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In this study, the effects of temperature and relative humidity on the resonant frequency of a micro-electro-mechanical system (MEMS) cantilever resonator under atmospheric pressure (p=101325 Pa) are discussed. The squeeze film damping (SFD) problem of MEMS cantilever resonators is modeled by solving the modified molecular gas lubrication (MMGL) equation, the equation of motion of micro-cantilever, and their appropriate boundary conditions, simultaneously in the eigen-value problem. The effective viscosity (µeff(RH, T)) of moist air is utilized to modify the MMGL equation to consider the effects of temperature and relative humidity under atmospheric pressure. Thus, the effects of temperature (T) and relative humidity (RH) on the resonant frequency of MEMS cantilever resonators over a wide range of gap thicknesses and under atmospheric pressure are discussed. The results showed that the frequency shift increases as the relative humidity and temperature increase. The influence of relative humidity on the resonant frequency becomes more significant under conditions of higher temperature and smaller gap thickness.

A CMOS-compatible three-axis fluxgate chip was implemented and characterized in this paper. The thin-film fluxgate core was fabricated onto a silicon chip with integrated planar excitation and sensing coils. A nickel-zinc ferrite fluxguide was aligned and attached to the center of the chip to enable the out-of-plane sensitivity to the external field. The feature size of the microfluxgate chip with a fluxguide is 4.1 mm, and the minimum noise level is 5–7 nT/ $\surd $ Hz at 1 Hz for the in-plane sensing axis. When the sensor is operated in the second-harmonic mode, the optimal excitation frequency is around 50 kHz. The performance of the vector magnetometer for geomagnetic measurement is demonstrated by rotating the device in the earth’s field and recording the azimuth response. The results showed that the proposed designs are valuable for simplifying the construction of miniature three-axis fluxgate, which is promising for applications in orientation determination and position detection, e.g., electronic compass and motion tracking.

In this study, the effects of temperature (T) and relative humidity (RH) of moist air are discussed on the quality factors (Q-factor) of micro-electro-mechanical-system (MEMS) cantilever resonators in atmospheric pressure (p = 101,325 Pa). The dominant squeeze film damping (SFD) of MEMS cantilever resonators is studied by solving the modified molecular gas lubrication (MMGL) equation. Dynamic viscosity and Poiseuille flow rate of moist air are utilized to modify the MMGL equation as functions of temperature and relative humidity for wide range of accommodation coefficients (ACs). In atmospheric pressure, dynamic viscosity changes more significantly with temperature and relative humidity than that of Poiseuille flow rate. The dominant thermoelastic damping (TED) and support loss are also included to obtain the Q-factor in wide range of cantilever sizes (length, width, and thickness). Thus, dependence of Q-factors of MEMS cantilever resonators on temperature and relative humidity is discussed for wide range of ACs and cantilever sizes in atmospheric pressure. The results show that Q-factor could be increase at higher temperature and relative humidity or lower ACs. Dependence of Q-factor on temperature and relative humidity enhances considerably in greater length, greater width, and smaller thickness of cantilever. Maximum Q-factors with temperature and relative humidity can be obtained for wide range of ACs and cantilever sizes in atmospheric pressure.

This paper discussed the effect of environmental conditions (moisture and temperature) on the quality factors (Q-factor) of micro-electro-mechanical systems (MEMS) cantilever beam resonators in wide range of gas rarefaction (pressure (p), and accommodation coefficients (ACs)), and flexural mode of resonator. The modified molecular gas lubrication (MMGL) equation is applied for modeling the dominant squeeze film damping (SFD) problem on the quality factor of MEMS cantilever beam resonators to discuss the effect of environmental conditions. The external SFD and the internal structure damping (thermoelastic damping) and support loss) are accurately taken into account. Effective viscosity, which is ratio of dynamic viscosity and Poiseuille flow rate of moist air, is utilized to modify the MMGL equation to consider the environmental effects of moisture and temperature in gas rarefaction. In low pressures, mean free path changes more significantly with relative humidity and temperature than that of dynamic viscosity of moisture in gas rarefaction. Thus, effect of environmental conditions such as moisture and temperature must be discussed to improve Q-factors of MEMS cantilever beam resonators in wide range of gas rarefaction (p and ACs) and flexural modes of resonator. The results showed that Q-factor of SFD decreases significantly as moisture and temperature increase at higher gas rarefaction (lower p, and ACs), while Q-factor of SFD decreases and then increases slightly as moisture and temperature increase at lower gas rarefaction (higher p, and ACs). The total Q-factor is highly sensitive to the relative humidity and temperature in higher gas rarefaction (lower p and ACs) and lower flexural modes of resonator.

This paper proposes a time varying disturbance observer for the active magnetic bearing system. The first derivative disturbance value was considered different to zero to show the effectiveness and originality of the proposed methodology. A novel disturbance observer form was constructed based on the basic nonlinear disturbance observer, which was combined with a proportional integral derivative sliding mode control for designing a control system. The disturbance estimation error was converged exponentially to the zero when the time goes to infinite. The output distance of the active magnetic bearing was closely converged to the desired trajectory. The Lyapunov law was used to analyses the convergent condition of the control system. Simulation results were used to prove the effectiveness of the proposed theory.

In this research, we have investigated an application of eddy current probe-based on the GMR spin-valve for the flaw testing system. The eddy current probe consists of a GMR spin-valve sensor and a square modulation coil. The sensing direction is performed perpendicular to the modulation field generated by a modulation coil. The GMR spin-valve used in this work is a model GF708 from Sensitec Inc with a bare-die version. The scanning length is 80 mm for six cracks with a different depth on the surface of a metal specimen. The gap between the cracks to each other is about 14.5 mm. The experimental results are obtained by scanning the probe over six cracks of a specimen. The crack positions on the surface of a specimen are determined by the peak or valley values of in-phase and quadrature-phase differential defect field. Similarly, the depth of the cracks is estimated by the phase of the differential defect field.

A miniature tri-axis magnetometer with in-plane giant magnetoresistance (GMR) sensors and a fluxguide was designed, implemented, and characterized in this paper. Three GMR sensor dies were aligned on a printed circuit board with their sensing directions in the same plane. By using the flux bending effect of a fluxguide, the magnetic field components in the mounting plane of GMR sensors were generated, and hence, the effective sensing directions are not in the same plane. The tilt of effective sensing direction from the mounting plane allows the device to detect the out-of-plane field component. When the device was used as an electronic compass, the digitally demodulated sensor outputs were converted into the orthogonal geomagnetic field components by using a real-time conversion process with the voltage-to-field transfer matrix. The result shows that the device is suitable for compass application. Further works to implement the similar design on a CMOS chip with integrated GMR elements and a planar modulation coil will realize a compact and easy-to-fabricate tri-axis magnetic field sensor.

The solid-state magnetic field sensors developed in recent years are transducers that convert magnetic fields under test into digital or analog voltage outputs. [1] The system consists of the front-end sensing element and the rear-end signal processing unit. The key performances of magnetic field sensor are demonstrated by its sensitivity, noise, linear range, and frequency bandwidth. The ultimate frequency response and noise behavior of the sensing system are determined by the driving method for the front-end sensing element. For quasi-static geomagnetic applications, flipping or modulation techniques is used to minimized the hysteresis for high accuracy measurement of DC field [2], but the available flat bandwidth is limited to less than one tenth of modulation frequency [3]. In contrast, a flat bandwidth over 30 kHz is observed for the DC-field-biased GMR sensor with a magnetic field feedback [4], which is ideal for high frequency applications, e.g. eddy-current sensing. However, the output under a DC-biased field is hysteretic and hence it is not suitable for DC measurement. For industry and high-end consumer applications, a magnetometer with a large bandwidth is necessary for mixed AC and DC measurement. A straight forward implementation of high bandwidth DC/AC magnetometer is to combine the DC sensor with and an AC induction coil [5], [6]. However, the hybrid magnetometer of this kind has a feature size much larger than the solid-state sensor in it. In addition, the output levels for the two element sensors could be very different, inducing more complexity in signal processing. In this work, we explore the flat bandwidth expansion technique using two spinvalve GMR magnetic field sensors driven by different schemes, i.e. field modulation and DC-field-bias. Fig.1 shows the block diagram for the analog signal processing of the system. The low-frequency GMR sensor (LF sensor) is driven by AC magnetic modulation field to achieve high linearity and low hysteresis. A low-pass filter is used to extract the DC output induced by the nonlinear voltage-field relation of spin valve. In this way, the complexity of driving circuit with the inclusion of synchronous detection is avoided. The high-frequency GMR sensor (HF sensor) driven by a DC magnetic field bias has higher hysteresis in the low frequency range, but it exhibits high sensitivity and good linearity for high frequency field measurement. The LF sensor is suitable for detection of DC and low frequency magnetic field, while the HF sensor is capable of AC measurement at higher frequencies. The combined sensor output of the system has a wide bandwidth and is suitable for both DC and AC measurement. To combine the output of the two sensors, the output of HF sensor is high-pass (6 dB/oct) filtered at 100 Hz, and the output of LF sensor is low-pass (6 dB/oct) filtered at 100 Hz. The amplifier gains of the two outputs are fine tuned to achieve a uniform sensitivity, and the two outputs are combined with a summing amplifier. The observed outputs of LF and HF sensors as well as the combined signals are shown in Fig. 2. It was found that the front-end sensitivities are 9.8 V/T for LF sensor and 251 V/T for HF sensor. The total sensitivity of the combined GMR sensing system is 2312 V/T with the total amplifier gains of 500 for the LF sensor and 20 for the HF sensor, supply voltage is 0.69 V for LF sensor and 2.61 V for HF sensor. The linearity error of the combined output signal is 2.2% within the ± 4μT range. The field noise spectral density is 65 nT$/ \surd $ Hz at 1 Hz. The output of summing amplifier is well consistent with theoretical values predicted by numeral calculations from the circuit model. The flat bandwidth of the combined output is expanded to the range from DC to above 10 kHz. The maximum deviation of normalized sensitivity is 1.7% at 100 Hz and the 3-dB flat bandwidth is 40 kHz. The phase lag of the combined output changes slowly to from 0° to - 15° with an increasing frequency from 1 Hz to 1 kHz. The phase lag increases to -130° at 10 kHz and becomes random at frequencies above 100 kHz. Further improvement in the uniformity of frequency response is possible by optimizing the circuit parameters of low-pass and high-pass filters to fine tune their characteristic frequencies and gains. The observed frequency response of our system surpasses the existing GMR sensing systems reported by Tyler et al. [7], for which the 5% flat bandwidth is 530 Hz, and 10% flat bandwidth is 1.515 kHz. Our system exhibited a 5% flat bandwidth of 1.7 kHz and a 10% flat bandwidth of 8.3 kHz, while the response to quasi-static sweeping field at frequencies below 0.1 Hz shows negligible hysteresis. The broad bandwidth of our system makes it suitable for detecting the DC and AC magnetic fields in nondestructive evaluation [4]. It is also suitable for monitoring the environmental field in transient motion tracking with the software gyroscope [8] consisting of magnetic sensor and accelerometer. This work is supported by the Ministry of Science and Technology of Taiwan under Grant No. MOST MOST 105-2221-E-151-038.Fig. 1.Schematics of the signal processing unitFig. 2.Normalized sensitivity of LF sensor, HF sensor, and combined output of two sensors. Brown: LF sensor, Purple: HF sensor, Blue: Output of summing amplifier.

High-Al-content AlxGa1−xN layers, x ∼ 0.72, have been grown by metal organic chemical vapour deposition (MOCVD) at a temperature ranging from 1000 to 1100 °C, together with high flow rate of the dopant precursor silane (SiH4) in order to obtain highly Si-doped Al0.72Ga0.28N layers, ∼1 × 1019 cm−3 as measured by secondary ion mass spectrometry (SIMS). Further characterization of the layers by capacitance–voltage (C–V), electron paramagnetic resonance (EPR), and transmission electron microscopy (TEM) measurements reveals the complex role of growth temperature for the n-type conductivity of high-Al-content AlxGa1−xN. While increasing temperature is essential for reducing the incorporation of carbon and oxygen impurities in the layers, it also reduces the amount of silicon incorporated as a donor.

Two self-doped conjugated polyelectrolytes, having semiconducting and metallic behaviors, respectively, have been blended from aqueous solutions in order to produce materials with enhanced optical and electrical properties. The intimate blend of two anionic conjugated polyelectrolytes combine the electrical and optical properties of these, and can be tuned by blend stoichiometry. In situ conductance measurements have been done during doping of the blends, while UV–vis and EPR spectroelectrochemistry allowed the study of the nature of the involved redox species. We have constructed an accumulation/depletion mode organic electrochemical transistor whose characteristics can be tuned by balancing the stoichiometry of the active material.

We have studied the silicon donor behavior in intentionally silicon doped AlxGa1-xN (0.63≤x≤1) grown by hot-wall metal-organic chemical vapor deposition. Efficient silicon doping was obtained for l ...

The high-Al-content AlxGa1-xN alloys, x>0.70, and AlN is the fundamental wide-band-gap material system associated with the technology development of solid-state LEDs operating at the short wavelengths in the deep-UV (λ < 280 nm). Yet, their properties are insufficiently understood. The present study is intended to bring elucidation on the long-time debated and much speculated Si transition from shallow donor in GaN to a localized deep DX defect in AlxGa1-xN alloys with increasing Al content. For that purpose electron paramagnetic resonance is performed on a particular selection of high-Al-content epitaxial layers of Al0.77Ga0.23N, alternatively Al0.72Ga0.28N, alloy composition.

Defects in unintentionally Nb-doped 6H-SiC grown by high-temperature chemical vapor deposition were studied by electron paramagnetic resonance (EPR). An EPR spectrum with a hyperfine (hf) structure consisting of ten equal-intensity lines was observed. The hf structure is identified to be due to the hf interaction between an electron spin S=1/2 and a nuclear spin of 93Nb. The hf interaction due to the interaction three nearest Si neighbors was also observed, suggesting the involvement of the C vacancy (VC) in the defect. Only one EPR spectrum was observed in 6H-SiC polytype. The obtained spin-Hamiltonian parameters are similar to that of the Nb-related EPR defect in 4H-SiC, suggesting that the EPR center in 6H-SiC is the NbSiVC complex in the neutral charge state, NbSiVC0. Photoexcitation EPR experiments suggest that the single negative charge state of the NbSiVC complex is located at ~1.3 eV below the conduction band minimum.

In this experiment, a two-dimensional (2D) position detection device using a tunnel-magnetoresistance (TMR) sensor combined with orthogonal gradient coils was designed and fabricated. Typical magnetic trackers rely on three-axis field sensing to detect the AC or pulse DC fields induced by dipole transmitters [1]. In our design, a single axis TMR sensor is the target object which converts the position information into the output voltage with an in-phase and quadrature synchronous detector, as show in Fig. 1(a). The sensing direction of the TMR sensor was set perpendicular to the plane of two gradient coils. The two coils were driven by sine wave currents at 1 kHz with 90° phase difference to generate the fields with uniform gradients along the x-and y-axes of the plane, as shown in Fig. 1(b) and (c). The distances from the sensor to the two coils were analysed numerically to achieve the maximum linear range, which corresponds to the detection area of the device. The observed result shows that the device with gradient coils and a TMR sensor is promising in applications related to 2D magnetic field mapping to allow the sensor position be determined accurately in real-time during scanning.

Point defects in semiconductor materials are known to have important influence on the performance of electronic devices. For defect control, knowledge on the model of defects and their properties i ...

We carried out Heyd-Scuseria-Ernzerhof hybrid density functional theory plane wave supercell calculations in wurtzite aluminum nitride in order to characterize the geometry, formation energies, transition levels and hyperfine tensors of the nitrogen split interstitial defect. The calculated hyperfine tensors may provide useful fingerprint of this defect for electron paramagnetic resonance measurement., 5 pages, 3 figures

In freestandingn-type 4H-SiC epilayers irradiated with low-energy (250 keV) electrons at room temperature, the electron paramagnetic resonance (EPR) spectrum of the negative carbon vacancy at the hexagonal site, VC- (h), and a new signal were observed. From the similarity in defect formation and the spin-Hamiltonian parameters of the two defects, the new center is suggested to be the negative C vacancy at the quasi-cubic site, VC- (k). The identification is further supported by hyperfine calculations.

Electron paramagnetic resonance studies of Si-doped AlxGa1−xN (0.79 ≤ x ≤ 1.0) reveal two Si negative-U (or DX) centers, which can be separately observed for x ≥ 0.84. We found that for the stable DX center, the energy |EDX| of the negatively charged state DX−, which is also considered as the donor activation energy, abruptly increases with Al content for x ∼ 0.83–1.0 approaching ∼240 meV in AlN, whereas EDX remains to be close to the neutral charge state Ed for the metastable DX center (∼11 meV below Ed in AlN).

Electron paramagnetic resonance (EPR) spectrum of a shallow donor is observed at low temperatures in darkness in Si-doped Al0.77Ga0.23N epitaxial layers grown on 4H-SiC substrates. It is shown from the temperature dependence of the donor concentration on the neutral donor state measured by EPR that Si is a DX (or negative-U) center but behaves as a shallow donor due to a small separation of only ∼3 meV between the neutral state Ed and the lower-lying negative state EDX. The neutral state is found to follow the effective mass theory with Ed ∼ 52–59 meV.

Issues of major relevance to the n-type conductivity of Al0.77Ga0.23N associated with Si and O incorporation, their shallow donor or deep donor level behavior, and carrier compensation are elucidated by allying (i) study of Si and O incorporation kinetics at high process temperature and low growth rate, and (ii) electron paramagnetic resonance measurements. The Al0.77Ga0.23 Nc omposition correlates to that Al content for which a drastic reduction of the conductivity of AlxGa1� x Ni s commonly reported. We note the incorporation of carbon, the role of which for the transport properties of AlxGa1� xN has not been widely discussed. V C 2013 American Institute of Physics.

Using electron paramagnetic resonance (EPR), energy levels of the carbon vacancy (V(C)) in 4H-SiC and its negative-U properties have been determined. Combining EPR and deep-level transient spectroscopy we show that the two most common defects in as-grown 4H-SiC--the Z(1/2) lifetime-limiting defect and the EH(7) deep defect--are related to the double acceptor (2-|0) and single donor (0|+) levels of V(C), respectively.

High purity silicon carbide (SiC) materials are of interest from high-power high temperature applications across recent photo-voltaic cells to hosting solid state quantum bits, where the tight control of electrically, optically, and magnetically active point defects is pivotal in these areas. 4H- and 6H-SiC substrates are grown at high temperatures and the incorporation of transition metal impurities is common. In unintentionally Nb-doped 4H- and 6H-SiC substrates grown by high-temperature chemical vapor deposition, an electron paramagnetic resonance (EPR) spectrum with C-1h symmetry and a clear hyperfine (hf) structure consisting of ten equal intensity hf lines was observed. The hf structure can be identified as due to the interaction between the electron spin S - 1/2 and the nuclear spin of Nb-93. Additional hf structures due to the interaction with three Si neighbors were also detected. In 4H-SiC, a considerable spin density of similar to 37.4% was found on three Si neighbors, suggesting the defect to be a complex between Nb and a nearby carbon vacancy (V-C). Calculations of the Nb-93 and Si-29 hf constants of the neutral Nb on Si site, Nb-Si(0), and the Nb-vacancy defect, NbSiVC0, support previous reported results that Nb preferentially forms an asymmetric split-vacancy (ASV) defect. In both 4H- and 6H-SiC, only one Nb-related EPR spectrum has been observed, supporting the prediction from calculations that the hexagonal-hexagonal defect configuration of the ASV complex is more stable than others. Funding Agencies|Swedish Energy Agency||Swedish Research Council VR/Linne Environment LiLI-NFM, FP7|270197|NHDP|TAMOP-4.2.1/B-09/1/KMR-2010-0002|Swedish National Infrastructure for Computing||Knut and Alice Wallenberg Foundation

In this study, to reveal the origin of the Z(1/2) center, a lifetime killer in n-type 4H-SiC, the concentrations of the Z(1/2) center and point defects are compared in the same samples, using deep level transient spectroscopy (DLTS) and electron paramagnetic resonance (EPR). The Z(1/2) concentration in the samples is varied by irradiation with 250 keV electrons with various fluences. The concentration of a single carbon vacancy (V-C) measured by EPR under light illumination can well be explained with the Z(1/2) concentration derived from C-V and DLTS irrespective of the doping concentration and the electron fluence, indicating that the Z(1/2) center originates from a single V-C.

Motivated by recent experimental findings on the hyperfine signal of nitrogen donor (N-C) in 4H and 6H SiC, we calculate the hyperfine tensors within the framework of density functional theory. We find that there is negligible hyperfine coupling with Si-29 isotopes when NC resides at h site both in 4H and 6H SiC. We observe measurable hyperfine coupling to a single Si-29 at k site in 4H SiC and k(1) site in 6H SiC. Our calculations unravel that such Si-29 hyperfine coupling does not occur at k(2) site in 6H SiC. Our findings are well corroborated by our new electron paramagnetic resonance studies in nitrogen doped 6H SiC.

The Z[1/2] center in n-type 4H-SiC epilayers—a dominant deep level limiting the carrier lifetime—has been investigated. Using capacitance versus voltage (C-V) measurements and deep level transient spectroscopy (DLTS), we show that the Z[1/2] center is responsible for the carrier compensation in n-type 4H-SiC epilayers irradiated by low-energy (250 keV) electrons. The concentration of the Z[1/2] defect obtained by C-V and DLTS correlates well with that of the carbon vacancy ( Vc ) determined by electron paramagnetic resonance, suggesting that the Z[1/2] deep level originates from Vc.