Printed Electronics

Combination of transparent Clevios™ coating with silver ink grid, both layers applied by screen printing. Printed electronics is a new way to simple and cheap electronics. The basic idea is to use mass production printing technologies based on wet processable organic or inorganic compounds. Like in conventional electronics conductors, semiconductors and isolators (dielectrics) are needed to construct the circuits. Printed electronics targets markets like OLEDs, OSCs, smart labels, printed bi-stable displays, touchscreens and membrane switches and many more.

Heraeus offers its Clevios product range as conductive material for various printing technologies including:

Heraeus also offers semiconductors based on Oligothiophenes for organic TFTs and OSCs which can be applied by various printing methods.

An almost traditional technique in the field of printed electronics is inorganic electroluminescence (EL). EL lamps are based on the principle that a suitable semiconductor (in this case doped zinc oxide) emits light when a strong electrical field is applied.

EL-lamps are flat, quite robust and can be produced by using only screenprinting steps. The operation conditions for EL lamps are U = 100 - 300 volts AC, F = 100 - 400 Hz. The layer sequence is shown below, Clevios™ serves as the transparent top electrode.

EL lamps can be printed on glass or plastic film substrates. Flexible lamps which can be shaped are possible. Clevios™ products for this application are:

Clevios™ S HTClevios™ S V3Clevios™ S V4

Inkjet printing is a direct printing method without an intermediate form. The layout is created with the help of a computer program and directly transferred to a printer. The most common setup is a piezo-electric printhead which is triggered by voltage pulses so that it emits defined drops of liquid. The printhead is moved in x,y-direction over a substrate table. Inkjet printing allows liquids to be deposited very exactly and layouts can be changed very quickly just by changing the bitmaps in the software.

Heraeus offers a range of Clevios™ P Jet inks for inkjet printing which are either designed for good hole injection (like P Jet OLED and P Jet UA) properties or high conductivity (all other inks). The Clevios™ P Jet inks are specially prepared and filtered to meet the high standards of inkjet inks.

Organic Field Effect Transistors (OFETs) form the basic elements in printed electronic logic circuits. An OFET works on the principle that a conductive channel is induced in the organic semiconductor when a voltage is applied between source and drain. Printable organic semiconductors enable mass production in large volumes and low process times to make OFETs candidates for low cost applications like printed radio frequency identification (RFID) tags.

Printed OFETs require materials that can be deposited from solution and that preserve the flexibility of the substrate. Heraeus provides organic semiconductors (see Semiconductors) and conductive polymers for this application. Conductive polymer disperions based on Clevios™ PEDOT:PSS can be used as source, drain, and gate electrodes in OFETs. Additionally Clevios™ PEDOT:PSS is able to form vias which connect the contacts of adjacent transistors.

Several high-conductive formulations have been tailor made to support different deposition techniques:

Ink-Jet Printing:

Clevios™ P JET NClevios™ P JET N V2Clevios™ P JET HCClevios™ P JET HC V2

Sceen-Printing:
Clevios™ S V3

Structuring by etching:

Clevios™ Etch

Screen printing is a method in which the ink is pressed through the open mesh parts of a photolithographically structured screen. Screen printing inks have to be highly viscous inks.

The paste is squeezed through the mesh by a moving squeegee. Heraeus offers pastes for area printing as well as fine line printing. Feature sizes <80 µm (lines and gaps) have been printed successfully. Application examples are: touch screens, membrane switches, transparent electrodes for inorganic electroluminescent lamps and various e-paper like displays.

Printed smart labels with electronic functions can help to protect products from counterfeiting or grey-market re-selling. Smart labels and security features on plastics and paper can enable traceability throughout the whole supply chain.

The labels could be applied by printing technologies directly during the production of the packaging or high value paper based items. Customized formulations based on Clevios™ are available for a range of security applications.