KR20070022651A - Variable capacitor and process for fabricating the same - Google Patents

Abstract

A lower movable electrode 35 having line portions 35a and 35a at both ends and a capacitor portion 35b at the center side, and a lower portion having line portions 37a and 37a at both ends and a capacitor portion 37b at the center side. The movable electrodes 37 are disposed so that the capacitor portions 35b and 37b face each other, and the lower movable electrode actuators 27a, 27b, 27c, 27d and the upper movable electrode 37 which drive the lower movable electrode 35 are provided. The drive electrodes of the upper movable electrode actuators 29a, 29b, 29c, and 29d for driving the electrical electrodes are electrically separated from the lower movable electrode 35 and the upper movable electrode 37. These actuators 27a-27d and / or 29a-29d move the lower movable electrode 35 and / or the upper movable electrode 37 to adjust the distance between both capacitor sections 35b and 37b. Control the capacitance.

Variable Capacitors, MEMS, Moving Electrodes, Actuators, Capacitance

Description

Variable Capacitor and Manufacturing Method Thereof {VARIABLE CAPACITOR AND PROCESS FOR FABRICATING THE SAME}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable capacitor and a method of manufacturing the same, and more particularly, to a variable capacitor having an opposing movable electrode using MEMS (Micro Electro Mechanical System) technology and a method of manufacturing the same.

The variable capacitor is an important component in an electric circuit including a variable frequency oscillator, a tuning amplifier, a phase shifter, an impedance matching circuit, and the like, and mounting in portable devices is increasing recently. Compared with varactor diodes, which are currently used mainly, variable capacitors manufactured using MEMS technology have the advantage of low loss and high Q value, and hastened their development.

1 (a) and 1 (b) are cross-sectional views and plan views showing the structure of a conventional variable capacitor (e.g., non-patent document Jan Y. Park, et al., "MICROMACHINED RF MEMS TUNABLE CAPACITORS USING PIEZOELECTRIC ACTUATORS"). IEEE International Microwave Symposium, 2001). The variable capacitor includes a movable electrode substrate 11 having a unimorph piezoelectric actuator 12 and a movable electrode 13, and a fixed electrode substrate provided with a fixed electrode 16 ( 15 is bonded to a solder bump 14 so that the movable electrode 13 and the fixed electrode 16 face each other. The capacitance of the capacitor is controlled by moving the movable electrode 13 by driving the piezoelectric actuator 12 to vary the distance between the movable electrode 13 and the fixed electrode 16.

Problems to be Solved by the Invention

However, the above-mentioned conventional variable capacitor has the following problems. Since the movable electrode 13 and the fixed electrode 16 are joined by the solder bumps 14, the distance between both electrodes is controlled by the solder bumps 14, and the distance is reduced to a state close to zero. It is impossible, and the capacitance of the capacitor when the piezoelectric actuator 12 is in the initial state does not increase.

Between the capacitance C of the capacitor and the distance d between the electrodes constituting the capacitor, the relationship between C = ε ₀ ε _r S / d (ε ₀ : permittivity in vacuum, ε _r : relative dielectric constant, S: area of electrode) And a relationship between the capacitance C and the distance d between the electrodes is shown in FIG. 2. In FIG. 2, the scales of the vertical axis and the horizontal axis are normalized to initial states C and d. When the change amount of the piezoelectric actuator is constant, the ratio of the change in the capacitance becomes larger in the state in which it is closer than in the state where both electrodes are separated. Therefore, the fact that the capacitance in the initial state does not become large (small) means that the change in the capacitance does not become large (small).

In the variable capacitor of this conventional example, as shown in Fig. 1 (b), the movable electrode 13 and the piezoelectric actuator 12 are connected by a torsion bar 17, and the movable electrode 13 and the piezoelectric element are connected. The drive electrode for the actuator 12 is integrally formed and electrically connected. Since the narrow torsion bar 17 is included in the line to the movable electrode 13 constituting the capacitor, this portion becomes an equivalent series resistance (ESR), resulting in a loss of resistance. Since the signal line electrically connected to the variable capacitor and the drive electrode for the piezoelectric actuator 12 are used together, the signal line is connected to a piezoelectric element, which is a high dielectric material, resulting in a dielectric loss and a very small Q value. There is. In addition, the line to the movable electrode 13 is not subjected to impedance matching, but also loses input energy, that is, insertion loss. Therefore, the present inventors are pushing for technical development to solve this problem.

The present inventor also proposes a variable capacitor in which two opposing electrodes are configured to be driven by a voltage actuator (see Japanese Patent Laid-Open No. 2004-127973). In the variable capacitor having the configuration in which the two movable electrodes are opposed to each other, since no bump is provided, the distance between the two electrodes can be easily reduced, so that a large capacitance can be obtained even with a small configuration. This brings about the effect of large change in capacitance.

The present invention has been devised in view of such a situation. Even in a small configuration, the capacitance can be increased, the rate of change in capacitance can be increased, and the capacitance can be fine-tuned, and the Q value is high. An object of the present invention is to provide a variable capacitor and a method of manufacturing the same.

Still another object of the present invention is to provide a variable capacitor capable of preventing energy loss (insertion loss) of a signal input from the outside and a method of manufacturing the same.

It is still another object of the present invention to provide a variable capacitor capable of obtaining a large change in capacitance and a large change in capacitance at which the driving voltage of the piezoelectric actuator is at least.

Means for solving the problem

A variable capacitor according to the present invention is a variable capacitor in which an opposite electrode is movable, comprising a substrate, a movable electrode having a first electrode portion and a second electrode portion, and a plurality of piezoelectric actuators for driving the movable electrode. The movable electrodes face each other to form a capacitor, and the movable electrodes and the signal pad are electrically connected to each other.

In this invention, since the voltage actuator which drives a movable electrode and a movable electrode is provided in the same board | substrate, it is a compact structure. Moreover, since each movable electrode can be moved, the distance between both movable electrodes can be made small, large capacitance and large change of an electrostatic capacitance are realized, and fine adjustment of an electrostatic capacitance is also easy. In addition, since the first electrode portion corresponding to the line (signal line) to the second electrode portion constituting the capacitor and the driving electrode for driving the piezoelectric actuator are electrically separated from each other, the first electrode portion of the piezoelectric element of the piezoelectric actuator ( High dielectric constant), and the insertion loss can be suppressed to improve the Q value.

In the variable capacitor according to the present invention, the movable electrode has the first electrode portion and the second electrode portion, and the movable electrode is disposed up and down.

In the present invention, the first electrode portion corresponding to the line to the second electrode portion constituting the capacitor does not include the narrow torsion bar as in the conventional example, and since the equivalent series resistance can be reduced, the Q value Can improve.

In the variable capacitor according to the present invention, each of the plurality of piezoelectric actuators includes a drive electrode and a piezoelectric element provided between the drive electrodes, and is separate from the drive electrode and the movable electrode. It is done.

In the present invention, since the movable electrode for the capacitor and the driving electrode for the voltage actuator are configured separately, the line portion does not come into contact with the piezoelectric element (dielectric) as in the conventional example, so that the Q value can be improved. have.

In the variable capacitor according to the present invention, the piezoelectric actuators are provided on both sides of the first electrode portion of the movable electrode, and a CPW line is formed by the first electrode portion and the drive electrode of the voltage actuator. It is done.

In the present invention, impedance matching can be easily performed by adjusting the width of the first electrode portion and the distance between the driving electrode of the first electrode portion and the voltage actuator in the CPW line, so that insertion loss is eliminated and the Q value is improved. Can be designed.

The variable capacitor according to the present invention is characterized in that a dielectric layer is provided between the second electrode portions of the movable electrode that face each other.

In the present invention, since the dielectric layer is provided between the second electrode portions constituting the capacitor, the capacitance and the amount of change thereof can be increased.

In the variable capacitor according to the present invention, at least one of the movable electrodes is connected to a ground electrode.

In the present invention, the stray capacitance is suppressed by connecting one movable electrode to the ground electrode.

In the variable capacitor according to the present invention, the vicinity of the boundary between the first electrode portion and the second electrode portion of one of the movable electrodes is electrically separated.

In the present invention, since one movable electrode is electrically separated near the boundary between the first electrode portion and the second electrode portion, the signal inputted to the first electrode portion passes through the second electrode portion and the other side thereof. It reaches to the stage of the 1st electrode part, and there is no thing reflecting there, and the energy loss (insertion loss) of an input signal is reduced.

A variable capacitor according to the present invention is a variable capacitor having a movable electrode which is movable in an opposite direction and a plurality of piezoelectric actuators for driving the movable electrode, comprising a voltage applying means for applying a voltage between the movable electrodes. The voltage application means is adapted to apply a voltage between the movable electrodes in a state in which the movable electrode is brought close in driving the piezoelectric actuator.

In the present invention, the distance between the two movable electrodes due to the electrostatic attraction generated between the pair of movable electrodes by applying a voltage between the pair of movable electrodes in a state in which the pair of movable electrodes is approached by driving the piezoelectric actuator. Make it even smaller.

In the method of manufacturing a variable capacitor according to the present invention, a method of manufacturing a variable capacitor in which an electrode is movable by driving a piezoelectric actuator, the method comprising: forming a plurality of the piezoelectric actuators on a substrate; And forming a movable electrode having a second electrode portion on the substrate, forming a sacrificial layer for forming a gap between the movable electrodes, removing the sacrificial layer, and removing the plurality of sacrificial layers. And a cutting step of cutting off portions of the piezoelectric actuator of the piezoelectric actuator from the substrate except for an end portion of the piezoelectric actuator and an end portion of the first electrode portion of the movable electrode.

In the present invention, a pair of movable electrodes and a piezoelectric actuator for driving these are easily formed on the same substrate.

In the method of manufacturing a variable actuator according to the present invention, there is provided a method of manufacturing a variable capacitor in which an electrode is movable by driving a piezoelectric actuator, the method comprising: forming a plurality of the piezoelectric actuators on a substrate; Forming a movable electrode having a second electrode portion on the substrate, forming a dielectric layer between the movable electrodes, forming a sacrificial layer for forming a gap between any one of the movable electrodes and the dielectric layer; And a removing step of removing the sacrificial layer, and a cutting step of cutting off portions of the plurality of piezoelectric actuators, excluding end portions of the first electrode portion of the movable electrode, from the substrate.

In the present invention, a dielectric layer between a pair of movable electrodes, a voltage actuator for driving them, and a pair of movable electrodes is easily formed on the same substrate.

The manufacturing method of the variable capacitor which concerns on this invention is characterized by performing the said removal process and the said cutting process simultaneously.

In the present invention, the work efficiency is improved by simultaneously performing the step of removing the sacrificial layer and the step of cutting the movable electrode and the voltage actuator from the substrate excluding the end.

Effect of the Invention

In the present invention, even in a small configuration, it is possible to increase the capacitance and to increase the rate of change of the capacitance, to fine-tune the capacitance, and to provide a variable capacitor excellent in impact resistance. . In addition, by electrically separating the movable electrode and the piezoelectric actuator, the structure of the torsion bar causing the equivalent series resistance is eliminated, and a wide line portion (first electrode portion) to the capacitor forming portion (second electrode portion) is secured. As a result, a high Q value can be obtained.

In addition, in the present invention, since the capacitor formation portion and the peripheral portion thereof are floated in the air from the substrate, the influence of the dielectric constant of the substrate or the like is eliminated, and a high Q value can be obtained.

In the present invention, since one of the variable electrodes is electrically separated near the boundary between the first electrode portion and the second electrode portion, it is possible to prevent energy loss (insertion loss) of the signal input from the outside.

In addition, in the present invention, the voltage is applied between the pair of movable electrodes while the pair of movable electrodes is approached by driving the piezoelectric actuator. It is possible to make it even smaller, so that a large capacitance and a large change in capacitance can be obtained. In addition, since the electrostatic attraction is generated in a state where the pair of movable electrodes are brought close by the driving of the voltage actuator, a large electrostatic attraction can be generated with a small driving voltage.

1 is a cross-sectional view showing a configuration of a conventional variable capacitor, a plan view.

2 is a graph showing the relationship between the capacitance of a capacitor and the distance between electrodes.

3 is a perspective view of a variable capacitor according to the first embodiment.

4 is an exploded perspective view of the variable capacitor according to the first embodiment.

FIG. 5 is a sectional view taken along line B-B and line C-C in FIG. 3; FIG.

6 is a cross-sectional view illustrating a process for manufacturing the variable capacitor according to the first embodiment.

7 is a cross-sectional view illustrating a process of manufacturing the variable capacitor according to the first embodiment.

8 is a cross-sectional view showing a modification of the manufacturing process of the variable capacitor according to the first embodiment.

9 is an exploded perspective view of a modification of the variable capacitor according to the first embodiment.

10 is an exploded perspective view of a variable capacitor according to a second embodiment.

11 is a cross-sectional view illustrating a process for manufacturing the variable capacitor according to the second embodiment.

12 is a cross-sectional view showing a step of manufacturing a variable capacitor according to the second embodiment.

Fig. 13 is an exploded perspective view of a variable capacitor (only movable electrode and voltage actuator) according to the third embodiment.

14 is a cross-sectional view showing an example of a process of manufacturing a variable capacitor according to the third embodiment.

15 is a cross-sectional view showing another example of the process of manufacturing the variable capacitor according to the third embodiment.

Fig. 16 is a diagram for explaining the effect of a dielectric layer on a variable capacitor according to the third embodiment.

17 is a top view and an enlarged view of a variable capacitor according to a fourth embodiment.

18 is a top view of a variable capacitor according to a fifth embodiment.

19 is a diagram for explaining a bimorph piezoelectric actuator.

<Description of the code>

21 boards

23 insulation layer

27, 27a, 27b, 27c, 27d actuator for lower movable electrode

29, 29a, 29b, 27c, 27d actuator for upper movable electrode

31 Lower electrode for actuator

33 Upper electrode for actuator

34 Piezoelectric Layer

35 Lower movable electrode

37 Upper movable electrode

35a, 37a line part (first electrode part)

35b, 37b capacitor section (second electrode section)

40 openings

41 Sacrifice

44 Grounding Electrode

45 signal pad

46 dielectric layers

47 cavity

48 power supply circuit

50 spaces

51 Second Sacrificial Layer

The present invention will be specifically described with reference to the drawings showing the embodiments thereof. In addition, this invention is not limited to the following embodiment.

(1st embodiment)

3 is a perspective view of the variable capacitor according to the first embodiment, and FIG. 4 is an exploded perspective view thereof. 21 is a board | substrate formed with silicon, a compound semiconductor, etc. In FIG. The cross-shaped opening 40 is provided in the center part of the board | substrate 21, and the insulating layer 23 is provided in the upper surface of the board | substrate 21. As shown in FIG.

In the drawings, 35 and 37 are the lower movable electrodes and the upper movable electrodes made of A1 (aluminum). The lower movable electrode 35 is composed of line portions 35a and 35a on both ends as the first electrode portion and a capacitor portion 35b in the center as the second electrode portion, and an end portion of one line portion 35a is formed. It is connected to a signal pad 45 to which a signal is input from an external high frequency signal source (not shown), and an end of the other line portion 35a is connected to the insulating layer 23 to be electrically connected to the ground electrode 44. Separated by. At these ends, the lower movable electrode 35 is supported by the substrate 21, and other portions of the lower movable electrode 35 except for the ends thereof are located on the opening 40. As shown in FIG. Moreover, the upper movable electrode 37 is comprised from the line part 37a, 37a of the both ends as a 1st electrode part, and the capacitor part 37b of the center as a 2nd electrode part, and both the line part 37a, 37a. Both ends are connected to the ground electrode 44. At their ends, the upper movable electrode 37 is supported on the substrate 21, and other portions of the upper movable electrode 37 except for the ends thereof are located on the opening 40. As shown in FIG.

The lower movable electrode 35 and the upper movable electrode 37 are arranged crosswise in accordance with the opening 40 of the substrate 21, and the capacitor portion 35b of the lower movable electrode 35 and the upper movable electrode ( The capacitor portion 37b of 37 is opposed through the air layer. It functions as a capacitor in the opposing capacitor section 35b and capacitor section 37b. In addition, although the lower movable electrode 35 and the upper movable electrode 37 which are electrically separated from each other may be used in a state of being floated from the ground, the upper movable electrode 37 may be grounded for the purpose of suppressing floating capacitance. (44).

The lower movable electrode 35 and the upper movable electrode 37 are driven by four lower movable electrode actuators 27a, 27b, 27c, 27d and upper movable electrode actuators 29a, 29b, 29c, 29d, respectively. . These lower movable electrode actuators 27a, 27b, 27c, 27d and the upper movable electrode actuators 29a, 29b, 29c, and 29d face the opening 40 of the substrate 21. Actuator 27 for the lower movable electrode (in the case of describing an actuator for one lower movable electrode as a representative, reference numeral 27 is simply used) and actuator 29 for the upper movable electrode (actuator for the lower movable electrode as a representative) In the following description, reference numeral 29 is simply used to indicate a piezoelectric actuator, and the insulating layer 23, the lower electrode 31 for the actuator, the piezoelectric layer 34, and the upper electrode 33 for the actuator are in this order below. The unimorph type laminated | stacked from the side is comprised. The actuator lower electrode 31 is formed of Pt / Ti (platinum / titanium), the actuator upper electrode 33 is formed from Pt, and the lower movable electrode 35 and the upper movable electrode 37 are both. Is different from the other. The signal input to the signal pad 45 from the high frequency signal source (not shown) is opposed to the capacitor portion 35b through the air layer from the capacitor portion 35b through the line portion 35a of the lower movable electrode 35. It flows into the ground electrode 44 via the capacitor portion 37b and the line portion 37a of the upper movable electrode 37. By inverting the polarization directions of the piezoelectric layers 34 of the lower movable electrode actuator 27 and the upper movable electrode actuator 29, the movement direction at the time of actuator driving is reversed.

By applying a voltage to the lower movable electrode driving pad 42 from the lower movable electrode driving power supply (not shown) to the upper electrode 33 for the actuator of the lower movable electrode actuator 27, the lower movable electrode 35 is A voltage is applied to the upper movable electrode driving pad 43 from the upper movable electrode driving power supply (not shown) to the upper electrode 33 for the actuator of the upper movable electrode actuator 29 toward the movable electrode 37. The movable electrodes 37 move independently of the lower movable electrodes 35, respectively. Therefore, by driving the lower movable electrode actuator 27 and / or the upper movable electrode actuator 29, the upper movable electrode 37 (capacitor portion 37b) and the lower movable electrode 35 (capacitor portion 35b). Since the distance with)) can be changed, the desired capacitance can be obtained.

In the present invention, the line portion and the capacitor portion through which signals from the high frequency signal source flow, and the drive electrode for driving the actuator are electrically separated. Therefore, since the line portion and the capacitor portion do not come into contact with the piezoelectric layer (dielectric) in the actuator, and because the surrounding is air, there is no dielectric loss and the Q value can be increased. FIG. 5 shows cross sections taken along lines B-B and C-C in FIG. 3. The line portion 35a of the lower movable electrode 35 and the line portion 37a of the upper movable electrode 37 are fitted to the actuator lower electrode 31 connected to the ground electrode 44. That is, these line portions 35a and 37a become CPW-type lines, and the interval w1 between the actuator lower electrode 31 and the line portion 35a or the line portion 37a and the line portion ( By adjusting the width w2 of the line portion 35a or the line portion 37a, the impedance of the line portion 35a or the line portion 37a is set to 50? To eliminate insertion loss.

Next, with reference to FIGS. 6 and 7, a method of manufacturing a variable capacitor having the above configuration will be described. 6 and 7 show cross sections taken along the line A-A in FIG.

On the substrate 21 made of silicon, a low stress nitrogen silicon layer 23a is formed by LPCVD (Low Pressure Chemical Vapor Deposition) method, and thereafter, Pt / Ti (for example, 0.5 µm thick). / 50nm layer 31a, lithium niobate, barium titanate, lead titanate, lead zirconate titanate, bismuth titanate, and the like The piezoelectric layer 34a (for example, 0.5 micrometer in thickness) made of a material is formed sequentially (FIG. 6A).

Then, by the patterning process of the photolithographic technique, a piezoelectric layer 34 having a predetermined shape and a lower electrode 31 for an actuator are formed from the piezoelectric layer 34a and the Pt / Ti layer 31a (Fig. 6 (b), (c)). In this case, a RIE (Reactive Ion Etching) device or an ion milling device using Cl ₂ / Ar (chlorine / argon) -based gas is used.

By the photolithographic technique, the upper electrode 33 for the actuator made of Pt is formed on the piezoelectric layer 34 (FIG. 6 (d)), and the silicon nitride layer 23a is patterned to form an insulating layer. (23) is obtained (Fig. 6 (e)). As the insulating layer 23, in addition to the silicon nitride layer, a silicon oxide layer formed by sputtering, thermal oxidation, or CVD may be used.

Next, a lower movable electrode 35 made of Al having a predetermined shape is formed on the substrate 21 (FIG. 7 (f)), and then a sacrificial layer 41 of a predetermined shape made of a resist material is formed. 7 (g), an upper movable electrode 37 made of Al having a predetermined shape is formed at a position opposite to the lower movable electrode 35 (FIG. 7 (h)).

The lower movable electrode 35, the upper movable electrode 37, the lower movable electrode actuator 27, and the substrate 21 around the upper movable electrode actuator 29 are removed from the rear surface thereof with a deep reactive ion. Etching to form an opening 40 (Fig. 7 (i)). By this etching, the end portions of the line portions 35a and the line portions 37a of the lower movable electrode 35 and the upper movable electrode 37, the actuator 27 for the lower movable electrode and the actuator 29 for the upper movable electrode 29 The remaining part except for each end of) is cut out from the substrate 21. Further, the etching gas is a mask for forming the use of SF _6, and opening 40, for example in the process is a register.

Finally, the sacrificial layer 41 is etched away to secure a gap 42 between the lower movable electrode 35 and the upper movable electrode 37, thereby producing a variable capacitor (FIG. 7 (j)).

Unlike the manufacturing procedure described above, after the process of FIG. 7H, the sacrificial layer 41 is first removed to secure the gap 42 between the lower movable electrode 35 and the upper movable electrode 37. After that, the substrate 21 may be etched to form the opening 40. As the material of the sacrificial layer 41, oxides such as MgO (magnesium oxide) can also be used in addition to the above-described resistors. Acetic acid or acetic acid may be used for etching in this case.

8 shows a modification of the manufacturing method of the variable capacitor. The manufacturing process of the first half in this modification is the same as the above-mentioned example (FIGS. 6 (a)-7 (f)). A sacrificial layer 41 of a predetermined type made of silicon of the same material as the substrate 21 is formed (Fig. 8 (a)), and the upper movable electrode made of Al having a predetermined shape at a position opposite to the lower movable electrode 35. 37 is formed (FIG. 8 (b)).

Then, for example, SF ₆ from the surface of the substrate 21 Using the gas, the sacrificial layer 41 and the substrate 21 are simultaneously etched to form a cavity 47 (Fig. 8 (c)). By this etching, the end portions of the line portions 35a and the line portions 37a of the lower movable electrode 35 and the upper movable electrode 37, the actuator for the lower movable electrode 27 and the actuator for the upper movable electrode 29 The remaining portion except for each end portion of) is cut out from the substrate 21 in the same manner as the above-described example. However, since the portion is etched toward the surface side of the substrate 21, the cavity is not opened as in the above-described example. 47 is formed.

9 is an exploded perspective view of the variable capacitor manufactured by this modification. A cross-shaped cavity 47 is provided in the center of the substrate 21. 9, the same code | symbol is attached | subjected to the same part as FIG. 3, FIG. 4, and description is abbreviate | omitted.

(2nd embodiment)

Fig. 10 is an exploded perspective view of the variable capacitor according to the second embodiment, and Figs. 11 and 12 are sectional views showing the manufacturing process of the variable capacitor.

In the second embodiment, the lower movable electrode 35 is provided around the lower movable electrode 35, the upper movable electrode 37, the lower movable electrode actuator 27, and the upper movable electrode actuator 29. The space 50 is provided between the upper movable electrode 37 and the insulating layer 23 and the substrate 21. The substrate 21 is formed of a material such as glass, sapphire, alumina, glass ceramics, gallium arsenide, or the like, rather than silicon. Configurations other than these are the same as that of 1st Embodiment, and the same code | symbol was attached | subjected to the same part.

For example, after forming the second sacrificial layer 51 of silicon by the sputtering method on the substrate 21 made of glass, the nitrogen silicon layer 23a and Pt / like the first embodiment. The Ti layer 31a and the piezoelectric layer 34a are sequentially formed (FIG. 11 (a)). Then, similarly to the first embodiment, a piezoelectric layer 34 of a predetermined shape, an actuator lower electrode 31, an actuator upper electrode 33, and an insulating layer 23 are obtained (Fig. 11 (b)-( e)).

Next, after forming the lower movable electrode 35 made of Al having a predetermined shape on the second sacrificial layer 51 (FIG. 12 (f)), a sacrificial layer 41 made of a resist material is formed throughout ( 12 (g)), an upper movable electrode 37 made of Al having a predetermined shape is formed at a position opposite to the lower movable electrode 35 (FIG. 12 (h)).

Then, the sacrificial layer 41 is etched away to secure a gap 42 between the lower movable electrode 35 and the upper movable electrode 37 (FIG. 12 (i)), and the second sacrificial layer ( 51 is removed by etching to secure a space 50 between the substrate 21, the lower movable electrode 35, and the insulating layer 23, thereby producing a variable capacitor (Fig. 12 (j)). In addition, the material of the sacrificial layer 41 and the second sacrificial layer 51 may be made the same, and the etching of the sacrificial layer 41 and the etching of the second sacrificial layer 51 may be performed simultaneously.

In the second embodiment, since the lower movable electrode 35 can be lifted from the substrate 21 in the air by etching the second sacrificial layer 51, the substrate 21 does not need to be etched and thus the substrate ( 21, the kind of material which can be used increases. For example, materials such as glass ceramics having a low dielectric constant and difficulty in etching can also be used as the substrate 21. For this reason, it becomes possible to improve Q value further.

(Third embodiment)

FIG. 13 is an exploded perspective view of the variable capacitor (only the movable electrode and the voltage actuator) according to the third embodiment, and FIG. 14 and FIG. 15 are sectional views showing the manufacturing process of this variable capacitor.

In the third embodiment, the dielectric layer 46 is provided between the lower movable electrode 35 (capacitor portion 35b) and the upper movable electrode 37 (capacitor portion 37b). The other structure is the same as that of 1st Embodiment, and attaches | subjects the same code | symbol to the same part, and abbreviate | omits description.

This dielectric layer 46 may be provided on the upper movable electrode 37 (capacitor portion 37b) side as shown in FIG. 13, and is not shown, but is shown on the lower movable electrode 35 (capacitor portion 35b) side. It may be installed in. The provision of the dielectric layer 46 increases the mass of the movable portion, resulting in a slight decrease in the resonant frequency or a decrease in the operating speed. However, as described later, the capacitance and its rate of change can be greatly increased.

16 shows the effect of the dielectric layer 46. As shown in Fig. 16A, the case where the dielectric layer 46 is provided on the capacitor portion 37b side of the upper movable electrode 37 will be described. When the thickness of the dielectric layer 46 is d1 and the thickness of the air layer formed between the dielectric layer 46 and the capacitor portion 35b of the lower movable electrode 35 is d2, the thickness of the capacitor portion 37b and the capacitor portion 35b The distance d between them becomes d = d1 + d2.

FIG. 16B is a graph showing a change in capacitance C when the capacitor portion 35b and / or the capacitor portion 37b are moved to change the thickness d2 of the air layer. The capacitor portion 35b and the capacitor portion 37b are square (one side: 230 μm), and the distance d between the electrodes in the initial state and the thickness d 2 of the air layer are d = 0.75 μm and d2 = 0.3 μm (d2 / d = 0.4). As the dielectric layer 46, Al ₂ O ₃ (alumina) (dielectric constant? = 10), which is a material having a low dielectric loss, is used. In addition, the change of the capacitance C in the comparative example which differed only by not providing such a dielectric layer is also shown by FIG. 16 (b).

As shown in Fig. 16B, in the variable capacitor of the example of the present invention in which the dielectric layer 46 is provided, about 1.36pF in the initial state and about 10.4pF in the state where the capacitor portion 35b is in contact with the dielectric layer 46. It has capacitance and the rate of change is about 7.6 times. Thus, by providing the dielectric layer 46, the capacitance and its variable range can be made very large.

FIG. 14 is a cross-sectional view showing an example of the manufacturing process of the variable capacitor of the third embodiment (the dielectric layer 46 is provided on the upper movable electrode 37 (capacitor portion 37b) side). The process of the first half is the same as the process (FIG. 6 (a)-7 (g)) of 1st Embodiment mentioned above.

By photolithographic technique, a dielectric layer 46 made of Al ₂ O ₃ is patterned on the sacrificial layer 41 (Fig. 14 (a)), and a predetermined shape is formed at a position opposite to the lower movable electrode 35. An upper movable electrode 37 made of Al is formed (Fig. 14 (b)). Then, the lower movable electrode 35, the upper movable electrode 37, the lower movable electrode actuator 27, and the substrate 21 around the upper movable electrode actuator 29 are removed from the rear surface of the DRIE apparatus. Etching to form an opening 40 (FIG. 14 (c)), and finally, the sacrificial layer 41 is etched away to remove the gap 42 between the lower movable electrode 35 and the dielectric layer 46. FIG. ), A variable capacitor is produced (Fig. 14 (d)).

FIG. 15 is a cross-sectional view showing another example of the manufacturing process of the variable capacitor of the third embodiment (the dielectric layer 46 is provided on the upper movable electrode 35 (capacitor portion 35b) side). The process of the first half is the same as the process (FIGS. 6 (a)-7 (f)) of 1st Embodiment mentioned above.

By photolithographic technology, a dielectric layer 46 made of Al ₂ O ₃ is patterned on the lower movable electrode 35 (Fig. 15 (a)). A sacrificial layer 41 made of a resistor material or MgO is formed into a predetermined shape (Fig. 15 (b)), and an upper movable electrode 37 made of Al of a predetermined shape is formed at a position opposite to the lower movable electrode 35. (FIG. 15 (c)). Then, the lower movable electrode 35, the upper movable electrode 37, the lower movable electrode actuator 27, and the substrate 21 around the upper movable electrode actuator 29 are moved from the rear surface to the DRIE apparatus. Etching to form an opening 40 (FIG. 15 (d)), and finally, the sacrificial layer 41 is etched away to remove the gap 42 between the dielectric layer 46 and the upper movable electrode 37. FIG. By ensuring that the variable capacitor is produced (Fig. 15 (e)).

Unlike the manufacturing procedure of FIGS. 14 and 15 described above, after the processes of FIGS. 14B and 15C, the sacrificial layer 41 is first removed to secure the gap 42, and then the substrate ( 21 may be etched to form the opening 40. Also in this third embodiment, as described above (see FIG. 8), the material of the sacrificial layer 41 is the same as that of the substrate 21, and the sacrificial layer 41 and the substrate 21 are replaced with each other. You may make it etch from the back side of the board | substrate 21 sequentially or simultaneously.

(4th embodiment)

FIG. 17 shows a fourth embodiment, FIG. 17A is a top view of a variable capacitor according to the fourth embodiment, and FIG. 17B is an enlarged view at a portion D of FIG. 17A. It is also.

In the fourth embodiment, in the lower movable electrode 35 in which one line portion 35a is connected to the signal pad 45, the other line portion 35a is different from the capacitor portion 35b. Is electrically isolated. That is, the lower movable electrode 35 is viewed from the signal pad 45, and the lower movable electrode 35 and the upper movable electrode 37 face each other to form a capacitor (capacitor portion 35b and capacitor portion 37b). At the opposite side of), it is electrically separated in two. The separated line portion 35a may be connected to the ground electrode 44 to have a grand potential.

In the fourth embodiment, a signal input from the signal pad 45 passes through the capacitor portion 35b through one line portion 35a, and with the signal pad 45 of the other line portion 35a. It is possible to prevent the energy loss of the input signal since it arrives at the opposite end, and there is no such thing as being reflected there, and this reflected signal can be eliminated.

(5th embodiment)

18 is a top view of a variable capacitor according to the fifth embodiment. In Fig. 18, a power supply circuit 48 is provided between the signal pad 45 and the ground electrode 44, and the signal pad 45 (the lower movable electrode 35 and the ground electrode 44) (the upper movable electrode) A voltage can be applied between 37).

The fifth embodiment relates to a method of adjusting the distance between the lower movable electrode 35 (capacitor portion 35b) and the upper movable electrode 37 (capacitor portion 37b). After driving the lower movable electrode actuator 27 and / or the upper movable electrode actuator 29 to reduce the gap between the capacitor portion 35b and the capacitor portion 37b, the lower movable electrode 48 is operated by the power supply circuit 48. A voltage is applied between the electrode 35 and the upper movable electrode 37 to make the distance between the two electrodes even smaller by the electrostatic force generated between the two electrodes.

As described above, in the fifth embodiment, distance control in two stages, namely, piezoelectric actuator driving and electrostatic actuator (human force) driving, is performed. You can get it. Since the electrostatic attraction is generated in the state where the piezoelectric actuator approaches the positive electrode, a large capacitance and a change in capacitance can be obtained. In addition, since the electrostatic attraction is generated in the state where the positive electrode is approached by the piezoelectric actuator, it is possible to generate a large electrostatic attraction with a small driving voltage.

In addition, in the above-mentioned example, although the lower movable electrode actuator 27 and the upper movable electrode actuator 29 were unimorph type, it is not limited to this. For example, the bimorph of the parallel connection type shown in FIG. 19A, or the bimorph of the series connection type shown in FIG. 19B may be sufficient. 19 (a) and 19 (b), piezoelectric elements 54a and 54b polarized in the direction of the arrow shown above and below the intermediate electrode 63 are provided. The lower movable electrode 53 is provided in the piezoelectric element 54a, and the upper movable electrode 55 is provided in the piezoelectric element 54b. And as shown, the bimorph deforms by applying the DC voltage V. As shown in FIG. When the lower movable electrode actuator 27 and the upper movable electrode actuator 29 are bimorphed, the insulating layer 23 in contact with the lower electrode 31 for the actuator in each of the above-described embodiments is It is not necessary.

This invention is not limited to each embodiment or modification mentioned above, and includes other various types of embodiment or modification. For example, in the above-described example, the piezoelectric actuators are driven to reduce the distance between the positive electrodes or the distance between the movable electrode and the dielectric layer (the capacitance becomes large). The piezoelectric actuator may be driven. In this case, the direction in which the unimorph piezoelectric actuator deforms may be reversed. Moreover, you may accommodate the variable capacitor in embodiment or modification mentioned above in the ceramic package. In such a case, various pads such as an external connection terminal provided in the package and a signal pad 45 provided on the substrate 21 are connected by a connection member such as a wire or bump.

Even in a small configuration, the capacitance can be increased, the rate of change in capacitance can be increased, and the capacitance can be fine-tuned, and a variable capacitor having a high Q value and a manufacturing method thereof can be provided. In addition, a variable capacitor capable of preventing energy loss (insertion loss) of a signal input from the outside and a method of manufacturing the same can be provided.

Claims (11)

A variable capacitor capable of moving an opposite electrode, comprising: a substrate, a movable electrode having a first electrode portion and a second electrode portion, and a plurality of piezoelectric actuators for driving the movable electrode, wherein the movable electrode is opposed to the capacitor; And a movable capacitor and a signal pad are electrically connected to each other. The method of claim 1, The movable electrode has the first electrode portion and the second electrode portion, and the movable electrode is disposed up and down. The method according to claim 1 or 2, Each of the plurality of piezoelectric actuators includes a drive electrode and a piezoelectric element provided between the drive electrodes, and the variable capacitor is separate from the drive electrode and the movable electrode. The method of claim 3, The piezoelectric actuators are provided on both sides of the first electrode portion of the movable electrode, and the variable capacitor comprises a CPW line formed by the first electrode portion and the drive electrode of the voltage actuator. The method according to any one of claims 1 to 4, A variable capacitor, wherein a dielectric layer is provided between the second electrode portions facing the movable electrode. The method according to any one of claims 1 to 5, At least one of the movable electrodes is connected to the ground electrode. The method according to any one of claims 1 to 6, The vicinity of the boundary part of the said 1st electrode part and the said 2nd electrode part of the said movable electrode is electrically isolate | separated, The variable capacitor characterized by the above-mentioned. A variable capacitor having a movable electrode whose opposite direction is movable, and a plurality of piezoelectric actuators for driving the movable electrode, comprising a voltage applying means for applying a voltage between the movable electrodes, wherein the piezoelectric actuator is driven. And the voltage applying means is configured to apply a voltage between the movable electrodes in a state in which the movable electrode is brought close to each other. A method of manufacturing a variable capacitor in which an electrode is movable by driving a piezoelectric actuator, the method comprising: forming a plurality of the piezoelectric actuators on a substrate, and a movable electrode having a first electrode portion and a second electrode portion on the substrate. Forming a sacrificial layer; forming a sacrificial layer for forming a gap between the movable electrodes; removing the sacrificial layer; and end portions of the plurality of piezoelectric actuators; 1. A manufacturing method of a variable capacitor, comprising a cutting step of cutting off a portion except an end of an electrode portion from the substrate. A method of manufacturing a variable capacitor in which an electrode is movable by driving a piezoelectric actuator, the method comprising: forming a plurality of the piezoelectric actuators on a substrate, and forming a movable electrode having a first electrode portion and a second electrode portion on the substrate A step of forming a dielectric layer between the movable electrodes, a step of forming a sacrificial layer for forming a gap between one of the movable electrodes and the dielectric layer, a removing step of removing the sacrificial layer, and the plurality of And a cutting process of cutting off portions of the piezoelectric actuators of the piezoelectric actuator and the end portions of the first electrode portion of the movable electrode from the substrate. The method of claim 9 or 10, A method of manufacturing a variable capacitor, characterized in that the removal step and the cutting step are performed simultaneously.

Images