Plastic bioelectronics is a research field that takes advantage of the inherent properties of polymers and soft organic electronics for applications at the interface of biology and electronics. The resulting electronic materials and devices are soft, stretchable and mechanically conformable, which are important qualities for interacting with biological systems in both wearable and implantable devices. Work is currently aimed at improving these devices with a view to making the electronic-biological interface as seamless as possible.

The rise of plastic bioelectronics

One of the advantages of organic over inorganic semiconductors is they can be grown from solution, but their electrical mobility is often poor. Yuan et al. report a technique for fabricating organic transistors with mobilities far beyond that of amorphous silicon and close to that of polycrystalline silicon.

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Ultra-high mobility transparent organic thin film transistors grown by an off-centre spin-coating method

Flexible, stretchable, and spanning microelectrodes that carry signals from one circuit element to another are needed for many emerging forms of electronic and optoelectronic devices. We have patterned silver microelectrodes by omnidirectional printing of concentrated nanoparticle inks in both uniform and high-aspect ratio motifs with minimum widths of approximately 2 micrometers onto semiconductor, plastic, and glass substrates. The patterned microelectrodes can withstand repeated bending and stretching to large levels of strain with minimal degradation of their electrical properties. With this approach, wire bonding to fragile three-dimensional devices and spanning interconnects for solar cell and light-emitting diode arrays are demonstrated.

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Omnidirectional Printing of Flexible, Stretchable, and Spanning Silver Microelectrodes

New microproducts need the utilization of a diversity of materials and have complicated three-dimensional (3D) microstructures with high aspect ratios. To date, many micromanufacturing processes have been developed but specific class of such processes are applicable for fabrication of functional and true 3D microcomponents/assemblies. The aptitude to process a broad range of materials and the ability to fabricate functional and geometrically complicated 3D microstructures provides the additive manufacturing (AM) processes some profits over traditional methods, such as lithography-based or micromachining approaches investigated widely in the past. In this paper, 3D micro-AM processes have been classified into three main groups, including scalable micro-AM systems, 3D direct writing, and hybrid processes, and the key processes have been reviewed comprehensively. Principle and recent progress of each 3D micro-AM process has been described, and the advantages and disadvantages of each process have been presented.

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A review on 3D micro-additive manufacturing technologies

The cost-effective production of flexible electronic components will profit considerably from the development of solution-processable, organic semiconductor materials. Particular attention is focused on soluble semiconductors for organic field-effect transistors (OFETs). The hitherto differentiation between "small molecules" and polymeric materials no longer plays a role, rather more the ability to process materials from solution to homogeneous semiconducting films with optimal electronic properties (high charge-carrier mobility, low threshold voltage, high on/off ratio) is pivotal. Key classes of materials for this purpose are soluble oligoacenes, soluble oligo- and polythiophenes and their respective copolymers, and oligo- and polytriarylamines. In this context, micro- or nanocrystalline materials have the general advantage of somewhat higher charge-carrier mobilities, which, however, could be offset in the case of amorphous, glassy materials by simpler and more reproducible processing.

Organic semiconductors for solution-processable field-effect transistors (OFETs).

Printed electronics provides a promising potential pathway toward the realization of ultralow-cost RFID tags for item-level tracking of consumer goods. Here, we report on our progress in developing materials, processes, and devices for the realization of ultralow-cost printed RFID tags. Using printed nanoparticle patterns that are subsequently sintered at plastic-compatible temperatures, low-resistance interconnects and passive components have been realized. Simultaneously, printed transistors with mobilities >10/sup -1/ cm/sup 2//V-s have been realized using novel pentacene and oligothiophene precursors for pMOS and ZnO nanoparticles for nMOS. AC performance of these devices is adequate for 135-kHz RFID, though significant work remains to be done to achieve 13.56-MHz operation.

http://delab.csd.auth.gr/~dimitris/courses/mpc_fall05/presentation_papers/Proceedings_IEEE_July_05_rfid.pdf

Progress Toward Development of All-Printed RFID Tags: Materials, Processes, and Devices

In recent years, printing has received substantial interest as a technique for realizing low cost, large area electronic systems. Printing allows the use of purely additive processing, thus lowering process complexity and material usage. Coupled with the use of low-cost substrates such as plastic, metal foils, etc., it is expected that printed electronics will enable the realization of a wide range of easily deployable electronic systems, including displays, sensors, and RFID tags. We review our work on the development of technologies and applications for printed electronics. By combining synthetically derived inorganic nanoparticles and organic materials, we have realized a range of printable electronic ldquoinksrdquo, and used these to demonstrate printed passive components, multilayer interconnection, diodes, transistors, memories, batteries, and various types of gas and biosensors. By exploiting the ability of printing to cheaply allow for the integration of diverse functionalities and materials onto the same substrate, therefore, it is possible to realize printed systems that exploit the advantages of printing while working around the disadvantages of the same.

Printed electronics for low-cost electronic systems: Technology status and application development

In recent years, there has been tremendous interest in all-printed electronics as a means of achieving ultra-low-cost electronic circuits with uses in displays and disposable electronics applications such as RFID tags. While there have been a few demonstrations of printed organic transistors to date, there has been little work on the associated passive component and interconnection technologies required to enable the development of all-printed RFID circuits. In particular, low-resistance conductors are crucial to achieve the high-Q inductors necessary for RFID. Here, we demonstrate inkjetted nanoparticle-Au conductors on plastic with sheet resistances as low as 0.03 ohms/square. We describe the optimization of the jetting parameters, and their impact on final film morphology and electrical properties. We also demonstrate a bridging technology based on an inkjetted polyimide interlevel dielectric. Using this process, we demonstrate multilevel interconnect and passive component structures including conductor patterns, crossover bridges, and tapped planar spiral inductors. Together, these represent an important step towards the realization of all-printed RFID.

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High-quality inkjet-printed multilevel interconnects and inductive components on plastic for ultra-low-cost RFID applications

Printed electronics holds promise for realizing ultra-low-cost RFID tags for item-level tracking of consumer goods. We report on our progress in developing all-printed RFID tags. We review the development of printable materials for these applications, summarize the characteristics of printed devices, and discuss the implications of these on circuit performance limits and needs. Based on this assessment, we discuss the outlook for all-printed RFID tags and identify the problems remaining to be solved and the efforts taking place in this regard.

All-printed RFID tags: materials, devices, and circuit implications

Printed electronics is attractive as a pathway towards the realization of ultra-low-cost RFID tags for replacement of conventional optical barcodes. While this application has received tremendous attention in recent years, it also represents one of the most challenging applications for organic transistors, based on both the performance requirements and the process complexity and cost implications. Here, we report on our progress in developing materials and processes for the realization of printed transistors for low-cost RFID applications. Using inkjet printing of novel conductors, dielectrics, and organic semiconductors, we have realized printed transistors with mobilities >0.1cm 2 /V-s, which is approaching the requirements of certain RFID applications. We review the performance of these devices, and discuss optimization strategies for achieving the ultimate performance goals requisite for realizing printed RFID.

D. C. Huang

Papers

Progress Toward Development of All-Printed RFID Tags: Materials, Processes, and Devices

Printed electronics for low-cost electronic systems: Technology status and application development

High-quality inkjet-printed multilevel interconnects and inductive components on plastic for ultra-low-cost RFID applications

All-printed RFID tags: materials, devices, and circuit implications

Printed organic transistors for low-cost RFID applications