Vibration element, oscillator, and method for manufacturing vibration element

Abstract

To provide a vibration element, an oscillator, and a method for manufacturing a vibration element that enable efficient and precise adjustment of the resonant frequency.SOLUTION: A vibration element 1 includes a base 21 and vibrating arms 22 extending from the base 21 in a planar view and having weight portions 40 provided thereon. The weight portions 40 are each provided on a first surface 10a of the vibrating arm 22 and includes a coarse tuning portion 41 having a first metal and a fine tuning portion 42 having a second metal different from the first metal.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a vibration element, an oscillator, and a method for manufacturing a vibration element.

Background Art

[0002] Conventionally, a technique for adjusting the resonance frequency of a vibration element by adjusting the mass of the vibration element is known. For example, in Patent Document 1, a first weight portion disposed on one main surface of the tip portion of a vibrating arm and a second weight portion disposed closer to the base end side than the first weight portion and having a thickness thinner than that of the first weight portion are included. The first weight portion is a weight portion for roughly adjusting the resonance frequency of the vibration element, and the second weight portion is a weight portion for finely adjusting the resonance frequency of the vibration element. Thus, it is described that by having the weight portion with the first weight portion for rough adjustment and the second weight portion for fine adjustment, the resonance frequency of the vibration element can be adjusted efficiently and accurately.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the vibration element described in Patent Document 1, since the same metal is used for the first weight portion and the second weight portion, it is necessary to increase the processing rate to improve efficiency during rough adjustment and to decrease the processing rate to improve accuracy during fine adjustment. That is, it is necessary to vary the laser irradiation conditions between the first weight portion for rough adjustment and the second weight portion for fine adjustment, resulting in a problem that the adjustment time becomes long due to the time required for changing the conditions.

Means for Solving the Problems

[0005] The vibrating element includes a base portion and a vibrating arm that extends from the base portion in a plan view and is provided with a weight portion. The weight portion is provided on a first surface of the vibrating arm and includes a coarse adjustment portion having a first metal and a fine adjustment portion having a second metal different from the first metal.

[0006] An oscillator comprising the vibrating element described above and an oscillation circuit.

[0007] The method for manufacturing a vibrating element has a frequency adjustment step of adjusting the resonance frequency of the vibrating element. The vibrating element includes a base portion and a vibrating arm that extends from the base portion in a plan view and is provided with a weight portion. The weight portion is provided on a first surface of the vibrating arm and includes a coarse adjustment portion having a first metal and a fine adjustment portion having a second metal different from the first metal.

Brief Description of the Drawings

[0008]

Figure 1

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Figure 6A

Figure 6B

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Embodiments for Carrying Out the Invention

[0009] 1. First Embodiment First, the vibration element 1 according to the first embodiment will be described with reference to FIGS. 1, 2, and 3.

[0010] The vibration element 1 according to the present embodiment can be manufactured by processing an SOI (Silicon on Insulator) substrate 10. The SOI substrate 10 is a substrate in which a silicon substrate 11, a buried oxide film (BOX: Buried Oxide) 12, and a surface silicon layer 13 are laminated in this order. For example, the silicon substrate 11 and the surface silicon layer 13 are made of single crystal silicon (Si), and the buried oxide film 12 is made of silicon dioxide (SiO2) or the like. In the present embodiment, the surface silicon layer 13 corresponds to the base material constituting the base portion 21 and the vibrating arm 22.

[0011] As shown in FIGS. 1, 2, and 3, the vibration element 1 includes a silicon substrate 11, a buried oxide film 12 disposed in a partial region of the silicon substrate 11, a vibrating body 20 made of silicon in the surface silicon layer 13, a piezoelectric driving unit 30, and a weight portion 40.

[0012] The vibrating body 20 has a base portion 21 supported by the buried oxide film 12 and a vibrating arm 22 separated from the surrounding silicon other than the base portion 21 on the region where the buried oxide film 12 is removed. That is, the vibrating body 20 has a base portion 21 and a vibrating arm 22 extending from the base portion 21 in a plan view and provided with a weight portion 40. In the example shown in FIGS. 1 to 3, the vibrating body 20 has three vibrating arms 22. A recess 11a that is recessed on the opposite side to the vibrating body 20 is formed in the silicon substrate 11 at a position facing the vibrating arm 22, constituting a cavity 11b.

[0013] The piezoelectric driving unit 30 vibrates the vibrating arm 22 and includes a first electrode 31, a piezoelectric layer 32, a second electrode 33, and a plurality of wirings 34. The first electrode 31 and the second electrode 33 are arranged to sandwich the piezoelectric layer 32. That is, the first electrode 31 arranged on the first surface 10a of the vibrating arm 22, the piezoelectric layer 32 arranged on the opposite side of the first surface 10a of the first electrode 31, and the second electrode 33 arranged on the opposite side of the piezoelectric layer 32 to the first electrode 31 are laminated in this order. In the example shown in Figs. 1 to 3, three piezoelectric driving units 30 each consisting of the first electrode 31, the piezoelectric layer 32, and the second electrode 33 are provided corresponding to the three vibrating arms 22.

[0014] The multiple wirings 34 are electrically connected to the first electrode 31 and the second electrode 33 so as to vibrate the adjacent vibrating arms 22 in opposite phases. Specifically, the first electrode 31 of the first vibrating arm 22a, the second electrode 33 of the second vibrating arm 22b, and the first electrode 31 of the third vibrating arm 22c are electrically connected by the wirings 34, and the second electrode 33 of the first vibrating arm 22a, the first electrode 31 of the second vibrating arm 22b, and the second electrode 33 of the third vibrating arm 22c are electrically connected by the wirings 34. In addition, the multiple wirings 34 are electrically connected to electrode pads 35, and the adjacent vibrating arms 22 can be vibrated in opposite phases by applying a voltage between the two electrode pads 35 from the outside.

[0015] As for the materials constituting these, for example, the piezoelectric layer 32 is made of aluminum nitride (AlN) or the like, the first electrode 31 and the second electrode 33 are made of titanium nitride (TiN) or the like, and the multiple wirings 34 and the electrode pads 35 are made of titanium nitride (TiN), aluminum (Al), copper (Cu), or the like.

[0016] When a voltage is applied between the first electrode 31 and the second electrode 33 via the two electrode pads 35, the piezoelectric layer 32 expands and contracts, causing the vibrating arm 22 to vibrate. The vibration is greatly excited at the natural resonant frequency, and the impedance becomes minimum. As a result, the oscillator using this vibration element 1 oscillates at an oscillation frequency determined mainly by the resonant frequency of the vibrating arm 22.

[0017] The weight portion 40 is used to adjust the resonance frequency of the vibration element 1. The weight portion 40 is provided on the first surface 10a of the vibration arm 22, and includes a coarse adjustment portion 41 having a first metal and a fine adjustment portion 42 having a second metal different from the first metal. The coarse adjustment portion 41 is provided on the side of the vibration arm 22 opposite to the base portion 21, and the fine adjustment portion 42 is provided on the base portion 21 side of the vibration arm 22. Specifically, the coarse adjustment portion 41 is arranged on the tip side of the vibration arm 22 where the frequency change amount is large with respect to the mass change, and the fine adjustment portion 42 is arranged between the coarse adjustment portion 41, which is on the base portion 21 side of the vibration arm 22 where the frequency change amount is small with respect to the mass change, and the piezoelectric drive portion 30. Thus, the coarse adjustment portion 41 and the fine adjustment portion 42 are provided on the first surface 10a, which is the same surface of the vibration arm 22.

[0018] In the weight portion 40, the first metal of the coarse adjustment portion 41 is gold (Au), and the second metal of the fine adjustment portion 42 is aluminum copper (AlCu) or titanium nitride (TiN).

[0019] Here, the processing rate of the metal used for the weight portion 40 by a laser, an ion beam, etc. will be described with reference to FIG. 4. FIG. 4 shows the results of measuring the processing rates of gold (Au), aluminum copper (AlCu), and titanium nitride (TiN) by an argon ion beam, and shows the processing amounts of each metal with respect to the processing time under the same irradiation conditions.

[0020] From FIG. 4, the processing rates decrease in the order of gold (Au), aluminum copper (AlCu), and titanium nitride (TiN). In particular, under the same irradiation conditions, the processing rates of aluminum copper (AlCu) and titanium nitride (TiN) are extremely small, about 1 / 10 or less compared to the processing rate of gold (Au). Also, gold (Au) has a larger specific gravity than aluminum copper (AlCu) and titanium nitride (TiN). Therefore, by using gold (Au), which has a large specific gravity and a large processing rate, as the first metal of the coarse adjustment portion 41, coarse adjustment can be performed at high speed. Also, by using aluminum copper (AlCu) or titanium nitride (TiN), which have a small specific gravity and a small processing rate, as the second metal of the fine adjustment portion 42, fine adjustment can be performed with high precision.

[0021] For the adjustment of the weight portion 40, it may be a laser or an ion beam. However, for the same energy, the shorter the pulse width, the higher the intensity of the generated laser. Therefore, it is preferable to use a femtosecond laser with a very short pulse width.

[0022] In addition, in this embodiment, the weight portion 40 is composed of two areas, a coarse adjustment portion 41 and a fine adjustment portion 42, but it is not limited thereto. For example, it may be composed of three areas such as a coarse adjustment portion 41, a fine adjustment portion 42, and an ultra-fine adjustment portion.

[0023] In addition, in this embodiment, the three-legged vibration element 1 having three vibrating arms 22 is taken as an example for explanation, but it may also be a crystal tuning fork vibration element, a MEMS (Micro Electro Mechanical Systems) tuning fork vibration element, a crystal gyro sensor element, and a MEMS gyro sensor element.

[0024] As described above, in the vibration element 1 according to this embodiment, on the first surface 10a of the vibrating arm 22, there are arranged a coarse adjustment portion 41 having a first metal with a large processing rate and a fine adjustment portion 42 having a second metal with a smaller processing rate than the first metal under the same laser irradiation conditions. Therefore, without changing the laser irradiation conditions during coarse adjustment or fine adjustment, the resonance frequency of the vibration element 1 can be efficiently and accurately adjusted to a desired resonance frequency in a short time, and a vibration element 1 with a desired resonance frequency accuracy at low cost can be obtained.

[0025] Next, a manufacturing method of the vibration element 1 according to this embodiment will be described with reference to FIGS. 5, 6A, and 6B.

[0026] As shown in FIG. 5, the manufacturing method of the vibration element 1 includes a substrate preparation step S1, a piezoelectric driving portion formation step S2, a protective film formation step S3, an etching process step S4, a frequency adjustment step S5, a sealing step S6, and a singulation step S7.

[0027] First, as the substrate preparation step S1, the vibrating element 1 is batch-processed, and a large SOI substrate 10 is prepared to enhance mass productivity.

[0028] Next, in the piezoelectric drive unit formation step S2, a piezoelectric drive unit 30, wiring 34, electrode pads 35, and a weight unit 40 are formed by photolithography on the SOI substrate 10 on which a base portion 21 and vibrating arms 22 are formed.

[0029] Next, in the protective film formation step S3, a photoresist is applied on the SOI substrate 10 on which the piezoelectric drive unit 30 and the like are formed, and an element outer shape mask pattern is formed by photolithography to serve as an etching protective film.

[0030] Next, in the etching process step S4, the surface silicon layer 13 exposed from the etching protective film is etched using an etching solution of TMAH (tetramethylammonium hydroxide) or potassium hydroxide (KOH). Then, the buried oxide film 12 exposed from the surface silicon layer 13 is etched using an etching solution of BHF (buffered hydrofluoric acid). Next, again using an etching solution of TMAH (tetramethylammonium hydroxide) or potassium hydroxide (KOH), the silicon substrate 11 exposed from the buried oxide film 12 is etched to form a recess 11a below the vibrating arm 22 and constitute a cavity 11b. By peeling off the etching protective film, a vibrating element 1 is completed, which includes a base portion 21 and a vibrating arm 22 extending from the base portion 21 in a plan view and provided with a weight portion 40. The weight portion 40 is provided on the first surface 10a of the vibrating arm 22 and includes a coarse adjustment portion 41 having a first metal and a fine adjustment portion 42 having a second metal different from the first metal.

[0031] Next, in the frequency adjustment step S5, a voltage is externally applied between the two electrode pads 35 of the vibration element 1, and the resonance frequency of the vibration element 1 is measured. Based on the difference from the desired resonance frequency, the rough adjustment section 41 is irradiated with a laser for a predetermined processing time to roughly adjust the resonance frequency to about 100 ppm of the desired resonance frequency. Next, the resonance frequency of the vibration element 1 is measured again, and the fine adjustment section 42 is irradiated with a laser under the same laser irradiation conditions as the rough adjustment to finely adjust the resonance frequency to have a variation of several ppm with respect to the desired resonance frequency. In the case of a laser, the processing position is changed from the position of the rough adjustment section 41 to the position of the fine adjustment section 42 by moving the galvano mirror or the stage holding the SOI substrate 10. In the case of an ion beam, the processing position is changed from the position of the rough adjustment section 41 to the position of the fine adjustment section 42 by moving the mask 50 or the stage holding the SOI substrate 10. That is, in the case of frequency adjustment by an ion beam using the mask 50, for rough adjustment, as shown in FIG. 6A, the opening of the mask 50 is arranged on the rough adjustment section 41 and irradiated with an ion beam to remove the first metal to adjust the resonance frequency. For fine adjustment, as shown in FIG. 6B, after moving the opening of the mask 50 onto the fine adjustment section 42, the ion beam is irradiated to remove the second metal to adjust the resonance frequency.

[0032] Next, in the sealing step S6, a lid 60 used in the oscillator 100 described later is joined. The lid 60 may be in a piece state, but it is preferably joined in a state of being integrally formed on a large substrate. Thereafter, in the singulation step S7, the large SOI substrate 10 to which the lid 60 is joined is cut by a dicing saw, a laser, or the like and singulated, whereby the vibration element 1 whose frequency has been adjusted is completed.

[0033] In the manufacturing method of the vibration element 1 according to the present embodiment, in the frequency adjustment step, the resonance frequency of the vibration element 1 in which the rough adjustment section 41 having the first metal with a large processing rate and the fine adjustment section 42 having the second metal with a smaller processing rate than the first metal under the same laser irradiation conditions are arranged on the first surface 10a of the vibrating arm 22 is adjusted. Therefore, without changing the laser irradiation conditions during rough adjustment and fine adjustment, the resonance frequency of the vibration element 1 can be efficiently and accurately adjusted to the desired resonance frequency in a short time, so that a vibration element 1 having the desired resonance frequency accuracy at low cost can be manufactured.

[0034] 2. Second Embodiment Next, the vibration element 1a according to the second embodiment will be described with reference to FIG. 7. For the same components as those in the first embodiment described above, the same reference numerals are given and the description thereof is omitted. The vibration element 1a of the second embodiment is the same as the vibration element 1 of the first embodiment, except that the types of constituent materials of the coarse adjustment portion 41a and the fine adjustment portion 42a of the weight portion 40 are different.

[0035] As shown in FIG. 7, the vibration element 1a includes an SOI substrate 10, a vibrating body 20 made of silicon in the surface silicon layer 13 of the SOI substrate 10, a piezoelectric driving portion 30, and a weight portion 40.

[0036] In the weight portion 40, the first metal of the coarse adjustment portion 41a is aluminum copper (AlCu), and the second metal of the fine adjustment portion 42a is titanium nitride (TiN). Since the processing rate of titanium nitride (TiN) in the fine adjustment portion 42a is lower than the processing rate of aluminum copper (AlCu) in the coarse adjustment portion 41a as shown in FIG. 4, the same effects as those in the first embodiment can be obtained.

[0037] In addition, titanium nitride (TiN) in the fine adjustment portion 42a has the same configuration as the first electrode 31, the wiring 34, and the electrode pad 35, and the fine adjustment portion 42a can be formed in the same process.

[0038] With such a configuration, the same effects as those in the first embodiment can be obtained.

[0039] 3. Third Embodiment Next, the oscillator 100 including the vibration elements 1 and 1a according to the third embodiment will be described with reference to FIGS. 8 and 9. In the following description, a configuration applying the vibration element 1 will be exemplified. In FIG. 8, for the convenience of explaining the internal configuration of the oscillator 100, a state where the lid 60 is removed is illustrated.

[0040] As shown in FIGS. 8 and 9, the oscillator 100 includes a vibration element 1, an oscillation circuit 71 provided on a circuit board 70, and a lid body 60.

[0041] The oscillation circuit 71 vibrates the vibration arm 22 of the vibrating body 20 and outputs an oscillation frequency. It is disposed between two electrode pads 35 in a plan view and is electrically connected to the electrode pads 35 via bonding wires 72. The oscillation circuit 71 is electrically connected to a plurality of external terminals 73 provided on a surface opposite to the surface on which the buried oxide film 12 of the silicon substrate 11 is disposed via a through electrode (not shown) or the like. The external terminals 73 supply power to the oscillation circuit 71 and output the oscillation frequency output from the oscillation circuit 71 to the outside.

[0042] The lid body 60 has a recess 61 recessed on the side opposite to the vibration element 1, and constitutes a cavity 62. The lid body 60 is joined to the surface of the outer peripheral portion of the recess 61 facing the vibration element 1 via a joining member 63 to the surface surrounding the vibrating body 20 of the surface silicon layer 13, and constitutes an accommodation space for accommodating the vibrating body 20 together with the cavity 11b. Further, the inside of the accommodation space is in a depressurized state, preferably a state closer to a vacuum. Thereby, the viscous resistance is reduced and the oscillation characteristics of the vibrating body 20 are improved. Further, as the constituent material of the lid body 60, silicon is suitable, and glass, ceramic, or the like may be used.

[0043] The oscillator 100 according to the present embodiment includes a vibration element 1 on which a coarse adjustment portion 41 having a first metal with a large processing rate and a fine adjustment portion 42 having a second metal with a smaller processing rate than the first metal under the same laser irradiation conditions are arranged on the first surface 10a of the vibration arm 22. Therefore, the resonance frequency of the vibration element 1 can be efficiently and accurately adjusted to a desired resonance frequency in a short time without changing the laser irradiation conditions during coarse adjustment and fine adjustment, so that an oscillator 100 with low cost and excellent oscillation frequency accuracy can be obtained.

Description of reference numerals

[0044] 1, 1a... vibration element, 10... SOI substrate, 10a... first surface, 11... silicon substrate, 11a... recess, 11b... cavity, 12... buried oxide film, 13... surface silicon layer, 20... vibrating body, 21... base, 22... vibrating arm, 30... piezoelectric drive unit, 31... first electrode, 32... piezoelectric layer, 33... second electrode, 34... wiring, 35... electrode pad, 40... weight portion, 41... coarse adjustment portion, 42... fine adjustment portion, 60... cover, 61... recess, 63... joining member, 70... circuit board, 71... oscillation circuit, 72... bonding wire, 73... external terminal, 100... oscillator.

Claims

1. A base, and a vibrating arm that extends from the base in a plan view and is provided with a weight portion, wherein the weight portion is provided on a first surface of the vibrating arm and includes a coarse adjustment portion having a first metal and a fine adjustment portion having a second metal different from the first metal. A vibration element.

2. The processing rate of the second metal is lower than that of the first metal. The vibration element according to Claim 1.

3. The coarse adjustment portion is provided on the side of the vibrating arm opposite to the base. The fine adjustment portion is provided on the base side of the vibrating arm. The vibration element according to Claim 1 or Claim 2.

4. The first metal is Au. The second metal is AlCu or TiN. The vibration element according to any one of Claims 1 to 3.

5. The first metal is AlCu. The second metal is TiN. The vibration element according to any one of Claims 1 to 3.

6. Any one of the vibration elements according to Claims 1 to 5, and an oscillation circuit. An oscillator.

7. A frequency adjustment step of adjusting the resonance frequency of the vibration element, wherein the vibration element includes a base and a vibrating arm that extends from the base in a plan view and is provided with a weight portion, and the weight portion is provided on a first surface of the vibrating arm and includes a coarse adjustment portion having a first metal and a fine adjustment portion having a second metal different from the first metal. A method for manufacturing a vibration element.

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