Method of manufacturing a metallisation on a piezoelectric substrate

The invention relates to a method of producing a metallization on the piezoelectric substrates for surface acoustic wave devices.

Such metal coatings are known from the prior art.

In "Thin Solid Films", 16 (1973) pp 227-236 for example, Al-Cu-metallization cited. Further, in "Jpn. J. Appl. Phys.", Vol.32 (1993), pp 2351-2354 described Al-Ti alloys. The stated metallizations are used to increase performance of surface acoustic wave elements.

Attempts have also been made to produce doped and undoped epitaxial layers ( "Electronics and Communications in Japan", Part 3, Vol. 76, No. 10, 1993, pp 33-42) and Bekeimungen to improve the epitaxial growth have also been proposed ( "NEC Res. § Develop.", Vol. 35, No. 2, April 1994 S.156-164).

However, all the known metallization have under unfavorable operating conditions may not have the required strength against Acousto- or electromigration on. This Acousto- or electromigration is caused by an applied high electric power.

Object of the present invention is to provide a method for producing a two- or multi-layer metallization for surface acoustic wave elements, which ensures a high resistance to acousto- or electro-migration and thus to increase the life and reliability of electrical surface wave elements.

This object is achieved by first applying a thin, closed and mechanically stable base layer of a is applied to the substrate reacting metal or metal alloy in a conventional thin-film technology on the substrate, and that then a layer of aluminum or aluminum alloy on this base layer becomes.

Advantageous embodiments of the subject matter of the invention are set forth in the subclaims.

The invention will be explained in the following with reference to embodiments.

On a piezoelectric unheated substrate such as quartz, LiTaO₃ or LiNbO₃ applying a thin closed mechanically stable base layer of thickness d≥15nm after the usual cleaning. The base layer consists of a metal, in particular titanium, or an alloy that reacts with the substrate and is applied in a conventional thin-film technology (no easy adhesion layer or seeding). On this base layer, the actual conductive layer of aluminum with a thickness d≥80nm is applied, whereby this conductive layer in turn connects well with the base layer.

Surface acoustic wave elements with a metallization according to the invention show over conventionally metallized surface acoustic wave elements with a metallization of an Al-Cu alloy, a substantially increased power compatibility and a longer life, which is due to a significantly improved performance over acousto- or electro-migration.

On the base layer can also be applied first an intermediate layer. It may further be disposed on the entire layer structure has a cover layer. Intermediate and outer layer can optionally also be made of titanium or other suitable metal or metal alloy.

Further processing of the surface wave components, such as the separation and the assembly can be effected in a known manner.