Cross-section reflective surface acoustic wave device and filter device including same

Abstract

A cross-section reflective surface acoustic wave device and a filter device including same are provided. The cross-section reflective surface acoustic wave device comprises: a substrate; an interdigital (IDT) including a plurality of electrodes spaced apart from each other in a first direction on the substrate and extending in a second direction perpendicular to the first direction; and a cross-section reflective portion spaced apart from an outermost electrode of the IDT by a separation distance in the first direction and formed in a depth direction of the substrate, wherein the separation distance is determined to be any one within a range increased by at least 3.13% of λ from a natural-number multiple of λ / 2, where λ is the wavelength of a surface acoustic wave of the surface acoustic wave device.

Description

Sectional reflection type elastic surface wave device and filter device including the same

[0001] The present invention relates to a cross-sectional reflective elastic surface wave device and a filter device including the same. More specifically, the invention relates to a cross-sectional reflective elastic surface wave device and a filter device including the same, in which elastic surface waves radiated from an IDT (Interdigital) electrode are reflected by cross-sectional reflectors installed on both sides of the IDT electrode, thereby improving ripple generation and Q values ​​in the passband and outside the band.

[0002] A Surface Acoustic Wave Resonator consists of an IDT that receives an electrical signal and converts it into an elastic surface wave, and reflectors located on both sides of the IDT that trap the elastic surface wave radiated from the IDT by reflecting it.

[0003] FIG. 1a illustrates an elastic surface wave resonator equipped with a reflector of the prior art. Referring to FIG. 1a, the resonator comprises an IDT (10) including an electrode (13) extending from a bus bar (11, 12) and reflectors (20, 21) located on both sides of the IDT (10), wherein the reflectors (20, 21) correspond to a Shortened Metal Strop Array (SMSA) type reflector in which electrodes (22) arranged periodically are electrically short-circuited.

[0004] These SMSA-type reflectors obtain an increased reflection coefficient by superimposing elastic surface waves reflected by periodically arranged electrodes. As the number of electrodes in the reflectors (20, 21) increases, the reflection coefficient increases, and the occurrence of Q degradation of the resonator can be suppressed. However, there is a limitation that the number of electrodes cannot be increased indefinitely in terms of chip area.

[0005] Meanwhile, FIG. 1b illustrates a resonator equipped with a cross-sectional reflector. The resonator of FIG. 1b is composed of an IDT (50) including an electrode (53) extending from a busbar (51) and a cross-sectional reflector (61) of a substrate (60) on which the IDT (50) is placed. A resonator equipped with such a cross-sectional reflector does not need to include the periodically arranged electrodes of an SMSA-type reflector, thereby having the effect of reducing the area.

[0006] A substrate (60) on which an IDT (50) is placed may include a cross-section (61) formed along the center of the outermost electrode (54) as shown in FIG. 1b. Meanwhile, according to the prior art, the formation of the cross-section (61) is mainly achieved by cutting the substrate (60) through a dicing process, so there was a risk of defects such as the cutting of the outermost electrode (54) due to process errors. Accordingly, methods such as forming the cross-section (61) with a distance between the outermost electrode (54) and the cross-section (61), or forming the cross-section (61) through dry etching, have been proposed.

[0007] However, cross-sectional reflection type resonators formed with a certain distance between the outermost electrode and the cross-section have a problem in that there is insufficient research on whether ripple within and outside the passband is reduced according to the arrangement, and on the increase or decrease of ripple and improvement of the Q value depending on the distance between the outermost electrode and the cross-section.

[0008] The technical problem that the present invention aims to solve is to provide a cross-sectional reflection type elastic surface wave device and a filter device including the same, in which elastic surface waves radiated from an IDT (Interdigital) electrode are reflected by cross-sectional reflectors installed on both sides of the IDT electrode, thereby improving ripple generation and Q values ​​in the passband and outside the band.

[0009] The technical problems of the present invention are not limited to those mentioned above, and other unmentioned technical problems will be clearly understood by those skilled in the art from the description below.

[0010] A cross-sectional reflective surface acoustic wave device according to an embodiment of the present invention for solving the aforementioned technical problem comprises: a substrate; an IDT (Interdigital) comprising a plurality of electrodes spaced apart from each other in a first direction and extending in a second direction perpendicular to the first direction on the substrate; and a cross-sectional reflective part formed in the depth direction of the substrate, spaced apart from the outermost electrode of the IDT by a distance in the first direction, wherein the distance is determined to be any one of a range in which the elastic surface wave wavelength of the surface acoustic wave device is λ, and the range is increased by at least 3.13% of λ from a natural number multiple of λ / 2.

[0011] In some embodiments of the present invention, the elastic surface wave of the surface elastic wave device may have at least one of a Shear wave (SH wave) or a Love wave (L wave) as a main component.

[0012] In some embodiments of the present invention, the cross-sectional reflector includes the shape of a trench, and the side cross-section of the trench may face the outermost electrode.

[0013] In some embodiments of the present invention, the side cross-section may form an angle of less than 90 degrees with the bottom surface of the trench.

[0014] In some embodiments of the present invention, the side cross-section may form an angle of 75 to 85 degrees with the bottom surface of the trench.

[0015] In some embodiments of the present invention, the spacing distance may be located within any one of the ranges of 34λ / 64 to 39λ / 64, 70λ / 64 to 77λ / 64, 106λ / 64 to 114λ / 64, and 144λ / 64 to 150λ / 64.

[0016] In some embodiments of the present invention, the spacing distance may be located within any one of the ranges of 39λ / 64 to 45λ / 64, 74λ / 64 to 81λ / 64, 109λ / 64 to 115λ / 64, and 144λ / 64 to 150λ / 64.

[0017] A filter device according to an embodiment of the present invention for solving the technical problem described above includes a cross-sectional reflective surface acoustic wave device, wherein the cross-sectional reflective surface acoustic wave device comprises: a substrate; an IDT (Interdigital) comprising a plurality of electrodes spaced apart from each other in a first direction on the substrate and extending in a second direction perpendicular to the first direction; and a cross-sectional reflective portion formed in the depth direction of the substrate, spaced apart from the outermost electrode of the IDT by a distance in the first direction, wherein the distance is determined to be any one of a range in which the elastic surface wave wavelength of the surface acoustic wave device is λ, and the range is increased by at least 3.13% of λ from a natural number multiple of λ / 2.

[0018] In some embodiments of the present invention, the magnitude of the ripple in the passband may be 0.2dB or less.

[0019] Specific details of other embodiments are included in the detailed description and drawings.

[0020] The cross-sectional reflective surface acoustic wave device according to the present invention can effectively eliminate longitudinal mode ripple by forming the separation distance with a slight difference from a natural number multiple of λ / 2. In particular, this difference is caused by the tapered side profile shape formed by the cross-sectional reflective portion through a dry etching process, which reduces unnecessary process deviations and enables the realization of a filter with an improved Q value and reduced longitudinal mode ripple.

[0021] The effects of the present invention are not limited to those mentioned above, and other unmentioned effects will be clearly understood by those skilled in the art from the description in the claims.

[0022] Figures 1a and 1b are drawings for explaining the configuration of a resonator according to the prior art.

[0023] FIG. 2 is a diagram illustrating the configuration of a cross-sectional reflective resonator according to an embodiment of the present invention.

[0024] FIG. 3a is a cross-sectional view illustrating the configuration of a cross-sectional reflector included in a cross-sectional reflective resonator according to an embodiment of the present invention.

[0025] FIG. 3b is a cross-sectional view illustrating the configuration of a cross-sectional reflector included in a cross-sectional reflective resonator according to another embodiment of the present invention.

[0026] Figure 4 is a graph showing the magnitude of the passband ripple with respect to the separation distance in a cross-sectional reflective surface elastic wave device according to an embodiment of the present invention.

[0027] FIG. 5 is a graph comparing the admittance and conductance characteristics of a cross-sectional reflection type surface elastic wave device according to an embodiment of the present invention and an SMSA type resonator of FIG. 1a.

[0028] Figure 6 is a graph showing the pass characteristics of a ladder filter including a cross-sectional reflective surface acoustic wave device according to an embodiment of the present invention, compared with an SMSA type reflector.

[0029] Figure 7 is a graph showing the magnitude of the Q value with respect to the separation distance in a cross-sectional reflective surface elastic wave device according to an embodiment of the present invention.

[0030] FIG. 8 is a graph showing the magnitude of the Q value for the separation distance in a cross-sectional reflective surface elastic wave device (100) according to an embodiment of the present invention.

[0031] FIGS. 9a to 9f are drawings for explaining frequency response characteristics when a cross-sectional reflective surface elastic wave device according to an embodiment of the present invention has different separation distances.

[0032] FIGS. 10a to 10c are drawings illustrating cross-sectional reflectors of various shapes in a cross-sectional reflective surface elastic wave device according to an embodiment of the present invention.

[0033] FIGS. 11a and 11b are drawings illustrating cross-sectional reflectors of various shapes in a cross-sectional reflective surface elastic wave device according to an embodiment of the present invention.

[0034] The advantages and features of the present invention and the methods for achieving them will become clear by referring to the embodiments described below in detail together with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below but may be implemented in various different forms. These embodiments are provided merely to ensure that the disclosure of the present invention is complete and to fully inform those skilled in the art of the scope of the invention, and the present invention is defined only by the scope of the claims. Throughout the specification, the same reference numerals refer to the same components.

[0035] When one component is referred to as being "connected to" or "coupled to" another component, it includes cases where it is directly connected or coupled to the other component, or cases where another component is interposed. Conversely, when one component is referred to as being "directly connected to" or "directly coupled to" another component, it indicates that no other component is interposed. "And / or" includes each of the mentioned items and all combinations of one or more of them.

[0036] The terms used herein are for describing the embodiments and are not intended to limit the invention. In this specification, the singular form includes the plural form unless specifically stated otherwise in the text. As used herein, "comprises" and / or "comprising" do not exclude the presence or addition of one or more other components, steps, actions, and / or elements to the mentioned components, steps, actions, and / or elements.

[0037] Although terms such as "first," "second," etc., are used to describe various components, it goes without saying that these components are not limited by these terms. These terms are used merely to distinguish one component from another. Therefore, it goes without saying that the "first component" mentioned below may be the "second component" within the technical scope of the present invention.

[0038] Unless otherwise defined, all terms used in this specification (including technical and scientific terms) may be used in a meaning commonly understood by those skilled in the art to which the present invention pertains. Additionally, terms defined in commonly used dictionaries are not to be interpreted ideally or excessively unless explicitly and specifically defined otherwise.

[0039] FIG. 2 is a diagram illustrating the configuration of a cross-sectional reflective resonator according to an embodiment of the present invention. At the bottom of FIG. 2, a cross-sectional view is shown by cutting a cross-sectional reflective elastic surface wave device (100) in the AA' direction.

[0040]

[0041] * Referring to FIG. 2, a cross-sectional reflective elastic surface wave device (100) according to an embodiment of the present invention may include an IDT (110) and a cross-sectional reflective part (130), etc.

[0042] The elastic surface wave propagated by the cross-sectional reflective elastic surface wave device (100) of Fig. 2 may have at least one of a Shear wave (SH wave) or a Love wave (L wave) as a main component.

[0043] The IDT (110) may be placed on a substrate (120). The substrate (120) may be a multilayer substrate comprising a plurality of films, for example, a support substrate (124) comprising any one of Si, SiC, sapphire, and quartz, a high-sonic film (123) comprising at least one material of amorphous silicon (a-Si), polysilicon, and SiN that transmits a sound speed faster than the elastic wave propagated by the piezoelectric film (121), a low-sonic film (122) comprising any one of SiO2, doped SiO2, TaO2, and TeO2 that transmits a sound speed slower than the elastic wave propagated by the piezoelectric film (121), and a piezoelectric film (121) located at the top comprising a material such as LiTaO3 (LT) and LiNbO3 (LN).

[0044] Meanwhile, the configuration of the substrate (120) of the cross-sectional reflective elastic surface wave device (100) according to an embodiment of the present invention is not limited in this way, and the configuration of the high-sounding film (123) and / or the low-sounding film (122) may be omitted.

[0045] The IDT (110) disposed on the substrate (120) may include first and second busbars (111, 112) spaced apart in the second direction (Y) and extended in the first direction (X), a first electrode (113) extending from the first busbar (111) toward the second busbar (112), a second electrode (114) disposed alternately with the first electrode (113) and extending from the second busbar (112) toward the first busbar (111), etc.

[0046] The first and second busbars (111, 112) may include a conductive material such as aluminum, for example, or have a structure in which a conductive material and an insulating material are stacked in sequence.

[0047] The first electrode (113) and the second electrode (114) can be arranged alternately. As shown in FIG. 2, the distance in the first direction (X) between two first electrodes (113) with one second electrode (114) or two second electrodes (114) with one first electrode (113) is called the period and is denoted by λ. Thus, the distance between adjacent first electrodes (113) and second electrodes (114) can be λ / 2.

[0048] Meanwhile, cross-sectional reflective sections (130) may be formed on both sides of the IDT (10) with a spacing distance (D). The cross-sectional reflective sections (130) may be formed inside the substrate (120) to provide a side cross-section (131) facing the outer electrode (115) of the IDT (110) in a first direction (X). The structure of the cross-sectional reflective sections (130) will be explained with reference to FIGS. 3a and 3b.

[0049] FIGS. 3a and 3b are drawings illustrating the structure of a cross-sectional reflector included in a cross-sectional reflective surface elastic wave resonator according to an embodiment of the present invention. FIGS. 3a and 3b correspond to drawings showing an enlarged portion of a cross-sectional view in the A-A' direction of FIG. 2.

[0050] Referring to FIGS. 2 and 3a, the cross-sectional reflection portion (130) may have the shape of a trench formed by removing the substrate (120) in the depth direction of the substrate (120), i.e., in the third direction (Z). The cross-sectional reflection type surface elastic wave elastic surface wave device (100) according to an embodiment of the present invention may form the cross-sectional reflection portion (130) by removing the substrate (120) by dry etching.

[0051] The cross-sectional reflector (130) may be spaced apart from the outermost electrode (115) of the IDT (110) by a distance (D). Here, the distance (D) may refer to the distance between the position on the surface of the substrate (120) of the side cross-section (131) defining the inner surface of the cross-sectional reflector (130) and the center of the first direction (X) of the outermost electrode (115). As illustrated in FIGS. 3a and 3b, the side cross-section (131) may not be perfectly perpendicular to the bottom surface (133) due to problems arising from the etching process forming the cross-sectional reflector (130), and if it is formed at a tapered angle (θ), the distance (D) may vary depending on the position of the third direction (Z) of the side cross-section (131).

[0052] As the cross-sectional reflective portion (130) is formed at a distance (D) from the outermost electrode (115), the width of the outermost electrode (115) in the first direction (X) may be the same as the width of the other electrodes (113, 114).

[0053] As illustrated in FIG. 3a, the cross-sectional reflective portion (130) is etched at least up to the upper surface of the support substrate (124) so ​​that the level of the lower surface (132) is the same as the level of the upper surface of the support substrate (124). By the side cross-sectional portion (131), the sides of the piezoelectric film (121), the high-sonic film (123), and the low-sonic film (122) forming the substrate (120) can all be exposed.

[0054] Meanwhile, as illustrated in FIG. 3b, it is preferable that the level of the bottom surface (132) of the cross-sectional reflector (130) be lower than the level of the top surface of the support substrate (124). That is, when the substrate (120) is etched to etch the cross-sectional reflector (130), parameters such as the etching time can be adjusted so that the support substrate (124) is over-etched and a portion of the support substrate (124) is removed. Importantly, for efficient reflection of surface acoustic waves radiated from the IDT (110), no portion of the high-sonic film (123) should remain in the cross-sectional reflector (130), and it is preferable that the depth of the third direction (Z) of the cross-sectional reflector (130) be equal to or greater than the sum of the thicknesses of the piezoelectric film (121), the low-sonic film (122), and the high-sonic film (123).

[0055] In some embodiments of the present invention, the width (W) of the short side of the cross-sectional reflective portion (130) may be greater than the depth (H) of the cross-sectional reflective portion (130) for stable etching. That is, the ratio of the depth (H) of the cross-sectional reflective portion (130) to the width (W) of the short side may be 1:1 or greater.

[0056] Meanwhile, by providing a separation distance (D), the occurrence of deviations caused by damage to the outermost electrode (115) or mask misalignment during the etching process for forming the cross-sectional reflection portion (130) can be reduced, and the occurrence of longitudinal mode ripples in the cross-sectional reflection type elastic surface wave device (100) can be prevented. The separation distance (D) for effectively preventing the occurrence of longitudinal mode ripples will be explained using FIG. 4, etc.

[0057] FIG. 4 is a graph showing the magnitude of the ripple in the passband with respect to the separation distance in a cross-sectional reflective surface elastic wave device (100) according to an embodiment of the present invention.

[0058] Referring to FIG. 4, the horizontal axis represents the distance (D) between the outermost electrode (115) and the cross-sectional reflector (130) in the cross-sectional reflector surface acoustic wave device (100) of the present invention as a magnitude relative to the elastic surface wave wavelength λ of the resonator, and the vertical axis represents the magnitude of the ripple in the passband according to the arrangement. For comparison, the ripple in a ladder filter composed of a surface acoustic wave device including a conventional SMSA type reflector is shown to have a magnitude of 0.2 dB.

[0059] According to FIG. 4, when the separation distance (D) is 1) 34λ / 64 to 39λ / 64, 2) 70λ / 64 to 77λ / 64, 3) 106λ / 64 to 114λ / 64, and 4) 144λ / 64 to 150λ / 64, it can be seen that the size of the ripple is smaller than that of a ladder filter using a conventional SMSA type reflector. This corresponds to 1) approximately 53.13% to 60.94%, 2) approximately 109.38 to 120.31%, 3) approximately 165.63% to 178.13%, and 4) approximately 225% to 234.38%, respectively, with respect to wavelength λ.

[0060] It is known that the distance between the end surface and the outermost electrode is an integer multiple of λ / 2, as in Japanese Patent Publication No. 60-41809. However, the cross-sectional reflection type elastic surface wave device (100) according to the embodiment of the present invention has a separation distance (D) at which the ripple is at least 0.2 dB or less, as obtained from the experimental results of FIG. 4, which is a natural multiple of λ / 2 (excluding 0), such as 32λ / 64, 64λ / 64, 96λ / 64, and 128λ / 64, which is increased from 3.13% to 34%, respectively. In particular, it can be seen that as the order of N, which is a natural multiple, increases, the range deviates more significantly from the natural multiple of λ / 2.

[0061] This may be due to the fact that the side cross-section (131) has a tapered shape of 75 to 85 degrees as the cross-sectional reflection portion (130) described in FIG. 3a and 3b is formed by dry etching. Since the surface elastic waves radiated from the outermost electrode (115) are not completely reflected by the tapered side cross-section (131), the longitudinal mode ripple is not completely eliminated when the separation distance (D) is a natural number multiple of λ / 2.

[0062] On the other hand, in the case of the elastic surface wave device introduced in Japanese Patent Publication No. Sho 60-41809, when a side cross-section forming a 90-degree angle with the upper surface of the substrate is formed using dicing, it may be possible to reduce longitudinal mode ripple by making the separation distance (D) a natural number multiple of λ / 2. However, due to the wear of the dicing blade, the thickness variation of the dicing blade, the alignment precision of the dicing blade and the IDT electrode, and the influence of chipping occurring during dicing, it is practically impossible to manage the formation of the cross-section through dicing to have a process variation of within 5% when the wavelength λ is 5μm in an RF SAW filter of 800MHz or higher. Accordingly, by forming a cross-sectional reflective portion (130) through a dry etching process as in the cross-sectional reflective surface elastic wave device (100) of the present invention, precise process control and adjustment of the separation distance (D) are achieved, and by forming the separation distance (D) with a slight difference from a natural number multiple of λ / 2 to match the shape of the side cross-section (131), a ladder filter having reduced longitudinal mode ripple can be implemented.

[0063] FIG. 5 is a graph comparing the admittance and conductance characteristics of a cross-sectional reflective surface acoustic wave device (100) according to an embodiment of the present invention and an SMSA-type resonator of FIG. 1a. In the graph, the horizontal axis represents frequency (MHz) and the vertical axis represents gain (dB).

[0064] Referring to FIG. 5, it can be seen that the admittance characteristic (REF) of a resonator according to the prior art shows that the reflection characteristic of an SMSA-type reflector and the radiation characteristic of an IDT overlap, and large ripple occurs in the region below the resonance frequency (approx. 760 MHz). In contrast, the admittance characteristic (ER) of a cross-sectional reflective surface acoustic wave device (100) according to an embodiment of the present invention shows a smooth shape without ripple in the region below the resonance frequency. Here, the separation distance (D) is set to 36λ / 64.

[0065] In addition, as revealed by the comparison of the conductance graph (ER') of the cross-sectional reflective surface acoustic wave device (100) according to an embodiment of the present invention and the conductance graph (REF') of the SMSA type reflector, the surface acoustic wave device (100) of the present invention has no wavelength dependence on reflection characteristics and does not have a stopband, so it can be seen that it exhibits a smooth shape without stopband ripple at frequencies above the anti-resonant frequency (approx. 800 MHz). Thus, the cross-sectional reflective surface acoustic wave device (100) of the present invention can have smoother conductance and admittance characteristics compared to using an SMSA type reflector, even above the anti-resonant frequency.

[0066] The pass characteristics of a ladder filter configured to include a cross-sectional reflective surface elastic wave device (100) according to an embodiment of the present invention are explained using the graph of FIG. 6.

[0067] Figure 6 is a graph showing the pass characteristics of a ladder filter including a cross-sectional reflective surface acoustic wave device according to an embodiment of the present invention, compared with an SMSA type reflector.

[0068] Referring to FIG. 6, a graph (ER') centered on the pass characteristics (ER) and passband of a ladder filter including a cross-sectional reflection type surface acoustic wave device according to an embodiment of the present invention is shown, along with the pass characteristics (REF and REF') of a ladder filter configured with a conventional SMSA type reflector. Each of the ladder filters is configured to include one series resonator and one parallel resonator.

[0069] As can be expected from the results obtained from the graph in Fig. 5, it is clearly evident that a ladder filter configured to include a cross-sectional reflective surface acoustic wave device (100) according to an embodiment of the present invention has characteristics of having little ripple within and outside the passband.

[0070] Meanwhile, in the cross-sectional reflection type surface elastic wave device (100) according to an embodiment of the present invention, the separation distance (D) of the range where the longitudinal mode ripple is minimized and the separation distance (D) of the range where the Q value is maximized may not coincide. This is explained using FIG. 7, etc.

[0071] FIG. 7 is a graph showing the magnitude of the Q value with respect to the separation distance in a cross-sectional reflective surface elastic wave device (100) according to an embodiment of the present invention, and separately indicates the range in which the Q value changes within 5% from the maximum value for each order. It was found that the maximum Q value of an elastic surface wave resonator having a conventional SMSA type reflector is approximately 4000.

[0072] According to FIG. 7, the separation distance (D) that causes the Q value to change from the maximum value may correspond to 1) 39λ / 64 to 45λ / 64, 2) 74λ / 64 to 81λ / 64, 3) 109λ / 64 to 115λ / 64, and 4) 144λ / 64 to 150λ / 64. That is, the range that gives the maximum Q value is different from 32λ / 64, 64λ / 64, 96λ / 64, and 128λ / 64, which are natural multiples of λ / 2. Also, as the multiple of the natural number increases, the difference between the range of the separation distance (D) that makes the Q value the maximum value and the natural multiple of λ / 2 increases.

[0073] Meanwhile, the separation distance (D) having the minimum ripple and the separation distance (D) having the maximum Q value may not coincide. This is explained using FIG. 8.

[0074] FIG. 8 is a graph showing the magnitude of the Q value with respect to the separation distance in a cross-sectional reflective surface elastic wave device (100) according to an embodiment of the present invention. For reference, a separation distance (D) determined to minimize the vertical mode ripple described using FIG. 4 is displayed on the graph.

[0075] As illustrated in FIG. 8, the range of separation distance (D) determined to minimize vertical mode ripple and the range where the Q value is maximized may not coincide. However, as the order of the natural number multiple of λ / 2 increases, that is, as the separation distance (D) increases, the magnitude of the discrepancy decreases, and a tendency can be observed that the range where the Q value is maximized is included within the separation distance (D) determined to minimize vertical mode ripple.

[0076] Meanwhile, in the lower order region of a natural number multiple of λ / 2, the range of separation distance (D) that provides the maximum Q is greater than the range with the minimum ripple, but as the multiple increases, the difference decreases, and in the range from 144λ / 64 to 150λ / 64, the range with the minimum ripple and the range with the maximum Q value coincide.

[0077] FIGS. 9a to 9f are drawings for explaining frequency response characteristics when a cross-sectional reflective surface elastic wave device (100) according to an embodiment of the present invention has different separation distances (D).

[0078] First, referring to FIG. 9a, the frequency response characteristics around the filter's passband are illustrated using the ladder filter of a conventional SMSA type reflector (REF graph), the range that generates minimum ripple (36L / 64 graph), and the range that provides the maximum Q value (42L64, 78L64, 112L / 64, 146L / 64 graphs). As illustrated in FIG. 9a and FIG. 9b (which is an enlarged view of the passband with the respective center frequencies shifted for comparison), it can be observed that ripple occurs in the passband and in the frequency ranges above and below the passband. However, when the separation distance (D) is 36L / 64, it can be observed that almost no ripple occurs compared to the reference (REF), resulting in a smooth passband. In the range that provides the maximum Q value, the ripple decreases as the separation distance (D) increases.

[0079] The pass characteristics for cases where the separation distance (D) is 36λ / 64 and 146λ / 64 are illustrated in FIG. 9c. As previously explained, the maximum Q value is assigned at a separation distance (D) of 146λ / 64 compared to the case of 36λ / 64, which is also revealed by the fact that the insertion loss of the graph with a separation distance (D) of 146λ / 64 appears good in the right region of the passband in the graph of FIG. 9c.

[0080] Meanwhile, Figures 9d and 9e are graphs illustrating the attenuation region of frequencies below the passband and the attenuation region of frequencies above the passband, respectively. At frequencies below the passband, at the separation distance (graphs 42L64, 78L64, 112L / 64, and 146L / 64) that grants the maximum Q value, it can be seen that the ripple improves as the order increases. However, at frequencies above the passband, the change in the amount of attenuation increases as the order increases, and in particular, when the separation distance (D) is 146λ / 64, it can be observed that a dip occurs around 830 MHz.

[0081] This may be related to the admittance and conductance characteristics of each case. Figure 9f shows a graph comparing the admittance and conductance characteristics for the previous case. The 36λ / 64, where ripple is minimized, is measured to have smooth resonance characteristics with no stopband ripple above the anti-resonance frequency as previously explained, but at the separation distance that gives the maximum Q value, it can be seen that the change in conductance above the anti-resonance frequency increases as the order increases.

[0082] Accordingly, in order to suppress the generation of ripple within the passband as much as possible in the cross-sectional reflection type surface elastic wave device (100) according to the embodiment of the present invention, the separation distance (D) is preferably set to a range having a minimum ripple that differs slightly from a natural number multiple of λ / 2, preferably 34λ / 64 to 39λ / 64, but when the generation of ripple is allowed to some extent, it is preferable to set the separation distance (D) to a range that gives a maximum Q value as shown in FIG. 7.

[0083] FIGS. 10a to 10c are drawings illustrating cross-sectional reflectors of various shapes in a cross-sectional reflective surface elastic wave device according to an embodiment of the present invention.

[0084] Referring to FIG. 10a, the cross section (134) in the second direction (Y) of the cross section (130) may be located on the extension of the first direction (X) of the second direction (Y) end (117) of the electrode (116) immediately adjacent to the outermost electrode (115). The other cross section in the second direction (Y) of the cross section (130) may be located parallel to the second direction (Y) end of the outermost electrode (115) as shown in FIG. 2. The strip shape of such a cross section (130), i.e., the length of the long and short sides, may be determined to be minimal within a range that does not completely surround the IDT (110) as in the prior art.

[0085] However, the shape of the cross-sectional reflector (130) of the present invention is not limited to this embodiment. FIGS. 10b to 10c respectively show that the cross-section (134) in the second direction (Y) of the cross-sectional reflector (130) is located at the end of the second direction (Y) of the dummy electrode (118) (Fig. 10b) and at a position parallel to the long side of the bus bar (111) (Fig. 10c). That is, the length in the second direction (Y) of the cross-sectional reflector (130) is based on the minimum length (Fig. 10a) capable of reflecting elastic surface waves radiated from the IDT (110), but can vary as much as the process variation.

[0086] FIGS. 11a and 11b are drawings illustrating cross-sectional reflectors of various shapes in a cross-sectional reflective surface elastic wave device according to an embodiment of the present invention.

[0087] Referring to FIGS. 11a and 11b, the shape of the cross-sectional reflector (130) is based on a strip-shaped rectangle, but each corner (135) may be rounded. That is, in order to prevent the shape of the cross-sectional reflector (130) from being distorted due to process variation during the etching process for forming the cross-sectional reflector (130), the corners (135) of the cross-sectional reflector (130) are formed with a rounded shape from the initial design.

[0088] At this time, the cross-section (134) in the second direction (Y) of the cross-section reflection part (130) may be located on the extension line of the first direction (X) of the second direction (Y) end (117) of the electrode (116) immediately adjacent to the outermost electrode (115) (Fig. 11a), or may be over-etched (Fig. 11b).

[0089] Although embodiments of the present invention have been described above with reference to the attached drawings, those skilled in the art will understand that the present invention may be implemented in other specific forms without changing its technical concept or essential features. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

Claims

1. In a surface acoustic wave device including a cross-sectional reflector, Substrate; An IDT (Interdigital) comprising a plurality of electrodes spaced apart from each other in a first direction on the substrate and extending in a second direction perpendicular to the first direction; and It includes a cross-sectional reflective portion formed in the depth direction of the substrate, spaced apart from the outermost electrode of the above IDT by a distance in the first direction, A cross-sectional reflective surface acoustic wave device, wherein the above separation distance is determined to be any one of a range from a natural number multiple of λ / 2 to an increase of at least 3.13% of λ, where λ is the elastic surface wave wavelength of the surface acoustic wave device.

2. In Paragraph 1, The elastic surface wave of the above-described surface elastic wave device is a cross-sectional reflection type surface elastic wave device having at least one of a Shear wave (SH wave) or a Love wave (L wave) as a main component.

3. In Paragraph 1, The above cross-sectional reflective portion includes the shape of a trench, and A cross-sectional reflective surface elastic wave device in which the side cross-section of the above trench faces the outermost electrode.

4. In Paragraph 3, A cross-sectional reflective surface elastic wave device in which the above-mentioned side surface forms an angle of less than 90 degrees with the bottom surface of the trench.

5. In Paragraph 4, A cross-sectional reflective surface elastic wave device in which the above-mentioned side surface forms an angle of 75 to 85 degrees with the bottom surface of the trench.

6. In Paragraph 1, The above separation distance is, A cross-sectional reflective surface acoustic wave device located within any one of the ranges of 34λ / 64 to 39λ / 64, 70λ / 64 to 77λ / 64, 106λ / 64 to 114λ / 64, and 144λ / 64 to 150λ / 64.

7. In Paragraph 1, The above separation distance is, A cross-sectional reflective surface acoustic wave device located within any one of the ranges of 39λ / 64 to 45λ / 64, 74λ / 64 to 81λ / 64, 109λ / 64 to 115λ / 64, and 144λ / 64 to 150λ / 64.

8. In any one of paragraphs 1 through 7, The above substrate is, Support substrate, A cross-sectional reflective surface elastic wave device comprising a high-sonic film, a low-sonic film, and a piezoelectric film formed sequentially on the above-mentioned support substrate.

9. Includes a cross-sectional reflective surface elastic wave device, The above cross-sectional reflection type surface elastic wave device is, Substrate; An IDT (Interdigital) comprising a plurality of electrodes spaced apart from each other in a first direction on the substrate and extending in a second direction perpendicular to the first direction; and It includes a cross-sectional reflective portion formed in the depth direction of the substrate, spaced apart from the outermost electrode of the above IDT by a distance in the first direction, A filter device in which the above separation distance is determined to be any one of a range from a natural number multiple of λ / 2 to at least 3.13% of λ, where λ is the elastic surface wave wavelength of the surface elastic wave device.

10. In Paragraph 9, A filter device having a ripple magnitude of 0.2dB or less in the passband.

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