Parts of an EPD

An electronic paper display (also known as electrophoretic display or EPD) is composed of five main structures: FPL, TFT, CoG, PS, and FPC.

E-ink imaging film (Front Panel Laminate or FPL)

This is the laminate layer that contains the electronic ink material or tiny capsules filled with charged ink particles. When a proper charge is applied, an EPD creates highly detailed images with the contrast ratio and readability of printed material. PDi (Pervasive Displays inc.) uses many types of FPLs. Click here to understand the features and differences.

For a more detailed description of FPL, visit Electronic Ink Film｜E Ink Technology .

TFT thin-film transistor

A thin-film transistor (TFT) is a special type of field-effect transistor (FET) where the transistor is thin relative to the plane of the device. A common substrate is glass because the traditional application of TFTs is in liquid-crystal displays (LCDs) (or our EPDs). This differs from the conventional bulk metal oxide field effect transistor (MOSFET), where the semiconductor material typically is the substrate, such as a silicon wafer.

Driver IC and CoG

To implement the desired patterns on the FPL, the motion of charged particles in the neutral suspension is influenced by controlling the pixel electrode or gate voltage. This requires a driving waveform to be supplied by a driver IC or timing controller (Tcon). The driver a driver IC (or the “Chip on Glass”/COG) is needed for interfacing. The CoG is bonded to the TFT (transistor FT) backplane

Charge pump, a kind of DC to DC converter that uses capacitors for energetic charge storage to raise or lower voltages. A positive charge pump and a negative charge pump to provide adjustable regulated output voltages. EPD needs charge pumps to step up the voltages to supply different voltage levels to drive different color pigments in EPD module. When the DC/DC is embedded in the CoG and driving waveform is pre-programmed in CoG, we call it internal timing controller (iTC). If the DC/DC circuit is arranged outside the EPD module and driving waveform is controlled from the MCU, it is called external timing controller (eTC).

PS protective sheet

A scratch-resistant hard plastic layer to protect the FPL from the environment. Refer to this article for more information on how we develop this material in-house.

FPC

A normal 24-pin flexible printed circuit (FPC) cable allows for CoG interfacing through evaluation boards or controller boards.