Foturan

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Foturan demonstrator in different processing steps (UV-exposure, tempering, etching, ceramization) Foturan (photosensitive glass) - Group-shot of processing steps of demonstrator.jpg
Foturan demonstrator in different processing steps (UV-exposure, tempering, etching, ceramization)

Foturan (notation of the manufacturer: 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.

Contents

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. [1]

Composition and Properties

Composition
IngredientSiO2LiO2Al2O3K2ONa2OZnOB2O3Sb2O3Ag2OCeO2
Proportions (%)75-857-113-63-61-20-20-10.2-10.1-0.30.01-0.2
Mechanical Properties
Knoop Hardness in N/mm2 (0.1/20)480
Vickers-Härte in N/mm2 (0.2/25)520
Density in g/cm32.37
Thermal Properties
Coefficient of mean linear thermal expansion a20-300 in 10−6·K−18.49
Thermal Conductivity at 90 °C in W/mK
[ clarification needed ]
1.28
Transformation Temperature Tg in °C455
Electrical Properties at different frequencies
Frequency (GHz)1.11.95
Relative Permittivity
Glass-state (annealed at 40 °C/h)6.46.46.4
Ceramic-state (ceramized at 560 °C)5.85.95.8
Ceramic-state (ceramized at 810 °C)5.45.55.4
Dissipation factor tanα(·10−4)
Glass-state (annealed at 40 °C/h)8490109
Ceramic-state (ceramized at 560 °C)586579
Ceramic-state (ceramized at 810 °C)394455
Chemical Properties
Hydrolytic resistance acc. to DIN ISO 719 in μgNa2O/g (class)578 (HGB 4)
Acid resistance acc. to DIN 12116 in mg/dm2 (class)0.48 (S1)
Alkali resistance acc. to DIN ISO 695 in mg/dm2 (class)100 (A2)
Optical properties
Refractive Index
Wavelength (nm), λ=300486.1 (nF)546.1 (ne)567.6 (nd)656.3 (nC)
Glass-state (annealed at 40 °C/h)1.5491.5181.5151.5121.510
Ceramic-state (ceramized at 560 °C)n/a1.5191.5151.5131.511
Ceramic-state (ceramized at 810 °C)n/a1.5321.5281.5261.523
Spectral Transmittance
τ(λ)t250t270t280t295t350
in (%, 1mm)[ clarification needed ]0.13112989

Foturan is a lithium aluminosilicate glass system doped with small amounts of silver oxides and cerium oxides. [2]

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. [3]

Exposure

If Foturan is exposed to light in the ultra-violet-range with a wavelength of 320 nm (eventually via photomask, contact lithography or proximity lithography to expose certain patterns), a chemical reaction is started in the exposed areas: The containing Ce3+ transforms into Ce4+ and frees an electron. [4]

Tempering

During the nucleation tempering (~ 500 °C), 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 (~560-600 °C), lithium metasilicates (Li2SiO3 glass-ceramic) forms on the silver cluster nucleation in the exposed areas. The unexposed glass, otherwise amorphous, remains unchanged. [4]

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. [4]

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. [4]

Product characteristics

Foturan 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. [5]

Many of those deal with topics such as

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:

By thermal diffusion bonding it is possible to bond multiple Foturan layers on top of each other to create complex 3-dimensional microstructures.

References

  1. "Schott Press Release 02-16-2016". 2016-02-16. Retrieved 2016-02-16.
  2. "Foturan Schott Website" . Retrieved 2016-02-12.
  3. Höland, Wolfram (1999). Glass Ceramic Technology (1 ed.). Wiley. p. 236. ISBN   0470487879.
  4. 1 2 3 4 Livingston, F.E.; Adams, P.M.; Helvajian, Henry (2005). "Influence of cerium on the pulsed UV nanosecond laser processing of photostructurable glass ceramic materials". Applied Surface Science. 247 (1–4): 527. Bibcode:2005ApSS..247..526L. doi:10.1016/j.apsusc.2005.01.158.
  5. "Foturan on Google Scholar". Google Scholar. Retrieved 30 October 2015.
  6. Rajta, I. (September 2003). "Proton beam micromachining on PMMA, Foturan and CR-39 materials". Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms. 210: 260–265. Bibcode:2003NIMPB.210..260R. doi:10.1016/s0168-583x(03)01025-5.
  7. Wang, Zhongke (October 2008). "Fabrication of integrated microchip for optical sensing by femtosecond laser direct writing of Foturan glass". Applied Physics A. 93 (1): 225–229. Bibcode:2008ApPhA..93..225W. doi:10.1007/s00339-008-4664-2. S2CID   19174537.
  8. An, R. (March 2007). "Optical waveguide writing inside Foturan glass with femtosecond laser pulses". Applied Physics A. 86 (3): 343–346. Bibcode:2007ApPhA..86..343A. doi:10.1007/s00339-006-3773-z. S2CID   98597105.
  9. He, Fei (December 2009). "Rapid fabrication of optical volume gratings in Foturan glass by femtosecond laser micromachining". Applied Physics A. 97 (4): 853–857. Bibcode:2009ApPhA..97..853H. doi:10.1007/s00339-009-5338-4. S2CID   98824071.
  10. Kim, Joohan (January 25, 2003). Pique, Alberto; Sugioka, Koji; Herman, Peter R; Fieret, Jim; Bachmann, Friedrich G; Dubowski, Jan J; Hoving, Willem; Washio, Kunihiko; Geohegan, David B; Traeger, Frank; Murakami, Kouichi (eds.). Fabrication of microstructures in FOTURAN using excimer and femtosecond lasers. Photon Processing in Microelectronics and Photonics II. Vol. 4977. SPIE. p. 324. Bibcode:2003SPIE.4977..324K. doi:10.1117/12.479239. S2CID   137683384.