ABSTRACT
Understanding the density of state (DOS) distribution in solution-processed indium-zinc-oxide (IZO) thin-film transistors (TFTs) is crucial for addressing electrical instability. This paper presents quantitative calculations of the acceptor-like state distribution of solution-processed IZO TFTs using thermal energy analysis. To extract the acceptor-like state distribution, the electrical characteristics of IZO TFTs with various In molarity ratios were analyzed with respect to temperature. An Arrhenius plot was used to determine electrical parameters such as the activation energy, flat band energy, and flat band voltage. Two calculation methods, the simplified charge approximation and the Meyer-Neldel (MN) rule-based carrier-surface potential field-effect analysis, were proposed to estimate the acceptor-like state distribution. The simplified charge approximation established the modeling of acceptor-like states using the charge-voltage relationship. The MN rule-based field-effect analysis validated the DOS distribution through the carrier-surface potential relationship. In addition, this study introduces practical and effective approaches for determining the DOS distribution of solution-processed IZO semiconductors based on the In molarity ratio. The profiles of the acceptor-like state distribution provide insights into the electrical behavior depending on the doping concentration of the solution-processed IZO semiconductors.
ABSTRACT
The atomic composition ratio of solution-processed oxide semiconductors is crucial in controlling the electrical performance of thin-film transistors (TFTs) because the crystallinity and defects of the random network structure of oxide semiconductors change critically with respect to the atomic composition ratio. Herein, the relationship between the film properties of nitrate precursor-based indium-zinc-oxide (IZO) semiconductors and electrical performance of solution-processed IZO TFTs with respect to the In molar ratio was investigated. The thickness, morphological characteristics, crystallinity, and depth profile of the IZO semiconductor film were measured to analyze the correlation between the structural properties of IZO film and electrical performances of the IZO TFT. In addition, the stoichiometric and electrical properties of the IZO semiconductor films were analyzed using film density, atomic composition profile, and Hall effect measurements. Based on the structural and stoichiometric results for the IZO semiconductor, the doping effect of the IZO film with respect to the In molar ratio was theoretically explained. The atomic bonding structure by the In doping in solution-processed IZO semiconductor and resulting increase in free carriers are discussed through a simple bonding model and band gap formation energy.
ABSTRACT
Understanding the chemical reaction pathway of the metal-salt precursor is essential for modifying the properties of solution-processed metal-oxide thin films and further improving their electrical performance. In this study, we focused on the structural growth of solution-processed amorphous indium-zinc-oxide (a-IZO) films and the electrical behavior of a-IZO thin-film transistors (TFT). To this end, solution-processed a-IZO films were prepared with respect to the Zn molar ratio, and their structural characteristics were analyzed. For the structural characteristic analysis of the a-IZO film, the cross-section, morphology, crystallinity, and atomic composition characteristics were used as the measurement results. Furthermore, the chemical reaction pathway of the nitrate precursor-based IZO solution was evaluated for the growth process of the a-IZO film structure. These interpretations of the growth process and chemical reaction pathway of the a-IZO film were assumed to be due to the thermal decomposition of the IZO solution and the structural rearrangement after annealing. Finally, based on the structural/chemical results, the electrical performance of the fabricated a-IZO TFT depending on the Zn concentration was evaluated, and the electrical behavior was discussed in relation to the structural characteristics.
ABSTRACT
Semitransparent dual-metal electrodes comprising several thin layers of metals, such as Ni, Ag, Cu, and Al, were developed for designing flexible red-phosphorescent organic light-emitting diodes (OLEDs). The said diodes were fabricated by first depositing a Ni layer on four glass and polyethylene terephthalate (PET) substrates each to facilitate adhesion with glass and a flexible PET substrate. Subsequently, a conductive layer of Ni, Ag, Cu, and Al was stacked atop the first Ni layer on the four glass and PET substrates each, respectively. The proof of principles has been employed to demonstrate the performance potential via optical, physical, and electrical analyses of dual-as well as single-metal layers prior to device realization. In addition, their electrical and optical characteristics were compared against those of In-Sn-oxide-based OLEDs to demonstrate their potential with regard to application flexibility.
ABSTRACT
We investigate the electrical characteristics of solution-processed poly(3-hexylthiophene-2,5-diyl) (P3HT) thin-film transistors (TFTs) under monochromatic illumination conditions at different wavelengths of 700, 655, 515, and 315 nm. The TFT characteristics measured under light illumination at the wavelengths of 700 and 655 nm were comparable to those measured in the dark state. In addition, light illumination at a wavelength of 515 nm, of which photon energy (~2.4 eV) is higher than the band gap energy of P3HT (~1.7 eV), had a little effect on the electrical characteristics of P3HT TFTs. On the other hand, the TFT performance was notably changed by light illumination at a wavelength of 315 nm. These results indicate that the photon energy, which cause the characteristic degradation in the solution-processed P3HT TFTs, is much higher than the band gap energy of P3HT. Consequently, the illumination-induced variation in the TFT performance can be understood through a broad distribution of energetic states in the solution-processed P3HT semiconductor.
ABSTRACT
Microwave breast tumor detection uses the electrical property contrast between normal tissues and malignancies to detect the latter in an early development stage. However, previous works on the microwave imaging uses 2-D or more complicated models of the breast and electromagnetic wave propagation. We present a computationally efficient and physically instructive electromagnetic wave channel modeling for confocal microwave imaging system for the breast tumor detection. The proposed model covers all of the factors that have been examined in the previous 2-D model, such as the radial spreading, path loss, partial reflection and transmission of the backscattered electromagnetic wave from the tumor cell. The characteristics of the reconstructed images of the tumor using the proposed 1-D model are compared with them of the previous 2-D FDTD method. Previous 2-D model of the cancerous breast utilizes the MRI-derived discretized cell model to simulate the realistic perturbation, but there has been no consideration on the system noise that can be detrimental to the reconstruction of the tumor. The effect of the system noise level to the reconstruction algorithm will be addressed as well.
