We report the control of threshold voltage (Vth) for low voltage (5V) operation in OFET by using double gate dielectric layers composed of poly (vinyl cinnamate) and SiO2. We succeeded in realizing a driving voltage of -5V and Vth shift by c.a. 1.0V. And programmed Vth was almost unchanged for 104s, where the relative change of Vth remains more than 99%.

We examined single crystal growth of benzothienobenzothiophene-based organic semiconductors by solution coating method using liquid crystal and investigated its electrical characteristics. As the results, we revealed that the averaged mobility in the saturation region reached 2.08 cm2/Vs along crystalline b-axis, and 1.08 cm2/Vs along crystalline a-axis.

The performance of devices based on two dimensional (2D) materials is significantly affected upon prolonged exposure to atmosphere. We analyzed time based environmental degradation of electrical properties of HfS2 field effect transistors. Atmospheric entities like oxygen and moisture adversely affect the device surface and reduction in drain current is observed over period of 48 hours. Two corrective measures, namely, PMMA passivation and vacuum annealing, have been studied to address the diminution of current by contaminants. PMMA passivation prevents the device from environment and reduces the effect of Coulomb scattering. Improvement in current characteristics signifies the importance of dielectric passivation for 2D materials. On the other hand, vacuum annealing is useful in removing contaminants from the affected surface. In order to figure out optimum process conditions, properties have been studied at various annealing temperatures. The improvement in drain current level was observed upon vacuum annealing within optimum range of annealing temperature.

The novel ladder-shaped polydiacetylene with a terephthalamide linker in the molecular center, namely poly(TPh-bisDA) was synthesized by photo-polymerization. The characteristics of thin films of polymer were dependent upon a casting solvent, but no significant change of backbone conformation of the PDA was observed. Obtained film is expected to be applied to the semi-conducting materials for organic field effect transistors (OFET).

A two-dimensional microarray of ten thousand (100100) chondrocyte-spheroids was successfully constructed with a 100-µm spacing on a micropatterned gold electrodes that were coated with poly(ethylene glycol) (PEG) hydrogels. The PEGylated surface as a cytophobic region was regulated by controlling the gel structure through photolithography. In this way, a PEG hydrogel was modulated enough to inhibit outgrowth of chondrocytes from cell adhering region in the horizontal direction. These structural control of PEG hydrogel was critical for inducing formation of three-dimensional chondrocyte condensations (spheroids) within 24 hours. We report noninvasive monitoring of the cellular functional change at the cell membrane using a chondrocyte-based field effect transistor (FET), which is based on detection of extracellular potential change induced as a result of the interaction between extracellular matrix (ECM) protein secreted from spheroid and substrate at the cell membrane. The interface potential change at the cell membrane/gate insulator interface can be monitored during the uptake of substrate without any labeling materials. Our findings on the time course of the interface potential would provide important information to understand the uptake kinetics for cellular differentiation.

We fabricated both thin film transistors (TFTs) and diodes using zinc oxide (ZnO) and pentacene, and investigated their basic characteristics. We found that field-effect mobility is influenced by the interface state between the semiconductor and dielectric layers. Furthermore, the complementary metal oxide semiconductor (CMOS) inverter using a p-channel pentacene field-effect transistor (FET) and an n-channel ZnO FET showed a relatively high voltage gain (8-12) by optimizing the device structure. The hybrid complementary inverters described here are expected for application in flexible displays, radio frequency identification cards (RFID) tags, and others.

Plasma oscillations in nanometer field effect transistors are used for detection and generation of electromagnetic radiation of THz frequency. Following first observations of resonant detection in 150 nm gate length GaAs HEMT, we describe recent observations of room temperature detection in nanometer Si MOSFETs, resonant detection in GaN/AlGaN HEMTs and improvement of room temperature detection in GaAs HEMTs due to the drain current. Experiments on spectrally resolved THz emission are described that involve room and liquid helium temperature emission from nanometer GaInAs and GaN HEMTs.

The carbon nanotube field-effect transistors show the hysteresis characteristic in their electrical characteristics owing to the amorphous carbon around the carbon nanotube. It is shown here the reduction of the hysteresis characteristic by the refining process applied repeatedly to the carbon nanotube. Moreover, after the refining processes, the transconductance of carbon nanotube field-effect transistor becomes 2.0 µS the ten times larger than before the refining process. Almost all carbon nanotubes without the refining processes, grown by thermal chemical vapor deposition, show the p type semiconductor characteristics. After the refining processes on the other hand, almost all carbon nanotube show the ambipolar type semiconductor characteristics.

This paper describes high power density and low distortion characteristics of a novel InGaP channel field-modulating plate FET (InGaP FP-FET) under high voltage operation of over 50 V. The developed InGaP FP-FET exhibited an extremely high breakdown voltage of 100 V with an impact ionization coefficient about 103 times smaller than that of GaAs. These superior breakdown characteristics indicate that the InGaP FP-FET is one of the most desirable device structures for high-voltage high-power operation. The InGaP FP-FET delivered an output power density of 1.6 W/mm at 1.95 GHz operated at a drain bias voltage of 55 V. As power operation moves from class A to class AB, both 3rd-order intermodulation distortion (IM3) and power-added efficiency (PAE) at higher output-power region were improved, resulting from a suppressed gate leakage current near the power saturation point. These results promise that the developed InGaP FP-FET is suited for applications in which both high efficiency and low distortion are required.

We present novel semiconductor technologies of ZnO epitaxial films with using laser molecular-beam epitaxy method. Exciting optical properties such as room temperature lasing in ZnO nanocrystalline films and quantum size effects in ZnO/MgxZn1-xO superlattices were observed. By developing crystalline quality with using lattice-matched substrates, we could control resistivity of the doped ZnO films from 10-3 Ωcm to 104 Ωcm. These results would provide us an opportunity to construct a monolithic array consisted of light emitting devices and field effect transistors towards a possible flat panel display.

We have analyzed a very short channel tunneling field effect transistor which uses new heterostructures (CoSi2/Si/CdF2/CaF2) lattice-matched to the Si substrate. In device operation, the drain current from source (CoSi2) to drain (CoSi2) through tunnel barriers (Si) and the channel (CdF2) is controlled by a gate electric field applied to the barrier between the source and the channel through the gate insulator (CaF2). Theoretical analysis shows that this transistor has characteristics similar to those of conventional metal-oxide-semiconductor field effect transistors even with channel lengths as short as 5 nm. In addition, we have estimated the theoretical response time of this transistor and showed the possibility of subpicosecond response.