Piezoelectric resonator

Abstract

To reduce the phase noise by increasing the crystal orientation of a piezoelectric film 3.SOLUTION: A piezoelectric resonator 100 includes a diaphragm 1 made of silicon, a support portion 2 that supports the diaphragm 1, a piezoelectric film 3 made of a single-crystal piezoelectric body that is laminated above a first main surface 1A of the diaphragm 1, and upper electrodes 41 and 42 that are laminated on the piezoelectric film 3. A crystal plane that is at an off-angle of -4° or more to 4° or less with respect to the (111) plane is exposed on the first main surface 1A.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to piezoelectric resonators. [Background technology]

[0002] Non-Patent Document 1 describes a resonator constructed by sandwiching a piezoelectric thin film (a thin film of aluminum nitride) between a single-crystal silicon layer and a metal layer. The single-crystal silicon layer is highly doped and conductive, and is used as the ground electrode of the resonator. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Yi Zhang et la, Fully-Differential TPoS Resonators Based on Dual Interdigital Electrodes for Feedthrough Suppression, 2. Resonator Model and Design, lines 5-9, [online], published January 21, 2020, MDPI Open Access Journals, [searched February 2, 2020],<URL:https: / / www.mdpi.com / 2072-666X / 11 / 2 / 119>

[0004] [overview] As described above, thin-film piezoelectric-on-silicon (TPoS), which combines single-crystal silicon with a piezoelectric thin film, can achieve low motional resistance and a high Q value by combining a piezoelectric thin film with a silicon substrate.

[0005] One of the factors that determines the performance of TPoS is the crystal orientation of the piezoelectric thin film. A piezoelectric thin film with high crystal orientation has a high electromechanical coupling coefficient (k 2) is a good value. By improving the electromechanical coupling coefficient, it becomes possible to transmit power with high efficiency, and the motional resistance (Rm) in the resonator is reduced. The term in Leeson's formula that expresses the phase noise of a resonator includes a coefficient (Po) that indicates power. By lowering the motional resistance and improving power efficiency, it is possible to reduce phase noise.

[0006] An object of the present disclosure is to provide a piezoelectric resonator with low phase noise by improving the crystal orientation of the piezoelectric film.

[0007] In order to solve the above-mentioned problems, one aspect of the present disclosure is a piezoelectric resonator including a diaphragm made of silicon, a support portion that supports the diaphragm, a piezoelectric film made of a single-crystal piezoelectric material laminated above a first main surface of the diaphragm, and an upper electrode laminated on the piezoelectric film. The first main surface exposes a crystal plane that is at an off-angle of -4° to 4° with respect to the (111) plane. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a plan view showing the configuration of a piezoelectric resonator 100 according to a first embodiment. [Figure 2] FIG. 2 is a cross-sectional view showing the configuration of the piezoelectric resonator 100 taken along the line II-II in FIG. [Figure 3] FIG. 3 is a cross-sectional view showing the configuration of the piezoelectric resonator 100 taken along the line III-III in FIG. [Figure 4A] FIG. 4A is a cross-sectional view (part 1) illustrating a process for manufacturing the piezoelectric resonator 100 shown in FIGS. 1 to 3. FIG. [Figure 4B] FIG. 4B is a cross-sectional view (part 2) illustrating a process for manufacturing the piezoelectric resonator 100 shown in FIGS. [Figure 4C] FIG. 4C is a cross-sectional view (part 3) illustrating a process for manufacturing the piezoelectric resonator 100 shown in FIGS. [Figure 4D] FIG. 4D is a cross-sectional view (part 4) illustrating a process for manufacturing the piezoelectric resonator 100 shown in FIGS. [Figure 5]FIG. 5 is a cross-sectional view showing the configuration of a piezoelectric resonator 101 according to the second embodiment. [Figure 6] FIG. 6 is a plan view showing the configuration of a piezoelectric resonator 102 according to the third embodiment. [Figure 7] FIG. 7 is a cross-sectional view showing the configuration of a piezoelectric resonator 103 according to a fourth embodiment. [Figure 8] FIG. 8 is a cross-sectional view showing the configuration of a piezoelectric resonator 104 having a temperature compensation film 11 formed on the first main surface 1A side of the diaphragm 1. As shown in FIG. [Figure 9] FIG. 9 is a cross-sectional view showing the configuration of a piezoelectric resonator 105 having temperature compensation films 11 and 12 formed on both the first main surface 1A side and the second main surface 1B side of the diaphragm 1. As shown in FIG. [Figure 10] FIG. 10 is a cross-sectional view showing the configuration of a piezoelectric resonator 106 having a temperature compensation film 12 formed on the second main surface 1B side of the diaphragm 1. As shown in FIG.

[0009] [Detailed explanation] Piezoelectric resonators and methods for manufacturing piezoelectric resonators according to several embodiments will be described in detail below with reference to the drawings. However, it should be noted that the drawings are schematic, and the relationship between thickness and planar dimensions, thickness ratios of various parts, etc. may differ from the actual ones. Furthermore, it goes without saying that the dimensional relationships or ratios may differ between the drawings.

[0010] The embodiments described below are comprehensive or specific examples. The numerical values, shapes, materials, components, installation positions, and connection forms of the components shown in the following embodiments are merely examples and are not intended to limit the scope of the present disclosure. Furthermore, among the components in the following embodiments, components that are not recited in the independent claims that represent the highest concepts are described as optional components. Furthermore, the following embodiments and their variations may include similar components, and the same reference numerals will be used to denote similar components, and redundant descriptions will be omitted.

[0011] (First embodiment) Fig. 1 is a plan view showing the configuration of a piezoelectric resonator 100 according to a first embodiment. Fig. 2 is a cross-sectional view showing the configuration of the piezoelectric resonator 100 taken along the II-II cross section of Fig. 1. Fig. 3 is a cross-sectional view showing the configuration of the piezoelectric resonator 100 taken along the III-III cross section of Fig. 1.

[0012] The piezoelectric resonator 100 includes a diaphragm 1, a support portion 2 that supports the diaphragm 1, a piezoelectric film 3 made of a single-crystal piezoelectric material laminated above a first main surface 1A of the diaphragm 1, and a first upper electrode 41 and a second upper electrode 42 laminated on the piezoelectric film 3. The first upper electrode 41 and the second upper electrode 42 may be collectively referred to as "upper electrodes 4." The piezoelectric resonator 100 is an example of a MEMS (Micro Electro Mechanical Systems).

[0013] Diaphragm 1 is a flexible thin film made of single-crystal silicon. Here, the film thickness direction of diaphragm 1 is defined as the Z direction. The shape of diaphragm 1 within the plane of first main surface 1A perpendicular to the Z direction, i.e., the planar shape of diaphragm 1, is not limited, but for example, as shown in FIG. 1, it has a rectangular shape consisting of a pair of opposing long sides 1a, 1b and a pair of short sides connecting the ends of long sides 1a, 1b. FIG. 1 shows an example in which the pair of long sides 1a, 1b and the pair of short sides are parallel line segments, but the planar shape of diaphragm 1 is not limited to this.

[0014] The direction of the long sides 1a and 1b of the diaphragm 1 is defined as the longitudinal direction (Y direction), and the direction of the short side of the diaphragm 1 perpendicular to the Y direction in the plane of the first main surface 1A is defined as the lateral direction (X direction). The X direction, Y direction, and Z direction are perpendicular to each other.

[0015] A crystal plane having an off angle of -4° to 4° with respect to the (111) plane, which is a crystal plane of single crystal silicon, is exposed on first main surface 1A of diaphragm 1. Below, we will continue to explain the case where the (111) plane of single crystal silicon is exposed on first main surface 1A.

[0016] The diaphragm 1 contains 1.0 × 10 trivalent elements such as boron (B) and gallium (Ga), or pentavalent elements such as phosphorus (P) and arsenic (As). 19 cm -3 The diaphragm 1 is doped at a concentration of 0.01 to 0.01g. This makes the diaphragm 1 conductive and allows it to function as the lower electrode of the piezoelectric element. It also improves the temperature coefficient of frequency (TCF). This means that the change in the resonant frequency of the piezoelectric resonator 100 due to temperature fluctuations can be minimized.

[0017] 1, when viewed from the Z direction, the support part 2 has a frame-like shape that surrounds the outer periphery of the diaphragm 1. The inner periphery of the support part 2 is connected to the outer periphery of the diaphragm 1 by two beams 51 and 52 (tether beams). The two beams 51 and 52 may be collectively referred to as "beam 5."

[0018] Beams 51 and 52 are connected to the center of a pair of short sides of the outer periphery of diaphragm 1. Support portion 2 supports diaphragm 1 via beams 5.

[0019] 1, a slit 6 (gap) is formed between the inner periphery of the support part 2 and the outer periphery of the diaphragm 1, excluding the beams 51 and 52. The slit 6 allows the diaphragm 1 to freely deform elastically relative to the support part 2.

[0020] 2 and 3, the support portion 2 has a layered structure made up of multiple members. In the cross-sectional structure of the piezoelectric resonator 100, the direction in which the piezoelectric film 3 and upper electrode 4 are located relative to the diaphragm 1 is referred to as the upper side, and the opposite direction is referred to as the lower side. The upper surface of the member is referred to as the upper surface, and the lower surface of the member is referred to as the lower surface.

[0021] The support section 2 has a structure in which, from bottom to top, a support substrate 2e, a buried insulating layer 2f, an active layer 2g, and a piezoelectric layer 2h are layered. The planar shapes of each component of the support section 2 are approximately the same. The support substrate 2e is made of polycrystalline silicon or single crystal silicon. A hollow section 7 is formed, surrounded by the inner peripheral surface of the support substrate 2e and the underside of the diaphragm 1 (the second main surface of the diaphragm 1 facing in the opposite direction to the first main surface 1A). The presence of the hollow section 7 allows the diaphragm 1 to elastically deform downward.

[0022] The buried insulating layer 2f is a layer made of silicon oxide (SiO2). The active layer 2g is a layer made of single crystal silicon. The support substrate 2e, the buried insulating layer 2f, and the active layer 2g form the same layered structure as an SOI (Silicon On Insulator) substrate.

[0023] As shown in Figures 2 and 3, the layer in which the active layer 2g is located is the same layer as the diaphragm 1 and the beams 5, and is made of the same material. The piezoelectric layer 2h is the same layer as the piezoelectric film 3, and is made of the same material. As shown in Figure 3, the active layer 2g is formed integrally with the diaphragm 1 via the beams 51 and 52. The piezoelectric layer 2h is formed integrally with the piezoelectric film 3 via the beams 51 and 52.

[0024] The piezoelectric film 3 has a piezoelectric property in that it is distorted in response to an increase or decrease in the strength of an applied electric field. For example, the piezoelectric film 3 may be made of lead zirconate titanate (PZT(Pb(Zr,Ti)O)), bismuth titanate (BTO(BiTiO)), or the like. 12 )), bismuth lanthanum titanate (BLT((Bi,La)4Ti3O 12 )), strontium bismuth tantalate (SBT(SrBi2Ta2O9)), lead lanthanum zirconate titanate (PLZT((PbLa)(ZrTi)O3)), aluminum nitride (AlN), zinc oxide (ZnO), lead titanate (PbTiO3), potassium sodium niobate (KNN), scandium aluminum nitride (ScAlN), or the like. The piezoelectric film 3 has a thickness of, for example, 0.5 μm or more and 5 μm or less.

[0025] The piezoelectric film 3 may have a crystal structure that inherits the lattice arrangement on the first main surface 1A of the diaphragm 1. For example, the (111) plane of single crystal silicon may be exposed on the first main surface 1A of the diaphragm 1, and the (002) plane of the piezoelectric film 3 made of single crystal AlN may face the first main surface 1A of the diaphragm 1. The (111) plane of silicon has a hexagonal lattice arrangement, which has good compatibility with the (002) plane of an AlN film, which is an example of a piezoelectric film 3, making it possible to obtain a piezoelectric film 3 with good crystal orientation.

[0026] The upper electrode 4 includes a first upper electrode 41 and a second upper electrode 42. As shown in FIG. 1, the upper electrode 4 has comb-like portions elongated in the longitudinal direction (Y direction) of the diaphragm 1. The comb-like portions of the first upper electrode 41 and the second upper electrode 42 are alternately arranged at predetermined intervals in the lateral direction (X direction) of the diaphragm 1. In the example shown in FIG. 1, one comb-like portion of the first upper electrode 41 is sandwiched between two comb-like portions of the second upper electrode 42. The upper electrode 4 is led to the support 2 via the beams 5 and connected to an electrode terminal (not shown). As shown in FIG. 3, the first upper electrode 41 is led from the second beam 52 to the support 2, and the second upper electrode 42 is led from the first beam 51 to the support 2. The number of comb-like portions of the upper electrode 4 is arbitrary and is not limited to the examples shown in FIGS. 1 to 3. The upper electrode 4 may have a laminated structure in which iridium oxide (IrO2) and iridium (Ir) are laminated in this order, or the upper electrode 4 may contain platinum (Pt) or molybdenum (Mo).

[0027] The basic operation and main uses of the piezoelectric resonator 100 will be explained. In the piezoelectric resonator 100, a piezoelectric film 3 is sandwiched between a diaphragm 1 made of single-crystal silicon and an upper electrode 4. The diaphragm 1 is electrically conductive due to the addition of a high concentration of impurities, and therefore also functions as the lower electrode of the piezoelectric element. When a voltage is applied between the diaphragm 1 and the upper electrode 4, an electric field is generated between the diaphragm 1 and the upper electrode 4. This electric field causes the piezoelectric film 3 to expand and contract in directions parallel to the XY plane, causing the diaphragm 1 to bend.

[0028] In the piezoelectric resonator 100, for example, a ground potential is applied to the diaphragm 1, and an AC voltage is applied between the first upper electrode 41 and the second upper electrode 42, causing the diaphragm 1 to vibrate. When the vibration frequency matches the resonant frequency, which is a value specific to the piezoelectric resonator 100, the vibration amplitude of the diaphragm 1 increases, and the resistance value between the first upper electrode 41 and the second upper electrode 42 reaches a minimum value. The frequency of the AC voltage can be determined from the change in the resistance value. Therefore, for example, the piezoelectric resonator 100 can be used to control the periodic speed of a computer. The piezoelectric resonator 100 can also function as a filter that passes only specific frequencies. Other uses of the piezoelectric resonator 100 include sensors.

[0029] Next, a method for manufacturing the piezoelectric resonator 100 shown in Figures 1 to 3 will be described with reference to Figures 4A to 4D. Note that the method for manufacturing the piezoelectric resonator 100 described below is just one example, and it goes without saying that various other manufacturing methods are also possible.

[0030] As shown in Figure 4A, an SOI substrate is prepared in which a support substrate 91, a buried insulating layer 92, and an active layer 93 are stacked in this order from the bottom up. The support substrate 91 is made of polycrystalline silicon or single crystal silicon. The buried insulating layer 92 is made of silicon oxide. The active layer 93 is made of single crystal silicon.

[0031] The active layer 93 contains 1.0×10 19 cm -3 The doping is performed at the above concentration. As a method for doping impurities, for example, ion implantation or thermal diffusion can be used. By doping the active layer 93 with a high concentration of impurities, it is possible to use the active layer 93 as a conductive electrode.

[0032] A piezoelectric layer 94 made of a single-crystal piezoelectric material is formed on the active layer 93. The film formation method can be metal organic chemical vapor deposition (MOCVD) or sputtering. For example, a single-crystal AlN film can be epitaxially grown on the (111) plane of single-crystal silicon at room temperature using magnetron sputtering. A single-crystal AlN film having a crystal structure that inherits the lattice arrangement of the active layer 93 can be formed. The single-crystal AlN film can be formed so that the (002) plane of the AlN film faces the (111) plane of the active layer 93. The crystal orientation of the AlN film can be improved by forming a thin aluminum (Al) film of approximately 1.5 nm to 5 nm between the active layer 93 and the AlN film.

[0033] By using the silicon (111) crystal plane as the crystal plane of the active layer 93 on which the piezoelectric layer 94 is epitaxially grown, residual stress after crystal growth can be reduced compared to other silicon crystal planes such as the (100) and (110) planes, thereby improving the crystal orientation of the piezoelectric layer 94. This effect is maintained even when the crystal plane of the active layer 93 is off-angled from the (111) plane by an angle of -4° to 4°.

[0034] An electrode film 95 is formed on the piezoelectric layer 94. For example, iridium oxide (IrO2) and iridium (Ir) are formed in this order as the electrode film 95 using a vapor deposition method or a sputtering method. The state after the above steps are performed is shown in FIG. 4A.

[0035] Next, as shown in Fig. 4B, the electrode film 95 of Fig. 4A is patterned into a predetermined planar shape using photolithography and etching, thereby forming the first upper electrode 41 and the second upper electrode 42 shown in Figs. 1 to 3 on the piezoelectric layer 94.

[0036] 4C, the piezoelectric layer 94 is patterned into a predetermined planar shape, thereby forming the piezoelectric film 3 and part of the support portion 2 (piezoelectric layer 2h) shown in FIGS.

[0037] Next, as shown in Fig. 4D, the active layer 93 is patterned into a predetermined planar shape. Specifically, the active layer 93 where the slits 6 shown in Figs. 1 to 3 are located is selectively etched using an anisotropic etching method such as reactive ion etching (RIE). As a result, the diaphragm 1 and a part of the support portion 2 (active layer 2g) shown in Figs. 1 to 3 are formed on the buried insulating layer 92.

[0038] Next, photolithography and etching are used to selectively etch the support substrate 91 from its lower surface using an anisotropic etching method, thereby forming the hollow portion 7 and a part of the support portion 2 (support substrate 2e) shown in Figures 1 to 3. Finally, the embedded insulating layer 2f remaining on the lower surfaces of the diaphragm 1, beams 5, and slits 6 is removed by hydrofluoric acid treatment, thereby completing the piezoelectric resonator 100 shown in Figures 1 to 3.

[0039] (Second embodiment) In the piezoelectric resonator 100 according to the first embodiment, the piezoelectric film 3 is formed in contact with the first main surface 1A of the vibration plate 1, but a layer made of another material may be interposed between the vibration plate 1 and the piezoelectric film 3. In the second embodiment, a piezoelectric resonator 101 will be described in which a seed layer 10 is stacked as a layer made of another material, as shown in FIG.

[0040] 5 is a cross-sectional view showing the configuration of a piezoelectric resonator 101 according to the second embodiment. Except for the fact that a seed layer 10 is laminated between the diaphragm 1 and the piezoelectric film 3, the configuration is the same as that of the piezoelectric resonator 100 shown in FIGS. 1 to 3, and the explanation will focus on the difference, the seed layer 10.

[0041] The piezoelectric resonator 101 further includes a seed layer 10 disposed between the diaphragm 1 and the piezoelectric film 3. The planar shape of the seed layer 10 is the same as that of the piezoelectric film 3 shown in FIG. 1. Materials that can be used for the seed layer 10 include strontium ruthenate (SR0), lithium nickel oxide (LNO), ruthenium oxide (RuOx), iridium oxide (IrOx), and LaSrCoO3. Alternatively, the seed layer 10 may be formed of zirconium oxide (ZrO2) or hafnium oxide (HfO2), and a single-crystal PZT film (an example of the piezoelectric film 3) may be formed thereon. Alternatively, the seed layer 10 may be formed of hafnium oxide (HFO2), and a single-crystal PbTiO3 film (PT film) may be disposed thereon.

[0042] The seed layer 10 is made of a crystallized metal oxide. That is, the seed layer 10 functions as a seed crystal layer intended to improve the crystal orientation of the piezoelectric film 3. The seed layer 10 has a thickness of, for example, 2 nm or more and 40 nm or less. By providing the seed layer 10, the crystal orientation of the piezoelectric film 3 formed on the seed layer 10 can be further improved.

[0043] The support portion 2A of the piezoelectric resonator 101 further includes a seed film 2i made of the same material as the seed layer .

[0044] (Third embodiment) In the piezoelectric resonator 100 shown in FIG. 1, the long sides 1a and 1b of the diaphragm 1 are line segments, but the long sides 1a-1 and 1b-1 of the diaphragm 1 may have a curvature.

[0045] The configuration of a piezoelectric resonator 102 according to the third embodiment will be described with reference to FIG. 6. In the piezoelectric resonator 102 according to the third embodiment, the long sides 1a-1 and 1b-1 of the diaphragm 1 have a convex shape when viewed from the normal direction (Z direction) of the first main surface 1A of the diaphragm 1. The curvature of the long sides 1a-1 and 1b-1 may be constant or may vary continuously from the first end to the second end of the long sides 1a-1 and 1b-1. The first and second ends of the long sides 1a-1 and 1b-1 are ends connected to the short sides of the diaphragm 1.

[0046] By having the long sides 1a-1 and 1b-1 of the diaphragm 1 have a convex shape, vibration energy can be concentrated at the center of the piezoelectric resonator 102, reducing the dissipation of vibration energy from the beam 5 to the support part 2 and improving the Q value of the piezoelectric resonator 102.

[0047] (Fourth embodiment) In the fourth embodiment and its modifications, piezoelectric resonators (103, 104, 105, 106) further having temperature compensation structures (11, 12, 13) that minimize changes in resonant frequency due to temperature fluctuations will be described.

[0048] A piezoelectric resonator 103 according to the fourth embodiment will be described with reference to Fig. 7. The piezoelectric resonator 103 further includes a temperature compensation member 13 embedded in the diaphragm 1. The temperature compensation member 13 has an embedded pillar structure. Specifically, the temperature compensation member 13 is a member containing silicon oxide embedded in a groove that penetrates from the upper surface (first main surface 1A) to the lower surface (second main surface 1B) of the diaphragm 1.

[0049] The piezoelectric film 3 and upper electrodes 41 and 42 are arranged in the center of the first main surface 1A of the diaphragm 1. The temperature compensation member 13 is arranged on the outer periphery of the diaphragm 1. The piezoelectric film 3 and upper electrodes 41 and 42 are not arranged on the temperature compensation member 13. The temperature compensation member 13 is arranged on the outer periphery of the diaphragm 1 so as to surround the periphery of the piezoelectric film 3 and upper electrodes 41 and 42. The number of temperature compensation members 13 (embedded pillars) is arbitrary.

[0050] An example of a method for manufacturing temperature compensation member 13 is as follows: In the step of forming slits 6 shown in Fig. 4D, grooves are formed on the outer periphery of diaphragm 1 at the same time as slits 6, and silicon oxide is selectively filled into the grooves using photolithography.

[0051] (Variation) In a modified example of the fourth embodiment, a piezoelectric resonator (104, 105, 106) having a temperature compensation film (11, 12) formed on at least one of the first main surface 1A side or the second main surface 1B side of the diaphragm 1 is described as a temperature compensation structure (11, 12).

[0052] 8 is a cross-sectional view showing the configuration of a piezoelectric resonator 104 having a temperature compensation film 11 formed on the first main surface side of the diaphragm 1. The temperature compensation film 11 is formed on the piezoelectric film 3 and the upper electrode 4. Furthermore, a film made of the same material as the temperature compensation film 11 is also formed on the support portion 2B, constituting a part 2j of the support portion 2.

[0053] An example of a method for manufacturing the temperature compensation film 11 is as follows: After forming the upper electrode 4 shown in Fig. 4B, the temperature compensation film 11 made of silicon oxide is formed using a CVD (chemical vapor deposition) method, and then patterned into the same shape as the piezoelectric film 3, etc. by selectively etching using the same photomask as the piezoelectric film 3, etc.

[0054] 9 is a cross-sectional view showing the configuration of a piezoelectric resonator 105 having temperature compensation films 11, 12 formed on both the first main surface 1A side and the second main surface 1B side of the diaphragm 1. The temperature compensation film 11 is formed on the first main surface 1A side, and the temperature compensation film 12 is formed on the second main surface 1B side. The buried insulating layer 92 shown in FIG. 4D can be left as it is when forming the hollow portion 7, rather than being removed, to form the temperature compensation film 12. The temperature compensation film 11 in FIG. 9 is the same as that in FIG. 8, and a description thereof will be omitted.

[0055] As shown in FIG. 10, the piezoelectric resonator 106 may have a temperature compensation film 12 formed on the second main surface 1B side of the diaphragm 1.

[0056] In this way, the piezoelectric resonators (103, 104, 105, 106) further having the temperature compensation structures (11, 12, 13) can improve the temperature coefficient of frequency (TCF), that is, can minimize changes in resonant frequency due to temperature fluctuations.

[0057] (Other embodiments) One known method for singulating the piezoelectric resonators 100-106 is to focus a pulsed laser inside the wafer and create controlled cracks to divide the wafer. When singulating the piezoelectric resonators 100-106 using this method, the support 2 is irradiated with laser light. By reducing the resistivity of the support substrate 2e, the absorption rate of the laser light can be improved, which reduces damage to the wafer, such as chipping, and shortens the processing time.

[0058] Therefore, the support part 2 contains 1.0E19 cm of a trivalent or pentavalent element. -3 The support substrate 2e may be doped with the following concentration: -3 The doping may be carried out at the following concentration: This reduces the resistivity of the support substrate 2e, thereby improving the laser light absorption rate.

[0059] The support portions 2, 2A, and 2B (support substrate 2e) may include single crystal silicon, and a (100) plane may be exposed on a side surface of the support portions 2, 2A, and 2B (support substrate 2e) parallel to the normal direction (Z direction) of the first main surface 1A. Specifically, as shown in FIGS. 1 and 2, the (100) plane of single crystal silicon may be exposed on any of the four side surfaces (2a to 2d) of the support portions 2, 2A, and 2B (support substrate 2e). Because cleavage planes are exposed on the side surfaces of the support portions 2, 2A, and 2B (support substrate 2e), damage to the wafer, such as chipping, can be reduced, and the piezoelectric resonators 100 to 106 can be easily separated into individual pieces.

[0060] When viewed from the normal direction (Z direction) of the first main surface 1A of the diaphragm 1, at least one side of the diaphragm 1 may be aligned with the cleavage plane of the piezoelectric film 3. Specifically, as shown in FIG. 1, at least one side of the pair of long sides 1a, 1b and the pair of short sides of the diaphragm 1 may be aligned with the cleavage plane of the piezoelectric film 3. The side surfaces of the diaphragm 1 and the side surfaces of the piezoelectric film 3 are substantially parallel. By exposing the cleavage planes on the side surfaces of the piezoelectric film 3, damage to the piezoelectric film 3 can be reduced when the piezoelectric film 3 is patterned.

[0061] With reference to FIG. 5, a piezoelectric resonator 101 in which a seed layer 10 is disposed between a diaphragm 1 and a piezoelectric film 3 has been described. Piezoelectric resonators according to other embodiments may have a lower electrode made of metal instead of the seed layer 10. For example, an aluminum (Al) film as the lower electrode can be formed on the (111) surface of a diaphragm 1 made of single-crystal silicon, and then a single-crystal AlN film can be formed as the piezoelectric film 3. The MOCVD method can be used as the film formation method. By inserting the lower electrode (Al film) between the diaphragm 1 and the piezoelectric film 3, the crystal orientation of the piezoelectric film 3 can be improved.

[0062] Although the present disclosure has been described in detail above, it will be apparent to those skilled in the art that the present disclosure is not limited to the embodiments described herein. One or more elements of one embodiment may be combined with one or more elements of another embodiment. The present disclosure can be implemented in modified and altered forms without departing from the spirit and scope of the present disclosure, as defined by the claims. Therefore, the description of the present disclosure is intended to be illustrative and explanatory and is not intended to be limiting of the present disclosure.

[0063] (Addendum) The technical ideas that can be understood from this disclosure are described below. The components described in the appendices are given the reference numerals of the corresponding components in the embodiments. The reference numerals are provided as examples to aid understanding, and the components described in each appendix should not be limited to the components indicated by the reference numerals.

[0064] (Appendix 1) Each of the piezoelectric resonators 100 to 106 comprises a diaphragm 1 made of single-crystal silicon, a support portion 2 that supports the diaphragm 1, a piezoelectric film 3 made of a single-crystal piezoelectric body that is laminated above a first main surface 1A of the diaphragm 1, and an upper electrode 4 that is laminated on the piezoelectric film 3. A crystal plane that is at an off-angle of -4° to 4° with respect to the (111) plane is exposed on the first main surface 1A. This improves the crystal orientation of the piezoelectric film, thereby providing a piezoelectric resonator with low phase noise.

[0065] (Appendix 2) In the piezoelectric resonator described in Supplementary Note 1, the (111) plane is exposed on the first main surface 1A, which can further improve the crystal orientation of the piezoelectric film, thereby further reducing phase noise.

[0066] (Appendix 3) The piezoelectric resonator 101 described in Supplementary Note 1 or 2 further includes a seed layer 10 disposed between the vibration plate 1 and the piezoelectric film 3. This can further improve the crystal orientation of the piezoelectric film 3 formed on the seed layer 10.

[0067] (Appendix 4) In the piezoelectric resonator 102 described in any one of Supplementary Notes 1 to 3, the long sides 1a-1 and 1b-1 of the diaphragm 1 have a convex shape when viewed from the normal direction (Z direction) of the first main surface 1A. This allows the vibration energy to be concentrated at the center of the piezoelectric resonator 102, reducing the dissipation of the vibration energy from the beams 5 to the support parts 2 and improving the Q value of the piezoelectric resonator 102.

[0068] (Appendix 5) In the piezoelectric resonators 100 to 106 described in any one of Supplementary Notes 1 to 4, the diaphragm 1 contains a trivalent or pentavalent element at a concentration of 1.0E19 cm -3 The diaphragm 1 is doped at a concentration of 0.01 to 0.01g. This makes the diaphragm 1 conductive and allows it to function as the lower electrode of the piezoelectric element. It also improves the temperature coefficient of frequency (TCF). This means that the change in the resonant frequency of the piezoelectric resonator 100 due to temperature fluctuations can be minimized.

[0069] (Appendix 6) In the piezoelectric resonators 100 to 106 described in Supplementary Note 5, the diaphragm 1 is the lower electrode. The piezoelectric film 3 in contact with the diaphragm 1 can be formed to have a high crystal orientation.

[0070] (Appendix 7) In the piezoelectric resonators 100 to 106 according to any one of Supplementary Notes 1 to 6, the piezoelectric film 3 has a crystal structure that inherits the lattice arrangement on the first main surface 1A of the diaphragm 1. This makes it possible to obtain a piezoelectric film 3 with good crystal orientation.

[0071] (Appendix 8) In the piezoelectric resonators 100 to 106 described in Appendix 7, the (002) plane of the piezoelectric film 3 faces the (111) plane of the diaphragm 1. The (111) plane of single crystal silicon is a hexagonal lattice arrangement, which has good compatibility with the (002) plane of an AlN film, which is an example of the piezoelectric film 3. This reduces residual stress after crystal growth, and allows for the production of a piezoelectric film 3 with good crystal orientation.

[0072] (Appendix 9) The piezoelectric resonator 103 according to any one of Supplementary Notes 1 to 8 further includes a temperature compensation member 13 embedded in the diaphragm 1. This improves the temperature coefficient of frequency (TCF), i.e., it is possible to minimize changes in the resonant frequency due to temperature fluctuations.

[0073] (Appendix 10) The piezoelectric resonators 104 to 106 described in any one of Supplementary Notes 1 to 9 further include temperature compensation films 11, 12 formed on at least one of the first main surface 1A side of the diaphragm 1 and the second main surface 1B side facing in the opposite direction to the first main surface 1A. This improves the temperature coefficient of frequency (TCF). In other words, it is possible to minimize changes in the resonant frequency due to temperature fluctuations.

[0074] (Appendix 11) In the piezoelectric resonators 100 to 106 described in any one of Supplementary Notes 1 to 10, the support portions 2, 2A, and 2B contain a trivalent or pentavalent element at a concentration of 1.0E19 cm -3 The concentration of the additive is as follows: By lowering the resistivity of the support parts 2, 2A, and 2B (support substrate 2e), the absorption rate of the laser light in the singulation process can be improved, damage to the wafer such as chipping can be reduced, and the processing time can be shortened.

[0075] (Appendix 12) In the piezoelectric resonators 104 to 106 according to any one of Supplementary Notes 1 to 9, the support portions 2, 2A, and 2B include single-crystal silicon, and the (100) plane of the single-crystal silicon is exposed on the side surfaces of the support portions 2, 2A, and 2B parallel to the normal direction (Z direction) of the first main surface 1A. Because cleavage planes are exposed on the side surfaces of the support portions 2, 2A, and 2B (support substrate 2e), damage to the wafer, such as chipping, is reduced, and the piezoelectric resonators 100 to 106 can be easily singulated.

[0076] (Appendix 13) In the piezoelectric resonators 100 to 106 according to any one of Supplementary Notes 1 to 12, when viewed from the normal direction (Z direction) of the first main surface 1A, at least one side of the vibration plate 1 is aligned along a cleavage plane of the piezoelectric film 3. By exposing the cleavage plane on the side surface of the piezoelectric film 3, damage to the piezoelectric film 3 during patterning can be reduced.

[0077] (Appendix 14) In the method for manufacturing the piezoelectric resonators 100 to 106 according to any one of Supplementary Notes 1 to 13, the piezoelectric film 3 is formed by MOCVD. By using MOCVD, the crystal orientation of the piezoelectric film 3 can be improved. [Explanation of symbols]

[0078] 1 diaphragm 1a, 1a-1, 1b, 1b-1 long side 1A First principal surface 1B Second main surface 2, 2A, 2B Support part 2a, 2b, 2c, 2d side 2e Support board 2f Buried insulating layer 2g active layer 2h Piezoelectric layer 2i Seed film 3 Piezoelectric film 4 Upper electrode 5 Beam 6 Slits 7 Hollow part 10 seed layer 11, 12 Temperature compensation membrane 13 Temperature compensation material 41 1st upper electrode 42 2nd upper electrode 51 1st beam 52 2nd beam 91 Support substrate 92 Buried insulating layer 93 Active layer 94 Piezoelectric layer 95 Electrode membrane 100~106 Piezoelectric resonator

Claims

1. a diaphragm made of silicon; a support portion that supports the diaphragm; a piezoelectric film made of a single crystal piezoelectric material laminated above a first main surface of the vibration plate; an upper electrode laminated on the piezoelectric film, The piezoelectric resonator has a crystal plane exposed on the first main surface that is off-angled from the (111) plane by an angle of −4° to 4°.

2. 2. The piezoelectric resonator according to claim 1, wherein a (111) plane is exposed on said first main surface.

3. 10. The piezoelectric resonator of claim 1, further comprising a seed layer disposed between the diaphragm and the piezoelectric film.

4. 2. The piezoelectric resonator according to claim 1, wherein the long side of the diaphragm has a convex shape when viewed in the normal direction of the first main surface.

5. The diaphragm contains 1.0×10 trivalent or pentavalent elements. １９ cm －３ 2. The piezoelectric resonator according to claim 1, wherein the doping concentration is equal to or greater than 100 ppm.

6. 6. The piezoelectric resonator according to claim 5, wherein the diaphragm is a lower electrode.

7. 2. The piezoelectric resonator according to claim 1, wherein the piezoelectric film has a crystal structure that inherits a lattice arrangement on the first main surface of the diaphragm.

8. 2. The piezoelectric resonator according to claim 1, further comprising a temperature compensation member embedded in said diaphragm.

9. 2. The piezoelectric resonator according to claim 1, further comprising a temperature compensation film formed on at least one of a first main surface side and a second main surface side of said diaphragm facing in the opposite direction to said first main surface side.

10. The support portion contains 1.0×10 trivalent or pentavalent elements. １９ cm －３ 2. The piezoelectric resonator of claim 1, wherein the piezoelectric resonator is doped with the following concentration:

11. 2. The piezoelectric resonator according to claim 1, wherein at least one side of said vibration plate is aligned with a cleavage plane of said piezoelectric film when viewed in the normal direction of said first main surface.

Images