JPH0311687B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a surface acoustic wave element in which electrodes, reflectors, and lead electrodes for guiding the electrodes to an external circuit are formed on the surface of a piezoelectric substrate.

[Technical background and conventional technology]

Recently, surface acoustic wave elements have been attracting attention as elements constituting filters and resonators. Figure 2 shows chip 1 of the surface acoustic wave device that makes up the resonator.
is shown in a plan view, and the third
The figure shows this enlarged. This chip 1 has two sets of resonators 3 and 4 on the surface of a piezoelectric substrate 2.
is arranged. The resonator 3 on one side is composed of a blind-shaped electrode 31 located at the center and reflectors 32 located on both sides thereof. Similarly, the resonator 4 has an interdigital electrode 41 located at the center.
and reflectors 42 located on both sides thereof. The above electrodes 31 and 41 are made of conductive material such as aluminum or gold, and these electrodes 31 and 41 are connected to a pair of interdigital conductors 31a, 31b and 41a, 41b facing each other. This is how it is structured. In addition, the reflectors 32 and 42 are made of the same conductive material as the electrodes 31 and 41, so that the piezoelectric substrate 2
The piezoelectric substrate 2 is provided by adhesion on the surface of the piezoelectric substrate 2, or by forming grooves on the surface of the piezoelectric substrate 2. The reflectors 32, 42 are made up of stripes 32a, 42a arranged in a lattice pattern at predetermined pitches and connectors 32b, 42b that connect these stripes to each other.

In a surface acoustic wave element that constitutes a resonator with such a configuration, when a predetermined voltage is applied to the electrodes 31 or 41 and a surface acoustic wave is generated on the surface of the piezoelectric substrate 2, this generates a surface acoustic wave on each of the reflectors 32 and 42. The waves are reflected by each stripe 32a, 42a, and the reflected waves are aligned in phase to cause resonance.

The chip 1 having the above-mentioned surface configuration is generally used while being packaged within a hermetic seal 5 as shown in FIG. This hermetic seal 5 is composed of a stem 51 and a metal case 52 covering the upper part of the stem 51. The tip 1 is fixed on the upper surface of the stem 51. Further, a bonding post 6 for connecting to an external circuit is fixed to the stem 51.
On the other hand, a bonding pad 7 is provided on the surface of the piezoelectric substrate 2 of the chip 1. This bonding pad 7 has lead electrodes 9, 10 or 11.
Each electrode 31a, 31b, 41a, 41b
is connected to. These lead electrodes 9, 10, 11 and bonding pad 7
are molded from the same conductive material as the electrodes 31 and 41. With the chip 1 assembled in the hermetic seal 5, each bonding post 6 and the bonding pad 7 are connected by wires 8. This wire 8 is made of the same conductive material as the bonding pad 7.

[Problems with conventional technology]

When forming the hermetic seal 5 shown in FIG. 1, the chip 1 is placed on the stem 51, and bonding is performed between the bonding pad 7 of the chip 1 and the bonding post 6 using the wire 8. Generally, when connecting by wire bonding using aluminum wire, the movement of the bonding tool is linear and unidirectional with respect to the bonded element, so this is to improve the efficiency of this bonding work. In order to do so, the bonding post 6 and the bonding pad 7 must be placed side by side. Additionally, in order to improve the reliability of the surface acoustic wave device, the wire 8 must be arranged so that it does not pass over the electrodes or reflectors. For these reasons, in the conventional chip 1, as shown in FIGS. 2 and 3, the lead electrodes 9, 10 and 11 are
It was deposited at a position avoiding the electrodes 31, 41 and reflectors 32, 42. However, in surface acoustic wave elements for consumer use, the external dimensions of the package are often limited. Therefore, in order to downsize the piezoelectric substrate 2, it is necessary to , 41, or the stripes 32a, 42 of the reflectors 32, 42.
This will reduce the number of a. As a result, the characteristics of the element may deteriorate and the degree of freedom in design may be reduced.

[Object of the present invention]

The present invention has been made by focusing on the above-mentioned conventional problems, and has made it possible to freely arrange lead electrodes without reducing the number of pairs of electrodes or the number of stripes of reflectors, and also to realize miniaturization of the chip. The purpose is to provide a surface acoustic wave device.

[Means for solving problems]

The surface acoustic wave element according to the present invention includes, on the surface of a piezoelectric substrate, a lattice-shaped conductor, a bonding pad for connecting to an external circuit, and a lead electrode for connecting an electrode of the lattice-shaped conductor to the bonding pad. In the surface acoustic wave device, an insulating layer is formed on the surface of the grid-like conductor, and the lead electrode is attached and formed on the insulating layer. be.

[Effect]

In the above method, since the lead electrodes are stacked on the grid-like conductor through the insulating layer, there is no need to form a lead electrode arrangement space outside the arrangement space of the grid-like conductor, and the piezoelectric substrate can be made smaller. You will be able to do it.

[Example of the present invention]

Embodiments of the present invention will be described below with reference to FIG. 4 and the subsequent drawings.

Fig. 4 is a plan view of the first embodiment showing the surface of the piezoelectric substrate of the surface acoustic wave element constituting the resonator, Fig. 5 is an enlarged view of the - cross section of Fig. 4, and Fig. 6 is the second embodiment. FIG.

(First Example) In the surface acoustic wave device shown in FIG.
Similar to what is shown in the figure, two
A pair of resonators 3 and 4 are arranged.
One resonator 3 is composed of an interdigital electrode 31 located at the center and reflectors 32 located on both sides thereof, and the other resonator 4 is also composed of an electrode 41 and reflectors 42. ing. Each of the above electrodes 3
1 and 41 are formed by depositing a conductive material such as aluminum or gold. Further, the electrode 31 consists of a pair of interdigital conductors 31a and 31b facing each other, and the electrode 41 also consists of a pair of interdigital conductors 4
It consists of 1a and 41b. On the other hand, reflector 3
2 consists of stripes 32a arranged in a lattice pattern and connectors 32b connecting each stripe 32a. Similarly, the reflector 42 consists of stripes 42a and connections 42b. These stripes 32a, 42a and connecting bodies 32b, 42b
are formed by adhering to a conductive material or a dielectric material like the electrodes 31 and 41,
Alternatively, it is constituted by a groove provided on the surface of the piezoelectric substrate 2.

On the other hand, in order to connect the chip 1 of this surface acoustic wave element to the bonding post 6 (the same as shown in FIG. 1) in the hermetic seal 5,
Three bonding pads 7 are formed on the piezoelectric substrate 2. The bonding pad 7 at the right end in FIG. 4 is connected to one of the interdigital conductors 31b and 41b of each electrode 31, 41 by a lead electrode 21. This lead electrode 21
A portion indicated by 21 a is directly attached to the upper surface of the piezoelectric substrate 2 , and a portion indicated by 21 b is attached and formed on the insulating layer 24 . On the other hand, the fourth
The bonding pad 7 at the left end of the figure is the lead electrode 2.
2 to the interdigital conductor 31a of the electrode 31. This lead electrode 22 is
A portion 22 a is directly attached to the surface of the piezoelectric substrate 2 , and a portion 22 b is attached and formed on the insulating layer 25 . One insulating layer 24 is formed over the reflector 42, and the other insulating layer 25 is formed between the reflectors 32 and 42.
(See Figure 5). Further, the bonding pad 7 in the center of FIG. 4 is connected to the interdigital conductor 41a by a lead electrode 23.

The chip 1 having the surface configuration shown in FIG. 4 is fixed on the stem 51 within the hermetic seal 5 (see FIG.
and the bonding post 6 are connected by a wire 8.

As described above, in the surface acoustic wave element, there is no need to secure space for the lead electrodes 21 and 22 on the surface of the piezoelectric substrate 2, so the chip can be made smaller, and the logarithm of the electrodes 31, 41 and the reflection Vessel 32,
There is no need to reduce the number of 42 stripes 32a, 42a.

Note that the insulating material forming the insulating layers 24 and 25 may be organic or inorganic;
In the case of a surface acoustic wave element constituting a resonator as shown in the figure, an inorganic material is preferable in order to prevent a decrease in the quality factor of the resonator and a fluctuation in the resonant frequency. Furthermore, among these inorganic substances, it is preferable to use a material having a small density, denseness, and high rigidity, such as silicon dioxide (SiO ₂ ).

Further, the insulating layer 24 or 25 is connected to the electrodes 31 and 4.
The lead electrode 21 or 22 may be provided on the electrodes 31 and 41.

(Second Example) Next, the surface acoustic wave element shown in FIG. 6 has the same basic configuration as that shown in FIG.
Two sets of resonators 3 and 4 are provided on the surface of. In addition, two electrodes for connecting each electrode 31 and 41 are
Book lead electrodes 21 and 22 are formed on insulating layers 24 and 25. Further, in this embodiment, the interdigital conductor 31 of the two electrodes 31, 41
A common lead electrode 21 connecting the terminals b and 41b is grounded via a bonding pad 7a. Further, each of the reflectors 32 and 42 of the two sets of resonators 3 and 4 is made of a conductive material, similarly to the electrodes 31 and 41, respectively. The two reflectors 32 and 42 on the left side of the figure are connected to the bonding pad 7b at ground potential by lead electrodes 27a and 27b. Similarly, the two reflectors 32 and 42 located on the right side of the figure are also connected to the lead electrode 2.
6a, 26b to bonding pad 7b at ground potential. Note that the left lead electrode 22 is connected to the stripe 32 of each reflector 32, 42.
a and 42a are arranged in parallel.

In the configuration shown in FIG. 6, each electrode 31, 4
Interdigital conductors 31b and 41b on one side of 1
is at ground potential, and reflectors 32 and 42 are also at ground potential. On the other hand, the interdigital conductors 31a and 41 are connected by the lead electrodes 22 and 23.
A is given a predetermined potential, and a predetermined voltage is applied to the electrodes 31 and 41. Therefore, each electrode 3 is provided between the lead electrode 22 and each reflector 32, 42.
The same voltage as that applied to 1 and 41 will be applied. Moreover, the lead electrode 22 is connected to the insulating layer 2.
The reflectors 32, 42 and the lead electrode 2 extend parallel to the stripes 32a, 42a through the
2, a predetermined parallel capacitance will occur between the two. Further, the lead electrodes 21 and 22 can be placed at arbitrary positions on the piezoelectric substrate 2 by the insulating layers 24 and 25. Therefore, by adjusting the position of the bonding pad 7, the lead electrodes 21, 2
It is also possible to freely change the arrangement length of 2 and freely set the series inductance within a certain range.
By utilizing each of these effects, for example, a surface acoustic wave element filter can be constructed and used for impedance matching.

The surface acoustic wave elements according to the above two embodiments both have a reflector and constitute a resonator, but the present invention is applied to the surface acoustic wave element constituting a filter, and the input An insulating layer may be formed on the electrode, the output electrode, and even the shield electrode, and the lead electrode may be disposed in an overlapping manner on top of the insulating layer.

[Effects of the present invention]

As described above, according to the present invention, the following effects can be achieved.

(1) An insulating layer is provided on the surface of the piezoelectric substrate, and lead electrodes are placed on top of the grid conductor.
There is no need to provide a space for arranging the lead electrodes on the piezoelectric substrate, and the chip can be made smaller.

(2) Since the lead electrode can be placed over the interdigital electrode or reflector, there is no need to reduce the number of pairs of electrodes or the number of stripes on the reflector, and the characteristics of the surface acoustic wave device are not affected. You can design the bonding pad layout.

(3) Lead electrodes can be placed in any position, so
The position of the bonding pad can also be set arbitrarily,
The degree of freedom in design is improved.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view showing the package structure of a surface acoustic wave element, Figure 2 is a plan view of a surface acoustic wave element that constitutes a conventional reflector, and Figure 3 is an enlarged view of the surface of the piezoelectric substrate in Figure 2. FIG. 4 and subsequent figures show embodiments of the present invention. FIG. 4 is an enlarged plan view showing the surface of the piezoelectric substrate of the surface acoustic wave element according to the first embodiment, and FIG. 4 is an enlarged cross-sectional view of FIG. 4, and FIG. 6 is an enlarged plan view showing the surface of the piezoelectric substrate of the surface acoustic wave element according to the second embodiment. 1... Chip, 2... Piezoelectric substrate, 3, 4... Reflector, 6... Bonding post, 7, 7a, 7
b... Bonding pad, 31, 41... Electrode, 32, 42... Reflector, 32a, 42a...
Stripe, 24, 25...insulating layer.

Claims (1)

[Claims] 1. On the surface of a piezoelectric substrate, a grid conductor, a bonding pad for connecting to an external circuit, and a lead electrode connecting the electrode of the grid conductor and the bonding pad are provided. In the surface acoustic wave device provided, an insulating layer is formed on the surface of the grid-like conductor, and the lead electrode is attached and formed on the insulating layer. . 2. The surface acoustic wave element according to claim 1, wherein the insulating layer is formed overlying the grid-like conductor constituting the reflector provided on the surface of the piezoelectric substrate. 3. The surface acoustic wave device according to claim 2, wherein the grid conductor of the reflector and the lead electrode are arranged in parallel, and a predetermined capacitance is provided between the reflector and the lead electrode. 4. The surface acoustic wave device according to claim 1, wherein the insulating layer is formed of an inorganic material that has low density, is dense, and has high rigidity. 5. The surface acoustic wave device according to claim 4, wherein the inorganic material is silicon dioxide.