Mingun Lee

Selective atomic layer deposition with electron-beam patterned self-assembled monolayers

The authors selectively deposited nanolines of titanium oxide (TiO2) through atomic layer deposition (ALD) using an octadecyltrichlorosilane (OTS) self-assembled monolayer (SAM) as a nucleation inhibition layer. Electron-beam (e-beam) patterning is used to prepare nanoline patterns in the OTS SAM on SiO2/Si substrates suitable for selective ALD. The authors have investigated the effect of an e-beam dose on the pattern width of the selectively deposited TiO2 lines. A high dose (e.g., 20 nC/cm) causes broadening of the linewidth possibly due to scattering, while a low dose (e.g., 5 nC/cm) results in a low TiO2 deposition rate because of incomplete exposure of the OTS SAMs. The authors have confirmed that sub-30 nm isolated TiO2 lines can be achieved by selective ALD combined with OTS patterned by EBL at an accelerating voltage of 2 kV and line dose of 10 nC/cm. This research offers a new approach for patterned gate dielectric layer fabrication, as well as potential applications for nanosensors and solar cells.

One-dimensional Nanomaterials for Field Effect Transistor (FET) Type Biosensor Applications

One-dimensional, nanomaterial field effect transistors (FET) are promising sensors for bio-molecule detection applications. In this paper, we review fabrication and characteristics of 1-D nanomaterial FET type biosensors. Materials such as single wall carbon nanotubes, Si nanowires, metal oxide nanowires and nanotubes, and conducting polymer nanowires have been widely investigated for biosensors, because of their high sensitivity to bio-substances, with some capable of detecting a single biomolecule. In particular, we focus on three important aspects of biosensors: alignment of nanomaterials for biosensors, surface modification of the nanostructures, and electrical detection mechanism of the 1-D nanomaterial sensors.

7-Octenyltrichrolosilane/trimethyaluminum hybrid dielectrics fabricated by molecular-atomic layer deposition on ZnO thin film transistors

We demonstrate the fabrication of 7-octenytrichlorosilane (7-OTS)/trimethylaluminum (TMA) organic–inorganic hybrid films using molecular-atomic layer deposition (MALD). The properties of 7-OTS/TMA hybrid films are extensively investigated using transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), and electrical measurements. Our results suggest that uniform and smooth amorphous hybrid thin films with excellent insulating properties are obtained using the MALD process. Films have a relatively high dielectric constant of approximately 5.0 and low leakage current density. We fabricate zinc oxide (ZnO) based thin film transistors (TFTs) using 7-OTS/TMA hybrid material as a back gate dielectric with the top ZnO channel layer deposited in-situ via MALD. The ZnO TFTs exhibit a field effect mobility of approximately 0.43 cm2 V−1 s−1, a threshold voltage of approximately 1 V, and an on/off ratio of approximately 103 under low voltage operation (from −3 to 9 V). This work demonstrates an organic–inorganic hybrid gate dielectric material potentially useful in flexible electronics application.

Functionalization of a Single TiO2 Nanotube for Bio Sensor Applications

Interests in one-dimensional structures as a material for emerging applications in chemical and bio sensors increase due to their unique physical properties, which arises from their dimensionality and size effects [1]. Single TiO2 nanotubes can be employed as biochemical detectors because they are nontoxic and provide not only a large surface area to volume ratio, but also an open capped structure. Even though the TiO2 nanotubular structure is suitable for sensor applications, it is necessary to improve their selectivity and detection limit in order to identify certain chemical and biological species. In this research, we discuss the effects of functionalizing stand-alone TiO2 nanotube devices in order to enhance their sensing capabilities.

Fabrication of single TiO2 nanotube devices with Pt interconnections using electron-and ion-beam-assisted deposition

Device fabrication using nanostructured materials, such as nanotubes, requires appropriate metal interconnections between nanotubes and electrical probing pads. Here, electron-beam-assisted deposition (EBAD) and ion-beam-assisted deposition (IBAD) techniques for fabrication of Pt interconnections for single TiO2 nanotube devices are investigated. IBAD conditions were optimized to reduce the leakage current as a result of Pt spreading. The resistivity of the IBAD-Pt was about three orders of magnitude less than that of the EBAD-Pt, due to low carbon concentration and Ga doping, as indicated by X-ray photoelectron spectroscopy analysis. The total resistances of single TiO2 nanotube devices with EBAD- or IBAD-Pt interconnections were 3.82 × 1010 and 4.76 × 108 Ω, respectively. When the resistivity of a single nanotube is low, the high series resistance of EBAD-Pt cannot be ignored. IBAD is a suitable method for nanotechnology applications, such as photocatalysis and biosensors.

Fabrication and surface functionalization of single TiO 2 nanotubes devices for bio-chemical sensors applications

A single TiO2 nanotube device has been successfully fabricated using both FIB deposition technique and conventional Si process. The device shows linear I–V characteristics implying ohmic contact. The device shows conductance modulation when it is functionalized by lysine and GABA. Surface modification is confirmed by monitoring the resistance change of TiO2 nanotube. In this study, fabrication of single TiO2 nanotube devices and the effect on conductance of the nanotube devices by surface modification will be discussed for bio-chemcial sensor applications.