Thin-film Magnetoresistive Sensors Research Articles

Thin-film magnetoresistive sensors and measuring transducers of magnetic induction

The article presents some features of thin-film magnetoresistive magnetic induction sensors ММКК247, ММКК247-01, МЧЭ033 and the digital measurement gauge МРД009 that was developed in JSC NPO IT for aviation and cosmic apparatus navigation systems.

Biosensors based on the thin-film magnetoresistive sensors

The review considered the state-of-the-art in the development of devices for detection of the agents of disease on the basis of the Lab on a chip (LOC) biosensors whose detecting element is a matrix of thin-film anisotropic magnetoresistive (AMR), magnetoresistive (GMR), or spin-tunnel magnetoresistive (STMR) magnetic field sensors based on the multi-chip planar technology. Data were presented on the nanospherical superparamagnetics used in many biological applications as the magnetic labels. The review is oriented to the technical experts, and in this connection the biological fundamentals of the method of determination of biological activity with the use of the MR biosensor were given in a nutshell.

Magnetovision [magnetic field scanning system

The experimental analysis of magnetic fields by scanning methods can effectively support and verify modern numerical methods. The scanning methods are especially suitable for testing the material structure and as a method for material evaluation. By applying the appropriate imaging techniques it is possible to reconstruct the magnetic field strength in an arbitrary plane. In the Magnetovision system, the specific area of a material is magnetized using a C-yoke. A line of miniature thin-film magnetoresistive sensors measures the magnetic field strength above the magnetized sample. Graphical results of the magnetic field strength scanned around steel samples are presented, showing that Magnetovision could be an effective system for nondestructive materials testing.

Magnetoresistive sensors

This paper reviews magnetoresistive sensors for detecting magnetic fields. These sensors are based on an effect which has been known for more than 100 years, but it has only come to prominence since 1971 when a thin-film magnetoresistive sensor was shown to have good signal-to-noise performance in a field-sensing application in magnetic recording.A large amount of research has been carried out to explore the limits of magnetoresistive sensors in their thin-film form and many novel structures have been published. Despite this there are application limits relating to non-linearity of response characteristics, presence of demagnetising fields, hysteresis and Barkhausen noise.The paper will present the basic theory of these sensors and deal with some technical limitations. A range of magnetic biasing techniques are discussed. The shape and structure of these sensors affects sensitivity through the form and magnitude of the demagnetising field. Improvements in performance can be gained by making thinner sensor films and films with transverse shape-anisotropy.Research has led to a reduction in coercivity of sensor film materials and a corresponding improvement in hysteresis. Barkhausen noise reduces in thinner films due to the transition from predominantly Bloch-type to predominantly Néel-type magnetic domain walls. This paper considers two types of sensor application. The first is for general magnetic field detection and the second, detecting magnetic fields on informaiton storage media.

Suppression of Barkhausen noise in magnetoresistive sensors employing AC bias

A magnetic field rotating in the plane of a thin-film magnetoresistive sensor provides continuous saturation of the ferromagnetic material if the magnitude of the field is sufficiently large. This mode of excitation allows operation free of errors related to remanence and at the same time helps in suppressing Barkhausen noise. The experiment demonstrates that the contribution of the magnetic noise in the sensor output is negligible when the period of the field rotation is less than 1 ms. This enables resolution of dc and low-frequency magnetic fields of the order of 10/sup -10/ T//spl radic/Hz. This result can be improved by decreasing the sensor induced anisotropy and a resolution of 10/sup -11/-10/sup -12/ T//spl radic/Hz might be attainable.

Current measurements based on thin-film magnetoresistive sensors

Abstract As is well known, the magnetoresistive effect is the basic principle of a large number of sensors. The potential-free measurement of current is one way of applying magnetoresistive sensors. For the measurement of currents lower than about 50 A, it is necessary to reduce the distance between the conductor the magnetoresistive sensor to one millimeter or less. We have developed two different kinds of current-sensor devices containing both a conductor and a sensor. The first one is a hybrid magnetoresistive current sensor suitable for measurements of currents between 1 and 10 A. This device contains a barberpole elementary magnetoresistive sensor chip the conductor, also a permanent magnet in order to generate the stabilizing magnetic field. The second device, suitable for the measurement of currents between 1 and 30 mA, contains a sensor chip with integrated thin-film conductor and a thin-film insulator between the conductor and magnetoresistive layer. The advantages disadvantages of our sensor devices are described the typical sensor parameters are explained.

Grooved bar-code pattern recognition system with magnetoresistive sensor

A magnetic bar-code pattern recognition system with a magnetoresistive sensor is proposed. The bar-code consists of a set of grooves on an iron plate, similar to an optical bar-code pattern. When a magnet passes above the grooves on an iron plate, the magnetic field produced by the magnet is bent by the grooves. The bar-code pattern of grooves can be reconstructed by detecting the bend using the magnetoresistive sensor. Computer simulation results on magnetic flux density distribution near the grooves are presented, and prototype recognition systems with a magnetoresistive sensor are described. It is shown that a two-groove bar-code configuration with different groove depths depending on groove width and a thin-film magnetoresistive sensor construction are useful in realizing high-resolution detection systems. >

Investigations of silicon iron sheets by means of permalloy magnetoresistive sensors

The paper presents the results of application of permalloy thin film magnetoresistive sensors for investigation of silicon iron sheets. The following parameters have been measured - the single point value of magnetic field intensity and anisotropy, sheet texture, losses and uniformity. Determination of these parameters has been based on the measurement of stray field at the sheet surface.

Analysis of magnetoresistors with high coercivity biassing films

It is necessary to bias permalloy thin-film magnetoresistive sensors in order to increase their sensitivity to applied fields and prevent domain wall formation giving rise to Barkhausen noise. This is possible by patterning the device from a three layer film consisting of the NiFe magnetoresistive layer and a high coercivity Co-25at.%Pt over layer separated by an insulating SiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> layer. Magnetic measurements have been made on this multilayer system and show that the spacing layer must be a minimum of 2000 Å thick in order to prevent increases in anisotropy magnitude and dispersion of the NiFe layer. A model has been developed for the behaviour of this multilayer system. The model predicts an increase in performance for overlayer biassed sensors compared with linear bias. The increase in zero bias sensitivity is found to be due to the non linear bias field from the permanent magnet layer partially compensating for the increase in demagnetising field near to the edge of the magnetoresistor strip. Both single strip sensors and strip arrays are considered and the sensitivity is found to depend strongly on spacer thickness for strip arrays but is much less dependent on spacer thickness for single strips.

Thin film magnetoresistive vector sensors with submicron gap width

The size of gap between adjacent conducting strips In the folded resistor track of a thin film magnetoresistive sensor element has an important effect on its performance. Pattern fabrication methods using electron-beam lithography enable conductor spacings in the submicron range to be used. Sensors with smaller conductor spacing have an enhanced sensitivity and require a much smaller orthogonal bias field than devices made using conventional photolithography. The parameters for optimum linearity of the signal are considered in terms of the amount of harmonic distortion introduced by the sensor when its working range of ±1 oersted is swept by an input field of sinusoidal form. The distortion values are extremely low and the orthogonal field for best linearity is established to be close to that for peak sensitivity. immunity to fields at right angles to the measurement vector is also a function of the bias field: the optimum value in this case is about 75% of that for peak sensitivity. Noise measurements indicate that levels are sufficiently low to permit magnetic signals of less than one gamma to be detected.