Vibration element, oscillator, and method for manufacturing vibration element

Abstract

To provide a vibration element that can increase the amount of adjustment of a resonance frequency, an oscillator, and a method for manufacturing a vibration element.SOLUTION: A vibration element 1 includes a base part 21, and a vibration arm 22 extended from the base part 21 in plan view and provided with weight parts 40. The weight part 40 is provided on a first surface 10a of the vibration arm 22, and has a lamination structure in which first metal layers 41 with a first ablation rate, and second metal layers 42 with a second ablation rate lower than the first ablation rate are alternately laminated in plurality with each other.SELECTED DRAWING: Figure 4

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 weight portion including a first weight portion disposed on one main surface of the tip portion of a vibrating arm and a second weight portion disposed on the base end side of the first weight portion and having a thickness thinner than that of the first weight portion is provided. 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 include 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, the vibration element described in Patent Document 1 has a problem that the thick film region in the weight portion is only the first weight portion, and the frequency range that can be roughly adjusted is narrow. That is, there are cases where adjustment of a vibration element with a large frequency variation cannot be performed. Such an element becomes defective, leading to a reduction in yield.

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 has a laminated structure in which a plurality of first metal layers having a first ablation rate and second metal layers having a second ablation rate lower than the first ablation rate are alternately laminated.

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

[0007] The method for manufacturing a vibrating element includes 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 has a laminated structure in which a plurality of first metal layers having a first ablation rate and second metal layers having a second ablation rate lower than the first ablation rate are alternately laminated.

Brief Description of the Drawings

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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, 3, and 4.

[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-crystalline 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 of the surface silicon layer 13, a piezoelectric drive unit 30, and a weight unit 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 a 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 that extends from the base portion 21 in a plan view and is provided with a weight portion 40. In the examples shown in FIGS. 1 to 3, the vibrating body 20 has three vibrating arms 22. A recess 11a that is recessed on the side opposite 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 drive 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 sets 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. As shown in FIG. 4, the weight portion 40 is provided on the first surface 10a of the vibrating arm 22 and has a laminated structure in which a plurality of first metal layers 41 and second metal layers 42 are laminated. A second metal layer 42a is disposed in the lowermost layer, and a second metal layer 42b is disposed in the outermost layer. For example, the first metal layer 41 is titanium (Ti), and the second metal layer 42 is molybdenum (Mo). However, the materials of the first metal layer 41 and the second metal layer 42 are not limited thereto, and the second ablation rate, which is the ablation rate of the second metal layer 42, may be lower than the first ablation rate, which is the ablation rate of the first metal layer 41. Such a combination of materials may be selected as the materials of the first metal layer 41 and the second metal layer 42.

[0018] In the laminated structure, the film thickness of the second metal layer 42 is thicker than that of the first metal layer 41, and the film thickness of the second metal layer 42a in the lowermost layer is thicker than that of the second metal layer 42b in the outermost layer.

[0019] Next, a configuration of the weight portion 40 that can increase the frequency adjustment range as the frequency variation of the vibration element 1 increases will be described. Generally, to increase the frequency adjustment range, it can be achieved by increasing the film thickness of the thick film region for coarse adjustment. However, the amount of etching removal after film formation increases, resulting in an increase in loss and a decrease in productivity due to an increase in film formation time, leading to high costs. Therefore, an adjustment method using ablation processing with an ultrashort pulse laser that can perform the same role as the fine adjustment layer in the thick film layer was investigated. In ablation processing, it is possible to adjust the ablation amount corresponding to the film thickness of one pulse by adjusting the laser fluence.

[0020] Ablation processing will be described with reference to Fig. 5. Fig. 5 is Fig. 2 of the cited reference "J. Plasma Fusion Res. Vol. 94, No. 5 (2018) 244 - 247", which shows the laser fluence dependence of the ablation rates of materials titanium (Ti) and molybdenum (Mo) by femtosecond lasers. Note that since a femtosecond laser has a pulse width shorter than the thermal relaxation time of a solid, it can ablate (scatter) the solid non-thermally and perform processing. Therefore, the ablation rate refers to the processing rate by a femtosecond laser.

[0021] From Fig. 5, for example, when the laser fluence is 150 mJ / cm 2 then, the ablation rate of titanium (Ti) is 16 nm / pulse, and the ablation rate of molybdenum (Mo) is 3 nm / pulse. Therefore, at the same laser fluence value, the ablation rate of titanium (Ti) can be about 5 times that of molybdenum (Mo).

[0022] Therefore, by using titanium (Ti) with a large ablation rate as the coarse adjustment layer, molybdenum (Mo) with a small ablation rate as the fine adjustment layer, and alternately stacking a plurality of the coarse adjustment layer and the fine adjustment layer to form a thick film layer, the frequency adjustment range can be increased. Also, since the coarse adjustment layer and the fine adjustment layer are alternately stacked a plurality of times, it can also cope with those with a small frequency adjustment range.

[0023] The film thickness of the thick film layer is determined design-wise according to the setting of the frequency adjustment range. Or, from the perspective of productivity, it is also possible to determine the film thickness from the number of coarse adjustment times. For example, if the number of coarse adjustment times is 10, and in addition to setting the resolution of the path for scanning the pulse spot over the entire 40 regions of the anvil part to be 5 - 7 passes per time, the number of fine adjustment times is 5 and the resolution per time is 5 passes, then the coarse adjustment layer is 10 nm and the fine adjustment layer is 13 nm. Since one coarse adjustment is 10 nm + 13 nm, the total film thickness is 230 nm after 10 coarse adjustments. Also, when the laser fluence is 140 mJ / cm near the threshold 2When set to this, only one condition can create coarse adjustment and fine adjustment based on the number of pulses, and the frequency adjustment accuracy can also be improved.

[0024] Therefore, the first metal layer 41 is titanium (Ti), and the second metal layer 42 is molybdenum (Mo). Also, when the ablation rate of the first metal layer 41 is defined as the first ablation rate and the ablation rate of the second metal layer 42 is defined as the second ablation rate, the weight portion 40 has a laminated structure in which a plurality of the first metal layer 41 with the first ablation rate and the second metal layer 42 with the second ablation rate lower than the first ablation rate are alternately laminated.

[0025] In the laminated structure, the second metal layer 42a with a small ablation rate and a thick film thickness is disposed at the lowermost layer to serve as a stopper and to prevent damage to the vibrating arm 22.

[0026] In addition, in the present embodiment, the three-pronged vibration element 1 having three vibrating arms 22 is taken as an example for explanation, but it may be a crystal tuning fork vibration element, a MEMS tuning fork vibration element, a crystal gyro sensor element, or a MEMS gyro sensor element.

[0027] As described above, since the vibration element 1 according to the present embodiment has a laminated structure in which the weight portion 40 is a laminated structure in which a plurality of the first metal layer 41 with the first ablation rate and the second metal layer 42 with the second ablation rate lower than the first ablation rate are alternately laminated, the film thickness of the weight portion 40 can be increased. Therefore, the adjustment amount can be increased, and the vibration element 1 with a large frequency adjustment range can be accurately adjusted to a desired resonance frequency. Further, since it is excellent in productivity, a vibration element 1 having a desired resonance frequency accuracy at low cost can be obtained.

[0028] Next, a method for manufacturing the vibration element 1 according to the present embodiment will be described with reference to FIGS. 6, 7, and 8.

[0029] As shown in FIG. 6, the manufacturing method of the vibration element 1 includes a substrate preparation step S1, a piezoelectric drive unit 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 dicing step S7.

[0030] First, as the substrate preparation step S1, in order to batch-process the vibration element 1 and improve mass productivity, a large-sized SOI substrate 10 is prepared.

[0031] Next, in the piezoelectric drive unit formation step S2, a piezoelectric drive unit 30, wiring 34, electrode pads 35, and a weight portion 40 are formed by photolithography on the SOI substrate 10 on which a base portion 21 and vibration arms 22 are formed.

[0032] 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.

[0033] 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 vibration arm 22 and constitute a cavity 11b. By peeling off the etching protective film, a vibration element 1 is completed, which includes a base portion 21 and a vibration arm 22 extending from the base portion 21 in a plan view and provided with a weight portion 40, and on the first surface 10a of the vibration arm 22, a first metal layer 41 having a first ablation rate and a second metal layer 42 having a second ablation rate lower than the first ablation rate are alternately stacked in a plurality.

[0034] Next, in the frequency adjustment step S5, a femtosecond laser is used as the laser. First, an external voltage is applied between the two electrode pads 35 of the vibrating element 1 to measure the resonance frequency of the vibrating element 1. A predetermined processing range and processing amount are calculated from the difference from the desired resonance frequency, and the weight portion 40 is irradiated with a femtosecond laser. The laminated layer of the first metal layer 41 and the second metal layer 42 is ablated as shown in FIG. 7 to roughly adjust it to about 100 ppm of the desired resonance frequency. Next, the resonance frequency of the vibrating element 1 is measured again, a predetermined processing range and processing amount are recalculated from the difference from the desired resonance frequency, and the weight portion 40 is irradiated with a femtosecond laser. The outermost second metal layer 42b is ablated as shown in FIG. 8 to finely adjust it to have a variation of several ppm with respect to the desired resonance frequency. In addition, in the present embodiment, in the rough adjustment, a part of the weight portion 40 is ablated. However, when the frequency adjustment range is large, the entire region of the weight portion 40 may be ablated for rough adjustment. Also, in the fine adjustment, the outermost second metal layer 42b is ablated. However, the lowermost second metal layer 42a shown in FIG. 7 may be ablated for fine adjustment.

[0035] 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 vibrating element 1 whose frequency has been adjusted is completed.

[0036] In the manufacturing method of the vibrating element 1 according to the present embodiment, since the weight portion 40 with an increased film thickness is ablated and adjusted as a laminated structure in which a plurality of first metal layers 41 with a first ablation rate and second metal layers 42 with a second ablation rate lower than the first ablation rate are alternately laminated, the vibrating element 1 with a large frequency adjustment range can be accurately adjusted to the desired resonance frequency. Also, since it is excellent in productivity, a vibrating element 1 having a desired resonance frequency accuracy at low cost can be manufactured.

[0037] 2. Second Embodiment Next, an oscillator 100 including the vibration element 1 according to the second embodiment will be described with reference to FIGS. 9 and 10. In FIG. 9, for the sake of convenience in explaining the internal configuration of the oscillator 100, a state in which the lid 60 is removed is illustrated.

[0038] As shown in FIGS. 9 and 10, the oscillator 100 includes a vibration element 1, an oscillation circuit 71 provided on a circuit board 70, and a lid 60.

[0039] The oscillation circuit 71 vibrates the vibrating arm 22 of the vibrator 20 and outputs an oscillation frequency. It is disposed between the 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.

[0040] The lid 60 has a recess 61 recessed on the side opposite to the vibration element 1, which constitutes a cavity 62. The lid 60 is joined to the surface of the vibration element 1 on the outer periphery of the recess 61 facing the vibrator 20 of the surface silicon layer 13 via a joining member 63, and together with the cavity 11b, constitutes a housing space for housing the vibrator 20. Further, the inside of the housing 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 vibrator 20 are improved. Further, as a constituent material of the lid 60, silicon is preferable, and glass, ceramic, or the like may also be used.

[0041] The oscillator 100 according to this embodiment includes a vibration element 1 in which a plurality of stacked structures are alternately stacked with a first metal layer 41 having a first ablation rate and a second metal layer 42 having a second ablation rate lower than the first ablation rate, and a weight portion 40 having a thick film thickness is disposed. Therefore, since the vibration element 1 having a large frequency adjustment range can be accurately adjusted to a desired resonance frequency, an oscillator 100 excellent in oscillation frequency accuracy can be obtained.

Explanation of Signs

[0042] 1... Vibration element, 10... SOI substrate, 10a... First surface, 11... Silicon substrate, 11a... Recess, 11b... Cavity, 12... Buried oxide film, 13... Surface silicon layer, 20... Vibration body, 21... Base portion, 22... Vibration arm, 30... Piezoelectric drive portion, 31... First electrode, 32... Piezoelectric layer, 33... Second electrode, 34... Wiring, 35... Electrode pad, 40... Weight portion, 41... First metal layer, 42... Second metal layer, 60... Cover body, 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 extending from the base in a plan view and provided with a weight portion, wherein the weight portion is provided on a first surface of the vibrating arm and has a laminated structure in which a plurality of first metal layers having a first ablation rate and second metal layers having a second ablation rate lower than the first ablation rate are alternately laminated. A vibration element.

2. The outermost layer and the lowermost layer of the laminated structure are the second metal layers. The vibration element according to Claim 1.

3. In the laminated structure, the film thickness of the second metal layer is thicker than that of the first metal layer. The vibration element according to Claim 1 or Claim 2.

4. In the laminated structure, the film thickness of the second metal layer of the lowermost layer is thicker than that of the second metal layer of the outermost layer. The vibration element according to Claim 1 or Claim 2.

5. The first metal layer is Ti, The second metal layer is Mo. The vibration element according to Claim 1 or Claim 2.

6. An oscillator comprising the vibration element according to any one of Claims 1 to 5 and an oscillation circuit. An oscillator.

7. A method for manufacturing a vibration element, the method having a frequency adjustment step of adjusting a resonance frequency of the vibration element, wherein the vibration element includes a base and a vibrating arm extending from the base in a plan view and provided with a weight portion, wherein the weight portion is provided on a first surface of the vibrating arm and has a laminated structure in which a plurality of first metal layers having a first ablation rate and second metal layers having a second ablation rate lower than the first ablation rate are alternately laminated. A method for manufacturing a vibration element.

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