JP2001345666A - Elastic surface wave device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a balanced elastic surface wave device of high quality, which operates as a balanced type and is excellent in filter characteristic. SOLUTION: In the elastic surface wave device, a resonator electrode pattern is formed by providing a plurality of odd-numbered IDT electrodes in propagation direction of the elastic surface wave, and is provided in a plurality of stages on a piezoelectric substrate. One of the resonator electrode patterns formed in stages at both ends of the resonator electrode patterns is made a balanced or unbalanced input, and the other is made an unbalanced or balanced output. A resonator electrode pattern wherein an unbalanced input or an unbalanced output is formed is formed so that IDT electrodes arranged at both sides of a center IDT electrode become the same phase mutually, and a resonator electrode pattern wherein a balanced input or a balanced output is formed is formed so that IDT electrodes arranged at both sides of a center IDT electrode become reverse phase mutually.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an unbalanced input-balanced output type or a balanced input-unbalanced output type, for example, a frequency band filter incorporated in a mobile radio device such as a mobile phone and a mobile phone. Surface acoustic wave device.

[0002]

2. Description of the Related Art In recent years, in order to reduce the size, weight, and cost of mobile communication devices, the number of parts used has been reduced.
Surface acoustic wave (Surface Acoustic Wav)
e, hereinafter also referred to as SAW). One of the demands is to be able to configure an unbalanced input-balanced output type or a balanced input-unbalanced output type. Here, the balanced input or balanced output means a signal that is input or output as a potential difference between two signal lines, and the signals on each signal line have the same amplitude and opposite phases. On the other hand, an unbalanced input or an unbalanced output means that a signal is input or output as a potential of one line with respect to a ground potential.

A conventional SAW filter is generally an unbalanced input-unbalanced output type SAW filter (hereinafter referred to as an unbalanced type SW filter).
AW filter), if the circuit and electronic components downstream of the SAW filter are of the balanced input type, S
A circuit configuration in which an unbalanced-balanced converter (hereinafter, also referred to as a balun) is inserted between the AW filter and the subsequent stage.
Similarly, when the circuits and electronic components in the preceding stage of the SAW filter are of a balanced output type, the circuit configuration has a balun inserted between the preceding stage and the SAW filter.

At present, an unbalanced-to-balanced output type SAW filter or a balanced-to-unbalanced output type in which a SAW filter is provided with an unbalanced-to-balanced conversion function or a balanced-to-unbalanced conversion function in order to eliminate a balun. SAW filter
(Hereinafter, abbreviated as a balanced SAW filter) is being put to practical use.

FIG. 3 shows a basic configuration of a conventional balanced SAW element.
(See Japanese Patent Application Laid-Open No. 9-321574). 42
A pair of comb-shaped electrodes made of Al, Al-Cu, or the like, an IDT (Inter Digital) is formed on a piezoelectric substrate made of a YTa-X single crystal or the like that propagates in °
Transducer) Multiple electrodes (three in Fig. 3)
A reflector for efficiently resonating the SAW is provided at both ends of the SAW propagation path of the IDT electrode. Such an electrode pattern is generally called a resonator type electrode pattern. Since the number of electrode fingers of the IDT electrode and the reflector ranges from several to several hundred, the shapes are simplified.

[0006] Of the three IDT electrodes, the IDT electrode arranged at the center is an unbalanced input or unbalanced output IDT electrode, and the IDT electrodes at both ends thereof are balanced input or balanced output IDT electrodes, respectively. Assuming that one of the pair of electrodes forming the output IDT electrode is an output 1, the other is an output 2 in which the amplitude is the same as that of the output 1 and the phase is opposite to the output 1. Of the operation.

In a SAW device using such a SAW element, the driving frequency and the pass band are increased to several hundred MHz to several GHz, and at the same time, the insertion loss in the pass band and the attenuation outside the pass band are increased. Has been required.
In particular, in order to achieve the demand for higher attenuation, the SAW element needs to have a configuration in which the SAW devices of FIG. 3 are connected in a plurality of stages as shown in FIG.

In the figure, reference numeral 11 denotes an unbalanced input or unbalanced output terminal (hereinafter, also referred to as unbalanced input / output terminal), and reference numeral 12 denotes a balanced output or balanced input 1 terminal (hereinafter, also referred to as balanced input / output 1 terminal). ) And 13 are terminals for balanced output or balanced input 2 (hereinafter also referred to as terminals for balanced input / output 2), and 14 is a ground terminal. In order to ensure a low insertion loss and a high out-of-band attenuation, it is desired that the number of stages is about two as shown in FIG. At one stage, the insertion loss is low, but the attenuation is deteriorated. At three or more stages, the insertion loss is high, but the attenuation is high.

The SAW element is mounted and fixed on an external casing made of a ceramic substrate or the like by using a Si resin or the like. Next, a wire wire made of Au or an Al-Si alloy is used to connect the electrode terminal of the SAW element to the outside. The electrode terminals of the housing are connected, and then a cap made of Kovar or the like is placed over the outer housing and sealed to form a SAW device for wire bonding wiring.

[0010] Alternatively, a bump made of Au or the like is formed on the electrode terminal of the SAW element, and then the SAW element is placed on an external housing made of a ceramic substrate or the like with the surface on which the bump is formed and the SAW propagates as a lower surface. The SAW device is mounted and fixed by a flip-chip mounting method, and is covered with an external housing with a cap and sealed, thereby forming a flip-chip mounted SAW device.

[0011]

However, in the configuration of the conventional SAW element, the balanced input / output 1 terminal is formed between the first-stage SAW element and the second-stage SAW element.
The balanced input / output 2 terminal is formed on the opposite side of the balanced input / output 1 terminal of the second-stage SAW element.

In the conventional SAW device of the wire bonding wiring using the SAW element, the wire wired to the terminal for balanced input / output 1 and the wire wired to the terminal for balanced input / output 2 as shown in FIG. The length of the wire and the shape of the peripheral electrode pattern are each electrically asymmetric. Alternatively, in the flip-chip mounted SAW device using the above-described conventional SAW element, as shown in FIG. 7, the electrode pattern of the external housing connected to the balanced input / output 1 terminal and the balanced input / output 2 terminal are connected. In addition, the shapes of the electrode patterns of the external housing are electrically asymmetric.

As described above, when the wires and electrode patterns become asymmetric between the balanced input / output 1 and the balanced input / output 2, the electrical characteristics of the SAW device are affected by inductor components and capacitance components generated by the wires and electrode patterns. Input / output 1,
The balanced input / output 2 has different electrical characteristics. As a result, there is a problem that the condition of the balanced SAW device that the amplitude is equal and the phase is opposite is not satisfied, and the filter characteristic is significantly deteriorated.

Accordingly, the present invention has been made in view of the above circumstances,
It is an object of the present invention to provide a high-quality balanced surface acoustic wave device that operates as a balanced type and has good filter characteristics.

[0015]

According to the present invention, there is provided a surface acoustic wave device comprising: an odd number of IDTs on a piezoelectric substrate;
Resonator-type electrode patterns formed by arranging a plurality of electrodes in parallel along the propagation direction of the surface acoustic wave are arranged in a plurality of stages, and the resonator-type electrodes formed on both ends of these resonator-type electrode patterns A surface acoustic wave device in which one of the patterns is a balanced or unbalanced input section and the other is an unbalanced or balanced output section, and a resonator-type electrode pattern in which an unbalanced input section or an unbalanced output section is formed, The IDT electrodes disposed on both sides of the centrally located IDT electrode are formed so as to be in phase with each other, and the resonator-type electrode pattern in which the balanced input portion or the balanced output portion is formed is located at the center. The IDT electrodes provided on both sides of the located IDT electrode are formed so as to have opposite phases to each other.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a SAW device according to the present invention will be described in detail with reference to the drawings.

FIG. 1 shows an example of the electrode configuration of the present invention. The SAW element shown in FIG. 1 is a device in which three IDT electrodes are arranged in parallel in the SAW propagation direction, and a resonator type electrode pattern in which reflectors are arranged so as to sandwich the IDT electrode is connected in two stages. A feature of the present invention is a resonator type SAW connected in two stages.
The element has an electrode structure that can make the shape of the two output terminals symmetrical.

That is, first, the IDs at both ends formed on the electrode pattern on which the unbalanced input / output electrode pattern is formed.
The T electrodes are formed so as to have the same phase. Next, the IDT electrodes at both ends of the electrode pattern on which the balanced input / output electrode pattern is formed are different from the electrode pattern on which the unbalanced input / output electrode pattern is formed. It is formed so that

Regarding the method of connecting the electrodes, first,
The unbalanced input / output electrode terminal is connected to the IDT electrode arranged at the center of the electrode pattern on which the unbalanced input / output electrode pattern is formed. Next, the IDT formed in the center
The two IDT electrodes on both sides of the electrode and the IDT electrode at the center of the electrode pattern on which the balanced input / output electrode pattern is formed are connected by an electrode pattern.

Next, two IDT electrodes on both sides of the electrode pattern on which the balanced input / output electrode pattern is formed are respectively connected to balanced input / output terminals. Thereby, the output I of the electrode pattern on which the balanced input / output electrode pattern is formed is formed.
Since the DT electrode can form an output terminal in the same direction,
It is characterized in that two output electrode terminals can be formed in a symmetrical shape.

If the SAW element having the above structure is used, as shown in FIG. 4, the symmetrical structure can be obtained up to the output terminal of the external housing even if the SAW element is mounted on the external housing and wired by wire bonding. Can be. In addition, as shown in FIG. 6, even when flip-chip mounting is employed, a symmetrical structure can be provided up to the output terminal of the external housing.

If the SAW device has the above structure,
Since the electrode structure from the unbalanced input / output terminal to the balanced input / output terminal 1 and the balanced input / output terminal 2 has a symmetrical shape, the inductor component and the capacitance component included in the electrode structure become equal at each output. As a result, Thus, a filter having excellent balance operation can be manufactured.

As a piezoelectric substrate for a SAW device, 3
6 ° ± 3 ° Y-cut X-propagating lithium tantalate single crystal,
42 ° ± 3 ° Y-cut X-propagating lithium tantalate single crystal, 64 ° ± 3 ° Y-cut X-propagating lithium niobate single crystal, 41 ° ± 3 ° Y-cut X-propagating lithium single crystal, 45
° ± 3 ° X-cut Z-propagating lithium tetraborate single crystal is preferable as a piezoelectric substrate because of its large electromechanical coupling coefficient and small frequency temperature coefficient. The thickness of the piezoelectric substrate is 0.1
If the thickness is less than 0.1 mm, the piezoelectric substrate becomes brittle, and if it exceeds 0.5 mm, the material cost and component dimensions increase, and the piezoelectric substrate cannot be used.

The IDT electrode and the reflector are made of Al or an Al alloy (Al—Cu, Al—Ti) and are formed by a thin film forming method such as a vapor deposition method, a sputtering method, or a CVD method. Electrode thickness is 0.1μm ~ 0.5μ
It is preferable to set it to about m in order to obtain characteristics as a SAW device.

Further, the electrode of the SAW device according to the present invention and the SAW propagation portion on the piezoelectric substrate are provided with Si, SiO 2, Si
N, Al2O3 may be formed as a protective film to prevent conduction by a conductive foreign substance and to improve power resistance.

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.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A more specific embodiment according to the present invention will be described below.

SAW having center frequency in 900 MHz band
An element was manufactured. It was fabricated by forming an electrode pattern having the structure shown in FIG. 1 on a piezoelectric substrate made of a 42 ° Y-cut X-propagating lithium tantalate single crystal.

First, an Al-Cu electrode was formed on the cleaned substrate by a sputtering method. The thickness is about 0.4 μm. Next, a resist is applied to a thickness of about 1 μm,
Baking was performed in two atmospheres. Next, a large number of resist positive patterns of a SAW filter were formed on the substrate by a photolithography method using a reduction projection exposure apparatus using ultraviolet rays. The minimum line width at this time is about 1.0 μm.

Next, RIE (Reactive Io)
n Etching) was performed to form an electrode pattern. Next, CVD (Che
A SiO2 layer was formed to a thickness of about 0.02 μm on the electrode pattern and the piezoelectric substrate by a mechanical vapor deposition (apparatus). Next, a resist was applied in a film thickness of about 1 μm, and baked in an N 2 atmosphere.

Next, Si on the SAW resonator is formed by a photolithography method using a reduction projection exposure apparatus using ultraviolet rays.
A resist pattern was formed so that a protective film of O2 could be formed. Next, RIE (Reactive Ion E)
tching) device to perform dry etching.
A protective film pattern of iO2 was formed.

Next, the SAW elements were individually cut out by dicing. Next, a 3 mm square ceramic package was coated with silicon resin, and the SA cut out individually was cut out.
One W element is bonded in a ceramic package, and N2
Baking was performed in an atmosphere. Next, by arranging a 30 μm diameter Au wire by wire bonding, S
An AW device was manufactured.

Thereafter, the SAW device was connected to a network analyzer, and the frequency characteristics of the insertion loss of each output were measured with a circuit configuration as shown in FIG. FIG. 8 shows a graph in which the frequency characteristics of each output near the pass band are overwritten. The characteristics of each output of the product of the present invention matched very well, and it was confirmed that balanced operation was performed. The difference between the insertion loss of each output was reduced to about 0.5 dB or less.

In this experiment, for comparison, in addition to the product of the present invention, the SAW of the conventional electrode pattern as shown in FIG.
An apparatus was also manufactured, and a similar evaluation of the frequency characteristics of insertion loss was performed. FIG. 9 shows a graph in which the frequency characteristics of each output near the pass band are overwritten. The characteristics of each output of the conventional product showed different characteristics within the pass band, and did not perform balanced operation. The difference between the insertion loss of each output reached about 1.8 dB. The filter characteristics were inferior in quality as compared with the product of the present invention.

From these results, it can be seen that the difference of the insertion loss of each output of the product of the present invention is improved by 1.3 dB as compared with the conventional product, and that the filter characteristic of the product of the present invention is improved as compared with the conventional product. Was confirmed.

[0036]

As described above, in the surface acoustic wave device of the present invention, the resonator type electrode pattern having the unbalanced input portion or the unbalanced output portion is formed on both sides of the IDT electrode located at the center. The disposed IDT electrodes are formed so as to have the same phase, and the resonator-type electrode pattern in which the balanced input portion or the balanced output portion is formed is disposed on both sides of the IDT electrode located at the center. IDT electrodes are formed so as to be mutually inverted and have opposite phases, and in an adjacent resonator-type electrode pattern, an IDT electrode positioned at the center of one resonator-type electrode pattern and the other resonator-type electrode pattern. By connecting the IDT electrode located at a position other than the center of the pattern electrode pattern, it is possible to provide a high-quality balanced surface acoustic wave device having good filter characteristics.

[Brief description of the drawings]

FIG. 1 is a schematic electrode diagram schematically illustrating a two-stage connected SAW element according to the present invention.

FIG. 2 is a schematic electrode diagram schematically illustrating a conventional two-stage connected SAW element.

FIG. 3 is a schematic electrode diagram schematically illustrating a conventional one-stage connection SAW element.

FIG. 4 is a diagram schematically illustrating a surface acoustic wave device according to the present invention, and is a top view and a cross-sectional view of the surface acoustic wave device wired by wire bonding.

FIG. 5 is a top view of a conventional surface acoustic wave device wired by wire bonding.

FIG. 6 is a top view and a cross-sectional view of a flip-chip surface acoustic wave device according to the present invention.

FIG. 7 is a top view of a conventional flip-chip mounted surface acoustic wave device.

FIG. 8 is a graph showing frequency characteristics near a pass band in the surface acoustic wave device of the present invention.

FIG. 9 is a graph showing frequency characteristics near a pass band in a conventional surface acoustic wave device.

FIG. 10 is a measurement circuit diagram of a frequency characteristic of the surface acoustic wave device.

FIG. 11 is a schematic electrode diagram illustrating another embodiment of the surface acoustic wave device according to the present invention.

FIG. 12 is a schematic electrode diagram illustrating another embodiment of the surface acoustic wave device according to the present invention.

[Explanation of symbols]

 1: SAW element 2: SAW device of wire bonding wiring 3: SAW device mounted on flip chip 11: Unbalanced input / output terminal 12: Balanced input / output terminal 13: Balanced input / output terminal 14: Ground terminal 21: External housing Unbalanced input / output terminal 22: balanced input / output terminal 1 of external housing 23: balanced input / output terminal 2 of external housing 24: ground terminal of external housing

Claims (1)

[Claims] 1. A resonator-type electrode pattern comprising a plurality of odd-numbered IDT electrodes arranged in parallel along the propagation direction of a surface acoustic wave on a piezoelectric substrate. A surface acoustic wave device in which one of the resonator-type electrode patterns formed at both ends of the electrode pattern is a balanced or unbalanced input portion and the other is an unbalanced or balanced output portion. The resonator-type electrode pattern on which the balanced output section is formed is such that the IDT electrodes disposed on both sides of the centrally located IDT electrode are formed so as to be in phase with each other, and the balanced input section or the balanced output section is formed. The surface acoustic wave device characterized in that the resonator-type electrode pattern in which the portions are formed is such that the IDT electrodes disposed on both sides of the IDT electrode located at the center have phases opposite to each other.