Piezoelectric resonator, method of manufacturing the same and electronic part using the same

The object of the present invention is to provide a piezoelectric resonator of which vibration frequency can be accurately adjusted and the adjustment accuracy of the vibration frequency can be improved. The piezoelectric resonator of the present invention includes an vibrating arm extended from a base, and a metal film for adjusting frequency formed along the longitudinal direction from the tip of the vibrating arm, in which the metal film for adjusting frequency is provided with a block pattern divided into a plurality of blocks in compliance with the amount of frequency adjustment. Structuring as above, the frequency adjustment of the piezoelectric resonator is conducted by eliminating the blocks in compliance with the amount of frequency adjustment one by one, which makes it possible to adjust the vibration frequency with accuracy.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a tuning fork type piezoelectric resonator made of, for instance, quartz crystal or the like, a method of manufacturing the same and an electronic part using the same.

2. Description of the Related Art

The tuning fork type quartz resonator has long been adopted as a signal source for pacing a wrist watch owing to its being compact, inexpensive and having a low power consumption, and the uses thereof are still expanding. The CI (crystal impedance) value of this quartz resonator is required to be as low as possible to reduce power loss, and a quartz resonator with a groove formed therein to enhance vibration efficiency is being used for this purpose.

The tuning fork type quartz resonator is provided with a pair of vibrating arms2aand2bon a base1as shown inFIG. 9, and grooves31and32are respectively provided on both main surfaces of the respective vibrating arms2aand2b. Excitation electrodes (not shown) for exciting fork vibration based on bending vibration are formed on these grooves31,32and the respective vibrating arms2a,2b. Metal films50aand50bfor adjusting frequency by adjusting the weight of the vibrating arms are formed on both front and back surfaces at the tips of the vibrating arms2aand2b.

The metal films50aand50bfor adjusting frequency include a chromium (Cr) film10, a gold (Au) film11, and a chromium (Cr) film13, which are stacked on the surface of the vibrating arms2aand2bin this order as shown inFIG. 10, and further include a gold (Au) film12serving as an adjusting weight being stacked further thereon. Incidentally,FIG. 10is a schematic sectional view of a sectional part along the A-A line inFIG. 9. The metal films50aand50bfor adjusting frequency thus structured are used to adjust the vibration frequency of the tuning fork type quartz resonator to, for instance, 32.768 kHz. Specific description of making adjustment to the vibration frequency is as follows. First, an oscillation circuit is connected to one quartz resonator among plural pieces of quartz resonators which are formed on a sheet of quartz wafer to measure the frequency before adjustment. Then, the metal films50aand50bfor adjusting frequency are irradiated with a laser beam so that the gold (Au) film of the adjusting weight is sputtered to conduct rough adjustment to adjust the frequency close to 32 kHz. At this time, irradiation pulse number of the laser is counted. Thereafter, ionized argon particles obtained by discharging argon (Ar) are allowed to hit at the metal films50aand50bfor adjusting frequency so that the gold (Au) film is sputtered to complete fine adjustment to the target frequency. The fine adjustment is conducted by sputtering the gold (Au) film with argon ions while monitoring the vibration frequency of the quartz resonator so as to adjust the thickness of the gold (Au) film. At this time, the irradiation amount of the argon (Ar) plasma is counted.

Next, based on the irradiation pulse number of the laser and the irradiation amount of the argon (Ar) plasma obtained from the above-described quartz resonator, the metal films50aand50bfor adjusting frequency are shaved by a laser and argon (Ar) plasma for plural quartz resonators formed on a sheet of quartz wafer so as to match with the vibration frequency.

However, the above-described adjustment of the vibration frequency has the following problems. In a rough adjustment of the frequency of each quartz resonator, accurate positioning between the laser and the quartz wafer stage and degrees of melting of the metal films50aand50bfor adjusting frequency with a laser are varied. Accordingly, time required for the rough adjustment is varied, which creates variation of time duration for the fine adjustment. When time for the fine adjustment is prolonged, time for irradiation with the argon (Ar) plasma also increases. As a result, the heating value of the quartz resonator increases. Since the vibration frequency of the tuning fork type quartz resonator is apt to be affected by heat, in other words, sensitive to heat, it is difficult to realize adjustment accuracy of high vibration frequency if the heating value varies in this manner.

Whereas the Patent Document 1 describes that the electrodes for finely adjusting frequency are formed in stripes on both front and back surfaces of a tuning fork arm, and, a beam of laser is allowed to irradiate the electrodes for finely adjusting frequency on the front surface of the tuning fork arm so as to perform fine adjustment of frequency. However, it is impossible to adjust the vibration frequency with high accuracy using this technology.

SUMMARY OF THE INVENTION

The present invention has been achieved under such circumstances, and the objects thereof are to provide a piezoelectric resonator whose vibration frequency can be accurately adjusted so that the adjustment accuracy of the vibration frequency is improved, a method of manufacturing the same and electronic parts using the same.

A piezoelectric resonator of the present invention has an vibrating arm extended from a base, and is provided with metal films for adjusting frequency formed along the longitudinal direction at the tip of the vibrating arm, in which

the above-described metal film for adjusting frequency includes a block pattern divided into a plurality of blocks.

In the above-described piezoelectric resonator, the aforementioned blocks may be provided in plurality in the longitudinal direction of the vibrating arm, or may be provided in plurality in the width direction of the vibrating arm. In addition, the blocks may be provided in plurality in the longitudinal and in the width directions of the vibrating arm or may include a plurality of block groups different in block size from each other. It is preferable that the metal films for adjusting frequency are formed on both front and back surfaces of the vibrating arm, and the block pattern formed on the front surface and that formed on the back surface correspond to each other. It is preferable that the above-described metal film for adjusting frequency includes a metal film for rough adjustment and a metal film for fine adjustment, and the block pattern is formed on the metal film for rough adjustment.

A method of manufacturing the piezoelectric resonator of the present invention includes the steps of:

forming an outer shape corresponding to a plurality of piezoelectric oscillating pieces from a piezoelectric substrate by etching, and forming grooves in plurality of vibrating arms extending from the base respectively;

forming the metal film for adjusting frequency at the tip of the vibrating arm;

forming a resist mask on the surface of the metal film to form a block pattern divided into more than one of blocks by etching the metal film;

removing the plurality of the blocks to perform rough adjustment of the vibration frequency; and

performing fine adjustment of the vibration frequency by shaving the metal film at a position where no block pattern is formed to adjust the thickness thereof.

The electronic part of the present invention includes the piezoelectric resonator manufactured by the above-described method; a vessel to house the piezoelectric resonator; and an external electrode formed on the outer surface of the vessel and electrically connected to the electrode of the piezoelectric resonator.

In the present invention, a metal film for adjusting frequency is formed along the longitudinal direction from the tip of the vibrating arm, and a block pattern divided into a plurality of blocks in compliance with the amount of frequency adjustment is formed on the metal film for adjusting frequency. The frequency adjustment of the piezoelectric resonator is conducted by shaving the metal film for adjusting frequency formed on the vibrating arm. The frequency adjustment of the piezoelectric resonator in the present invention is conducted by eliminating the blocks in compliance with the amount of frequency adjustment one by one. As a result, it is possible to perform adjustment of the vibration frequency accurately so that the adjustment accuracy of the vibration frequency is improved.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

An embodiment of the present invention will be explained. As for the structure of a quartz resonator being a piezoelectric resonator relating to the present embodiment, metal films50aand50bfor adjusting frequency are formed on both front and back surfaces along the longitudinal direction from the tip of vibrating arms2aand2b, and a block pattern divided into a plurality of blocks in compliance with the amount of frequency adjustment is formed on the metal films50aand50bfor adjusting frequency. Since other points excepting the above are the same as the quartz resonator explained in the section of related art usingFIG. 9, explanation of these identical portions will be omitted, and parts of the same structure are attached with the same symbols and numerals.

FIG. 1is a schematic plan view of the quartz resonator relating to the embodiment of the present invention, andFIG. 2is an enlarged view of the tip of the vibrating arms2a(2b) of the quartz resonator. As shown in FIGS.1and2, the metal films50aand50bfor adjusting frequency, which are formed on both front and back surfaces of the tip of the vibrating arms2aand2binclude metal films51aand51bfor rough adjustment formed near the tip of the vibrating arms2aand2b, and metal films52aand52bfor fine adjustment formed near the base of the vibrating arms2aand2b, and a block pattern divided into a plurality of blocks is formed on the metal films51aand51bfor rough adjustment. In other words, the metal films51aand51bfor rough adjustment are divided into blocks having a plurality of sizes, and as will be described later, an approximate amount of change in frequency at the time of eliminating the block is determined for every block. Note that, as shown inFIG. 2, rectangular blocks having different sizes are arranged from a block having a larger amount of frequency adjustment to a block having a smaller amount of frequency adjustment in sequence from the tip of the vibrating arms2aand2btoward the base in this example. These blocks include those having a surface area of, for instance, 10 μm×10 μm to 40 μm×40 μm. The shape of the block is not limited to a rectangle, but may be, for instance, a circle, a trapezoid, a triangle, and so on. As for the arrangement of the blocks, it is not limited to this example, they may be arranged from a block having the largest amount of frequency adjustment to those having smaller amounts in the width direction of the vibrating arms2aand2bin sequence, or, for instance, a block having a larger amount of frequency adjustment and a block having a smaller amount of frequency adjustment are made into one group, and such groups may be arranged from the tip of the vibrating arms2aand2bin the longitudinal direction. Note that, in a case where blocks having a size smaller than the diameter of the laser irradiating the metal films50aand50bfor adjusting frequency are arranged vertically and horizontally, some space is taken between blocks lest a block adjacent to the block to be eliminated should be eliminated when the block is eliminated by the laser. In other words, the space between block patterns is adjusted in compliance with the diameter of the laser.

Returning the explanation toFIG. 1, the quartz resonator is composed of one electrode and the other electrode making a pair. Focusing on the vibrating arm2afirst, the one excitation electrode41is formed on the whole inner surface of two grooves31,32of the vibrating arm2aand a space between these grooves31,32. In other words, the excitation electrodes41in the respective grooves31and32of the vibrating arm2aare connected via the excitation electrode41formed on, what is called, a bridge corresponding to the space between the grooves31and32. The other excitation electrodes51(not shown) are formed on both side surfaces of the vibrating arm2a.

Focusing on the vibrating arm2b, the other excitation electrode51is formed on the whole inner surface of two grooves31,32of the vibrating arm2band a space between these grooves31,32. The one excitation electrode41(not shown) is formed on both side surfaces of the vibrating arm2b. The arrangements of the electrodes provided on the vibrating arms2aand2bare the same with each other except that the excitation electrodes41and51are in opposite relation. A pull-out electrode42is formed on the surface of a base1so that the one excitation electrode41and the one excitation electrode41are electrically connected, and a pull-out electrode52is formed on the surface of the base1so that the other excitation electrode51and the other excitation electrode51are connected. Note that the excitation electrodes41,51, the pull-out electrodes42,52, and the metal films50a,50bfor adjusting frequency inFIGS. 1 and 2are expressed by using slash lines and black dots separately for each area so that the drawing is easily seen. Accordingly, the slash lines inFIGS. 1 and 2are not for expressing the sections of a quartz piece.

A method of manufacturing the quartz resonator shown inFIGS. 1 and 2will be explained with reference toFIG. 3. Since the process of forming a quartz wafer in a tuning fork shape having grooves from a quartz wafer cut out along the X axis of quartz crystal is conducted by a known method combining photolithography and etching, the explanation of the process will be omitted, and the process of forming the metal film for adjusting frequency on the tip of the vibrating arms2aand2band the following processes thereafter will be explained.FIG. 3is a view showing a manufacturing process of the side surface parts of the vibrating arms2aand2bshown inFIG. 2. First, a metal film, for instance, a chromium (Cr) film6, which is a backing film having good adherence to the quartz wafer, is formed on both front and back surfaces of the tip of the vibrating arms2aand2bin a thickness of, for instance, 50 Å to 500 Å by the sputtering method (FIG. 3A). Then, a metal film, for instance, a gold (Au) film61having good adherence to the metal film6, is formed on the metal film6in a thickness of, for instance, 1000 Å to 10,000 Å by the sputtering method (FIG. 3B). To be precise, the metal films6and61are formed at the tips of the vibrating arms2aand2bby lithography. Next, a metal film, for instance, a chromium (Cr) film62, which is a backing film having good adherence to the quartz wafer, is formed on the whole surface of the quartz wafer, namely, on both main surfaces and side surfaces of the quartz wafer in a thickness of, for instance, 50 Å to 500 Å by the sputtering method (FIG. 3C). Then, a metal film, for instance, a gold (Au) film63having good adherence to the metal film62, is formed on the whole surface of the quartz wafer, namely, on both main surfaces and side surfaces of the quartz wafer in a thickness of, for instance, 500 Å to 2000 Å by the sputtering method (FIG. 3D). Thereafter, photoresist is applied on the whole surface of the quartz wafer by, for instance, the spray method to form a resist film64(FIG. 3E). Then, the resist film64except the resist film64for electrode patterns is eliminated (this state is not illustrated on the side surface side) by photolithography, and at the same time, the resist film64except the resist film64for block patterns is eliminated (FIG. 3F). Thereafter, the gold (Au) film63and the chromium (Cr) film62on the spots where the resist film64is eliminated are etched to form the electrode patterns and the block patterns (FIG. 4G). Next, the gold (Au) film61and the chromium (Cr) film6on the spots where the gold (Au) film63and the chromium (Cr) film62formed at the tip of the vibrating arms2aand2bare eliminated are etched to form block patterns (FIG. 4H). Thereafter, the resist film64left on the quartz wafer is completely eliminated (FIG. 4I).

As shown inFIG. 4I, areas80where the chromium (Cr) film62and the gold (Au) film63are stacked in this order are metal films for electrodes (excitation electrodes41,51and pull-out electrodes42,52), and areas81where the chromium (Cr) film6, the gold (Au) film61, the chromium (Cr) film62, and the gold (Au) film63are stacked in this order are metal films50aand50bfor adjusting frequency. In the metal films50aand50bfor adjusting frequency, the areas where block patterns are formed on the metal films6,61,62and63are the metal films51aand51bfor rough adjustment, and the areas where block patterns are not formed on the metal films6,61,62and63are the metal films52aand52bfor fine adjustment. The metal films51a,51bfor rough adjustment and the metal films52a,52bfor fine adjustment structured in this manner are used for adjusting the vibration frequency of the tuning fork type quartz resonator to, for instance, 32.768 kHz.

Next, in the tip of the vibrating arms2aand2b, adjustment of the vibration frequency is conducted by shaving the surface of the metal films50aand50bfor adjusting frequency formed on the tip with a laser or the like. Describing the adjustment of frequency more specifically, an oscillation circuit is connected to one quartz resonator among plural pieces of quartz resonators formed on a sheet of quartz wafer first, and the frequency before adjustment is measured. Next, blocks required for adjusting frequency to the target frequency is irradiated with a laser. In other words, when a block formed on one surface of the vibrating arms2aand2bis irradiated with a laser, the block formed on one surface is eliminated, and thereafter, the laser penetrates through the quartz wafer and irradiates the same sized block formed on the other surface of the vibrating arms2aand2b. In this embodiment, it becomes possible to adjust its frequency in the order of 500 ppm to 10 ppm by irradiating a block pattern formed on the metal films51aand51bfor rough adjustment with a laser to eliminate the block pattern. Thus, the same block formed on both front and back surfaces of the vibrating arms2aand2bare eliminated to conduct rough adjustment so as to bring its frequency close to 32 kMz (refer toFIG. 5). The number of blocks eliminated at this time is counted. Thereafter, one piece of the quartz resonator is cut out from the quartz wafer, argon particles prepared by discharging and ionizing argon (Ar) are allowed to hit on the metal films52aand52bfor fine adjustment formed on one surface of the vibrating arms2aand2bof the cut out quartz resonator so as to gradually sputter the gold (Au) film63to conduct fine adjustment to the target frequency. For this fine adjustment, as shown inFIG. 6, an apparatus mainly composed of a tray90made of metal such as SUS or the like and being capable of holding a plurality of the quartz resonators, a drive means91capable of sliding the tray90in a prescribed direction, and an ion gun92irradiating charged particle beams (argon ion beam) to the vibrating arms2aand2bof the quartz resonator held by the tray90, is used.

The above-described tray90is provided with a recessed93capable of fitting a case7awhich houses the quartz resonator as shown inFIG. 8to be described later, and an opening94is provided at the position where the meat films for fine adjustment52aand52bof the quartz resonator as shown inFIG. 7on the bottom of the recess93. The case7ais fitted into the recess93of the tray90formed as described above such that the opening of the case7afaces toward the bottom side of the recess93. This structure makes it possible to get an unobstructed view of the metal film52aand52bof the quartz resonator from the outside through the opening94at the bottom of the recess93. Then, the argon ion beam from the ion gun92provided on the bottom side of the tray90hits the metal film52aand52bfor fine adjustment of the quartz resonator through the opening94of the tray90. That is, the tray90works as a mask.

In an apparatus of such a structure, when conducting fine adjustment, one piece of roughly adjusted quartz resonator from the quarts wafer first, and the quartz resonator is bonded to the bottom of the case7awith a conductive adhesive7d. Next, the case7ais placed in the recess93of the tray90. Then it is irradiated with the argon ion beam from the ion gun92. Since the irradiation area of the argon ion beam is limited by the tray90, only the metal film52aand52bfor fine adjustment of the quartz resonator are eliminated. An electrode pad95is connected to electrodes72and73arranged on the outside bottom of the case7a, and by sputtering the gold (Au) film63with argon ions while monitoring the vibration frequency of the quartz resonator using a frequency measuring instrument96via the electrode pad95so as to adjust the film thickness of the gold (Au) film63. The irradiation amount of the argon (Ar) plasma at this time is counted.

Next, based on the number of eliminated blocks and the irradiation amount of the argon (Ar) plasma obtained from the quartz resonator, matching of the vibration frequency is conducted for a plurality of quartz resonators formed on a sheet of quartz wafer. That is, the same amount of the blocks are eliminated in the metal films51aand51bfor rough adjustment of each quartz resonator, and the same amount of argon (Ar) plasma is allowed to beam at the metal films52aand52bfor fine adjustment of each quartz resonator. Explaining concretely, first, plural quartz resonators formed on a sheet of quartz wafer are roughly adjusted respectively. Then, all quartz resonators are cut out from the sheet of the quartz wafer and housed in the cases7arespectively. Then, these cases7aare arranged in the recesses93of the trays90respectively, and the trays90are transferred from the right side to the left side inFIG. 7in turn by the drive means91so as to match the respective openings94of the trays90with the irradiating point of the ion gun92. By this process, fine adjustment is conducted for each quartz resonator.

According to the above-described embodiment, adjustment of the vibration frequency of the quartz resonator is conducted by eliminating the blocks of which approximate amounts of change in frequency are known one by one. As a result, it becomes possible to perform adjustment of the vibration frequency accurately so that the adjustment accuracy of the vibration frequency is improved. It also becomes possible to perform rough adjustment without being affected by various variations by eliminating blocks required for matching the frequency to the target frequency with a laser irradiation. Further, it is possible to easily calculate the amount of rough adjustment of frequency by checking the eliminated blocks. In addition, since the frequency after the rough adjustment of frequency is stabilized, the difference in the amount of frequency adjustment at the time of fine adjustment among the respective quartz resonators is reduced, and the heat effect is made uniform, so that the variations in final frequency are diminished.

The adjustment of the frequency may be conducted as follows. First, a piece of quartz resonator is cut out from plural pieces of quartz resonators formed in one sheet of quartz wafer, this one piece of the quartz resonator is set in an oscillation circuit, and the frequency is measured under the condition that the metal films51a,51bfor rough adjustment and the metal films52aand52bfor fine adjustment are arranged. Then, the difference between the measured frequency and the target frequency, 32.768 kHz, is calculated. Next, based on the difference between the measured frequency and the target frequency, among the metal films51aand51bfor rough adjustment, the blocks required for matching with the target frequency are irradiated with a laser. Then, rough adjustment is conducted by eliminating the same sized blocks formed on both front and back surfaces of the vibrating arms2aand2bso that the frequency is brought close to 32 kHz. Thereafter, similarly to the above, ionized argon particles obtained by discharging argon (Ar) are allowed to beam at the metal films52aand52bfor fine adjustment formed on one surface of the vibrating arms2aand2bso that the gold (Au) film63is sputtered to conduct fine adjustment to the target frequency. Such a frequency adjustment is conducted for cut-out quartz resonators in sequence.

It should be noted that in the above-described embodiment, the metal films50aand50bfor adjusting frequency are formed on both front and back surfaces of the vibrating arms2aand2b, it is also possible to form the metal films50aand50bfor adjusting frequency only on the front surface of the vibrating arms2aand2b. Furthermore, the fine adjustment process may be performed with a laser.

The quartz resonator, for which adjustment of the vibration frequency has been completed as described above is housed, for instance, as shown inFIG. 8, in a package7made of ceramics in a surface mounted device (SMD) structure. The package7includes a case7amade of, for instance, ceramics, of which upper surface is open, and a lid7bmade of, for instance, metal. The above-described case7aand the lid7bare seam-welded via a sealing compound7cmade from, for instance, a welding material, and the inside thereof is maintained under vacuum. The above-described tuning fork type quartz resonator70is placed in the package7in the following manner that the pull-out electrodes42and52of the base1are fixed on a pedestal71placed in the inside of the package7via a conductive adhesive7d, and the quartz resonator70is fixed on the pedestal71in a horizontal posture in which the vibrating arms2aand2bare extending into a space inside the package7. In addition, conductive paths72and73(73is a conductive path on the inner side of the paper) are wired on the surface of the above-described pedestal71, the pull-out electrodes42and52of the base1are connected to the above-described conductive paths72and73via the conductive adhesive7d. The conductive paths72and73are connected to electrodes74and75, which are arranged to face in the longitudinal direction of the outside bottom surface of the case7a. Owing to this structure, the quartz resonator is oscillated by application of a voltage to the pull-out electrodes42and52of the base1through the electrodes74,75, the conductive paths72,73, and the conductive adhesive7d. Electric parts are composed in this manner, and the electric part is installed on a circuit board (not shown) on which circuit parts of an oscillation circuit are installed.