Kazuma Hayasaka

Fabrication of Ultra-Thin printed organic TFT CMOS logic circuits optimized for low-voltage wearable sensor applications

Ultrathin electronic circuits that can be manufactured by using conventional printing technologies are key elements necessary to realize wearable health sensors and next-generation flexible electronic devices. Due to their low level of power consumption, complementary (CMOS) circuits using both types of semiconductors can be easily employed in wireless devices. Here, we describe ultrathin CMOS logic circuits, for which not only the source/drain electrodes but also the semiconductor layers were printed. Both p-type and n-type organic thin film transistor devices were employed in a D-flip flop circuit in the newly developed stacked structure and exhibited excellent electrical characteristics, including good carrier mobilities of 0.34 and 0.21 cm2 V−1 sec−1, and threshold voltages of nearly 0 V with low operating voltages. These printed organic CMOS D-flip flop circuits exhibit operating frequencies of 75 Hz and demonstrate great potential for flexible and printed electronics technology, particularly for wearable sensor applications with wireless connectivity.

A Printed Organic Circuit System for Wearable Amperometric Electrochemical Sensors

Wearable sensor device technologies, which enable continuous monitoring of biological information from the human body, are promising in the fields of sports, healthcare, and medical applications. Further thinness, light weight, flexibility and low-cost are significant requirements for making the devices attachable onto human tissues or clothes like a patch. Here we demonstrate a flexible and printed circuit system consisting of an enzyme-based amperometric sensor, feedback control and amplification circuits based on organic thin-film transistors. The feedback control and amplification circuits based on pseudo-CMOS inverters were successfuly integrated by printing methods on a plastic film. This simple system worked very well like a potentiostat for electrochemical measurements, and enabled the quantitative and real-time measurement of lactate concentration with high sensitivity of 1 V/mM and a short response time of a hundred seconds.

Printed 5-V organic operational amplifiers for various signal processing

The important concept of printable functional materials is about to cause a paradigm shift that we will be able to fabricate electronic devices by printing methods in air at room temperature. One of the promising applications of the printed electronics is a disposable electronic patch sensing system which can monitor the health conditions without any restraint. Operational amplifiers (OPAs) are an essential component for such sensing system, since an OPA enables a wide variety of signal processing. Here we demonstrate printed OPAs based on complementary organic semiconductor technology. They can be operated with a standard safe power source of 5 V with a minimal power consumption of 150 nW, and used as amplifiers, a variety of mathematical operators, signal converters, and oscillators. The printed micropower organic OPAs with the low voltage operation and the high versatility will open up the disposable electronic patch sensing system in near future.

A Printed Organic Amplification System for Wearable Potentiometric Electrochemical Sensors

Electrochemical sensor systems with integrated amplifier circuits play an important role in measuring physiological signals via in situ human perspiration analysis. Signal processing circuitry based on organic thin-film transistors (OTFTs) have significant potential in realizing wearable sensor devices due to their superior mechanical flexibility and biocompatibility. Here, we demonstrate a novel potentiometric electrochemical sensing system comprised of a potassium ion (K+) sensor and amplifier circuits employing OTFT-based pseudo-CMOS inverters, which have a highly controllable switching voltage and closed-loop gain. The ion concentration sensitivity of the fabricated K+ sensor was 34 mV/dec, which was amplified to 160 mV/dec (by a factor of 4.6) with high linearity. The developed system is expected to help further the realization of ultra-thin and flexible wearable sensor devices for healthcare applications.