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(d)Electrochromic

Below the aforementioned E-paper technologies are presented in details.

2.4.1 Bichromal Displays

The term Bichromal refers to the technique where dipole microscopic plastic beads are

encapsulated in oil to rotate freely within a plastic sheet. Applying voltage across the plastic

sheet will cause the beads to rotate according to their charge and thus generates a different

pattern.

2.4.1.1 Gyricon

Gyricon was developed by a researcher Nicholas K. Sheridon in 1970 at Xerox Palo Alto

Research Center [3]. The technology itself is explained by the name given to it by the

inventor, “Gyricon means ‘rotating image’ in Greek”, and the technology is achieved by

embedding millions of small beads in an oily liquid to rotate freely beneath a thin layer of

transparent plastic. The beads are bicolored i.e. black on one side and white on the other,

placing different charge on each colored side make them act like a dipole. Applying a voltage

on a bead will cause it to rotate and the corresponding image can be viewed at the surface of

the plastic, because different text or image have different voltage pattern it can be controlled

by control logic Thin Film Transistor (TFT). Gyricon is bistable, it has about 100 dpi printing

resolution, which is not enough to fulfill all the demands of current display market. To refresh

a screen gyricon requires a special voltage pattern hence it needs a relative long response

time.

2.4.2 Electrophoretic

Electrophoresis is the migration of spherical molecules to an electrode with the opposite

charge when a voltage is applied to a biological process. The same principle is applied to

Electrophoretic displays; spherical microcapsules with particles of opposite charges are

suspended in a dielectric fluid medium. Conductive plates of cathode and anode are placed

between the embedded microcapsules. The application of voltage in the system will make the

particles in the microcapsules to migrate to the electrode with the opposite charge. If these

particles are colored according to their charge, then a viewer will notice a pattern change in

the display.

2.4.2.1 E-Ink

E-Ink, uses Electrophoretic Display (EPD) technology, it was developed in 1996 at MIT

Media Lab by Professor Joseph Jacobson [4]. The basic concept is to laminate millions of

microcapsules into a plastic circuitry. "Each microcapsule contains positively charged white

particles and negatively charged black particles suspended in a clear fluid" [5]. By placing say

a negative charge on the electrodes that are part of the circuitry a kind of dipole is formed and

the positively charged particles are attracted to the electrode while the negatively charged

particles are repelled. A viewer will then see the negatively charged particles as black spot. E-

Ink has a printing resolution of about 170 dpi. The response time is about 400 ms –1s

(compare LCD 12ms – 15ms). The contrast is ca 10:1, it is bistable.

Seiko Epson corporation used E-Ink's Electrophoretic technology in combination with both of

it's own proprietary technologies namely; low temperature polysilicon thin film transistors

(LTPS-TFT) technology and SUFTLA technology to produce a new electronic paper that

achieves Quad-XGA resolution (1536 x 2048 pixels). This resolution is considered as the

highest in the e-paper industry presently [32].

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