Ferroelectric material supports both pyro- and piezoelectric effects that can be used for sensing pressures on large, bended surfaces. We present PyzoFlex, a pressure-sensing input device that is based on a ferroelectric material (PVDF:TrFE). It is constructed by a sandwich structure of four layers that can easily be printed on any substrate. The PyzoFlex foil is sensitive to pressure- and temperature changes, bendable, energy-efficient, and it can easily be produced by a screen-printing routine. Even a hovering input-mode is feasible due to its pyroelectric effect. In this paper, we introduce this novel, fully printed input technology and discuss its benefits and limitations.
This work demonstrates a novel surface scanning method for the quantitative determination of the local pyroelectric coefficient in ferroelectric thin films. Such films find application in flexible and large-area printed ferroelectric sensors for gesture-controlled non-touch human-machine interface devices.
The method is called Pyroelectric Scanning Probe Microscopy (PyroSPM)[1] and allows generating a map of the pyroelectric response with very high spatial resolution. In domains of previously aligned dipole moments small heat fluctuations are achieved by laser diode excitation from the bottom side thus inducing changes in the surface potential due to the pyroelectric effect. Simultaneously, the surface potential variations are detected by scanning surface potential microscopy thus forming the base for the pyroelectric coefficient map. The potential of the method is demonstrated on the basis of ferroelectric semi-crystalline copolymer thin films yielding local maxima of the pyroelectric coefficients around 40µC/m2K. Another promising feature of PyroSPM is the ability to visualize “screened” polarization thus enabling in-depth profiling of polarization distributions and domain formation and to study the composition dependence and the time and frequency behavior of ferroelectric nano-domains.
We demonstrate the printing of a complex smart integrated system using only five functional inks: the fluoropolymer
P(VDF:TrFE) (Poly(vinylidene fluoride trifluoroethylene) sensor ink, the conductive polymer PEDOT:PSS (poly(3,4
ethylenedioxythiophene):poly(styrene sulfonic acid) ink, a conductive carbon paste, a polymeric electrolyte and SU8 for
separation. The result is a touchless human-machine interface, including piezo- and pyroelectric sensor pixels (sensitive
to pressure changes and impinging infrared light), transistors for impedance matching and signal conditioning, and an
electrochromic display. Applications may not only emerge in human-machine interfaces, but also in transient
temperature or pressure sensing used in safety technology, in artificial skins and in disposable sensor labels.
Here we report on the fabrication and detailed characterization of flexible low-voltage organic thin-film transistors
directly integrated with pyro- and piezoelectric sensors. The functional layer of the capacitive sensors is a ferroelectric
fluoropolymer. The transistors on the other hand are based on a high-k nanocomposite gate dielectric and on pentacene
as the organic semiconductor and can be operated well below 5V. It is shown, that the transistors can be fabricated on the
fluororpolymer layer. Since the control of parameter spread is a very important topic in large area electronics, it was
attempted to investigate the homogeneity of a significant set of devices by individual assessment of the layer
composition and thickness, the pentacene morphology, the actual geometry and the electrical parameters. It turned out
that starting from the measured device parameters such as layer thickness, capacitance, channel dimension, grain size
and threshold voltage, the drain current can be calculated with high accuracy in a specified operation point. In addition, it
is shown that the main influence on the parameter spread originates from the variations in the threshold voltage. Storage
in air destroys the transistors on the long term, whereas bias stress measurements under inert conditions reveal that the
interfaces are very stable.
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