JP2006050591A - High frequency filter and manufacturing method thereof - Google Patents

Abstract

A high-frequency filter having uniform frequency characteristics can be realized by adjusting the resonance frequencies of piezoelectric resonators formed on a substrate to different frequencies without complicating the process.
A plurality of first piezoelectric resonators 11 that are held on a substrate 1 and are composed of a piezoelectric film 31, a first upper electrode 41, and a first lower electrode 43, and are held on the substrate 1 and A high frequency filter is formed by the plurality of second piezoelectric resonators 12 including the piezoelectric film 31, the second upper electrode 42, and the second lower electrode 44. At least one of the first upper electrode 41 and the first lower electrode 43 is formed of the first electrode forming material, and at least one of the second upper electrode 42 and the second lower electrode 44 is the first electrode. The second electrode forming material is different from the forming material.
[Selection] Figure 1

Description

  The present invention relates to a high-frequency filter using a piezoelectric resonator and a manufacturing method thereof.

  In recent years, with the spread of mobile phones worldwide, the number of mobile phones used is increasing at an accelerating rate. In mobile phones, it is necessary to process a plurality of high-frequency signals having different frequencies, and it is generally necessary to remove high-frequency signals of frequencies other than the target frequency. For example, in a terminal called a front end that receives a signal having a frequency transmitted from a base station in a terminal, it is always necessary to remove a high-frequency signal other than the signal having the received frequency. In addition, in a circuit that converts a received frequency signal into an intermediate frequency signal that is a frequency for signal processing inside the terminal, it is necessary to remove signals of frequencies other than the intermediate frequency. In order to remove such a high-frequency signal having an unnecessary frequency and pass only a high-frequency signal having a desired frequency, a component called a high-frequency filter is generally used.

  The characteristics required for a high-frequency filter are required to have a small loss when passing a signal having a desired frequency and to greatly attenuate a signal having a frequency other than the desired frequency. At this time, the frequency characteristics of the high-frequency filter are important so that signals having frequencies other than the desired frequency are not passed or signals having the desired frequency are not attenuated. In particular, since the frequency of the high-frequency signal transmitted from the terminal to the base station and the frequency of the high-frequency signal transmitted from the base station to the terminal are generally close to each other, it is required that the frequency characteristics are strictly as designed. The

  One of the components that constitute such a filter is a resonator. In order to obtain the desired frequency characteristics of the high-frequency filter, it is very important to accurately realize the resonance frequency of the resonator used in the high-frequency filter as designed. In recent years, attempts have been made to use SAW resonators that use surface acoustic waves as resonators, piezoelectric resonators that use bulk acoustic waves, and the like in order to reduce the size and performance of filters.

  In order to make the resonance frequency of the piezoelectric resonator as designed, the total thickness of the piezoelectric film thickness, upper electrode thickness, and lower electrode thickness must be made exactly as designed. . However, in general, it is difficult to make the thickness of the thin film exactly as designed. Therefore, in the piezoelectric resonator, after forming the piezoelectric resonator, it is necessary to make an adjustment for accurately setting the resonance frequency to a desired value.

  For example, in Patent Document 1, the upper electrode is formed to be thicker than the lower electrode, and the upper electrode is made thinner while measuring the resonance frequency, thereby adjusting the resonance frequency to a desired value.

Further, in Patent Document 2, the thickness deviation of the lower electrode is determined by measuring the deviation of the thickness of the substrate on which the piezoelectric resonator is formed and determining the deposition condition of the lower electrode, and then depositing the lower electrode according to the condition. And the resonance frequency is adjusted to a desired value.
Japanese Patent Laid-Open No. 2001-196883 US Pat. No. 6,507,983

  However, there are the following problems in adjusting the resonance frequency of the piezoelectric resonator by using the conventional method to obtain the desired frequency characteristics of the high frequency filter.

  The high frequency filter is formed by combining at least two piezoelectric resonators having different resonance frequencies. For this reason, it is generally necessary to make adjustments so that the plurality of piezoelectric resonators formed on the substrate have at least two different resonance frequencies. However, in the conventional method, all the piezoelectric resonators formed on the substrate can only be adjusted to have the same resonance frequency. For this reason, when trying to adjust the piezoelectric resonator using the conventional method, there is a problem that the adjustment process becomes very complicated.

  For example, first, a part of the piezoelectric resonator formed on the substrate is masked, and the resonance frequency of the piezoelectric resonator that is not masked is adjusted. Next, the adjusted piezoelectric resonator is masked, the mask of the unadjusted piezoelectric resonator is removed, and the resonance frequency is adjusted. This method increases the number of steps for applying a mask.

  The present invention solves the above-mentioned conventional problems and can adjust the resonance frequency of the piezoelectric resonator formed on the substrate to different frequencies without complicating the process, thereby realizing a high-frequency filter having a uniform frequency characteristic. The purpose is to do so.

  In order to achieve the above object, the present invention has a high-frequency filter including two types of resonators in which at least one of the upper electrode and the lower electrode is formed of different materials.

  Specifically, a first high-frequency filter according to the present invention is held along a main surface of a substrate and the substrate, the first piezoelectric film, and the upper and lower surfaces of the first piezoelectric film. A first piezoelectric resonator formed of a first upper electrode and a first lower electrode respectively formed at positions facing each other, and held on the main surface of the substrate along the main surface; And a second upper electrode and a second lower electrode formed at positions facing each other on the upper surface and the lower surface of the second piezoelectric film, respectively, and having a resonance frequency different from that of the first piezoelectric resonator. And at least one of the first upper electrode and the first lower electrode is made of a first electrode forming material, and is formed of the second upper electrode and the second lower electrode. At least one of them is made of the second electrode forming material. That.

  According to the first high frequency filter, at least one of the first upper electrode and the first lower electrode is made of the first electrode forming material, and the second upper electrode and the second lower electrode are Since at least one is made of the second electrode forming material, the resonance frequency of the first piezoelectric resonator is adjusted by etching the first electrode forming material, and the second electrode forming material is etched. The resonance frequency of the second piezoelectric resonator can be adjusted. Therefore, it is easy to adjust the resonance frequency of the first piezoelectric resonator and the resonance frequency of the second piezoelectric resonator to different frequencies, so that it is possible to realize a high-frequency filter with uniform frequency characteristics. It becomes.

  In the first high-frequency filter, it is preferable that the first electrode forming material has an etching resistance to the second etchant that is etched by the first etchant and etches the second electrode forming material. By adopting such a configuration, when the resonance frequency of the second piezoelectric resonator is adjusted using the second etchant, it is possible to reliably prevent the resonance frequency of the first piezoelectric resonator from fluctuating. Therefore, it is possible to adjust the high frequency filter without increasing the mask formation process and the like.

  In this case, it is preferable that the first electrode forming material is platinum and the second electrode forming material is gold.

  In this case, the second electrode forming material preferably has etching resistance to the first etchant, the first electrode forming material is gold, and the second electrode forming material is titanium or aluminum. It is preferable.

  The first high-frequency filter includes a first additional film formed of at least one of the upper surface of the first upper electrode and the lower surface of the first lower electrode and made of the first material, and the upper surface of the second upper electrode. And at least one of a second additional film formed on at least one of the lower surfaces of the second lower electrode and made of the second material. With such a configuration, since the resonance frequency of at least one of the first piezoelectric resonator and the second piezoelectric resonator can be adjusted by etching the additional film, the resonance frequency of the piezoelectric resonator can be adjusted. The adjustment becomes easier.

  In the first high-frequency filter, one of the second upper electrode and the second lower electrode is electrically connected to the first upper electrode or the first lower electrode, and the second upper electrode and the second lower electrode are electrically connected. The other unit of the electrode is a basic unit of a ladder type resonator that is electrically connected to the ground. The combination of the first electrode forming material and the second electrode forming material is the same as that of the first piezoelectric resonator. A combination in which the insertion loss is smaller than the insertion loss of the second piezoelectric resonator is preferable. With such a configuration, the insertion loss of the high frequency filter can be reduced.

  In this case, it is preferable that an inductor is electrically connected between the second upper electrode or the second lower electrode and the ground.

  The first high-frequency filter further includes a first input / output terminal, a second input / output terminal, a third input / output terminal, and a fourth input / output terminal, and there are two first resonators, One of the two first resonators is electrically connected between the first input / output terminal and the second input / output terminal, and the other of the two first resonators is a third input / output. The second resonator is electrically connected between the terminal and the fourth input / output terminal, and one of the two second resonators is connected to the first input / output terminal and the fourth input / output terminal. And the other of the two second resonators is electrically connected between the third input / output terminal and the second input / output terminal. The combination of the electrode forming material and the second electrode forming material is such that the insertion loss of the first piezoelectric resonator is smaller than the insertion loss of the second piezoelectric resonator. Preferred. By adopting such a configuration, it is possible to reduce the insertion loss of the high frequency filter and to realize a parallel input and parallel output type high frequency filter.

  The second high-frequency filter according to the present invention is held on the main surface of the substrate along the main surface, and the first piezoelectric film and the upper surface and the lower surface of the first piezoelectric film are opposed to each other. A first piezoelectric resonator composed of a first upper electrode and a first lower electrode respectively formed at a position where the second piezoelectric film is formed, and held on the main surface of the substrate along the main surface; And a second upper electrode and a second lower electrode respectively formed at opposite positions on the upper and lower surfaces of the second piezoelectric film and having a resonance frequency different from that of the first piezoelectric resonator. And at least one of the first upper electrode additional film formed on the upper surface of the first upper electrode and the first lower electrode additional film formed on the lower surface of the first lower electrode, A second upper electrode additional film formed on the upper surface of the second upper electrode; At least one of the second lower electrode addition films formed on the lower surface of the partial electrode, and at least one of the first upper electrode addition film and the first lower electrode addition film is the first addition It is made of a film forming material, and at least one of the second upper electrode additional film and the second lower electrode additional film is made of a second additional film forming material.

  According to the second high frequency filter, at least one of the first upper electrode additional film and the first lower electrode additional film is made of the first additional film forming material, and the second upper electrode additional film and the first upper electrode additional film Since at least one of the two lower electrode additional films is made of the second additional film forming material, the resonance of the first piezoelectric resonator and the second piezoelectric resonator is obtained by etching two films of different materials. Each frequency can be adjusted. Therefore, it becomes easy to adjust the resonance frequency of the first piezoelectric resonator and the resonance frequency of the second piezoelectric resonator to different frequencies. Further, since an insulating film can be used as the additional film, the effect of facilitating the formation and etching of the additional film is also obtained.

  In the second high-frequency filter, it is preferable that the first additional film forming material has etching resistance to the second etchant that is etched by the first etchant and etches the second additional film forming material. In this case, it is preferable that the first additional film forming material is platinum and the second additional film forming material is gold. With this configuration, the resonance frequency of the second piezoelectric resonator can be adjusted without changing the resonance frequency of the first piezoelectric resonator.

  In the second high frequency filter, it is preferable that the second additional film forming material has etching resistance with respect to the first etchant. In this case, it is preferable that the first additional film forming material is silicon nitride, the second additional film forming material is silicon oxide, the first additional film forming material is gold, and the second additional film forming material is gold. The forming material may be titanium or aluminum.

  In the second high frequency filter, one of the second upper electrode and the second lower electrode is electrically connected to the first upper electrode or the first lower electrode, and the second upper electrode and the second lower electrode are electrically connected. A basic unit of a ladder type resonator in which the other electrode is grounded is formed. The combination of the first additional film forming material and the second additional film forming material has an insertion loss of the first piezoelectric resonator. A combination that is smaller than the insertion loss of the second piezoelectric resonator is preferable.

  In this case, it is preferable that an inductor is electrically connected between the second upper electrode or the second lower electrode and the ground.

  The second high-frequency filter further includes a first input / output terminal, a second input / output terminal, a third input / output terminal, and a fourth input / output terminal, and the first resonator has two, One of the two first resonators is electrically connected between the first input / output terminal and the second input / output terminal, and the other of the two first resonators is a third input / output. The second resonator is electrically connected between the terminal and the fourth input / output terminal, and one of the two second resonators is connected to the first input / output terminal and the fourth input / output terminal. And the other of the two second resonators is electrically connected between the third input / output terminal and the second input / output terminal. The combination of the additional film forming material and the second additional film forming material is a combination in which the insertion loss of the first piezoelectric resonator is smaller than the insertion loss of the second piezoelectric resonator. Door is preferable.

  The first high-frequency filter manufacturing method according to the present invention includes a first piezoelectric film and a first upper portion formed on the main surface of the substrate so as to face the upper surface and the lower surface of the first piezoelectric film. A first piezoelectric resonator comprising an electrode and a first lower electrode; a second piezoelectric film; a second upper electrode formed on the upper surface and the lower surface of the second piezoelectric film so as to face each other; Using the first etchant capable of etching at least one of the first upper electrode and the first lower electrode, and a step of holding the second piezoelectric resonator including two lower electrodes. The step of adjusting the resonance frequency of the resonator and the second etchant capable of etching at least one of the second upper electrode and the second lower electrode are used to adjust the resonance frequency of the second piezoelectric resonator. And that it has a process And butterflies.

  According to the first high-frequency filter manufacturing method, the resonance frequency of the first piezoelectric resonator is adjusted using the first etchant capable of etching at least one of the first upper electrode and the first lower electrode. And adjusting the resonance frequency of the second piezoelectric resonator using a second etchant capable of etching at least one of the second upper electrode and the second lower electrode. The resonance frequency of the second piezoelectric resonator can be adjusted without changing the resonance frequency of the first piezoelectric resonator. Therefore, it is not necessary to form a complicated mask, and it is possible to easily obtain a high frequency filter having a uniform frequency characteristic.

  In the first high-frequency filter manufacturing method, at least one of the first upper electrode and the first lower electrode is made of gold, and at least one of the second upper electrode and the second lower electrode is titanium or The first etchant is preferably an iodine-based etchant, and the second etchant is preferably a hydrofluoric acid-based etchant. With this configuration, the resonance frequency of the first piezoelectric resonator can be adjusted without changing the resonance frequency of the second piezoelectric resonator, and the resonance frequency of the first piezoelectric resonator can be changed. The resonance frequency of the second piezoelectric resonator can be adjusted without causing it to occur.

  In the first high-frequency filter manufacturing method, at least one of the first upper electrode and the first lower electrode is made of platinum, and at least one of the second upper electrode and the second lower electrode is made of gold. Thus, it is preferable that the first etchant is aqua regia and the second etchant is a potassium hydroxide solution. With this configuration, the resonance frequency of the second piezoelectric resonator can be adjusted without changing the resonance frequency of the first piezoelectric resonator.

  The second high-frequency filter manufacturing method includes a first piezoelectric film on a main surface of a substrate, a first upper electrode formed on the upper surface and the lower surface of the first piezoelectric film so as to face each other, and a first A first piezoelectric resonator composed of a lower electrode, a second piezoelectric film, and a second upper electrode and a second lower electrode formed on the upper and lower surfaces of the second piezoelectric film so as to face each other. Holding the second piezoelectric resonator comprising: a first addition on a surface opposite to the surface in contact with the first piezoelectric film in at least one of the first upper electrode and the first lower electrode Forming a film, forming a second additional film on a surface opposite to the surface in contact with the second piezoelectric film in at least one of the second upper electrode and the second lower electrode, The first etchant that can etch one additional film is used for the first Adjusting the resonance frequency of the piezoelectric resonator, and adjusting the resonance frequency of the second piezoelectric resonator using a second etchant capable of etching the second additional film. To do.

  According to the second high-frequency filter manufacturing method, the step of adjusting the resonance frequency of the first piezoelectric resonator using the first etchant that etches the first additional film, and the second additional film are etched. And adjusting the resonance frequency of the second piezoelectric resonator using the second etchant, so that the resonance frequency of the second piezoelectric resonator is not changed without changing the resonance frequency of the first piezoelectric resonator. Can be adjusted. Therefore, it is not necessary to form a complicated mask, and it is possible to easily obtain a high frequency filter having a uniform frequency characteristic.

  In the second high frequency filter manufacturing method, the first additional film is made of silicon nitride, the second additional film is made of silicon oxide, the first etchant is phosphoric acid, and the second etchant is hydrofluoric acid. Preferably there is. With such a configuration, the additional film can be reliably formed. Further, the resonance frequency of the first piezoelectric resonator and the resonance frequency of the second piezoelectric resonator can be adjusted independently of each other without forming a mask.

  According to the high frequency filter and the manufacturing method thereof of the present invention, the resonance frequency of the piezoelectric resonator formed on the substrate is adjusted to different frequencies without complicating the process, thereby realizing a high frequency filter having uniform frequency characteristics. it can.

(First embodiment)
A high frequency filter and a manufacturing method thereof according to a first embodiment of the present invention will be described with reference to the drawings. FIG. 1A shows the basic circuit configuration of the high-frequency filter of this embodiment. As shown in FIG. 1A, the first piezoelectric resonator 11, which is a series element connected between the input / output terminal 21 and the input / output terminal 22, is connected between the output terminal 22 and the ground. A ladder type filter is formed by the second piezoelectric resonator 12 which is a parallel element.

  The resonance frequency of the first piezoelectric resonator 11 that is a series element is adjusted to the highest frequency in the pass band of the high-frequency filter, and the resonance frequency of the second piezoelectric resonator 12 that is a parallel element is that of the pass band of the high-frequency filter. It is necessary to adjust to the lowest frequency. FIG. 1A shows the minimum structural unit of the high-frequency filter in which the first piezoelectric resonator 11 and the second piezoelectric resonator 12 are connected one by one. A plurality of minimum structural units shown in FIG. 1A are connected in series.

  Moreover, as shown in FIG.1 (b), the 1st resonator which is a serial element may be further connected to the terminal. In addition, as shown in FIG. 1C, an inductor 15 may be connected between the second piezoelectric resonator 12 and the ground.

  FIG. 2 shows a cross-sectional configuration of the piezoelectric resonator used in the high-frequency filter according to the first embodiment. As shown in FIG. 2, a piezoelectric film 31 made of aluminum nitride (AlN) is held on a holding substrate 1 made of silicon having two air gaps 1a formed at intervals. A first lower electrode 43 made of the first electrode forming material is formed on an upper portion of one air gap 1a on the lower surface of the piezoelectric film 31, and a second portion is formed on the upper portion of the other air gap 1a. A second lower electrode 44 made of the electrode forming material is formed. A first upper electrode 41 made of the first electrode forming material is formed on a portion of the upper surface of the piezoelectric film 31 facing the first lower electrode 43, and a second portion of the upper surface of the piezoelectric film 31 is opposed to the second lower electrode 44. A second upper electrode 42 made of the electrode forming material is formed.

  The upper part of the air gap 1 a of the piezoelectric film 31 is a cavity part that can vibrate freely, and the first piezoelectric resonator 11 is constituted by the piezoelectric film 31, the first upper electrode 41, and the first lower electrode 43. The second piezoelectric resonator 12 is formed by the piezoelectric film 31, the second upper electrode 42, and the second lower electrode 44. Although not shown, wiring is connected to the first upper electrode 41, the first lower electrode 43, the second upper electrode 42, and the second lower electrode 44, respectively, and FIG. ) Is formed.

  FIG. 2 shows a state in which two piezoelectric resonators are held on the holding substrate 1, but two or more first piezoelectric resonators 11 and second ones are provided on the holding substrate 1, respectively. The piezoelectric resonator 12 may be held. Further, although an example in which the piezoelectric film 31 is common to all the piezoelectric resonators is shown, each may be independent.

  In the high frequency filter of the present embodiment, gold (Au) is used as the first electrode forming material, and titanium (Ti) is used as the second electrode forming material. Au, which is the first electrode forming material, is etched by an iodine-based etching solution, but Ti, which is the second electrode forming material, is hardly etched. Conversely, Ti is etched by a hydrofluoric acid-based etching solution, but Au is hardly etched.

  Therefore, by performing wet etching using an iodine-based etching solution, the first upper electrode 41 and the first lower electrode 43 are not etched without etching the second upper electrode 42 and the second lower electrode 44. It can be etched. Therefore, the resonance frequency of the first piezoelectric resonator 11 can be adjusted without substantially changing the resonance frequency of the second piezoelectric resonator 12. On the other hand, by performing wet etching using a hydrofluoric acid-based etchant, the second upper electrode 42 and the second lower electrode 44 are formed without etching the first upper electrode 41 and the first lower electrode 43. It can be etched. Therefore, the resonance frequency of the second piezoelectric resonator 12 can be adjusted without substantially changing the resonance frequency of the first piezoelectric resonator 11.

  For this reason, the first piezoelectric resonator 11 and the second piezoelectric resonator 12 can be adjusted to have different resonance frequencies without forming a mask, and a high-frequency filter can be easily manufactured. it can.

Note that a mixed solution of iodine (I) and an alkali iodide such as potassium iodide (KI) or ammonium iodide (NH ₄ I) may be used as the iodine-based etching solution. Further, dilute hydrofluoric acid or the like may be used as the hydrofluoric acid-based etching solution.

  Hereinafter, a manufacturing process of a high frequency filter having a band of about 2 GHz will be described as an example of a manufacturing process of the high frequency filter with reference to the drawings. 3 and 4 show the manufacturing process of the high-frequency filter of this embodiment in the order of processes. First, as shown in FIG. 3A, a piezoelectric film 31 made of aluminum nitride having a thickness of 500 nm is formed on a forming substrate 51 made of sapphire or silicon carbide (SiC). Subsequently, a conductive film made of Au having a thickness of 230 nm is formed on the piezoelectric film 31 and then patterned to form the first lower electrode 43. Subsequently, a conductive film made of Ti having a thickness of 600 nm is formed on the piezoelectric film 31 and then patterned to form the second lower electrode 44. Subsequently, the holding substrate 1 made of silicon in which the air gap 1a is formed in advance and the forming substrate 51 on which the piezoelectric film 31 is formed are aligned and then bonded together.

  Next, as shown in FIG. 3B, after the formation substrate 51 is peeled off, a conductive film made of Au having a thickness of 230 nm is formed on the exposed surface of the piezoelectric film 31, and then patterned to form the first The upper electrode 41 is formed.

  Next, as shown in FIG. 3C, a conductive film made of Ti having a thickness of 600 nm is formed and then patterned to form the second upper electrode 42, whereby the first piezoelectric resonator 11 and A second piezoelectric resonator 12 is formed.

  Next, as shown in FIG. 4A, wet etching is performed using a first etchant 61 made of a mixed solution of iodine and potassium iodide while monitoring the resonance frequency, whereby the first piezoelectric resonator is obtained. 11 resonance frequency is adjusted to the highest frequency in the pass band of the high frequency filter.

  Next, as shown in FIG. 4B, wet etching is performed using the second etchant 62 made of dilute hydrofluoric acid while monitoring the resonance frequency, whereby the resonance frequency of the second piezoelectric resonator 12 is increased. Adjust to the lowest frequency in the pass band of the filter. Note that the adjustment order of the resonance frequency may be reversed.

  Furthermore, as necessary, unnecessary portions of the piezoelectric film 31 may be removed by etching as shown in FIG. By doing so, it is possible to prevent the spurious characteristics from deteriorating even when the distance between adjacent piezoelectric resonators is narrow.

  As described above, according to the high frequency filter manufacturing method of the first embodiment, the first piezoelectric resonator 11 and the second piezoelectric resonator 12 have different resonance frequencies without using a mask. Can be adjusted.

  In the present embodiment, the first upper electrode 41 and the first lower electrode 43 are made of Au as the first electrode forming material, and the second upper electrode 42 and the second lower electrode 44 are formed of the second electrode. An example of Ti as a material was shown. However, the first electrode forming material and the second electrode forming material may be materials that are etched by different etchants, for example, a combination of gold (Au) and aluminum (Al). In this case as well, an iodine-based etchant may be used for the first etchant 61 and a hydrofluoric acid-based etchant may be used for the second etchant 62.

  Further, the first electrode material and the second electrode material are interchanged to form the first upper electrode 41 and the first lower electrode 43 with the second electrode material, and the second upper electrode 42 and the second electrode material are formed. The lower electrode 44 may be formed of the first electrode material. Further, the order of adjusting the resonance frequency may be reversed, and the resonance frequency of the first resonator 11 may be adjusted after adjusting the resonance frequency of the second resonator 12.

  Further, the first electrode forming material and the second electrode forming material that are etched together by the first etchant 61 and the first electrode forming material that is not etched by the second etchant 62 may be used in combination. . For example, platinum (Pt) is used as the first electrode forming material, gold (Au) is used as the second electrode forming material, the first etchant 61 is aqua regia, and the second etchant 62 is potassium hydroxide ( KOH) solution.

  In this case, first, the resonance frequency of the first piezoelectric resonator 11 is adjusted using the first etchant 61. Next, the resonance frequency of the second piezoelectric resonator 12 may be adjusted using the second etchant 62. When the resonance frequency of the first piezoelectric resonator 11 is adjusted, the resonance frequency of the second piezoelectric resonator 12 also fluctuates. However, since the resonance frequency of the second piezoelectric resonator 12 is adjusted thereafter, no problem occurs. A sodium hydroxide solution may be used instead of the potassium hydroxide solution.

  In the present embodiment, the first upper electrode 41, the first lower electrode 43, the second upper electrode 42, and the second lower electrode 44 are formed of the same material. In this case, both the upper electrode and the lower electrode are etched when adjusting the resonance frequency. However, if the thickness of one of the upper electrode and the lower electrode can be adjusted, the resonance frequency can be adjusted. Therefore, as shown in FIG. 5, the first lower electrode 43 and the second lower electrode 44 may be formed of the third electrode forming material that is not affected by both the first etchant 61 and the second etchant 62. Good.

  For example, the first lower electrode 43 and the second lower electrode 44 are made of molybdenum (Mo), the first upper electrode 41 is made of gold (Au), and the second upper electrode 42 is made of titanium (Ti). An etchant of iodine type may be used for the etchant 61 and a hydrofluoric acid etchant may be used for the second etchant 62. In this case, since the number of steps for forming the conductive film is three, the manufacturing process can be simplified. Further, the material of the upper electrode and the material of the lower electrode may be reversed.

  Further, only one of the first upper electrode 41, the first lower electrode 43, the second upper electrode 42, and the second lower electrode 44 is formed of a material that is etched by a different etching solution. Even in this case, the resonance frequency of the first piezoelectric resonator 11 and the resonance frequency of the second piezoelectric resonator 12 can be adjusted to different frequencies without using a mask. For example, as shown in FIG. 6, the first upper electrode 41, the first lower electrode 43, and the second lower electrode 44 are formed of a material etched by the first etchant 61, and only the second upper electrode 42 is formed. May be formed of a material etched by the second etchant 62.

  Specifically, the first upper electrode 41, the first lower electrode 43, and the second lower electrode 44 are formed of gold (Au), and the second upper electrode 42 is formed of titanium (Ti). In this case, since the first upper electrode 41, the first lower electrode 43, and the second lower electrode 44 are etched by the iodine-based etchant, the resonance frequency of the first piezoelectric resonator 11 and the second piezoelectric electrode are etched. The resonance frequency of the resonator 12 can be varied. On the other hand, depending on the hydrofluoric acid-based etching solution, only the second upper electrode 42 is etched, so that only the resonance frequency of the second piezoelectric resonator 12 can be varied.

  In the present embodiment, the first upper electrode 41 and the first lower electrode 43 constituting the first piezoelectric resonator 11 are Au, and the second upper electrode constituting the second piezoelectric resonator 12 is used. 42 and the second lower electrode 44 are made of Ti. Since Au is harder and has lower acoustic impedance than Ti, the insertion loss of the first piezoelectric resonator 11 is smaller than that of the second piezoelectric resonator 12.

  The first piezoelectric resonator 11 with a small insertion loss is a series element connected in series between the input / output terminal 21 and the input / output terminal 22, and the second piezoelectric resonator 12 is input / output with the input / output terminal 21. A parallel element connected in parallel with the terminal 22 is preferable because the insertion loss of the entire high-frequency filter can be reduced.

  In the present embodiment, the high frequency filter is a ladder type filter, but the same effect can be obtained with a lattice type high frequency filter as shown in FIG. In this case, the piezoelectric resonator 13 connected between the input / output terminal 23 and the input / output terminal 24 and between the input / output terminal 25 and the input / output terminal 26 has a resonance frequency at the highest passband frequency. The piezoelectric resonator 14 adjusted and connected between the input / output terminal 23 and the input / output terminal 26 and between the input / output terminal 25 and the input / output terminal 24 adjusts the resonance frequency to the lowest frequency in the pass band. .

  In addition, it is better to use a piezoelectric resonator having a smaller insertion loss using an electrode forming material that is harder and has a smaller acoustic impedance for the piezoelectric resonator 13 connected between the input / output terminals having the same polarity. It is preferable because the insertion loss as a whole of the high frequency filter can be reduced.

  In this embodiment, an example in which a piezoelectric film having a cavity portion is formed by bonding a piezoelectric film to a holding substrate in which an air gap is formed has been shown. However, by providing a convex portion on a lower electrode, You may form a cavity part in. In addition to the bonding, the piezoelectric resonator may be formed by a method using a sacrificial layer. Further, instead of an air gap, a piezoelectric resonator having an acoustic multilayer film may be used.

(Second Embodiment)
Hereinafter, a high frequency filter and a method for manufacturing the same according to a second embodiment of the present invention will be described with reference to the drawings. FIG. 8 shows a cross-sectional configuration of a piezoelectric resonator used in the high-frequency filter according to the second embodiment. In FIG. 8, the same components as those in FIG.

  The high-frequency filter of the second embodiment is a ladder type filter similar to that of the first embodiment, and the circuit configuration is the same as that in FIG.

  As shown in FIG. 8, in the present embodiment, the first upper electrode 41, the first lower electrode 43, the second upper electrode 42, and the second lower electrode 44 each have a thickness of 400 nm of molybdenum (Mo). It is formed by. A first additional film 71 made of the first material is formed on the first upper electrode 41, and a second additional film 72 made of the second material is formed on the second upper electrode 42. Has been.

The first material and the second material may be materials etched by different etchants. In this embodiment, the first material is silicon nitride (SiN), and the first additional film is used. The thickness of 71 was 200 nm. Further, silicon oxide (SiO ₂ ) was used as the second material, and the thickness of the second additional film 72 was 200 nm.

The first additional film 71 made of SiN is etched by phosphoric acid, but the second additional film 72 made of SiO ₂ is hardly etched. On the other hand, the second additional film 72 made of SiO ₂ is etched by hydrofluoric acid, but the first additional film 71 made of SiN is hardly etched.

  Therefore, the first additional film 71 is wet-etched using phosphoric acid as the first etchant 61, so that the resonance frequency of the first piezoelectric resonator 11 hardly fluctuates without substantially changing the resonance frequency of the second piezoelectric resonator 12. Can be adjusted to the highest frequency in the passband of the high frequency filter.

  Further, the second additional film 72 is wet-etched using hydrofluoric acid as the second etchant 62, so that the resonance frequency of the second piezoelectric resonator 12 is hardly changed without substantially changing the resonance frequency of the first piezoelectric resonator 11. It can be adjusted to the lowest frequency in the pass band of the high frequency filter. As described above, even when the additional film formed on the electrode, not the electrode itself, is etched, the resonance frequency can be adjusted.

Note that the first additional film 71 may be formed of SiN, and the second additional film 72 may be formed of SiO ₂ by switching the first material and the second material. Further, after adjusting the resonance frequency of the second resonator 12, the resonance frequency of the first resonator 11 may be adjusted.

  Further, the additional film is not limited to the insulating film, and for example, platinum (Pt) may be used as the first material and gold (Au) may be used as the second material. In this case, similarly to the first embodiment, aqua regia may be used as the first etchant 61 and a potassium hydroxide solution may be used as the second etchant 62.

  Moreover, it is good also as a structure where not the upper electrode but a lower electrode has an additional film, or all the electrodes have an additional film. Further, as shown in FIG. 9, one piezoelectric resonator may have an additional film formed on the upper electrode, and the other piezoelectric resonator may have an additional film formed on the lower electrode. Further, one piezoelectric resonator may be configured to adjust the resonance frequency by etching the electrode itself, and the other piezoelectric resonator may be configured to adjust the resonance frequency by etching the additional film.

  Also in the second embodiment, the insertion loss of the entire high-frequency filter is reduced by using a material that is harder and has a lower acoustic impedance for the additional film formed on the electrodes constituting the piezoelectric resonator that is a series element. Can be suppressed.

  The same effect can also be obtained when forming a lattice-type filter as shown in FIG.

  The high-frequency filter and the manufacturing method thereof according to the present invention can realize a high-frequency filter having uniform frequency characteristics by adjusting the resonance frequencies of the piezoelectric resonators formed on the substrate to different frequencies without complicating the process. It has an effect and is useful as a high-frequency filter using a piezoelectric resonator, a manufacturing method thereof, and the like.

(A)-(c) is a circuit diagram which shows the high frequency filter which concerns on the 1st implementation of this invention. It is sectional drawing which shows the piezoelectric resonator used for the high frequency filter which concerns on the 1st Embodiment of this invention. It is sectional drawing which shows the manufacturing method of the piezoelectric resonator used for the high frequency filter which concerns on the 1st Embodiment of this invention in process order. It is sectional drawing which shows the piezoelectric resonator used for the high frequency filter which concerns on the 1st Embodiment of this invention in process order. It is sectional drawing which shows another example of the piezoelectric resonator used for the high frequency filter which concerns on the 1st Embodiment of this invention. It is sectional drawing which shows another example of the piezoelectric resonator used for the high frequency filter which concerns on the 1st Embodiment of this invention. It is a circuit diagram which shows another example of the high frequency filter which concerns on the 1st Embodiment of this invention. It is sectional drawing which shows the piezoelectric resonator used for the high frequency filter which concerns on the 2nd Embodiment of this invention. It is sectional drawing which shows another example of the piezoelectric resonator used for the high frequency filter which concerns on the 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Holding substrate 1a Air gap 11 1st piezoelectric resonator 12 2nd piezoelectric resonator 13 1st resonator 14 2nd resonator 15 Inductor 21 Input / output terminal 22 Input / output terminal 23 Input / output terminal 24 Input / output terminal 25 Input / Output Terminal 26 Input / Output Terminal 31 Piezoelectric Film 41 First Upper Electrode 42 Second Lower Electrode 43 First Lower Electrode 44 Second Lower Electrode 51 Formation Substrate 61 First Etchant 62 Second Etchant 71 First additional film 72 Second additional film

Claims (23)

A substrate,
The first piezoelectric film and the first upper electrode and the first lower electrode formed on the upper surface and the lower surface of the first piezoelectric film, which are held on the main surface of the substrate, respectively, are opposed to each other. A first piezoelectric resonator comprising:
The second piezoelectric film is held on the main surface of the substrate, and the second upper electrode and the second lower electrode formed on the upper surface and the lower surface of the second piezoelectric film, respectively, facing each other. A second piezoelectric resonator having a resonance frequency different from that of the first piezoelectric resonator,
At least one of the first upper electrode and the first lower electrode is made of a first electrode forming material, and at least one of the second upper electrode and the second lower electrode is a second electrode. A high frequency filter comprising an electrode forming material.   2. The radio frequency according to claim 1, wherein the first electrode forming material is etched by a first etchant and has etching resistance to a second etchant that etches the second electrode forming material. filter. The first electrode forming material is platinum,
The high frequency filter according to claim 2, wherein the second electrode forming material is gold.   The high frequency filter according to claim 2, wherein the second electrode forming material has etching resistance with respect to the first etchant. The first electrode forming material is gold;
5. The high frequency filter according to claim 4, wherein the second electrode forming material is titanium or aluminum.   A first additional film made of a first material and formed on at least one of the upper surface of the first upper electrode and the lower surface of the first lower electrode; the upper surface and the second lower portion of the second upper electrode; 2. The high frequency filter according to claim 1, further comprising at least one of a second additional film formed on at least one of the lower surfaces of the electrodes and made of the second material. One of the second upper electrode and the second lower electrode is electrically connected to the first upper electrode or the first lower electrode, and of the second upper electrode and the second lower electrode A basic unit of a ladder type resonator in which the other side is grounded is formed,
The combination of the first electrode forming material and the second electrode forming material is a combination in which the insertion loss of the first piezoelectric resonator is smaller than the insertion loss of the second piezoelectric resonator. The high frequency filter according to claim 1.   8. The high frequency filter according to claim 7, wherein an inductor is electrically connected between the second upper electrode or the second lower electrode and the ground. A first input / output terminal, a second input / output terminal, a third input / output terminal, and a fourth input / output terminal;
The first resonator has two, and one of the two first resonators is electrically connected between the first input / output terminal and the second input / output terminal, The other one of the two first resonators is electrically connected between the third input / output terminal and the fourth input / output terminal,
The number of the second resonators is two, and one of the two second resonators is electrically connected between the first input / output terminal and the fourth input / output terminal, The other of the two second resonators is electrically connected between the third input / output terminal and the second input / output terminal,
The combination of the first electrode forming material and the second electrode forming material is a combination in which the insertion loss of the first piezoelectric resonator is smaller than the insertion loss of the second piezoelectric resonator. The high frequency filter according to claim 1. A substrate,
The first piezoelectric film and the first upper electrode and the first lower electrode formed on the upper surface and the lower surface of the first piezoelectric film, which are held on the main surface of the substrate, respectively, are opposed to each other. A first piezoelectric resonator comprising:
The second piezoelectric film is held on the main surface of the substrate, and the second upper electrode and the second lower electrode formed on the upper surface and the lower surface of the second piezoelectric film, respectively, facing each other. A second piezoelectric resonator having a resonance frequency different from that of the first piezoelectric resonator,
At least one of a first upper electrode additional film formed on the upper surface of the first upper electrode and a first lower electrode additional film formed on the lower surface of the first lower electrode;
At least one of a second upper electrode additional film formed on the upper surface of the second upper electrode and a second lower electrode additional film formed on the lower surface of the second lower electrode;
At least one of the first upper electrode additional film and the first lower electrode additional film is made of a first additional film forming material,
At least one of the second upper electrode additional film and the second lower electrode additional film is made of a second additional film forming material.   The high frequency according to claim 10, wherein the first additional film forming material has etching resistance to a second etchant that is etched by the first etchant and etches the second additional film forming material. filter. The first additional film forming material is platinum,
12. The high frequency filter according to claim 11, wherein the second additional film forming material is gold.   The high-frequency filter according to claim 11, wherein the second additional film forming material has etching resistance to the first etchant. The first additional film forming material is silicon nitride,
The high frequency filter according to claim 13, wherein the second additional film forming material is silicon oxide. The first additional film forming material is gold,
14. The high frequency filter according to claim 13, wherein the second additional film forming material is titanium or aluminum. One of the second upper electrode and the second lower electrode is electrically connected to the first upper electrode or the first lower electrode, and the second upper electrode and the second lower electrode A ladder-type resonator basic unit is formed, the other of which is grounded,
The combination of the first additional film forming material and the second additional film forming material is a combination in which the insertion loss of the first piezoelectric resonator is smaller than the insertion loss of the second piezoelectric resonator. The high-frequency filter according to claim 10.   The high frequency filter according to claim 16, wherein an inductor is electrically connected between the second upper electrode or the second lower electrode and the ground. A first input / output terminal, a second input / output terminal, a third input / output terminal, and a fourth input / output terminal;
The first resonator has two, and one of the two first resonators is electrically connected between the first input / output terminal and the second input / output terminal, The other of the two first resonators is electrically connected between the third input / output terminal and the fourth input / output terminal,
The number of the second resonators is two, and one of the two second resonators is electrically connected between the first input / output terminal and the fourth input / output terminal, The other of the two second resonators is electrically connected between the third input / output terminal and the second input / output terminal,
The combination of the first additional film forming material and the second additional film forming material is a combination in which the insertion loss of the first piezoelectric resonator is smaller than the insertion loss of the second piezoelectric resonator. The high-frequency filter according to claim 10. A first piezoelectric resonance comprising a first piezoelectric film and a first upper electrode and a first lower electrode formed on the main surface of the substrate so as to face the upper and lower surfaces of the first piezoelectric film. And a second piezoelectric resonator comprising a second piezoelectric film and a second upper electrode and a second lower electrode formed on the upper and lower surfaces of the second piezoelectric film so as to face each other. Holding, and
Adjusting a resonance frequency of the first piezoelectric resonator using a first etchant capable of etching at least one of the first upper electrode and the first lower electrode;
Adjusting a resonance frequency of the second piezoelectric resonator using a second etchant capable of etching at least one of the second upper electrode and the second lower electrode. A method for manufacturing a high-frequency filter.   At least one of the first upper electrode and the first lower electrode is made of gold, at least one of the second upper electrode and the second lower electrode is made of titanium or aluminum, and the first 20. The method of manufacturing a high frequency filter according to claim 19, wherein the etchant is an iodine-based etchant, and the second etchant is a hydrofluoric acid-based etchant.   At least one of the first upper electrode and the first lower electrode is made of platinum, at least one of the second upper electrode and the second lower electrode is made of gold, and the first etchant is 20. The method of manufacturing a high frequency filter according to claim 19, wherein the method is aqua regia, and the second etchant is a potassium hydroxide solution. A first piezoelectric resonance comprising a first piezoelectric film and a first upper electrode and a first lower electrode formed on the main surface of the substrate so as to face the upper and lower surfaces of the first piezoelectric film. And a second piezoelectric resonator comprising a second piezoelectric film and a second upper electrode and a second lower electrode formed on the upper and lower surfaces of the second piezoelectric film so as to face each other. And a process of
Forming a first additional film on a surface opposite to the surface in contact with the first piezoelectric film in at least one of the first upper electrode and the first lower electrode;
Forming a second additional film on a surface opposite to the surface in contact with the second piezoelectric film in at least one of the second upper electrode and the second lower electrode;
Adjusting a resonance frequency of the first piezoelectric resonator using a first etchant capable of etching the first additional film;
And a step of adjusting a resonance frequency of the second piezoelectric resonator using a second etchant capable of etching the second additional film. The first additional film is made of silicon nitride,
The second additional film is made of silicon oxide,
The first etchant is phosphoric acid;
23. The method of manufacturing a high frequency filter according to claim 22, wherein the second etchant is hydrofluoric acid.

Images