JP5716833B2 - Piezoelectric bulk wave device and manufacturing method thereof - Google Patents

Description

The present invention relates to a piezoelectric bulk wave device using LiTaO ₃ and a manufacturing method thereof, and more particularly to a piezoelectric bulk wave device using a thickness shear mode bulk wave as a bulk wave and a manufacturing method thereof.

Conventionally, piezoelectric thin film devices are used for oscillators, filters, and the like. For example, Patent Document 1 below discloses a piezoelectric thin film device shown in FIG. The piezoelectric thin film device 1001 has a piezoelectric thin film 1002. It is described that the piezoelectric thin film 1002 is preferably made of a piezoelectric single crystal such as quartz, LiTaO ₃ , or LiNbO ₃ . Electrodes 1003 and 1004 are formed on the upper surface of the piezoelectric thin film 1002. Electrodes 1005 to 1007 are formed on the lower surface of the piezoelectric thin film 1002. By using these electrodes 1003 to 1007, the piezoelectric thin film device 1001 includes four piezoelectric thin film resonators using the thickness shear mode.

JP 2007-228356 A

Conventionally, as described in Patent Document 1, a piezoelectric thin film device using a thickness sliding mode of LiTaO ₃ has been known. However, when a thickness-shear vibration mode is used using a piezoelectric thin film made of LiTaO ₃ , it is difficult to increase the frequency. That is, for example, when trying to obtain a resonance frequency or center frequency of 1.5 GHz or more, the total thickness of the electrode and LiTaO ₃ is thinned, and the mechanical strength tends to decrease.

An object of the present invention is to use a LiTaO ₃ thickness-slip mode, and a piezoelectric bulk wave device capable of forming a filter or a resonator capable of high frequency using a LiTaO ₃ thin plate having a relatively large thickness. And a manufacturing method thereof.

The piezoelectric bulk acoustic wave device according to the present invention uses a bulk shear mode bulk wave of a piezoelectric thin plate made of LiTaO ₃ . The piezoelectric bulk acoustic wave device of the present invention includes a piezoelectric thin plate made of LiTaO ₃ and first and second electrodes provided so as to be in contact with the piezoelectric thin plate. In the present invention, the Euler angles (φ, θ, ψ) of the LiTaO ₃ are φ = 0 °, 54 ° ≦ θ ≦ 107 °, and ψ = 0 °. The first and second electrodes are made of a conductor having a specific acoustic impedance smaller than the specific acoustic impedance of a transverse wave propagating through LiTaO ₃ . In the present invention, when the total thickness of the first and second electrodes is the electrode thickness and the thickness of LiTaO ₃ is the LT thickness, the electrode thickness / (LT thickness + electrode thickness) is greater than 5% and 70% Smaller than.

In the present invention, the electrode thickness / (LT thickness + electrode thickness) is preferably larger than 5% and smaller than 40%. Within this range, the change of the electromechanical coupling coefficient k ² is small. Accordingly, it is possible to provide a piezoelectric bulk acoustic wave device with a small variation in bandwidth due to manufacturing variations.

In the present invention, the electrode thickness / (LT thickness + electrode thickness) may exceed 40%. In that case, it is possible to increase the damping capacity C _0.

In the present invention, the material constituting the first and second electrodes is preferably at least one metal selected from the group consisting of Al, Ag, Cu, Ni and Ti, or the metal as a main component. Or a laminate in which the metal occupies a majority of the weight ratio or more. Since these metals have a lower specific acoustic impedance than that of LiTaO ₃ , the piezoelectric bulk wave device can be increased in frequency according to the present invention. More preferably, Al is used. In this case, the piezoelectric bulk wave device of the present invention can be provided without increasing the cost.

A method for manufacturing a piezoelectric bulk wave device according to the present invention is a method for manufacturing a piezoelectric bulk wave device using a thickness-shear mode bulk wave of a piezoelectric thin plate made of LiTaO ₃ , and in terms of Euler angles (φ, θ, ψ). , φ = 0 °, 54 ° ≦ θ ≦ 107 °, preparing a piezoelectric thin plate made of LiTaO ₃ is [psi = 0 °, so as to be in contact with the piezoelectric thin, transverse to specific acoustic impedance propagates LiTaO ₃ and forming a first and a second electrode that Do from less conductive than specific acoustic impedance of. The electrode thickness, which is the sum of the thicknesses of the first and second electrodes, is the ratio of the thickness to the sum of the LiTaO ₃ thickness and the electrode thickness, and the electrode thickness / (LT thickness + electrode thickness) is 5%. larger, form the first and second electrodes from the small Kunar so 70%.

In a specific aspect of the method for manufacturing a piezoelectric bulk wave device of the present invention, the step of preparing the piezoelectric thin plate is performed by implanting ions from one surface of a piezoelectric substrate made of LiTaO ₃ , and having the implanted ion concentration most on the one surface side. A step of forming a high concentration ion implantation portion, a step of bonding a support substrate to the one surface side of the piezoelectric substrate, and heating the piezoelectric substrate, while the piezoelectric substrate is heated at the high concentration ion implantation portion. Separating the piezoelectric thin plate from the one surface of the substrate to the high-concentration ion-implanted portion and the remaining piezoelectric substrate portion. In this case, the position of the high concentration ion implantation portion can be easily controlled by controlling the ion implantation conditions. In general, the ion beam of the ion implantation apparatus is irradiated to the substrate linearly with a uniform intensity, and the same portion is irradiated many times at substantially the same irradiation angle while the ion beam sweeps the entire substrate. Therefore, in comparison with the thickness variation due to film forming methods such as sputtering, CVD, and vapor deposition, the position of the high concentration ion implantation portion is uniform over the entire surface of the substrate and the depth variation is small. Therefore, a piezoelectric thin plate with an accurate thickness can be easily obtained over the entire surface of the substrate.

In another specific aspect of the method for manufacturing a piezoelectric bulk wave device of the present invention, the step of preparing the piezoelectric thin plate is performed by implanting ions from one surface of a piezoelectric substrate made of LiTaO ₃ , and the concentration of implanted ions on the one surface side. The step of forming the highest concentration ion implantation portion, the step of bonding a temporary support member to the one surface side of the piezoelectric substrate, and the high concentration while heating the piezoelectric substrate bonded to the temporary support member Separating the piezoelectric substrate from the one surface of the piezoelectric substrate to the high-concentration ion-implanted portion at the ion-implanted portion and the remaining piezoelectric substrate portion, and temporarily supporting the piezoelectric substrate from the piezoelectric thin plate And a step of peeling the member.

  In this case, at the time of separating the piezoelectric thin plate, it is possible to suppress the possibility that a failure occurs in the piezoelectric thin plate due to thermal stress.

  In still another specific aspect of the method for manufacturing a piezoelectric bulk wave device according to the present invention, prior to peeling the temporary support member from the piezoelectric thin plate, a step of forming a first electrode on the piezoelectric thin plate; A step of forming a sacrificial layer so as to cover the first electrode and a step of laminating a support substrate on the sacrificial layer are performed. Furthermore, after peeling the temporary support member from the piezoelectric thin plate, a step of forming a second electrode on the other surface of the piezoelectric thin plate exposed by peeling of the temporary support member, and a step of eliminating the sacrificial layer Prepare. In this case, a piezoelectric bulk acoustic wave device having a structure in which the vibrating portions in which the first and second electrodes are formed above and below the piezoelectric thin plate are floated from the support substrate can be provided according to the present invention.

In the piezoelectric bulk wave device according to the present invention, a piezoelectric thin plate made of LiTaO ₃ is used, and the first and second electrodes are made of a conductor having a specific acoustic impedance smaller than that of the transverse wave of LiTaO ₃ , and Since the electrode thickness / (LT thickness + electrode thickness) is larger than 5% and smaller than 70%, higher frequency can be achieved. That is, even if a piezoelectric thin plate made of relatively thick LiTaO ₃ is used, a piezoelectric bulk wave device used in a high frequency band of 1.5 GHz or more can be provided. Therefore, it is possible to provide a piezoelectric bulk wave device that has excellent mechanical strength and can be used in a high frequency range.

  According to the method for manufacturing a piezoelectric bulk wave device according to the present invention, since the specific process is provided, it is possible to provide a piezoelectric bulk wave device that is easy to increase the frequency and has excellent mechanical strength according to the present invention.

1A and 1B are a front sectional view and a plan view of a piezoelectric bulk acoustic wave device according to an embodiment of the present invention. FIG. 2 is a diagram showing the relationship between the resonance frequency and the electrode thickness / (electrode thickness + LT thickness) of the first and second electrodes made of Al in one embodiment of the present invention. FIG. 3 is a diagram showing the relationship between the electrode thickness / (electrode thickness + LT thickness) of the first and second electrodes made of Al and the electromechanical coupling coefficient k ² in one embodiment of the present invention. FIG. 4 is a diagram showing the relationship between the electrode thickness / (electrode thickness + LT thickness) of the first and second electrodes made of Al and the braking capacity C ₀ in one embodiment of the present invention. FIG. 5 is a diagram showing the relationship between the upper electrode thickness = the lower electrode thickness and the LiTaO ₃ thickness when the first and second electrodes are made of Al and the resonance frequency is 880 MHz in one embodiment of the present invention. It is. FIG. 6 is a diagram showing the relationship between upper electrode thickness = lower electrode thickness and braking capacity C ₀ when the first and second electrodes are made of Al and the resonance frequency is 880 MHz in one embodiment of the present invention. It is. FIG. 7 shows the relationship between the upper electrode thickness = the lower electrode thickness and the electromechanical coupling coefficient k ² when the first and second electrodes are made of Al and the resonance frequency is 880 MHz in one embodiment of the present invention. FIG. FIG. 8 is a diagram showing the relationship between the upper electrode thickness = lower electrode thickness and the LiTaO ₃ thickness when the first and second electrodes are made of Al and the resonance frequency is 1960 MHz in one embodiment of the present invention. It is. FIG. 9 is a diagram showing the relationship between upper electrode thickness = lower electrode thickness and braking capacity C ₀ when the first and second electrodes are made of Al and the resonance frequency is 1960 MHz in one embodiment of the present invention. It is. FIG. 10 shows the relationship between the upper electrode thickness = the lower electrode thickness and the electromechanical coupling coefficient k ² when the first and second electrodes are made of Al and the resonance frequency is 1960 MHz in one embodiment of the present invention. FIG. FIG. 11 is a diagram illustrating the relationship between the Euler angle θ of LiTaO ₃ and the resonance frequency Fr and antiresonance frequency Fa of the thickness-shear mode. FIG. 12 is a diagram illustrating the relationship between the Euler angle θ of LiTaO ₃ and the electromechanical coupling coefficient k ^{2 in} the thickness-slip mode. FIG. 13 is a diagram showing the relationship between the Euler angle θ of LiTaO ₃ and the frequency temperature coefficient TCF in the thickness-shear mode. FIG. 14 is a diagram showing the relationship between the Euler angle θ of LiTaO ₃ and the electromechanical coupling coefficient k sp ² of the thickness longitudinal vibration mode that becomes spurious. FIG. 15 is a diagram showing the relationship between the Euler angle θ of LiTaO ₃ and the resonance frequency Fr and antiresonance frequency Fa of the thickness longitudinal vibration. FIG. 16 is a diagram showing the relationship between the Euler angle θ of LiTaO ₃ and the electromechanical coupling coefficient k ^{2 of} thickness longitudinal vibration. FIG. 17 is a diagram showing the relationship between the Euler angle θ of LiTaO ₃ and the frequency temperature coefficient TCF. FIG. 18 is a diagram showing the relationship between the Euler angle θ and the frequency temperature coefficient TCF in the thickness shear vibration mode when LiNbO ₃ is used. FIG. 19 is a diagram illustrating impedance characteristics and phase characteristics of the piezoelectric bulk acoustic wave device according to the first embodiment. FIG. 20 is a diagram illustrating an impedance Smith chart of the piezoelectric bulk wave device according to the first embodiment. 21A to 21D are schematic front sectional views for explaining a method for manufacturing a piezoelectric bulk acoustic wave device according to an embodiment of the present invention. 22A to 22C are schematic front sectional views for explaining a method for manufacturing a piezoelectric bulk acoustic wave device according to an embodiment of the present invention. 23A to 23C are schematic front sectional views for explaining a method for manufacturing a piezoelectric bulk acoustic wave device according to an embodiment of the present invention. 24A to 24C are schematic front sectional views for explaining a method for manufacturing a piezoelectric bulk wave device according to an embodiment of the present invention. FIG. 25 is a schematic cross-sectional view showing an example of a conventional piezoelectric thin film device.

  Hereinafter, the present invention will be clarified by describing specific embodiments of the present invention with reference to the drawings.

  1A and 1B are a front sectional view and a plan view of a piezoelectric bulk acoustic wave device according to an embodiment of the present invention.

  The piezoelectric bulk wave device 1 of the present embodiment has a support substrate 2. The support substrate 2 is made of an appropriate insulator or piezoelectric material. In the present embodiment, the support substrate 2 is made of alumina.

An insulating layer 3 is formed on the support substrate 2. The insulating layer 3 is made of silicon oxide in the present embodiment, but can be formed of an appropriate insulating material such as LiTaO ₃ , LiNbO ₃ , sapphire, or glass. Alumina, glass, and LiNbO ₃ are desirable because they are cheaper and easier to manufacture than LiTaO ₃ and sapphire. A recess 3 a is formed on the upper surface of the insulating layer 3. The piezoelectric thin plate vibrating portion 4 is disposed above the portion where the recess 3a is provided. The piezoelectric thin plate vibrating section 4 includes a piezoelectric thin plate 5, a first electrode 6 formed on the upper surface of the piezoelectric thin plate 5, and a second electrode 7 formed on the lower surface.

The piezoelectric thin plate 5 is made of LiTaO ₃ . The piezoelectric thin plate 5 refers to a thin piezoelectric body having a thickness of about 2 μm or less, for example. According to the manufacturing method to be described later, a piezoelectric thin plate made of LiTaO _{3 having} such a small thickness can be obtained with high accuracy by using the ion implantation-division method.

  The piezoelectric thin plate 5 is a thin piezoelectric body having a thickness of about 2 μm or less as described above, but in this embodiment, the piezoelectric bulk acoustic wave device having a resonance frequency of 1.5 GHz or more has a thickness of 1.01-1. The total thickness of the piezoelectric thin plate 5 and the first and second electrodes 6 and 7 can be made relatively thick as compared to the conventional piezoelectric bulk acoustic wave device of about 2 μm. This is because the first and second electrodes 6 and 7 are configured as follows.

That is, a feature of the present invention is a piezoelectric bulk acoustic wave device utilizing a bulk shear mode bulk wave of LiTaO ₃ , wherein the first and second electrodes 6, 7 are inherent acoustic waves of a transverse wave propagating through LiTaO _3. It is characterized by comprising a conductor having a lower specific acoustic impedance than the impedance. In the present invention, the electrode thickness / (LT thickness + electrode thickness) is greater than 5%, where the total thickness of the first and second electrodes 6 and 7 is the electrode thickness and the thickness of LiTaO ₃ is the LT thickness. , Less than 70% is another feature. Thereby, even when the LiTaO ₃ and the electrode having a relatively large total thickness are used, a high frequency can be realized. Therefore, it is possible to provide a high-frequency piezoelectric bulk wave device having excellent mechanical strength. This will be described in more detail below.

In addition, as a conductor whose specific acoustic impedance is smaller than LiTaO ₃ , at least one selected from the group consisting of Al, Ag, Cu, Ni, and Ti, or a laminate in which the metal occupies a majority of the weight ratio or more. Can be mentioned. More preferably, Al is desirable because it is inexpensive and readily available.

  As described above, the first and second electrodes 6 and 7 have the electrode thickness / (electrode thickness + LT thickness) larger than 5% and smaller than 70% by such a conductor having a low specific acoustic impedance. In addition, high frequency can be easily realized. This will be described with reference to FIGS.

  2 to 10 are based on the following configuration.

A structure in which a first electrode 6 is laminated on the upper surface of a piezoelectric thin plate made of LiTaO ₃ and a second electrode 7 is laminated on the lower surface. The thickness of LiTaO ₃ , that is, the LT thickness and the electrode thickness = (thickness of the first electrode 6 + thickness of the second electrode 7) are set to 1000 nm. That is, electrode thickness = upper electrode thickness + lower electrode thickness. Here, the electrode thickness / (LT thickness + electrode thickness) was changed in the range of 5 to 95%. A region where the first electrode 6 and the second electrode 7 face each other has a square shape, and the area thereof is 44.7 μm × 44.7 μm = 2000 μm ² . The Euler angles of LiTaO ₃ were (0 °, 73 °, 0 °).

FIG. 2 shows the relationship between the electrode thickness / (electrode thickness + LT thickness) and the resonance frequency. Figure 3 shows the relationship between the electrode thickness / (the electrode thickness + LT thickness) and the electromechanical coupling coefficient k ^2, 4, the relationship between the electrode thickness / (the electrode thickness + LT thickness) and damping capacitance C ₀ FIG.

As is apparent from FIG. 2, even when the total thickness of the above laminated structure is constant at 1000 nm, the resonance occurs when the electrode thickness / (LT thickness + electrode thickness) is greater than 5% and less than 70%. It can be seen that the frequency can be increased to 1960 MHz or higher, that is, 1.96 GHz or higher. In other words, even if the total thickness of LiTaO ₃ or the electrodes is increased, a resonance frequency of 1.5 GHz or more can be obtained. A decrease in electrode thickness / (electrode thickness + LT thickness) means that the thickness of LiTaO ₃ is relatively increased. Therefore, according to this embodiment, it can be seen that a piezoelectric bulk wave device that is excellent in mechanical strength and can cope with high frequency can be provided. Note that if the electrode thickness is less than 5%, the electrical resistance increases, which causes deterioration of the resonance resistance of the resonator configured as the piezoelectric bulk wave device and deterioration of the insertion loss of the filter.

On the other hand, from FIG. 3, in the range electrode thickness / (electrode thickness + LT thickness) is less than 40%, it can be seen that a change in electromechanical coupling coefficient k ² is small. Electromechanical coupling coefficient k ² is proportional to the bandwidth of the filter. Therefore, since the change of the electromechanical coupling coefficient k ² is small, if the electrode thickness / (LT thickness + electrode thickness) in the range of 40% or less, even variations in electrode thickness and LT thickness occurs, the bandwidth The variation of is small. Therefore, a piezoelectric bulk wave device with little frequency variation can be provided.

Further, when the electrode thickness / (electrode thickness + LT thickness) is 40% or less, the absolute value of the electromechanical coupling coefficient k ² as high as 14% or more, thus it can be seen that can provide a broadband filter.

On the other hand, as is clear from FIG. 4, when the electrode thickness / (electrode thickness + LT thickness) is 40% or more, the braking capacity C ₀ increases. As C ₀ increases, the impedance of the resonator decreases. The impedance of the RF filter needs to be matched with the impedance of an antenna or a device such as a power amplifier or a low noise amplifier connected to the front and rear. Usually, this impedance is 50Ω or 150Ω.

The impedance of the resonator is inversely proportional to the area of the resonator. Therefore, when a plurality of resonators are combined, for example, a ladder type filter is configured, the impedance of the filter is proportional to the impedance of the resonator. Therefore, the area of the resonator is inversely proportional to the impedance of the filter. Therefore, damping capacity C ₀ is large resonator per unit area, that is, by the impedance per unit area having a low resonator, it is possible to miniaturize the filter. Therefore, in order to reduce the size of the filter and the resonator, the electrode thickness / (electrode thickness + LT thickness) is desirably 40% or more.

By the way, in the conventional bulk wave resonator, AlN is used as the piezoelectric body. The relative dielectric constant of AlN is about 12, whereas the relative dielectric constant of LiTaO ₃ is 40.9 to 42.5, which is about 3.4 times as large. In addition, the sound velocity of the transverse wave of the bulk wave is 0.68 times lower in LiTaO ₃ than in AlN. Therefore, when the ratio of the same frequency, the electrode thickness / (electrode thickness + LT thickness) is the same, and the impedance is the same, the area of the bulk wave resonator using LiTaO ₃ is the same as that of the bulk wave resonator using AlN. It can be about 1/5 of the area. Therefore, it is possible to reduce the size of the piezoelectric bulk wave device.

In addition, as described above, in the range where the braking capacity C ₀ increases rapidly, that is, in the above range where the electrode thickness / (LT thickness + electrode thickness) is 40% or more, the piezoelectric bulk wave device can be further downsized. Can be planned.

In FIGS. 2 to 10, the Euler angles of LiTaO ₃ are (0 °, 73 °, 0 °), but similar results are also obtained in the case of Euler angles (90 °, 90 °, 0 °). It was. That is, it can be seen that the same effect can be obtained even in a crystal orientation in which the c-axis of LiTaO ₃ is close to the plane direction.

As described above, when the first and second electrodes 6 and 7 made of Al are used and the electrode thickness / (LT thickness + electrode thickness) is 40% or less, the electrode thickness / (LT thickness + As the electrode thickness increases, the resonance frequency Fr increases. When the electrode thickness exceeds this, the resonance frequency Fr decreases as the ratio increases. Therefore, when the first and second electrodes 6 and 7 made of Al are used, as described above, the electrode thickness / (LT thickness + electrode thickness) is in a range of 40%, that is, a range of 70% or less. Therefore, it is possible to increase the frequency. This is because the intrinsic acoustic impedance of Al is lower than the intrinsic acoustic impedance of the transverse wave propagating through LiTaO ₃ , so that the reflection coefficient viewed from LiTaO ₃ is negative. In addition, the specific acoustic impedance of the transverse wave propagating through LiTaO ₃ is 29.6 kg · s / m ² , and the specific acoustic impedance of Al is 8.4 kg · s / m ² . Accordingly, in the above embodiment, the first and second electrodes 6, 7 are formed with Al, not limited to Al, low specific acoustic impedance than _{LiTaO 3, Ag, Cu, Ni} , Ti and first Also, it may be used as a material constituting the second electrodes 6 and 7.

5, the upper portion electrode thickness = lower electrode thickness in the case of forming the laminated structure to the resonator and 880 MHz, shows the relationship between the thickness of the LiTaO _3, 6 upper electrode thickness = lower electrode thickness If, damping capacity shows the relationship between C _0, Fig. 7 shows the relationship between the upper electrode thickness = lower electrode thickness and the electromechanical coupling coefficient k ^2. The upper electrode thickness = the lower electrode thickness is equal to the thicknesses of the first electrode 6 and the second electrode 7, respectively, and in FIGS. 5 to 7, the thickness of the electrode on one side, the thickness of LiTaO ₃ , The relationship between the braking capacity C ₀ or the electromechanical coupling coefficient k ² is shown.

8 shows the relationship between the upper electrode thickness = lower electrode thickness and the LiTaO ₃ thickness when the resonator is configured to be 1960 MHz, and FIG. 9 shows the upper electrode thickness = lower electrode thickness and braking capacitance C. ₀ shows the relationship between, FIG. 10 shows the thickness upper electrode thickness = lower electrode, the relationship between the electromechanical coupling factor k ^2.

As is clear from a comparison between FIGS. 5 to 7 and FIGS. 8 to 10, the upper electrode thickness = the lower electrode thickness and the LiTaO ₃ thickness when the resonator is set to either 880 MHz or 1960 MHz. It can be seen that there is a similar change tendency between the magnitude of the braking capacity C ₀ and the electromechanical coupling coefficient k ² .

  The first and second electrodes 6 and 7 may be formed of a laminated metal film formed by laminating a plurality of metal films.

  The method for forming the first and second electrodes 6 and 7 is not particularly limited. An appropriate method such as electron beam evaporation, chemical vapor deposition, sputtering, or CVD can be used.

  Note that FIG. 1A corresponds to a cross-sectional view of a portion along the line AA in FIG. The piezoelectric thin plate 5 has slits 5a and 5b on both sides in the direction along the line AA of the recess 3a. Therefore, as shown in FIG. 1A, the piezoelectric thin plate vibrating portion 4 is in a floating state above the recess 3a. A wiring electrode 8 is formed on the insulating layer 3 outside the slit 5a. The wiring electrode 8 is connected to the second electrode 7 at a portion not shown. A wiring electrode 9 is formed outside the slit 5b. The wiring electrode 9 is formed on the piezoelectric thin plate 5 and is electrically connected to the first electrode 6 at a portion not shown. The wiring electrodes 8 and 9 are made of an appropriate conductive material. As such a conductive material, Cu, Al, or an alloy thereof can be used.

A bump 10 made of gold is provided on the wiring electrode 9. A via hole electrode 11 is provided on the piezoelectric thin plate 5 so as to be electrically connected to the wiring electrode 8. A bump 12 made of gold is bonded to the upper end of the via-hole electrode 11. Therefore, the piezoelectric thin plate vibrating portion 4 can be vibrated by applying an alternating electric field from the gold bumps 10 and 12. In addition, since the wiring electrode 8 for transmitting the main electrical signal is separated from the bonding interface between the insulating layer 3 and the support substrate 2, semiconductor resistance deterioration and skin effect due to diffusion and non-uniformity of the bonding interface. The main electrical signal can be transmitted with low loss without being affected.

Bulk acoustic wave device of the present embodiment, in the piezoelectric thin vibrating portion 4, utilizes a thickness shear vibration mode of the piezoelectric thin plate 5 made of LiTaO _3, preferably, the Euler angles of the LiTaO ₃ (phi, theta, In (ψ), it is desirable that φ is 0 ° and θ is in the range of 54 ° to 107 °. Thereby, good resonance characteristics using the thickness shear vibration mode can be obtained. This will be described more specifically below.

A bulk wave vibrator using a thickness shear vibration mode and a thickness longitudinal vibration mode using LiTaO ₃ was analyzed by a finite element method. The thickness of LiTaO ₃ was 1000 nm. A model in which electrodes made of Al with a thickness of 100 nm were formed on the top and bottom of this LiTaO ₃ was used as a model. The overlapping area of the upper and lower electrodes was 2000 μm ² .

At the Euler angles (0 °, θ, 0 °) of LiTaO ₃ , θ was changed, and the states of the thickness shear vibration mode and the thickness longitudinal vibration mode were analyzed. The results are shown in FIGS.

FIG. 11 is a diagram illustrating the relationship between the Euler angle θ and the resonance frequency Fr and anti-resonance frequency Fa of the thickness-shear vibration mode, where the solid line indicates the resonance frequency and the broken line indicates the anti-resonance frequency. FIG. 12 is a diagram illustrating the relationship between the Euler angle θ and the electromechanical coupling coefficient k ^{2 in the} thickness-shear vibration mode. As apparent from FIG. 12, the electromechanical coupling coefficient k ² of the thickness shear vibration mode utilized, theta is maximum in the vicinity of 80 °, a 14.3% value. Here, when θ is in the range of 54 ° or more and 107 ° or less, the electromechanical coupling coefficient k ² exceeds 5%, and the electromechanical coupling necessary for forming the bandwidth of the filter for the portable terminal is used. coefficient ^{k 2} can be obtained. Further, when θ is in the range of 63 ° or more and 97 ° or less, the electromechanical coupling coefficient k ² maintains a large value of 9.5% or more, which is 2/3 of the maximum value. Electromechanical coupling coefficient k ² is proportional to the bandwidth of the filter. Therefore, it can be seen that when the Euler angle θ is set to 54 ° or more and 107 ° or less, the electromechanical coupling coefficient k ² can be increased and a broadband bulk wave filter can be configured.

Therefore, in this embodiment, it is understood that a broadband bulk wave device can be provided by setting the Euler angle θ to 54 ° or more and 107 ° or less. However, depending on the application, the wider the bandwidth, the better. However, if a capacitance is added in parallel or in series with the bulk wave resonator, the bandwidth can be reduced. Therefore, when the electromechanical coupling coefficient k ² is large, it is possible to increase the freedom of design. Therefore, since the Euler angle θ is 54 ° or more and 107 ° or less and the electromechanical coupling coefficient k ² is large, bulk wave devices with various bandwidths can be easily provided.

On the other hand, as is apparent from FIG. 14, the electromechanical coupling coefficient k sp ² in the thickness longitudinal vibration mode serving as a spurious becomes substantially zero when θ is 73 °. This is consistent with the result of FIG. That is, FIG. 15 to FIG. 17 are diagrams for explaining changes due to θ of Euler angles in a thickness longitudinal vibration mode that becomes spurious. FIG. 15 shows the relationship between the Euler angle θ and the resonance frequency Fr and antiresonance frequency Fa of the thickness longitudinal vibration. The solid line shows the result of the resonance frequency, and the broken line shows the result of the anti-resonance frequency. Further, FIG. 16 shows the relationship between the electromechanical coefficient k ² of θ and the thickness longitudinal vibration of Euler angles, Figure 17 shows the relationship between θ and the temperature coefficient of frequency TCF of Euler angles. As is apparent from FIGS. 15 to 17, when the Euler angle θ is 73 °, the electromechanical coupling coefficient k ^{2 in the} thickness longitudinal vibration mode that becomes spurious becomes almost zero, and θ is 55 ° or more and 85 ° or less. If it is within the range, as is apparent from FIG. 14, the electromechanical coupling coefficient k sp ^{2 in the} thickness longitudinal vibration mode that becomes spurious is as small as 1.5% or less.

  Therefore, it is more preferable that the Euler angle θ is in the range of 55 ° to 85 °. Thereby, the response of the thickness longitudinal vibration mode which becomes spurious can be reduced. Therefore, when the piezoelectric bulk acoustic wave device of the above embodiment is configured, the attenuation characteristic in the stop band of the filter can be improved.

  On the other hand, as is apparent from FIG. 13, the absolute value of the frequency temperature coefficient TCF in the thickness-shear vibration mode is as small as 21.4 ppm / ° C. when θ = 75 °. Further, in the range of θ between 62 ° and 87 °, the absolute value of TCF is as small as 30 ppm / ° C. or less. Therefore, more preferably, θ is in the range of 62 ° to 87 °. As a result, the pass band and stop band of the filter in the piezoelectric bulk wave device 1 are difficult to shift due to changes in the environmental temperature. That is, it is possible to provide the piezoelectric bulk acoustic wave device 1 that is stable against frequency fluctuations.

Here, FIG. 18 shows the relationship between the Euler angle θ and the frequency temperature coefficient TCF in the thickness shear vibration mode when LiNbO ₃ is used. In LiNbO ₃ , as in the case of LiTaO ₃ , TCF in the vicinity of θ = 73 ° where the electromechanical coupling coefficient k ^{2 in the} thickness longitudinal vibration mode that becomes spurious becomes small is confirmed to be 96 ppm / ° C. and 21.4 ppm / It can be seen that it is nearly 5 times larger than LiTaO ₃ which is at a temperature. Therefore, it can be said that it is preferable to use LiTaO ₃ as the piezoelectric thin plate.

In FIGS. 11 to 17, the upper and lower surfaces of LiTaO _3, was examined structure formed an electrode made of Al as a model. However, even if the electrode material is changed to another metal, even if the absolute value of the electromechanical coupling coefficient k ² changes, the electromechanical coupling coefficient can be reduced by setting the Euler angle θ within the same range as described above. enhance k ^2, and further by a θ of the desired range, it is confirmed that suppressing spurious, or can decrease the absolute value of TCF.

19 and 20 are diagrams showing impedance characteristics and phase characteristics, and an impedance Smith chart of the piezoelectric bulk acoustic wave device 1 of the present embodiment described above. Here, the Euler angles of the piezoelectric thin plate 5 made of LiTaO ₃ are (0 °, 85 °, 0 °), and the thickness thereof is 0.85 μm. The first electrode 6 and the second electrode 7 are made of aluminum and have a thickness of 75 nm. Further, Ti as thin as 10 nm was disposed as an adhesion layer between aluminum and LiTaO ₃ . As apparent from FIGS. 19 and 20, the resonance frequency is 1990 MHz, the anti-resonance frequency is 2196 MHz, and a wide resonance characteristic with a bandwidth of 10.3% is obtained.

  Next, an example of a method for manufacturing the piezoelectric bulk wave device 1 will be described with reference to FIGS. 21 (a) to 24 (c).

As shown in FIG. 21A, a piezoelectric substrate 5A made of LiTaO ₃ is prepared. Hydrogen ions are implanted from one surface of the piezoelectric substrate 5A as indicated by an arrow. The ions to be implanted are not limited to hydrogen but helium or the like may be used. The energy at the time of ion implantation is not particularly limited, but in this embodiment, it is 150 KeV and the dose amount is 8 × 10 ¹⁷ atoms / cm ² . The ion implantation conditions may be selected according to the thickness of the target piezoelectric thin plate. That is, the position of the implanted ion high concentration portion can be controlled by selecting the ion implantation conditions.

  When ion implantation is performed, an ion concentration distribution is generated in the thickness direction in the piezoelectric substrate 5A. A portion having the highest ion concentration is indicated by a broken line in FIG. The implanted ion high concentration portion 5x, which is the portion having the highest ion concentration indicated by the broken line, is easily separated by stress when heated. A method of separating by such an implanted ion high concentration portion 5x is disclosed in JP-T-2002-534886.

Next, as shown in FIG. 21B, a temporary bonding layer 21 is formed on the surface of the piezoelectric substrate 5A on which ion implantation has been performed. The temporary bonding layer 21 is provided to bond a temporary support member 22 described later and to protect the finally obtained piezoelectric thin plate 5. The temporary bonding layer 21 is made of a material that is removed by an etching process described later. That is, it is made of an appropriate material which is removed by etching and does not damage the piezoelectric thin plate 5 at the time of etching. As a material constituting the temporary bonding layer 21, an appropriate material such as an inorganic material or an organic material can be used. Examples of the inorganic material include insulating inorganic materials such as ZnO, SiO ₂ , and AlN, and metal materials such as Cu, Al, and Ti. Examples of the organic material include polyimide. The temporary bonding layer 21 may be a laminate of a plurality of films made of these materials. In the present embodiment, the temporary bonding layer 21 is made of SiO ₂ .

  As shown in FIG. 21C, the temporary support member 22 is laminated and bonded to the temporary bonding layer 21. The temporary support member 22 can be formed of an appropriate rigid material. As such a material, an appropriate material such as insulating ceramics or piezoelectric ceramics can be used. Here, the temporary support member has almost no thermal stress acting on the interface with the piezoelectric substrate, or when the support substrate and the piezoelectric substrate are joined, the thermal stress acting on the interface between the support substrate and the piezoelectric substrate. Rather, it is made of a material having a smaller thermal stress acting on the interface between the temporary support member and the piezoelectric substrate. For this reason, it is possible to suppress the possibility that the piezoelectric thin plate is defective due to thermal stress when the piezoelectric thin plate is separated. On the other hand, since the support substrate is formed on the piezoelectric thin plate after heating for dividing the piezoelectric thin plate, the constituent material of the support substrate is not considered thermal stress acting on the interface between the support substrate and the piezoelectric thin plate. A material having an arbitrary linear expansion coefficient can be selected.

  Therefore, the selectivity of the combination of the constituent material of the piezoelectric thin plate and the constituent material of the support substrate can be enhanced. For example, in a filter device, the temperature-frequency characteristics of the filter can be improved by making the linear expansion coefficient of the constituent material of the support substrate significantly smaller than the linear expansion coefficient of the piezoelectric thin plate. Further, by selecting a material having high thermal conductivity for the support substrate, it is possible to improve heat dissipation and power durability. Moreover, it becomes possible to lower the manufacturing cost of the device by selecting an inexpensive constituent material.

  Next, heating is performed to facilitate the division of the piezoelectric substrate 5A in the implanted ion high concentration portion 5x. In this embodiment, the heating temperature for easily dividing the piezoelectric substrate 5A in the implanted ion high concentration portion 5x is maintained at a temperature of about 250 ° C. to 400 ° C.

  In this state, an external force is applied to divide the piezoelectric substrate 5A. That is, the piezoelectric thin plate 5 and the remaining piezoelectric substrate portion are separated from each other in the implanted ion high concentration portion 5x so as to leave the piezoelectric thin plate 5 shown in FIG. 21D, and the remaining piezoelectric substrate portion is removed.

  In addition, after dividing | segmenting by heating, it is desirable to perform the heat processing which recovers piezoelectricity suitably. Such heat treatment may be maintained at a temperature of 400 ° C. to 500 ° C. for about 3 hours.

The heating temperature required for the piezoelectric recovery may be higher than the heating temperature for facilitating the division. Thereby, the piezoelectricity can be effectively recovered.

  Next, as shown in FIG. 22A, an electrode structure including the second electrode 7 and the wiring electrode 8 is formed on the piezoelectric thin plate 5 by photolithography. Further, a protective film 8 a is formed so as to cover the wiring electrode 8.

Next, as shown in FIG. 22B, a sacrificial layer 23 is formed so as to cover the second electrode 7. The sacrificial layer 23 is made of a material that can be removed by etching. As such a sacrificial layer forming material, an insulating film such as SiO ₂ ZnO PSG (phosphosilicate glass), various organic films, a metal having a high solubility selectivity with respect to the passivation film covering the lower electrode and the lower electrode, or the like is used. be able to. In this embodiment, Cu is used. As the etchant for the etching, an appropriate material that can remove only the sacrificial layer by etching without etching the second electrode 7 can be used.

As shown in FIG. 22C, the insulating layer 3 is formed on the entire surface so as to cover the sacrificial layer 23, the protective film 8a, and the like. Insulating layer 3 _can be formed by a suitable insulating ceramic such as _{SiO 2, SiN, Ta 2 O} 5, AlN. Further, an insulating material such as glass or resin may be used.

  Thereafter, as shown in FIG. 23A, the insulating layer 3 is polished and the upper surface thereof is flattened.

  Next, as shown in FIG. 23B, the support substrate 2 is laminated on the planarized insulating layer 3.

  Next, the temporary bonding layer 21 described above is removed by etching and separated from the piezoelectric thin plate 5. Thereby, the piezoelectric thin plate 5 can be peeled from the temporary support member 22. In this way, as shown in FIG. 23C, a structure is obtained in which the sacrificial layer 23, the second electrode 7, and the piezoelectric thin plate 5 are laminated on the lower surface of the support substrate 2 with the insulating layer 3 interposed therebetween. It is done.

  Next, as shown in FIG. 24A, the first electrode 6 and the wiring electrode 9 are formed on the piezoelectric thin plate 5 by photolithography by turning upside down.

  Thereafter, slits 5a and 5b and via hole forming electrode holes are formed in the piezoelectric thin plate 5 by etching. Next, as shown in FIG. 24B, the via hole electrode 11 is formed.

  Thereafter, the sacrificial layer 23 is removed by etching. In this way, as shown in FIG. 24C, the recess 3a is formed, and the piezoelectric thin plate vibrating portion 4 is in a floating state. Finally, as shown in FIG. 1A, bumps 12 and 10 are formed on the via hole electrode 11 and the wiring electrode 9. Thus, the piezoelectric bulk wave device 1 of the above embodiment can be obtained. According to the manufacturing method, ions are previously implanted into the thick piezoelectric substrate 5A. Therefore, the piezoelectric thin plate 5 can be easily obtained by dividing the implanted ion high concentration portion 5x. According to this method, the piezoelectric thin plate 5 having a relatively small thickness can be obtained with high accuracy.

  The piezoelectric bulk wave device of the present invention can be manufactured by the manufacturing method shown in the above embodiment, but may be manufactured by other methods.

For example, in the above embodiment, after the temporary support member 22 is bonded to one surface of the piezoelectric substrate, the piezoelectric thin plate and the remaining piezoelectric substrate portion are separated. The steps for preparing the piezoelectric thin plate are as follows: May be implemented. That is, a step of ion-implanting from one surface of a piezoelectric substrate made of LiTaO ₃ to form the above-described high-concentration ion-implanted portion, a step of bonding a support substrate to the one surface side of the piezoelectric substrate, and a piezoelectric substrate And a step of separating the piezoelectric substrate from the one surface of the piezoelectric substrate to the high concentration ion implantation portion and the remaining piezoelectric substrate portion at the high concentration ion implantation portion. A piezoelectric thin plate may be prepared. More specifically, as shown in FIG. 21A, a piezoelectric substrate 5A having a high concentration ion implanted portion 5x is prepared by ion implantation. Next, a first electrode is formed on the surface of the piezoelectric substrate 5A on which ion implantation has been performed. Thereafter, the support substrate 2 is bonded to the surface on which the ion implantation of the piezoelectric substrate 5A, that is, the surface on which the first electrode is formed. In this state, the piezoelectric substrate 5A is heated and separated into the piezoelectric thin plate and the remaining piezoelectric substrate portions in the same manner as in the above-described embodiment. Next, the second electrode may be formed on the surface of the piezoelectric thin plate opposite to the surface on which the first electrode is formed.

The piezoelectric thin plate can be formed by ion implantation and division into a piezoelectric substrate made of LiTaO ₃ , or by grinding the piezoelectric substrate, etching the piezoelectric substrate, or the like.

The piezoelectric bulk acoustic wave device 1 is only an example of the piezoelectric bulk acoustic wave device of the present invention. The feature of the present invention is that the first and second electrodes 6 and 7 constituting the piezoelectric bulk acoustic wave device are LiTaO _3. When the total thickness of the first and second electrodes 6 and 7 is an electrode thickness and the thickness of LiTaO ₃ is an LT thickness, the electrode has an intrinsic acoustic impedance lower than that of a transverse wave propagating through the transverse wave. That is, the thickness / (LT thickness + electrode thickness) is larger than 5% and smaller than 70%, and the resonance characteristic by the thickness shear vibration mode is effectively used. Therefore, the materials and shapes of the first and second electrodes are not particularly limited. In addition to the resonator, the piezoelectric bulk wave device may be configured to have an electrode structure that functions as various band-pass filters.

DESCRIPTION OF SYMBOLS 1 ... Piezoelectric bulk wave apparatus 2 ... Support substrate 3 ... Insulating layer 3a ... Concave 4 ... Piezoelectric thin plate vibration part 5 ... Piezoelectric thin plate 5A ... Piezoelectric substrate 5a, 5b ... Slit 5x ... Implanted ion high concentration part 6 ... 1st electrode 7 ... second electrode 8 ... wiring electrode 8a ... protective film 9 ... wiring electrode 10 ... bump 11 ... via hole electrode 12 ... bump 21 ... temporary bonding layer 22 ... temporary support member 23 ... sacrificial layer

Claims (9)

A piezoelectric thin plate made of LiTaO ₃ ;
A first electrode and a second electrode provided in contact with the piezoelectric thin plate;
A bulk wave in the thickness-shear mode of the piezoelectric thin plate made of LiTaO ₃ is used, and at Euler angles (φ, θ, ψ) of LiTaO ₃ , φ = 0 °, 54 ° ≦ θ ≦ 107 °, ψ = 0 °,
Wherein the first and second electrodes, than specific acoustic impedance of transverse waves propagating LiTaO _3, consists specific acoustic impedance is small conductor, the first, electrode thickness is the sum of the thickness of the second electrode, A piezoelectric bulk acoustic wave device in which electrode thickness / (LT thickness + electrode thickness), which is a ratio of thickness to the sum of LiTaO ₃ thickness and electrode thickness, is greater than 5% and less than 70%.   2. The piezoelectric bulk acoustic wave device according to claim 1, wherein the electrode thickness / (LT thickness + electrode thickness) is larger than 5% and smaller than 40%.   The piezoelectric bulk acoustic wave device according to claim 1, wherein the electrode thickness / (LT thickness + electrode thickness) exceeds 40%.   The first and second electrodes are at least one metal selected from the group consisting of Al, Ag, Cu, Ni, and Ti, an alloy based on the metal, or the metal is a majority of the weight ratio. The piezoelectric bulk wave device according to any one of claims 1 to 3, wherein the piezoelectric bulk wave device is a laminated body that occupies the above. The piezoelectric bulk acoustic wave device according to claim 4, wherein the first and second electrodes are made of Al. A method of manufacturing a piezoelectric bulk wave device using a bulk shear mode bulk wave of a piezoelectric thin plate made of LiTaO ₃ , comprising:
Preparing a piezoelectric thin plate made of LiTaO _{3 with} Euler angles (φ, θ, ψ) of φ = 0 °, 54 ° ≦ θ ≦ 107 °, and ψ = 0 ° ;
Said to be in contact with the piezoelectric thin, and a step than specific acoustic impedance of transverse waves propagating LiTaO ₃ to form the first and second electrodes that Do from specific acoustic impedance is small conductor,
The electrode thickness, which is the sum of the thicknesses of the first and second electrodes, is the ratio of the thickness to the sum of the LiTaO ₃ thickness and the electrode thickness, and the electrode thickness / (LT thickness + electrode thickness) is 5%. larger, you form the first and second electrodes from the small Kunar so 70%, the production method of the piezoelectric bulk acoustic wave device. The step of preparing the piezoelectric thin plate includes:
A step of ion-implanting from one surface of a piezoelectric substrate made of LiTaO ₃ and forming a high-concentration ion-implanted portion having the highest implantation ion concentration on the one surface side;
Bonding a support substrate to the one surface side of the piezoelectric substrate;
Separating the piezoelectric substrate into a piezoelectric thin plate extending from the one surface of the piezoelectric substrate to the high concentration ion implanted portion and the remaining piezoelectric substrate portion while heating the piezoelectric substrate; A method for manufacturing a piezoelectric bulk acoustic wave device according to claim 6. The step of preparing the piezoelectric thin plate includes:
A step of ion-implanting from one surface of a piezoelectric substrate made of LiTaO ₃ and forming a high-concentration ion-implanted portion having the highest implantation ion concentration on the one surface side;
Bonding a temporary support member to the one surface side of the piezoelectric substrate;
While heating the piezoelectric substrate bonded to the temporary support member, the piezoelectric substrate at the high-concentration ion-implanted portion is moved from the one surface of the piezoelectric substrate to the high-concentration ion-implanted portion, and the remaining piezoelectric material. A step of separating into a substrate portion,
The method for manufacturing a piezoelectric bulk wave device according to claim 6, further comprising a step of peeling the temporary support member from the piezoelectric thin plate. Prior to peeling off the temporary support member from the piezoelectric thin plate, a step of forming a first electrode on the piezoelectric thin plate, a step of forming a sacrificial layer so as to cover the first electrode, and a step on the sacrificial layer And laminating a support substrate on the substrate,
After peeling the temporary support member from the piezoelectric thin plate, further comprising a step of forming a second electrode on the other surface of the piezoelectric thin plate exposed by peeling of the temporary support member, and a step of eliminating the sacrificial layer; A method for manufacturing a piezoelectric bulk wave device according to claim 8.

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