Inkyu Park

ZnO nanowire network transistor fabrication on a polymer substrate by low-temperature, all-inorganic nanoparticle solution process

All-solution processed, low-temperature zinc oxide nanowire network transistor fabrication on a polymer substrate was demonstrated. This simple process can produce high resolution metal electrode transistors with inorganic semiconductor nanowire active material in a fully maskless sequence, eliminating the need for lithographic and vacuum processes. The temperature throughout the processing was under 140°C, which will enable further applications to electronics on low-cost, large-area flexible polymer substrates.

Sub-10 nm nanoimprint lithography by wafer bowing.

We introduce the concept of wafer bowing to affect nanoimprinting. This approach allows a design that can fit the key imprinting mechanism into a compact module, which we have constructed and demonstrated with an overlay and resolution of <0.5 microm and <10 nm, respectively. In the short term, this wafer bowing approach makes nanoimprint lithography much more accessible to a broad range of researchers. More importantly, this approach eliminates machine movement other than wafer bowing and shortens the mechanical path; these will enable the achievement of excellent patterning and overlay at a much lower cost. In the long term, wafer bowing is extensible to step-and-repeat printing for volume manufacturing.

Low temperature, low pressure nanoimprinting of chitosan as a biomaterial for bionanotechnology applications

Micro- and nanoscale structures of chitosan were fabricated by nanoimprinting lithography and biochemically functionalized for bionanodevice applications. Chitosan solutions were prepared and a nanoimprinting process was developed for it, where chitosan solution is used as a functional resist for nanoimprinting lithography. A low temperature (90°C) and low pressure (5–25psi) nanoimprinting with polydimethylsiloxane mold could achieve not only microscale structures but also nanoscale features such as nanowire and nanodots down to 150nm dimensions. The nanoimprinted structures were chemically modified and used for the immobilization of protein molecules.

Thermal oxidation of tantalum films at various oxidation states from 300 to 700°C

This paper presents the combined use of mathematical modeling and Auger depth profiling to study and quantify the oxidation of Ta films over a wide range of temperatures. The thermal oxidation of tantalum films (∼700nm) is studied using direct measurements of species concentration by means of Auger depth profiling. The oxidation temperature range of this study extends from 300 to 700°C and the oxidation period varies from 5s to 12.5h. The Auger depth profiles revealed that the metallic film oxidizes to first form low valence oxides of Ta that progressively convert to tantalum pentoxide with increasing temperature and time. A first-order reaction diffusion model is used to quantify the diffusion of oxygen through a film that is evolving in composition. The Auger depth profiling and reaction-diffusion model are used to estimate the actual diffusivity values for oxygen in the evolving Ta/Ta-oxide thin-film matrix, rather than more conventional techniques that estimate either the initial diffusion of oxygen t...

Selective Functionalization of Silicon Micro/Nanowire Sensors via Localized Joule Heating

A novel approach to achieve localized surface functionalization of silicon-based micro and nanoscale linear structures (e.g., silicon nanowire sensors) is proposed in this paper. This method is based upon the protection of silicon surface by hydrophobic polymer layers such as polytetrafluoroethylene (PTFE). These layers are used as a protective, patterning barrier against surface functionalization of silicon or silicon oxide surface. Subsequently, these polymer layers undergo selective thermal ablation along the silicon micro / nanowire sensors by localized Joule heating. This local ablation is then followed by a brief low power O2 plasma for activating the surface of silicon oxide with more hydroxyl (-OH) groups for further surface functionalization. Next, organosilane groups including amino-propyltriethoxysilane (APTES) and 3-mercaptopropyltri-methoxysilane (3-MPTMS) are used as a chemical linker between silicon oxide surface and protein or DNA molecules. We first present a finite element analysis (FEA) of localized Joule heating of silicon nanowires and experimental results of localized ablation of the protective polymer by Joule heating. We also verify localized surface modification of ablated surface of silicon with 3-MPTMS by selective binding of gold nanoparticles on the thiolized silicon surface. This localized functionalization is expected to have great advantages such as increasing the sensitivity and lowering the detection limit of silicon micro/nanowire-based sensors.

Infrared absorption study of neutron-transmutation-doped germanium

Using high‐resolution far‐infrared Fourier transform absorption spectroscopy and Hall effect measurements we have studied the evolution of the shallow acceptor and donor impurity levels in germanium during and after the neutron transmutation doping process. Our results show unambiguously that the gallium acceptor level concentration equals the concentration of transmutated 70 Ge atoms during the whole process indicating that neither recoil during transmutation nor gallium‐defect complex formation play significant roles. The arsenic donor levels appear at full concentration only after annealing for 1 h at 450 °C. We show that this is due to donor‐radiation‐defect complex formation. Again recoil does not play a significant role.

nDSE-based overlay alignment: enabling technology for nano metrology and fabrication

Displacement sensing and estimation (DSE) is important preprocessing task for many image-based processing systems that extract information from multiple images. In last two years, we gained significant insight of the nature of DSE and developed theory and algorithm framework named nanoscale displacement sensing and estimation (nDSE). We also build procedures to apply nDSE to overlay alignment down to the nanoscale. We will introduce two basic theories: Phase Delay Detection (PDD) and Derivatives-based Maximum Likelihood Estimation (DML) and associated DSE algorithms, noticeably Near-Neighbor-Navigation (N-Cubed) algorithm. We presented our best nDSE experimental result of 1 nm (1σ) while tracking 5 nm stepping. To develop nDSE-based nanoscale alignment, we introduced our definition of displacement, alignment and pseudo-displacement. We presented both theoretical and practical procedures to use nDSE to achieve nano-alignment down to the 10s of nano-meters and beyond. Then we compared nDSE-based nano-alignment to other industry standard alignment method and attempt to show the substantial advantages of nDSE based alignment in terms of cost and simplicity of the system design.

Micro/Nanoscale Structure Fabrication by Direct Nanoimprinting of Metallic and Semiconducting Nanoparticles

In this paper, we present our recent development of direct nanoimprinting of metal and semiconductor nanoparticles for a simple but high-throughput fabrication of micro/nanoscale structures. Nanoparticle suspension with self-assembled-monolayer (SAM) protected-nanoparticles (Au, Ag, and CdSe-ZnS core-shell quantum dots) suspended in alpha-terpineol carrier solvent are used as solutions for direct nanoimprinting. Polydimethylsiloxane (PDMS)-based soft imprinting molds with micro/nanoscale features are used. Process and material flexibility enable a very low temperature (80°C) and low pressure (5psi) nanoimprinting process and results in superfine features from micrometers down to ∼100nm resolutions. We will show the geometrical and electrical characterization of nanoimprinted structures and demonstrate working electronic components such as resistors or organic field effect transistors (OFET).Copyright

Nanoscale Joule Heating Along Silicon Nanowire and Its Nanoscale Heater Application

In this paper, we present numerical and experimental studies on the nanoscale Joule heating along the single crystalline silicon nanowires. 50–100nm wide single crystalline silicon nanowires are heated via Joule heating by applying an electrical potential across them. Numerical simulation result predicts an extremely localized temperature field by resistive heating of silicon nanowire. We experimentally verified this highly localized heating of silicon nanowires by AFM imaging of localized thermal ablation of polytetrafluoroethylene (PTFE) thin film. This result implies potential applications of silicon nanowires as nanoscale heaters for the generation of highly localized temperature fields.Copyright

LOW TEMPERATURE OFET (ORGANIC FIELD EFFECT TRANSISTOR) FABRICATION BY METAL NANOPARTICLE IMPRINTING

The low temperature fabrication of OFET (organic field effect transistor) is presented in this paper. PDMS imprinting mold was used to pattern gold nano-particles suspended in Alpha-Terpineol solvent. After imprinting, nanoparticles was dried and then sintered at plastic compatible low temperature. Finally, air stable semiconductor polymer (modified polythiophene) in dichlorobenzene (o-DCB) solution to fabricate OFETs on flexible polymer substrates. The performance of the transistors were characterized and discussed.Copyright