Thermal Oxidation Technique Research Articles

A novel fabrication method based on an after thermal oxidation process for the realization of silicon-beams with normative polygon cross sections shapes

This paper presents a novel method to obtain structures with normative polygon cross section (PCS) shapes in a single crystal silicon substrate. A combination of wet etching and an after thermal oxidation (ATO) technique was used to fabricate several novel, complex structures with PCS shapes, which can hardly be fabricated by traditional wet etching. Based on such an innovative method, this paper proposes and develops three varieties of PCS silicon-beams. The subsequent experiment of fabricating silicon-beams with hexagonal sections has been taken as an example to validate the technique principle. Furthermore, the dimension parameters of the fabricated structures have been tested. Through this novel fabrication method, the sidewall arris of the fabricated silicon-beams can be maintained due to the protection of the ATO SiO2 layers, the arris disfigurement of the silicon-beam decreases dramatically and the quality of the silicon-beam is improved greatly.

Comparison of oxidized/nitrided Zr thin films on Si and SiC substrates

This work utilizes simultaneous thermal oxidation and nitridation technique to transform sputtered Zr to ZrO2 and to Zr-oxynitride thin films on Si and SiC substrates, respectively, in nitrous oxide gas ambient. Various characterization techniques such as X-ray photoelectron spectroscopy, energy-filtered transmission electron spectroscopy, atomic force microscopy, X-ray diffraction, capacitance–voltage measurements, and leakage current density-electric field measurements were carried out to evaluate and compare the structural, chemical, and electrical properties of the films produced on both Si and SiC substrates.

Enhancement-mode InAlN/GaN MISHEMT with low gate leakage current

We report an enhancement-mode InAlN/GaN MISHEMT with a low gate leakage current by a thermal oxidation technique under gate. The off-state source-drain current density is as low as ∼10−7 A/mm at VGS = 0 V and VDS = 5 V. The threshold voltage is measured to be +0.8 V by linear extrapolation from the transfer characteristics. The E-mode device exhibits a peak transconductance of 179 mS/mm at a gate bias of 3.4 V. A low reverse gate leakage current density of 4.9 × 10−7 A/mm is measured at VGS = −15 V.

Field emission properties of zinc oxide/zinc tungstate (ZnO/ZnWO4) composite nanorods

Zinc oxide/zinc tungstate (ZnO/ZnWO4) nanorods were synthesized as composite nanostructure on the tungsten/glass substrates by thermal oxidation technique for field emission cathodes. The ZnWO4 wolframite structure in the ZnO film formed the ZnO/ZnWO4 composite nanostructure, as indicated by the XRD patterns and Raman spectrum. An ohmic contact was transformed to a Schottky contact between a silver electrode and the ZnO/ZnWO4 composite nanorods from I–V measurement given that the work function of the ZnO/ZnWO4 composite nanorods was lower than that of ZnO nanorods. The field emission properties of the ZnO/ZnWO4 composite nanorods includes a turn-on electric field (Eon) of 2.1V/μm and a threshold electric field (Eth) of 2.9V/μm, both much lower than that found in ZnO nanorods without ZnWO4 nanostructures. The novel ZnO/ZnWO4 composite nanorod shows excellent potential for application in field emission cathodes and related devices.

Zinc Oxide Nanowires Deposited on Polymeric Hotplates for Low-power Gas Sensors

Zinc oxides (ZnO) nanowires were successfully deposited on plastic low-power micro-hotplates using the thermal oxidation technique. Metallic zinc layer was deposited on the sensing transducer by RF magnetron sputtering and then oxidized in a controlled atmosphere in order to obtain ZnO nanostructures. Morphological investigations confirmed the nanometric dimensions of the fabricated nanostructures. The n-type behavior of the nanostructured material was evaluated towards different chemical species to highlight the electrical properties of the materials. Calibration curves for the detection of several chemical species were defined. © 2012 The Authors. Published by Elsevier Ltd.

Growth Kinetic and Characterization of Mg<SUB><I>x</I></SUB>Zn<SUB>1−<I>x</I></SUB>O Nanoneedles Synthesized by Thermal Oxidation

Mg(x)Zn1-xO nanoneedles were synthesized on alumina substrate by using thermal oxidation technique under normal atmosphere. Zn powder and MgO powder were mixed and heated to form Mg(x)Zn1-xO with x content of 0-0.3 by mol at heating temperature and time of 400-1000 degrees C and 24 h. The morphology of Mg(x)Zn1-xO nanoneedle was characterized by filed emission scanning electron microscope (FE-SEM). It was found that the needle-like nanostructures with the sharp ends were observed outward from microparticles at 400-800 degrees C. From EDS, XRD, and TEM analysis, it was suggested that Mg(x)Zn1-xO alloy was formed with no segregation of MgO in Mg(x)Zn1-xO alloy after thermal oxidation process. Also, from reflectance spectra, the Mg(x)Zn1-xO nanoneedle exhibited higher energy gap than that of ZnO films for entire Mg content indicating widening band gap energy due to alloying effect. Moreover, we have proposed the growth mechanism of Mg(x)Zn1-xO nanoneedles based on growth kinetic of nucleation formation. This growth model can be explored to explain nanostructure of other metal-oxide alloy prepared by thermal oxidation.

Thermal oxidation as a simple method to increase resolution in nanoimprint lithography

We introduce a simple thermal oxidation technique for decreasing feature sizes of nanoimprint lithography (NIL) masters. During oxidation, the dimensions of negative features are reduced (e.g., gaps become narrower), and the dimensions of positive features increase (e.g., lines become wider). We demonstrate that positive feature sizes can also be reduced after oxidation by selective etching of the oxide. We show that 74 nm gaps can be reduced to 10 nm and 226 nm lines can be narrowed to 55 nm. The reduction in feature size achieved in both positive and negative structures directly translates into increased imprint resolution, and we demonstrate improved resolution in a complete NIL pattern transfer using thermally oxidized NIL masters.

Effect of sputtering time on physical and electrical properties of ZrOx thin film on Si

PurposeThe purpose of this paper is to report the effect of sputtering time on the electrical and physical properties of ZrOx. ZrOx (measured thickness is ranging from 20.5 to 51.3 nm) thin films as gate oxide materials are formed by metal deposition at different sputtering time and thermal oxidation techniques.Design/methodology/approachZirconium is deposited on silicon substrate at three different sputtering time; 30‐, 60‐ and 120‐s continued with an oxidation process conducted at 500°C for 15 min to form ZrOx thin films. High‐resolution X‐ray diffraction (HR‐XRD), Fourier transform infrared (FTIR) spectroscopy and electrical characterizations were used to examine the properties of the thin film.FindingsA broad ZrOx peak lies in between 26° and 31° from HR‐XRD is presumed as the effect of small thickness of ZrOx and or the ZrOx is still partially crystalline. FTIR spectroscopy results suggested that besides ZrOx, SiOx interfacial layer (IL) has also formed in all of the investigated samples. As the sputtering time increases, hysteresis between the forward and reverse bias of capacitance‐voltage curve has reduced. The lowest leakage current density and the highest oxide breakdown voltage have been demonstrated by 60‐s sputtered sample. These may be attributed to a lower effective oxide charge and interface trap density. The extracted dielectric constant (κ) of these oxides is ranging from 9.4 to 18, in which the κ value increases with the increase in sputtering time.Originality/valueZrOx thin film which was fabricated by sputtering method at different sputtering time and thermal oxidation techniques showed distinctive electrical results. SiOx IL formed in the samples.

Enhancement of Sensor Response by Au Nanoparticles Doping on ZnO Tetrapod Sensor

Zinc oxide tetrapods (T-ZnO) were synthesized using thermal oxidation technique from Zn powders mixed with hydrogen per oxide (H2O2). Through a detailed field emission scanning electron microscopy (FE-SEM), energy dispersive spectroscopy (EDS), and x-ray diffraction (XRD) showed that the T-ZnO exhibited single crystalline hexagonal wurtzite structure. The leg tip of the T-ZnO was about 8.17±1.17 µm in length and 47.80 nm in diameter. The ethanol sensors, based on the T-ZnO and the T-ZnO doped with Au nanoparticles (Au/T-ZnO), were fabricated and investigated for the ethanol sensing properties. The ethanol sensor response of the T-ZnO and the Au/T-ZnO sensors was tested at the operating temperature of 260-360°C with the ethanol concentration of 50, 100, 500, and 1000 ppm. The results showed that the Au/T-ZnO sensors exhibited exceptionally higher sensitivity than the pure T-ZnO sensors for entire ethanol concentration with optimum temperature of 340°C and 320°C, respectively. This enhancement can be explained in terms of the electron concentration of sensor in air, n0 and the reaction rate constant, kEth between the adsorbed oxygen species and the ethanol vapor due to the increase of effective surface for adsorption of ethanol on the surface. With an excellent catalytic ability, the Au nanoparticles doping on the T-ZnO sensors would result in higher reaction rate constant than the undoped T-ZnO sensors.

Fabrication of Silicon Nano-wire by Oxidation

In this paper, we report a method of fabricating silicon nano-wire based on thermal oxidation technique. In this method, we first fabricate a wider structure with traditional lithography, and then use a layer of silicon nitride as mask to oxidize silicon. At the same time, due to the lateral diffusion and oxidation of oxidant, silicon is consumed by oxidant and the width of the silicon structure will be reduced to nano range when we remove the silicon dioxide. The factors affecting the ratio of vertical and lateral oxidation, for example, the gentle slope caused by isotropic oxidation and the inhomogeneity of the sidewall of silicon nano-wire, are discussed at last. Our results should be useful in generating silicon–based nanospintronics devices with careful selection of the oxide parameters.

STRUCTURAL AND OPTICAL PROPERTIES OF ZnO SYNTHESIZED BY TEMPERATURE GRADIENT THERMAL OXIDATION

In this work, a series of polycrystalline ZnO samples have been synthesized from Zn thin films deposited on Si (100) substrates by using thermal oxidation technique. The ZnO thin film samples grown by this technique were then characterized by a variety of structural and optical characterization tools. The results revealed that the use of novel annealing process i.e. the application of temperature gradient in the thermal treatment could enhance the structural and optical quality of the ZnO thin films significantly as compared to the normal annealing process, i.e. a fixed temperature under different durations. Apart from the improvement of structural and optical properties of ZnO thin films, another striking feature of this novel annealing process was the promotion of the growth of ZnO nanostructures.

Fabrication of nanowires with high aspect ratios utilized by dry etching with SF6:C4F8 and self-limiting thermal oxidation on Si substrate

Si-based nanowires with high aspect ratios have been fabricated using an inductively coupled plasma reactive ion etching (ICP-RIE) with a continuous processing gas mixture of fluorine-based SF6:C4F8 combined with a thermal oxidation technique. The subsequent thermal oxidation further reduced the nanowire diameter utilizing the self-limiting oxidation effect below the lithographic dimensions. Transmission electron microscopy analysis of the completed nanostructures revealed the total oxide thickness and the consumption of the Si core which determines the inner nanowire diameter. The final dimensions of the inner Si nanowire are about 600 nm tall and less than 25 nm wide using top-down processing techniques.

Silicon-on-SiC, a Novel Semiconductor Structure for Power Devices

A physical and electrical analysis of Si/SiC heterojunctions formed by layer transfer based on the smartcut® process is presented in this paper. AFM and SEM have revealed a high bonding quality when Si wafers are transferred to SiC on-axis wafers. XRD points to the fact that the layers are monocrystalline in nature. A surface AFM analysis of the bonded wafers demonstrated a smooth surface (rms = 5.8 nm) suitable for semiconductor device fabrication. Capacitors have been fabricated from the Si/SiC heterojunctions, which have been totally oxidised. Oxidised Si/SiC structures yielded a lower density of interface states than conventional thermal oxidation techniques.

Enhancement of sensor response by TiO 2 mixing and Au coating on ZnO tetrapod sensor

The sensors based on ZnO tetrapods (T-ZnO) and ZnO tetrapods with TiO 2 mixing (T-TiZnO) and Au coating (Au/T-TiZnO) were investigated. The T-ZnO and T-TiZnO were synthesized by a simple thermal oxidation technique. The leg of the tetrapod is about 1–10 μm in length and 160–500 nm in diameter. Au coating was performed by sputtering technique and annealed at 550 °C for 6 h under normal atmosphere. The ethanol sensor response of the T-ZnO, T-TiZnO and Au/T-TiZnO sensors was tested at the operating temperature of 260–360 °C with the ethanol concentration of 50, 100, 200, 500, and 1000 ppm. It was found that at the optimum temperature the Au/T-TiZnO sensor exhibited the highest sensor response and the T-TiZnO sensor exhibited higher sensor response than that of the T-ZnO sensor. The Au/T-TiZnO sensor exhibited the highest sensor response up to 240 at 340 °C under the ethanol concentration of 1000 ppm. The enhancement of the sensor response based on the T-ZnO by TiO 2 mixing and Au coating can be explained by alloying effect and metal catalytic effect, respectively. The response enhancement can be explained in terms of electron concentration, n 0 in air and reaction rate constant, k Eth . The evidence for both effects can be found in higher sensor resistance in air and lower sensor resistance in the ethanol ambient.

Experimental analysis of current conduction through thermally grown SiO2 on thick epitaxial 4H-SiC employing Poole-Frenkel mechanism

Electrical properties of SiO2 grown on the Si-face of the epitaxial 4H-SiC substrate by wet thermal oxidation technique have been experimentally investigated in metal oxide-silicon carbide (MOSiC) structure with varying oxide thicknesses employing Poole-Frenkel (P-F) conduction mechanism. The quality of SiO2 with increasing thickness in MOSiC structure has been analysed on the basis of variation in multiple oxide traps due to effective P-F conduction range. Validity of Poole-Frenkel conduction is established quantitatively employing electric field and the oxide thickness using forward I–V characteristics across MOSiC structures. From P-F conduction plot (ln(J/E) vs. E 1/2), it is revealed that Poole-Frenkel conduction retains its validation after a fixed electric field range. The experimental methodology adopted is useful for the characterization of oxide films grown on 4H-SiC substrate.

Au-doped zinc oxide nanostructure sensors for detection and discrimination of volatile organic compounds

Pure and 10% w/w Au-doped zinc oxide (ZnO) nanostructure sensors were produced and used as sensing devices in a portable electronic nose (E-nose). The nanosensors were prepared using thermal oxidation technique with sintering temperature at 700°C under oxygen atmosphere at a flow rate of 500 mL min–1. The sensors were demonstrated to be sensitive to various volatile organic compounds (VOCs), especially ethanol vapour. The E-nose even with only two sensors was efficient to discriminate a number of selected VOCs. The Au-doped sensor shows a significant improvement of sensitivity. The portable E-nose can detect the difference between alcohol beverages and alcohol solutions and can distinguish the difference of white and red wines having the same percentage of alcohol.

Zinc oxide nanostructures for applications as ethanol sensors and dye-sensitized solar cells

ZnO nanostructures were prepared by thermal oxidation technique for applying as ethanol sensors and dye-sensitized solar cells. To improve sensitivity of the sensor based on ZnO nanostructures, gold doping was performed in ZnO nanostructures. Gold-doped with 0%, 5%, and 10% by weight were investigated. The improvement of sensor sensitivity toward ethanol due to gold doping was observed at entire operating temperature and ethanol concentration. The sensitivity up to 145 was obtained for 10% Au-doped ZnO sensor. This can be explained by an increase of the quantity of oxygen ion due to catalytic effect of gold. Also, it was found that oxygen ion species at the surface of the Au-doped ZnO sensor remained O 2− as pure ZnO sensor. For dye-sensitized solar cell application, the dye-sensitized solar cell structure based on ZnO as a photoelectrode was FTO/ZnO/Eosin-Y/electrolyte/Pt counter electrode. ZnO with different morphologies of nanobelt, nano-tetrapod, and powder were investigated. It was found that DSSCs with ZnO powder showed higher photocurrent, photovoltage and overall energy conversion efficiencies than that of ZnO nanobelt and ZnO nano-tetrapod. The best results of DSSCs were the short circuit current ( J sc) of 1.25 mA/cm 2, the open circuit voltage ( V oc) of 0.45 V, the fill factor (FF) of 0.65 and the overall energy conversion efficiency ( η) of 0.68%.

Investigation on the electrocatalytic characteristics of SnO2 electrodes with nanocoating prepared by electrodeposition method

SnO2 electrodes have many advantages in the degradation of toxic or bio-refractory organic wastewater, and SnO2 is a kind of anode material which has the potential to be widely used. Electrocatalytic efficiency and service life of TiSnO2 electrodes are key factors that can influence its applications. In order to enhance the electrocatalytic characteristics of TiSnO2 electrodes, a type of electrocatalytic electrode with nanocoating was prepared by direct current (DC) electrodeposition method and thermal oxidation technique. With phenol as the model pollutant, the electrochemical degradation efficiencies of electrodes with nanocoating and non-nanocoating were investigated. It was demonstrated that the electrodes with nanocoating have higher efficiency than that of electrodes with non-nanocoating. The degradation time was decreased 33.3% for the same amount of phenol’s degradation. The crystal structure of surface coating, the micrograph of electrode surface and the chemical environment of Sn and Sb in the electrode surface were analyzed with the help of XRD, SEM and XPS. The results showed that the surface of electrode was mainly SnO2 crystal with rutile structure and that much adsorbed oxygen in nanocoating was the dominant factor for enhancing the electrocatalytic characteristics.

Semiconducting tin oxide nanowires and thin films for Chemical Warfare Agents detection

In this work we report the preparation and structural characterization of tin oxide nanowires as functional materials for the development of chemical sensors. Aspects of material preparation relevant for gas sensing applications, such as the control of the wire diameter, are emphasized. The functional characterization is focused on the detection of Chemical Warfare Agents (CWAs) simulants, with particular regard to poisoning effects induced by dimethyl methyl phosphonate (DMMP), a simulant for Sarin nerve agent. Tin oxide thin films, prepared by means of rheotaxial growth and thermal oxidation (RGTO) technique, are used as reference to better compare the performance of nanowires with thin films traditionally used in gas sensing field.

Comparative study of ethanol sensor based on gold nanoparticles: ZnO nanostructure and gold: ZnO nanostructure

Gold colloid:ZnO nanostructures were prepared from Zn powder by using thermal oxidation technique on alumina substrates, then it was impregnated by gold colloid for comparative study. The gold colloid is the solution prepared by chemical reduction technique; it appeared red color for gold nanoparticle solution and yellow color for gold solution. The heating temperature and sintering time of thermal oxidation were 700 °C and 24 h, respectively under oxygen atmosphere. The structural characteristics of gold colloid:ZnO nanostructures and pure ZnO nanostructures were studied using filed emission scanning electron microscope (FE-SEM). From FE-SEM images, the diameter and length of gold colloid:ZnO nanostructures and ZnO nanostructures were in the ranges of 100–500 nm and 2.0–7.0 μm, respectively. The ethanol sensing characteristics of gold colloid:ZnO nanostructures and ZnO nanostructures were observed from the resistance alteration under ethanol vapor atmosphere at concentrations of 50, 100, 200, 500, and 1000 ppm with the operating temperature of 260–360 °C. It was found that the sensitivity of sensor depends on the operating temperature and ethanol vapor concentrations. The sensitivity of gold colloid:ZnO nanostructures were improved with comparative pure ZnO nanostructures, while the optimum operating temperature was 300 °C. The mechanism analysis of sensor revealed that the oxygen species on the surface was O 2−.