JP4730126B2 - Bulk acoustic wave resonance element, manufacturing method thereof, and filter circuit - Google Patents

Description

  The present invention relates to a bulk acoustic wave resonator element that can further improve element characteristics and a method for manufacturing the same. The present invention also relates to a filter circuit using this bulk acoustic wave resonant element.

  For example, a bulk acoustic wave (hereinafter abbreviated as “BAW resonant element”) resonant element is known as an element applicable as a high frequency filter, a high frequency oscillator, or the like. The BAW resonant element includes a substrate, a first electrode formed on the substrate, a piezoelectric thin film formed on the first electrode, and a second electrode formed on the piezoelectric thin film. For example, it is disclosed in Patent Document 1. The first electrode in the piezoelectric thin film element disclosed in Patent Document 1 is formed by laminating a base film, an adhesion layer, and a lower electrode from the substrate toward the piezoelectric thin film. Further, at the end of paragraph [0021] of Patent Document 1, it is described that “an additional electrode thin film may be provided between the adhesion layer 3 and the lower electrode 4 as necessary”.

Further, as shown in Patent Document 2, aluminum nitride (AlN), zinc oxide (ZnO), or the like is used for a piezoelectric thin film in a conventional BAW resonant element. For this reason, there is a problem that the pass band is narrow and cannot be used for UWB (Ultra WideBand) communication or the like. In this case, such a problem can be addressed by using lead zirconate titanate having a high mechanical coupling coefficient for the piezoelectric thin film.
JP 2001-250995 A JP 2005-295250 A

  By the way, in the piezoelectric thin film element described in Patent Document 1, when lead zirconate titanate (hereinafter abbreviated as “PZT”) is used for the piezoelectric body, the (111) orientation of the PZT film is insufficient. There was a problem of being.

  [0021] The paragraph [0021] of Patent Document 1 has the above description, but there is no description about the effect of the electrode thin film and the material of the electrode thin film. There is no.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a bulk acoustic wave resonant element that can improve the (111) orientation of a PZT film and further improve element characteristics.

As a result of various studies, the present inventor has found that the above object is achieved by the present invention described below. That is, in one aspect according to the present invention, the bulk acoustic wave resonance element is mainly composed of a substrate, a first electrode formed on the substrate, and lead zirconate titanate formed on the first electrode. And a second electrode formed on the piezoelectric film. The first electrode includes a first adhesion layer mainly composed of titanium or chromium , iridium (Ir), and iridium oxide (IrO). ₂ ), a main conductive layer mainly composed of any one of rubidium (Ru), rubidium oxide (RuO), lanthanum nickel oxide (LaNiO ₃ ), yttrium barium copper oxide (YBCO), and strontium ruthenium oxide (SrRuO ₃ ). the second adhesion layer composed mainly of titanium or chromium, that sub conductive layer made of platinum as a main component are laminated toward from the substrate to the piezoelectric film And butterflies.

  In the bulk acoustic wave resonance element described above, an acoustic mirror layer is further formed between the substrate and the first electrode.

  Further, in the above-described bulk acoustic wave resonance elements, an opening reaching the first electrode is formed in the substrate.

In another aspect of the present invention, a substrate, a first electrode formed on the substrate, a piezoelectric film mainly composed of lead zirconate titanate formed on the first electrode, In the method of manufacturing a bulk acoustic wave resonator including the second electrode formed on the piezoelectric film, the step of forming the first electrode includes a step of forming titanium or chromium as a main component on the substrate. A step of forming one adhesion layer, and iridium (Ir), iridium oxide (IrO ₂ ), rubidium (Ru), rubidium oxide (RuO), lanthanum nickel oxide (LaNiO ₃ ), yttrium barium oxide on the first adhesion layer copper (YBCO) and forming a main conductive layer composed mainly of any one of strontium ruthenium oxide (SrRuO _3), titanium or chromium on the main conductive layer Forming a second contact layer composed as a main component, characterized in that it comprises a step of forming a sub conductive layer composed as a main component platinum to the second contact layer.

  Furthermore, in another aspect of the present invention, the filter circuit includes a pair of input terminals, two bulk acoustic wave resonance elements connected in series connected between the pair of input terminals, and one of the two filter circuits. And a pair of output terminals connected to one of the pair of input terminals, and the bulk acoustic wave resonant element includes the bulk acoustic wave resonant element described above. It is any one of these. A plurality of the filter circuits may be connected in cascade.

  In such a BAW resonant element and a method for manufacturing the BAW resonant element, the (111) orientation of the PZT film is improved, and the element characteristics can be further improved. Since such a filter circuit uses a BAW resonant element having good element characteristics, the filter characteristics can be improved.

  Embodiments according to the present invention will be described below with reference to the drawings. In addition, the structure which attached | subjected the same code | symbol in each figure shows that it is the same structure, The description is abbreviate | omitted.

  The BAW resonant element of the present embodiment is an element in which a piezoelectric film mainly composed of PZT is formed between a pair of electrodes facing each other, and is an element using the bulk vibration of the piezoelectric film.

  FIG. 1 is a schematic diagram illustrating a cross-sectional structure of a BAW resonant element according to an embodiment. In FIG. 1, the BAW resonant element 1 is formed on a substrate 11, an acoustic mirror layer 12 formed on the substrate 11, a first electrode 13 formed on the acoustic mirror layer 12, and a first electrode 13. The piezoelectric thin film 14 mainly composed of PZT and the second electrode 15 formed on the piezoelectric thin film 14 are configured.

The substrate 11 is a plate-like member made of a semiconductor material such as silicon (Si). The acoustic mirror layer 12 is a layer that reflects acoustic vibrations, particularly ultrasonic waves, and is composed of a multilayer film in which materials with high acoustic impedance and materials with low acoustic impedance are alternately stacked. An example of a material with low acoustic impedance is silicon dioxide (SiO ₂ ). Examples of the material having high acoustic impedance include zinc oxide (ZnO), tungsten (W), tantalum acid (Ta ₂ O ₅ ), and iridium (Ir). A combination of any of these and the above silicon dioxide can be used for the acoustic mirror layer 12.

  The first electrode 13 includes a first adhesion layer 131 formed on the acoustic mirror layer 12, a main conductive layer 132 formed on the first adhesion layer 131, and a second adhesion formed on the main conductive layer 132. The vibrating electrode thin film of the piezoelectric thin film 14 includes the layer 133 and the sub-conductive layer 134 formed on the second adhesion layer 133. That is, the first adhesion layer 131, the main conductive layer 132, the second adhesion layer 133, and the sub conductive layer 134 are sequentially laminated from the substrate 11 toward the piezoelectric thin film 14.

  The first adhesion layer 131 is a thin film that reduces the stress between the acoustic mirror layer 12 and the main conductive layer 132 and improves the adhesion between the acoustic mirror layer 12 and the main conductive layer 132. The main component is titanium (Ti) having good adhesion to the main conductive layer 132. The main conductive layer 132 is a thin film for obtaining high conductive characteristics. The main conductive layer 132 is, for example, a thin film mainly composed of iridium (Ir). If the film thickness is less than 10 nm, it is difficult to uniformly generate PZT. The film thickness is preferably 10 nm or more and 100 nm or less because it decreases. The second adhesion layer 133 is a thin film that reduces the stress between the main conductive layer 132 and the sub conductive layer 134 and improves the adhesion between the main conductive layer 132 and the sub conductive layer 134. The main component is titanium having good adhesion to the sub-conductive layer 134. The sub conductive layer 134 is a thin film for growing PZT. For example, the sub-conductive layer 134 is a thin film containing platinum (Pt) as a main component. When the film thickness is less than 20 nm, the conductivity is lowered. Therefore, the film thickness is preferably 20 nm or more and 100 nm or less. Here, when the piezoelectric thin film 14 is formed by the sol-gel method, the first and second adhesion layers 131 and 133 reduce occurrence of cracks in the firing process.

In addition to the above, the first and second adhesion layers 131 and 133 may be formed using chromium (Cr) as a main component. The main conductive layer 132 is any of iridium oxide (IrO ₂ ), rubidium (Ru), rubidium oxide (RuO), lanthanum nickel oxide (LaNiO ₃ ), yttrium barium copper oxide (YBCO), and strontium ruthenium oxide (SrRuO ₃ ). You may form one as a main component.

The piezoelectric thin film 14 is a thin film mainly composed of PZT, which is a piezoelectric material that generates a piezoelectric phenomenon, and bulk vibration is generated when a predetermined electrical signal is applied to the first and second electrodes. The second electrode 15, for applying an electrical signal to the piezoelectric thin film 14 becomes the first electrode 13 and the pair, for example, gold (Au), aluminum (Al), iridium (Ir), iridium oxide (IrO ₂ ) And a conductive metal material (including an alloy) such as rubidium (Ru) as a main component. The second electrode 15 may be further provided with an adhesive layer of titanium or chromium, for example, between the piezoelectric thin film 14 in order to improve adhesion with the piezoelectric thin film 14.

  The BAW resonant element having such a structure is formed by, for example, the following steps.

  First, the acoustic mirror layer 12 was formed on the silicon single crystal substrate 11 by sputtering. The acoustic mirror layer 12 is made of a combination of low acoustic impedance silicon dioxide and high acoustic impedance zinc oxide or tungsten, and has a film thickness of about 2 μm. Silicon dioxide and zinc oxide use argon (Ar) gas and oxygen as the reaction gas, and the substrate temperature is set to about 200 to 300 ° C., and tungsten uses argon gas as the reaction gas and the substrate. Film formation was performed at a temperature of about 200 to 300 ° C.

  Next, a first adhesion layer 131 made of titanium having a thickness of about 5 to 10 nm was formed on the acoustic mirror layer 12 by a high-frequency magnetron sputtering method. The distance between the substrate 11 and the target is set to about 6 to 12 cm, 100% argon gas is used as the sputtering gas, the argon gas flow rate is about 30 to 50 sccm, the pressure is about 5 to 10 mTorr, and the deposition power Was about 300-500 W and deposited at room temperature.

  Next, a main conductive layer 132 made of iridium having a thickness of about 20 to 80 nm was formed on the first adhesion layer 131 by high frequency magnetron sputtering. The distance between the substrate 11 and the target is set to about 6 to 12 cm, 100% argon gas is used as the sputtering gas, the argon gas flow rate is about 30 to 50 sccm, the pressure is about 5 to 10 mTorr, and the deposition power Was about 100-300 W and deposited at room temperature.

  Next, a second adhesion layer 133 made of titanium having a thickness of about 5 to 10 nm was formed on the main conductive layer 132 by high frequency magnetron sputtering under the same conditions as the first adhesion layer 131.

  Next, a sub-conductive layer 134 made of platinum having a thickness of about 20 to 50 nm was formed on the second adhesion layer 133 by high frequency magnetron sputtering. The distance between the substrate 11 and the target is set to about 6 to 12 cm, argon (Ar) gas 100% is used as the sputtering gas, the argon gas flow rate is about 30 to 50 sccm, the pressure is about 1 to 5 mTorr, The film formation power was about 300 W, and the film was formed at room temperature.

  The first electrode 13 was formed by such steps.

  Next, the piezoelectric thin film 14 made of PZT was formed on the first electrode 13 (sub conductive layer 134) by sol-gel method, CVD or MOCVD, and the second electrode 15 was formed by high frequency magnetron sputtering.

  Through these steps, the BAW resonant element having the structure shown in FIG. 1 is formed.

  In addition, in the said process, each layer can be made into a desired shape by performing a chemical or physical process in a required step.

  In the BAW resonant element 1 having such a configuration, when a predetermined electrical signal is applied to the first electrode 13 and the second electrode 15, the piezoelectric thin film 14 undergoes bulk vibration and resonates. Therefore, the BAW resonant element 1 can be applied to a resonator, a filter, and an oscillator. Further, ultrasonic waves generated by this resonance are reflected by the acoustic mirror layer 12. For this reason, since this ultrasonic wave is suppressed from escaping to the substrate 11, that is, the loss is reduced, the efficiency is further improved.

  Since the first electrode 13 has a four-layer structure of the first adhesion layer 131, the main conductive layer 132, the second adhesion layer 133, and the sub-conductive layer 134, the (111) orientation of the PZT of the piezoelectric thin film 14 is improved. To do. For example, when the first electrode 13 has a laminated structure of a Ti adhesion layer / Ir main conductive layer / Pt electrode layer, the (111) orientation of PZT is about 50% according to the X-ray diffraction method. However, in this embodiment, according to the X-ray diffraction method, the (111) orientation of PZT is about 90%, which is remarkably improved. In addition, the adhesion of the first electrode 13 to the acoustic mirror layer 12 is also improved. For this reason, the piezoelectric thin film 14 of PZT is densely formed with high crystallinity, and the element characteristics of the BAW resonant element are further improved. Even when the acoustic mirror layer 12 is not provided and the first electrode 13 is formed on the substrate 11, the (111) orientation of the PZT of the piezoelectric thin film 14 is improved.

  FIG. 2 is a schematic diagram showing a cross-sectional structure of a BAW resonant element according to a modified embodiment. Here, in the above-described embodiment, in the region of the piezoelectric thin film 14 sandwiched between the first and second electrodes 13 and 15, as shown in FIG. In the case where is a silicon substrate, the opening 11 may be provided by removing the substrate 11 immediately below by anisotropic etching of silicon.

  The region of the piezoelectric thin film 14 sandwiched between the first and second electrodes 13 and 15 is a vibration region that undergoes bulk vibration. By providing such an opening 18, the first and second piezoelectric thin films 14 have a first vibration region. The region sandwiched between the second electrodes 13 and 15 has a floating structure, and the bulk vibration of the piezoelectric thin film 14 is not inhibited by the substrate 11 (acoustic mirror layer 12), and the bulk vibration of the piezoelectric thin film 14 becomes easy. . As a result, the element characteristics of the BWA resonant element 1 'can be further improved.

  A filter circuit can be configured using the BAW resonant elements 1, 1 ′ having such a structure. FIG. 3 is a circuit diagram showing the configuration of the filter circuit. 3A shows the configuration of a one-stage filter circuit, and FIG. 3B shows the configuration of a three-stage filter circuit.

  3A, the filter circuit 2 includes a pair of input terminals Tina and Tinb, two BAW resonant elements 21 and 22, and a pair of output terminals Touta and Toutb.

  The two BAW resonant elements 21 and 22 are the BAW resonant elements 1 and 1 'shown in FIGS. 1 and 2, and are connected in series. The two BAW resonant elements 21 and 22 connected in series are connected between the pair of input terminals Tina and Tinb. One of the pair of output terminals Touta and Toutb, for example, the output terminal Touta is connected to a connection portion a to which the BAW resonance element 21 and the BAW resonance element 22 are connected, and the other of the pair of output terminals Touta and Toutb. The output terminal Toutb is connected to the input terminal Tinb.

  Further, a filter circuit may be configured by connecting a plurality of filter circuits 2 having such a configuration in cascade. As an example, FIG. 3B illustrates a filter circuit 3 in which three filter circuits 2 are connected in cascade. The filter circuit 3 includes three filter circuits 2-1, 2-2, and 2-3. These three filter circuits 2-1; 2-2; 2-3 have a pair of input terminals Tina-1, Tinb-1; Tina-2, Tinb-2; Tina-3, Tinb-3, Two BAW resonant elements 21-1, 22-1; 21-2, 22-2; 21-3, 22-3 and a pair of output terminals Touta-1, Toutb-1; Touta-2, Toutb-2 ; Touta-3 and Toutb-3, which are configured in the same manner as in FIG. The pair of output terminals Touta-1 and Toutb-1 in the filter circuit 2-1 are respectively connected to the pair of input terminals Tina-2 and Tinb-2 in the filter circuit 2-2, and the pair of output terminals Tona-1 and Tinb-2 in the filter circuit 2-2. The output terminal Touta-2 and Toutb-2 are connected to the pair of input terminals Tina-3 and Tinb-3 in the filter circuit 2-3, respectively, thereby configuring the filter circuit 3.

  In the filter circuits 2 and 3 having such a configuration, since the BAW resonant elements 1 and 1 'having good element characteristics are used, the filter characteristics can be improved.

It is a schematic diagram which shows the cross-sectional structure of the BAW resonant element which concerns on embodiment. It is a schematic diagram which shows the cross-section of the BAW resonant element which concerns on a deformation | transformation form. It is a circuit diagram which shows the structure of a filter circuit.

1, 1 ′, 21, 22 Bulk acoustic wave resonance element 2, 3 Filter circuit 11 Substrate 12 Acoustic mirror layer 13 First electrode 14 Piezoelectric thin film 15 Second electrode 18 Opening 131 First adhesion layer 132 Main conductive layer 133 2 Adhesion layer 134 Sub-conductive layer Tina, Tinb Input terminal ToutaToutb Output terminal

Claims (6)

A substrate,
A first electrode formed on the substrate;
A piezoelectric film mainly composed of lead zirconate titanate formed on the first electrode;
A second electrode formed on the piezoelectric film,
The first electrode includes a first adhesion layer mainly composed of titanium or chromium , iridium (Ir), iridium oxide (IrO ₂ ), rubidium (Ru), rubidium oxide (RuO), lanthanum nickel oxide (LaNiO ₃ ), A main conductive layer mainly composed of one of yttrium barium copper oxide (YBCO) and strontium ruthenium oxide (SrRuO ₃ ), a second adhesion layer mainly composed of titanium or chromium, and a sub-conductivity composed mainly of platinum. A bulk acoustic wave resonance element comprising: a layer laminated from the substrate toward the piezoelectric film. Bulk acoustic wave resonator according to claim 1, characterized in Rukoto acoustic mirror layer has been further formed between the substrate and the first electrode. The bulk acoustic wave resonance element according to claim 1, wherein an opening reaching the first electrode is formed in the substrate. A substrate; a first electrode formed on the substrate; a piezoelectric film mainly composed of lead zirconate titanate formed on the first electrode; and a second film formed on the piezoelectric film. In a method of manufacturing a bulk acoustic wave resonant element comprising an electrode,
The step of forming the first electrode includes:
Forming a first adhesion layer mainly composed of titanium or chromium on the substrate;
On the first adhesion layer, iridium (Ir), iridium oxide (IrO ₂ ), rubidium (Ru), rubidium oxide (RuO), lanthanum nickel oxide (LaNiO ₃ ), yttrium barium copper oxide (YBCO), and strontium ruthenium oxide ( Forming a main conductive layer containing as a main component any one of SrRuO ₃ );
Forming a second adhesion layer mainly composed of titanium or chromium on the main conductive layer;
Forming a sub-conductive layer mainly composed of platinum on the second adhesion layer.
A method for manufacturing a bulk acoustic wave resonance element . A pair of input terminals;
Two bulk acoustic wave resonant elements connected in series connected between the pair of input terminals;
One is connected between the two bulk acoustic wave resonance elements, the other comprises a pair of output terminals connected to one of the pair of input terminals,
The bulk acoustic wave resonator is the bulk acoustic wave resonator according to any one of claims 1 to 3.
A filter circuit characterized by the above . Filter circuit filter circuit is characterized in that it is connected to the plurality cascade according to claim 5.

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