A nonvacuum and low temperature process for passivating transparent metal oxides based thin-film transistors is presented. This process uses the epoxy-based SU-8 resist which prevents device degradation against environmental conditions, vacuum or sputtering surface damage. The incorporation of SU-8 as a passivation layer is based on the ability of this polymer to provide features with high mechanical and chemical stability. With this approach, lithography is performed to pattern the resist over the active area of the device in order to form the passivation layer. The resulting transistors demonstrate very good electrical characteristics, such as μFE=61 cm2/V s, VON=−3 V, ON/OFF=4.4×109, and S=0.28 V/dec. Electrical behavior due to the SU-8/metal oxide interface characteristics is also reported on the basis of Fourier transform infrared analysis. In contrast, we demonstrate how sputtering of SiO2 as a passivation layer results in severely degraded devices that cannot be switched-off. In order to obtain proper working devices, it is shown that SU-8 should be hard baked at 200 °C for 1 h in order to obtain a highly cross-linked polymer network. The stability of SU-8 passivated devices over the time of storage, under current bias stress and vacuum conditions is also demonstrated.
Room-temperature deep Si etching using time-multiplexed deep reactive ion etching (DRIE) processes is investigated to fabricate ultra-high aspect ratio Si nanowires (SiNWs) perpendicular to the silicon substrate. Nanopatterning is achieved using either top-down techniques (e.g. electron beam lithography) or colloidal polystyrene (PS) sphere self-assembly. The latter is a faster and more economical method if imperfections in diameter and position can be tolerated. We demonstrate wire radii from below 100 nm to several micrometers, and aspect ratios (ARs) above 100:1 with etching rates above 1 μm min(-1) using classical mass flow controllers with pulsing rise times of seconds. The mechanical stability of these nanowires is studied theoretically and experimentally against adhesion and capillary forces. It is shown that above ARs of the order of 50:1 for spacing 1 μm, SiNWs tend to bend due to adhesion forces between them. Such large adhesion forces are due to the high surface energy of silicon. Wetting the SiNWs with water and drying also gives rise to capillary forces. We find that capillary forces may be less important for SiNW collapse/bending compared to adhesion forces of dry SiNWs, contrary to what is observed for polymeric nanowires/nanopillars which have a much lower surface energy compared to silicon. Finally we show that SiNW arrays have oleophobic and superoleophobic properties, i.e. they exhibit excellent anti-wetting properties for a wide range of liquids and oils due to the re-entrant profile produced by the DRIE process and the well-designed spacing.
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.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.