STRUCTURE FOR HOLDING ULTRATHIN PLATE PIEZOELECTRIC RESONATOR IN PACKAGE

Abstract: A piezoelectric resonator constituted in one body of an ultrathin vibrating part and a thick annular enclosing part surrounding the vibrating part, in which a groove for an excess adhesive agent, etc., is formed between an appropriate area which is a portion of the surface of the annular enclosing part and on which adhesive is applied, and the inner periphery of a recessed part facing the area, adhesive is applied in the z-axis direction on the peripheral surface of the annular enclosing part to hold the resonator in a package, the resonator is held in the package not by the adhesive but by an elastic claw, or one peripheral part of the annular enclosing part being the surface opposed to a pad positioned in one peripheral part on one of the surfaces of the piezoelectric resonator is bonded to the inner bottom surface of the package. Owing to the holding structures, change of the resonance frequency of the piezoelectric vibrating plate which is caused by flowing of the adhesive into the recessed part is prevented, variation of the temperature-frequency characteristic of the resonator held in the package which is caused in the case of mass production is reduced, and the mechanical strength of the electrical connection by bonding of the piezoelectric resonator incorporated in the package can be improved too.

Description: The present invention relates to a structure by which a resonator using an ultrathin piezoelectric plate, capable of providing resonance frequencies as high as tens to hundreds of megahertz, is supported in a package. In recent years there has been a strong and growing demand for high frequency operation and high frequency stability of various pieces of electronic and communication equipment. An ordinary AT cut quartz crystal resonator, which has heretofore been used widely as a piezoelectric device (such as a resonator or filter), has a very excellent temperature-frequency characteristic. However, since its resonance frequency is in inverse proportion to its thickness, the fundamental frequency of this kind of resonator with a mechanical strength sufficient for practical use is around 40 MH z at the highest. There has also been widely employed what is called overtone oscillation means which extracts a higher order harmonic mode vibration of an AT cut quartz crystal resonator to obtain a frequency which is an odd multiple of the fundamental resonance frequency, but its oscillation circuit calls for an LC tuning circuit including a coil, and hence is not suitable for fabrication as a semiconductor IC, besides the overtone oscillation circuit may sometimes be difficult to activate because such a resonator has a large capacitance ratio and consequently a high impedance level. On the other hand, a surface acoustic wave (SAW) resonator, whose oscillation frequency is determined by the pitch of electrodes of an interdigital transducer, has come to be able to output a maximum of 1 GH z or so due to the progress in photolithography, but a piezoelectric substrate usable for the SAW resonator is remarkably inferior to the AT cut quartz crystal in terms of temperature-frequency characteristic. To solve the above-mentioned problems, there has been proposed in house, but not disclosed publicly, a piezoelectric resonator such as shown in Figs. 1(a), 1(b), 2(a) and 2(b). That is, a cavity or recess 5 is formed, by machining or etching, in one side of a block 1 of AT cut quartz crystal substantially centrally thereof as depicted in Figs. 1(a) and (b) and the thickness of a vibratory portion 2 forming the bottom of the cavity 5 is selected about 16µm, for example, if a fundamental resonance frequency of 100 MH z is desired. On the side of the block where the cavity 5 is formed, the ultrathin vibratory portion 2 is edged with a thick frame-like marginal rib portion 3 formed integrally therewith. The ultrathin vibratory portion 2 can be retained in its required shape by the frame-like rib 3. In this instance, it is preferable that excitation electrodes for the piezoelectric block be composed of an overall electrode 12 formed on the side of the block where the cavity 5 is provided and a partial electrode 11 and an electrode lead pattern 14a on the opposite side of the cavity 5, the electrode lead member 14a extending from the partial electrode 14 to one end face of the block. It is technically advantageous to house such a resonator of the above construction upside down--with the cavity 5 facing downward--in a ceramic or similar package 11 which has a concave housing space 10 centrally thereof and to mechanically bond and electrically connect the top 3a of one side of the frame-like marginal portion 3, by a conductive adhesive 15 coated in line thereon, to a conductive film 16 which is exposed on the bottom of the housing space 10, hermetically passes through the package and is connected to an external lead member 17 projecting out of or exposed on the outside of the package, as shown in Figs. 2(a) and 2(b). The piezoelectric device of such a construction has sometimes turned out to be defective in that since the resonator is very small, it is hard to control the amount of conductive adhesive used for bonding the top 3a of one side of the frame-shaped rib 3 to the bottom of the package 11, and consequently, the excess adhesive may sometimes flow into the cavity 5 and hence increases the thickness of the vibratory portion 2, causing a variation in the resonance frequency. In view of the above-noted defects the object of the present invention is to provide a piezoelectric resonator support structure with which it is possible to support, in a package, a piezoelectric resonator of the type having an ultrathin vibratory portion formed by the bottom of a cavity made in a block of quartz crystal or the like, without causing a variation in the resonance frequency of the resonator which is attributable to the inflow of the excess adhesive into the cavity which is likely to occur when fixing the top of one marginal portion of the frame-shaped rib of the resonator to the bottom of the package. US-A-4517485 discloses a resonator having an ultrathin vibratory portion formed by a cavity made in one side of a quartz crystal block substantially centrally thereof and a thick rectangular frame-like rib formed integrally with and surrounding the vibrating portion. JP-A-60105309 discloses a piezoelectric vibrator in a casing having adhesive-receiving grooves to avoid swelling of the adhesive and hence disturbance of casing end caps. According to the present invention, in a structure of a piezoelectric resonator housed within a package, the resonator having an ultrathin vibratory portion formed by a cavity made in one side of a piezoelectric block substantially centrally thereof and a thick frame-like rib formed integrally with and surrounding the vibrating portion; the resonator has an excess adhesive receiving groove or slit cut in one marginal portion of the frame-like rib along one side of the cavity between an adhesive coated region at which the resonator is secured to the package and the edge of the cavity for preventing the adhesive from flowing into the cavity from the adhesive coated region. In the accompanying drawings: Figs. 1(a) and (b) are, respectively, a perspective view showing the construction of a previously proposed but undisclosed resonator using an ultrathin piezoelectric plate; and a sectional view taken on the line X-X in Fig. 1(a), showing how the resonator is housed in a package; Figs. 2(a) and (b) are, respectively, a sectional view and a plan view showing how the previously proposed resonator using an ultrathin piezoelectric plate is housed in the package; Figs. 3(a), (b) and (c) are, respectively, a perspective view, a plan view and a sectional view taken on the line A-A in Fig. 3(b) showing the construction of a quartz crystal resonator according to the present invention; Figs. 4(a) and (b) are plan views of modified forms of the Fig. 1 embodiment; and, Fig. 4 (c) is a partial plan view of another modification. The AT cut quartz crystal resonator of Figs. 3 has the cavity 5 formed by etching or machining in one side of the rectangular parallelepiped block 1 of AT cut quartz crystal substantially centrally thereof so that the bottom of the cavity 5 forms the ultrathin vibratory portion 2 edged with the thick frame-like marginal portion (rib) 3. In this embodiment, however, the AT cut quartz crystal resonator has an excess adhesive receiving groove 40 cut in the top of the marginal portion of the rib 3 along the conductive adhesive coated portion (for fixing the quartz crystal) 3a near the cavity 5 so that excess adhesive 15, which oozes from the adhesive coated portion when bonding the resonator to the package, flows into the groove 40, and hence is prevented from flowing into the cavity 5. The groove 40 can be formed by etching simultaneously with the formation of the cavity 5, and accordingly, no particular manufacturing step is needed therefor. It is necessary that the groove 40 be formed substantially in parallel to the conductive adhesive coated region 3a and that its width, length, depth and shape be set so that the overflowing excess adhesive 15 can be prevented from flowing into the cavity 5. From this point of view, the groove 40 may also be a slit extending through the frame-like marginal portion of the rib 3. The groove 40 need not always be limited specifically to such a straight-shaped one as shown but may also be provided at both ends with large adhesive reservoirs 41 as depicted in Fig. 4(a). Alternatively, it is possible to open the groove 40 at an edge of the quartz crystal block 1 near the adhesive coated region 3a to let the excess adhesive 15 run down to the bottom of the package through the open ends 42. Thus, the area of bonding the quartz crystal block 1 to the bottom of the package can be defined. In the above embodiment the resonator is fixedly held in a cantilever fashion at one marginal portion of the frame-like rib. Such a structure is effective in the reduction of variation of the resonance frequency of the resonator, improving its temperature-frequency characteristic and other characteristics. With the structure, however, the resonator is very likely to be broken down by flapping due to vibration or shock applied thereto. To avoid this, the marginal portion 3b of the frame-like rib opposite the adhesive coated region 3a across the cavity 5 may sometimes be joined at one corner 3b' to the bottom of the package at the sacrifice of improvement in the above-mentioned various characteristics of the resonator. Also, in such an instance, a groove 45 may preferably be provided as shown in Figs. 4(c) so as to define the area of joining the portion 3b to the bottom of the package. The gist of each of the Figs. 3 and 4 embodiments resides in the structure for preventing the adhesive from flowing into the cavity by forming the excess adhesive receiving groove in the top of one marginal portion of the frame like rib between the adhesive coated region and the cavity as described above. Although in the above the piezoelectric resonator is housed with its cavity facing toward the bottom of the package, it is needless to say that the present invention is also applicable to the case where the resonator is housed with its planar surface facing toward the bottom of the package. The above embodiments have been described with respect to the case where the piezoelectric resonator is a AT cut quartz crystal resonator, but this should be construed as being merely illustrative of the invention and the invention is applicable as well to devices which utilize piezoelectric materials other than the AT quartz crystal. Moreover, while the embodiments have been described to employ the rectangular block of a piezoelectric material, this configuration is needed merely for providing enhanced mass productivity of the resonator by use of a batch system, and hence the present invention is not limited specifically thereto. Accordingly, the present invention can equally be applied to resonators of circular, polygonal and other forms as viewed from above. Thus, the embodiments shown in Figs. 3(a) to (c) and 4(a) to (c) according to the present invention are intended to solve the afore-mentioned object of the invention and are capable of substantially completely preventing that when the resonator having the ultrathin vibratory portion is joined to the bottom of its package, the excess adhesive flows into the vibratory portion of the resonator, causing a variation in its resonance frequency. Furthermore, these embodiments do not call for any high precision adhesive dispenser, and hence do not require any particular equipment, and they permit simultaneous formation of the excess adhesive receiving groove with the cavity. Accordingly, the structures of the above embodiments not only improves the yield rate of product but also cheapens the manufacturing cost of the type of piezoelectric resonator.

Claims: A structure of a piezoelectric resonator housed within a package (11), the resonator having an ultrathin vibratory portion (2) formed by a cavity (5) made in one side of a piezoelectric block (1) substantially centrally thereof and a thick frame-like rib (3) formed integrally with and surrounding the vibrating portion, wherein the resonator has an excess adhesive receiving groove or slit (40) cut in one marginal portion of the frame-like rib along one side of the cavity between an adhesive coated region (3a) at which the resonator is secured to the package and the edge of the cavity for preventing the adhesive from flowing into the cavity from the adhesive coated region.

Inventors: ISHII OSAMU, KUROSAKI TAKEBUMI, MORITA TAKAO, ISHII, OSAMU, KUROSAKI, TAKEBUMI, MORITA, TAKAO, ISHII, OSAMU, TOYO COMMUNICATION EQUIP. CO., LTD, KUROSAKI, TAKEBUMI, TOYO COMMUNICATION EQU. COLTDO, MORITA, TAKAO, TOYO COMMUNICATION EQUIP. CO., LTD.
Applicants: TOYO COMMUNICATION EQUIP, TOYO COMMUNICATION EQUIPMENT CO. LTD.
Application year: 1990
Main classification: H03H9
IPC codes: H03H9, H03H3