LABORATORY
ACOUSTOELECTRONICS

HEAD: Prof. Lozan Spassov, Dr.Sci.
tel: 772 510; e-mail: lspassov@issp.bas.bg

TOTAL STAFF: 17
RESEARCH SCIENTISTS: 6

Assoc.Prof. A.Manov, Ph.D.
Assoc.Prof. I.Avramov, Ph.D.
Assoc.Prof. V.Georgieva, Ph.D.
E.Radeva, Ph.D.
Ts.Yordanov
M.Atanassov
Z.Raicheva
L.Vergov
R.Velcheva
S.Sokolova-Shumkova
J.Lazarov
V.Nikolova
S.Harbova

RESEARCH ACTIVITIES:

1. THERMOSENSITIVE QUARTZ RESONATORS

    Based on finite element analysis, high degree interpolation techniques and lagrangian writing of the variation formulation at the kernal level, experimental miniature strip type thermosensitive quartz resonators were designed and produced. This is the smallest device from the thermosensitive quartz resonator's family. A special package for strip resonators was designed in Acoustoelectronics laboratory. Using X-ray topography, the modes corresponding to the different mechanical resonance have been identified. The results obtained from the X-ray topography and the parameters measurements were confirmed by the theoretical simulations proceeded in Ecole Nationale Superieure de Mecanique et des Microtechniques, Besanson, France.

2. RAPID THERMAL ANNEALING OF THE RESONATOR S STRUCTURES

    The influence of rapid thermal annealing (RTA) on quartz resonators equivalent dynamic parameters has been investigated, aiming to establish the parameters changes resulting from such treatment. A correlation between the measured resonator characteristics and the RTA parameters was detected. As a result, the conditions of RTA were determined under which resonator characteristics were improved or deteriorated (depending on the electrode's material). The resonance frequency mode could be transformed from the thickness - shear (TS) mode to the thickness - extension (TE) mode at the same condition. The result of this investigation could be used for the purposes of improving the resonators equivalent dynamic parameters at determined RTA conditions.

3. QUARTZ RESONATOR WITH THIN TiO2 FOR NH3 DETECTION

    The sorption properties of TiO₂ thin films are investigated, in order to detect ammonium vapor existence. For that purpose mass sensitive quartz resonators covered by TiO₂ film are used. TiO₂ thin films are prepared using a new method called Liquid Phase Deposition (LPD). By this method metal oxide layers are deposited on surfaces dipped in solutions. The layers are obtained as a result from a balance reaction, which happens between the metal fluourocomplex and metal oxide in aqueous solution.

    The main advantage of this method is its low synthesis temperature - up to 200°C. The sorption sensitivity of the created structure is registered by the Quartz Crystal Microbalance (QCM) method. A range of ammonium concentration (from 100 ppm to 10000 ppm) is investigated. Dependence is obtained between relative change of resonator frequency (Af/f) and ammonium solution concentration.

    The obtained initial results show that this sort of systems could be used for creating sensor elements aiming the detection of ammonium contamination in the air.

4. PLASMA POLYMER FILMS FOR NEUTRON SENSORS AND ELECTROLUMINESCENT STRUCTURES

    The investigations on boron containing polymer films obtained from hexametyl disiloxane in a glow discharge on quartz resonators for neutron sensor applications are continued. The samples were exposed to neutrons. The results show that such devices may be used as neutron sensitive elements for neutron flux measurements.

    Polymers obtained from hexametyldisiloxane in plasma on hybrid electroluminescent structures with yellow emission. The established increased brightness values of these structures shows, that they could be used for displays with various size, shapes and configurations.

5. X-RAY PHOTOELECTRON SPECTOGRAPHY AND ATOMIC FORCE MICROSCOPY STUDIES OF Ge_XSb_40-xS₆₀ FILMS

    Thermally evaporated films of Ge_xSb_40-xS₆₀ were studied further by XPS and Atomic Force Microscopy (AFM). The analyses of XPS of fresh and treated (illuminated and/or annealed) films show the coordination number correction necessity, as well as the complicated Sb contribution to film peculiarity. The surface of fresh and double treated (x = 5) films was observed by AFM. It can be suggested through AFM images that the roughness scale changes like mechanical stress with the film composition variation.

6. APPLICATIONS OF SURFACE AND BULK ACOUSTIC WAVES

    A novel method for phase noise reduction in surface acoustic wave (SAW) and surface transverse wave (STW) based microwave oscillators has been developed. Substantial phase noise reduction is achieved by implementing nonlinear amplifiers with a controlled conduction angle as active circuits in the oscillators.

    A unique passive wireless sensor, based on a RF-powered SAW/STW sensor oscillator for remote measurements of different physical measurements, has been demonstrated. The sensor oscillator is remotely interrogated by means of electromagnetic waves and does not need a separate power supply. It is immune to interference with multiple path signals, launched by the interrogation source, and allows much higher measurement precision and resolution, compared to traditional passive wireless SAW sensors. In addition, transmission of identification information and data from more than one nonacoustic sensors at the location of the measurement is possible with one single sensor oscillator.

    A new method and oscillator for precise measurement of the series resonant frequency and motional resistance of a thickness-shear quartz crystal microbalance (QCM) under highly viscous liquid load has been developed. The measurement oscillator allows much better measurement accuracy and resolution compared to traditional methods, even if the viscosity of the characterized liquid changes by three orders of magnitude.

1. V.Lazarova, Ts.Yordanov, L.Spassov, G.Beshkov. Vacuum rapid thermal annealing of quartz resonators. Vacuum, 69, 379-383 (2003).
2. K. Christova, A. Manov, V Pamukchieva, AG Fitzgerald, L. Jiang. Mechanical stress studies of amorphous Ge_xSb_40-xS₆₀ film. J. of Non - Crystalline Solids, 325, 142-149 (2003).
3. I. D. Avramov. Analysis and design of negative resistance oscillators using surface transverse wave based single port resonators. Transactions IEEE Ultrasonics, Ferroelectrics and Frequency Control, UFFC-50, 3, March, 220-229 (2003).
4. V.Georgieva, P.Stevchev, P.Vitanov, L.Spassov, Quartz resonator with thin TiO₂ for NH₃ detection, Vacuum (in press).
5. E. Radeva, D. Radev, H. Borner and T. Soldner, Neutron sensitive devices with boron containing plasma polymer films, Vacuum (in press).
6. L. Yourukova, K. Kolentcov, E. Radeva, Effect of second protective layer in AC EL display structures on their characteristics, Vacuum (in press).
7. L.Spassov, R.Velcheva, Ts.Yordanov, L.Vergov, B.Dulmet, R.Bourquin, Investigations of thermo-sensitive quartz resonators NLC-cut at cryogenic temperatures. Proc. 16-th EFTF, St. Petersburg 2002, 'European frequency and time forum', Eds Y.V. Gyliaev, R. Besson, S. Kulakov, G. Mansfeld, 2003, p. D-037-D-041.
8. B.Dulmet, R.Bourquin, L.Spassov, R.Velcheva, 'Finite element analysis of activity-dips in NLC-cut quartz temperature sensors'. Proc. 16-th EFTF, St. Petersburg 2002, 'European frequency and time forum', Eds Y.V. Gyliaev, R. Besson, S. Kulakov, G. Mansfeld, 2003, p. D-033-D-036.
9. B.Dulmet, R.Bourquin, R.Velcheva, L.Spassov, 'Study of NLC-cut resonators by X-ray topography'. Proc. 16-th EFTF, St. Petersburg 2002, 'European frequency and time forum', Eds Y.V. Gyliaev, R. Besson, S. Kulakov, G. Mansfeld, 2003, p. D-060-D-063.
10. R.Velcheva, L.Spassov, Yu.Filipov, V.Miklayev, E.Kulagin, 'Radiation resistance of thermosensitive quartz crystal resonators'. Proc. 16-th EFTF, St. Petersburg 2002, 'European frequency and time forum', Eds Y.V. Gyliaev, R. Besson, S. Kulakov, G. Mansfeld, 2003, p. D-048-D-050.
11. V.Georgieva, L.Spassov, Ts. Yordanov, M. Marinov, 'The effect of rapid thermal annealing on quartz resonators'. Proc. 16-th EFTF, St. Petersburg 2002, 'European frequency and time forum', Eds Y.V. Gyliaev, R. Besson, S. Kulakov, G. Mansfeld, 2003, p. D-061-D-064.
12. I. D. Avramov, 'Phase noise reduction in surface wave oscillators by using nonlinear sustaining amplifiers', Proc. '2003 IEEE International Frequency Control Symposium and PDA Exhibition Jointly with the 17th European Frequency and Time Forum', Tampa, Florida, USA, 2003, p. 478-486.
13. I. D. Avramov, 'The RF-Powered surface wave sensor oscillator - a successful alternative to passive wireless sensing', Proc. '2003 IEEE International Frequency Control Symposium and PDA Exhibition Jointly with the 17th European Frequency and Time Forum', Tampa, Florida, USA, 2003, p. 911-918.
14. E. Radeva, 'Thin plasma polymer films for sensor applications', 'Nanoscience& Nanotechnology'2003', Nov. 2003, Sofia.

1. Applications of surface transverse waves (STW) in devices for frequency control and selection and systems for wireless data transfer in the 3 GHz frequency range. Measurement circuits for quartz crystal microbalance (QCM) based sensors for characterizing liquid properties.

1. F-902 "Investigation of Resonators Systems Quartz-metal After Rapid Thermal Annealing"

1. Bulgarian Academy of Sciences - CNRS, France: "Thermosensitive Quartz Resonators at Cryogenic Temperatures", Joint Research Project with ENSMM - Besancon, France.
2. Institute of Solid State Physics - Joint Institute of Nuclear Research, Dubna, Russia: "Measurements of Helium Flow in Cryogenic Accelerator Complex - "Nuclotron".
3. Institute of Solid State Physics - Bulgarian State Railways "Creation of software and implementation of automated system "Dynamic Integrator".
4. Institute of Solid State Physics - Russian Academy of Sciences - GEOHI "Research of Chemical Sensors based on piezoresonance type for pollution detection in the environment".
5. "Optimized Raleigh wave two-port sensor resonator operating at 433 MHz with maximum suppression of parasitic modes for operation with gas sensitive coatings in highly reactive gaseous environments" - Research Center Karlsruhe, Germany

1. Growth Programme of 5 FP of EU: "Multi - Channel Measurement and Control System Based on Resonant Piezoelectric Crystal Sensors - QxSens"

1. "Thermosensitive Quartz Resonators at Cryogenic Temperature" - Ecole Nationale Superiore de Mecanique et Microtecniques, Besancon, France
2. "Measurements of Helium Flow in Cryogenic Accelerator Complex - "Nuclotron" - Joint Institute for Nuclear Research, Dubna, Russia
3. "Research of Chemical Sensors based on piezoresonance type for pollution detection in the environment" - Russian Academy of Sciences
4. "Optimized Raleigh wave two-port sensor resonator operating at 433 MHz with maximum suppression of parasitic modes for operation with gas sensitive coatings in highly reactive gaseous environments" - Research Center Karlsruhe, Germany

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