Semiconductor device manufacturing: process – Making device or circuit responsive to nonelectrical signal – Physical stress responsive
Reexamination Certificate
2000-06-02
2002-11-05
Fahmy, Wael (Department: 2823)
Semiconductor device manufacturing: process
Making device or circuit responsive to nonelectrical signal
Physical stress responsive
C257S419000, C029S025350, C310S366000
Reexamination Certificate
active
06475823
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a piezoelectric device that may be utilized as, for instance, a filter, a resonator or a vibrator, and a method of manufacturing this piezoelectric device.
2. Discussion of the Background
A sealed vibration space must be formed around a first electrode and a second electrode in this type of piezoelectric device. The degree of airtightness in such a vibration space and its volumetric capacity directly affect the characteristics of the piezoelectric device. Thus, when forming a vibration space, it is crucial to ensure that the vibration space achieves a high degree of airtightness, that it is supported by a film structure that does not cause any reduction in the degree of airtightness and that it maintains a constant spatial volume. In addition, it is also essential to ensure that no residue from the manufacturing process remains, in order to prevent the occurrence of characteristics defects.
The publications in the known art disclosing technologies for vibration space formation include Japanese Unexamined Patent Publication No. 41309/1989 and Japanese Unexamined Patent Publication No. 167381/1993. Japanese Unexamined Patent Publication No. 41309/1989 discloses that after applying a resist resin to a vibration portion of a piezoelectric element, a cover resin (a hollow layer) is applied onto a surface of the piezoelectric element while securing an opening communicating with a portion of an end edge of the resist resin. Next, after the cover resin is dried, the resist resin is dissolved by using an organic solvent or the like and is further discharged to the outside through the opening in the cover resin. In addition, the cavity formed by removing the resist resin is washed by means such as ultrasonic cleaning. Then, the opening is sealed to form a sealed vibration space.
Japanese Unexamined Patent Publication No. 167381/1993 discloses that after applying a resist resin to a vibration portion of a piezoelectric element, a resin layer (hollow layer) having an opening ranging over an area smaller than the planar area of the resist resin layer is formed on the resist resin. Then, after the resin layer (hollow layer) is dried, the resist resin is dissolved and discharged to the outside through the opening in the cover resin. By sealing the opening with a sealing layer, a sealed vibration space is formed. The sealing layer includes a first sealing layer and a second sealing layer. The first sealing layer has an indented portion to enclose the cavity area and is pasted onto the hollow layer. The second sealing layer is pasted onto the first sealing layer to seal the indented portion of the first sealing layer and the opening continuous with the cavity.
However, the prior art technologies described above do not readily satisfy the requirement of the vibration space discussed earlier. For instance, in the invention disclosed in Japanese Unexamined Patent Publication 41309/1989, the opening provided to facilitate the removal of the resist resin and to wash out the resist resin is located at the end edge of the hollow layer and residue of the resist resin tends to remain inside the cavity. In addition, since the thickness of the hollow layer around the opening is extremely small, cracks and the like occurring in this area may reduce the degree of airtightness.
In the invention disclosed in Japanese Unexamined Patent Publication No. 16738 1/1993, the airtightness cannot be sustained if a misalignment which occurs between the opening continuous with the cavity and the indented portion of the first sealing layer or between the cavity and the indented portion at the first sealing layer.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a piezoelectric device having a vibration space that achieves a high degree of airtightness, and a manufacturing method thereof.
It is a further object of the present invention to provide a piezoelectric device having a vibration space of which the airtightness is not readily reduced, and a manufacturing method thereof.
It is a still further object of the present invention to provide a piezoelectric device having a vibration space that maintains a constant spatial volume, and a manufacturing method thereof.
It is a still further object of the present invention to provide a piezoelectric device achieving a structure that does not readily allow residue from the manufacturing process to remain in the vibration space, and a manufacturing method thereof.
In order to achieve the objects described above, the present invention discloses a piezoelectric device realized in two modes.
Piezoelectric Device in First Mode
The piezoelectric device in the first mode comprises a piezoelectric element, a first film structure and a second film structure. The piezoelectric element includes a piezoelectric substrate, at least one first electrode and at least one second electrode. The first electrode is provided at a first surface of the piezoelectric substrate, whereas the second electrode is provided at a second surface of the piezoelectric substrate which faces opposite the first electrode.
The first film structure includes a first hollow layer and a first sealing layer. The first hollow layer has a first surface, an opposing second surface and at least one first cavity. The first cavity has a uniform width and extends between the first and second surfaces of the first hollow layer around a vibration portion of the piezoelectric element where the first electrode is provided. The first surface of the first hollow layer is disposed on the first surface of the piezoelectric substrate, and the first sealing layer is disposed on the second surface of the first hollow layer to seal the first cavity.
The second film structure includes a second hollow layer and a second sealing layer. The second hollow layer has a first surface, an opposing second surface and at least one second cavity. The second cavity has a uniform width and extends between the first and second surfaces of the second hollow layer around a vibration portion of the piezoelectric element where the second electrode is provided. The first surface of the second hollow layer is disposed on the second surface of the piezoelectric substrate, and the second sealing layer is disposed on the second surface of the second hollow layer to seal the second cavity.
As described above, in the piezoelectric device according to the present invention, the first electrode is provided at the first surface of the piezoelectric substrate. The second electrode, located at the second surface of the piezoelectric substrate, faces opposite the first electrode. The first and second electrodes constitute a vibration portion. As a result, piezoelectric vibration characteristics determined by the first and second electrodes are achieved.
The first hollow layer forms the first cavity around the vibration portion where the first electrode is provided. The first sealing layer is disposed on the first hollow layer to seal the first cavity. The second hollow layer forms the second cavity around the vibration portion where the second electrode is provided. The second sealing layer is disposed on the second hollow layer to seal the second cavity. Consequently, piezoelectric vibration occurs in the first and second cavities sealed by the first and second film structures respectively.
Since the first cavity has a uniform width and extends between the first and second surfaces of the first hollow layer, the resist resin, which is utilized under normal circumstances to form the first cavity, can be completely removed. Thus, characteristics defects caused by the presence of residual resist resin can be prevented.
The first sealing layer is disposed on the second surface of the first hollow layer to seal the first cavity. Since such a first sealing layer only needs to be disposed on the plane of the first hollow layer, the alignment of the first sealing layer relative to the first hollow layer, which is essential in the prior art, does not need to be p
Katoh Ikuo
Kiriyama Takahito
Sakano Shigeru
Suzuki Akira
Tajima Seiichi
Fahmy Wael
TDK Corporation
Toledo Fernando
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