Flexible electronics : materials and sensor fabrication

FLEXIBLE ELECTRONICS: MATERIALS AND SENSOR FABRICATION by Katherine J Duncan This dissertation demonstrates how to fabricate piezoelectric/pyroelectric thin films by using different printing techniques. These techniques could replace vacuum techniques for manufacturing piezoelectric/pyroelectric sensors. Ink-jet, screen and stencil printing techniques were developed to print these devices. This work outlines attempts to develop a solution processable conductive ink for ink-jet printing. It then details the printing of commercial conductive ink on flexible substrates employing the three printing methods. Raman spectroscopy and Fourier transform infrared spectroscopy, are both used to investigate the structure of the P(VDF-TrFE) films. Optical microscopy is used to investigate the thickness and uniformity of the deposited films. The formulation of P(VDF-TrFE) for printing is also described for the three printing methods. Piezoelectric accelerometers have been developed and demonstrated. The sensors are axial compression piezoelectric accelerometers which measure impacts in the direction perpendicular to the sensors themselves. When the sensors are moved downward the top electrode tends to move upward, inducing charge via the piezoelectric effect. The sensors were mounted on an electrodynamic shaker and tested with an input vibration up to 1.5 g's at 100 Hz. The test data show that the accelerometers track the frequency of the input vibration; the output increases with increasing input acceleration. A comparison of the three printing methods to fabricate sensors on flexible substrates with commercial conductive inks and formulated P(VDF-TrFE) ink specific to the print method with similar geometries produces the following conclusions: Excellent adhesion of the commercial silver ink for screen and stencil printing has been achieved. The stencil printed silver films are smoother and more uniform than the screen printed films. Adhesion of the commercial PEDOT/PSS ink-jettable was successful. However, smoothness and uniformity were issues that need to be resolved. Also, when the ink-jetted PDOT/PSS films were exposed to high temperatures the films tended to crack and adhesion was lost. Functional devices were fabricated with screen and stencil printing quickly. In a one day period, multiple sheets of functional devices were obtained with both printing methods. Ink-jet printing, on the other hand, required greater then twenty four hours to fabricate one sheet of sensors even when the sensor size was reduced. The cost of masks/cartridges was $0.75, $1.68 and $59 per layer for stencil, screen and ink-jet printing respectively. The ink-jet print system cartridges were manufactured for one time use, whereas the masks were reusable for both screen and stencil printing. The best stencil and screen printed accelerometers demonstrated a voltage sensitivity of 145 mV/g. It is believed that the performance of these sensors can be enhanced with an automated printing system that is equipped with optical vision and automated alignment systems. The successful development of printed devices demonstrates that these print methods will be beneficial to the future of flexible electronics. FLEXIBLE ELECTRONICS: MATERIALS AND SENSOR FABRICATION by Katherine J. Duncan A Dissertation Submitted to the Faculty of New Jersey Institute of Technology and Rutgers, The State University of New Jersey-Newark in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in Applied Physics Federated Physics Department August 2008 Copyright