Bulk Acoustic Wave Resonator

Abstract

The present disclosure provides a bulk acoustic wave resonator, comprising: a first electrode; a piezoelectric layer disposed on at least a portion of the first electrode; and a second electrode disposed on the piezoelectric layer. The piezoelectric layer contains a dopant, and a value of [thickness (nm) of the piezoelectric layer × concentration (at %) of the dopant] / 100 is less than or equal to 80, wherein the concentration (at %) of the dopant is calculated based on 100 at % of the total content of aluminum and the dopant in the piezoelectric layer.

Description

[0001] This application claims the benefit of priority from Korean Patent Application No. 10-2019-0141129 filed on November 6, 2019, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety for all purposes by reference. Technical Field

[0002] The following description relates to a bulk acoustic wave resonator. Background Art

[0003] With the advent of fifth-generation (5G) communications, bulk acoustic wave (BAW) filters for 5G have been developed. BAW filters for 5G have significantly wider bandwidths and shorter communication distances than existing filters, thereby improving signal strength and power.

[0004] To increase the bandwidth of BAW filters in line with this trend, it is necessary to increase the piezoelectric constant of the piezoelectric element to enhance the performance of the resonator. In addition, to withstand high power, it is necessary to reduce the loss of the piezoelectric film to improve the reliability of the BAW filter. Summary of the Invention

[0005] This summary is provided to introduce selected concepts in a simplified form and further describe the concepts in the detailed description below. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

[0006] The present disclosure provides a bulk acoustic wave resonator that can suppress abnormal growth of a piezoelectric layer.

[0007] In one general aspect, a bulk acoustic wave resonator includes: a first electrode; a piezoelectric layer disposed on at least a portion of the first electrode; and a second electrode disposed on the piezoelectric layer, wherein the piezoelectric layer contains a dopant and a value of [thickness of the piezoelectric layer (nm) × concentration of the dopant (at %)] / 100 is less than or equal to 80, wherein the concentration of the dopant (at %) is calculated based on 100 at % of the total content of aluminum and the dopant in the piezoelectric layer.

[0008] The piezoelectric layer may include aluminum nitride (AlN).

[0009] The dopant may be at least one of scandium (Sc), erbium (Er), yttrium (Y), lanthanum (La), titanium (Ti), zirconium (Zr), hafnium (Hf), tantalum (Ta), and niobium (Nb).

[0010] The dopant may be scandium (Sc), and the content of scandium (Sc) in the piezoelectric layer may be 0.1 at % to 30 at % based on 100 at % of the total content of aluminum and the dopant in the piezoelectric layer.

[0011] The content of scandium (Sc) in the piezoelectric layer may be 10 at % to 30 at % based on 100 at % of the total content of aluminum and the dopant in the piezoelectric layer.

[0012] The BAW resonator may further include a substrate disposed on the other side of the first electrode opposite to the side on which the piezoelectric layer and the second electrode are disposed; and a membrane layer disposed between the substrate and the first electrode and defining a cavity together with the substrate.

[0013] The BAW resonator may further include an etching preventing portion disposed between the substrate and the first electrode and disposed around a circumference of the cavity.

[0014] The BAW resonator may further include a sacrificial layer disposed to surround the etching preventing portion.

[0015] The membrane layer may include a seed layer comprising aluminum nitride (AlN).

[0016] The BAW resonator may further include an insertion layer at least partially disposed below a portion of the piezoelectric layer.

[0017] One or both of the first electrode and the second electrode may be formed using 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 thereof.

[0018] The root mean square (RMS) of the surface roughness of the first electrode may be less than 5 nm.

[0019] One or both of the first electrode and the second electrode may include an aluminum alloy layer including scandium (Sc).

[0020] The BAW resonator may further include a substrate disposed on the other side of the first electrode opposite to the side on which the piezoelectric layer and the second electrode are disposed, and the substrate may include a reflective layer overlapping an effective area where the first electrode, the piezoelectric layer, and the second electrode overlap each other.

[0021] The bulk acoustic wave resonator may further include: a substrate disposed on the other side of the first electrode opposite to the side on which the piezoelectric layer and the second electrode are disposed, and the substrate may include a cavity-forming groove that overlaps an effective area where the first electrode, the piezoelectric layer, and the second electrode overlap each other.

[0022] The BAW resonator may further include an insulating layer disposed on the cavity-forming groove.

[0023] In another general aspect, a bulk acoustic wave resonator includes: an input electrode; an output electrode; and a doped piezoelectric layer disposed between the input electrode and the output electrode, wherein the product of a thickness of the piezoelectric layer in nanometers and an atomic concentration percentage of a dopant in the piezoelectric layer based on 100 at % of aluminum and a total content of the dopant in the piezoelectric layer is less than or equal to 8000.

[0024] The dopant may be a rare earth metal or a transition metal.

[0025] The dopant may be scandium.

[0026] The atomic concentration percentage of the dopant may be greater than or equal to 6.25% and less than or equal to 20% based on 100 at % of the total content of aluminum and the dopant in the piezoelectric layer.

[0027] Other features and aspects will be apparent from the following detailed description, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a schematic plan view illustrating a bulk acoustic wave resonator according to an example.

[0029] Figure 2 It is along Figure 1 A cross-sectional view taken along line II'.

[0030] Figure 3 It is along Figure 1 A cross-sectional view taken along line II-II'.

[0031] Figure 4 It is along Figure 1 A cross-sectional view taken along line III-III'.

[0032] Figure 5 is a diagram used to describe the wurtzite grain structure of aluminum nitride.

[0033] Figure 6 A photograph used to depict abnormal growth of grains that are larger than normal.

[0034] Figure 7: is a table showing the abnormal growth density according to the thickness of the piezoelectric layer and the concentration of the dopant.

[0035] Figure 8 is a graph showing abnormal growth density according to the thickness of the piezoelectric layer and the concentration of the dopant.

[0036] Figure 9 is a diagram used to describe the area where abnormal growth occurs.

[0037] Figure 10 A photograph is used to depict an area where abnormal growth has occurred.

[0038] Figure 11 This is a table showing the values ​​of [thickness of the piezoelectric layer (nm)×concentration of the dopant (at%)] / 100.

[0039] Figure 12 is a schematic cross-sectional view illustrating a bulk acoustic wave resonator according to an example.

[0040] Figure 13 is a schematic cross-sectional view illustrating a bulk acoustic wave resonator according to an example.

[0041] Throughout the drawings and detailed description, like reference numerals refer to like elements. The drawings may not be drawn to scale, and the relative sizes, proportions, and depictions of elements in the drawings may be exaggerated for clarity, illustration, and convenience. DETAILED DESCRIPTION

[0042] The following detailed description is provided to help the reader gain a comprehensive understanding of the methods, devices, and / or systems described herein. However, various modifications, variations, and equivalents of the methods, devices, and / or systems described herein will be apparent to those skilled in the art. The order of operations described herein is merely an example and is not limited to the examples set forth herein. Rather, except for operations that must occur in a specific order, modifications that will be apparent to those skilled in the art may be made. In addition, for the sake of clarity and brevity, descriptions of functions and configurations that are well known to those skilled in the art may be omitted.

[0043] The features described herein may be implemented in different forms and should not be construed as limited to the examples described herein. Rather, the examples described herein are provided so that this disclosure will be thorough and complete and will fully convey the scope of the disclosure to those skilled in the art.

[0044] It is worth noting here that the use of the term "may" with respect to an example or embodiment (e.g., with respect to what an example or embodiment may include or implement) means that there is at least one example or embodiment that includes or implements such features, but all examples and embodiments are not limited thereto.

[0045] Throughout the specification, when an element such as a layer, a region, or a substrate is described as being “on,” “connected to,” or “coupled to” another element, the element may be directly “on,” “connected to,” or “coupled to” the other element, or one or more other elements may be present intervening. In contrast, when an element is described as being “directly on,” “directly connected to,” or “directly coupled to” another element, there may be no intervening elements.

[0046] As used herein, the term "and / or" includes any one and any combination of any two or more of the associated listed items.

[0047] Although terms such as "first," "second," and "third" may be used herein to describe various members, components, regions, layers, or portions, these members, components, regions, layers, or portions are not limited by these terms. Rather, these terms are used only to distinguish one member, component, region, layer, or portion from another member, component, region, layer, or portion. Thus, a first member, component, region, layer, or portion in the examples described herein may also be referred to as a second member, component, region, layer, or portion without departing from the teachings of the examples.

[0048] For ease of description, spatially relative terms such as "above," "up," "below," and "below" may be used herein to describe the relationship of one element to another element as shown in the accompanying drawings. Such spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the accompanying drawings. For example, if the device in the accompanying drawings is turned over, an element described as being "above" or "up" relative to another element would subsequently be located "below" or "below" relative to the other element. Thus, the term "above" includes both the orientations "above" and "below," depending on the spatial orientation of the device. The device may also be positioned in other ways (e.g., rotated 90 degrees or in other orientations), and the spatially relative terms used herein will be interpreted accordingly.

[0049] The terms used herein are intended only to describe various examples and are not intended to limit the present disclosure. Unless the context clearly indicates otherwise, the singular is intended to include the plural. The terms "comprising," "including," and "having" enumerate the presence of the stated features, numbers, operations, components, elements, and / or combinations thereof, but do not preclude the presence or addition of one or more other features, numbers, operations, components, elements, and / or combinations thereof.

[0050] Due to manufacturing techniques and / or tolerances, variations in the shapes shown in the drawings may occur. Therefore, the examples described herein are not limited to the specific shapes shown in the drawings but include variations in shapes that occur during manufacturing.

[0051] The features of the examples described herein may be combined in various ways that will be apparent after understanding the disclosure of the present application. In addition, although the examples described herein have various configurations, other configurations that will be apparent after understanding the disclosure of the present application are feasible.

[0052] Hereinafter, examples will be described in detail with reference to the accompanying drawings.

[0053] Figure 1 is a schematic plan view showing a bulk acoustic wave resonator according to an example, Figure 2 It is along Figure 1 A cross-sectional view taken along line II' of Figure 3 It is along Figure 1 A cross-sectional view taken along line II-II', Figure 4 It is along Figure 1 A cross-sectional view taken along line III-III'.

[0054] Reference Figures 1 to 4 The BAW resonator 100 may include a substrate 110 , a sacrificial layer 120 , an etch preventing 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 .

[0055] The substrate 110 may be a silicon substrate. For example, a silicon wafer or a silicon-on-insulator (SOI) type substrate may be used as the substrate 110 .

[0056] The insulating layer 112 may be formed on the upper surface of the substrate 110 and may electrically insulate components disposed on the substrate 110 and the substrate 110 from each other. The insulating layer 112 may be used to prevent the substrate 110 from being etched by etching gas when the cavity C is formed during a manufacturing process.

[0057] In this case, the insulating layer 112 can be formed using at least one of silicon dioxide (SiO2), silicon nitride (Si3N4), aluminum oxide (Al2O3) and aluminum nitride (AlN), and can be formed by any one of a chemical vapor deposition process, a radio frequency (RF) magnetron sputtering process and an evaporation process.

[0058] The sacrificial layer 120 may be formed on the insulating layer 112, and the cavity C and the etching preventing portion 130 may be provided in the sacrificial layer 120. The cavity C may be formed by removing a portion of the sacrificial layer 120 when being manufactured. As described above, the cavity C may be formed inside the sacrificial layer 120, and thus the first electrode 150 and the like provided on the sacrificial layer 120 may be formed to be flat.

[0059] The etch preventing portion 130 may be provided along a boundary of the cavity C. The etch preventing portion 130 may prevent etching from being performed outside the cavity region during formation of the cavity C.

[0060] The film layer 140 may form a cavity C together with the substrate 110. The film layer 140 may be formed using a material having low reactivity with an etching gas when the sacrificial layer 120 is removed. The etching preventing portion 130 may be inserted and disposed in a groove 142 formed by the film layer 140. A dielectric layer including any one of silicon nitride (Si3N4), silicon dioxide (SiO2), magnesium 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) may be used as the film layer 140.

[0061] A seed layer (not shown) formed of aluminum nitride (AlN) may be formed on the membrane layer 140. That is, the seed layer may be provided between the membrane layer 140 and the first electrode 150. In addition to aluminum nitride (AlN), the seed layer may also be formed using a dielectric material or metal having a hexagonal close-packed (HCP) grain structure. As an example, when the seed layer is formed of metal, the seed layer may be formed of titanium (Ti).

[0062] The first electrode 150 may be formed on the membrane layer 140 and may be partially disposed above the cavity C. The first electrode 150 may function as either an input electrode for inputting an electrical signal (such as a radio frequency (RF) signal) or an output electrode for outputting an electrical signal (such as a radio frequency (RF) signal).

[0063] The first electrode 150 can be formed using, for example, an aluminum alloy containing scandium (Sc). Since the first electrode 150 is formed using an aluminum alloy containing scandium (Sc), the mechanical strength of the first electrode 150 can be improved, allowing high-power reactive sputtering to be performed. Under such deposition conditions, the surface roughness of the first electrode 150 can be prevented from increasing, and highly directional growth of the piezoelectric layer 160 can be induced.

[0064] By using an aluminum alloy containing scandium (Sc) as the material for the first electrode 150, the chemical resistance of the first electrode 150 can be increased to compensate for the disadvantages of forming the first electrode using pure aluminum. Furthermore, the stability of processes such as dry etching and wet etching during the manufacture of the bulk acoustic wave resonator can be ensured. Furthermore, while oxidation is easily caused when the first electrode is formed using pure aluminum, forming the first electrode 150 using an aluminum alloy containing scandium can improve chemical resistance to oxidation.

[0065] However, the first electrode 150 is not limited to such a composition and may be formed using, for example, a conductive material such as molybdenum (Mo) or an alloy thereof. However, the first electrode 150 is not limited to such a composition and may be formed using a conductive material such as ruthenium (Ru), tungsten (W), iridium (Ir), platinum (Pt), copper (Cu), titanium (Ti), tantalum (Ta), nickel (Ni), chromium (Cr), etc., or an alloy thereof.

[0066] The piezoelectric layer 160 may be formed to cover at least the first electrode 150 disposed above the cavity C. The piezoelectric layer 160 may generate a piezoelectric effect that converts electrical energy into mechanical energy in the form of acoustic waves, and may include, for example, aluminum nitride (AlN).

[0067] The piezoelectric layer 160 may be doped with a dopant such as a rare earth metal or a transition metal. For example, the rare earth metal used as a dopant may include at least one of scandium (Sc), erbium (Er), yttrium (Y), and lanthanum (La). In addition, the transition metal used as a dopant may include at least one of titanium (Ti), zirconium (Zr), hafnium (Hf), tantalum (Ta), and niobium (Nb). The piezoelectric layer 160 may also include magnesium (Mg) as a divalent metal.

[0068] The piezoelectric layer 160 may be formed such that the value of the following formula is 80 or less.

[0069] Mode:

[0070] [Thickness of piezoelectric layer (nm) × concentration of dopant (at%)] / 100

[0071] In more detail, first, aluminum nitride (AlN) may be used as a base material of the piezoelectric layer 160. In order to continuously increase the bandwidth of the piezoelectric layer 160, the content of a dopant (such as scandium (Sc)) contained in the piezoelectric layer 160 needs to be continuously increased. However, as the content of the dopant such as scandium increases, it may become difficult to achieve a highly oriented aluminum nitride layer.

[0072] In more detail, Figure 5As shown in , aluminum nitride may have a wurtzite grain structure with an HCP structure. However, in the case where aluminum nitride is doped with a dopant such as scandium, the dopant element such as scandium may replace the position of the aluminum element. However, when the content of the dopant such as scandium increases, rapid grain growth may occur in the edge grain direction in the HCP grain structure, resulting in abnormal growth of grains larger than normal grains, such as Figure 6 As shown in .

[0073] In particular, when the content of a dopant such as scandium is further increased, the probability that such abnormal growth will occur increases, resulting in an exponential increase in the frequency of occurrence of abnormal growth.

[0074] The dopant for improving the piezoelectric characteristics of the piezoelectric layer 160 may correspond to an element having an atomic diameter greater than that of aluminum (Al). That is, since aluminum (Al) is substituted with an element having an atomic diameter greater than that of aluminum (Al), deformation may occur in the grain structure, and as the content of the dopant increases, the possibility of abnormal growth occurring due to the increase in such deformation also increases.

[0075] Abnormal growth can often be described by the grain boundary relaxation model. Abnormal film growth can occur in gaps existing at grain boundaries (the boundaries between grains), and these gaps can be sites for nucleation of abnormal growth. Abnormal growth occurring within open grain boundaries can reduce the surface free energy during film growth, a common environment.

[0076] The surface roughness of the first electrode 150 before depositing the piezoelectric layer 160 may also have a significant impact on abnormal growth. In the case where the root mean square (RMS) of the surface roughness of the first electrode 150 in the active area where the first electrode 150 and the second electrode 170 overlap each other is 5 nm or greater, the possibility of abnormal growth will increase. As described above, in the case where abnormal growth occurs in a state where the surface roughness increases, there may be a risk that the bulk acoustic wave resonator 100 will be damaged due to the abnormal growth under high output and high voltage environments. The surface roughness can be analyzed by performing atomic force microscopy (AFM) analysis or by measuring the surface roughness of the first electrode 150 obtained using a transmission electron microscope (TEM). Therefore, the RMS of the surface roughness of the first electrode 150 can be less than 5 nm.

[0077] As the content of dopants such as scandium (Sc) increases, the frequency of abnormal growth may increase. This may be because as the content of dopants such as scandium (Sc) increases, the number of open grain boundary sites increases, so that the possibility that abnormal growth will occur also increases.

[0078] In addition, for the content of each dopant (such as scandium (Sc)), sputtering deposition can be performed using an AlSc alloy target through a reactive reaction with nitrogen. The density of abnormal growth can be confirmed by scanning electron microscopy (SEM) while gradually increasing the thickness of the AlScN film from 200 nm to 1300 nm at intervals of 100 nm. Generally, the composition analysis of the dopant (such as scandium (Sc)) in the AlScN film can be performed by TEM, and when the total content of aluminum (Al) and the dopant (such as scandium (Sc)) is 100 at%, the dopant composition can be expressed by the content ratio (at%) of the dopant (such as scandium (Sc)).

[0079] like Figure 7 and Figure 8 As shown in FIG, even if the contents of the dopant (such as scandium (Sc)) contained in the piezoelectric layer 160 are the same as each other, the occurrence of abnormal growth may increase and the size of the abnormal growth may also increase in the case where the thickness of the piezoelectric layer 160 increases. This phenomenon may occur because not only normal grain growth but also abnormal grain growth occurs in terms of grain growth according to the increase in the thickness of the piezoelectric layer 160.

[0080] from Figure 9 As can be seen from FIG, the abnormal growth of the piezoelectric layer 160 does not occur in the initial stage, but starts from the piezoelectric layer 160 having a predetermined thickness or greater. Figure 10 As can be seen in FIG. 1 , in the case where a focused ion beam (FIB) cross-sectional analysis is performed on the piezoelectric layer 160 where abnormal growth actually occurs, the abnormal growth starts from the piezoelectric layer 160 having a predetermined thickness or more.

[0081] from Figure 7 and Figure 8 As can be seen from FIG, when the content of the dopant such as scandium (Sc) is 6.25 at%, abnormal growth is observed from when the thickness of the piezoelectric layer 160 is 1300 nm. Figure 7 and Figure 8 As can be seen from FIG, when the content of the dopant such as scandium (Sc) is 12.5 at%, abnormal growth is observed from when the thickness of the piezoelectric layer 160 is 700 nm. Figure 7 and Figure 8 As can be seen from FIG. 1 , in the case where the content of the dopant such as scandium (Sc) is 20 at %, abnormal growth is observed starting when the thickness of the piezoelectric layer 160 is 500 nm.

[0082] Therefore, when the state in which abnormal growth does not occur is confirmed by the above formula, it can be seen that the value of [thickness of the piezoelectric layer (nm)×concentration of the dopant (at%)] / 100 is 80 or less. That is, Figure 11As shown in , abnormal growth may occur in a portion surrounded by a thick line (that is, in a case where the value of [thickness of the piezoelectric layer (nm)×concentration of the dopant (at %)] / 100 is greater than 80).

[0083] As a result, when a bulk acoustic wave (BAW) filter is manufactured using a piezoelectric layer having a thickness at which abnormal growth does not occur depending on the content of a dopant such as scandium (Sc), the BAW filter can be manufactured without causing defects in the piezoelectric layer 160. Without defects in the piezoelectric layer 160, the piezoelectric layer 160 of the bulk acoustic wave resonator 100 having high reliability under high output and high voltage conditions can be realized, thereby contributing to improved reliability of the bulk acoustic wave resonator 100.

[0084] When the dopant is scandium (Sc), the content of scandium (Sc) in the piezoelectric layer 160 may be 0.1 at % to 30 at %. Compared to the case where the piezoelectric layer is formed using aluminum nitride (AlN), the content of scandium (Sc) as a dopant needs to be 0.1 at % or more to achieve high piezoelectric performance. When the content of scandium (Sc) is greater than 30 at %, it may be difficult to manufacture an AlSc alloy target. When the content of scandium (Sc) is greater than 30 at %, when the AlSc alloy target is manufactured by a melting method, there may be a problem that the AlSc alloy target is brittle, making it difficult to produce and process the AlSc alloy target.

[0085] In addition, when the dopant is scandium (Sc), the content of scandium (Sc) in the piezoelectric layer 160 may be 10 at % to 30 at %. That is, when the content of scandium (Sc) is less than 10 at %, the frequency of abnormal growth may be small as the thickness of the piezoelectric layer 160 increases, but when the content of scandium (Sc) is 10 at % or more, the frequency of abnormal growth of the piezoelectric layer 160 may increase rapidly.

[0086] In particular, when the content of a dopant such as scandium (Sc) is 10at% or greater, the frequency of abnormal growth may increase, and therefore it may be more preferable to manufacture the piezoelectric layer 160 having a dopant content within this numerical range. That is, when the scandium (Sc) content in the piezoelectric layer 160 is controlled to be 10at% to 30at% in order to achieve high piezoelectric performance, it may be more effective to control the dopant content and the thickness of the piezoelectric layer 160 according to the above formula. In addition, according to an embodiment of the present invention, the atomic concentration percentage of the dopant may be greater than or equal to 6.25% and less than or equal to 20%.

[0087] The piezoelectric layer 160 may include a piezoelectric portion 162 disposed in the flat portion S and a bent portion 164 disposed in the extended portion E.

[0088] The piezoelectric portion 162 may be a portion directly stacked on the upper surface of the first electrode 150. Therefore, the piezoelectric portion 162 may be interposed between the first electrode 150 and the second electrode 170 and formed flat together with the first electrode 150 and the second electrode 170.

[0089] The bent portion 164 may refer to a region extending outward from the piezoelectric portion 162 and located in the extension portion E.

[0090] The bent portion 164 may be provided on the insertion layer 180 and may have a form protruding along the shape of the insertion layer 180. Therefore, the piezoelectric layer 160 may be bent at the boundary between the piezoelectric portion 162 and the bent portion 164, and the bent portion 164 may protrude according to the thickness and shape of the insertion layer 180.

[0091] The bent portion 164 may be divided into an inclined portion 164 a and an extending portion 164 b .

[0092] The inclined portion 164a may refer to a portion inclined along the inclined surface L of the insert layer 180. The extending portion 164b may refer to a portion extending outward from the inclined portion 164a.

[0093] The inclined portion 164 a may be formed in parallel with the inclined surface L of the insertion layer 180 , and an inclination angle of the inclined portion 164 a may be the same as an inclination angle of the inclined surface L of the insertion layer 180 .

[0094] The second electrode 170 may be formed to cover at least the piezoelectric layer 160 disposed above the cavity C. The second electrode 170 may be used as either an input electrode for inputting an electrical signal (such as a radio frequency (RF) signal) or an output electrode for outputting an electrical signal (such as a radio frequency (RF) signal). That is, when the first electrode 150 is used as an input electrode, the second electrode 170 may be used as an output electrode, and when the first electrode 150 is used as an output electrode, the second electrode 170 may be used as an input electrode.

[0095] The second electrode 170 may be formed using, for example, an aluminum alloy containing scandium (Sc). However, the second electrode 170 is not limited to such a composition and may be formed using, for example, a conductive material such as molybdenum (Mo) or an alloy thereof. However, the second electrode 170 is not limited to such a composition and may be formed using 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.

[0096] The insertion layer 180 may be formed between the first electrode 150 and the piezoelectric layer 160. The insertion layer 180 may be formed using a dielectric material such as silicon dioxide (SiO2), aluminum nitride (AlN), aluminum oxide (Al2O3), silicon nitride (Si3N4), magnesium oxide (MgO), zirconium oxide (ZrO2), lead zirconate titanate (PZT), gallium arsenide (GaAs), hafnium oxide (HfO2), titanium oxide (TiO2), zinc oxide (ZnO), etc., but may be formed using a material different from that of the piezoelectric layer 160. If desired, the region in which the insertion layer 180 is provided may be formed as air. This air can be achieved by removing the insertion layer 180 during the manufacturing process.

[0097] The insertion layer 180 may be formed to have a thickness that is the same as or similar to that of the first electrode 150. The insertion layer 180 may be formed to have a thickness that is similar to or smaller than that of the piezoelectric layer 160. For example, the insertion layer 180 may be formed to have or greater, and may be formed to have a thickness smaller than that of the piezoelectric layer 160. However, the configuration of the insertion layer 180 and the piezoelectric layer 160 is not limited to this configuration.

[0098] The insertion layer 180 may be disposed along a surface formed by the membrane layer 140 , the first electrode 150 , and the etch preventing portion 130 .

[0099] The insertion layer 180 may be disposed near the flat portion S and support the bent portion 164 of the piezoelectric layer 160 . Therefore, the bent portion 164 of the piezoelectric layer 160 may be divided into an inclined portion 164 a and an extended portion 164 b along the shape of the insertion layer 180 .

[0100] The insertion layer 180 may be provided in the region except the flat portion S. For example, the insertion layer 180 may be provided over the entire region except the flat portion S, or may be provided in a portion of the region except the flat portion S.

[0101] At least a portion of the insertion layer 180 may be disposed between the piezoelectric layer 160 and the first electrode 150 .

[0102] The side surface of the insertion layer 180 disposed along the boundary of the flat portion S may have a thickness that increases with distance from the flat portion S. Therefore, the side surface of the insertion layer 180 disposed adjacent to the flat portion S may be formed as an inclined surface L having a predetermined inclination angle θ.

[0103] When the inclination angle θ of the side surface of the insertion layer 180 is less than 5°, the thickness of the insertion layer 180 needs to be very small, or the area of ​​the inclined surface L needs to be too large, so as to manufacture the insertion layer 180 with the inclination angle θ of the side surface less than 5°, which is basically difficult to achieve.

[0104] When 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 stacked on the insertion layer 180 may be greater than 70°. In this case, the piezoelectric layer 160 is excessively bent, so that cracks may occur in the bent portion of the piezoelectric layer 160.

[0105] Therefore, in an example, the inclination angle θ of the inclined surface L may be within a range of greater than or equal to 5° and less than or equal to 70°.

[0106] The passivation layer 190 may be formed in both a region where a portion of the first electrode 150 overlaps a portion of the second electrode 170 and a region where a portion of the first electrode 150 does not overlap a portion of the second electrode 170. The passivation layer 190 may be used to prevent the second electrode 170 and the first electrode 150 from being damaged during processing.

[0107] Furthermore, a portion of the passivation layer 190 can be etched and removed to adjust the frequency in the final process. That is, the thickness of the passivation layer 190 can be adjusted. For example, a dielectric layer containing any one of silicon nitride (Si3N4), silicon dioxide (SiO2), magnesium 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) can be used as the passivation layer 190.

[0108] Metal pad 195 may be formed in portions of first electrode 150 and second electrode 170 where passivation layer 190 is not formed. As an example, metal pad 195 may be formed using a material such as gold (Au), a gold-tin (Au-Sn) alloy, copper (Cu), a copper-tin (Cu-Sn) alloy, aluminum (Al), an aluminum alloy, etc. For example, the aluminum alloy may be an aluminum-germanium (Al-Ge) alloy.

[0109] As described above, the value of [thickness of the piezoelectric layer (nm)×concentration of the dopant (at %)] / 100 may be 80 or less, and thus abnormal growth of the piezoelectric layer 160 may be prevented.

[0110] Figure 12 is a schematic cross-sectional view illustrating a bulk acoustic wave resonator according to an example.

[0111] Reference Figure 12 The BAW resonator 200 may include 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 .

[0112] The substrate 210 may be a substrate in which silicon is stacked. For example, a silicon wafer may be used as the substrate 210. The substrate 210 may be provided with a reflective layer 211.

[0113] The reflective layer 211 may be disposed under the active region. Here, the active region may refer to a region where the first electrode 230, the piezoelectric layer 240, and the second electrode 250 are disposed to overlap each other.

[0114] The reflective layer 211 may include a first reflective member 212 and a second reflective member 214 disposed in the groove. The first reflective member 212 and the second reflective member 214 may be formed using different materials.

[0115] The first reflective member 212 can be formed using a conductive material such as molybdenum (Mo) or its alloy. However, the first reflective member 212 is not limited to such a composition and can be formed using ruthenium (Ru), tungsten (W), iridium (Ir), platinum (Pt), copper (Cu), aluminum (Al), titanium (Ti), tantalum (Ta), nickel (Ni), chromium (Cr), etc. A dielectric layer containing any one of silicon nitride (Si3N4), silicon dioxide (SiO2), magnesium 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) can be used as the second reflective member 214. A total of four first reflective members 212 and second reflective members 214 can be provided, that is, two pairs of first reflective members 212 and second reflective members 214. However, the first and second reflective members 212 and 214 are not limited to this configuration, and a pair of the first and second reflective members 212 and 214 may be provided, or three or more pairs of the first and second reflective members 212 and 214 may be provided.

[0116] The first reflective member 212 may be formed using a material having a higher density than that of the second reflective member 214 .

[0117] The film layer 220 may be formed as the reflective layer 211 covering the substrate 210. A dielectric layer including any one of silicon nitride (Si3N4), silicon dioxide (SiO2), magnesium 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) may be used as the film layer 220.

[0118] A seed layer (not shown) formed of aluminum nitride (AlN) may be formed on the film layer 220. That is, the seed layer may be disposed between the film layer 220 and the first electrode 230. In addition to aluminum nitride (AlN), the seed layer may also be formed using a dielectric material or metal having a hexagonal close-packed (HCP) grain structure. As an example, when the seed layer is formed of metal, the seed layer may be formed of titanium (Ti).

[0119] The first electrode 230 may be formed on the film layer 220. The first electrode 230 may be used as either an input electrode for inputting an electrical signal such as a radio frequency (RF) signal or an output electrode for outputting an electrical signal such as a radio frequency (RF) signal.

[0120] The first electrode 230 can be formed using, for example, an aluminum alloy containing scandium (Sc). Since the first electrode 230 is formed using an aluminum alloy containing scandium (Sc), the mechanical strength of the first electrode 230 can be improved, allowing high-power reactive sputtering to be performed. Under such deposition conditions, the surface roughness of the first electrode 230 can be prevented from increasing, and highly oriented growth of the piezoelectric layer 240 can be induced.

[0121] By using an aluminum alloy containing scandium (Sc) as the material for the first electrode 230, the chemical resistance of the first electrode 230 can be increased, thereby compensating for the disadvantages of forming the first electrode using pure aluminum. Furthermore, the stability of processes such as dry etching and wet etching processes during the manufacture of the bulk acoustic wave resonator can be ensured. Furthermore, while the first electrode 230 is susceptible to oxidation when formed using pure aluminum, forming the first electrode 230 using an aluminum alloy containing scandium can improve chemical resistance to oxidation.

[0122] However, the first electrode 230 is not limited to such a composition and may be formed using, for example, a conductive material such as molybdenum (Mo) or an alloy thereof. However, the first electrode 230 is not limited to such a composition and may be formed using a conductive material such as ruthenium (Ru), tungsten (W), iridium (Ir), platinum (Pt), copper (Cu), titanium (Ti), tantalum (Ta), nickel (Ni), chromium (Cr), etc., or alloys thereof.

[0123] The first electrode 230 may have a surface roughness RMS of less than 5 nm.

[0124] The piezoelectric layer 240 may be formed to cover at least the first electrode 230 disposed above the reflective layer 211. The piezoelectric layer 240 may generate a piezoelectric effect that converts electrical energy into mechanical energy in the form of acoustic waves, and may include, for example, aluminum nitride (AlN).

[0125] 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 a dopant may include at least one of scandium (Sc), erbium (Er), yttrium (Y), and lanthanum (La). In addition, the transition metal used as a dopant may include at least one of titanium (Ti), zirconium (Zr), hafnium (Hf), tantalum (Ta), and niobium (Nb). The piezoelectric layer 240 may also include magnesium (Mg) as a divalent metal.

[0126] The piezoelectric layer 240 may be formed such that the value of the following formula is 80 or less.

[0127] Mode:

[0128] [Thickness of piezoelectric layer (nm) × concentration of dopant (at%)] / 100

[0129] The piezoelectric layer 240 may include a piezoelectric portion 242 disposed in the flat portion S and a bent portion 244 disposed in the extended portion E.

[0130] The piezoelectric portion 242 may be a portion directly stacked on the upper surface of the first electrode 230. Therefore, the piezoelectric portion 242 may be interposed between the first electrode 230 and the second electrode 250 and may be formed flat together with the first electrode 230 and the second electrode 250.

[0131] The bent portion 244 may refer to a region extending outward from the piezoelectric portion 242 and located in the extension portion E.

[0132] The bent portion 244 may be provided on the insertion layer 260 and may have a form protruding along the shape of the insertion layer 260. Therefore, the piezoelectric layer 240 may be bent at the boundary between the piezoelectric portion 242 and the bent portion 244, and the bent portion 244 may protrude according to the thickness and shape of the insertion layer 260.

[0133] The bent portion 244 may be divided into an inclined portion 244 a and an extended portion 244 b .

[0134] The inclined portion 244a may refer to a portion inclined along the inclined surface L of the insertion layer 260. The extending portion 244b may refer to a portion extending outward from the inclined portion 244a.

[0135] The inclined portion 244 a may be formed in parallel with the inclined surface L of the insertion layer 260 , and an inclination angle of the inclined portion 244 a may be the same as an inclination angle of the inclined surface L of the insertion layer 260 .

[0136] The second electrode 250 may be formed to cover at least the piezoelectric layer 240 disposed above the reflective layer 211. The second electrode 250 may be used as either an input electrode for inputting an electrical signal (such as a radio frequency (RF) signal) or an output electrode for outputting an electrical signal (such as a radio frequency (RF) signal). That is, when the first electrode 230 is used as an input electrode, the second electrode 250 may be used as an output electrode, and when the first electrode 230 is used as an output electrode, the second electrode 250 may be used as an input electrode.

[0137] The second electrode 250 may be formed using, for example, a conductive material such as molybdenum (Mo) or an alloy thereof. However, the second electrode 250 is not limited to this configuration and may be formed using 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.

[0138] The insertion layer 260 may be formed between the first electrode 230 and the piezoelectric layer 240. The insertion layer 260 may be formed using a dielectric material such as silicon dioxide (SiO2), aluminum nitride (AlN), aluminum oxide (Al2O3), silicon nitride (Si3N4), magnesium oxide (MgO), zirconium oxide (ZrO2), lead zirconate titanate (PZT), gallium arsenide (GaAs), hafnium oxide (HfO2), titanium oxide (TiO2), zinc oxide (ZnO), etc., but may be formed using a material different from that of the piezoelectric layer 240. If desired, the region in which the insertion layer 260 is provided may be formed as air. This air can be achieved by removing the insertion layer 260 during the manufacturing process.

[0139] The insertion layer 260 may be formed to have a thickness that is the same as or similar to that of the first electrode 230. The insertion layer 260 may be formed to have a thickness that is similar to or smaller than that of the piezoelectric layer 240. For example, the insertion layer 260 may be formed to have or greater, and may be formed to have a thickness smaller than that of the piezoelectric layer 240. However, the configuration of the insertion layer 260 and the piezoelectric layer 240 is not limited to this configuration.

[0140] The insertion layer 260 may be disposed along a surface formed by the membrane layer 220 and the first electrode 230 .

[0141] The insertion layer 260 may be disposed near the flat portion S and support the bent portion 244 of the piezoelectric layer 240 . Therefore, the bent portion 244 of the piezoelectric layer 240 may be divided into an inclined portion 244 a and an extended portion 244 b along the shape of the insertion layer 260 .

[0142] The insertion layer 260 may be provided in a region other than the flat portion S. For example, the insertion layer 260 may be provided over the entire region other than the flat portion S, or may be provided in a portion of the region other than the flat portion S.

[0143] At least a portion of the insertion layer 260 may be disposed between the piezoelectric layer 240 and the first electrode 230 .

[0144] The passivation layer 270 may be formed in both the region where a portion of the first electrode 230 overlaps a portion of the second electrode 250 and the region where a portion of the first electrode 230 does not overlap a portion of the second electrode 250. The passivation layer 270 may be used to prevent the second electrode 250 and the first electrode 230 from being damaged during the process.

[0145] Furthermore, a portion of the passivation layer 270 can be etched and removed to adjust the frequency in the final process. That is, the thickness of the passivation layer 270 can be adjusted. For example, a dielectric layer containing any one of silicon nitride (Si3N4), silicon dioxide (SiO2), magnesium 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) can be used as the passivation layer 270.

[0146] Metal pad 280 may be formed in portions of first electrode 230 and second electrode 250 where passivation layer 270 is not formed. As an example, metal pad 280 may be formed using a material such as gold (Au), a gold-tin (Au-Sn) alloy, copper (Cu), a copper-tin (Cu-Sn) alloy, aluminum (Al), an aluminum alloy, etc. For example, the aluminum alloy may be an aluminum-germanium (Al-Ge) alloy.

[0147] As described above, the value of [thickness of the piezoelectric layer (nm)×concentration of the dopant (at %)] / 100 may be 80 or less, and thus abnormal growth of the piezoelectric layer 240 may be prevented.

[0148] Figure 13 is a schematic cross-sectional view illustrating a bulk acoustic wave resonator according to an example.

[0149] Reference Figure 13 The BAW resonator 300 may include 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 .

[0150] Since 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 Figure 12The 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 included in the BAW resonator 200 shown in FIG. 1 are substantially the same, and thus a detailed description thereof is omitted.

[0151] The substrate 310 may be a substrate in which silicon is stacked. For example, a silicon wafer may be used as the substrate 310 .

[0152] The substrate 310 may be provided with a cavity forming groove 311 for forming the cavity C. An insulating layer 312 may be formed on the substrate 310 and may electrically insulate the components provided on the substrate 310 and the substrate 310 from each other. The insulating layer 312 may be used to prevent the substrate 310 from being etched by an etching gas when the cavity C is formed during the manufacturing process.

[0153] In this case, the insulating layer 312 can be formed using at least one of silicon dioxide (SiO2), silicon nitride (Si3N4), aluminum oxide (Al2O3) and aluminum nitride (AlN), and can be formed by any one of a chemical vapor deposition process, a radio frequency (RF) magnetron sputtering process and an evaporation process.

[0154] As described above, according to various examples, abnormal growth of the piezoelectric layer can be suppressed.

[0155] Although the present disclosure includes specific examples, it will be apparent to those skilled in the art that various changes in form and detail may be made in these examples without departing from the spirit and scope of the claims and their equivalents. The examples described herein are to be considered as descriptive only and not for purposes of limitation. The description of the features or aspects in each example will be considered to be applicable to similar features or aspects in other examples. Suitable results may be obtained if the described techniques are performed in a different order, and / or if the components in the described systems, architectures, devices, or circuits are combined in a different manner, and / or if the components in the described systems, architectures, devices, or circuits are replaced or added by other components or their equivalents. Therefore, the scope of the present disclosure is not limited by specific embodiments, but by the claims and their equivalents, and all changes within the scope of the claims and their equivalents will be interpreted as being included in the present disclosure.

Claims

1. A bulk acoustic wave resonator, comprising: a first electrode; a piezoelectric layer disposed on at least a portion of the first electrode; as well as a second electrode, disposed on the piezoelectric layer, The piezoelectric layer comprises aluminum nitride, which has a close-packed hexagonal wurtzite grain structure, and further comprises a dopant. a value of [thickness of the piezoelectric layer×concentration of the dopant] / 100 is less than or equal to 80, wherein the thickness of the piezoelectric layer is in nm and the concentration of the dopant in at % is calculated based on 100 at % of the total content of aluminum and the dopant in the piezoelectric layer, The dopant is scandium, and the content of scandium in the piezoelectric layer is 10 at % to 30 at % based on 100 at % of the total content of aluminum and the dopant in the piezoelectric layer.

2. The bulk acoustic wave resonator according to claim 1, wherein The thickness of the piezoelectric layer is 200 nm to 1200 nm.

3. The BAW resonator according to claim 1, wherein The content of scandium in the piezoelectric layer is 12.5 at % to 20 at % based on 100 at % of the total content of aluminum and dopants in the piezoelectric layer.

4. The bulk acoustic wave resonator according to claim 3, wherein The thickness of the piezoelectric layer is 200 nm to 600 nm.

5. The BAW resonator according to claim 1 , further comprising: a substrate provided on the other side of the first electrode opposite to the side on which the piezoelectric layer and the second electrode are provided; as well as The membrane layer is disposed between the substrate and the first electrode and defines a cavity together with the substrate.

6. The BAW resonator according to claim 5, further comprising: An etching preventing portion is provided between the substrate and the first electrode and is provided around the outer periphery of the cavity.

7. The BAW resonator according to claim 6, further comprising: The sacrificial layer is disposed to surround the etching preventing portion.

8. The BAW resonator according to claim 5, wherein The membrane layer includes a seed layer comprising aluminum nitride.

9. The BAW resonator according to claim 1, further comprising: An insertion layer is at least partially disposed below a portion of the piezoelectric layer.

10. The BAW resonator according to claim 1, wherein One or both of the first electrode and the second electrode is formed using one of molybdenum, ruthenium, tungsten, iridium, platinum, copper, titanium, tantalum, nickel, and chromium, or an alloy thereof.

11. The BAW resonator according to claim 1, wherein The root mean square of the surface roughness of the first electrode is less than 5 nm.

12. The BAW resonator according to claim 1, wherein One or both of the first electrode and the second electrode includes an aluminum alloy layer including scandium.

13. The BAW resonator according to claim 1, further comprising: A substrate is arranged on the other side of the first electrode opposite to the side on which the piezoelectric layer and the second electrode are arranged, wherein the substrate includes a reflective layer that overlaps an effective area where the first electrode, the piezoelectric layer, and the second electrode overlap each other.

14. The BAW resonator according to claim 1, further comprising: A substrate is arranged on the other side of the first electrode opposite to the side on which the piezoelectric layer and the second electrode are arranged, wherein the substrate includes a cavity-forming groove, and the cavity-forming groove overlaps an effective area where the first electrode, the piezoelectric layer and the second electrode overlap each other.

15. The BAW resonator according to claim 14, further comprising: An insulating layer is provided on the cavity forming groove.

16. A bulk acoustic wave resonator, comprising: Input electrodes; output electrode; as well as A doped piezoelectric layer is provided between the input electrode and the output electrode, wherein the piezoelectric layer comprises aluminum nitride having a close-packed hexagonal wurtzite grain structure, wherein: The product of the thickness of the piezoelectric layer in nanometers and the atomic concentration percentage of the dopant in the piezoelectric layer based on 100 at % of the total content of aluminum and the dopant in the piezoelectric layer is less than or equal to 8000, and The dopant is scandium, and the content of scandium in the piezoelectric layer is 10 at % to 30 at % based on 100 at % of the total content of aluminum and the dopant in the piezoelectric layer.

17. The BAW resonator according to claim 16, wherein: The thickness of the piezoelectric layer is 200 nm to 1200 nm.

18. The BAW resonator according to claim 16, wherein Based on 100 at % of the total content of aluminum and the dopant in the piezoelectric layer, the atomic concentration percentage of the dopant is greater than or equal to 12.5% ​​and less than or equal to 20%, and the thickness of the piezoelectric layer is 200 nm to 600 nm.

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