Hydrogen sensors based on AlGaN/AIN/GaN HEMT

Pt/AlGaN/AIN/GaN high electron mobility transistors (HEMT) were fabricated and characterized for hydrogen sensing. Pt and Ti/Al/Ni/Au metals were evaporated to form the Schottky contact and the ohmic contact, respectively. The sensors can be operated in either the field effect transistor (FET) mode or the Schottky diode mode. Current changes and time dependence of the sensors under the FET and diode modes were compared. When the sensor was operated in the FET mode, the sensor can have larger current change of 8 mA, but its sensitivity is only about 0.2. In the diode mode, the current change was very small under the reverse bias but it increased greatly and gradually saturated at 0.8 mA under the forward bias. The sensor had much higher sensitivity when operated in the diode mode than in the FET mode. The oxygen in the air could accelerate the desorption of the hydrogen and the recovery of the sensor. (c) 2007 Elsevier Ltd. All rights reserved.

Hydrogen sensors based on AlGaN/AIN/GaN Schottky diodes

Pt/AlGaN/AIN/GaN Schottky diodes are fabricated and characterized for hydrogen sensing. The Pt Schottky contact and the Ti/Al/Ni/Au ohmic contact are formed by evaporation. Both the forward and reverse currents of the device increase greatly when exposed to hydrogen gas. A shift of 0.3 V at 300K is obtained at a fixed forward current after switching from N-2 to 10%H-2+N-2. The sensor responses under different concentrations from 50ppm H-2 to 10%H-2+N-2 at 373K are investigated. Time dependences of the device forward current at 0.5 V forward bias in N-2 and air atmosphere at 300 and 373K are compared. Oxygen in air accelerates the desorption of the hydrogen and the recovery of the sensor. Finally, the decrease of the Schottky barrier height and sensitivity of the sensor are calculated.

Development of current-based microscopic defect analysis method using optical filling techniques for the defect study on heavily irradiated high-resistivity Si sensors/detectors

Current-based microscopic defect analysis method such as current deep level transient spectroscopy (I-DLTS) and thermally stimulated current have been developed over the years at Brookhaven National Laboratory (BNL) for the defect characterizations on heavily irradiated (Phi(n) >= 10(13) n/cm(2)) high-resistivity (>= 2 k Omega cm) Si sensors/detectors. The conventional DLTS method using a capacitance transient is not valid on heavily irradiated high-resistivity Si sensors/detectors. A new optical filling method, using lasers with various wavelengths, has been applied, which is more efficient and suitable than the traditional voltage-pulse filling. Optimum defect-filling schemes and conditions have been suggested for heavily irradiated high-resistivity Si sensors/detectors. (c) 2006 Published by Elsevier Ltd.

Hydrogen sensors based on Pt-AlGaN/GaN back-to-back Schottky diode

In this paper, platinum (Pt) with a thickness of 45 nm was sputtered on the surface of AlGaN/GaN heterostructure to form the Schottky contact and the back-to-back Schottky diodes were characterized for H-2 sensing at room temperature. Both the forward and reverse current of the devices increased with exposure to H-2 gas, which was attributed to Schottky barrier height reduction caused by hydrogen absorption in the catalytic metals. A shift of 0.7 V at 297 K was obtained at a fixed forward current of 0.1 mA after switching from N-2 to 40% H-2 in N-2. The sensor's responses under different concentrations from 2500 ppm H-2 to 40% H-2 in N-2 at 297 K were investigated. Time response of the sensor at a fixed bias of 1 V was given. Finally, the decrease of the Schottky barrier height and the sensitivity of the sensor were calculated. (C) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Hydrogen sensors based on Pt-AlGN/AIN/GaN Schottky diode - art. no. 68291R

Pt/AlGaN/AlN/GaN Schottky diodes have been fabricated and characterized for H-2 sensing. Platinum (Pt) with a thickness of 20nm was evaporated on the sample to form the Schottky contact. The ohmic contact, formed by evaporated Ti/Al/Ni/Au metals, was subsequently annealed by a rapid thermal treatment at 860 degrees C for 30 s in N-2 ambience. Both the forward and reverse current of the device increased greatly when exposed to H-2 gas. The sensor's responses under different hydrogen concentrations from 500ppm to 10% H-2 in N-2 at 300K were investigated. A shift of 0.45V at 297K is obtained at a fixed forward current for switching from N-2 to 10% H-2 in N-2. Time response of the sensor at a fixed bias of 0.5 V was also measured. The turn-on response of the device was rapid, while the recovery of the sensor at N-2 atmosphere was rather slow. But it recovered quickly when the device was exposed to the air. The decrease in the barrier height of the diode was calculated to be about 160meV upon introduction of 10% H-2 into the ambient. The sensitivity of the sensor is also calculated. Some thermodynamics analyses have been done according to the Langmuir isotherm equation.

A Novel Low-Power Digital Baseband Circuit for UHF RFID Tag with Sensors

A novel low-power digital baseband circuit for UHF RFID tag with sensors is presented in this paper. It proposes a novel baseband architecture and a new operating scheme to fulfill the sensor functions and to reduce power consumption. It is also compatible with the EPC C1G2 UHF RFID protocol. It adopts some advanced low power techniques for system design and circuit design: adaptive clock-gating, multi-clock domain and asynchronous circuit. The baseband circuit is implemented in 0.18um 1P3M standard CMOS process. ne chip area is 0.28 mm(2) excluding test pads. Its power consumption is 25uW under 1.1V power supply.

High resolution interrogation technique based on linear photodiode array spectrometer for fiber Bragg grating Sensors - art. no. 65952C

A linear photodiode array spectrometer based, high resolution interrogation technique for fiber Bragg grating sensors is demonstrated. Spline interpolation and Polynomial Approximation Algorithm (PAA) are applied to the data points acquired by the spectrometer to improve the original PAA based interrogation method. Thereby fewer pixels are required to achieve the same resolution as original. Theoretical analysis indicates that if the FWHM of a FBG covers more than 3 pixels, the resolution of central wavelength shift will arrive at less than 1 pm. While the number of pixels increases to 6, the nominal resolution will decrease to 0.001 pm. Experimental result shows that Bragg wavelength resolution of similar to 1 pm is obtained for a FBG with FWHM of similar to 0.2 nm using a spectrometer with a pixel resolution of similar to 70 pm.

Experiment on Qinghai-Tibet railroad subgrade temperature monitoring based on FBG sensors

Qinghai-Tibet Railway is the longest and highest plateau railway in the world. A long term monitoring system of the stability of the subgrade in the permafrost regions should be put forward immediately to prevent damage to the railway. As it's very difficult to set up the long-distance automatic monitoring system which contains a lot of measure points along the 550 kilometers railway in the permafrost area, we present a subgrade temperature monitor system based on fiber Bragg grating (FBG). In this paper the principles of the FBG was presented, and the feasibility of the FBG sensors in the permafrost area of Qinghai-Tibet plateau was analysized. We embedded fifteen FBG temperature sensors and thermal resistance temperature sensors. A contrast experiment is made while the two kinds of sensors are arranged in the same position. The result of the experiment shows that the accuracy of the FBG temperature sensors is less than 0.1 degrees C. and the FBG sensors can do well in the measurement of pattern which the temperature varies with the depth of the permafrost soil. The result also shows the stability of the FBG sensors in the bad environmental condition of Qinghai-Tibet plateau, which proves the feasibility of the application of FBG sensors and our monitoring system on the Qinghai-Tibet railway.

Development of current-based microscopic defect analysis method using optical filling techniques for the defect study on heavily irradiated high-resistivity Si sensors/detectors

Current-based microscopic defect analysis method such as current deep level transient spectroscopy (I-DLTS) and thermally stimulated current have been developed over the years at Brookhaven National Laboratory (BNL) for the defect characterizations on heavily irradiated (Phi(n) >= 10(13) n/cm(2)) high-resistivity (>= 2 k Omega cm) Si sensors/detectors. The conventional DLTS method using a capacitance transient is not valid on heavily irradiated high-resistivity Si sensors/detectors. A new optical filling method, using lasers with various wavelengths, has been applied, which is more efficient and suitable than the traditional voltage-pulse filling. Optimum defect-filling schemes and conditions have been suggested for heavily irradiated high-resistivity Si sensors/detectors. (c) 2006 Published by Elsevier Ltd.

Potentiometric glucose sensors

The determination of glucose is possible with the enzymatic reaction of glucose oxidase and potentiometric detection. The signal is proportional to the concentration up to 50 mg/dl. This value is fixed by the concentration of oxygen in the sample. By adding catalase, concentrations up to 2000 mg/dl are detectable. The steepness of the calibration curve is not affected by oxygen concentrations greater than 4 mg/l. In contrast to amperometric sensors, an influence of deposits on the electrodes surface on the signal cannot be found with potentiometric sensors

Ion recognition: application of symmetric and asymmetric schiff bases and their complexes for the fabrication of cationic and anionic membrane sensors to determine ions in real samples

Schiff base compounds refer to the branch of supra-molecules and can be used as sensing material in the construction of potentiometric ion selective electrodes (ISEs). This relatively modern field has been subject to extensive research in the period of 1999-2007 when more than 100 ISEs employing Schiff bases were constructed. The quantitative high-throughput detection of 29 cations and 7 anions has been demonstrated in various scientific branches, such as biomedicine, pharmacy, biochemistry, pharmacology, environmental chemistry, food technology, and agriculture. This review discusses Schiff base compounds and their applications in the design and development of ion selective sensors and microsensors.

Mercury(II) ion sensing with PVC-matrix based membrane sensors

Thiosemicarbazone derivatives have been used as ion carriers for the preparation of PVC-matrix based mercury(II)-selective membrane sensors. The electrodes give near-Nernstian responses in the linear concentration range of 1.0×10-1-5.0×10-6 M with detection limits of the order of 10-6 M. The stable potentiometric signals are obtained within a short time period of 20-25s. The effect of different plasticizers has been studied and dioctylsebacate (DOS) found to give a better response in comparison to other plasticizers. Selectivity coefficient values (log KPotHg,M) have been evaluated using fixed interference method. Better selectivity for mercury(II) ions is observed over many of the monovalent (Na+, K+ and NH4+) and divalent ions (Mg2+, Ca2+, Zn2+, Pb2+, Ni2+, Co2+, etc.). The sensors have also been used as indicator electrodes in potentiometric titration of mercury(II) ions with EDTA and its determination in synthetic water samples.