Alexey Vasiliev

Metal-oxide gas sensor high-selective to ammonia

Metrological and performance characteristics of a metal-oxide sensor high-selective to ammonia in the presence of methane, carbon monoxide, and water vapors are presented. The specific feature of the design consists in using pulsed sensor heating as the main factor for improved selectivity to ammonia. The ammonia threshold achieved during the pulse-type temperature modulation is 5 × 10−4% vol.

Sensors Based on Technology “Nano-on-Micro” for Wireless Instruments Preventing Ecological and Industrial Catastrophes

The problem of gas analyzers compatible with wireless networks can be solved by using sensors based on the “nano-on-micro” technology. The basis of this technology consists in nano-composite sensing metal oxide semiconductor or thermocatalytic materials deposited on a microhotplate fabricated using silicon or alumina microelectronic technology. As a result, the sensor combines the advantages of both technologies: on the one hand, high stability and sufficient selectivity of nano-composite materials, and, on the other hand, microprocessor compatibility, low-cost, mass-production possibilities, and low power consumption of microelectronic substrates. Two methods for the fabrication of microhotplates are the most promising: the silicon based technology of silicon oxide/silicon nitride membranes and the CeraMEMS technology of thin alumina films (TAF). The first technology enables the fabrication of microheaters with a power consumption around 20 mW for an operating temperature below 450°C. Advantages of CeraMEMS platforms are: (1) operation at temperature up to 600°C and, potentially, up to 800°C; (2) robustness compared with silicon chip with thin membrane; (3) perfect Pt and sensing layer adhesion without any adhesive layers; (4) low cost of middle scale production (104–107 chips per year) compared with the silicon technology. The CeraMEMS platform can be used for the fabrication of semiconductor and thermocatalytic gas sensors, as a source of IR radiation for optical gas sensors and as bolometers. The sensor withstands ∼7 × 106 on-off cycles. Heater resistance drift is below 3% per year at 550°C.

Room-Temperature Hydrogen Sensitivity of a MIS-Structure Based on the

An LaF3 layer was shown to improve the characteristics of field-effect gas sensors for room-temperature hydrogen monitoring. The Pt/LaF3 interface leads to a Nernst-type response and a detection limit of 10-ppm hydrogen in atmospheric air. The response time was shown to be about 110 s and was independent of hydrogen concentration. A method for the stabilization of a long-term behavior of the sensor was successfully demonstrated. The mechanism of the sensors response to hydrogen was shown to be different from that of the metal/insulator/semiconductor (MIS)-type sensors

hboxPt/LaF_3

The sensitivity of metal‐insulator‐semiconductor structure gas sensors based on silicon or silicon carbide to different fluorinecontaining gases was studied in the temperature range 20‐5308C. Silicon based gas sensors could be used for the determination of fluorine and hydrogen fluoride at room temperature. The sensitivity to fluorine is 28.00.5 mV/lg(p(F2)), the sensitivity to HF is 44.41.6 mV/(p(HF)), and the detection is about 10 ppb in both instances. High temperature silicon carbide sensors can be applied for the determination of fluorine and fluorocarbons (CF3CH2F, CF3CCl3 ,C F 3CH2Cl, CHClF2, CCl2F2, CCl3F) up to 5308C. The sensor signal for fluorocarbon concentration measurements demonstrates a Nernstian concentration dependence. The detection limit for these gases is ca. 10 ppm. # 1999 Elsevier Science B.V. All rights reserved.

Interface

Abstract For the detection of fluorine, two different preparation methods for semiconductor gas sensors were developed, the first for concentrations between 10 and 1000 ppm (type I) and another for concentrations between 0.01 and 10 ppm (type II). The sensitivity of type I sensors is about 116 mV/lg(p(F 2 )). It is possible to detect gas concentrations down to 0.1 ppm using this sensor. The main disadvantage is that the sensor response kinetics depends strongly on concentration. The sensors response is fast for measurement of high concentrations (between 10 and 1000 ppm) but the response time is not acceptable for the detection of small concentrations. Type II sensors show a sensitivity of 28 mV/lg(p(F 2 )) for gas concentrations between 0.006 and 10 ppm. This sensor is very fast in the detection of small concentrations of gas.

Semiconductor sensors for the detection of fluorocarbons, fluorine and hydrogen fluoride

An increase in the number of gases detectable by sensors based on Pd-SiO₂-Si (MIS) and Pt-LaF₃-Si₃N₄-SiO₂-Si (MEIS) structures was achieved by the application of an external catalyst element (CE). It was shown that as a result of the decomposition of hydrocarbon and fluorocarbon molecules on a Ni coil (CE), the products detectable by metal-insulator-semiconductor (MIS) and metal-electrolyte-insulator-semiconductor (MEIS) sensors are formed. The simultaneous catalytic oxidation of hydrocarbons and their thermal decomposition result in an optimum CE temperature of about 1050 K for propane. The kinetics of the thermal decomposition of gases on Ni were investigated. The activation energy of the reaction for C₃H₈ and the enthalpy in the case of CF₃-CCl were estimated

Semiconductor sensors for fluorine detection — optimization for low and high concentrations

Abstract The new large band gap semiconductor material SiC was used to develop a high temperature field-effect structure SiC/epi-SiC/SiO 2 /LaF 3 /Pt. The response to different fluorocarbons as CF 3 CH 2 F, CF 3 CCl 3 , CHClF 2 , CF 3 CH 2 Cl and CCl 3 F was investigated. A complex behaviour was found for the temperature range 200–300°C. The selective detection of fluorine containing molecules was shown for a temperature of 380°C. The fluoride ion conducting material LaF 3 was proven to have the substantial role for the sensor detection principal.

Hydrocarbon and Fluorocarbon Monitoring by MIS Sensors Using an Ni Catalytic Thermodestructor

Abstract A chemical semiconductor sensor for the temperature range up to 400°C was developed using silicon carbide with an epitaxial layer of SiC as the substrate. Thin layers of LaF 3 and Pt were deposited on the semiconductor/insulator structure to form a three-phase boundary with the gas under investigation. The sensor was shown to be sensitive to fluorine, hydrogen fluoride and different fluorocarbons. The influence of the operation temperature on the sensor response signal was investigated in the range from room temperature up to 400°C. For the fluorocarbons CF 3 CH 2 F, CF 3 CCl 3 , CHClF 2, CF 3 CH 2 Cl and CCl 3 F a selective detection was achieved at temperatures near to 400°C. The substantial role of the fluoride ion conducting material LaF 3 for the sensor detection principle was proven. A mechanism including the chemisorption of the fluorocarbon at the Pt surface and an insertion of fluorine into LaF 3 was discussed.

Silicon carbide based semiconductor sensor for the detection of fluorocarbons

Application of solid electrolytes as undergate layers accelerates the response of a sensor at room temperature as compared with ordinary hydrogen sensors manufactured on the basis of the metal-insulator-semiconductor (MIS) structures with a palladium gate. The proton-conducting solid electrolytes under study include NAFION, zirconium hydrophosphate, and etherified polyvinyl alcohol (PVA) with heteropolyacids and phenoldisulfonic acid, which can be deposited under the platinum gate. Sensors based on the MIS structures with these solid electrolytes show a high sensitivity toward hydrogen (∼120 mV per concentration decade). The response time τ0.63 of a freshly manufactured sensor with a layer of zirconium hydrophosphate amounts to about 2 min. The maximum mechanical stability, especially at relative humidities in excess of 80% is intrinsic to sensors containing layers of PVA with heteropolyacids. The response time of such sensors is nearly 10 min.

FIELD-EFFECT SENSOR FOR THE SELECTIVE DETECTION OF FLUOROCARBONS

A silicon based semiconductor sensor structure Pd/LaF3/Si3N4/SiO2/Si was prepared using thin layer technology. The sensor can be used for hydrogen detection at room temperature. Therefore, the power consumption is reduced by a factor 10 compared to the best low power consumption hydrogen sensors. In contrast to other sensors it can be used for measurements at very low and high hydrogen partial pressure. The limit of detection was determined to be 0.5 ppm. Measurements at high concentrations near to and above the Lower Explosion Level (LEL) of 4 % hydrogen in air are demonstrated. A method to achieve long lifetime of the sensor was developed.