Solid-state Magnetic Sensors Research Articles

Noise Suppression of Nitrogen-Vacancy Magnetometer in Lock-In Detection Method by Using Common Mode Rejection.

Nitrogen-vacancy (NV) centers in diamonds are promising solid-state magnetic sensors with potential applications in power systems, geomagnetic navigation, and diamond NV color center current transformers, in which both high bandwidth and high magnetic field resolution are required. The wide bandwidth requirement often necessitates high laser power, but this induces significant laser fluctuation noise that affects the detection magnetic field resolution severely. Therefore, enhancement of the magnetic field resolution of wide-bandwidth NV center magnetic sensors is highly important because of the reciprocal effects of the bandwidth and magnetic field resolution. In this article, we develop a common mode rejection (CMR) model to eliminate the laser noise effectively. The simulation results show that the noise level of the light-detected magnetic resonance signal is significantly reduced by a factor of 6.2 after applying the CMR technique. After optimization of the laser power and modulation frequency parameters, the optimal system bandwidth was found to be 75 Hz. Simultaneously, the system's detection magnetic field resolution was enhanced significantly, increasing from 4.49 nT/Hz1/2 to 790.8 pT/Hz1/2, which represents an improvement of nearly 5.7 times. This wide-bandwidth, high-magnetic field resolution NV color center magnetic sensor will have applications including power systems, geomagnetic navigation, and diamond NV color center current transformers.

An Integrated Magnetometer Module With MFCs Based on Diamond NV Centers

In recent years, nitrogen vacancy (NV) centers in diamond have become a promising solid-state magnetic sensor for applications due to their high sensitivity to magnetic field and excellent spatial resolution at room temperature. However, diamond magnetometer has complex and large optical system and microwave system, it is necessary to address the requirements of the measured environment for the small space and high sensitivity of the magnetometer in practical applications. In this paper, we propose an integrated magnetometer module with magnetic flux concentrators (MFCs) shaped like the wings of an airplane. The fiber coupler, diamond, microwave antenna, filters, photodetector and a weak signal processing circuit are integrated in the integrated module. MFCs are also integrated to collect flux from a larger area and concentrate it into the center of diamond magnetometer, which are used to improve the sensitivity of the diamond magnetometer. The volume of the integrated module is limited to 3.81 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> and achieve the actual magnetic sensitivity of sub-0.34 nT/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> . In the designed magnetometer module, the devices are assembled more easily and tightly, which provides a new degree of freedom for the production of diamond magnetometer.

Structure and 3-D Model of a Solid State Thin-Film Magnetic Sensor

Vector 3-D magnetic sensors form the basis of measurement devices for magnetic field mapping and magnetic tracking. Typically, such sensors utilize specific constructions based on split Hall structures (SHS). An SHS-based 3-D magnetic sensor is a bulk semiconductor integrated structure with 8 or more contacts. Combining current flow directions through the contacts and measuring the corresponding voltages, one defines projections BX, BY, BZ of the magnetic field vector. This work presents a novel design of 3-D solid state magnetic sensors that requires no insulation by p-n junctions and can be implemented by thin-film technology traditionally used for fabrication of Hall sensors including those based on InSb films. Besides, a SPICE model of the 3-D magnetic sensor is provided, which helps design the proposed sensor and refine techniques of its calibration.

PicoTesla magnetic tunneling junction sensors integrated with double staged magnetic flux concentrators

Ultra-sensitive solid-state magnetic sensors are in strong demand in many applications where currently available sensors are inadequate. We have used high performance magnetic tunneling junction (MTJ) sensors and pushed the magnetic sensing limit to a high level. We have incorporated double-staged magnetic flux concentrators, one on the MTJ chip level and the other on a more macroscopic level, to amplify the external field of interest. With this approach and undergoing a process of optimization on the flux concentrators, we have increased the sensitivity of the MTJ sensor by a large factor of 517 to 775.4%/Oe in terms of magnetoresistance response. The coercivity of the sensor is only 0.12 Oe. We have achieved a detectable field limit of 30 pT/Hz at 10 kHz. We have presented the noise spectrum and the sensitivity spectrum up to a maximum frequency of 100 kHz.

Magnetometer Error Models of Low-Cost Land Vehicle Navigation System

This article implies a method of magnetometer error determination. Using solid-state magnetic sensors, vehicle odometer and GPS sensor, low-cost complex navigation system for land vehicles can be realized. The methods and algorithms of magnetometer calibration are shown. Results of magnetometer calibration experiments and possibility to detect magnetometer error parameters in process of car driving are analysed. To acquire vehicle heading output, navigation system described here is developed. DOI: http://dx.doi.org/10.5755/j01.eie.22.6.17225

Magnetic stability under magnetic cycling of MgO-based magnetic tunneling junctions with an exchange-biased synthetic antiferromagnetic pinned layer

We investigate the magnetic stability and endurance of MgO-based magnetic tunnel junctions (MTJs) with an exchange-biased synthetic antiferromagnetic (SAF) pinned layer. When a uniaxially cycling switching field is applied along the easy axis of the free magnetic layer, the magnetoresistance varies only by 1.7% logarithmically with the number of cycles, while no such change appears in the case of a rotating field. This observation is consistent with the effect of the formation and motion of domain walls in the free layer, which create significant stray fields within the pinned hard layer. Unlike in previous studies, the decay we observed only occurs during the first few starting cycles (&amp;lt;20), at which point there is no further variance in all performance parameters up to 107 cycles. Exchange-biased SAF structure is ideally suited for solid-state magnetic sensors and magnetic memory devices.

Thin Film of Giant Magnetoresistance (GMR) Material Prepared by Sputtering Method

In recent decades, a new magnetic sensor based on magnetoresistance effect is highly researched and developed intensively. GMR material has great potential as next generation magnetic field sensing devices. It has also good magnetic and electric properties, and high potential to be developed into various applications of electronic devices such as: magnetic field sensor, current measurements, linear and rotational position sensor, data storage, head recording, and non-volatile magnetic random access memory. GMR material can be developed to be solid state magnetic sensors that are widely used in low field magnetic sensing applications. A solid state magnetic sensor can directly convert magnetic field into resistance, which can be easily detected by applying a sense current or voltage. Generally, there are many sensors for measuring the low magnetic field, such as: fluxgate sensor, Hall sensor, induction coil, GMR sensor, and SQUID sensor. Compared to other low magnetic field sensing techniques, solid state sensors have demonstrated many advantages, such as: small size (&lt;0.1mm2), low power, high sensitivity (~0.1Oe) and good compatibility with CMOS technology. The thin film of GMR is usually prepared using: sputtering, electro deposition or molecular beam epitaxy (MBE) techniques. But so far, not many researchers reported the manufacture of thin film of GMR by dc-Opposed Target Magnetron Sputtering (dc-OTMS). In this paper, we inform the development of GMR thin film with sandwich and spin valve structures using dc-OTMS method. We have also developed organic GMR with Alq3 as a spacer layer.

Magnetic Field Sensors Based on Giant Magnetoresistance (GMR) Technology: Applications in Electrical Current Sensing

The 2007 Nobel Prize in Physics can be understood as a global recognition to the rapid development of the Giant Magnetoresistance (GMR), from both the physics and engineering points of view. Behind the utilization of GMR structures as read heads for massive storage magnetic hard disks, important applications as solid state magnetic sensors have emerged. Low cost, compatibility with standard CMOS technologies and high sensitivity are common advantages of these sensors. This way, they have been successfully applied in a lot different environments. In this work, we are trying to collect the Spanish contributions to the progress of the research related to the GMR based sensors covering, among other subjects, the applications, the sensor design, the modelling and the electronic interfaces, focusing on electrical current sensing applications.

The sheer-contact MAGRES – a magnetic field sensor with minimal manufacturing complexity

Abstract This paper analyzes a solid state magnetic sensor called the “sheer-contact magnetic field sensitive resistor” (SC-MAGRES). The geometry of this device features no lateral insulation and is determined by the contacts only, thus, it can be manufactured with a minimal number of masking steps. Its applications are in the micro-electro-mechanical-systems (MEMS)-area with low-cost sensor-applications using non-standard processes. An equivalent circuit for use in circuit simulators as well as models of the device resistors and sensitivity are presented and compared to measurements which show a maximum sensitivity of 17 μA/VT. Other measurements show a maximum resolution of 120 nT as well as the offset of the device. A comparison to similar magnetic sensors concludes the analysis, together with an investigation of optimization strategies.

Circular arrays of magnetic sensors for current measurement

A single solid-state magnetic sensor can measure a current flowing in a conductor in a noncontact way. In order to improve the accuracy of the measuring system and to reduce the crosstalk effects of other magnetic fields, circular arrays of magnetic sensors can be fabricated, still preserving low costs. In those kind of arrays, the sensing elements are assembled on a circle around the conductor. The sum of the sensor output signals is an approximation of Ampere's circulation. A quite satisfactory crosstalk effects reduction can be thus achieved. More sophisticated algorithms that combine sensor output signals are necessary in order to further reduce crosstalk effects. This paper presents an algorithm that is able to calculate the intensity of a dc current flowing in a rectangular bus-bar, in the presence of crosstalk fields.

Interference rejection algorithm for current measurement using magnetic sensor arrays

Solid state magnetic sensors can measure a current by sensing the field near the conductor. Means are required to distinguish between useful and interference fields and that are those of conductors near the current under measurement and environmental fields. Starting from analytical expressions of the magnetic field, spatial harmonic analysis is performed. It is then possible to separate the effects of the field generated by the current under measurement from those of interference fields. A new algorithm based on spatial Discrete Fourier Transform (DFT) capable of calculating the current to be measured is presented. The algorithm can be implemented by a DSP that processes output signals of solid state magnetic sensors forming a circular array centred in the current conductor.

Considerations for applying solid state sensors to high density magnetic disc recording

To compete with optical recording densities of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> or greater bits per square centimeter, equal magnetic disc areal densities must be achieved. Based on signal to noise considerations, inductive sensing of magnetic transitions written on magnetic media must give way to solid state magnetic sensors. There are fundamental considerations involved with implementing solid state sensors as read heads. These considerations embrace the basic sensor characteristics of size, resolution, sensitivity, signal to noise ratio and frequency response. Other equally important considerations involve packaging and head-wear resulting from head-media proximity demanded by the nature of the field to be sensed from the media. Finally, the solutions to these considerations must be simple and inexpensive.