Nano-oxidation Process Research Articles

Prediction Surface Morphology of Nanostructure Fabricated by Nano-Oxidation Technology.

Atomic force microscopy (AFM) was used for visualization of a nano-oxidation technique performed on diamond-like carbon (DLC) thin film. Experiments of the nano-oxidation technique of the DLC thin film include those on nano-oxidation points and nano-oxidation lines. The feature sizes of the DLC thin film, including surface morphology, depth, and width, were explored after application of a nano-oxidation technique to the DLC thin film under different process parameters. A databank for process parameters and feature sizes of thin films was then established, and multiple regression analysis (MRA) and a back-propagation neural network (BPN) were used to carry out the algorithm. The algorithmic results are compared with the feature sizes acquired from experiments, thus obtaining a prediction model of the nano-oxidation technique of the DLC thin film. The comparative results show that the prediction accuracy of BPN is superior to that of MRA. When the BPN algorithm is used to predict nano-point machining, the mean absolute percentage errors (MAPE) of depth, left side, and right side are 8.02%, 9.68%, and 7.34%, respectively. When nano-line machining is being predicted, the MAPEs of depth, left side, and right side are 4.96%, 8.09%, and 6.77%, respectively. The obtained data can also be used to predict cross-sectional morphology in the DLC thin film treated with a nano-oxidation process.

A study on the construction of nano-oxidation process parameter prediction model by combining a processing database and multiple regression equation

This study conducted nano-oxidation experiments in an exploration of applied voltage, time of voltage application, and relative humidity, in order to establish a nano-oxidation processing database. Multiple regression analysis (MRA) was then used to construct the impact of nano-oxidation process parameters on the oxide weight and height relationship. Finally, this study conducted a confirmation experiment and explored the impact of additional parameter amplification on the predictive power of the relationship equation. It was found that the relationship equation of the oxide height and width generated by combining the nano-oxidation processing database and the process parameters obtained using MRA was quite reasonable, and that the addition of database parameters that are in line with physical meaning could improve the predictive power of the relationship equation.

Precise Control of Nanofabrication by Atomic Force Microscopy

With an aim of the precise control of the anodic oxidation process by atomic force microscopy, the technical improvement has been carried out based on the mechanism studies. The accuracy and reliability of the nanofabrication have been improved by the combination of ambient humidity control, improvement of instrumental performance and meniscus lifetime control. In parallel, the mechanism study has been proceeded through the detection of Faradaic current. The in situ Faradaic current detection of the nano-oxidation process can actually work as a sensitive monitor for the nano-oxidation process with a high reliability. From an engineering viewpoint with an eye to practical applications, controllable physical parameters which affect on the product size are enumerated to consider what we should do to raise the precision of nano-oxidation. Then the fast fabrication in a large area by a patchwork method, Faradaic current detection during oxidation-reduction reaction, and nanofabrication by current-control are shown as examples.

The influence of sample conductivity on local anodic oxidation by the tip of atomic force microscope

We analyze the role of the electric field distribution in the nano-oxidation process realized by the tip of atomic force microscope (AFM) experimentally and theoretically as well. We show the importance of the sample conductivity and the water bridge in the process applied to bulk GaAs and Ga[Al]As heterostructures in both contact and noncontact AFM modes. The experimental results show that the lines written in contact mode are much wider then those written in noncontact mode. Moreover, saddlelike profile lines can appear for high-resistive samples. These effects are explained by the numerical simulations using finite-element method. We show that the electric field distribution in the system tip-sample is controlled by the sample conductivity. In the case of low-conductive samples, maximum field is located apart from the tip apex for both contact and noncontact AFM modes.

Why nano-oxidation with carbon nanotube probes is so stable: I. Linkage betweenhydrophobicity and stability

Carbon nanotube (CNT) probes enhance the stability of the nano-oxidation process underdynamic-mode operation. In this paper we investigate how the hydrophobic nature of theCNT allows oxide nanostructures to be fabricated with constant aspect ratio overa wide range of relative humidity values. In particular, we characterize oxidegrowth by measuring both the integrated ionic current and volume expansion.Behaviour of different CNT probes was compared to assess individual stabilityand performance under identical voltage and humidity conditions. While muchremains to be established about the relationship between exposure conditionsand dynamic-mode parameters on nanoscale oxide fabrication, hydrophobicity isa key factor in the improved reliability of CNT probes over conventional ones.

AFM nanooxidation process – Technology perspective for mesoscopic structures

We study the technology of local anodic oxidation (LAO) by the AFM tip applied to semiconductor heterostructures with two-dimensional electron gas. The aim is to design mesoscopic rings with persistent current and one subband occupied. For this purpose the need is to oxidize narrow lines that represent energy barriers high enough. Using the electrostatic model, we explain the electric field distribution in the system tip–sample just before LAO starts. We study the influence of the conductivity of the cap layer on LAO and explain the origin of the saddle-like profile lines, observed in the experiment. Using Monte Carlo simulation we show that the carrier redistribution in the system with LAO energy barriers effectively lowers the barrier height. In the experimental part we have grown InGaP/AlGaAs/GaAs heterostructures by organometalic vapor phase epitaxy with an active layer only 31 nm below the surface. We have prepared oxide lines on the heterostructures by LAO and characterized them by the temperature-dependent transport measurement.

Room Temperature Coulomb Diamond Characteristic of Single Electron Transistor Made by AFM Nano-Oxidation Process

To obtain a clear signal of the single electron transistor (SET) at room temperature, low capacitance of the SET is indispensable. This SET also has need of the fabrication of the tunnel junction and island with extremely small size. In this paper, three new processes will be proposed to achieve these requirements. First, we applied a single-wall carbon nanotube (SWNT) atomic force microscopy (AFM) cantilever in the AFM nano-oxidation process to obtain less than 10-nm-wide tunnel junctions and a smaller island size of the SET. Secondly, we have succeeded in developing an atomically flat quartz (SiO2) substrate with a smaller relative dielectric constant, which could reduce the SET capacitance to half that of our previous SET on the Al2O3 substrate. Finally, we established the thermal oxidation squeezing process, which can make the island smaller in size after the fabrication of the SET. The thermally squeezed SET showed a clearer Coulomb diamond characteristic than the previously fabricated SET at room temperature.

Single Wall Carbon Nanotube Cantilever: Fabrication and Application.

A single wall carbon nanotube (SWNT) has an extremely small diameter of 1∼2 nm and a high aspect ratio. For the use of the SWNT as an atomic force microscopy (AFM) cantilever, the SWNT was grown directly onto the top of the conventional silicon (Si) AFM cantilever using chemical vapor deposition (CVD) at 900oC in flowing CH4 gas. The length of the SWNT was hardly controlled in the growing process. Therefore, we cut the SWNT and adjusted its length at the top of the cantilever by bending and by applying the bias between the cantilever and the conductive substrate with monitoring the force curve and the vibration amplitude of the cantilever. The resolution of AFM using the optimized SWNT cantilever was compared with the one using conventional Si cantilever by observing the Au surface and TiOx lines fabricated utilizing the AFM nano-oxidation process. The radius of the SWNT cantilever was estimated by observing the width of the DNA in air.

Single Electron Memory at Room Temperature: Experiment and Simulation

We study a single-electron room temperature memory device. The device was fabricated by a pulse mode atomic force microscopy nano-oxidation process on an atomically flat α-Al2O3 substrate. We model the operation using a Monte Carlo simulation. There is a general agreement between theory and experiment. The observed differences stem from noise and the uncertainty in determining the geometry of the fabricated circuit.

Basic properties of GaAs oxide generated by scanning probe microscope tip-induced nano-oxidation process

The basic properties of GaAs oxide generated by atomic force microscope (AFM) tip-induced nano-oxidation process have been investigated. The chemical analysis of the AFM tip-generated GaAs oxide was performed by using scanning microprobe x-ray photoelectron spectroscopy, and the main constituents of GaAs anodic oxide were determined to be Ga2O3 and As2O3. The electrical characterization showed that the electron transport across a GaAs oxide nanodot of ∼5.7 nm thickness, from a doped n+-Si tip into the n+-GaAs substrate follows the Fowler–Nordheim tunneling mechanism over a range of applied bias. Further, the tip-generated GaAs oxide nanodots were found to withstand moderate thermal treatments, but some volume reduction was observed.

Experimental and theoretical results of room-temperature single-electron transistor formed by the atomic force microscope nano-oxidation process

The single-walled carbon-nanotube (SWNT) was grown directly onto the top of the conventional Si atomic force microscopy (AFM) cantilever. This SWNT AFM cantilever was introduced into the AFM nano-oxidation process, which oxidized the titanium (Ti) metal film on the atomically flat α-Al2O3 substrate and formed the ultranarrow oxidized titanium (TiOx) line of 5 nm width. This TiOx line was used as the tunnel junction of the single-electron transistor (SET), and the SET fabricated by this process showed room-temperature Coulomb oscillation with periods of 1 V. It was determined by three-dimensional simulation that the tunnel-junction capacitance shows only weak dependence on the tunnel-junction width.

Scanning probe microscope tip-induced oxidation of GaAs using modulated tip bias

We have investigated the basic mechanisms that determine the lateral resolution limits in the tip-induced nano-oxidation process of n+-GaAs(100) substrates. For this purpose, a set of systematic experiments and measurements were conducted. First, the cross-sectional profiles of GaAs oxide nanodots were investigated upon which the relationship between the measured profiles and oxidation parameters were studied. The current that flows during oxidation was monitored and analyzed. It is shown that the fundamental mechanism that governs the lateral resolution would be a finite electrical conductance of an adsorbed thin water film existing between the substrate and the tip, which then acts to defocus the electric field required for the oxidation. Second, the use of a modulated or pulsed bias with a short voltage duration in the range of 10–100 ms upon oxidation was proposed in order to improve the lithographic performance. The lateral resolution and aspect ratio were significantly improved with the modulated/pulsed tip bias scheme.

Experimental and Simulated Results of Room Temperature Single Electron Transistor Formed by Atomic Force Microscopy Nano-Oxidation Process

A planar-type single electron transistor (SET) was fabricated by the atomic force microscopy (AFM) nano-oxidation process. The fabricated SET showed the Coulomb oscillation characteristic with the period of about 2 V at room temperature. From the three-dimensional simulation, it is found out that the smaller the SET island size, the smaller the tunnel junction capacitance, and the tunnel junction capacitance shows a weak dependence on the tunnel junction width. Using the analytical model, the reason for this weak dependence was clarified.

Room-Temperature Single Electron Devices by Scanning Probe Process

A single electron transistor (SET) and a single electron memory were fabricated using the improved pulse-mode AFM nano-oxidation process. A single electron transistor which works as an electrometer for detecting the potential of the memory node of the single electron memory showed clear Coulomb oscillation characteristics with the period of 2.1 V at room temperature. A single electron memory exhibited a hysteresis loop as the memory bias was scanned from 0 to 10 V and then back down to 0 V.

ROOM-TEMPERATURE SINGLE ELECTRON DEVICES BY SCANNING PROBE PROCESS

A single electron transistor (SET) and a single electron memory were fabricated using the improved pulse-mode AFM nano-oxidation process. A single electron transistor which works as an electrometer for detecting the potential of the memory node of the single electron memory showed clear Coulomb oscillation characteristics with the period of 2.1 V at room temperature. A single electron memory exhibited a hysteresis loop as the memory bias was scanned from 0 to 10 V and then back down to 0 V.

Room-temperature single-electron memory made by pulse-mode atomic force microscopy nano oxidation process on atomically flat α-alumina substrate

A single-electron memory was fabricated using the improved pulse-mode atomic force microscopy nano oxidation process which oxidized the surface of the thin titanium (Ti) metal on the atomically flat α-alumina (α-Al2O3) substrate and formed the narrow oxidized titanium (TiOx) line that works as a tunnel junction for the device. This single-electron memory consists of the multitunnel junction and a memory capacitance. The single-electron transistor, which works as an electrometer, was connected to the memory node of the single-electron memory to detect the potential change of the memory node by the injection of the individual electrons. The fabricated single-electron memory showed the hysteresis loop even at room temperature by the return trip of the memory bias when starting from 0 to 10 V and again coming back to 0 V. About 25 electrons were stored at the memory node.

Nanomachining of (110)-oriented silicon by scanning probe lithography and anisotropic wet etching

We have demonstrated that silicon nanostructures with high aspect ratios, having ∼400 nm structural height and ∼55 nm lateral dimension, may be fabricated by scanning probe lithography and aqueous KOH orientation-dependent etching on the H-passivated (110) Si wafer. The high spatial resolution of fabricated features is achieved by using the atomic force microscope based nano-oxidation process in ambient. Due to the large (110)/(111) anisotropic ratio of etch rate and the large Si/SiO2 etch selectivity at a relatively low etching temperature and an optimal KOH concentration, high-aspect-ratio gratings with (111)-oriented structural sidewalls as well as hexagonal etch pit structures determined by the terminal etch geometry can be obtained.

Room temperature operated single electron transistor made by a scanning tunnelling microscopy/atomic force microscopy nano-oxidation process

Application of scanning tunnelling microscopy (STM) and atomic force microscopy (AFM) to an electron device is introduced in this paper. Using a STM tip/AFM cantilever as a cathode, the surface of a metal is oxidized to form a few tens of nanometre wide oxidized metal line, which works as an energy barrier for an electron. A single electron transistor (SET) is fabricated using this fabrication process. As a STM/AFM, nano-oxidation process could fabricate the device size of the order of 10 nm, the fabricated SET operates even at a higher temperature than room temperature and shows the large Coulomb gap and staircase of 200 mV periods. An atomically flat α-A12O3 substrate is proposed for improving the uniformity and reproducibility of the oxidized line made by a STM/AFM nano-oxidation process.

Metal-Based Room-Temperature Operating Single Electron Devices Using Scanning Probe Oxidation

Coulomb oscillation was clearly observed at room temperature in the single electron transistor fabricated by atomic force microscopy (AFM) nano-oxidation process. In order to obtain a clear Coulomb oscillation at room temperature, new and improved fabrication processes and measurement systems such as a pulse-mode AFM nano-oxidation process and a triaxial active feedback measurement system are introduced. The Coulomb oscillation peaks appear with the period of 1.9 V at the drain bias conditions of 0.25 V and 0.3 V. The current modulation rate ranges from 20% to 30%.

Single electron transistors fabricated with AFM ultrafine nanooxidation process

Single electron transistors fabricated with AFM ultrafine nanooxidation process