JPS6228095Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a surface acoustic wave device that exhibits stable characteristics against changes in the surrounding temperature environment and thermal environment.

Examples of surface acoustic wave devices include surface acoustic wave filters, surface acoustic wave resonators, and surface acoustic wave delay lines. Such surface acoustic wave devices generally use ceramic materials that have a piezoelectric effect. Examples of such piezoelectric ceramic materials include barium titanate, lead titanate, and lead zirconate titanate.

Recently, these surface acoustic wave devices are required to be highly reliable, and are required to have stable characteristics against the external environment, especially the temperature environment and thermal environment.

However, in the past, it has often been observed that when a material is placed in a severe temperature or thermal environment, its piezoelectric properties deteriorate when it is subjected to a test called a special test such as a high temperature storage test or a thermal shock test. To this end, various improvement plans have been attempted in the past, but the current situation is that the best solution has not yet been found.

In other words, for ferroelectric substrates used in surface acoustic wave devices, etc., it is important that (1) the frequency and insertion loss do not change even with temperature changes, and (2) the electromechanical coupling coefficient is large. required as a characteristic. For example, various additives are added to the main component of lead zirconate titanate ceramics in order to improve the properties of the material itself. However, when adding additives, even if characteristic (1) above is satisfied, conversely, characteristic (2)
properties may deteriorate. In addition, attempts have been made to improve the property (1) by examining various firing conditions; however, (2)
The drawback is that the properties of the calcinations vary or deteriorate, and it is also difficult to control the firing conditions, making them unsuitable for industrial production.

By the way, there is a leadless type surface acoustic wave device as shown in FIG. In the figure, 1 is a surface acoustic wave device unit. The unit 1 includes a ferroelectric ceramic substrate 11 based on lead zirconate titanate, for example. On one main surface of this substrate 11, there are interdigital electrodes 12 on the input side and interdigital electrodes 13 on the output side.
are made of a conductive material, and a shield electrode 14 is formed between the two as necessary. A ground electrode 15 is formed on the other main surface of the ferroelectric ceramic substrate 11 as required. A pair of comb-shaped electrodes of the interdigital electrodes 12 on the input side are each individually connected to an extraction electrode 1.
6a and 16b are connected. Furthermore, extraction electrodes 17a and 17b are electrically connected to the pair of comb-shaped electrodes of the interdigital electrodes on the output side, respectively. Further, an extraction electrode 16b is electrically connected to the shield electrode 14. At this time, the ground electrode 15 formed on the back surface of the substrate 11 may be electrically connected to the shield electrode 14, that is, the extraction electrode 16b, by a conductive paste or a resistive paste (not shown). Such surface acoustic wave device unit 1
is known as a unit constituting a surface acoustic wave device.

On the other hand, 2 is an insulating base with extraction electrodes 16a, 16
For example, four lead terminal electrodes 21a, 21b, 22a, and 22b corresponding to electrodes b, 17a, and 17b are provided by a metallization method. The back side of the substrate 11 is adhered to the insulating base 2 with an insulating adhesive (not shown). Bonding wire (not shown)
, the extraction electrode 16a and the extraction terminal electrode 21a, the extraction electrode 16b and the extraction terminal electrode 21b, and the extraction electrode 1
7a and the extraction terminal electrode 22a, and the extraction electrode 17b and the extraction terminal electrode 22b are connected, respectively. Reference numeral 3 designates a cap whose lower surface is open in the figure, and is fixed to the insulating base 2 so as to cover the surface acoustic wave device unit 1 with the lead terminal electrodes 21a, 21b, 22a, and 22b partially exposed.

The purpose of this invention is to provide a surface acoustic wave device whose characteristics do not change much in severe temperature or thermal environments by making maximum use of such a structure.

In summary, this idea is to provide an interdigital electrode on one surface of a polarized ferroelectric ceramic substrate, and to provide a lead terminal electrode on a semiconductor board or a resistor board, which has a conductive or resistive component. By bonding the other surface of the ferroelectric ceramic substrate onto a semiconductor or resistor plate with an adhesive and by connecting the electrode provided on one surface of the ceramic substrate and the lead terminal electrode, the temperature of the ferroelectric ceramic substrate can be adjusted. This is a surface acoustic wave device in which a discharge circuit for the accumulated charges is constructed between parts where positive and negative charges are accumulated due to changes.

The above objects and other objects and features of the present invention will become clearer from the following detailed description with reference to the drawings.

FIG. 2 is an exploded perspective view showing an embodiment of this invention. In FIG. 2, the same parts as in FIG. 1 are given the same numbers and their explanations will be omitted.

Reference numeral 4 denotes a base made of ceramic resin having semiconductivity or resistance, and the base 4 has respective lead terminal electrodes 21a, 21b, 22 as shown in the figure.
For example, a conductive adhesive 24 is applied within a range 23 that does not reach a and 22b so as to satisfy the conditions described below.
The back side of the substrate 11 is adhered to the semiconductor or resistor base 4 by applying the following. Conductive adhesive 24
A resistant adhesive may be used instead. At this time, each lead terminal electrode 21a, 21b, 22a, 22
It may be applied to a range reaching b. As in the conventional case, each extraction electrode 16a, 16b, 17a, 1
7b are connected to the lead terminal electrodes 21a, 21b, 22a, and 22b by bonding wires, respectively. Therefore, as illustrated in FIG.
1, that is, the interdigital electrode 12, 1
3, extraction electrodes 16a, 16b, 17a, 17b,
In some cases, the surface on which the shield electrode 14 is provided may be connected to the back side of the substrate 11 via a bonding wire, a semiconductor or resistor base 4, or a conductive or resistive adhesive 24. Become. When considering such a circuit, the resistance value between the surfaces of the ferroelectric ceramic substrate 11 where electric charges are generated due to thermal shock is set as _R1 , and the total resistance value of the circuit externally connected between these surfaces is R. ₂ , the experimental results showed that when R ₂ <R ₁ , the charge due to thermal shock was quickly discharged through the above circuit, and it showed satisfactory stability against changes in the surrounding temperature environment and thermal environment.

With this configuration, for thermal shock tests,
Although the insertion loss and center frequency do not change, it is presumed that the reason why such stable characteristics are obtained is as follows.

In other words, in surface acoustic wave devices made of ferroelectric ceramics such as barium titanate, lead zirconate titanate, and lead titanate, when the ambient temperature changes, a change in spontaneous polarization occurs in the plane intersecting the polarization direction. The pyroelectric effect is created by
A charge is generated on that surface. It is thought that this charge acts as an anti-electric field that takes polarization, which is opposite to the direction of the DC electric field during the polarization process, and as a result, the piezoelectric properties of the substrate deteriorate. However, as in the above-mentioned embodiment, both sides of the board can be formed by using the semiconductivity or resistance of the base itself, which forms part of the casing, or by using the resistance of the adhesive in addition to this. When electrically connected, the charge generated by the pyro effect is discharged through this resistance, and as a result, no counter-electric field is generated, presumably preventing deterioration of the piezoelectric properties of the substrate. Therefore, as described above, the resistance used at this time must have a resistance value lower than the resistance value of the substrate itself.

In the above-described embodiments, the electrodes formed on the surface of the substrate 11 were made of a conductive material. , or may be formed by sputtering. At this time,
It will be necessary to select the resistance value of the circuits connected to both sides of the above-mentioned substrate in relation to the resistance value of the electrodes.
Materials for the semiconductor or resistor base 4 include:
Examples include semiconductor ceramic materials and resistive resins. The material of the cap 3 may be a ceramic material such as alumina or holsterite, an insulating resin such as an epoxy resin, or the same material as the base 4 described above. Note that the surface acoustic wave device unit 1 with the ground electrode 15 may be used instead of the surface acoustic wave device unit 1 without the ground electrode 15;
Care must be taken to avoid unnecessary electrical short circuits between 2a and 22b. Further, the number of lead-out terminal electrodes connected to the back surface of the surface acoustic wave device unit 1 using the conductive or resistive adhesive 24 may be, for example, only one, and it is not necessarily necessary to connect all four. Furthermore, when the shield electrode 14 is an independent electrode, a shield electrode lead electrode is provided on the semiconductor or resistor base 4, and this and the shield electrode 1
4 may be simply wire-bonded, or it may be combined with the preceding embodiment.

As described above, according to this invention, a material that exhibits semiconductivity or resistance is used as the base that forms part of the casing, and instead of the conventional insulating adhesive, it is possible to use conductive or By simply bonding the surface acoustic wave device unit to a semiconductor or a resistive base using a resistive adhesive that has Deterioration of the surface acoustic wave device is almost eliminated, and a highly stable surface acoustic wave device can be obtained. Moreover, such surface acoustic wave devices can be efficiently produced with a high yield rate and without any additional steps.

[Brief explanation of the drawing]

Figure 1 is an exploded perspective view of a conventional surface acoustic wave device.
FIG. 2 is an exploded perspective view of a surface acoustic wave device according to an embodiment of this invention, and FIG. 3 is a diagram showing the principle of a surface acoustic wave device according to an embodiment of this invention. In the figure, 1 is a surface acoustic wave device unit;
1 is a ferroelectric substrate, 12 and 13 are interdigital electrodes, 14 is a shield electrode, 15 is a ground electrode, 16a, 16b, 17a, and 17b are extraction electrodes, 21a, 21b, 22a, and 22b are extraction terminal electrodes, and 24 is an extraction terminal electrode. Conductive or resistive adhesive, 4 is the base.

Claims (1)

[Scope of utility model registration request] An inder digital electrode is provided on one surface of a polarized ferroelectric ceramic substrate, and a lead terminal electrode is provided on a semiconductor board or a resistor board.
By bonding the other surface of the ferroelectric ceramic substrate onto the semiconductor or resistor plate with an adhesive having conductivity or resistance, and by connecting the electrode provided on one surface of the ceramic substrate and the lead terminal electrode, A surface acoustic wave device in which a circuit for discharging accumulated charges is constructed between portions of a ferroelectric ceramic substrate in which positive and negative charges are accumulated due to temperature changes.