Source: http://patents.com/us-7279824.html
Timestamp: 2013-05-25 21:55:15
Document Index: 559231995

Matched Legal Cases: ['arts 100', 'arts 100', 'art 100', 'art 100', 'art 62', 'art 62', 'art 62', 'art 42', 'art 550', 'art 550', 'art 550', 'arts 100', 'art 100', 'art 550']

US Patent # 7,279,824. Piezoelectric resonator element, piezoelectric device, method of
manufacturing the same, cellular phone device utilizing piezoelectric
device, and electronic equipment utilizing piezoelectric device - Patents.com
United States Patent 7,279,824
Piezoelectric resonator element, piezoelectric device, method of
device, and electronic equipment utilizing piezoelectric device
A piezoelectric resonator element is provided including a base portion and
a plurality of resonating arms extending from the base portion. A notch
part is formed in the base portion. Grooves are formed in the front and
back surfaces of the resonating arms. A driving electrode is provided at
least in the grooves of the resonating arms. The driving electrode has a
lower layer and an electrode layer formed on the lower layer. The
thickness t of the lower layer is in the range 0.07<t<0.3
Inventors: Tanaya; Hideo (Suwa, JP), Jokura; Toshinari (Okaya, JP), Oshiro; Atsushi (Minowa-machi, JP) Assignee:
10/976,246
Foreign Application Priority Data Oct 28, 2003
2003-367743
310/344 ; 310/370
Field of Search: 310/364,370,344,348
6587009
6768247
6894428
Tanaya et al.
6927530
2002/0121175
2003/0067248
52-052597
55-138916
2002-261575
Other References Patent Abstracts of Japan for No. JP2002261575 (Sep. 13, 2002). cited by other
.1 Page Abstract for 04025568.9 (date unknown). cited by other
.Communication from European Patent Office re: counterpart application, date unknown. cited by other
.Communication from European patent Office re: related application, date unknown. cited by other. Primary Examiner: Budd; Mark
Claims What is claimed is: 1. A piezoelectric device comprising: a package including a first substrate, a second substrate, and a through hole formed through the first substrate and the second
substrate, the through hole including a first hole formed in the first substrate and a second hole formed in the second substrate, the second hole having a diameter that is less than a diameter of the first hole; a metal sealant disposed in the first
hole and the second hole; an electrode portion formed on the second substrate and spaced apart from the second hole; a base portion disposed on the electrode portion and including a notch part; a plurality of resonating arms disposed on the package
and extending from and parallel to the base portion, the plurality of resonating arms including a groove part formed on a front surface and a back surface of the resonating arms; and a driving electrode disposed in the groove part of the resonating arms
and including a lower layer and an electrode layer formed on the lower layer, the lower layer including a thickness t in a range of 0.07 micrometers<t<0.3 micrometers; wherein the second substrate is disposed between the first substrate and the
plurality of resonating arms.
5. A cellular phone device obtaining a clock signal for control by using a piezoelectric device, comprising: a package including a first substrate, a second substrate, and a through hole formed through the first substrate and the second
6. Electronic equipment obtaining a clock signal for control by using a piezoelectric device, comprising: a package including a first substrate, a second substrate, and a through hole formed through the first substrate and the second substrate,
the through hole including a first hole formed in the first substrate and a second hole formed in the second substrate, the second hole having a diameter that is less than a diameter of the first hole; a metal sealant disposed in the first hole and the
second hole; an electrode portion formed on the second substrate and spaced apart from the second hole; a base portion disposed on the electrode portion and including a notch part; a plurality of resonating arms disposed on the package and extending
from and parallel to the base portion, the plurality of resonating arms including a groove part formed on a front surface and a back surface of the resonating arms; and a driving electrode disposed in the groove part of the resonating arms and including
a lower layer and an electrode layer formed on the lower layer, the lower layer including a thickness t in a range of 0.07 micrometers<t<0.3 micrometers; wherein the second substrate is disposed between the first substrate and the plurality of
resonating arms.
9. The piezoelectric device according to claim 8 further comprising a lid extending over the base and the plurality of resonating arms and attached to the third substrate by a sealant. Description RELATED APPLICATIONS
In small information equipment such as a hard disc drive (HDD), a mobile computer, or an integrated circuit (IC) card, and mobile communication equipment such as a cellular phone, a car-phone, or a paging system, a piezoelectric device such as a
crystal resonator and a crystal oscillator that contains a piezoelectric resonator element in a package has been widely used.
A piezoelectric resonator element contained in a conventional piezoelectric device has a structure including a base portion and a pair of resonating arm portions formed in a manner of protruding from the base portion (Refer to Japanese Unexamined
Patent Publication No. 2002-261575 (FIG. 1, Page 5 and 7)).
However, in a tuning fork type resonator element with so-called grooves, which is a conventional piezoelectric resonator element, a temperature characteristic (frequency) that is the relationship between temperature changes and frequency
tolerance changes shows a quadratic curve. Therefore, there is a problem that the changes of frequency tolerance due to temperature changes become large.
The present invention is devised in order to solve the above problem, and is intended to provide a piezoelectric resonator element, a piezoelectric device in which the changes of frequency tolerance in response to temperature changes is reduced
so as to obtain an excellent temperature characteristic, a method of manufacturing them, a cellular phone device utilizing a piezoelectric device, and electronic equipment utilizing a piezoelectric device.
According to a first aspect of the invention, the above aim is achieved by a piezoelectric resonator element comprising: a base portion; and a plurality of resonating arms extending from the base portion parallel to the base portion, wherein: a
notch part is formed in the base portion, and a groove part is formed on a front surface and a back surface of the resonating arms; an electrode for driving is provided at least in the groove part of the resonating arms; and the electrode for driving has
a lower layer and an electrode layer formed on the lower layer, and the thickness t of the lower layer is in the range 0.07 micrometers<t<0.3 micrometers.
If the thickness t of the lower layer is 0.07 micrometers or less, in the working temperature range in the view of practical use, the changes of frequency tolerance in response to temperature changes become large. Moreover, if the thickness t of
the lower layer is 0.3 micrometers or more, side etching by an etchant for the lower layer is intensely caused when forming an electrode pattern by etching, so that the patterning of electrodes with high accuracy becomes impossible.
Thus, since the thickness t of the lower layer is in the above range, the second order coefficient of the temperature characteristic curve is decreased considerably so that a flat part in the temperature characteristic is obtained. Therefore,
the changes of frequency tolerance due to temperature changes can be reduced. Because the thickness t of the lower layer is large as described above, by forming electrodes for driving, stress is caused in the forming portion so as to affect the
oscillation characteristic, and thus the temperature characteristic is improved.
According to the configuration of the third aspect, the thickness t of the lower layer is preferably in the range 0.07 micrometers<t<0.15 micrometers. If the thickness t of the lower layer is 0.07 micrometers or less, in the working
temperature range in the view of practical use, the changes of frequency tolerance in response to temperature changes become large. Furthermore, if the thickness t of the lower layer is 0.15 micrometers or more, side etching against the lower layer is
easily caused when forming an electrode pattern by etching, and thus the degree of side etching may surpass the practical use level in which the patterning of the lower layer when etching is carried out sharply.
According to the configuration of the fourth aspect, the thickness t of the lower layer is most preferably in the range 0.09 micrometers<t<0.11 micrometers. If the thickness t of the lower layer is 0.09 micrometers or less, frequency
fluctuation may be slightly caused in the range of practical use temperatures. Furthermore, if the thickness t of the lower layer is 0.11 micrometers or more, side etching against the lower layer is easily caused when forming an electrode pattern by
etching, and thus it may become hard to form the sharp pattern of the lower layer when etching.
According to a fifth aspect of the invention, the above aim is achieved by a piezoelectric device comprising: a piezoelectric resonator element contained in a package, wherein: the piezoelectric resonator element comprises a base portion and a
plurality of resonating arms extending from the base portion parallel to the base portion; a notch part is formed in the base portion, and a groove part is formed on a front surface and a back surface of the resonating arms; an electrode for driving is
provided at least in the groove part of the resonating arms; and the electrode for driving has a lower layer and an electrode layer formed on the lower layer, and the thickness t of the lower layer is in the range 0.07 micrometers<t<0.3
According to a sixth aspect of the invention, the above aim is achieved by a method of manufacturing a piezoelectric resonator element including a base portion, a plurality of resonating arms extending from the base portion parallel to the base
portion, a notch part in the base portion, a groove part on a front surface and a back surface of the resonating arms, and an electrode for driving provided at least in the groove part, the method comprising: an outer shape etching step for etching a
substrate composed of a piezoelectric material so as to form an outer shape; an electrode forming step for, after forming of the outer shape, forming the electrode for driving that has a lower layer and an electrode layer at least in the groove part of
the resonating arms, wherein, in the electrode forming step, the lower layer is formed so that the thickness t of the lower layer is in the range 0.07 micrometers<t<0.3 micrometers.
According to a seventh aspect of the invention, the above aim is achieved by a method of manufacturing a piezoelectric device containing, in a package, a piezoelectric resonator element that includes a base portion, a plurality of resonating arms
extending from the base portion parallel to the base portion, a notch part in the base portion, a groove part on a front surface and a back surface of the resonating arms, and an electrode for driving provided at least in the groove part, the method
comprising: an outer shape etching step for etching a substrate composed of a piezoelectric material so as to form an outer shape; an electrode forming step for, after forming of the outer shape, forming the electrode for driving that has a lower layer
and an electrode layer at least in the groove part of the resonating arms, wherein, in the electrode forming step, the lower layer is formed so that the thickness t of the lower layer is in the range 0.07 micrometers<t<0.3 micrometers.
According to an eighth aspect of the invention, the above aim is achieved by a cellular phone device obtaining a clock signal for control by using a piezoelectric device, comprising: a piezoelectric resonator element contained in a package of the
piezoelectric device, wherein: the piezoelectric resonator element comprises a base portion and a plurality of resonating arms extending from the base portion parallel to the base portion; a notch part is formed in the base portion, and a groove part is
formed on a front surface and a back surface of the resonating arms; an electrode for driving is provided at least in the groove part of the resonating arms; and the electrode for driving has a lower layer and an electrode layer formed on the lower
layer, and the thickness t of the lower layer is in the range 0.07 micrometers<t<0.3 micrometers.
According to a ninth aspect of the invention, the above aim is achieved by electronic equipment obtaining a clock signal for control by using a piezoelectric device, comprising: a piezoelectric resonator element contained in a package of the
oscillation characteristic, and thus the temperature characteristic is improved. BRIEF DESCRIPTION OF THE DRAWINGS
Referring to FIGS. 1 and 2, in a piezoelectric device 30, an example in which a crystal resonator is constituted is shown. The piezoelectric device 30 contains a piezoelectric resonator element 32 in a package 36. The package 36 is formed by
stacking a plurality of substrates formed by shaping ceramic green sheets composed of aluminum oxide as an insulating material, and then sintering it, for example. A given hole is formed inside each of the plurality of substrates in order to form a
given inner space S2 inside when stacked.
Near the left end part in the diagram of the inner space S2 of the package 36, on the second stacked substrate 64, which is exposed to the inner space S2 and constitutes the inner bottom part, the electrode portions 31 and 31 formed by
implementing nickel-plating or gold-plating for a tungsten metalized portion are provided, for example.
These electrode portions 31 and 31 are coupled to the outside so as to provide a driving voltage. Conductive adhesives 43 and 43 are applied onto the electrode portions 31 and 31, and a base portion 51 of the piezoelectric resonator element 32
is disposed on the conductive adhesives 43 and 43. Then, the conductive adhesives 43 and 43 are cured. As the conductive adhesives 43 and 43, an adhesive in which conductive particles such as silver fine particles are included in a synthetic resin
agent as an adhesive component exerting adhesiveness can be used, and a silicone, epoxy, polyimide conductive adhesive or the like can be utilized.
The piezoelectric resonator element 32 shown in FIGS. 1 and 2 is formed by etching a quartz crystal, for example, as a piezoelectric material through manufacturing processes to be described later. In the present embodiment, the piezoelectric
resonator element 32 is formed into the shape shown by a schematic perspective view of FIG. 3 particularly in order to obtain required performance with a small form.
The piezoelectric resonator element 32 of FIG. 3 comprises the base portion 51 fixed to the package 36 shown in FIGS. 1 and 2, and a pair of resonating arms 34 and 35 that extend from the base portion 51 as a base end toward the left in the
drawing parallel to the Y direction in a manner of being bifurcated. As the piezoelectric resonator element 32, a so-called tuning fork type piezoelectric resonator element, whose entire shape is like a tuning fork, is utilized. The pair of resonating
arms 34 and 35 is an example of a plurality of resonating arms.
In each of the resonating arms 34 and 35 of the piezoelectric resonator element 32 shown in FIG. 3, long bottomed grooves 56 and 57 extending along the length direction (Y-direction) are formed. The grooves 56 and 57 are formed on both sides of
the front and back surfaces of the resonating arms 34 and 35, as shown in FIG. 4, which is an end surface view cut along C-C line of FIG. 3. The resonating arms 34 and 35 have a substantially H-shaped section.
Referring to FIG. 3, near both ends in the width direction at the end part (right end part in FIG. 3) of the base portion 51 of the piezoelectric resonator element 32, extraction electrodes 52 and 53 are formed. The extraction electrodes 52 and
53 are also formed on the back surface (not shown) of the base portion 51 of the piezoelectric resonator element 32 similarly.
These extraction electrodes 52 and 53 are portions connected to the electrode portions 31 and 31 on the package side shown in FIG. 1 with the conductive adhesives 43 and 43 as described above. The extraction electrodes 52 and 53 are electrically
coupled to excitation electrodes (electrodes for driving) 54 and 55 provided in the grooves 56 and 57 of the resonating arms 34 and 35 as shown in the drawing.
The excitation electrodes 54 and 55 are also formed on both side surfaces of the resonating arms 34 and 35 as shown in FIG. 4. For example, with respect to the resonating arm 34, the polarity of the excitation electrode 54 in the groove 57 and
that of the excitation electrode 55 on the side surface part are different from each other. With respect to the resonating arm 35, the polarity of the excitation electrode 55 in the groove 56 and that of the excitation electrode 54 on the side surface
part are different from each other.
As is apparent from FIGS. 3 and 4, the polarities of side electrode portions 54a and 55a formed on the inner side surfaces of the resonating arms 34 and 35 that face each other are different from each other.
Groove width E of the grooves 56 and 57 in FIG. 3 is equal to or greater than 40% of the width W of the resonating arms 35 and 34. Groove depth G of the grooves 56 and 57 is equal to or greater than 30% and less than 50% with respect to the
depth D of the resonating arms 34 and 35. That the groove width E is preferably equal to or greater than 40% of the width W of the resonating arm is a condition for reducing the rigidity of the resonating arms 34 and 35.
That the groove depth G is preferably equal to or greater than 30% and less than 50% of the depth D of the resonating arms 34 and 35 is a condition for reducing the rigidity of the resonating arms 34 and 35. If the groove depth G is 50% or more,
the groove on the front surface side and the groove on the back surface side lead to each other.
As described above, the notch parts 100 and 100 shown in FIG. 3 are provided in one end part and the other end part of the base portion 51. It has been known that the temperature characteristic curve becomes straight instead of becoming a
quadratic curve if the notch parts 100 and 100 are not provided in the base portion 51, and the existence of the notch part 100 prevents the temperature characteristic curve from becoming straight.
As the reason for this, it has been considered that, if there is no notch part 100, on the part in which the base portion 51 is mounted above the electrode portion 31 by using the conductive adhesive 43 as shown in FIG. 2, stress affects the
resonating arms 35 and 34 so as to have an influence on the oscillation mode (oscillation characteristic).
As shown in FIG. 2, around substantially the center of the bottom surface of the package 36, successive through holes 37a and 37b are formed in two stacked substrates constituting the package 36, and thereby a through hole 37 opened outward is
formed. Of two through holes constituting the through hole 37, compared to the first hole 37b opened to the inside of the package, the outside through hole 37a, which is the second hole, has the larger inside diameter. Thus, the through hole 37 is a
stepped opening having a downward step part 62 in FIG. 2. On the surface of the step part 62, a metal-covered portion is preferably provided.
As a metal sealant 38 provided in the through hole 37, for example, a sealant not including lead is preferably selected. For example, it is selected from silver solder, Au/Sn alloy, Au/Ge alloy, and so forth. Corresponding to this, on the
metal-covered part of surface of the stepped part 62, nickel-plating or gold-plating is preferably formed on a tungsten metalized portion.
For the opened upper end of the package 36, a lid 39 is bonded with a sealant 33 so as to carry out sealing. The lid 39 is preferably formed of a material that transmits light, particularly thin plate glass. This is because, after the lid 39 is
sealingly fixed to the package 36, a metal-covered portion to be described later of the piezoelectric resonator element 32 is irradiated with laser light L2 from the outside so as to control the frequency by a mass reduction method as shown in FIG. 2.
Furthermore, in FIG. 2, by removing part of inside of the second substrate 64, a concave part 42 is formed. Thus, even if the tip of the piezoelectric resonator element 32 is displaced toward the arrowhead D1 direction when an external impact is
given to the piezoelectric device 30, the tip of the piezoelectric resonator element 32 is prevented from colliding with the inside bottom part of the package 36 and being broken, effectively.
FIG. 4 shows a structural example of an end surface along C-C line of the piezoelectric resonator element 32 shown in FIG. 3. Namely, the end surface of the resonating arms 34 and 35 shown in FIG. 4 is on a plane formed by the X-direction and
Z-direction in FIG. 3.
The excitation electrodes 54 and 55 are a stacked structure of a lower layer 75A and an electrode layer 75B. The lower layer 75A is a Cr layer for example. The electrode layer 75B is an Au layer. The lower layer 75A may be a Ni layer or a Ti
film instead of a Cr layer. The electrode layer 75B is not limited to an Au layer but may be an Ag layer.
The lower layer 75A of the excitation electrodes 54 and 55 shown in FIG. 4 is formed directly on the surface of the resonating arms 35 and 34. The electrode layer 75B is formed in a manner of being stacked on the lower layer 75A. Between the
excitation electrode 54 and the other excitation electrode 55 of the resonating arm 34 shown in FIG. 4, a distance 180 for preventing a short-circuit is formed. Similarly, also between the excitation electrode 55 and the other excitation electrode 54 of
the resonating arm 35, the distance 180 for preventing short-circuit is formed.
An oxide film such as SiO.sub.2 is preferably provided around the distance 180 for preventing short-circuit, and thereby a short-circuit between the excitation electrodes 54 and 55 can surely be avoided. In the resonating arm 34, the excitation
electrode 54 is formed on the groove 57 side, while the excitation electrode 55 is formed as the electrode on the side surface side. Similarly, in the resonating arm 35, the excitation electrode 55 is formed on the groove 56 side, while the excitation
electrode 54 is formed as the electrode on the side surface side.
In the pair of resonating arms 34 and 35 shown in FIG. 4, electric fields are indicated by using arrowheads. When driving voltage is applied to the excitation electrodes 54 and 55, electric fields exemplified by arrowheads are caused in the
resonating arms 34 and 35.
The present inventors have found a phenomenon in which the second order coefficient of the temperature characteristic becomes smaller as the thickness of the lower layer 75A, of the layered structure of the excitation electrodes 54 and 55 shown
in FIG. 4, is increased.
Referring to FIG. 5, as the thickness of Cr, which is the lower layer, is increased, the value of second order temperature coefficient becomes smaller regardless of the thickness of the electrode layer (Au layer). Namely, the research in the
present invention has revealed that the second order coefficient of temperature characteristic becomes smaller while advancing along the T-direction in FIG. 5, namely, as the thickness of chromium of the lower layer is increased.
In FIG. 6, examples of a tuning fork type piezoelectric resonator element of the embodiment of the present invention and a conventional one are shown. The conventional tuning fork type piezoelectric resonator element indicates a quadratic
temperature characteristic curve 400 that has a turnover temperature and is upwardly convex. The thickness t1 of chromium that is a lower layer in a conventional usual tuning fork type piezoelectric resonator element is in the range 300
angstrom<t1<700 angstrom. In the case of the temperature characteristic curve 400 shown in FIG. 6, the thickness t1 of chromium was 700 angstrom.
A temperature characteristic curve 500 from the piezoelectric resonator element of the embodiment of the present invention shown in FIG. 6 does not become a quadratic temperature characteristic curve, which is symmetrical, but includes a
substantially flat part 550. The temperature characteristic curve 500 of the embodiment of the present invention became not a quadratic curve but a cubic curve. The temperature characteristic curve 500 was obtained when the thickness t of chromium was
900 angstrom. The flat part 550 in the temperature characteristic curve 500 of the embodiment of the present invention is in the temperature range from -20 degrees centigrade to 50 degrees centigrade, for example.
By obtaining the temperature characteristic curve 500 of the embodiment of the present invention that includes such a flat part 550, an accurate temperature characteristic curve in which the changes of frequency tolerance due to temperature
changes are small can be obtained.
As shown in FIG. 5, for example, the value of the second order temperature coefficient when the film thickness of chromium of the lower layer is 900 angstrom (0.09 micrometers) for example, is substantially half as compared to the case in which
the thickness of chromium is 300 angstrom.
If the thickness t of the lower layer is 0.07 micrometers or less, in the working temperature range in the view of practical use, the changes of frequency tolerance in response to temperature changes become large. Furthermore, if the thickness t
of the lower layer is 0.15 micrometers or more, side etching against the lower layer is easily caused when forming an electrode pattern by etching, and thus the degree of side etching may surpass the practical use level in which the patterning of the
lower layer when etching is carried out sharply.
If the thickness t of the lower layer is 0.09 micrometers or less, frequency fluctuation may be caused slightly in the range of practical use temperatures. Furthermore, if the thickness t of the lower layer is 0.11 micrometers or more, side
etching against the lower layer is easily caused when forming an electrode pattern by etching, and thus it may become hard to form the sharp pattern of the lower layer when etching.
In an AT piezoelectric resonator element, among the structures of an excitation electrode, particularly the thickness of the lower layer and so forth has a significant effect. Meanwhile, in the tuning fork type piezoelectric resonator element of
the present invention, the excitation electrode may not exist in an extreme case. It has not been considered that the thickness of the lower layer of the excitation electrode has an effect on the temperature characteristic curve of a piezoelectric
resonator element.
As shown in FIG. 2, the base portion 51 of the piezoelectric resonator element is mounted with the conductive adhesive 43 such as Si-based Ag paste for example. Stress caused by this mounting seems to also affect the oscillation mode of the
piezoelectric resonator element so as to affect the temperature characteristic. If the temperature moves toward the high temperature side or the low temperature side, the effect of stress by the conductive adhesive becomes significant. This seems to
affect the temperature characteristic curve on the low temperature side. Even if the same Si-based conductive adhesive is used, the difference in the second order coefficient of the temperature characteristic curve is caused.
Since the notch parts 100 and 100 are formed in the base portion 51 as shown in FIG. 3, the crystal impedance (CI) value varies. It has been known that, since the notch part 100 is formed in the base portion 51, the existence of the notch part
allows the temperature characteristic curve to become not straight but a quadratic curve so as to prevent the temperature characteristic curve from becoming straight. As the reason for this, it is considered that, if the notch part does not exist,
stress of the mounted part affects the resonating arm so as to affect the oscillation mode.
The grooves 56 and 57 are formed in the resonating arms 34 and 35, and therefore the rigidity of the resonating arms 34 and 35 is reduced. Thus, the temperature characteristic curve 500 as shown in FIG. 6 is obtained. Since the groove depth G
shown in FIG. 3 is set to be equal to or greater than 30% and less than 50% of the thickness of the resonating arm, the rigidity of the resonating arm is reduced so that the temperature characteristic curve 500 as shown in FIG. 6 can be obtained. The
groove width E shown in FIG. 3 is set to be equal to or greater than 40% of the width W of the resonating arm. Thus, the rigidity is reduced, and thereby obtaining the temperature characteristic curve 500 shown in FIG. 6.
In the piezoelectric resonator element 32 with a so-called groove as the embodiment of the present invention, the film thickness of the electrode, particularly the thickness of the lower layer is controlled. Thus, the second order coefficient is
considerably reduced in the temperature characteristic curve 500 as shown in FIG. 6 so that the flat part 550 can be obtained. This enables the changes of frequency tolerance due to temperature changes to be reduced, and therefore an accurate
piezoelectric resonator element and piezoelectric device can be obtained.
Also in the Au layer, which is the electrode layer of the excitation electrode, a thinner Au film shows the trend toward a smaller second order coefficient in the temperature characteristic curve although the effect is less significant than that
of chromium layer being the lower layer as shown in FIG. 5.
Moreover, in the piezoelectric resonator element of the present invention, practically, the Au film in the groove forming portion (important portion determining the oscillation mode and characteristic) is removed, and SiO.sub.2 coating (insulator
for preventing short-circuit between electrodes) is implemented therefore.
Next, FIGS. 7 through 10 are process diagrams for explaining one example of a method of manufacturing the piezoelectric resonator element 32 of the present embodiment. Each process of FIGS. 7 through 10 is shown in the order of processes with
respect to a region corresponding to the cut surface of the resonating arms 34 and 35 that is shown with a cut end surface diagram of the part corresponding to FIG. 4.
One example of a method of manufacturing the piezoelectric resonator element 32 will be described with sequentially referring to FIGS. 7A through 7F. Next, one example of a method of manufacturing the piezoelectric device 30 will be described
based on FIG. 11.
Referring to FIG. 7A, a substrate 71 composed of a piezoelectric material whose size is such that a plurality or a number of the piezoelectric resonator elements 32 can be obtained is prepared. The substrate 71 is cut from a piezoelectric
material, for example a single crystal of a quartz crystal so that, when the substrate 71 is processed into the tuning fork type piezoelectric resonator element 32 through the processes, X, Y, and Z-axes shown in FIG. 3 become an electrical axis, a
mechanical axis, and an optical axis, respectively. Also, when the substrate is cut from a single crystal of a quartz crystal, in the orthogonal coordinate system made up of the above X, Y, and Z-axes, the cutting is made with inclining the XY-plane
constituted by X and Y-axes by about -5 degrees or 5 degrees clockwise around the X-axis.
As shown in FIG. 7A, corrosion resistant films 72 are formed on the surfaces (front and back surfaces) of the substrate 71 with methods such as sputtering or vapor deposition. As shown in the drawing, the corrosion resistant films 72 are formed
on both the front and back surfaces of the substrate 71 composed of a quartz crystal, and the corrosion resistant film 72 comprises, for example, a chromium layer as a lower layer and a gold covering layer that is provided thereon.
Then, as shown in FIG. 7B, resist 73 is applied on the entire surface of the corrosion resistant films 72 on the front and back of the substrate 71 (resist applying process). The resist 73 is applied in order to pattern the outer shape. As the
resist 73, for example, ECA-based, or PGMEA-based positive resist can favorably be used.
Then, as shown in FIG. 7C, a mask (not shown) with given pattern width is disposed in order to pattern the outer shape and exposure is implemented. Thereafter, the exposed resist 73 is removed, and then the corrosion resistant films 72 are also
removed in the order Au and Cr with corresponding to the part from which resist is removed.
Then, as shown in FIG. 8G, for the substrate 71 exposed as the part outside the outer shape of the piezoelectric resonator element 32, the outer shape of the piezoelectric resonator element is etched with using a hydrofluoric acid solution as an
etchant, for example (etching process). The time required for the etching process is from 2 to 3 hours, and varies depending on the concentration, kind, temperature, and so forth of the hydrofluoric acid solution. In the embodiment, hydrofluoric acid
and ammonium fluoride are used as the etchant. The volume ratio thereof as the concentration is 1:1, and the temperature thereof is 65.+-.1 degrees centigrade. With these conditions, the etching process is completed in about two and a half hours.
In the embodiment, hydrofluoric acid and ammonium fluoride are used as the etchant. The volume ratio thereof as the concentration is 1:1, and the temperature thereof is 65.+-.1 degrees centigrade. With these conditions, the etching process is
completed in 30-60 minutes.
Next, as shown in FIG. 8J, the resist 74 is removed from the corrosion resistant film 72, and the corrosion resistant film 72 is also removed so as to obtain a state of FIG. 9K. This is the state in which the electrodes of the piezoelectric
resonator element 32 of FIG. 3 are not formed.
Subsequently, as shown in FIG. 9L, metal films 75 for forming electrodes on the entire surface are formed with methods such as vapor deposition or sputtering. The metal films 75 are made up of a chromium layer as the lower layer 75A, which is
the same as the corrosion resistant film, and the electrode layer (gold covering layer) 75B provided thereon.
Next, as shown in FIG. 9M, resist 76 is ejected at an angle in which the ejecting orientation intersects the front and back surfaces of the substrate 71 as shown by arrowheads T, so as to be applied. In the embodiment, the resist 76 is so-called
spray resist. The ejecting angle is about 90 degrees with respect to the front and back surfaces of the substrate 71.
As the resist 76, in view of the suitability for the manufacturing process of the present embodiment, a material diluted with a solvent of high volatility and adhering to the substrate 71 in a half-dried state is suitable. Specifically,
ECA-based or PGMEA-based positive resist is used, for example, as a resist solution having the viscosity of about 5-40 cp. The number of ejecting is from 2 to 4 so that the resist thickness becomes from 1 micrometer to 3 micrometers.
In a state where the resist 76 is thus applied as shown in FIG. 9M, masking (not shown) for separating a region on which electrodes are formed (refer to FIG. 3) from the other region, and exposure are implemented as shown in FIG. 10N. Then, the
unnecessary resist 76 is removed so as to expose the metal film 75 to be removed.
Therefore, the piezoelectric resonator element 32 that is completed as shown in FIG. 3 is bonded to the inside of the package 36 by utilizing the conductive adhesive 43 as shown in FIGS. 1 and 2. Thereafter, the lid 39 is joined to the package
36 by using a brazing material (for example, low-melting glass). Then, the package 36 is heated in a vacuum so as to de-gas the package 36 via the through hole 37, and the through hole 37 is vacuum-sealed with the sealant 38. Thus, the piezoelectric
device 30 is completed.
Next, in a step ST111, which is a first step of the forming process for a piezoelectric resonator element, for example, the outer shape of the piezoelectric resonator element is formed by punching a through hole in a quartz crystal wafer or
etching a quartz crystal wafer. Then, the quartz crystal wafer is cut in a rectangle shape in accordance with a given orientation so as to obtain the piezoelectric resonator element 32 shown in FIG. 1. The piezoelectric resonator element 32 is formed
by etching the outer shape thereof through manufacturing processes shown in FIGS. 7, 8 and 9K.
Then, in a step ST112, which is a second step of the forming process, the above described excitation electrodes 54 and 55 and the extraction electrodes 52 and 53 are formed in the piezoelectric resonator element 32 shown in FIG. 3. The
excitation electrodes 54 and 55, and the extraction electrodes 52 and 53 are constituted by stacking the lower layer (lower metal layer) formed of chromium and so forth, and the electrode layer of silver (Ag) or gold (Au), for example. These electrodes
are sequentially deposited with sputtering and are formed by a photo process using a mask. For example, the excitation electrodes 54 and 55 are formed through manufacturing processes shown in FIG. 9L, 9M and 10.
Subsequently, in a step ST113 of FIG. 11, driving voltage is applied to the piezoelectric resonator element 32 so as to measure the frequency. Then, by adding an electrode film and trimming a part thereof with laser light and so forth, the
coarse adjustment of the frequency is carried out.
Referring to the drawing, a microphone 308 receiving audio of a transmitter, and a speaker 309 for converting a received matter into an audio output are included. In addition, a controller (CPU) 301 made up of integrated circuits and so forth is
included as a control unit connected to a modulation unit and demodulation unit of a sent and received signal.
The controller 301, in addition to modulation and demodulation of sent and received signals, controls an information input-output unit 302 made up of an LCD as an image display unit, operation keys for inputting information and so forth. The
controller 301 also controls information storage means (memory) 303 including a random access memory (RAM), a read only memory (ROM) and so forth. Therefore, the piezoelectric device 30 is attached to the controller 301, and thus the output frequency is
utilized as a clock signal matched to the controlling by a given divider (not shown) and so forth incorporated in the controller 301. The piezoelectric device 30 attached to the controller 301 may be, instead of a single piece of the piezoelectric
device 30, an oscillator obtained by combining the piezoelectric device 30 and a given divider and so forth.
In this manner, the piezoelectric device 30 according to the above embodiment of the present invention or other modifications of a piezoelectric device is applicable to electronic equipment such as the digital cellular phone device 300 including
a control unit. In this case, since there is a flat part in the temperature characteristic curve, the changes of frequency tolerance due to temperature changes are reduced so that the operation accuracy of electronic equipment is improved.
FIG. 13 shows another sectional structure example along C-C line in the resonating arm of the piezoelectric resonator element of FIG. 3. In the sectional structure example of the resonating arms 34 and 35 of FIG. 13, the resonating arms 34 and
35 have a substantially H-shape. Grooves 757 are formed on both front and back surface sides of one resonating arm 34. Grooves 756 are formed on both front and back surface sides of the other resonating arm 35.
A center line CL1 of the groove 757 of the resonating arm 34 and a center line CL2 of the groove 757 on the back surface side are positioned in such a manner that the directions thereof are offset relative to each other. Namely, the grooves 757
and 757 are offset relative to each other in the X-direction (horizontal direction). Thus, on the front surface side of the resonating arm 34, width W3 is larger than width W1. On the back surface side, width W2 is larger than width W4.
Similarly, a center line CL3 of the groove 756 on the front surface side of the resonating arm 35 and a center line CL4 of the groove 756 on the back surface side are offset, relative to each other, in the horizontal direction, which is the
If the grooves of the resonating arms 34 and 35 are disposed as shown in FIG. 13, when the resonating arms 34 and 35 oscillate in the horizontal direction, which is the X-direction, the vibration component in the perpendicular direction, which is
the Z-direction, is caused in addition to the vibration in the horizontal direction. As a result, the vibration in the M direction, which is an oblique direction, is caused. This is because the difference in the magnitude of the electric field between
the front surface side and the back surface side is caused with respect to the X-direction, which is the horizontal direction. In order to cause flexural vibration in the horizontal direction, the mechanical value of expansion and contraction of the
tuning fork arm portion that are caused by the electric field needs to be in equilibrium between the front surface side and the back surface side. However, if the magnitude of an electric field is different between the front surface side and the back
surface side as shown in FIG. 13, the mechanical value of expansion and contraction of the tuning fork arm portion is disrupted, and therefore the vibration component in the Z-direction is added to the flexural vibration in the X-direction so as to
generate the vibration in the M-direction.
In this manner, by making the grooves on the front and back surface sides of the resonating arm be offset relative to each other so as to make the positions of the grooves on the front and back surface sides be asymmetric, the temperature
characteristic curve with small second order temperature coefficient that has a flat part as shown in FIG. 6 can be obtained so that the temperature characteristic becomes favorable.
Furthermore, this invention can be applied to all piezoelectric resonator elements and piezoelectric devices utilizing a piezoelectric resonator element regardless of the kinds such as a crystal resonator, a crystal oscillator, a gyro sensor, and
an angle sensor, if they are constituted by containing a piezoelectric resonator element in a package or a box-manner lid.
In the above embodiment, a box-shaped body made up of ceramic is utilized as a package. However, the present invention is not limited to such a conformation but also applies to equivalent devices including any package or case if the devices are
constituted by containing a piezoelectric resonator element as a package such as a metal cylinder.