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Organic thin-film transistors (OTFTs) using high-k polymeric materials have attracted considerable attention. Their fabrication processes based on printing can dramatically reduce material waste and manufacturing costs compared with conventional photolithography. However, the high operating voltage of printed OTFTs remains a significant problem. In this study, we fabricated OTFTs that can operate in low voltages by using a high-k dielectric bilayer and a paraelectric polymers. The bilayer structure provided a much higher dielectric constant (>18). The bilayer dielectric exhibited a residual polarization value of 0.3 μC cm−2 and the measured field-effect mobility of the printed OTFT was 0.91 cm2 V s−1.

A newly developed silver nanoparticle ink for gravure offset printing has been prepared through the thermal decomposition reaction of silver oxalate. The resistivity of silver thin films made of the ink was estimated to be 3.1 µΩ cm by sintering at 250 °C, which is comparable to that of bulk silver. In addition, we achieved the patterning of fine lines with a width of 20 µm using the combination of the ink and gravure offset printing. The prepared ink could be used to fabricate various printed electronic circuits in the near future.

We report on the fabrication and demonstration of fully printed ferroelectric capacitors using poly(vinylidene fluoridetrifluoroethylene) [P(VDF–TrFE)]. The printed ferroelectric capacitors were primarily fabricated by ink-jet printing on a thin plastic film substrate. The annealing process for the P(VDF–TrFE) layer was optimized from the viewpoints of surface morphology and crystallinity. A good ferroelectric polarization–electric field loop and piezoelectricity in the P(VDF–TrFE) were achieved for the printed ferroelectric capacitors. We have succeeded in the detection of a weak pressure of 150 mbar using the printed ferroelectric capacitor, which is an indication of a potential application to health-care biosensors. These results were realized by the optimization of the annealing temperature for the P(VDF–TrFE) layer.

Here, we demonstrate ultrathin, flexible nonvolatile memory devices with excellent durability under compressive strain. Ferroelectric-gate field-effect transistors (FeFETs) employing organic semiconductor and polymer ferroelectric layers are fabricated on a 1-µm-thick plastic film substrate. The FeFETs are characterized by measuring their transfer characteristics, programming time, and data retention time. The data retention time is almost unchanged even when a 50% compressive strain is applied to the devices. To clarify the origin of the excellent durability of the devices against compressive strain, an intermediate plane is calculated. From the calculation result, the intermediate plane is placed close to the channel region of the FeFETs. The high flexibility of the ferroelectric polymer and ultrathin device structure contributes to achieving a bending radius of 0.8 µm without the degradation of memory characteristics.

Fully solution-processed organic thin-film transistor (OTFT) devices have been fabricated with simple patterning process at a relatively low process temperature of 100 °C. In the patterning process, a hydrophobic amorphous fluoropolymer material, which was used as the gate dielectric layer and the underlying base layer, was treated with an oxygen plasma to selectively change its surface wetting properties from hydrophobic to hydrophilic. Silver source and drain electrodes were successfully formed in the treated areas with highly uniform line widths and without residues between the electrodes. Nonuniformities in the thickness of the silver electrodes originating from the “coffee-ring” effect were suppressed by optimizing the blend of solvents used with the silver nanoparticles, such that the printed electrodes are appropriate for bottom-gate OTFT devices. A fully solution-processed OTFT device using a polymer semiconductor material (PB16TTT) exhibited good electrical performance with no hysteresis in its transfer characteristics and with good linearity in its output characteristics. A relatively high carrier mobility of 0.14 cm2 V-1 s-1 and an on/off ratio of 1×105 were obtained with the fabricated TFT device.