JPH07107967B2 - Surface acoustic wave device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improving the reliability of a surface acoustic wave device, and particularly relates to a surface acoustic wave device that transmits a large amount of electric power or a surface acoustic wave with a large amplitude standing wave. The present invention relates to an electrode and a reflector suitable for a surface acoustic wave resonator.

[Background of the Invention]

The range of applications of surface acoustic wave devices has expanded, and surface acoustic wave filters that transmit large amounts of power and surface acoustic wave resonators that have large amplitude surface wave waves as standing waves have come to be used.

However, in the surface acoustic wave device as described above, the transmitting and receiving electrodes and the fine Al electrode fingers of the reflector are shown in the IEICE Transactions, Vol. J67C, pp. 278-285 (March 1984). Similarly, defects similar to defects such as protrusions (hillox) and voids due to electromigration that occur in the Al wiring electrodes of the semiconductor integrated circuit, that is,
Al migration frequently occurred, and the surface acoustic wave resonator had frequent deviations in the resonance frequency, and surface acoustic wave filters that transmitted large amounts of power often suffered short-circuiting and disconnection due to hillox growth.

In the above-mentioned literature, the mechanism of occurrence of such a defect is that "the strain on the substrate surface caused by surface acoustic waves causes internal stress in the Al thin film formed on the surface, and the stress exceeds a certain value. Grain boundary migration occurs, resulting in voids and hillocks.Grain boundary migration due to internal stress is caused by eye triple e transaction parts hybrids
And Packaging, Volume PHP-7, Issue 3, pp. 13-13
Page 8 (September 1971) (IEEE Trans, Parts, Hybrids and Pa
It is considered that the mechanism is the same as in the temperature cycle of the integrated circuit shown in ckag). ". The above-mentioned first document describes a method of adding a trace amount (1 to 4%) of copper (Cu) to Al as used in a semiconductor integrated circuit as a countermeasure against such defects due to Al migration. It shows the effectiveness against the suppression of migration.

However, when Cu is used, the hardness of the film tends to increase, and there is a drawback that wire bonding becomes difficult to hit. Further, when introducing a dry etching method for achieving high frequency and forming a fine electrode with high precision, there is a problem that corrosion of the electrode is likely to occur and the yield is significantly reduced. Furthermore, at high frequencies, the surface wave distortion increases even if the transmitted power or amplitude does not change.
With electrodes, a sufficient life cannot be guaranteed when operating at high power (large amplitude).

[Object of the Invention]

An object of the present invention is to facilitate wire bonding, to easily introduce dry etching that facilitates high precision and high yield of fine electrodes, and at the same time, suppresses Al migration to operate at high power (large amplitude). An object of the present invention is to provide a surface acoustic wave device having an electrode that enables the above.

[Outline of Invention]

In the present invention, in order to achieve the above object, not the Cu having a high boiling point of the reaction product chloride CuCl ₃ as an element to be added to Al, instead the boiling point of the chloride TiCl ₄ is low, and dry etching is also easy. It was decided to use Ti, which could not be usually considered by adding it to Al, which is an electrode material, because it causes a large increase in electric resistance. Moreover, the electrode of the high frequency surface acoustic wave device was formed by applying a sputtering method with stable composition control instead of the vapor deposition method, for example, a DC sputtering method.

As a result, the chloride produced by the reaction does not volatilize during the dry etching, and the electrodes do not corrode. In addition, since the surface acoustic wave substrate is equipped with an Al electrode added with Ti distributed over the entire cross section of the thin film, the logical consequence is that it is strengthened not only within the crystal grain boundaries but also within the crystal grains. As a result, excellent power resistance was confirmed. It should be noted that although the electrical resistance increases because Ti is added to the electrode Al, there is no problem that actually affects the operation.

[Embodiment of the Invention] An embodiment of the present invention will be described below with reference to FIG.

In this figure, reference numeral 1 is a surface acoustic wave substrate using STcut quartz, and a pair of transmitting and receiving electrodes 2, 2 ′ has an opening 1000 on the surface of the substrate.
μm, 28 pairs, which are provided so as to transmit and receive surface acoustic waves to each other. The electrodes are connected to the bonding pads 3, 3 ′ through bus bar electrodes (not shown), and the bonding pads 3, 3 ′ are Al wires. Alternatively, a gold wire bonding wire (not shown) is electrically connected to the input / output pins 4, 4'of the stem of the can package, and the ground side busbar electrode (not shown) of the transmitting / receiving electrode is the ground side. It is grounded to the stem 6 of the can package through a bonding pad (not shown). Further, reflector electrodes 10 and 10 'made up of 750 metal strips are provided on both sides of the above-mentioned pair of transmitting / receiving electrodes 2 and 2', thus forming a two-port surface acoustic wave resonator. The thickness of the transmitting / receiving electrodes 2, 2'and the reflector electrodes 10, 10 'is 0.1
In μm, the resonance frequency is 697 MHz and Q≈4000.
The electrode material is Al to which 2 wt% of Ti has been added, which is deposited by the DC magnetron sputtering method and then patterned by photo-etching. In this example, since 2 wt% of Ti was added to Al, the electric resistance of the electrode increased, but there was no problem that affected the operation. Further, since the excessive film hardness as seen in Cu addition is eliminated, wire bonding can be easily performed.

The results of the accelerated deterioration test of the surface acoustic wave resonator of this example are shown in FIG. As a comparative example, test results of a sample obtained by EB vapor deposition of Cu-containing Al are shown. The horizontal axis shows the concentration of the additive element in the film in wt%, and the vertical axis shows the deterioration time TF (Time to Failur).
e) is shown. In this case, TF is shown as the time when the resonance frequency changes. The accelerated deterioration test conditions are a temperature of 120 ° C and an input power of 100 mW. Reference numeral 11 in FIG. 2 is an experimental result of a sample obtained by EB vapor deposition of Cu-added Al shown as a comparative example, but the embodiment using the Ti-added Al sputtered electrode of the present invention shown in 12 in the figure is a comparative example. On the other hand, the deterioration time is more than 10 times, and the power resistance is greatly improved. In addition, in FIG. 12, when Ti is not added, that is, in the case of pure Al, the same FIG.
TF is larger than. The increase in TF is the effect of changing the electrode film deposition method to the EB vapor deposition method or the resistance heat vapor deposition method and using the sputtering method. This is considered to reflect the fact that the effect of a slight increase in electric resistance due to the addition of Ti can be ignored and that the mechanical strength of the film is increased by the sputtering method.

The above-mentioned embodiment is a case of a 2-aperture surface acoustic wave resonator using a reflector made of a metal film strip, but the present invention is not limited thereto, and the 1-aperture surface acoustic wave resonator and the output from the input side electrode are output. Even if it is a surface acoustic wave filter that sends a large amount of power to the side electrode, or one that uses a surface acoustic wave transmitter / receiver as a resonator, the effect is the same.
Also, the surface acoustic wave substrate is not limited to STcut quartz, but is also effective for various substrates such as LiNbO ₃ and LiTaO ₃ and cut plane orientations.

〔The invention's effect〕

In the present invention, by adding Ti to the electrode Al,
Since the Al migration is suppressed, the power resistance is significantly improved, and a surface acoustic wave device having a deterioration time of 10 times or more can be obtained. Furthermore, at the same time, conventional Cu addition
Instead of the electrode by Al EB heating evaporation or resistance heating evaporation, Ti
By using the added Al thin film as the electrode formed by the sputtering method, the introduction of dry etching was facilitated, so that the precision of the fine electrode and the yield were improved. Also,
The addition of Ti eliminates the excessive film hardness seen in addition of Cu, thus increasing the wire bonding yield.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a surface acoustic wave device as a surface acoustic wave double aperture resonator of an embodiment of the present invention, and FIG. 2 is a diagram showing results of accelerated deterioration test showing effects of the present invention. 1 ... Surface acoustic wave device 2, 2 '... Transceiver electrode 3, 3' ... Bonding pad 4, 4 '... Input / output pin 6 ... Can package stem 10, 10' ... Surface acoustic wave reflection Vessel 11 …… Comparative example with Cu added Al by EB deposition 12 …… Example showing effect of Ti addition of the present invention

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroki Isomae 1410 Inada, Katsuta City, Ibaraki Prefecture, Toda Factory, Hitachi Ltd. Inside the factory (72) Inventor Jun Yamada 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Inside Electric Appliances Research Laboratory, Hitachi, Ltd.

Claims (2)

[Claims] 1. A surface acoustic wave device comprising a surface acoustic wave substrate provided with electrodes of an Al thin film obtained by distributing and adding Ti over the entire cross section of the thin film. 2. The surface acoustic wave device according to claim 1, wherein the Al thin film has a Ti addition amount of 2 wt% or less.