JPH0463010A - Surface acoustic wave resonator - Google Patents

Abstract

PURPOSE:To prevent spurious resonation due to the influence of a neighboring surface acoustic wave resonator by arranging an accessory pattern which distorts the wave front of a leaked surface acoustic wave at an area outside a grating reflector. CONSTITUTION:The accessory pattern 20 consisting of the same material(Al, etc.,) as that of the IDT 13 or the grating reflector 14 and which distorts the wave front of a surface acoustic wave(SAW) leaked from the grating reflector 14 to the outside is provided in the area outside the grating reflector 14 in a direction to propagate the SAW excited by an IDT 13. Deviation occurs between the upper and lower sides in the wave front of the SAW while the SAW leaking from the grating reflector 14 to the neighboring surface acoustic wave resonator 12 on the left side arrives at the surface acoustic wave resonator 12. When the SAW is reflected on the grating reflector 14 of a neighboring pattern and is propagated again on a propagation path, the deviation occurs further between the upper and lower sides. In such a way, the resonation between the neighboring patterns can be suppressed.

Description

Detailed Description of the Invention [Object of the Invention] (Industrial Application Field) The present invention relates to a surface acoustic wave resonator used as an oscillator for various communication means.

(Prior Art) In general, a surface acoustic wave resonator includes at least one interdigital transducer (hereinafter referred to as IDT) formed on a piezoelectric substrate and an excited surface acoustic wave (
It is composed of grating reflectors and the like formed to sandwich the IDT in the propagation direction of the SAW (hereinafter referred to as SAW). Since such surface acoustic wave resonators can directly oscillate fundamental waves at frequencies from VHF to UHF, they can be used as RF modulators in VTRs, local oscillators in CATV converters, local oscillators in mobile communication devices such as cordless phones and car phones, etc. It is widely used.

When applying a surface acoustic wave resonator to an oscillator in this way,
System requirements often require high oscillation frequency accuracy. For example, in a local oscillator application for a CATV converter, it is necessary to keep the oscillation frequency accuracy within +100KH2. This corresponds to ±150 ppm, which is extremely severe.

On the other hand, in the manufacturing process of surface acoustic wave resonators, processing variations (film thickness, line width, etc.) of the resonator pattern (metal thin film pattern of A℃, Au, etc.) in the PEP process, The resonant frequency of the formed surface acoustic wave resonator varies due to variations in alignment (mask alignment accuracy) or variations in the surface acoustic wave velocity of the piezoelectric wafer itself.

For this reason, usually, as shown in FIG. 7, a piezoelectric wafer 1 is patterned by a PEP patterning process to form a large number of surface acoustic wave resonators 2, and then these surface acoustic wave resonators are directly placed in the wafer state using a prober or the like. The frequency characteristics of the surface acoustic wave resonator 2 are measured, and the pattern is judged to be pass/fail.Based on the measurement results, the frequency characteristics are adjusted to the desired range through reprocessing, which is called trimming. The method is to improve the manufacturing yield after packaging.

FIG. 8 shows the state of blobbing when the wafer is in the first state. Piezoelectric ueno which is a piezoelectric substrate
A large number of surface acoustic wave resonators 2 formed in 1 have two IDs.
T3 and grating reflectors 4 placed on both sides of it
I believe in Then, the probe 6 of the prober is brought into contact with the butt part 5 of the IDT 3, and the transmission characteristics are measured using a network analyzer or the like.

At this time, most of the SAW excited by the IDT 3 is reflected by the grating reflector 4 and resonates within the surface acoustic wave resonator 2 being measured. The SAW leaking from the grating reflector 4 is
It is reflected by the grating reflector 4 of the adjacent surface acoustic wave resonator 2 in the SAW propagation direction, and returns again to the surface acoustic wave resonator 2 where the measurement is being performed. For this reason, spurious resonance occurs between the grating reflector 4 of the surface acoustic wave resonator 2 that is being measured and the grating reflector 4 of the adjacent surface acoustic wave resonator 2, and the network analyzer As shown in FIG. 9, this spurious resonance is superimposed on the resonance of the main pattern, and a characteristic having two peaks, A (main pattern) and B (spurious), is measured.

On the other hand, in measurement in a wafer state, when the surface acoustic wave resonator 2 exhibiting such characteristics is cut into chips and evaluated after being mounted in a package, the above-mentioned spurious does not occur. In other words, after cutting into each chip in this way, the leakage S described earlier
The AW is reflected at the edge of the chip, but the edge of the chip cut with a dicing saw or the like is microscopically non-linear and wobbling due to minute chips.
AW is diffusely reflected, and S at the edge of such a chip
Since the reflection of the AW is mode-converted into a bulk wave that penetrates into the substrate, no spurious resonance occurs.

(Problem to be Solved by the Invention) As described above, in conventional surface acoustic wave resonators, when trying to measure frequency characteristics in the wafer state using a blower or the like, spurious resonance occurs due to the influence of adjacent surface acoustic wave resonators. As a result, characteristics such as the resonance frequency cannot be accurately measured, resulting in errors in pattern pass/fail determination or frequency shift target value determination by trimming.

The present invention has been made in response to such conventional circumstances, and can prevent spurious resonance due to the influence of adjacent surface acoustic wave resonators, and enables accurate measurement of frequency characteristics in the Ueno state. The present invention aims to provide a surface acoustic wave resonator that can perform accurate pass/fail determination and accurate evaluation for trimming, thereby improving productivity.

[Configuration of the Invention (Means for Solving the Problems) In other words, the present invention comprises a piezoelectric substrate having a predetermined shape, at least one interdigital transducer formed on one main surface of the piezoelectric substrate, and the piezoelectric substrate. In a surface acoustic wave resonator comprising a grating reflector formed to sandwich the interdigital transducer on one principal surface, the grating reflection in the direction in which the surface acoustic wave excited by the interdigital transducer propagates. An attached pattern made of the same material as the interdigital transducer or the grating reflector, which distorts the wavefront of the surface acoustic wave leaking outward from the grating reflector, is provided in an area outside the device. It is characterized by having been placed.

(Function) In the surface acoustic wave resonator of the present invention having the above configuration, the surface acoustic wave leaking from the grating reflector propagates through the attached pattern before reaching the adjacent surface acoustic wave resonator on the wafer. , during this time the wavefront (equiphase front) is distorted. and,
When reflected and returned to the surface acoustic wave resonator where measurement is being performed again, the wavefront is further distorted by propagating through the attached pattern again.

Therefore, spurious resonance due to the influence of adjacent surface acoustic wave resonators can be prevented, and accurate frequency characteristics can be measured in the wafer state.

Therefore, accurate pass/fail judgment and accurate bias for trimming can be performed, and productivity can be improved.

(Example) Hereinafter, details of the present invention will be described with reference to the drawings.

FIG. 1 shows the configuration of a surface acoustic wave resonator in an embodiment of the wafer state after patterning.

In the figure, reference numeral 11 denotes a piezoelectric wafer 11 which is a piezoelectric substrate.
A large number of surface acoustic wave resonators 12 are formed so as to be regularly arranged on one main surface of the piezoelectric wafer 11 (only a part of which is shown in FIG. 1).

The surface acoustic wave resonator 12 includes two IDTs 13 and a total of two grating reflectors 14, one on each side of the IDTs. In addition, the pad portion 1 is attached to the IDTl3.
5 is provided, and is configured so that a blow μ probe (not shown) can be brought into contact thereto and the transmission characteristics can be measured using a network analyzer or the like.

Further, in the area outside the grating reflector 14 in the direction in which the SAW excited by the ID 713 propagates, the IDT 1
3 or the grating reflector 14 (such as AJ2), and is provided with an attached pattern 20 for distorting the wavefront of the SAW leaking outward from the grating reflector 14.

That is, this additional pattern 20 is set to have a width that is approximately half the width of the IDT 13 and the grating reflector 14, and is provided so as to be located only in the half (lower half in FIG. 1). . Therefore, in FIG. 1, the SAW leaking from the grating reflector 14 of the surface acoustic wave resonator 12 in the center to the adjacent surface acoustic wave resonator 12 on the left is the SAW that propagates in the upper free portion of the propagation path. The propagation speed is different between the SAW and the SAW propagating in the lower attached pattern 20 part (the propagation speed of the SAW is lower in the pattern part than in the fringe part due to the surface short-path effect and the mass addition effect of the thin film). , on each of the upper and lower sides,
Since the wavelength of the propagating SAW is different, the wavefront of the SAW is shifted upward and downward while reaching the left surface acoustic wave resonator 12 (indicated by the dotted line in the figure). This SAW with a shifted wavefront
However, when the light is reflected by the grating reflector 14 of the adjacent pattern and propagates through this propagation path again, a shift in the wavefront occurs between the upper and lower sides.

In this way, resonance between adjacent patterns is effectively suppressed.

Therefore, it is possible to accurately measure frequency characteristics in the wafer state, and based on this, accurate pass/fail judgment and accurate evaluation for trimming can be performed.
Productivity can be improved.

In addition, since the attached pattern 20 is made of the same material as the IDT 13 or the grating reflector 14, it can be formed at the same time as these patterns, and compared to conventional methods, only the mass needs to be changed. , there is no need to increase the number of processes.

After completing a wafer process such as blowing, the surface acoustic wave resonator 12 is diced into chips along the dashed lines shown in the figure, and mounted on a package to form a device. Therefore, the attached pattern 20 will remain in the area between the grating reflector 14 on the chip and the end of the piezoelectric substrate, but in this mounted state, the grating reflector 14 will be removed as described above. Since the leaked SAW causes diffuse reflection or mode conversion to a bulk wave at the chip end, spurious resonance does not occur regardless of the presence or absence of the attached pattern 20.

Furthermore, when looking at the occupancy rate when viewed on a straight line parallel to the SAW propagation direction of the attached pattern 20, it is 0 on the upper side and approximately 1 on the lower side, so the distribution of the occupancy rate in the direction perpendicular to this straight line is , will be different on the upper and lower sides. If there is something that can distort the wavefront of the leaked SAW due to such a difference in the distribution of the occupancy rate, the shape of the attached pattern 20 can be changed as appropriate. Further, in the embodiment shown in FIG. 1, it is not necessary to make the shapes of the attached patterns 20 on both sides the same, or to make the shapes of the attached patterns 20 on both sides the same.

Modifications of such an attached pattern 20 are shown in FIGS. 2 to 6.

FIG. 2 shows an example in which a diamond-shaped attached pattern 20a is provided. In this case, the SAW propagating near the center of the attached pattern 20a will mostly propagate within the attached pattern, and the It is delayed compared to the SAW that propagates in the other upper and lower parts. Therefore, the wavefront of the SAW is distorted as shown by the dotted line in the figure, and no spurious resonance occurs.

The attached pattern 20b shown in FIG. 3 has a shape in which the pattern part and the fringe part of the diamond-shaped attached pattern 20a shown in FIG. 2 are reversed. Further, FIG. 4 shows a triangular attached pattern 20c, FIG. 5 shows an attached pattern 20d in the shape of a combination of three rhombuses, and FIG. 6 shows the attached pattern 20 of FIG.
An attached pattern 20d having a rounded corner is shown.

Similar effects can be obtained with these attached patterns 20b to 20d, and these can also be used in combination.

[Effects of the Invention] As explained above, according to the surface acoustic wave resonator of the present invention, spurious resonance due to the influence of adjacent surface acoustic wave resonators can be prevented, and accurate frequency characteristics can be achieved in the wafer state. can be measured.

Therefore, accurate pass/fail determination and accurate evaluation for trimming can be performed, and productivity can be improved.

In addition, the attached pattern can be formed simultaneously when patterning the IDT and grating reflector,
Compared to the conventional method, it is only necessary to change the mask, and the number of manufacturing steps does not increase.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of an embodiment of the present invention, FIGS. 2 to 6 are diagrams showing the configuration of a modification of the embodiment shown in FIG. 1, and FIG. 7 is a diagram showing the state of the piezoelectric wafer. Figure 8 is a diagram for explaining how to measure the characteristics of a conventional surface acoustic wave resonator in a wafer state, and Figure 9 is a diagram to explain how to measure the characteristics of a conventional surface acoustic wave resonator in a wafer state. It is a figure showing a result. 11...Piezoelectric wafer 12...
......Surface acoustic wave resonator 13...
・・・・・・・・・・・・・IDT14・・・・・・・
......Grating reflector 15...
・・・・・・・・・Pad part 20・・・・・・・・・
・・・・・・Applicant of attached pattern: Toshiba Corporation

Claims (1)

[Scope of Claims] A piezoelectric substrate having a predetermined shape, at least one interdigital transducer formed on one main surface of the piezoelectric substrate, and one main surface of the piezoelectric substrate forming the interdigital transducer so as to sandwich the interdigital transducer. In a surface acoustic wave resonator comprising a grating reflector, the interdigital transducer or the grating reflector is provided in a region outside the grating reflector in a direction in which the surface acoustic wave excited by the interdigital transducer propagates. A surface acoustic wave resonator characterized in that an attached pattern made of the same material is arranged to distort the wavefront of a surface acoustic wave leaking outward from the grating reflector.