JP2006270770A - Thin film bulk wave element and high frequency device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thin film bulk wave element and a high frequency device having a high Q-value and superior resonance characteristics. <P>SOLUTION: The thin film bulk wave element has a rectangular plane shaped recess 2 on the surface of a board 1, and a thin film resonator 6 formed across the center of the recess 2. The resonator 6 is composed of a piezoelectric thin film 3 and electrodes 4, 5 formed on the upside and the underside of the thin film 3. Openings 7, 7 of lengths L are formed between a set of opposite sides 6b, 6d and the board, respectively, at the marginal edge of the resonator 6, and the sides 6b, 6d are distant from the board 1 at their centers over the lengths L. The electrodes 4, 5 are connected to pad electrodes 8, 9 formed on the board 1, respectively, and also to a not-shown external circuit through the pad electrodes 8, 9. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a thin film bulk wave device and a high frequency device.

  Conventionally, a thin film bulk acoustic wave device using an elastic wave (bulk wave) inside a piezoelectric thin film is known (see, for example, Patent Document 1).

  FIG. 10 is a plan view and a cross-sectional view for explaining the structure of a conventional thin film bulk acoustic wave device. FIG. 10A is a plan view of a conventional thin film bulk acoustic wave device, and FIG. 10B is a cross-sectional view of the conventional thin film bulk acoustic wave device as viewed from the direction of arrow B. With reference to FIG. 10, the structure of a conventional thin film bulk acoustic wave device will be described.

  In the conventional thin film bulk acoustic wave device, as shown in FIGS. 10A and 10B, a concave portion 104 having a rectangular planar shape is formed on the surface of the substrate 101. A thin film resonator (FBAR) 105 is formed on the recess 104 so as to cover the entire recess 104. The thin film resonator 105 includes a piezoelectric thin film 106 and electrodes 107 and 108 formed on the upper and lower surfaces of the piezoelectric thin film 106.

  Further, etching holes 109, 109,... Penetrating from the surface of the thin film resonator 105 to the recess 104 are formed in the thin film resonator 105. The etching holes 109, 109,... Are used for removing a sacrificial material such as phosphosilicate glass (PSG) filled in the recess 104 by etching before the thin film resonator 105 is disposed on the recess 104. Used.

  The electrodes 107 and 108 are connected to pad electrodes 110 and 111 formed on the substrate 101, respectively, and are connected to an external circuit (not shown) via the pad electrodes 110 and 111. . In this way, a conventional thin film bulk wave device is configured.

In the conventional thin film bulk wave device, a bulk wave is generated inside the piezoelectric thin film 106 by the high frequency power applied to the electrodes 107 and 108. At this time, since the bulk wave is reflected on the upper surface and the lower surface of the thin film resonator 105 in the thin film resonator r _{1 formed} of a region having a rectangular planar shape located on the concave portion 104 of the thin film resonator 107, the thin film resonator r ₁ resonates in the thickness direction (longitudinal direction) at a frequency having a wavelength about twice the thickness h of the region r ₁ (the total thickness of the piezoelectric thin film 106 and the thickness of the electrodes 107 and 108). (Longitudinal vibration).

Further, in the region other than the thin film resonator r ₁ of the thin film resonator 106, the bulk wave leaks toward the substrate 101, and thus the above resonance phenomenon does not occur. That is, in the conventional thin film bulk acoustic wave device, the thin film resonator r ₁ composed of a region located on the recess 104 of the thin film resonator 105 substantially functions as a resonator.

In the conventional thin film bulk acoustic wave device, the thickness h of the thin film resonator r ₁ is set to the μm order so that the resonance frequency f _h of the longitudinal vibration is in the GHz order.

In the conventional thin film bulk acoustic wave device, the thin film resonator r ₁ resonates not only in the thickness direction (longitudinal direction) but also in the plane direction (lateral direction). The resonance frequency f _w of the resonance (lateral vibration) in the horizontal direction is the frequency having a wavelength of about twice the width W of the planar shape of the thin film resonator r ₁ (or length L). Here, in the conventional thin film resonator r ₁ , the width W of the thin film resonator r ₁ is on the order of several hundred μm, which is about two orders of magnitude larger than the thickness h of the thin film resonator r _1. the resonance frequency f _w of the lateral vibration of the vessel 106, two orders of magnitude less than the resonant frequency f _h of the longitudinal vibration. Therefore, in the thin film bulk acoustic wave device is set to the resonance frequency of the GHz order, the resonance frequency f _w of the lateral vibration was hardly utilized.

In general, the film bulk acoustic elements, as well as other resonator has a double resonance characteristic, the above resonance frequency, the resonance frequency f _r or impedance impedance is substantially zero up to which means the anti-resonance frequency f _a made.
JP 2002-314368 A

As described above, in the conventional thin film bulk acoustic wave device, since the resonance frequency f _h of the longitudinal vibration is controlled by the thickness h of the thin film resonator r ₁ , in order to obtain a thin film bulk acoustic wave device having a higher resonance frequency. Therefore, it was necessary to further reduce the thickness h of the thin film resonator r ₁ . In this case, there is a problem in that the strength of the thin film resonator 106 is reduced, or the thickness is easily distributed in the planar direction (lateral direction) of the thin film resonator r ₁ . As a result, the conventional thin film bulk acoustic wave device has a problem that a high resonance frequency cannot be easily obtained.

The present invention has been made to solve the above problems,
One object of the present invention is to provide a thin film bulk acoustic wave device capable of easily obtaining a high resonance frequency.

  Another object of the present invention is to provide a high-frequency device capable of easily obtaining a high resonance frequency.

  In order to achieve the above object, a thin film bulk acoustic wave device according to a first aspect of the present invention includes a substrate having a recess on its surface, a piezoelectric thin film formed on the recess, and upper and lower surfaces of the piezoelectric thin film. A ratio of a thickness (h) of a thin film resonator including a region located on the concave portion of the thin film resonator and a width (w) of the thin film resonator (w) w / h) is 10 or less. The “thickness of the thin film resonator” in the present invention is the thickness of the region located on the concave portion of the thin film resonator, that is, the thickness of the piezoelectric thin film and the thickness of the electrodes formed on the upper and lower surfaces thereof. And the total. The “width of the thin film resonator” in the present invention is the length in the plane direction of the region located on the concave portion of the thin film resonator, that is, the region in the direction orthogonal to the “thickness of the thin film resonator” direction. Is the length of Further, when the thin film resonator has a rectangular planar shape composed of a long side and a short side, the length of the short side of the rectangle becomes the “width of the thin film resonator”.

In the thin film bulk acoustic wave device according to the first aspect, as described above, the thin film resonator composed of the region located on the concave portion of the thin film resonator substantially functions as a resonator. Is less than 10 times the thickness h, and therefore, the resonance frequency f _h of resonance (longitudinal vibration) in the thickness direction (longitudinal direction) and the resonance frequency f of resonance (lateral vibration) in the plane direction (lateral direction) _w can be of equal order. Thereby, the longitudinal vibration and the transverse vibration are easily coupled to generate a new resonance mode having a resonance frequency f _c higher than the resonance frequency f _h of the longitudinal vibration. On the other hand, when the width w of the thin film resonator is larger than 10 times the thickness h, the resonance frequency f _h of the longitudinal vibration and the resonance frequency f _{w of the} lateral vibration are too far apart, so that a new resonance mode in which these are combined is Hard to occur. Here, the resonance frequency f _c of the new resonance mode is expressed by the following equation using the resonance frequency f _{h of} longitudinal vibration and the resonance frequency f _w of transverse vibration.

(f _c ) ² = (f _h ) ² + (f _w ) ² (1)
By utilizing the resonant mode this and the newly generated longitudinal vibration and lateral vibration are bonded, without reducing the thickness of the thin film resonator, it is possible to increase the resonance frequency f _c, the thin film resonator The strength of is difficult to decrease. Further, since it is not necessary to reduce the thickness of the thin film resonator, the thickness h of the thin film resonator is hardly distributed in the lateral direction. As a result, a thin film bulk acoustic wave device having a high resonance frequency can be obtained with high reliability.

  Therefore, in this first aspect, a thin film bulk acoustic wave device having a high resonance frequency can be easily obtained.

In general, a thin film bulk acoustic wave device has a double resonance characteristic like other resonators, and in the present invention, the above resonance frequency is a narrow definition in which the impedance is almost zero (or minimum). the resonance frequency f _rc and impedance in the sense of it include both anti-resonance frequency f _ac to be infinite (or maximum).

  In the thin film bulk acoustic wave device according to the first aspect of the present invention, since the resonance frequency of the thin film resonator can be controlled by changing the width of the thin film resonator, the thin film resonator is used to adjust the resonance frequency. There is no need to change the thickness. Thereby, the resonance frequency of the thin film resonator can be easily adjusted.

  The thin film bulk acoustic wave device according to the first aspect preferably includes a plurality of thin film resonators separated from each other by an opening, and the plurality of thin film resonators are electrically connected in parallel to each other and are equal to each other. It has a resonance frequency. With this configuration, since the plurality of thin film resonators are acoustically separated from each other, bulk waves generated in each thin film resonator do not interfere with each other, and each thin film resonator is independent of each other. And can resonate. Thereby, even when a plurality of thin film resonators are arranged close to each other, the resonance frequency does not change.

  And by connecting these thin film resonators having the same resonance frequency in parallel, the impedance of the thin film bulk acoustic wave device can be controlled without changing the resonance frequency. In the present invention, “equal resonance frequency” means a substantially equal resonance frequency, and specifically, within a range of about ± 0.5% of the center frequency of the thin film bulk acoustic wave device. It can be treated as a substantially equal resonance frequency.

  In the thin film bulk acoustic wave device according to the first aspect, preferably, the plurality of thin film resonators have the same thickness and the same width. With this configuration, the resonance frequencies of the plurality of thin film resonators can be easily equalized. In the present invention, “equal thickness” and “equal width” mean a thickness and a width at which substantially the same resonance frequency can be obtained, and specifically, ± 0. A range of about 5% can be handled as being substantially equal.

  The thin film bulk acoustic wave device according to the first aspect preferably includes a plurality of thin film resonators that are separated from each other by an opening, and the plurality of thin film resonators are electrically connected in parallel to each other and are different. It has a resonance frequency. With this configuration, a plurality of thin film resonators can be acoustically separated from each other, so that bulk waves generated in each thin film resonator do not interfere with each other, and each thin film resonator is independent of each other. And can resonate. Furthermore, the resonance frequency of each thin film resonator is made different from each other, and these thin film resonators are electrically connected in parallel, so that the thin film resonator has a frequency characteristic obtained by superimposing the frequency characteristics of the respective thin film resonators. Can be obtained. As a result, the band-pass or band-stop filter characteristics can be easily obtained with one thin film resonator.

  In the thin film bulk acoustic wave device according to the first aspect, the plurality of thin film resonators preferably have the same thickness and different widths. With this configuration, the resonance frequencies of the plurality of thin film resonators can be easily changed.

  A high frequency device according to a second aspect of the present invention includes the thin film bulk acoustic wave element according to the first aspect. That is, the high-frequency device includes a thin film resonator including a substrate having a concave portion on the surface, a piezoelectric thin film formed on the concave portion, and electrodes formed on the upper surface and the lower surface of the piezoelectric thin film. The ratio (w / h) of the thickness (h) of the thin film resonator comprising the region located on the concave portion of the thin film resonator to the width (w) of the thin film resonator is 10 or less. Including.

In the high-frequency device according to the second aspect, as described above, the width w of the thin film resonator formed of the region located on the concave portion of the thin film resonator is set to 10 times or less the thickness h, thereby The resonance frequency f _h of resonance (longitudinal vibration) in the thickness direction (longitudinal direction) and the resonance frequency f _w of resonance (lateral vibration) in the plane direction (lateral direction) can be set to substantially the same order. As a result, the longitudinal vibration and the transverse vibration are easily coupled to generate a new resonance mode having a resonance frequency f _c higher than the resonance frequency f _h of the longitudinal vibration. In addition, by using the resonance mode in which the newly generated longitudinal vibration and lateral vibration are combined, the resonance frequency can be increased without reducing the thickness of the thin film resonator, so that the strength of the thin film resonator can be increased. In addition, the thickness of the thin film resonator is less likely to be distributed in the lateral direction. Thereby, the high frequency device which consists of a thin film bulk wave element which has a high resonant frequency can be obtained reliably.

  The “high-frequency device” in the present invention includes, for example, a high-frequency filter such as a high-frequency resonator and a bandpass filter, a duplexer, and the like.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
In the first embodiment, a thin film bulk acoustic wave device including one thin film resonator having the same thickness and width will be described.

  FIG. 1 is a plan view and a cross-sectional view of a thin film bulk acoustic wave device according to a first embodiment of the present invention. FIG. 1A is a plan view of a thin film bulk acoustic wave device, and FIG. 1B is a cross-sectional view of the thin film bulk acoustic wave device as viewed from the direction of arrow A.

  First, the structure of a thin film bulk acoustic wave device according to a first embodiment of the present invention will be described with reference to FIG. In the thin film bulk acoustic wave device according to the first embodiment, as shown in FIGS. 1A and 1B, on the upper and lower surfaces of the substrate 1 made of Si (100) having a thickness of about 300 μm, Protective films 2 and 3 comprising Si oxide films 2a and 3a having a thickness of about 1 μm and Si nitride films 2b and 3b having a thickness of about 0.2 μm formed on Si oxide films 2a and 3a, respectively. Is formed.

  A through-hole 4 having a rectangular planar shape with a length L of about 150 μm and a width W of about 11.4 μm is formed at the center between the substrate 1 and the protective films 2 and 3.

  A thin film resonator 5 having a rectangular planar shape with a length L1 and a width W1 of about 1.4 μm is formed on the through hole 4 so as to straddle the center of the through hole 4. This thin film resonator 5 includes a piezoelectric thin film 6 made of AlN having a thickness of about 1 μm, and an electrode made of Mo having a thickness of about 0.2 μm formed on the upper and lower surfaces of the piezoelectric thin film 6, respectively. 7 and 8. The thickness h of the thin film resonator 5 is such that the film thickness of the piezoelectric thin film 6 (about 1 μm) and the film thicknesses of the electrodes 7 and 8 formed on the upper and lower surfaces thereof (about 0.2 μm respectively). (About 1.4 μm), which is equal to the width W 1 of the thin film resonator 5.

The peripheral edge portion of the thin film resonator r ₁ , which is a region having a rectangular planar shape located on the through hole 4 of the thin film resonator 5, is composed of four sides having a length L and a width W 1, respectively. A pair of opposing sides is fixed on the protective film 2 over its entire length. In addition, between the sides having the length L and the substrate _{1 in} the peripheral portion of the thin film resonator r ₁ , openings 9 and 9 having a length L (about 150 μm) and a width of about 5 μm, respectively. Is formed. Thereby, a pair of opposing sides having the length L of the peripheral edge portion of the thin film resonator r ₁ are located on the through hole 4 away from the substrate 1 and the protective film 2 over the entire length.

  The electrodes 7 and 8 are connected to pad electrodes 10 and 11 formed on the protective film 2 and connected to an external circuit (not shown) via the pad electrodes 10 and 11, respectively. Yes. Thus, the thin film bulk acoustic wave device according to the first embodiment of the present invention is configured.

In the thin film bulk acoustic wave device according to the first embodiment of the present invention, bulk waves are generated inside the piezoelectric thin film 6 by the high frequency power applied to the electrodes 7 and 8. The thin film resonator r ₁ composed of a region having a rectangular planar shape having a length L and a width W 1 located on the through hole 4 of the thin film resonator 5 substantially functions as a resonator.

  Next, a method for manufacturing the thin film bulk acoustic wave device according to the first embodiment shown in FIG. 1 will be described. First, Si oxide films 2a and 3a having a thickness of about 1 μm are respectively formed on the upper surface and the lower surface of the substrate 1 made of Si (100) having a thickness of about 300 μm by thermal oxidation. Next, Si nitride films 2b and 3b having a thickness of about 0.2 μm are formed on Si oxide films 2a and 3a by sputtering, respectively. Thereby, the protective film 2 made of the Si oxide film 2a and the Si nitride film 2b and the protective film 3 made of the Si oxynitride film 3a and the Si nitride film 3b are formed on the upper surface and the lower surface of the substrate 1, respectively. To do.

  Next, using the resist pattern formed by the photolithography process as a mask, the central portion of the protective film 3 on the lower surface of the substrate 1 is etched so that the planar shape is rectangular. Further, etching is performed from the lower surface to the upper surface of the substrate 1 using the protective film 3 as a mask. At this time, the etching is stopped halfway so that the thickness of Si and the protective film 2 on the upper surface side of the substrate 1 remains about 50 μm. As a result, a recess that becomes a part of the through hole 4 is formed on the lower surface of the substrate 1. At this time, it is preferable to use an aqueous solution containing about 22% of TMAH (tetramethylammonium hydrate) as the etching solution. Thereby, the (100) plane of the substrate 1 made of Si (100) is selectively etched, and the through holes 4 are etched mainly in the depth direction of the substrate 1. Each side surface of the recess is inclined with respect to the lower surface of the substrate 1 so that the cross-sectional shape decreases from the lower surface to the upper surface of the substrate 1.

  Next, after forming a Mo thin film having a thickness of about 0.2 μm on the protective film 2 by sputtering, the Mo thin film is partially etched, so that the length L1 and about An electrode 8 having a rectangular planar shape with a width W1 of 1.4 μm and a pad electrode 11 connected to the electrode 8 are formed.

  Next, an AlN thin film having a high orientation is formed on the protective film 2 and the electrode 8 by sputtering using an inductively coupled plasma (ICP) assisted RF magnetron sputtering apparatus. The AlN thin film formed in the region on the protective film 2 is removed by etching. Thereby, the piezoelectric thin film 6 made of AlN having a rectangular planar shape with a length L1 and a width W1 is formed on the electrode 8.

  Further, a Mo thin film having a thickness of about 0.2 μm is formed on the piezoelectric thin film 6 and the protective film 2, and then the Mo thin film is partially etched so that a length L 1 is formed on the piezoelectric thin film 6. An electrode 7 made of Mo having a rectangular planar shape with a width W1 and a pad electrode 10 connected to the electrode 7 are formed on the protective film 2. Thereby, the thin film resonator 5 composed of the piezoelectric thin film 6 and the electrodes 7 and 8 formed on the upper surface and the lower surface of the piezoelectric thin film 6 is formed.

  Thereafter, the central portion of the substrate 1 and the protective film 2 is etched from the upper surface of the recess formed on the lower surface of the substrate 1, thereby penetrating the substrate 1 and the protective films 2 and 3. A through-hole 4 having a rectangular planar shape having a length L and a width W is formed on the upper surface side. Thus, the thin film bulk acoustic wave device according to the first embodiment of the present invention is manufactured.

  FIG. 2 is a schematic view of the ICP-assisted RF magnetron sputtering apparatus. In this apparatus, the target 53 can be sputtered by introducing a reactive gas into the chamber 51 and applying RF power to the target 53 using the RF power source 52. A thin film can be formed on the substrate 54 disposed above the target 53. At this time, in this apparatus, simultaneously with sputtering of the target 53, the RF power is applied to the coil 56 installed between the target 53 and the substrate 54 using the RF power source 55, thereby the particles sputtered from the target 53. Ionization can be promoted. This makes it difficult to damage the substrate 54, so that a thin film having high orientation and a dense film structure can be formed on the substrate 54.

When the AlN thin film used for the piezoelectric thin film 6 is formed by the ICP-assisted RF magnetron sputtering apparatus, in the apparatus, the target 53 is made of Al. Further, it is preferable to use a mixed gas of Ar and N ₂ as the reaction gas. Furthermore, when forming an AlN thin film, it is preferable to heat the substrate 54 by a heater 57 on the back surface of the substrate 54. Table 1 shows the main film forming conditions for forming an AlN thin film using the above-described ICP-assisted RF magnetron sputtering apparatus.

図３は、上記のＩＣＰ支援ＲＦマグネトロンスパッタ装置を用いて形成したＡｌＮ薄膜（０００２）面の結晶性と形成条件との関係を示す特性図である。図３において、ＡｌＮ薄膜（０００２）面の結晶性は、そのロッキングカーブ半値幅（ＦＷＨＭ）により評価した。圧電体薄膜６に用いるＡｌＮ薄膜は、結晶性が高いものほど好ましい。即ち、上記ＦＷＨＭが小さいものほど圧電体薄膜６として用いるのに適している。図３より、ＡｌＮ薄膜の結晶性は、基板温度およびコイル５５に印加したＲＦ電力により変化するが、基板温度２００℃、コイルＲＦ電力２００Ｗの条件で最もＦＷＨＭが小さく、ｃ軸配向性が最も高いＡｌＮ薄膜が得られることがわかる。

FIG. 3 is a characteristic diagram showing the relationship between the crystallinity of the AlN thin film (0002) surface formed using the ICP-assisted RF magnetron sputtering apparatus and the formation conditions. In FIG. 3, the crystallinity of the AlN thin film (0002) plane was evaluated by its rocking curve half width (FWHM). The higher the crystallinity of the AlN thin film used for the piezoelectric thin film 6, the better. That is, the smaller the FWHM, the more suitable for use as the piezoelectric thin film 6. From FIG. 3, the crystallinity of the AlN thin film varies depending on the substrate temperature and the RF power applied to the coil 55, but the FWHM is the smallest and the c-axis orientation is the highest at the substrate temperature of 200 ° C. and the coil RF power of 200 W. It can be seen that an AlN thin film can be obtained.

In the thin film bulk acoustic wave device of the present embodiment, as described above, the thickness h (about 1.4 μm) and the width W1 (about 1) of the thin film resonator r ₁ composed of the region located on the through hole 4 of the thin film resonator 5. .4 μm) (W1 / h) is about 1, the resonance frequency f _h of resonance (longitudinal vibration) in the thickness direction (longitudinal direction) of this thin film resonator r ₁ and the plane direction (lateral direction). The resonance frequency f _w of the resonance (lateral vibration) can be made equal. As a result, the longitudinal vibration and the transverse vibration are easily coupled to generate a new resonance mode having a resonance frequency f _c higher than the resonance frequency f _h of the longitudinal vibration.

By utilizing the resonant mode this and the newly generated longitudinal vibration and lateral vibration are bonded, without reducing the thickness h of the thin film resonator r _1, to increase the resonance frequency f _c of the thin film resonator r ₁ As a result, the strength of the thin film resonator r ₁ is unlikely to decrease, and the thickness h of the thin film resonator r ₁ is also unlikely to be distributed in the lateral direction. As a result, a thin film bulk acoustic wave device having a high resonance frequency can be obtained with high reliability.

  Therefore, in this embodiment, a thin film bulk acoustic wave device having a high resonance frequency can be easily obtained.

(Second Embodiment)
In the second embodiment, a thin film bulk acoustic wave device including a plurality of thin film resonators having equal resonance frequencies will be described.

  FIG. 4 is a plan view and a cross-sectional view of a thin film bulk acoustic wave device according to a second embodiment of the present invention. 4A is a plan view of the thin film bulk acoustic wave device, and FIG. 4B is a cross-sectional view of the thin film bulk acoustic wave device as viewed from the direction of arrow A.

  First, the structure of a thin film bulk acoustic wave device according to a second embodiment of the present invention will be described with reference to FIG. In addition, description is abbreviate | omitted about the structure which is common in the thin film bulk acoustic wave device by 1st Embodiment.

  In the thin film bulk acoustic wave device according to the second embodiment, a ladder-like plane is formed so as to straddle the through hole 4 on the through hole 4 having a rectangular planar shape with a length L of about 150 μm and a width W of about 37 μm. A thin film resonator 15 having a shape is formed. The thin film resonator 15 includes a piezoelectric thin film 16 made of AlN having a thickness of about 1 μm, and an electrode made of Mo having a thickness of about 0.2 μm formed on the upper surface and the lower surface of the piezoelectric thin film 16, respectively. 17 and 18.

The thicknesses h of the five thin film resonators r ₁ , r ₁ ,..., Each of which has a rectangular planar shape with a length L and a width W 1 located on the through hole 4 of the thin film resonator 15, respectively, The total thickness (about 1.4 μm) of the film thickness (about 1 μm) of the piezoelectric thin film 16 and the film thicknesses of the electrodes 17 and 18 (about 0.2 μm, respectively) formed on the upper and lower surfaces thereof, Are equal.

The peripheral portions of the thin film resonators r ₁ , r ₁ ,..., Each of which has a rectangular planar shape located on the through-hole 4 of the thin film resonator 15, have four sides each having a length L or W 1. It is fixed on the protective film 2 over the entire length W1 on both opposing sides of a set having a length W1. .. Of the thin film resonators r ₁ , r ₁ ,... Between the side having the length L and the substrate 1 and between the sides having the length L are about 150 μm. Openings 9, 9,... Having a length and a width of about 5 μm are formed. Thereby, a pair of opposing sides having the length L of the peripheral edge of the thin film resonators r ₁ , r ₁ ,... Are separated from the substrate 1 and the protective film 3 over the entire length L, and the through-hole 4 Located on the top. The thin film resonators r ₁ , r ₁ ,... Are separated from each other by the openings 9, 9.

  The electrodes 17 and 18 are connected to pad electrodes 10 and 11 formed on the protective film 2 and are connected to an external circuit (not shown) via the pad electrodes 10 and 11. ing. Thus, the thin film bulk acoustic wave device according to the second embodiment of the present invention is configured.

In the thin film bulk acoustic wave device according to the second embodiment of the present invention, the ratio between the thickness h (about 1.4 μm) and the width W1 (about 1.4 μm) of the five thin film resonators r ₁ , r ₁ ,. W1 / h) is about 1, so that each of the thin film resonators r ₁ , r ₁ ,... Also has a longitudinal vibration and a lateral vibration having a resonance frequency f _c higher than the resonance frequency f _{h of the} longitudinal vibration. A new resonance mode combined with vibration is generated. At this time, since each thin film resonator r ₁ , r ₁ ,... Has the same thickness h and the same width W1, each thin film resonator r ₁ , r ₁ ,. Can be easily equalized.

Further, since the thin film resonators r ₁ , r ₁ ,... Are separated from each other by the openings 9, 9,... On the through-hole 4, the thin film resonators r ₁ , r ₁ ,. Can be acoustically separated from each other. Thereby, the bulk waves generated in each thin film resonator r ₁ , r ₁ ,... Do not interfere with each other. As a result, each of the thin film resonator _{r 1, r} 1, · · · each independently can resonate at resonant frequency equal _{f c.}

Furthermore, five thin film resonator _{r 1, r} 1, electrodes 7,7 are formed on the upper surface and on the lower surface of ..., ... and 8,8, ..., respectively common pad electrode 10 and 11, the five thin film resonators r ₁ , r ₁ ,... Are electrically connected in parallel. These results, in the thin film bulk acoustic wave device of this embodiment, without changing the resonance frequency f _c of the thin film resonator 15, it is possible to change the impedance of the thin film bulk acoustic wave device.

(Evaluation 1)
Next, the resonance characteristics of the thin film bulk acoustic wave device according to the first embodiment and the second embodiment of the present invention were evaluated by simulation.

FIG. 5 is an equivalent circuit diagram used for evaluating the resonance characteristics of the thin film bulk acoustic wave device according to the first and second embodiments of the present invention and a characteristic diagram showing the resonance characteristics. The thin film bulk acoustic wave element R1 used for the simulation in the evaluation 1 is connected to each other in parallel and has a thin film resonator 25 having n (n = 1, 5 and 10) thin film resonators r _{s1 to} r _sn. It has. As shown in the equivalent circuit diagram of FIG. 5, the thin film resonator 25 is connected in series to one signal line. Each thin film resonator r _{s1 to} r _sn has the same thickness h and width W1, that is, the ratio (W1 / h) of the thickness h to the width W1 is about 1. Therefore, in the thin film bulk acoustic wave element R1 used in this evaluation 1, the resonance frequency f _w of the resonance (lateral vibration) in the plane direction (lateral direction) of each of the thin film resonators r _{s1 to} r _sn is the resonance frequency f of the longitudinal vibration. equal to _h .

In FIG. 5, the horizontal axis indicates the frequency of the input signal to the thin film bulk acoustic wave element R <b _{> 1} with the resonance frequency f _h of resonance (longitudinal vibration) in the thickness direction (longitudinal direction) of each thin film resonator r _{s1 to} r _sn. The vertical axis represents the magnitude (transmittance) of the output signal from the thin film bulk acoustic wave element R1 at each frequency. In this evaluation 1, the resonance frequency f _h means the anti-resonance frequency f _ah where the impedance between the input and output terminals is maximized.

As shown in FIG. 5, in the resonance characteristics of each thin film bulk acoustic wave element R1, a downward peak due to longitudinal vibration (direction in which the transmittance decreases) is observed at the resonance frequency _fah , and about _fah . A larger downward peak is also seen at a frequency f _ac near 1.414 times. From the above equation (1), it is found that this resonance frequency f _ac substantially coincides with the resonance frequency of a new resonance mode in which the resonance frequency f _{ah of} longitudinal vibration and the resonance frequency f _{aw of} transverse vibration are combined.

Further, the resonance frequency f _ac does not change even when the number (n) of the thin film resonators r _{s1 to} r _sn connected in parallel increases, and the peak of the downward resonance decreases as n increases, It has been found that the transmittance at the resonance frequency f _ac increases.

(Evaluation 2)
FIG. 6 is an equivalent circuit diagram used to evaluate the resonance characteristics of the thin film bulk acoustic wave device according to the first and second embodiments of the present invention and a characteristic diagram showing the resonance characteristics. The thin film bulk acoustic wave element R2 used for the simulation in the evaluation 2 is connected to each other in parallel and has a thin film resonator 35 having n (n = 1, 5 and 10) thin film resonators r _{p1 to} r _pn. It has. As shown in the equivalent circuit diagram of FIG. 6, the thin film resonator 35 is connected in parallel to two signal lines (one is grounded). Each thin film resonator r _{p1 to} r _pn has a ratio (W1 / h) of the thickness h to the width W1 of about 2. Therefore, in the thin film bulk acoustic wave element R2 used in this evaluation 2, the resonance frequency f _w of the resonance (lateral vibration) in the plane direction (lateral direction) of each of the thin film resonators r _{p1 to} r _pn is the resonance frequency f of the longitudinal vibration. The value is about 1/2 times _h .

In FIG. 6, the horizontal axis indicates a value obtained by normalizing the frequency of the input signal to the thin film bulk acoustic wave element R2 by the resonance frequency f _h of the longitudinal vibration of each thin film resonator r _{p1 to} r _pn. Indicates the magnitude (transmittance) of the output signal from the thin film bulk acoustic wave element R2 at each frequency. In this evaluation 2, the resonance frequency f _h means a resonance frequency _{frh in a} narrow sense in which the impedance between the input and output terminals is minimized.

As shown in FIG. 6, in the resonance characteristic of the film bulk acoustic wave device R2, respectively, at the resonant frequency f _rh, with peak downward resonance by longitudinal vibration is observed, in the vicinity of about 1.118 times f _rh A larger downward peak is also seen at the frequency _frc . The resonance frequency f _rc, from the equation (1), the resonance frequency f _rh of the longitudinal vibration and the resonance frequency f _rw of the lateral vibration is substantially coincident with the resonance frequency of the new resonant modes bound was found.

Further, even if the number (n) of the thin film resonators r _{p1 to} r _pn connected in parallel increases, the resonance frequency f _rc does not change, and as n increases, the downward resonance peak increases. It was found that the transmittance at the resonance frequency _frc is small.

(Evaluation 3-7)
Furthermore, in evaluations 3 to 5, the resonance characteristics of the other thin film bulk acoustic wave devices according to the first and second embodiments of the present invention were also evaluated using the same equivalent circuit as in the evaluation 2. In Evaluations 3 to 5, as shown in Table 2 below, the ratio (W1 / h) of the thickness (h) to the width (W1) of each thin film resonator r _{p1 to} r _pn is about 0.5, about Thin film bulk wave devices of 5.0 and about 10 were used.

  For comparison, instead of the thin film bulk acoustic wave element used in the above evaluations 3 to 5, a thin film resonator having a width of about 20 times the thickness was evaluated in evaluation 6, and a width was about 100 in thickness in evaluation 7. A conventional thin-film bulk acoustic wave device having one double-thin film resonator was used.

In the evaluation 1 Evaluation 7 above shows the resonant frequency f _c of the new resonance mode, the transmittance at the resonance frequency f _c in Table 2. Note that the resonance frequency f _c in Table 2 is the frequency normalized by the value of the resonance frequency _frh of the longitudinal vibration in the evaluation 2 for the evaluations 2 to 7, and the resonance frequency f _c of the evaluation 1 is for the evaluation 1 Each frequency normalized by the value of the resonance frequency _fah was used.

表２より、薄膜共振子の厚みｈと幅Ｗ１との比（Ｗ１／ｈ）が２０を超えると、新たな共振モードの共振周波数ｆ_ｃは、縦振動の共振周波数ｆ_ｈと略等しく、縦振動と横振動との結合はほとんど生じていない。これより、Ｗ１／ｈが２０を超えると、共振周波数を大きくする効果はほとんど見られないことが判明した。

According to Table 2, when the ratio (W1 / h) between the thickness h and the width W1 of the thin film resonator exceeds 20, the resonance frequency f _c of the new resonance mode is substantially equal to the resonance frequency f _h of the longitudinal vibration. There is almost no coupling between vibration and transverse vibration. From this, it was found that when W1 / h exceeds 20, the effect of increasing the resonance frequency is hardly seen.

On the other hand, when W1 / h is 10 or less, a new resonance mode having a resonance frequency f _c higher than the resonance frequency f _ah of the longitudinal vibration in which the longitudinal vibration and the transverse vibration are combined is generated. I understood. Further, as the W1 / h is small, the resonance frequency f _c of the new resonance mode was found to increase.

Further, each evaluation, regardless of the number of thin-film resonator are connected in parallel, with the resonance frequency f _c is equal new resonance mode, the larger the number of thin-film resonator are connected in parallel to each other, evaluate in 1, a large transmittance at the resonance frequency f _c, the evaluation 2-5, conversely, it was found that the transmittance at the resonance frequency f _c is smaller. Than this, a thin film bulk acoustic wave device according to the first embodiment and the second embodiment of the present invention, without changing the resonance frequency f _c, it was found that it is possible to change the impedance of the thin film bulk acoustic wave device.

(Third embodiment)
In the third embodiment, a thin film bulk acoustic wave device including a plurality of thin film resonators having different resonance frequencies will be described.

  FIG. 7 is a plan view and a cross-sectional view of a thin film bulk acoustic wave device according to a third embodiment of the present invention. FIG. 7A is a plan view of the thin film bulk acoustic wave device, and FIG. 7B is a cross-sectional view of the thin film bulk acoustic wave device as viewed from the direction of arrow A.

  First, the structure of a thin film bulk acoustic wave device according to a third embodiment of the present invention will be described with reference to FIG. In addition, description is abbreviate | omitted about the structure which is common in the thin film bulk acoustic wave device by 2nd Embodiment.

  In the thin film bulk acoustic wave device according to the third embodiment, a ladder shape is formed so as to straddle the through hole 4 on the through hole 4 having a rectangular planar shape with a length L of about 50 μm and a width W of about 33.05 μm. A thin film resonator 45 having a planar shape is formed. The thin film resonator 45 includes a piezoelectric thin film 46 made of AlN having a thickness of about 1 μm, and an electrode made of Mo having a thickness of about 0.2 μm formed on the upper and lower surfaces of the piezoelectric thin film 46, respectively. 47 and 48.

A length L located on the through hole 4 of the thin film resonator 25 and a width W1 of about 1.4 μm, a width W2 of about 1.75 μm, a width W3 of about 2.1 μm and a width W4 of about 2.8 μm. The thicknesses h of the _four thin film resonators r _{1 to} r 4 each having a rectangular planar shape are respectively formed on the film thickness (about 1 μm) of the piezoelectric thin film 26 and on the upper and lower surfaces thereof. It is the sum (about 1.4 μm) with the film thicknesses of the electrodes 47 and 48 (each about 0.2 μm), which are equal.

  The electrodes 47 and 48 are connected to pad electrodes 10 and 11 formed on the protective film 2, respectively, and are connected to an external circuit (not shown) via the pad electrodes 10 and 11. ing. Thus, the thin film bulk acoustic wave device according to the third embodiment of the present invention is configured.

In the thin film bulk acoustic wave device according to the third embodiment of the present invention, as in the second embodiment, the four thin film resonators r _{1 to} r ₄ can resonate independently.

Further, the ratio (W1 / h, W2 / h, W3 /) of the thickness h (about 1.4 μm) and the width W1 to W4 (about 1.4 μm to about 2.8 μm) of each thin film resonator r _{1 to} r _4. h, W4 / h) are about 1, about 1.25, about 1.5, and about 2.0, respectively, and are on the same order, so that the resonance frequency f _c is higher than the resonance frequency f _h of the longitudinal vibration. It is possible to vibrate in a new resonance mode in which longitudinal vibration and transverse vibration having In this case, the width W1~W4 of each of the thin film resonator _r 1 ~r ₄ are different, varying the resonant frequency _{f c} of the new resonance mode occurring in each of the thin film resonator _r 1 ~r ₄ facilitate Can do.

Furthermore, since these thin film resonators r _{1 to} r ₄ are electrically connected in parallel, a thin film resonator having a frequency characteristic obtained by superimposing the frequency characteristics of the thin film resonators r _{1 to} r ₄ is obtained. Can do.

(Evaluation 8)
Here, the resonance characteristics of the thin film bulk acoustic wave device according to the third embodiment were evaluated by simulation.

FIG. 8 is an equivalent circuit diagram used for evaluating the resonance characteristics of the thin film bulk acoustic wave device according to the third embodiment of the present invention and a characteristic diagram showing the resonance characteristics. Film bulk acoustic wave device used in the simulation in this evaluation. 8, along with being connected in parallel with each other, provided with a thin film resonator 45 having four thin film resonator r _p1 ~r _p4 having a different resonance frequency f _c from each other Yes. As shown in the equivalent circuit diagram of FIG. 8, the thin film resonator 45 is connected in parallel to two signal lines (one is grounded).

In FIG. 8, the horizontal axis indicates a value obtained by normalizing the frequency of the input signal to the thin film bulk acoustic wave element by the resonance frequency f _h of the longitudinal vibration of each of the thin film resonators r _{p1 to} r _4. Indicates the magnitude (transmittance) of the output signal from the thin film bulk acoustic wave element at each frequency. In this evaluation 8, the resonance frequency f _h means a narrowly defined resonance frequency _fr that minimizes the impedance between the input and output terminals.

As shown in FIG. 8, in the resonance characteristics of the thin film bulk acoustic wave device according to the present embodiment, a small peak of downward resonance due to longitudinal vibration is seen at the resonance frequency _frh , and about 1.1 to about _frh of frh. Greater transmission attenuation is seen over 1.4 times the frequency. Thereby, in the thin film bulk acoustic wave device of this embodiment, it is possible to obtain a band rejection type filter characteristic that blocks an input signal in a frequency band of about 1.1 to about 1.4 times the resonance frequency _frh. all right.

(Fourth embodiment)
In the fourth embodiment, a high frequency filter including two thin film bulk acoustic wave devices according to the second embodiment will be described.

  FIG. 9 is an equivalent circuit diagram of a high frequency filter according to a fourth embodiment of the present invention and a characteristic diagram showing frequency characteristics thereof.

As shown in this equivalent circuit diagram, the high frequency filter of the present embodiment includes the thin film bulk acoustic wave element R1 used in Evaluation 1 and the thin film bulk acoustic wave element R2 used in Evaluation 2. The thin film resonator 25 in the thin film bulk acoustic wave element R1 is connected in series to one signal line and has five thin film resonators r _{s1 to} r _s5 . Each thin film resonator r _{s1 to} r _s5 has a ratio (W1 / h) of the thickness h to the width W1 of about 1. The thin film resonator 35 in the thin film bulk wave element R2 is connected in parallel to two signal lines (one is grounded) and has five thin film resonators r _{p1 to} r _p5 . ing. Each of the thin film resonators r _{p1 to} r _p5 has a ratio (W2 / h) of the thickness h to the width W2 of about 0.5.

In the characteristic diagram of FIG. 9, the horizontal axis normalizes the frequency of the input signal to the high frequency filter by the resonance frequency f _h of the longitudinal vibration of each thin film resonator r _{s1 to} r _s5 and r _{p1 to} r _p5 . The vertical axis represents the magnitude (transmittance) of the output signal from the high frequency filter at each frequency. In this embodiment, the resonance frequency f _h means an anti-resonance frequency f _ah that maximizes the impedance between the input and output terminals.

As shown in FIG. 9, in the high frequency filter according to the present embodiment, large downward peaks are observed at frequencies about 1.1 times and about 1.4 times the resonance frequency _fah . It was found that a passband type filter characteristic that allows an input signal to pass through can be obtained in a frequency band between.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above description of the embodiments but by the scope of claims for patent, and further includes all modifications within the meaning and scope equivalent to the scope of claims for patent.

For example, in each of the embodiments described above, the through hole 4 is formed in the substrate 1. However, the present invention is not limited to this, and the region to be the thin film resonator r ₁ is separated from the substrate 1 and the protective film 2. A recess may be formed on the upper surface of the substrate 1 and the protective film 2.

  In each of the above embodiments, the thin film resonator is configured from a region having a rectangular planar shape. However, the present invention is not limited to this, and may be a square planar shape. Moreover, even if it is a polygon other than a rectangle or one of the sides is a curved line, it may have a substantially rectangular or substantially square planar shape.

  In each of the above embodiments, the protective films 2 and 3 are formed on the upper surface and the lower surface of the substrate 1. However, the present invention is not limited to this, and the protective films 2 and 3 are not formed. Also good.

  In addition, the high frequency filter of the fourth embodiment is configured by the thin film bulk acoustic wave device according to the present embodiment, but the present invention is not limited thereto, and may include a thin film bulk acoustic wave device other than the present embodiment. Alternatively, other electric elements may be included.

It is the top view and sectional drawing of a thin film bulk acoustic wave device by a 1st embodiment of the present invention. It is the schematic of an ICP assistance RF magnetron sputtering apparatus. It is a characteristic view which shows the relationship between the crystallinity of AlN thin film (0002) surface formed using the ICP assistance RF magnetron sputtering apparatus, and formation conditions. It is the top view and sectional drawing of a thin film bulk acoustic wave device by a 2nd embodiment of the present invention. It is the equivalent circuit figure used in order to evaluate the resonance characteristic of the thin film bulk wave element by 1st Embodiment of this invention, and 2nd Embodiment, and the characteristic figure which shows the resonance characteristic. It is the equivalent circuit figure used in order to evaluate the resonance characteristic of the thin film bulk wave element by 1st Embodiment of this invention, and 2nd Embodiment, and the characteristic figure which shows the resonance characteristic. It is the top view and sectional drawing of a thin film bulk acoustic wave device by a 3rd embodiment of the present invention. It is the characteristic diagram which shows the equivalent circuit diagram used in order to evaluate the resonance characteristic of the thin film bulk acoustic wave device by 3rd Embodiment of this invention, and its resonance characteristic. It is the equivalent circuit schematic of the high frequency filter of 4th Embodiment of this invention, and the characteristic view which shows the frequency characteristic. It is the top view and sectional drawing for demonstrating the structure of the conventional thin film bulk acoustic wave element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2, 3 Protective film 2a, 3a Si oxide film 2b, 3b Si nitride film 4 Through hole 5 Thin film resonator 5a Thin film resonator 6 Piezoelectric thin film 7, 8 Electrode 9 Opening 10, 11 Pad electrode

Claims (6)

A substrate having a recess on the surface;
A piezoelectric thin film formed on the recess;
A thin film resonator including electrodes formed on the upper surface and the lower surface of the piezoelectric thin film;
A thin film bulk wave having a ratio (w / h) of a thickness (h) of a thin film resonator formed of a region located on the concave portion of the thin film resonator to a width (w) of the thin film resonator is 10 or less element. A plurality of the thin film resonators separated from each other by an opening,
The thin film bulk acoustic wave device according to claim 1, wherein the plurality of thin film resonators are electrically connected to each other in parallel and have the same resonance frequency.   The thin film bulk acoustic wave device according to claim 2, wherein the plurality of thin film resonators have the same thickness and the same width. A plurality of the thin film resonators separated from each other by an opening,
The thin film bulk acoustic wave device according to claim 1, wherein the plurality of thin film resonators are electrically connected to each other in parallel and have different resonance frequencies.   The thin film bulk acoustic wave device according to claim 4, wherein the plurality of thin film resonators have the same thickness and different widths.   A high-frequency device comprising the thin film bulk acoustic wave device according to claim 1.

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