Electro-Active Paper(EAPap) has been recognized as a new smart material that can be used for sensors, actuators, biomimetic robots, and smart wallpapers. EAPap is made with cellulose paper by coating thin electrodes on both sides of it. This paper can produce a bending or longitudinal strain in the presence of an electric field. Also, it can produce an induced charge under the external stress. This EAPap material has many advantages in terms of large displacement output, low actuation voltage, low power consumption, dryness, flexibility, sensing capability, and biodegradable characteristics.

The Micro-Transfer Printing process includes (a) micro-patterning on cellulose paper, (b) fabrication of microelectronics, and (c) microstructure fabrication with cellulose paper.
This work was to develop a biodegradable microelectromechanical system (MEMS) fabrication with cellulose-based EAPap. A micro-transfer printing (MTP) technique was successfully demonstrated by making an interdigit transducer (IDT) pattern for a surface acoustic wave (SAW) sensor, and a microstrip pattern for a rectenna. However, there were some technical difficulties including adhesion control and contact pressure control. Thus, this work serves to improve the quality of the MTP by studying the adhesive coating, contact pressure, and depth control.

In developing biodegradable MEMS fabrication with cellulose EAPap, there are several sub-technologies: micro-patterning on cellulose paper, fabrication of microelectronics, and microstructure fabrication with cellulose paper. The MTP process has been studied to improve the quality of micro-transferred pattern. Studies included adhesion control between gold and cellulose paper, and contact alignment for pattern transfer. Several adhesive layers were tried to improve the adhesion between gold and cellulose papers. Also, the contact aligner machine was revised so as to precisely control the contact pressure and contact depth. This contact control capability allows high yield ratio on the MTP process. To demonstrate its success, dipole rectenna patterns were made.

As a microelectronic device, Schottky diodes were fabricated. Instead of using semiconductor materials such as GaAs or GaNb, nanoparticles were mixed in a resin polymer such as PEDOT, and their processability on cellulose paper was studied. MTP was used to make a pattern of semiconductor element on cellulose EAPap.

Cellulose paper fabrication was successfully established. To make microstructures with cellulose paper, micromolding can be a solution. Cellulose solution can be poured onto a micromold and cured. After that, however, washing and drying processes should be followed, which may affect the quality of the micro-molding.

The paper contained cellulose nanofibers, composed of cellulose crystalline and cellulose chains. The cellulose chains could be ordered by electrical poling and stretching. The diameters of the cellulose nanofibers were gradually reduced by increasing the stretching ratio. Dense crystalline in nanofibers of diameter 50-100 nm and ordering of cellulose chains resulted. Preliminary measurements revealed existence of direct piezoelectricity and converse piezoelectricity.

This work was done by Jaehwan Kim of South Korea’s Inha University for the Asian Office of Aerospace Research and Development. For more information, download the Technical Support Package (free white paper) at www.defensetechbriefs.com/tsp under the Materials category. AFRL-0160

This Brief includes a Technical Support Package (TSP).
Biodegradable MEMS Based on Cellulose Paper

(reference AFRL-0160) is currently available for download from the TSP library.

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This article first appeared in the December, 2010 issue of Defense Tech Briefs Magazine.

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