JP4855508B2 - MEMS variable capacitor and filter device using the same - Google Patents

Description

  The present invention relates to a MEMS variable capacitor manufactured using MEMS (Microelectromechanical System) technology and a filter device using the same.

  In recent years, the demand for RF (Radio Frequency) technology has increased rapidly. Various functions have come to be demanded for RF devices due to the diversity of functions and the rapid increase in users. In particular, a function that operates in a wide band in addition to downsizing and cost reduction is desired for the filter as the RF frequency becomes broadband. From such a social background, the MEMS technology has been attracting attention in the application of portable radio terminal equipment. This is because the MEMS device has characteristics such as low power consumption, high-density packaging, and broadband characteristics.

  Research on MEMS filters has been active mainly in the United States since the late 1990s. Currently, a few companies have provided samples. However, these products mainly replace quartz and are characterized by miniaturization of devices, and filters have not yet been applied. In the case where the MEMS technology is applied to a filter, a technique for changing the interval between capacitors has been published at an academic conference. However, there is a problem that the variable rate is about 3 and relatively small, and the application range is limited.

  The MEMS variable capacitor is reported in, for example, Non-Patent Documents 1 to 3, but as an example, the technique described in Non-Patent Document 1 will be described below with reference to FIG. 19 as a conventional example.

  FIG. 19 is a perspective view showing a configuration of a conventional MEMS variable capacitor. In FIG. 19, spring beams 91 and 92 are provided on a dielectric substrate 90, have curling 97, each tip is connected via a connection portion 98, and one end is fixed by an anchor 93, and the other end is A capacitor portion facing the fixed electrode 94 is configured. The spring beams 91 and 92 have a bimorph structure of the piezoelectric material AlN, and are connected by reversing the direction of polarization in order to suppress warping (see reverse electric fields 95 and 96). On the other hand, when a DC voltage is applied, the spring beams 91 and 92 are deformed by the inverse piezoelectric effect, so that the distance between one end of the spring beam 92 and the fixed electrode 94 changes, and as a result, the capacitance value changes. It is.

  In the conventional example of FIG. 19, the capacitance value changes about three times. However, when this is applied to a filter, since the cutoff frequency is inversely proportional to the square root of the capacitance, only a change of about 1.7 times occurs, which is not much different from the performance of a semiconductor varicap. . For this reason, it was not particularly excellent as a new technology. Further, the process of depositing the piezoelectric material is different from the standard LSI process, and there is a problem that a special apparatus is required.

Japanese Patent Application Laid-Open No. 2008-098609. JP2009-135359A.

T. Kawakubo et al., "Piezoelectric RF MEMS tunable capacitor with 3V operation using CMOS compatible materials and process", IEDM Technical Digest, IEEE International Electron Devices Meeting, Washington, DC, U.S.A., pp. 294-297, December 2005. Robert L. Borwick III et al., "A high Q, Large tuning range, tunable capacitor for RF applications", The Fifteenth IEEE International Conference on Micro Electro Mechanical Systems, pp.669-672, January 2002. J.K.Luo et al., "MEMS based digital variable capacitors with a high-k dielectric insulator", Sensors and Actuators, A 132, pp. 139-146, May 2006. T. Yasuda et al., "Microfluidic Dispensing Device Using Wettability Gradient and Electrowetting", Proceeding of the 24th Sensor symposium, Vol. 24, pp.138-141, Tokyo Japan, 2007. Sung Kwon Cho et al., "Creating, Transporting, Cutting, and Merging Liquid Droplets by Electrowetting-Based Actuation for Digital Microfluidic Circuits", Journal of Microelectromechanical Systems, Vol. 12, No. 1, February 2003.

  In order to solve the above problems, Patent Documents 1 and 2 disclose the following variable capacitors.

  For example, in Patent Document 1, in order to provide a variable capacitor using an electrowetting phenomenon that facilitates the manufacturing process, is excellent in reliability and durability, and has no limitation on the tuning range, A second electrode provided apart from the first electrode; a fluid channel formed between the first electrode and the second electrode; and a first insulating film provided between the first electrode and the fluid channel. And a conductive fluid that moves along the fluid channel by generating a DC potential difference between the first and second electrodes. In Patent Document 1, it is described as “a variable capacitor with no limitation on the tuning range”. However, in an actual device, the capacitance range is limited, and thus, based on the limited capacitance range. It is considered to be limited to the tuning range.

  Further, in Patent Document 2, in order to provide a variable capacitor that can reduce mechanical wear and extend the life compared to a conventional product, two electrodes are provided to face each other, and a pair of electrodes is provided inside these electrodes. A dielectric plate is attached, and a container configured to allow two types of fluid containing liquid metal to flow between the dielectric plates, a tank for storing the fluid, and the fluid is transferred between the container and the tank. It is characterized by having a pump 3 that is configured to change the capacitance according to the amount of liquid metal.

  However, the above prior art has a problem that the capacitance of the capacitor cannot be changed digitally and the control circuit for fluid movement in the variable capacitor is complicated. That is, in Patent Document 1, two DC power sources are necessary, and in Patent Document 2, a pump that moves fluid is necessary.

  The object of the present invention is to solve the above-mentioned problems, the fluid movement control circuit is simpler than the prior art, and the capacitance of the capacitor can be changed digitally within a large change range of, for example, three digits or more. An object of the present invention is to provide a MEMS variable capacitor, a MEMS variable capacitor device including a plurality of MEMS variable capacitors, and a filter device using the MEMS variable capacitor device.

The MEMS variable capacitor according to the present invention is a MEMS variable capacitor that digitally changes the capacitance between the pair of electrodes by selectively switching whether or not to allow fluid to flow into a fluid channel between the pair of electrodes facing each other. A capacitor,
A first drive electrode provided in the fluid channel and applying a drive voltage for allowing the fluid to flow into the fluid channel by dielectric electrowetting drive;
A tank having a second drive electrode and supplying fluid to the fluid channel;
Fluid control means provided in the tank for controlling the fluid in the tank to be retained in the tank without flowing into the fluid channel by capillary action;
When the drive voltage is applied between the first drive electrode and the second drive electrode, the stress when the fluid flows into the fluid channel by the dielectric electrowetting drive is expressed as the fluid. Configured to be greater than the stress on the fluid by the control means,
When the drive voltage is not applied between the first drive electrode and the second drive electrode, the fluid is retained in the tank, while the first drive electrode and the second drive electrode When the drive voltage is applied between the drive electrodes, the fluid flows into the fluid channel and is filled, so that the pair of interelectrode capacitances can be digitally generated using only one drive voltage. It is characterized by changing.

  In the MEMS variable capacitor, the fluid control means is a slit portion including a plurality of slits.

  Further, in the MEMS variable capacitor, the fluid control means is configured such that the internal height of the tank is set so as to be thin so that the fluid is retained in the tank by a capillary phenomenon. And

A MEMS variable capacitor device according to the present invention is a MEMS variable capacitor device including a plurality of N of the above MEMS variable capacitors,
A plurality of N MEMS variable capacitors are connected in parallel, and a drive voltage for each MEMS variable capacitor is turned on / off to digitally change the overall capacitance of the MEMS variable capacitor device.

  In the MEMS variable capacitor device, the capacitances of the MEMS variable capacitors are configured to have different values.

In the MEMS variable capacitor device, each of the MEMS variable capacitors is configured to have a capacitance nC ₀ (n = 1, 2,..., N) with a basic capacitance C ₀ , The total capacity is changed digitally with a resolution of N bits.

  A filter device according to the present invention includes the MEMS variable capacitor device and at least one inductor connected to the MEMS variable capacitor device.

  According to the present invention, as compared with the prior art using two DC voltage sources in Patent Document 1, when no EWOD driving voltage is applied, the fluid flows into the tank side due to capillary action in the fluid control means of the slit portion or tank. However, it is possible to change the capacitance of one MEMS variable capacitor digitally with one DC voltage source with a very simple configuration by conducting water to the fluid channel side when an EWOD driving voltage is applied. . Further, by connecting a plurality of the MEMS variable capacitors in parallel, it is possible to realize a MEMS variable capacitor device that has a large capacitance change range and can change the capacitance digitally as compared with the prior art. Furthermore, a filter apparatus can be comprised using the said MEMS variable capacitor apparatus and an inductor.

It is a side view which shows the principle of the fluid variable MEMS capacitor which concerns on this invention. It is a circuit diagram which shows the digital variable circuit using the three fluid variable MEMS capacitors of FIG. (A) is a top view which shows the structure of the 2 tank type MEMS variable capacitor based on the 1st Embodiment of this invention, (b) is a front view which shows the structure of the 2 tank type MEMS variable capacitor of (a). is there. It is a graph which shows the electrostatic capacitance with respect to the water filling number in the 2 tank type MEMS variable capacitor of FIG.2 and FIG.3. FIG. 4 is a longitudinal sectional view for illustrating the fluid driving principle used in the two-tank MEMS variable capacitor of FIGS. 2 and 3, wherein (a) is a longitudinal sectional view showing the position of the fluid 25 when no DC voltage is applied. (B) It is a longitudinal cross-sectional view which shows the position of the fluid 25 at the time of the start of application of DC voltage, (c) is a longitudinal cross-sectional view which shows the position of the fluid 25 after sufficient time passes after the application of DC voltage is started. It is. FIG. 4 is a circuit diagram showing a MEMS variable low-pass filter configured using the four 2-tank MEMS variable capacitors of FIGS. 2 and 3. It is a table | surface which shows the step change of the MEMS variable low-pass filter of FIG. 6, and a cut-off frequency measurement result. It is a graph showing the frequency characteristics of the MEMS variable low-pass filter in the pass coefficient _{S 21} of FIG. 6 (0.001GHz~8GHz). It is a graph showing the frequency characteristics of the MEMS variable low-pass filter in the pass coefficient _{S 21} of FIG. 6 (0.001GHz~1GHz). It is a perspective view which shows the structure of the digital variable type MEMS variable capacitor based on the 2nd Embodiment of this invention. It is an enlarged view of the principal part of FIG. It is a longitudinal cross-sectional view of the fluid channel part of FIG. It is a cross-sectional view about the A-A 'line of FIG. 11 is a table showing a list of electrode sizes and the like of the digital variable MEMS variable capacitor in FIG. 10. FIG. 11 is a circuit diagram of the digital variable MEMS variable capacitor of FIG. 10. It is a longitudinal cross-sectional view which shows the structure of the MEMS variable capacitor using the two fluids 26 and 27 in the sealed fluid channel which concerns on the 1st modification of this invention. It is a longitudinal cross-sectional view which shows the structure of the MEMS variable capacitor using the fluid 26 which has the particle | grains 26a in the fluid channel based on the 2nd modification of this invention. It is a longitudinal cross-sectional view which shows the structure of the MEMS variable capacitor using the bubble 28 in the fluid 27 in the sealed fluid channel which concerns on the 3rd modification of this invention. It is a perspective view which shows the structure of the MEMS variable capacitor which concerns on a prior art example.

  Hereinafter, embodiments according to the present invention will be described with reference to the drawings. In addition, in each following embodiment, the same code | symbol is attached | subjected about the same component.

Basic principle.
In the following embodiments of the present invention, it is possible to realize a capacitance change of 80 times which is significantly higher than the current state by inserting water having a high dielectric constant (relative permittivity ε _r = 80) between the electrodes of the capacitor. In addition, a description will be given of trial evaluation of an RF filter using the same. In addition, by adopting the principle of dielectric electrowetting (hereinafter referred to as EWOD (Electrowetting on dielectric)) (for example, Non-Patent Documents 4 and 5) for transporting fluid (liquid) between electrodes, the fluid is electrically controlled. The fact that a structure having no mechanical movable part can be realized will be described.

FIG. 1 is a side view showing the principle of a fluid variable MEMS capacitor according to the present invention, and FIG. 2 is a circuit diagram showing a digital variable circuit using the three fluid variable MEMS capacitors of FIG. The fluid variable MEMS capacitor realizes a large capacitance change by inserting water (relative permittivity ε _r = 80) between the electrodes 11 and 12. When the dielectric constant in vacuum is ε ₀ , the relative dielectric constant is ε _r , the area of the electrodes 11 and 12 is A, and the distance between the electrodes 11 and 12 is d, the capacitance C is expressed by the following equation.

As shown in FIG. 1, when out of the water between the two electrodes 11 and 12 facing each other, the dielectric constant epsilon _r is changed to capacitance _{C 0} is the capacitance 80C ₀ next to the formula (1), 80 Double capacitance variation can be obtained. In addition, digital change is possible by changing the number of channels filled with water (FIG. 2). In FIG. 2, the MEMS variable capacitor C1 is composed of a pair of electrodes 11a and 12a, the MEMS variable capacitor C2 is composed of a pair of drive electrodes 11b and 12b, and the MEMS variable capacitor C3 is composed of a pair of electrodes 11c and 12c. Composed. Here, the pair of electrodes 11a and 12a, the pair of drive electrodes 11b and 12b, and the pair of electrodes 11c and 12c have different electrode areas (in the example of FIG. 2, the area ratio is 1: 2: 4). Each of the electrodes is filled with a fluid 25 such as water so as to fill and fill almost the entire electrode area. By switching between full filling and non-filling, the total capacity Ct can be changed digitally for each C _{0 in} the range from 0 to 7 C ₀ as shown in the following table.

[Table 1]
―――――――――――――――――――――
C3 C2 C1 Total capacity Ct
―――――――――――――――――――――
0 0 0 0
0 0 1 C ₀
0 1 0 2C ₀
0 1 1 3C ₀
1 0 0 4C ₀
1 0 1 5C ₀
1 1 0 6C ₀
1 1 1 7C ₀
―――――――――――――――――――――

First embodiment.
FIG. 3A is a plan view showing a configuration of the two-tank MEMS variable capacitor according to the first embodiment of the present invention, and FIG. 3B is a diagram of the two-tank MEMS variable capacitor of FIG. It is a front view which shows a structure.

  In FIG. 3, the MEMS variable capacitor according to the present embodiment has two fluid replenishing tanks 14a and 14b, and is extremely thin compared to the internal height of the fluid channels 15a and 15b (35 μm in the example of FIG. 3). The tanks 14a and 14b having a thickness or an internal height (7 μm in the example of FIG. 3) are filled with fluid by capillary action. Next, when the EWOD drive voltage is applied between the drive electrode 21a and the drive electrode 22a of the tank 14a or between the drive electrode 21b and the drive electrode 22b of the tank 14b, fluid is transferred from the tanks 14a and 14b by the EWOD drive. When the fluid channel 15a, 15b flows out into the fluid channels 15a, 15b between the two electrodes 11, 12 constituting the capacitor portions C11, C12, respectively, and the fluid channels 15a, 15b are filled with the fluid, the capillary action on the fluid is stopped when the voltage application is stopped. Can be controlled so that the fluid due to the EWOD driving voltage becomes larger than the stress due to the EWOD driving voltage and the fluid returns from the fluid channels 15a and 15b to the tanks 14a and 14b, respectively. Here, fluid channels 15a and 15b, which are narrower than the tanks 141 and 14b but do not generate capillary action, are electrically formed by the silicon structure 13 from the tanks 14 and 14b on the near side of the electrodes 11 and 12, respectively. Capacitor portions C21 and C22 are constituted by a pair of electrodes 11 and 12 facing each other. The EWOD drive voltage application drive electrodes 22a and 22b are formed on both sides of the lower electrodes 11 and 11 so as to extend to the vicinity of the tanks 14a and 14b so as to guide the fluid in the tanks 14a and 14b. . Note that the stress due to capillary action on the fluid generally increases as the height of the tanks 14a, 14b or the fluid channels 15a, 15b is reduced.

  In this embodiment, the dimensions of the silicon structure 13 are designed so as to have a capacitance of 1 pF when the fluid channels 15a and 15b are not filled with fluid. For this reason, if the fluid is filled only in one of the flow channels 15a and 15b, the entire capacitance changes to 40.5 pF, and if both are filled, the overall capacitance changes to 80 pF, and a three-stage capacitance change is obtained. In the present embodiment, the device was fabricated by electrostatic bonding the silicon structure 13 processed by bulk micromachining on a 6 mm square glass substrate 10.

  FIG. 4 is a graph showing the capacitance with respect to the number of water fillings in the two-tank MEMS variable capacitor of FIGS. As is clear from FIG. 4, it is shown that the capacitance changes in three stages as expected when the fluid channels 15a and 15b are not filled with fluid, when one is filled, and when both are filled. It was.

FIG. 5 is a longitudinal sectional view for illustrating the fluid drive principle used in the two-tank MEMS variable capacitor of FIGS. 2 and 3, and FIG. 5 (a) shows the position of the fluid 25 when no DC voltage is applied. FIG. 5 (b) is a longitudinal sectional view showing the position of the fluid 25 at the start of application of the DC voltage, and FIG. 5 (c) is a view after a sufficient time has elapsed after the start of application of the DC voltage. 3 is a longitudinal sectional view showing the position of a fluid 25. FIG. That is, FIG. 5 is a diagram showing a principle using EWOD (Electrowetting on dielectric) drive in order to perform electrical control of fluid movement. In FIG. 5, the EWOD driving circuit includes driving electrodes 21 and 22 divided on the glass substrate 10, an insulating film 23 made of, for example, SiO ₂ on the surface of the glass substrate 10, and CYTOP (registered trademark), for example. The water-repellent film 24 is covered. When the DC voltage source 20 is connected between the drive electrodes 21 and 22 and the electric field applied to the fluid 25 on the electrodes 11 and 12 is changed, fluid transport occurs because the wettability of water changes. Here, the contact angle of the fluid 25 is θ ₀ , the dielectric constant in vacuum and the relative dielectric constant of the insulating film are ε ₀ and ε _r , the thickness of the insulating layer is t, and the surface tension between the fluid and the solid is γ _SL. Then, the contact angle θ _V when the voltage V is applied is expressed by the following equation.

  Here, when a conductive fluid such as pure water or a metal fluid such as a gallium alloy is used as the fluid 25, it is necessary to form the insulating layer 23. For example, a nonconductive fluid such as silicon oil or deionized water is required. When using the insulating layer 23, the insulating layer 23 may not be formed. Here, the fluid 25 may be a conductive fluid or a non-conductive fluid.

  FIG. 6 is a circuit diagram showing a MEMS variable low-pass filter configured using the four 2-tank MEMS variable capacitors shown in FIGS. That is, the MEMS variable low-pass filter of FIG. 6 is an improved design based on a Butterworth cubic filter. In FIG. 6, the MEMS variable low-pass filter is configured between terminals T1 and T2, and includes two 15nH inductors L1 and L2, and four MEMS variable capacitors C21 to C24 connected in parallel to each other. Composed. Here, each of the MEMS variable capacitors C21 to C24 has a minimum capacitance of 4 pF, and a maximum capacitance of 320 pF when all the fluid channels 15a and 15b are filled with fluid can be varied in nine steps. .

FIG. 7 is a table showing stepwise variable and cutoff frequency measurement results of the MEMS variable low-pass filter of FIG. Further, FIG. 8 is a graph showing the frequency characteristics of the MEMS variable low-pass filter in the pass coefficient _{S 21} of FIG. 6 (0.001GHz~8GHz), 9 frequency of the pass coefficient _{S 21} of the MEMS variable low-pass filter in FIG. 6 It is a graph which shows a characteristic (0.001 GHz-1 GHz). 8 and 9, the numbers N0 to N9 indicate the number of water fillings.

In the MEMS variable low-pass filter in FIG. 6, to 8GHz using Agilent E5071B network analyzer to measure the frequency characteristic of the pass coefficient _{S 21} showing the insertion loss (FIGS. 8 and 9). The cut-off frequency is shown in FIGS. As is clear from the measurements in FIGS. 7 to 9, it was confirmed that the filter frequency characteristics were variable in eight stages. The measured cutoff frequency was in the range of 49.4 to 672 MHz, and a variable rate of 13.6 times could be realized. This corresponds to a change of 185 times the capacitance.

  As described above, a fluid variable MEMS capacitor using the principle of changing the capacitance by changing the relative dielectric constant is created, and 80 times the capacitance variable rate can be realized using pure water. Demonstrated. In addition, a low-pass filter was prototyped using the MEMS variable capacitor, and its frequency characteristics were evaluated. The cut-off frequency of the low-pass filter was changed from 49.4 to 672 MHz in 8 steps. This corresponds to a variable ratio of 185 times that of the MEMS variable capacitor.

  Therefore, according to the present embodiment, as compared with the conventional technique using two DC voltage sources in Patent Document 1, when the EWOD driving voltage is not applied, the fluid flows into the fluid channels 15a and 15b due to the capillary action of the tanks 14a and 14b. However, when the EWOD drive voltage is applied, water is introduced to the fluid channels 15a and 15b to digitally use one DC voltage source to generate one MEMS. The capacitance of the variable capacitor can be changed with a very simple configuration. In addition, since a pump like patent document 2 is not required, a control apparatus is simple. Further, by connecting a plurality of the MEMS variable capacitors in parallel, it is possible to realize a MEMS variable capacitor device that has a large capacitance change range and can change the capacitance digitally as compared with the prior art. Furthermore, a low-pass filter can be configured using the MEMS variable capacitor device and the inductor.

  In the above embodiment, a low-pass filter is configured. However, the present invention is not limited to this, and a high-pass filter, a band-pass filter, or the like can be obtained by combining the MEMS variable capacitor device and the inductor by a known method. A filter device may be configured.

Second embodiment.
FIG. 10 is a perspective view showing a configuration of a digital variable MEMS variable capacitor according to the second embodiment of the present invention, and FIG. 11 is an enlarged view of a main part of FIG. 12 is a longitudinal sectional view of the fluid channel portion of FIG. 10, and FIG. 13 is a transverse sectional view taken along line AA ′ of FIG.

  In FIG. 10, a tank 14 in which a fluid such as pure water is placed is formed on a glass substrate 10 by circular weir walls 14 c and 14 d having different diameters, and a fluid channel 15 ( 12), a MEMS variable capacitor device 40 including a plurality of MEMS variable capacitors is provided, and a slit portion 41 including a plurality of slits is provided on the other side of the tank 14, which is the side facing the MEMS variable capacitor device 40. ing. Here, the slit portion 41 is configured by arranging silicon plates in parallel so as to form slits at predetermined thin intervals so as to draw the fluid by capillary action, and the fluid in the tank 14 is used as the fluid of the MEMS variable capacitor device 40. The channel 15 does not conduct water (when the EWOD driving voltage is not applied) and operates so as to be placed in the tank 14. A drive electrode 21 is formed below the tank 14, and the drive electrode 21 is connected to the electrode pad 21p. In mounting, the tank 14 is sealed with a lid (not shown) so that fluid does not flow out. Note that the stress due to capillary action on the fluid generally increases as the slit interval of the slit portion 41 is reduced.

  12 and 13 show the configuration of one MEMS variable capacitor in the MEMS variable capacitor device 40, which is configured using a silicon structure 31 on the glass substrate 10, and has a width W and a width on the glass substrate 10. A lower electrode 11 having a length L is formed, and drive electrodes 22 for guiding fluid from the tank to the fluid channel 15 by EWOD extend on both sides of the lower electrode 11 in the vicinity of the tank 14 and the vicinity of the drive electrode 21. It is formed as follows. An upper electrode 12 is formed on the upper side of the lower electrode 11 via a fluid channel 15 having a substantially rectangular parallelepiped shape, and constitutes a MEMS variable capacitor. For example, the MEMS variable capacitor device 40 is configured by connecting nine MEMS variable capacitors in parallel. As shown in FIGS. 10 and 11, the lower electrode 11 is connected to the electrode pad 11p, the upper electrode 12 is connected to the electrode pad 12p, and the drive electrode 22 is connected to the electrode pad 22p. Further, the silicon structure 31 and the upper electrode 12 are electrically insulated by an insulating layer 32. Here, the fluid channel 15 is electrically connected to the tank 14 from the MEMS variable capacitor side, and is configured to guide the fluid in the tank 14 to the fluid channel 15 when the EWOD driving voltage is applied to the electrodes 11 and 12. ing. That is, the stress of the slit portion 41 with respect to the fluid is set to be larger than the stress of the EWOD drive with respect to the fluid.

  In one MEMS variable capacitor in the MEMS variable capacitor device 40 configured as described above, when the EWOD drive voltage is not applied to the drive electrodes 21 and 22, the fluid is on the tank 14 side and the fluid channel 15. Since no water is conducted, the space between the electrodes 11 and 12 of the MEMS variable capacitor becomes air, and has a predetermined capacity (hereinafter referred to as an unfilled capacity). When the EWOD drive voltage is applied to the drive electrodes 21 and 22, the fluid is guided to the fluid channel 15, so that the fluid between the electrodes 11 and 12 of the MEMS variable capacitor becomes a fluid larger than the unfilled capacity. (Hereinafter referred to as the filling capacity). In this state, when the EWOD driving voltage is not applied, the stress of the slit portion 41 with respect to the fluid is set to be larger than the stress of the EWOD driving with respect to the fluid, so that the fluid in the fluid channel 15 is contained in the tank 14. Can be controlled to return to

As is apparent from FIGS. 12 and 13, by changing the width W and length L of the lower electrode 11 of each MEMS variable capacitor, the unfilled capacity and the filled capacity can be changed. FIG. 14 is a table showing a list of electrode sizes and the like of the digital variable MEMS variable capacitor of FIG. FIG. 14 shows a case where the filling capacity and non-filling capacity of each MEMS variable capacitor are set to nC ₀ (n = 1, 2,..., 256).

FIG. 15 is a circuit diagram of the digital variable MEMS variable capacitor of FIG. In FIG. 15, 13 MEMS variable capacitors C1 to C13 are connected in parallel, and the capacitance of each MEMS variable capacitor C1 to C13 is filled by turning on and off the EWOD drive voltage from the controller 50 having a DC voltage source. And non-filled volume can be changed digitally. As is apparent from FIG. 14, when 13 MEMS variable capacitors are connected in parallel, 2 ¹³ (= 8192 types) with a capacitance change of 100 times from the minimum capacitance Cmin = 0.302 pF to the maximum capacitance Cmax = 30.16 pF. The resolution can be changed.

In addition, the filling capacity and the non-filling capacity of each MEMS variable capacitor may be set as nC ₀ (n = 1, 2,..., N; N ≧ 2), and in this case, it changes with a resolution of 2 ^N. Can be made.

  As described above, according to the present embodiment, the capillary tube of the slit portion 41 connected to the tank 14 when no EWOD driving voltage is applied, as compared with the prior art using two DC voltage sources in Patent Document 1. The fluid is on the tank 14 side due to the phenomenon, but when the EWOD driving voltage is applied, the fluid is guided to the fluid channel 15 side of each MEMS variable capacitor, thereby digitally using the controller 50 having the DC voltage source 40. Capacitance of the MEMS variable capacitor can be changed with a very simple configuration. By connecting a plurality of the MEMS variable capacitors in parallel, the capacitance can be changed digitally with a large capacitance change range compared to the prior art. A variable MEMS variable capacitor device can be realized. In addition, since a pump like patent document 2 is not required, a control apparatus is simple. Furthermore, a filter device such as a low-pass filter can be configured using the MEMS variable capacitor device and the inductor.

  FIG. 16 is a longitudinal sectional view showing a configuration of a MEMS variable capacitor using two fluids 26 and 27 in a sealed fluid channel according to a first modification of the present invention. In FIG. 16, for example, two kinds of fluids (combination of pure water and silicon oil or alcohol) 26 and 27 are confined in a fluid channel in a sealed space between the glass substrate 10 and the sealed dielectric substrate 10a, so that the relative dielectric constant is obtained. Alternatively, the capacitance of the MEMS variable capacitor may be changed by moving only the large fluid 26.

  FIG. 17 is a longitudinal sectional view showing a configuration of a MEMS variable capacitor using a fluid 26 having particles 26a in a fluid channel according to a second modification of the present invention. The capacitance of the MEMS variable capacitor may be changed by diffusing the particles 26a having a large dielectric constant into the small fluid 26 and moving the particles 26a as the fluid 26 moves.

  FIG. 18 is a longitudinal sectional view showing a configuration of a MEMS variable capacitor using bubbles 28 in a fluid 27 in a sealed fluid channel according to a third modification of the present invention. You may comprise so that the capacity | capacitance of a MEMS variable capacitor may be changed by moving the bubble (for example, air is included) 28 in the fluid 27 with a large dielectric constant.

  It is possible to change the relative dielectric constant between the electrodes 11 and 12 in the fluid channel 15 by the method according to any modification of FIGS. 16 to 18, and various forms are taken depending on the ease of movement of the fluid. be able to.

Further, in FIG. 14, the filling capacity and the non-filling capacity of each MEMS variable capacitor are changed to nC ₀ (n = 1, 2,..., 256), but the present invention is not limited to this, and each MEMS variable is variable. You may comprise so that the filling capacity | capacitance and non-filling capacity | capacitance of a capacitor may mutually differ, or may become the same.

  As described above in detail, according to the present invention, compared with the prior art using two DC voltage sources in Patent Document 1, when no EWOD driving voltage is applied, the fluid control means of the slit portion or tank Although the fluid is on the tank side due to capillary action, the capacitance of one MEMS variable capacitor can be digitally simplified using one DC voltage source by conducting water to the fluid channel side when the EWOD driving voltage is applied. Can vary with configuration. Further, by connecting a plurality of the MEMS variable capacitors in parallel, it is possible to realize a MEMS variable capacitor device that has a large capacitance change range and can change the capacitance digitally as compared with the prior art. Furthermore, a filter apparatus can be comprised using the said MEMS variable capacitor apparatus and an inductor.

10 ... Glass substrate,
10a: sealed dielectric substrate,
11, 12, 11a, 12a, 11b, 12b, 11c, 12c ... electrodes,
11p, 12p, 21p, 22p ... electrode pads,
13 ... silicon structure,
14, 14a, 14b ... tanks
14c, 14d ... dam wall,
15, 15a, 15b ... fluid channels,
20: DC voltage source,
21, 22 ... drive electrodes,
23. Insulating layer,
24 ... water-repellent layer,
25 ... Fluid,
26, 27 ... fluid,
26a ... particles,
28 ... bubbles,
31 ... silicon layer,
32. Insulating layer,
40 ... MEMS variable capacitor device,
41 ... slit group,
50 ... Controller,
C1 to C13, C21 to C24 ... variable capacitors,
L1, L2 ... inductors,
T1, T2 ... terminals.

Claims (7)

A MEMS variable capacitor that digitally changes the capacitance between a pair of electrodes by selectively switching whether or not a fluid flows into a fluid channel between a pair of electrodes facing each other,
A first drive electrode provided in the fluid channel and applying a drive voltage for allowing the fluid to flow into the fluid channel by dielectric electrowetting drive;
A tank having a second drive electrode and supplying fluid to the fluid channel;
Fluid control means provided in the tank for controlling the fluid in the tank to be retained in the tank without flowing into the fluid channel by capillary action;
When the drive voltage is applied between the first drive electrode and the second drive electrode, the stress when the fluid flows into the fluid channel by the dielectric electrowetting drive is expressed as the fluid. Configured to be greater than the stress on the fluid by the control means,
When the drive voltage is not applied between the first drive electrode and the second drive electrode, the fluid is retained in the tank, while the first drive electrode and the second drive electrode When the drive voltage is applied between the drive electrodes, the fluid flows into the fluid channel and is filled, so that the pair of interelectrode capacitances can be digitally generated using only one drive voltage. A MEMS variable capacitor characterized by being changed.   2. The MEMS variable capacitor according to claim 1, wherein the fluid control means is a slit portion including a plurality of slits.   2. The MEMS according to claim 1, wherein the fluid control means is configured such that an internal height of the tank is set so as to be thin so that the fluid is retained in the tank by capillary action. Variable capacitor. A MEMS variable capacitor device comprising a plurality of N MEMS variable capacitors according to any one of claims 1 to 3,
A MEMS variable capacitor characterized in that a plurality of N MEMS variable capacitors are connected in parallel, and a drive voltage for each MEMS variable capacitor is turned on / off to digitally change the overall capacitance of the MEMS variable capacitor device. apparatus.   5. The MEMS variable capacitor device according to claim 4, wherein the capacitances of the MEMS variable capacitors have different values. Each of the MEMS variable capacitors is configured to have a capacitance nC ₀ (n = 1, 2,..., N ≧ 2) with a basic capacitance C ₀ , and the total capacitance of the MEMS variable capacitor device is N bits. The MEMS variable capacitor device according to claim 4, wherein the MEMS variable capacitor device is digitally changed with a resolution of 5. A MEMS variable capacitor device according to any one of claims 4 to 6,
A filter device comprising: at least one inductor connected to the MEMS variable capacitor device.

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