JP2013090442A - Electrostatic drive type actuator, variable capacitance element and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrostatic drive type actuator and a variable capacitance element capable of suppressing occurrence of a sticking phenomenon, and a method of manufacturing the same with high yield and high form accuracy.SOLUTION: In a variable capacitance element 1, a movable beam 3 faces a fixed plate 2, movable beam side drive capacitance electrodes 8A, 8B and a movable beam side RF capacitance electrode 9 are provided in the movable beam 3, fixed plate side drive capacitance electrodes 5A, 5B are provided in the fixed plate 2 so as to face the movable beam side drive capacitance electrodes 8A, 8B, the fixed plate side RF capacitance electrodes 6A, 6B are provided in the fixed plate 2 so as to face the movable beam side RF capacitance electrode 9, a dielectric film 4 is formed so as to cover the fixed plate side drive capacitance electrodes 5A, 5B and the fixed plate side RF capacitance electrodes 6A, 6B and the movable beam 3 is configured so that its tip is bent to a side of the fixed plate 2 in the initial state.

Description

  The present invention can continuously change an RF (Radio Frequency) capacity using an electrostatic drive actuator that is driven by electrostatic force using MEMS (Micro Electro Mechanical Systems) and the electrostatic drive actuator. The present invention relates to a variable capacitance element and a manufacturing method thereof.

  An electrostatic drive type actuator may be employed in various devices (see, for example, Patent Document 1).

FIG. 1A is a diagram illustrating a configuration example of a switch element 101 that employs an electrostatic drive actuator.
The illustrated switch element 101 includes a fixed portion 102, a movable portion 103, a contact electrode 104, a drive capacitance electrode 105, and a stopper 106. The fixing part 102 is a substrate. The movable portion 103 is a metal cantilever, and includes a fixed end portion 103A fixed to the fixed portion 102 and a movable end portion 103B facing the main surface of the fixed portion 102 at a constant interval. The contact electrode 104, the drive capacitance electrode 105, and the stopper 106 are provided to face the movable end portion 103B. In this switch element 101, the drive voltage is applied between the drive capacitance electrode 105 and the movable portion 103, so that the movable portion 103 is deformed, the movable end portion 103 </ b> B contacts the contact electrode 104, and the movable portion 103 An electrical contact with the contact electrode 104 is obtained.

  In addition, as a device using such an electrostatic drive actuator, a variable capacitance element has been developed in which the RF capacitance can be continuously controlled.

  FIG. 1B is a diagram illustrating a configuration example of a variable capacitance element 201 that employs an electrostatic drive type actuator.

The illustrated variable capacitor 201 includes a fixed portion 202, a movable portion 203, a fixed portion-side RF capacitor electrode 204, a movable portion-side RF capacitor electrode 205, a dielectric film 206, and a fixed portion-side drive capacitor electrode (not fixed). And a movable portion side drive capacitance electrode (not shown). The fixing part 202 is a substrate. The movable portion 203 is a cantilever made of an insulating material, and includes a fixed end portion 203A fixed to the fixed portion 202 and a movable end portion 203B facing the main surface of the fixed portion 202 at a predetermined interval. . The movable part side RF capacitance electrode 205 is provided on the surface of the movable end 203B facing the fixed part 202. The fixed part side RF capacitive electrode 204 is provided so as to face the movable end part 203 </ b> B and the movable part side RF capacitive electrode 205. The movable portion side drive capacitance electrode (not shown) is provided on the surface of the movable end portion 203B facing the fixed portion 202 so as to be adjacent to the movable portion side RF capacitance electrode 205. The fixed portion side drive capacitance electrode (not shown) is provided so as to face the movable end portion 203B and the movable portion side drive capacitance electrode. Note that the fixed portion side drive capacitance electrode and the movable portion side drive capacitance electrode are not shown in FIG. The dielectric film 206 is provided so as to cover the fixed portion side RF capacitor electrode 204 and the fixed portion side drive capacitor electrode (not shown).
In this variable capacitance element 201, the movable portion 203 is displaced by the drive capacitance generated by applying a drive voltage between the fixed portion side drive capacitance electrode and the movable portion side drive capacitance electrode, and the movable portion side RF capacitance electrode 205 is displaced. Contacts the dielectric film 206. The contact area between the movable part side RF capacitive electrode 205 and the dielectric film 206 changes according to the driving voltage, and the fixed part side RF capacitive electrode 204 and the movable part side RF capacitive electrode 205 that face each other through the dielectric film 206. In the meantime, an RF capacitance having a capacitance value corresponding to the contact area between the movable portion side RF capacitance electrode 205 and the dielectric film 206 is generated. In the variable capacitance device 201, the dielectric film 206 is made of a material having a high dielectric constant and is formed with a very thin film thickness.

JP 2009-152194 A

  In a variable capacitance element employing an electrostatic drive type actuator, the movable part is displaced by the application of a drive voltage, and both surfaces of the dielectric film are in contact with the electrodes. In this state, electrons move between the surface of the dielectric film and the electrode, and the surface of the dielectric film is charged (hereinafter, this phenomenon is referred to as charge-up). The charging due to the charge-up continues even if the application of the drive voltage is stopped. If the amount of charge due to the charge-up is large, a sticking phenomenon in which the movable part sticks to the fixed part even if the application of the drive voltage is stopped is caused. . Then, it becomes difficult to control the movable part with the drive voltage, and even if the application of the drive voltage is stopped, the RF capacity cannot be lowered to the lower limit value.

  Therefore, the present invention realizes an electrostatic drive type actuator and variable capacitance element that can suppress the occurrence of sticking phenomenon, and produces these electrostatic drive type actuators and variable capacitance elements with high yield and high shape accuracy. The purpose is to do.

The electrostatic drive actuator according to the present invention includes a fixed plate, a movable beam, a movable beam side electrode, a fixed plate side electrode, and a dielectric film. The movable beam is provided to face the fixed plate at an interval. The movable beam side electrode is provided on the movable beam. The fixed plate side electrode is provided on the fixed plate so as to face the movable beam side electrode. The dielectric film is disposed between the movable beam side electrode and the fixed plate side electrode. In the initial state, the movable beam is convex on the side opposite to the fixed plate side.
The electrostatic drive actuator according to the present invention includes a fixed plate, a movable beam, a movable beam side electrode, a fixed plate side electrode, and a dielectric film, and the movable beam is fixed in the initial state. The tip is configured to bend toward the plate side.

The variable capacitor according to the present invention includes a fixed plate, a movable beam, a drive capacitor, and an RF capacitor. The drive capacitor unit is fixed to the movable beam side drive capacitance electrode provided on the movable beam, the fixed plate side drive capacitance electrode provided on the fixed plate so as to face the movable beam side drive capacitance electrode, and the movable beam side drive capacitance electrode. It consists of a dielectric film formed between the plate-side drive capacitance electrode, and deforms the movable beam based on the drive capacitance generated between the movable beam-side drive capacitance electrode and the fixed plate-side drive capacitance electrode. The RF capacitor unit includes a movable beam-side RF capacitive electrode provided on the movable beam, a fixed plate-side RF capacitive electrode provided on the fixed plate so as to face the movable beam-side RF capacitive electrode, and the movable beam-side RF capacitive electrode. It consists of a dielectric film formed between the plate-side RF capacitor electrodes. In the initial state, the movable beam is convex on the side opposite to the fixed plate side.
In addition, the variable capacitance element according to the present invention includes a fixed plate, a movable beam, a drive capacitance portion, and an RF capacitance portion, and the tip of the movable beam is bent toward the fixed plate in the initial state. It is configured.

  When the movable beam is configured so that the tip is bent toward the fixed plate in the initial state, when the drive capacity is increased, the first region close to the fixed plate (hereinafter referred to as the initial proximity region). In order to make it close to the fixed plate, it is necessary to deform the initial proximity region into a convex shape with respect to the fixed plate side. The electrostatic attractive force required to deform the initial proximity region convexly with respect to the fixed plate side is small when the movable beam is configured so that the tip does not bend toward the fixed plate in the initial state. When the movable beam is configured such that the tip is bent toward the fixed plate in the initial state, the size becomes large. Even when the dielectric film charge-up causes a sticking phenomenon, the initial proximity region is deformed into a convex shape, but the movable beam is configured so that the tip is bent toward the fixed plate in the initial state. In the variable capacitance element, the initial proximity region cannot be deformed into a convex shape unless the electrostatic attraction and charge amount due to the charge-up of the dielectric film are considerably large. Therefore, with this configuration, the occurrence of the sticking phenomenon can be suppressed.

In the above-described variable capacitance element, it is preferable that at least one of the movable beam side drive capacitance electrode and the movable beam side RF capacitance electrode is a compressive stress layer. In the above-described variable capacitance element, it is preferable that the movable beam is provided with a tensile stress film on the surface opposite to the surface facing the fixed plate.
In these configurations, it is easy to make the movable beam in a state where the tip is bent toward the fixed plate in the initial state.

In the above-described variable capacitance element, it is preferable that the dielectric film includes a thin portion and a protruding portion that locally protrudes.
By configuring the dielectric film to have a thin part and a protruding part as in this configuration, the contact area between the electrode on the movable beam side and the dielectric film is reduced. The amount of electrification caused by the decrease can be reduced, and the sticking phenomenon of the movable beam can be prevented more reliably.

  The manufacturing method of the electrostatic drive actuator and the manufacturing method of the variable capacitance element according to the present invention includes a film forming step of forming a metal film forming the movable beam side electrode on a substrate forming the movable beam by a sputtering method. In the film formation process, the substrate deflection is recognized by irradiating the substrate with laser light and detecting the light receiving angle of the laser reflected light reflected by the substrate, and the sputtering conditions are controlled based on the substrate deflection. The metal film is formed as a compressive stress film.

  By this method, it is possible to produce an electrostatic drive actuator or variable capacitance element whose tip is bent toward the fixed plate in the initial state with a high yield and high shape accuracy.

  According to the configuration of the present invention, it is possible to realize an electrostatic drive type actuator and a variable capacitance element that can suppress the occurrence of the sticking phenomenon, and to obtain these electrostatic drive type actuators and variable capacitance elements with high yield and high shape accuracy. Can be produced.

It is a figure explaining the structural example of the device using the conventional electrostatic drive type actuator. It is a figure explaining the structure of the variable capacitance element which concerns on the 1st Embodiment of this invention. It is a top view in the state where the variable capacity element concerning a 1st embodiment of the present invention was disassembled. It is sectional drawing of the variable capacitance element which concerns on the 1st Embodiment of this invention. It is a figure explaining the deformation | transformation aspect of the movable beam in the variable capacitance element which concerns on the 1st Embodiment of this invention. It is a figure explaining the relationship between the drive voltage of the variable capacitance element which concerns on the Example of the 1st Embodiment of this invention, and RF capacity | capacitance. It is a figure explaining the relationship between the drive voltage and RF capacity | capacitance of the variable capacitance element which concerns on a comparative example. It is a figure explaining the film-forming process of the metal film of the variable capacitance element which concerns on the 1st Embodiment of this invention. It is a figure explaining the structure of the variable capacitance element which concerns on the 2nd Embodiment of this invention. It is a figure explaining the structure of the variable capacitance element which concerns on the 3rd Embodiment of this invention. It is a figure explaining the structure of the variable capacitance element which concerns on the 4th Embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In each figure, an orthogonal coordinate XYZ axis is attached, the thickness direction of the movable beam is the Z-axis direction, the beam length direction is the X-axis direction, and the beam width direction is the Y-axis direction.

<< First Embodiment >>
First, the electrostatic drive actuator according to the first embodiment of the present invention will be described taking a variable capacitance element as an example.

  FIG. 2A is a plan view (XY plane plan view) of the variable capacitance element 1 according to the first embodiment of the present invention.

As shown in FIG. 2, the variable capacitance element 1 includes a fixed plate 2, a movable beam 3, and a dielectric film 4.
The fixed plate 2 is made of, for example, a glass substrate and is configured in a rectangular shape in plan view. The fixing plate 2 may be made of another insulating substrate such as a silicon single crystal substrate.
The dielectric film 4 is formed on the upper surface (the surface in the positive Z-axis direction) of the fixed plate 2 in a rectangular shape smaller than the fixed plate 2 in plan view. The dielectric film 4 is a thin film having a high dielectric constant such as tantalum pentoxide.

The movable beam 3 has a cantilever structure supported by the fixed plate 2 at one end, and includes a support portion 3A, a connecting portion 3B, and a movable portion 3C. The movable beam 3 is made of an insulating substrate such as a high resistance silicon substrate or a conductive substrate. Moreover, the movable beam 3 may not be a cantilever structure, but may be a cantilever structure supported by the fixed plate 2 at both ends.
The support portion 3 </ b> A has a rectangular shape that is long in the Y-axis direction in plan view, and is erected in the positive direction of the Z-axis from the upper surface of the fixed plate 2. 3 A of support parts are provided in the X-axis negative direction edge part of the movable beam 3. As shown in FIG.
Each of the connecting portions 3B has a meander line shape meandering with respect to the X axis in plan view, and is erected in the X axis positive direction from both ends of the supporting portion 3A in the Y axis direction.
The movable portion 3 </ b> C has a flat plate shape that is long in the X-axis direction in plan view, and is provided at the end portion of the movable beam 3 in the X-axis positive direction. The movable portion 3 </ b> C has an outer peripheral portion located inside the outer peripheral portion of the dielectric film 4. 3 C of movable parts are connected with the connection part 3B by the edge part of the X-axis negative direction.
The connecting portion 3B and the movable portion 3C are supported by the support portion 3A in a state of being separated from the fixed plate 2 and the dielectric film 4.

  The movable portion 3C includes two divided areas 3D1 and 3D2 and three partition areas 3E1, 3E2, and 3E3. The divided areas 3D1 and 3D2 are areas in which a plurality of through holes are arranged along the X axis. The partitioned areas 3E1, 3E2, and 3E3 are long areas along the X-axis direction partitioned by the divided areas 3D1 and 3D2.

FIG. 2B is an exploded plan view (XY plane plan view) of the variable capacitance element 1 with the movable beam 3 removed.
The dielectric film 4 includes a thin portion 4A configured to be thinner than a region on the X axis negative direction side on the X axis positive direction side. In addition, the dielectric film 4 includes a columnar protrusion 4B that locally protrudes from the periphery in a region facing the above-described partition regions 3E1, 3E2, and 3E3 in the thin portion 4A. The thin wall portion 4A and the protruding portion 4B are provided to reduce the contact area between the electrode on the movable beam 3 described later and the dielectric film 4. By reducing the contact area, the charge amount due to the charge-up of the dielectric film 4 is reduced, and the sticking phenomenon of the movable beam 3 can be suppressed.

FIG. 3A is an exploded plan view (XY plane plan view) of the variable capacitance element 1 with the movable beam 3 and the dielectric film 4 removed.
As shown in FIG. 3A, the variable capacitance element 1 includes fixed plate side drive capacitance electrodes 5A and 5B and fixed plate side RF capacitance electrodes 6A and 6B. The fixed plate side drive capacitance electrodes 5A and 5B and the fixed plate side RF capacitance electrodes 6A and 6B are formed on the upper surface of the fixed plate 2, respectively.

The fixed plate side drive capacitance electrodes 5A and 5B and the fixed plate side RF capacitance electrodes 6A and 6B are line-shaped electrodes that are long in the X-axis direction, and are arranged in the Y-axis direction. The fixed plate side drive capacitance electrodes 5A and 5B and the fixed plate side RF capacitance electrodes 6A and 6B may be configured as, for example, a single layer electrode of a metal layer made of Cr, Pt, Au, or the like, or a laminated electrode thereof.
The fixed plate side drive capacitance electrodes 5A and 5B are provided in regions facing the partition regions 3E1 and 3E3, and one end thereof is connected to the drive voltage terminal DC. The fixed plate side drive capacitance electrodes 5A and 5B are provided on both sides of the fixed plate side RF capacitance electrodes 6A and 6B in the Y-axis direction.
The fixed plate side RF capacitive electrodes 6A and 6B are provided in a region facing the partition region 3E2, and one end of the fixed plate side RF capacitive electrode 6A is connected to an RF signal input terminal (or output terminal). One end of the fixed plate side RF capacitor electrode 6B is connected to an output terminal (or input terminal) of an RF signal. The fixed plate side RF capacitive electrodes 6A and 6B are provided between the fixed plate side drive capacitive electrodes 5A and 5B. The dielectric film 4 is formed so as to cover the fixed plate side drive capacitance electrodes 5A and 5B and the fixed plate side RF capacitance electrodes 6A and 6B.

FIG. 3B is an exploded plan view (XY plane plan view) of the variable capacitance element 1 with the movable beam 3 turned upside down except for the fixed plate 2 and the dielectric film 4.
As shown in FIG. 3B, the variable capacitance element 1 includes movable beam side drive capacitance electrodes 8A and 8B and a movable beam side RF capacitance electrode 9. The movable beam side drive capacitance electrodes 8A and 8B and the movable beam side RF capacitance electrode 9 are formed on the lower surface of the movable beam 3, respectively. The movable beam side drive capacitance electrodes 8A and 8B and the movable beam side RF capacitance electrode 9 are line-like electrodes that are long in the X-axis direction, and are arranged in the Y-axis direction.

The movable beam side drive capacitance electrodes 8A and 8B are provided on both sides of the movable beam side RF capacitance electrode 9 in the Y-axis direction. The movable beam side drive capacitance electrode 8A is provided in the partition region 3E1 so as to face the fixed plate side drive capacitance electrode 5A and the dielectric film 4, and one end thereof is connected to the ground terminal GND. The movable beam side drive capacitance electrode 8B is provided in the partition region 3E3 so as to face the fixed plate side drive capacitance electrode 5B and the dielectric film 4, and one end thereof is connected to the ground terminal GND.
The movable beam side RF capacitive electrode 9 is provided between the movable beam side drive capacitive electrodes 8A and 8B. Specifically, the movable beam side RF capacitive electrode 9 is provided in the partition region 3E2 so as to face the fixed plate side RF capacitive electrodes 6A and 6B and the dielectric film 4.

  These movable beam side drive capacitive electrodes 8A and 8B and movable beam side RF capacitive electrode 9 are, for example, a single layer electrode of a metal layer made of tungsten or molybdenum, or a titanium / tungsten alloy layer on an underlayer made of tungsten. A laminated electrode provided may be configured.

  4A is a cross-sectional view (YZ plane cross-sectional view) of the variable capacitance element 1 at a position indicated by A-A ′ in FIG. 2.

  The movable beam side drive capacitance electrodes 8A and 8B are opposed to the fixed plate side drive capacitance electrodes 5A and 5B and the dielectric film 4, respectively. The movable beam side drive capacitance electrode 8 </ b> A constitutes a drive capacitance section together with the opposing region of the fixed plate side drive capacitance electrode 5 </ b> A and the dielectric film 4. The movable beam side drive capacitance electrode 8B constitutes a drive capacitance section together with the opposing region of the fixed plate side drive capacitance electrode 5B and the dielectric film 4. When a drive voltage (DC voltage) is applied from the drive voltage terminal DC to the fixed plate side drive capacitance electrodes 5A and 5B, an electrostatic attractive force is generated in the drive capacitance section. The drive capacitor unit functions as a drive capacitor that attracts the movable beam 3 to the fixed plate 2 side by the electrostatic attractive force and brings the movable beam 3 into contact with the dielectric film 4 from the tip (end on the X axis positive direction side). The higher the drive voltage, the larger the contact area between the movable beam 3 and the dielectric film 4.

  The movable beam side RF capacitive electrode 9 faces the fixed plate side RF capacitive electrodes 6A and 6B and the dielectric film 4. The movable beam-side RF capacitive electrode 9 constitutes an RF capacitive portion together with the opposed regions of the fixed plate-side RF capacitive electrodes 6A and 6B and the dielectric film 4. The RF capacitor portion is formed between the movable beam side RF capacitor electrode 9 and the fixed plate side RF capacitor electrodes 6A and 6B, and the size of the capacitance changes according to the contact area between the movable beam 3 and the dielectric film 4. Functions as an RF capacitor.

  In addition, since the drive capacity unit is connected in parallel between the drive voltage terminal DC and the ground terminal GND, the electrostatic attraction per unit area is larger than the configuration in which both are connected in series, compared to the case where both are connected in series. Is also advantageous in reducing the electrode area. On the other hand, since the RF capacitor is connected in series between the input terminal and the output terminal of the RF signal, the electrostatic attraction per unit area is smaller than the configuration in which both are connected in parallel, and compared to the case where both are connected in parallel. Is also advantageous in suppressing the deformation (self-activation) of the movable beam 3 by the RF signal.

  4B is a cross-sectional view (XZ plane cross-sectional view) of the variable capacitance element 1 at a position indicated by B-B ′ in FIG. 2.

  The movable beam side drive capacitive electrodes 8A and 8B and the movable beam side RF capacitive electrode 9 are configured to be compressive stress layers. In other words, the movable beam 3 has its distal end (end on the X-axis positive direction side) bent toward the fixed plate 2 in a state where the driving voltage is not applied (initial state) due to the compressive stress of the compressive stress layer. It is configured as follows. In other words, the movable beam 3 protrudes on the opposite side to the fixed plate 2 side in the state where the driving voltage is not applied (initial state), and the tip of the movable part 3C (the end part on the X axis positive direction side) The distance between the fixed plate 2 and the fixed plate 2 is shorter than the distance between the fixed plate 2 and the connecting portion of the movable portion 3C with the connecting portion 3B.

  FIG. 5 is a diagram for explaining a deformation mode of the movable beam 3 in the variable capacitance element 1.

  The drive voltage applied from the drive voltage terminal DC to the fixed plate side drive capacitance electrodes 5A and 5B is increased from 0V, and between the fixed plate side drive capacitance electrodes 5A and 5B and the movable beam side drive capacitance electrodes 8A and 8B. When the drive capacity formed on the movable plate 3 is increased, the movable beam 3 is attracted to the fixed plate 2 side by electrostatic attraction, the bending of the movable beam 3 at the connecting portion 3B increases, and the movable portion 3C is moved to the tip (X axis). The dielectric film 4 approaches from the positive direction end. Then, as shown in FIG. 5A, the movable beam side drive capacitance electrodes 8 A and 8 B (not shown) and the movable beam side RF capacitance electrode 9 are in contact with the protrusion 4 B of the dielectric film 4.

  As the drive capacity is further increased, the bending of the movable portion 3C of the movable beam 3 increases, and the movable portion 3C deforms into a convex shape with respect to the fixed plate 2 side, as shown in FIG. The movable beam 3 approaches the fixed plate 2 so that the vicinity of the tip (end on the X axis positive direction side) of the movable beam 3 is parallel to the fixed plate 2. Note that the first area close to the fixing plate 2 in parallel is the initial proximity area. In this embodiment, the thin portion 4A is provided in the area of the dielectric film 4 that coincides with the initial proximity area.

  As the driving voltage is further increased, the bending of the movable portion 3C of the movable beam 3 is further increased, and the movable beam side RF capacitive electrode 9 is in contact with the dielectric film 4 as shown in FIG. As the capacity expands, the variable capacity increases.

  In the variable capacitance element 1 having such a deformation mode, the electrostatic attraction necessary for changing from the state of the movable beam 3 shown in FIG. 5A to the state of the movable beam 3 shown in FIG. Big. This indicates that the sticking phenomenon hardly occurs even when an electrostatic attractive force due to the charge-up of the dielectric film 4 acts.

  FIG. 6 is a diagram for explaining the relationship between the driving voltage of the variable capacitance element 11 and the RF capacitance according to an example of the present embodiment. FIG. 7 is a diagram for explaining the relationship between the drive voltage and the RF capacitance of the variable capacitance element 111 according to the comparative example.

The variable capacitance element 11 shown in FIG. 6 is configured to include a dielectric film 14 having a flat surface. Other configurations are the same as those of the variable capacitance element 1 of the present embodiment. The variable capacitance element 11 has a distance between the tip of the movable portion 3C (end on the X axis positive direction side) and the fixed plate 2 of about 400 nm in a state where no drive voltage is applied (initial state), The distance between the connecting part of the movable part 3C and the connecting part 3B and the fixed plate 2 is about 600 nm.
In this variable capacitance element 11, when the drive voltage is increased from 0V and the drive capacitance is increased, the drive voltage is about 2V and the state shown in FIG. The state shown in FIG. When this drive voltage was from 0 V to about 10 V, the magnitude of the RF capacity was substantially constant. As the drive voltage was increased from about 10V to about 30V, the RF capacity gradually increased.
Further, when the drive voltage was lowered from about 30V, the RF capacity decreased according to the drive voltage up to about 10V. While the drive voltage was lowered from about 10 V to 0 V, the RF capacity was substantially constant near the lower limit value.

The variable capacitance element 111 of the comparative example shown in FIG. 7 is bent at the tip (end on the X axis positive direction side) on the side opposite to the fixed plate 2 in a state where the drive voltage is not applied (initial state). Thus, the movable beam 113 is configured. In other words, in the movable beam 113, the distance between the tip of the movable part (the end on the X-axis positive direction side) and the fixed plate 2 in the state where the drive voltage is not applied (initial state) is the connection of the movable part. This is longer than the distance between the connecting portion and the fixed plate 2. The variable capacitance element 111 has a distance between the tip of the movable part (the end on the X-axis positive direction side) and the fixed plate 2 of about 700 nm in a state where no driving voltage is applied. The distance between the connecting portion and the fixing plate 2 is about 600 nm. In addition, the variable capacitance element 111 includes a dielectric film 114 having a flat surface, similar to the variable capacitance element 11 shown in FIG. The other configuration of the variable capacitance element 111 shown in FIG. 7 is the same as that of the variable capacitance element 11.
In the variable capacitance element 111, when the drive voltage was increased from 0V and the drive capacitance was increased, the drive voltage was about 4V and the state shown in FIG. When this drive voltage was from 0V to about 4V, the magnitude of the RF capacity was substantially constant. As the drive voltage was increased from about 4V to about 30V, the RF capacity gradually increased.
Further, when the drive voltage was lowered from about 30 V, the RF capacity decreased according to the drive voltage. However, even when the drive voltage was lowered to 0V, the RF capacity did not reach the lower limit. This is because the sticking phenomenon occurs due to the charge-up of the dielectric film 4 because the drive voltage is increased.

  As described above, in the embodiment as well, it is effective to prevent the sticking phenomenon from causing the tip of the movable beam to bend toward the fixed plate when no driving voltage is applied (initial state). I was able to confirm that there was. Also, when lowering the driving voltage of the variable capacitance element, it is confirmed that the RF capacitance does not remain high without decreasing to the lower limit value, and it becomes possible to prevent the variable capacitance element from becoming uncontrollable. We were able to.

  Next, an example of a manufacturing method for making the tip of the movable beam 3 bend toward the fixed plate in a state where the driving voltage is not applied (initial state) will be described.

  FIG. 8A is a schematic diagram illustrating a sputtering apparatus 21 used for manufacturing the variable capacitance element 1 of the present embodiment and a film forming process using the sputtering apparatus 21.

  The sputtering apparatus 21 includes a laser beam irradiation unit 22, a laser reflected light detection unit 23, a sputtering condition control unit 24, and a chamber 25.

The chamber 25 accommodates the target 20 and the substrate 31. In the sputtering apparatus 21, metal particles are scattered from the target 20 using a sputtering gas, and a metal film 32 made of, for example, tungsten is formed on the substrate 31. The metal film 32 has an internal stress corresponding to the sputtering gas pressure and sputtering power at the time of film formation, and the substrate 31 is bent by the internal stress of the metal film 32.
The laser light irradiation unit 22 irradiates the substrate 31 accommodated in the chamber 25 with laser light.
The laser reflected light detector 23 receives the laser reflected light reflected by the substrate 31 irradiated with the laser light, and detects the light receiving angle (or light receiving position) of the laser reflected light.
The sputtering condition control unit 24 recognizes the amount of bending of the substrate 31 based on the light receiving angle (or light receiving position) of the laser reflected light detected by the laser reflected light detecting unit 23 so that the substrate 31 has a desired amount of bending. The sputtering gas pressure and sputtering power are controlled.

In such a film forming process using the sputtering apparatus 21, the deflection amount of the substrate 31 can be controlled with high accuracy by controlling the sputtering gas pressure and the sputtering power while detecting the deflection amount of the substrate 31. .
Therefore, after this film forming step, the metal film 32 is etched to form the movable beam side drive capacitance electrodes 8A and 8B and the movable beam side RF capacitance electrode 9. In the film forming step, a metal film 32 is formed in a state where a resist pattern having openings corresponding to the movable beam side drive capacitance electrodes 8A and 8B and the movable beam side RF capacitance electrode 9 is formed on the substrate 31, Thereafter, the movable beam side drive capacitance electrodes 8A and 8B and the movable beam side RF capacitance electrode 9 may be formed by a lift-off process for removing the resist pattern. After forming the movable beam side drive capacitance electrodes 8A and 8B and the movable beam side RF capacitance electrode 9 in this way, the substrate 31 is processed as a movable beam to manufacture the variable capacitance element of this embodiment. With such a manufacturing method, it is possible to manufacture the variable capacitance element of the present embodiment with a high yield.

  Here, a specific relationship between the internal stress of the metal film 32 to be the movable beam side drive capacitance electrodes 8A and 8B and the movable beam side RF capacitance electrode 9 and the sputtering conditions will be described.

  FIG. 8B is a diagram showing the relationship between the sputtering gas pressure and the internal stress of the metal film 32 in the process of forming the metal film 32 in the manufacture of the variable capacitance element 1 of the present embodiment. Here, an example is shown in which a metal film 32 having a thickness of about 200 nm is formed by DC sputtering using argon gas with a DC power of about 1500 W and a film formation time of about 1000 seconds.

When the metal film 32 is formed by changing the sputtering gas pressure to about 0.7 Pa, about 0.75 Pa, about 0.76 Pa, and about 0.8 Pa, and the internal stress of each is examined, the sputtering gas pressure is about 0.1. When the pressure was 76 Pa, the metal film 32 having substantially zero internal stress was formed. At a sputtering gas pressure lower than about 0.76 Pa, the metal film 32 having an internal stress of tensile stress was formed. Conversely, the metal film 32 having an internal stress of compressive stress was formed at a sputtering gas pressure higher than about 0.76 Pa. This is presumably because the implantation energy of the sputtering gas or metal particles into the metal film 32 is large when the sputtering gas pressure is low, and is small when the sputtering gas pressure is high.
Therefore, since the metal film 32 is formed to be a compressive stress layer at a high sputtering gas pressure, the substrate 31 is formed in a shape warped toward the metal film 32 side. Further, since the metal film 32 is formed to be a tensile stress layer at a low sputtering gas pressure, the substrate 31 is formed in a shape warped on the opposite side to the metal film 32.

FIG. 8C is a diagram showing the relationship between the DC power and the internal stress of the metal film 32 in the metal film 32 deposition process in the manufacture of the variable capacitance element 1 of the present embodiment.
After the film formation time was set to about 1000 seconds, the DC power and the film thickness were varied to form the metal film 32, and when the internal stress was examined, the internal power was reduced to about 1500 W. A metal film 32 having a tensile stress of 2600 Pa was formed. When the DC power was about 1000 W, the metal film 32 having a tensile stress with an internal stress of about 1000 Pa was formed. When the DC power was about 500 W, the metal film 32 having a compressive stress with an internal stress of about 1200 Pa was formed.

  Further, when the metal film 32 is formed by changing the DC power and the film formation time after the film thickness of the metal film 32 to be formed is about 200 nm, and the internal stress of each is examined, the DC power is about 1500 W. As a result, the metal film 32 having an internal stress of about 2600 Pa and a tensile stress was formed. When the DC power was about 1000 W, the metal film 32 having a tensile stress with an internal stress of about 2000 Pa was formed. When the DC power was about 500 W, a metal film having a compressive stress with an internal stress of about 1800 Pa was formed.

  By adopting the configuration and the manufacturing method of the present embodiment described above, a movable beam configured such that the tip is bent toward the fixed plate in a state where the driving voltage is not applied (initial state) is provided. In addition, the variable capacitance element that can suppress the occurrence of the sticking phenomenon can be manufactured with high shape accuracy and high yield.

<< Second Embodiment >>
Next, a variable capacitance element according to the second embodiment of the present invention will be described.

  FIG. 9A is an exploded plan view (XY plane plan view) of the variable capacitance element 31 according to the second embodiment of the present invention with the movable beam removed.

The variable capacitance element 31 includes a dielectric film 34 having a shape different from that of the variable capacitance element 1 of the first embodiment, and other configurations are the same as those of the variable capacitance element 1 of the first embodiment.
The dielectric film 34 includes a thin portion 34A in which a region facing the partition regions 3E1 and 3E3 is configured thinner than other regions. Further, the dielectric film 34 is provided with a columnar protruding portion 4B that is evenly disposed in a region facing the partition regions 3E1, 3E2, and 3E3 in the thin portion 34A and locally protrudes from the periphery. The thin portion 34A and the protruding portion 34B are provided in order to reduce the contact area between the electrode on the movable beam side and the dielectric film 34, similarly to the thin portion 4A and the protruding portion 4B described above. By configuring the dielectric film 34 in this manner, the charge amount due to the charge-up of the dielectric film 34 is reduced, and the occurrence of the sticking phenomenon can be prevented.

  FIG. 9B is an exploded plan view (XY plane plan view) of the variable capacitance element 41 according to a modification of the second embodiment of the present invention with the movable beam removed.

The variable capacitance element 41 includes a dielectric film 44 having a shape different from that of the variable capacitance element 1 of the first embodiment, and other configurations are the same as those of the variable capacitance element 1 of the first embodiment.
The dielectric film 44 includes a thin portion 44A configured to be thinner than a region on the X-axis negative direction side in a half region on the X-axis positive direction side in a region facing the partition regions 3E1, 3E2, and 3E3. Further, the dielectric film 44 is provided with a columnar protruding portion 44B that is evenly disposed in a region facing the partition regions 3E1, 3E2, and 3E3 in the thin portion 44A and locally protrudes from the periphery. Even if the dielectric film 44 is configured in this way, the charge amount due to the charge-up of the dielectric film 44 is reduced, and the occurrence of the sticking phenomenon can be prevented.

<< Third Embodiment >>
Next, a variable capacitor according to a third embodiment of the present invention will be described.

  FIG. 10A is a cross-sectional view (XZ plane cross-sectional view) perpendicular to the Y-axis of the variable capacitance element 51 according to the third embodiment of the present invention. FIG. 10A is a cross-sectional view at the same position as that in FIG.

The variable capacitance element 51 is provided with a tensile stress film 53 on the surface opposite to the surface facing the fixed plate 2 of the movable beam 3 (surface in the positive direction of the Z axis), and the movable beam side drive capacitance electrodes 8A and 8B ( (Not shown) and the internal stress of the movable beam side RF capacitive electrode 9 are made substantially zero, and the other configurations are the same as those of the first embodiment.
The tensile stress film 53 applies a force in the compression direction to the movable beam 3 and deforms the distal end of the movable beam 3 to be bent toward the fixed plate in a state where no driving voltage is applied (initial state). Even in such a configuration, the tensile stress film 53 can be formed by the film forming process described in the first embodiment, and in a state where the driving voltage is not applied (initial state), It is possible to manufacture the variable capacitance element 51 that includes the movable beam configured to be bent at the tip on the fixed plate side and can suppress the occurrence of the sticking phenomenon with high shape accuracy and high yield.

  FIG. 10B is a cross-sectional view (XZ plane cross-sectional view) perpendicular to the Y-axis of the variable capacitance element 61 according to a modification of the third embodiment of the present invention. FIG. 10B is a cross-sectional view at the same position as that in FIG.

The variable capacitance element 61 is provided with a tensile stress film 63 on a surface opposite to the surface facing the fixed plate 2 of the movable beam 3 (a surface in the positive Z-axis direction) in a region overlapping the initial proximity region. In this configuration, the internal stresses of the side drive capacitance electrodes 8A and 8B (not shown) and the movable beam side RF capacitance electrode 9 are made substantially zero.
The tensile stress film 63 applies a force in the compression direction to a part of the movable beam 3 located in the initial proximity region, and in a state where the driving voltage is not applied (initial state), the tip of the movable beam 3 is located on the fixed plate side. It is deformed as if it is bent. Even when the variable capacitance element 61 is configured as described above, the tensile stress film 63 can be formed by the film forming process described in the first embodiment, and thus, a state in which no driving voltage is applied (initial state) In the state), the variable capacitance element 51 that includes the movable beam configured to be bent on the fixed plate side and can suppress the occurrence of the sticking phenomenon can be manufactured with high shape accuracy and high yield.

<< Fourth Embodiment >>
Next, a variable capacitor according to a fourth embodiment of the present invention will be described.

FIG. 11A is an exploded plan view (XY plane plan view) of the variable capacitance element 71 according to the fourth embodiment of the present invention with the movable beam and the dielectric film removed.
The variable capacitance element 71 includes fixed plate side drive capacitance electrodes 75A and 75B that are narrower than those in the above-described embodiment. In addition, a ground electrode 77 formed in a meander line shape and having one end connected to the ground terminal GND is provided.

FIG. 11B is an exploded plan view (XY plane plan view) of the variable capacitance element 71 according to the fourth embodiment of the present invention with the movable beam removed.
The variable capacitance element 71 includes a dielectric film 74 having a shape different from that of the above-described embodiment. The dielectric film 74 includes a thin portion 74A in which a region overlapping the fixed plate side drive capacitance electrodes 75A and 75B is formed thinner than other regions.

  The variable capacitance element 71 is a region overlapping the fixed plate side drive capacitance electrodes 75A and 75B, and the dielectric film 74 does not contact the movable beam side drive capacitance electrodes 8A and 8B (not shown) and overlaps the ground electrode 77. Thus, the dielectric film 74 comes into contact with the movable beam side drive capacitance electrodes 8A and 8B (not shown). The ground electrode 77 is connected to the same potential (ground potential) as the movable beam side drive capacitance electrodes 8A and 8B (not shown), and the movable beam side drive capacitance electrodes 8A and 8B (not shown) and the fixed plate side drive capacitance electrode 75A. , 75B is prevented from acting on the dielectric film 74 in the region facing it. For this reason, the drive voltage is not directly applied to the dielectric film 74, and the charge-up in the dielectric film 74 can be significantly suppressed. For this reason, generation | occurrence | production of a sticking phenomenon can be prevented more reliably.

  The present invention is not limited to the description of the embodiments and modifications described above, and the scope of the present invention is defined by the scope of claims, and all meanings within the scope and meaning equivalent to the scope of claims are within the scope of the present invention. It is intended to include changes.

1, 11, 31, 41, 51, 61, 71 ... variable capacitance element 2 ... fixed plate 3 ... movable beam 3A ... support portion 3B ... connecting portion 3C ... movable portion 3D1, 3D2 ... divided regions 3E1, 3E2, 3E3 ... section Regions 4, 14, 34, 44, 74 ... dielectric films 4A, 34A, 44A, 74A ... thin portions 4B, 34B, 44B ... projections 5A, 5B, 75A, 75B ... fixed plate side drive capacitance electrodes 6A, 6B ... Fixed plate side RF capacitive electrodes 8A, 8B ... Movable beam side drive capacitive electrode 9 ... Movable beam side RF capacitive electrode 20 ... Target 21 ... Sputtering device 22 ... Laser beam irradiation unit 23 ... Laser reflected light detection unit 24 ... Sputtering condition control unit 25 ... Chamber 31 ... Substrate 32 ... Metal film 53, 63 ... Tensile stress film 77 ... Ground electrode

Claims (9)

A fixed plate,
A movable beam provided to face the fixed plate with a gap therebetween;
A movable beam side electrode provided on the movable beam;
A fixed plate side electrode provided on the fixed plate so as to face the movable beam side electrode;
A dielectric film disposed between the movable beam side electrode and the fixed plate side electrode;
With
In the initial state, the movable beam is an electrostatic drive type actuator that is convex on the side opposite to the fixed plate side. A fixed plate,
A movable beam provided to face the fixed plate with a gap therebetween;
A movable beam side electrode provided on the movable beam;
A fixed plate side electrode provided on the fixed plate so as to face the movable beam side electrode;
A dielectric film disposed between the movable beam side electrode and the fixed plate side electrode;
With
In the initial state, the movable beam is an electrostatic drive type actuator configured such that a tip is bent toward the fixed plate. A fixed plate,
A movable beam provided to face the fixed plate with a gap therebetween;
The movable beam side drive capacitance electrode provided on the movable beam, the fixed plate side drive capacitance electrode provided on the fixed plate so as to face the movable beam side drive capacitance electrode, the movable beam side drive capacitance electrode, and the fixed A dielectric film formed between the plate-side drive capacitance electrode and deforming the movable beam based on a drive capacitance generated between the movable beam-side drive capacitance electrode and the fixed plate-side drive capacitance electrode. A drive capacity section;
A movable beam side RF capacitive electrode provided on the movable beam, a fixed plate side RF capacitive electrode provided on the fixed plate so as to face the movable beam side RF capacitive electrode, the movable beam side RF capacitive electrode, and the fixed An RF capacitor portion comprising a dielectric film formed between the plate-side RF capacitor electrode;
With
In the initial state, the movable beam is a variable capacitance element that is convex on the side opposite to the fixed plate side. A fixed plate,
A movable beam provided to face the fixed plate with a gap therebetween;
The movable beam side drive capacitance electrode provided on the movable beam, the fixed plate side drive capacitance electrode provided on the fixed plate so as to face the movable beam side drive capacitance electrode, the movable beam side drive capacitance electrode, and the fixed A dielectric film formed between the plate-side drive capacitance electrode and deforming the movable beam based on a drive capacitance generated between the movable beam-side drive capacitance electrode and the fixed plate-side drive capacitance electrode. A drive capacity section;
A movable beam side RF capacitive electrode provided on the movable beam, a fixed plate side RF capacitive electrode provided on the fixed plate so as to face the movable beam side RF capacitive electrode, the movable beam side RF capacitive electrode, and the fixed An RF capacitor portion comprising a dielectric film formed between the plate-side RF capacitor electrode;
With
In the initial state, the movable beam is a variable capacitance element configured such that a tip is bent toward the fixed plate.   5. The variable capacitance element according to claim 3, wherein at least one of the movable beam side drive capacitance electrode and the movable beam side RF capacitance electrode is a compressive stress layer. 6.   The variable capacitance element according to claim 3, wherein the movable beam is provided with a tensile stress film on a surface opposite to a surface facing the fixed plate.   The variable capacitance element according to claim 3, wherein the dielectric film includes a thin portion and a protruding portion that protrudes locally. A fixed plate,
A movable beam provided to face the fixed plate with a gap therebetween;
A movable beam side electrode provided on the movable beam;
A fixed plate side electrode provided on the fixed plate so as to face the movable beam side electrode;
A dielectric film disposed between the movable beam side electrode and the fixed plate side electrode;
A method of manufacturing an electrostatic drive actuator comprising:
A film forming step of forming a metal film constituting the movable beam side electrode on a substrate constituting the movable beam by a sputtering method;
In the film forming step, a laser beam is irradiated on the substrate to detect a light receiving angle of laser reflected light reflected by the substrate, thereby recognizing the amount of bending of the substrate, and sputtering conditions based on the amount of bending of the substrate. A method for manufacturing an electrostatically driven actuator, wherein the metal film is formed as a compressive stress layer by controlling the above. A fixed plate,
A movable beam provided to face the fixed plate with a gap therebetween;
The movable beam side drive capacitance electrode provided on the movable beam, the fixed plate side drive capacitance electrode provided on the fixed plate so as to face the movable beam side drive capacitance electrode, the movable beam side drive capacitance electrode, and the fixed A dielectric film formed between the plate-side drive capacitance electrode and deforming the movable beam based on a drive capacitance generated between the movable beam-side drive capacitance electrode and the fixed plate-side drive capacitance electrode. A drive capacity section;
A movable beam side RF capacitive electrode provided on the movable beam, a fixed plate side RF capacitive electrode provided on the fixed plate so as to face the movable beam side RF capacitive electrode, the movable beam side RF capacitive electrode, and the fixed An RF capacitor portion comprising a dielectric film formed between the plate-side RF capacitor electrode;
A method of manufacturing a variable capacitance element comprising:
A film forming step of forming a metal film forming the movable beam side driving capacitive electrode and the movable beam side RF capacitive electrode on a substrate constituting the movable beam by a sputtering method;
In the film forming step, a laser beam is irradiated on the substrate to detect a light receiving angle of laser reflected light reflected by the substrate, thereby recognizing the amount of bending of the substrate, and sputtering conditions based on the amount of bending of the substrate. And manufacturing the variable capacitance element, wherein the metal film is formed as a compressive stress layer.

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