JP4849445B2 - Thin film resonator - Google Patents

Description

  The present invention relates to a thin film resonator for extracting a signal of a specific frequency from a broadband signal used in communication equipment such as a mobile phone.

  An RF filter for extracting a signal in a specific frequency band is used in a communication device such as a mobile phone or a wireless LAN transmitter / receiver. In an RF filter, a large number of resonators that resonate at a frequency within a used frequency band are usually used. Since the frequency band used in these communication devices is as high as several hundred MHz to several GHz, the resonator needs to cope with such a high frequency.

  In recent years, a thin film resonator called FBAR (Film Bulk Acoustic Resonator) has attracted attention as a resonator capable of realizing a high resonance frequency (see Patent Document 1). The FBAR has a structure in which a piezoelectric thin film is placed on a substrate having a cavity, and a pair of electrodes is provided so as to sandwich the piezoelectric thin film. Here, the cavity is provided in the substrate so that the piezoelectric thin film can freely vibrate without being constrained by the substrate. In FBAR, since the resonance frequency is inversely proportional to the thickness of the piezoelectric thin film, the resonance frequency can be increased as the thickness of the thin film is reduced. In fact, it has been confirmed that a frequency filter using FBAR can obtain good filter characteristics even at a high frequency of several GHz.

Japanese Patent Laid-Open No. 2001-203558 ([0003] to [0004], FIG. 1)

However, the conventional FBAR has the following problems.
The resonance frequency of the FBAR depends on the elastic constant of the piezoelectric body, and this elastic constant changes with the temperature of the piezoelectric body. That is, the conventional FBAR has a problem that the resonance frequency changes due to a temperature change. In particular, in mobile communication devices, it is necessary to supply a large power of about 100 mW to an FBAR of about 0.1 mm square, so that the FBAR is greatly affected by temperature rise.

  In addition, a conventional FBAR usually uses a piezoelectric body in which resonance due to a longitudinal wave propagating in a direction perpendicular to the film surface is formed because it is easy to manufacture. Longitudinal waves can propagate to the air outside the membrane and vibration energy is likely to be lost. In order to prevent this loss of vibration energy, some FBARs have a piezoelectric body sealed in a vacuum vessel. However, in that case, it becomes difficult to dissipate heat from the piezoelectric body, so that the temperature of the piezoelectric body rises and the resonance frequency changes (decreases).

  Further, in the conventional FBAR, unnecessary vibration (spurious mode) different from the original resonance of the resonator is generated in a region in the piezoelectric thin film that is directly above or below the electrode. In many cases, the frequency of the spurious mode is a value close to the original resonance frequency of the resonator, which causes an error in the vibration frequency of the main body.

  The problem to be solved by the present invention is to provide a thin film resonator in which a change in resonance frequency due to a temperature change is small and spurious mode vibration can be suppressed.

The thin film resonator according to the present invention, which has been made to solve the above problems,
a) A resonator body comprising a piezoelectric film provided between upper and lower electrodes, and a transverse wave standing wave propagating in the thickness direction of the piezoelectric film is formed when an AC voltage is applied between the electrodes;
b) having a characteristic that the viscosity coefficient decreases as the temperature rises, and a contact liquid that contacts at least a part of the resonator body;
It is characterized by providing.

In order to obtain a resonator body in which a transverse standing wave is formed, the piezoelectric film made of either ZnO or AlN and having the [0001] direction oriented in one direction substantially parallel to the film surface is used. be able to.
As shown in FIG. 1, both ZnO and AlN have a wurtzite structure represented by the general formula ^{An + Bn-} (n is an integer) and a hexagonal crystal. In the wurtzite structure, layers composed of ^{An +} (layer A) and layers composed of B ^n- (layer B) are alternately stacked, and the layer B is located at a distance from the two layers A above and below the same distance. It exists at a position shifted in one direction of the c-axis. That is, the wurtzite structure has polarity in the c-axis direction. In the present application, the direction in which the A layer deviates from the B layer is defined as the [0001] direction.

  The piezoelectric film is made of either ZnO or AlN and has the same material and thickness as the first piezoelectric film, with the [0001] direction oriented in one direction substantially parallel to the film surface. It is possible to use a laminated body in which the [0001] direction and the second piezoelectric film oriented in a direction different from the first piezoelectric film by 180 ° are stacked. Furthermore, a laminated body in which a plurality of first piezoelectric films and second piezoelectric films are alternately stacked can also be used.

The “contact liquid” used in the present invention has a function of suppressing the temperature change of the frequency of the resonator main body by the temperature change of the viscosity, and specifically, is a liquid having the following characteristics.
(1) The viscosity coefficient decreases with increasing temperature.
(2) Better thermal conductivity than air.
(3) Longitudinal waves propagate more easily than air.
Due to such characteristics, in the present invention, the contact liquid that contacts at least a part of the resonator body performs the following action.
(1) When the temperature of the resonator body rises, the elastic constant of the piezoelectric film decreases and the resonance frequency changes to the lower frequency side. On the other hand, since the viscosity coefficient of the contact liquid is lowered, the contact liquid acts to change the resonance frequency of the piezoelectric film to the high frequency side. Similarly, when the temperature of the resonator body decreases, the elastic constant of the piezoelectric film increases and its resonance frequency changes to the high frequency side, whereas the contact liquid increases in viscosity coefficient and the piezoelectric film It acts to change the resonance frequency to the low frequency side. The action due to the temperature change of the elastic constant and the action due to the temperature change of the viscosity coefficient are at least partially offset, thereby suppressing the change in the resonance frequency due to the temperature change of the resonator.
(2) The heat generated in the piezoelectric film can be transmitted better than the conventional air (or vacuum) and released to the outside. Thereby, the temperature change itself of the piezoelectric film can be suppressed.
(3) Among the spurious modes generated in the piezoelectric film, a sound wave having a displacement component other than the direction parallel to the piezoelectric film leaks into the contact liquid and attenuates the spurious mode vibration of the piezoelectric film.

  In the thin film resonator of the present invention, when the temperature rises, the elastic constant of the piezoelectric film is lowered and the resonance frequency is changed to the lower frequency side, and the viscosity coefficient of the contact liquid is lowered to resonate. It acts so that the frequency changes to the high frequency side. Similarly, when the temperature is lowered, the elastic constant is increased and the resonance frequency is changed to the higher frequency side, and the viscosity coefficient is increased and the resonance frequency is changed to the lower frequency side. By canceling out the effect due to the change in the elastic constant of the piezoelectric film and the effect due to the change in the viscosity of the contact liquid, the change in the resonance frequency due to the temperature change in the resonator is suppressed.

  In addition, since the resonator main body is in contact with the contact liquid, the thin film resonator according to the present invention easily releases heat generated from the main body to the outside through the contact liquid. Thereby, the change of the resonant frequency by the temperature change (rise) of a resonator is further suppressed.

  Furthermore, in the thin film resonator of the present invention, since the sound wave having a displacement component other than the direction parallel to the piezoelectric film in the spurious mode leaks into the contact liquid, the spurious mode can be attenuated.

  The main body of the thin film resonator of the present invention has a pair of electrodes (upper electrode and lower electrode) arranged so as to sandwich the upper and lower sides of a film made of a piezoelectric material. This is the same as the conventional thin film resonator such as the FBAR described above. As this resonator main body, one that forms a transverse standing wave that propagates in the thickness direction of the piezoelectric film when an AC voltage is applied between the electrodes is used.

  An example of such a resonator body is a thin film resonator using ZnO or AlN whose [0001] direction is oriented in one direction substantially parallel to the surface of the thin film as a piezoelectric film. When an AC voltage is applied between the electrodes of the resonator body, a standing wave of a transverse wave that propagates in a direction substantially perpendicular to the piezoelectric film and has a displacement in a substantially parallel direction is formed. When only one piezoelectric film is provided, the wavelength of the transverse wave is twice the thickness of the piezoelectric film. Also, as the piezoelectric film of the main body, a laminated body in which a first piezoelectric film and a second piezoelectric film made of ZnO or AlN and having different [0001] directions by 180 ° can be used. In this case, the wavelength of the transverse wave is the same as the thickness of the laminated body, that is, 1/2 of the case where only one layer of ZnO or AlN is provided. Furthermore, a laminate in which a plurality of first piezoelectric films and second piezoelectric films are alternately laminated can also be used.

  A contact liquid is brought into contact with at least a part of the resonator body. The contact liquid may contact only a part of the main body, and the part may be a piezoelectric film, an upper electrode, or a lower electrode. However, in order to obtain the maximum effect of the present invention, the contact liquid is preferably brought into contact with the entire surface of the resonator body. When a conductive contact liquid is used, it is desirable to provide an insulating member between the upper electrode and / or the lower electrode and the contact liquid.

  In the present invention, since the resonator body is brought into contact with the liquid, if a resonator body in which a longitudinal standing wave is formed is used, the vibration of the longitudinal wave propagates in the liquid and the resonance intensity is attenuated. End up. Therefore, in the present invention, the propagation of vibration into the liquid is prevented by using a resonator body in which a transverse standing wave is formed.

と表される。温度が上昇すると、圧電体膜の弾性定数c_pは小さくなる（密度及び厚さは弾性定数よりも温度変化が十分に小さい）ため、共振周波数f₀は低くなる。 The operation of the thin film resonator of the present invention will be described.
First, for comparison, a resonance frequency f ₀ of a thin film resonator in which the piezoelectric film is in contact with a vacuum (not a liquid as in the present invention) and the other configuration is the same as that of the present invention. Indicates. The resonance frequency f ₀ is obtained by using the density ρ _p , the elastic constant c _p and the thickness d _p of the piezoelectric film,

It is expressed. As the temperature increases, the elastic constant c _p of the piezoelectric film becomes small (density and thickness is sufficiently small temperature changes than the elastic constant) Therefore, the resonance frequency f ₀ is lowered.

と表される。ここで、ρ_lは接触液の密度、η_lは接触液の粘性係数である。(3)式より、Δfはc _p ^1/4 及びη_l ^1/2に比例する。温度が上昇すると、粘性係数η_lが小さくなると共に、前述のように圧電体膜の弾性定数c_pも小さくなるため、Δfは小さくなる。(2)式の第2項より、このΔfの温度変化は、温度上昇と共に共振周波数fを大きくするように作用する。それに対して、(2)式の第1項のf₀は、温度上昇と共に共振周波数fを小さくするように作用する。これにより、(2)式第2項の温度変化と(2)式第1項の温度変化が相殺されるため、本発明の薄膜共振器の共振周波数fは、圧電体膜が真空に接する薄膜共振器よりも温度による変化が小さくなる。 On the other hand, in the thin film resonator of the present invention, since the piezoelectric film is in contact with the contact liquid, the resonance frequency f is
f = f ₀ -Δf (2)
Thus, the piezoelectric film is smaller than the thin film resonator in contact with the vacuum by a change amount Δf. This change Δf is

It is expressed. Here, ρ _l is the density of the contact liquid, and η _l is the viscosity coefficient of the contact liquid. From equation (3), Δf is proportional to c _p ^1/4 and η _l ^1/2 . As the temperature increases, the viscosity coefficient eta _l decreases, since the smaller elastic constant c _p of the piezoelectric film as described above, Delta] f becomes smaller. From the second term of equation (2), the temperature change of Δf acts to increase the resonance frequency f as the temperature rises. On the other hand, f _{0 in} the first term of equation (2) acts to decrease the resonance frequency f as the temperature rises. This cancels out the temperature change in the second term of equation (2) and the temperature change in the first term of equation (2), so the resonance frequency f of the thin film resonator of the present invention is a thin film in which the piezoelectric film is in contact with vacuum The change with temperature becomes smaller than the resonator.

  In the thin film resonator of the present invention, heat generated in the resonator body during use is discharged to the outside through the contact liquid. Therefore, since the temperature change itself of the thin film resonator can be suppressed, the temperature change of the resonance frequency f can be further suppressed.

  Furthermore, according to the present invention, a thin film resonator that is not affected by the spurious mode can be obtained. This is because the spurious mode consists of plate waves and surface waves propagating in a direction parallel to the piezoelectric film, and the vibration of these waves leaks into the contact liquid, thereby attenuating the spurious mode for the fundamental mode of the transverse wave. Because it can.

Usually, a liquid has a viscosity coefficient several orders of magnitude greater than that of a gas. For example, when the temperature is 25 ° C. and normal pressure, the viscosity coefficient of air is 1.82 × 10 ⁻⁵ Pa · s, while the viscosity coefficient of water is 8.90 × 10, which is about 50 times that of air. ^-4 Pa · s. And the change by the temperature of the viscosity coefficient is also large according to it. Also, regarding the thermal conductivity and the longitudinal wave propagation characteristics, naturally, a liquid having a higher density than the gas has a higher value. Since the liquid has such general characteristics, most of the liquid that can be usually considered can be used as the contact liquid used in the present invention.

  In order to increase the Q value of the thin film resonator main body, it is desirable to use a contact liquid having a viscosity coefficient as small as possible and also having a sufficiently large temperature change in the viscosity coefficient in order to suppress a temperature change in the resonance frequency. The contact liquid is desirably chemically inert.

  One suitable example of the contact liquid used in the present invention is silicone oil. Silicone oil differs in absolute value and temperature dependence of viscosity coefficient depending on the type of side chain of the component polymer. Therefore, the silicone oil has an advantage that an appropriate one can be selected according to the material of the piezoelectric film to be used. Silicone oil also has the advantage of being chemically inert.

An FBAR which is an embodiment of a thin film resonator according to the present invention will be described with reference to FIGS.
(1) Configuration of FBAR of this embodiment FIG. 2 is a longitudinal sectional view of the FBAR 10 of this embodiment. The Si substrate 11 made of silicon has a cavity 12 passing through it at the center. A lower electrode 13 is provided on the Si substrate 11, a ZnO thin film 14 made of ZnO is provided thereon, and an upper electrode 15 is provided on the ZnO thin film 14. In the ZnO thin film 14, the [0001] direction is oriented in one direction in the plane of the thin film (the left-right direction in FIG. 2). Hereinafter, such an orientation is referred to as “parallel orientation”.

  These Si substrate 11, ZnO thin film 14, and upper and lower electrodes are enclosed in a container 17 together with a contact liquid 16. The exposed surfaces of the ZnO thin film 14, the lower electrode 13, and the upper electrode 15 are in contact with the contact liquid 16. One end of each of the lower electrode 13 and the upper electrode 15 is connected to terminals 181 and 182 provided on the container 17. An insulator that is not eroded by the contact liquid 16 is used as the material of the container 17.

ここで、動粘度は粘性係数η_lを密度ρ_lで除したものであり、表１に挙げた値は25℃におけるものである。粘度温度係数は次式

で表される。粘度温度係数が大きいほど、温度による粘度の変化は大きい。 In this embodiment, the contact liquid 16 is composed of KF-54 silicone oil (this embodiment 1), KF-96-10cs silicone oil (this embodiment 2) and KF-96L-1cs silicone oil (this embodiment 3) (whichever Also manufactured three types of FBARs using Shin-Etsu Chemical Co., Ltd.). The characteristics of these silicone oils are shown in Table 1.

Here, the kinematic viscosity is obtained by dividing the viscosity coefficient η _l by the density ρ _l , and the values listed in Table 1 are those at 25 ° C. Viscosity temperature coefficient is

It is represented by The greater the viscosity temperature coefficient, the greater the change in viscosity with temperature.

(2) Manufacturing method of FBAR 10 of this embodiment A manufacturing method of FBAR 10 of this embodiment will be described with reference to FIGS. Here, first, (i) the entire flow of the FBAR manufacturing method will be described with reference to FIG. 3, and then (ii) a method of manufacturing the ZnO thin film 14 will be described with reference to FIG. 4.
(i) FBAR Manufacturing Method First, a mask 21 having a window in a region where the lower electrode 13 is formed is formed on the surface of the Si substrate 11, and a lower electrode metal is deposited thereon (FIG. 3 (a)). Thereby, the lower electrode 13 is produced. After removing the mask 21 (b), a ZnO thin film 14 is formed on the Si substrate 11 and the lower electrode 13 using the method described in (ii) (c). Further, a mask 22 having a window in a region where the upper electrode 15 is to be formed is formed thereon, and an upper electrode metal is vapor-deposited (d) thereon to produce the upper electrode 15. After removing the mask 22 (e), the cavity 12 is formed by selectively etching Si in the region of the Si substrate 11 near the center of the ZnO thin film 14 (f). The main body of the FBAR thus obtained is fixed in a separately prepared container 17, and after the contact liquid 16 is injected into the container 17, the container 17 is sealed. Thereby, FBAR10 of a present Example is obtained (g).

(ii) Preparation method of ZnO thin film 14 (step of FIG. 3 (c))
The ZnO thin film 14 was produced using the magnetron sputtering apparatus 30 shown in FIG. First, the configuration of the magnetron sputtering apparatus 30 will be described. In this apparatus, a magnetron circuit 32 and a cathode 33 are provided in the lower part of the film forming chamber 31, and an anode 34 is provided in the upper part. Immediately below the anode 34, a substrate stage 35 is disposed at a position deviating from a line connecting the centers of the cathode 33 and the anode 34 (a chain line in the figure) and being inclined with respect to this line. Yes. On the cathode 33, a ZnO target 36 as a raw material for the ZnO thin film 14 is placed. A gas source 37 of argon (Ar) gas and oxygen (O ₂ ) gas is connected to the film forming chamber 31.
A method for producing the ZnO thin film 14 will be described. The substrate (bottom 38) in which the lower electrode 13 is formed on the surface of the Si substrate 11 shown in FIG. 3B is attached to the substrate base 35 so that the lower electrode 13 is on the lower side. Ar gas and O ₂ gas are introduced into the film forming chamber 31, and high frequency power is supplied to the cathode 33. As a result, a high-frequency electromagnetic field is formed in the film forming chamber 31, whereby Ar gas and O ₂ gas are ionized to emit electrons. The electrons move while drawing a toroidal curve by an electric field and a magnetic field in the vicinity of the ZnO target 36, whereby plasma is generated in the vicinity of the ZnO target 36 and the ZnO target 36 is sputtered. The sputtered ZnO forms a uniaxial flow (raw material flow 39) toward the anode 34, the raw material flow 39 reaches the surface of the substrate 38, and ZnO is deposited on this surface. At this time, by arranging the substrate 38 to be inclined as described above, a temperature gradient in one direction parallel to the surface is formed on the substrate 38, whereby the parallel-oriented ZnO thin film 14 is formed.

(3) Measurement results of characteristics of FBAR 10 of this example For the FBARs 10 of Examples 1 to 3, admittance characteristics and changes in temperature of the resonance frequency were measured. In addition, as a comparative example, a container 17 filled with air 19 instead of the contact liquid 16 of this example (Comparative Example 1, FIG. 5A), instead of the ZnO thin film 14 of this example [ [0001] Using a ZnO thin film whose direction is perpendicular to the film surface (hereinafter referred to as "vertical alignment") (Comparative Example 2, FIG. 5 (b)), and the contact liquid 16 of Comparative Example 2 Instead, a container 17 filled with air 19 (Comparative Example 3, FIG. 5 (c)) was prepared, and the same measurement was performed. When an AC voltage is applied between the lower electrode 13 and the upper electrode 15, a transverse standing wave that vibrates in a direction parallel to the film surface is formed in the ZnO thin film 14 in the FBARs of the present example and the comparative example 1. On the other hand, in the FBARs of Comparative Examples 2 and 3, a longitudinal standing wave that vibrates in a direction perpendicular to the film surface is formed in the ZnO thin film 14. In each of Examples 1 to 3 and Comparative Examples 1 to 3, the thickness of the ZnO thin film 14 was 6.5 μm, and the thicknesses of the lower electrode and the upper electrode were each 0.15 μm. Note that all of Examples 1 to 3 and Comparative Examples 1 to 3 were measured without the Si substrate 11.

In FIG. 6, the measurement result of the admittance characteristic of FBAR10 of the present Example 3 and FBAR of Comparative Examples 1-3 is shown. For the contact liquid 16 of Comparative Example 2, the same KF-96L-1cs silicone oil as in Example 3 was used. The resonance frequency is about 200 MHz for the FBARs of the present Example 3 and Comparative Example 1, and is about 450 MHz for the FBARs of Comparative Example 2 and Comparative Example 3. In Comparative Example 2 and Comparative Example 3 in which a longitudinal standing wave is formed, the admittance decreased by an order of magnitude when the contact liquid 16 (Comparative Example 2) was used instead of the air 19 (Comparative Example 3). This is because in the case of the comparative example 2, the vibration of the longitudinal wave formed when the vertically oriented ZnO thin film 14 is used is attenuated by the contact liquid 16. On the other hand, in this Example 3 and Comparative Example 1 in which a standing wave of a transverse wave is formed, a decrease in admittance when the contact liquid 16 (this Example 3) is used instead of the air 19 (Comparative Example 1). Is suppressed more than the longitudinal wave. This is considered to be because the vibration of the transverse wave is not attenuated by the contact liquid 16 in the third embodiment.
Note that the peak seen in the vicinity of 200 MHz in Comparative Examples 2 and 3 is due to a transverse wave that is generated when the [0001] axis of the ZnO thin film is slightly inclined from the direction perpendicular to the thin film. Similarly, in Comparative Example 1, a peak due to a longitudinal wave generated when the [0001] axis is slightly inclined from the direction parallel to the thin film is observed near 440 MHz. In Example 3, this longitudinal wave is observed. Is not observed because it is attenuated by the contact liquid 16. Moreover, the peak seen in the vicinity of 600 MHz in the present Example 3 and Comparative Examples 1 to 3 is due to the third-order mode of transverse wave vibration.

  FIG. 7 shows an enlarged view of a graph of admittance characteristics in the vicinity of the resonance frequency for Example 3 and Comparative Example 1. FIG. 7 shows that in the comparative example 1, a large number of spurious modes are superimposed on the main peak. On the other hand, in Example 3, no peak due to the spurious mode is observed. This is because in this embodiment, a sound wave having a displacement component other than the direction parallel to the piezoelectric film in the spurious mode leaks into the contact liquid, and the spurious mode vibration is attenuated.

In FIG. 8, the result of having measured the change with the temperature of the resonant frequency in FBAR of the Examples 1-3 and the comparative example 1 is shown with a graph. In Comparative Example 1, a change represented by a linear function having a negative slope was shown in the entire temperature range where the measurement was performed. The value of TCF (Temperature coefficient of Frequency) representing the change with respect to temperature is 31.4 ppm / ° C. Here, TCF is obtained by dividing the slope of this graph by the value of the resonance frequency at the reference temperature (25 ° C. in this example). In contrast, in Example 3, the TCF value is 24.3 ppm / ° C., and in Example 2, the TCF value is 19.7 ppm / ° C., both of which have a smaller temperature change than Comparative Example 1. Furthermore, in Example 1, the resonance frequency hardly changes in the temperature range of 25 ° C. to 50 ° C. In addition, in the temperature range of 50 ° C to 80 ° C, the resonance frequency shows a change represented by a linear function having a negative slope as in the other examples, but the TCF value is 16.0 ppm / ° C. Smaller than one. From the above, it can be said that all of the FBARs 10 of Examples 1 to 3 have higher stability against temperature change than the FBAR of Comparative Example 1 in the entire temperature range in which the measurement was performed. Further, the present embodiment 1, when comparing the embodiment 2 and the embodiment 3, it can be said that the higher the temperature stability viscosity temperature coefficient of the contact liquid 16 is high becomes higher.

Another embodiment of the thin film resonator according to the present invention is shown in FIGS.
The FBAR 10 a shown in FIG. 9 is one in which the contact liquid 16 is sealed only in the cavity 12 using the lid 41 without using the container 17. Other configurations are the same as those of the FBAR 10. In this FBAR 10 ′, only a part of the ZnO thin film 14 and a part of the lower electrode 13 are in contact with the contact liquid 16 in the resonator body. Thus, even if only a part of the resonator body is in contact with the contact liquid, the effect of the present invention can be obtained that suppresses the change in the resonance frequency with respect to temperature and the spurious mode. However, in order to obtain these effects more strongly, it is desirable that a wider part of the resonator body, like the FBAR 10, be in contact with the contact liquid.

In the FBAR 10b shown in FIG. 10, instead of the ZnO thin film 14, the [0001] direction is oriented in a direction 180 ° different from the ZnO thin film 141 in which the [0001] direction is oriented in one direction parallel to the film surface. A laminated body 14 ′ of the ZnO thin film 142 is provided. Other configurations are the same as those of the FBAR 10. Comparing the FBAR 10b with the FBAR 10 described above, the FBAR 10 forms a standing wave of the first mode having a wavelength twice the thickness of the ZnO thin film 14, whereas the FBAR 10b has the thickness of the stacked body 14 '. Since a standing wave of a secondary mode having the same wavelength is formed, the resonance frequency of the FBAR 10b is twice that of the FBAR 10 if the thickness of the ZnO thin film 14 and the stacked body 14 'is the same. . Therefore, the FBAR 10b can obtain a higher resonance frequency than the FBAR 10 without reducing the mechanical strength of the resonator.
Moreover, what laminated | stacked more than one laminated body 14 'can also be used instead of the ZnO thin film 14. FIG. By making the thickness the same as that of the ZnO thin film 14, the resonance frequency can be further increased.

FIG. 11 shows an SMR (Solidly Mounted Resonator) 50 which is another embodiment of the present invention. This SMR50 is [0001] direction has a lower electrode 53 and upper electrode 55 above and below the ZnO thin film 54 oriented in one direction parallel to the film plane, under the lower electrode 53, a low sound of SiO ₂ An acoustic multilayer film 51 in which a large number of high acoustic impedance layers 512 made of Mo and impedance layers 511 are alternately laminated is provided. Each of the low acoustic impedance layer 511 and the high acoustic impedance layer 512 has a thickness of 1/4 times the wavelength of the ultrasonic wave having a resonance frequency determined by the thickness of the ZnO thin film 54. The ZnO thin film 54, the lower electrode 53, the upper electrode 55, and the acoustic multilayer film 51 are arranged in a container 57, and the same contact liquid 56 as that used in the FBAR 10 is brought into contact with the upper electrode 55.
In the SMR 50, ultrasonic waves from the ZnO thin film 54 generated by applying an AC voltage between the electrodes are reflected at the boundary between each low acoustic impedance layer 511 and high acoustic impedance layer 512, and these reflected waves are in phase with each other. Do not cancel each other. Thereby, the vibration of the ZnO thin film 54 is suppressed from leaking to the outside. Since the contact liquid is in contact with one surface of the resonator body composed of the ZnO thin film 54, the lower electrode 53, and the upper electrode 55, the same effect as that of the FBAR 10 can be obtained.
Similar to the above-described various FBARs, a stacked body 14 ′ or a stack of a plurality of the stacked bodies 14 ′ can be used instead of the ZnO thin film 54.

The crystal structure figure which shows a wurtzite structure. The longitudinal cross-sectional view which shows one Example (FBAR10) of the thin film resonator which concerns on this invention. The longitudinal cross-sectional view which shows the manufacturing method of FBAR10 of a present Example. The longitudinal cross-sectional view which shows the apparatus for manufacturing the ZnO thin film in which the c axis | shaft orientated in the surface. The longitudinal cross-sectional view which shows FBAR of a comparative example. The graph which shows the admittance characteristic of FBAR of the present Example 3 and Comparative Examples 1-3. The enlarged view of the graph of FIG. The graph which shows the temperature change of the resonant frequency in FBAR of the Examples 1-3 and the comparative example 1. FIG. The longitudinal cross-sectional view which shows FBAR10a which enclosed the contact liquid 16 only in the cavity 12, which is the other Example of this invention. The longitudinal cross-sectional view which shows FBAR10b using the laminated body 14 'which is another Example of this invention. The longitudinal cross-sectional view which shows SMR50 which is the other Example of this invention.

Explanation of symbols

10, 10a, 10b ... FBAR
DESCRIPTION OF SYMBOLS 11 ... Si substrate 12 ... Cavity 13, 53 ... Lower electrode 14, 141, 142, 54 ... ZnO thin film 14 '... Laminated body 15, 55 ... Upper electrode 16, 56 ... Contact liquid 17, 57 ... Container 181, 182 ... Terminal DESCRIPTION OF SYMBOLS 19 ... Air 21, 22 ... Mask 30 ... Magnetron sputtering apparatus 31 ... Film formation chamber 32 ... Magnetron circuit 33 ... Cathode 34 ... Anode 35 ... Substrate stand 36 ... ZnO target 37 ... Gas source 38 ... Substrate 39 ... Raw material flow 41 ... Cover 50 ... SMR
51 ... Acoustic multilayer film 511 ... Low acoustic impedance layer 512 ... High acoustic impedance layer

Claims (7)

a) A resonator body comprising a piezoelectric film provided between upper and lower electrodes, and a transverse wave standing wave propagating in the thickness direction of the piezoelectric film is formed when an AC voltage is applied between the electrodes;
b) having a characteristic that the viscosity coefficient decreases as the temperature rises, and a contact liquid that contacts at least a part of the resonator body;
A thin film resonator comprising:   2. The thin film resonator according to claim 1, wherein the piezoelectric film is made of any one of ZnO and AlN and has a [0001] direction oriented in one direction substantially parallel to the film surface.   The piezoelectric film is made of either ZnO or AlN, and the [0001] direction is aligned in one direction substantially parallel to the film surface, and the material and thickness are the same as the first piezoelectric film. 2. The thin film resonator according to claim 1, comprising a laminated body in which a second [0001] direction and a second piezoelectric film oriented in a direction different from the first piezoelectric film by 180 ° are stacked.   4. The thin film resonator according to claim 3, wherein the laminated body is formed by alternately stacking a plurality of first piezoelectric films and second piezoelectric films.   The thin film resonator according to claim 1, wherein the contact liquid is silicone oil.   The thin film resonator according to claim 1, wherein the resonator main body is fixed on a substrate having a cavity.   The resonator main body is an acoustic multilayer film in which two types of layers having a thickness of 1/4 of an ultrasonic wave having the same frequency as the resonance frequency of the resonator main body and having different acoustic impedances are alternately stacked. The thin film resonator according to claim 1, wherein the thin film resonator is fixed.

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