Vibration device

Abstract

We provide low-impedance vibration devices. [Solution] The vibration device 1 comprises three or more vibrating arms 22 extending along a first direction, a support portion 210 connected to one end of the three or more vibrating arms 22, a fixing portion 211 that fixes the support portion 210 to a base portion 131, and a drive portion 23 provided on the three or more vibrating arms 22 and having laminates 23A, 23B, 23C having at least a piezoelectric layer 232 and electrodes 231, 233, wherein the laminates 23A, 23B, 23C are arranged to straddle a part of the support portion 210 from above the three or more vibrating arms 22.

Description

Technical Field

[0001] The present invention relates to a vibration device.

Background Art

[0002] Patent Document 1 discloses a vibration piece including a base portion, and three arms connected to the base portion and extending along one direction. The base portion and the three arms are made of a silicon substrate, and a laminated structure including a first electrode, a piezoelectric layer, and a second electrode is formed on the base portion and the three arms.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, further improvement in vibration characteristics such as impedance reduction is required for the vibration piece described in Patent Document 1.

Means for Solving the Problems

[0005] The vibration device includes three or more vibration arms extending along a first direction, a support portion connected to one end of the three or more vibration arms, a fixing portion fixing the support portion to a base portion, and a driving portion provided on the three or more vibration arms and having a laminate including at least a piezoelectric layer and an electrode. The laminate is disposed so as to straddle from above the three or more vibration arms to a part of the support portion.

Brief Description of the Drawings

[0006] [Figure 1] A plan view showing a schematic structure of the vibration device according to the present embodiment. [Figure 2] A cross-sectional view taken along line A-A in FIG. 1. [Figure 3] Plan view of the vibrating element of a vibration device. [Figure 4] Cross-sectional view of the vibrating arm of the vibrating piece. [Figure 5] A graph showing the relationship between L2 / L1 and normalized impedance. [Modes for carrying out the invention]

[0007] Regarding the vibration device 1 according to this embodiment, a vibrating piece 20 having three or more vibrating arms 22 will be given as an example and described with reference to Figures 1 to 5. In embodiments of the present invention, the components shown in each drawing may be shown at different dimensional scales for clarity. For the sake of clarity, the following plan and cross-sectional diagrams will show the X, Y, and Z axes as three mutually orthogonal axes. The direction along the X axis will also be referred to as the "X-axis direction," the direction along the Y axis as the "Y-axis direction," and the direction along the Z axis as the "Z-axis direction." The X-axis direction corresponds to the "second direction," and the Y-axis direction corresponds to the "first direction." The side of each axis indicated by the arrow will also be referred to as the "positive side," and the side opposite the arrow as the "negative side." The positive side of the Z-axis direction will also be referred to as "up," and the negative side of the Z-axis direction will also be referred to as "down."

[0008] As shown in Figures 1 and 2, the vibration device 1 comprises an SOI (Silicon on Insulator) substrate 10 on which a vibrating piece 20 is formed, and a lid portion 5 that hermetically seals the vibrating piece 20 between itself and the SOI substrate 10. The lid portion 5 is made of single-crystal silicon or the like and has a recess opening on its lower surface. The lower surface of the lid portion 5 is joined to the upper surface of the SOI substrate 10. As shown in Figure 2, the SOI substrate 10 is a multilayer substrate in which a silicon layer 11, a BOX (Buried Oxide) layer 12, and a surface silicon layer 13, which is the device layer, are stacked in this order from the bottom. For example, the silicon layer 11 and the surface silicon layer 13 are each made of single-crystal silicon, and the BOX layer 12 is made of silicon oxide (SiO2) layer.

[0009] As shown in Figure 1, the surface silicon layer 13 has a vibrating substrate 21 equipped with a vibrating piece 20 and a frame-shaped base 131 surrounding the vibrating substrate 21. A pair of electrode pads PAD1 and PAD2 are arranged on the upper surface of the base 131. As shown in Figure 2, through electrodes 14 and 15 are formed at positions overlapping with each electrode pad PAD1 and PAD2, penetrating the SOI substrate 10 in the thickness direction. Through electrode 14 is electrically connected to electrode pad PAD1, and through electrode 15 is electrically connected to electrode pad PAD2. As a result, electrode pads PAD1 and PAD2 are drawn out from the lower surface of the vibration device 1. Therefore, electrical connection to external devices such as oscillation circuits is made easy.

[0010] Furthermore, the vibrating element 20 has a vibrating substrate 21 formed on the surface silicon layer 13. In other words, the vibrating substrate 21 is formed from a silicon substrate. By forming the vibrating substrate 21 from a silicon substrate, the vibrating substrate 21 can be formed using a silicon wafer process, which makes it easier to process the vibrating substrate 21 and allows the vibrating substrate 21 to be formed with high processing accuracy.

[0011] The vibrating substrate 21 is plate-shaped and has an upper and lower surface that are in a front-back relationship. As shown in Figure 3, the vibrating substrate 21 has a support portion 210, three vibrating arms 22 extending from the support portion 210, and a fixing portion 211 that fixes the support portion 210 to the base portion 131. As shown in Figure 4, the base portion 131 is supported by the silicon layer 11 and the BOX layer 12 located below it, whereas the vibrating arms 22, the support portion 210, and the fixing portion 211 are separated from the silicon layer 11 as there is no BOX layer 12 below them. Therefore, the vibrating arms 22, the support portion 210, and the fixing portion 211 are fixed to the base portion 131 at the side surface of the fixing portion 211 that faces the base portion 131. Furthermore, the entire vibrating substrate 21 is formed to the same thickness as the surface silicon layer 13.

[0012] As shown in Figure 3, the vibrating arms 22A, 22B, and 22C each extend from the support portion 210 toward the positive side of the first direction, the Y-axis, and are arranged at equal intervals in the second direction, the X-axis. Specifically, vibrating arm 22A is located in the center of the arrangement, vibrating arm 22B is located toward the positive side of vibrating arm 22A toward the X-axis, and vibrating arm 22C is located toward the negative side of the X-axis. Each of these vibrating arms 22A, 22B, and 22C has an arm portion 221 that extends from the support portion 210 toward the positive side of the Y-axis, and a wide portion 222 located toward the tip of the arm portion 221 and wider than the arm portion 221. For the sake of explanation, in the following, the length of each vibrating arm 22A, 22B, 22C and the support portion 210 along the Y-axis will be referred to as "length," and the length along the X-axis will be referred to as "width."

[0013] Each arm 221 is straight and has a constant width along the Y-axis. The width of the wide section 222 is greater than the width of the arm 221. Each wide section 222 is also straight and has a constant width along the Y-axis. With this configuration, the mass of the tips of the vibrating arms 22A, 22B, and 22C increases due to the mass effect of the wide section 222. Therefore, if the resonant frequency of the vibrating piece 20 is the same, the overall length of the vibrating arms 22A, 22B, and 22C can be shortened compared to when there is no wide section 222, thereby enabling miniaturization of the vibrating piece 20. Alternatively, if the overall length of the vibrating arms 22A, 22B, and 22C is the same, the resonant frequency of the vibrating piece 20 can be lowered compared to when there is no wide section 222.

[0014] Furthermore, the vibrating piece 20 has a film-like weight portion M positioned on the upper surface of the wide portion 222 of each vibrating arm 22A, 22B, 22C. By positioning the weight portion M, the mass of the wide portion 222 increases, and the aforementioned mass effect becomes more pronounced. The constituent material of the weight portion M is not particularly limited, but it is preferable to include at least one of the following: aluminum (Al), titanium (Ti), chromium (Cr), gold (Au), silver (Ag), copper (Cu), and polysilicon (Si). Note that "aluminum (Al)" above includes aluminum, as well as aluminum compounds such as aluminum oxide and aluminum nitride. The same applies to the other materials. Although not shown in the figures, the weight portion M in this embodiment has a structure in which a gold (Au) surface layer is laminated on a titanium (Ti) underlayer. With these materials, a weight portion M with high specific gravity can be easily formed. However, the weight portion M may be omitted.

[0015] As shown in Figure 3, the vibrating piece 20 has a drive unit 23 that bends and deforms the vibrating arms 22A, 22B, and 22C in the Z-axis direction. The drive unit 23 has a laminate 23A positioned on the upper surface of vibrating arm 22A, a laminate 23B positioned on the upper surface of vibrating arm 22B, and a laminate 23C positioned on the upper surface of vibrating arm 22C. The laminates 23A, 23B, and 23C are shorter than the arm portion 221 and are positioned in an area of ​​about half the base end of the vibrating arms 22A, 22B, and 22C. Furthermore, the laminates 23A, 23B, and 23C are shorter than the length L of the vibrating arms 22A, 22B, and 22C, and in this embodiment, are positioned in an area of ​​about half the base end of the vibrating arms 22A, 22B, and 22C. In addition, the laminates 23A, 23B, and 23C are positioned so as to straddle a part of the support portion 210 from above the three vibrating arms 22. Furthermore, in order to balance the vibrations, the vibrating arms 22B and 22C located at at least both ends of the arrangement of the vibrating piece 20 have the same configuration (shape and size), while the central vibrating arm 22A has a different configuration (shape and size) from the vibrating arms 22B and 22C as needed.

[0016] Each of these laminates 23A, 23B, and 23C expands and contracts in the Y-axis direction when a driving voltage is applied. By expanding and contracting the laminates 23A, 23B, and 23C in the Y-axis direction, the vibrating arms 22A, 22B, and 22C vibrate in the Z-axis direction.

[0017] The drive unit 23, consisting of laminates 23A, 23B, and 23C, has a similar configuration to each other. As shown in Figure 4, it comprises a laminate with a first electrode 231, a piezoelectric layer 232 positioned on the upper surface of the first electrode 231, and a second electrode 233 positioned on the upper surface of the piezoelectric layer 232. The constituent materials of each part of the laminates 23A, 23B, and 23C are not particularly limited, but for example, the piezoelectric layer 232 is made of aluminum nitride (AlN), and the first electrode 231 and second electrode 233 are made of titanium nitride (TiN), etc. However, the configuration of the laminates 23A, 23B, and 23C is not particularly limited, and other layers may be interposed between each layer. Furthermore, the first electrode 231 may be realized using a surface silicon layer 13. In other words, the three vibrating arms 22, each made of a surface silicon layer 13, also serve as the first electrode 231, and the drive unit 23, positioned on the upper surface of the three vibrating arms 22, may have laminates 23A, 23B, and 23C, each comprising at least a piezoelectric layer and electrodes.

[0018] As shown in FIG. 3, such laminates 23A, 23B, and 23C are wired so that the adjacent vibrating arms 22A, 22B, and 22C bend and vibrate in opposite phases. That is, there are a first state in which the vibrating arms 22B and 22C bend and deform upward while the vibrating arm 22A bends and deform downward, and a second state in which the vibrating arms 22B and 22C bend and deform downward while the vibrating arm 22A bends and deform upward, and the laminates 23A, 23B, and 23C are wired so that these states are alternately repeated. Specifically, the first electrodes 231 of the laminates 23B and 23C and the second electrode 233 of the laminate 23A are electrically connected to the electrode pad PAD1 via wiring not shown, and the second electrodes 233 of the laminates 23B and 23C and the first electrode 231 of the laminate 23A are electrically connected to the electrode pad PAD2 via wiring not shown. Further, the connection method is not limited to the above, and various connection methods are conceivable, such as connecting the first electrodes 231 of the laminates 23B and 23C to the electrode pad PAD1 and the electrode pad PAD2, respectively, with the first electrode 231 having a floating potential.

[0019] In this way, by bending and vibrating the adjacent vibrating arms 22A, 22B, and 22C in opposite phases, at least a part of the vibrations of the vibrating arms 22A, 22B, and 22C is canceled, and the vibration leakage of the vibrating piece 20 can be effectively suppressed. The bending vibration of the vibrating arms 22A, 22B, and 22C is greatly excited at the resonance frequency and the impedance Z becomes minimum. As a result, by connecting this vibration device 1 to an oscillation circuit, an oscillator that oscillates at an oscillation frequency determined by the resonance frequency can be obtained.

[0020] Next, the impedance Z of the vibration device 1 when the laminates 23A, 23B, and 23C are arranged so as to straddle a part of the support portion 210 from above the vibrating arm 22 in a state where the vibrating arm 22 and the support portion 210 are separated from the silicon layer 11 will be described. FIG. 5 shows the relationship between the length L2 of the overlapping portion 234, which is the portion of the laminates 23A, 23B, and 23C located above the support portion 210, with respect to the length L1 of the support portion 210 in the first direction, and the normalized impedance (Z / Z0). FIG. 5 is a graph showing the result of simulating the relationship between L2 / L1 and the normalized impedance (Z / Z0). Note that the normalized impedance (Z / Z0) on the vertical axis is obtained by normalizing the impedance Z when L2 is changed with the impedance Z0 when L2 is 0. From FIG. 5, by setting 0 < L2 / L1 < 0.58, the normalized impedance (Z / Z0) can be made less than 1.0. That is, it can be made less than or equal to the impedance Z0 when the reference L2 is 0. Further, preferably, by setting 0.05 ≤ L2 / L1 ≤ 0.47, the normalized impedance (Z / Z0) can be made less than or equal to 0.98. More preferably, by setting 0.1 ≤ L2 / L1 ≤ 0.35, the normalized impedance (Z / Z0) can be made less than or equal to 0.96.

[0021] Note that the length L1 of the support portion 210 satisfies 3% ≤ L1 / L ≤ 10% with respect to the length L of the vibrating arm 22. When L1 / L < 3%, the vibration of the vibrating arm 22 is transmitted to the base portion 131 fixed to the silicon layer 11 and the BOX layer 12 through the fixing portion 211, and the vibration is attenuated at the base portion 131, so it is difficult to achieve a low impedance. When 10% < L1 / L, the overall length of the vibrating piece 20 becomes long, and it is difficult to miniaturize the vibration device 1. Therefore, by satisfying 3% ≤ L1 / L ≤ 10%, a vibration device 1 that can be miniaturized and has a low impedance can be obtained.

[0022] This is because the support portion 210 is separated from the silicon layer 11 together with the vibrating arm 22, so the distortion of the vibration by the vibrating arm 22 occurs up to a part of the support portion 210. That is, the vibration by the vibrating arm 22 is transmitted up to the range of 0 < L2 / L1 < 0.58, and by arranging the laminate bodies 23A, 23B, 23C so as to straddle from above the vibrating arm 22 to a part of the support portion 210, vibration can be efficiently performed. Therefore, the impedance Z can be made small, and the minimum impedance can be obtained when L2 / L1 is around 0.2. When L2 / L1 is within the range of 0.58 < L2 / L1, since an attempt is made to vibrate the region where no distortion of vibration by the vibrating arm 22 occurs, the impedance Z is considered to increase conversely.

[0023] As described above, in the vibration device 1 of the present embodiment, since the lower part of the support portion 210 is separated from the silicon layer 11 in the same manner as the vibrating arm 22, the vibration by the vibrating arm 22 is transmitted to the range of 0 < L2 / L1 < 0.58. Therefore, by arranging the laminate 23A, 23B, 23C so as to straddle from above the vibrating arm 22 to a part of the support portion 210, particularly in the range of 0 < L2 / L1 < 0.58, it is possible to vibrate efficiently and achieve a low impedance.

Explanation of Reference Numerals

[0024] 1... Vibration device, 5... Cover portion, 10... SOI substrate, 11... Silicon layer, 12... BOX layer, 13... Surface silicon layer, 131... Base portion, 14, 15... Through electrodes, 20... Vibration piece, 21... Vibration substrate, 210... Support portion, 211... Fixed portion, 22, 22A, 22B, 22C... Vibrating arms, 221... Arm portion, 222... Wide portion, 23... Driving portion, 23A, 23B, 23C... Laminate, 231... First electrode, 232... Piezoelectric layer, 233... Second electrode, 234... Overlapping portion, M... Weight portion, L, L1, L2... Lengths, PAD1, PAD2... Electrode pads, Z, Z0... Impedance.

Claims

1. Three or more vibrating arms extending along the first direction, A support part connected to one end of three or more of the vibrating arms, A fixing part for fixing the support part to the base, The device comprises a drive unit having a laminate provided on three or more of the aforementioned vibrating arms, and having at least a piezoelectric layer and electrodes, The laminate is arranged so as to span over a part of the support portion from above three or more of the vibrating arms. Vibration device.

2. When the length of the support portion in the first direction is L1, and the length of the overlapping portion of the laminate, which is the part located above the support portion, is L2, Satisfying 0 < L2 / L1 < 0.58, The vibration device according to claim 1.

3. When the length of the vibrating arm is L, Satisfying 3% ≤ L1 / L ≤ 10%, The vibration device according to claim 2.

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