Foturan
Foturan is a photosensitive glass by SCHOTT Corporation developed in 1984. It is a technical glass-ceramic which can be structured without photoresist when it is exposed to shortwave radiation such as ultraviolet light and subsequently etched.
In February 2016, Schott announced the introduction of Foturan II at Photonics West. Foturan II is characterized by higher homogeneity of the photosensitivity which allows finer microstructures.
Composition and Properties
Foturan is a lithium aluminosilicate glass system doped with small amounts of silver oxides and cerium oxides.Processing
Foturan can be structured via UV-exposure, tempering and etching: Crystal nucleation grow in Foturan when exposed to UV and heat treated afterwards. The crystalized areas react much faster to hydrofluoric acid than the surrounding vitreous material, resulting in very fine microstructures, tight tolerance and high aspect ratio.Exposure
If Foturan is exposed to light in the ultra-violet-range with a wavelength of 320 nm, a chemical reaction is started in the exposed areas: The containing Ce3+ transforms into Ce4+ and frees an electron.Tempering
During the nucleation tempering, the Silver-ion Ag+ will be transferred into Ag0 by scavenging the electron released from Ce3+.This activates the agglomeration of atomic silver to form nanometer-scale silver clusters
During the subsequent crystallization tempering, lithium metasilicates forms on the silver cluster nucleation in the exposed areas. The unexposed glass, otherwise amorphous, remains unchanged.
Etching
After tempering, the crystallized areas can be etched with hydrofluoric acid 20 times faster than the unexposed, still amorphous glass. Thus, structures with an aspect ratio of ca. 10:1 can be created.Ceramization (Optional)
After etching, a ceramization of the entire substrate after a 2nd UV-exposure and thermal treatment is possible. The crystalline phase in this stage is lithium disilicate Li2Si2O5.Product characteristics
Small structure size: Structure sizes of ~ 25 μm are possibleHigh aspect ratio: Etchingratios of > 20:1 make aspect ratio of > 10:1 and a wall angle of ~ 1-2° possibleHigh optical transmission in visible and non-visible spectrum: More than 90% transmission between 350 nm and 2.700 nmHigh temperature resistance: Tg > 450°CelsiusPore-free: Suitable for biotech / microfluidics applicationLow self fluorescenceHydrolytic resistance : HGB 4Acid resistance : S 1Alkali resistance : A 2Foturan in the scientific community
Foturan is a widely known material in the material science community. As of October 30, 2015, Google Scholar showed more than 1.000 results of Foturan in scholarly literatures across an array of publishing formats and disciplines.Many of those deal with topics such as
- Micromachining Foturan
- 3D / laser direct writing in Foturan
- Using Foturan for optical waveguides
- Using Foturan for volume gratings
- Processing Foturan via excimer / femtosecond laser
Applications
Foturan is mainly used for microstructure applications, where small and complex structures have to be created out of a solid and robust base material. Overall there are five main areas for which Foturan is used:Microfluidics / Biotech Semiconductor Sensors RF / MEMS TelecomBy thermal diffusion bonding it is possible to bond multiple Foturan layers on top of each other to create complex 3-dimensional microstructures.