Synthesis and Properties of Al-Based Amorphous and Microcrystalline Thin Films
- PDF / 493,252 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 8 Downloads / 215 Views
Synthesis and Properties of Al-Based Amorphous and Microcrystalline Thin Films Christoph Ettl, Lothar Berger, Joachim W. Mrosk and Hans-Jörg Fecht Center for Micromaterials, Ulm University, Albert-Einstein-Allee 47, D-89081 Ulm, Germany ABSTRACT Amorphous metal alloys are ideally suited for interconnects in micro-electromechanical systems (MEMS) because of their resistance against stress- and electromigration, and their stability in chemically aggressive environments, which should both lead to a substantial improvement of lifetime and reliability of robust sensors. While amorphous refractory metal alloys and amorphous silicides are excellent interconnect materials for devices operating at elevated temperatures, these systems lack the cost-effective and easy interconnect processing of the prevalent polycrystalline aluminum alloy metallizations. Amorphous aluminum alloys are applicable to devices operating at up to 200°C, and their stressmigration resistance and chemical stability is far superior to conventional polycrystalline aluminum alloys. These new metallizations are very promising for processing interconnects, in particular because of their high strength and ductility, though having low density, and their relatively low electrical resistivity compared to other amorphous metal alloys. Therefore these metallizations are especially suited for surface acoustic wave (SAW) sensors, where the interconnects are exposed to considerable mechanical strains. In this work amorphous Aluminum Yttrium alloy thin film metallizations deposited on appropriate substrates at room temperature (R.T.) by ultra-high vacuum (UHV) electron beam evaporation will be presented, and their mechanical and electronic properties together with their temperature stability will be investigated. INTRODUCTION Surface acoustic wave (SAW) devices have found widespread application in the telecommunication, consumer electronics, and automotive industry, both as passive analogous filters [1] and robust sensors [2]. They consist of one or two comb-shaped electrodes (interdigital transducers, IDTs) sitting on a piezoelectric substrate, where high frequency current is converted into mechanical displacements and vice versa. Aggressive environments place great demands on interconnect materials in SAW sensors, whereas in passive SAW devices mechanical strains produced by surface acoustic waves are the main cause for fatigue. Electromigration and stress-migration,material transport along grain boundaries, promoted by strong electric field gradients, electron flux, and mechanical strains [35], and thermal diffusion [6] generate voids in widely used polycrystalline Al and AlCu metallizations and lead to interconnect failure. The material diffuses into the substrate or grows lateral formations, known as hillocks and whiskers [7], out of the interconnects. These problems may be approached in two ways. First, a decrease of migration in polycrystalline metallizations is achieved by a diffusion barrier. This is particularly effective for operation in hot environments,
Data Loading...
