Magnetic Microsensors Research Articles

New Fabrication of Multiple-Layer Microcoil Using Anodic Oxidized Aluminum

A multiple-layer microcoil is a promising candidate for micromagnetic sensors for probing cracks in pipes in power stations and plants. We proposed fabrication of multiple-layer microcoils combining Al anodic oxidation and photolithography, and conducted experiments with the following results: 1) Sputter-deposited Al was anodically oxidized and thickness of Al2O3 formed controlled by anodic-oxidation time. 2) A pattern with Al and Al2O3 was made by masking Al with photoresist to prevent anodic oxidation. 3) A multiple-layer Al and Al2O3 was fabricated by combining Al anodic oxidation and photolithography. 4) As these results shown, multiple-layer microcoils having both high inductance and low resistance were fabricated as proposed using a simple process and having a high potential application to smaller multiple-layer microcoils.

Improvement of radiation resistance of magnetic field microsensors

Magnetic microsensors with the active area volume of 10 −5 mm 3 are fabricated on the basis of III–V semiconductor microcrystals. To improve the radiation resistance of magnetic microsensors complex metallurgical doping was applied to semiconductor microcrystals during growth. In addition to a basic donor dopant, rare-earth elements and special extras which are able to bind oxygen and act as drains for radiation defects are introduced. All that slows down the process of deep acceptor level complexation by means of radiation defects and background impurities, and improves the radiation resistance of sensors. Studies of effect of fast neutrons irradiation with energies from 0.1÷13 MeV and fluence of 10 14 n cm −2 were carried out. It has been shown that at the mean sensitivity change of 0.12% for the set of InSb-based microsensors with the electron concentration of (1÷3)·10 17 cm −3, for 60% of these microsensors the change does not exceed the determination error ±0.04%. The investigations have shown the relevance of the continuation of works directed to further improvement of the magnetic microsensor radiation resistance.

Magnetic microsensors: technology, properties, application

A number of Hall magnetic microsensors based on InAs and InSb microcrystals have been developed. Microcrystals are grown with the chemical transport reaction method, which ensures the formation of microcrystals with the required doping and shape. The electrophysical parameters of the microcrystals are similar to those of bulk crystals. Microcrystal-based microsensors have minimum dimensions, weight and power consumption. These microsensors are resistant to radiation exposure with fast neutrons and high-energy protons. They can operate in a temperature range reaching cryogenic temperatures, within a large range of magnetic induction. They are used for solving specific measurement problems in complicated magnetic systems, under conditions characterized by non-uniform magnetic induction distribution or high radiation. The design and characteristics can be customized.

MI Magnetic Sensor Using a C-MOS IC and Amorphous Wire

This paper presents new micromagnetic sensors with high sensitivity and stability and low power consumption using an amorphous wire MI head and a C-MOS inverter IC. The sensors employ the pulse response MI effect. The basic properties of the pulse response MI effect in amorphous wire ( (Fe0.06Co0.94)72.5Si12.5B15) and two kind of sensor circuits are reported. The impedance in the MI head is sensitively changed to more than 80%/Oe owing to a sharp current magnetization. The sensor circuits operate with a high stability because of a current-source-like operation in the C-MOS IC, and the independence of the field detection sensitivity with respect to the oscillation frequency of the multivibrator. The power consumption in the sensor circuit is less than 0.5 mW.

Detection of the Shaft-Edge Field of an Induction Motor for Stable Torque Control

To achieve stable torque control, rotor information on squirrel-cage induction motors was obtained for the first time by using highly sensitive magneto-impedance micromagnetic sensor. The magnetic field detected near the edge of the rotor shaft was estimated to be proportional to the rotor current with a slip frequency (psf/2) and a torque when the motor was driven with a constant V/f inverter. Stable control of the stationary torque was realized independently of the motor temperature variation.

Two-dimensional magnetic microsensor with on-chip signal processing for contactless angle measurement

The reported CMOS microsystem is the key element for accurate angle measurements. In combination with a permanent magnet, it is used for various wear free angular positioning control systems for automotive and industrial applications covering the full 360/spl deg/ range. The integrated system includes a two-dimensional (2-D) magnetic microsensor (30/spl times/30 /spl mu/m/sup 2/ active area), offset compensation, and signal conditioning circuitry. A novel approach for the angle calculation is presented using an on-board incremental ADC. A bitstream representing the angular position of the applied permanent magnet is provided at the system output. The system achieves a 1/spl deg/ angular resolution with 9 mW power consumption and a permanent magnet of 100 mT. The chip is fabricated in a generic 2-/spl mu/m, double-poly, double-metal CMOS process and covers an area of 2.6/spl times/4.1 mm/sup 2/.

A fully integrated planar toroidal inductor with a micromachined nickel-iron magnetic bar

A fully integrated toroidal inductor is realized on a silicon wafer by using a multilevel metallization technique to fabricate a wrapped coil wound around a micromachined bar of high-permeability magnetic material. In particular, efforts are made to minimize the coil resistance by using thick conductor lines and electroplated vias. In this structure, a 30 /spl mu/m thick nickel-iron permalloy magnetic core is wrapped with 40 /spl mu/m thick multilevel copper conductor lines, constructing a conventional toroidal inductor in planar shape. A closed magnetic circuit (i.e., toroidal) in this inductive component is adopted, where magnetic core bar and wrapped conductor lines are tightly interlinked, so that leakage flux and electromagnetic interference are minimized. For an inductor size of 4 mm/spl times/1 mm/spl times/130 /spl mu/m thickness having 33 turns of multilevel coils, the achieved inductance is approximately 0.4-0.1 /spl mu/H at 1 kHz-1 MHz, corresponding to a core permeability of approximately 800. The measured dc resistance of the conductor lines is approximately 0.3 /spl Omega/. Since this inductive component shows favorable magnetic characteristics as well as electrical properties, it is potentially very useful as a basic inductive component in applications for magnetic microsensors, microactuators, and micromagnetic power devices such as a dc/dc converter.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Thermal effects in magnetic microsensor modeling

Abstract We present the three-dimensional vector equations governing carrier and heat transport in a semiconductor by drift, diffusion, and thermal diffusion under the influence of a magnetic field. The equations are derived in the framework of Onsager's principles of irreversible, thermodynamics.

Fabrication of atomically sharp tungsten tips

Atomically sharp tungsten tips (&amp;lt;20 Å) have been grown on a silicon substrate by chemical vapor reaction of WF6 with atomically sharp preformed silicon tips. Transmission electron microscope studies show that a thickness of about 50 Å of tungsten is optimum for complete coverage of silicon while retaining atomic sharpness at the tip. The tungsten is nearly amorphous and is porous. These tips have potential applications in vacuum microelectronics as electron emitters and can also be used as electronic and magnetic microsensors and probes.