Surface acoustic wave resonator, surface acoustic wave resonator unit, surface mounting type surface acoustic wave resonator unit

A surface acoustic wave resonator unit using surface acoustic wave, in which a surface acoustic wave resonator formed by disposing an IDT and reflectors on a piezoelectric member thereof is mounted by a cantilever method so that a surface acoustic wave resonator unit exhibiting very stable resonance frequency, a low resonance resistance and a large Q-value is realized. By accommodating the surface acoustic wave resonator in a housing in a vacuum state, the Q-value can be enlarged. By anodic-oxidizing the electrodes forming the IDT, a thick oxide film can be formed, the oxide film enabling the electrodes to be protected from problems, such as short circuit taking due to foreign matters, such as dust, with the characteristics maintained. If the high performance surface acoustic wave resonator unit is molded together with a lead frame by resin, a surface acoustic wave device, that can be mounted on the surface, and that exhibits excellent reliability and high quality, can be provided.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a surface acoustic wave resonator unit 
suitable to form a high-frequency oscillation circuit and an apparatus 
that exhibit excellent stability. 
2. Description of Related Art 
A technique for machining small articles, such as integrated circuits, 
causes fine electrodes to be formed on the surface of a piezoelectric 
member, thus enabling surface acoustic waves (SAW) to be electrically 
driven or detected. By using this technique, high frequency waves from 
about 100 MHz to the GHz level have been stably obtained. A surface 
acoustic wave device using the surface acoustic waves has been used to 
form a high-frequency filter (a surface acoustic wave filter) or a surface 
acoustic wave resonator unit (a SAW resonator unit) for forming an 
oscillation circuit. 
FIG. 27 shows a known surface acoustic wave device. The device 90 has a 
surface acoustic wave resonator 92 that is, by an adhesive agent 93, 
secured to a supporting metal portion 91 and sealed in a case 96, by 
resistance welding or the like, performed in a nitrogen atmosphere. Leads 
94 for establishing the electrical connection with the surface acoustic 
wave resonator 92, penetrate an insulating portion in the metal portion 
91, which is a sealing glass 97. The leads 94 are electrically connected 
to electrodes disposed on the surface acoustic wave device by bonding 
wires 95. 
The known surface acoustic wave device 90 shown in FIG. 28 is a so-called 
entire-surface adhesive type surface acoustic wave device that has: a base 
101 made of ceramic or the like; and a surface acoustic wave resonator 92 
attached to the base 101 by an adhesive agent 93. The base 101 has 
electrodes metallized thereon for establishing the electrical connection 
with the surface acoustic wave resonator 92 so that the electrodes on the 
base 101 and the electrodes on the surface acoustic wave resonator 92 are 
electrically connected to one another by bonding wires 95 similarly to the 
foregoing structure. Furthermore, a cap 102 is, by an adhesive agent or 
the like, attached above the base 101 in an atmosphere of nitrogen. The 
cap 102 is sometimes attached by brazing, welding or the like. 
FIG. 29 shows a surface acoustic wave resonator 110 to be accommodated in 
the foregoing surface acoustic wave device. The surface acoustic wave 
resonator 110 is formed by using a piezoelectric member 111, such as a 
quartz crystal member. The piezoelectric member 111 is obtained by cutting 
a flat piezoelectric substrate to a predetermined size and dimension, the 
piezoelectric member 111 being usually formed into a rectangular shape as 
later described by cutting because an area for disposing a reflector can 
be obtained, a satisfactory mass productivity can be realized, and 
machining can easily be performed. An interdigital transducer (IDT) 112 is 
formed in a substantially central portion of either side (the main 
surface) of the piezoelectric member 111 by using a thin film electrodes 
made of aluminum material or the like. Furthermore, reflectors 113, each 
of which is made of a thin film of aluminum material or the like similar 
to the electrodes, are disposed on the two sides of the IDT 112 in the 
lengthwise direction of the same, that is, on the two sides of the longer 
sides of the piezoelectric member 111. Along the lengthwise directional 
edges of the piezoelectric member 111, connection lands 114 are connected 
to the IDT 112 for conducting electric power are formed by using the same 
material as that of the IDT 112. Therefore, the electrical connection can 
be established by performing wire-bonding to the connection lands 114. 
To form a high-frequency-range and stable oscillator by using the surface 
acoustic wave device, a surface acoustic wave device having a large 
Q-value (sharpness of resonance) and a low resonance resistance and, 
therefore capable of resonating a stable resonance frequency, is required. 
A conventional surface acoustic wave device of the foregoing type 
comprises a surface acoustic wave resonator brought into close contact 
with a support substrate by an adhesive agent. Therefore, the difference 
in the coefficient of thermal expansion between the surface acoustic wave 
resonator and a portion for supporting the same, contraction of the 
adhesive agent, deformation of the supporting portion and the like cause 
the surface acoustic wave resonator to be distorted, as a result of which 
the resonance frequency to be made instable or the resonance resistance, 
is increased. Since many of these surface acoustic wave devices have been 
used as surface acoustic wave filters, considerably large Q-values have 
not been required. However, a surface acoustic wave resonator that forms 
an oscillator must be capable of generating resonance frequencies more 
stably than that required for the filter. Therefore, it is important to 
use a surface acoustic wave resonator unit having a low resonance 
resistance and a large Q-value in order to realize a stable oscillator. 
In order to obtain a reliable oscillator, the device for forming the same 
must have excellent reliability. In a surface acoustic wave device, 
adhesion of foreign matter, such as dust, to the surface, on which the IDT 
has been formed, causes a problem to arise in that the frequency is 
changed or stable resonance characteristics cannot be obtained. If the 
connection between the IDT and the lead becomes defective, stable 
oscillation characteristics cannot, of course, be obtained, and an 
increase in the connection resistance occurring due to the defective 
connection causes the frequency to be changed and the Q-value to be 
lowered. Accordingly, it is also important to provide a reliable device by 
eliminating influence of foreign matter and preventing a defective state 
of connection while preventing influence of distortion on the surface of 
the surface acoustic wave resonator. 
SUMMARY OF THE INVENTION 
In the present invention, influence of a supporting member or an adhesive 
agent on a surface acoustic wave resonator is prevented by supporting only 
an end of the surface acoustic wave resonator. That is, only either end of 
a surface acoustic wave resonator in the lengthwise direction of the 
surface acoustic wave resonator having an interdigital transducer formed 
in a substantially central portion of the surface thereof, that is cut 
into a substantially rectangular shape, is connected to the supporting 
member so that portions, which are affected by the supporting member, are 
decreased. Furthermore, the surface acoustic wave resonator floats from a 
housing, such as a case. As a result, the surface acoustic wave resonator 
is free from external stress and influence, due to distortion, can be 
eliminated so that a surface acoustic wave resonator unit having a very 
stable resonance frequency and exhibiting excellent aging characteristics 
is obtained. That is, mounting of a portion more adjacent to the end than 
the reflectors (hereinafter called "mounting by a cantilever method") 
enables influence of distortion upon the surface acoustic wave resonator 
to be eliminated satisfactorily. 
As the structure of the housing for mounting the surface acoustic wave 
resonator by the cantilever method to form a surface acoustic wave 
resonator unit, a metal case formed into a cylindrical shape; a round can 
shape; or a box-like shape and sealed by a supporting member may be 
employed. The "cylindrical shape" includes a structure having a circular 
cross sectional shape and that having an oval cross sectional shape. If a 
cylindrical case is used, the surface acoustic wave resonator is mounted 
substantially in parallel to a direction in which the case is attached. If 
a round can or box-like case is used, it is mounted substantially 
perpendicular to the direction in which the case is attached. The 
electrical conduction with the surface acoustic wave resonator, thus 
sealed in the housing, can be maintained by a plurality of leads of the 
supporting member. The box-like ceramic case may be used to perform 
sealing. In this case, a deducing pattern may be used to maintain the 
electrical connection. 
The present invention results in a fact to be found that a Q-value of the 
surface acoustic wave resonator unit, which is a device using surface 
acoustic wave of a piezoelectric member thereof, is changed due to the 
atmosphere in the housing. It was found that making of the atmosphere in 
the housing to be substantially a vacuum will enable a surface acoustic 
wave resonator unit exhibiting a large Q-value to be obtained. 
When the surface acoustic wave resonator is sealed in the housing, inclined 
mounting such that a central axis of the housing and the surface of a 
surface acoustic wave resonator intersect enables space in the housing to 
be used effectively. Thus, problems, such as undesirable contact between 
the housing and the surface acoustic wave resonator, can be prevented. 
Therefore, the portion in which the leads are in contact with the surface 
acoustic wave resonator may be inclined with respect to the central axis 
of the housing. 
To mount the surface acoustic wave resonator by the cantilever method, the 
piezoelectric member may be supported through a non-conductive adhesive 
agent. As an alternative to this, the supporting may be performed with 
conduction established in such a manner that leads are used to establish 
the connection with connection lands formed on the surface acoustic wave 
resonator. The foregoing methods may be employed simultaneously or, either 
of the two methods may be employed as the main method and the other method 
may be employed as a second method. 
When the leads are connected to the connection lands, it is desirable to 
provide flat connection ends for the leads to maintain an area for 
conduction or to branch the leading end of the connection end into at 
least two sections. Since the connection lands usually comprise aluminum 
based electrodes, connection by means of a usual soldering method cannot 
easily be established. Since a very thin oxide film is naturally formed on 
the surface of the electrode, stable electrical conduction cannot easily 
be maintained using a usual conductive adhesive agent. Therefore, a 
conductive adhesive agent that contains an oxidation inhibitor mixed 
thereto is effective when used. To prevent influence of the oxide film on 
the electrode, it is desirable to form at least one scratch on the 
connection land after the conductive adhesive agent has been applied or to 
form a bump on the connection land. 
The surface acoustic wave device easily raises a problem due to foreign 
matter such as dust in the housing. By subjecting at least either of a 
pair of electrodes forming the interdigital transducer to an anodic 
oxidation process to form an oxide film having at least a thickness of 280 
.ANG., the foregoing problem can be prevented. If either of the pair of 
electrodes forming the interdigital transducer is subjected to an anodic 
oxidation process, the resonance frequency in a wafer state can be 
measured. Furthermore, a resonance frequency of the surface acoustic wave 
resonator can be adjusted by the anodic oxidation process. 
By integrally molding a surface acoustic wave resonator unit and a lead 
frame electrically connected to the leads by using resin, a surface 
mounting type device suitable to be mounted on the surface can be 
provided. In a case where the housing is made of metal, molding of a lead 
frame electrically connected to the housing and grounding of the housing 
enable a surface mounting type surface acoustic wave device capable of 
withstanding noise to be realized.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 shows a surface acoustic wave resonator according to the present 
invention. The surface acoustic wave resonator 1 is formed into a base (a 
chip) 2 formed by cutting a piezoelectric member made of quartz crystal, 
lithium tantalate or lithium niobate into a rectangular shape. The 
piezoelectric chip 2 according to this embodiment is, by cutting, formed 
into a flat rectangular shape that has, in the central portion of a 
surface (a main surface) 3 thereof, an IDT 5 consisting of a pair of 
electrodes 4a and 4b. Furthermore, reflectors 6a and 6b in the form of a 
lattice are formed on the two sides of the IDT 5 in the lengthwise 
direction of the same. The pair of electrodes 4a and 4b forming the IDT 5 
are allowed to pass through the outside of the reflector 6a, that is, the 
edge of the chip 2, so as to be introduced into an end 2a of the chip 2 so 
that connection lands 7a and 7b each having a relatively large area are 
formed. The electrodes 4, the reflectors 6 and the connection lands 7 are 
usually made of an electrically conductive material, such as gold, 
aluminum, or aluminum-copper alloy. In view of manufacturing easiness and 
cost reduction, aluminum based material has been most widely employed. 
Mounting a Surface Acoustic Wave Resonator 
FIG. 2(a) shows change in the resonance frequency (Fr) and the quantity of 
deformation of the chip 2 attained when the end 2a of the chip 2 of a 145 
MHz Rayleigh wave type surface acoustic wave resonator 1 (having a length 
of 6.5 mm, a width of 1.6 mm and a thickness of 0.4 mm) formed by using ST 
cut quartz crystal was supported. Furthermore, FIG. 2(b) shows change in 
the resonance frequency (Fr) and the quantity of deformation of the chip 2 
attained when an entire reverse surface 9 opposing the main surface 3 of 
the chip 2 was supported by using a known adhesive agent. The quantity of 
deformation of the chip 2 is, as shown in FIG. 2(b), indicated by a 
maximum quantity of deformation of the main surface 3 in order to reflect 
distortion and warp of the chip 2. 
As can be understood from FIG. 2, in a case where only the end 2a of the 
chip 2 is supported, that is, in a so-called cantilever mounting method is 
employed, the frequency is not substantially changed, and also the 
quantity of deformation of the chip is very small. On the contrary, in the 
case where the reverse surface 9 of the chip is bonded, that is, in the 
case of a so-called entire-surface bonding mounting method, the change in 
the frequency is 100 ppm or larger and also the quantity of deformation of 
the chip is 500 nm or larger, each of which is excessively large. Since 
the surface acoustic wave device obtains its resonance frequency from the 
surface acoustic wave on the main surface, it has been supported by a 
method such that the reverse surface is strongly connected and influence 
on the main surface is expected to be eliminated. However, the foregoing 
has confirmed that the mounting method considerably affects the state of 
the chip and the resonance frequency. The entire-surface bonding mounting 
method, which has been expected to be able to stably secure the 
conventional chip and obtain stable frequency, causes the quantity of the 
deformation of the chip to be enlarged excessively and the resonance 
frequency to be changed excessively. On the contrary, where the chip is 
mounted by the cantilever method the change in the frequency and the 
quantity of deformation of the chip are reduced considerably. Therefore, 
to obtain stable and excellent performance, it is preferable that a 
surface acoustic wave resonator be mounted by the cantilever method. 
FIGS. 3(a) and 3(b) and 4(a) and 4(b) show aging characteristics where the 
foregoing surface acoustic wave resonator is mounted by the cantilever 
method and where the same is mounted by an entire-surface bonding method. 
The foregoing figures show results of a measured .DELTA.Fr of the 
resonance frequency and .DELTA.Rr of the resonance resistance attained in 
a state where surface acoustic wave resonators were mounted by the 
foregoing respective methods, allowed to stand at 85.degree. C. and a 
predetermined time has passed. The surface acoustic wave resonator mounted 
by the cantilever method encounters .DELTA.Fr of the resonance frequency 
by about 10 ppm or smaller after 1000 hours have passed. On the other 
hand, the surface acoustic wave resonator mounted by the entire-surface 
bonding method has a tendency of resulting in a change of about 30 ppm. 
Also, results of the measured .DELTA.Rr of the resonance resistance gather 
in the vicinity of about 0 .OMEGA. in the case of the cantilever mounting 
method; on the other hand the entire-surface bonding mounting method 
results in a tendency of having an increase in the resonance resistance Rr 
of about 1 .OMEGA. to 3 .OMEGA.. The foregoing aging tendency is due to 
hardening of the adhesive agent taking place when the entire-surface 
bonding mounting process is performed and due to a difference in the 
coefficients of thermal expansion from the mounted member. The foregoing 
influences can be eliminated by employing a cantilever mounting method. 
The surface acoustic wave resonator mounted by the cantilever method has 
excellent aging characteristics that are superior to those attainable from 
conventional entire-surface bonding mounting methods. That is, by mounting 
a surface acoustic wave resonator by the cantilever method, a resonator 
having long term stable characteristics can be obtained, and an increase 
in the resonance resistance Rr can be prevented. Thus, a surface acoustic 
wave resonator unit having a large Q-value suitable to a stable oscillator 
can be obtained. 
The surface acoustic wave resonator 1 can be mounted by any of the 
following cantilever methods. FIG. 5 shows a schematic structure of a 
surface acoustic wave resonator unit having a surface acoustic wave 
resonator 1 mounted by the cantilever method by using its leads. The 
surface acoustic wave resonator unit 20 comprises a metal case 21 formed 
into a cylinder having an opening at either end thereof and accommodating 
the surface acoustic wave resonator 1. The opening of the metal case 21 
receives a hermetic terminal 22 so that the surface acoustic wave 
resonator 1 is sealed up in the case 21. The hermetic terminal 22 has a 
glass portion 23 that is provided with a metal ring 24 disposed on the 
outer periphery thereof. Two leads 25 penetrate the glass portion 23. Ends 
25c and 25d of the leads 25 located in the case 21 are connected to 
corresponding connection lands 7a and 7b of the surface acoustic wave 
resonator 1. Thus, the surface acoustic wave resonator 1 is mounted by the 
cantilever method in the case 21 by the hermetic terminal 22 (hereinafter 
called a "plug member" including the leads) through the foregoing leads 
25. 
The leads 25c and 25d are secured to the connection lands 7a and 7b by a 
coupling agent 26. In order to obtain an electrical conduction, the 
coupling agent 26 is made of solder or other electrically conductive 
adhesive agent. It is important to connect the leads 25c and 25d to the 
connection lands 7a and 7b with a low resistance, as will be described 
later in detail. The case 21 and the metal ring 24 of the plug member are 
applied with plug plating 27 and case plating 28 in order to maintain 
airtightness in the case, the foregoing plating serving as a sealing 
member, also as will be described later. 
FIG. 6 shows the surface acoustic wave resonator unit 20 viewed from a 
position on the side portion of the surface acoustic wave resonator 1. The 
surface acoustic wave resonator 1 is connected to the leads 25 in such a 
manner that its main surface 3 is inclined with respect to a central axis 
29 of the case 21 so that the central axis 29 and the surface acoustic 
wave resonator 1 intersect. By mounting the surface acoustic wave 
resonator 1 as described above, the surface acoustic wave resonator 1 can 
be mounted at a substantially central portion of the case 21, even if the 
leads 25 are disposed at the center of the plug member, whereby a 
sufficiently large gap can be maintained from the surface acoustic wave 
resonator 1 and the inner surface 21a of the case 21. By creating this gap 
as described above, contact between the case 21 and the surface acoustic 
wave resonator 1 can be prevented when the surface acoustic wave resonator 
1 is accommodated in the case 21, whereby a factor that makes oscillation 
instable can be eliminated. Furthermore, a problem that the resonator 
comes in contact with the inner surface of the case 21 and thus dust is 
generated can be prevented. 
It is preferable that the angle at which the surface acoustic wave 
resonator 1 is inclined be determined to be in a range from a position, at 
which the surface acoustic wave resonator 1 is in parallel to the central 
axis 29, to a degree at which the other end surface 8d of the chip 2 
having no connection land intersects the central axis 29. Since the end 
25c of the leads 25 is connected by the adhesive agent 26 and therefore, 
the necessity of direct contact with the connection lands can be 
eliminated, the mounting angle can easily be provided. As a matter of 
course, the end 25c of the leads 25 may be inclined to make a 
predetermined angle or the end 25c of the leads 25 may be cut or deformed 
to use the cut surface or the deformed surface to establish the connection 
with the connection lands 7. 
FIG. 7 shows an example in which a non-conductive adhesive agent 30 is used 
to mount the surface acoustic wave resonator 1 on the plug member by the 
cantilever method. Since the leads 25c and 25d are, in the illustrated 
example, connected to the connection lands 7a and 7b using the conductive 
adhesive agent 26, the non-conductive adhesive agent 30 is used to 
reinforce the portion mounted by the cantilever method. The oscillations 
of the surface acoustic waves are generated on the surface of the chip 2, 
and the chip must have a thickness that enables the characteristics of the 
surface acoustic wave resonator 1 to be maintained. The thickness is 
sufficient to be about 10 times the wavelength of the surface acoustic 
wave. If the resonance frequency is low, the chip is thickened, and 
therefore the weight of the surface acoustic wave resonator is enlarged. 
In the foregoing case, it is preferable that both conductive adhesive 
agent 26 and the non-conductive adhesive agent 30 be used to mount the 
surface acoustic wave resonator 1 by the cantilever method with the 
strength enabling the same to withstand impact and vibrations. It is 
preferable that the area for the non-conductive adhesive agent 30 to cover 
the surface acoustic wave resonator 1 be minimized. In consideration of 
the characteristics of the surface acoustic wave resonator, it is 
preferable that the area covers the connection lands 7, that is, so the 
adhesive agent 30 does not reach the reflector 6a adjacent to the end 2a 
at which the chip is mounted by the cantilever method. 
FIGS. 8 and 9(a) and 9(b) show the surface acoustic wave resonator 1 
mounted into a flat-box-like case 21 formed into a substantially oval 
shape. As shown in FIG. 9, two leads 25 penetrate an insulating member 31a 
at an end of a flat base 31 having a substantially oval shape. The leads 
25 have, at leading ends thereof, flat connection ends 25c extending along 
the base 31. On the connection ends 25c, the connection lands 7 of the 
surface acoustic wave resonator 1 are mounted. The leads 25 and the 
connection lands 7 are secured by the conductive adhesive agent 26. 
Furthermore, the end 2a of the surface acoustic wave resonator 1 is 
secured by the non-conductive adhesive agent 30. The above securing method 
enables the surface acoustic wave resonator 1 to be mounted in a thin case 
21 by the cantilever method. The case 21 may, of course, be formed into a 
round can shape or a square box-like shape. 
The surface acoustic wave resonator 1 may be attached in such a manner that 
its main surface 3, having the IDT formed thereon, faces the base 31 in a 
manner contrary to FIGS. 9(a) and 9(b). In the foregoing case, the space 
from the main surface 3 and the base 31 is narrow, whereby foreign matter 
cannot easily be introduced and satisfactory reliability can be obtained. 
By employing the cantilever mounting method, the main surface may be 
caused to face either side. The positions of the connection lands 7 may be 
suitably positioned, except on the main surface 3 having the IDT formed 
thereon. They may be formed on the reverse surface 9, the side surfaces 8a 
and 8c or the side surface 8b shown in FIG. 1. Also where the connection 
lands 7 are formed on the reverse surface 9 or the side surfaces 8a and 
8c, it is preferable that the positions of the connection lands 7 be at 
the end 2a at which the chip is secured, in order to prevent deterioration 
in the characteristics of the surface acoustic wave resonator. It is 
preferable that the connection lands 7 be disposed adjacent to the 
reflector 6a near the end 2a at which the chip 2 is secured, or disposed 
at a position more adjacent to the end 2a at which the chip 2 is secured, 
than the reflector 6a. In particular, it is preferable that the connection 
lands 7 be formed more adjacent to the securing end 2a than the reflector 
6a, similar to the case where they are disposed on the main surface 3. 
Since a conductive pattern must be formed by using a technique, such as 
the diagonal evaporation, the connection lands are formed at positions 
except on the main surface, attention must be paid to prevent defective 
conduction. To prevent defective conduction, it is important to maintain a 
sufficiently large area for fixing the conductive pattern. In view of the 
foregoing, it is preferable that connection lands be formed on the main 
surface. 
FIG. 10(a) and 10(b) shows an example of the surface acoustic wave 
resonator unit 20 having the surface acoustic wave resonator 1 mounted by 
the cantilever method in a ceramic case 32. The ceramic case 32 is formed 
in a box-like shape having wall surfaces on all sides, at least one of the 
wall surfaces having a stepped portion 32a. The stepped portion 32a has, 
on the surface thereof, a pattern 33 extending to the outside of the 
ceramic case 32. By aligning the position of the conductive pattern 33 and 
those of the connection lands 7 of the surface acoustic wave resonator 1 
to one another, the surface acoustic wave resonator 1 can be mounted by 
the cantilever method. When the surface acoustic wave resonator 1 is 
mounted, the connection lands 7 and the conductive pattern 33 are 
connected to one another by the conductive adhesive agent 26 and the chip 
securing end 2a is secured to the stepped portion 32a by the 
non-conductive adhesive agent 30. After the surface acoustic wave 
resonator 1 has been mounted, a cover 34 is put on the ceramic case 32 and 
the case is sealed by seam welding. 
FIG. 11 shows another embodiment in which the surface acoustic wave 
resonator 1 is mounted into the ceramic case 32 by the cantilever method. 
In this example, the securing end 2a of the surface acoustic wave 
resonator 1 floats from a bottom surface 32b of the ceramic case 32 by 
means of a non-conductive adhesive agent or a spacer 35 made of, for 
example, ceramic so as to be secured. Furthermore, a bonding wire 36 
establishes the electrical connection between the surface acoustic wave 
resonator 1 and the conductive pattern 33. 
For the non-conductive adhesive agent for fixing the surface acoustic wave 
resonator 1 when the surface acoustic wave resonator 1 is mounted, it is 
preferable that a thermosetting resin which has a heat resistance capable 
of sufficiently maintaining the strength thereof in the temperature range 
so the surface acoustic wave resonator unit can be operated and that does 
not generate a gas that affects the atmosphere in the case that 
accommodates the surface acoustic wave, be used. Furthermore, it is 
preferable that the resin not drop, to prevent spreading to reach the 
surface acoustic wave resonator and the outer surface of the plug member 
during hardening. In addition, it is preferable that the resin have a low 
stress, to prevent accumulation of stress of the surface acoustic wave 
resonator chip during hardening and the same be hardened at low 
temperatures. As a non-conductive adhesive agent that satisfies the 
foregoing conditions, an epoxy adhesive agent can be employed, which can 
be hardened when it is irradiated with ultraviolet rays or when it is 
heated. 
When the surface acoustic wave resonator is mounted by the cantilever 
method, its overall body, except the secured end thereof, is caused to 
float so that dynamical influences, such as pressure and distortion, and 
thermal influence from the base can be eliminated satisfactorily, as 
compared with the case where conventional entire-surface bonding mounting 
method, is employed. Although influences, such as distortion, upon the 
secured end cannot be prevented, the portions that can be distorted are 
made to be the outsides of the two reflectors interposing the IDT that 
entraps the oscillation energy, so that the influence on the oscillation 
portion can be eliminated. Therefore, the foregoing cantilever mounting 
method enables a surface acoustic wave resonator unit that is free from 
machining distortion to be obtained. Thus, a high quality surface acoustic 
wave device that is not affected by change in the atmosphere can be 
provided. 
Atmosphere In The Housing Accommodating The Resonator 
To mount a surface acoustic wave device without any influence of the 
atmosphere, the surface acoustic wave resonator is accommodated in a 
hollow housing, such as a cylindrical case, a flat case in the form of a 
box or a ceramic case. FIGS. 12 and 13 represent influences of the 
atmosphere in the housing upon the resonator unit. 
FIG. 12 shows a resonance resistance Rr of surface acoustic wave resonator 
units shown in FIG. 7, which comprise an ST-cut Rayleigh wave of 145 MHz 
type surface acoustic wave resonator that is sealed in a vacuum state in a 
cylindrical metal case having an opening at an end thereof, the pressure 
in which is 1.times.10.sup.-5 torr or lower; and a surface acoustic wave 
resonator unit that is sealed under the atmospheric pressure. As can be 
understood from FIG. 12, the resonance resistance Rr can be reduced by 
about 3.OMEGA. to 5.OMEGA. by sealing the surface acoustic wave resonator 
unit under vacuum pressure as compared with the surface acoustic wave 
resonator unit that is sealed under atmospheric pressure. Thus, the 
surface acoustic wave device, which is a device using the surface acoustic 
wave of a piezoelectric member, is affected by the atmosphere surrounding 
the device and that making the atmosphere surrounding the surface acoustic 
wave resonator to be a vacuum atmosphere will realize a resonator the 
deterioration of which can be prevented. If the value of the resonance 
resistance Rr can be reduced, a surface acoustic wave resonator unit 
having a large Q-value can be provided. 
FIG. 13 shows the Q-values of surface acoustic wave resonator units of an 
ST-cut Rayleigh wave type having a resonance frequency of 100 MHz to 300 
MHz that are respectively sealed in the atmosphere and vacuum. The 
Q-values undesirably decrease in inverse proportion to the frequency. 
Therefore, it is, as described above, important that a surface acoustic 
wave resonator unit having a large Q-value in a high frequency range is 
obtained in order to realize a stable and high-frequency oscillator. As 
can be understood from the figure above, sealing in a vacuum will provide 
a resonator having a Q-value at about 200 MHz that is larger by about 60%, 
as compared with that attained from the case where sealing under the 
atmosphere pressure is employed. 
To seal the inside portion of the housing in a vacuum, a cylindrical case 
of a type as shown in FIG. 5 can be employed preferably. The shape shown 
in FIG. 5 is a press-fitting type cylindrical shape for sealing the inside 
of the housing in an airtight manner. The case 21 is made of a material, 
such as nickel silver, so that when the plug member is press-fit, a 
tightening force, generated in the case 21, enables airtightness to be 
maintained. Between the case 21 and the plug member, there is applied a 
case plating and plug plating using soft metal having malleability, such 
as solder or gold, solder being employed in this embodiment, because the 
cost of which is low and exhibits excellent mass productivity. Therefore, 
the solder acts as a sealing member so that the gap between the case and 
the plug member can be plugged. The plating process is usually performed 
by a plating technique, such as a barrel method or a dipping method. At 
least an internal surface of the case, with which the plug member is 
brought into contact, is applied with plating, while the metal ring 24 and 
the leads of the plug member are applied with plating. Plating exhibiting 
excellent sealing performance and having malleability may be applied to at 
least the plug member or case, while other plating processes may be 
performed by nickel or the like. 
If the foregoing press-fitting case is employed, sealing performed in such 
a manner that the plug member to which the surface acoustic wave resonator 
is secured is mounted, will make the inside portion of the case to be the 
same as the atmosphere in which the sealing operation is performed. 
Therefore, if machining in an atmosphere of a vacuum is employed, the 
inside portion of the case can be made to be a vacuum. If machining in an 
atmosphere of nitrogen is performed, the inside portion of the case can be 
made to be a nitrogen atmosphere. Therefore, a surface acoustic wave 
resonator unit having a case, the inside of which has been made vacuum and 
that exhibits a large Q-value, can be manufactured in large quantities and 
with a low cost by simply aligning the position by using a jig. 
By making vacuum the inside of the housing that seals the surface acoustic 
wave resonator, oxidation of the electrodes can be prevented. Furthermore, 
a short circuit of the IDT, which is formed in the order of microns, due 
to dew condensation can be prevented so that the aging prevention is 
improved. The effects of preventing oxidation of the electrodes and a 
short circuit due to dew condensation are also obtained from sealing of 
the inside portion of the housing with an inactive gas, such as nitrogen. 
By sealing inactive gas in the housing and raising the internal pressure, 
the generation of harmful gas from the adhesive agent or the like can be 
prevented. 
Conduction Among Connection Lands, Leads and the like 
The surface acoustic wave resonator according to this embodiment has 
electrodes made of aluminum or aluminum based material. Where aluminum 
electrodes are used, the surface is naturally oxidized to cause an oxide 
film to be formed, thus resulting in that soldering cannot be performed. 
Although soldering may be performed by using flux for aluminum, a process, 
such as washing for maintaining the quality, is required. Thus, mass 
productivity deteriorates and manufacturing cost is undesirably raised. 
Accordingly, the connection lands 7 as shown in FIG. 14 are connected to 
the leads 25 or the deducing pattern by using the conductive adhesive 
agent 26. It is preferable that the conductive adhesive agent 26 be mixed 
with an oxidation inhibitor to prevent oxidation of the electrodes. To 
obtain excellent electrical conduction, it is preferable that silver or 
copper be employed to make the filler (a material for realizing the 
conductive characteristic in the conductive adhesive agent). 
By using a conductive adhesive agent, a low resistance surface acoustic 
wave resonator unit can be obtained with a low cost required. Since the 
non-processed oxide film 37 is left on the surface of the aluminum 
electrodes, a direct-current conduction cannot be established. Therefore, 
to reduce the resonance resistance Rr and obtain a surface acoustic wave 
resonator unit having a larger Q-value, the oxide film 37 must be 
processed. 
FIG. 15 shows a bump 40 provided at the connection land 7. The connection 
land 7 made of aluminum or aluminum-copper alloy has the bump 40 formed 
thereon, which cannot easily be oxidized and exhibits excellent 
conductivity, for example, gold, silver, solder or the like, by a 
machining technique, such as sputtering, ion plating or the like. The bump 
40 is not affected by the oxide film or the like. Therefore, if the leads 
25 or the like including the bump 40, are attached on the connection land 
7 by the conductive adhesive agent 26, direct-current conduction can be 
established and a surface acoustic wave resonator unit having a low 
resonance resistance Rr and a large Q-value can be obtained. If a 
soldering plating covering the leads 25 is melted, in place of fixing, 
using the conductive adhesive agent, the connection with the bump 40 can 
be established without using flux. In the foregoing case, it is preferable 
that a non-conductive adhesive agent be used for a reinforcement to obtain 
the strength required to mount the surface acoustic wave resonator 1 by 
the cantilever method. 
FIG. 16 shows the leads 25 connected to the connection lands 7 viewed from 
a position above the main surface 3. The connection end 25c of the leads 
25 according to this embodiment is deformed into a flat shape and branches 
into two sections. The two branched sections are attached by the 
conductive adhesive agent 26 so they extend on the two sides of the bump 
40. By deforming the connection end 25c of the lead, its area that is in 
contact with the conductive adhesive agent 26 can be enlarged, whereby the 
contact resistance can be reduced. Simultaneously, a large adhesive force 
can be obtained. By branching the connection end 25c into two or more 
sections, disposition while being combined with the bump 40 formed on the 
connection lands 7 can easily be performed. Therefore, areas of the 
connection lands 7 can effectively be used and an excellent conduction 
with the bump 40 can be established. By providing the foregoing branch, 
the leads 25 can be strongly secured by the adhesive agent 26 so the 
surface acoustic wave resonator 1 is mounted by the cantilever method 
using the leads 25. 
FIG. 17 shows a stud bump 41 provided for the connection land 7 by the wire 
bonding method. The stud bump 41 can be formed by removing the oxide film 
37 by ultrasonic vibration and by wire-bonding metal, such as gold or 
copper. Even if the oxide film 37 is relatively thick, the stud bump 41 
can be provided at a low cost and with simple work. In a case where the 
bump is formed by evaporation or the like, large energy is required if the 
oxide film is thick, and thus a large cost is required. Therefore, the 
stud bump 41 according to this embodiment exhibits excellent mass 
productivity and enables the cost required for manufacturing to be 
reduced. As a matter of course, a similar effect can be obtained from the 
stud bump 41 even where a wire is arranged on the connection land 7. By 
providing the bump for the connection land 7 as described above, the 
contact resistance with the leads can considerably be reduced. As a 
result, the resonance resistances Rr of a surface acoustic wave resonator 
unit (a cylindrical surface acoustic wave resonator unit oscillating a 
resonance frequency of 145 MHz) having no bump at the connection land 
distribute widely to about 20.OMEGA. to 40.OMEGA., whereas provision of 
the bump is able to reduce the resonance resistance to about 10.OMEGA. to 
20.OMEGA.. By providing a bump, variation of the resonance resistance Rr 
can be within a narrow range, whereby a surface acoustic wave resonator 
unit exhibiting stable performance can be obtained. 
FIGS. 18 and 19 show another embodiment for establishing a conduction with 
the connection land 7. In this embodiment, the lead 25 is mounted on the 
connection land 7, followed by an application of the conductive adhesive 
agent 26. The surface of the connection land 7, covered with the adhesive 
agent 26, is scratched by a jig having a sharp leading end before the 
adhesive agent 26 is hardened. The scratch 42 may consist of one or more 
lines to run parallel to the leads 25 or perpendicular to the same. By 
forming the scratch 42, a portion from which the oxide film 37 has been 
removed can be formed to cause the aluminum portion of the connection land 
7 to be exposed. Therefore, direct-current conduction can be established 
between the connection land 7 and the leads 25 through the conductive 
adhesive agent 26. If a scratch is formed on the outside of the range for 
the adhesive agent 26, the exposed portion is initially oxidized and an 
oxide film is again synthesized, thus requiring attention to be directed 
there. If the connection land is separated by the scratch 42, the 
conduction of the electrodes cannot easily be established and the scratch 
out of the adhesive agent causes the oxide film to be formed, thus 
requiring attention to be directed there. 
The scratch 42 can be formed by pressing the leads 25 against the 
connection lands 7, by mechanically vibrating the same with ultrasonic 
vibrations or the like. If the adhesive agent 26 is applied by a dispenser 
or the like, the scratch may be formed by the leading end of a nozzle of 
the dispenser, when the agent 26 is applied. As an alternative metal, 
except the lead, may be vibrated or rubbed to form the scratch. The 
thus-formed scratch is able to reduce conduction loss of the connection 
land due to contamination or the like. Note that the process must be 
performed before the adhesive agent 26 is hardened. The scratch is able to 
improve the value of the resonance resistance Rr, similarly to the case 
where the bump is formed. In particular, it is preferable that the scratch 
be formed in a line rather than formed as a dot. Furthermore, random 
formation of three or more lines of scratches will attain an effect 
similar or superior to that obtainable from the formed bump. In addition 
to the resonance resistance Rr, the inventor has measured change in the 
direct-current resistance value. In accordance with the results of the 
measurement, no process of the oxide film results in a wide range of the 
direct-current resistance from 5.OMEGA. to infinite, whereas the scratch 
or the bump results in accurate convergence to values about 1.OMEGA. to 
2.OMEGA.. Thus, the formed scratch or bump enables the influence of the 
oxide film to be eliminated, so that a surface acoustic wave resonator 
unit having a low connection resistance (direct-current resistance) and 
exhibiting a large Q-value is realized. 
To obtain the foregoing effects, a scratch where the oxide film has been 
removed is required for the connection land. Therefore, the scratch is 
provided for the connection land after the conductive adhesive agent has 
been applied. In a contrary case where the scratched connection lands and 
the leads are connected to one other in a state of a low connection 
resistance, the foregoing scratches are formed after an adhesive agent has 
been applied. If the scratches are formed and the internal surface of the 
scratch is again oxidized, a satisfactory conductive state cannot be 
obtained. Accordingly, it is preferable that a conductive adhesive agent 
of a type containing an oxidation inhibitor mixed thereto be employed. As 
the oxidation inhibitor, a reducing type inhibitor, such as hydroquinone, 
catechol, or phenol, is employed. Furthermore, mixing of different type 
metals, such as nickel, may be mixed, in addition to silver particles, to 
stabilize the contact resistance and to attain an effect of preventing 
oxide film being formed. 
Also, the effect of the oxidation inhibitor has been confirmed due to 
experiments performed by the inventor. A surface acoustic wave resonator 
unit, in which an adhesive agent having no oxidation inhibitor was used 
encountered change in the resonance frequency by 100 ppm or more due to 
annealing at 230.degree. C. for 10 hours after the adhesive agent had been 
hardened. Also the value of the resonance resistance Rr was resulted in 
rise to 30.OMEGA. to 40.OMEGA. as compared with a value of 20.OMEGA. or 
less before annealing was performed. If an adhesive agent containing an 
oxidation inhibitor is used, the change in resonance frequency can be 
converged within about 20 ppm, and a satisfactory value of the resonance 
resistance Rr of 20.OMEGA. or less can be maintained. 
Protection of Electrodes 
In the present invention, the surface acoustic wave resonator is mounted by 
the cantilever method in such a manner that it is supported while being 
caused to float from the housing, such as a cylindrical or ceramic case. 
Furthermore, a space is provided around the surface acoustic wave 
resonator to protect the surface acoustic wave resonator from being 
affected from the surrounding atmosphere. In the foregoing surface 
acoustic wave resonator unit, the space formed around the surface acoustic 
wave resonator serves as a space in which foreign matter, such as dust of 
SUS or solder dust, that can be mixed when the surface acoustic wave 
resonator is sealed, can move. The foregoing foreign matter is able to 
move between the electrodes of the surface acoustic wave resonator, for 
example, the electrodes of the IDT or the electrodes that establish the 
connection between the IDT and the connection land. Since the IDT is in 
the order of microns, existence of the conductive foreign matter between 
the electrodes causes a short circuit to take place. Thus, the stable 
operation of the surface acoustic wave resonator unit is inhibited. 
Furthermore, it is difficult to completely prevent the mixture of foreign 
matter. Since the surface acoustic wave resonator unit is used in a 
variety of purposes, the foreign matters can move due to impact during 
mounting or transporting or due to the angle of mounting. Therefore, it is 
difficult to completely prevent the foregoing problem at the time of 
assembling the surface acoustic wave resonator unit or mounting the same. 
To prevent the problem raised due to foreign matter, the IDT or the like 
may be applied with a coating, such as silicon oxide. However, the layer 
of different material formed on the chip causes the resonance frequency to 
be changed and the Q-value to be lowered. Thus, the effect of the 
cantilever mounting method is minimized. Accordingly, the inventor paid 
attention on the effect of the oxide film formed on the surfaces of the 
aluminum electrodes. As described above, oxide films are naturally formed 
on the surfaces of the aluminum electrodes these formed oxide films are 
able to prevent short circuit. However, since the oxide film that is 
naturally formed is very thin having a thickness of 10 .ANG. to 30 .ANG., 
it cannot completely protect the electrodes from foreign matter that moves 
due to impact, such as falling. 
Accordingly, in the present invention, the aluminum electrodes of the 
surface acoustic wave resonator are anodic-oxidized, so that a thick oxide 
film having a thickness about 280 .ANG. or thicker is formed on the 
surfaces of the electrodes, in order to prevent problems taking place due 
to foreign matter. 
The anodic oxidation is performed by using a structure in which a plurality 
of surface acoustic wave patterns 51 are formed on a wafer 50 of a 
piezoelectric member, as shown in FIG. 20. In this embodiment, either of 
the electrodes 4a and 4b, that form the IDT 5, is subjected to the anodic 
oxidation. Therefore, the wafer 50 is provided with, in addition to a 
surface acoustic wave pattern, a connection line 52 that establishes the 
connection with the electrode 4a of the surface acoustic wave pattern 51 
and a terminal 53 that establishes a connection with a power source for 
anodic oxidation. 
FIG. 21 shows an outline of an apparatus for performing the anodic 
oxidation. A tank 55 includes anodic oxidation liquid 59 and a clip 56 
that holds the terminal 53 of the wafer 50 so the wafer 50 is immersed in 
the oxidizing liquid 59. A power source 57 is used to supply electric 
current so that the portion including the wafer 50, is made to be an 
anode. Also, a cathode 58 immersed in the oxidizing liquid 59, is 
connected to the power source 57. In this embodiment, anodic oxidation 
enables a non-porous oxide film to be formed. Therefore, the oxidizing 
liquid 59 is water solution of phosphate or liquid mixture of a water 
solution of borate. As an alternative, a water solution of a salt near 
neutral, such as citric acid or adipic acid, may be used. It is preferable 
that the temperature of the liquid be near room temperature in order to 
prevent porous film being formed. For example, in a case where water 
solution of borate is used, it is preferable that the temperature be about 
20.degree. C. to about 30.degree. C. 
If anodic oxidation is performed under the foregoing conditions, oxide 
films each having a thickness that is substantially in proportion to the 
applied voltage can be formed on the surfaces of the electrodes. To 
control the thickness of the oxide film and to control the electric 
current flowing when the electric current is supplied to be a level lower 
than a predetermined level, it is preferable that a constant-voltage and 
constant electric current power source be employed as the processing power 
source. Since it is preferable that portions of the electrodes 
corresponding to the connection lands be subjected to a process for 
removing the oxide film as described above, it is preferable that the 
portions corresponding to the connection lands be applied with a resist or 
the like, to prevent an increase in the thickness of the oxide film. 
The inventor has measured frequency of generation of problems in a case 
where foreign matter (SUS dust having diameters from 5 .mu.m to 10 .mu.m) 
of SUS was forcibly mixed into a cylindrical case. As a result, about 100% 
of resonators that were not subjected to anodic oxidation encountered a 
short circuit after a repeated falling test (results of the falling tests 
repeated five times from height of 75 cm to 150 cm). On the other hand, 
surface acoustic wave resonator units having the electrodes on either side 
of the IDT being subjected to the anodic oxidation resulted in the 
frequency in the generation of short circuits being decreased. Where the 
anodic oxidation voltage was made to be about 30 V, the frequency in the 
generation of short circuits can be substantially halved. If the anodic 
oxidation voltage was raised to a level higher than 50 V, the frequency in 
the generation of short circuits can be substantially eliminated. 
Electrodes on the two sides of the IDT can be anodic-oxidized by using a 
pattern shown in FIG. 22 or by a similar method. Resonators of this type 
resulted in the frequency in the generation of short circuits being 
substantially eliminated when the anodic oxidation voltage was made to be 
20 V or higher. As shown in FIG. 23, when the anodic oxidation voltage was 
20 V, the thickness of the oxide film was about 280 .ANG., whereas it was 
about 700 .ANG. when the anodic oxidation voltage was 50 V. 
Where an oxide film is forcibly formed on the electrodes on either side of 
the IDT, the film must have a thickness thicker than the oxide films 
formed on the electrodes on the two sides, the required thickness being 
about two times as a result of conducted experiments. However, since the 
electrodes on either side of the IDT can be individually formed for each 
pattern, the resonance frequency for each pattern can be previously 
measured in a wafer state, before chips are formed by cutting. In 
accordance with the measured resonance frequency, the process for forming 
the oxide film is repeated to enable the operations for adjusting the 
resonance frequency during the manufacturing process, such as the major 
adjustment in the wafer state and the minor adjustment for each surface 
acoustic wave resonator to be performed. 
FIG. 24 shows changes in the resonance frequency of a plurality of wafers 
with respect to the anodic oxidation voltages where the anodic oxidation 
voltage is about 50 V. As can be understood from the above figure, 
adjustment of the oxidation voltage enables resonance frequency to be 
adjusted in units of ppm. Therefore, if the electrodes on either side of 
the IDT are anodicoxidized, the resonance frequency can be measured in the 
wafer state. In accordance with the measurements, anodic oxidation is 
further performed, and therefore surface acoustic wave resonators having 
arranged resonance frequencies can be easily obtained. Thus, the anodic 
oxidation of the electrodes will enable devices to be realized that 
exhibit durability against problems due to dust, so that the foregoing 
excellent characteristics can be maintained. 
Surface Mounting Type Device 
FIG. 25 is a perspective view in which the surface acoustic wave resonator 
unit 20 having the surface acoustic wave resonator shown in FIG. 5 
accommodated in a cylindrical case by the cantilever mounting method so as 
to be formed into a surface mounting type device 60. In the device 60, 
leads 25a and 25b outwardly project over the case 21, in which the surface 
acoustic wave resonator is airtight-sealed, and are attached to 
corresponding lead frames 61a and 61b by, for example, welding, soldering 
or a conductive adhesive agent. Furthermore, a lead frame 62 is disposed 
on a side of the cylindrical case 21 opposing the side on which the leads 
project. The lead frames 61 and 62 and the case 21 are integrated by a 
resin 65. The lead frames 61a and 61b are used to establish electrical 
connection with the surface mounting type surface acoustic wave resonator 
unit 60. The lead frame 62 is used as a dummy lead to maintain the 
strength when the surface acoustic wave resonator unit 60 is mounted on 
the board. Since the elements are integrally molded into a rectangular 
parallelpiped by resin 65, mounting on the substrate can be performed 
using an automatic mounting technique. 
FIG. 26 shows a surface mounting type surface acoustic wave resonator unit 
60 in which the lead frame 62 is used, in the foregoing embodiment, as the 
dummy lead, and is electrically connected to the cylindrical case 21. The 
lead frame 62 can be electrically connected to the case 21 at a position 
69 which comes in contact with the case 21 by a method, such as contact, 
press fit, soldering or a conductive adhesive agent. By bringing the lead 
frame 62 into contact with the case 21, as described above, the metal case 
21 can be connected to the ground, that is grounded through the lead frame 
62. The surface acoustic wave resonator unit is usually used at a 
high-frequency of several hundred MHz. Thus, grounding of the case 21 can 
shield noise existing as electric waves in space. Furthermore, the surface 
acoustic wave resonator unit serving as the noise source can be prevented. 
By grounding a metal case, such as the box-like case, as well as the 
cylindrical case grounded through the lead frame, a surface acoustic wave 
device of a surface mounting type able to withstand noise can be provided. 
Each of the foregoing surface acoustic wave devices has the surface 
acoustic wave resonator mounted in the case by the cantilever method. 
Thus, a surface acoustic wave resonator unit capable of generating very 
stable resonance frequency can be obtained. Furthermore, the surface 
acoustic wave resonator unit has excellent characteristics, such as a low 
resonance resistance and a large Q-value. In addition, integral-molding 
with the lead frame by a resin enables a surface mounting type device 
exhibiting excellent surface mounting characteristics to be easily 
obtained. Since the surface acoustic wave resonator is mounted by a 
cantilever method by using a conductive adhesive agent or non-conductive 
adhesive agent, it has excellent impact resistance. If anodic-oxidized 
films are formed on the electrodes, problems, such as short circuit due to 
shock can be prevented. Thus, the present invention enables a surface 
acoustic wave resonator unit exhibiting excellent conductivity and high 
quality to be provided.