Method for designing a SAW resonator, a SAW filter and a method for designing the same, and a computer program having program instructions for carrying out the same

Abstract

The present invention provides a method for designing a SAW resonator, a SAW filter and a method for designing the same, and a computer program having program instructions for executing the same, which can improve the quality factor of a SAW resonator by optimally designing the structures of the input IDT fingers, output IDT fingers, and spacing between the fingers in the IDT electrodes of the SAW resonator without changing the material of the SAW resonator or the manufacturing process, and can provide a SAW filter using such a SAW resonator to obtain low insertion loss and improved frequency characteristics.

Description

[Technical field]

[0001] The present invention relates to a surface acoustic wave resonator (hereinafter referred to as "SAW resonator") and a surface acoustic wave filter (hereinafter referred to as "SAW filter") that are resonators and bandpass filters used in mobile communication devices and the like, and that convert an electrical signal into a surface acoustic wave (SAW) of a piezoelectric material by using the piezoelectric effect of the piezoelectric material, and then converts the converted surface acoustic wave (SAW) back into an electrical signal. [Background technology]

[0002] Mobile devices such as smartphones and tablets require small-sized RF filters, so acoustic filters using surface acoustic waves (SAW) or bulk acoustic waves (BAW), which have a radio wave speed much slower than EM waves, are mainly used.

[0003] With the development of mobile communication systems, the currently available frequency band below 3 GHz is saturated, so RF (Radio Frequency) filters operating in the frequency band below 3 GHz are required to have high selectivity, low insertion loss, small size, etc.

[0004] The filter that meets all of these requirements and is currently most widely used is the filter that uses surface acoustic waves. In order to improve the selectivity and insertion loss of a SAW filter, the quality factor (Q-factor) of the SAW resonator that constitutes the filter must be improved.

[0005] Since a SAW filter is designed by connecting many one-port or two-port SAW resonators in series or parallel, in order to improve the quality factor (Q value) of the SAW filter, the quality factor (Q value) of the one-port or two-port SAW resonators must be fundamentally improved.

[0006] Conventionally, improvements in the quality factor of SAW resonators have been achieved by changing the crystal orientation of the piezoelectric material or piezoelectric material of the piezoelectric substrate constituting the SAW resonator, or by modifying the process.

[0007] However, methods for improving the quality factor of a SAW resonator, such as changing the piezoelectric material constituting the piezoelectric substrate, changing its crystal orientation, or changing the manufacturing process, have problems such as increasing the price of the SAW resonator. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Special Publication No. 2021-500838

[0009] [Patent Document 2] Korean Patent Publication No. 2014-0077463

[0010] [Patent Document 3] Korean Patent Publication No. 2006-0120007 Summary of the Invention [Problem to be solved by the invention]

[0011] The present invention provides a method for designing a SAW resonator, a SAW filter and a method for designing the same, which can provide an optimal quality factor that can be realized by the SAW resonator itself by modifying the wave motion of a surface acoustic wave (SAW) generated by an IDT electrode by changing the structure of the IDT electrode of the SAW resonator without changing the material of the SAW resonator or the manufacturing process, and a computer program having program instructions for executing the same. [Means for solving the problem]

[0012] A method for designing a SAW resonator according to one embodiment of the present invention includes a piezoelectric substrate and an IDT electrode provided on the piezoelectric substrate for converting between an electrical signal and a surface acoustic wave, the IDT electrode including a plurality of input IDT fingers and a plurality of output IDT fingers, an input gap portion is formed between the input IDT fingers and the output IDT fingers, and an output gap portion is formed between the output IDT fingers and a next input IDT finger. In the SAW resonator, the method includes the steps of: defining an input finger metallization, which is the ratio of the input IDT finger in a region including the input IDT fingers and the input gap portion, and an output finger metallization, which is the ratio of the output IDT finger in a region including the output IDT fingers and the output gap portion, as parameters; and searching for setting values ​​that satisfy a range of a quality factor of the selected SAW resonator while changing the setting values ​​of each of the input finger metallization and the output finger metallization.

[0013] In addition, preferably, the step of defining the parameters further includes a step of defining a section length, defined as half the period from the input IDT finger to the output interval, together with the input finger metallization and the output finger metallization as parameters, and the step of finding setting values ​​that satisfy the quality factor range includes a step of finding setting values ​​for each of the section length, input finger metallization, and output finger metallization so as to satisfy the quality factor range of the SAW resonator.

[0014] Also preferably, the input finger metallization and the output finger metallization are set to values ​​each selected within the range of 0.40-0.60.

[0015] Meanwhile, a method for designing a SAW filter according to an embodiment of the present invention is a method for designing a SAW filter by connecting in series and parallel a plurality of SAW resonators, each including a piezoelectric substrate and an IDT electrode provided on the piezoelectric substrate and performing conversion between an electrical signal and a surface acoustic wave, the IDT electrode including a plurality of input IDT fingers and a plurality of output IDT fingers, an input gap portion is formed between the input IDT finger and the output IDT finger, and an output gap portion is formed between the output IDT finger and a next input IDT finger, the SAW filter connecting in series and parallel a plurality of SAW resonators. The method includes the steps of: defining an input finger metallization, which is a ratio of the input IDT fingers to an area including the input IDT fingers and an input gap, and an output finger metallization, which is a ratio of the output IDT fingers to an area including the output IDT fingers and an output gap, as parameters for each SAW resonator connected in series and in parallel; and searching for setting values ​​that satisfy a range of quality factors of a selected SAW filter while changing the setting values ​​of the input finger metallization and the output finger metallization.

[0016] Also, preferably, in each of a plurality of SAW resonators connected in series in the SAW filter, the input finger metallization is set to a value selected within a range of 0.41 to 0.48, and the output finger metallization is set to a value selected within a range of 0.52 to 0.59.

[0017] Also, preferably, in each of a plurality of SAW resonators connected in parallel in the SAW filter, the input finger metallization is set to a value selected within a range of 0.52 to 0.55, and the output finger metallization is set to a value selected within a range of 0.48 to 0.55.

[0018] The invention also includes a computer program comprising program instructions capable of carrying out the method for designing a SAW filter as described above.

[0019] Meanwhile, a SAW filter according to an embodiment of the present invention is a SAW filter including a piezoelectric substrate and a plurality of SAW resonators, each including an IDT electrode provided on the piezoelectric substrate for converting between an electric signal and a surface acoustic wave, connected in series and in parallel, wherein the IDT electrode in each of the plurality of SAW resonators includes a plurality of input IDT fingers and a plurality of output IDT fingers, an input gap portion is formed between the input IDT finger and the output IDT finger, and an output gap portion is formed between the output IDT finger and a next input IDT finger, and the input IDT finger is connected to the input IDT finger in series with the output IDT finger. an input finger metallization, which is the ratio of the input IDT fingers to a region including the input fingers and the input gap, is configured to have a value in the range of 0.41 to 0.48, and an output finger metallization, which is the ratio of the output IDT fingers to a region including the output IDT fingers and the output gap, is configured to have a value in the range of 0.52 to 0.59, and in each of a plurality of SAW resonators connected in parallel, the input finger metallization is configured to have a value in the range of 0.52 to 0.55, and the output finger metallization is configured to have a value in the range of 0.48 to 0.55. Effect of the Invention

[0020] The method for designing a SAW resonator, a SAW filter and the method for designing the same, as well as a computer program having program instructions capable of executing the same according to the present invention, can improve the quality factor of a SAW resonator by optimally designing the structures of the input IDT fingers, output IDT fingers, and spacing between fingers in the IDT electrodes of the SAW resonator without changing the material of the SAW resonator or the manufacturing process, and by constructing a SAW filter using such a SAW resonator, it is possible to obtain low insertion loss and improved frequency characteristics. [Brief description of the drawings]

[0021] [Figure 1] 1 is a diagram showing a structure of a SAW resonator on an xy plane for explaining a method of designing a SAW resonator according to an embodiment of the present invention. FIG.

[0022] [Diagram 2] 2A is an enlarged view of part R in FIG. 1, and (b) is a front view (xz plane) of the part shown in (a).

[0023] [Diagram 3] 1 is a graph showing the change in capacitance of an IDT electrode due to a change in input finger metallization (Mi).

[0024] [Figure 4] This figure shows that as the input finger metallization changes, the resonant frequency of the IDT electrodes of the resonators connected in series of a SAW filter changes to an Srf curve shape, and the resonant frequency of the IDT electrodes of the resonators connected in parallel changes to a Prf curve shape.

[0025] [Diagram 5] FIG. 13 is a diagram showing the change in quality factor depending on the frequency range when the values ​​of the input finger metallization and the output finger metallization are changed while keeping the same section length of the IDT electrode in a SAW resonator.

[0026] [Figure 6] This is a graph showing the relationship between frequency and insertion loss by changing the values ​​of the input finger metallization of a SAW resonator S1 connected in series and the input finger metallization of a SAW resonator P1 connected in parallel in a SAW filter composed of multiple SAW resonators connected in series and in parallel. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] The specific contents of the SAW resonator design method, SAW filter and the design method thereof, and a computer program having program instructions for executing the same according to the present invention will be described in detail with reference to the drawings.

[0028] First, the configuration of a SAW resonator according to an embodiment of the present invention and a method of designing a SAW resonator using the same will be described with reference to FIGS.

[0029] FIG. 1 is a diagram showing the structure of a SAW resonator on an xy plane to explain a method of designing a SAW resonator according to one embodiment of the present invention, FIG. 2(a) is an enlarged diagram of part R in FIG. 1, and FIG. 2(b) is a diagram showing the part shown in (a) on the front (xz plane).

[0030] As shown in FIG. 1, a SAW resonator may include a piezoelectric substrate 100 that converts electrical energy into acoustic energy by a piezoelectric effect, an IDT electrode 200 that is provided on the piezoelectric substrate 100 and generates a surface acoustic wave (SAW) on the piezoelectric substrate 100 in response to an electrical signal or converts the surface acoustic wave into an electrical signal, and reflectors 110 and 120 that are provided on both sides of the IDT electrode 200 to reflect the surface acoustic wave generated in the IDT electrode 200 to the IDT electrode 200 so as to prevent the surface acoustic wave from traveling to the outside.

[0031] In a SAW resonator, the surface acoustic wave generated by the IDT electrode is generated by the deformation of the piezoelectric material particles of the piezoelectric substrate due to the effect of the electric field generated by the IDT electrode, and has the following mathematical relationship (1).

[0032]

number

[0033] Here, S is stress, T is strain, u is particle placement of the piezoelectric material, v is particlevelocity of the piezoelectric material, and ρ is mass density. The above-mentioned T and S satisfy the following mathematical formula 2.

[0034]

number

[0035] Here, c is the stiffness tensor and η is the viscosity tensor. Assuming a lossless medium with no body force, T and S can be expressed as the following mathematical formula 3.

[0036]

number

[0037] From Equation 3, the velocity v of the surface acoustic wave generated by the IDT electrode can be expressed as Equation 4 below.

[0038]

number

[0039] Therefore, by changing the structure of the IDT electrodes of the SAW resonator, for example by changing the width of the input IDT fingers, the width of the output IDT fingers, the width of the input gap, the width of the output gap, etc., the strain T applied to the piezoelectric substrate, the velocity v of the surface acoustic wave as it passes through the piezoelectric material, the strain T applied to the output IDT fingers from the surface acoustic wave generated by the IDT electrodes, etc., can be changed, thereby improving the quality factor.

[0040] 1, the IDT electrode 200 is divided into an input IDT electrode section 210 and an output IDT electrode section 220. The input IDT electrode section 210 has a positive potential, and the output IDT electrode section 220 has a negative potential.

[0041] The input IDT electrode section 210 includes a number of input IDT fingers (214, 215, etc.) and an input bus bar 212 electrically connecting each of the input IDT fingers, and the output IDT electrode section 220 includes a number of output IDT fingers 224, 225, etc. and an output bus bar 222 electrically connecting each of the output IDT fingers.

[0042] The input IDT fingers 214, 215, etc. and the output IDT fingers 224, 225, etc. are alternately arranged one by one, and spacers 234, 235, etc. are formed between the input IDT fingers and the output IDT fingers at a predetermined distance.

[0043] The gaps between the fingers are divided into an input gap 234 and an output gap 235, with the input gap 234 being formed between an input IDT finger 214 and its adjacent output IDT finger 225, and the output gap 235 being formed between an output IDT finger 225 and its adjacent next input IDT finger 215.

[0044] FIG. 2(a) shows an enlarged view of portion R shown in FIG. 1, and shows an enlarged view of the i-th input IDT finger 214, the i-th input spacing portion 234, the i-th output IDT finger 225, and a portion of the i+1-th input IDT finger 215.

[0045] FIG. 2(a) shows part R in FIG. 1 on the xy plane, while FIG. 2(b) shows part R in FIG. 1 on the xz plane so as to correspond to the part shown in FIG. 2(a).

[0046] As shown in (b) of FIG. 2, assuming that the thicknesses t of the i-th input IDT finger 214, the i-th output IDT finger 225, and the i+1-th input IDT finger 215 are the same, an i-th input gap 234 is formed between the i-th input IDT finger 214 and the i-th output IDT finger 225, and an i-th output gap 235 is formed between the i-th output IDT finger 225 and the i+1-th input IDT finger 215.

[0047] Here, as shown in FIG. 2B, the width of the i-th input IDT finger 214 is Wi (i) and the width of the i-th output IDT finger 225 is Wo (i) and the width of the i+1-th input IDT finger 215 is Wi (i+1) The width of the input gap 234 between the i-th input IDT finger 214 and the i-th output IDT finger 225 is Si (i) and the width of the output gap 235 between the i-th output IDT finger 225 and the i+1-th input IDT finger 215 is So (i) It is.

[0048] As shown in FIG. 2B, the length from the end of the i-th input IDT finger 214 to the point where the i-th output gap 235 and the (i+1)-th input IDT finger 215 intersect in the x direction is called the period λ.

[0049] That is, the period λ of the IDT electrodes can be defined as follows:

[0050]

number

[0051] A method for designing a SAW resonator and a SAW filter according to one embodiment of the present invention provides a method for improving the quality factor of a SAW resonator by optimally designing structures such as input IDT fingers, output IDT fingers, and spacing between fingers in an IDT electrode of a SAW resonator without changing the material of the SAW resonator or the manufacturing process. For such a design, it is necessary to define several parameters related to the structure of the IDT electrode.

[0052] In the design method of the SAW resonator and the SAW filter according to an embodiment of the present invention, a period length (Lp), which is half the period λ of the IDT electrodes, can be defined and used as an important parameter.

[0053] In addition, as the important parameters mentioned above, the input finger metallization (Mi), which is the ratio of the input IDT finger 214 to the area including the input IDT finger 214 and the input spacing portion 234, and the output finger metallization (Mo), which is the ratio of the output IDT finger 225 to the area including the output IDT finger 225 and the output spacing portion 235, can be defined and used.

[0054] That is, the input finger metallization (Mi) can be defined as the ratio of the input IDT finger (metal) to the total area of ​​the input IDT electrode, and the output finger metallization (Mo) can be defined as the ratio of the output IDT finger (metal) to the total area of ​​the output IDT electrode. In mathematical terms, the i-th input finger metallization Mi(i) and the i-th output finger metallization Mo(i) can be defined as the following mathematical formula 1.

[0055]

number

[0056] In a method for designing a SAW resonator and a SAW filter according to one embodiment of the present invention, the aforementioned section length Lp and the aforementioned input finger metallization (Mi) and output finger metallization (Mo) are defined as parameters, and the setting values ​​of each of the section length Lp, the input finger metallization (Mi), and the output finger metallization (Mo) can be changed to find setting values ​​that satisfy the range of the quality factor of the selected SAW resonator, and by adjusting such parameters, a SAW resonator having an optimal quality factor and a SAW filter using the same can be designed.

[0057] FIG. 3 is a graph showing the change in capacitance of an IDT electrode due to changes in input finger metallization (Mi).

[0058] As shown in FIG. 3, it can be seen that the capacitance changes proportionally as the input finger metallization (Mi) changes in the IDT electrode of the SAW resonator.

[0059] That is, FIG. 3 shows that as the input finger metallization (Mi) varies in the range of 0.4 to 0.6, the capacitance of the IDT electrode varies proportionately together.

[0060] When a SAW filter is constructed by connecting multiple SAW resonators having the same conditions as described above in series and parallel, as shown in FIG. 4, as the input finger metallization (Mi) changes, the resonant frequency of the IDT electrodes of the resonators connected in series of the SAW filter changes to an Srf curve shape, and the resonant frequency of the IDT electrodes of the resonators connected in parallel changes to a Prf curve shape.

[0061] FIG. 4 shows that when the input finger metallization (Mi) and output finger metallization (Mo) values ​​are the same and are changed from 0.4 to 0.6, the resonant frequency of the SAW resonators connected in series changes to an Srf curve, and the resonant frequency of the SAW resonators connected in parallel changes to a Prf curve.

[0062] As shown in FIG. 4, by appropriately selecting a combination of input finger metallization and output finger metallization, a SAW filter constructed by connecting SAW resonators having such a combination in series and parallel can be made to have desired series resonance frequencies and parallel resonance frequencies.

[0063] Here, the quality factor (Q) of the SAW resonator can be expressed as Equation 7 below.

[0064]

number

[0065] Here, ω is the angular frequency, and τ gd is the group delay,

number

[0066] As shown in Equation 7, the quality factor Q(ω) is a function of frequency (ω). Therefore, by appropriately selecting the combination of input finger metallization and output finger metallization in the SAW resonator, it is possible to design a SAW filter having desired resonant frequency characteristics, and the quality factor, which is a function of frequency, can also be improved.

[0067] That is, one can find the combination of input finger metallization and output finger metallization that has the highest quality factor at a desired frequency in a SAW resonator, thereby enabling the design of SAW resonators and SAW filters with improved quality factors.

[0068] FIG. 5 shows the change in quality factor (Q) over the frequency range when the values ​​of the input finger metallization (Mi) and output finger metallization (Mo) are changed while keeping the same section length Lp of the IDT electrode in a SAW resonator.

[0069] In FIG. 5, when the section length Lp of the IDT electrode of the SAW resonator is 0.8 μm, curve A1 is the curve when the input finger metallization and output finger metallization are 0.525, curve A2 is the curve when the input finger metallization and output finger metallization are 0.5, and curve A3 is the curve when the input finger metallization and output finger metallization are 0.475.

[0070] As shown in FIG. 5, it can be seen that the quality factor of the SAW resonator can be improved by varying the input finger metallization and the output finger metallization.

[0071] Figure 6 is a graph showing the relationship between frequency and insertion loss by changing the values ​​of the input finger metallization of SAW resonator S1 connected in series and the input finger metallization of SAW resonator P1 connected in parallel in a SAW filter constructed by connecting multiple SAW resonators in series and in parallel.

[0072] In FIG. 6, curve B1 shows a graph of insertion loss versus frequency of a SAW filter when the input finger metallization value of the series-connected SAW resonator S1 and the input finger metallization value of the parallel-connected SAW resonator P1 are each 0.5, and curve B2 shows a graph of insertion loss versus frequency of a SAW filter when the input finger metallization value of the series-connected SAW resonator S1 is 0.4730 and the input finger metallization value of the parallel-connected SAW resonator P1 is 0.55.

[0073] As shown in FIG. 6, by changing the input finger metallization value to change from curve B1 to curve B2, the frequency range from the passband to the rejection band becomes shorter by a as shown in FIG. 6, and the insertion loss is also improved in the case of curve B2 compared to the case of curve B1.

[0074] A SAW filter according to one embodiment of the present invention is configured by connecting a plurality of SAW resonators in series and in parallel, and the input finger metallization of the plurality of SAW resonators connected in series has a value in the range of 0.41 to 0.48, the output finger metallization has a value in the range of 0.52 to 0.59, and the input finger metallization of the plurality of SAW resonators connected in parallel has a value in the range of 0.52 to 0.55, and the output finger metallization has a value in the range of 0.48 to 0.55, thereby obtaining a SAW filter with an improved quality factor.

[0075] As described above, the SAW resonator design method and SAW filter and its design method according to the present invention have the features and advantages that the quality factor of the SAW resonator can be improved by optimally designing the structures of the input IDT fingers, output IDT fingers, and the spacing between the fingers in the IDT electrodes of the SAW resonator without changing the material of the SAW resonator or the manufacturing process, and that a SAW filter can be constructed using such a SAW resonator, resulting in low insertion loss and improved frequency characteristics. [Industrial Applicability]

[0076] The SAW resonator design method, SAW filter and the design method thereof according to the present invention, as well as a computer program having program instructions capable of executing the same, are industrially applicable in the technical field of designing SAW resonators and SAW filters when applied to software that embodies the process of the design method as an algorithm and performs the corresponding function, or a computer that performs such function, or equipment for designing or manufacturing SAW resonators or filters.

Claims

1. A method for designing a SAW resonator including a piezoelectric substrate and an IDT electrode provided on the piezoelectric substrate for converting between an electrical signal and a surface acoustic wave, comprising the steps of: In a SAW resonator, the IDT electrode includes a plurality of input IDT fingers and a plurality of output IDT fingers, an input gap is formed between the input IDT finger and the output IDT finger, and an output gap is formed between the output IDT finger and a next input IDT finger, defining an input finger metallization, which is a ratio of the input IDT finger to an area including the input IDT finger and the input gap, and an output finger metallization, which is a ratio of the output IDT finger to an area including the output IDT finger and the output gap, as parameters; Varying the settings of each of the input finger metallization and the output finger metallization to find settings that satisfy a range of quality factors for a selected SAW resonator.

2. The step of defining the parameters includes: defining a section length, which is defined as half a period from the input IDT finger to the output space, together with the input finger metallization and the output finger metallization as a parameter; The step of searching for a set value that satisfies the range of the quality factor includes:

2. The method of claim 1, further comprising the step of searching for settings for each of the section length, input finger metallization, and output finger metallization to satisfy a range of quality factors of the SAW resonator.

3. 2. The method of claim 1, wherein the input finger metallization and the output finger metallization are set to respective selected values ​​within the range of 0.40-0.

60.

4. A method for designing a SAW filter by connecting a plurality of SAW resonators in series and parallel, the SAW resonators including a piezoelectric substrate and an IDT electrode provided on the piezoelectric substrate for converting between an electric signal and a surface acoustic wave, comprising: The IDT electrode includes a plurality of input IDT fingers and a plurality of output IDT fingers, an input gap is formed between the input IDT finger and the output IDT finger, and an output gap is formed between the output IDT finger and a next input IDT finger. In a SAW filter, defining an input finger metallization, which is a ratio of the input IDT fingers to an area including the input IDT fingers and an input gap, and an output finger metallization, which is a ratio of the output IDT fingers to an area including the output IDT fingers and an output gap, as parameters for each of the SAW resonators connected in series and in parallel; and varying the settings of the input finger metallization and the output finger metallization to find settings that satisfy a range of quality factors of a selected SAW filter.

5. In each of the plurality of SAW resonators connected in series in the SAW filter, 5. The method of claim 4, wherein the input finger metallization is set to a value selected within the range of 0.41 to 0.48 and the output finger metallization is set to a value selected within the range of 0.52 to 0.

59.

6. In each of the plurality of SAW resonators connected in parallel in the SAW filter, 5. The method of claim 4, wherein the input finger metallization is set to a value selected within a range of 0.52 to 0.55 and the output finger metallization is set to a value selected within a range of 0.48 to 0.

55.

7. A computer program comprising program instructions capable of carrying out the method for designing a SAW filter according to any one of claims 4 to 6.

8. A SAW filter including a piezoelectric substrate and a plurality of SAW resonators connected in series and in parallel, the SAW resonators including an IDT electrode provided on the piezoelectric substrate for converting between an electric signal and a surface acoustic wave, In each of the plurality of SAW resonators, the IDT electrode includes a plurality of input IDT fingers and a plurality of output IDT fingers, an input gap is formed between the input IDT finger and the output IDT finger, and an output gap is formed between the output IDT finger and a next input IDT finger; In each of the plurality of SAW resonators connected in series, an input finger metallization, which is a ratio of the input IDT finger to a region including the input IDT finger and the input gap, is configured to have a value in the range of 0.41 to 0.48, and an output finger metallization, which is a ratio of the output IDT finger to a region including the output IDT finger and the output gap, is configured to have a value in the range of 0.52 to 0.59, 1. A SAW filter comprising: a first input finger metallization configured to have a value in a range of 0.52 to 0.55 and a second output finger metallization configured to have a value in a range of 0.48 to 0.55 for each of a plurality of SAW resonators coupled in parallel.

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