Wave transmission lines and networks – Plural channel systems – Having branched circuits
Reexamination Certificate
2001-06-05
2003-04-15
Ham, Seungsook (Department: 2817)
Wave transmission lines and networks
Plural channel systems
Having branched circuits
C333S202000, C333S206000, C333S219000, C333S219100, C501S134000, C501S136000
Reexamination Certificate
active
06549094
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a high frequency ceramic compact for use in the microwave region, millimeter wave region, and other high frequency regions, and to a method of producing the same. Additionally, the present invention relates to a dielectric antenna, support for dielectric resonator, dielectric resonator, dielectric filer, dielectric duplexer and communication system, which are mounted on, for example, mobile phones, personal radios, satellite receivers, local area wireless networks and millimeter wave radars.
2. Description of the Related Art
Ceramic compacts are conventionally widely used in, for example, dielectric resonators and circuit boards for use in the microwave region, millimeter wave region and other high frequency regions.
Such high frequency ceramic compacts must have (1) a low dielectric loss, that is, a high Q-value, and (2) a thermally stable resonant frequency, that is, a temperature coefficient of resonant frequency (&tgr;
f
) that can be optionally controlled in the vicinity of 0 ppm/° C.
In order to miniaturize the resulting device, a high relative dielectric constant (∈
r
) of the ceramic is preferable since the wavelength of an electromagnetic wave in the dielectric is shortened to 1/(∈
r
)
1/2
. However, demands have also been made to provide a material having a low relative dielectric constant, as the dielectric device becomes excessively small in size to deteriorate workability when the device is used at high frequencies.
This type of conventional high frequency ceramic compacts includes, for example, a Ba(Sn,Mg,Ta)0
3
based ceramic as described in Japanese Examined Patent Application Publication No. 3-34164, and a MgO—SiO
2
—Al
2
O
3
based ceramic as described in Japanese Examined Patent Application Publication No. 6-103603 and Japanese Unexamined Patent Application Publication No. 8-69715.
The Ba(Sn,Mg,Ta)0
3
based ceramic compact can control the temperature coefficient of resonant frequency (&tgr;
f
) in the vicinity of 0 ppm/° C. and has a high Q-value at 10 GHz from 20,000 to 30,000. However, the ceramic compact has a high relative dielectric constant (∈
r
) of 24 and the resulting device is excessively small in size to thereby deteriorate workability when it is used in a microwave region or millimeter wave region.
In contrast, the MgO—SiO
2
—Al
2
O
3
based ceramic compacts and alumina ceramics have a low relative dielectric constant (∈
r
) from 7 to 10 and a high Q-value at 10 GHz from 6,000 to 29,000. These ceramics, however, have a high absolute value of the temperature coefficient of resonant frequency (&tgr;
f
) from −30 to −50 ppm/° C. and are limited in application as dielectric materials for use in a microwave region or millimeter wave region.
A possible solution to control the temperature coefficient of resonant frequency (&tgr;
f
) of the alumina ceramic compacts is a combination use with TiO
2
which has a positive temperature coefficient of resonant frequency (&tgr;
f
). This type of raw material, however, must be sintered by firing at temperatures not lower than 1350° C., and firing at such high temperatures invites the formation of an Al
2
TiO
5
crystal phase to thereby deteriorate the Q-value and other characteristics.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to solve the above problems and to provide a high frequency ceramic compact that is excellent in high frequency characteristics and temperature characteristics, has a relative dielectric constant (∈
r
) of about 20 or less and a Q-value at 10 GHz of about 10,000 or more and can optionally control the temperature coefficient of resonant frequency (&tgr;
f
) around 0 ppm/° C., and to provide a method of producing the high frequency ceramic.
Another object of the present invention is to provide, using the aforementioned ceramic compact, a dielectric antenna, support for dielectric resonator, dielectric resonator, dielectric filter or dielectric duplexer, each of which is excellent in electric characteristics, and a high-performance communication system of small size.
Specifically, the present invention provides, in an aspect, a high frequency ceramic compact which includes Al, Ti and Mn as metallic elements and contains substantially no Al
2
TiO
5
crystal phase.
The high frequency ceramic compact is preferably obtained by firing at a temperature not exceeding about 1310° C.
In another aspect, the present invention provides a high frequency ceramic compact which has a Q-value at 10 GHz of 10000 or more and includes Al, Ti and Mn as metallic elements, is represented by the following formula: (100−x−y)AlO
3/2
−xTiO
2
−yMnO, wherein x and y are % by mole and x and y satisfy the following conditions: 3.0≦x≦9.0; and 0.1≦y≦1.0.
Specifically, x and y in the compositional formula preferably further satisfy the following conditions: 3.0≦x≦7.0 and 0.1<y≦0.25. Preferably, substantially no Al
2
TiO
5
crystal phase is contained in the high frequency ceramic.
The compositional formula is the compositional formula of the high frequency ceramic compact after sintering. As raw materials for the high frequency ceramic compact, an alumina powder having a specific surface area of about 4 m
2
/g or more and a titanium dioxide powder having a specific surface area of about 3 m
2
/g or more are preferably used as the raw material of AlO
3/2
component and the raw material of TiO
2
component, respectively. An alumina powder having a specific surface area from about 4 m
2
/g to 5 m
2
/g is particularly preferably used as the raw material of AlO
3/2
component.
The present invention provides, in a further aspect, a method of producing a high frequency ceramic compact represented by the following formula: (100−x−y)AlO
3/2
−xTiO
2
−yMnO, wherein x and y are % by mole and x and y satisfy the following conditions: 3.0≦x≦9.0; and 0.1≦y≦1.0, which method includes the steps of:
mixing a raw material containing Al, a raw material containing Ti and a raw material containing Mn;
molding the resulting mixture to yield a green compact; and
firing the green compact at a temperature not exceeding about 1310° C.
Preferably, an alumina powder having a specific surface area of about 4 m
2
/g or more is used as the raw material containing Al, and a titanium dioxide powder having a specific surface area of about 3 m
2
/g is used as the raw material containing Ti in the above method. The alumina powder preferably has a specific surface area from about 4 to 5 m
2
/g. Additionally, the firing temperature is preferably about 1300° C. or lower.
REFERENCES:
patent: 4721692 (1988-01-01), Nishioka et al.
patent: 5175132 (1992-12-01), Ketcham et al.
patent: 5340783 (1994-08-01), Anderson et al.
patent: 6242376 (2001-06-01), Jacquin et al.
patent: 6245702 (2001-06-01), Tatekawa et al.
patent: 61168562 (1986-07-01), None
patent: 62278704 (1987-12-01), None
patent: 9-052760 (1997-02-01), None
patent: 09052761 (1997-02-01), None
patent: 9-052762 (1997-02-01), None
patent: 9-221355 (1997-08-01), None
I.B. Cutler, C. Bradshaw, C.J. Christensen, E.P. Hyatt, “Sintering of Alumina at Temperatures of 1400°C. and Below,” Journal of the American Ceramic Society, Apr. 1957, pp. 134-139, vol. 40, No. 4.
M.C. Moreira & M. Segadaes, “Phase Equilibrium Relationships in the System A12O3—TiO2—MnO, Relevant to the Low-Temperature Sintering of Alumina,” Journal of the European Ceramic Society, 1996, pp. 1089-1098, vol. 16, No. 10, Elsevier Science Limited, Great Britain.
Kono Mizuki
Takagi Hitoshi
Tatekawa Tsutomu
Dickstein Shapiro Morin & Oshinsky LLP.
Ham Seungsook
Murata Manufacturing Co. Ltd
LandOfFree
High frequency ceramic compact, use thereof, and method of... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with High frequency ceramic compact, use thereof, and method of..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and High frequency ceramic compact, use thereof, and method of... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3078746