed conductor pattern 3 is formed are left, and the other surface of the substrate 2 is left. A concave portion 27 is formed by digging the portion by etching to a depth of about 1 μm. After this etching step, an SiO ₂ insulating film 11 having a thickness of, for example, about 100 nm is formed on the entire surface of the substrate 2 using a sputtering means or the like.

  Thereafter, the fixing portion 5 shown in FIG. 5 (f) and the substrate 2 shown in FIG. 6 (e) are bonded by an anodic bonding method as shown in FIG. 7 (a). As a result, the movable portion 4 is locked to the fixed conductor patterns 3a and 3b via the insulating layer 10, and the tops of the curved portions 17 of the beams 6a and 6b are in contact with the driving fixed electrode 8, so that the driving fixed electrode The curved portion 17 is elastically deformed toward the substrate 2 by the pressing force from 8. Thereafter, as shown in FIG. 7B, the surface of the substrate 2 is ground and polished to reduce the thickness of the substrate 2 to about 100 μm, for example. Thereafter, each hole part constituting the external connection terminal corresponding to each of the fixed conductor patterns 3a and 3b, the movable conductor pattern 7 and the like is formed by, for example, sandblasting, and a conductor material is respectively placed in each hole part. Provide.

  Through the manufacturing process as described above, the variable capacitor 1 of the first embodiment can be manufactured.

  In the first embodiment, the movable part 4 is supported and fixed by the two beams 6a and 6b. For example, as shown in the schematic plan view of FIG. It is good also as a structure currently supported and fixed to the fixing | fixed part 5 by the four beams 6a-6d. As described above, the number of beams and the shapes of the beams that support and fix the movable portion are limited as long as the beams can be bent and deformed in the perspective direction with respect to the substrate and the movable portion can be displaced in the normal direction of the surface of the substrate. It is not a thing. However, the beam is provided with a material portion having a coefficient of expansion different from that of the constituent material of the beam, and a curved portion having a convex shape is formed on the substrate, and the top of the curved portion of the beam is located above the beam. The curved portion of the beam is elastically deformed by being brought into contact with the fixed electrode for driving in a pressed state.

  The second embodiment will be described below. In the description of the second embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and the duplicate description of the common portions is omitted.

  FIG. 9A is a schematic plan view showing main components of a shunt-type switch element that is an electrostatic drive element according to the second embodiment, and FIG. A schematic cross-sectional view of the switch element corresponding to the A-A position is shown. In the switch element 30 of the second embodiment, three fixed conductor patterns 3s, 3g1, and 3g2 are formed on the surface side of the substrate 2. The fixed conductor patterns 3s, 3g1, and 3g2 constitute a coplanar line (CPW line), and the fixed conductor pattern 3s is a signal line (line pattern) for high-frequency signal conduction of, for example, 5 GHz or more. The fixed conductor patterns 3g1 and 3g2 arranged in such a manner as to sandwich the pattern 3s with an interval are formed as a ground line (line pattern).

  The movable part 4 is arranged above the fixed conductor patterns 3s, 3g1, 3g2, and the movable conductor pattern 7 is formed on the surface of the movable part 4 on the fixed conductor patterns 3s, 3g1, 3g2 side. The position and size of the movable conductor pattern 7 are set so as to face the three fixed conductor patterns 3s, 3g1, and 3g2 in common.

  The rest of the configuration of the switch element 30 of the second embodiment is the same as that of the variable capacitance element 1 that is an electrostatic drive element of the first embodiment, and the first embodiment is also the first embodiment. Similarly to the embodiment, each of the beams 6 a and 6 b is provided with a metal layer 18, and a curved portion 17 having a convex shape with respect to the substrate 2 is provided by the metal layer 18. The convex top of the curved portion 17 is in contact with the driving fixed electrode 8, and the curved portion 17 is disposed in an elastically deformed state on the substrate 2 side.

  The switch element 30 of the second embodiment is connected to the voltage applying means 20 shown in FIG. 9B and is packaged to constitute an electrostatic drive device. As shown in FIG. 9B, when the switch means 22 of the voltage application means 20 is in an off state and no electrostatic attractive force is generated between the movable part 4 and the driving fixed electrode 8, the beams 6a, The movable portion 4 is displaced to the substrate 2 side by the elastic force of the curved portion 17 of 6b, and the distance between the fixed conductor patterns 3s, 3g1, 3g2 and the movable conductor pattern 7 becomes very narrow, and the fixed conductor patterns 3s, 3g1. , 3g2 and the movable conductor pattern 7 increase in capacitance. In this state, the signal line 3s is equivalent to a state where the signal line 3s is short-circuited to the ground lines 3g1 and 3g2 via the movable conductor pattern 7. For this reason, the high-frequency signal conducted through the signal line 3s is reflected at the position of the signal line 3s facing the movable conductor pattern 7, and the conduction of the high-frequency signal through the signal line 3s (CPW line) is turned off. Become. When the switch means 22 is turned on and an electrostatic attractive force is generated between the movable part 4 and the driving fixed electrode 8, the moving part 4 moves away from the substrate 2 side (approaching the driving fixed electrode 8). Direction) to increase the distance between the fixed conductor patterns 3s, 3g1, 3g2 and the movable conductor pattern 7, and the capacitance between the fixed conductor patterns 3s, 3g1, 3g2 and the movable conductor pattern 7 is reduced. . In this state, when the ground lines 3g1 and 3g2 are viewed from the signal line 3s through the movable conductor pattern 7, this is equivalent to open. For this reason, the conduction of the high-frequency signal of the signal line 3s is turned on. Thus, between the movable conductor pattern 7 and the fixed conductor patterns 3s, 3g1, and 3g2 due to the wide and narrow spaces between the movable conductor pattern 7 and the fixed conductor patterns 3s, 3g1, and 3g2 by driving (displacement) of the movable part 4 as described above. The conduction on / off of the high-frequency signal of the signal line 3s is controlled by the magnitude of the electrostatic capacity of the signal line 3s.

  The third embodiment will be described below. In the description of the third embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and overlapping description of common portions is omitted.

  FIG. 10A is a schematic plan view showing main components of a contact-type switch element that is an electrostatic drive element of the third embodiment, and FIG. ) Is a schematic cross-sectional view of the switch element corresponding to the A-A position. In the switch element 31 of the third embodiment, the fixed conductor patterns 3a and 3b constitute a microstrip line, and are arranged in a state where one end sides face each other with a gap therebetween. In the third embodiment, the insulating film 11 on the fixed conductor patterns 3a and 3b shown in the first embodiment is omitted. Further, instead of the insulating film 10 on the movable conductor pattern 7, On the movable conductor pattern 7, a conductor film 32 such as gold (Au) is formed as a buffer member. The other configuration of the switch element 31 of the third embodiment is the same as that of the capacitance variable element 1 that is an electrostatic drive element of the first embodiment. Also in this third embodiment, each beam 6a. , 6b has a curved portion 17 in which a metal layer 18 is formed and is curved and deformed upwardly with respect to the substrate 2 by the metal layer 18. The top of the curved portion 17 abuts against the driving fixed electrode 8 and the curved portion 17 is arranged in a state of being elastically deformed toward the substrate 2 by the pressing force from the driving fixed electrode 8.

  The switch element 31 of the third embodiment is connected to the voltage applying means 20 shown in FIG. 10B and is packaged to form an electrostatic drive device. When the switch means 22 of the voltage application means 20 is in an OFF state and no electrostatic attractive force is generated between the movable part 4 and the driving fixed electrode 8, the movable part 4 is moved by the elastic force of the curved portions 17 of the beams 6a and 6b. Displaced to the substrate 2 side, the movable conductor pattern 7 is electrically connected directly to both the fixed conductor patterns 3a and 3b via the conductor film 32 (becomes in contact). As a result, the fixed conductor patterns 3 a and 3 b become conductive via the movable conductor pattern 7. When the switch means 22 is turned on and an electrostatic attractive force is generated between the movable portion 4 and the driving fixed electrode 8, the direction in which the movable portion 4 is separated from the substrate 2 by the electrostatic attractive force (fixing for driving). The movable conductor pattern 7 moves away from the fixed conductor patterns 3a and 3b (becomes a non-contact state). Thereby, the signal conduction between the fixed conductor patterns 3a and 3b is turned off.

  As described above, the movable conductor pattern 7 and the fixed conductor patterns 3a and 3b are in contact with each other or are not in contact with each other by driving (displacement) of the movable portion 4 that changes the distance between the movable conductor pattern 7 and the fixed conductor patterns 3a and 3b. A contact state is established, and signal conduction between the fixed conductor patterns 3a and 3b is controlled.

  In addition, this invention is not limited to the form of each 1st-3rd embodiment, Various embodiments can be taken. For example, in each of the first to third embodiments, the metal layer 18 having a larger expansion coefficient than Si, which is a constituent material of the beams 6a and 6b, is formed on the substrate 2 side of the M region of the beams 6a and 6b. Thus, the convex curved portion 17 is formed on the substrate 2. For example, on the driving fixed electrode 8 side of the M region of the beams 6 a and 6 b, the constituent materials of the beams 6 a and 6 b are used. Alternatively, for example, an oxide layer having a small expansion coefficient may be formed, and the convex curved portion 17 may be formed on the substrate 2 by the stress of the oxide layer.

  Further, for example, in each of the first to third embodiments, the curved portions 17 of the beams 6a and 6b are convex upward with respect to the substrate 2. For example, FIG. As described above, the curved portion 17 may have a convex shape (a shape bulging and deformed toward the substrate side) with respect to the substrate 2, and the top of the convex curved portion 17 is pressed against the substrate 2 below the curved portion 17. The curved portion 17 may be disposed in an elastically deformed state. Under the convex curved portion 17, an insulating layer (material portion) 33 such as an oxide layer having a smaller expansion coefficient than Si, which is a constituent material of the beams 6a and 6b, is formed on the substrate 2 side of the beams 6a and 6b. The insulating layer 33 can be formed by the stress. Alternatively, the downwardly convex curved portion 17 forms a metal layer (material portion) having a larger expansion coefficient than the constituent material (Si) of the beams 6a and 6b on the driving fixed electrode 8 side of the beams 6a and 6b. It can be formed by the stress of the metal layer.

  When the curved portion 17 is convex downward with respect to the substrate 2, a DC voltage is applied between the fixed conductor patterns 3 a and 3 b and the movable conductor pattern 7 by the voltage applying means 20 to drive the movable portion 4 to be displaced. Let That is, when the switch means 22 of the voltage applying means 20 is in the OFF state, no DC voltage is applied between the fixed conductor patterns 3a and 3b and the movable conductor pattern 7, and between the fixed conductor patterns 3a and 3b and the movable conductor pattern 7 No electrostatic attraction occurs. At this time, the movable portion 4 is in a state of being pressed and locked to the driving fixed electrode 8 by the elastic force of the curved portions 17 of the beams 6a and 6b. When the switch means 22 is turned on, a DC voltage based on the voltage source 21 is applied between the fixed conductor patterns 3 a and 3 b and the movable conductor pattern 7, and between the fixed conductor patterns 3 a and 3 b and the movable conductor pattern 7. Electrostatic attraction occurs. Due to this electrostatic attraction, the movable portion 4 is displaced toward the substrate 2 with a contact portion between the top of the curved portion 17 of the beams 6a and 6b and the substrate 2 as a fulcrum. Thereby, the space | interval between fixed conductor pattern 3a, 3b and the movable conductor pattern 7 becomes narrow. As described above, the distance between the fixed conductor patterns 3a and 3b and the movable conductor pattern 7 changes widely, and the capacitance between the fixed conductor patterns 3a and 3b and the movable conductor pattern 7 changes to a large or small value.

  In the switch elements 30 and 31 of the second and third embodiments, the movable portion 4 is supported and fixed to the fixed portion 5 by the two beams 6a and 6b. As shown in FIG. 8, the movable part 4 is also supported and fixed to the fixed part 5 by four beams 6a to 6d, as shown in FIG. Also good. Thus, the number and shape of the beams are not limited to the configuration shown in the drawing.

  Furthermore, although the electrostatic drive element of each of the first to third embodiments is provided with only one variable capacitance element or switch element, for example, each of the first to third embodiments. An electrostatic drive element having a configuration in which a plurality of variable capacitance elements 1 or switch elements 30 and 31 as shown in the example are provided in an array with a common substrate 2 and spaced from each other may be used. Moreover, you may comprise the electrostatic drive device which has an array-shaped electrostatic drive element.

It is a figure for demonstrating the electrostatic drive element (variable capacitive element) of the example of 1st Embodiment. FIG. 2 is a schematic exploded view of the electrostatic driving element shown in FIG. 1. It is a figure for demonstrating the operation example of the electrostatic drive element shown by FIG. It is a figure of the equivalent circuit which the electrostatic drive element shown by FIG. 1 has. It is a figure for demonstrating an example of the manufacturing process of the electrostatic drive element shown by FIG. FIG. 6 is a diagram for explaining an example of a manufacturing process of the electrostatic drive element of FIG. 1 following FIG. 5. FIG. 7 is a diagram for explaining an example of a manufacturing process of the electrostatic drive element of FIG. 1 following FIG. 6. It is a figure for demonstrating the other example of a form of the beam which supports a movable part. It is a figure for demonstrating the electrostatic drive element (switch element) of the example of 2nd Embodiment. It is a figure for demonstrating the electrostatic drive element (switch element) of the example of 3rd Embodiment. It is a figure for demonstrating other example embodiments. It is a figure for demonstrating one example of an electrostatic drive element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Variable capacitance element 2 Board | substrate 3 Fixed conductor pattern 4 Movable part 5 Fixed part 6 Beam 7 Movable conductor pattern 8 Driving fixed electrode 10 Insulating film 17 Curved part 18 Metal layer 30, 31 Switch element 33 Insulating layer

Claims (5)

A substrate,
A fixed conductor pattern formed on the surface of the substrate;
A fixed portion fixed to the surface of the substrate;
A beam having one end connected to the fixed portion;
A movable part connected to the other end of the beam and arranged to face the substrate;
A movable conductor pattern formed on the substrate-side surface of the movable portion and facing the fixed conductor pattern;
A material part having an expansion coefficient different from that of the beam in order to make the shape of the beam formed on the beam convex upward with respect to the substrate;
A driving fixed electrode that presses the convex top of the beam;
Have
Due to the generation of electrostatic attraction by applying a voltage between the driving fixed electrode and the movable part, the movable part is displaced in a direction approaching the driving fixed electrode with the convex top of the beam as a fulcrum. An electrostatic driving element characterized in that a distance between a conductor pattern and the fixed conductor pattern changes in a direction in which the distance increases. A substrate,
A fixed conductor pattern formed on the surface of the substrate;
A fixed portion fixed to the surface of the substrate;
A beam having one end connected to the fixed portion;
A movable part connected to the other end of the beam and arranged to face the substrate;
A movable conductor pattern formed on the substrate-side surface of the movable portion and facing the fixed conductor pattern;
A material part having an expansion coefficient different from that of the beam in order to make the shape of the beam formed on the beam convex downward with respect to the substrate;
Have
The convex top of the beam is configured to be in contact with the substrate in a pressed state,
Due to the generation of electrostatic attraction by applying a voltage between the movable conductor pattern and the fixed conductor pattern, the movable portion is displaced in a direction approaching the substrate with the convex top of the beam as a fulcrum, and the movable conductor pattern and The electrostatic drive element according to claim 1, wherein a distance between the fixed conductor pattern and the fixed conductor pattern changes in a narrowing direction.   The electrostatic drive element according to claim 1, wherein an insulating film is formed on a surface of the movable conductor pattern. The electrostatic driving element according to claim 1 or 3,
Voltage application means for applying a voltage between the fixed electrode for driving the electrostatic drive element and the movable part;
Have
The fixed conductor pattern of the electrostatic drive element is a line pattern through which a high-frequency signal is conducted, and the on / off of the high-frequency signal of the fixed conductor pattern is controlled by the size of the capacitance between the fixed conductor pattern and the movable conductor pattern. An electrostatic drive device characterized by being made. The electrostatic driving element according to claim 2 or 3,
Voltage applying means for applying a voltage between the movable conductor pattern and the fixed conductor pattern of the electrostatic drive element;
Have
The fixed conductor pattern of the electrostatic drive element is a line pattern through which a high-frequency signal is conducted, and the on / off of the high-frequency signal of the fixed conductor pattern is controlled by the size of the capacitance between the fixed conductor pattern and the movable conductor pattern. An electrostatic drive device characterized by being made.

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