JPH05102782A - Surface acoustic wave element - Google Patents

Abstract

PURPOSE:To surely make the element size small while preventing occurrence of large out-band spurious radiation. CONSTITUTION:An comb-line electrode 12, a reflector 13 arranged respectively at both sides and a damping part 2 arranged at the outside of each reflector 13 are formed on a crystal substrate 11 side by side. In the surface acoustic wave 1, the width W along with the propagation direction of a surface acoustic wave of the damping section 2 is selected to be the multiple of 5 of a reflector wavelength lambda or more and the multiple of 20 or less.

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.

[0002]

2. Description of the Related Art Conventionally, VH such as television broadcasting is used.
A surface acoustic wave element is used when performing signal processing from the F band to the UHF band. One example is a surface acoustic wave element.
A SAW filter 10 configured as shown in FIG. 6 is known. That is, this SAW filter 10 has 8
It is called a crystal laterally coupled 1-port dual-mode type used in the 0 to 90 MHz band, and a comb-shaped electrode (IDT) 12 that excites surface acoustic waves is formed on the surface of a crystal substrate 11 in the shape of a rectangular plate. And reflectors (reflectors) 13 arranged at both side positions sandwiching the IDT 12 and reflecting surface acoustic waves. At this time, of course, the reflectors 13 are divided by the number (cycle) corresponding to the wavelength synchronized with the desired center frequency (f ₀ ).

Therefore, in this SAW filter 10, the surface acoustic wave is excited by the impulse voltage applied to the IDT 12 and is propagated along the surface acoustic wave propagation direction (indicated by arrow A in the figure). The surface waves will be reflected by the respective reflectors 13, and standing waves will be formed between these reflectors 13. As a result, the function as a resonator having a high Q value will be exhibited. .. In the figure, reference numeral 14 is a signal line pad formed by connecting to each IDT 12, and 15 is a reflector 1.
3 is a ground pad formed by connecting to each of the three.

[0004]

By the way, in order to miniaturize the SAW filter 10 as a surface acoustic wave element, it is important to minimize the number of the reflectors 13 within a range in which the characteristics thereof are not deteriorated. Become. However, when considering the relationship between the in-band loss and the out-of-band spurious in the SAW filter 10, when the number of reflectors reaches a certain number, the spurious is not satisfied even though the loss is still sufficiently satisfied. It will happen that a large amount of. Then, if such a situation occurs, as shown in FIG. 7, for example, when the image frequency (f ₀ +1) is at the high frequency side 910 KHz detuning point of f ₀ , the attenuation amount at this point is sufficient. Even if the image frequency (f ₀ -1) is at the detuning point of 910 KHz on the low frequency side of f ₀ , the standard will be broken and the yield will be reduced. ..

Therefore, in order to improve such spurious characteristics, conventionally, a damping portion (not shown) for the surface acoustic wave is formed by coating a silicon resin or the like on the outer portion of each reflector 13. It is being set. However, the necessary and sufficient width dimension of the damping portion along the surface acoustic wave propagation direction A has not been examined, and the width dimension of the damping portion is set appropriately. Therefore, the width dimension of these damping portions may be too large, and eventually the size reduction of the SAW filter 10 may be halfway completed.

The present invention was devised in view of such inconveniences, and it is possible to prevent the occurrence of only the out-of-band spurious noise, and at the same time, it is possible to reduce the size of the element reliably. The purpose is to provide a surface acoustic wave element.

[0007]

In order to achieve such an object, the present invention provides a comb-shaped electrode (IDT), reflectors (reflectors) arranged on both sides of the comb-shaped electrode, and the outside of each reflector. In a surface acoustic wave device in which a damping part disposed in the part is formed in parallel on the surface of a quartz substrate, the width dimension along the surface acoustic wave propagation direction of the damping part is set to 5 times or more and 20 times or less of the reflector wavelength. It is characterized by being present.

[0008]

According to the above construction, the damping portion is formed on the outer side of each reflector, so that not only the loss but also the spurious can be sufficiently satisfied. At this time, the width dimension of the damping portion is set to be 5 times or more and 20 times or less of the reflector wavelength, so that the element size can be sufficiently reduced.

[0009]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a plan view showing a schematic structure of a SAW filter as a surface acoustic wave element, and FIG. 2 is a plan view showing a modification thereof. Reference numeral 1 in these drawings is a SAW filter. Since the overall structure of the SAW filter 1 is basically the same as that of the conventional example, the same or corresponding parts and portions as those in FIG. 6 are denoted by the same reference numerals in FIGS. 1 and 2.

Like the conventional example, the SAW filter 1 according to the present embodiment is called a crystal horizontal coupling 1-port double mode type, and has a crystal substrate 11 formed in a rectangular flat plate shape. Then, on the surface of the crystal substrate 11, a comb-shaped electrode (IDT) 12 for exciting surface acoustic waves is formed.
And reflectors (reflectors) 13 arranged on both sides sandwiching the IDT 12 and reflecting surface acoustic waves, respectively. Each reflector 13 has a desired center frequency f.
It is divided by the number (cycle) corresponding to the wavelength synchronized with ₀ . The period that divides the reflector 13 is generally referred to as the reflector wavelength λ.

Furthermore, damping portions 2 for preventing the surface acoustic waves from leaking out are formed on the outer portions of the respective reflectors 13 formed on the surface of the quartz substrate 11 by applying a silicone resin or the like. Therefore, the width W of each damping portion 2 along the surface acoustic wave propagation direction A is set to 5 times or more and 20 times or less of the reflector wavelength λ. That is, the width W of the damping part 2 when the reflector wavelength λ is 35 μm is 175 μm.
It is set to (= 5 × λ) or more and 700 μm (= 20 × λ) or less. By the way, in FIG. 1, the damping part 2 is formed in a state of being separated from the reflector 13. However, the present invention is not limited to this, and as shown in FIG. 1
It may be formed in such a manner that it hangs on the outer side portion of 3.

Here, the width dimension W of the damping portion 2
The reason why is restricted to 5 times or more and 20 times or less of the reflector wavelength λ is as follows. First, when the width W of the damping part 2 is 5 times or less of the reflector wavelength λ, the damping effect becomes insufficient and spurious cannot be suppressed sufficiently. Further, if the width dimension W of the damping section 2 is set to be 20 times or more the reflector wavelength λ, the width dimension W will be widened by that amount. Therefore, when the element size is limited, By reducing the size, the property must be sacrificed.

By the way, the inventor of the present invention has found that the SAW having the same element size and used in the 90 MHz band is used.
A characteristic comparison experiment was performed when the width W of the damping part 2 in the filter 1 was changed. That is, the sample 1 in which the width dimension W of the damping part 2 is less than 5 times the reflector wavelength λ, the sample 2 in which the width dimension W of the damping part 2 is about 10 times the reflector wavelength λ, and the width dimension of the damping part 2 Sample 3 in which W exceeds 20 times the reflector wavelength λ, and a part of this damping part 2 hangs on the reflector 13
When an experiment was carried out after preparing and, the insertion loss (attenuation) -frequency characteristics as shown in FIGS. In this characteristic comparison experiment, only sample 2 corresponds to this example, and samples 1 and 3 are out of the corresponding range of this example.

[0015] Then, according to these characteristics comparison experiment result, the attenuation in the image frequency (f ₀ +1) in the high frequency side 910KHz detuning point samples f ₀ 1 (see FIG. 3)
It is 61 dB, whereas it is 80 dB in the sample 2 (see FIG. 4) corresponding to the present example, which is a significant improvement. In addition, the sample 3 (see FIG. 5) is replaced with the sample 2
When compared with, the attenuation amount at the center frequency (f ₀ ) increases from 3 dB to 5 dB, and the 3 dB band width decreases from 53 KHz to 47 KHz.
It can be seen that the characteristics are degraded.

The present invention is not applied only to a SAW filter called a crystal laterally coupled 1-port double-mode type, but is also applicable to a surface acoustic wave device having another structure such as a 2-port type. It goes without saying that it is also applicable.

[0017]

As described above, according to the surface acoustic wave element of the present invention, the propagation direction of the surface acoustic wave of the damping portion disposed on the outer side of the reflector disposed on each side of the comb-shaped electrode. Since the width dimension along with is not less than 5 times and not more than 20 times the reflector wavelength, it is possible to effectively prevent a large out-of-band spurious from occurring while keeping the in-band loss low. The effect that it is possible to achieve a reliable miniaturization is obtained.

[Brief description of drawings]

FIG. 1 is an SA as a surface acoustic wave device according to the present embodiment.
It is a top view which shows schematic structure of a W filter.

FIG. 2 is a plan view showing a modification thereof.

FIG. 3 is a characteristic diagram showing an insertion loss-frequency characteristic of Sample 1.

FIG. 4 is a characteristic diagram showing an insertion loss-frequency characteristic of sample 2.

FIG. 5 is a characteristic diagram showing insertion loss-frequency characteristics of sample 3.

FIG. 6 is a SAW as a surface acoustic wave device according to a conventional example.
It is a top view which shows schematic structure of a filter.

FIG. 7 is a characteristic diagram showing the insertion loss-frequency characteristics.

[Explanation of symbols]

 1 SAW filter (surface acoustic wave element) 2 Damping part 11 Crystal substrate 12 IDT (comb-shaped electrode) 13 Reflector (reflector) W Width width of damping part λ Reflector wavelength

Claims (1)

[Claims] 1. A quartz substrate (1) comprising a comb-shaped electrode (12), reflectors (13) arranged on both sides of the comb-shaped electrode (12), and a damping portion (2) arranged on the outer side of each reflector (13). In the surface acoustic wave device formed in parallel on the surface of 11), the width dimension (W) along the surface acoustic wave propagation direction of the damping part (2) is set to be 5 times or more and 20 times or less of the reflector wavelength (λ). A surface acoustic wave device characterized in that