Method of manufacturing a metallisation on a piezoelectric substrate

The invention relates to a method of producing a metallization on 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 metallizations cited. Furthermore, in "Jpn. J. Appl. Phys. ", Vol.32 (1993), pp 2351-2354 Al-Ti alloys described. The stated metallizations for enhanced performance used by surface-wave components.

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

However, all the known metallization have unfavorable Operating conditions may not be required Resistance Acousto- or electromigration on. This Acousto- or electromigration is due to an applied high electric power.

From US 4,445,066 is an electrode structure for a Zinc oxide film is known which consists of a titanium base layer and a Aluminum electrode. is from US 5233261 Multi-layer structure known of a quartz substrate, in which provided under a zinc coating a titanium bonding layer is. From JP-A-2-048811, it is known between the piezoelectric substrate and made of aluminum Electrode of a SAW component a titanium bonding layer provide.

Object of the present invention is a process for Producing a two- or multilayer metallization specify for surface acoustic wave devices, having a high resistance to electromigration or Acousto- guarantees and thus to increase the life and Reliability of electrical surface wave elements leads.

This object is achieved according to a method according to Claim 1 dissolved.

Advantageous embodiments of the subject invention are given in the subclaims.

It is first a thin, closed and mechanically stable base layer of a substrate reacting with the Metal or metal alloy in a conventional thin-film technology applied to the substrate and then this base layer a layer: made of aluminum or an aluminum alloy applied. Over the thus formed layer structure applying a cover layer, wherein for elementary and Cover layer of titanium is used.

The invention will in the following by means of embodiments explained.

On a piezoelectric substrate such as unheated Quartz, LiTaO₃ or LiNbO₃ is after the usual cleaning a thin closed mechanically stable base layer the thickness d≥15nm applied. The base layer consists of a metal, in particular titanium, or an alloy reacts with the substrate and is in a conventional thin-film technology applied (not a simple adhesive layer or seeding). This base layer is the actual conductive layer applied aluminum in a thickness d≥80nm wherein these conductive again excellent with the Base layer connects.

Surface acoustic wave devices according to a metallization the invention show opposite metallized conventionally Surface acoustic wave elements with a metallization an Al-Cu alloy, a substantially increased Leistungsver compatibility and a longer life, which substantially on a improved performance over Acousto- or Electromigration is due.

On the base layer can also first an intermediate layer be applied. The intermediate layer may also consists of titanium or a other suitable metal or metal alloy.

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