The electrical characteristics and device applications of metal oxide nanowires.

摘要

Metal oxide and semiconductor nanowires have shown great potential as the basis for electronic devices which are compatible with a wide range of device substrates, including transparent or flexible substrates. The development of such nanowire-based devices, however, currently presents several outstanding challenges. Besides the various issues related to the growth of nanowires, the commercial applications of these materials depend critically on the development of scalable methods for achieving nanowire assembly and integration. In order to address such manufacturability issues, a thin-film transistor (TFT) based upon metal oxide nanowires is characterized in order to show that it is possible to fabricate nanowire devices which offer both high-performance levels and compatibility with transparent and flexible device substrates.;Instead of directly depositing semiconductor materials on glass or plastic as with typical TFT designs, in this work the low-temperature requirements of glass and plastic substrates are satisfied by employing a contact printing process to transfer synthesized nanowires from their growth substrate directly onto the device substrate. This method was shown to effectively achieve the isolation of the high-temperature processes required by single-crystalline material growth from the low-temperature conditions mandated by the device substrate.;Semiconductor nanowires, such as metal oxide SnO2 or Ge-based nanowires, were employed as the TFT channel material. Optimization of the growth process of these nanowires is discussed. For instance, the diameter controlled growth of 30 nm diameter SnO2 nanowires is examined. Electrical characterization results of such SnO2 nanowires showed that they possess field-effect mobilities that averaged 156 cm2/V·s. Moreover, by properly controlling the amount of extrinsic dopants during the nanowire growth, the conductivity of the nanowires may be adjusted from semiconducting to metallic.;Although the DC performance of nanowire-based transistors has been extensively examined; in circuit applications, the high frequency characteristics of the nanowirebased transistors are more relevant. In order to demonstrate their suitability for high frequency circuit applications, direct RF measurements are carried out on nanowire-based TFTs fabricated on glass. Operational speeds in excess of 300 MHz were reached. Additionally, the suitability of these TFTs in logic circuits is demonstrated with the fabrication and successful operation of a two-transistor inverter.