JP3439750B2 - Surface acoustic wave device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave filter device comprising a surface acoustic wave resonator,
The present invention relates to a surface acoustic wave resonator composite filter in which a plurality of surface acoustic wave resonators each having an interdigital electrode finger disposed on a piezoelectric substrate are combined. 2. Description of the Related Art In recent years, mobile phones and mobile phones have become smaller and lighter, and are rapidly spreading. Filters are used in the radio signal processing units of these telephone devices. Recently, the above-mentioned filters using surface acoustic wave elements have been developed and used in order to reduce the size, weight, and performance of devices. 2. Description of the Related Art A so-called transversal type surface acoustic filter is composed of an input interdigital transducer for converting an electric signal into a surface acoustic wave and an output interdigital transducer for converting the surface acoustic wave back into an electric signal again. It is arranged on a substrate. FIG. 9 shows a basic configuration of a surface acoustic wave resonator. In the figure, 1 is a piezoelectric single crystal substrate, 2 is a comb-shaped drive electrode, and interdigitated electrode fingers 2a and 2b made of, for example, A1 are interleaved (interdigital electrode fingers). Numeral 3 is a reflective electrode made of, for example, the same A1, and has a structure in which a number of electrode fingers 3a are arranged, and is shown as a short strip type reflective electrode in the figure. As shown in FIG. 10, a surface acoustic wave resonator has a double resonance characteristic of a resonance frequency fr and an anti-resonance frequency fa. The method of forming a filter using a resonator is as follows. FIG. 10A shows the pass characteristics when one surface acoustic wave resonator is connected in series, and FIG. 10B shows the pass characteristics when one surface acoustic wave resonator is connected in parallel. . From FIG. 10C combining these, it can be seen that a bandpass filter is formed when the resonance frequency fr of the series resonator is substantially equal to the anti-resonance frequency fa of the parallel resonator. To obtain desired filter characteristics, it is necessary to optimize the combination of the resonance characteristics of each series resonator and the parallel arm resonator and the ladder. Heretofore, in a filter in which a surface acoustic wave resonator is formed in a ladder shape, the arrangement on the chip is such that the propagation path of the surface acoustic wave of the resonator is common as shown in Japanese Patent Application Laid-Open No. 1-260911. It was something like that. That is, a configuration of a multi-mode filter in which resonators are arranged on the same propagation path and mutual interference is used has been used. FIG. 11 shows a specific example of a chip arrangement structure in which five resonators R1 to R5 are arranged on a piezoelectric substrate 1 of, for example, about 1.5 mm × 2.25 mm. As can be seen from the equivalent circuit shown at the bottom of the figure, the resonators R2 and R5 are in parallel between the input and output terminals. In other words, a chip arrangement for realizing an equivalent circuit as shown in FIG. 11 is formed, for example, as shown in FIG. [0006] However, the conventional chip arrangement focuses only on how to reduce the chip area, and the signal lines in a case where a plurality of serial arms and parallel arms are arranged in a ladder form. The transmission loss due to routing and the interference of elastic waves between the serial arm and the parallel arm can be said at all,
Interest was not paid. As a result, as shown in FIG. 12, the insertion loss and the in-band ripple of the filter were increased. SUMMARY OF THE INVENTION It is an object of the present invention to obtain a good filter characteristic by suppressing transmission loss due to signal line routing and interference between elastic waves of a serial arm and a parallel arm. [0008] In order to understand the present invention, the arrangement of FIGS. 1 to 3 will be described first. In FIG. 1, the serial arm resonators 11 and 12 are arranged on a linear pattern substantially orthogonal to the elastic wave propagation path.
1 and 12 are connected by a straight connection line (signal line) 13 having no corner portion (bent portion). Further, the parallel arm resonator 21 is connected to the propagation path 5 of the elastic wave of the series arm resonators 11 and 12.
0 (horizontal direction in the figure) and a position avoiding the signal line 13 connecting the serial arm resonators, and the acoustic wave propagation path is arranged so as to intersect with the linear pattern portion of the serial arm resonator. In FIG. 2, when at least one of the input / output units (for example, the output unit) is constituted by the parallel arm resonator 22, the parallel arm resonator 22 provided in at least one of the input / output units and the series arm resonance The resonator 12 is arranged on a straight line, and the series arm / parallel arm resonators 12 and 22 are also connected by a straight connection line (signal line 13 ') having no corner (bent portion). In FIG. 3, the elastic wave propagation path of the parallel arm resonator 21 sandwiched between the series arm resonators 11 and 12 is set between the elastic wave propagation paths of the series arm resonators 11 and 12 sandwiching the parallel arm resonator. Form. On the other hand, according to the present invention, as shown in FIGS. 4 and 7, at least one of the series arm resonators sandwiching the parallel arm resonator is connected to the series arm resonance of the input / output section of the filter circuit. When configured as a resonator, the parallel arm resonator 21 (FIG. 10) is provided so that the elastic wave propagation path is provided outside (the chip end side) of the elastic wave propagation path of the series arm resonator provided in at least one input / output unit. 7, a parallel arm resonator 22) is arranged, and at least a part of the parallel arm resonator is arranged so as to be located on an extension of a linear signal line connecting the series arm resonators. I do. As shown in FIGS. 1, 2 and 3, the series arm resonator has no corner, that is, a connection (signal) having no bent portion.
Since the connection is made by the wire, the capacitance generated at the corner of the high-frequency line can be reduced, and therefore, the transmission loss at the connection line is extremely small. Therefore, the insertion loss of the filter can be reduced. Further, since the parallel arm resonators are arranged so as to avoid the elastic wave propagation path of the series arm resonator, good filter characteristics can be obtained without the elastic waves of the series and parallel arm resonators interfering with each other. Further, by arranging the parallel arm resonator so as to intersect with the pattern portion of the series arm resonator, the size of the element can be reduced. According to the present invention, as shown in FIGS. 4 and 7, the propagation path of the parallel arm resonator 21 (the parallel arm resonator 22 in FIG. 7) is provided outside the pattern connecting the elements. Therefore, the logarithm can be increased and the element area can be reduced. In particular, in FIG. 7, the circuit configuration is the same as that of FIG. 5, but by disposing the propagation path of the parallel arm resonator 22 outside the input side series arm resonator 11 (chip end side), The area can be reduced. FIG. 5 shows an actual on-chip layout of a filter for realizing the equivalent circuit configuration shown in FIG. The filter chip is A1-C on a 36 ° YX LiTaO ₃ substrate 1.
The surface acoustic wave resonators 11, 12A, 12B, 21, and 22 constituted by a comb-shaped electrode and a reflector made of a u film are used as circuit elements, and these are connected in series and parallel in a pattern to form a circuit. By appropriately adjusting the period, logarithm, and aperture length of the resonator, desired characteristics can be obtained. In this embodiment, the series arm resonators 11, 12A,
The period of 12B is 4.10 μm, and the parallel arm resonators 21 and 22 are used.
Is 4.30 μm, and the aperture length and logarithm are 8
0 μm and 150 pairs. FIG. 6 shows the characteristics. When the same circuit configuration is formed by the connection line 13 'having a corner as shown in FIG. 11 under the same conditions, the result becomes as shown by the broken line in FIG. 6, and it can be seen that according to the present invention, the insertion loss is improved by 0.2 dB. Understand. Preferably, as shown in FIG. 5, the position detecting pattern 8 is provided at two corner portions on the diagonal line of the chip or in the vicinity thereof, avoiding the elements and wiring. As a result, when the chip is mounted on the package and wire-bonded, the relative position of the bonding pad position with respect to the position detection pattern 8 is constant even if the position of the chip varies, thereby improving the reliability of automatic bonding. it can. FIG. 5 shows an example in which the position detecting pattern 8 is formed on the same plane as the element simultaneously with the pattern formation. The size of the detection pattern 8 is 100 μm × 150 μ
m, the center of the figure was provided on a diagonal line 200 μm away from the edge of the chip. With respect to this position detection pattern, the input / output and the positional relationship between the ground pads 5 and 6 are constant. In addition, even if chipping or the like occurs during wafer cutting, it is not affected. As described above, by recognizing the position detection pattern 8, the wire at the time of automatic bonding can be accurately connected to the electrode pad portion. The shape of the position detection pattern 8 is not particularly limited as long as it can be recognized by the reading device, and is preferably a circle, a star, or the like in which a difference from the shape of the element can be clearly seen. In FIGS. 1 to 12, corresponding parts are denoted by the same reference numerals, and redundant description is omitted. Further, in the chip pattern diagram, the equivalent lines are shown at the bottom as necessary. As described above, according to the present invention, when a surface acoustic wave resonator is arranged in a ladder form to form a band-pass filter, a reduction in insertion loss and a large out-of-band suppression degree can be achieved. realizable. In addition, the size of the chip can be reduced while maintaining good filter characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a structural diagram showing a basic pattern shape of a surface acoustic wave device. FIG. 2 is a structural diagram showing another pattern shape of FIG. 1; FIG. 3 is a structural view showing still another pattern shape of FIG. 1; FIG. 4 is a structural diagram showing an arrangement of the present invention showing still another pattern shape of FIG. 1; FIG. 5 is a structural diagram showing still another pattern shape of FIG. 1; FIG. 6 is a graph showing the insertion loss characteristics of a surface acoustic wave device. FIG. 7 is a structural diagram showing an arrangement of the present invention showing still another pattern shape of FIG. 5; 8 is an equivalent circuit diagram of the pattern shape shown in FIG. FIG. 9 is an illustrative view showing a basic structure of a surface acoustic wave resonator; FIG. 10 is an explanatory diagram for configuring a filter using a resonator. FIG. 11 is a structural diagram showing an example of an electrode layout of a conventional filter chip. FIG. 12 is a characteristic diagram showing an in-band ripple of a conventional filter. [Description of Signs] 11, 12 ... series arm resonators 21, 22 ... parallel arm resonators 13, 13 '... signal lines

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Osamu Igata 1015 Uedanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture Inside Fujitsu Limited (72) Inventor Tsutomu Miyashita 1015, Kamiodanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture Fujitsu Limited (56) References JP-A-4-95208 (JP, A) JP-A-4-54011 (JP, A) JP-A-61-151430 (JP, U) JP-B-58-1850 (JP, B1) Yuki Yu, Kazuo Okuno, Yoichi Kobayashi, High Bandwidth Stable Surface Acoustic Wave Filter, Electronic Ceramics, January 1, 1977, Vol. 8, Winter No. 46, p. 65-70 Supervised by Tadashi Shiozaki, Manufacture and Application of Piezoelectric Materials, CMC Corporation, February 24, 1984, p. 153-154 (58) Field surveyed (Int. Cl. ⁷ , DB name) H03H 9/64

Claims (1)

(57) [Claim 1] A band-pass filter circuit configured by providing a surface acoustic wave resonator in a series arm and a parallel arm of a ladder type circuit is formed on a chip in a predetermined pattern. When at least one of the series arm resonators sandwiching the parallel arm resonator is configured as at least one series arm resonator of the input / output part of the filter circuit, the series arm resonator Along with being arranged on a linear pattern that is substantially orthogonal to the propagation path,
The parallel arm resonators are connected by a linear signal line, and the parallel arm resonator is disposed outside the propagation path of the series arm resonator provided in the at least one input / output unit. A surface acoustic wave element which is arranged so as to be located on an extension of the linear signal line connecting a series arm resonator.