KR20180001426A - Bulk acoustic wave resonator and filter including the same - Google Patents

Abstract

The present invention relates to a volume acoustic resonator having excellent electric resistance and acoustic impedance characteristics and improved process efficiency compared to existing electrodes, and a filter including the same. The volume acoustic resonator according to an embodiment of the present invention comprises: a substrate; a first electrode and a second electrode formed on the substrate; and a piezoelectric layer provided between the first electrode and the second electrode, wherein either or both the first electrode or/and the second electrode comprises a molybdenum-tungsten alloy, and the weight ratio of molybdenum to tungsten in the molybdenum-tungsten alloy is 3 : 1 to 1 : 3.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a volume acoustic resonator and a filter including the same,

The present invention relates to a volume acoustic resonator and a filter including the same.

2. Description of the Related Art Demand for small and lightweight filters, oscillators, resonant elements, and acoustic resonant mass sensors used in such devices has been rapidly increasing due to recent rapid development of mobile communication devices, Is also increasing.

A thin film bulk acoustic resonator (hereinafter referred to as "FBAR") is known as a means for realizing such a compact lightweight filter, an oscillator, a resonant element, and an acoustic resonance mass sensor. FBARs can be mass-produced at a minimum cost and can be implemented in a very small size. In addition, it is possible to implement a high quality factor (Q) value, which is a major characteristic of a filter, and can be used in a microwave frequency band. Particularly, a PCS (Personal Communication System) and a DCS (Digital Cordless System) There is an advantage that it can be.

2. Description of the Related Art Generally, an FBAR has a structure including a resonator formed by sequentially stacking a first electrode, a piezoelectric layer, and a second electrode on a substrate.

The principle of operation of the FBAR is as follows. First, electric energy is applied to the first and second electrodes to induce an electric field in the piezoelectric layer. This electric field induces a piezoelectric phenomenon of the piezoelectric layer so that the resonator part vibrates in a predetermined direction. As a result, a bulk acoustic wave is generated in the same direction as the vibration direction, causing resonance.

It is an object of the present invention to provide a bulk acoustic resonator having an electrode having excellent electrical resistance and acoustic impedance characteristics and further improved process efficiency as compared with a conventional electrode.

According to an aspect of the present invention, there is provided a volume acoustic resonator comprising: a substrate; a first electrode and a second electrode formed on the substrate; Wherein at least one of the first electrode and the second electrode comprises a molybdenum-tungsten alloy, and the molybdenum-tungsten alloy comprises molybdenum and tungsten in the molybdenum-tungsten alloy. The ratio is between 3: 1 and 1: 3.

In one embodiment, the ratio of molybdenum to tungsten in the molybdenum-tungsten alloy may range from 3: 1 to 1: 1.

In one embodiment, the molybdenum-tungsten alloy may be oriented in a (110) crystal plane.

In one embodiment, the piezoelectric layer may be aluminum nitride.

In one embodiment, the piezoelectric layer may comprise a rare earth metal or a transition metal.

In one embodiment, a seed layer may be formed between at least one of the first and second electrodes and the substrate.

In one embodiment, the seed layer may comprise at least one of Ti and TiW.

According to another aspect of the present invention,

At least one of the plurality of volume acoustic resonators includes a substrate, a first electrode and a second electrode formed on the substrate, and a second electrode formed between the first electrode and the second electrode, Wherein at least one of the first electrode and the second electrode comprises a molybdenum-tungsten alloy, and the ratio of molybdenum to tungsten in the molybdenum-tungsten alloy is 3: 1 to 1: 3 Filter.

In one embodiment, the ratio of molybdenum to tungsten in the molybdenum-tungsten alloy may range from 3: 1 to 1: 1.

In one embodiment, the molybdenum-tungsten alloy may be oriented in a (110) crystal plane.

In one embodiment, the piezoelectric layer may be aluminum nitride.

In one embodiment, the piezoelectric layer may comprise a rare earth metal or a transition metal.

In one embodiment, the plurality of volume acoustic resonators may be a ladder type or a lattice type.

In the case of the bulk acoustic resonator according to an embodiment of the present invention, the electrical resistance and the acoustic impedance characteristics are excellent, and the process efficiency can be improved.

1 is a cross-sectional view illustrating an acoustic resonator according to an embodiment of the present invention.
2 is a schematic view showing the orientation of an aluminum nitride (0002) crystal face and a molybdenum (110) crystal face.
FIGS. 3 and 4 are XRD analysis results for examining the orientation of the molybdenum-tungsten alloy.
5 is a graph showing changes in electrical characteristics and acoustic impedance characteristics depending on the ratio of molybdenum and tungsten.
FIG. 6 shows calculation of acoustic impedance / surface resistance according to the ratio of molybdenum to tungsten.
7 is a graph showing changes in Qp characteristics depending on the ratio of molybdenum and tungsten.
8 is a cross-sectional view showing a volume acoustic resonator according to another embodiment of the present invention.
9 and 10 are schematic circuit diagrams of a filter according to one embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described with reference to specific embodiments and the accompanying drawings. However, the embodiments of the present invention can be modified into various other forms, and the scope of the present invention is not limited to the embodiments described below. Further, the embodiments of the present invention are provided for a more complete description of the present invention to the ordinary artisan. Accordingly, the shapes and sizes of the elements in the drawings may be exaggerated for clarity of description, and the elements denoted by the same reference numerals in the drawings are the same elements.

It is to be understood that, although the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, Will be described using the symbols. Further, throughout the specification, when an element is referred to as "including" an element, it means that the element may include other elements as well, without departing from the other elements unless specifically stated otherwise.

1 is a cross-sectional view illustrating an acoustic resonator according to an embodiment of the present invention.

Referring to FIG. 1, the acoustic resonator 100 of the present invention may be a thin film bulk acoustic resonator (FBAR), and may include a substrate 110, an insulating layer 120, an air cavity 112 and a resonant portion 135. [

The substrate 110 may be formed of a silicon substrate and an insulating layer 120 may be provided on the upper surface of the substrate 110 to electrically isolate the substrate 110 from the resonator 135. In this case, the insulating layer 120 is silicon dioxide (SiO _2), silicon nitride (Si ₃ N _4), aluminum oxide (Al ₂ O _2), and aluminum nitride (AlN) at least one of a chemical vapor deposition (Chemical of (RF Magnetron Sputtering), and Evaporation (vapor deposition), RF magnetron sputtering, and Evaporation.

The air cavity 112 may be formed on the substrate 110 and may be positioned below the resonator 135 such that the resonator 135 vibrates in a predetermined direction. The air cavity 112 is formed by forming an air cavity sacrificial layer pattern on the insulating layer 120 and then forming a membrane 130 on the air cavity sacrificial layer pattern and etching the air cavity sacrificial layer pattern by etching . In this case, the membrane 130 may function as a protective oxide layer or as a protective layer for protecting the substrate 110. Although not shown in FIG. 1, a seed layer made of aluminum nitride (AlN) may be formed on the membrane 130, or a metal having an HCP structure, particularly a Ti or Ti alloy metal. Specifically, a seed layer may be disposed between the membrane 130 and the first electrode 140.

The resonator unit 135 includes a first electrode 140, a piezoelectric layer 150, and a second electrode 160 that are sequentially stacked on top of the air cavity 112. In this case, the first electrode 140 is formed on the upper surface of the membrane 130 so as to cover a part of the membrane 130. The piezoelectric layer 150 is formed on the upper surface of the membrane 130 and the first electrode 140 to cover a portion of the membrane 130 and a portion of the first electrode 140. The piezoelectric layer 150 is formed of aluminum nitride (AlN), zinc oxide (ZnO), lead zirconium titanium oxide (PZT), or the like, which causes a piezoelectric effect to convert electrical energy into mechanical energy in the form of elastic waves. The second electrode 160 is formed on the piezoelectric layer 150. In addition, when the piezoelectric layer 150 is formed of aluminum nitride (AlN), the piezoelectric layer 150 may further include a rare earth metal or a transition metal. As an example, the rare earth metal may include at least one of scandium (Sc), erbium (Er), yttrium (Y), and lanthanum (La). The transition metal may include at least one of hafnium (Hf), titanium (Ti), zirconium (Zr), and magnesium (Mg).

1, the resonance part 135 is divided into an active area and a non-active area. The active region of the resonance unit 135 is formed by applying electric energy such as an RF (Radio Frequency) signal to the first and second electrodes 140 and 160 to generate electric field in the piezoelectric layer 150, The first electrode 140, the piezoelectric layer 150, and the second electrode 160 are all overlapped in the vertical direction in the upper portion of the air cavity 112. In this case, The inactive region of the resonance portion 135 corresponds to a region outside the active region that is not resonated by the piezoelectric phenomenon even if the first and second electrodes 140 and 160 are applied with electrical energy.

The resonator unit 135 configured as described above can filter a radio signal having a specific frequency by using the piezoelectric effect of the piezoelectric layer 150 described above.

More specifically, the resonator 135 resonates the piezoelectric layer 150 according to an RF signal applied to the first electrode 140 and the second electrode 160 to generate an acoustic wave having a specific resonance frequency and an anti- Wave can be generated. The resonance phenomenon of the piezoelectric layer 150 occurs when 1/2 of the wavelength of the applied RF signal coincides with the thickness of the piezoelectric layer 150. Since the electrical impedance rapidly changes when a resonance phenomenon occurs, The acoustic resonator according to the example can be used as a filter for selecting a frequency. Specifically, since the resonance unit 135 has a constant resonance frequency according to the vibration generated in the piezoelectric layer 150, only a signal that matches the resonance frequency of the resonance unit 135 among the input RF signals is output.

The passivation layer 170 may be disposed on the second electrode 160 of the resonator 135 to prevent the second electrode layer 160 from being exposed to the outside and oxidized, 140 and the second electrode 160 may be formed with an electrode pad 180 for applying an electrical signal.

In this embodiment, at least one of the first electrode 140 and the second electrode 160 includes a molybdenum-tungsten alloy, and the ratio of molybdenum to tungsten in the molybdenum-tungsten alloy is 3: 1 to 1: 3 Is satisfied. The inventors of the present invention have found that when the molybdenum-tungsten alloy is used in a ratio of 3: 1 to 1: 3 as the material of the first and second electrodes 140 and 160, the electric resistance and the acoustic impedance characteristic are improved, Furthermore, process efficiency has also improved. Here, the ratio of molybdenum to tungsten is based on% by weight. When the acoustic impedance of the electrodes 140 and 160 in the acoustic resonator 100 increases, the Kt2 and attenuation characteristics of the resonator can be improved.

Specifically, the present inventors have found that when molybdenum-tungsten alloy is used, the acoustic impedance is improved as compared with molybdenum which is commonly used as an electrode material. This increase in acoustic impedance is understood to be due to the effect of tungsten. However, when tungsten is increased to a certain level or more, it is difficult to form an electrode structure due to high difficulty in the deposition or patterning process. Considering these factors together, the weight ratio of molybdenum and tungsten suitable for the electrode material in the electrical characteristic, the acoustic characteristic, and the process characteristic is derived from 3: 1 to 1: 3 as described above. In addition, since the molybdenum-tungsten alloy has a low thermal expansion coefficient compared to pure molybdenum, the TCF (rate of change of temperature due to temperature protection) characteristics can be improved when applied to an FBAR.

Referring to FIG. 2, aluminum nitride (AlN) corresponding to the piezoelectric layer may have a hexagonal close packing (HCP) structure. In this case, a BCC (Body-Centered Cubic) structure It is necessary to make the crystal orientation of molybdenum (Mo) having a (110) crystal face. Under these crystal orientation conditions, the lattice mismatch between aluminum nitride and molybdenum is the least. The present inventors have made a molybdenum-tungsten alloy by the sputtering method and confirmed that it has the same crystal plane as that of pure molybdenum. The molybdenum-tungsten alloy is formed, but has a body-centered cubic (BCC) structure such as molybdenum.

FIGS. 3 and 4 are XRD analysis results for examining the orientation of the molybdenum-tungsten alloy produced by the present inventors. In the case of FIG. 3, molybdenum and tungsten were deposited at a thickness of 2000 Å in a ratio of 75:25, that is, 3: 1. The deposition conditions for each sample are shown in Table 1 below.

Sample number Molybdenum: tungsten Sheet resistance
(ohm / sq) Deposition conditions # 1-1 3: 1 0.669 Deposition on a Si wafer to a thickness of 2000 angstroms # 2-1 3: 1 0.623 Deposition on a Si wafer / Ti seed layer (500 ANGSTROM) at a thickness of 2000 ANGSTROM # 3-1 3: 1 0.634 Deposition on a Si wafer / TiW seed layer (500 ANGSTROM) at a thickness of 2000 ANGSTROM

In the case of FIG. 4, the ratio of molybdenum to tungsten was 50: 50, that is, 1: 1. The deposition conditions for each sample are shown in Table 2 below.

Sample number Molybdenum: tungsten Sheet resistance
(ohm / sq) Deposition conditions # 1-2 1: 1 0.81 Deposition on a Si wafer to a thickness of 2000 angstroms # 2-2 1: 1 0.78 Deposition on a Si wafer / Ti seed layer (500 ANGSTROM) at a thickness of 2000 ANGSTROM # 3-2 1: 1 0.789 Deposition on a Si wafer / TiW seed layer (500 ANGSTROM) at a thickness of 2000 ANGSTROM

Referring to the results of the XRD analysis of FIGS. 3 and 4, it can be confirmed that the crystal orientation was oriented to the (110) crystal face with no significant difference according to the composition of the molybdenum-tungsten alloy. In addition, the present inventors analyzed the surface morphology of the molybdenum-tungsten alloy produced by the above process and found that the second phase due to the nonuniformity of the composition on the surface after deposition with no significant difference according to the condition of 3: 1, 1: Not observed.

Further, according to the results of Tables 1 and 2, it was found that the samples (# 2-1, # 3-1, # 2-2, # 3-2) in which the molybdenum- tungsten alloy was formed on the Ti or TiW seed layer The surface resistance characteristic was improved. That is, the samples (# 2-1, # 3-1, # 2-2, # 3-2) in which a molybdenum-tungsten alloy is formed on the Ti or TiW seed layer, 1-1, and # 1-2).

5 is a graph showing changes in electrical characteristics and acoustic impedance characteristics depending on the ratio of molybdenum and tungsten. In this case, the electrical properties were measured by measuring the surface resistance of the alloy sample produced. 5, the left side of the vertical axis represents the acoustic impedance (unit: kg / m ² / s), and the right side represents the surface resistance (unit: ohm / sq). 6 is a graph showing the calculated values of acoustic impedance / surface resistance according to the ratio of molybdenum to tungsten. FIG. 7 is a graph showing changes in Qp characteristics depending on the ratio of molybdenum and tungsten.

5 and FIG. 6, the molybdenum-tungsten alloy has an acoustic impedance greater than that due to an increase in surface resistance in the range of 3: 1 to 1: 3 by weight of molybdenum and tungsten, , Which is an electrode material suitable for use in FABR. The Qp characteristic of the resonator is strongly influenced by the acoustic impedance. In the case of the molybdenum-tungsten alloy having a weight ratio of 3: 1 to 1: 3, the acoustic impedance is higher than that of pure Mo, and the Kt2 and the attenuation characteristic Can be improved.

However, as the amount of tungsten increased and the ratio of tungsten to molybdenum exceeded 3: 1, the acoustic impedance / surface resistance value decreased due to the increase of the surface resistance rather than the increase of acoustic impedance. The ratio of tungsten to molybdenum Acoustic impedance / surface resistance tends to decrease suddenly when it approaches 1: 3. If the ratio of tungsten to molybdenum and tungsten is greater than 1: 3, the slope at which the surface resistance increases is significantly increased, while the disadvantage of increasing the surface resistance is greater than the performance improvement due to the increase in acoustic impedance . From these results, it can be seen that the preferred weight ratio of molybdenum to tungsten is 3: 1 to 1: 1. 8, the Qp characteristic was the best when the molybdenum-tungsten ratio was 1: 1, and the characteristic was similar to pure tungsten when the ratio was 3: 1. From these results, it can be seen that the more preferable range of molybdenum and tungsten is 3: 1 to 1: 1.

8 is a cross-sectional view showing a volume acoustic resonator according to another embodiment of the present invention. In the case of this embodiment, there is a difference in the shape of the air cavity 212 and the embodiment of Fig. The volume acoustic resonator of Figure 8 includes a substrate 210, an insulating layer 220, an etch stop layer 223, an etch stop 225, an air cavity 212, a sacrificial layer pattern 230, And a resonator portion including a piezoelectric layer 250 and a second electrode 260. The first electrode layer 240 may further include a protective layer 270 and an electrode pad 280. [

The etching stop layer 223 may be formed on the insulating layer 220 and the etching stop layer 223 may be formed on the substrate 210 and the insulating layer 220 ), And so on. The etch stopper 225, the air cavity 212 and the sacrificial layer pattern 230 may be formed on the etch stop layer 223 and the etch stopper 225, the air cavity 212, The pattern 230 is formed to be substantially equal in height so that one side of the layers can be substantially flat.

The air cavity 212 is positioned below the resonance part so that the resonance part composed of the first electrode 240, the piezoelectric layer 250, and the second electrode 260 can vibrate in a predetermined direction. The air cavity 212 is formed by forming a sacrificial layer on the etch stop layer 223 and stacking the first electrode 240, the piezoelectric layer 250 and the second electrode 260 on the sacrificial layer, The etching process may be performed.

An etching stopper 225 may be formed on the outer side of the air cavity 212. The etch stopper 225 may be formed to protrude from the etching stopper layer 223 so that the outer circumferential boundary surface of the air cavity 212 may be defined by the side surface of the etch stopper 225. In the case of the present embodiment, the cross section of the etching stopper 225 may have a substantially trapezoidal shape. Specifically, the width of the upper surface of the etching stopper 225 may be wider than the width of the lower surface, and the side connecting the upper surface and the lower surface may be inclined. The etch stop layer 223 and the etch stop 225 may be formed of a material that is not etched in the etching process for removing the sacrificial layer. For example, the etch stop layer 223 and the etch stop 225 And may be formed of the same material. The shape of the air cavity 212 after the sacrificial layer is removed can be defined by the space enclosed by the etching stopper layer 223 and the etching stopper 225. Specifically, the lower boundary surface of the air cavity 212 can be defined by the etching stop layer 223, and the outer circumferential boundary surface of the air cavity 212 can be defined by the etching stopper 225.

The sacrificial layer pattern 230 may be formed on the opposite side of the air cavity 212 with respect to the outer-etching stopper 225 of the etching stopper 225. The sacrificial layer pattern 230 may extend outside the etching stopper 225. The sacrificial layer pattern 230 may correspond to a portion of the sacrificial layer formed on the etch stop layer 223 remaining after the etching process.

The first electrode 240, the piezoelectric layer 250 and the second electrode 260 form a resonance part 235 and the first electrode 240, the piezoelectric layer 250, The common area superimposed in the direction of the air cavity 212 may be located at the top of the air cavity 212. As in the previous embodiment, the piezoelectric layer 250 is a part causing a piezoelectric effect to convert electrical energy into mechanical energy in the form of elastic waves. The piezoelectric layer 250 is made of aluminum nitride (AlN), zinc oxide (ZnO), lead zirconium titanium oxide (PZT; PbZrTiO , And the second electrode 160 is formed on the piezoelectric layer 150. [ In addition, when the piezoelectric layer 150 is formed of aluminum nitride (AlN), the piezoelectric layer 150 may further include a rare earth metal or a transition metal. As an example, the rare earth metal may include at least one of scandium (Sc), erbium (Er), yttrium (Y), and lanthanum (La). In addition, the transition metal may include at least one of hafnium (Hf), titanium (Ti), zirconium (Zr), and magnesium (Mg).

In this embodiment, at least one of the first electrode 240 and the second electrode 260 includes a molybdenum-tungsten alloy, and the ratio of molybdenum to tungsten in the molybdenum-tungsten alloy is 3: 1 to 1: 3 Is satisfied.

9 and 10 are schematic circuit diagrams of a filter according to one embodiment of the present invention. Each of the plurality of volume acoustic resonators employed in the filters of Figs. 9 and 10 corresponds to the volume acoustic resonator shown in Fig.

Referring to FIG. 9, the filter 1000 according to an embodiment of the present invention may be formed of a ladder type filter structure. Specifically, the filter 1000 includes a plurality of volume acoustic resonators 1100, 1200. The first volume acoustic resonator 1100 may be connected in series between a signal input terminal to which the input signal RFin is input and a signal output terminal to which the output signal RFout is output and the second volume acoustic resonator 1200 may be connected to the signal output terminal It is connected between ground.

Referring to FIG. 10, the filter 2000 according to an embodiment of the present invention may be formed of a lattice type filter structure. Specifically, the filter 2000 includes a plurality of volume acoustic resonators 2100, 2200, 2300, 2400 to filter the balanced input signals RFin +, RFin- to produce balanced output signals RFout +, RFout- Can be output.

The present invention is not limited to the above-described embodiments and the accompanying drawings, but is intended to be limited only by the appended claims. It will be apparent to those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. something to do.

110: substrate
112: air cavity
120: insulating layer
125: etch stop layer
130: Membrane
135:
140: first electrode
150: piezoelectric layer
160: Second electrode
170: protective layer
180: Electrode pad
1000, 2000: filter
1100, 1200, 2100, 2200, 2300, 2400: volume acoustic resonator

Claims (15)

Board;
A first electrode and a second electrode formed on the substrate; And
And a piezoelectric layer provided between the first electrode and the second electrode,
Wherein at least one of the first electrode and the second electrode comprises a molybdenum-tungsten alloy, and the weight ratio of molybdenum to tungsten in the molybdenum-tungsten alloy is 3: 1 to 1: 3.
The method according to claim 1,
Wherein the weight ratio of molybdenum to tungsten in the molybdenum-tungsten alloy is 3: 1 to 1: 1.
The method according to claim 1,
The molybdenum-tungsten alloy is oriented in a (110) crystal plane.
The method according to claim 1,
Wherein the piezoelectric layer is aluminum nitride.
5. The method of claim 4,
Wherein the piezoelectric layer comprises a rare earth metal or a transition metal.
The method according to claim 1,
And a seed layer formed between at least one of the first and second electrodes and the substrate.
The method according to claim 6,
Wherein the seed layer comprises at least one of Ti and TiW.
In a filter including a plurality of volume acoustic resonators,
Wherein at least one of the plurality of volume acoustic resonators comprises:
Board;
A first electrode and a second electrode formed on the substrate; And
And a piezoelectric layer provided between the first electrode and the second electrode,
Wherein at least one of the first electrode and the second electrode comprises a molybdenum-tungsten alloy and the weight ratio of molybdenum to tungsten in the molybdenum-tungsten alloy is 3: 1 to 1: 3.
9. The method of claim 8,
Wherein the weight ratio of molybdenum to tungsten in the molybdenum-tungsten alloy is from 3: 1 to 1: 1.
9. The method of claim 8,
Wherein the molybdenum-tungsten alloy is oriented in a (110) crystal plane.
9. The method of claim 8,
Wherein the piezoelectric layer is aluminum nitride.
12. The method of claim 11,
Wherein the piezoelectric layer comprises a rare earth metal or a transition metal.
9. The method of claim 8,
Wherein the plurality of volume acoustic resonators comprise a ladder type or a lattice type.
9. The method of claim 8,
And a seed layer formed between at least one of the first and second electrodes and the substrate.
15. The method of claim 14,
Wherein the seed layer comprises at least one of Ti and TiW.

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