Printed Electronics- An Innovation to Printed Circuits
Printed Electronics (PE) is showing a trending growth in different applications. Smart labels, flexible displays, smart clothing and animation posters are the common users of PE. Creating printed electrical traces, circuits, and designs on paper makes Printed Electronics to be one of the promising technologies.
- conductive ink,
- paper or other substrates and
- a modified printer;
PE can bring out different circuits which are recyclable, flexible, and reliable and at the same time cheap.
“Defined as a set of printing methods that helps to create electrical devices on different substrates.” Here the printing uses equipments like inkjet, lithography, screen printing and flexography that are helpful to define patterns on the material. In PE, electric functioning electronic and optical inks are deposited to the substrate.
Resolution and Thickness of Printed Electronics
Resolution of the structures is determined by the human eye. In printed electronics, high resolution, small structure is essential. This is because these features are necessary to obtain better functioning and low circuit density.
Selection of the printing technology depends upon the properties and requirements of the materials to be printed and technical and economic considerations of the products. Commonly screen printing and sheet based inkjet are used for high precision and low volume work. For solar cells; flexography and offset printing technology is used. Organic FETs and different Integrated Circuits are made by using other types of printing methods. Inkjet printing is most commonly used for PE. But it has many disadvantages like low throughput and low resolution. Organic semiconductors like Organic FETs, OLEDs, and Organic Photovoltaic cells can make use of inkjet printing.
Screen printing is helpful for making conducting lines for antennas and circuit boards. Aerosol Jet printing is a deposition printing technology for PE. Beginning from atomization of ink, and then heating to 80°C, atomized droplets are being produced. The jet of droplets is allowed to impinge on to the substrate. Evaporation printing helps to print features of 5µm size. Nano imprint lithography and micro contact lithography are other techniques that can be used.
Organic and Inorganic Printed Electronics
Organic PE is the combination of chemistry, PE and material science. Since they differ from conventional electronics on the basis of structure and functionality it will affect the device functions, circuit design and even the fabrication process. Inorganic PE provides better interfaces and ordered layers.
PE generally uses substrates that are flexible which has the advantage of low cost. Screen and inkjet printing uses glass and silicon to imprint. Many printing technologies use paper to imprint. Low rough, low costs, less wet are some of the features that a substrate must have. Flexible coils, polyethylene terephthalate foil and polyethylene naphthalate are some other alternatives that can be used as substrates in PE.
The name “Conductive Ink” defines to be a type of ink which transmits electricity. Conductive Ink finds great applications in the field of printed electronics. Using this ink and different printing methods one can print circuits or designs on materials ranging from polyester to paper. The conductive particles in the ink allow the ink to expand on the substrate and thereby conduct electricity. Transforming a liquid ink to solid printing involves process like dry, cure and melts. Usually, the conductivity or resistance values of the ink are given in ohm/square /25µm. Always a high conductive ink will have low resistance.
Printed Electronics Using Conductive Ink
What is Conductive Ink made of?
The main components of conductive ink are:
- Polymer Binder
- Conductive Material
Polymer Binder: It function is to keep the pigment particles together and determine the properties of the ink. The main properties of the ink are adhesion, hardness, flexibility.
Solvent: Usually, the solvent is determined by the technique of printing or printing technology being used. For screen printing technology, generally high boiling point solvents are being used.
Conductive Material: It determines the conductivity of the final ink being produced. Silver is the commonly used to conductive material. Other materials like carbon, copper and conducting polymers are used as the conductive particles in the ink. Surface area, type of lubricant used and particle size of the conductive material has great influence on the conductivity of the ink. To improve conductivity, additives can also be added which also helps to improve adhesion, wetting and even flexibility.
After the printing process, conductive design will appear on the substrate.. Many applications of conductive ink include in RFIDs, sensors, batteries, medical applications etc.
Types of Conductive Inks
- Graphene Based Ink
Graphene based ink from Graphene NanoChem is now used widely for PE. The properties like conductivity, flexibility, transparency makes them good for PE applications like smart cards, printed displays, RF tags etc.
- Circuit Scribe
It is water based reactive, silver ink pen which is developed by Electroninks. This ink pen is good to draw circuits or designs on a paper. This pen uses a non-toxic silver conductive ink with resistance of 2-10ohms.
- Nano-silver and nano- carbon inks
Methode Electronics developed nano-carbon and nano-silver inks for PE involving inkjet printing method.
- Reactive Silver Inks
These inks are particle free. They contain diamine silver complexes due to which silver particles are developed on to the substrate after the printing purpose.
- Dielectric Inks
Screen printable ink from MINICO and ELECTRODAG can be used for both paper and other substrates. Applications like keyboards, PC desktops etc can make use of this ink.
Disadvantages of Conductive Inks
- Includes toxic materials.
- Conductivity is poor.
- Inkjet printing using conductive inks is difficult.