Włodzimierz Strupiński

Sensitivity and Offset Voltage Testing in the Hall-Effect Sensors Made of Graphene

Paper presents the results of the hall effect testing in the graphene structures. Special hall effect structures were designed and build, using large graphene sheets. Laboratory testing stand was developed to test sensitivity and offset voltage in hall effect structures under external magnetic field. Characteristics of investigated structures were measured, including such impacting factors as structure size, external magnetic field strength, temperature and time.

Low-noise epitaxial graphene on SiC Hall effect element for commercial applications

In this report, we demonstrate a complete Hall effect element that is based on quasi-free-standing monolayer graphene synthesized on a semi-insulating on-axis Si-terminated 6H-SiC substrate in an epitaxial Chemical Vapor Deposition process. The device offers the current-mode sensitivity of 87 V/AT and low excess noise (Hooges parameter αH < 2 × 10−3) enabling room-temperature magnetic resolution of 650 nT/Hz0.5 at 10 Hz, 95 nT/Hz0.5 at 1 kHz, and 14 nT/Hz0.5 at 100 kHz at the total active area of 0.1275 mm2. The element is passivated with a silicone encapsulant to ensure its electrical stability and environmental resistance. Its processing cycle is suitable for large-scale commercial production and it is available in large quantities through a single growth run on an up to 4-in SiC wafer.

Study on Graphene Growth Process on Various Bronzes and Copper-Plated Steel Substrates

The paper presents the aim, way of proceeding and results obtained during the research made in the project GRAPHTRIB to determine the metallic substrates, other than copper, to realize graphene growth process. The various silicon and silicon free bronzes were the objects of investigations. The obtained results presented in the paper aren’t encouraging.

High frequency electromagnetic detection by nonlinear conduction modulation in graphene nanowire diodes

We present graphene nanowires implemented as dispersion free self switched microwave diode detectors. The microwave properties of the detectors are investigated using vector corrected large signal measurements in order to determine the detector responsivity and noise equivalent power (NEP) as a function of frequency, input power, and device geometry. We identify two distinct conductance nonlinearities which generate detector responsivity: an edge effect nonlinearity near zero bias due to lateral gating of the nanowire structures, and a velocity saturation nonlinearity which generates current compression at high power levels. The scaling study shows that detector responsivity obeys an exponential scaling law with respect to nanowire width, and a peak responsivity (NEP) of 250 V/W (50 pW/ Hz) is observed in detectors of the smallest width. The results are promising as the devices exhibit responsivities which are comparable to state of the art self switched detectors in semiconductor technologies.

Characterization and physical modeling of MOS capacitors in epitaxial graphene monolayers and bilayers on 6H-SiC

Capacitance voltage (CV) measurements are performed on planar MOS capacitors with an Al2O3 dielectric fabricated in hydrogen intercalated monolayer and bilayer graphene grown on 6H-SiC as a function of frequency and temperature. Quantitative models of the CV data are presented in conjunction with the measurements in order to facilitate a physical understanding of graphene MOS systems. An interface state density of order 2 . 10(12)eV(-1)cm(-2) is found in both material systems. Surface potential fluctuations of order 80-90meV are also assessed in the context of measured data. In bilayer material, a narrow bandgap of 260meV is observed consequent to the spontaneous polarization in the substrate. Supporting measurements of material anisotropy and temperature dependent hysteresis are also presented in the context of the CV data and provide valuable insight into measured and modeled data. The methods outlined in this work should be applicable to most graphene MOS systems.

Temperature Dependence of Functional Properties of Graphene Hall-Effect Sensors Grown on Si Face and C Face of 4H-SiC Substrate

Paper presents the results of investigation of the temperature influence on the basic functional properties of graphene Hall-effect sensors. The measurement system utilizing Helmholtz coils as a source of external magnetic field and environmental chamber for setting temperature was developed. Two types of monolayer graphene structures grown on both Si and C face of SiC substrate were investigated in the room temperature (about 20 oC) and their functional properties were compared. Next, the temperature influence on functional properties of both types of graphene structures was investigated using environmental chamber. The results of measurements are presented as charts and analyzed in the paper. On the basis of the results, conclusions were formulated, which are included in the last section of the paper.

Investigation of the Functional and Environmental Characteristics of Elements with Graphene Coating

This paper presents environmental and functional tests to determine the areas for graphene coated element application. The researches were held for the following environmental testing of samples with graphene: cold, dry heat, rapid temperature changes and sinusoidal vibrations.

Influence of Protective Layer on the Functional Properties of Monolayer and Bilayer Graphene Hall-Effect Sensors

Paper presents the results of investigation of the influence of protective layer on the basic functional properties of experimental graphene Hall-effect sensors. Both monolayer and bilayer type of graphene structure was investigated under external magnetic field. Measurement system for obtaining U H(B) characteristics of Hall-effect sensors was developed using Helmholtz coils as a source of magnetic field. Results of executed tests are presented in the paper as charts, which were analyzed and discussed. Finally, the conclusions were formulated, which are included in the last section of the paper.

New method for determination of the peak‐velocity in epitaxial semiconductor structures by dc measurements on microbridges

A simple current‐voltage measurement technique using microbridge patterns is described as a fast method for the determination of the effective peak electron velocity in III‐V semiconducting materials. The method is tested for GaAs samples. Microbridge patterns with different geometries were investigated and the influence of ‘‘self‐heating’’ by power dissipation was examined. Some other potential sources of errors deteriorating the accuracy of measurements were determined.