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Herein, we propose an ionic liquid–polymer dielectric layer for flexible electronics reinforced by a chemical interaction between the polymer matrix (PVP) and the ionic liquid. Due to the robust structures of the cross-linked PVP matrix and hydrogen bonding between the ionic liquid and PVP, the ionic liquid–PVP (IL–PVP) layer exhibited a good mechanical strength when bending up to 1000 times and a stable thermal behaviour up to 300 °C. Furthermore, the IL–PVP dielectric layer showed a high capacitance value of ∼2 μF cm−2 and was operated well as a gate insulator for flexible ZnO thin film transistors with a linear field-effect mobility of ∼3.3 cm2 V−1 s−1 at a gate bias of 3 V.

Solution-processed oxide semiconductors (OSs) used as channel layer have been presented as a solution to the demand for flexible, cheap, and transparent thin-film transistors (TFTs). In order to produce high-performance and long-sustainable portable devices with the solution-processed OS TFTs, the low-operational voltage driving current is a key issue. Experimentally, increasing the gate-insulator capacitances by high-k dielectrics in the OS TFTs has significantly improved the field-effect mobility of the OS TFTs. But, methodical examinations of how the field-effect mobility depends on gate capacitance have not been presented yet. Here, a systematic analysis of the field-effect mobility on the gate capacitances in the solution-processed OS TFTs is presented, where the multiple-trapping-and-release and hopping percolation mechanism are used to describe the electrical conductivity of the nanocrystalline and amorphous OSs, respectively. An intuitive single-piece expression showing how the field-effect mobility depends on gate capacitance is developed based on the aforementioned mechanisms. The field-effect mobility, depending on the gate capacitances, of the fabricated ZnO and ZnSnO TFTs clearly follows the theoretical prediction. In addition, the way in which the gate insulator properties (e.g., gate capacitance or dielectric constant) affect the field-effect mobility maximum in the nanocrystalline ZnO and amorphous ZnSnO TFTs are investigated.

Solution-processed high-K dielectrics for oxide thin-film transistors (TFTs) have been widely studied with the objective of achieving high performance and low-cost TFTs for next-generation displays. In this study, we introduce an amorphous hafnium-lanthanum oxide (HfLaOx) gate insulator with high electrical permittivity which was fabricated by the simple spin-coating method. In particular, the solution-processed HfLaOx dielectric layer, which was achieved by a mixture of two Hf and La metal hydroxide precursors, showed amorphous properties, a low leakage current and a high dielectric constant. The solution-processed HfLaOx dielectric layers showed a breakdown voltage as high as 5 MV cm−1 in strength and a dielectric constant above 22. Based on their implementation as a gate insulator, the solution-processed ZnO/HfLaOx TFTs showed good and stable performances during operation at a low voltage. A mobility of μ = 1.6 cm2 V−1 s−1, an on/off current ratio of 106, and a threshold voltage of 0.0015 V were obtained under a 5 V gate bias. Our results show the possibility of the solution-processed amorphous HfLaOx dielectric layer as a gate insulator for oxide TFTs. We believe that this amorphous HfLaOx dielectric has good potential for next-generation high-performance TFT devices.

Solution-processed and alkali metals, such as Li and Na, are introduced in doped amorphous zinc tin oxide (ZTO) semiconductor TFTs, which show better electrical performance, such as improved field effect mobility, than intrinsic amorphous ZTO semiconductor TFTs. Furthermore, by using spectroscopic UV-visible analysis we propose a comprehensive technique for monitoring the improved electrical performance induced by alkali metal doping in terms of the change in optical properties. The change in the optical bandgap supported by the Burstein-Moss theory could successfully show a mobility increase that is related to interstitial doping of alkali metal in ZTO semiconductors.

) and its dep-osition requires a high-cost vacuum process. More importantly, the poor transparency of silicon makes it unsuitable for trans-parent applications, and transparency is one of the key issues for future display technology. Consequently, in a search for alterna-tives for amorphous silicon, considerable interest has focused on metal oxide semiconductors, such as In, Ga, or Zn oxides, as these exhibit high optical transparencies, and have excel-lent electrical properties with high electron mobility, chemical stability, and solution processability. For example, ZnO-based semiconductors have been successfully incorporated into var-ious electronic devices, such as electron transfer layers for solar cells

As transparent displays become recog-nized as next-generation displays, the transparent thin-fi lm transistor (TTFT) is becoming an important device in the display industry. In addition, because the transparent device is causing a strong ripple effect through the whole industry, it has been spotlighted in response to changing markets and technological demands. For example, this technology can be applied to ultra-mobile PCs, smart windows, transparent tablets, and paper-thin displays. In particular, one anticipated application is the smart window. The smart window could transmit visual information onto the windshields of automobiles and airplanes. The use of transparent window displays has no limitations in space and visibility. Therefore, the transparent device has the potential to drive the future of the IT industry. From a technological standpoint, advances in trans-parent devices mean an increase in the transmittance in order to enhance the aperture ratio of device. Higher transmittance of the thin fi lm transistor (TFT) allows the effective use of back light and improves power consumption effi ciency. In order to achieve the TTFT, the development of transparent materials must be fi rst addressed. Of prime importance is zinc oxide (ZnO) with extensive applications in the industry. ZnO is a wide bandgap (

We report a compact design for a coarse approach mechanism, the so-called `walker', for a lowtemperature ultra-high-vacuum scanning probe microscope. We adapted the slip-stick principle with three actuators driven by the time sequential scheme suggested by Pan et al. The shear piezo-stack was replaced by three rectangular pieces of a piezoelectric (PZT) actuator to reduce the walker volume. Three slip-stick actuators were used rather than six actuators in the original design. By using polished sapphire and rough alumina plates, we implemented perfect sticking and a sliding interface. Our design minimizes usage of glue or epoxy, where attachment strength would be deteriorated by repeated temperature cycling. By using te on material, we reduced the frictional force of sliding parts. Without a metallic spring, elastic motion was provided by the te on material against the holding force. A moving velocity of 18 m/s and a step distance of 0.3 m were measured at room temperature.

We fabricated a novel in-line conductive atomic force microscopy (C-AFM), which can analyze the resistive failures and examine process variance with an exact-positioning capability across the whole wafer scale in in-line DRAM fabrication process. Using this in-line C-AFM, we introduced a new, non-destructive diagnosis for resistive failure in mobile DRAM structures. Specially, we focused on the self-aligned contact (SAC) process, because the failure of the SAC process is one of the dominant factors that induces the degradation of yield performance, and is a physically invisible defect. We successfully suggested the accurate pass mark for resistive-failure screening in the fabrication of SAC structures and established that the cause of SAC failures is the bottom silicon oxide layer. Through the accurate pass mark for the SAC process configured by the in-line C-AFM analyses, we secured a good potential method for preventing the yield loss caused by failures in DRAM fabrication.

We theoretically and experimentally investigate how the field-effect mobility (MFE) depends on the gate capacitances (CI) in solution-processed oxide semiconductor (OS) thin-film transistors (TFTs). With recently developed solution-based techniques, high quality OS films can be deposited onto flexible substrates at low temperatures, which accelerate applying of flexible, transparent, and ink-jet printable OS TFTs to future mobile display and electronics. Meanwhile, another important issue is to sustainably use of portable devices using integrated OS TFT circuits for a long time. Empirically, Increasing CI has been used to increase the drain current (ID) for high-performance and low-energy consuming OS TFTs, which is based on a theory of conventional metal-oxide-semiconductor field-effect transistors (MOSFETs): ID∝CI. However, it has been observed that incremental features of ID as increasing CI in solution-processed OS TFTs are quite different to that of MOSFETs. It is because disordered metal ions and dense grain boundaries in the solution-processed OSs make MFE depend on total number of accumulated electrons. Thus, MFE relies on CI, and ID cannot be linear relationship to CI. Therefore, grasping the relationship between MFE and CI in theoretical manner is important to realize high-performance, low-operational voltage devices, and it is also useful to design, optimize, and integrate OS TFT circuits. The disordering nature of solution-processed OSs can be classified into nanocrystalline and amorphous states, which are determined by how many numbers of metal ions component are contained. When the number of metal ion component is ‘1’, such as ZnO, InO2, and SnO2, the solution-processed OS films have nanocrystalline phase. As the number of metal ion component is larger than ‘1’(for example, ZnSnO, InGaZnO, InZnO), the states of the OS films are amorphous. Although electronic properties of both amorphous and nanocrystalline OS films arising from their atomic arrangements are different to each other, the CI-dependent-MFE characteristics have been observed by two following features experimentally. First, with high-CI conditions, the maximum-MFE values of the OS TFTs can be achieved with low gate voltages (VG) than that with low-CI conditions. Second, the maximum-MFE values with gate insulator comprising of high-k dielectric materials is higher than that comprising of low-k dielectric materials, within the associated VG regimes. However, how the MFE values is determined by the CI values and how gate-insulator properties (ex, dielectric constant) affects the maximum-MFE values have not been intensively investigated yet. Here, we systematically performed an investigation of the CI-dependent MFE features. We developed theoretical models representative of the solution-processed OS TFTs, where multiple-trapping-and-release (MTR) and hopping percolation mechanisms are used for explaining the electrical conductivity of nanocrystalline and amorphous OS films, respectively. For both theoretical models, we derived a single-piece expression that shows how the MFE value and the operational voltage can be determined by the CI value. We successfully verified the developed analytic formula by using fabricated solution-processed ZnO and ZnSnO TFTs. At low-VG regions (~4 V), the ZnO TFTs shows that its MFE varies from 0.066 to 6.01 cm2 / V sec following MFE ∝~ CI1.66, while the ZnSnO TFTs shows MFE∝~CI0.41. Furthermore, we investigated how the dielectric constant of gate insulators affects the maximum MFE values.

Recently, alkali metal doped ZnO has received much positive attention owing to its high performance and good electrical stability. In particular, since alkali metals such as Li and Na are general elements and show good potential as doping elements in ZnO semiconductors, several researchers have been interested in alkali metal doping process of polycrystalline zinc oxide semiconductors. However, only a few studies have been reported the doping mechanism to enhance the mobility. In addition, there have been few studies on alkali metal doping mechanism in amorphous metal oxide semiconductors. Most studies about alkali metal doped oxide semiconductor have been inquired in term of crystallinity, oxygen vacancy, and surface morphology properties. For these reasons, we also studied the mechanism of alkali metal doping in view of oxygen vacancy by spectroscopic study using XPS and surface morphology using AFM. However, although we observed that oxygen vacancy contents are reduced slightly with a correlation by interstitial or substitutional mechanism, it seems to be difficult to identify the correlation between the enhancement of electrical properties induced by interstitial doping and the changes of oxygen vacancy contents, because the difference of XPS spectra in doped ZTO films is too small. Also, as the decrease of oxygen vacancy contents means the decrease of electron mobility in metal oxide semiconductors, the tendency of oxygen vacancy spectra in XPS is inconsistence with general phenomena. It means that other mechanisms are required to precisely explain the electrical properties of the doped amorphous ZTO TFTs related to alkali metal doping mechanism. Otherwise, the change in the optical band gap supported by the Burstein-moss theory showed successfully that the enhancement of mobility was related to the interstitial doping of alkali metals. This result shows that the change of the optical band gap clearly applied to the study of the relationship between the change in mobility and interstitial doping concentrations. Here in, we introduce alkali metals doped and solution processed amorphous zinc tin oxide (ZTO) semiconductor TFTs, which show better electrical properties, such as field effect mobility and conductivity, than that of intrinsic amorphous ZTO based TFTs. We also analyze that the doping mechanism of alkali metals in the amorphous ZTO based TFTs using various techniques such as, atomic force microscopy (AFM), X-ray photoemission spectroscopy (XPS), Hall mobility. Furthermore, through the UV-visible spectroscopy, we suggest a comprehensive technique for investigating the enhanced electrical performance induced by alkali metal doping in terms of the change in optical band gap. Specially, we showed that UV-visible spectroscopic analysis for investigating the electrical performance of alkali metal doped metal oxide semiconductor TFTs has good potential as a fast and non-destructive analytical technique.

We fabricated zinc oxide (ZnO) TFTs using a zinc ammine complex with various zinc oxide sources such as ZnO, intrinsic Zn(OH)2, and precipitated Zn(OH)2. From the analyses of the reaction mechanism, surface morphology, crystal structure, and oxygen vacancy in the ZnO films, we confirmed the same intermediate in ZnO semiconductor films irrespective of the type of zinc oxide source in the zinc ammine complex precursor. The results showed the analogous value of the average field effect mobility, on/off current ratio, and turn-on voltage in all solution-processed ZnO TFTs. In conclusion, we confirmed that directly dissolving pristine ZnO into ammonia water is the most efficient method for preparing the ZnO semiconductor precursor, the zinc ammine complex, for low-temperature, solution-processed, and high performance ZnO TFTs.

Chemical imprinting was conducted on ZnO semiconductor films via a chemical reaction at the contact regions between a micro-patterned PDMS stamp and ZnO films. In addition, we applied the chemical imprinting on Li doped ZnO thin films for high performance TFTs fabrication. The representative micro-patterned Li doped ZnO TFTs showed a field effect mobility of 4.2 cm(2) V(-1) s(-1) after sintering at 300 °C.

Flexible and transparent thin film transistors (FTTFTs) can lead to next generation displays that involve large area, future-oriented flexible and transparent displays. In order to achieve stable FTTFTs, solution processes of organic and inorganic compounds have received significant attention. Above all, transparent oxide semiconductors such as ZnO have been studied to enhance flexibility with high electrical performance by integration with organic dielectrics. However, interfacial traps between inorganic and organic compounds are derived by interface dipole, which induce a considerable flat band shift. Herein, we have developed a self-assembled inorganic layer (SAIL) via the photo-induced transformation of a mono-poly(dimethylsiloxane) (PDMS) layer as interface engineering. Especially, the shifting of flat band voltage (VFB) was effectively suppressed by the SAIL process, which was analyzed with a single-piece analytical model for ZnO TFTs. In addition, flexible ZnO/SAIL/polymer dielectric TFTs with low process temperature as high as 200 °C exhibited a good field-effect mobility μ = 0.28 cm2 V−1 s−1, more than 106 on–off current ratio and excellent device operational stability and flexibility.

A solution-processed ionic amorphous Al2O3 dielectric with a low temperature annealing process at 350 °C shows good compatibility and high performance in metal oxide semiconductor thin film transitors (TFTs) such as Li–ZnO TFTs and In–ZnO TFTs. The Li–ZnO/Al2O3 and In–ZnO/Al2O3 TFTs, with solution-processability and low temperature annealing at a maximum of 350 °C, exhibited field-effect mobilities of 46.9 cm2 V−1 s−1 in crystalline Li–ZnO/Al2O3 TFTs and 44.2 cm2 V−1 s−1 in amorphous In–ZnO/Al2O3 TFTs with an on/off current ratio of more than 105. The proton mobile ion, such as hydrogen ion (H+) from chemisorbed water, in the ionic Al2O3 dielectric remarkably induces a high performance capacitance by the formation of an electrical double layer. The chemisorbed water was monitored by FT-IR and ellipsometric porosimetry measurements. Furthermore, the addition of H2O2 to the ionic Al2O3 dielectric precursor successfully suppressed the oxygen vacancies in the dielectric layer, which caused the electrical trap and pass, and confirmed the stable operation. These ionic amorphous Al2O3 dielectrics show good potential as switching TFTs devices in advanced displays, because they can satisfy the various demands of next-generation high-performance TFTs, such as low-cost, solution-processability, and a relatively low-temperature process.

The structural, electrical and optical properties of high-performance, low-temperature and solution-processed alkali metal-doped ZnO TFTs were studied using various analytic instruments, including HR-TEM, AFM, XPS, EDS, electrical bias stability test and UV-vis spectroscopy. Furthermore, we successfully demonstrated that a change in the optical bandgap energy of Li-doped ZnO semiconductor films supported by Burstein–Moss theory can show a trade-off relationship between the field effect mobility of Li-ZnO TFTs and the Li doping concentrations. The relative broadening of the Eopt values, which are strongly related to the amount of excited electrons from the Fermi level in the valance band to the conduction band, was observed from the undoped ZnO film to the Li-doped ZnO film (10 mol%). The increase in the electron donor concentration was the dominant reason for the enhancement in the electron mobility of the alkali metal-doped ZnO TFTs.

We introduce high performance, low-temperature (

A transparent thin film transistor (TTFT), including zinc oxide (ZnO), has come into the spotlight as an innovative TFT that has the potential to drive the future of the information technology industry. Herein, we developed a new direct patterning method, drop-casting with a new developing method, through the combination of an aqueous ammonia–ZnO process with the doping of Na ions and surface engineering for high n-type semiconducting performance with good operational stability at low temperature. In particular, the effective decomposition and removal of the residual ammonia compounds using methanol have a successful effect on both intrinsic and Na doped ZnO precursor processes for TFTs and they showed the extensive possibility of ammonia based metal oxide precursor solutions. In this method, the Na doped ZnO TTFTs showed good operational stability even with the process of low temperature sintering. The mobility μ = 0.80 cm2 V−1 s−1 was obtained at 200 °C sintering and the mobility μ = 0.10 cm2 V−1 s−1 at 100 °C sintering. In addition, in ambient conditions, the patterned Na doped ZnO TTFT exhibited high electron mobility μ = 1.84 cm2 V−1 s−1 with excellent device operational stability and scant hysteresis with sintering at 300 °C. This method is not only simple as compared with photolithography and inkjet printing, but is also a sophisticated patterning process with good fidelity for solution-processed ZnO TFTs. Moreover, the proposed method can be extended to plastic substrates on a large scale because of the low temperature development process of the ammonia–ZnO precursor using methanol and continuous patterning at ambient conditions. We believe that this method can be adapted to the advanced process toward future printed transparent electronic devices.