We have designed gate arrays using low-temperature poly-Si thin-film transistors and confirmed the correct operations. Various kinds of logic gates are beforehand prepared, contact holes are later bored, and mutual wiring is formed between the logic gates on demand. A half adder, two-bit decoder, and flip flop are composed as examples. The static behaviors are evaluated, and it is confirmed that the correct waveforms are output. The dynamic behaviors are also evaluated, and it is concluded that the dynamic behaviors of the gate array are less deteriorated than that of the independent circuit.

A novel driving concept, "pulse-width modulation with current uniformization," is proposed for thin-film transistor driven organic light-emitting diode displays (TFT-OLEDs). An example of this driving concept is the combination of "pulse-width modulation with a self-biased inverter" and a "time-ratio grayscale with current uniformization." Its driving operation is confirmed by circuit simulation. It is found that this driving method can compensate the characteristic deviations and degradations of both TFTs and OLEDs and immensely improve luminance uniformity. Finally, its driving operation is also confirmed by an actual pixel equivalent circuit.

Driving methods for TFT-OLEDs are explained with their features and classified from the viewpoints of grayscale methods and uniformizing methods. This classification leads us to a novel proposal using time ratio grayscale and current uniformization. This driving method maintains current uniformity and simultaneously overcomes charging shortage of the pixel circuit for low grayscale levels and current variation due to the shift of operating points. Tolerance toward degraded characteristics, linearity of grayscale and luminance uniformity against degraded characteristics are confirmed using circuit simulation.

The pseudo-lattice method has been developed for dynamic 3-D liquid-crystal director simulation in thin-film-transistor liquid-crystal displays. Its feature is that the equation of motion of the director is not formularized from the real-lattices, but from the pseudo-lattices organized between the real-lattices. The director on the pseudo-lattice is calculated from the real-lattices by insertion. The objective is to simulate the continuous nematic symmetry correctly and to reduce time and memory needed for the calculation. Especially in this paper, the pseudo-lattice method is explained in detail. Moreover, experiments have been done, and the simulated behavior and location of the bright line, which is caused by the distortion of the director profile, were confirmed to be the same as the actual ones. In particular, the movement and elimination process of the bright line were simulated for the first time.

Thermoelectric effect of Ga-Sn-O (GTO) thin films has been investigated for Internet-of-Things application. It is found that the amorphous GTO thin films provide higher power factors (PF) than the polycrystalline ones, which is because grain boundaries block the electron conduction in the polycrystalline ones. It is also found that the GTO thin films annealed in vacuum provide higher PF than those annealed in air, which is because oxygen vacancies are terminated in those annealed in air. The PF and dimensionless figure of merit (ZT) is not so excellent, but the cost effectiveness is excellent, which is the most important for some examples of the Internet-of-Things application.

Promising proposals of a material, deposition process, and storage device have been demonstrated for neuromorphic systems. The material is Ga-Sn-O (GTO), amorphous metal-oxide semiconductor, and does not contain rare metals such as In. The deposition process is a mist chemical-vapor-deposition (CVD) method, atmospheric pressure process. Therefore, the material and fabrication costs can be simultaneously saved, and three-dimensional stacked structures will be possible. The storage device is an analog memristor, a kind of memristors, but has continuous conductance, and analog computing will be possible owing to continuous weights of synapse elements in neural networks. These structures and computing are the same as those in living brains. We have succeeded in attaining an analog memristive characteristic by optimizing the Ga:Sn composition rate, namely, completing an analog memristor. The analog memristor of the GTO thin film by the mist CVD method can be expected to be a key component for neuromorphic systems.

A numerical model of thin-film transistors for circuit simulation has been developed. This model utilizes three schemes. First, the spline interpolation with transformation by y=x+log(x) achieves excellent preciseness for both on-current and off-current simultaneously. Second, the square polynomial supplement solves an anomaly near the points where drain voltage equal to zero. Third, the linear extrapolation achieves continuities of the current and its derivatives as a function of voltages out of the area where the spline interpolation is performed, and improves convergence during circuit simulation.

We propose a temperature sensor employing a ring oscillator composed of poly-Si thin-film transistors (TFTs). Particularly in this research, we compare temperature sensors using TFTs with lightly-doped drain structure (LDD TFTs) and TFTs with offset drain structure (offset TFTs). First, temperature dependences of transistor characteristics are compared between the LDD and offset TFTs. It is confirmed that the offset TFTs have larger temperature dependence of the on current. Next, temperature dependences of oscillation frequencies are compared between ring oscillators using the LDD and offset TFTs. It is clarified that the ring oscillator using the offset TFTs is suitable to detect the temperature. We think that this kind of temperature sensor is available as a digital device.

We have developed a capacitance sensor of frequency modulation for integrated touchpanels using amorphous In-Sn-Zn-O (α-ITZO) thin-film transistors (TFTs). This capacitance sensor consists of a ring oscillator, whose one stage is replaced by a reset transistor, sensing transistor, and sensing electrode. The sensing electrode is prepared as one terminal to form a sensing capacitor when the other terminal is added by a finger. The ring oscillator consists of pseudo CMOS inverters. We confirm that the oscillation frequency changes when the other terminal is added. This result suggests that this capacitance sensor can be applied to integrated touchpanels on flatpanel displays.

Two types of thin-film phototransistors (TFPTs), p/i/n TFPT and n/i/n TFPT, are characterized from the viewpoint of operation condition and device behavior. It is found that the detected current can be both independent of the applied voltage (Vapply) and linearly dependent on the photo-illuminance in the saturation region of the p/i/n TFPT. This characteristic is because even if Vapply increases, the depletion layer remains in the whole intrinsic region, and the electric field changes only near the p-type/intrinsic interface and intrinsic/n-type interface but remains in the most intrinsic region. This characteristic is preferable for some kinds of photosensor applications. Finally, an application example of the p/i/n TFPT, artificial retina, is introduced.