Piezoelectric vibrator and manufacturing method thereof

Abstract: In the piezoelectric vibrator, a plate includes a thin quartz plate portion for generating vibrations, and non-contact electrodes for applying an alternating electric field are arranged above the thin quartz plate portion at both sides thereof so as not to contact with the thin quartz plate portion. The electrodes may be formed on a supporter which can be bonded directly with the thin quartz plate. The electrodes may also be formed above the thin quartz plate and supported by the plate outside the thin quartz plate portion. The piezoelectric vibrator has a superior Q of resonance at high frequencies.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a piezoelectric vibrator having good high frequency characteristics and a manufacturing method thereof. Description of the Prior Art Recently, communication devices are made more compact and operate at higher frequencies according to the development of mobile communication technology. These devices need vibrators and high frequency filters, and piezoelectric vibrators can be used for such vibrators and high frequency filters. A prior art piezoelectric vibrator such as a quartz vibrator is prepared by forming a quartz plate of a prescribed shape and by forming electrodes on the top and bottom planes thereof. Vibrations are generated in the piezoelectric vibrator by applying an alternating electric voltage between the electrodes. A quartz vibrator having good characteristics at high frequencies is needed for mobile communication devices. Among high frequency characteristics, vibration frequency and Q of resonance (which is in correspondence to an inverse of loss) are important. The vibration frequency of quartz vibrator is inversely proportional to the thickness of quartz plate if thickness-shear vibration of quartz is used. Usually, a quartz vibrator which can be produced easily usually has vibration frequency of 50 MHz or less in the fundamental mode and has 30 µ m or more of thickness of quartz plate. In order to increase the vibration frequency, it is needed to make the thickness of quartz plate thinner. For example, the vibration frequency of 167 MHz can be available for a thickness of 10 µ m, and the vibration frequency of 330 MHz can be available for a thickness of 5 µ m. For example, E. A. Gerber et al. produces quartz vibrators for frequencies of hundreds MHz to more than 1 GHz by using polishing, etching, ion trimming or the like ("Advances in Microwave Acoustic Frequency Sources", IEEE Transactions on Microwave Theory and Techniques, Vol. MTT-34, No. 10, October 1986, 1004). However, the Q of resonance decreases with increasing frequency. This is ascribed partly to the increase in electrode loss due to the skin effect at the electrodes. This is also ascribed to the weight of the electrode itself which contributes the loss more with decreasing thickness. Then, there is an upper limit on the thickness of the electrode though the increase in thickness decreases the resistance of the electrode. Therefore, if quartz is formed to be thin with polishing or the like, the vibration frequency increases whereas the Q of resonance decreases, or a piezoelectric vibrator of good high frequency characteristics cannot be produced. On the other hand, a quartz vibrator with a non-contact electrode is also known. For example, a quartz vibrator disclosed in Japanese Patent laid open Publication 2-121512/1990 intends to decrease temperature hysteresis. A quartz plate having a concave section is interposed and fixed between top and bottom plates on which an electrode is formed. Gaps are provided between the quartz plate and the electrodes. A specified metal (SUS 630) is used for metallic plates for holding the quartz plate, and the quartz plate is fixed with the metallic plates or holders with screws at a fixing angle of the quartz plate determined so that the thermal expansion coefficient of the metallic plates agrees with that of the quartz plate at the fixing angle. The thermal hysteresis decreases because the thermal expansion coefficient of the metallic plates is chosen to agree with that of the quartz plate. In the structure of the quartz vibrator, the effect of the mass of the electrodes on the vibration can be vanished so that Q at high frequencies can be improved. However, because screws are used, it is difficult to provide a constant gap of micrometer order reproducibly. If the gap cannot be adjusted at a high precision for a quartz plate of thickness of 10 µ m or less, the stability of Q on production and on the characteristics under operation are not sufficient. Further, because screws are used, it is difficult to seal the vibration element in a compact size. The thermal expansion coefficient cannot be agreed only at a certain direction, and it is difficult to realize stability in a wide temperature range. The characteristics are liable to change due to drop or mechanical vibrations. It is also known to use an adhesive instead of screws to provide gaps and to fix the holders. However, an adhesive is an organic material and has low heat-resisting property, and the characteristics may change for soldering at 220 °C or more and the temperature characteristics on use or on transport are not stable. Further, if the sealing is performed, gas may be generated from the adhesive and this may change the characteristics. A similar quartz vibrator is also disclosed in Japanese Patent laid open Publication 5-22071/1993, wherein a quartz plate and a pair of plates each having a non-contact electrode are fixed mechanically with screws. Further, an elastic surface wave element disclosed in Japanese Patent laid open Publication 3-6912/1991 has a non-contact type electrode with a gap between the piezoelectric plate and the electrode. This element also uses the non-contact type electrodes like the present invention. However, the structure of the electrode is different from that of the present invention because an elastic surface wave is generated. Further, a bridge or supporter of the electrode is formed by using deposition on the piezoelectric plate, while the supporter of the electrode is bonded directly with the piezoelectric plate in the present invention. SUMMARY OF THE INVENTION An object of the present invention is to provide a quartz vibrator having a good Q at high frequencies. A second object of the present invention is to provide a quartz vibrator which can be sealed in a compact size. A third object of the present invention is to provide a quartz vibrator having good temperature characteristics. A fourth object of the present invention is to provide a quartz vibrator stable against mechanical vibrations. A fifth object of the present invention is to provide a quartz vibrator which can be produced in a large amount. In an aspect of the invention, a piezoelectric vibrator comprises a plate and a pair of electrodes. The plate comprises a thin plate portion made of quartz and a thick plate portion around the thin plate portion. The electrodes are arranged at the opposite side of the plate, and they are arranged above the thin plate portion and supported by the thick plate portion, and the thin plate portion is located near the electrodes without contact with the thin plate portion when the thin plate portion vibrates. In a manufacturing method of a quartz vibrator, a plate including a thin plate portion made of quartz is provided. A material different from quartz is coated on the thin plate portion, and a metallic electrode is formed on the material. Then, the material is removed to form a gap between the metallic electrode and the thin plate portion. Such an electrode is formed above both sides of the thin plate portion. Then, the non-contact electrodes are arranged near the thin film portion for piezoelectric vibrations. An advantage of the present invention is that a piezoelectric vibrator has good Q of resonance at high frequencies. Another advantage of the present invention is that a piezoelectric vibrator has good temperature characteristics. A third advantage of the present invention is that a compact piezoelectric vibrator can be provided. A fourth advantage of the present invention is that the mechanical stability of a piezoelectric vibrator can be improved. A fifth advantage of the present invention is that the productivity of a piezoelectric vibrator can be improved. BRIEF DESCRIPTION OF THE DRAWINGS These and other objects and features of the present invention will become clear from the following description taken in conjunction with the preferred embodiments thereof with reference to the accompanying drawings, and in which: Figures 1 to 5 were deleted in the course of examination. Fig. 6(a) is a schematic sectional view of a first example of a piezoelectric vibrator of the present invention, and Fig. 6(b) is a plan view of the piezoelectric vibrator; Fig. 7 is a diagram of a manufacturing method of the piezoelectric vibrator shown in Figs. 6(a) and (b) ; Fig. 8 is a schematic sectional view of a second example of a piezoelectric vibrator of the present invention; Fig. 9 is a diagram of a manufacturing method of the piezoelectric vibrator shown in Fig. 8; Fig. 10 is a schematic sectional view of a third example of a piezoelectric vibrator of the present invention; Fig. 11 is a schematic sectional view of a fourth example of a piezoelectric vibrator of the present invention; Fig. 12 is a schematic sectional view of a fifth example of a piezoelectric vibrator of the present invention; and Fig. 13 is a schematic sectional view of a sixth example of a piezoelectric vibrator of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings, wherein like reference characters designate like or corresponding parts throughout the views, examples of structures and manufacturing methods of piezoelectric vibrators of the present invention will be explained below. Embodiment 1 Different types of non-contact electrodes are used for piezoelectric vibrators of the examples explained below. Figs. 6(a) and (b) show a first example of a structure of a piezoelectric vibrator of Embodiment 1. Fig. 6(a) shows a section of the structure of a piezoelectric vibrator, wherein reference numeral 31 denotes a quartz plate comprising a thin plate portion 32 provided at the center of the quartz plate 31. The quartz plate 31 comprises the thin plate portion 32, a thick portion at the periphery and a shoulder portion 32' between the thin plate portion 32 and the thick portion at the periphery. Non-contact electrodes 33, 33' are formed above the recess 32 at both sides thereof and are supported by the shoulder portion 32', and gaps 34, 34' are provided between the thin plate portion 32 and the non-contact electrode 33, 33'. As shown in Fig. 6(b), the quartz plate 31 comprises further a concave portion 32' for forming an exposed portion necessary to etch and remove a material for forming a gap 34, 34', as will be explained later. The non-contact electrodes 33, 33' are opposed to each other at to the vibration portion 32, while the connection portions 35, 35' are provided at different directions from the center to the periphery. The electrodes 33, 33' do not contact with the thin plate portion 32 of the quartz plate directly due to the gaps 34, 34' when the thin plate portion 32 vibrates, and the distance between the electrodes 33, 33' is smaller than the thickness of the thick portion of the quartz plate 31. Therefore, a strong electric field is applied to the thin plate portion 32 when an electric field is applied between the top and bottom electrodes 33, 33'. By using this structure, a quartz vibrator of very good Q of resonance at high frequencies can be produced. For example, if the thick portion of the quartz plate 31 has 40 µ m of thickness, the thin plate portion 32 has about 1.7 µ m thickness, the electrodes 33, 33' have 0.5 µ m of thickness and the gap 34, 34' have about 1 µ m of thickness, about 1 Ghz of resonance frequency and Q of about 950 are realized. On the contrary, if the gaps 34, 34' are not provided, Q decreases to about 200. Thus, the loss at high frequencies can be improved to a large extent. Next, an example of a manufacturing method of the piezoelectric vibrator shown in Figs. 6(a) and (b) is explained below with reference to Fig. 7. First, a quartz plate of 40 µm thickness is provided and the two surfaces of the quartz plate is covered with a mask made of a metallic thin film of chromium-gold or the like except a portion to be used as a thin plate portion 32 used for vibration (step S11). Then, by using the mask, a thin plate portion 32 is formed in the quartz plate with an etchant of hydrofluoric acid (step S12). By controlling the temperature and the time, the thickness of the thin plate portion 32 can be reduced to for example 2 µ m. A shoulder portion 32' is also fabricated. Then, the mask for etching is removed (step S13). Next, a photosensitive polyimide layer is coated on the entire surface with spin coating, and a polyimide layer is formed on the thin plate portion 32 with photolithography technique to cover the thin plate portion 32 (step S21). Next, a chromium-gold layer is deposited on the entire surface with vacuum deposition (step S22), and prescribed patterns of electrodes 33, 33' above the thin plate portion 32 and on the shoulder portion 32' and the thick portion at the periphery are formed with conventional photolithography and etching techniques (step S23). In this process, a part of the polyimide film has been remained to be exposed, and the polyimide film on the thin plate portion 32 is removed with a solvent of polyimide through the concave portion 32' (step S24). Thus, the electrode 33 and the thin plate portion 32 of quartz do not contact directly, and the electrode 33 is held by the shoulder portion 32'. This process is repeated for the electrode 33' (steps S31 - S34), to produce a quartz vibrator shown in Figs. 6(a) and (b). The gaps 34, 34' between the thin plate portion 32 and the non-contact electrodes 33, 33' can be controlled between 0.1 and 5 µ m freely. The thickness of the electrodes 33, 33' is set for example to be 0.5 µ m. Another example of a manufacturing method of the piezoelectric vibrator shown in Figs. 6(a) and (b) is explained below. The manufacturing method is the same as that explained above until a thin plate portion 32 of 2 µ m thickness is formed. Then, aluminum is deposited on the entire surface of the quartz plate 31 with vacuum deposition process, and an aluminum film is formed on the thin plate portion 32 so as to cover the thin plate portion 32 with use of conventional photolithography and etching techniques. The etchant used is hydrochloric acid or the like. Next, chromium-gold is deposited on the entire surface with vacuum deposition, and prescribed patterns of electrodes 33, 33' above the thin plate portion 32 and on the shoulders and the thick portion at the periphery are formed with conventional photolithography and etching techniques. In this process, a part of the aluminum film is remained to be exposed, and the aluminum film on the thin plate portion 32 is removed with a solvent such as hydrochloric acid which dissolves aluminum but does not dissolve chromium-gold and quartz. Thus, the non-contact electrode 33, 33' and the quartz 32 do not contact directly with each other in the thin plate portion 32, and the electrode 33, 33' is held by the shoulder portion 32' of the quartz plate 31. This process is repeated on the two surfaces to produce a quartz vibrator shown in Figs. 6(a) and (b). The gaps 34, 34' between the thin plate portion 32 and the non-contact electrodes 33, 33' can be controlled between 0.1 and 5 µ m freely. The thickness of the chromium-gold electrodes 33, 33' can be set between 0.1 and 5 µ m, for example at 0.5 µ m. Embodiment 2 Fig. 8 shows a second example of a structure of a piezoelectric vibrator, wherein reference numeral 41 denotes a thin quartz plate used to generate vibrations, reference numerals 43, 43' denote non-contact electrodes, and reference numeral 45 denotes a supporter, made of quartz, silicon or glass for supporting the electrodes 43, 43'. The supporter 45 having an opening at the center is bonded directly to the quartz plate 41. The electrode 43 is formed above the entire quartz plate 41, while the other electrode 43' is formed above the quartz plate 41 at the other side from the electrode 43 in the above-mentioned opening of the supporter 45. Thus, the electrodes 43, 43' are opposed to each other at to the quartz plate 41. Reference numerals 44, 44' denote gaps between the quartz plate 41 and the electrode 43, 43', and the electrodes 43, 43' do not contact with the quartz 41 directly due to the gaps 44, 44' when the quartz plate 41 vibrates. Therefore, a strong electric field is applied to the quartz plate 41 when an electric field is applied between the top and bottom electrodes 43, 43'. By using this structure, a quartz vibrator of very good Q of resonance at high frequencies can be provided. As an example, if the sizes similar to those in Embodiment 1 are used, about 1 GHz of resonance frequency and Q of about 950 are realized. On the contrary, if the gaps 44, 44' are not provided for the electrodes, Q decreases to about 200. Thus, the loss at high frequencies can be improved to a large extent. An example of manufacturing method of a piezoelectric vibrator shown in Fig. 8 is explained below with reference to Fig. 9. First, a quartz plate of thickness of 40 µ m and a supporter 45 made of quartz, glass or silicon wafer are provided, and they are bonded directly with each other. That is, first, the surfaces of the quartz plate and the supporter 45 are made hydrophile (steps S101 and S111), and they are immersed in pure water(steps S102 and S112). Then, they are layered (step S120) and heated at 300 - 500 °C in air to complete the direct bonding (step S121). Next, the supporter 45 is masked with a chromium-gold layer, and only the quartz plate is etched to 2 µ m of thickness to form the quartz plate 41 (step S122). Then, the supporter 45 just below the quartz plate 41 is etched with conventional photolithography and etching techniques from the side not bonded with the quartz plate 41 to expose the rear plane of the quartz plate 41 to form a hole at the center of the supporter 45 (step S123). If the supporter 45 is made of silicon, the etchant used is a mixed acid of hydrofluoric acid with nitric acid, potassium hydroxide or the like. If the supporter 45 is made of quarts or glass, the etchant used is a hydrofluoric acid. Then, the entire surface of the quartz plate 41 is coated with a photosensitive polyimide film with spin coating. Next, processes (steps S130 - S133 and steps S140 - S143) similar to the above-mentioned example (steps S21 - S24 and steps S31 - S34) are used to complete a structure shown in Fig. 8, wherein the non-contact electrodes 43, 43' do not contact with a portion of the quartz plate 41 for vibration. Embodiment 3 Fig. 10 shows a third example of a piezoelectric vibrator, wherein reference numerals 31 - 34 denote parts having names and functions similar to the piezoelectric vibrator of Embodiment 1 shown in Figs 6(a) and (b). Reference numerals 36, 36' denote reenforcing layers formed on the whole surface at both sides including the non-contact electrodes 33, 33'. By using this structure, the strength of the non-contact electrodes 33, 33' is increased by the reinforcing layers 36, 36' or the mechanical reliability against drop, vibrations or the like can be improved to a large extent, while keeping the high frequency characteristics as in Embodiment 1. The reinforcing layers 36, 36' may be made of for example a thermosetting film of an organic polyimide resin or a metallic plating film of gold or the like. Next, an example of a manufacturing method of piezoelectric vibrator shown in Fig. 10 is explained. The processes for manufacturing the piezoelectric vibrator shown in Figs. 6(a) and (b) is performed as explained in Embodiment 1. Then, the thin plate portion 32 has been coated with a chromium-gold layer. Next, the thickness of the chromium-gold layer is increased with gold plating for example up to 10 µ m. Then, the polyimide film is removed. Thus, the mechanical strength of the electrodes 33, 33' is reinforced for the structure shown in Fig. 8. The thickness of the reinforcing layer 36, 36' can be increased further by selecting a material for the plating and a plating process. For example, it can be increased easily to 30 µ m with nickel plating. Embodiment 4 Fig. 11 shows a fourth example of a structure of a piezoelectric vibrator, wherein reference numerals 41 - 45 denote parts having names and functions similar to Embodiment 2 shown in Fig. 8. Reinforcing layers 46, 46' are applied to the non-contact electrodes 43, 43'. By using this structure, the mechanical reliability against drop, vibrations or the like can be improved to a large extent, while keeping the high frequency characteristics as in Embodiment 2. The reinforcing layers 46, 46' may be made of for example a thermosetting film of an organic polyimide resin or a metallic plating film of gold or the like, as in Embodiment 8. Next, an example of a manufacturing method of piezoelectric vibrator shown in Fig. 11 is explained. Processes of the manufacturing method of the piezoelectric vibrator shown in Fig. 8 are carried out until the chromium-gold film for the electrodes 43, 43' are formed. Next, a photosensitive polyimide film is coated on the entire surface at both sides of the piezoelectric vibrator. Then, the polyimide film and the chromium-gold layer are processed with the conventional photolithography and etching to form the prescribed pattern of electrodes 43, 43'. Then, the polyimide film is set thermally and the aluminum is removed with etching to form gaps, to complete a quartz vibrator shown in Fig. 11. Thus, the mechanical strength of the non-contact electrodes 43, 43' is reinforced by the polyimide layer 46, 46'. Next, another example of a manufacturing method of piezoelectric vibrator shown in Fig. 11 is explained. Similarly to the above-mentioned method, the processes of the above-mentioned method are carried out until the chromium-gold electrode 43, 43' are formed. Next, a photosensitive polyimide film 46, 46' is coated except a small exposed area of the aluminum for forming gaps later. Then, the polyimide film is set thermally and the aluminum is removed with etching to form gaps 44, 44' from the exposed area. Thus, the mechanical strength of the non-contact electrodes 43, 43' is reinforced with the polyimide layer 46, 46'. Thus, a quartz vibrator shown in Fig. 11 is obtained. Embodiment 5 Fig. 12 shows a fifth example of a piezoelectric vibrator. This piezoelectric vibrator is different from that shown in Figs. 6(a) and (b) as to the structure of a quartz plate 31. The quartz plate 31 comprises a vibration portion 37 and a thin portion 38 around the vibration portion 37. The thickness of the vibration portion 37 is larger than the thin portion 38. Reference numerals 33 and 34 denote the same as in Fig. 6(a). By using this structure, vibrating waves in the quartz plate attenuate in the thin portion 38 rapidly so that the Q of resonance is improved further and the spurious mode is reduced. These advantages can be obtained if the thickness of the thin portion 38 is selected to be thinner by 10 % or more than the vibration portion 37. In order to manufacture this structure of piezoelectric vibrator, the manufacturing method of the piezoelectric vibrator of Embodiment 1 is modified. That is, after the thin quartz portion 32 is formed, the thickness of the periphery of the thin portion 32 is further reduced with the photolithography and etching to form the thin portion 38 while remaining the vibration portion 37. Embodiment 6 Fig. 13 shows a sixth, example of a piezoelectric vibrator of Embodiment 11. The piezoelectric vibrator is the same as that of Embodiment 2 shown in Fig. 8 except the structure of the quartz plate 41 which comprises a vibration portion 47 and a thinner portion 48 around the vibration portion 47. Reference numerals 43, 44 and 45 denote the same as in Fig. 8. The thickness of the vibration portion 47 is larger than that of the thinner portion 48 around the vibration portion 47. By using this structure, vibrating waves in the quartz plate attenuate in the thinner portion 48 rapidly so that the Q of resonance is improved further and the spurious mode is reduced. The advantages can be obtained if the thickness of the peripheral thinner portion 48 is selected to be thinner by 10 % or more than that of the central vibration portion 47. In order to manufacture this structure of piezoelectric vibrator, the manufacturing method in Embodiment 2 is modified. That is, after the thickness of the quartz plate is reduced, the periphery of the quartz plate is further formed thinner with the photolithography and etching. The above-mentioned examples are explained further below. The improvement of Q at high frequencies is remarkable if the thickness of the quartz plate is 10 µ m or less. The thickness at the vibration portion of the quartz plate is not limited to 2 µ m adopted in the Embodiments 1-6. However, if the thickness of the quartz vibration portion exceeds 10 µ m, the advantages of the non-contact electrodes become small. Therefore, it is preferable that the thickness of the quartz vibration portion is 10 µ m or less. The initial thickness of the quartz plate is not limited to be 40 µ m as adopted in the examples, or it may be thicker or thinner than 40 µ m as far as the handling is not hindered. The gap between the thin quartz plate and the non-contact electrode have a thickness of 1 µ m. However, by controlling the vacuum deposition or the etching for forming the thin quartz plate, the gap can be made larger or smaller between 0.1 - 5 µ m. The gaps for the non-contact electrodes can be formed with good reproducibility with use of wet etching, pin coating, vacuum deposition and the like. The intensity of electric field increases with decreasing the thickness of the gap, while it is needed to increase the gap to overcome the bending of the electrodes when the area of the vibration portion is wide. Practically, the thickness up to 5 µ m is sufficient for such a case. The Q of resonance does not decrease so low at high frequencies due to electrode loss because the gaps are formed between the piezoelectric vibration portion and the non-contact electrodes so as not to contact directly with each other, and the high frequency characteristics can be improved to a large extent. In the above-mentioned Examples 1 - 6, the electrodes are made of chromium-gold layers (for example successive layers of a chromium layer of 0.02 µ m thickness and a gold layer of 0.48 µ m thickness), and the thickness thereof is for example 2 µ m. On the other hand, the electrodes may also be made of an ordinary metal such as titanium, platinum, copper, silver, tungsten or nickel. Aluminum can also be used if aluminum is not used for forming the gap. The thickness of the electrodes can be controlled between 0.1 - 5 µ m with vacuum deposition. In the Embodiments 1-6, a photosensitive polyimide of an organic material and aluminum of an inorganic material are used for forming the gaps between the quartz vibration plate and the electrodes. However, any material which does not dissolve the quartz, the electrodes and the supporter, but dissolves itself with a solvent or an etchant. For example, an organic material such as a conventional photoresist, an oxide such as silicon oxide, a nitride such as silicon nitride and a metal such as titanium or chromium can be used. By using the reinforcing layer as in Embodiments 3 and 4, the mechanical reliability against drop or the like can be improved while keeping the high frequency resonance characteristics good. Although the present invention has been fully described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications are apparent to those skilled in the art. Such changes and modifications are to be understood as included within the scope of the present invention as defined by the appended claims unless they depart therefrom.

Claims: A piezoelectric vibrator comprising: a plate comprising a thin plate portion and a thick plate portion around the thin plate portion, which thin plate portion being made of quartz; and a pair of electrodes arranged at opposite sides of the plate, which electrodes being arranged above said thin plate portion and supported by the thick plate portion, the thin plate portion of said plate being located near said electrodes without contact with the thin plate portion when the thin plate portion vibrates. The piezoelectric vibrator according to Claim 1, wherein said thick plate portion of said plate is made of quartz. The piezoelectric vibrator according to Claim 1, wherein said thick plate portion of said plate is made of a material which can be bonded directly with said thick plate portion and said thick plate portion is bonded directly to the periphery of said thin plate portion. The piezoelectric vibrator according to Claim 3, wherein said thick plate portion is made of glass. The piezoelectric vibrator according to Claim 3, wherein said thick plate portion is made of silicon. The piezoelectric vibrator according to Claim 1, wherein the thickness of said thin plate portion of said piezoelectric vibration plate is between 10 and 0.1 µ m. The piezoelectric vibrator according to Claim 6, wherein the thickness of said thin plate portion of said piezoelectric vibration plate is between 5 and 0.1 µ m. The piezoelectric vibrator according to Claim 1, wherein said thick plate portion comprises a central portion and a peripheral portion having a thickness smaller than the central portion, whereby vibration energy can be confined in the central portion. The piezoelectric vibrator according to Claim 1, further comprising a reinforcing layer applied to said electrode, whereby the mechanical strength of said electrode is increased. A manufacturing method of a quartz vibrator comprising the steps of: providing a plate including a thin plate portion made of quartz; coating the thin plate portion with a material different from quartz; coating the material with a metallic film except a portion not belonging to the thin plate portion, which metallic film being provided as an electrode; and removing said material from said portion to form a gap between the metallic film and the thin plate portion; whereby said metallic film is held by said quartz plate except the recess and said metallic film is used as an electrode for activating vibrations. The manufacturing method according to Claim 10, wherein said step of providing a plate including a thin plate portion made of quartz comprises the steps of: providing a quartz plate; and forming a thin plate portion in said quartz plate. The manufacturing method according to Claim 10, wherein said step of providing a plate including a thin plate portion made of quartz comprises the steps of: providing a first plate made of quartz; providing a second plate made of a material which can be bonded directly with the second plate; bonding said first plate directly to said second plate; decreasing the thickness of said first plate; and forming a hole in said second plate so as to expose said first plate. The manufacturing method according to Claim 10, wherein said coating material is an organic material. The manufacturing method according to Claim 13, wherein said organic material is a photosensitive polyimide. The manufacturing method according to Claim 10, wherein said coating material is aluminum. The manufacturing method according to Claim 10, further comprising the step of forming a metallic layer on said electrode to reinforce said electrode. The manufacturing method according to Claim 16, further comprising the step of forming a thermosetting organic layer on said electrode to reinforce said electrode. The manufacturing method according to Claim 10, wherein said supporter is made of quartz, silicon or quartz.

Inventors: EDA KAZUO, NAGATA TAKASHI, EDA, KAZUO, NAGATA, TAKASHI
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1993
Main classification: H03H3
IPC codes: H03H3, H03H9