High performance transparent thin-film transistors deposited on glass substrates and entirely processed at a low temperature not exceeding 150°C are presented and analyzed in this paper. Besides being based on an amorphous oxide semiconductor, the main innovation of this work relies on the use of sputtered multicomponent oxides as dielectric materials based on mixtures of Ta 2 O 5 with SiO 2 or Al 2 O 3 . These multicomponent dielectrics allow to obtain amorphous structures and low leakage currents while preserving a high dielectric constant. This results in transistors with remarkable electrical properties, such as field-effect mobility exceeding 35 cm 2 V −1 s −1 , close to 0 V turn-on voltage, on/off ratio higher than 10 6 , and a subthreshold slope of 0.24 V decade −1 , obtained with a Ta 2 O 5 :SiO 2 dielectric. When subjected to severe current stress tests, optimized devices show little and reversible variation in their electrical characteristics. The devices presented here have properties comparable to the ones using plasma-enhanced chemical vapor deposited SiO 2 at 400°C, reinforcing the success of this amorphous multicomponent dielectric approach for low temperature, high performance, and transparent electronic circuits.Transparent electronics is one of the most fascinating and fastgrowing research areas since the first fully transparent thin-film transistors ͑TFTs͒ based on ZnO were presented in 2003. 1 A significant effort has been made in enhancing the devices' performance and lowering their maximum processing temperature 2 down to at least 150°C because this is normally seen as the upper limit for the socalled low temperature electronics, where low cost and flexible substrates are used. More recently, it was proved that multicomponent amorphous oxide semiconductors based on combinations of metallic cations with a ͑n − 1͒d 10 ns 0 ͑n Ն 4͒ electronic configuration, such as gallium indium zinc oxide ͑GIZO͒, 3-6 provide an enhanced performance over single binary oxides. Besides that, due to their amorphous structure, these materials also allow lower processing temperature, improved reproducibility and uniformity in large areas, and smoother surfaces when compared with polycrystalline materials. 7,8 The TFTs based on amorphous oxide semiconductors present remarkable characteristics, even when postprocessing temperatures of only 150°C are used. 3 However, most of the times the overall maximum processing temperature of these devices is much higher than 150°C and is dictated by the nature and the fabrication process of the dielectric layer. Most of the oxide semiconductor based TFTs rely on conventional dielectrics from Si technology, such as plasmaenhanced chemical vapor deposited ͑PECVD͒ SiO 2 9,10 and SiN x :H, 11,12 or even thermally grown SiO 2 when Si wafers are used as substrates. 3,13,14 While good performance can be obtained with these dielectrics when processed above 250-300°C, their properties are degraded when a temperature of around 150°C is established as the maximum for transistor fabrication....

No abstract

Abstract— This paper discusses the properties of sputtered multicomponent amorphous dielectrics based on mixtures of high‐κ and high‐bandgap materials and their integration in oxide TFTs, with processing temperatures not exceeding 150°C. Even if Ta2O5 films are already amorphous, multicomponent materials such as Ta2O5—SiO2 and Ta2O5—Al2O3 allow an increase in the bandgap and the smoothness of the films, reducing their leakage current and improving (in the case of Ta2O5—SiO2) the dielectric/semiconductor interface properties when these dielectrics are integrated in TFTs. For HfO2‐ based dielectrics, the advantages of multicomponent materials are even clearer: while HfO2 films present a polycrystalline structure and a rough surface, HfO2—SiO2 films exhibit an amorphous structure and a very smooth surface. The integration of the multicomponent dielectrics in GIZO TFTs allows remarkable performance, comparable with that of GIZO TFTs using SiO2 deposited at 400°C by PECVD. For instance, with Ta2O5—SiO2 as the dielectric layer, field‐effect mobility of 35 cm2/(V‐sec), close to 0 V turn‐on voltage, an on/off ratio higher than 106, a subthreshold slope of 0.24 V/dec, and a small/recoverable threshold voltage shifts under constant current (ID= 10 μA) stress during 24 hours are achieved. Initial results with multilayers of SiO2/HfO2—SiO2/SiO2 are also shown, allowing a lower leakage current with lower thickness and excellent device performance.

We present a general protocol for processing cost‐beneficial, environmentally benign aqueous‐type suspensions containing metal‐oxide nanostructured particles, and their patterning with piezoelectric ink‐jet printing technology. The critical issues relevant to ink‐jet printing are the preparation and stabilization of nanosized particles in a fluid and adjusting its physical properties to the values appropriate for a particular ink‐jet printer mechanism. We discuss and illustrate, on a model titania system, the processing of a highly stable, colloidal, water‐based suspension containing particles not bigger than 570 nm, prepared by a ball‐milling process. For the ink‐jet printing experiments, the surface tension and the viscosity of the suspension were modified by the addition of a small amount of the appropriate non‐ionic amphiphiles and glycerol. The formation of droplets, their positioning on the substrate, and the shape and uniformity of the dots on the substrate are discussed and correlated with the fluid properties via the inverse Ohnesorge number Z. It was shown successfully that uniform, regular‐shaped TiO2 dots with a diameter of 30 μm and a good positioning accuracy on Si/SiO2 substrates could be obtained by jetting a fluid with Z values of 5 and 9 using a piezoelectric ink‐jet printer with a nozzle diameter of 21 μm operating at an amplitude of 13 V and a frequency of 5 kHz.

The synthesis of Pb(Mg 1/3 Nb 2/3 )O 3 (PMN) with high-energy milling was studied by X-ray powder diffraction (XRD) using the Rietveld-refinement method. The results are discussed in terms of the qualitative and quantitative composition of the crystalline and amorphous phases as a function of milling time. The mechano-synthesis of PbO, Nb 2 O 5 , and MgO leads to the formation of perovskite PMN. In the initial stage of milling, particle size reduction and a high degree of amorphization were observed, together with the simultaneous formation of perovskite and pyrochlore-type structures. A mechanism for the formation of PMN by the mechano-synthesis route is proposed.

We developed a new, simple method to prepare pure perovskite Pb(Mg1/3Nb2/3)O3 (PMN) from an aqueous suspension in a single annealing step. In this synthesis it is crucial to suppress the reaction between PbO and Nb2O5, which leads to secondary pyrochlore PbxNbyOz phases. Our method is based on the designed arrangement of particles of the starting compounds. The self‐assembly of the colloidal aggregates was governed by particle surface charge, which was adjusted by the suspension pH. At pH below 11.8 particle–particle interactions lead to close contacts between lead oxide and niobium oxide particles in the suspension as well as in the dried powders, whereas at pH above 11.8 close contacts between lead and niobium oxide particles are avoided. The suspensions of the starting powders were prepared at pH 10.0, 11.4, 12.5, and in acetone. After heating of the dried suspension with the pH set at 12.5 at 900°C, a pure perovskite PMN powder was obtained. On the contrary, the powders prepared from the pH 11.4, 10.0, and acetone suspensions still contained the detrimental pyrochlore phase after heating at 900°C. The properties of the ceramics prepared from the pH 12.5 suspension are superior in comparison with the other samples.

No abstract

No abstract