JP2008091167A - Micromechanical device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a micromechanical device having a piezo-electric drive actuator which does not use a lead system material for a piezo-electric film, is easy to manufacture and can eliminate sticking even if it happens. <P>SOLUTION: The micromechanical device includes an actuator 10 which is installed on a substrate 1 and has a piezo-electric film 4, a lower electrode 3 provided on a face opposed to the substrate 1 of the piezo-electric film 4, and an upper electrode 5 provided on an opposed face to the face on which the lower electrode 3 of the piezo-electric film 4 is provided, and has a fixing part 10a fixed on the substrate 1 and an action part 10b extending from the fixing part 10a, a voltage applying means 13 to apply voltage between the lower electrode 3 and the upper electrode 5, and a polarity switching means 14 to switch over polarity of the voltage applied. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a micromechanical device, and more particularly to a micromechanical device driven by a piezoelectric actuator.

  In recent years, there has been an interest in a technique for manufacturing a micromechanical device such as a switch or a variable capacitor by using a thin film actuator manufactured by a micro-electro-mechanical system (MEMS) technique.

  As one of thin film actuators manufactured by such MEMS technology, an electrostatic actuator using an electrostatic force as a driving force is known. This electrostatic actuator has an advantage in that it requires only a very simple operation mechanism that only applies a driving voltage to a pair of electrodes spaced apart from each other. On the other hand, due to the property that the electrostatic force is proportional to the minus square of the distance, the applied voltage and the amount of movement are non-linear, and a phenomenon called pull-in occurs in which the interval closes discontinuously below about 2/3 of the initial interval. In order to drive a distance of 1 μm or more with a narrow driving range, generally, a high driving voltage of 20 V or more is necessary, and charges are injected into the movable electrode by voltage application, resulting in sticking between the electrodes. . At present, due to these disadvantages, particularly the problem of high driving voltage, it has not been applied to general consumer devices.

In order to solve such a problem, a piezoelectric actuator using piezoelectric power as a driving force is generally known (for example, Patent Document 1). In such a piezoelectric actuator, a PZT system (lead zirconate titanate) having high piezoelectricity and high workability is suitably used as the piezoelectric film. Therefore, actuators with various shapes can be easily manufactured.
JP 2006-87231 A

  However, when manufacturing an actuator using a PZT-based piezoelectric film by thin film technology, there are various difficulties. For example, a lead-based material has a high melting point and vapor pressure, and it is difficult to control the composition during film formation. Further, in a normal semiconductor production line, there is a problem that the use of lead-based materials is restricted due to problems such as environmental pollution.

  Furthermore, the piezoelectric actuator manufactured by the thin film technology also has a problem of sticking like the electrostatic actuator. This sticking occurs, for example, mainly due to van der Waals force between the metal electrode and the dielectric film, or between the dielectric films, and in a MEMS switch that opens and closes by ohmic contact between the metal electrodes, This phenomenon is physically unavoidable because it is caused by cohesive force.

  Accordingly, an object of the present invention is to provide a micromechanical device including a piezoelectric actuator that does not use a lead-based material for a piezoelectric film, is easy to manufacture, and can eliminate the occurrence of sticking. And

  The micromechanical device according to the present invention includes a substrate, a piezoelectric film provided on the substrate, a first electrode provided on a surface of the piezoelectric film facing the substrate, and the first of the piezoelectric film. A second electrode provided on a surface opposite to the surface on which the electrode is provided, and an actuator comprising a fixed portion fixed on the substrate and an action portion extending from the fixed portion; The fixed electrode disposed on the surface of the substrate facing the action portion, the voltage applying means for applying a voltage between the first electrode and the second electrode, and the polarity of the voltage are switched. And polarity switching means for bending and moving the actuator in a direction approaching the substrate or in a direction away from the substrate.

  According to the present invention, there is provided a micromechanical device including a piezoelectric actuator that does not use a lead-based material for the piezoelectric film, is easy to manufacture, and can eliminate the occurrence of sticking.

As a result of various studies on piezoelectric materials that can be produced by a thin film method in order to solve the above-described problems, the present inventor has found that the c-axis of aluminum nitride (AlN) or zinc oxide (ZnO) having a wurtzite crystal system. It has been found that an alignment film is suitable. However, the piezoelectricity of AlN or ZnO is as small as 1/10 or less compared to the case of the PZT system described above. For this reason, when fabricating a piezoelectric actuator provided with a piezoelectric film of AlN or ZnO, in order to increase the amount of displacement, it is necessary to reduce the thickness of the actuator and increase the length, that is, to increase the aspect ratio. . However, when such an actuator structure with a large aspect ratio is adopted, the rigidity of the actuator becomes small, and there arises a problem that operation failure is more likely to occur due to sticking between the contacts.

  The sticking phenomenon will be described with reference to the drawings. FIG. 11 is a diagram showing the structure of a variable capacitor having a conventional piezoelectric actuator. 1 is a substrate, 2 is an anchor, 3 is a lower electrode of an actuator, 4 is a piezoelectric film, 5 is an upper electrode, 6 is a support film, 7 is a movable electrode constituting a variable capacitor, 8 is a fixed electrode, 9 is a dielectric film, Reference numeral 10 denotes an actuator, and 12 denotes a voltage applying means (DC power supply).

In FIG. 11, when a voltage V is applied between the lower electrode 3 and the upper electrode 5 sandwiching the piezoelectric film 4 using the voltage applying means 12, the piezoelectric film 4 expands in the film thickness direction and contracts in the major axis direction. . Therefore, the actuator 10 is in the figure, bent toward the x-direction, the movable electrode 7 when displaced by x _t is in contact with the dielectric film 9 on the fixed electrode 8.

FIG. 12 is a diagram illustrating a driving mechanism when the piezoelectric driving voltages V _{0 to} V _t are applied to the actuator 10 shown in FIG.

The actuator 10 has inherent rigidity and generates a spring elastic force F proportional to the displacement x of the actuator 10. On the other hand, by applying the piezoelectric driving voltages V _{0 to} V _t to the actuator 10, the piezoelectric driving forces F _{0 to} F _t are generated, and the displacement in which the piezoelectric driving forces F _{0 to} F _t and the spring elastic force F of the actuator are balanced. x _{0 to} x _t are generated. When the actuator 10 is in contact with the dielectric film 9 by the displacement x _t, because more can not be displaced, relationship of the piezoelectric drive voltage V and the actuator displacement x is as shown in FIG. 13 (a).

However, as described above, a piezoelectric actuator using AlN or ZnO having a small piezoelectric constant as a piezoelectric film has a thin and long structure and is characterized by rigidity, in other words, the aforementioned spring elastic force F is small. In addition to the elastic force F and the piezoelectric driving forces F _{0 to} F _t , sticking (sticking) due to the cohesive force when the electrodes come into contact with each other cannot be ignored. That is, the movable electrode 7 by the displacement x _t by applying a piezoelectric driving voltage V _t in FIG. 12 after contact with the dielectric layer 9, when returning the piezoelectric driving voltage to V _0, pull back the F _t to the actuator 10 Power works. If the fixing force between the movable electrode 7 and the dielectric film 9 is larger than the force F _t , the actuator 10 sticks to the dielectric film 9 and does not function as a variable capacitor (FIG. 13B).

  As a result of various studies, the inventors have found a new structure and driving method that can be applied to a piezoelectric actuator in order to cope with the problem of sticking.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following description of the drawings, the same portions are denoted by the same reference numerals, and overlapping descriptions are omitted. The drawings are schematic, and the relationship between the thickness and the planar dimensions, the ratio of the thickness of each layer, and the like are different from the actual ones. Further, there are included portions having different dimensional relationships and ratios between the drawings.

(First embodiment)
FIG. 1 is a diagram showing a cross-sectional structure of a micromechanical device according to a first embodiment of the present invention. The micromechanical device according to the present embodiment relates to a unimorph type piezoelectric drive variable capacitor, and an actuator 10 is provided on a substrate 1 as shown in FIG. The actuator 10 has, for example, a fixed portion 10a fixed via an anchor 2 and an action portion 10b having a movable electrode 7 extending from the fixed portion 10a. The electrode 3, the piezoelectric film 4, the upper electrode 5, and the support film 6 have a structure in which they are stacked in this order. The movable electrode 7 of the action part 10 b is provided in the same layer and the same material as the lower electrode 3, and an electrode slit 11 is provided between the lower electrode 3 and the movable electrode 7.

  A fixed electrode 8 is provided on the surface of the substrate 1 so as to face the movable electrode 7 of the action portion 10 b of the actuator 10, and the fixed electrode 8 is covered with a dielectric film 9. The total height of the fixed electrode 8 and the dielectric film 9 is designed to be smaller than the height of the anchor 2 so that a gap (space) is generated between the movable electrode 7 and the dielectric film 9.

  The actuator 10 is connected with voltage application means 13 for applying a voltage between the lower electrode 3 and the upper electrode 5, and between the lower electrode 3 and the upper electrode 5 and the voltage application means 13, an application voltage is applied. Polarity switching means 14 for switching the polarity of the voltage to be applied is provided.

  As shown in FIG. 1, the voltage applying unit 13 includes unipolar DC power sources 15 and 16. The DC power supplies 15 and 16 are arranged in the voltage applying means 13 with the polarities reversed. For this reason, the voltage applying means 13 has bipolar characteristics.

Polarity switching means 14 includes a changeover switch _{S 1} and the changeover switch _{S 2.} Changeover switch S ₁ is between the first switching terminal S _1a connected to the upper electrode 5, and the third switch terminal S _1c which is the second switching terminal S _1b or ground connected to the negative DC power supply 15 This is a switch for switching between. Changeover switch S ₂ is between the fourth switch terminal S _2a which is connected to the lower electrode 3, and the sixth switch terminal S _2c which is connected to the negative polarity of the fifth switch terminal S _2b or DC power source 16 which is grounded It is a switch for switching. The positive polarity of the DC power supplies 15 and 16 is grounded.

The polarity switching means 14 is driven in a state where the first switching terminal S _{1a is connected} to the second switching terminal S _1b and the fourth switching terminal S _2a is connected to the fifth switching terminal S _2b (hereinafter referred to as the first state). Thus, a voltage having the lower electrode 3 as positive polarity and the upper electrode 5 as negative polarity can be applied. Further, in a state where the first switching end S _{1a is connected} to the third switching end S _1c and the fourth switching end S _2a is connected to the sixth switching end S _2c (hereinafter referred to as the second state), the lower electrode 3 is A voltage having a negative polarity and a positive polarity of the upper electrode 5 can be applied. That is, the polarity switching unit 14 is a switching unit that switches between the first state and the second state. The polarity switching means 14 is composed of a semiconductor switch or a mechanical switch.

  In the micromechanical device according to the present embodiment, when a voltage having the lower electrode 3 as positive polarity and the upper electrode 5 as negative polarity is applied, the piezoelectric film 4 extends in the major axis direction, and the actuator 10 main body is the substrate 1. Bend towards the side. Conversely, when a voltage with the lower electrode 3 being negative and the upper electrode 5 being positive is applied, the piezoelectric film 4 shrinks in the major axis direction, and the actuator 10 body faces in a direction opposite to the substrate 1 side. And bend.

  FIG. 2 is a view for explaining the drive mechanism in the present embodiment.

The micromechanical device according to the present embodiment uses the voltage application unit 13 and the polarity switching unit 14 to bring the movable electrode 7 and the dielectric film 9 into contact between the piezoelectric drive electrodes (the lower electrode 3 and the upper electrode 5). it is possible to apply a driving voltage V _t of can further apply a reverse polarity of electrostatic driving pressure -V _t for separating the movable electrode 7 and the dielectric film 9. That is, even when sticking occurs between the movable electrode 7 and the dielectric film 9, in addition to the force (here, spring elastic force) −F _t for pulling back to the actuator, the pulling according to the drive voltage −V _t is performed. Since a directional force (here, piezoelectric power) -F _t is further applied, sticking can be easily eliminated.

  FIG. 3 is a diagram for explaining the operation mechanism of the micromechanical device according to this embodiment.

When a voltage V _t is first applied to the accumulator 10 at the point A, the acceler 10 is bent and displaced by x _{t in the} x direction shown in FIG. 1 so that the movable electrode 7 becomes the dielectric film 9 on the fixed electrode 8 at the point B. To touch. If strong sticking occurs at this time, sticking is not eliminated even if the applied voltage is returned to V ₀ (point C). Here sticking a driving voltage -V _r by the actuator 10 applies the driving voltage -V _t of reverse direction away is eliminated (point D), the bending displacement of the actuator 10 which corresponds to the driving voltage -V _r Return to position (point E) and leave to point F. Thereafter, the position of the actuator 10 returns to the first point A by returning the drive voltage to V ₀ .

  As the substrate 1, an insulating glass substrate or a semiconductor substrate such as silicon (Si) is used.

The anchor 2 is preferably an insulating film such as silicon oxide (SiO ₂ ).

  As electrode materials such as the lower electrode 3, the upper electrode 5, the movable electrode 7 and the fixed electrode 8, aluminum (Al), gold (Au), platinum (Pt), copper (Cu), indium (Ir), tungsten (W ), Molybdenum (Mo) and the like, which are easily processed, are preferably used.

  As the support film 6, for example, a poly-Si film is preferably used.

As the dielectric film 8, an insulating film such as silicon oxide (SiO ₂ ) or silicon nitride (Si ₃ N ₄ ) is used.

  The piezoelectric film 4 is preferably a c-axis oriented film of aluminum nitride (AlN) or zinc oxide (ZnO) having a wurtzite crystal system. A drive mechanism when a PZT material is used for the piezoelectric film 4 will be described with reference to FIGS.

  FIG. 4 is a relationship diagram between the electric field E applied to a ferroelectric film such as PZT and the polarization P, generally called a PE hysteresis curve. First, when a positive electric field is applied from the unpolarized state A point, ferroelectric polarization occurs, and at point B, the polarization is saturated and reaches point C. When the electric field is run in the negative direction from the point C, the ferroelectric polarization starts to reverse at the point D, the inversion is saturated at the point E, and reaches the point F. When the applied electric field is again run in the positive direction, the ferroelectric polarization starts to reverse again at the point G, saturates at the point H, and returns to the point C. In this way, in the case of a ferroelectric, a ferroelectric hysteresis of C → D → E → F → G → H → C is drawn corresponding to application of positive and negative electric fields.

  Next, the relationship between the electrostriction ε generated in the ferroelectric and the applied electric field E is shown in FIG. The electrostriction ε substantially depends on the product of the polarization amount and the electric field E. That is, when a positive electric field is applied from the unpolarized state A point, the electrostriction ε increases as the polarization and the electric field E increase, and reaches the C point via the B point. When the electric field E is run in the negative direction from the point C, the electrostriction ε decreases as the electric field E decreases. When the electric field E becomes negative, the ferroelectric polarization is reversed between the point D and the point E, and the directions of the polarization and the electric field E coincide with each other, so that the electrostriction ε increases again to reach the point F. When the applied electric field is run again in the positive direction, the electrostriction ε also decreases as the electric field E decreases. However, when the electric field E becomes positive, the ferroelectric polarization is inverted between the G point and the H point, and the polarization And the direction of the electric field E coincide with each other, so that the electrostriction ε increases again and returns to the point C. Thus, in the case of a ferroelectric material, the electrostriction ε is stronger than the point A when the electric field E is not polarized and the electric field E is 0, and when the electric field E is applied positively (point C), the electric field is strongly negative. When E is added, the electrostriction ε also occurs in the same direction at the point F. Therefore, it can be seen that the merit is extremely limited even if the electric field E is switched between positive and negative.

  On the other hand, FIG. 6 shows the relationship between the electric field E and the polarization P and FIG. 7 shows the relationship between the electric field E and the electrostriction ε when a piezoelectric material such as AlN or ZnO that does not cause polarization inversion is used in the piezoelectric actuator. In the case of a piezoelectric material such as AlN or ZnO, the amount of polarization and electrostriction ε is simply proportional to the applied electric field E, and if a positive electric field E is applied, electrostriction ε is generated in the positive direction. When a negative electric field E is applied, negative electrostriction ε is generated. Therefore, as described above, applying a positive and negative electric field E is a very effective means for the piezoelectric actuator.

  As described above, the micromechanical device according to the present embodiment is provided with polarity switching means for switching the polarity of the voltage between the lower electrode 3 and the upper electrode 5 even when AlN or ZnO having low piezoelectricity is used as the piezoelectric film. Therefore, even if sticking occurs, it can be canceled, and a micromechanical device that can be easily manufactured can be realized without using a lead-based material.

  Hereinafter, specific examples in the present embodiment will be described.

  A micromechanical device having the configuration shown in FIG. 1 was prepared under the following conditions.

-Lower electrode: Al (thickness 200 nm)
Piezoelectric film: c-axis oriented AlN (thickness 500 nm)
-Upper electrode: Al (thickness 200 nm)
Support film: SiO2 film (thickness 300 nm)
Fixed electrode: Al (thickness 200 nm)
-Movable electrode: Al (thickness 200 nm)
・ Equivalent area of variable capacitor 6400μm ²
・ Long axis 200μm of actuator 10
・ Short axis 100μm of actuator 10
FIG. 8 shows a relationship diagram between the drive voltage and the capacitance when the manufactured variable capacitor is driven.

  As shown in FIG. 8, when the drive voltage was increased from 0 V to 3 V, the capacitance continuously increased from 0.22 pF to 1.85 pF (point A). However, when the drive voltage was continuously set to 0 V, the capacitance value hardly changed because of sticking between the electrodes (point B). Then, when the drive voltage was applied by applying a negative voltage from 0 V to -3 V, the sticking was eliminated at around -2 V, and the capacitance decreased discontinuously from 1.82 pF to 0.13 pF (point C). . Thereafter, when the drive voltage was decreased from −3 V to 0 V, the capacitance continuously increased from 0.12 pF to 0.22 pF (point D).

  As described above, it was confirmed that sticking was eliminated by applying a reverse polarity voltage when sticking occurred between the electrodes.

  In addition to the capacitance change range of 0.22 pF to 1.85 pF when a positive voltage of 0 to 3 V is applied, from the capacitance change range of 0.12 pF when a negative voltage of -3 V to 0 V is applied. It was confirmed that the 0.22 pF region can be used, and the capacitance change magnification increased from 8.4 times to 15.4 times.

  The same tendency was confirmed even when c-axis oriented ZnO (thickness: 500 nm) was used as the piezoelectric film.

(Second Embodiment)
FIG. 9 is a diagram showing a cross-sectional structure of a micromechanical device according to the second embodiment of the present invention. The micromechanical device according to the present embodiment relates to a bimorph piezoelectric drive MEMS variable capacitor, and an actuator 40 is provided on a substrate 21 as shown in FIG. The actuator 40 has, for example, a fixed portion 40a fixed via an anchor 22 and an action portion 40b having a movable electrode 28 extending from the fixed portion 40a. The electrode 23, the lower piezoelectric film 24, the intermediate electrode 25, the upper piezoelectric film 26, and the upper electrode 27 are stacked in this order. The movable electrode 28 of the action part 40 b is provided in the same layer as the lower electrode 23, and an electrode slit 29 is provided between the lower electrode 23 and the movable electrode 28.

  Further, a fixed electrode 30 is provided on the surface of the substrate 21 so as to face the movable electrode 28 of the action portion 40 b, and the fixed electrode 30 is covered with a dielectric film 31.

  The total height of the dielectric film 31 and the fixed electrode 30 is designed to be smaller than the height of the anchor 22 so that a gap (space) is generated between the movable electrode 28 and the dielectric film 31.

  The actuator 40 is connected with voltage application means 32 for applying a voltage between the lower electrode 23 and the intermediate electrode 25 and between the intermediate electrode 25 and the upper electrode 27. Between the upper electrode 27 and the voltage applying means 32, a polarity switching means 33 for switching the polarity of the applied voltage is provided.

  As shown in FIG. 9, the voltage applying unit 32 includes a unipolar DC power supply 34.

Polarity switching means 33 is provided with a selector switch _{S 3} and the changeover switch _{S 4.} Selector switch S _3, the third switching terminal S which is a second switching terminal S _3b connected to a negative polarity or ground and the first switching terminal S _3a connected to the lower electrode 23 and upper electrode 27, a DC power source 34 It is a switch for switching between _3c . Selector switch S ₄ switches the fourth switching terminal S _4a which is connected to the intermediate electrode 25, and a sixth switch terminal S _4c which is connected to the negative polarity of the fifth switch terminal S _4b or DC power source 34 which is grounded Switch. That is, the second switching terminal S _3b and the sixth switching terminal S _4c are connected in parallel to the negative polarity of the DC power supply 34, and the third switching terminal S _3c and the fifth switching terminal S _4b are grounded. The positive polarity of the DC power supply 34 is grounded.

The polarity switching means 33 is driven in a state where the first switching end _{S3a is connected} to the second switching end _S3b and the fourth switching end _S4a is connected to the fifth switching end _S4b (hereinafter referred to as the first state). Thus, a voltage with the intermediate electrode 25 having a positive polarity and the lower electrode 23 and the upper electrode 27 having a negative polarity can be applied. Further, the first switching terminal S _{3a is connected} to the third switching terminal S _3c and the fourth switching terminal S _4a is connected to the sixth switching terminal S _4c (hereinafter referred to as the second state), so that A voltage having the electrode 25 as a negative polarity and the lower electrode 23 and the upper electrode 27 as a positive polarity can be applied. That is, the polarity switching unit 33 is a switching unit that switches between the first state and the second state. The polarity switching means 33 is composed of a semiconductor switch or a mechanical switch.

  In the micromechanical device according to the present embodiment, when a negative voltage is applied to the intermediate electrode 25 and a positive voltage is applied to the lower electrode 23 and the upper electrode 27, the upper piezoelectric film 26 extends in the major axis direction. Then, the lower piezoelectric film 24 is reduced in the major axis direction, and the actuator 40 body is bent toward the substrate 21 side. Conversely, when a positive voltage is applied to the intermediate electrode 25 and a negative voltage is applied to the lower electrode 23 and the upper electrode 27, the upper piezoelectric film 26 is reduced in the major axis direction, and the lower piezoelectric film 24 is The actuator 40 main body bends in the direction opposite to the substrate 21 side.

  As the substrate 21, an insulating glass substrate or a semiconductor substrate such as silicon (Si) is used.

As the anchor 22, an insulating film such as silicon oxide (SiO ₂ ) is preferably used.

  Examples of electrode materials for the lower electrode 23, the intermediate electrode 25, the upper electrode 27, the movable electrode 28, and the fixed electrode 30 include aluminum (Al), gold (Au), platinum (Pt), copper (Cu), and indium (Ir). Metals that can be easily processed, such as tungsten (W) and molybdenum (Mo), are preferably used.

As the dielectric film 31, an insulating film such as silicon oxide (SiO ₂ ) or silicon nitride (Si ₃ N ₄ ) is used.

  For the lower piezoelectric film 24 and the upper piezoelectric film 26, it is preferable to use a c-axis oriented film of aluminum nitride (AlN) or zinc oxide (ZnO) having a wurtzite crystal system.

  Since other driving principles and effects are the same as those in the first embodiment, description thereof is omitted.

  Hereinafter, specific examples in the present embodiment will be described.

A variable capacitor having the configuration shown in FIG. 9 was created under the following conditions.

-Lower electrode: Al (thickness 200 nm)
Piezoelectric film: c-axis oriented AlN (thickness 500 nm)
Intermediate electrode: Al (thickness 200 nm)
-Upper electrode: Al (thickness 200 nm)
Fixed electrode: Al (thickness 200 nm)
-Movable electrode: Al (thickness 200 nm)
・ Equivalent area of variable capacitor 6400μm ²
・ Long axis 200μm of actuator 10
・ Short axis 100μm of actuator 10
When the manufactured variable capacitor was driven, a capacitance change about 1.8 times larger than that of the unimorph-type piezoelectric drive MEMS variable capacitor described in the first embodiment was confirmed. As in the first embodiment, Sticking occurred between the electrodes of the variable capacitor, and sticking was not eliminated even when the drive voltage was returned to 0V.

  Therefore, when a voltage having a reverse characteristic was applied, it was confirmed that sticking was eliminated at around -1.5 V and the operation was stable.

  The same tendency was confirmed even when c-axis oriented ZnO (thickness: 500 nm) was used as the piezoelectric film.

(Third embodiment)
FIG. 10 is a diagram showing a cross-sectional structure of a micromechanical device according to the third embodiment of the present invention. The micro mechanical device according to the present embodiment is similar in configuration to the variable capacitor described in the first embodiment, but relates to an RF switch as a function. The micro mechanical device according to the present embodiment has a configuration without the dielectric film 9 as compared with the micro mechanical device according to the first embodiment, and other configurations, driving principles, effects, and the like are the same as those in the first embodiment. Since it is the same as that of a form, description is abbreviate | omitted.

  The micro mechanical device according to the present embodiment enables ohmic contact when the movable electrode 7 and the fixed electrode 8 are in direct contact, and functions as an RF switch.

Hereinafter, specific examples in the present embodiment will be described.

An RF switch having the configuration shown in FIG. 4 was created under the following conditions.

-Lower electrode: Au (thickness 200 nm)
Piezoelectric film: c-axis oriented AlN (thickness 500 nm)
-Upper electrode: Au (thickness 200 nm)
Support film: SiO2 film (thickness 300 nm)
Fixed electrode: Au (thickness 200 nm)
-Movable electrode: Au (thickness 200 nm)
・ Long axis 200μm of actuator 10
・ Short axis 100μm of actuator 10
When a driving voltage of 3 V was applied to the manufactured piezoelectric actuator, an ohmic contact was obtained between the movable electrode and the fixed electrode, and the loss at 2 GHz was as small as 0.3 dB. However, the drive voltage was subsequently returned to 0 V, but the resistance value hardly changed because sticking occurred between the electrodes. Then, when a negative voltage was applied from 0 V to -3 V, the sticking was eliminated at around -1.2 V and conduction was lost, and the isolation at -3 V was as high as 32 dB at 2 GHz. After that, when the drive voltage was returned to 0V, the isolation was 25 dB.

As described above, when sticking occurs after the electrode is brought into contact, it becomes possible to eliminate sticking by applying a voltage having a reverse polarity, and it is possible to operate stably. That is, the conduction is achieved by applying a positive voltage to the piezoelectric actuator, and the conduction is achieved by once applying a negative voltage and returning it to 0V. When large insulation isolation is required, this can be achieved by continuing to apply a negative voltage. In addition, the piezoelectric film composed of AlN and ZnO can easily achieve high insulation. In this embodiment, even when 3V is applied, the flowing current is 10 ⁻¹⁰ A or less, and the power consumption can be ignored. It was.

(Other embodiments)
The actuators according to the first to third embodiments described above relate to a cantilever structure in which one end is a fixed part. However, the present invention includes various types such as a double-end structure and a folded structure. Needless to say, the structure is applicable. Also, in the voltage applying means and the polarity switching means, it is only necessary to apply a reverse polarity voltage between the electrodes of the piezoelectric actuator, so that various forms of voltage applying means and polarity switching means can be used. For example, the voltage application unit 13 and the polarity switching unit 14 described in the first embodiment can be replaced with the voltage application unit 32 and the polarity switching unit 33 described in the second embodiment, and vice versa. Is also possible.

The figure which shows the cross-section of the micromechanical device which concerns on the 1st Embodiment of this invention. The figure explaining the drive mechanism in 1st Embodiment. The figure explaining the operation | movement mechanism of the micro mechanical device which concerns on 1st Embodiment. FIG. 4 is a diagram illustrating a driving mechanism when a PZT material is used for the piezoelectric film. FIG. 4 is a diagram illustrating a driving mechanism when a PZT material is used for the piezoelectric film. The figure which shows the relationship between an electric field at the time of using piezoelectric materials, such as AlN and ZnO, and polarization. The figure which shows the relationship between an electric field at the time of using piezoelectric materials, such as AlN and ZnO, and electrostriction. The figure which shows the relationship between the drive voltage at the time of driving the produced variable capacitor, and capacity | capacitance. The figure which shows the cross-section of the micromechanical device which concerns on the 2nd Embodiment of this invention. The figure which shows the cross-section of the micromechanical device which concerns on the 3rd Embodiment of this invention. The figure which shows the structure of the variable capacitor provided with the conventional piezoelectric actuator. FIG. 12 is a diagram illustrating a drive mechanism when piezoelectric drive voltages V _{0 to} V _t are applied to the actuator 10 illustrated in FIG. 11. The figure which shows the relationship between the piezoelectric drive voltage V and the displacement x.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Board | substrate 2 Anchor 3 Lower electrode 4 Piezoelectric film 5 Upper electrode 6 Support film 7 Movable electrode 8 Fixed electrode 9 Dielectric film 10 Actuator 10a Fixed part 10b Action part 11 Electrode slit 12 Voltage application means 13 Voltage application means 14 Polarity switching means 15 DC lower power source 16 a DC power source 21 lower electrode 24 substrate 22 anchor 23 piezoelectric film 25 intermediate electrode 26 upper piezoelectric film 27 upper electrode 28 movable electrode 29 the electrode slit 30 fixed electrode 31 dielectric layer _S 1 to S ₄ switch

Claims (9)

A substrate,
A piezoelectric film provided on the substrate; a first electrode provided on a surface of the piezoelectric film facing the substrate; and a surface of the piezoelectric film facing the surface on which the first electrode is provided. An actuator comprising: a second electrode provided; a fixed portion fixed on the substrate; and an action portion extending from the fixed portion;
A fixed electrode disposed on the surface of the substrate so as to face the action portion;
Polarity for switching the voltage application means for applying a voltage between the first electrode and the second electrode and the polarity of the voltage to bend and displace the actuator in a direction approaching the substrate or away from the substrate And a switching means. 2. The micromechanical device according to claim 1, wherein the voltage applying means is a unipolar DC power source. 2. The micromechanical device according to claim 1, wherein the voltage applying means is a bipolar DC power source.   4. The micromechanical device according to claim 1, wherein the piezoelectric film is made of a c-axis alignment film of aluminum nitride or zinc oxide. 5. A substrate,
A stacked structure in which a first electrode, a first piezoelectric film, a second electrode, a second piezoelectric film, and a third electrode are stacked in this order from the side facing the substrate provided on the substrate. An actuator having a fixed portion fixed on the substrate, and an action portion extending from the fixed portion;
A fixed electrode disposed on the surface of the substrate so as to face the action portion;
The voltage application means for applying a voltage between the second electrode and the third electrode, and the second electrode and the first electrode, and switching the polarity of each voltage, A micromechanical device comprising: a polarity switching unit that bends and displaces in a direction approaching the substrate or away from the substrate. 6. The micromechanical device according to claim 5, wherein the voltage applying means is a unipolar DC power source. 6. The micromechanical device according to claim 5, wherein the voltage applying means is a bipolar DC power source.   8. The micromechanical device according to claim 5, wherein the first piezoelectric film and the second piezoelectric film are made of a c-axis alignment film of aluminum nitride or zinc oxide. .   The micromechanical device according to any one of claims 1 to 8, wherein the micromechanical device is a variable capacitor or a switch.

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