R2R patterned antenna structures

ExpertisePrinted Electronic Technologies

Printed Electronic Technologies

A lot of global research efforts have been spent during recent years on developing components in the field of printed electronics. Some of the components have shown excellent performance and also printability. Electronic components and systems manufactured by printing and coating techniques are therefore predicted to dramatically change the utilization of electronics in many application areas, mainly thanks to the novel form factor enabling various kinds of electronic functionalities on flexible paper or plastic substrates; a few examples of targeted applications are sensors and indicators incorporated in packages, matrix-addressed displays utilized for advertising purposes and electroluminescent lighting. However, despite the efforts, the integration of components into useful printed electronic systems and products has proven more challenging than expected. One of the major challenges is the large variety of materials and processes that are used during manufacturing, which often results in complex processing lines. Another challenge is how to design electronic systems that can accommodate the differences in drive voltage between different components. RISE Acreo is therefore providing a technology platform based on printed electronics primarily consisting of electrolyte-based components; electrochromic displays, thin film transistors, and systems thereof. These components have the benefit of being based on a small set of materials, and at the same time the components show switching times in the millisecond to second range at drive voltages around 1 volt. The latter is critical upon system integration of thin film transistors with batteries, displays and sensors.

Acreo DisplayAcreo display

The Acreo display is a printed electrochromic display (ECD) that is structured either as a lateral or a vertical electrochemical cell with a pixel electrode and a counter electrode bridged by a solid electrolyte, see the figure below. The pixel electrode, which is made from the conducting polymer PEDOT:PSS, serves both as electrochromic material and electrical conductor. When a voltage is applied across the electrodes, a redox reaction occurs, in which a negatively biased pixel electrode becomes electrochemically reduced and dark blue, while the opposite voltage polarity results in an oxidized and transparent pixel electrode. The lateral display is typically printed on paper, while the vertically structured display in most cases is printed on a plastic substrate where an opaque electrolyte hides the counter electrode, hence, both architectures are said to operate in reflection mode, that is, no backlight is used to light up the pixels.

The major advantages of the Acreo display is the wide viewing angle, the form factor, the low weight and the low manufacturing cost. Energy is mainly consumed when the display is switched. The required voltage is low, typically in the range 0.5-3 V, which allows for standard battery operation. Keeping the display updated only takes a small sustain current. The display is flexible and it can even be folded without damage.

The display elements can also be combined into a passive or active matrix addressed display. An arbitrary message or image can be presented in such matrix displays by applying a specific voltage pattern across the rows and columns, see the photograph of the chess board pattern below. The most recent research activities, that were performed in collaboration with Lintec Corp., have resulted in improved switching characteristics of the electrochemical addressing transistors used in active-matrix displays, improved color contrast of the electrochromic pixels and a novel patterning technique that can be used in the manufacturing process. Furthermore, an electrochromic pixel device showing non-linear switch characteristics has also been developed recently, such that passive matrix addressing of printed displays can be obtained, see the 16 x 16 passive-matrix display shown in the lower right photograph. 

Passive matrix addressed display

References
• Printed passive matrix addressed electrochromic displays, Organic Electronics, vol. 14, pp. 3371-3378, 2013
• Flexible active matrix addressed displays manufactured by printing and coating techniques, Journal of Polymer Science Part B: Polymer Physics, 51, 265-271, 2013
• Improving the color switch contrast in PEDOT:PSS-based electrochromic displays, Organic electronics, 13, 469-474, 2012

Electrochemical transistors

The electrochromic property of PEDOT:PSS was used in the printed Acreo display. But the electrical conductivity of PEDOT:PSS can also be modulated by electrochemical switching, which in turn makes this material suitable for use in electrochemical transistors (ECT).

By applying a positive potential to the gate electrode, relative the source and drain electrodes, the current between the source and drain electrodes can be modulated. In the ECT a high current is delivered in its on-state upon applying a negative drain potential and zero gate potential, while the transistor channel is switched off by combining a negative drain potential by a positive gate potential, that is, the ECT is a depletion mode transistor. One of the major advantages of the ECT is the low operating potentials, typically around 0.5-2 V. Such low operating potentials, which originate from the fact that the transistor is gated by an electrolyte, are desired within the field of printed electronics since printed batteries, supercapacitors or solar cells potentially can be used for powering the devices. Another important feature is that the ECT conducts current through the complete thickness of the material in the channel, which enables on-current levels in the milliampere range without device degradation. This, in turn, makes the ECT a suitable device in e.g. printed display driver circuits and smart pixel devices in active-matrix displays. The lateral design of an ECT is illustrated in the figure above, but the gate electrode can of course also be vertically deposited on top of the electrolyte. The switching behavior of a printed ECT is shown below.

  

References
• Fast-switching all-printed organic electrochemical transistors, Organic Electronics, vol. 14, no. 5, pp. 1276-1280, 2013
• Fast-Switching Printed Organic Electrochemical Transistors Including Electronic Vias Through Plastic and Paper Substrates, IEEE Transactions on Electron Devices, vol. 60, no. 6, pp. 2052-2056, 2013
• Bi-stable and dynamic current modulation in electrochemical organic transistors, Advanced Materials, 14, 51-54, 2002

Electrolyte-gated field-effect transistors

Together with the LOE research group at Linköping University we have developed the so-called electrolyte-gated OFETElectrolyte-gated field-effect transistor where the gate insulator in an OFET is replaced with a solid polyelectrolyte. This forms a transistor with low-voltage (< 1V) operation and short switching time (~50 µs) for use in e.g. logic circuits. When a negative voltage is applied to the gate electrode, cations are attracted to the negatively charged gate electrode, while anions migrate towards the interface between the electrolyte and the organic semiconductor layers, as illustrated in the figure to the right. This polarization of the electrolyte results in the formation of electric Helmholtz double-layers along the two interfaces being in contact with the electrolyte. For the electrolyte/organic semiconductor interface this sheet of charges is balanced by holes injected into the organic semiconductor from the source contact, thus establishing the transistor channel. Courtesy of Linköping University.

In the photograph to the left the OFET operates at 1 V despite the 0.2 mm thick solid electrolyte drop. Here the gate electrode is the metal wire dipped into the drop. The independence of the operating voltage with the thickness of the insulating layer makes this new kind of transistor compatible with low-cost manufacturing techniques, such as printing. Courtesy of Linköping University.

 

 

References
• Low-voltage polymer field-effect transistors gated via a proton conductor, Advanced Materials vol. 19, pp. 97-101, 2007
• Polymer field effect transistor gated via a poly(styrenesulfonic acid) thin film, Applied Physics Letters vol. 89, p. 143507, 2006

Printed diodes

Printed electronic components are predicted to contribute to the concept of Internet-of-things (IoT), in e.g. wireless electronic tags and sensors. However, printed semiconductors typically show too low charge carrier mobility, hence, the operational frequency of printed rectifiers is not high enough to enable direct communication and powering between mobile phones and printed electronic tags. We have, in collaboration with Linköping University and De La Rue, changed this viewpoint by the development of an all-printed diode operating in the GHz frequency range. The device is based on inorganic semiconducting microparticles stacked in between the patterned electrode layers, which results in an all-printed diode manufactured on a flexible plastic substrate. Furthermore, an all-printed electronic tag has been created by combining the printed diode with a patterned antenna and an electrochromic display. The concept was proven by harvesting the energy transmitted by the antenna of a mobile phone operating in the GSM band, while making a phone call, rectifying the signal by using the printed diode, and finally using the converted signal to update a printed electrochromic display. This demonstration of direct communication between an all-printed electronic label and a mobile phone has been realized and published.

References

Link to full publication

Official URL

Published in: Proceedings of the National Academy of Sciences of the United States of America (PNAS), vol. 111, pp. 11943-11948

People

Göran Gustafsson
Department Manager
+46 (0)705 82 29 04
goran.gustafsson [at] ri.se

Roman Lassnig
Development Engineer
+46 (0)70 347 56 27
roman.lassnig [at] ri.se

Negar Sani
Researcher
+46 (0)70 367 86 72
negar.sani [at] ri.se

News
In media