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Semiconductor gas-sensitive sensors

The scientific – research laboratory "Omega" has developed the production technology of semiconductor gas-sensitive sensors which are successfully applied in devices of chemical investigation and environmental monitoring. Together with technology algorithms and physical and chemical bases of detection of trace concentration of toxic and chemically dangerous substances in water and the atmosphere are developed.

The technology allows to make the semiconductor gas-sensitive sensors meeting the modern requirements of chemical safety of Russia and Europe. The developed technology significantly expanded a class of gas sensors and reduced their prime cost. For example, gas semiconductor sensors of the leader of world electronic industry  "Figaro" (Japan) are capable to define the concentration of carbon monoxide, vapors of ammonia, methane and oxygen exceeding maximum permissible values. The sensors made on our technology allow to define concentration of vapors of toxic agents, toxic and explosive gases, strong poisons, vapors of components of rocket fuels below maximum permissible level more than  1000 – 10000 times at their cost much less then Japanese.

The method of the kinetic analysis on the basis of nanodisperse semiconductor adsorptive sensors and analytical systems created on their base is the basis for the developed technology. As sensitive layers the nanodisperse oxides of metals (SnO2, ZnO, NiO, Cu2O, In2O3, etc.) with pronounced semiconductor properties alloyed by catalysts Pb, Pd, Ag, Co, Mn, etc. are used. The developed structure of a surface of the formed materials of a gas-sensitive layer is reached by processing methods and makes 60 - 90 sq.m/g.

The principle of operation of semiconductor adsorptive sensors is based on measurement of change of conductivity of a gas-sensitive layer at adsorption on its surface of molecules from a gas phase. At adsorption of molecules on a surface of a gas-sensitive layer equilibrium value of current in a zone of conductivity is broken and occurs or increase in concentration of carriers of a charge (in case of a donor gas hemosorbtion), or decrease in their concentration (in case of a gas acceptor hemosorbtion). Changes of concentration of carriers define an analytical response of the sensor which depends on a chemical composition of the occluded gas and its concentration.

Management of selectivity and sensitivity of a gas-sensitive layer is reached by introduction to structure of the semiconductor of metals catalysts and the operated heating which allows to maintain sensor surface temperature in range from 100 to 800os with high precision.

The use of semiconductor adsorptive sensors allows to carry out, first, miniaturization of the designed devices, secondly, to expand a class of the defined substances at the qualitative level, and also to carry out the quantitative analysis with a satisfactory error. The use of semiconductor adsorptive sensors and special methods of processing the results of measurements allows to realize both threshold, and quantitative methods of analytical control of a wide range of gases of various chemical composition and vapors of toxic substances.

The tests which are carried out in coordination with Management of chemical troops of Russian Armed Forces on base  of the Central research test institute No.33 of the Ministry of Defence of the Russian Federation, showed that the semiconductor sensors established in prototypes of gas-signaling devices conform to the modern requirements imposed to technical means of chemical investigation of subgroup 1.4 "Chemical sensors of complex monitors for protection of mobile objects of armored equipment and air-vehicle from the weapons of mass distraction".

Tests showed that the main advantages of our development are:

- the wide list of the found substances with possibility of replenishment or replacement of a database (besides fighting toxic agents, by means of the device it is possible to find the most widespread strong toxic agents, such as hydrocianic acid, chlorine, ammonia, sulphurous anhydride, etc., toxins, and also explosive and combustible gases);

- the sensitivity, specificity, speed and an after-effect of detection of toksikant conforming to requirements of OTT 7.1.306-2005;

- information transfer about a chemical situation to canals of an automated control system;

- absence in devices of sources of ionizing radiation;

- simplicity in operation and service;

- lack of expendables at operation of devices;

- mass-dimensional characteristics of the developed gas analyzers significantly surpass characteristics of devices of similar appointment.

Sensitivity, speed, selectivity of detection of fighting toxic agents by means of the sensors developed by us on three orders surpass characteristics of the devices consisting on supply in NATO such as JCAD and ICAD.

The list of the developed gas-sensitive sensors includes as the selective sensors focused on definition of one concrete substance, and the multitouch systems allowing to define more than one hundred different substances at the same time. And, target substances can be defined both in atmospheric air, and in water.

Synthesis of gas-sensitive material

Synthesis and its modifications allow to receive the applied zol-gel nanostructural kserogel with further transfer to a crystal form. Thus the sizes of polycrystals are distributed in the range of 10 - 50 nanometers. The most probable size of particles is defined by calcinating temperature kserogelya.

Formation of nanodimensional structures

Gas-sensitive microchips

Classical design mikrochipovseriya

"Mono"                                     Duo N-p series                              Kvadro series

 The manufacturing techniques of gas-sensitive microchips allow to let out 3 – 5 thousand sensors a month, to form multitouch systems for installation in gas analyzers.

In devices of the SNIFF series detectors with semiconductor sensors on the basis of dioxide of tin (SnO2) with the alloying impurity are used: La, Ni, Co, Ag, Pd, Bi and Mo. Control of a basic level of conductivity is exercised at a synthesis stage with introduction of the corresponding amount of oxide of antimony (Sb2O3).

The algorithm of work and mathematical apparatus of processing of results of measurement and decision-making allows to establish the list of the defined substances in the on-line mode.

Design of gaz sensitive sensors

                     

Gas-sensitive layer                            Heating element

Options of installation of microchips                                                    

 The board of gas-sensitive sensors       Gas dynamic flowing chamber

NEW!!! Use of four gas-sensitive sensors on one board and installation of two boards in one gas chamber. That allows to provide selectivity.