Bulk Acoustic Resonator

Abstract

To provide a bulk acoustic wave resonator in which abnormal growth of a piezoelectric layer may be suppressed.SOLUTION: A bulk acoustic wave resonator 100 includes a piezoelectric layer 160, a first electrode 150, and a second electrode 170. The piezoelectric layer 160 covers at least a portion of the first electrode. The second electrode is disposed atop the piezoelectric layer. The piezoelectric layer contains a dopant, and satisfies a mathematical expression for a thickness and a scandium (Sc) content in the piezoelectric layer, [piezoelectric layer thickness (nm)×dopant concentration (at.%)] / 100≤80.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to bulk acoustic resonators. [Background technology]

[0002] Recently, with 5G communications emerging as a new topic, the development of BAW filters for 5G is underway. Compared to conventional filters, 5G BAW filters have the following characteristics: the bandwidth is much increased, and as the communication distance becomes shorter, the signal strength and power increases.

[0003] In order to broaden the bandwidth of BAW filters in line with this trend, it is necessary to improve the performance of the resonator by increasing the piezoelectric constant of the piezoelectric material, and to withstand high power, it is also necessary to reduce the loss in the piezoelectric thin film and improve the reliability of the BAW filter. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5994850 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a bulk acoustic resonator capable of suppressing abnormal growth of a piezoelectric layer. [Means for solving the problem]

[0006] According to an embodiment of the present invention, there is provided a bulk acoustic resonator including a first electrode, a piezoelectric layer covering at least a portion of the first electrode, and a second electrode disposed on an upper portion of the piezoelectric layer, wherein the piezoelectric layer contains a dopant, and a value of [thickness of the piezoelectric layer (nm)×dopant concentration (at%)] / 100, which is a mathematical expression for a thickness of the piezoelectric layer and a content of the dopant, may be 80 or less. Effect of the Invention

[0007] According to the present invention, there is an effect that abnormal growth of the piezoelectric layer can be suppressed. [Brief description of the drawings]

[0008] [Figure 1] 1 is a schematic plan view showing a bulk acoustic resonator according to a first embodiment of the present invention. [Diagram 2] 2 is a cross-sectional view taken along line II' in FIG. [Diagram 3] 2 is a cross-sectional view taken along line II-II' in FIG. [Figure 4] FIG. 2 is a cross-sectional view taken along line III-III' in FIG. [Diagram 5] FIG. 2 is an explanatory diagram showing the crystal structure of wurtzite of aluminum nitride. [Figure 6] This is a photograph to explain the abnormal growth of grains that are larger than normal grains. [Figure 7] 1 is a table showing the density of abnormal growth as a function of the thickness and dopant concentration of the piezoelectric layer. [Figure 8] 1 is a graph showing the density of abnormal growth as a function of the thickness and dopant concentration of the piezoelectric layer. [Figure 9] FIG. 11 is an explanatory diagram for explaining a region where abnormal growth occurs. [Figure 10] 13 is a photograph for explaining an area where abnormal growth occurs. [Figure 11] 1 is a table showing values ​​of [piezoelectric layer thickness (nm)×dopant concentration (at %)] / 100. [Figure 12]FIG. 4 is a schematic cross-sectional view showing a bulk acoustic resonator according to a second embodiment of the present invention. [Figure 13] FIG. 11 is a schematic cross-sectional view showing a bulk acoustic resonator according to a third embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, an embodiment of the present invention will be described with reference to a specific embodiment and the attached drawings. However, the embodiment of the present invention may be modified into several other forms, and the scope of the present invention is not limited to the embodiment described below. Furthermore, the embodiment of the present invention is provided to more completely explain the present invention to those having average knowledge in the art. Therefore, the shape and size of elements in the drawings may be enlarged or reduced (or highlighted or simplified) for clearer explanation, and elements indicated by the same reference numerals in the drawings are the same elements.

[0010] FIG. 1 is a schematic plan view showing a bulk acoustic resonator according to a first embodiment of the present invention, FIG. 2 is a cross-sectional view taken along line II' in FIG. 1, FIG. 3 is a cross-sectional view taken along line II-II' in FIG. 1, and FIG. 4 is a cross-sectional view taken along line III-III' in FIG. 1.

[0011] 1 to 4, a bulk acoustic resonator 100 according to a first embodiment of the present invention may include, for example, a substrate 110, a sacrificial layer 120, an etching prevention portion 130, a membrane layer 140, a first electrode 150, a piezoelectric layer 160, a second electrode 170, an insertion layer 180, a passivation layer 190, and a metal pad 195.

[0012] The substrate 110 may be a silicon substrate. For example, the substrate 110 may be a silicon wafer or a silicon on insulator (SOI) type substrate.

[0013] An insulating layer 112 may be formed on the upper surface of the substrate 110 to electrically insulate the substrate 110 from an upper structure. In addition, the insulating layer 112 may serve to prevent the substrate 110 from being etched by an etching gas when a cavity C is formed during a manufacturing process.

[0014] In this case, the insulating layer 112 may be formed of at least one of silicon dioxide (SiO2), silicon nitride (Si3N4), aluminum oxide (Al2O2), and aluminum nitride (AlN), and may be formed through any one of chemical vapor deposition, RF magnetron sputtering, and evaporation processes.

[0015] The sacrificial layer 120 is formed on the insulating layer 112, and the cavity C and the etch stopper 130 may be disposed inside the sacrificial layer 120. The cavity C is formed by removing a portion of the sacrificial layer 120 during manufacturing. Since the cavity C is formed inside the sacrificial layer 120, the first electrode 150, etc. disposed on the upper portion of the sacrificial layer 120 may be formed flat.

[0016] The etching prevention portion 130 is disposed along the boundary of the cavity C. The etching prevention portion 130 prevents etching beyond the cavity region during the process of forming the cavity C.

[0017] The film layer 140 forms a cavity C together with the substrate 110. The film layer 140 may be made of a material that is less reactive with an etching gas when the sacrificial layer 120 is removed. Meanwhile, the etching prevention portion 130 is inserted and disposed in a groove portion 142 formed by the film layer 140. Meanwhile, the film layer 140 may be a dielectric layer containing any of the following materials: silicon nitride (Si3N4), silicon oxide (SiO2), manganese oxide (MgO), zirconium oxide (ZrO2), aluminum nitride (AlN), lead zirconate titanate (PZT), gallium arsenide (GaAs), hafnium oxide (HfO2), aluminum oxide (Al2O3), titanium oxide (TiO2), and zinc oxide (ZnO).

[0018] Meanwhile, a seed layer (not shown) made of aluminum nitride (AlN) may be formed on the film layer 140. That is, the seed layer may be disposed between the film layer 140 and the first electrode 150. The seed layer may be formed by using a dielectric or metal having an HCP crystal structure other than aluminum nitride (AlN). As an example, when the seed layer is a metal, the seed layer may be formed of titanium (Ti).

[0019] The first electrode 150 is formed on the film layer 140, and a portion of it is disposed above the cavity C. In addition, the first electrode 150 can be used as either an input electrode or an output electrode for inputting and outputting an electric signal such as an RF (Radio Frequency) signal.

[0020] Meanwhile, the first electrode 150 may be made of an aluminum alloy material containing scandium (Sc), for example. Since the first electrode 150 is made of an aluminum alloy material containing scandium (Sc), the mechanical strength increases and high power reactive sputtering is possible. Under such deposition conditions, an increase in the surface roughness of the first electrode 150 can be prevented, and highly oriented growth of the piezoelectric layer 160 can also be induced.

[0021] In addition, the inclusion of scandium (Sc) increases the chemical resistance of the first electrode 150, thereby making up for the drawbacks that arise when the first electrode is made of pure aluminum. In addition, process stability such as dry etching or wet process during manufacture can be ensured. Furthermore, when the first electrode is made of pure aluminum, oxidation easily occurs, but since the first electrode 150 is made of an aluminum alloy material containing scandium, the chemical resistance against oxidation can be improved.

[0022] The first electrode 150 may be formed using a conductive material such as molybdenum (Mo) or an alloy thereof, but is not limited thereto. The first electrode 150 may be formed of a conductive material such as ruthenium (Ru), tungsten (W), iridium (Ir), platinum (Pt), copper (Cu), titanium (Ti), tantalum (Ta), nickel (Ni), chromium (Cr), or an alloy thereof.

[0023] The piezoelectric layer 160 is formed to cover at least the first electrode 150 disposed on the upper portion of the cavity C. Meanwhile, the piezoelectric layer 160 is a portion that causes a piezoelectric effect that converts electrical energy into mechanical energy in the form of an elastic wave, and includes, for example, an aluminum nitride (AlN) material.

[0024] In addition, the piezoelectric layer 160 may be doped with a dopant such as a rare earth metal or a transition metal. As an example, the rare earth metal used as the dopant may include at least one of scandium (Sc), erbium (Er), yttrium (Y), and lanthanum (La). In addition, the transition metal used as the dopant may include at least one of titanium (Ti), zirconium (Zr), hafnium (Hf), tantalum (Ta), and niobium (Nb). In addition, the piezoelectric layer 160 may also include magnesium (Mg), which is a divalent metal.

[0025] On the other hand, the piezoelectric layer 160 has a value of 80 or less in the following formula: Formula: [Piezoelectric layer thickness (nm) × dopant concentration (at%)] / 100

[0026] To explain this in more detail, first, the piezoelectric layer 160 uses aluminum nitride (AlN) as a basic base material. In order to continuously expand the usable bandwidth of the piezoelectric layer 160, the content of the dopant, for example, scandium (Sc), contained in the piezoelectric layer 160 needs to be continuously increased. However, as the content of the dopant, for example, scandium, increases, it becomes difficult to realize a highly oriented aluminum nitride layer.

[0027] More specifically, aluminum nitride has a wurtzite crystal structure with an HCP structure, as shown in Figure 5. However, when aluminum nitride is doped with a dopant, for example, scandium, the dopant element, for example, scandium, substitutes for the aluminum element site. However, as the content of the dopant, for example, scandium, increases, rapid crystal growth occurs in the edge crystal direction in the HCP crystal structure, resulting in abnormal growth of grains that are larger than normal grains, as shown in Figure 6.

[0028] In particular, as the content of a dopant, for example, scandium, increases, the probability of such abnormal growth occurring increases, and the frequency of occurrence of abnormal growth increases exponentially.

[0029] The dopant used to improve the piezoelectric properties of the piezoelectric layer 160 corresponds to an element having an atomic diameter larger than that of aluminum (Al). That is, an element having an atomic diameter larger than that of aluminum (Al) is substituted for aluminum (Al), causing deformation in the crystal structure, and as the content of the dopant increases, the probability of abnormal growth occurring increases due to the increase in the deformation.

[0030] In general, abnormal growth can be explained by the grain boundary relaxation model. Abnormal growth of thin films can occur in gaps at grain boundaries, which are the boundaries between normal crystals. This can be a site for nucleation of abnormal growth. In this way, when abnormal growth occurs at open grain boundaries, it reduces the surface free energy during thin film growth, which can generally become an environment in which abnormal growth occurs.

[0031] In addition, before the deposition of the piezoelectric layer 160, the surface roughness of the first electrode 150 also has an important effect on the abnormal growth. When the surface roughness (RMS, Root Mean Square) of the first electrode 150 in the active region where the first electrode 150 and the second electrode 170 overlap is 5 nm or more, the possibility of abnormal growth is high. In this way, when abnormal growth occurs in a state where the surface roughness is high, the bulk acoustic resonator 100 may be damaged due to the abnormal growth in a high power and high voltage environment. The surface roughness can be analyzed by performing an AFM analysis or from the surface roughness of the first electrode 150 in a TEM cross section. Thus, the surface roughness (RMS) of the first electrode 150 can be less than 5 nm.

[0032] Meanwhile, as the content of a dopant, for example, scandium (Sc), increases, the frequency of occurrence of abnormal growth increases. This is because as the content of a dopant, for example, scandium (Sc), increases, the number of open grain boundary sites increases, and the probability of occurrence of abnormal growth also increases.

[0033] In addition, sputtering deposition is performed by reactive reaction with nitrogen gas using an AlSc target with each content of dopant, e.g., scandium (Sc). Then, the thickness of the AlScN thin film is increased by 100 nm from 200 nm to 1300 nm, and the density of abnormal growth is confirmed by SEM. In general, a component analysis is performed on the dopant, e.g., scandium (Sc), in the AlScN piezoelectric thin film by TEM, and the content of aluminum (Al) and the dopant, e.g., scandium (Sc), is expressed as the at% content ratio of the dopant, e.g., scandium (Sc), when the content of aluminum (Al) and the dopant, e.g., scandium (Sc) is regarded as 100 at%.

[0034] 7 and 8, even if the piezoelectric layer 160 has the same dopant, for example, the same scandium (Sc) content, when the thickness of the piezoelectric layer 160 increases, the occurrence rate of abnormal growth also increases and the size of the abnormal growth also increases. This phenomenon occurs because, in terms of grain growth accompanying the increase in thickness, not only normal grain growth but also abnormal growth occurs.

[0035] 9, abnormal growth in the piezoelectric layer 160 does not occur in the early stages, but occurs when the thickness exceeds a certain level. Also, as shown in FIG 10, when FIB cross-sectional analysis is performed on the piezoelectric layer 160 where abnormal growth actually occurs, it is found that the abnormal growth occurs when the thickness exceeds a certain level.

[0036] 7 and 8, when the content of the dopant, for example, scandium (Sc), is 6.25 at%, abnormal growth begins to be observed when the thickness of the piezoelectric layer 160 is 1300 nm. When the content of the dopant, for example, scandium (Sc), is 12.5 at%, abnormal growth begins to be observed when the thickness of the piezoelectric layer 160 is 700 nm. Furthermore, when the content of the dopant, for example, scandium (Sc), is 20 at%, abnormal growth begins to be observed when the thickness of the piezoelectric layer 160 is 500 nm.

[0037] Thus, when checking the state where abnormal growth does not occur through a formula, it is found that the value of [piezoelectric layer thickness (nm) × dopant concentration (at%)] / 100 is less than or equal to 80. That is, as shown in Fig. 11, when the value of [piezoelectric layer thickness (nm) × dopant concentration (at%)] / 100 is greater than 80 in the area surrounded by the thick line, abnormal growth occurs.

[0038] As a result, when a BAW filter is manufactured using a piezoelectric layer thickness that does not cause abnormal growth depending on the content of a dopant, for example, scandium (Sc), it can be manufactured without defects in the piezoelectric layer 160. When there are no defects in the piezoelectric layer 160, it is possible to realize a piezoelectric layer 160 of the bulk acoustic resonator 100 that is highly reliable under high output and high voltage conditions, which can contribute to improving reliability.

[0039] On the other hand, when the dopant is scandium (Sc), the content of scandium (Sc) in the piezoelectric layer 160 may be 0.1 to 30 at%. In order to realize high piezoelectric characteristics, the content of scandium (Sc) as the dopant needs to be 0.1 at% or more, compared to the case where the piezoelectric layer is made of aluminum nitride (AlN). In addition, when the content of scandium (Sc) is 30 at% or more, it is not easy to manufacture an AlSc alloy target. When the content of scandium (Sc) is 30 at% or more, there is a problem that the AlSc target becomes brittle when the target is manufactured through a melting method, so that it is not easy to manufacture and process the AlSc alloy target.

[0040] Furthermore, when the dopant is scandium (Sc), the content of scandium (Sc) in the piezoelectric layer 160 may be 10 to 30 at %. That is, when the content of scandium (Sc) is 10 at % or less, the frequency of occurrence of abnormal growth accompanying an increase in the thickness of the piezoelectric layer 160 is low, but when the content of scandium (Sc) is 10 at % or more, the frequency of occurrence of abnormal growth of the piezoelectric layer 160 increases rapidly.

[0041] In particular, when the content of a dopant, for example, scandium (Sc), is 10 at % or more, the frequency of occurrence of abnormal growth increases, so it is more preferable to manufacture the crystal within such a numerical range.

[0042] On the other hand, the piezoelectric layer 160 includes a piezoelectric portion 162 disposed on the flat portion S and a bent portion 164 disposed on the extended portion E.

[0043] The piezoelectric part 162 is a part that is directly laminated on the upper surface of the first electrode 150. As a result, the piezoelectric part 162 is interposed between the first electrode 150 and the second electrode 170 and is formed in a flat shape together with the first electrode 150 and the second electrode 170.

[0044] Bend portion 164 can be defined as the area that extends outward from piezoelectric portion 162 and is located within extension E.

[0045] The bent portion 164 is disposed on the insertion layer 180, which will be described later, and is formed to protrude along the shape of the insertion layer 180. As a result, the piezoelectric layer 160 is bent at the boundary between the piezoelectric portion 162 and the bent portion 164, and the bent portion 164 protrudes in accordance with the thickness and shape of the insertion layer 180.

[0046] The bent portion 164 may be divided into an inclined portion 164a and an extended portion 164b.

[0047] The inclined portion 164a refers to a portion formed to be inclined along an inclined surface L of the insertion layer 180, which will be described later, and the extended portion 164b refers to a portion extended outward from the inclined portion 164a.

[0048] The inclined portion 164 a is formed parallel to the inclined surface L of the insertion layer 180 , and the inclination angle of the inclined portion 164 a may be formed to be the same as the inclination angle of the inclined surface L of the insertion layer 180 .

[0049] The second electrode 170 is formed to cover at least the piezoelectric layer 160 disposed on the upper portion of the cavity C. The second electrode 170 can be used as either an input electrode or an output electrode for inputting and outputting an electrical signal such as an RF (Radio Frequency) signal. That is, when the first electrode 150 is used as an input electrode, the second electrode 170 is used as an output electrode. Also, when the first electrode 150 is used as an output electrode, the second electrode 170 can be used as an input electrode.

[0050] The second electrode 170 may be formed using a conductive material such as molybdenum (Mo) or an alloy thereof, but is not limited thereto. The second electrode 170 may be formed of a conductive material such as ruthenium (Ru), tungsten (W), iridium (Ir), platinum (Pt), copper (Cu), titanium (Ti), tantalum (Ta), nickel (Ni), chromium (Cr), or an alloy thereof.

[0051] The insertion layer 180 is disposed between the first electrode 150 and the piezoelectric layer 160. The insertion layer 180 may be formed of a dielectric material such as silicon oxide (SiO2), aluminum nitride (AlN), aluminum oxide (Al2O3), silicon nitride (Si3N4), manganese oxide (MgO), zirconium oxide (ZrO2), lead zirconate titanate (PZT), gallium arsenide (GaAs), hafnium oxide (HfO2), aluminum oxide (Al2O3), titanium oxide (TiO2), zinc oxide (ZnO), etc., but may be formed of a material different from that of the piezoelectric layer 160. Also, if necessary, the region where the insertion layer 180 is provided may be formed as an air region. This can be achieved by removing the insertion layer 180 during the manufacturing process.

[0052] In this embodiment, the thickness of the insertion layer 180 may be the same as or similar to the thickness of the first electrode 150. Also, the insertion layer 180 may be formed to be similar to or thinner than the piezoelectric layer 160. For example, the insertion layer 180 may be formed to a thickness of 100 Å or more and thinner than the piezoelectric layer 160. However, the configuration of the present invention is not limited thereto.

[0053] Meanwhile, the insertion layer 180 is disposed along the surface formed by the membrane layer 140, the first electrode 150, and the etch stopper .

[0054] The insertion layer 180 is disposed around the flat portion S to support the bending portion 164 of the piezoelectric layer 160. Thus, the bending portion 164 of the piezoelectric layer 160 may be divided into an inclined portion 164a and an extended portion 164b according to the shape of the insertion layer 180.

[0055] The insertion layer 180 is disposed in a region excluding the flat portion S. For example, the insertion layer 180 may be disposed in the entire region excluding the flat portion S, or may be disposed in a portion of the region.

[0056] Additionally, the insertion layer 180 is at least partially disposed between the piezoelectric layer 160 and the first electrode 150 .

[0057] The side of the insertion layer 180 arranged along the boundary of the flat portion S is formed to have a shape that increases in thickness as it moves away from the flat portion S. As a result, the side of the insertion layer 180 arranged adjacent to the flat portion S is formed as an inclined surface L having a certain inclination angle θ.

[0058] If the inclination angle θ of the side of the insertion layer 180 is formed to be less than 5°, it is difficult to actually realize this because the thickness of the insertion layer 180 must be made very thin or the area of ​​the inclined surface L must be made excessively large in order to manufacture it.

[0059] In addition, if the inclination angle θ of the side surface of the insertion layer 180 is greater than 70°, the inclination angle of the inclined portion 164a of the piezoelectric layer 160 laminated on the insertion layer 180 is also greater than 70°. In this case, the piezoelectric layer 160 is bent excessively, which may cause cracks to occur in the bent portion of the piezoelectric layer 160.

[0060] Therefore, in this embodiment, the inclination angle θ of the inclined surface L is in the range of 5° to 70°.

[0061] The passivation layer 190 is formed on an area excluding a portion of the first electrode 150 and the second electrode 170. Meanwhile, the passivation layer 190 serves to prevent the second electrode 170 and the first electrode 150 from being damaged during the process.

[0062] Furthermore, in the final process, the passivation layer 190 may be partially removed by etching for frequency adjustment. That is, the thickness of the passivation layer 190 may be adjusted. The passivation layer 190 may be, for example, a dielectric layer containing any of the following materials: silicon nitride (Si3N4), silicon oxide (SiO2), manganese oxide (MgO), zirconium oxide (ZrO2), aluminum nitride (AlN), lead zirconate titanate (PZT), gallium arsenide (GaAs), hafnium oxide (HfO2), aluminum oxide (Al2O3), titanium oxide (TiO2), and zinc oxide (ZnO).

[0063] The metal pad 195 is formed on a portion of the first electrode 150 and the second electrode 170 where the passivation layer 190 is not formed. As an example, the metal pad 195 may be made of a material such as gold (Au), a gold-tin (Au-Sn) alloy, copper (Cu), a copper-tin (Cu-Sn) alloy, aluminum (Al), and an aluminum alloy. The aluminum alloy may be, for example, an aluminum-germanium (Al-Ge) alloy.

[0064] As described above, since the value of the formula [thickness of piezoelectric layer (nm)×dopant concentration (at %)] / 100 is 80 or less, abnormal growth of the piezoelectric layer 160 can be prevented.

[0065] FIG. 12 is a schematic cross-sectional view showing a bulk acoustic resonator according to a second embodiment of the present invention.

[0066] Referring to FIG. 12, the bulk acoustic resonator 200 according to the second embodiment of the present invention may include, for example, a substrate 210, a membrane layer 220, a first electrode 230, a piezoelectric layer 240, a second electrode 250, an insertion layer 260, a passivation layer 270, and a metal pad 280.

[0067] The substrate 210 may be a substrate on which silicon is laminated. For example, a silicon wafer may be used as the substrate. Meanwhile, the substrate 210 may be provided with a reflective layer 211.

[0068] The reflective layer 211 may be disposed under an active area, where the active area is an area where the first electrode 230, the piezoelectric layer 240, and the second electrode 250 are all arranged to overlap each other.

[0069] Meanwhile, the reflective layer 211 may include first and second reflective members 212 and 214 disposed in the grooves. The first and second reflective members 212 and 214 may be made of different materials.

[0070] The first reflecting member 212 may be formed using a conductive material such as molybdenum (Mo) or an alloy thereof, but is not limited thereto, and other usable materials include ruthenium (Ru), tungsten (W), iridium (Ir), platinum (Pt), copper (Cu), aluminum (Al), titanium (Ti), tantalum (Ta), nickel (Ni), and chromium (Cr). Also, the second reflecting member 214 may be a dielectric layer containing any of silicon nitride (Si3N4), silicon oxide (SiO2), manganese oxide (MgO), zirconium oxide (ZrO2), aluminum nitride (AlN), lead zirconate titanate (PZT), gallium arsenide (GaAs), hafnium oxide (HfO2), aluminum oxide (Al2O3), titanium oxide (TiO2), and zinc oxide (ZnO). Meanwhile, the first and second reflecting members 212 and 214 may be provided with four layers, that is, two pairs of the first and second reflecting members 212 and 214. However, the present invention is not limited thereto, and the first and second reflecting members 212 and 214 may be provided as a pair, or three or more pairs of the first and second reflecting members may be provided.

[0071] On the other hand, the first reflective member 212 can be made of a material having a higher density than the second reflective member 214 .

[0072] The film layer 220 can be formed to cover the reflective layer 211 of the substrate 210. The film layer 220 can be a dielectric layer containing any of the following materials: silicon nitride (Si3N4), silicon oxide (SiO2), manganese oxide (MgO), zirconium oxide (ZrO2), aluminum nitride (AlN), lead zirconate titanate (PZT), gallium arsenide (GaAs), hafnium oxide (HfO2), aluminum oxide (Al2O3), titanium oxide (TiO2), and zinc oxide (ZnO).

[0073] Meanwhile, a seed layer (not shown) made of aluminum nitride (AlN) may be formed on the membrane layer 220. That is, the seed layer may be disposed between the membrane layer 220 and the first electrode 230. The seed layer may be formed using a dielectric material or a metal having an HCP crystal structure other than aluminum nitride (AlN). As an example, when the seed layer is a metal, the seed layer may be formed of titanium (Ti).

[0074] The first electrode 230 is formed on the film layer 220. The first electrode 230 can be used as either an input electrode or an output electrode for inputting and outputting an electric signal such as an RF (Radio Frequency) signal.

[0075] Meanwhile, the first electrode 230 may be made of an aluminum alloy material containing scandium (Sc), for example. Since the first electrode 230 is made of an aluminum alloy material containing scandium (Sc), the mechanical strength increases and high power reactive sputtering is possible. Under such deposition conditions, an increase in the surface roughness of the first electrode 230 can be prevented, and highly oriented growth of the piezoelectric layer 240 can also be induced.

[0076] In addition, the inclusion of scandium (Sc) increases the chemical resistance of the first electrode 230, thereby making up for the drawbacks that arise when the first electrode is made of pure aluminum. In addition, process stability such as dry etching or wet process during manufacturing can be ensured. Furthermore, when the first electrode is made of pure aluminum, oxidation easily occurs, but since the first electrode 150 is made of an aluminum alloy material containing scandium, the chemical resistance against oxidation can be improved.

[0077] The first electrode 230 may be formed using a conductive material such as molybdenum (Mo) or an alloy thereof, but is not limited thereto. The first electrode 230 may be formed of a conductive material such as ruthenium (Ru), tungsten (W), iridium (Ir), platinum (Pt), copper (Cu), titanium (Ti), tantalum (Ta), nickel (Ni), chromium (Cr), or an alloy thereof.

[0078] Meanwhile, the surface roughness (RMS) of the first electrode 230 may be less than 5 nm.

[0079] The piezoelectric layer 240 is formed to cover at least the first electrode 230 disposed on the upper portion of the reflective layer 211. Meanwhile, the piezoelectric layer 240 is a portion that causes a piezoelectric effect that converts electrical energy into mechanical energy in the form of an elastic wave, and includes, for example, an aluminum nitride (AlN) material.

[0080] In addition, the piezoelectric layer 240 may be doped with a dopant such as a rare earth metal or a transition metal. As an example, the rare earth metal used as the dopant may include at least one of scandium (Sc), erbium (Er), yttrium (Y), and lanthanum (La). In addition, the transition metal used as the dopant may include at least one of titanium (Ti), zirconium (Zr), hafnium (Hf), tantalum (Ta), and niobium (Nb). In addition, the piezoelectric layer 240 may also include magnesium (Mg), which is a divalent metal.

[0081] On the other hand, the piezoelectric layer 240 has a value of 80 or less in the following formula: Formula: [Piezoelectric layer thickness (nm) × dopant concentration (at%)] / 100

[0082] On the other hand, the piezoelectric layer 240 includes a piezoelectric portion 242 disposed on the flat portion S and a bent portion 244 disposed on the extended portion E.

[0083] The piezoelectric part 242 is a part that is directly laminated on the upper surface of the first electrode 230. Thus, the piezoelectric part 242 is interposed between the first electrode 230 and the second electrode 250 and is formed in a flat shape together with the first electrode 230 and the second electrode 250.

[0084] Bend portion 244 can be defined as the area that extends outward from piezoelectric portion 242 and is located within extension E.

[0085] The bent portion 244 is disposed on the insertion layer 260, which will be described later, and is formed to protrude along the shape of the insertion layer 260. As a result, the piezoelectric layer 240 is bent at the boundary between the piezoelectric portion 242 and the bent portion 244, and the bent portion 244 protrudes in accordance with the thickness and shape of the insertion layer 260.

[0086] The bent portion 244 may be divided into an inclined portion 244a and an extended portion 244b.

[0087] The inclined portion 244a refers to a portion formed to be inclined along an inclined surface L of the insertion layer 260, which will be described later, and the extended portion 244b refers to a portion extended outward from the inclined portion 244a.

[0088] The inclined portion 244 a is formed parallel to the inclined surface L of the insertion layer 260 , and the inclination angle of the inclined portion 244 a may be formed to be the same as the inclination angle of the inclined surface L of the insertion layer 260 .

[0089] The second electrode 250 is formed to cover at least the piezoelectric layer 240 disposed on the upper part of the reflective layer 211. The second electrode 250 can be used as either an input electrode or an output electrode for inputting and outputting an electric signal such as an RF (Radio Frequency) signal. That is, when the first electrode 230 is used as an input electrode, the second electrode 250 can be used as an output electrode, and when the first electrode 230 is used as an output electrode, the second electrode 250 can be used as an input electrode.

[0090] The second electrode 250 may be formed using a conductive material such as molybdenum (Mo) or an alloy thereof, but is not limited thereto. The second electrode 250 may be formed of a conductive material such as ruthenium (Ru), tungsten (W), iridium (Ir), platinum (Pt), copper (Cu), titanium (Ti), tantalum (Ta), nickel (Ni), chromium (Cr), or an alloy thereof.

[0091] The insertion layer 260 is disposed between the first electrode 230 and the piezoelectric layer 240. The insertion layer 260 may be formed of a dielectric material such as silicon oxide (SiO2), aluminum nitride (AlN), aluminum oxide (Al2O3), silicon nitride (Si3N4), manganese oxide (MgO), zirconium oxide (ZrO2), lead zirconate titanate (PZT), gallium arsenide (GaAs), hafnium oxide (HfO2), aluminum oxide (Al2O3), titanium oxide (TiO2), zinc oxide (ZnO), etc., but may be formed of a material different from that of the piezoelectric layer 240. Also, if necessary, the region where the insertion layer 260 is provided may be formed as an empty region (air). This can be implemented by removing the insertion layer 260 during the manufacturing process.

[0092] In this embodiment, the thickness of the insertion layer 260 may be the same as or similar to the thickness of the first electrode 230. Also, the insertion layer 260 may be formed to be the same as or thinner than the piezoelectric layer 240. For example, the insertion layer 260 may be formed to a thickness of 100 Å or more and thinner than the piezoelectric layer 240. However, the configuration of the present invention is not limited thereto.

[0093] On the other hand, the insertion layer 260 is disposed along the surface formed by the membrane layer 220 and the first electrode 230 .

[0094] The insertion layer 260 is disposed around the flat portion S to support the bending portion 244 of the piezoelectric layer 240. Thus, the bending portion 244 of the piezoelectric layer 240 may be divided into an inclined portion 244a and an extended portion 244b according to the shape of the insertion layer 260.

[0095] The insertion layer 260 is disposed in a region excluding the flat portion S. For example, the insertion layer 260 may be disposed in the entire region excluding the flat portion S, or may be disposed in a portion of the region.

[0096] Additionally, the insertion layer 260 is at least partially disposed between the piezoelectric layer 240 and the first electrode 230 .

[0097] The passivation layer 270 is formed on an area excluding a portion of the first electrode 230 and the second electrode 250. Meanwhile, the passivation layer 270 serves to prevent the second electrode 250 and the first electrode 230 from being damaged during the process.

[0098] Furthermore, in the final process, the passivation layer 270 may be partially removed by etching for frequency adjustment. That is, the thickness of the passivation layer 270 may be adjusted. The passivation layer 270 may be, for example, a dielectric layer containing any of silicon nitride (Si3N4), silicon oxide (SiO2), manganese oxide (MgO), zirconium oxide (ZrO2), aluminum nitride (AlN), lead zirconate titanate (PZT), gallium arsenide (GaAs), hafnium oxide (HfO2), aluminum oxide (Al2O3), titanium oxide (TiO2), and zinc oxide (ZnO).

[0099] The metal pad 280 is formed on a portion of the first electrode 230 and the second electrode 250 where the passivation layer 270 is not formed. As an example, the metal pad 280 may be made of a material such as gold (Au), a gold-tin (Au-Sn) alloy, copper (Cu), a copper-tin (Cu-Sn) alloy, aluminum (Al), and an aluminum alloy. The aluminum alloy may be, for example, an aluminum-germanium (Al-Ge) alloy.

[0100] As described above, since the value of the formula [thickness of piezoelectric layer (nm)×concentration of dopant (at %)] / 100 is 80 or less, abnormal growth of the piezoelectric layer 240 can be prevented.

[0101] FIG. 13 is a schematic cross-sectional view showing a bulk acoustic resonator according to a third embodiment of the present invention.

[0102] Referring to FIG. 13, a bulk acoustic resonator 300 according to the third embodiment of the present invention may include, for example, a substrate 310, a membrane layer 220, a first electrode 230, a piezoelectric layer 240, a second electrode 250, an insertion layer 260, a passivation layer 270, and a metal pad 280.

[0103] Meanwhile, the membrane layer 220, the first electrode 230, the piezoelectric layer 240, the second electrode 250, the insertion layer 260, the passivation layer 270, and the metal pad 280 are substantially the same as those in the bulk acoustic resonator 200 according to the second embodiment of the present invention described above, and therefore, detailed description thereof will be omitted and the above description will be used instead.

[0104] The substrate 310 may be a substrate on which silicon is stacked, for example, a silicon wafer may be used as the substrate.

[0105] Meanwhile, the substrate 310 may be provided with a cavity forming groove 311 for forming a cavity C. Also, an insulating layer 312 may be formed on the substrate 310 to electrically insulate the substrate 310 from a structure disposed thereon. Also, the insulating layer 312 serves to prevent the substrate 310 from being etched by an etching gas when the cavity C is formed during the manufacturing process.

[0106] In this case, the insulating layer 312 may be formed of at least one of silicon dioxide (SiO2), silicon nitride (Si3N4), aluminum oxide (Al2O2), and aluminum nitride (AlN), and may be formed through any one of chemical vapor deposition, RF magnetron sputtering, and evaporation processes.

[0107] Although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and it will be obvious to those having ordinary skill in the art that various modifications and variations are possible within the scope that does not deviate from the technical idea of ​​the present invention described in the claims. [Explanation of symbols]

[0108] 100, 200, 300 Bulk Acoustic Resonators 110, 210, 310 board 120 Sacrificial Layer 130 Etching prevention part 140, 220 membrane layers 150, 230 1st electrode 160, 240 Piezoelectric layer 170, 250 2nd electrode 180, 260 Insertion layer 190, 270 Passivation layer 195, 280 Metal pad

Claims

1. A first electrode; a piezoelectric layer covering at least a portion of the first electrode; a second electrode disposed on top of the piezoelectric layer; Including, the piezoelectric layer contains a dopant; a value of [piezoelectric layer thickness (nm) x dopant concentration (at %)] / 100, which is a mathematical expression of the thickness of the piezoelectric layer and the content of the dopant, is 80 or less; the piezoelectric layer comprises aluminum nitride having a wurtzite crystal structure of a HCP structure; the dopant is scandium (Sc); A bulk acoustic resonator, wherein the content of scandium (Sc) in the piezoelectric layer is 10 to 30 at %.

2. a substrate disposed under the first electrode; a membrane layer forming a cavity with said substrate and on which said first electrode is disposed; 10. The bulk acoustic resonator of claim 1 further comprising:

3. The bulk acoustic resonator of claim 2 further comprising an etch stop disposed between said substrate and said first electrode and disposed about a periphery of a cavity.

4. The bulk acoustic resonator of claim 3 further comprising a sacrificial layer disposed over the etch stop.

5. The bulk acoustic resonator according to claim 1 , further comprising an insertion layer disposed under a portion of the piezoelectric layer.

6. The bulk acoustic resonator of claim 2 , wherein the membrane layer comprises a seed layer of aluminum nitride (AlN).

7. 7. The bulk acoustic resonator according to claim 1, wherein at least one of the first electrode and the second electrode is made of any one of molybdenum (Mo), ruthenium (Ru), tungsten (W), iridium (Ir), platinum (Pt), copper (Cu), titanium (Ti), tantalum (Ta), nickel (Ni), and chromium (Cr), or an alloy containing any one of them.

8. The bulk acoustic resonator of claim 1 , wherein the first electrode has a surface roughness (RMS) of 5 nm or less.

9. 9. The bulk acoustic resonator of claim 1, wherein at least one of the first electrode and the second electrode comprises an aluminum alloy layer containing scandium (Sc).

10. The bulk acoustic resonator of claim 2 , wherein the substrate is provided with a reflective layer disposed below an active area in which the first electrode, the piezoelectric layer, and the second electrode are all arranged to overlap each other.

11. The bulk acoustic resonator of claim 2 , wherein the substrate is provided with a cavity-forming groove disposed under an active region in which the first electrode, the piezoelectric layer, and the second electrode are all arranged to overlap each other.

12. The bulk acoustic resonator of claim 2 , wherein an insulating layer is provided on the top surface of the substrate and on the cavity forming groove.

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