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Printed Electronics World
Posted on December 4, 2007 by  & 

A step closer to ultra low-cost disposable printed organic RFID tags

Organic materials are of great interest for electronics applications, as they have many advantages over their inorganic counterparts.
 
Communication between objects as well as objects and people allows for an unprecedented level of automation and improvement in efficiency. By putting an electronic device on every item, products within the supply chain could communicate if they have been shipped to the wrong place or warn the consumer from using them if they have expired - resulting in a demand of 10 trillion such devices a year (replacing barcodes).
 
These devices can even go further by incorporating the devices with sensors and displays which provide diagnostics and information. To be able to do this the cost of the circuit should be no more than the cost of the inks - just like the barcode. If organic semiconductors can be perfected, they promise to be inexpensive enough for practical use in disposable applications such as these.
 
Researchers at the University of Washington (Seattle) and Stanford University (Palo Alto, Calif.) have been working towards this goal and have created the first all organic nanowire integrated circuit and although others have demonstrated organic n-type and p-type thin-film transistors fabricated via high-temperature thermal evaporation, graduate researcher Alejandro Briseno at the University of Washington states that their method not only provides a simple solution-processable method of fabricating inverters, but it also demonstrates the possibility of fabricating single-crystal nanowire transistors from both p- and n-type transistors at room temperature.
 
 
According to eetimes.com, "The complementary organic semiconductor (COS) circuitry was created from nanowires that self assembled at room temperature from solutions of organic semiconductors. The semiconductor inverter gate that was produced (hexathiapentacene for p-type and perylenetetracarboxyldiimide for n-type) had a gain exceeding of 8, an on or off ratio of 104 and electron mobility on the order of one-hundredth of a square centimeter per volt-second.
 
The organic nanowire transistors are called one-dimensional because their channels self-assemble into nanowires so narrow that, mathematically, they can be treated as having only length. Compared with silicon semiconductors, organics ordinarily have much lower gain, on or off ratio and electron mobility, but by going to one-dimensional nanowires, much of that performance loss can be regained, say the researchers.
 
Because the nanowires' diameters are measured in nanometers and their growth patterns were random in the demonstration chip, arrays of nanowires were grown atop the respective source and drain electrodes to the p- and n-type transistors. First, the nanowires were self-assembled in a solution spread as a thin film, resulting in random nanowire arrays precipitated out of the organic semiconductor solution atop the electrodes."
 
According to Briseno the use of organic nanomaterials in a basic complementary inverter has not yet been demonstrated until now. They were able to accomplish this by synthesizing large quantities of crystalline nanowires from a variety of low-cost, commercially available semiconductors via a solution-phase process.
 
 
The electron mobility of the transistors in the organic inverter was measured by the research team as one-hundredth of a square centimeter per volt-second, compared with just under one square meter per volt-second for silicon - a 1,000-fold difference. However, the team has high hopes of improving the electron mobility of organic semiconductor circuitry.
 
Complementary organic semiconductors use the same energy-efficient complementary architecture as complementary metal oxide semiconductors (CMOS) but are cast in inexpensive organics instead of inorganic metal oxides.
 
Complementary metal oxide semiconductors are one of several semiconductor fabrication technologies and currently the most popular, partly because it conserves power by putting p and n type transistors back to back. This is also possible with silicon film TFTCs and ones made using organic semiconducting films. However, achieving both p and n type with polymer films based on printing inks is a relatively recent development. CMOS advantages for chip cards, tickets and tags are that it has low power consumption, operates faster and is resistant to electronic noise. CMOS can operate over a wide range of supply voltages. CMOS circuits are susceptible to damage by static electricity so care is required when handling them. They are Field Effect Transistors FETs.
 
 
Briseno also says in eetimes.com "that now, they need to work on synthesizing new organic materials that are solution-processable and that also have efficient charge transport. He says this is a challenge that the entire scientific community is actively pursuing."
 
Many organizations, research institutes and consortiums like PolyApply are working towards the realization of low-cost high-volume organic RFID tags. Printed Electronics World covered an article "Flexible Organic 13.56-MHz RFID Tag is a Cost Breakthrough."
 

Authored By:

Business Development Director, Research

Posted on: December 4, 2007

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