Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2001-08-17
2003-06-03
Budd, Mark D. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S344000
Reexamination Certificate
active
06573635
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a surface acoustic wave (SAW) device, and, more particularly, to a surface acoustic wave device enabling packaging to be effected in a wafer process.
2. Description of the Related Art
Mobile communication equipment such as cellular phones and cordless telephones is rapidly prevailing with recent progress toward miniaturization and lightness of electronic devices. A high frequency circuit of a radio communication circuit included in such mobile communication equipment uses a multiplicity of electronic devices mounted with filter elements.
For the purpose of realizing the miniaturization and lightness in particular, surface acoustic wave (SAW) elements are employed as the filter elements.
FIG. 1
is a schematic diagram showing in section a conventional surface acoustic wave device having a surface acoustic wave element, and its wiring connection structure for connecting the surface acoustic wave element to external connection terminals.
A package for the surface acoustic wave device is constructed from a multilayer ceramic package
100
and a metal cap
101
. The surface acoustic wave element
104
is adhered by an electroconductive resin
105
to the top of a substrate
103
disposed within the interior of the package, with input and output terminals of the surface acoustic wave element
104
being electrically connected via aluminum wires
106
to a ground terminal. The reverse side of the substrate
103
is formed with an external connection terminal
107
.
FIG. 2
shows the structure of another conventional surface acoustic wave device, in which the surface acoustic wave element
104
is connected by connection bumps
108
to the substrate
103
disposed on the bottom of the package, to provide physical fixation and electrical connection wiring.
Thus, in the structure shown in
FIGS. 1 and 2
, electric wirings (the aluminum wires
106
in FIG.
1
and the connection bumps
108
in
FIG. 2
) are both formed within the interior of the ceramic package
100
.
The cap
101
has a sealing material
109
formed in a region in contact with the ceramic package
100
. This provides a hermetic sealing between the ceramic package
100
and the cap
101
so that airtightness is held within the interior of the package.
Thus, to achieve a miniaturization of the surface acoustic wave device, the structure shown in
FIGS. 1 and 2
can not neglect the space which is used for the aluminum wire connection and the hermetic sealing structure between the package
100
and the cap
101
.
The manufacturing procedure includes making electrode wiring on a piezoelectric substrate wafer by patterning and thereafter cutting and separating the wafer into chip elements to thereby obtain individual surface acoustic wave (SAW) elements
104
.
The cut chip elements are mounted on the package
100
, which is then fitted with the cap
101
for sealing to obtain a surface acoustic wave device. For this reason, the cost of the cap
101
is a factor greatly affecting the price of product of the surface acoustic wave device. On the contrary, another technique is also known where the package is formed in the state of a wafer (Japan Patent Laid-open Pub. No. 2000-261285).
In the technique described in Japan Patent Laid-open Pub. No.2000-261285, electrodes are formed on a piezoelectric substrate wafer by patterning and a cover forming member is formed from a separate and independent substrate wafer. The cover forming member is then laminated to the piezoelectric substrate wafer having the electrodes formed thereon by patterning, to thereby obtain a surface acoustic wave device having a surface acoustic wave element function.
However, such a technique disclosed in the above patent laid-open publication also imposes a limitation on miniaturization of the surface acoustic wave device and needs a separate provision of the cover forming member, which may be disadvantageous in the number of manufacturing steps. This leads to increase the price of the device.
SUMMARY OF THE INVENTION
The present invention was conceived in view of the problems involved in the prior art. It is therefore an object of the present invention to provide a lightweight and chip-sized surface acoustic wave device.
It is another object to provide a surface acoustic wave device capable of being manufactured up to packaging in the state of a piezoelectric substrate wafer by a less number of steps.
In order to achieve the above objects, according to a first aspect of the present invention there is provided a surface acoustic wave device comprising a piezoelectric substrate; a drive electrode unit formed on the piezoelectric substrate, for generating surface acoustic waves; and an electrically conductive electrode protecting unit for covering the drive electrode unit with a hollow therebetween, wherein the electrode protecting unit is formed on the piezoelectric substrate by use of a film forming technique.
In order to achieve the above objects, according to a second aspect of the present invention there is provided a surface acoustic wave device comprising a piezoelectric substrate; an electrode unit formed on the piezoelectric substrate, the electrode unit including a drive electrode unit for generating surface acoustic waves and an external connection electrode unit; an electrically conductive electrode protecting unit for covering the drive electrode unit with a hollow therebetween, the electrode protecting unit being formed on the piezoelectric substrate by use of a film forming technique; an electroconductive column formed on the external connection electrode unit; and an external connection terminal formed at the extremity of the electroconductive column, wherein the piezoelectric substrate is sealed by a resin with the exception of the external connection terminal and the electrode protecting unit.
In order to achieve the above objects, according to a third aspect of the present invention there is provided a method of manufacturing a surface acoustic wave device, comprising the steps of forming a drive electrode having a surface acoustic wave element function on a piezoelectric substrate wafer; resist coating an upper region of the drive electrode; effecting a metal film coating in dome form so as to cover the resist coat; removing the resist lying within the metal dome coated; and providing a resin seal thereon.
REFERENCES:
patent: 4047129 (1977-09-01), Ishiyama
patent: 4699682 (1987-10-01), Takishima
patent: 5831369 (1998-11-01), Furbacher et al.
patent: 5991989 (1999-11-01), Onishi et al.
patent: 6310420 (2001-10-01), Pahl et al.
patent: 2000-261284 (2000-09-01), None
Suga Akira
Ueda Masanori
Arent Fox Kintner & Plotkin & Kahn, PLLC
Budd Mark D.
Fujitsu Media Devices Limited
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