(Keynote) Ferroelectric Polymers for Flexible Electronics
Authors: Stadlober Barbara , Groten Jonas , Schäffner Philipp , Scheipl Gregor , Adler Manfred , Abu Ali Taher , Tschepp Andreas , Belegratis Maria , Amon Clemens , Maurer Dietmar , Rendl Christian , Greindl Patrick , Domann Gerhard , Collin Daniela , Zirkl Martin 
Published: February 2020

Ferroelectric polymers from the PVDF-family have proven to be multifunctional and self-sustaining materials with a broad deployment in printed and flexible electronics. They can be used in large and flexible form factors for detecting mechanical excitations such as pressure variations, force touch and impact, for sensing human-body radiation and proximity, as vibration sensors for structure-borne sound detection and acoustics, as fast and high-precise strain sensors, as stretchable vital parameter sensors for movement, ECG and respiratory rate monitoring, as well as piezoelectric energy harvesting elements, just to name a few.

This talk will provide an overview of the most attractive applications of PVDF-based devices such as pressure-sensitive human-machine interfaces on planar, flexible and 3D-shaped surfaces (also in combination with flexible displays), large-area impact sensing films for material and crash testing, sensors for structural health monitoring, ultrathin microphones smoothly integrated on versatile, arbitrary shaped object surfaces, smart skin patches for vital monitoring and intelligent floor for smart home applications and energy supply for low-power sensor networks.

The sensors are entirely fabricated by screen printing which is one of the most common techniques used in printed electronics for the fabrication of large-area flexible components and multifunctional devices. Screen printing is highly tolerant to the type and form factor of substrates, the rheology of ink materials, provides sufficient alignment accuracy for multilayer printing and can be done in a sheet-to-sheet or roll-to-roll scheme.

The printed ferroelectric polymer sensors come in two versions; (i) either they have a sandwich-type structure of four layers that are printed onto a flexible or stretchable substrate (e. g. plastic films, paper, and textiles up to A3) and response accurately, fast and reproducibly to pressure and temperature changes over large dynamic ranges or (ii) a two layer structure that is highly sensitive to lateral strain and vibrations.

By optimizing the design, the printing and annealing process as well as the poling conditions and the source material, functional sensors with a soft yield of more than 98% with less than ± 5% deviation in the remnant polarization were demonstrated. It is also interesting to note that extended aging tests under definite climate and shock conditions revealed more than 98% preservation of the remnant polarization for high molecular weight PVDF-TrFE polymers. Based on these sensors applications such as flexible 3D user interfaces [1,2] (Fig. 1) and large-area force, impact and proximity sensors, ultrathin object-integrated microphones as well as medical patches will be presented either in a passive-matrix or an active-matrix ferroelectric sensor configuration with OTFT- or OECT-backplane.

Finally, a novel printable nanocomposite material, which allows reducing the cross-sensitivity between the pyro- and piezoelectric sensing modes, will be presented. This material is composed of inorganic ferroelectric nanoparticles blended in a ferroelectric polymer matrix. By exploiting the fact that the piezoelectric coefficient in inorganic ceramics has an opposite sign to that one of the ferroelectric polymer either the piezo- or the pyroelectric activity can be suppressed by independently defining the poling direction of particles and matrix in a clever poling procedure [3].

M. Zirkl, A. Sawatdee, U. Helbig, M. Krause, P. Bodö, P. Andersson Ersman, D. Platt, S. Bauer, G. Domann, and B. Stadlober, Adv. Mat. 23, 2069 (2011)

C. Rendl, D. Kim, P. Parzer, S. Fanello, M. Zirkl, G. Scheipl, M. Haller, S. Izadi, FlexCase: Enhancing Mobile Interaction with a Flexible Sensing and Display Cover, Proceedings of the 2016 CHI Conference on Human Factors in Computing Systems, San Jose, California, USA, pp. 5138-5150, doi: 10.1145/2858036.2858314 (2016)

I. Graz, M. Krause, S. Bauer-Gogonea, S. Bauer, S. P. Lacour, B. Ploss, M. Zirkl, B. Stadlober, and S. Wagner, J. Appl. Phys. 106, p. 034503 (2009)

Figure 1