Design, fabrication and characterization of gallium nitridebased circular schottky diode for hydrogen sensing

Recent revolutionary progress of the internet and wireless technologies has create a concept of the “ubiquitous network” society for this 21st century. A so called Intelligent Quantum (IQ) chip has been proposed as the promising electronic device for the ubiquitous network society environment. An IQ chip is an III-V semiconductor chip with sizes of millimeter square where not only nanometer scale quantum processors and memories are integrated on this chip but also other devices such as wireless power supply and various sensing devices so that such ideal concept can be realized. This research is carried out to reveal a possibility of utilizing III-V base material as a sensing device, in particular as a hydrogen (H2) gas sensor. High temperature operation and long term stability are important requirements for a H2 sensor, thus an undoped-Alluminium Nitride/Gallium Nitride (AlGaN/GaN) high-electron-mobility-transistor (HEMT) structure is chosen as the base material. The sheet concentration and mobility of epitaxial layers determined by Hall measurement were 6.61×1012 cm-2 and 1860 cm2/Vsec, respectively. The devices fabrication were etched by an inductively-couple-plasma reactive ion etching (ICP-RIE) system for mesa isolation? with a Chlorine (Cl)-based gas system consisting of Boron Trychloride (BCl3) and Chlorine (Cl2) gases. The ohmic contacts are formed by deposition of Titanium/Aluminium/Titanium/Aurum (Ti/Al/Ti/Au) (20/50/35/50 nm) multilayers followed by rapid thermal annealing at 850 °C for 30 s in nitrogen (N2) ambient. The Schottky contact was produced by evaporating 5 nm thick catalytic Platinum (Pt) metal. Finally, Titanium/Aurum (Ti/Au) was evaporated as interconnection contact. Typical I-V characteristics measured in vacuum and high purity H2 ambient at room temperature show that both the forward and reverse currents give only a slight change of current upon exposure to H2 because the diffusion rate for H2 atom through the catalytic metal is very slow at room temperature. Thus, it can be said that the sensitivity of gas sensor is quite low at room temperature. However, a large current change by the same amount of H2 concentration is observed as the temperatures increase up to 200 °C because more effective catalytic dissociation of H2 on the Pt surface can be realized at higher temperature. The time-transient response measured at temperature of 200 °C and forward bias of 1 V shows that there is sufficient cracking of H2 for the diode to be a sensitive gas sensor. A constant speed is obtained at each cycle where the average of increment and decrement speed of current are estimated to be 27.6 nA/sec and 17.6 nA/sec, respectively. The increment speed is much faster than the decrement speed for each cycle meaning that the absorption of H2 is faster than desorption. This is because a desorption process requires thermal energy supply, leading to a longer decrement time. These preliminary results indicate that the proposed sensing devices are capable of detecting H2 gas with acceptable performance

THE OPTIMAL ABSORPTION OF BILIRUBIN USING AN OPTICAL FIBRE SENSOR

This paper describes an optical fiber sensor for the monitoring of bilirubin concentration and commonly called jaundice An open path optical technique is used to analyze the absorption lines of bilirubin within the Ultra Violet/ Visible region. By using a wavelength corresponding to a bilirubin absorption peak, the Beer-Lambert Law can be used to relate the concentration of bilirubin surrounding the sensing portion to the amount of absorbed light. In the initial experiment, the absorption cross section for MAS bilirubin a product from Thermo Scientific was investigated and compare with theoretical data. Initially, an empty cuvette was used to measure incident intensity when the light passes through the empty cuvette. Then a cuvette was filled with bilirubin sample before measured the transmitted intensity. The theoretical absorbance of bilirubin shows maximum absorption in the range of 400 nm to 600 nm. The experimental result shows the absorption line for measured MAS bilirubin is in similar pattern but the maximum absorbance shows in range 600 nm to 700 nm. This is due to the type of sample used in the experiment and high attenuation of the optical fiber used at the lower wavelength of UV light. Future work would be carried out to study the cross sensitivity of bilirubin absorption spectrum with other human blood molecules like hemoglobin (Hb), oxygen (O2) and carbon dioxide (CO2) to yield the best wavelength for the absorption

Bilirubin Sensing and a Cross Sensitivity Evaluation with Co2 and O2 Using Optical Fiber Sensor

This paper describes an optical fiber sensor for the monitoring of bilirubin concentration and commonly called jaundice. An open path optical technique is used to analyze the absorption lines of bilirubin within the Ultra Violet/ Visible region. By using a wavelength corresponding to a bilirubin absorption peak, the Beer-Lambert Law can be used to relate the concentration of bilirubin surrounding the sensing portion to the amount of absorbed light. In the initial experiment, the absorption cross section for MAS bilirubin a product from Thermo Scientific was investigated and compare with theoretical data. an empty cuvette was used to measure incident intensity when the light passes through the empty cuvette. Then a cuvette was filled with bilirubin sample before measured the transmitted intensity. The theoretical absorbance of bilirubin shows maximum absorption in the range of 400 nm to 500 nm. The experimental result shows the absorption line for measured MAS bilirubin is in similar pattern and the maximum absorbance shows in range 400 nm to 500 nm. Cross sensitivity evaluation would be carried out to study the cross sensitivity of bilirubin absoprtion spectrum with other human blood molecules like oxygen (O2) and carbon dioxide (CO2) to yield the best wavelength for the absorption

An Overview of Optical Fibre Sensors for Medical Application

Optical techniques developed for sensing purposes proved ti be completely realized in many application fields, ranging from aerospace, industry, process control and medical. The capabilities of these sensors are generally enhanced when a bulk optical fibre technology. There is a growing need for a real time and low cost technology because of the expense and time constraints associated with modern laboratory analysis. This us certainly due the growing interest in aptoelectronics, but also the very satisfactory performance and reliability that optical fibre sensor are now able to provide. This paper focuses on the advantages that optical fibre sensos offer to the biomedical field, recalls the basic working principles of sensing and discusses some example

The sensing performance of undoped-AlGaN/GaN/sapphire HEMT hydrogen gas sensor

The hydrogen sensing characteristics of undoped-AlGaN/GaN/sapphire circular Schottky diodes are systematically studied and compared over wide hydrogen concentration and temperature ranges. High purity hydrogen gas was exposed to the sample together with the ambient gas of either air or pure nitrogen or without ambient gas (vacuum) at pressure in the range of 50 Torr to 200 Torr was used for both types of ambient gases. The sensing characteristics at different hydrogen concentration are investigated. The sensitivity to hydrogen gas was also investigated in dependence of various catalytic metals thickness and operating temperatures

Uric acid detection using uv-vis spectrometer

The aim of this research is to detect uric acid (UA) concentration using Ultraviolet-Visible (UV-Vis) spectrometer in the Ultraviolet (UV) region. Absorption technique was proposed to detect different uric acid concentrations and its UV absorption wavelength. Current practices commonly take a lot of times or require complicated structures for the detection process. By this proposed spectroscopic technique, every concentration can be detected and interpreted into an absorbance value at a constant wavelength peak in the UV region. This is due to the chemical characteristics belong to the uric acid since it has a particular absorption cross-section, σ which can be calculated using Beer’s Lambert law formula. The detection performance was displayed using Spectrasuite sofware. It showed fast time response about 3 seconds. The experiment proved that the concentrations of uric acid were successfully detected using UV-Vis pectrometer at a constant absorption UV wavelength, 294.46 nm in a low time response. Even by an artificial sample of uric acid, it successfully displayed a close value as the ones reported with the use of the medical sample. It is applicable in the medical field and can be implemented in the future for earlier detection of abnormal concentration of uric acid

UV detection on artificial uric acid using UV-Vis spectrometer

The aim of this research work is to measure the concentration and absorption cross-section of artificial uric acid in the Ultraviolet (UV) region using UV-Vis spectrometer. The uric acid sample comes in powder form which has to be dissolved with distilled water to convert it into liquid form. Therefore, it can be placed in the cuvette for the analysis purposes. This research study was proposed to make a comparison with the previous research studies that uric acid was normally extracted from human serum as a real sample. This research study was carried out using an artificial sample of uric acid with the suspended or grits of uric acid which were not totally dissolved. These grits might be artificially assumed as crystallites which is common with Gout disease. Based on the medical perspective, crystallites normally inhibit the human joints which may cause intense pain to the human bones or tissues. In the experiment, the distilled water was used a background or reference spectrum which can be stored and automatically deducted using the Spectra suite software application. Thus, Spectra suite only measures the pure concentration and UV absorption wavelength of the uric acid through the use of the spectrometer. The absorbance data was extracted and substituted into Beer’s Lambert Law formula to calculate the value of absorption cross-section. The result shows that the value of UV absorption wavelength and absorption cross-section is really close as reported in the previous research studies. It proves that even the artificial sample of uric acid with the grits still can give a very close result. The UV absorption of uric acid was obtained at 293.99 nm by four different concentrations. The response time was successfully done in 3 seconds. The resulting curves have noise signals which can be analyzed and reduced using an averaging method to make the curve look sharper and lack of noise

Uric Acid Detection in UV Region

The aim of this research is to analyze uric acid (UA) concentration using Ultraviolet (UV) spectrometer. Absorption technique was proposed in the application to detect different uric acid concentrations. Current practice is commonly done by using enzymatic or colorimetric technique which may drag take a lot of times especially at the analysis phase. By this proposed spectroscopic technique, every concentration can be contemplated into UV absorption wavelength displaying on Spectrasuite. It shows fast time response i.e., 1s. Each value of diluted uric acid concentration indicates a different absorption potential. Absorption cross-section of uric acid can be calculated by Beer’s Lambert law formula. The experiment proves that different concentrations of uric acid were successfully detected using UV spectrometer at wavelength, 294.46 nm, every concentration showing a different absorbance value. Meanwhile, the absorption cross-section of uric acid molecules shows the close values for the different concentrations

The sensing performance of hydrogen gas sensor utilizing undoped-AlGaN/GaN HEMT (a)

High temperature operation and long term stability are important requirements for gas sensor. The response of Pt-circular Schottky diodes fabricated on undoped AlGaN/GaN high-electron-mobility-transistor (HEMT) structure to hydrogen gas at various temperatures, ranging from 25 to 200°C has been investigated. A 5 nm-thick of catalytic Pt Schottky contact is formed by electron beam evaporation. Both forward and reverse currents of the device increase upon exposing to hydrogen gas. Although a slight change of forward and reverse current is obtained at room temperature upon exposure to hydrogen but both currents drastically increase with the increase of temperatures. The time-transient characteristics show the average current increment and decrement speed of 27.6 and 17.6 nA sec-1, respectively at constant forward bias of 1 V and temperature of 200°C