MUVAST: Microfabrication with ultra violet-assisted sol-gel technology

• Research unit: EU RFP
• Project number: 98.0116

Key words (English)

Thin films; sol-gel deposition; ultra violet-assisted deposition; PZT; optical waveguides

Alternative project number (English)

EU project number: BRPR-CT98-0777

Research programs (English)

EU-programme: 4. Frame Research Programme - 2.1 Industrial and materials technologies

Short description (English)

See abstract

Partners and International Organizations (English)

NMRC Cork (IRL); Dublin City University (IRL); CSIC Madrid (E); Thomson-CSF Paris (F) JIPELEC Grenoble (F); DaimlerChrysler AG Munich (D)

Abstract (English)

Sol-gel technology emerges as a possibility to manufacture thin film oxides on a versatile low-cost basis for applications as optical coatings and waveguides, on-chip capacitors and memory cells, ferroelectric films for sensors and nonvolatile random access memories (FRAMs). The advantages of the sol-gel technique in respect to conventional thin film deposition methods are low investment costs for tooling, rapid processing, good homogenity over large areas, film thicknesses in excess of 1 µm and the possibility to largely tailor the film properties. At present, the crystallization of these films demands temperatures in the order of 600°C to 700°C. Such a high crystallisation temperature of ferroelectrics like lead titanate is prohibitive for many applications, since internal aluminum metallisations of standard CMOS processes of the electronics embedded in the silicon wafer do not withstand temperatures in excess of 500°C.
The MUVAST project directly addresses this demand by implementing ultra violet radiation into the sol gel processing technique in order to lower the processing temperature. The main goal of the project is the development of a ultra violet (UV)-assisted sol-gel processing for ferroelectric (PbTiO3, PT) films for silicon micromachined detectors and the development of a ultra violet-assisted sol-gel SiO2 film for telecommunication waveguides integrated on silicon.
The goal of the project has been achieved, for both ferroelectric processing and silica waveguide processing. The optimized UV-assisted sol-gel deposition technology enables a considerable reduction of the annealing temperature. In particular, the crystallisation of the ferroelectric perovskite phase of modified lead titanate from sol-gel layer has been achieved at a temperature as low as 550°C using ultraviolet-assisted rapid thermal processing. This compares well to the temperature of 650°C required to develop the same perovskite phase using purely thermal annealing. This decrease of the processing temperature provokes virtually no deterioration of the ferroelectric and piezoelectric properties of the films. Specifically, for La-modified PT the best values of piezoelectric constants d33 and e31 were 39 pm/V and 1.7 C/m2, respectively. These values were even slightly higher than the values measured on the films processed in the standard way (650°C) using the same precursors. More ambitious goals to reach the processing temperatures as low as 450-500°C failed because of the dramatic degradation of the film quality for processing temperature lower than 550°C.
In conclusion, the reduction in the maximum processing temperature achieved by UV-assisted sol-gel opens the possibilities for wider applications of ferroelectrics, high-k and oxide materials on thermally sensitive substrates and structures.

References in databases (English)

Swiss Database: Euro-DB of the
State Secretariat for Education and Research
Hallwylstrasse 4
CH-3003 Berne, Switzerland
Tel. [phone]
Swiss Project-Number: 98.0116