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2.4.3.1 Liquavista: (High Efficiency Optical System, HEOS™)

The HEOS trademark based on Electrowetting was developed inside Philips Research Labs

after decades of work. Presently the trademark and technology is being championed by

Liquavista, which is an offshoot of Philips since 2006 [12, 34]. Depicted below is one pixel of

Electro-wetting display showing optical stack of electrode, a hydrophobic insulator, a colored

oil layer and water. In a display these layers will be sandwiched between glass substrate or

polymeric substrates.

Equilibrium state (off state) On-state

Figure: 2. 4: Cross-section of HEOS (courtesy of Liquavista [34])

Applying a voltage difference across the insulator adds an electrostatic term to the energy

balance and the system mode changes leading to a state that is no longer energetically

favorable. The energy gain can be lowered by moving the water into contact with the

insulator, thereby pushing the oil to one side exposing the underlying reflecting surface. The

question about, how far the oil is pushed to the side is determined by the balance between

electrostatic and surface tension forces.

This provides a way of tuning a pixel between two states, off-state represents a colored pixel

and on-state represents white pixel. Electrowetting like all E-Paper technology does not

require backlight, its switching response speed is less than 10 milliseconds and true color can

be realized by using RGB filters.

2.4.3.2 Advanced Display Technologies (adt)

The Advanced Display Technologies is a Swiss-German company and their main focus is on

the development of innovative display technology. The company uses Electrowetting

frontplane principle in combination with their own Droplet-Driven-Display Technology, short

as D

-Technology to produce bi-stable displays. The D

-Technology allows Advanced

Display Technologies to produced Printing-like Display (PLD) in various formats, e.g. for

small, medium and large scale applications [44].

Main features of D

-Technology are high resolution and contrast, video capability, bistability

and back lighting option.

2.4.4 Cholesteric Crystal Displays

Cholesteric Liquid Crystal Displays technology is achieved by electrically manipulating the

wounded spirals of a liquid crystal molecule. These liquid crystals will reflect 50% of certain

visible wavelength depending on the alignment of the spiral with regard to the vertical or the

horizontal axis. Spirals change their alignment orthogonally when an electric field is applied

to the material. A horizontally aligned spiral will reflect the incoming light while a vertically

aligned one will allow the light to pass through. If the backplane of the display is painted

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Amazon Kindle D00111 Manuale Utente Pagina 9