New Technique for Advanced Printed Electronics

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Figure 2: (a) Schematic of synchrotron X-ray diffraction experiment and diffraction pattern of plate-like crystal, (b) Molecular packing structure within crystals, (c) Schematic of molecular chain and polarization alignment on substrate surface.

A capacitor-type device using the plate-like crystals with about 1 μm thickness exhibited quasi-rectangular loops in the electric polarization (P) versus electric field (E) hysteresis experiments without additional thermal annealing (Fig. 3a). The devices exhibited polarization switching at a very low voltage of about 3–4 V at 10 Hz. The fatigue characteristics of switching were evaluated at frequencies of 10, 100, and 1000 Hz. The ferroelectric properties could be maintained until hundreds of thousands cycles at 1000 Hz (Fig. 3b). The researchers expected that the fatigue characteristics could be improved by optimizing the device structure.

Figure 3: Ferroelectric properties of the developed single-crystalline thin film

(a) Electric polarization (P) versus electric field (E) hysteresis loops. (b) Fatigue characteristics at frequencies of 10, 100, and 1000 Hz

Piezoresponse force microscope (PFM) characterization provides microscopic information about the polarization reversal. Figure 4a shows various sizes of polarization reversal domains obtained by applying a constant DC bias of +20 V to the tip with a pulse duration varying from 10 to 1000 ms for a 1.0 µm thick film. The minimum domain size was ≈500 nm, whereas it increases logarithmically with increasing a pulse duration (Fig. 4b). This domain was found to be stable for at least 40 h under ambient pressure at room temperature. Phases of PFM images reveal that the polarization changes by not 90 degrees but 180 degrees (Fig. 4c).

Figure 4: Local polarization reversal by using a piezoresponse force microscope (PFM)

(a) PFM phase image of written domains. (b) Size variation of polarization reversal domains as a function of pulse duration for an applied electric field. (c) Phase images of vertical and lateral directions

Future Plans

The researchers aim to develop manufacturing technologies of all-printed electronics devices by combining the developed printing technique for thin film formation and other printing techniques for fabricating metal wires and semiconductor thin films.

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