View source for Foturan

[[File:Foturan_(photosensitive_glass)_-_Group-shot_of_processing_steps_of_demonstrator.jpg|thumb|400px|right|Foturan demonstrator in different processing steps (UV-exposure, tempering, etching, ceramization)]]

'''Foturan''' (notation of the manufacturer: FOTURAN) is a [[photosensitive glass]] by [[Schott AG|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 [[SPIE|Photonics West]]. Foturan II is characterized by higher homogeneity  of the photosensitivity which allows finer microstructures.<ref>{{cite web|title=Schott Press Release 02-16-2016 |url=http://www.schott.com/uk/english/news/press.html?NID=com4894|date=2016-02-16|access-date=2016-02-16}}</ref>

==  Composition and Properties ==
{| class="wikitable floatright" style="text-align:center; font-size:90%"
| style="background:#B3B7FF" colspan="13" | '''Composition'''
|-
| style="background:#E0E0E0" align="left"|Ingredient
| style="background:#E0E0E0"| SiO<sub>2</sub>
| style="background:#E0E0E0"| LiO<sub>2</sub>
| style="background:#E0E0E0"| Al<sub>2</sub>O<sub>3</sub>
| style="background:#E0E0E0"| K<sub>2</sub>O
| style="background:#E0E0E0"| Na<sub>2</sub>O
| style="background:#E0E0E0"| ZnO
| style="background:#E0E0E0"| B<sub>2</sub>O<sub>3</sub>
| style="background:#E0E0E0"| Sb<sub>2</sub>O<sub>3</sub>
| style="background:#E0E0E0"| Ag<sub>2</sub>O
| style="background:#E0E0E0"| CeO<sub>2</sub>
|-
| style="background:#E0E0E0" align="left"|Proportions (%)
| 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
|-
| style="background:#B3B7FF" colspan='13'| '''Mechanical Properties'''
|-
| style="background:#E0E0E0" align="left" colspan='10'|[[Knoop hardness test|Knoop Hardness]] in N/mm<sup>2</sup> (0.1/20)||align="right"| 480 
|-
| style="background:#E0E0E0" align="left" colspan='10'|[[Vickers hardness test|Vickers-Härte]] in N/mm<sup>2</sup> (0.2/25)||align="right"| 520 
|-
| style="background:#E0E0E0" align="left" colspan='10'| [[Density]] in g/cm<sup>3</sup> ||align="right"| 2.37 
|-
| style="background:#B3B7FF" colspan='13'| '''Thermal Properties'''
|-
| style="background:#E0E0E0" align="left" colspan='10'| [[Thermal expansion|Coefficient of mean linear thermal expansion]] a<sub>20-300</sub> in 10<sup>−6</sup>·K<sup>−1</sup> ||align="right"| 8.49
|-
| style="background:#E0E0E0" align="left" colspan='10'| [[Thermal Conductivity]] at 90&nbsp;°C in W/mK<br>{{clarify|date=August 2022}} ||align="right"| 1.28 
|-
| style="background:#E0E0E0" align="left" colspan='10'| [[Glass transition|Transformation Temperature]] T<sub>g</sub> in °C ||align="right"| 455 
|-
! style="background:#B3B7FF" colspan="11" | Electrical Properties at different frequencies
|-
| style="background:#E0E0E0" align="left" colspan='8'| Frequency (GHz)
| style="background:#E0E0E0"| 1.1
| style="background:#E0E0E0"| 1.9
| style="background:#E0E0E0"| 5
|-
! style="background:lightblue" colspan="13" | [[Relative Permittivity]]
 |-
| style="background:#E0E0E0" align="left" colspan='8'| Glass-state (annealed at 40&nbsp;°C/h)
| 6.4
| 6.4
| 6.4
|-
| style="background:#E0E0E0" align="left" colspan='8'| Ceramic-state (ceramized at 560&nbsp;°C)
| 5.8
| 5.9
| 5.8
|-
| style="background:#E0E0E0" align="left" colspan='8'| Ceramic-state (ceramized at 810&nbsp;°C)
| 5.4 
| 5.5
| 5.4
|-
| style="background:lightblue" colspan="13" | ''' [[Dissipation factor]] tan&alpha;(·10<sup>−4</sup>) '''
|-
| style="background:#E0E0E0" align="left" colspan='8'| Glass-state (annealed at 40&nbsp;°C/h)
| 84
| 90
| 109
|-
| style="background:#E0E0E0" align="left" colspan='8'| Ceramic-state (ceramized at 560&nbsp;°C)
| 58
| 65
| 79
|-
| style="background:#E0E0E0" align="left" colspan='8'| Ceramic-state (ceramized at 810&nbsp;°C)
| 39 
| 44
| 55
|-
| style="background:#B3B7FF" colspan='11'|'''Chemical Properties'''
|-
| style="background:#E0E0E0" align="left" colspan='9'| [[Hydrolytic resistance]] acc. to DIN ISO 719 in μgNa<sub>2</sub>O/g (class) ||align="right" colspan=2|  578 (HGB 4)
|-
| style="background:#E0E0E0" align="left" colspan='9'|Acid resistance acc. to DIN 12116 in mg/dm<sup>2</sup> (class) ||align="right" colspan=2|  0.48 (S1)
|-
| style="background:#E0E0E0" align="left" colspan='9'| Alkali resistance acc. to DIN ISO 695 in mg/dm<sup>2</sup> (class) ||align="right" colspan=2|  100 (A2)
|-
! style="background:#B3B7FF" colspan='13'| Optical properties
|-
! style="background:lightblue" colspan="13" | [[Refractive Index]]
|-
| style="background:#E0E0E0" align="left" colspan='6'| Wavelength (nm), &lambda;=
| style="background:#E0E0E0"| 300
| style="background:#E0E0E0"| 486.1 (n<sub>F</sub>)
| style="background:#E0E0E0"| 546.1 (n<sub>e</sub>)
| style="background:#E0E0E0"|567.6 (n<sub>d</sub>)
| style="background:#E0E0E0"|656.3 (n<sub>C</sub>)
|-
| style="background:#E0E0E0" align="left" colspan='6'| Glass-state (annealed at 40&nbsp;°C/h)
| 1.549
| 1.518
| 1.515
| 1.512
| 1.510
|-
| style="background:#E0E0E0" align="left" colspan='6'| Ceramic-state (ceramized at 560&nbsp;°C)
| n/a
| 1.519
| 1.515
| 1.513
| 1.511
|-
| style="background:#E0E0E0" align="left" colspan='6'| Ceramic-state (ceramized at 810&nbsp;°C)
| n/a 
| 1.532
| 1.528
| 1.526
| 1.523
|-
| style="background:lightblue" colspan="13" | '''[[transmittance|Spectral Transmittance]]'''
|-
| style="background:#E0E0E0" align="left" colspan='6'| &tau;(&lambda;)
| style="background:#E0E0E0"| t<sub>250</sub>
| style="background:#E0E0E0"| t<sub>270</sub>
| style="background:#E0E0E0"| t<sub>280</sub>
| style="background:#E0E0E0"| t<sub>295</sub>
| style="background:#E0E0E0"| t<sub>350</sub>
|-
| style="background:#E0E0E0" align="left" colspan='6'| in (%, 1mm){{clarify|date=August 2022}}
| 0.1
| 3
| 11
| 29
| 89
|}

Foturan is a [[lithium]] [[aluminosilicate]] glass system doped with small amounts of [[silver]] oxides and [[cerium]] oxides.<ref>{{cite web|title=Foturan Schott Website |url=http://www.schott.com/advanced_optics/english/products/optical-materials/thin-glass/foturan-2/index.html
|access-date=2016-02-12}}</ref>

== Processing ==
Foturan can be structured via [[ultra-violet|UV]]-exposure, tempering and [[Etching (microfabrication)|etching]]: Crystal [[nucleation]] grow in Foturan when exposed to [[ultraviolet|UV]] and heat treated afterwards. The [[crystal]]ized areas react much faster to [[hydrofluoric acid]] than the surrounding [[Glass|vitreous]] material, resulting in very fine [[microstructures]], tight [[tolerances|tolerance]] and high [[aspect ratios|aspect ratio]].<ref>{{cite book|last1=Höland|first1=Wolfram|title=Glass Ceramic Technology|date=1999|publisher=Wiley|isbn=0470487879|pages=236|edition=1}}</ref>

===  Exposure ===

If Foturan is exposed to [[light]] in the [[UV|ultra-violet]]-range with a [[wavelength]] of 320&nbsp;nm (eventually via [[photomask]], [[contact lithography]] or [[Photolithography#Contact and proximity|proximity lithography]] to expose certain patterns), a chemical reaction is started in the exposed areas: The containing Ce<sup>3+</sup> transforms into Ce<sup>4+</sup> and frees an electron.<ref name="ASS">{{cite journal|last1=Livingston|first1=F.E.|last2=Adams|first2=P.M.|last3=Helvajian|first3=Henry|title=Influence of cerium on the pulsed UV nanosecond laser processing of photostructurable glass ceramic materials|journal=Applied Surface Science|date=2005|volume=247|issue=1–4|page=527|doi=10.1016/j.apsusc.2005.01.158|bibcode=2005ApSS..247..526L}}</ref>
:<math>\mathrm{Ce^{3+} + h\nu(312\ \mathrm{nm}) \longrightarrow Ce^{4+} + e^- }</math>

===  Tempering ===
During the [[nucleation]] tempering (~ 500&nbsp;°C), the Silver-ion Ag<sup>+</sup> will be transferred into Ag<sup>0</sup> by scavenging the electron released from Ce<sup>3+</sup>.
:<math>\mathrm{Ag^{+} + e^- + \Delta H \longrightarrow Ag^{0} }</math>

This activates the agglomeration of atomic silver to form nanometer-scale silver clusters
:<math>\mathrm{xAg^{0} + \Delta H \longrightarrow (Ag^{0})x }</math>

During the subsequent crystallization tempering (~560-600&nbsp;°C), lithium metasilicates (Li<sub>2</sub>SiO<sub>3</sub> [[glass-ceramic]]) forms on the silver cluster nucleation in the exposed areas. The unexposed glass, otherwise [[amorphous]], remains unchanged.<ref name="ASS"/>

=== 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.<ref name="ASS"/>

=== Ceramization (Optional) ===
After [[Etching (microfabrication)|etching]], a [[ceramization]] of the entire substrate after a 2nd [[ultra-violet|UV]]-exposure and thermal treatment is possible. The crystalline phase in this stage is lithium disilicate Li<sub>2</sub>Si<sub>2</sub>O<sub>5</sub>.<ref name="ASS"/>

== Product characteristics ==
* '''Small structure size:''' Structure sizes of ~ 25 μm are possible
* '''High aspect ratio:''' [[Etching (microfabrication)|Etching]]ratios of > 20:1 make [[aspect ratio]] of > 10:1 and a wall angle of ~ 1-2° possible
* '''High optical transmission in visible and non-visible spectrum:''' More than 90% [[Transmittance|transmission]] (substrate thickness 1&nbsp;mm) between 350&nbsp;nm and 2.700&nbsp;nm
* '''High temperature resistance:''' [[Glass transition|Tg]] > 450°Celsius
* '''Pore-free:''' Suitable for [[biotech]] / [[microfluidics]] application
* '''Low [[Autofluorescence|self fluorescence]]'''
* '''Hydrolytic resistance''' (acc. to DIN ISO 719): HGB 4
* '''Acid resistance''' (acc. to DIN 12116): S 1
* '''Alkali resistance''' (acc. to DIN ISO 695): A 2

== 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.<ref>{{cite web|title=Foturan on Google Scholar|url=https://scholar.google.com/scholar?hl=en&q=foturan&btnG=&as_sdt=1%2C5&as_sdtp=|website=Google Scholar|access-date=30 October 2015}}</ref>

Many of those deal with topics such as
* Micromachining Foturan<ref>{{cite journal|last1=Rajta|first1=I.|title=Proton beam micromachining on PMMA, Foturan and CR-39 materials|journal=Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms|date=September 2003|volume=210|pages=260–265|doi=10.1016/s0168-583x(03)01025-5|bibcode=2003NIMPB.210..260R}}</ref>
* 3D / laser direct writing in Foturan<ref>{{cite journal|last1=Wang|first1=Zhongke|title=Fabrication of integrated microchip for optical sensing by femtosecond laser direct writing of Foturan glass|journal=Applied Physics A|date=October 2008|volume=93|issue=1|pages=225–229|doi=10.1007/s00339-008-4664-2|bibcode=2008ApPhA..93..225W|s2cid=19174537}}</ref>
* Using Foturan for [[Waveguide (optics)|optical waveguides]]<ref>{{cite journal|last1=An|first1=R.|title=[[Waveguide (optics)|Optical waveguide]] writing inside Foturan glass with femtosecond laser pulses|journal=Applied Physics A|date=March 2007|volume=86|issue=3|pages=343–346|doi=10.1007/s00339-006-3773-z|bibcode=2007ApPhA..86..343A|s2cid=98597105}}</ref>
* Using Foturan for volume gratings<ref>{{cite journal|last1=He|first1=Fei|title=Rapid fabrication of optical volume gratings in Foturan glass by femtosecond laser micromachining|journal=Applied Physics A|date=December 2009|volume=97|issue=4|pages=853–857|doi=10.1007/s00339-009-5338-4|bibcode=2009ApPhA..97..853H|s2cid=98824071}}</ref>
* Processing Foturan via [[Excimer laser|excimer]] / [[Ultrashort pulse|femtosecond laser]]<ref>{{cite conference|last1=Kim|first1=Joohan|editor1-first=Alberto|editor1-last=Pique|editor2-first=Koji|editor2-last=Sugioka|editor3-first=Peter R|editor3-last=Herman|editor4-first=Jim|editor4-last=Fieret|editor5-first=Friedrich G|editor5-last=Bachmann|editor6-first=Jan J|editor6-last=Dubowski|editor7-first=Willem|editor7-last=Hoving|editor8-first=Kunihiko|editor8-last=Washio|editor9-first=David B|editor9-last=Geohegan|editor10-first=Frank|editor10-last=Traeger|editor11-first=Kouichi|editor11-last=Murakami|title=Fabrication of microstructures in FOTURAN using excimer and femtosecond lasers|conference=Photon Processing in Microelectronics and Photonics II|publisher=SPIE|date=January 25, 2003|volume=4977|page=324|doi=10.1117/12.479239|bibcode=2003SPIE.4977..324K|s2cid=137683384}}</ref>

== 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]]''' (such as [[lab-on-a-chip]] or [[organ-on-a-chip]] components, [[micro mixer]], [[micro reactor]], [[Inkjet printing#Head design|printheads]], [[Microtiter plate|titer plates]], [[chip electrophoresis]])
* '''[[Semiconductor]]''' (such FED spacer, packaging elements or interposer for IC components, [[CMOS]] or [[memory module]]s)
* '''[[Semiconductor detector|Sensors]]''' (such as [[Flow sensor|flow]]- or [[temperature sensors]], [[gyroscope]]s or [[accelerometer]]s)
* '''[[Radio frequency|RF]] / [[MEMS]]''' (such as substrates or packaging elements for antennas, [[capacitor]]s, [[RF and microwave filter|filter]], [[duplexer]]s, [[RF switch|switches]] or [[Electronic oscillator|oscillators]])
* '''[[Telecommunication|Telecom]]''' (such as optical alignment chips, [[Waveguide (optics)|optical waveguides]] or optical interconnects)

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

== References ==
{{Reflist}}

== External links ==
{{Glass science}}
{{Glass makers and brands}}

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[[Category:Glass-ceramics]]
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