JPH11330899A - Saw device and manufacture of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the structure of an SAW device with excellent electric power resistance, and a method for manufacturing this device. SOLUTION: This SAW device is constituted so that one part or the entire part of a piezoelectric substrate 1 is made thin. Heat generated during the operation of the SAW device is transferred through the thin substrate to the outside part so that the increase of temperature due to the heat accumulation of an SAW chip can be prevented, and the increase of the temperature of the chip can be reduced, and the power resistance of the SAW device can be improved. Moreover, since this SAW device is constituted so that only one part of the substrate 1 is made thin like a groove, a conventional pattern forming technique and process can be used, and cracks of the substrate 1 in the process can be hardly generated, and simple handling can be realized, and the influence of the reflection of a bulk wave when this substrate is made thin can be suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a substrate structure for improving the power durability of a SAW device.
The present invention relates to a device and a method for manufacturing the device.

[0002]

2. Description of the Related Art Generally, a SAW device forms an interdigital transducer by arranging an electrode made of an aluminum film in a comb shape on the surface of a piezoelectric substrate to constitute a filter or a resonator.

In recent years, with the increase in the frequency of mobile communication,
The operating frequency of the SAW device is also increased from several hundred MHz to several GHz, and high output is desired. As the frequency increases, the pattern width of the interdigital transducer electrode also needs to be reduced, and the electrode line width needs to be formed to about 0.7 μm in a center frequency 1.5 GHz band filter.

When a large electric power is applied to a SAW device having such a fine line width, heat is generated well over 150 ° C. due to conversion of Joule heat due to wiring resistance and partial vibration into heat. In addition, the strain generated by the surface acoustic wave generates stress in the electrode film, and when the stress exceeds the critical stress of the electrode film, the stress is relaxed. Therefore, aluminum atoms as the electrode material move through crystal grain boundaries (stress migration). As a result, protrusions (hillocks) and voids (voids) are generated to cause destruction of the electrodes, leading to deterioration of the characteristics of the SAW device. In a high temperature state, stress due to the difference in thermal expansion coefficient between the substrate and the electrode film is applied to the electrode film, and the specific resistance increases, so that the destruction of the electrode film is accelerated.

Conventionally, as a technique for improving the power durability of a SAW device, efforts have been made to develop electrode materials having excellent power durability, such as alloy electrodes made by adding a small amount of copper or the like to aluminum, or aluminum and other metal materials. Studies have been made to increase the stress migration resistance of the electrode film itself by using a stacked electrode or the like in which the electrodes are alternately formed.

As the substrate, a substrate having a thickness of about 350 μm is often used from the viewpoint of SAW device characteristics or handling. When the thickness is reduced, the substrate is easily broken, the warpage is increased, and the pattern forming accuracy is deteriorated. In addition, there is a concern that adverse effects such as generation of spurious vibrations due to the reflection of the bulk wave on the back surface may occur.

[0007]

The SAW device has a problem that it generates heat during its operation, and this high temperature accelerates the destruction of the electrode film.

[0008] Alloy electrodes that are obtained by adding other metals to aluminum and laminated electrodes that are formed by laminating aluminum and other metals, which have been developed by the conventional electrode material technology, have been improved by increasing the stress migration resistance of the electrode films themselves. Although the power performance is improved, an increase in heat generation due to an increase in specific resistance is expected in each case.

On the other hand, the present invention shows that the power durability can be improved from a new viewpoint of improving the heat radiation of the substrate, and can be used in combination with the electrode material technology.

An object of the present invention is to provide a SAW device having excellent power durability.

[0011]

In order to solve this problem, in a SAW device according to the present invention, a part or the whole of a substrate is thinned to improve heat radiation from the substrate.

Thus, the heat generated during the operation of the SAW device is transmitted to the outside through the thinned substrate,
It is possible to prevent an increase in temperature due to heat storage of the SAW chip, and to improve the power durability of the SAW device by suppressing a rise in chip temperature. Furthermore, if the structure is such that only a part of the substrate is thinned in a groove shape, the conventional pattern forming technology and process can be used, and the substrate is hardly cracked during the process, handling is easy, and the thinning is achieved. In this case, the influence of the reflection of the bulk wave can be suppressed.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS According to the first aspect of the present invention, the thickness of a part or the whole of a piezoelectric substrate is 100 to 2 mm.
The heat generated during the operation of the SAW device is transmitted to the outside through the thinned substrate, and can prevent the SAW chip from being heated to a high temperature due to the heat storage of the SAW chip. The power durability of the SAW device can be improved. By setting the thickness to 100 to 250 μm, there is an effect of providing a SAW device that has a heat radiation effect, hardly causes cracks in the substrate during the process, and is easy to handle.

According to a second aspect of the present invention, the thickness of the piezoelectric substrate is partially or entirely 100 to 250 μm.
The surface roughness Ra of the surface on which no pattern is formed is set to approximately 0.5 μm, and the heat generated during the operation of the SAW device is transmitted to the outside through the thinned substrate, and the surface of the SAW chip is It is possible to prevent an increase in temperature due to heat storage and suppress an increase in chip temperature, thereby improving the power durability of the SAW device. By setting the thickness to 100 to 250 μm, there is an effect of radiating heat, the substrate is hardly cracked during the process, and the handling becomes easy. And by setting the surface roughness Ra to approximately 0.5 μm,
This has the effect of providing a SAW device in which the bulk wave is irregularly reflected on the back surface of the substrate and the influence of spurious due to reflection is suppressed.

According to a third aspect of the present invention, at least one groove is provided in a part of the piezoelectric substrate, and heat generated during operation of the SAW device is reduced. By transmitting the heat to the outside through the substrate, it is possible to prevent the temperature of the SAW chip from becoming high due to heat storage, and to suppress the rise in the chip temperature, thereby improving the power durability of the SAW device. In addition, since only a part of the substrate is thinned in a groove shape, the substrate has a function of preventing the substrate from being cracked during the process and providing a SAW device which is easy to handle.

According to a fourth aspect of the present invention, a groove is provided in a part of the piezoelectric substrate, and the thickness of the groove is set to 100 to 250 μm.
m, the heat generated during the operation of the SAW device is transmitted to the outside through the thinned substrate,
A high temperature due to heat storage of the W chip can be prevented, and a rise in the chip temperature can be suppressed, whereby the power durability of the SAW device can be improved. 100 to 250 μm thickness
By doing so, there is an effect of providing a SAW device which has an effect of heat radiation, hardly causes cracks in the substrate during the process, and is easy to handle.

According to a fifth aspect of the present invention, the cross section of the groove of the piezoelectric substrate is substantially semicircular, and the heat generated during the operation of the SAW device is reduced. The heat can be transmitted to the outside through the substrate, and the temperature of the SAW chip can be prevented from rising due to heat storage. By suppressing the rise in chip temperature, the power durability of the SAW device can be improved. In addition, the cross-sectional shape of the groove is substantially semicircular, so that the substrate is unlikely to crack during the process, and handling is easy. In addition, since the bulk wave is irregularly reflected on the curved surface of the groove, the SAW in which the influence of spurious due to reflection is suppressed.
It has the effect of providing a device.

According to the invention described in claim 6 of the present invention, the surface roughness Ra of the processing surface of the groove provided in a part of the piezoelectric substrate is set to approximately 0.1.
The heat generated during the operation of the SAW device is transmitted to the outside through the thinned substrate,
It is possible to prevent an increase in temperature due to heat storage of the SAW chip, and to improve the power durability of the SAW device by suppressing a rise in chip temperature. In addition, the surface roughness is set to approximately 0.
By setting the thickness to 5 μm, the bulk wave is irregularly reflected on the back surface of the substrate, thereby providing an SAW device in which the influence of spurious due to reflection is suppressed.

According to a seventh aspect of the present invention, there is provided a resonator comprising at least an interdigital transducer electrode and a reflector provided on a surface of a piezoelectric substrate, and an interdigital transducer is provided substantially immediately below the resonator. It has a configuration in which at least one or more grooves are formed in a direction parallel to the electrodes, and heat generated during operation of the SAW device is:
The power is transmitted to the outside through the thinned substrate, so that the temperature of the SAW chip can be prevented from rising due to heat storage. By suppressing a rise in the chip temperature, the power durability of the SAW device can be improved. In addition, by making the curved surface directly under the resonator where bulk wave reflection occurs most, the bulk wave is irregularly reflected, suppressing the influence of spurious due to reflection, and the substrate is less likely to crack during the process and handling is easy. Easy SA
It has the effect of providing a W device.

According to an eighth aspect of the present invention, there is provided an interdigital transducer having a resonator comprising at least an interdigital transducer electrode and a reflector provided on the surface of a piezoelectric substrate, and being displaced from immediately below the resonator. At least one groove is formed in the direction perpendicular to the electrodes. During operation of the SAW device, the substrate is thin and heat radiation is improved, so that the rise in chip temperature can be suppressed and the power durability improved. it can. In addition, by reducing the thickness of the part shifted from immediately below the resonator where reflection of bulk waves occurs most, the effect of spurious due to reflection of bulk waves is suppressed, and the substrate is less likely to crack during processing. Provides an easy-to-use SAW device.

According to a ninth aspect of the present invention, the piezoelectric substrate on which the interdigital transducer electrodes are formed is fixed to a package using a conductive resin, and the substrate is fixed with the conductive resin. Accordingly, by improving the heat conduction from the substrate, the heat radiation is further improved, the rise in the chip temperature can be suppressed, and the power durability can be improved. During the operation of the SAW device, the substrate is made thinner and the heat radiation is improved, so that an increase in chip temperature can be suppressed, and an effect of providing a SAW device with improved power durability can be provided.

According to a tenth aspect of the present invention, an aluminum film or an aluminum alloy film is uniformly formed on a piezoelectric substrate by a sputtering method or a vacuum evaporation method, and a resist is formed thereon by using a photolithography technique. After removing the unnecessary electrode parts by reactive ion etching and washing with water, apply a low-melting resin soluble in solvents such as wax to the pattern forming surface and fix it to the substrate holding jig. Fabrication of SAW devices in which grooves are formed in a part of the substrate by grinding with a grindstone to which abrasive grains such as diamond are bonded, or the entire surface of the substrate is thinned, and finally, wax and resist are simultaneously dissolved and removed with a solvent. This method uses conventional SAW filter processing techniques and processes, and can reduce the thickness of the substrate by forming a thinner substrate after pattern formation. An effect that it is possible to prevent the deterioration of over emissions formation accuracy.

According to the present invention, a low-melting resin soluble in a solvent such as wax is applied before the conventional pattern forming process such as the formation of an aluminum electrode, or the substrate is vacuum-adsorbed. After fixing the pattern forming surface side to the substrate holding jig, a SAW device in which predetermined grooves are formed in advance on the surface opposite to the pattern forming surface of the piezoelectric substrate by grinding using a grindstone to which abrasive grains such as diamond are adhered. This is a manufacturing method.
It has an effect that the processing technology and process of the AW filter can be used, and deterioration of pattern formation accuracy caused by substrate warpage due to substrate processing distortion can be prevented.

Hereinafter, embodiments of the present invention will be described. (Embodiment 1) FIG. 1A is a perspective view showing a configuration of a ladder-type SAW filter created in this embodiment.
FIG. 1B is a diagram showing the configuration. Reference numeral 1 denotes a piezoelectric substrate whose thickness is reduced to about 150 μm. In this embodiment, 36 ° Y-cut X-propagation LiTa
An O ₃ substrate was used. Reference numeral 2 denotes a SAW resonator which includes a comb-shaped electrode and a reflector and is formed by processing an aluminum film. Reference numeral 4 denotes a ceramic package, reference numeral 3 denotes a die bond resin for fixing the SAW chip to the ceramic package, and in this embodiment, S
A silver paste was used as a conductive resin to improve heat conduction from the AW chip. Reference numeral 7 denotes a bonding wire made of a thin aluminum wire. The electrical connection between the SAW chip and the ceramic package was performed by wire bonding to the input terminal 5, the output terminal 6, and the GND terminal 8, respectively.

FIG. 4 shows a manufacturing flow of the SAW filter according to the first embodiment. First, the conventional thickness of about 35
Wash the 0 μm LT substrate. Next, an electrode film made of Al1% Cu is formed to a thickness of about 4000 ° by sputtering. Next, a photoresist is applied by a spin coater and dried. Next, a predetermined pattern formed on the photomask is exposed and transferred. Next, development is performed to remove unnecessary resist. Next, the unnecessary Al1% Cu electrode film is removed by dry etching, and a desired pattern of the Al1% Cu electrode film is realized on the LT substrate. Up to this point, it is exactly the same as the conventional manufacturing flow.

Next, for example, a wax, which is soluble in a solvent and has a low melting point of 100 ° C. or less, is applied to the pattern forming surface of the substrate and adhered to the substrate holder. Next, the substrate is placed on the stage of the grinding machine with the substrate holder down, and fixed by vacuum suction. Then, the substrate is thinly ground with a grinder to which # 1000 diamond abrasive grains are bonded, and finished to about 150 μm. By processing with a grinding machine to which # 1000 diamond abrasive grains are bonded,
The surface roughness Ra of the processed surface is about 0.5 μm. Next, the wax and the resist are dissolved and removed with an organic solvent such as acetone.

Finally, similarly to the conventional manufacturing method, the SAW chips formed on the wafer are singulated by dicing. As a result, a SAW chip having a configuration in which the LT substrate is thinned can be manufactured using the conventional pattern forming technique without deteriorating the pattern accuracy. The SAW chip is fixed in the ceramic package with a die bond resin, the SAW chip and the ceramic package are electrically connected by wire bonding, and hermetically sealed by seam welding. Note that by using a conductive resin as the die bond resin, it is expected that the heat dissipation of the substrate is improved and the power durability is improved.

After dicing into individual pieces, it is also possible to reduce the thickness by grinding.

(Embodiment 2) FIG. 2 is a perspective view showing the configuration of a ladder-type SAW filter produced in this embodiment. The configuration of the embodiment of the present invention shown in FIG.
Since the configuration is basically the same as that shown in FIG. 1, the same components will be denoted by the same reference symbols and detailed description thereof will be omitted. However, a feature of the second embodiment is that a groove having a semicircular cross section is formed almost directly below the first-stage parallel resonator from the input side in parallel with the interdigital transducer electrode.
The thickness of the thinnest portion of the substrate is reduced to about 150 μm. Since the resonator in which electrode breakdown is most likely to occur differs depending on the design and usage of the SAW filter, it is necessary to check in advance the resonator having the weakest power durability and form a groove substantially immediately below the resonator. desirable. In many cases, it is a parallel resonator or a series resonator of the first stage from the input side, and it is desirable to target both or one of them.

FIG. 5 shows a manufacturing flow of the SAW filter according to the second embodiment. First, the conventional thickness of about 35
Wash the 0 μm LT substrate. Next, a resin that is soluble in a solvent and has a low melting point of 100 ° C. or less, for example, wax, is applied to the surface of the substrate on which the pattern is to be formed, and is adhered to the substrate holder. Next, the substrate is placed on the stage of the grinding machine with the substrate holder down, and fixed by vacuum suction. Then, a portion of the portion directly under the first-stage parallel resonator from the input side is formed by a disc-shaped grinding machine having a width of about 300 μm and having a semicircular tip, to which the # 1000 diamond abrasive is adhered. Thin the board and reduce the thickness of the thinnest part to about 1
Finish to 50 μm. After that, an electrode film made of Al1% Cu is formed in a thickness of about 4000 ° by sputtering in exactly the same manner as in the conventional manufacturing process.

Next, a photoresist is applied by a spin coater and dried. Next, a predetermined pattern formed on the photomask is exposed and transferred. Next, development is performed to remove unnecessary resist. Next, unnecessary Al1% Cu electrode film is removed by dry etching, and Al1% Cu electrode film is removed.
A desired pattern by the electrode film is realized on the LT substrate.

Finally, the SAW chips formed on the wafer are singulated by dicing. As a result, a SAW chip having a configuration in which the LT substrate is thinned can be manufactured using the conventional pattern forming technique without deteriorating the pattern accuracy. Fix the SAW chip in the ceramic package with die bond resin and wire bond S
The AW chip is electrically connected to the ceramic package, and hermetically sealed by seam welding. Note that by using a conductive resin as the die bond resin, it is expected that the heat dissipation of the substrate is improved and the power durability is improved.

(Embodiment 3) FIG. 3 is a perspective view showing the configuration of a ladder-type SAW filter produced in this embodiment. The configuration of the embodiment of the present invention shown in FIG.
Since the configuration is basically the same as that shown in FIG. 1, the same components will be denoted by the same reference symbols and detailed description thereof will be omitted. However, the feature of the third embodiment is that two grooves each having a semicircular cross section are formed substantially perpendicular to the interdigital transducer electrode by being shifted from immediately below the first-stage parallel resonator from the input side. , The thickness of the thinnest part of the substrate is about 150μ
m. Since the resonator in which electrode breakdown is most likely to occur differs depending on the design and usage of the SAW filter, it is necessary to check in advance the resonator having the weakest power durability and form a groove substantially immediately below the resonator. desirable. In many cases, the first stage is a parallel resonator or a series resonator from the input side, and it is desirable to target both or one of them.

The manufacturing flow of the SAW filter according to the third embodiment is basically shown in FIG. 5, and is basically the same as that described in the second embodiment.

Although it is difficult to actually measure the substrate temperature of the SAW chip, the substrate having a thickness of 250 μm and 150 μm has a 5-fold and 10-fold improvement in power durability compared to a substrate having a thickness of 350 μm. I do. Further, from the relationship between the power withstand test temperature and the power withstand life, it is expected that the temperatures of the operating chips can be lowered by about 20 ° C. and 35 ° C., respectively.

[0036]

As described above, the piezoelectric substrate is partially or entirely thinned, and the heat generated during the operation of the SAW device is transmitted to the outside through the thinned substrate, and the heat of the SAW chip is stored. Temperature can be prevented, and by suppressing the rise in chip temperature, the power durability of the SAW device can be improved. Furthermore, if the structure is such that only a part of the substrate is thinned in a groove shape, the conventional pattern forming technology and process can be used. A SAW device that suppresses the influence of bulk wave reflection when the filter is used can be obtained, and a SAW filter that can be used in a duplexer of a mobile phone to which a large amount of power is applied, a resonator used in a keyless entry system, and the like This is effective in that it can be created with high reliability.

[Brief description of the drawings]

FIG. 1A is a schematic diagram illustrating a schematic configuration of a SAW filter according to a first embodiment of the present invention; FIG.

FIG. 2 is a schematic diagram showing a schematic configuration of a SAW filter according to a second embodiment of the present invention.

FIG. 3 is a schematic diagram illustrating a schematic configuration of a SAW filter according to a third embodiment of the present invention.

FIG. 4 is a process chart showing a manufacturing flow of the SAW filter according to the first embodiment of the present invention.

FIG. 5 is a process chart showing a manufacturing flow of a SAW filter according to the second and third embodiments of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Piezoelectric substrate 2 Resonator 3 Die bond resin 4 Ceramic package 5 Input terminal 6 Output terminal 7 Bonding wire 8 GND terminal

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Kazunari Nishihara 1006 Kazuma Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd.

Claims (11)

[Claims] A piezoelectric substrate having at least an interdigital transducer electrode provided on a surface of the piezoelectric substrate, wherein a thickness of a part or the entire surface of the piezoelectric substrate is 1
A SAW device having a configuration of 00 to 250 μm. 2. The SAW device according to claim 1, wherein the surface of the piezoelectric substrate on which the interdigital transducer electrode is not formed has a surface roughness Ra of about 0.5 μm. 3. A SAW device having a piezoelectric substrate and at least an interdigital transducer electrode provided on the surface of the piezoelectric substrate, wherein at least one groove is provided in a part of the piezoelectric substrate. 4. The SAW device according to claim 3, wherein a groove is provided in a part of the piezoelectric substrate, and the thickness of the groove is 100 to 250 μm. 5. The SAW device according to claim 3, wherein the cross-sectional shape of the groove in a part of the piezoelectric substrate is substantially semicircular. 6. The SAW device according to claim 3, wherein a surface roughness Ra of a processing surface of the groove provided in a part of the piezoelectric substrate is approximately 0.5 μm. 7. A piezoelectric substrate, and a resonator comprising at least an interdigital transducer electrode and a reflector provided on the surface of the piezoelectric substrate, and substantially parallel to the interdigital transducer electrode substantially under the resonator. The SAW device according to any one of claims 4 to 6, wherein at least one or more grooves are formed in the direction. 8. A piezoelectric substrate, and a resonator including at least an interdigital transducer electrode and a reflector provided on the surface of the piezoelectric substrate, and is displaced from immediately below the resonator to be perpendicular to the interdigital transducer electrode. The SAW device according to any one of claims 4 to 6, wherein at least one or more grooves are formed in the direction. 9. The S according to claim 1, wherein a conductive resin is used for fixing the piezoelectric substrate on which the interdigital transducer electrodes are formed to a package.
AW device. 10. An aluminum film or an aluminum alloy film is uniformly formed on a piezoelectric substrate by a sputtering method or a vacuum evaporation method, and a desired pattern is formed thereon by a resist using a photolithography technique. After removing unnecessary electrode parts by ion etching and washing with water, a low-melting resin soluble in solvents such as wax was applied to the pattern formation surface, fixed to a substrate holding jig, and then abrasive grains such as diamond were bonded. A method of manufacturing a SAW device in which a groove is formed in a part of a substrate by grinding with a grindstone, or the entire surface of the substrate is thinned, and finally, wax and resist are simultaneously dissolved and removed with a solvent. 11. Prior to a conventional pattern forming process such as formation of an aluminum electrode, a low-melting resin soluble in a solvent such as wax is applied, or the pattern forming surface side of the substrate is placed on a substrate holding jig by vacuum suction. A method for manufacturing a SAW device in which predetermined grooves are formed in advance on a surface opposite to a pattern formation surface of a piezoelectric substrate by grinding using a grindstone to which abrasive grains such as diamond are adhered after fixing.