JP4645227B2 - Vibrator structure and manufacturing method thereof - Google Patents

Description

  The present invention relates to a vibrator structure and a method for manufacturing the vibrator structure, and more particularly to a vibrator structure suitable for a structure as a minute functional element manufactured using a semiconductor manufacturing technique called MEMS (Micro Electro Mechanical System). .

  In general, a resonator device such as a resonator is used in an oscillator that generates a reference signal or a filter for eliminating an electric signal in a desired band (for example, a band-pass filter or a low-pass filter) according to its vibration characteristics. Has been.

  In recent years, various new types of vibrators different from vibrators / resonators using crystals and dielectrics that have been mainly used so far have been proposed, one of which is a MEMS vibrator. There is. MEMS is an abbreviation for Micro Electro Mechanical System, and there are various interpretations in the concept range encompassed by it. There are cases where it is called a micromachine or MST (Micro System Technology). The term “fabricated micro functional element” is meant.

  The MEMS vibrator is made of finely processed silicon. As its manufacturing method, a surface layer semiconductor region (surface layer silicon) of an SOI (Semiconductor On Insulator) substrate is formed by etching or the like, and a surface structure (thin film) such as an oxide film or polycrystalline silicon on the silicon substrate. In general, the surface structure is formed by etching the surface structure. The MEMS vibrator formed in this way is driven by the same electromechanical principle as that of the MEMS actuator, for example, electrostatic driving, electromagnetic driving, thermal driving and the like.

  Representative examples of conventional MEMS vibrators include a comb-type vibrator that vibrates in the substrate surface direction and a beam-type (beam-type) vibrator that vibrates in the substrate thickness direction, both of which are technical documents. Etc. are widely known. As a beam type vibrator, a lower electrode is formed on a substrate, a band-shaped upper electrode is arranged above the lower electrode with a gap and fixed at both ends so as to straddle the lower electrode (Clamped -Clamped Beam) is disclosed in Patent Document 1 below. 9 and 10, the fixed electrode 2 and the movable electrode 3 facing the fixed electrode 2 are provided on the substrate 1, and the movable part 3a of the movable electrode 3 facing the fixed electrode 2 has a narrow left and right side. Non-Patent Document 1 below discloses a structure in which two sets are supported by a total of four support beam portions 3b (Flee-Flee Beam). The support beam portion 3b is fixed to a support fixing portion 5 made of an insulating material on the wiring 4, and thereby the movable electrode 3 is supported in a state where it can be elastically vibrated up and down.

As a driving method of the beam type vibrator, an electric field is formed by applying a potential difference between the movable electrode supported in a movable state as described above and a fixed electrode disposed opposite to the movable electrode, There are many electrostatic drive systems that are driven by the electrostatic attraction generated by this. That is, the movable electrode is vibrated by a change in electrostatic attraction force generated by applying a drive signal (AC voltage) between the movable electrode and the fixed electrode. In this case, a predetermined natural frequency (resonance frequency) is determined by the material, shape / size, support structure, etc. of the movable electrode. This resonance frequency f is roughly
f = (1 / 2π) · (k / m) ^0.5 (1)
Determined by. Here, k is the spring constant of the vibrating part of the movable electrode, and m is the mass of the vibrating part.
JP 7-333077 A Kay Wang, et al. “VHF Band Free Free High-Q Microresonator”, Micro Electromechanical Systems, 347-360, Vol. 9, No. 3, September 2000 (K. Wang, (ACWong, and Clark TCNguyen "VHF Free-Free Beam High-Q Micromechanical Resonators" Journal of Microelectromechanical Systems, Vol. 9, No. 3, September 2000)

  However, in recent years, in electronic circuits and systems using the same, for example, circuits and systems in the field of wireless communication, there is an increasing need to use a plurality of frequencies in parallel or simultaneously. A prominent example is the appearance of mobile phones that support multiple frequencies. In order to cope with such a device, for example, it is desirable to configure so that a clock signal serving as a reference signal can be generated at a plurality of frequencies.

  However, in the above-described beam type vibrator, since the resonance frequency is determined by the above equation (1), there is only one resonance frequency for each vibrator structure, and it is not possible to deal with the above-described plurality of frequencies. There is a problem. In order to cope with a plurality of frequencies with the above structure, it is necessary to form a plurality of beam-type vibrators on the substrate, which is contrary to downsizing of the apparatus and causes an increase in manufacturing cost due to an increase in the number of parts. There is a case. In addition, since the resonance frequency cannot be changed in a vibrator once formed with a predetermined structural dimension, it cannot be flexibly adapted to various applications. It is necessary to redo the design from the beginning.

  Therefore, the present invention solves the above-described problems, and the problem is that the resonance frequency can be changed or adjusted in the beam type vibrator, so that the vibrator can be flexibly adapted to various uses. Is to realize a simple vibrator structure.

In view of such circumstances, the vibrator structure according to the present invention includes a substrate, a fixed electrode formed on the substrate, and the fixed electrode opposed to the fixed electrode through a gap , around a portion facing the fixed electrode. In the vibrator structure having a movable electrode fixed to the support fixing portion on the substrate at a plurality of locations, an auxiliary electrode facing the movable electrode is provided between the fixed electrode and the support fixing portion. Auxiliary control means is provided for controlling the electrostatic force generated between the auxiliary electrode and the movable electrode so as to be variable.

  According to the present invention, the restraint state of the movable electrode can be changed by controlling the potential relation between the auxiliary electrode and the movable electrode by the auxiliary control means, and changing the electrostatic force generated between the two. The vibration characteristics can be changed without changing the structural dimensions. Therefore, for example, the natural frequency (resonance frequency) of the vibrator structure can be changed or adjusted.

  In the present invention, it is preferable that the plurality of auxiliary electrodes are respectively formed around the fixed electrode. Since the movable electrode is fixed to the support fixing portion on the substrate at a plurality of locations around the fixed electrode, the auxiliary electrode is provided between the support fixing portion around the fixed electrode, so that the movable electrode and the fixed electrode are provided. Since the movable electrode can be constrained at a plurality of locations around the opposite area of the electrode, a binding force can be applied symmetrically around the fixed electrode, so that the vibration of the movable electrode in a constrained state by the auxiliary electrode can be stabilized. It becomes possible.

  In the present invention, the movable electrode is preferably provided with an auxiliary driven portion that is wider than an adjacent portion at a position facing the auxiliary electrode. According to this, since the auxiliary driven portion is provided in a manner that is wider than the adjacent portion, the opposing area between the auxiliary electrode and the auxiliary driven portion can be increased, so that the movable electrode is reliably restrained by the auxiliary electrode. And it becomes possible to carry out easily.

  Specifically, the movable electrode is provided between a main driven portion provided at a position facing the fixed electrode, and between the main driven portion and the support fixing portion, and is narrower than the main driven portion. It is preferable to have a supporting beam portion formed on the support beam portion, and an auxiliary driven portion provided at a position facing the auxiliary electrode in the middle of the supporting beam portion and formed wider than the support beam portion. According to this, since the main driven part is formed wider than the support beam part, a sufficient area can be secured between the main driven part and the fixed electrode, so that it can be driven reliably and easily. . In addition, since the elastically deformed portion of the movable electrode that accompanies vibration can be concentrated on the support beam portion, it is easy to design the vibration characteristics depending on the shape and size of the support beam portion.

  In the present invention, the auxiliary control means sets the potential of the auxiliary electrode to a potential of the movable electrode or a first potential closer to the potential and a potential difference between the first potential and the potential of the movable electrode being large. It is preferable to include a switch that switches between two potentials. According to this, when the switch of the auxiliary control means switches the potential of the auxiliary electrode to the first potential, the potential difference between the movable electrode and the auxiliary electrode is 0 or small, so that the movable electrode is not constrained or weakened. Become. On the other hand, when the switch of the auxiliary control means switches the potential of the auxiliary electrode to the second potential, the potential difference between the movable electrode and the auxiliary electrode is increased, so that the constraint on the movable electrode becomes stronger. Therefore, since the strength of the movable electrode can be switched by the switch, the vibration characteristics of the movable electrode can be changed reliably and easily.

  In the present invention, it is preferable that a portion of the movable electrode facing the auxiliary electrode is disposed closer to the substrate than a portion of the movable electrode facing the fixed electrode in a state where no electrostatic force is received. According to this, since the distance between the movable electrode and the auxiliary electrode can be reduced, it is possible to reliably and easily realize the binding of the movable electrode by the electrostatic force of the auxiliary electrode. In addition, since the deformation amount of the movable electrode in the constrained state by the auxiliary electrode can be reduced, the reproducibility of the vibration state and the durability of the movable electrode can be improved.

  In the present invention, the movable range of the portion facing the auxiliary electrode in the movable electrode to the substrate side is smaller than the movable range of the portion facing the fixed electrode in the movable electrode to the substrate side. preferable. According to this, even if the movable electrode is maximally deformed to the limit of movement toward the auxiliary electrode, it can be configured so as not to reach the limit of movement toward the fixed electrode, so that the binding force of the movable electrode by the auxiliary electrode is increased. However, the movable electrode can be vibrated. Therefore, in a state where the movable electrode is constrained, the vibration state of the movable electrode can be further stabilized.

  In the present invention, an insulating film is preferably interposed between the auxiliary electrode and the movable electrode. According to this, since an insulating film is interposed between the auxiliary electrode and the movable electrode, excessive electrostatic attraction force is generated between the auxiliary electrode and the movable electrode, or external stress is applied. It is possible to prevent electrostatic breakdown from occurring due to proximity or contact between the two. In addition, it is possible to stabilize the bound state of the movable electrode by configuring the auxiliary electrode and the movable electrode so as to be fixed with the insulating film interposed therebetween.

  In this invention, it is preferable that the convex part which protrudes toward the other is provided on the at least one opposing surface of the said auxiliary | assistant driven part and the said auxiliary electrode. According to this, when the auxiliary driven part and the auxiliary electrode are in direct or indirect contact (that is, through the insulating film), a stable contact state can be obtained through the convex part, and vibration is stable and reproducible. It is possible to realize the operation of the child. Here, the convex portion only needs to be formed on at least one of the auxiliary driven portion and the auxiliary electrode, and when an insulating film is formed on the auxiliary electrode, the convex portion is formed on the insulating film. It doesn't matter.

  In the present invention, it is preferable that the auxiliary electrode is an impurity region formed in a surface layer portion of the substrate, and the insulating film is formed on a surface of the substrate. By making the auxiliary electrode an impurity region formed in the surface layer portion of the substrate, the auxiliary electrode can be configured on the substrate itself. Therefore, the insulating film formed on the surface of the substrate is formed of the auxiliary electrode and the movable electrode. Can be interposed. Therefore, the thickness of the vibrator structure can be reduced as compared with the case where the auxiliary electrode is formed on the substrate, and the step of forming a dedicated insulating film for covering the auxiliary electrode can be omitted.

The method for manufacturing a vibrator structure according to the present invention includes a substrate, a fixed electrode formed on the substrate, and the fixed electrode opposed to the fixed electrode through a gap at a plurality of locations around a portion facing the fixed electrode. In the manufacturing method of the vibrator structure having a movable electrode fixed to the upper support fixing portion, the step of forming the fixed electrode and another auxiliary electrode on the substrate or the substrate, and the auxiliary Forming a movable electrode that is opposed to the electrode and the fixed electrode with a gap and is supported and fixed on the substrate at a plurality of locations around the portion facing the auxiliary electrode and the fixed electrode. It is characterized by that.

  In the present invention, it is preferable that the method further includes a step of forming an insulating layer to be disposed between the auxiliary electrode and the movable electrode.

  In the present invention, the auxiliary electrode is preferably an impurity region formed in a surface layer portion of the substrate.

  In the present invention, the step of forming the movable electrode includes a step of forming a sacrificial layer on the substrate, a step of forming the movable electrode on the sacrificial layer, and removing the sacrificial layer to form the gap. Preferably comprising the steps of: In this case, in the step of forming the sacrificial layer, the layer thickness on the auxiliary electrode is preferably smaller than the layer thickness on the fixed electrode.

  Next, embodiments of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a schematic perspective view showing the vibrator structure of the present embodiment, and FIG. 2A is a cross-section of the vibrator structure of the same embodiment taken along a virtual vertical plane including line AA shown in FIG. It is a longitudinal cross-sectional view which shows a virtual cross section.

  The vibrator structure 100 includes a substrate 101 made of a single crystal silicon substrate or the like, and a structure provided on the surface. An auxiliary electrode 101A composed of an impurity region or the like is provided on the surface layer portion of the substrate 101, and an insulating layer 102 composed of silicon oxide or the like and a silicon nitride or the like are formed on the surface of the substrate 101. An insulating layer 103 is stacked. On the insulating layer 103, there are formed a fixed electrode 110 and a wiring 114 made of a conductor made of polycrystalline silicon whose resistivity is sufficiently lowered by doping. Here, a part of the wiring 114 is disposed on the left and right sides of the fixed electrode 110 in the figure.

  On the wiring 114, a movable electrode 120 is formed of a conductor such as polycrystalline silicon or metal via an insulating layer 115. The movable electrode 120 is configured to extend in the horizontal direction in the figure as a whole, and the fixed portion 125 at both ends in the horizontal direction is an insulating layer 115 and a support fixing portion configured by the wiring 114 connected through the insulating layer 115. It is fixed. Further, in FIG. 1, the signal path (input signal introduction path) of the wiring 114 is configured symmetrically with respect to the left and right fixed parts 125, and as a result, the wiring length for a plurality (left and right) fixed parts 125 is long. They are identical to each other. As a result, the phase difference of the input signal is unlikely to occur between the plurality of input paths, and the influence on the vibration can be minimized.

  The movable electrode 120 includes a main driven part 121 formed at the center in the horizontal direction in the figure, an inner support beam part 122 whose inner ends are connected to the left and right sides of the main driven part 121 in the figure, and an inner support beam part 122. The auxiliary driven part 123 whose outer end is connected to the inner end, the outer support beam part 124 connected to the outer end of the auxiliary driven part 123, and the fixed part to which the outer end of the outer support beam part 124 is connected 125.

  Here, the main driven portion 121 is formed wider than the inner support beam portion 122 and the outer support beam portion 124, and has a rectangular planar shape in the illustrated example. The main driven portion 121 has a shape that substantially overlaps the fixed electrode 110 disposed below, and is disposed at a position facing the fixed electrode 110. That is, the main driven part 121 is disposed at a position directly above the fixed electrode 110.

  Each of the inner support beam portion 122 and the outer support beam portion 124 has a shape extending in the left-right direction in the figure, and is configured in a band shape or a rod shape in the illustrated example. The inner support beam portion 122 and the outer support beam portion 124 constitute a support beam portion for supporting the main driven portion 121 from both left and right sides in the figure. In the case of the illustrated example, a total of four support beam portions are provided, two on each of the left and right sides.

  The auxiliary driven portion 123 is connected between the inner support beam portion 122 and the outer support beam portion 124, is formed wider than these support beam portions, and has a rectangular planar shape in the illustrated example. In the case of the illustrated example, a common auxiliary driven portion 123 is connected to the inner support beam portion 122 and the outer support beam portion 124 provided two by two. The auxiliary driven portion 123 has a shape that substantially overlaps the auxiliary electrode 101A in a plan view, and is arranged at a position facing the auxiliary electrode 101A. That is, the auxiliary driven portion 123 is disposed at a position immediately above the auxiliary electrode 101A.

  In the movable electrode 120, the portion excluding the fixed portion 115 is disposed on the substrate 101 with a gap with respect to the lower layer structure. That is, the main driven part 121, the inner support beam part 122, the auxiliary driven part 123, and the outer support beam part 124 of the movable electrode 120 are spaced upward from the insulating layer 103, the fixed electrode 110, and the wiring 114 on the substrate 101. It is provided in the state. Accordingly, the movable electrode 120 is in a state in which the respective parts 121 to 124 can be physically displaced in a direction perpendicular to the surface of the substrate 101 by elastic deformation thereof.

  In the present embodiment, an electrostatic attractive force is generated between the fixed electrode 110 and the main driven part 121 of the movable electrode 120 by applying a periodic fluctuation voltage between the fixed electrode 110 and the wiring 114, and Since the electrostatic attractive force periodically varies, the movable electrode 120 can be vibrated. In this case, as is well known, an AC voltage may be applied to the wiring 114 to generate a periodic voltage fluctuation between the DC-grounded fixed electrode 110 or the fixed electrode 110 and the wiring. An AC voltage may be supplied in a state where a DC bias is applied between the first and second electrodes 114. For example, a predetermined DC bias voltage can be set between the fixed electrode 110 and the wiring 114 and an input signal (alternating voltage) Vin can be supplied to the wiring 114.

  When the movable electrode 120 vibrates according to the input signal Vin as described above, the output signal Iout can be extracted from the fixed electrode 110. For example, since the electrostatic capacitance between the main driven portion 121 and the fixed electrode 110 periodically varies due to the vibration, a current Iout is generated in the fixed electrode 110 according to the variation of the electrostatic capacitance. An output signal obtained by converting the current Iout into a voltage by an external circuit connected to the fixed electrode 110 can also be obtained.

In general, the equivalent circuit constants of the beam type vibrator, that is, the equivalent resistance Rx, the equivalent inductance Lx, and the equivalent capacitance Cx are as follows.
Rx = (k ′ · m ′) ^0.5 / (Q · η ² ) (2)
Lx = m ′ / η ² (3)
Cx = η ² / k ′ (4)
Here, k ′ is an effective spring constant of the vibrator, m ′ is an effective mass of the vibrator, Q is a Q value of the vibrator, η is a mechanical / electrical conversion coefficient, and δC / δx is set between the movable electrode and the fixed electrode. If the capacitance displacement is taken and Vs is the potential difference between the movable electrode and the fixed electrode, η = Vs · (δC / δx). (Sengbae Lee, Clark Tee Neuen, "Influence of automatic level control on phase noise of mechanical resonators" IEEE International Frequency Control Symposium 2003-Influence of Automatic level Control on Mechanical resonator oscillator phase noise, Seungbae Lee and Clark TCNguyen, 2003 IEEE International Frequency Control Symposium-)

  Therefore, various oscillation circuits, filter circuits, and the like can be configured by incorporating the vibrator structure of the present embodiment having the above circuit constants into the circuit. In general, the greater the equivalent inductance and the smaller the equivalent resistance, the higher the Q value of the vibrator.

  In the present embodiment, auxiliary control means for switching the potential of the auxiliary electrode 101A is provided. The auxiliary control means includes a first potential (+ Vp in the illustrated example) substantially the same as the potential of the movable electrode 120 and a second potential (Vq in the illustrated example) different from the potential of the movable electrode 120. For example, the switching means includes a switch SW that switches the potential of the auxiliary electrode 101A between Vq = −Vp). In general, the first potential is a potential close to the potential of the movable electrode 120, and the second potential is a potential that causes a potential difference sufficiently larger than the first potential with respect to the potential of the movable electrode 120. That's fine. In the illustrated example, if the reference potential of the fixed electrode 110 is, for example, the ground potential (DC0v), a DC bias of Vp is set between the fixed electrode 110 and the movable electrode 120.

  Further, although the potential of the wiring 114 varies depending on the input signal Vin, the first potential may be basically set based on the center potential (bias potential) of the wiring 114. However, it is more preferable to set the first potential with reference to the actual potential of the wiring 114 that varies depending on the input signal Vin. For example, by making the first potential coincide with the fluctuation potential of the wiring 114, it can be configured such that no electrostatic force is always generated between the auxiliary electrode and the movable electrode.

  The switch SW is constituted by a semiconductor switch such as a MOSFET and is formed in the substrate 101. The substrate 101 at this time is a semiconductor substrate, and is particularly preferably the above-described single crystal silicon substrate. However, the switch SW is not limited to a semiconductor switch, but may be a mechanical switch, or may be a discrete switching element provided separately from the substrate. For example, the switch SW can be a minute mechanical switch constituted by a micromachine structure separately formed on the substrate 101, that is, a MEMS switch.

  Further, the auxiliary electrode 101A connected to the auxiliary control means including these switches SW has an input impedance set sufficiently large at the resonance frequency of the vibrator as viewed from the auxiliary driven portion 123 of the movable electrode. If the input impedance of the auxiliary electrode 101A is small, a part of the signal input from the wiring 114 is likely to leak from the auxiliary driven portion 123, and the performance as a vibrator is deteriorated. In order to prevent this, it is preferable that the wiring to the auxiliary electrode 101A and the switch SW has a layout having no unnecessary parasitic capacitance, and that a matching circuit having a high input impedance only at a specific frequency is inserted in the wiring.

  FIG. 3 is a partial longitudinal sectional view showing the positional relationship between the auxiliary electrode 101A and the auxiliary driven portion 123. As shown in FIG. FIG. 3A shows a state in which no electrostatic force is acting between the auxiliary electrode 101 </ b> A and the auxiliary driven portion 123. In this state, the movable electrode 120 maintains its original shape, and the auxiliary driven portion 123 is separated from the insulating layer 103 on the substrate 101. When a voltage is applied between the auxiliary electrode 101A and the auxiliary driven portion 123 and an electrostatic attractive force acts between the auxiliary electrode 101A and the auxiliary driven portion 123, the auxiliary driven portion 123 is attracted to the auxiliary electrode 101A as shown in FIG. The electrode 120 is partially deformed. However, since the electrostatic attraction is not so strong in the state shown in FIG. 3B, the auxiliary driven portion 123 is not in contact with the insulating layer 103, and in the case of FIG. It has a narrower predetermined interval. In this case, the auxiliary driven portion 123 is disposed at a position (height) where the above electrostatic attractive force and the elastic force of the movable electrode 120 are balanced. At this time, since the auxiliary driven portion 123 receives electrostatic attraction, the movable electrode 120 is constrained by the auxiliary driven portion 123. In this state, the fixed electrode 110, the main driven portion 121, When the main driven portion 121 vibrates due to the fluctuation of the electrostatic force generated during the period, the vibration state is different from the vibration state when there is no constraint as shown in FIG.

  Here, by increasing the potential difference between the auxiliary electrode 110 and the movable electrode 120, the amount of deformation of the movable electrode 120 due to the electrostatic attractive force received by the auxiliary driven portion 123 also increases. Conversely, by reducing the potential difference, the electrostatic attractive force is also reduced. Since it becomes small, the deformation amount of the movable electrode 120 decreases. Therefore, if the deformation range of the movable electrode 120 by the auxiliary control means is less than the elastic limit, preferably if it is smaller than the proportional limit, the movable electrode 120 will return to its original shape. However, a reproducible vibration state can be obtained. In order to secure a certain number of repeatable times (that is, durability) to some extent, it is desirable that the deformation amount of the movable electrode 120 be configured to be significantly smaller than the proportional limit.

  In general, in the beam type vibrator, the resonance frequency f is determined by the above equation (1), but the spring constant k of the vibrating body and the mass m of the vibrating body that determine the frequency are as shown in FIG. It is different in the state with the constraint in FIG. That is, the spring constant k increases and the mass m decreases due to the restraint of the auxiliary driven portion 123 of the movable electrode 120 as in the case where the length of the support beam portion is substantially shortened. Therefore, the resonance frequency f becomes higher due to the restraint of the movable electrode 120 by the auxiliary electrode 101A.

  Further, as shown in FIG. 3C, when a sufficient electrostatic attraction is generated between the auxiliary electrode 101 </ b> A and the auxiliary driven portion 123, the movable electrode 120 is greatly deformed, and the auxiliary driven portion 123 becomes the insulating layer 103. It can be made to contact. In this case, since the electrostatic attractive force exceeds the elastic force of the movable electrode 120, even if the main driven part 121 vibrates due to the electrostatic force generated between the fixed electrode 110 and the main driven part 121, the auxiliary driven part 123 is stabilized. Can increase the sex.

  That is, if the position of the auxiliary driven part 123 is unstable, the vibration energy given to the main driven part 121 is easily dissipated to the surroundings via the auxiliary driven part 123 and affects the vibration state of the main driven part 121. Therefore, a vibration mode other than the original vibration mode is likely to occur, and as a result, the characteristics of the vibrator structure as an element (increased loss, decreased Q value) and the like are caused. However, since the auxiliary driven portion 123 comes into contact with the insulating layer 103 on the substrate as described above, the positional stability of the auxiliary driven portion 123 increases, so that deterioration of element characteristics can be suppressed.

  In particular, if the electrostatic attractive force applied to the auxiliary driven portion 123 is set to be always larger than the elastic deformation force exerted on the auxiliary driven portion 123 caused by the vibration of the main driven portion 121, the auxiliary driven portion 123 is always insulated. Since the contact with the layer 103 remains, it is possible to eliminate the leakage of vibration energy through the auxiliary driven portion 123 and the influence on the vibration mode by the auxiliary driven portion 123, thereby further stabilizing the vibration characteristics of the main driven portion 121. Sex can be secured.

  Further, as shown by a two-dot chain line in FIG. 2A, by providing the convex portion 123x on the lower surface of the auxiliary driven portion 123, the posture and the contact state at the time of contact can be stabilized. As a result, the vibration state when the auxiliary driven portion 123 comes into contact with the substrate is stable, and it is possible to obtain element characteristics with high reproducibility. The convex portion may be formed by a plurality of dimples, or may be formed by a protrusion on a single long bar whose corners are chamfered. In short, any form that can realize a stable contact state at the time of contact with good reproducibility is acceptable. Further, the convex portion 101x may be provided on the auxiliary electrode 101A side. In this case, the convex portion 101x may be provided directly on the auxiliary electrode 101A or may be provided on the insulating layer 102.

  FIG. 2B is a longitudinal sectional view showing the structure of another embodiment obtained by further improving the above embodiment. In this embodiment, the shape of the movable electrode 120 is changed so that the height of the auxiliary driven portion 123 on the substrate 101 is lower than the height of the main driven portion 121 on the substrate 101. Thereby, the gap G2 between the auxiliary driven part 123 and the insulating layer 103 on the auxiliary electrode 101A is smaller than the gap G1 between the main driven part 121 and the fixed electrode 110. These intervals G1 and G2 indicate ranges in which the main driven portion 121 and the auxiliary driven portion 123 of the movable electrode 120 can move toward the substrate 101, respectively. In general, the interval G1 is preferably 1.5 times or more, and more preferably twice or more than the interval G2. The larger the difference between the two gaps, the better. However, if this difference is increased, the thickness of the vibrator structure increases. From the viewpoint of manufacturing, it is preferable that the gap G1 is not more than 5 times the gap G2. It is most desirable to set about 3 times.

  With this configuration, even when the auxiliary driven portion 123 is restrained by electrostatic attraction as described above, the interval between the main driven portion 121 and the fixed electrode 110 can be secured, and the main driven portion 121 is reliably vibrated. At the same time, the main driven part 121 and the fixed electrode 110 come into contact with each other and are electrically short-circuited, thereby eliminating the possibility of occurrence of problems such as damage to the electrode surface. In particular, as shown in FIG. 4, even when the movable electrode 120 is largely deformed so that the auxiliary driven portion 123 is in contact with the insulating layer 103, the main driven portion 121 and the fixed electrode 110 are not in contact, and the main driven portion 121 can be configured to be able to vibrate.

  Moreover, since the deformation amount of the movable electrode 120 controlled by the auxiliary control unit can be suppressed by configuring as described above, the reproducibility of the vibration state at the time of control by the auxiliary control unit can be improved. Furthermore, it becomes possible to increase the number of times that switching can be repeated.

FIG. 5 is a schematic perspective view showing the structure of a vibrator structure according to another embodiment. In this vibrator structure 200, the fixed electrode 210, the movable electrode 220, the auxiliary electrode 201A, the wiring 214, the insulating layer 215, the main driven part 221, the inner supporting beam part 222, the auxiliary driven part 223, the outer supporting beam part 224, The basic structure such as the fixing portion 225 is the same as that in each of the above embodiments.

  However, this embodiment differs from the above embodiment in that three support beam portions are connected to the main driven portion 221. Further, these three support beam portions are uniformly distributed in the circumferential direction around the main driven portion 221. That is, three support beam portions are arranged around the main driven portion 221 at intervals of 120 degrees. Similarly to the above-described embodiment, the inner support beam portion 222, the auxiliary driven portion 223, and the outer support beam portion 224 are connected to each support beam portion from the main driven portion 221 side to the outer side in order. The support beam portion is formed to extend linearly outward in the radial direction.

  In the present embodiment, since the three support beam portions are evenly arranged around the main driven portion 221, the stability of the main driven portion 221 can be improved, and the vibration in the original vertical direction can also be obtained with respect to the vibration mode. Generation of vibration components other than the components can be suppressed. Here, in the illustrated example, three support beam portions are provided, but the number is not limited to three, and an arbitrary number of three or more support beam portions can be provided.

  Note that each of the embodiments described above, which is configured so that the support beam portions extend on both the left and right sides of the main driven portion, and the present embodiment, each support beam at a plurality of locations around the main driven portion. It is the same in that the portion is configured, and the same operational effects as those of the above embodiments can be obtained. In this example, the wiring lengths of the wirings 214 for the three fixed portions 225 are not equal, but the above-described pattern of the wiring 214 is devised so that the wiring lengths for the three fixed portions 225 are the same. The influence of the phase difference can be reduced.

  FIG. 6 is a schematic perspective view showing still another embodiment. The vibrator structure 300 according to this embodiment is basically configured in the same manner as the embodiment shown in FIG. 1 and includes a fixed electrode 310, a movable electrode 320, a wiring 314, an insulating layer 315, and the like. The beam portion is different from the above in that two auxiliary driven portions 323 and 325 are provided in series. That is, in each support beam portion, the inner support beam portion 322, the inner auxiliary driven portion 323, the intermediate support beam portion 324, the outer auxiliary driven portion 325, and the outer support beam portion 326 are sequentially outward from the main driven portion 321. Are connected, and the outer support beam portion 326 is connected to the fixed portion 327.

  Further, as described above, the two auxiliary driven portions, that is, the inner auxiliary driven portion 323 and the outer auxiliary driven portion 325 are provided in the middle of each support beam portion, so that they differ in the radial direction corresponding to these. Two auxiliary electrodes, that is, an inner auxiliary electrode 301A and an outer auxiliary electrode 301B are provided at the position. Here, in the example shown in FIG. 6, the wiring 314 has a symmetrical shape with respect to the left and right fixed parts 327, and the input signal is supplied with the same wiring length for the left and right fixed parts 327. Care is taken so that no phase difference occurs.

  Furthermore, in the case of the present embodiment, the auxiliary control means is configured so that the potential of the inner auxiliary electrode 301A and the potential of the outer auxiliary electrode 301B can be switched separately. That is, among the movable electrodes 320, the inner auxiliary driven portion 323 and the outer auxiliary driven portion 325 can be switched independently. Thereby, the variation of the switching mode of the vibration state of the movable electrode 320 can be increased.

  In the present embodiment configured as described above, the potential difference between the inner auxiliary electrode 301A and the movable electrode 320 is increased by increasing the potential difference between the inner auxiliary electrode 301A and the movable electrode 320, and the potential difference between the outer auxiliary electrode 301B and the movable electrode 320 is increased. Since the effective spring constant k and the mass m of the movable electrode 320 can be made different from each other when the outer auxiliary driven portion 325 is constrained, any of the inner auxiliary driven portion 323 and the outer auxiliary driven portion 325 can be changed. In addition, a total of three vibration states can be switched to each other: a state in which only the inner auxiliary driven portion 323 is bound, and a state in which only the outer auxiliary driven portion 325 is bound. Therefore, the range of selection of the resonance frequency can be expanded.

  In this embodiment, it is also possible to bind both the inner auxiliary driven part 323 and the outer auxiliary driven part 325. In this case, basically, vibration close to a state in which only the inner auxiliary driven part 323 is restricted. Although the state is obtained, strictly speaking, the bound state of the inner auxiliary driven portion 323 is further enhanced by the binding of the outer auxiliary driven portion 325, and therefore, another vibration other than the above three vibration states. The state can be obtained.

  When a plurality of sets of auxiliary electrodes and auxiliary driven portions are provided in series along the support direction as described above, a plurality of switches are provided in the auxiliary control means so that each set is connected to a different potential. Constitute. In this case, it suffices that the number of branches by the switches is the same as the number of sets. In addition, the plurality of potentials in this case may be configured by dividing a single power supply voltage.

  7 and 8 are schematic process diagrams showing a method for manufacturing the vibrator structure 100 of the present embodiment. The following manufacturing method will be described for the vibrator structure shown in FIGS. 2B and 4, but the other embodiments can be easily manufactured by substantially the same procedure.

  In this embodiment, first, a substrate 101 shown in FIG. 7A is prepared. The substrate 101 is preferably a semiconductor substrate, and particularly preferably a single crystal silicon substrate.

Next, as shown in FIG. 7B, an impurity diffusion region is formed in the surface layer portion of the substrate 101 by a thermal diffusion method, an ion implantation method, or the like, so that an auxiliary electrode 101A having conductivity is formed. For example, when a p ⁻ type silicon substrate is used as the substrate 101, an n ⁺ type diffusion region is formed by doping P, As, or the like. Further, when a negative voltage is applied to the auxiliary electrode as described above, a P ⁺ type diffusion region is formed by doping B or the like after forming an n-well in the substrate 101.

Next, as shown in FIG. 7C, an insulating layer 102 made of silicon oxide (SiO ₂ ) or the like is formed on the surface of the substrate 101 by sputtering or thermal oxidation. The insulating layer 102 may be formed of a natural oxide film that is naturally formed on the substrate surface.

Further, as shown in FIG. 7D, an insulating layer 103 made of silicon nitride (Si ₃ N ₄ ) or the like is formed on the insulating layer 102 by sputtering or CVD. This insulating layer 103 also functions as an etching stop layer when etching a sacrificial layer described later.

  Next, as shown in FIG. 7E, a polycrystalline silicon layer is formed on the insulating layer 103 by a CVD method or the like, and is patterned by a photolithography method or an etching method, whereby the fixed electrode 110 and the wiring are formed. 114 is formed.

  Next, as shown in FIG. 8A, a silicon oxide layer 112 is formed on the surface of the insulating layer 103 made of silicon nitride, the fixed electrode 110 made of polycrystalline silicon, and the wiring 114 by thermal oxidation. Form. The silicon oxide layer 112 is formed by heating the insulating layer 103, the fixed electrode 110, and the wiring 114 themselves in an oxidizing atmosphere. As emphasized in the drawing, silicon nitride is formed of polycrystalline silicon. As a result, the portion on the insulating layer 103 is thin, and the portions on the fixed electrode 110 and the wiring 114 are thick.

  Further, as shown in FIG. 8B, a silicon oxide layer 113 is formed by forming a silicon oxide film on the silicon oxide layer 112 by a CVD method or the like. The silicon oxide layers 112 and 113 constitute a sacrificial layer for forming a gap between the movable electrode 120 and the substrate 101 described later. The silicon oxide layer 113 is formed in order to secure a sufficient thickness of the sacrificial layer and to control the thickness as designed.

  Further, the silicon oxide layers 112 and 113 serving as sacrificial layers are patterned so as to exist at least in a region including a region where the movable electrode 120 described later is formed. At this time, it is desirable that the patterning is performed so as to exist only in the region where the movable electrode 120 is formed. At the time of this patterning, contact holes 112 a and 113 a are formed in the silicon oxide layers 112 and 113 formed on the wiring 114.

  Next, as shown in FIG. 8C, a movable electrode 120 is formed by depositing a conductor such as polycrystalline silicon on the silicon oxide layer 113 by CVD or the like and patterning it. At this time, the contact holes 112a and 113a are also filled with a film forming material, whereby the movable electrode 120 and the wiring 114 are conductively connected. When this process is completed, all the structural elements constituting the vibrator structure 100 are formed on the substrate 101.

  Next, as shown in FIG. 8D, the substrate 101 is covered with a protective film 116 such as an acrylic resin, and an opening 116a is formed in a region of the protective film 116 substantially corresponding to the movable part of the movable electrode 120. Form. It is also possible to form the protective film 116 with the openings 116a in advance by screen printing or the like.

  Then, the sacrificial layer (silicon oxide layers 112 and 113) is removed at a portion corresponding to the opening 116a by performing wet etching using a hydrofluoric acid-based etching solution. At this time, the wet etching stops at the insulating layer 103. As a result, the gaps G <b> 1 and G <b> 2 are secured between the main driven portion 121, the inner support beam portion 122, the auxiliary driven portion 123, the outer support beam portion 124, and the insulating layer 103 in the movable electrode 120. That is, a small gap G2 is obtained in the region where the silicon oxide layer 112 is formed thin, and a large gap G1 is obtained in the region where the silicon oxide layer 112 is formed thick.

  Of the silicon oxide layers 112 and 113, a portion (anchor portion) existing below the fixed portion 125 of the movable electrode 120 is left without being removed by the wet etching, and the movable electrode 120 is placed on the substrate 101. It becomes the support fixing | fixed part 115 for fixing.

  According to the embodiment described above, a plurality of frequencies can be realized by a single vibrator structure. Therefore, in a circuit or device using a plurality of frequencies, the circuit can be downsized or simplified, or The cost can be reduced by reducing the number of parts.

  It should be noted that the vibrator structure of the present invention is not limited to the illustrated examples described above, and it is needless to say that various changes can be made without departing from the scope of the present invention. For example, in each of the above embodiments, the technology for switching the frequency of the vibrator structure by the auxiliary control unit has been described. However, the present invention is not limited to such a technology, and the potential of the vibrator structure can be controlled by the potential control by the auxiliary control unit. Includes all technologies that can change or adjust the vibration state. For example, the present invention may be applied only for the purpose of adjusting the frequency of the vibrator structure.

  Moreover, although each said embodiment demonstrated the structure containing a switch as an auxiliary | assistant control means, in this invention, since the electrostatic force between an auxiliary electrode and a movable electrode should just be changed, what includes a switch Or a potential control means capable of continuously changing the potential difference between the auxiliary electrode and the movable electrode or setting it to an arbitrary potential difference. It may be provided.

The schematic perspective view of embodiment. The longitudinal cross-sectional view (a) of embodiment, and the longitudinal cross-sectional view (b) of different embodiment. Explanatory drawing (a)-(c) which shows operation | movement of the auxiliary | assistant driven part of embodiment. The longitudinal cross-sectional view which shows the binding state of different embodiment. The schematic perspective view of another embodiment. The schematic perspective view of another embodiment. The schematic process drawing (a)-(e) which shows the manufacturing method of embodiment. The schematic process drawing (a)-(d) which shows the manufacturing method of embodiment. The schematic perspective view of the conventional beam type vibrator. FIG. 6 is a schematic longitudinal sectional view of a conventional beam type vibrator.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Vibrator structure, 101 ... Substrate, 101A ... Auxiliary electrode, 102, 103 ... Insulating layer, 110 ... Fixed electrode, 114 ... Wiring, 115 ... Insulating layer, 120 ... Movable electrode, 121 ... Main driven part, 122 ... Inner support beam part, 123 ... auxiliary driven part, 124 ... outer support beam part, 125 ... fixed part

Claims (14)

A substrate, a fixed electrode formed on the substrate, and a fixed electrode that is opposed to the fixed electrode via a gap, and is fixed to a supporting and fixing portion on the substrate at a plurality of locations around a portion facing the fixed electrode. A movable electrode,
Auxiliary control means for forming an auxiliary electrode facing the movable electrode between the fixed electrode and the support fixing portion, and configured to change an electrostatic force generated between the auxiliary electrode and the movable electrode by potential control. A vibrator structure provided with
The vibrator structure according to claim 1, wherein the movable electrode is provided with an auxiliary driven portion that is wider than an adjacent portion at a position facing the auxiliary electrode.   The vibrator structure according to claim 1, wherein the plurality of auxiliary electrodes are respectively formed around the fixed electrode.   The movable electrode is provided with a main driven portion provided at a position facing the fixed electrode, and a support provided between the main driven portion and the support fixing portion and formed narrower than the main driven portion. 3. The apparatus according to claim 1, further comprising: a beam portion; and an auxiliary driven portion provided at a position facing the auxiliary electrode in the middle of the support beam portion and formed wider than the support beam portion. The vibrator structure described. The auxiliary control means sets the potential of the auxiliary electrode between a potential of the movable electrode or a first potential closer to the potential and a second potential having a large potential difference between the first potential and the potential of the movable electrode. The vibrator structure according to any one of claims 1 to 3 , further comprising a switch that switches between them. The portion of the movable electrode facing the auxiliary electrode in a state where no electrostatic force is received is disposed closer to the substrate than the portion of the movable electrode facing the fixed electrode. The vibrator structure according to any one of 1 to 4 . The movable range of the portion of the movable electrode facing the auxiliary electrode toward the substrate is smaller than the movable range of the portion of the movable electrode facing the fixed electrode toward the substrate. The vibrator structure according to any one of claims 1 to 4 . Oscillator structure according to any one of claims 1 to 6, wherein an insulating film is interposed between the auxiliary electrode and the movable electrode. The vibrator structure according to claim 7 , wherein the auxiliary electrode is an impurity region formed in a surface layer portion of the substrate, and the insulating film is formed on a surface of the substrate. A substrate, a fixed electrode formed on the substrate, and a fixed electrode that is opposed to the fixed electrode via a gap, and is fixed to a supporting and fixing portion on the substrate at a plurality of locations around a portion facing the fixed electrode. In a method of manufacturing a vibrator structure having a movable electrode,
Forming the fixed electrode and an auxiliary electrode different from the fixed electrode on the substrate or the substrate;
Forming a movable electrode which is opposed to the auxiliary electrode and the fixed electrode via a gap and is supported and fixed on the substrate at a plurality of locations around a portion facing the auxiliary electrode and the fixed electrode;
I have a,
The method for manufacturing a vibrator structure further comprising a step of forming an insulating layer to be disposed between the auxiliary electrode and the movable electrode. The method for manufacturing a vibrator structure according to claim 9 , wherein the auxiliary electrode is an impurity region formed in a surface layer portion of the substrate. The step of forming the movable electrode includes a step of forming a sacrificial layer on the substrate, a step of forming the movable electrode on the sacrificial layer, and a step of forming the gap by removing the sacrificial layer. The method for producing a vibrator structure according to claim 9 or 10 , characterized by comprising: 12. The method for manufacturing a vibrator structure according to claim 11 , wherein in the step of forming the sacrificial layer, a layer thickness on the auxiliary electrode is formed smaller than a layer thickness on the fixed electrode. Vibrator according to any one of claims 1 to 8, characterized in that the provided protruding portion protruding toward the other at least one of the opposing surfaces shaped auxiliary driven portion and the auxiliary electrode Structure. The vibration according to any one of claims 9 to 12 , further comprising a step of forming a convex portion projecting toward the other on at least one of the auxiliary driven portion and the auxiliary electrode. A manufacturing method of a child structure.

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