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Printed Electronics World
Posted on June 8, 2007 by  & 

Flexible Electronics Pilot Lab and New Electronic Paper in Taiwan

Although we do not believe that the effort on printed electronics in Taiwan matches that in Germany, the UK, Japan or the USA as yet, very impressive things are happening there and the pace is accelerating. For example, Taiwan's Industrial Technology Research Institute (ITRI) recently inaugurated its Flexible Electronics Pilot Laboratory, the first such laboratory in Taiwan, devoted to research and development of flexible electronics and open for international cooperation. It will provide a comprehensive range of functions including synthesizing materials and developing production processes as well as product design and pilot production. It will serve as an important platform for cooperation between the international industrial and academic circles and it will facilitate the development of the flexible electronics industry in Taiwan.
Focus on production
The laboratory will initially focus on production process R&D for flexible electronic circuits, flexible solar cells, flexible reactors and flexible displays. Machinery for continuous processes will be prioritized. An industry alliance will be established to carry out joint efforts in establishing high performance flexible electronics production lines.
Photolithography, screen and ink jet
ITRI's flexible electronics pilot lab has already established a production process for 25-centimeter wide photolithography as well as three processes for ink jet printing and screen printing. The equipment and processes can be combined in a variety of ways to pave the way for the development of different types of flexible electronics products.
This will lead to the integration of chemical, manufacturing process and optoelectronics analysis as well as permit the development and pilot production, from components to entire products, on a single platform.
Domestic and international companies, academic institutions and research agencies will be welcome to engage in R&D at the laboratory. It will engage in specific cooperation projects with local companies and schools and will form international R&D alliances.
Ultrasonic paper for physiotherapy and sensing
ITRI is already releasing some exciting new inventions. This one could form a substrate for many types of co-deposited printed electronic component. They have written to us as follows:
"We successfully verified and demonstrated a novel device named polymer-based ultrasonic paper (PUP). By integrating a novel polymer-based material and innovative MEMS fabrication techniques, the prototype of polymer-based ultrasonic paper is developed.
Up to now, we believe this polymer-based ultrasonic paper is a first naturally flexible innovation in the field of capacitive micromachined ultrasonic transducers (CMUT). In some advanced application, eg, electronic paper with ultrasonic motion detector or ultrasound physiotherapy over large area, the ultrasonic transducers will be operated more or less under deformed situation to obtain the best results.
The main purpose to operate the transducers under deformation is to improve the ultrasound wave incidence efficiency and to eliminate the amount of transverse dissipated energy. The concept of flexible ultrasonic transducers is to keep each ultrasonic transducer within an array perpendicular to the relevant object's surface during ultrasonic energy transmission and/or reception stages. When compared with traditional piezoelectric transducers, CMUT seems to be a better candidate for evolving flexible variations from both structure and material viewpoints. However the flexibility of conventional silicon-based CMUT is limited because silicon wafer is known for its hardness and fragility in nature.
Nowadays, ultrasonic technology covers a wide range of measurement, diagnosing, and other applications. For most of ultrasonic devices, ultrasonic transducer is undoubtedly the most critical component that transforms electricity into mechanical energy, or vice versa. Without ultrasonic transducers, none of ultrasonic wave can be transmitted or received.
Piezoelectric material has been used as raw material of ultrasonic transducers for several decades, and its related design analysis or fabrication technologies are also mature after years of development. Because conventional piezoelectric technology can preclude the realisation of certain theoretically possible devices and configurations, the capacitive acoustic transducers have generated interest as a potential alternative to piezoelectric devices. Although capacitive acoustic transducers have been around for decades, novel developments in micro-fabrication technology have spurred the realisation of the innovative concept of capacitive micromachined ultrasonic transducers (CMUT).
Referring to most of available publications, CMUT outperforms conventional piezoelectric transducers in terms of bandwidth, sensitivity and electro-mechanical coupling efficiency. CMUT is in principle similar to a parallel plate capacitor and is like a kind of electrostatic transducer. In contrast to traditional electrostatic transducers, which are composed of a single membrane, CMUT is made of a plurality of small membranes with a diameter of 30 to 100 microns suspended over a conductive silicon substrate by insulating posts.
The corresponding operation frequency may range from a few kHz up to a hundred MHz. The gap between the opposite electrodes can be as small as 0.5 micron. The membranes are either conductive or coated with a conductive electrode and essentially create small capacitors together with the substrate. Either an electrical or acoustical force can change the distance between top and bottom electrodes within a membrane. Based on this principle, CMUT is able to transmit or receive ultrasound wave on desired frequency.
Silicon wafer has been the major constituent of CMUT since its advent. However its hardness and fragility keeps it from being candidates of other advanced applications requiring flexibility and conformity according to Snell's Law, an ultrasound wave produces both reflected and refracted waves when it passes through an interface between two materials at an oblique angle, and the materials have different indices of refraction.
The reflected wave will take away some ultrasound energy with it. If the transducers can be kept normal to the relevant surface, it will help decrease reflected and dissipated wave and then improve the efficiency of incidence. Obviously flexible ultrasonic transducers may fulfil the need in this regard. CMUT is superior to piezoelectric transducers in developing flexible variations due to its micro-scale structures. With this in mind, we proposed an innovative concept about developing an active ultrasonic device on a paper-thin polymer-base material.
After years of research, we successfully developed and demonstrated the prototype of polymer-based ultrasonic paper (PUP). These results prove that the idea of naturally flexible ultrasonic transducer can be realised other than just a concept."
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