Wave transmission lines and networks – Plural channel systems – Having branched circuits
Reexamination Certificate
2000-10-20
2002-09-24
Pascal, Robert (Department: 2817)
Wave transmission lines and networks
Plural channel systems
Having branched circuits
C333S204000, C333S193000
Reexamination Certificate
active
06456172
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a multilayered ceramic RF (radio frequency) device, and in particular but not exclusively, to a multilayered ceramic RF device used in high-frequency radio equipment such as a cellular telephone.
2. Description of the Related Art
Recently multilayered ceramic RF devices are attracting much attention for their ability to contribute greatly to the size reduction of high-frequency radio equipment such as a cellular telephone.
FIG. 15
is a block diagram showing an example of an RF circuit used in a cellular telephone. A duplexer
22
is formed of a transmitting filter and a receiving-filter. In such an RF circuit as show in
FIG. 15
, a transmitting signal amplified by a power amplifier
21
passes through a low-pass filter
20
and the transmitting filter in the duplexer
22
and is transmitted from an antenna
24
. A band-pass filter may be used instead of the low-pass filter
20
. A signal received by the antenna
24
is input to a low-noise amplifier
28
via the receiving filter in the duplexer
22
and a band-pass filter
26
. The signal is amplified by the low-noise amplifier
28
and, after that, the signal is subjected to a frequency conversion and a signal processing. While the low-pass filter
20
and the duplexer
22
can be constituted from multilayered filters or the like, the band-pass filter
26
is normally constituted from a SAW filter. The power amplifier
21
and the low-noise amplifier
28
are made by using semiconductor elements with excellent radio frequency characteristics.
Now an example of the multilayered ceramic RF device of the prior art will be described below with reference to FIG.
16
and FIG.
17
.
FIG. 16
is a sectional view of a multilayered ceramic RF device
100
of the prior art which constitutes a part of the RF circuit shown in FIG.
15
. In the multilayered ceramic RF device
100
of the prior art, electrode patterns
102
which constitute the RF circuit are formed in a low temperature-cofired multilayered ceramic body
101
. The electrode patterns
102
are electrically connected to each other by means of via holes
103
. Chip components
105
such as chip resistors, chip capacitors, chip inductors and packaged semiconductor elements are formed on the surface of the low temperature-cofired multilayered ceramic body
101
, and are shielded by a metal cap
107
.
The operation of the multilayered ceramic RF device
100
of the prior art constituted as described above will be described below.
The electrode patterns
102
form inner layer capacitors and inner layer inductors in the low temperature-cofired multilayered ceramic body
101
as well as providing electrical connection between the plurality of chip components
105
. These components collectively form the RF circuit and serve as a multilayered ceramic RF device such as, for example, a multilayer RF switch.
FIG. 17
schematically shows an example of the constitution of an RF device
120
of the prior art used in a cellular telephone that has the RF circuit as shown in FIG.
15
. As shown in
FIG. 17
, the RF device
120
of the prior art has been constituted from separate components such as an multilayered filter
110
, a SAW filter
112
covered with a ceramic package
111
, and the mutilayered ceramic RF device
100
formed of a multilayered ceramic body having an RF switching circuit
114
, which are independent from each other. Thus the RF device
120
of the prior art shown in
FIG. 17
has been made by mounting the multilayered filter
110
, the SAW filter
112
covered with a ceramic package
111
, and the multilayered ceramic RF device
100
that are independent from each other on a printed circuit board and connecting the components by soldering or using micro strip lines.
In the constitution of the RF device
120
of the prior art, however, there has been such a problem that the use of soldering lands or running the micro strip lines on the printed circuit board causes unmatched impedance and/or an increase in impedance loss. Also because connection of the components is carried out in the final packaging stage of the production process, even when the components have been certified for satisfactory radio frequency characteristics before connection, there occur variations in the high-frequency characteristics of the components due to unmatched impedance in junctions or the like after the components have been connected in the final packaging stage. As a result, it has been difficult to produce the RF device
120
of the prior art with excellent radio frequency characteristics and excellent reproducibility.
Also in the multilayered ceramic RF device
100
of the prior art shown in
FIG. 16
, since a bare semiconductor chip (i.e., a chip that is not molded) and a SAW filter need to be sealed, these components cannot be used in the device
100
. This is because the metal cap
107
of the prior art is used for the purpose of merely providing an electromagnetic shielding and does not have the sealing function. Therefore, it is necessary to use the semiconductor element and the SAW filter that are individually sealed, which makes it difficult to reduce the device size and leads to a complicated manufacturing process.
SUMMARY OF THE INVENTION
The present invention has been developed to overcome the above-described disadvantages.
It is accordingly an objective of the present invention to provide a multilayered ceramic RF device that has excellent radio frequency characteristics and high reliability.
Another object of the present invention is to provide a multilayered ceramic RF device that has high performance, and is small in size and in profile and easy to produce.
In accomplishing the above and other objectives, a multilayered ceramic RF device of the present invention having at least one radio frequency filter, includes a low temperature-cofired multilayered ceramic body having a plurality of ceramic layers laminated one upon another and fired together, the low temperature-cofired multilayered ceramic body also having a first electrode pattern formed therein and a second electrode pattern formed thereon. The first and second electrode patterns are electrically connected to-one another through a-via hole. A bare semiconductor chip (i.e., a chip that is not molded) is mounted on the low temperature-cofired multilayered ceramic body with a face down bonding, and the bare semiconductor chip is coated with a sealing resin. The least one radio frequency filter is a multilayered filter formed in the low temperature-cofired multilayered ceramic body, and the multilayered filter includes a part of the first and second electrode patterns.
In the multilayered ceramic RF device of the present invention, the electrode patterns formed on the surface and inside of the low temperature-cofired multilayered ceramic body are electrically connected with each other by via holes (holes that penetrate the ceramic layer and are filled with, for example, Ag or Cu), and the radio frequency filter is a multilayered filter formed inside of the multilayered ceramic body while including a part of the electrode patterns. Thus the connection between the multilayered filters, between the multilayered filter and another radio frequency filter or between the multilayered filter and a bare semiconductor chip can be made with very short wiring a distances by using the via holes or the like that are formed inside the multilayered ceramic body. As a result, unmatched impedance and impedance loss can be decreased, ripple in the pass band of the radio frequency filter can be prevented and proper performance of the filter can be realized, compared to the RF device of the prior art having components such as the radio frequency filter and the multilayered filter individually mounted on the printed circuit board. Therefore, the multilayered ceramic RF device that has excellent high-frequency characteristics and high reliability can be provided. Also the device can be made small in size and in profile with a reduced number of co
Ishizaki Toshio
Kagata Hiroshi
Sakakura Makoto
Yamada Toru
Matsushita Electric - Industrial Co., Ltd.
Pascal Robert
Takaoka Dean
Wenderoth , Lind & Ponack, L.L.P.
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