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Gas Sensors and Radiation Detectors for Monitoring

#2503


Research and Development of High-Sensitive Semiconductor Gas Sensors and Ionizing-Radiation Detectors for Environment Monitoring

Tech Area / Field

  • ENV-MIN/Monitoring and Instrumentation/Environment
  • FIR-INS/Nuclear Instrumentation/Fission Reactors
  • INS-DET/Detection Devices/Instrumentation

Status
8 Project completed

Registration date
25.04.2002

Completion date
01.04.2008

Senior Project Manager
Genisaretskaya S V

Leading Institute
Russian Academy of Sciences / Institute of Radioengineering and Electronics / Fryazino Branch, Russia, Moscow reg., Fryazino

Supporting institutes

  • NPO Orion, Russia, Moscow\nKurchatov Research Center, Russia, Moscow

Collaborators

  • CEA/Saclay/DRT/LIST/DIMRI/SIAR/LTD, France, Gif-sur-Yvette Cedex\nRuhr Universität Bochum, Germany, Bochum\nHumboldt-Universitat zu Berlin/Institut fur Chemie/Walther-Nernst-Institut fur Physikalische und Thearetische Chemie, Germany, Berlin

Project summary

Environment monitoring problems including the monitoring of ecological parameters of human living environment, especially mass crowding places, as well as the control of technological processes in industry challenge the enhancement of means for the analysis of gas medium chemistry and parameters of radiations and the development of more effective and inexpensive measuring devices. Rising danger of terrorism with the use of explosive, toxic, and radioactive materials makes this problem more urgent.

The existing semiconductor chemical sensors can detect only a limited amount of gaseous agents. Moreover, their sensitivity, selectivity, and response time are not very good. There are no compact cheap effective multi-sensors (i.e., sensors selectively sensitive to a wide range of gases simultaneously) integrated with signal processing units, with low power consumption.

Many present-day problems related to the detection and conversion of radiations could be solved with the use of diamond-based detectors. However, serious obstacles for manufacture of such detectors in necessary amounts are the expensiveness and inhomogeneity of natural row material, low content of crystals fit for detector application making matters worse, limited row material resource, as well as impossibility to change its parameters. Besides, dimensions of natural crystals are insufficient for some important applications.

These are the problems that determined the objectives of the Project: Research and development of compact semiconductor gas sensors, multi-sensors in that number, for Н2, СО, NOx, NH3, F2, HF, AsH3, PH3, CH4, fluorine carbons, etc. and detectors of ionizing, UV, and visible radiations based on synthetic and CVD diamond with enhanced performance, including sensitive units suitable for inexpensive measuring devices of wide application, in particular for environment monitoring. For synthetic-diamond ionizing-radiation detectors, the study of possibility of spectrometric detector development is planned particularly.

The most promising results of the Project could become advanced technologies related to the following researches and developments:

1. Prototypes of compact gas mono- and multi-sensors of resistive type with various sensitive layers (metal oxides on silicon) for measuring of concentrations of a wide range of gases integrated with microprocessor units will be developed possessing improved (as compared to available devices) sensitivity, selectivity, and operation speed (95% signal level is reached for 2-3 s), with the operation temperature interval 100-500 °C, power consumption below 100 mW, and low cost of production.

2. Principles and procedures for using a composite gate insulator in metal-insulator-semiconductor (MIS) sensors will be developed jointly with the method of molecule fragment detecting for selective gas detection and extension in principle of the range of detectable gases. Structures that use short-time heating of sensor surface (or an external catalytic destructor) and the composite gate insulator containing a layer of solid electrolyte will extend the potentialities of application of gas sensor systems to gases now undetectable with conventional MIS-sensors.

3. The feasibility in principle of creation of gas sensors with sensitivity close to the theoretical limit (one molecule) will be evaluated through studies of incoherent mesoscopics effects in structures near the percolation threshold. As a result of these studies, the structures most sensitive to absorption of gases will be revealed.

4. Proceeding from the studies carried out, optimum circuit-design solutions will be offered and prototypes of high-sensitive gas sensors are to be manufactured on the base of the method of thermal molecule destruction and the composite gate insulator for fragment-by-fragment detection of now undetectable gases, and on the base of incoherent mesoscopics effects for obtaining of sensors with the sensitivity close to the theoretical limit.

Presented in the table below are the main expected parameters of some (items 1 and 4 above) of the gas chemical sensor prototypes planned for development in the Project:

Remarks to the table: LDL is the Lowest Detectable Limit (concentration in air). LDL in the atmosphere of the chemically inert gases is approximately two orders lower for the MIS sensor. T is the sensor operating temperature in Celsius scale. MIS-sensors have a catalytically active electrode operating under heat pulses. MSS: Metal-Superionic-Semiconductor is the structure of the sensor with composite gate insulator.

5. Based on the studies of adsorption and desorption effects on the surface of diamond and diamond-like materials, selection and optimization of the effects most promising for gas detection will be conducted. Optimum solutions will be proposed and research and development of prototypes of high-sensitive (to a few molecules per mm2 expected) selective diamond sensors based on surface-state spectrum variation will be carried out.

One of the most important results of the Project could become the development of new-generation gas sensor prototypes containing all obtained achievements inside or with combinations of particular achievements. The work on gas sensors will be completed with the elaboration of the recommendations on creation of industrial application devices.

Application: Gas chemical mono- and multi-sensors can be used for the control of technological processes in industry, for environmental monitoring including the monitoring of ecological parameters of human living environment, especially mass crowding places, for the detection of explosive materials most of which contain molecular complexes of NOx type.

Based on the research and development of high-quality synthetic-diamond crystal and CVD film growth technology as well as of detector technology, prototypes of the following radiation detectors and phototransducers on these materials are expected as results of the development in Project.

6. Detectors for soft and hard X-ray as well as gamma and neutron radiations, including those with internal gain. Expected parameters: photon energy range E > 5 keV, responsivity > 10-4 Coul/Gy (10 A/W) at E 5 keV (with internal gain), dark current ~ 10-11 A, response time 10-300 s (with internal gain).

Internal gain will result in considerable increase of detector response (an increase of more than two orders of magnitude is expected). For natural-diamond detectors, with no gain, the responsivity cannot exceed 0.075 A/W.

The advantages in comparison with silicon detectors:

– tissue equivalence (radiation absorption factor for diamond [the element is carbon!] and its dependence on the energy of particles are close to corresponding characteristics of tissues of biological objects);


– far less dark and, consequently, noise current (related to gain unit) and, correspondingly, far lower minimum radiation power detected (or much higher sensitivity);
– much higher responsivity (for internal-gain detectors);
– much higher radiation hardness, especially to neutron radiation (by orders of magnitude);
– possibility to operate at increased temperatures (> 40 °C).

The advantages in comparison with natural-diamond detectors:

– much higher responsivity makes it possible to refuse, in some cases, from the preamplifiers placed close to the detector and, therefore, liable to the action of the same radiation, but possessing a lower radiation hardness than the detectors themselves; this could enhance the reliability and decrease the cost of signal processing devices;


– lower cost relative to natural-diamond detectors. So, the manufacture of such detectors could be of commercial interest.

Application: Dosimetry (and, probably, spectrometry) of mentioned kinds of radiation in industry, nuclear reactor control systems, medical radiotherapy, household equipment, science, nuclear waste storages, nuclear and thermonuclear diagnostics, ecological monitoring, space exploration.

7. Detectors and phototransducers for visible and UV radiation based on diamond and diamond-like films: photon energy range 2.5-6 eV, dark current ~ 10-10 A, response time Ј 1 ms, no-load voltage і 1 V, operation voltage Ј 10 V. The advantages in comparison with the similar natural-diamond detectors: Relatively low cost and unlimited row resource. Much higher responsivity due to internal gain. Reproducibility of artificial material properties. Possibility to manufacture large area CVD films.

Application: Solar UV-B dosimetry, ecological monitoring, UV sensors for sterilization equipment in medicine and food industry. Photovoltaic structures based on large area films can be used as high-efficient phototransducers of nuclear energy into electric one.

The developments proposed will be based on the basis founded by several well-known groups of Russian scientists in IREE RAS, RRC KI, and ORION RD&P Ctr., some part of whose employees, having multi-year experience of successful activity in these areas of semiconductor microelectronics (including the participation of ORION Ctr. in ISTC Project #447), will be involved in Project activities. The results of their work have been presented in many publications and reported at international conferences.

Previous activity of most of the Project participants concerned the development of military technologies. So, this Project will provide them alternative possibility to work in civil area and promote their involvement into international science community. Results of the work could be used in the areas of environmental protection, power production, anti-terrorism and nuclear safety.

In the Project, two trends, seemingly independent prima facie, will be developed: gas sensors and radiation detectors coupled by common technology elements and research techniques, being developed by the same groups, and having common application areas. All these can promote more efficient work, particularly at the cost of economy in labor expenses for similar procedures. The activity in the Project is pided into 5 tasks on gas sensors and 2 on radiation detectors.

Gas sensors:

The problem of resistive-type chemical sensors is pided into several main stages: selection of some proper composition of sensitive layers, development of their formation technology, study of physical and chemical processes occurring during gas adsorption, analysis of the influence of various conditions on electrical and physical properties in order to achieve the best parameter values, development of optimum basic design for chemical sensor structure, sensor manufacturing and testing in various gas ambient, and experiments in the formation of multi-sensor structures with data processing.

The Project envisages new approaches in development of sensors based on MIS -structures: 1) Extension of the range of detectable gases and increase of detection selectivity due to the application of composite gate insulator with a solid electrolyte layer that contains ions of the atoms presented in analyzed gas. 2) Drastic extension of the range of gases detectable with traditional silicon-based MIS sensors due to thermal destruction of the molecules and subsequent detection of their fragments. 3) Study of incoherent-mesoscopics effects with the intention to increase the sensitivity of semiconductor gas sensors up to the theoretical limit and development of the basis for a new generation of gas sensors.

For the development of a new type of sensors based on surface-state spectrum variation for the purpose of drastic increase of their sensitivity and essential increase of their selectivity, the study of adsorption and desorption effects on the surface of diamond and diamond-like materials will be carried out to select the effects most promising for gas detection.

All achievements will be combined and will make constituent parts of a new principle of gas sensor engineering.

Radiation detectors:

The development and optimization of diamond synthesis technology providing the desired single crystal and CVD quality will be the general purpose in the first stage of work. Detailed physical analysis and experimental study of diamond band structure, transport and transient processes in crystal volume will be required. Wafer classification criteria, improvements in selection and testing procedures promoting high quality diamond manufacturing will be developed at the same time. In the next stage of work, the investigations of properties of the contacts to synthetic and CVD diamond and corresponding technological experiments will be necessary. Detailed calculations of contact and the whole detector structure models will be carried out. This part of the work will be closely related to developments and particular improvements in the detector manufacturing processes. Except the experimental research, great attention will be paid to theoretical studies. In the final stage, most efforts will be applied to designing and manufacturing of various detectors with required properties, their metrology, calibration and testing at real application environment conditions. A lot of work concerning the optimization of device configuration, electric circuits and final design is foreseen.

The following materials will be used in the Project: Metal-oxide thin films with various additives. MIS structures based on silicon: 1) with inclusion of ion-conducting solid electrolytes containing ions of the atoms of gases under analyses into the composite gate dielectric layer; 2) with the electrode of catalytically-active metals of the platinum group. Catalytically-active materials for the use as external high-temperature destructors (e.g., platinum as a coil). Metal-dielectric nanocomposites based on Fe/SiO2. Diamond and diamond-like films, synthetic-diamond single crystals.

In the course of the Project, we suppose to conduct information exchange with foreign collaborators, including sending them quarter, year, and final reports through the ISTC. Joint investigations with the use of equipment and samples of Russian and foreign parties are planned, as well as meetings and work discussions during international conferences.


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