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Electrowetting

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Electrowetting is the change in how well a liquid wets a solid surface when an electric voltage is applied between the liquid and the surface. The voltage lowers the apparent contact angle of a conductive liquid, so a droplet spreads further or a liquid meniscus changes curvature.[1][2] In the typical electrowetting-on-dielectric (EWOD) configuration, a thin insulating layer separates the liquid from the electrode. Electrowetting is used in lab-on-a-chip devices, variable-focus liquid lenses and reflective displays.[2][3]

In virtual reality (VR) and augmented reality (AR) research, electrowetting liquid lenses have been used to change the focal distance of a head-mounted display and so address the vergence-accommodation conflict. Sheng Liu, Dewen Cheng and Hong Hua presented an optical see-through display with addressable focal planes built around such a lens at ISMAR 2008.[4][5] Later work has used electrowetting microlens arrays for focus-tunable integral imaging AR displays and electrowetting-driven droplets to steer light inside an AR waveguide combiner.[6][7]

Reviewed 13 October 2026. Checked every citation's authors, title, venue and year against Crossref and the abstracts or full texts, and the Lippmann equation, history dates, FluidFocus, Varioptic, Corning, Liquavista and VR/AR prototype figures against their cited sources. About review dates.

Principle

A droplet resting on a solid surface meets it at a contact angle set by the balance of interfacial tensions (Young's angle). In a typical EWOD configuration, a voltage is applied between a conductive liquid and a flat metal electrode coated with a thin dielectric layer. Electrostatic energy is then stored at the charged liquid/insulator interface, which favors a larger contact area, so the liquid spreads and its apparent contact angle falls.[2]

The relation between voltage and contact angle is known as the electrowetting equation, the Lippmann equation or the Young-Lippmann formula. In the form given by Dan Klarman, David Andelman and Michael Urbakh, cos θ(U) = cos θ0 + ε0εdU2/(2γd), where θ0 is the contact angle without voltage, U is the applied voltage, ε0 is the permittivity of vacuum, εd is the dielectric constant of the insulating layer, d is its thickness and γ is the tension of the liquid/ambient interface. The change in the cosine therefore grows with the square of the voltage. With alternating current, the root-mean-square voltage is commonly used in place of U.[8] The added term is a dimensionless quantity called the electrowetting number, which expresses the strength of electrostatic forces relative to surface tension.[2]

The equation holds well at low voltage, commonly for an electrowetting number below about 0.7. Above a threshold, the contact angle stops decreasing instead of reaching complete wetting as the equation predicts. This limit, called contact angle saturation, is a serious constraint on electrowetting devices. Proposed causes include the strong electric field near the three-phase contact line, charge trapping in the insulator, ionization of the surrounding medium and the ejection of tiny droplets, and a unified theory is still missing.[2][3] The insulating layer suppresses side reactions that would otherwise occur at high potentials, but according to a 2024 paper in Nanoscale Advances, EWOD has needed tens to hundreds of volts to change contact angles by about 70 degrees.[9]

History

The effect was first reported indirectly by Gabriel Lippmann in 1875, through his work on electrocapillarity. Lippmann explained how the position of a meniscus at a mercury/electrolyte interface shifted with applied potential as a change in interfacial energy.[9][1] For many decades the phenomenon received little attention, partly because the wetting effect could not easily be extended to solid conductors and because of side effects such as decomposition of the electrolyte and corrosion of the substrate. About half a century after Lippmann, A. N. Frumkin and colleagues studied oil droplets on mercury electrodes in electrolytes, building on Lippmann's theory.[9]

The term "electrowetting" was introduced by G. Beni and S. Hackwood in 1981.[1] Their paper in Applied Physics Letters proposed electrowetting as the basis of passive displays that switch reversibly from transparent to white, with a response time under 1.0 ms, operating voltages under 1.0 V and power consumption under 1.0 mW/cm2.[10] In 1993 Bruno Berge introduced a thin insulator between the conductive liquid and the metal electrode to eliminate the problem of electrolysis, the arrangement now called electrowetting-on-dielectric.[1]

Selected milestones
Year Development Ref.
1875 Gabriel Lippmann describes electrocapillarity at a mercury/electrolyte interface [9]
1981 Beni and Hackwood coin "electrowetting" and propose electrowetting displays [10]
1993 Berge adds a thin insulating layer (electrowetting-on-dielectric) [1]
2000 Pollack, Fair and Shenderov move droplets on an electrode array for microfluidics [11]
2000 Berge and Peseux publish a variable focal lens controlled by voltage [12]
2002 Bruno Berge founds Varioptic, a developer of programmable liquid lenses [13]
2003 Hayes and Feenstra (Philips Research) demonstrate video-speed electrowetting electronic paper [14]
2004 Philips shows its FluidFocus liquid lens; Kuiper and Hendriks publish the design [15][16]
2008 Liu, Cheng and Hua present an optical see-through HMD with addressable focal planes using a liquid lens [4]

The 2000 paper by Michael Pollack, Richard Fair and Alexander Shenderov described a linear array of seven electrodes at 1.5 mm pitch that moved droplets (0.7 to 1.0 µl) of potassium chloride solution between electrodes at 40 to 80 V, at switching rates of up to 20 Hz and average speeds of 30 mm/s.[11] This and related work helped popularize digital microfluidics, the droplet-based branch of lab-on-a-chip technology, and electrowetting research has also led to commercially available liquid lenses and diagnostic kits.[1]

Liquid lenses

In an electrowetting liquid lens, the curved boundary (meniscus) between two immiscible liquids acts as the lens surface. Changing the voltage changes the contact angle of the conductive liquid on the coated wall, which changes the curvature of the meniscus and therefore the focal length.[16][12] S. Kuiper and B. H. W. Hendriks of Philips showed in 2004 that two liquids in a tube form a self-centered lens of high optical quality, and they built a miniature achromatic camera module around it.[16] EE Times reported that the Philips "FluidFocus" demonstrator measured 3 mm in diameter by 2.2 mm in length, could focus from 5 cm to infinity and, according to Philips, switched over its full focal range in less than 10 milliseconds; Philips said it had tested more than 1 million focusing operations without loss of optical performance.[15]

Varioptic

Varioptic, founded in 2002 by the physicist Bruno Berge, built its products on research into electrically controlled liquid lenses carried out from the early 1990s at Joseph Fourier University in Grenoble and the physics laboratory of the École Normale Supérieure de Lyon. Parrot announced on 13 May 2011 that it had finalized the acquisition of a 100% stake in Varioptic; at that time Varioptic had 19 employees and reported 0.6 million euros of revenue for 2010.[13] Corning later announced that it had delivered its 2 millionth Corning Varioptic lens for industrial applications such as machine vision, barcode readers and medical imaging. In the announcement, John Duke, vice president and general manager of Corning Glass Microsystems, said that "Varioptic became a part of Corning in 2017 through an acquisition that included Varioptic and Invenios technologies".[17]

Varioptic's 2011 product pages described a sealed cell holding two immiscible, transparent liquids (oil and water) with different refractive indices but exactly the same density, which made the lens stable against mechanical shocks. The company stated that its "Arctic" autofocus lens changed focus from -10 to +30 diopters, that liquid lenses had been tested for over 30 million cycles, that reconfiguration could take as little as tens of milliseconds and that a typical lens dissipated about 15 mW including the driver. It also described lenses with four or eight electrodes that could tilt the liquid interface or add cylinder (astigmatism) correction, for optical image stabilization and beam control.[18]

Not every liquid lens uses electrowetting. A Meta Platforms Technologies patent on a polarization-selective varifocal liquid lens for near-eye displays lists electrowetting as one way to control the curvature of the boundary between two fluids, alongside an electrically responsive elastic membrane, mechanical force on a membrane and a pump that changes the fluid volume.[19] Electrically tunable lenses based on liquid crystals are a separate technology, described in liquid crystal lens.

Electrowetting displays

Robert A. Hayes and B. J. Feenstra of Philips Research Eindhoven reported in Nature in 2003 a reflective display in which a voltage moves a colored oil film lying next to a white substrate. They wrote that it was significantly faster than electrophoretic electronic paper, fast enough to show video, that its reflectivity and contrast approached those of paper and that their color concept was intrinsically four times brighter than reflective liquid-crystal displays.[14]

The technology was developed commercially by Liquavista, which was spun off from Philips in 2006, purchased by Samsung in 2011 and bought by Amazon in 2013.[20][21] Information Display noted at the time that Liquavista's electrowetting technology had for some time been considered a contender for color e-readers, and that neither company disclosed the price.[21] In November 2018 Display Daily reported that Amazon had confirmed to the blog The Digital Reader that Liquavista was no longer operating.[20]

Beam steering

Electrowetting can also shape a liquid into a tunable prism. Niel Smith, Jason Heikenfeld and colleagues reported electrowetting microprisms in 2006 that steered a beam continuously through 14 degrees (plus or minus 7 degrees) with a liquid of refractive index 1.359, with switching speeds of the order of milliseconds; they projected about 30 degrees of steering with higher-index liquids and discussed use in laser radar (LiDAR).[22]

Applications in VR and AR

Varifocal and multifocal head-mounted displays

Conventional stereoscopic head-mounted displays present images at a fixed focal distance, so they cannot render accommodation cues that match the vergence of the eyes. Liu, Cheng and Hua's 2008 prototype used a liquid lens with optical power variable from -5 to 20 diopters to place the display's focal plane anywhere from infinity to the near point of the eye. It was a monocular prototype built from off-the-shelf parts, and the authors measured viewers' accommodation responses to the presented focal distances.[4] In his 2016 survey of solutions to the vergence-accommodation conflict, Gregory Kramida describes the lens as an electrowetting varifocal lens and reports that it could change between any two states in that range within 74 ms, a rate of about 7 Hz; the team also tested alternative lenses with response times down to 9 ms.[5]

Liu and Hua then drove a faster liquid lens back and forth between two focal planes, synchronized with rendering of the two corresponding views, in a time-multiplexed dual-focal-plane display published in Optics Letters in 2009. Kramida reports that this reached 37.5 Hz, limited by the graphics card, and that the authors found the lens settling time shifted the focal planes and caused minor blur, a problem they expected a lens running at 60 Hz or faster to reduce.[5][23] A 2010 paper in IEEE Transactions on Visualization and Computer Graphics described a bench prototype of an optical see-through head-mounted display that could address focal distances from infinity to as close as 8 diopters, in either a vari-focal mode or a time-multiplexed multi-focal mode.[24] Kramida summarizes that this display was tested on ten subjects, with accommodation measured by a near-infrared autorefractor, and gave better accommodation cues than conventional stereoscopy. He also cites a critique by Love and colleagues that a switchable-focal-plane display needs at least four focal planes, which with a 60 Hz liquid lens would allow a refresh rate of only 12.5 Hz.[5] These designs are part of the wider family of varifocal displays.

Tunable lens arrays for integral imaging

Integral imaging avoids the vergence-accommodation conflict of stereoscopic displays, but it has a limited depth range. Cheoljoong Kim, Dooseub Shin, Gyohyun Koo and Yong Hyub Won fabricated an electrowetting liquid microlens array with a 1 mm lens pitch, 100 µm sidewalls, a total size of 20 x 14 mm, focus variable from -542 D to -89 D and a response time of 11.6 ms, and used it in a focus-tunable integral imaging system.[25] In a 2020 SPIE paper the same authors built an AR integral imaging display with a high-fill-factor hexagonal electrowetting lens array; by adjusting the voltage, they moved the central depth plane from tens of centimeters to the meter scale, a range they considered enough for typical AR use.[6] Related work is covered in Microlens Arrays and light field display.

Waveguide eyebox control

Chuan Luo and Yuzuru Takashima of the University of Arizona presented, at an SPIE AR, VR, MR conference in San Francisco in January 2025, an "active eyebox" AR combiner that adds a transparent EWOD device to a one-dimensional diffractive waveguide. Electrowetting moves liquid droplets that switch on selected sub-regions of the out-coupler, so light is sent toward the eye pupil instead of across the whole eye box, which the authors say raises light-transfer efficiency. They demonstrated the concept with an off-the-shelf EWOD device and a binary surface-relief grating waveguide.[7]

See also

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 Ya-Tang Yang, Tsung-Yi Ho (2021-05-26). "Conquering the Tyranny of Number With Digital Microfluidics". Frontiers in Chemistry, vol. 9, article 676365. doi:10.3389/fchem.2021.676365. https://doi.org/10.3389/fchem.2021.676365. Retrieved 2026-10-13.
  2. ↑ 2.0 2.1 2.2 2.3 2.4 Ioannis E. Markodimitrakis, Dionysios G. Sema, Nikolaos T. Chamakos, Periklis Papadopoulos, Athanasios G. Papathanasiou (2021). "Impact of substrate elasticity on contact angle saturation in electrowetting". Soft Matter, vol. 17, no. 16. Royal Society of Chemistry. pp. 4335-4341. doi:10.1039/d0sm02281k. https://doi.org/10.1039/d0sm02281k. Retrieved 2026-10-13.
  3. ↑ 3.0 3.1 Frieder Mugele, Jean-Christophe Baret (2005). "Electrowetting: from basics to applications". Journal of Physics: Condensed Matter, vol. 17, no. 28. IOP Publishing. pp. R705-R774. doi:10.1088/0953-8984/17/28/R01. https://doi.org/10.1088/0953-8984/17/28/R01. Retrieved 2026-10-13.
  4. ↑ 4.0 4.1 4.2 Sheng Liu, Dewen Cheng, Hong Hua (2008-09). "An optical see-through head mounted display with addressable focal planes". Proceedings of the 7th IEEE International Symposium on Mixed and Augmented Reality (ISMAR 2008), pp. 33-42. IEEE. doi:10.1109/ISMAR.2008.4637321. https://doi.org/10.1109/ISMAR.2008.4637321. Retrieved 2026-10-13.
  5. ↑ 5.0 5.1 5.2 5.3 Gregory Kramida (2016-07). "Resolving the Vergence-Accommodation Conflict in Head-Mounted Displays". IEEE Transactions on Visualization and Computer Graphics, vol. 22, no. 7. IEEE. pp. 1912-1931. doi:10.1109/TVCG.2015.2473855. https://doi.org/10.1109/TVCG.2015.2473855. Retrieved 2026-10-13.
  6. ↑ 6.0 6.1 Cheoljoong Kim, Dooseub Shin, Gyohyun Koo, Yong Hyub Won (2020-02-26). "Depth enhancement of integral imaging AR display with an electrowetting microlens array". Proceedings of SPIE, vol. 11304. SPIE. doi:10.1117/12.2546064. https://doi.org/10.1117/12.2546064. Retrieved 2026-10-13.
  7. ↑ 7.0 7.1 Chuan Luo, Yuzuru Takashima (2025). "Active eyebox waveguide combiner for augmented reality driven by electrowetting actuation". Optical Architectures for Displays and Sensing in Augmented, Virtual, and Mixed Reality (AR, VR, MR) VI, Proceedings of SPIE vol. 13414, article 134140L. SPIE. doi:10.1117/12.3044412. https://doi.org/10.1117/12.3044412. Retrieved 2026-10-13.
  8. ↑ Dan Klarman, David Andelman, Michael Urbakh (2011-04-21). "A Model of Electrowetting, Reversed Electrowetting, and Contact Angle Saturation". Langmuir, vol. 27, no. 10. American Chemical Society. pp. 6031-6041. doi:10.1021/la2004326. https://doi.org/10.1021/la2004326. Retrieved 2026-10-13.
  9. ↑ 9.0 9.1 9.2 9.3 Sittipong Kaewmorakot, Athanasios A. Papaderakis, Robert A. W. Dryfe (2024). "Electrowetting on glassy carbon substrates". Nanoscale Advances, vol. 6, no. 21. Royal Society of Chemistry. pp. 5441-5450. doi:10.1039/d4na00506f. https://doi.org/10.1039/d4na00506f. Retrieved 2026-10-13.
  10. ↑ 10.0 10.1 G. Beni, S. Hackwood (1981-02-15). "Electro-wetting displays". Applied Physics Letters, vol. 38, no. 4. American Institute of Physics. pp. 207-209. doi:10.1063/1.92322. https://doi.org/10.1063/1.92322. Retrieved 2026-10-13.
  11. ↑ 11.0 11.1 Michael G. Pollack, Richard B. Fair, Alexander D. Shenderov (2000-09-11). "Electrowetting-based actuation of liquid droplets for microfluidic applications". Applied Physics Letters, vol. 77, no. 11. American Institute of Physics. pp. 1725-1726. doi:10.1063/1.1308534. https://doi.org/10.1063/1.1308534. Retrieved 2026-10-13.
  12. ↑ 12.0 12.1 B. Berge, J. Peseux (2000-10). "Variable focal lens controlled by an external voltage: An application of electrowetting". The European Physical Journal E, vol. 3, no. 2. Springer. pp. 159-163. doi:10.1007/s101890070029. https://doi.org/10.1007/s101890070029. Retrieved 2026-10-13.
  13. ↑ 13.0 13.1 "Acquisition of a technological component in the optics sector". Parrot press release (AMF regulatory filing). Parrot. 2011-05-13. https://echanges.dila.gouv.fr/OPENDATA/AMF/ECO/2011/05/FCECO020903_20110513.pdf. Retrieved 2026-10-13.
  14. ↑ 14.0 14.1 Robert A. Hayes, B. J. Feenstra (2003-09). "Video-speed electronic paper based on electrowetting". Nature, vol. 425. Nature Publishing Group. pp. 383-385. doi:10.1038/nature01988. https://doi.org/10.1038/nature01988. Retrieved 2026-10-13.
  15. ↑ 15.0 15.1 Peter Clarke (2004-03). "Philips applies electrowetting to fluid lens". EE Times. https://www.eetimes.com/?p=1192286. Retrieved 2026-10-13.
  16. ↑ 16.0 16.1 16.2 S. Kuiper, B. H. W. Hendriks (2004-08-16). "Variable-focus liquid lens for miniature cameras". Applied Physics Letters, vol. 85, no. 7. American Institute of Physics. pp. 1128-1130. doi:10.1063/1.1779954. https://doi.org/10.1063/1.1779954. Retrieved 2026-10-13.
  17. ↑ "Corning delivers two million Varioptic lenses". Imaging and Machine Vision Europe. Corning Incorporated. https://www.imveurope.com/press-releases/corning-delivers-two-million-varioptic-lenses. Retrieved 2026-10-13.
  18. ↑ "Liquid Lens Technology". Varioptic. Varioptic. 2011. https://web.archive.org/web/20110305000132/http://www.varioptic.com/en/topmenu/liquid-lens-technology.html. Retrieved 2026-10-13.
  19. ↑ Afsoon Jamali, Changwon Jang, Sandro Pintz (2025-02-25). "US 12235458 B2: Polarization-selective varifocal liquid lens". Google Patents. Meta Platforms Technologies LLC. https://patents.google.com/patent/US12235458B2/en. Retrieved 2026-10-13.
  20. ↑ 20.0 20.1 Ken Werner (2018-11-22). "Over the River and through the Woods". Display Daily. https://displaydaily.com/over-the-river-and-through-the-woods/. Retrieved 2026-10-13.
  21. ↑ 21.0 21.1 "Industry News (July/August 2013)". Information Display. Society for Information Display. 2013-07. https://archive.informationdisplay.org/id-archive/2013/july-august/industry-news. Retrieved 2026-10-13.
  22. ↑ Niel R. Smith, Don C. Abeysinghe, Joseph W. Haus, Jason C. Heikenfeld (2006). "Agile wide-angle beam steering with electrowetting microprisms". Optics Express, vol. 14, no. 14, p. 6557. Optica Publishing Group. doi:10.1364/OE.14.006557. https://doi.org/10.1364/OE.14.006557. Retrieved 2026-10-13.
  23. ↑ Sheng Liu, Hong Hua (2009-06). "Time-multiplexed dual-focal plane head-mounted display with a liquid lens". Optics Letters, vol. 34, no. 11, p. 1642. Optica Publishing Group. doi:10.1364/OL.34.001642. https://doi.org/10.1364/OL.34.001642. Retrieved 2026-10-13.
  24. ↑ Sheng Liu, Hong Hua, Dewen Cheng (2010). "A novel prototype for an optical see-through head-mounted display with addressable focus cues". IEEE Transactions on Visualization and Computer Graphics, vol. 16, no. 3. IEEE. pp. 381-393. doi:10.1109/TVCG.2009.95. https://doi.org/10.1109/TVCG.2009.95. Retrieved 2026-10-13.
  25. ↑ Cheoljoong Kim, Dooseub Shin, Gyohyun Koo, Yong Hyub Won (2020-01-15). "Fabrication of an electrowetting liquid microlens array for a focus tunable integral imaging system". Optics Letters, vol. 45, no. 2, p. 511. Optica Publishing Group. doi:10.1364/OL.377865. https://doi.org/10.1364/OL.377865. Retrieved 2026-10-13.
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