Bulk acoustic wave resonator, method of determining a doping concentration, filter, and electronic device

Abstract

The present application relates to a bulk acoustic wave resonator, comprising: a substrate; an acoustic mirror; a bottom electrode; a piezoelectric layer; and a top electrode, wherein: the resonator has a resonance frequency lower than 2.5 GHz and has a layer thickness ratio E / P; the resonator has an electromechanical coupling coefficient Kt 2 , the doping concentration is not less than a1, a1 being the electromechanical coupling coefficient Kt 2 corresponding to a layer thickness ratio E / P = 1.5. The present application also relates to a doping concentration determination method, the doping concentration being the doping concentration of a doping element of a piezoelectric layer of a bulk acoustic wave resonator, the resonator having an electromechanical coupling coefficient Kt 2 , the resonator having a resonance frequency lower than 2.5 GHz and having a layer thickness ratio E / P, the method comprising the step of: based on the layer thickness ratio E / P, selecting the doping concentration to be not less than a1, a1 being the electromechanical coupling coefficient Kt 2 corresponding to a layer thickness ratio E / P = 1.5. The present application also relates to a filter and an electronic device.

Description

TECHNICAL FIELD

[0001] Embodiments of the present application relate to the field of semiconductor, and in particular, to a bulk acoustic wave resonator and a method for determining a doping concentration, and a filter and an electronic device. BACKGROUND

[0002] With the development of 5G communication technology, the communication technology puts forward higher and higher requirements on the large bandwidth of the filter. Under this premise, the design of the filter puts forward urgent needs for the resonator with larger effective electromechanical coupling coefficient (kt 2 ).

[0003] As a new type of MEMS device, the film bulk acoustic resonator (FBAR) has the advantages of small size, light weight, low insertion loss, wide frequency band, and high quality factor, which well adapts to the upgrading of wireless communication systems.

[0004] In the prior art, there is still a demand to improve the Q value of the resonator while keeping the kt 2 of the resonator large.

[0005] In addition, as the frequency of the resonator decreases, the area of the resonator will increase under the condition that the Kt 2 is fixed, and the area of the resonator increases, so the area of the filter also increases, thereby reducing the number of die output from a single wafer. Therefore, in the prior art, there is also a demand to make the area of the resonator small while keeping the kt 2 of the resonator large. SUMMARY

[0006] To alleviate or solve at least one aspect of the above problems in the prior art, the present application is proposed.

[0007] According to an aspect of an embodiment of the present application, a bulk acoustic wave resonator is provided, comprising:

[0008] a substrate;

[0009] an acoustic mirror;

[0010] a bottom electrode;

[0011] a piezoelectric layer, the piezoelectric layer being a piezoelectric layer comprising a doping element, the doping element having a corresponding doping concentration; and

[0012] a top electrode,

[0013] wherein:

[0014] the resonator has a resonant frequency lower than 2.5 GHz and has a layer thickness ratio E / P;

[0015] the resonator has an electromechanical coupling coefficient Kt2 corresponding to the doping concentration. 2 corresponding to the doping concentration.

[0016] Embodiments of the present application also relate to a method for determining a doping concentration of a piezoelectric layer of a bulk acoustic wave resonator, the resonator having an electromechanical coupling coefficient Kt 2 , the resonator having a resonance frequency lower than 2.5 GHz and having a layer thickness ratio E / P, the method comprising the steps of:

[0017] selecting, based on the layer thickness ratio E / P, the doping concentration not to be less than a1, a1 being the electromechanical coupling coefficient Kt 2 corresponding to the doping concentration.

[0018] Embodiments of the present application also relate to a filter comprising the resonator described above.

[0019] Embodiments of the present application also relate to an electronic device comprising the filter described above or the resonator described above. BRIEF DESCRIPTION OF DRAWINGS

[0020] The following description with the accompanying drawings can better help understand these and other features and advantages of the various embodiments disclosed by the present application, in which the same reference numerals always designate the same components, in which:

[0021] Figure 1 is a schematic cross-sectional view of a bulk acoustic wave resonator;

[0022] Figure 2 is a graph exemplarily showing the relationship between the E / P value and the width of the protruding structure and the Q value of the resonator;

[0023] Figure 3 is a graph exemplarily showing the relationship between the width of the protruding structure and the Q value of the resonator;

[0024] Figure 4 is a graph exemplarily showing the relationship between the E / P value and the Kt 2 ;

[0025] Figure 5 is a graph exemplarily showing the relationship between the doping concentration and the Kt 2 with the same E / P, wherein E / P = 1.5;

[0026] Figure 6 is a graph exemplarily showing the relationship between the doping concentration and the Kt 2 with the same E / P, wherein E / P = 1.7;

[0027] Figure 7Exemplary plot of doping concentration versus Kt for the same E / P, where E / P = 1.85. 2

[0028] Figure 8 Exemplary plot of doping concentration versus Kt for the same E / P, where E / P = 2. 2

[0029] Figure 9 Exemplary plot of doping concentration versus resonator area for a resonator with a frequency of 1.75 GHz for the same Kt. 2

[0030] Figure 10 Exemplary plot of doping concentration versus resonator area for a resonator with a frequency of 3.5 GHz for the same Kt. 2 DETAILED DESCRIPTION

[0031] The technical solutions of the present application will be further described below by way of examples in conjunction with the accompanying drawings. In the description, identical or similar reference numerals indicate identical or similar components. The following description of the embodiments of the present application with reference to the accompanying drawings is intended to explain the general inventive concept of the present application, and should not be understood as a limitation of the present application. The embodiments described below are only a part of the embodiments of the present application, and not all the embodiments of the present application. All other embodiments obtained by those skilled in the art based on the embodiments in the present application are within the scope of protection of the present application.

[0032] Figure 1 A cross-sectional view of a typical sandwich structure bulk acoustic wave resonator is shown. Figure 1 In the drawings, the following reference numerals are used:

[0033] 101: substrate, which can be made of single crystal silicon, gallium nitride, gallium arsenide, sapphire, quartz, silicon carbide, diamond, etc.

[0034] 102: acoustic mirror, which can be a cavity, or can be a Bragg reflection layer or other equivalent form. In the embodiments of the present application, the cavity form is used.

[0035] 103: bottom electrode (including bottom electrode pin), which can be made of molybdenum, ruthenium, gold, aluminum, magnesium, tungsten, copper, titanium, iridium, osmium, chromium, or a composite of the above metals or an alloy thereof, etc.

[0036] ​​​​104: piezoelectric layer, which can be a single crystal piezoelectric material, such as single crystal aluminum nitride, single crystal gallium nitride, single crystal lithium niobate, single crystal lead zirconate titanate (PZT), single crystal potassium niobate, single crystal quartz thin film, or single crystal lithium tantalate, or a polycrystalline piezoelectric material (as opposed to a single crystal material, a non-single crystal material), such as polycrystalline aluminum nitride, zinc oxide, PZT, or a rare earth element doped material containing the above materials in a certain atomic ratio, such as doped aluminum nitride containing at least one rare earth element, such as scandium (Sc), yttrium (Y), magnesium (Mg), titanium (Ti), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).

[0037] 105: top electrode (including top electrode pin), which can be made of molybdenum, ruthenium, gold, aluminum, magnesium, tungsten, copper, titanium, iridium, osmium, chromium, or a composite of the above metals or an alloy thereof.

[0038] 106: passivation layer or process layer, which can be aluminum nitride, silicon nitride, or silicon dioxide.

[0039] 107: protruding structure, which can be made of molybdenum, ruthenium, gold, aluminum, magnesium, tungsten, copper, titanium, iridium, osmium, chromium, or a composite of the above metals or an alloy thereof.

[0040] For a bulk acoustic wave resonator, the electromechanical coupling coefficient Kt 2 is related to the value of the layer thickness ratio E / P and the doping concentration of the doping element in the piezoelectric layer. In addition, the Q value of the bulk acoustic wave resonator is related to the value of the layer thickness ratio E / P.

[0041] Furthermore, the area of the resonator (referring to the area of the effective region of the resonator, and the effective region refers to the region formed by the overlapping of the top electrode, the piezoelectric layer, the bottom electrode, and the acoustic mirror in the thickness direction of the resonator) increases with the decrease of the resonant frequency of the resonator when the electromechanical coupling coefficient of the resonator is fixed.

[0042] The present application proposes a scheme for reducing the area of the resonator by selecting a doping concentration higher than the doping concentration based on a certain layer thickness ratio, so that both a higher resonator Q value and a higher Kt 2 value can be obtained, and the area of the resonator can be made smaller.

[0043] The layer thickness ratio E / P is briefly described below.

[0044] For example, the layer thickness ratio E / P can be expressed as follows: Figure 1As shown, the thickness of the bottom electrode 103 is t1, the thickness of the piezoelectric layer 104 is t2, the thickness of the top electrode 105 is t3, and the thickness of the passivation layer 106 above the top electrode is t4. When the passivation layer 106 is not provided, the ratio of the electrode thickness to the piezoelectric layer thickness, i.e., the layer thickness ratio E / P, is defined as (t1+t3) / t2. When the resonator has the passivation layer 106, the ratio of the electrode thickness to the piezoelectric layer thickness, i.e., the layer thickness ratio E / P, is defined as (t1+t3+t4*a) / t2, where a is related to the ratio of the rate of influence of the thickness of the passivation layer 106 on the resonant frequency Fs of the resonator to the rate of influence of the thickness of the top electrode 105 on the resonant frequency Fs of the resonator. Specifically, assuming that the rate of influence of the thickness of the passivation layer 106 on the resonant frequency Fs of the resonator is V1 nm / MHz and the rate of influence of the thickness of the top electrode 105 on the resonant frequency Fs of the resonator is V2 nm / MHz, then a = V2 / V1. If Mo is selected as the material of the top and bottom electrodes and AlN is selected as the material of the passivation layer, then the value of a is close to 1 / 3. If the stacked structure of the resonator is increased by other functional layers on the basis of the above, the layer thickness ratio E / P can also be calculated based on the above concept.

[0045] The doping concentration of the doped element in the piezoelectric layer will be briefly described below.

[0046] Doping means that part of one or more elements in the piezoelectric material that is originally not doped is replaced by a doped element. At this time, the doping concentration is defined as the ratio of the number of atoms of the doped element to the sum of the number of atoms of the one or more elements that are partially replaced by the doped element in a unit volume. For example, in the case where the piezoelectric layer is aluminum nitride and the doped element is scandium, part of the aluminum atoms is replaced by scandium atoms, and the doping concentration is the ratio of the number of scandium atoms to the sum of the number of aluminum atoms and the number of scandium atoms in a unit volume (Sc / Al+Sc).

[0047] In addition, the area A of the resonator satisfies the following formula:

[0048] A∝t2 / (Fs*ε)–(1)

[0049] A: area of the 50Ω resonator

[0050] t2: thickness of the piezoelectric layer

[0051] Fs: resonant frequency of the resonator

[0052] ε: dielectric constant of the piezoelectric layer

[0053] As the frequency decreases, the thickness t2 of the piezoelectric layer will become larger under the condition that kt 2 is fixed. It can be known from the above formula (1) that the area of the 50Ω resonator will become larger as the frequency Fs decreases. For example, in the case where the doping concentration is 0, when kt 2When kt 2 is 5.9%, the area of a 50Ω resonator at 1.75GHz is about 21000μm 2 (see Figure 9 ) and the area of a 50Ω resonator at 3.5GHz is about 5200μm 2 (see Figure 10 ). When the area of the resonator is increased, the area of the filter is forced to increase, which reduces the number of dies produced from a single wafer.

[0054] To reduce the area of the resonator, the layer thickness ratio E / P needs to be increased to reduce the thickness of the piezoelectric layer. However, when the thickness of the piezoelectric layer is reduced, the kt 2 of the resonator is reduced. Therefore, it is desirable to increase the kt 2 of the resonator to, for example, the original value (i.e. to maintain the kt 2 of the resonator at the original value) by doping. Therefore, when the layer thickness ratio E / P is increased (which results in the thickness of the piezoelectric layer being reduced and the kt 2 of the resonator being reduced), the doping concentration needs to be increased to maintain the kt 2 of the resonator (i.e. to maintain the kt 2 of the resonator at the original value or to maintain the kt 2 of the resonator within a range of 5% of the original value, in the embodiment of the present application, the kt 2 of the resonator is maintained at the original value). The final result is shown in Figure 9 . In Figure 9 , when the kt 2 is fixed (5.9% in Figure 9 ), the area of a 50Ω resonator is reduced as the doping concentration (in the example of Figure 9 , the doping concentration of scandium-doped aluminum nitride) is increased. Therefore, for a low frequency resonator, because of the fact that the area of a 50Ω resonator is large (which results in good heat dissipation), the power handling capacity of the resonator is not a concern and the kt 2 of the resonator can be maintained by increasing the doping concentration while the area of the resonator is reduced by increasing the layer thickness ratio E / P. Therefore, the size of the filter can be reduced, which increases the number of dies produced from a single wafer and reduces the cost of a single product. Obviously, reducing the size of the product also complies with the current trend of miniaturization of electronic devices.

[0055] Figure 4 An exemplary graph showing the relationship between the value of E / P and the kt 2 is shown in Figure 4 . More specifically, an exemplary graph showing the relationship between the value of E / P and the kt 2 when the piezoelectric layer is scandium-doped aluminum nitride is shown in 2 . It can be seen that the kt 2 is reduced as the value of E / P is increased.

[0056] Figure 5 An example is shown showing the relationship between doping concentration and Kt. 2 The relationship diagram. In Figure 5 In the diagram, the horizontal axis represents the doping concentration, and the vertical axis represents Kt. 2 Where E / P = 1.5, it can be seen that as the doping concentration increases, Kt 2 improve.

[0057] If it is necessary to reduce the resonator area by increasing the layer thickness ratio E / P (a higher layer thickness ratio E / P will lead to a decrease in the resonator's Kt). 2 To reduce Kt, the doping concentration needs to be increased. 2 To keep Kt 2 Stability. Since a larger reduction in resonator area necessitates a higher E / P value, a higher E / P value and corresponding doping concentration can be chosen. This ensures both a smaller resonator area and a stable Kt value. 2 Stablize.

[0058] For example, if the resonator's Kt 2 If it is 5.9%, then if Figure 8 As shown, a doping concentration of approximately 0.052 corresponds to an E / P value of 2. See also... Figure 9 As can be seen, for a frequency of 1.75GHz, Kt 2 A 50Ω resonator with a doping concentration of 5.9% has an area of ​​approximately 21000 μm when undoped (doping concentration of 0). 2 Corresponding to a doping concentration of approximately 0.052, the resonator area is approximately 12500 μm. 2 Clearly, in this example, by increasing the E / P value and through doping, the area of ​​the resonator can be significantly reduced, while still maintaining the Kt value of the resonator. 2 5.9% or remain at Kt 2 Stablize.

[0059] Clearly, by increasing the E / P value and through doping, the area of ​​the resonator can be significantly reduced, while still maintaining the Kt value of the resonator. 2 5.9% or remain at Kt 2 Stablize.

[0060] See Figure 2 and Figure 3 As can be seen, as the layer thickness ratio E / P increases, the high value of the resonator's Q value increases accordingly or can be stabilized in a relatively high range.

[0061] Figure 2 The diagram illustrates the relationship between the layer thickness ratio (E / P) and the width of the protrusion structure and the Q value of the resonator.Figure 2 In the diagram, the vertical axis represents the Q-value of the resonator, and the horizontal axis has two layers: the first layer represents the layer thickness ratio E / P of the resonator, and the second layer represents the width L (in μm) of the protrusion structure 107. Based on the first layer, Figure 2 An example is shown illustrating the relationship between the Q-factor of a resonator in the Band 1TX band (1920-1980MHz) and the layer thickness ratio E / P. Based on the second layer, Figure 2 An example is shown of the Q value of the resonator with different protrusion widths L for different layer thickness ratios E / P.

[0062] Figure 3 An exemplary diagram illustrates the relationship between the width L of the protrusion structure and the Q value of the resonator when the layer thickness ratio E / P = 1. Figure 3 It can be seen that the Q value of the resonator varies with the bump width L, and there are two peak values ​​when the bump width L = 1.25 μm and L = 5.25 μm. However, see... Figure 2 When the layer thickness ratio E / P is less than 1, Figure 3 The peak values ​​of both corresponding Q values ​​deteriorate as the layer thickness ratio E / P decreases. See also Figure 2 When E / P = 0.65, in Figure 3 Both maximum values ​​of Q in the data have deteriorated by more than 20%, and the maximum value at L = 1.25 no longer exists.

[0063] Therefore, the layer thickness ratio E / P directly affects the Q value of the resonator. When the E / P value is less than 1, the Q value of the resonator shows a significant decreasing trend as the E / P value decreases. To obtain a better Q value, the layer thickness ratio E / P should not be lower than 0.75. It can also be seen that when the E / P value is greater than 1, the Q value of the resonator remains in a relatively stable state.

[0064] To reduce the area of ​​the low-frequency resonator and to make Kt 2 Stability can be achieved by reducing the resonator area through a larger E / P value and by maintaining Kt through doping. 2 Stability is ensured, and a larger E / P value also guarantees that the Q value of the resonator remains within a high range. In this invention, the layer thickness ratio E / P is chosen to be no less than 1.5, and the lower limit of the doping concentration is determined based on this E / P value. This helps to reduce the resonator area and maintain Kt. 2 It is stable and can also ensure a high Q value for the resonator.

[0065] In other words, in this invention, for a bulk acoustic wave filter, the area of ​​the resonator can be reduced by selectively increasing the E / P value; however, in order to maintain the kt of the resonator... 2 Stable, or for those who have chosen kt 2resonator, it is also necessary to set the doping concentration in an optimal range, the lower limit of which is determined based on a higher value of the layer thickness ratio E / P (1.5 in the present application), so as to reduce the area of the resonator (by selecting a higher E / P value) and maintain Kt 2 stable, and also to ensure a higher resonator Q value. That is, in the present application, for a low-frequency resonator, if both the performance of the resonator and the size of the resonator are to be ensured, the doping concentration not only needs to meet the performance requirement, but also needs to have a minimum limit based on the area requirement of the resonator. For low-frequency products, in the present application, the E / P value is not less than 1.5 and the doping concentration is not less than the doping concentration corresponding to E / P = 1.5, so as to facilitate the miniaturization of the resonator area and meet the relevant performance requirements of the resonator.

[0066] Based on the above, the present application proposes a bulk acoustic wave resonator, a piezoelectric layer of which is a piezoelectric layer including a doping element having a corresponding doping concentration, the resonator having a resonant frequency lower than 2.5 GHz and having a layer thickness ratio E / P; the resonator having an electromechanical coupling coefficient Kt 2 , the doping concentration being not less than a1, a1 being the electromechanical coupling coefficient Kt 2 corresponding to the doping concentration.

[0067] Based on the above, the present application also proposes a method for determining the doping concentration of a piezoelectric layer of a bulk acoustic wave resonator, comprising the step of: based on the layer thickness ratio E / P, selecting the doping concentration to be not less than a1, a1 being the electromechanical coupling coefficient Kt 2 corresponding to the doping concentration.

[0068] In a more specific embodiment of the present application, when the piezoelectric layer is a piezoelectric layer of aluminum nitride doped with a metal scandium element, the lower limit value a1 of the doping concentration is the electromechanical coupling coefficient Kt 2 corresponding to the doping concentration, and is determined by the following formula: Kt 2 = 0.2845a1 2 + 0.2791a1+ 0.0488. In Figure 5 , a graph showing the relationship between the doping concentration a1 and Kt 2 at E / P = 1.5 is shown, in Figure 5 , y corresponds to Kt 2 , and x corresponds to the doping concentration a1.

[0069] In a further embodiment, the resonant frequency of the resonator is below 2.0 GHz, and the doping concentration is not less than a2, where a2 is the electromechanical coupling coefficient Kt when the resonator layer thickness ratio E / P = 1.7. 2 The corresponding doping concentration. More specifically, the piezoelectric layer is an aluminum nitride layer doped with scandium, and a2 is determined by the following formula: Kt 2 =0.2315a2 2 +0.283a2+0.0451. In Figure 6 The figure shows the relationship between doping concentration a2 and Kt when E / P = 1.7. 2 Relationship diagram, in Figure 6 In this context, y corresponds to Kt. 2 , where x corresponds to the doping concentration a2.

[0070] In a further embodiment, the resonant frequency of the resonator is below 1.5 GHz, and the doping concentration is not less than a3, where a3 is the electromechanical coupling coefficient Kt when the resonator layer thickness ratio E / P = 1.85. 2 The corresponding doping concentration. More specifically, the piezoelectric layer is an aluminum nitride layer doped with scandium, and a3 is determined by the following formula: Kt 2 =0.2196a3 2 +0.2771a3+0.0434. In Figure 7 The figure shows the relationship between doping concentration a3 and Kt when E / P = 1.85. 2 Relationship diagram, in Figure 7 In this context, y corresponds to Kt. 2 , where x corresponds to the doping concentration a3.

[0071] In a further embodiment, the resonant frequency of the resonator is below 1.0 GHz; the doping concentration is not less than a4, where a4 is the electromechanical coupling coefficient Kt when the resonator layer thickness ratio E / P = 2.0. 2 The corresponding doping concentration. More specifically, the piezoelectric layer is an aluminum nitride layer doped with scandium, and a4 is determined by the following formula: Kt 2 =0.407a4 2 +0.2315a4+0.0421. In Figure 8 The figure shows the relationship between doping concentration a4 and Kt when E / P = 2.0. 2 Relationship diagram, in Figure 8 In this context, y corresponds to Kt. 2 , where x corresponds to the doping concentration a4.

[0072] The above resonators (based on the layer thickness ratio E / P, select an appropriate doping concentration to reduce the resonator area while maintaining Kt) 2 Stability and a high Q value of the resonator can also be used in filters.

[0073] In one embodiment of the present application, the filter is a filter of Band 5 frequency band (TX (824MHz-849MHz), RX (869MHz-894MHz)); and the doping concentration of the resonator in the filter is not less than 15%. In the present application, TX represents a transmitting filter, and RX represents a receiving filter.

[0074] In one embodiment of the present application, the filter is a filter of Band 8 frequency band (TX (880MHz-915MHz), RX (925MHz-960MHz)); and the doping concentration of the resonator in the filter is not less than 14.5%.

[0075] In one embodiment of the present application, the filter is a filter of Band 3 frequency band (TX (1710MHz-1785MHz), RX (1805MHz-1880MHz)); and the doping concentration of the resonator in the filter is not less than 12%.

[0076] In one embodiment of the present application, the filter is a filter of Band 1 frequency band (TX (1920MHz-1980MHz), RX (2110MHz-2170MHz)); and the doping concentration of the resonator in the filter is not less than 11.5%.

[0077] In the above embodiments of the present application, the lower limit value of the doping concentration of the piezoelectric layer of the resonator is selected based on the value of the selected layer thickness ratio E / P, so that the Kt 2 The resonator has a smaller area while the Kt

[0078] As can be understood by those skilled in the art, the material of the piezoelectric layer is not limited to aluminum nitride, but can also be other piezoelectric materials listed in the present application, and the doping element is not limited to scandium metal, but can also be other dopable metal elements listed in the present application. Although in the specific embodiments of the present application, the doping of scandium element in aluminum nitride is taken as an example to illustrate how to determine the lower limit value of the doping concentration of the piezoelectric layer of the resonator based on the value of the selected layer thickness ratio E / P.

[0079] It should be noted that in the present application, each numerical range, in addition to explicitly indicating that it does not include the end point value, can also be the median value of each numerical range, which is within the protection scope of the present application.

[0080] As can be understood by those skilled in the art, the bulk acoustic wave resonator can be used to form other semiconductor devices in addition to filters.

[0081] Based on the above, the present application proposes the following technical solutions:

[0082] 1. A bulk acoustic wave resonator, comprising:

[0083] a substrate;

[0084] an acoustic mirror;

[0085] a bottom electrode;

[0086] a piezoelectric layer, the piezoelectric layer being a piezoelectric layer comprising a doping element, the doping element having a corresponding doping concentration; and

[0087] a top electrode,

[0088] wherein:

[0089] a resonant frequency of the resonator is lower than 2.5 GHz, and has a layer thickness ratio E / P;

[0090] the resonator has an electromechanical coupling coefficient Kt 2 , the doping concentration is not less than a1, a1 being the electromechanical coupling coefficient Kt 2 corresponding to the layer thickness ratio E / P = 1.5.

[0091] 2. The resonator according to 1, wherein:

[0092] the piezoelectric layer is an aluminum nitride layer doped with a scandium element, a1 being determined by the following formula: Kt 2 = 0.2845a1 2 + 0.2791a1 + 0.0488.

[0093] 3. The resonator according to 1, wherein:

[0094] the resonant frequency of the resonator is lower than 2.0 GHz;

[0095] the doping concentration is not less than a2, a2 being the electromechanical coupling coefficient Kt 2 corresponding to the layer thickness ratio E / P = 1.7 of the resonator.

[0096] 4. The resonator according to 3, wherein:

[0097] the piezoelectric layer is an aluminum nitride layer doped with a scandium element, a2 being determined by the following formula: Kt 2 = 0.2315a2 2 + 0.283a2 + 0.0451.

[0098] 5. The resonator according to 3, wherein:

[0099] The resonant frequency of the resonator is lower than 1.5 GHz;

[0100] The doping concentration is not less than a3, a3 being the electromechanical coupling coefficient Kt of the resonator layer when the thickness ratio E / P=1.85 2 The corresponding doping concentration.

[0101] 6. The resonator according to 5, wherein:

[0102] The piezoelectric layer is an aluminum nitride layer doped with a scandium element, and a3 is determined by the following formula: Kt 2 = 0.2196a3 2 + 0.2771a3+0.0434.

[0103] 7. The resonator according to 5, wherein:

[0104] The resonant frequency of the resonator is lower than 1.0 GHz;

[0105] The doping concentration is not less than a4, a4 being the electromechanical coupling coefficient Kt of the resonator layer when the thickness ratio E / P=2.0 2 The corresponding doping concentration.

[0106] 8. The resonator according to 7, wherein:

[0107] The piezoelectric layer is an aluminum nitride layer doped with a scandium element, and a4 is determined by the following formula: Kt 2 = 0.407a4 2 + 0.2315a4+0.0421.

[0108] 9. A filter comprising a plurality of bulk acoustic wave resonators according to any one of 1-8.

[0109] 10. The filter according to 9, wherein:

[0110] The filter is a filter of Band 5 frequency band; and

[0111] The doping concentration of the resonator in the filter is not less than 15%.

[0112] 11. The filter according to 9, wherein:

[0113] The filter is a filter of Band 8 frequency band; and

[0114] The doping concentration of the resonator in the filter is not less than 14.5%.

[0115] 12. The filter according to 9, wherein:

[0116] The filter is a filter of Band 3 frequency band; and

[0117] The doping concentration of the resonator in the filter is not less than 12%.

[0118] 13. The filter of 9, wherein:

[0119] The filter is a filter of Band1 frequency band; and

[0120] The doping concentration of the resonator in the filter is not less than 11.5%.

[0121] 14. A method for determining a doping concentration of a doping element in a piezoelectric layer of a bulk acoustic wave resonator, the resonator having an electromechanical coupling coefficient Kt 2 , the resonator having a resonance frequency lower than 2.5GHz and having a layer thickness ratio E / P, the method comprising the steps of:

[0122] selecting the doping concentration to be not less than a1 based on the layer thickness ratio E / P, a1 being the electromechanical coupling coefficient Kt 2 corresponding to the doping concentration when the layer thickness ratio E / P of the resonator is 1.5.

[0123] 15. The method of 14, wherein:

[0124] The piezoelectric layer is an aluminum nitride layer doped with a scandium element, a1 being determined by the following equation: Kt 2 = 0.2845a1 2 + 0.2791a1+0.0488.

[0125] 16. An electronic device comprising the filter of any one of 9-13, or the bulk acoustic wave resonator of any one of 1-8.

[0126] The electronic device herein includes but is not limited to intermediate products such as radio frequency front end, filter amplification module, and terminal products such as mobile phone, WIFI, and unmanned aerial vehicle.

[0127] Although the embodiments of the present application have been shown and described, it is to be understood that for the purpose of the present application, the embodiments can be changed and modified without departing from the principles and spirit of the present application, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A bulk acoustic resonator, comprising: Base; Acoustic mirror; Bottom electrode; A piezoelectric layer, wherein the piezoelectric layer includes doped elements, and the doped elements have a corresponding doping concentration; and Top electrode, in: The resonator has a resonant frequency of less than 2.5 GHz and a layer thickness ratio of E / P. The resonator has an electromechanical coupling coefficient Kt 2 The doping concentration is not less than a1, where a1 is the electromechanical coupling coefficient Kt when the layer thickness ratio E / P = 1.

5. 2 The corresponding doping concentration, the electromechanical coupling coefficient Kt of the bulk acoustic resonator 2 The Q value of the bulk acoustic resonator is related to the layer thickness ratio E / P and the doping concentration of the doped elements in the piezoelectric layer.

2. The resonator according to claim 1, wherein: The piezoelectric layer is an aluminum nitride layer doped with scandium, and a1 is determined by the following formula: Kt 2 =0.2845a1 2 +0.2791a1+0.0488。 3. The resonator according to claim 1, wherein: The resonant frequency of the resonator is below 2.0 GHz; The doping concentration is not less than a2, where a2 is the electromechanical coupling coefficient Kt when the resonator layer thickness ratio E / P = 1.

7. 2 The corresponding doping concentration.

4. The resonator according to claim 3, wherein: The piezoelectric layer is an aluminum nitride layer doped with scandium, and a2 is determined by the following formula: Kt 2 =0.2315a2 2 +0.283a2+0.0451。 5. The resonator according to claim 3, wherein: The resonant frequency of the resonator is below 1.5 GHz; The doping concentration is not less than a3, where a3 is the electromechanical coupling coefficient Kt when the resonator layer thickness ratio E / P = 1.

85. 2 The corresponding doping concentration.

6. The resonator according to claim 5, wherein: The piezoelectric layer is an aluminum nitride layer doped with scandium, and a3 is determined by the following formula: Kt 2 =0.2196a3 2 +0.2771a3+0.0434。 7. The resonator according to claim 5, wherein: The resonant frequency of the resonator is below 1.0 GHz; The doping concentration is not less than a4, where a4 is the electromechanical coupling coefficient Kt when the resonator layer thickness ratio E / P = 2.

0. 2 The corresponding doping concentration.

8. The resonator according to claim 7, wherein: The piezoelectric layer is an aluminum nitride layer doped with scandium, and a4 is determined by the following formula: Kt 2 =0.407a4 2 +0.2315a4+0.0421。 9. A filter comprising a plurality of bulk acoustic resonators according to any one of claims 1-8.

10. The filter according to claim 9, wherein: The filter is a Band 5 frequency band filter; and The doping concentration of the resonator in the filter is not less than 15%.

11. The filter according to claim 9, wherein: The filter is a Band 8 frequency band filter; and The doping concentration of the resonator in the filter is not less than 14.5%.

12. The filter according to claim 9, wherein: The filter is a Band 3 frequency band filter; and The doping concentration of the resonator in the filter is not less than 12%.

13. The filter according to claim 9, wherein: The filter is a Band 1 frequency band filter; and The doping concentration of the resonator in the filter is not less than 11.5%.

14. A method for determining doping concentration, wherein the doping concentration is the doping concentration of the doping element in the piezoelectric layer of a bulk acoustic wave resonator, the resonator having an electromechanical coupling coefficient Kt. 2 The resonator has a resonant frequency below 2.5 GHz and a layer thickness ratio E / P. The method includes the following steps: Based on the layer thickness ratio E / P, the doping concentration is selected to be not less than a1, where a1 is the electromechanical coupling coefficient Kt when the resonator layer thickness ratio E / P = 1.

5. 2 The corresponding doping concentration, the electromechanical coupling coefficient Kt of the bulk acoustic resonator 2 The Q value of the bulk acoustic resonator is related to the layer thickness ratio E / P and the doping concentration of the doped elements in the piezoelectric layer.

15. The method of claim 14, wherein: The piezoelectric layer is an aluminum nitride layer doped with scandium, and a1 is determined by the following formula: Kt 2 =0.2845a1 2 +0.2791a1+0.0488。 16. An electronic device comprising a filter according to any one of claims 9-13, or a bulk acoustic resonator according to any one of claims 1-8.

Images