Wave transmission lines and networks – Plural channel systems – Having branched circuits
Reexamination Certificate
2002-10-01
2004-08-17
Summons, Barbara (Department: 2817)
Wave transmission lines and networks
Plural channel systems
Having branched circuits
C333S189000, C333S191000, C228S110100, C029S025350
Reexamination Certificate
active
06778038
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a piezoelectric resonant filter including a thin-film piezoelectric resonator, a duplexer including the resonant filter, and manufacturing methods thereof.
2. Description of the Related Art
Mobile communications devices such as mobile phones, which have dramatically become widespread in recent years, have been miniaturized and have attained higher usable frequencies year by year. In response to this, it is desired that electronic components for use with such mobile communications devices also be miniaturized and made usable at higher frequencies.
Some mobile communications devices include a duplexer for switching between a transmission signal path and a reception signal path in order to share a single antenna for both transmitting and receiving signals. The duplexer has a filter for allowing a transmission signal to pass therethrough and interrupting a reception signal, and a filter for allowing the reception signal to pass therethrough and interrupting the transmission signal.
In recent years, some of the aforementioned duplexers incorporate a surface acoustic wave filter. The surface acoustic wave filters have features that they are usable at frequencies up to about several gigahertz and can be made more compact than ceramic filters. However, usable frequencies of mobile communications devices can become even higher in the future, while under the present situation there remain many technical problems for the surface acoustic wave filters to become usable at such high frequencies.
In this regard, attention has been focused lately on a thin-film piezoelectric resonator, which is also called a thin-film bulk acoustic resonator (hereinafter also referred to as FBAR). The thin-film piezoelectric resonator utilizes resonance of a piezoelectric thin film in a direction of its thickness. Changing the thickness of the piezoelectric thin film can change the resonant frequency of the thin-film piezoelectric resonator. The thin-film piezoelectric resonator is expected to be capable of responding to frequencies up to several gigahertz.
Such a thin-film piezoelectric resonator is described, for example, in the following documents:
Published Unexamined Japanese Patent Application (KOKAI) No. 2000-278078;
U.S. Pat. No. 5,872,493;
U.S. Pat. No. 4,642,508;
U.S. patent application Publication No. 2002/0070262 A1; and
a paper entitled “Thin Film Resonators and Filters”, Kiyoshi Nakamura et al., presented at International Symposium on Acoustic Wave Devices for Future Mobile Communication Systems, Mar. 5-7, 2001, pp. 93-99.
A thin-film piezoelectric resonator comprises a piezoelectric thin film, two electrodes disposed on both surfaces of the piezoelectric thin film, and a base body for supporting the piezoelectric thin film and the electrodes. The base body may have a cavity which forms an opening on a side opposite to the side on which the piezoelectric thin film and the two electrodes are disposed (see Published Unexamined Japanese Patent Application (KOKAI) No. 2000-278078 and U.S. Pat. No. 5,872,493). Otherwise, a gap may be formed between one of the electrodes and the base body (see U.S. Pat. No. 4,642,508). Otherwise, the piezoelectric thin film and the two electrodes may be disposed on an acoustic multi-layered film on the base body, without cavity or gap (see Kiyoshi Nakamura et al.).
Filters employing a resonator include a ladder filter. A ladder filter includes a series resonator and a parallel resonator, as a basic configuration. As necessary, a plurality of the basic configurations are connected in a cascaded manner to make up a ladder filter.
Now, for example, suppose that a filter including a plurality of resonators such as the aforementioned ladder filter is packaged. In this case, a chip including filter components is formed and then the chip is mounted onto a mounting substrate to thereby fabricate a packaged filter.
Conventionally, to package a filter including a plurality of resonators, a wire bonding method has been widely employed for establishing electrical connection between the chip and the mounting substrate (see U.S. Pat. No. 5,872,493).
Now, a method for establishing electrical connection between the chip and the mounting substrate by wire bonding will be briefly described. In this method, the chip including the base body and elements mounted thereon is placed on the mounting substrate such that the surface of the base body having the elements mounted thereon faces upward, and then bonded onto the mounting substrate using an adhesive or the like. The chip is provided with connection electrodes, and the mounting substrate is provided with connection pads. The connection electrodes and the connection pads are connected to each other with thin metal wires. For example, the thin metal wires are 20 to 30 &mgr;m in diameter. The thin metal wires are made of a material such as gold or aluminum. Connection between the thin metal wires and the connection electrodes, or connection between the thin metal wires and the connection pads is established by thermo-compression bonding, ultrasonic bonding, or a combination thereof.
When the electrical connection between the chip and the mounting substrate is established by wire bonding, the thin metal wires cause an extra parasitic inductance between the chip and the mounting substrate. The extra parasitic inductance caused by the aforementioned thin metal wires may result in a shift of the electrical properties of the filter from desired ones, even when the chip has been fabricated so as to obtain the desired electrical properties of the filter. The electrical properties of the filter include frequencies for determining the passband of the filter, center frequency of the passband, insertion loss, and the amount of attenuation in an attenuation band.
For conventional filters used in a frequency band of 1 GHz or less, for example, a shift of the electrical properties of the filters caused by the aforementioned extra parasitic inductance is slight and has been neglected.
However, for filters used in a high frequency band of several GHz to the order of 10 GHz such as piezoelectric resonant filters employing a thin-film piezoelectric resonator, a shift of the electrical properties of the filters caused by the aforementioned extra parasitic inductance is non-negligibly great.
To avoid such a problem as mentioned above, as a method for establishing electrical connection between the chip and the mounting substrate, it is proposed that a solder bumps provided on the chip are directly connected to the connection pads of the mounting substrate by flip chip bonding (see U.S. patent application Publication No. 2002/0070262 A1).
Now, briefly described is an example of a method for establishing electrical connection between the chip and the mounting substrate by the aforementioned flip chip bonding. In this method, first, fine solder bumps having a diameter of several tens to 100 &mgr;m or so are formed on the connection pads provided on the chip by using a high-melting solder. On the other hand, the connection pads provided on the mounting substrate are pre-coated with solder by using a procedure such as plating, thick-film printing of solder paste, and vapor deposition. The solder bumps are then soaked in flux. The chip is then positioned and mounted on the mounting substrate such that the solder bumps of the chip face the connection pads of the mounting substrate. Then, with this state remained unchanged, the solder with which the connection pads of the mounting substrate has been pre-coated is melted by using a reflow furnace or the like. After that, the solder is solidified so that the solder bumps of the chip and the connection pads of the mounting substrate are electrically and mechanically bonded to each other. Then, the flux is cleaned off as required. Then, to improve reliability of the connection between the solder bumps of the chip and the connection pads of the mounting substrate, an underfill resin may be filled in between the chip and the mounting substrate
Gunji Katsuhiko
Komuro Eiju
Takeishi Taku
Oliff & Berridg,e PLC
Summons Barbara
TDK Corporation
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