JPH09172339A - Surface acoustic wave device and manufacture of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remove the limit of miniaturization owing to the package of a surface acoustic wave device and to reduce the cost. SOLUTION: An IDT (reed screen-like interdigital electrode) 2 and enveloping electrodes 4 surrounding a surface acoustic wave exciting part by means of IDT are simultaneously formed on a wafer-like piezoelectric substrate 1. A sacrifice layer 5 and a resin layer 7 of silicon oxide and the like are stacked and formed on the whole surface of a wafer. Window holes 8 having the same areas as the terminal electrodes 3 are provided n positions corresponding to the terminal electrodes 3 of IDT. A hollow part 9 is formed at the inner side of the enveloping electrodes 4 and the resin layer 7 by immersing them in buffered hydrofluoric acid and eluding the sacrifice layer 5 from the window holes 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave device used as a high frequency functional element in telecommunications equipment and a method for manufacturing the same.

[0002]

2. Description of the Related Art A surface acoustic wave device (SAW resonator) used for a high frequency resonator, a filter, etc. is provided with a hollow portion in the vicinity of an electrode surface where a surface acoustic wave is excited and is airtight. It is sealed by welding using a package made of ceramic or the like.

[0003]

However, since the ceramic package and the like are expensive, they occupy a large proportion of the cost as parts, and the packaging is performed by cutting and separating a large number of SAW elements formed on one piezoelectric substrate wafer. Since it is carried out in a chip shape, a large number of steps are required for packaging each chip. In addition, since one surface acoustic wave element chip is housed in one package, the size of the device is determined by the size of the package when miniaturization is considered. In addition, a cap having a sufficient height is required so that the bonding wire and the cap do not come into contact with each other, and there is a limitation in reducing the thickness of parts. Further, if the surface acoustic wave element is not housed in a package and is mounted on a circuit board together with another IC circuit as a chip and is resin-sealed at the same time, the resin may touch the surface of the electrode to be excited, which may lead to a desired electrical characteristic. There is a problem that we cannot be satisfied.

It is an object of the present invention to provide a surface acoustic wave device and a method for manufacturing the same, which eliminates the limitations of downsizing and economy due to the use of the package of the prior art, and greatly simplifies the packaging man-hours. It is in.

[0005]

To achieve the above object, a surface acoustic wave device of the present invention comprises a piezoelectric substrate, an IDT electrode formed on the piezoelectric substrate, and a terminal electrode connected to the IDT electrode. The terminal electrode of the resin layer comprises: an enclosing electrode surrounding the surface acoustic wave excited portion by the IDT electrode; and a resin layer formed so as to cover the hollow portion inside the electrode surface of the enclosing electrode as a peripheral portion. It is characterized in that a window hole is provided in a portion corresponding to.

Further, according to the method of manufacturing the surface acoustic wave device described above, a large number of IDT electrodes and the I-electrodes are formed on a wafer-shaped piezoelectric substrate.
An electrode forming step of forming a terminal electrode connected to the DT electrode and a surrounding electrode surrounding the surface acoustic wave excited portion by the IDT electrode, and an etching solution that does not erode the electrode on the entire surface of the piezoelectric substrate on which the electrode is formed. A sacrificial layer forming step of depositing a sacrificial layer of a material that can be melted, and a first etching step of removing a peripheral portion of the sacrificial layer except an inner portion of the surrounding electrode to expose an electrode surface of the surrounding electrode. A resin layer forming step of forming a resin layer in which a window hole is provided in a portion corresponding to the terminal electrode on the surrounding electrode and a sacrificial layer inside thereof, and then, by immersing the resin layer in an etching solution and through the window hole The method is characterized by comprising a second etching step of eluting the sacrificial layer and a cutting step of cutting the outside of the surrounding electrode to obtain a large number of chip-shaped surface acoustic wave devices.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION As described above, after the silicon oxide (SiO ₂ ) film serving as a spacer or a sacrificial layer and the polyimide resin layer are provided on the surface of the surface acoustic wave excitation electrode, the window is formed in the terminal electrode portion. By making holes to elute the silicon oxide in the inner layer, a surface acoustic wave device having a hollow portion in the excitation portion of the excitation electrode surface covered with the polyimide resin layer can be obtained.

[0008]

EXAMPLES The details of the present invention will be specifically described below with reference to the drawings showing examples. 1 and 2 are explanatory views in the order of steps for explaining the manufacturing method of the present invention. FIG. 1 is a plan view (A) showing an electrode forming step, which is the first step of the manufacturing method of the present invention, and an end view (B) of a central transverse section. In the figure, 1 is a piezoelectric substrate made of, for example, lithium niobate (LiNbO ₃ ), 2 is a interdigitated interdigital electrode (IDT), 3 is a
Is the terminal electrode. Reference numeral 4 is an enclosing electrode on the piezoelectric substrate that surrounds the surface acoustic wave excited portion excited by the IDT 2. The IDT 2, the terminal electrode 3, and the surrounding electrode 4 have a thickness of 30 over the entire surface of the piezoelectric substrate 1 by vacuum deposition of gold (Au), for example.
After forming a film of 00Å, patterning is performed by photolithography using a positive photoresist, and etching is performed by ion milling or the like to form the film at the same time. Although FIGS. 1 and 2 all show one surface acoustic wave element, for example, about 700 surface acoustic wave elements are simultaneously formed in a 3-inch piezoelectric substrate material wafer. Therefore, all the steps of FIG. 1 and the step of FIG. 2 described below are simultaneously processed in the wafer state.

FIG. 2 is an explanatory view sequentially showing the manufacturing process of the present invention subsequent to FIG. 1, and (A) to (E) are all shown in FIG.
FIG. 7B is a similar end view of the central transverse section. FIG. 2A shows a sacrifice layer forming step, and 5 is, for example, silicon oxide (S
It is a sacrificial layer such as an iO ₂ ) film. After the electrode formation step of FIG. 1B, a 3 μm thick SiO ₂ film is deposited by sputtering on the entire surface of the wafer as shown in FIG. 2A. Next, FIG. 2B shows a first etching step.
In this step, a negative photoresist is used, and the SiO ₂ film on the upper surface of the surrounding electrode 4 is etched by buffered hydrofluoric acid by photolithography to expose the electrode surface of the surrounding electrode 4 as an adhesive surface 6. Buffered hydrofluoric acid is a buffer solution made up of ammonium fluoride and hydrogen fluoride.

Next, FIG. 2C shows a resin layer forming step, and 7 is a resin layer made of, for example, photosensitive polyimide. First, from the top of the sacrificial layer 5 formed in the previous step, a resin such as a photosensitive polyimide is used as a cover for the hollow portion by 12 μm.
Spin coating is performed with a thickness of m, and a window hole 8 having an area substantially the same as the area of the terminal electrode 3 (bonding pad) is formed at a position corresponding to the terminal electrode 3 by photolithography.

Next, FIG. 2D shows the second etching step, and 9 is a hollow portion. In this step, after the completion of the previous step, it is immersed in a buffered hydrofluoric acid solution for 30 minutes to elute (etch) the sacrificial layer (SiO ₂ ) filling the inside of the surrounding electrode 4 from the window hole 8 to make it hollow. Part 9
Is formed. This hollow portion 9 can be observed from the outside.
When 70 chips out of 700 chips formed in the surface of the 3-inch wafer were extracted and characteristic inspection was performed by the probe, the same electric characteristics as in the state of FIG. 1 were obtained, and the hollow portion 9 was It was judged to have been surely obtained.

FIG. 3 is a perspective view showing the appearance of the surface acoustic wave device of the present invention manufactured by the above manufacturing method. FIG.
After the second etching step (D), cleaning, drying, etc. are performed, and the outside of the surrounding electrode 4 is cut to obtain a large number of surface acoustic wave devices in a chip shape. FIG. 3 shows the appearance of one of the chips, in which the piezoelectric substrate 1 is covered with the polyimide resin layer 7 and the terminal electrode 3 serving as a bonding pad can be seen through the window hole 8.

The chip-type surface acoustic wave device of the present invention shown in FIG. 3 is surface-mounted on a circuit board such as a VCO (voltage controlled oscillator), and the pad portion of the conductor wiring on the circuit board and the terminal electrode 3 are provided. It is wire-bonded with aluminum (Al) or a gold wire, and is hermetically sealed with a high-viscosity epoxy resin together with other circuit elements for practical use.

[0014]

As described above in detail, by implementing the present invention, a chip-like surface acoustic wave device without using a conventional package and having an electromagnetic shield effect equivalent to that of a metal package. As a result, the miniaturization is further promoted, and a great effect can be exerted on the miniaturization of the equipment used by incorporating such a surface acoustic wave device. Further, since the packaging process can be performed on a wafer-by-wafer basis, the cost can be further reduced.

[Brief description of the drawings]

FIG. 1 is a manufacturing process explanatory view showing an embodiment of the present invention.

FIG. 2 is a manufacturing process explanatory view showing an embodiment of the present invention.

FIG. 3 is a perspective view of a chip-shaped surface acoustic wave device of the present invention.

[Explanation of symbols]

 1 Piezoelectric Substrate 2 IDT 3 Terminal Electrode 4 Surrounding Electrode 5 Sacrificial Layer 6 Adhesive Surface 7 Resin Layer 8 Window Hole 9 Hollow Part

Claims (2)

[Claims] 1. A piezoelectric substrate, an IDT electrode formed on the piezoelectric substrate, a terminal electrode connected to the IDT electrode, and the I electrode.
A surrounding electrode surrounding a surface acoustic wave excited portion by the DT electrode,
A resin layer formed so as to cover the hollow portion inside the electrode surface of the surrounding electrode as a peripheral portion, and a window hole is provided in a portion of the resin layer corresponding to the terminal electrode, Surface acoustic wave device. 2. A large number of IDTs are formed on a wafer-shaped piezoelectric substrate.
An electrode forming step of forming an electrode, a terminal electrode connected to the IDT electrode, and an enclosing electrode surrounding the surface acoustic wave excitation part by the IDT electrode; and not eroding the electrode on the entire surface of the piezoelectric substrate on which the electrode is formed A sacrificial layer forming step of depositing a sacrificial layer made of a material that can be melted by an etching solution; and a first part of exposing the electrode surface of the surrounding electrode by removing a peripheral portion of the sacrificial layer except an inner portion of the surrounding electrode. An etching step, a resin layer forming step of forming a resin layer in which a window hole is provided in a portion corresponding to the terminal electrode on the surrounding electrode and the sacrificial layer inside thereof, and then immersing in an etching solution to form the window A method of manufacturing a surface acoustic wave device, comprising: a second etching step of eluting the sacrificial layer from a hole; and a cutting step of cutting the outside of the surrounding electrode to obtain a large number of chip surface acoustic wave devices. .