Elastic wave element equipped with a reflector that has capacitance function

Abstract

To provide an acoustic wave element with a reflector having capacitance function that enables 5G front-end modules to be made lighter, thinner, shorter, and smaller, reducing costs, and meeting adjacent band blocking design specifications by improving skirt characteristics during filter design.SOLUTION: The present invention configures a reflector structure of an acoustic wave element such as a surface acoustic wave (SAW) resonator, a composite resonator, or a DMS (Double Mode SAW) as a capacitive reflector structure, thereby shifting the parallel resonance frequency to the series resonance frequency while maintaining the area of the acoustic wave element, without needing to connect an additional capacitor to the acoustic wave element, thereby more dramatically improving the skirt characteristics of the acoustic wave element and a bandpass filter including the same.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to an elastic wave device including a reflector having a capacitance function for improving the skirt characteristics of a bandpass filter. More specifically, it utilizes the piezoelectric effect of a piezoelectric material to convert an electrical signal into an elastic wave (Acoustic Wave) of the piezoelectric material, and is an elastic wave device used in filters that convert the converted elastic wave back into an electrical signal. It relates to an elastic wave device in which a capacitor function for moving the parallel resonance frequency toward the series resonance frequency side is embodied in the reflector to have a capacitive reflector structure. National Policy Issue Information [Issue Unique Number] 2021-0-00163 [Ministry Name] Ministry of Science and Technology, Information and Communications [Research Management Specialized Institution] Information and Communications Planning and Evaluation Institute [Research Project Name] Broadcast and Telecommunications Industry Technology Development Project [Research Topic Name] Development of High-Efficiency RF FEM for Wi-Fi (Registered Trademark) 6 / 6e AP [Contribution Rate] 1 / 1 [Supervising Agency] WiPAM, Incorporated [Research Period] Third Fiscal Year (January 1, 2023 to December 31, 2023)

Background Art

[0002] With the development of mobile communication devices such as smartphones and tablets, there is a demand for higher performance of surface acoustic wave resonators used in them, elastic wave devices such as filters using them, and devices. In particular, with the advent of the 5G era and the increase in frequencies available for use in mobile environments, the number of elastic wave filters included in mobile phones has increased significantly. As a result, more filters and RF elements must be added to the existing space, which requires miniaturization and integration of filter sizes.

[0003] With such a significant increase in the number of elements, it is necessary to minimize the mutual interference between each frequency, and for this purpose, the steep skirt characteristics on the response curve of the surface acoustic wave filter (SAW filter) become even more important.

[0004] Figure 1 shows the structure of a conventional surface acoustic wave resonator. Such a conventional surface acoustic wave resonator is an inter-digital transducer, or IDT structure (20), which is constructed by arranging metal electrodes in parallel and continuously on a piezoelectric substrate (10) made of piezoelectric material. When an AC signal voltage is applied to the IDT (20), an electric field is generated between the electrodes inside the IDT, and deformation occurs on the substrate surface due to the piezoelectric effect of the piezoelectric substrate (10), causing surface acoustic waves (SAW) to propagate in both directions of the IDT.

[0005] In this way, the surface acoustic waves generated on the surface of the piezoelectric substrate (10) by the IDT (20) can perform the function of a band-pass filter in the process of converting them back into electrical signals by the output electrode in the IDT or another IDT placed adjacent to it. This filter allows frequency components tuned to the frequency of the surface acoustic waves to pass through while attenuating the remaining signals.

[0006] At this time, reflectors (30, 40) are provided that form metal thin film gratings around the IDT (20) on the piezoelectric substrate (10), thereby reducing losses by reflecting the surface acoustic waves generated by the IDT (20) and propagating to the outside back to the IDT (20).

[0007] In a typical surface acoustic wave (IDT) resonator, the reflector reflects the surface acoustic waves generated by the IDT at both ends of the IDT according to the Bragg condition, thereby confining the surface acoustic waves within the resonator.

[0008] On the other hand, Figure 2 shows the response curve of a basic pass-through filter (FL) that has a series resonator (SAW(S)) and a parallel resonator (SAW(P)) with surface acoustic wave resonators connected in series, as described above.

[0009] Figure 2 shows the frequency-relative admittance curve (Y) of the series resonator (SAW(S)) of the filter (FL). 11S ) and the frequency-dependent admittance curve (Y) of the parallel resonator (SAW(P)) 11P ), and the frequency-dependent insertion loss curve (S) of a filter (FL) with a series resonator (SAW(S)) and a parallel resonator. 21 This indicates that...

[0010] Y 11S Curves and Y 11P On the curve, fs, s and fp, s are series resonance frequencies, while fs, p and fp, p are parallel resonance frequencies.

[0011] As shown in Figure 2, the skirt (sk) characteristics in the stopband on the filter's response curve are closely related to the series and parallel resonance frequencies of the surface acoustic wave resonators that constitute the filter.

[0012] In other words, as shown in Figure 2, in order to further dramatically improve the skirt characteristics of the surface acoustic wave transmission filter, the parallel resonance frequency (fs,p) of the surface acoustic wave resonator must be shifted towards the series resonance frequency (fs,s) to reduce the difference between the parallel and series resonance frequencies.

[0013] Therefore, conventionally, an IDT capacitor or manual capacitor was connected in parallel to the surface acoustic wave resonator to shift the parallel resonance frequency of the surface acoustic wave resonator towards the series resonance frequency.

[0014] However, this method has the problem that the area of ​​the surface acoustic wave resonator and filter increases due to the additional capacitors and connecting lines used to link them. This problem can act as a fatal obstacle that makes it difficult to miniaturize 5G front-end modules. [Prior art documents] [Patent Documents]

[0015] [Patent Document 1] Patent No. 6585459 [Patent Document 2] Patent No. 3487772 [Patent Document 3] Japanese Patent Publication No. 2011-130513 [Patent Document 4] Japanese Patent Publication No. 2001-237668 [Overview of the project] [Problems that the invention aims to solve]

[0016] The present invention aims to solve the aforementioned problems by providing an elastic wave element equipped with a reflector that has capacitance functionality. This reflector structure of the elastic wave element, such as a surface acoustic wave resonator, composite resonator, or DMS, is configured as a capacitive reflector structure. This allows the parallel resonance frequency to be shifted toward the series resonance frequency without adding a capacitor to the elastic wave element, while maintaining the area of ​​the elastic wave element. This enables a more rapid improvement in the skirt characteristics of the elastic wave element and the bandpass filter including it. [Means for solving the problem]

[0017] An elastic wave element comprising a reflector having capacitance function according to one embodiment of the present invention is an elastic wave element comprising a reflector having capacitance function, comprising: a piezoelectric substrate; an IDT electrode provided on the piezoelectric substrate that performs at least one of the following: converting an electrical signal into an elastic wave on the piezoelectric substrate and converting the elastic wave into an electrical signal; and a slit reflector arranged in the propagation direction of the elastic wave generated from the IDT electrode, which reflects the elastic wave to the IDT electrode and forms a slit capacitance which is a slit structure that performs capacitance function.

[0018] Preferably, the slit reflector includes a plurality of divided reflection units arranged in parallel in a direction perpendicular to the propagation direction of the elastic wave generated from the IDT electrode, and is configured to form at least one slit by separating each of the plurality of divided reflection units from each other. The slit is configured to function as the slit capacitance by connecting power supplies to the divided reflection units on one side and the other side of the slit, respectively.

[0019] Preferably, the slit reflector is configured such that the width of the slit formed between each of the plurality of divided reflection units is shorter than the wavelength of the elastic wave generated from the IDT electrode.

[0020] Preferably, the slit reflector is configured to adjust the capacitance value of the slit capacitance by adjusting the length of the slit formed by the plurality of divided reflection units and the number of the slits.

[0021] Preferably, each of the plurality of divided reflection units is configured in a closed form in which a large number of reflection electrodes having a length shorter than the length of the IDT fingers of the IDT electrode are arranged at a preset interval along the propagation direction of the elastic wave generated from the IDT electrode.

[0022] Preferably, a plurality of floating reflection electrodes are provided between the IDT electrode and the slit reflector without connecting a power supply, and are configured to reflect the elastic wave propagated from the IDT electrode in front of the slit reflector. Each of the plurality of floating reflection electrodes is arranged at a preset interval along the propagation direction of the elastic wave generated from the IDT electrode.

[0023] Preferably, the system further includes a plurality of floating reflective electrodes provided behind the slit reflector without power connection, which reflect elastic waves propagating from the IDT electrode behind the slit reflector, each of which is configured to be arranged at a predetermined interval along the propagation direction of the elastic waves generated from the IDT electrode.

[0024] Preferably, each of the multiple segmented reflection units of the slit reflector is configured in a closed form in which a number of reflection electrodes, each having a length shorter than the length of the IDT fingers of the IDT electrode, are arranged at predetermined intervals along the propagation direction of the elastic waves generated from the IDT electrode, and each of the multiple floating reflection electrodes is configured to have the same length as the length from the upper end to the lower end of the IDT electrode.

[0025] Preferably, the IDT electrode includes an input IDT electrode section having a number of input IDT fingers and an output IDT electrode section having a number of output IDT fingers, and the slit reflector is configured to include at least one slit formed by spacing out a plurality of divided reflection units arranged in parallel perpendicular to the propagation direction of elastic waves generated from the IDT electrode, and includes an input-side connection section that connects the input section of the power supply to the input IDT electrode section and the divided reflection unit on one side of the slit, respectively, and an output-side connection section that connects the output section of the power supply to the output IDT electrode section and the divided reflection unit on the other side of the slit, respectively.

[0026] Preferably, the slit reflector includes a first split reflecting unit, a second split reflecting unit, and a third split reflecting unit arranged in parallel perpendicular to the propagation direction of the elastic wave generated from the IDT electrode, wherein a first slit having a width smaller than the wavelength of the elastic wave is formed between the first split reflecting unit and the second split reflecting unit, and a second slit having a width smaller than the wavelength of the elastic wave is formed between the second split reflecting unit and the third split reflecting unit, and the slit capacitance includes the capacitance due to the first slit between the first split reflecting unit and the second split reflecting unit, and the capacitance due to the first slit between the second split reflecting unit and the third split reflecting unit, by connecting the input section of the power supply to the first split reflecting unit and the third split reflecting unit and connecting the output section of the power supply to the second split reflecting unit.

[0027] Preferably, the slit reflector includes a first split reflecting unit, a second split reflecting unit, a third split reflecting unit, and a fourth split reflecting unit, which are arranged in parallel perpendicular to the propagation direction of the elastic wave generated from the IDT electrode, and is configured to form a first slit between the first split reflecting unit and the second split reflecting unit having a width smaller than the wavelength of the elastic wave, a second slit between the second split reflecting unit and the third split reflecting unit having a width smaller than the wavelength of the elastic wave, and a third slit between the third split reflecting unit and the fourth split reflecting unit having a width smaller than the wavelength of the elastic wave, and the slit capacitance includes the capacitance due to the first slit between the first split reflecting unit and the second split reflecting unit, the capacitance due to the second slit between the second split reflecting unit and the third split reflecting unit, and the capacitance due to the third slit between the third split reflecting unit and the fourth split reflecting unit, by connecting the input section of the power supply to the first split reflecting unit and the third split reflecting unit and the output section of the power supply to the second split reflecting unit and the fourth split reflecting unit. [Effects of the Invention]

[0028] The elastic wave element equipped with a reflector having capacitance function according to the present invention, by configuring the reflector structure provided on the piezoelectric substrate to be a capacitive reflector structure, that is, including a slit reflector that embodies a slit capacitance in the form of a slit within the reflector, the parallel resonant frequency can be shifted toward the series resonant frequency without adding additional elements such as manual capacitors to the elastic wave element, while maintaining the area of ​​the elastic wave element as is. This further dramatically improves the skirt characteristics of the elastic wave element and the Bandpass filter including it, resulting in the miniaturization and reduction of 5G front-end modules, cost savings, and the ability to satisfy the blocking design specifications for adjacent bands by improving the skirt characteristics during filter design. [Brief explanation of the drawing]

[0029] [Figure 1] A diagram showing the configuration of a conventional surface acoustic wave resonator with a typical reflector structure. [Figure 2] This diagram shows the response curves of a basic surface acoustic wave (SWA) filter that has a series resonator (concurrently formed by connecting two SWA) and a parallel resonator (concurrently formed by connecting two SWA) in parallel. [Figure 3] A drawing shows an example of an elastic wave element according to one embodiment of the present invention, in which a surface acoustic wave resonator is equipped with a slit reflector with one slit. [Figure 4] A diagram showing the equivalent circuit models of a conventional surface acoustic wave resonator and a surface acoustic wave resonator according to one embodiment of the present invention. [Figure 5] A diagram showing the admittance response curves of a conventional surface acoustic wave resonator and a surface acoustic wave resonator according to one embodiment of the present invention. [Figure 6] This drawing shows an example of an elastic wave element according to another embodiment of the present invention, in which a surface acoustic wave resonator is equipped with a slit reflector with two slits. [Figure 7] This drawing shows an example of an elastic wave element according to another embodiment of the present invention, in which a surface acoustic wave resonator is equipped with a three-slit reflector. [Figure 8] Figures 3, 6, and 7 show the admittance response curves for a surface acoustic wave resonator with a 1-slit reflector, a surface acoustic wave resonator with a 2-slit reflector, and a surface acoustic wave resonator with a 3-slit reflector, respectively. [Figure 9] The drawings show an elastic wave element having a slit reflector structure for improving the skirt characteristics of a surface acoustic wave transmission filter according to another embodiment of the present invention. [Figure 10] This graph compares the response curve of a conventional surface acoustic wave filter having a surface acoustic wave resonator with a normal reflector with the response curve of a surface acoustic wave filter having a surface acoustic wave resonator with a slit reflector according to one embodiment of the present invention. [Figure 11] This graph shows the results of applying a slit reflector according to one embodiment of the present invention to a surface acoustic wave transmission filter of the DMS (Double Mode SAW) type, in comparison with a conventional filter. [Modes for carrying out the invention]

[0030] The specific details of the elastic wave element equipped with a reflector having capacitance function according to the present invention will be described in detail with reference to the drawings.

[0031] As mobile communication standards evolve, they must support more frequency bands, and to meet the demand for miniaturization, the area of ​​the elastic wave element must not increase, while still achieving a steep skirt characteristic on the filter's response curve.

[0032] To satisfy these conditions, an elastic wave element according to one embodiment of the present invention can shift the parallel resonance frequency toward the series resonance frequency and further improve the skirt characteristics by implementing the reflectors provided on both sides of the IDT (Inter-Digital Transducer) electrode on the piezoelectric substrate with a capacitive reflector structure.

[0033] The features of the present invention are applicable to all elastic wave elements, including surface acoustic wave (SAW) resonators, composite resonators, and DMS (Double Mode SAW) that utilize surface acoustic waves on a piezoelectric substrate. The following description uses the application of the features of the present invention to a surface acoustic wave resonator as an example, but the present invention is not limited to this and can be applied to elastic wave elements in general using the same method.

[0034] As an example of a capacitive reflector structure provided in an elastic wave element according to one embodiment of the present invention, Figures 3 to 6 show a surface acoustic wave resonator equipped with a slit reflector that embodies one or more slit capacitances within the reflector.

[0035] Figure 3 shows the configuration of a surface acoustic wave resonator having a 1-slit slit reflector as an example of an elastic wave element according to one embodiment of the present invention; Figure 4 shows the equivalent circuit models of a conventional surface acoustic wave resonator and a surface acoustic wave resonator according to one embodiment of the present invention; and Figure 5 shows the admittance response curves of a conventional surface acoustic wave resonator and a surface acoustic wave resonator according to one embodiment of the present invention.

[0036] Figure 6 shows an example of a configuration having a 2-slit slit reflector as a surface acoustic wave resonator, which is an elastic wave element according to another embodiment of the present invention, and Figure 7 shows an example of a configuration having a 3-slit slit reflector as a surface acoustic wave resonator, which is an elastic wave element according to yet another embodiment of the present invention.

[0037] As shown in Figure 3, a surface acoustic wave resonator, which is an example of an elastic wave element according to one embodiment of the present invention, basically comprises a piezoelectric substrate (100) made of a material that has a piezoelectric effect, and an IDT electrode (200) provided on the piezoelectric substrate (100) that converts electrical signals into surface acoustic waves on the piezoelectric substrate (100), or conversely, converts surface acoustic waves on the piezoelectric substrate (100) into electrical signals, or performs both.

[0038] The surface acoustic wave resonator according to the present invention is characterized by including a capacitive reflector, that is, a reflector with a capacitor function, which improves the structure of the reflector used in conventional surface acoustic wave resonators so that the parallel resonance frequency on the response curve is shifted toward the series resonance frequency, thereby realizing a steep skirt characteristic. Specific examples of such capacitive reflectors include slit reflectors (300, 400) that form a slit capacitance in the form of a slit within the reflector.

[0039] The slit reflector essentially functions as a normal reflector, positioned on the piezoelectric substrate (100) in the direction of propagation of surface acoustic waves generated by the IDT electrode (200), and reflecting the surface acoustic waves with the IDT electrode (200).

[0040] As shown in Figure 3, the IDT electrode (200) is divided into an input IDT electrode section (210) and an output IDT electrode section (220), with a comb-like structure consisting of numerous metal electrodes, i.e., numerous fingers. The structure has multiple input IDT fingers (212) and multiple output IDT fingers (222) arranged alternately. When an electrical signal is applied through the input IDT electrode section (210), surface acoustic waves are generated on the piezoelectric substrate (100) by the electric field between the multiple input fingers (212) and the output fingers. These surface acoustic waves are converted back into electrical signals and output to the output IDT electrode section (220).

[0041] At this time, the surface acoustic waves generated from the IDT electrode (200) propagate in both directions, i.e., left and right directions on the diagram.

[0042] As mentioned above, the slit reflectors (300, 400) are positioned in the direction of propagation of the surface acoustic waves generated by the IDT electrode (200), so it is desirable that they be provided on one end and the other end of the IDT electrode (200), respectively.

[0043] The aforementioned slit reflectors (300, 400) are positioned in the direction of propagation of the elastic wave generated by the IDT electrode (200), and reflect the propagating elastic wave back at the IDT electrode (200), thereby forming a slit capacitance, which is a slit structure that performs a capacitance function.

[0044] That is, the slit reflector (300, 400) may include a slit capacitance provided by connecting a power supply (600) to the split reflector unit (301, 401) on one side of the slit (301 or 401) and the split reflector unit (310 or 410) on the other side of the slit (320 or 420), respectively, and having a plurality of split reflector units (310 or 410) arranged in parallel perpendicular to the propagation direction of the elastic wave generated by the IDT electrode (200), and a slit reflector (301, 401) separated from each of the split reflector units.

[0045] Here, each segmented reflection unit (310, etc.) is constructed by arranging a number of reflection electrodes (312, etc.) that are shorter in length than the length of the IDT fingers (212, 222) of the IDT electrode (200) at predetermined intervals along the direction of propagation of elastic waves from the IDT electrode (200).

[0046] Each segmented reflection unit (such as 310) is configured in a closed configuration with numerous reflective electrodes, as shown in Figure 3, to prevent the generation of elastic waves.

[0047] Since a power supply is connected so that a slit capacitance function is realized between the segmented reflection units, if each segmented reflection unit is in an open configuration, each segmented reflection unit can generate elastic waves, which can alter the characteristics of the elastic waves generated at the IDT electrode (200).

[0048] However, elastic waves generated by an open-type split reflection unit may have completely different characteristics, such as resonant frequency, from those generated by the IDT electrode, potentially negatively impacting the characteristics of the elastic waves generated by the IDT electrode.

[0049] Therefore, as shown in Figure 3, it is desirable to configure each segmented reflection unit (such as 310) in a closed configuration to prevent the generation of elastic waves.

[0050] Furthermore, it is desirable that each segmented reflection unit (such as 310) be arranged in parallel so that a slit is formed between the lower end of one segmented reflection unit and the upper end of another segmented reflection unit, as shown in Figure 3.

[0051] If the two split reflective units are positioned so that there is a gap between the sides of one split reflective unit and the sides of another split reflective unit, this is undesirable because it may generate elastic waves between the two split reflective units.

[0052] As shown in Figure 3, an elastic wave element according to one embodiment of the present invention may include an input-side connection section (230) that connects the input section (630) of the power supply to the input IDT electrode section (210) and the first split reflection unit (310), respectively, and an output-side connection section (240) that connects the output section (640) of the power supply to the output IDT electrode section (220) and the second split reflection unit (320), respectively. The input-side connection section (230) can be configured to connect the input power supply to the input IDT electrode section (210) and the split reflection units (310, 410) on both sides thereof, while the output-side connection section (240) can be configured to connect the output power supply to the output IDT electrode section (220) and the split reflection units (320, 420) on both sides thereof.

[0053] As shown in Figure 3, in one slit reflector (300), a first split reflector unit (310) and a second split reflector unit (320) are arranged in parallel perpendicular to the propagation direction of surface acoustic waves (vertical direction in the drawing), with a slit (301) spaced apart between them. When the input section (630) of a power supply (600) is connected to the first split reflector unit (310) and the output section (640) is connected to the second split reflector unit (320), and current is applied, a potential difference is generated between the first split reflector unit (310) of the input power supply and the second split reflector unit (320) of the output power supply. As a result, charge is filled into the slit (301), which can become a slit capacitance that functions as a capacitor.

[0054] The configuration of one slit reflector (300) is similarly applied to the other slit reflector (400). That is, the configurations indicated by reference numerals 310, 320, and 301 for the one slit reflector (300) correspond to the configurations indicated by reference numerals 410, 420, and 401 for the other slit reflector (400).

[0055] As shown in Figure 2, the series and parallel resonance frequencies of the surface acoustic wave resonators that make up the filter are very important design variables that determine the passband and stopband of the filter.

[0056] As can be seen in the equivalent circuit model of a typical surface acoustic wave resonator shown in Figure 1, as shown in Figure 4(a), series resonance and parallel resonance coexist in a surface acoustic wave resonator, and the series resonance frequency and parallel resonance frequency at this time are expressed by Equation 1 below.

[0057]

number

[0058] Here, fs and fp are the series resonance frequency (fs) and parallel resonance frequency (fp) calculated through the equivalent circuit model of a typical surface acoustic wave resonator shown in Figure 4(a).

[0059] The series and parallel resonant frequencies are determined by the electromechanical coupling coefficient of the piezoelectric substrate of the surface acoustic wave resonator. To improve the skirt characteristics of the filter, the difference between the series and parallel resonant frequencies should be reduced, but conventionally, a method of connecting a manual capacitor element in parallel to a normal surface acoustic wave resonator has been used.

[0060] However, in such cases, the cost and size increase due to the addition of manual elements. Therefore, in order to solve this problem, the present invention presents a configuration equipped with a slit reflector that embodies slit capacitance, as described above. Figure 4(b) shows an equivalent circuit model of a surface acoustic wave resonator equipped with a slit reflector as shown in Figure 3.

[0061] The series and parallel resonant frequencies of a surface acoustic wave resonator equipped with such a slit reflector, according to the equivalent circuit model, can be expressed by the following equation 2.

[0062]

number

[0063] Here, fs and fpc are the series resonance frequency (fs) and parallel resonance frequency (fpc) ​​calculated through the equivalent circuit model of a surface acoustic wave resonator with a slit reflector shown in Figure 4(b).

[0064] Comparing the admittance response curve of a conventional surface acoustic wave resonator with a normal reflector as described above with the admittance response curve of a surface acoustic wave resonator with a slit reflector according to one embodiment of the present invention, we get the result shown in Figure 5.

[0065] In Figure 5, the Ccon curve, shown as a solid line, represents the admittance response curve of a conventional surface acoustic wave resonator with a normal reflector, while the Cirv curve, shown as a dotted line, represents the admittance response curve of a surface acoustic wave resonator with a slit reflector according to one embodiment of the present invention.

[0066] As shown in Figure 5, changing a conventional reflector to a slit reflector does not change the series resonant frequency, but the parallel resonant frequency (fp) on the curve of the resonator with a conventional reflector shifts to the parallel resonant frequency (fpc) ​​(i.e., shifts towards the series resonant frequency) due to the effect of the slit capacitance of the slit reflector.

[0067] In other words, as can be seen from the graph in Figure 5, the admittance response of a surface acoustic wave resonator with a slit reflector has the same effect as a conventional surface acoustic wave resonator with a manual capacitor connected in parallel.

[0068] In one embodiment of the present invention, the slit reflector (300, 400) of the elastic wave element, as shown in Figure 3, allows surface acoustic waves generated from the IDT electrode to leak through the slit if the width (Ws) of the slit (301, 401) formed between the first and second split reflection units is large. Therefore, by forming the slit width (Ws) shorter than the wavelength (SAW wavelength) of the surface acoustic wave generated from the IDT electrode (200), it is possible to prevent the leakage of surface acoustic waves through the slit. That is, it is desirable to ensure that (slit width (Ws)) < (wavelength of the surface acoustic wave).

[0069] On the other hand, as shown in Figure 3, the length (Ls) of the slits (301, 401) formed between the two split reflection units is related to the capacitance value. That is, the longer the slit length (Ls), the larger the capacitance.

[0070] Furthermore, the embodiment shown in Figure 3 relates to a structure in which the slit reflector is divided into two parts, a first divided reflective unit and a second divided reflective unit, with a slit formed between them. However, by changing the structure of the reflector to form two or more slits and realizing multiple slit capacitances, it is possible to obtain the effect of connecting multiple capacitors in series or parallel.

[0071] Therefore, the slit reflector of the elastic wave element according to the present invention is characterized in that the capacitance value of the slit capacitance can be adjusted by adjusting the length and / or number of slits formed by a plurality of segmented reflection units.

[0072] Examples of designs with two or more slits are shown in Figures 6 and 7, respectively.

[0073] The surface acoustic wave resonator with a 1-slit reflector structure shown in Figure 3, the surface acoustic wave resonator with a 2-slit reflector structure shown in Figure 6, and the surface acoustic wave resonator with a 3-slit reflector structure shown in Figure 7 differ in the structure of the slit reflector and the power supply connection structure, but the other configurations are substantially the same. In the following embodiments, explanations of identical configurations will be omitted.

[0074] In the embodiment shown in Figure 6, the slit reflector (300) includes a first split reflective unit (330), a second split reflective unit (340), and a third split reflective unit (350) arranged in parallel perpendicular to the propagation direction of the surface acoustic waves of the IDT electrode (200), and can be configured to form a first slit (302) between the first split reflective unit (330) and the second split reflective unit (340) having a width smaller than the wavelength of the surface acoustic wave, and a second slit (303) between the second split reflective unit (340) and the third split reflective unit (350) having a width smaller than the wavelength of the surface acoustic wave.

[0075] At this time, the split reflection unit on one side of each slit (302, 303) and the split reflection unit on the other side require power supply connections of different polarities. As shown in Figure 6, the input-side connection (250) connected to the power supply input (630) is preferably connected to the input IDT electrode (210), the first split reflection unit (330), and the third split reflection unit (350), while the output-side connection (260) connected to the power supply output (640) is preferably connected to the output IDT electrode (220) and the second split reflection unit (340).

[0076] As a result, the first slit (302) can act as a slit capacitance due to the potential difference between the first split reflection unit (330) of the input power supply and the second split reflection unit (340) of the output power supply, and the second slit (303) can act as a slit capacitance due to the potential difference between the third split reflection unit (350) of the input power supply and the second split reflection unit (340) of the output power supply.

[0077] In this case, each segmented reflection unit (such as 330) is configured in a closed form in which a number of reflection electrodes, each shorter in length than the length of the IDT finger of the IDT electrode (200), are arranged at predetermined intervals along the propagation direction of elastic waves from the IDT electrode (200), so as not to generate elastic waves, and it is desirable that they be arranged in parallel so that a slit is formed between the lower end of one segmented reflection unit and the upper end of another segmented reflection unit.

[0078] The configuration of the slit reflector (300) on one side is similarly applied to the slit reflector (400) on the other side. That is, the configurations indicated by reference numerals 330, 340, 350, 302, and 303 in the drawings for the slit reflector (300) on one side correspond to the configurations indicated by reference numerals 430, 440, 450, 402, and 403 in the drawings for the slit reflector (400) on the other side.

[0079] With the configuration described above, the surface acoustic wave resonator according to the embodiment shown in Figure 6 can embody a slit reflector having slit capacitance due to the 2-slit design.

[0080] On the other hand, in the embodiment shown in Figure 7, the slit reflector (300) includes a first segmented reflecting unit (360), a second segmented reflecting unit (370), a third segmented reflecting unit (380), and a fourth segmented reflecting unit (390) arranged in parallel perpendicular to the propagation direction of the surface acoustic waves of the IDT electrode (200), and can be configured to form a first slit (304) between the first segmented reflecting unit (360) and the second segmented reflecting unit (370) having a width smaller than the wavelength of the surface acoustic wave, a second slit (305) between the second segmented reflecting unit (370) and the third segmented reflecting unit (380) having a width smaller than the wavelength of the surface acoustic wave, and a third slit (306) between the third segmented reflecting unit (380) and the fourth segmented reflecting unit (390) having a width smaller than the wavelength of the surface acoustic wave.

[0081] At this time, the split reflection units on one side of each slit (304, 305, 306) and the split reflection units on the other side require power supply connections of different polarities. As shown in Figure 7, it is desirable that the input-side connection (270) connected to the power supply input (630) is connected to the input IDT electrode (210), the first split reflection unit (360), and the third split reflection unit (380), and that the output-side connection (280) connected to the power supply output (640) is connected to the output IDT electrode (220), the second split reflection unit, and the fourth split reflection unit (390).

[0082] As a result, the first slit (304) can act as a slit capacitance due to the potential difference between the first split reflection unit (360) of the input power supply and the second split reflection unit (370) of the output power supply, the second slit (305) can act as a slit capacitance due to the potential difference between the third split reflection unit (380) of the input power supply and the second split reflection unit (370) of the output power supply, and the third slit (306) can act as a slit capacitance due to the potential difference between the third split reflection unit (380) of the input power supply and the fourth split reflection unit (390) of the output power supply.

[0083] In this case, each segmented reflection unit (such as 360) is configured in a closed form in which a large number of reflection electrodes, each shorter in length than the length of the IDT finger of the IDT electrode (200), are arranged at predetermined intervals along the propagation direction of elastic waves from the IDT electrode (200), thereby preventing the generation of elastic waves. It is desirable that they be arranged in parallel so that a slit is formed between the lower end of one segmented reflection unit and the upper end of another segmented reflection unit.

[0084] The configuration of one slit reflector (300) is similarly applied to the other slit reflector (400). That is, the configurations indicated by drawing reference numerals 360, 370, 380, 390 and 304, 305, and 306 for the one slit reflector (300) correspond to the configurations indicated by drawing reference numerals 460, 470, 480, 490 and 404, 405, and 406 for the other slit reflector (400).

[0085] With the configuration described above, the surface acoustic wave resonator according to the embodiment shown in Figure 7 can embody a slit reflector having slit capacitance due to the 3-slit design.

[0086] Figure 8 shows the admittance response curves for a surface acoustic wave resonator with a 1-slit structure slit reflector (see Figure 3), a surface acoustic wave resonator with a 2-slit structure slit reflector (see Figure 6), and a surface acoustic wave resonator with a 3-slit structure slit reflector (see Figure 7), as described above.

[0087] In Figure 8, the Cs1 curve represents the response curve for the surface acoustic wave resonator of a 1-slit slit reflector, the Cs2 curve represents the response curve for the surface acoustic wave resonator of a 2-slit slit reflector, and the Cs3 curve represents the response curve for the surface acoustic wave resonator of a 3-slit slit reflector.

[0088] In Figure 8, the parallel resonance frequency of the surface acoustic wave resonator of the slit reflector with a 1-slit structure is f1, the parallel resonance frequency of the surface acoustic wave resonator of the slit reflector with a 2-slit structure is f2, and the parallel resonance frequency of the surface acoustic wave resonator of the slit reflector with a 3-slit structure is f3.

[0089] As shown in Figure 8, it can be seen that the parallel resonant frequency shifts towards the series resonant frequency as you move from 1-slit → 2-slit → 3-slit, f1 → f2 → f3.

[0090] By utilizing these characteristics and adjusting the number of slits in the slit reflector, the capacitance value of the slit capacitance can be adjusted to obtain the desired parallel resonance frequency shift effect. (As mentioned above, the closer the parallel resonance frequency shifts to the series resonance frequency, the steeper the skirt characteristic can be obtained in the response curve of the surface acoustic wave filter.)

[0091] On the other hand, with reference to Figure 9, an elastic wave element equipped with a reflector having capacitance function according to another embodiment of the present invention will be described.

[0092] Figure 9(a) shows an example of a reflector that includes a slit reflector and multiple floating reflective electrodes positioned in front of it, and Figure 9(b) shows an example of a reflector that includes a slit reflector and multiple floating reflective electrodes positioned behind it.

[0093] The surface acoustic wave resonator according to the embodiment shown in Figure 9(a) can be configured by providing slit reflectors (710, 810) on both sides of the IDT electrode (200), and forward reflectors (510, 520) between the IDT electrode (200) and the slit reflectors (710, 810).

[0094] The slit reflector (710) has a first split reflection unit (711) and a second split reflection unit (712) arranged in parallel perpendicular to the propagation direction of surface acoustic waves (vertical direction in the drawing), with a slit (702) spaced apart between them, and the input section (630) of the power supply (600) is connected to the first split reflection unit (711) and the output section (640) is connected to the second split reflection unit (712), and by applying current, a slit capacitance can be realized through the slit (702).

[0095] In this case, a floating reflective electrode (510) including one or more metal electrodes (512) can be provided between the slit reflector (710) and the IDT electrode (200) (in front of the slit reflector (710)) without power supply connection.

[0096] Therefore, the surface acoustic waves generated from the IDT electrode (200) are first reflected by the multiple floating reflective electrodes (510), and the remainder are reflected by the slit reflector (710).

[0097] By providing multiple floating reflective electrodes (510) without power supply connection, the normal reflector function can be performed, and at the same time, the slit capacitance effect of the slit reflector (710) can also be obtained.

[0098] The configuration of the slit reflector (710) on one side and the multiple floating reflective electrodes (510) provided in front of it is similarly applied to the slit reflector (810) on the other side and the floating reflective electrodes (520) on the other side. That is, the configurations indicated by reference numerals 711, 712, and 702 in the drawings for the slit reflector (710) on one side correspond to the configurations indicated by reference numerals 811, 812, and 802 in the drawings for the slit reflector (810) on the other side, and the configuration of the floating reflective electrode (510) on one side corresponds to the configuration of the floating reflective electrode (520) on the other side.

[0099] On the other hand, the surface acoustic wave resonator according to the embodiment shown in Figure 9(b) can be configured by providing slit reflectors (720, 820) on both sides of the IDT electrode (200), and a plurality of floating reflective electrodes (530, 540) behind them.

[0100] The slit reflector (720) has a first split reflection unit (721) and a second split reflection unit (722) arranged in parallel perpendicular to the propagation direction of surface acoustic waves (vertical direction in the drawing), with a slit (704) spaced apart between them, and the input section (630) of the power supply (600) is connected to the first split reflection unit (721), and the output section (640) is connected to the second split reflection unit (722). By applying current, a slit capacitance can be realized through the slit (704).

[0101] In this case, a floating reflective electrode (530) including one or more metal electrodes (532) can be provided behind the slit reflector (720) without power supply connection.

[0102] Therefore, the surface acoustic waves generated from the IDT electrode (200) are first reflected by the slit reflector (720), and the remainder are reflected by multiple floating reflective electrodes (530).

[0103] By providing multiple floating reflective electrodes (530) in this manner without power supply connection, the normal reflector function can be performed, and at the same time, the slit capacitance effect of the slit reflector (720) can also be obtained.

[0104] This configuration of one slit reflector (720) and the multiple floating reflective electrodes (530) behind it is similarly applied to the other slit reflector (820) and the other floating reflective electrodes (540). That is, the configurations indicated by reference numerals 721, 722, and 704 in the drawings for the one slit reflector (720) correspond to the configurations indicated by reference numerals 821, 822, and 804 in the drawings for the other slit reflector (820), and the configuration of the one floating reflective electrode (530) corresponds to the configuration of the other floating reflective electrode (540).

[0105] As mentioned above, through a configuration that includes a slit reflector and multiple floating reflective electrodes, the length of the slit realized within the slit reflector can be adjusted, thereby also adjusting the capacitance value due to the slit capacitance.

[0106] On the other hand, Figure 10 is a graph comparing the response curve of a surface acoustic wave filter composed of a conventional surface acoustic wave resonator with a normal reflector and the response curve of a surface acoustic wave filter composed of a surface acoustic wave resonator with a slit reflector as described above.

[0107] Looking at the section labeled A in the graph in Figure 10, we can see that the surface acoustic wave filter, composed of a surface acoustic wave resonator with a slit reflector, exhibits a more abrupt change in skirt characteristics compared to conventional filters. In this way, by improving the skirt characteristics of the filter using a slit reflector, the blocking effect in the counterband can be maximized.

[0108] This abrupt skirt characteristic is due to the slit reflector as described above, and the desired skirt characteristic can be obtained by adjusting the length and number of slits realized within the slit reflector.

[0109] Figure 11 shows a graph comparing the response curve of a conventional filter with a DMS (Double Mode SAW) type elastic wave-passing filter that has been fitted with the aforementioned slit reflector. Here, the solid line represents the response curve of a conventional filter with a resonator that has a normal reflector, and the dotted line represents the response curve of a filter with a resonator that has a slit reflector.

[0110] As shown in Figure 11, it can be seen that by using a surface acoustic wave resonator equipped with a slit reflector as described above, the right-hand blocking effect of the passband can be improved for a DMS-type acoustic wave pass filter.

[0111] In the surface acoustic wave resonator with a capacitive reflector structure according to the present invention, the position of the slit reflector can be freely positioned within an allowable range, the slit can be realized in a curved shape, and it can be formed in various directions. In this way, the capacitance value can be adjusted by utilizing various forms of slit capacitance.

[0112] As described above, the elastic wave element equipped with a reflector having capacitance function according to the present invention has the advantage of being able to shift the parallel resonance frequency toward the series resonance frequency without adding additional elements such as manual capacitors to the elastic wave element, while maintaining the area of ​​the elastic wave element, by configuring the reflector structure provided on the piezoelectric substrate to be a capacitive reflector structure, i.e., a slit reflector that embodies a slit capacitance in the form of a slit within the reflector. This further dramatically improves the skirt characteristics of the elastic wave element and the Bandpass filter including it, thus enabling miniaturization and cost reduction of 5G front-end modules, and satisfying the blocking design specifications for adjacent bands by improving the skirt characteristics during filter design.

Claims

1. An elastic wave element comprising a reflector having capacitance function, Piezoelectric substrate and The piezoelectric substrate is provided with an IDT electrode that performs at least one of the following: conversion from an electrical signal to an elastic wave on the piezoelectric substrate and conversion from the elastic wave to an electrical signal, The system includes a slit reflector positioned in the propagation direction of the elastic wave generated from the IDT electrode, which reflects the elastic wave back to the IDT electrode and performs a capacitance function, The aforementioned slit reflector is, It includes a plurality of segmented reflection units arranged in parallel in a direction perpendicular to the propagation direction of the elastic waves generated from the IDT electrode, Each of the plurality of segmented reflection units comprises a frame-shaped electrode and a plurality of reflection electrodes arranged within the frame-shaped electrode at predetermined intervals along the propagation direction of the elastic wave generated from the IDT electrode, and having a length shorter than the length of the IDT finger of the IDT electrode, with each end of the plurality of reflection electrodes connected to the inner wall of the frame-shaped electrode. An elastic wave element comprising a reflector having a capacitance function, configured to form at least one slit by separating each of the plurality of divided reflection units, and configured so that the slit performs the capacitance function by connecting a power supply to the divided reflection unit on one side of the slit and the divided reflection unit on the other side of the slit, respectively.

2. The aforementioned slit reflector is, An elastic wave element comprising a reflector having capacitance function according to claim 1, wherein the width of the slit, which is the distance between each of the plurality of divided reflection units, is formed to be shorter than the wavelength of the elastic wave generated from the IDT electrode.

3. The aforementioned slit reflector is, An elastic wave element comprising a reflector having a capacitance function according to claim 1, configured to adjust the capacitance value of the slit reflector by adjusting the length in the propagation direction of the elastic waves generated at the IDT electrodes of the slits formed by the plurality of divided reflection units and the number of slits.

4. An elastic wave element comprising a reflector having capacitance function, Piezoelectric substrate and The piezoelectric substrate is provided with an IDT electrode that performs at least one of the following: conversion from an electrical signal to an elastic wave on the piezoelectric substrate and conversion from the elastic wave to an electrical signal, The system includes a slit reflector positioned in the propagation direction of the elastic wave generated from the IDT electrode, which reflects the elastic wave back to the IDT electrode and performs a capacitance function, The aforementioned slit reflector is, The system is configured to have a plurality of segmented reflection units arranged in parallel perpendicular to the propagation direction of the elastic waves generated from the IDT electrode, and to form at least one slit by separating each of the plurality of segmented reflection units, and the slit is configured to perform the capacitance function by connecting a power supply to the segmented reflection unit on one side of the slit and the segmented reflection unit on the other side of the slit, respectively. An elastic wave element comprising a reflector having capacitance function, further comprising a plurality of floating reflective electrodes positioned between the IDT electrode and the slit reflector without power connection, which reflect the elastic waves propagating from the IDT electrode before they reach the slit reflector in the propagation direction of the elastic waves generated from the IDT electrode, each of the plurality of floating reflective electrodes extending perpendicular to the propagation direction of the elastic waves and arranged at predetermined intervals along the propagation direction of the elastic waves generated from the IDT electrode.

5. An elastic wave element comprising a reflector having capacitance function, Piezoelectric substrate and The piezoelectric substrate is provided with an IDT electrode that performs at least one of the following: conversion from an electrical signal to an elastic wave on the piezoelectric substrate and conversion from the elastic wave to an electrical signal, The system includes a slit reflector positioned in the propagation direction of the elastic wave generated from the IDT electrode, which reflects the elastic wave back to the IDT electrode and performs a capacitance function, The aforementioned slit reflector is, The system is configured to have a plurality of segmented reflection units arranged in parallel perpendicular to the propagation direction of the elastic waves generated from the IDT electrode, and to form at least one slit by separating each of the plurality of segmented reflection units, and the slit is configured to perform the capacitance function by connecting a power supply to the segmented reflection unit on one side of the slit and the segmented reflection unit on the other side of the slit, respectively. An elastic wave element comprising a reflector having capacitance function, further comprising a plurality of floating reflective electrodes arranged without power connection on the side of the slit reflector opposite to the side facing the IDT electrode, which reflect the elastic wave propagating from the IDT electrode in the propagation direction of the elastic wave generated from the IDT electrode, wherein each of the plurality of floating reflective electrodes extends perpendicular to the propagation direction of the elastic wave and is arranged at a predetermined interval along the propagation direction of the elastic wave generated from the IDT electrode.

6. Each of the multiple segmented reflection units of the slit reflector has a frame-shaped electrode and a plurality of reflective electrodes arranged within the frame-shaped electrode at predetermined intervals along the propagation direction of the elastic wave generated from the IDT electrode, and having a length shorter than the length of the IDT finger of the IDT electrode, with each end of the plurality of reflective electrodes connected to the inner wall of the frame-shaped electrode. An elastic wave element comprising a reflector having capacitance function according to claim 4, wherein each of the plurality of floating reflective electrodes is configured to have the same length as the length from the upper end to the lower end of the IDT electrode.

7. The IDT electrode includes an input IDT electrode section having a number of input IDT fingers and an output IDT electrode section having a number of output IDT fingers. An elastic wave element comprising a reflector having capacitance function according to claim 1, including an input-side connecting section that connects the input section of the power supply to the input IDT electrode section and the split reflection unit on one side of the slit, respectively, and an output-side connecting section that connects the output section of the power supply to the output IDT electrode section and the split reflection unit on the other side of the slit, respectively.

8. An elastic wave element comprising a reflector having capacitance function, Piezoelectric substrate and The piezoelectric substrate is provided with an IDT electrode that performs at least one of the following: conversion from an electrical signal to an elastic wave on the piezoelectric substrate and conversion from the elastic wave to an electrical signal, The system includes a slit reflector positioned in the propagation direction of the elastic wave generated from the IDT electrode, which reflects the elastic wave back to the IDT electrode and performs a capacitance function, The aforementioned slit reflector is, It includes a first split reflection unit, a second split reflection unit, and a third split reflection unit, which are arranged in parallel in a direction perpendicular to the propagation direction of the elastic waves generated from the IDT electrode. The device is configured to form a first slit with a width smaller than the wavelength of the elastic wave between the first and second segmented reflection units, and a second slit with a width smaller than the wavelength of the elastic wave between the second and third segmented reflection units. The slit reflector is an elastic wave element comprising a reflector having a capacitance function, configured such that the input section of the power supply is connected to the first segmented reflector unit and the third segmented reflector unit, and the output section of the power supply is connected to the second segmented reflector unit, thereby realizing the capacitance due to the first slit between the first segmented reflector unit and the second segmented reflector unit, and the capacitance due to the second slit between the second segmented reflector unit and the third segmented reflector unit.

9. An elastic wave element comprising a reflector having capacitance function, Piezoelectric substrate and The piezoelectric substrate is provided with an IDT electrode that performs at least one of the following: conversion from an electrical signal to an elastic wave on the piezoelectric substrate and conversion from the elastic wave to an electrical signal, The system includes a slit reflector positioned in the propagation direction of the elastic wave generated from the IDT electrode, which reflects the elastic wave back to the IDT electrode and performs a capacitance function, The aforementioned slit reflector is, It includes a first segmented reflection unit, a second segmented reflection unit, a third segmented reflection unit, and a fourth segmented reflection unit, which are arranged in parallel in a direction perpendicular to the propagation direction of the elastic waves generated from the IDT electrode. The device is configured to form a first slit between the first and second segmented reflection units having a width smaller than the wavelength of the elastic wave, a second slit between the second and third segmented reflection units having a width smaller than the wavelength of the elastic wave, and a third slit between the third and fourth segmented reflection units having a width smaller than the wavelength of the elastic wave. The slit reflector is an elastic wave element comprising a reflector having a capacitance function, configured such that the input section of the power supply is connected to the first segmented reflector unit and the third segmented reflector unit, and the output section of the power supply is connected to the second segmented reflector unit and the fourth segmented reflector unit, thereby realizing the capacitance due to the first slit between the first segmented reflector unit and the second segmented reflector unit, the capacitance due to the second slit between the second segmented reflector unit and the third segmented reflector unit, and the capacitance due to the third slit between the third segmented reflector unit and the fourth segmented reflector unit.

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