JPH11186867A - Surface acoustic wave device - Google Patents

Abstract

(57) [Summary] A multi-mode type S that can use a single SAW device in a plurality of different frequency bands and is significantly reduced in size.
An AW device. A piezoelectric substrate has at least a pair of I on a main surface thereof.
A SAW device D1 formed by forming DT electrodes 1 to 3, wherein the pair of IDT electrodes 1 to 3 is configured such that three IDT electrodes 1 to 3 are meshed with each other, and has a three-phase or two-phase structure. Drive with potential.

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 for a frequency band filter or an oscillator incorporated in a mobile radio device such as an automobile telephone and a portable telephone.

[0002]

2. Description of the Related Art Conventional surface acoustic waves (Surface Acoustic W)
The device D is shown in FIG. FIG. 3A shows a pair of comb-shaped electrodes I of the SAW device D.
Partial plan view of DT (Inter Digital Transducer) electrode,
(B) is sectional drawing in CC line of (a). In the drawing, reference numeral 4 denotes a piezoelectric substrate, and 5 denotes a potential excited by the IDT electrodes 7 and 8. The pair of IDT electrodes 7 and 8 are configured so as to mesh with each other, and resonate at a predetermined frequency with respect to an input high-frequency signal according to a configuration parameter such as a pitch of electrode fingers.

FIG. 7 shows an example of a conventional SAW filter. This figure is a circuit diagram of a 2.5-stage π-type ladder-type (ladder-type) SAW filter F for the GHz band for mobile communication. In the figure, 12 is a pair of IDT electrodes, 13 is a reflector provided at both ends of the SAW propagation path of the IDT electrode 12 for efficiently resonating the SAW,
15 is a series SAW resonator (series SAW device), 16 to 1
8 is a parallel SAW resonator.

[0004] The SAW filter F is formed on the main surface of a piezoelectric substrate (not shown) made of a 36 ° Y-cut-X propagating LiTaO ₃ single crystal or the like.
4, 15 and the parallel SAW resonators 16 to 18 are connected alternately in parallel and in series. In the figure, IN indicates an input terminal and OUT indicates an output terminal. The number of electrode fingers of the IDT electrode 12 and the reflectors 13 and 13 is several tens to several hundreds.
In order to cover a book, its shape is simplified.

[0005] Such a SAW filter F generally has a SAW resonator (SAW device D) shown in FIG. 5 as a basic component. Further, there is an oscillator as another application field of the SAW resonator.

In the ladder-type SAW filter F, the pass bandwidth is substantially determined by the stop bandwidth (≡Δf) of each SAW resonator. FIG.
5 is a graph in which an IDT electrode 12 of a W resonator is connected to an impedance analyzer or the like, and an absolute value | Z | -frequency characteristic of an input impedance is measured. In the figure, f1
Is the resonance frequency at which | Z | is the minimum, and f2 is | Z |
Is the maximum anti-resonance frequency. Stopband width Δ
f corresponds to the frequency interval between f1 and f2.

Using a material having a small Δf and a high Q (Q: resonance sharpness) such as a lithium tantalate (LiTaO ₃ ) single crystal, the sharpness of the resonance frequency and the anti-resonance frequency of the SAW resonator is increased. Is increased, the steepness of the SAW filter F has good characteristics.

[0008]

However, in a conventional SAW filter using a SAW resonator, an operable frequency and a frequency band are uniquely determined by its structure. For example, as a function of a mobile phone that has recently been growing in demand, there is a function of using two different frequency bands, a so-called dual mode function. In this case, two types of SAW filters are required in accordance with the two frequency bands. There was a problem of becoming. Further, an impedance matching circuit for electrically connecting the two types of SAW filters has been required. Therefore, in the case of a dual mode type mobile phone (dual mode device) or the like, the conventional SAW resonator has problems in miniaturization and cost reduction.

Accordingly, the present invention has been completed in view of the above circumstances, and has as its object to reduce the size of a multimode SAW device by using a single SAW device in a plurality of different frequency bands. In addition, in a SAW filter and an oscillator for a dual mode device, the number of SAW resonators is greatly reduced, and the impedance matching circuit is simplified, thereby achieving a significant reduction in size and cost. .

[0010]

A surface acoustic wave device according to the present invention comprises three or more comb-shaped electrodes arranged on a main surface of a piezoelectric substrate so as to mesh with each other, and a plurality of these comb-shaped electrodes are provided. It is characterized by being driven by the potential of each phase, whereby it is possible to resonate at two or more different frequencies by driving at different potentials of a plurality of phases and switching the drive potential by a switching circuit. Is given to one surface acoustic wave device, and a multi-mode type that is significantly reduced in size is realized.

In the present invention, preferably, when the number of comb-teeth electrodes is n (n is an integer of 3 or more) and the electrode finger pitch of the comb-teeth electrodes having the minimum electrode finger pitch is p, The electrode finger pitch is (n-
1) p-times n-1 comb-shaped electrodes are alternately meshed and arranged.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A SAW device according to the present invention will be described below. 1 and 2 show SAW devices D1 and D2 of the present invention. FIGS. 1 (a) and 2 (a) are partial plan views of an IDT electrode, and FIGS. 1 (b) and 2 (b) are IDT electrodes. 3 is a sectional view taken along line AA (FIG. 1) and line BB (FIG. 2). These are examples in which three IDT electrodes are driven by three-phase or two-phase potentials and are resonated at two kinds of frequencies. Of course, four or more IDT electrodes are driven by a plurality of
Resonance may be performed at more than one kind of frequency.

1 and 2, reference numeral 1 denotes an IDT electrode having a minimum electrode finger pitch and an electrode finger pitch of p, 2 denotes an IDT electrode having an electrode finger pitch 2p twice as large as the IDT electrode 1, and 3 denotes an electrode finger pitch. Another IDT electrode of 2p, 4 is LiT
A piezoelectric substrate made of aO ₃ single crystal or the like, 5 is a typical potential input to the IDT electrode, and 6 is a resistor for dividing the potential of the high frequency power supply. Also, the IDT electrode 2 and the IDT
Although the T electrodes 3 overlap, an insulating layer such as SiO ₂ is formed between them.

Then, depending on the frequency to be resonated, ID
The potential supplied to the T electrodes 1 to 3 can be switched by an external diode switch or the like.

The SAW device D1 shown in FIG. 1 is an example in which resonance is performed in a lower frequency band as compared with FIG.
Denotes a ground electrode, the IDT electrode 2 functions as a plus or minus electrode, and the IDT electrode 3 functions as a minus or plus electrode. As a result, as shown by the potential 5, an electrode finger pitch of 2p corresponds to one wavelength of the excited SAW.

The SAW device D2 shown in FIG. 2 is an example of a case where resonance occurs in a high frequency band. The IDT electrode 1 functions as a positive electrode or a negative electrode, and the IDT electrodes 2 and 3 function as a negative electrode or a positive electrode. As a result, as shown by the potential 5, the electrode finger pitch p corresponds to one wavelength of the excited SAW.

Here, the power supply shown in FIG. 1 and FIG. 2 is shared, and two types of power supply are switched by a switch, thereby enabling resonance in a low frequency band or a high frequency band.

The SAW devices D1 and D2 shown in FIGS.
The number of T electrodes can be four or more. More generalized, the number of IDT electrodes is n (n is an integer of 3 or more), and the electrode finger pitch of the IDT electrode having the minimum electrode finger interval is p. In this case, n-1 IDT electrodes having an electrode finger pitch of (n-1) p times are alternately meshed with the IDT electrodes having the minimum electrode finger spacing.

In this case, n = 3 is the example in FIGS. 1 and 2, and the drive frequency can be easily doubled (FIG. 2). Also, n ≧ 4, and
The basic operation is the same as that of FIGS. n = 4
3 is shown in FIG.
The DT electrodes 22 to 24 are arranged so as to mesh with each other. The present invention provides a transversal SAW having such a configuration.
Filter, resonator type SAW filter, etc., each ID
Adjusting the phase of the high-frequency signal input to the T electrode also has the effect that the passband width and phase characteristics can be varied.

An IDT in which the electrode finger spacing is the same as q
When the number of electrodes is m (m is an integer of 3 or more), m-1 IDT electrodes are meshed with one IDT electrode, and m-IDT electrodes are arranged between electrode fingers of the one IDT electrode. 1
It is possible to adopt a configuration in which the electrode fingers of the IDT electrodes are arranged. In this case, depending on the number of m, for example, if m is an odd number, the same operation as in FIGS. 1 and 2 can be performed. And a transversal type SAW filter and a resonator type SA
In a W filter or the like, by adjusting the phase of a high-frequency signal input to each IDT electrode, the pass band width and phase characteristics can be varied.

Further, a plurality of IDT electrodes can be configured to mesh with a plurality of IDT electrodes. Two IDTs for two IDT electrodes 31 and 32
FIG. 4 shows an example in which the electrodes 33 and 34 are arranged in engagement.

In the present invention, the IDT electrodes 1 to 3 are made of Al.
Alternatively, it is made of an Al alloy (Al-Cu system, Al-Ti system, etc.), and Al is particularly preferable because of its high excitation efficiency and low material cost. The IDT electrodes 1 to 3 are formed by a thin film forming method such as an evaporation method, a sputtering method, or a CVD method.

The number of pairs of the IDT electrodes 1 to 3 is about 50 to 200, and the line width of the electrode fingers is 0.1 to 10.0.
μm, the distance between the electrode fingers is about 0.1-10.0 μm,
The opening width (intersection width) of the electrode finger is about 10 to 100 μm,
It is preferable that the thickness of the DT electrode 1a be about 0.2 to 0.4 μm in order to obtain desired characteristics as a SAW resonator or a SAW filter. IDT electrode 1
It is preferable to form a piezoelectric material such as zinc oxide or aluminum oxide between the electrode fingers of (1) to (3) because the SAW resonance efficiency is improved.

As the piezoelectric substrate, a LiTaO ₃ single crystal of 36 ° Y cut-X propagation and a LTa of 64 ° Y cut-X propagation are used.
iNbO ₃ single crystal, 45 ° X cut-Z propagation LiB ₄
O ₇ single crystal or the like is preferable because it has a large electromechanical coupling coefficient and a small group delay time temperature coefficient. Particularly, a 36 ° Y cut-X propagating LiTaO ₃ single crystal having a large electromechanical coupling coefficient is preferable. The cut angle in the crystal Y-axis direction is 3
The angle may be within the range of 6 ° ± 10 °, in which case sufficient piezoelectric characteristics can be obtained. The thickness of the piezoelectric substrate is 0.1-0.5m
m is good. If it is less than 0.1 mm, the piezoelectric substrate becomes brittle, and if it exceeds 0.5 mm, the material cost increases.

Thus, according to the present invention, it is possible to resonate at two or more different frequencies by driving with different potentials of a plurality of phases and switching the driving potential by a switching circuit. It has the effect of realizing.

Further, in the SAW device of the present invention, a ladder-type SAW filter F as shown in FIG. 5, for example, can be formed by connecting a plurality of SAW devices on the main surface of the same piezoelectric substrate. In that case, 1.5-stage type, 2-stage type,
A 2.5-stage type, a 3-stage type, a 3.5-stage type, or a multi-stage type may be used. Or, not limited to the ladder type,
It can be used for various types of SAW filters such as a lattice type SAW filter and a notch type SAW filter. Further, a SAW device or a SAW filter may be provided on both main surfaces (front and back surfaces) of the piezoelectric substrate.

It should be noted that the present invention is not limited to the above embodiment, and various changes may be made without departing from the scope of the present invention.

[0028]

Embodiments of the present invention will be described below. Using a pattern of a SAW device D1 made of Al as shown in FIG. 1, a 2.5-stage π-type ladder-type SAW filter F as shown in FIG. 7 was converted to a 36 ° Y-cut X-propagation LiTaO ₃ single crystal. Formed on a piezoelectric substrate composed of Specifically, it was produced as follows.

(1) A negative pattern of a resist for the IDT electrodes 1 and 2 was formed on the piezoelectric substrate wafer by a photolithography method using a contact exposure device using ultraviolet rays (Deep UV).

(2) A
1 was formed, unnecessary Al was lifted off in the resist stripping solution, and a large number of fine patterns for the SAW filter F were produced.

(3) A resist was applied again and photolithography was performed, and an insulating layer made of SiO ₂ was formed by a sputtering method on the IDT electrode 2 where the IDT electrodes 2 and 3 overlap with each other at a thickness of 300 °.

(4) A resist was further applied and photolithography was performed to form a negative resist pattern corresponding to the IDT electrode 3.

(5) Al is deposited by an electron beam evaporator,
Unnecessary Al is lifted off in the resist stripper, and IDT
The fine patterns of the electrodes 1 to 3 were completed.

(6) The wafer after patterning was cut by a dicing method to cut out individual SAW filters F.

(7) Each chip of the SAW filter F is connected to an SMD (Surface Mounted Device).
It was adhered with epoxy resin in a package for mounting and mounted and fixed. An Al wire having a diameter of 35 μm (diameter of 35 μm) was ultrasonically bonded so as to connect the electrode pad of the package and the Al pad on the chip, and then covered and bonded with a package lid, thereby completing the packaging.

At this time, in one SAW device D1, the number of pairs of IDT electrodes 1 = 85 pairs, the line width of the electrode fingers of IDT electrode 1 = 1.1 μm, the distance between the electrode fingers of IDT electrode 1 =
1.1 μm, thickness of electrode finger of IDT electrode 1 = 3500
Å, number of electrode fingers of reflector = 20, line width of electrode finger of reflector = 1.1 μm, interval between electrode fingers of reflector = 1.1 μm,
The thickness of the electrode fingers of the reflector was 3500 °.

The logarithm of the IDT electrode 2 = 85 pairs, ID
Line width of electrode finger of T electrode 2 = 1.1 μm, distance between electrode fingers of IDT electrode 2 = 2.2 μm, thickness of electrode finger of IDT electrode 2 = 3500 °, number of pairs of IDT electrodes 3 = 85, IDT
The line width of the electrode finger of the electrode 3 was 1.1 μm, the interval between the electrode fingers of the IDT electrode 3 was 2.2 μm, and the thickness of the electrode finger of the IDT electrode 3 was 3500 °.

The SAW filter F of the present invention has a simplified impedance matching circuit as compared with the conventional SAW filter F, and its size has been greatly reduced to about 1/3.

Further, in the above configuration, about 900 MHz
, The IDT electrode 1 has a ground potential and ID
When a high-frequency signal is input to the T electrode 2 and a high-frequency signal having a phase opposite to that of the IDT electrode 2 is input to the IDT electrode 3,
The case where a high-frequency signal is input to the IDT electrode 1, a high-frequency signal having a phase opposite to that of the IDT electrode 1 is input to the IDT electrode 2, and the same high-frequency signal as the IDT electrode 2 is input to the IDT electrode 3 is set to , And two types of passbands were obtained with a single SAW filter F.

[0040]

According to the present invention, a single SAW device is used in a plurality of different frequency bands by configuring at least three IDT electrodes so as to mesh with each other and by driving with a plurality of phase potentials. A multi-mode SAW device can be manufactured in a reduced size, and in a SAW filter and an oscillator for a dual-mode device, the number of SAW devices can be significantly reduced, and the impedance matching circuit can be simplified, thereby greatly reducing the size. This has the effect of realizing cost reduction.

[Brief description of the drawings]

FIG. 1 shows a SAW device D1 of the present invention, wherein (a) shows an SAW device.
Partial plan view of the IDT electrode of the W device D1, (b) is (a)
FIG. 3 is a sectional view taken along line AA of FIG.

FIG. 2 shows a SAW device D2 according to the present invention, wherein (a) shows the SAW device;
Partial plan view of the IDT electrode of the W device D2, (b) is (a)
It is sectional drawing in the BB line of FIG.

FIG. 3 shows another embodiment of the SAW device of the present invention,
FIG. 4 is a partial plan view in a case where three IDT electrodes are arranged so as to mesh with one IDT electrode.

FIG. 4 shows another embodiment of the SAW device of the present invention,
FIG. 5 is a partial plan view in a case where two IDT electrodes are arranged so as to mesh with one IDT electrode.

5A and 5B show a conventional SAW device D, wherein FIG. 5A is a partial plan view of an IDT electrode of the SAW device D, and FIG.
It is sectional drawing in the C line.

FIG. 6 is a graph showing a frequency characteristic of an input impedance | Z | of the SAW resonator.

FIG. 7 is a circuit diagram of a conventional 2.5-stage π-type ladder-type SAW filter F.

[Explanation of symbols]

 1: IDT electrode 2: IDT electrode 3: IDT electrode 4: Piezoelectric substrate 5: Potential potential 6: Resistance

Claims (2)

[Claims] 1. A surface acoustic wave characterized in that three or more comb-shaped electrodes are arranged on a main surface of a piezoelectric substrate so as to mesh with each other, and these comb-shaped electrodes are driven with a plurality of phases of potentials. apparatus. 2. When the number of comb-teeth electrodes is n (n is an integer of 3 or more) and the electrode finger pitch of the comb-teeth electrodes having the minimum electrode finger pitch is p, the comb having the minimum electrode finger interval is provided. 2. The surface acoustic wave device according to claim 1, wherein n-1 comb-teeth electrodes having an electrode finger pitch of (n-1) p times are alternately meshed with the tooth electrodes.