JP3722642B2 - Surface acoustic wave device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a surface acoustic wave device such as a surface acoustic wave filter and a duplexer, which is used in mobile communication devices such as a mobile phone.
[0002]
[Prior art and its problems]
At present, surface acoustic wave filters used in mobile communication devices are desired to have a low mounting area, a low weight, and a low height to the limit in order to miniaturize mobile phone terminals.
[0003]
Conventionally, the surface acoustic wave filter J1 shown in FIGS. 9A to 9C is mainly composed of a substrate 102 made of a piezoelectric single crystal on which excitation electrodes are formed, and a ceramic package 108 for sealingly mounting the substrate.
[0004]
A substrate 102 includes a comb-like surface acoustic wave resonator electrode (excitation electrode) 103 made of aluminum, aluminum-copper alloy, etc., input / output electrodes 113a and 113b, a ground electrode (not shown), and connection electrodes thereof. Are formed on the same surface.
[0005]
A protective film 104 is formed on the top surface of the excitation electrode 103 to prevent foreign substances such as dust from attaching and corroding. The substrate 102 is fixed to the bottom of the ceramic package 108 by a resin 110, and input / output electrodes and a ground electrode (not shown) on the substrate 102 are respectively connected to the input / output terminal electrodes 113a and 113b of the ceramic package 108 using wires 114. Are connected.
[0006]
A protective film is not formed on the portion where the wire 114 is connected in order to ensure the stability of the connection. Since the board | substrate 102 is an elastic body, the space 105 which ensures free vibration is required. For this reason, a lid 109 is provided on the upper portion, and hermetically sealed with the ceramic package 108 and the resin 110 so as to prevent vibration damping due to moisture or moisture entering from the outside. In particular, the entry of moisture and the like is a serious problem in terms of reliability and the like since it has deliquescence when the piezoelectric substrate is a lithium tetraborate single crystal or the like.
[0007]
In such a surface acoustic wave filter, the substrate 102 and the ceramic package 108 are electrically connected by the wire 114, and this height hinders miniaturization. Further, the ceramic package 108 is much larger than the substrate 102, for example, about 1.5 to 2.1 mm in size per side, and the bottom area is about three times as large.
[0008]
Further, as shown in FIG. 9A, the ground terminal electrode 113b in the ceramic package 108 is connected to the back surface of the ceramic package 108 through the narrow end face ground electrode as shown in FIG. 9C. Therefore, an inductor component is generated, and the attenuation characteristics at the low frequency side of the pass band (hatched portion) and at 4 to 6 GHz are deteriorated as indicated by a circle in FIG.
[0009]
Further, the surface acoustic wave filter J2 as shown in FIGS. 11A to 11C is formed by connecting the input / output electrode 103a and the ground electrode (not shown) on the substrate 102 with a ceramic bump 111 therebetween. It is connected to the terminal electrodes 113a and 113b on the package 108, and is reinforced with a conductive resin 112 to compensate for the low connection strength between the bump 111 and the terminal electrodes 113a and 113b. Further, the conductive resin 112 also plays a role of absorbing the poor flatness of the bumps 111. With the above structure, the height can be reduced by the height of the wire loop.
[0010]
However, since the bottom area of the ceramic package 108 is reduced, the gap g between the input / output terminal electrodes 113a on the back surface is reduced, and a capacitance is generated between the electrodes. For this reason, as indicated by a circle in FIG. 12, the attenuation characteristics on the high frequency side of the pass band (hatched portion) and in the vicinity of 3 GHz have deteriorated. Further, the ceramic package 108 still occupies most of the filter shape, which hinders the reduction in size, weight, and height.
[0011]
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a surface acoustic wave device that can be miniaturized and is highly reliable without impairing attenuation characteristics.
[0012]
[Means for Solving the Problems]
In order to solve the above problems, a surface acoustic wave device according to the present invention is a surface acoustic wave device in which a lower surface side of a piezoelectric substrate on which an excitation electrode, an input / output electrode and a ground electrode are formed is mounted on a circuit board. The side surface of the piezoelectric substrate is formed at an acute angle with respect to the lower surface, and a conductive protective film is formed on the upper surface and the side surface of the piezoelectric substrate, and the ground electrode is formed on the lower surface of the piezoelectric substrate. It is characterized in that it is formed so as to surround the excitation electrode in an outer peripheral portion and to be in contact with the protective film.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of a surface acoustic wave device according to the present invention will be described below in detail with reference to the drawings.
[0014]
FIG. 1 shows a sectional view of a mounting structure of a surface acoustic wave filter 1 as a surface acoustic wave device, and FIG. 2 shows an electrode structure thereof. The surface acoustic wave filter 1 includes a lower surface 2a of a piezoelectric substrate 2 such as a lithium tantalate single crystal, a single crystal having a langasite-type crystal structure (for example, a lanthanum-gallium-niobium single crystal), or a lithium tetraborate single crystal. In addition, an electrode 3 such as an excitation electrode is formed. That is, a plurality of comb-shaped resonator electrodes 3c, which are excitation electrodes described later, are connected to the lower surface 2a of the piezoelectric substrate 2, for example, in a ladder circuit, and the connection electrodes 3d, input / output electrodes 3a, and grounding electrodes are connected. A semiconductive or insulating electrode protective film 4 such as silicon or silicon oxide is formed on the electrode 3b. In addition, a thin metal film 12 that is a conductive protective film is formed on the upper surface 2c and the side surface 2b of the piezoelectric substrate 2 by a thin film forming method, thereby realizing a chip surface acoustic wave filter having a structure with excellent weather resistance. .
[0015]
Here, the protective film formed on the upper surface and the side surface of the piezoelectric substrate 2 is conductive in order to shield outflow radio waves (such as harmonics), but can further ensure airtightness, and can form a film. For simplicity and ease, it is preferable to use a metal. In forming the metal thin film 12, the chip surface acoustic wave filter is individually separated by dicing, and then one or more kinds of metals made of Al, Au, Ti, Cr, etc. are formed by vapor deposition or an Al film. And a Cu film, a W film and an Au film, and the like.
[0016]
Although it is necessary to form the metal thin film 12 with an appropriate thickness also on the side surface of the piezoelectric substrate 2 separated by dicing, this film formation is most easily performed by a vapor deposition method. At this time, since the vapor deposition particles are formed in a direction substantially perpendicular to the surface to be vapor-deposited, uniform film formation is difficult when the side surface of the piezoelectric substrate 2 is vertical.
[0017]
Therefore, in the present invention, when the chip surface acoustic wave filter is individually separated by dicing, a dicing tooth having a convex shape (for example, a V shape) is used, and the chip surface acoustic wave filter is separated while forming a taper at the end portion of the element. Then, a metal thin film 12 having a thickness of 500 μm to 10 μm is formed on the upper surface and side surfaces of the piezoelectric substrate 2. Here, the film thickness is within the above range because if it is less than 500 mm, film formation becomes difficult on the side surface and upper surface edge of the piezoelectric substrate 2 and the weather resistance cannot be maintained, and if it exceeds 10 μm, the metal thin film 12 and This is because a difference in linear expansion coefficient of the piezoelectric substrate 2 causes a compressive stress at a low temperature or a tensile stress at a high temperature, which adversely affects the temperature characteristics.
[0018]
Further, the angle (taper angle) θ formed between the lower surface 2a and the side surface 2b of the piezoelectric substrate 2 clearly shown in FIGS. 1 and 6A is 45 to 80 degrees.
[0019]
The surface acoustic wave filter 1 configured as described above is mounted on the circuit board 6 by forming the grounding electrode 3 b surrounding the resonator electrode 3 c on the lower surface or side surface of the piezoelectric substrate 2. The distance h between the surface of the circuit board 6 and the surface of the resonator electrode 3c is set to a distance equal to or greater than the wavelength of the surface acoustic wave.
[0020]
In FIG. 1, 8 is a conductive adhesive made of conductive resin, 9 is a connection pad made of metal or the like formed on the filter substrate 10, 11 is a via electrode, and 13 is an external extraction electrode. is there. The surface acoustic wave filter 1 configured as described above is mounted on an external circuit board. As shown in FIG. 3, a surface acoustic wave filter in which the lower surface 2a side of the piezoelectric substrate 2 is directly face-down mounted on a circuit substrate 6 made of glass epoxy or the like instead of the filter substrate 10 of FIG. 1 ′ (same configuration as the surface acoustic wave filter 1 except that the circuit board 6 is used instead of the filter board 10) may be configured.
[0021]
Here, since the input / output electrode 3a and the grounding electrode 3b are formed by the same process, these electrodes are excellent in flatness. In addition, since the input / output electrodes and the grounding electrode protrude from the electrode protection film 4 made of semiconductive or insulating material, the space 5 for free vibration can be maintained, and the filter substrate 10 or the circuit substrate 6 remains as it is. It can be mounted face down. Further, since the grounding electrode 3b is formed all around the substrate 2, airtightness is ensured.
[0022]
Moreover, since the metal thin film is formed on the upper surface and the side surface of the piezoelectric substrate of the chip surface acoustic wave filter, unnecessary electromagnetic waves can be blocked by an RF (Radio Frequency) block.
[0023]
Although the ladder type filter has been described in the present invention, a surface acoustic wave device such as a resonator type or propagation type filter or a duplexer other than a filter may be used as long as it has an excitation electrode. Changes and modifications can be made as appropriate without departing from the scope.
[0024]
【Example】
Hereinafter, specific examples in which the chip surface acoustic wave filter according to the present invention was produced will be described.
[0025]
FIGS. 5A to 5H and FIGS. 6I to 6M are schematic cross-sectional views showing the manufacturing process of the chip surface acoustic wave filter, respectively. In the manufacture, photolithography was performed using a stepper (reduction projection exposure apparatus) and an RIE (Reactive Ion Etching) apparatus.
[0026]
(1) First, the substrate 2 (42 ° Y cut of lithium tantalate single crystal) was subjected to ultrasonic cleaning using acetone / IPA or the like to remove organic components. Next, after the substrate was sufficiently dried by a clean oven, the electrode 3 was formed as shown in FIG. A sputtering apparatus was used to form the electrode 3, and the electrode 3 made of an Al—Cu (2 wt%) alloy was formed. The electrode film thickness was about 2000 mm.
[0027]
(2) As shown in FIG. 5B, a photoresist 7 was applied to a thickness of about 0.5 μm by spin coating.
[0028]
(3) As shown in FIG. 5C, patterning was performed to a desired shape with a stepper, and unnecessary portions of the photoresist 7 were dissolved with an alkaline developer using a developing device to form a desired resist pattern.
[0029]
(4) As shown in FIG. 5D, the electrode 3 was etched into a desired pattern by an RIE apparatus.
[0030]
(5) As shown in FIG. 5E, the photoresist 7 was peeled off and the patterning was completed.
[0031]
(6) As shown in FIG. 5F, the electrode protective film 4 made of SiO _{2 was formed} to a thickness of 250 mm by a sputtering apparatus.
[0032]
(7) As shown in FIG. 5G, the photoresist 7 was applied again to the entire surface with a thickness of about 3 μm.
[0033]
(8) As shown in FIG. 5H, a portion of the photoresist 7 on the substrate 2 on which the input / output electrodes 3a and the grounding electrode 3b are formed was exposed and removed.
[0034]
(9) As shown in FIG. 6I, the SiO ₂ electrode protective film 4 on the substrate 2 on which the input / output electrodes 3a and the grounding electrode 3b are formed was removed by CDE.
[0035]
(10) As shown in FIG. 6 (j), an Al electrode was formed to a thickness of 2 μm by vapor deposition so as to be thicker than the electrode protective film 4.
[0036]
(11) As shown in FIG. 6K, the electrode material on the photoresist together with the photoresist 7 was removed by lift-off. .
[0037]
(12) As shown in FIG. 6 (l), the wafer is diced along the dicing line using V-shaped teeth and divided so that the taper angle θ of the chip end is 45 ° to 80 °. The chip was completed.
[0038]
Next, implementation will be described.
[0039]
(13) As shown in FIG. 6 (m), the chip is mounted face-down on the filter substrate 10, and the input / output electrode 3a and the ground electrode 3b are connected to the electrode on the substrate by a conductive resin (not shown). did.
[0040]
(14) As shown in FIG. 1, a thickness of 1000 mm was formed on the upper surface 2c and side surface 2b of the piezoelectric substrate 2 by vapor deposition of Al.
[0041]
(15) Finally, the filter substrate 10 was matched with the chip and divided into individual pieces by dicing to complete individual filters 1.
[0042]
In the above mounting, a reactive polyester resin or epoxy resin containing 90 to 93% by weight or 81 to 86% by weight of silver filler in the outer periphery and the input / output electrode part of the ground electrode 3b is screen-printed. It was applied by the method, temporarily cured at 80 ° C. for about 1 hour, and then cured at 120 to 225 ° C. for 10 to 60 minutes for mounting.
[0043]
According to the mounting structure of the surface acoustic wave filter, the outer peripheral portion of the piezoelectric substrate is surrounded by the metal material, and the periphery of the substrate 2 is surrounded by the grounding electrode 3b, so that airtightness can be secured at the same time. Further, since the input / output electrode 3a and the grounding electrode 3b are formed by the same process, the flatness is excellent and the conduction reliability can be extremely increased. Further, the height of the space 5 is secured to about 2 μm, and this height is almost equal to the wavelength at the center frequency of the surface acoustic wave filter. If there is a space height higher than this, the vibration of the surface acoustic wave is caused. There is no hindrance.
[0044]
As shown in FIG. 4, the electrical characteristics of the chip surface acoustic wave filter obtained in this way were not deteriorated in the attenuation characteristics that had occurred in the past, and good attenuation characteristics could be obtained. Further, an attenuation amount of 20 dB or more can be obtained on the higher frequency side than the pass band (hatched portion), and the attenuation characteristics in the vicinity of the pass band were not deteriorated.
[0045]
Good attenuation characteristics were obtained compared to the conventional configuration because the conventional ceramic package is not required, unnecessary inductance is not generated, and there is no ceramic package, so the input / output terminals are wide. Since no electrode is required and only an input / output electrode that is conductively connected to the circuit board is required, it is conceivable that the facing distance between the input / output electrodes is wide and the generated capacity is reduced.
[0046]
Further, in the surface acoustic wave filter of the present invention, there is a concern about characteristic deterioration due to the opposing capacitance between the input / output 3a and the grounding electrode 3b at the position indicated by d (opposite spacing) in FIG. It was confirmed that there was no problem at all. It is VSWR (standing wave ratio) that changes depending on the capacitance at this point, and it has been found that there is no problem with the attenuation characteristics if there is no change in VSWR.
[0047]
FIG. 7 is a graph showing the relationship between the facing distance d and the capacitance C generated at that location. It is shown that when the facing distance d is 20 μm or less, the capacity generated suddenly increases. Since the capacitance when d is 20 μm is about 0.14 pF, it has been found that the change in VSWR in this case is 0.08 at most, as shown in FIG. Therefore, it was confirmed that there was no deterioration in characteristics when the facing distance d was 20 μm or more.
[0048]
【The invention's effect】
According to the surface acoustic wave device of the present invention, the side surface of the piezoelectric substrate is formed at an acute angle with respect to the lower surface, and the protective film is deposited on the upper surface and the side surface of the piezoelectric substrate. It is possible to reduce the height, prevent damage to the piezoelectric substrate as much as possible, and form a protective film uniformly by a thin film forming method.
[0049]
Further, by using a conductive metal material as the protective film, the protective film can be easily formed, unnecessary electromagnetic waves can be shielded, and sufficient airtightness can be secured. Therefore, it is possible to provide a surface acoustic wave device that is easy to manufacture and excellent in reliability.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view schematically showing a mounting structure of a surface acoustic wave device according to the present invention.
FIG. 2 is a plan view schematically showing an electrode structure of another surface acoustic wave device according to the present invention.
FIG. 3 is a cross-sectional view schematically showing a mounting structure of another surface acoustic wave device according to the present invention.
FIGS. 4A to 4C are diagrams illustrating the electrical characteristics of the surface acoustic wave device according to the present invention. FIG.
FIGS. 5A to 5H are cross-sectional views illustrating manufacturing steps of the surface acoustic wave device of the present invention.
6 (a) to 6 (m) are cross-sectional views illustrating manufacturing steps of the surface acoustic wave device of the present invention.
FIG. 7 is a diagram showing a relationship between a facing distance and a capacity of the surface acoustic wave device of the present invention.
FIG. 8 is a diagram showing the relationship between the counter capacitance and the VSWR of the surface acoustic wave device of the present invention.
9A and 9B are diagrams for explaining a conventional surface acoustic wave filter, in which FIG. 9A is a top view in a non-sealed state, FIG. 9B is a bottom view, and FIG. It is an A line expanded sectional view.
FIGS. 10A to 10C are diagrams for explaining electrical characteristics of a conventional surface acoustic wave filter, respectively.
11A and 11B are diagrams for explaining another conventional surface acoustic wave filter, in which FIG. 11A is a top view in an unsealed state, FIG. 11B is a bottom view, and FIG. It is a BB line expanded sectional view.
FIGS. 12A to 12C are diagrams illustrating electrical characteristics of other conventional surface acoustic wave filters, respectively.
[Explanation of symbols]
1, 1 ': Chip surface acoustic wave filter (surface acoustic wave device)
2: Piezoelectric substrate 3: Electrode 3a: Input / output electrode 3b: Ground electrode 3c: Resonator electrode (excitation electrode)
3d: Connection electrode 4: Electrode protective film 5: Space 6: Circuit board 7: Photoresist 8: Adhesive 9: Connection pad 10: Filter substrate 11: Via electrode 12: Metal thin film

Claims (1)

A surface acoustic wave device in which a lower surface side of a piezoelectric substrate on which an excitation electrode , an input / output electrode and a grounding electrode are formed is mounted on a circuit board, and the side surface of the piezoelectric substrate is formed at an acute angle with respect to the lower surface. A conductive protective film is formed on the upper and side surfaces of the piezoelectric substrate, and the grounding electrode is formed on the outer periphery of the lower surface of the piezoelectric substrate so as to surround the excitation electrode and to be in contact with the protective film. A surface acoustic wave device.

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