S. Timoshenkov

Investigation of transport mechanisms in Bi doped Ge2Sb2Te5 thin films for phase change memory application

The influence of Bi doping on the charge carrier transport mechanism in GST225 thin films was investigated. The three regions with different current-voltage dependencies were established. The energy diagrams for Bi doped GST225 thin films for different regions were analyzed. Analysis of experimental data showed that space charge limited current is the most possible explanation for the nonlinear I-V dependence in the middle electrical field strength (103 < E < 104 V/cm). Position of the trap levels (Et) controlling transport mechanism, and density of traps (Nt) were estimated with using of Rose and Lampert theories. It was established that Bi doping can significantly change I-V characteristic, resistivity, mobility gap, Urbach energy, density distribution of localized states, and activation energy of conductivity. The most pronounced modification of current-voltage characteristic and parameters of the thin films was established for GST225 + 0,5 wt. % Bi. Thus, doping of Ge2Sb2Te5 by Bi expands the range of material properties, which is important for the optimization of PCM technology.

Error angle determination of the star sensor with liquid cooling

Design studies method of star sensor thermal stability with liquid cooling using modern CAD has been described. Optimal operation of two circuits for liquid cooling structure of star sensor has been chosen using a mathematical model for calculating the convective heat transfer coefficient. Study defined the angular displacement of the star sensor with liquid cooling (~ 0.3 arc seconds), which is acceptable for star sensors with 1 arc seconds accuracy. At this level of scientific investigation the developed 3D model of the star sensor assembly comprising a thermally stabilizing ground test equipment allows to determine the angular error due to the temperature loads and optimal parameters liquid of cooling system (for example, the flow rate of fluid , geometrical parameters of cooling circuits , etc.). In the future, this model should be improved, which will consider the impact of other factors (e.g. gravity, vibration, etc.) on the performance of the star sensor.

Influence of indium doping on the electrical properties of Ge2Sb2Te5 thin films for nonvolatile phase change memory devices

In this article the influence of different amounts of In (0, 0.5, 1 and 3 wt. %) on the thermal and electrical properties of Ge2Sb2Te5 thin films for nonvolatile phase change memory devices is investigated. Crystallization temperature, resistivity, width of the optical band gap, Urbach energy, activation energy and type of conductivity are estimated for all investigated compounds. Storage and data processing times of the PCM cells on the basis of investigated materials were calculated. Nonmonotonic concentration dependences of properties were observed.

Low-voltage field desorption in carbon nanotubes

Influence of gas sorption and desorption on field emission current evolution from carbon nanotube cathodes was investigated. Two types of nanotube cathodes were made: nanotubes grown from gas phase on stainless steel and nanotubes deposited from solution on Si substrate. Exposure of cathode to air at atmospheric pressure leads to increase of starting current with rapid decrease. We associate this effect of reversible degradation with some kind of field desorption. Sorbed gases reduce the work function and thus increase emission current. Different gases demonstrate different effect on the current behavior. We observed desorption process in low field values ~104−105 V/cm.

Angular Rate Sensors with Conformal Flexible Multilayer Polymer Wiring Boards

The usage possibility of conformal flexible boards for angular velocity sensors has been described. Production of such sensors allows us to solve the problem of constructing roll sensor for rapidly rotating body (20 Hz) along the longitudinal axis of which are speed reaching 200g, and also perpendicular speed up 20g. The paper also analyzed the possibility of using polyparaxylylene as dielectric and protective layer in conformal multilayer wiring boards (CMWB). Research tests for compliance with the requirements of the developed process conducted and research testing to the requirements of the developed technological process. The proposed approach has been developed and its efficiency has been demonstrated by various experimental scenarios.

Influence of Ti Doping on the Properties of Ge-Sb-Te Thin Films for Phase Change Memory

The influence of Ti doping on the resistivity, activation energy of conductivity, energy band gap, Urbach energy, crystallization temperature, heat effect and crystallization kinetic parameters in Ge2Sb2Te5 thin films for phase change memory was investigated. It was shown that introduction of Ti influences on the thermal properties, and kinetics of crystallization process. Results of analyzes showed that Ti doping affects crystallization time, and probability of spontaneous crystallization at room temperature, which must be taken into consideration at designing PCM cells with Ti electrodes.

Enhancement of the Schottky Effect in a Si(100)—Water System Using Porous Polymeric Track-Etched Membranes

The kinetics of variation in the electronic work function (EWF) of single-crystal silicon Si(100) exposed to liquid water is studied. It is shown that immersing porous film track-etched membranes (TEMs) with pore sizes of 3.0–0.1 μm in water containing Si(100) considerably reduces the EWF of single-crystal silicon. It is found that a similar effect is observed when TEMs in the form of caps are held over the surface of water containing Si(100) at a distances of around 1.5–2.0 cm. It is speculated that the occurrence of a developed surface of TEMs in an open system changes the supramolecular structure of the water and leads to the formation of associates (H2O)n with increased dipole moments (compared to molecular moments), enhancing the Schottky effect during sorption on Si(100) surfaces.

Research and development of capacitive transducer with linear acceleration

Paper presents the study results and modeling of functional characteristics of the linear acceleration transducers, enabling sensors creation with the specified parameters. Sensing element made for linear acceleration transducer with torsion cruciform section has been proposed on the based design and technological principles. It allows minimizing the impact of cross-acceleration and gives the maximum of center mass displacement for high sensors sensitivity in the given dimensions. The range of measured acceleration from ± 0.2g to ± 50g was provided by changing the torsion bar thickness n = 34 ÷ 56 microns. The transducers frequency range of linear acceleration 100-150 Hz depends on the gas pressure P = 700-800Pa in which the sensor element was located. Methods converting displacement of sensing element in the sensor output have been provided. On their basis the linear acceleration transducers with analog output signal having a predetermined frequency range and high linearity of the transformation (nonlinearity 0.2-1.5%) was developed. Also the linear acceleration transducers with digital signal consuming little (no more than 850 μA), low noisy (standard deviation to 0.1mg/rt-Hz) and high sensitivity (up to 0.1mg) to the accelerations was made. Errors in manufacturing process of sensitive elements and operating environment temperature affect the changes in the characteristics of the linear acceleration transducers. It has been established that different plate thickness up to 3.6% leads to the scale factor error to 4.7%. Irreproducibility of depth anisotropic etching of silicon up to 6.6% introduces an error in the output signal of 2.9 ... 13.8mg.

Comb structure analysis of the capacitive sensitive element in MEMS-accelerometer

In this paper analysis of comb design for the sensing element MEMS accelerometer with longitudinal displacement of the inertial mass under the influence of acceleration to obtain the necessary parameters for the further construction of an electronic circuit for removal and signal processing has been done. Fixed on the stator the inertia mass has the ability to move under the influence of acceleration along the longitudinal structure. As a result the distance between the fixed and movable combs, and hence the capacitance in the capacitors have been changed. Measuring the difference of these capacitances you can estimate the value of the applied acceleration. Furthermore, managing combs that should apply an electrostatic force for artificial deviation of the inertial mass may be used for the initial sensitive elements culling. Also in this case there is a change of capacitances, which can be measured by the comb and make a decision about the spoilage presence or absence.

Design and fabrication of piezoelectric MEMS

Lead-zirconate-titanate (PZT) is a typical piezoelectric material with outstanding properties. The preparation behavior of Lead Zirconate Titanate (PZT) composite films comprised of Si, SiO2, Pt, PZT and Pt for MEMS applications was investigated. The choice of precursors can affect the microstructures and properties of the product, so in this paper we compared the crystallization behavior of PZT films derived from different precursors, stressing the influence of experiment conditions. Dense PZT films were prepared by electrophoretic deposition method (EPD), using commercial powder PZT precursor and metal alkoxide components for the same composition. Some specific comments were underlined about structure of PZT films.