Ryo Sugano

Fully printed and flexible ferroelectric capacitors based on a ferroelectric polymer for pressure detection

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.

Ultrathin flexible memory devices based on organic ferroelectric transistors

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.

Enhanced memory characteristics in organic ferroelectric field-effect transistors through thermal annealing

We report on the memory characteristics of organic ferroelectric field-effect transistors (FeFETs) using spin-coated poly(vinylidene difluoride/trifluoroethylene) (P(VDF/TrFE)) as a gate insulating layer. By thermal annealing the P(VDF/TrFE) layer at temperatures above its melting point, we could significantly improve the on/off current ratio to over 104. Considerable changes in the surface morphology and x-ray diffraction patterns were also observed in the P(VDF/TrFE) layer as a result of the annealing process. The enhanced memory effect is attributed to large polarization effects caused by rearranged ferroelectric polymer chains and improved crystallinity in the organic semiconductor layer of the FeFET devices.

Fully Printed Wearable Vital Sensor for Human Pulse Rate Monitoring using Ferroelectric Polymer

The ability to monitor subtle changes in vital and arterial signals using flexible devices attached to the human skin can be valuable for the detection of various health conditions such as cardiovascular disease. Conventional Si device technologies are being utilised in traditional clinical systems; however, its fabrication is not easy owing to the difficulties in adapting to conventional processes. Here, we present the development of a fully printed, wearable, ferroelectric-polymer vital sensor for monitoring the human pulse wave/rate on the skin. This vital sensor is compact, thin, sufficiently flexible, and conforms to the skin while providing high pressure sensitivity, fast response time, superior operational stability, and excellent mechanical fatigue properties. Moreover, the vital sensor is connected to a communication amplifier circuit for monitoring the pulse waves with a wireless sensing system. This sensor system can realise the development of new healthcare devices for wearable sensor applications.

Fine patterning method for silver nanoparticle electrodes using differential hydrophobic and hydrophilic surface properties

Using a simple spin-coating process, we have demonstrated a fine patterning method for silver nanoparticle ink by combining hydrophobic and hydrophilic substrate surface properties. The hydrophobic/hydrophilic treated areas were precisely formed on a glass substrate by employing a hydrophobic photoresist and a hydrophilic polymer with a conventional photolithographic patterning process. Using this technique, fine silver electrodes with spaces of 5 µm were successfully formed. We applied this method to the short-channel source/drain electrodes in organic thin-film transistor (TFT) devices and succeeded in fabricating a TFT electrode array with a resolution of 100 ppi. The short-channel pentacene TFT with silver nanoparticle electrodes showed good electrical characteristics with high yields and no hysteresis.

Development of a silver nanoparticle ink for fine line patterning using gravure offset printing

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.

Author Correction: Fully Printed Wearable Vital Sensor for Human Pulse Rate Monitoring using Ferroelectric Polymer

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has been fixed in the paper.

Fine Patterning Method for Silver Nanoparticle Electrodes Using Difference of Hydrophilic and Hydrophobic Surface Properties

By using a UV curable hydrophobic photoresist, short channel silver nanoparticle electrodes (less than 10 μm) were successfully formed by simple spin-coating process. The channel length was varied with a photomask, and we succeeded in a fabrication of a 100 ppi electrode array. This method was applied to source/drain electrodes of organic thin-film transistor, and a mobility of 0.03 cm 2 /Vs and on/off ratio of 10 6