Foturan

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Foturan (spelling of the manufacturer: FOTURAN®) is a photosensitive glass that was developed in 1984 by Schott AG from Mainz . It is a technical glass ceramic whose structuring - in contrast to conventional processes - is possible without the use of photoresist . Instead, the material is exposed to short-wave radiation, such as ultraviolet light , and then etched.

In February 2016, Schott announced the market launch of Foturan II at Photonics West , which is characterized by higher homogeneity of photosensitivity, which enables finer microstructures.

Composition and properties

composition
component SiO 2 LiO 2 Al 2 O 3 K 2 O Na 2 O ZnO B 2 O 3 Sb 2 O 3 Ag 2 O CeO 2
Proportion of [%] 75-85 7-11 3-6 3-6 1-2 0-2 0-1 0.2-1 0.1-0.3 0.01-0.2
Mechanical properties
Knoop hardness in N / mm² (0.1 / 20) 480
Vickers hardness in N / mm² (0.2 / 25) 520
Density in g / cm³ 2.37
Thermal properties
Expansion coefficient a 20-300 in 10 −6 K −1 8.49
Thermal diffusivity at 90 ° C in W / (m K) 1.28
Transformation temperature T g in ° C 455
Electrical Properties
Dielectric constant
Frequency [GHz] 1.1 1.9 5
Glass condition (tempered at 40 ° C / h) 6.4 6.4 6.4
Ceramic condition (ceramized at 560 ° C) 5.8 5.9 5.8
Ceramic condition (ceramized at 810 ° C) 5.4 5.5 5.4
Loss factor tanδ (10 −4 )
Frequency [GHz] 1.1 1.9 5
Glass condition (tempered at 40 ° C / h) 84 90 109
Ceramic condition (ceramized at 560 ° C) 58 65 79
Ceramic condition (ceramized at 810 ° C) 39 44 55
Chemical properties
Hydrolysis resistance according to DIN ISO 719 in µg Na 2 O / g (class) 578 (HGB 4)
Acid resistance according to DIN 12116 in mg / dm² (class) 0.48 (S1)
Alkali resistance according to DIN ISO 695 in mg / dm² (class) 100 (A2)
Optical properties
Refractive index
Wavelength [nm], λ = 300 486.1 (n F ) 546.1 (n e ) 567.6 (n d ) 656.3 (n C )
Glass condition (tempered at 40 ° C / h) 1,549 1,518 1,515 1,512 1,510
Ceramic condition (ceramized at 560 ° C) n / A 1,519 1,515 1,513 1,511
Ceramic condition (ceramized at 810 ° C) n / A 1,532 1,528 1,526 1,523
Spectral transmittance
τ (λ) t 250 t 270 t 280 t 295 t 350
in [%, 1 mm] 0.1 3 11 29 89

Foturan is a glass system made of lithium and aluminosilicates that is doped with small amounts of silver and cerium oxides.

processing

Foturan - processing steps (schematic representation)

The structuring of Foturan consists of UV exposure, tempering and etching . The UV exposure through a photo mask excites the electrons in the illuminated areas, which triggers the crystalline nucleus growth during the subsequent heat treatment. The crystallized areas react much faster with hydrofluoric acid than the surrounding (previously not irradiated) glass-like material, which results in very fine microstructures that are characterized by a narrow tolerance and a high aspect ratio .

1) Exposure to UV light

If Foturan is exposed to UV light with a wavelength of around 320 nm (e.g. via a photo mask , contact exposure , proximity exposure to expose certain patterns), this triggers a chemical reaction in the irradiated areas: the Ce 3+ contained in it is converted into Ce 4 + and releases an electron in the process.

2) annealing

During the annealing process (approx. 500 ° C) nucleation begins in the previously exposed areas, as a result of which the silver ion Ag + absorbs the previously released electron from Ce 3+ and converts it into Ag 0 . This process is similar to a photo , or a photolithographic silicon structuring process for the production of integrated circuits and microsystems .

Through the formation of silver nuclei, further silver atoms accumulate and gradually form silver clusters on the order of a few nanometers.

During the subsequent crystallization process (tempering at 560–600 ° C), lithium metasilicates (Li 2 SiO 3 glass ceramic ) are formed in the exposed areas due to the silver clusters . This creates a crystalline structure. The previously not irradiated areas retain their amorphous glass structure.

3) etching

After the tempering process, the crystallized areas can be etched away using hydrofluoric acid , which happens 20 times faster with a crystalline structure than with an amorphous structure (the remaining unexposed areas of the photo uranium). Structures can thus be produced which have an aspect ratio of approximately 10: 1.

4) Exposure to UV light and ceramizing

After the etching process, the entire substrate can be converted into a ceramic by irradiating the material with UV light a second time and heat-treating it (at 800–900 ° C). In this state, the crystalline phase is Li 2 Si 2 O 5 .

Product features

  • Small structure sizes: structures of approx. 25 µm are possible
  • High aspect ratio: an etching ratio of> 20: 1 enables an aspect ratio of> 10: 1 and an angular deviation of the structural wall of 1–2 °
  • High optical transmission in the visible and invisible spectrum: transmission over 90% (with a substrate thickness of 1 mm) between 350 and 2700 nm
  • High temperature resistance: T g > 450 ° C
  • No pore formation: can be used for biotech / microfluidic applications
  • Low self-fluorescence
  • hydrolytic resistance (according to DIN ISO 719): HGB 4
  • Acid resistance (according to DIN 12116): S 1
  • Alkali resistance (according to DIN ISO 695): A 2

scientific publications

Foturan is widely known in the field of materials science , as can be seen from over 1000 results in the Google Scholar science database (accessed on October 30, 2015) on a wide variety of topics.

Frequently treated topics of these publications are

  • Microstructuring of Foturan
  • 3D / direct laser structuring in Foturan
  • Use of Foturan for fiber optics
  • Use of Foturan for volume grating
  • Processing of Foturan using excimer and ultrashort pulse lasers

Possible applications

Foturan is mainly used to realize microstructure applications where small and complex structures are required within a solid and robust material. There are five main areas for which Foturan can be used:

Using thermal diffusion bonding, it is also possible to connect several structured layers of Foturan glass with one another in order to produce complex three-dimensional microreactors.

Web links

Individual evidence

  1. SCHOTT brand overview. SCHOTT AG, accessed on February 7, 2016 .
  2. SCHOTT press release February 16, 2016. SCHOTT AG, February 16, 2016, accessed on February 16, 2016 .
  3. Foturan Schott website . Retrieved February 12, 2016.
  4. ^ Wolfram Höland: Glass Ceramic Technology , 1st edition, Wiley, 1999, ISBN 0470487879 , p. 236.
  5. a b c d F.E. Livingston, PM Adams, Henry Helvajian: Influence of cerium on the pulsed UV nanosecond laser processing of photostructurable glass ceramic materials . In: Applied Surface Science . No. 247, 2005, p. 527.
  6. Foturan on Google Scholar . Retrieved October 30, 2015.
  7. I. Rajta: Proton beam micromachining on PMMA, Foturan and CR-39 material . In: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms . 210, September 2003, pp. 260-265.
  8. Zhongke Wang: Fabrication of integrated microchip for optical sensing by femtosecond laser direct writing of Foturan glass . In: Applied Physics A . 93, No. 1, October 2008, pp. 225-229.
  9. R. To: Optical waveguide writing inside Foturan glass with femtosecond laser pulses . In: Applied Physics A . 86, No. 3, March 2007, pp. 343-346.
  10. Fei He: Rapid fabrication of optical volume gratings in Foturan glass by femtosecond laser micromachining . In: Applied Physics A . 97, No. 4, December 2009, pp. 853-857.
  11. Joohan Kim: Fabrication of microstructures in FOTURAN using excimer and femtosecond lasers . In: SPIE Conference Volume 4977 . January 25, 2003.