• High-precision automotive magnetic position sensor is immune to stray magnetic fields (AS5161-HSOP-500)

    AMS is a global leader in the design and manufacture of high performance analog ICs.
    The AMS AS5161 is a contactless Hall-based automotive magnetic position sensor designed for accurate angular measurement over a full 360 degree turn. A sub-range can be programmed to achieve the best output characteristic for the application. A simple diametrical 2-pole magnet rotating on the centre of the IC is required. The magnet may be placed above or below the IC.

    AS5161_Supramagnets

    AS5161-HSOP-500

    The AS5161 is a compact integrated solution which provides the absolute angle measurement with a resolution of 0.09 degrees over a full revolution as PWM output signal. The internal 14-bit core of the AS5161 enables a new programming of the start and stop positions with a resolution of 0.02 degrees to allow the finest system mechanical adjustments. High level of flexibility is assured by the programmability through the UART interface shared with the output pin, to reduce the number of pins in the application. The angular output data can be linearized in the final production to further increase the precision of the measurement. With embedded over-voltage protection and reverse battery protection, the AS5161 can fulfil the most demanding automotive safety standards.

    Typical applications include transmission gearbox position sensors, valve position sensing, contactless potentiometers and chassis ride height control.

  • How AMR Sensors (Magnetic Switches) Works ?

    Outline

    AMR sensor is a sensor using a magnetic resistance value changing according to the strength of the magnetic field.
    It uses together with a magnet.

    AMR: Anisotropic Magneto Resistance

    Because the lineup of sensitivity and the size is wide, you can choose the optimal product according to the usage.

    • There is a product of two types depending on the direction of the magnetic field detection.
      Horizontal direction type: AS-M series
      Vertical direction type: AS-V series
    • There are large variations, such as a package, high accuracy type and a sampling period.
      (low consumption current, high – speed sampling, always drive)

    AMR sensor is independent of magnetic pole. (One output for S or N pole)

    The horizontal detection type has the following features.

    • Compared to Hall IC, our sensor has wide detection area.
      It is more flexible for design. (mount location)
    • AMR sensor is not mechanical components like the lead switch.
      So it holds small size and high reliability.
    Compared to Hall IC, our sensor has wide detection area. It is more flexible for design. (mount location)

    As for vertical detection type, the replacement from Hall IC is possible.

    Applications

    AMR sensor is the best for the usage such as the mobile devices for the noncontact switch.

    Open/Close detection

    • For Mobile phones, Note – size PCs, Digital cameras and more…
    • For Refrigerators, Washing machines and other Home appliances
    • For Security equipments
    Open/Close detection

    Flow meter for boiler (Detection of vane’s rotation)

    Flow meter for boiler (Detection of vane's rotation)

    Pulse encoder (Detection of Ring type Magnet)

    Pulse encoderPulse encoder

    2pieces of Magnetic switches and Ring type Magnet

    Land 2 sensors on the board, one slant 45 deg.
    When the magnet rotates, it can detect rotation and direction depend on 2 sensors detect phase difference.

     

     

    Principle

    Basic characteristic

    • AMR element is made of a perm alloy (Fe, Ni) thin film resistor.
    • It can be same motion, if it reverse N and S of the magnet, because plus side and minus side have symmetry characteristics.
    Operation image in the horizontal detection typeOperation image in the horizontal detection type

    Block diagram

    • AMR sensors incorporate 1 package both AMR element and CMOS IC piggyback type.
    • It designs 3 terminals; VDD, VSS and VOUT.
    • It include sampling circuit to prevent current draw.
    Block diagram

    Chattering prevention

    • Magnetic field has hysteresis to prevent chattering.
      (Chattering is a phenomenon in which an electric signal repeats intermittence by detailed and very quick mechanical vibration, when the point of contact of a relay or a switch changes.)
    • When the magnet approach to the sensor and the magnetic flux density exceeds MOP, VOUT changes from H to L.
    • When the magnet leaves and the magnetic flux density decreases below MRP, VOUT changes from L to H.
    Chattering prevention

     

    Horizontal direction type: Features of AS-M series

    Difference from Hall IC

    Difference from Hall IC
    AMR sensor
    (Horizontal direction type)
    Hall IC
    Detection direction Magnetic
    resistance effect
    Hall effect
    Sensor Material Ni and Fe Si type
    InSb type
    Detection Magnet Field Horizontal Vertical
    Detection area Wide Narrow
    • AMR sensor has wide detection area because AMR sensor can use wide magnetic field.
      More flexible for design (Mount location)
    • It can make up for error of soldering. It can design magnet smaller and flatter than Hall IC.
    Relation between sensor and magnetic fieldRelation between sensor and magnetic field

    Difference from a reed switch

    AS-M series (Horizontal direction type) has the following features compared with a reed switch.

    • Small size and low price
    • Available for low supply voltage
    • It is high reliability against the impact and the fall
    Usage exampleUsage example

     

    Vertical direction type: Features of AS-V series

    • Available at same type magnet as a Hall IC by our original process.
    • Two kinds of packages.
      AS-V20TA-R ⇒ Land compatibility as SOT23 package
      AS-V20NA-R ⇒ Land compatibility as SON4 package

    Vertical direction type: Features of AS-V series

  • AMR vs. GMR Vs. TMR magnetic sensors

    Many companies are working hard in the design, development and fabrication of Anisotropic Magneto-Resistance (AMR), Giant Magneto-Resistance (GMR), and Magnetic Tunneling Junction (MTJ) magnetic thin film sensors.

    Working with a variety of magnetic materials (see table below) AMS deposition techniques achieve optimal conditions (uniformity, composition control, easy/hard axis orientation). The thickness range of these materials spans from <10Å (1nm) for GMR and MTJ applications to >10µ for magnetic shields and flux-concentrators.


    Materials Magnetic Properties Application Deposition Technique Typical Layer Thk.
    NiFe (Permalloy) Soft AMR, GMR sensors Sputtered 10Ǻ – 1000Ǻ
    NiFe (Permalloy) Soft Shields, Poles Plated 1µm – 10µm
    NiFe (45/55) Soft, higher moment Shields, Poles Plated 1µm-10µm
    CoPt Hard, high coercivity Permanent magnets Sputtered 500 Ǻ – 10 µm
    Co ternary alloy Soft, higher moment Shields, Inductors, Poles Sputtered 1 µm – 10 µm
    IrMn, PtMn Anti-ferromagnetic GMR, MTJ sensors Sputtered 50 – 250 Ǻ

    We use several different vacuum deposition tools to deposit a variety of magnetic materials, including the GMR / MTJ cluster disposition system seen below. The metrology equipment for the characterization of magnetic materials includes BH loopers, VSM (Vibrating Sample Magnetometer), MFM (Magnetic Force Microscopy) and RMM (Remanent Moment Magnetization).

     

    Typical AMR sensors transfer curve
    Typical AMR transfer curve

  • What is GMR magnetic sensors ?

    What’s GMR sensor : “Giant Magnetoresistance”?

    The “giant magnetoresistive” (GMR) effect was discovered in the late 1980s by two European scientists working independently: Peter Gruenberg of the KFA research institute in Julich, Germany, and Albert Fert of the University of Paris-Sud .

    In 1988, scientists discovered the “Giant Magneto Resistive” effect – a large change in electrical resistance that occurs when thin stacked layers of ferromagnetic and non-magnetic materials are exposed to a magnetic field. Since then, many companies have sought to develop practical applications for this intriguing technology.

    Although the term “giant” in giant magnetoresistance (GMR) seems incongruous for a nanotechnology device, it refers to a large change in resistance (typically 10 to 20%) when the devices are subjected to a magnetic field, compared with a maximum sensitivity of a few percent for other types of magnetic sensors.

    Nanotechnology Structure
    GMR structures are ferromagnetic alloys sandwiched around an ultrathin nonmagnetic conducting middle layer:

    GMR Without Applied Field

    (A) is a conductive, nonmagnetic interlayer. Magnetic moment in alloy (B) layers face opposite directions due to antiferromagnetic coupling. Resistance to current (C) is high. The nonmagnetic conducting layer is often copper. Copper is normally an excellent conductor, but when it is only a few atoms thick, electron scattering causes copper’s resistance to increase significantly. This resistance changes depending on the relative orientation of electron spins surrounding the conducting layer

    Applying an external magnetic field (D) overcomes antiferromagnetic coupling, aligning magnetic moments in alloy (B) layers:

    GMR With Field Applied

    GMR With Field Applied

    Such exposure changes the device resistance so the structure can be used to sense an external field. Practical devices are often made of multiple layers of alternating magnetic and nonmagnetic layers to improve sensitivity.

    The Quantum Mechanics of GMR
    To understand how GMR works on the atomic level, consider the following analogies: If a person throws a ball (analogous to a conduction electron) between two sets of rollers turning the same direction (analogous to parallel spin-aligned magnetic layers), the ball tends to go through smoothly. But if the top and bottom rollers turn in opposite directions, the ball tends to bounce and scatter. Alternatively, the GMR effect may be compared to light passing through polarizers. When the polarizers are aligned, light passes through; when their optical axes are rotated with respect to each other, light is blocked.

    The resistance of metals depends on the mean free path of their conduction electrons, which, in GMR devices, depends on the spin orientation. In ferromagnetic materials, conduction electrons either spin up when their spin is parallel to the magnetic moment of the ferromagnet, or spin down when they are antiparallel. In nonmagnetic conductors, there are equal numbers of spin-up and spin-down electrons in all energy bands. Because of the ferromagnetic exchange interaction, there is a difference between the number of spin-up and spin-down electrons in the conduction bands. Quantum mechanics dictates that the probability of an electron being scattered when it passes into a ferromagnetic conductor depends on the direction of its spin. In general, electrons with a spin aligned with the majority of spins in the ferromagnets will travel further without being scattered.

    In a GMR spintronic device, the first magnetic layer polarizes the electron spins. The second layer scatters the spins strongly if its moment is not aligned with the polarizer’s moment. If the second layer’s moment is aligned, it allows the spins to pass. The resistance therefore changes depending on whether the moments of the magnetic layers are parallel (low resistance) or antiparallel (high resistance).

    Optimal layer thicknesses enhance magnetic-layer antiparallel coupling, which is necessary to keep the sensor in the high-resistance state when no field is applied. When an external field overcomes the antiparallel coupling, the moments in the magnetic layers align and reduce the resistance. If the layers are not the proper thickness, however, the coupling mechanism can destroy the GMR effect by causing ferromagnetic coupling between the magnetic layers.

    For spin-dependent scattering to be a significant part of the total resistance, the layers must be thinner (to a magnitude of several nanometers) than the mean free path of electrons in most spintronic materials. A typical GMR medical sensor has a conducting layer approximately 3 nm (or one ten-millionth of an inch) thick. For reference, that is less than 10 atomic layers of copper, and less than one ten-thousandth the thickness of a piece of tissue paper.

    Spintronic GMR Bridge Sensors
    A photomicrograph of a typical GMR magnetic sensor, also known as a magnetometer is shown below:

    A spintronic sensor bridge

    The thin metal-alloy films are vacuum deposited onto silicon wafers. Other manufacturing steps include thermal annealing, magnetic annealing, and photolithography. GMR resistors are generally patterned into serpentine resistors using photolithography. The serpentine configuration maximizes resistance per unit area. Maximizing resistance minimizes power consumption when the sensor is sampled.

    In a typical sensor, four GMR resistors are configured as a Wheatstone bridge. A bridge configuration provides an easy-to-use voltage output that is proportional to the magnetic field applied but insensitive to any variations in the absolute resistance of the GMR device.

    Two of the resistors are sensing resistors; the other two are reference resistors. The reference resistors are covered by a nickel-iron magnetic shield that measures 0.0004 in. thick. In response to an external magnetic field, the exposed sensing resistors decrease in electrical resistance while the reference resistors remain unchanged, causing a voltage at the bridge output.

    The shield may also serve as a flux concentrator for the sensing resistors, increasing the sensitivity of the device and improving its spatial specificity. Because of the small geometries of spintronic sensors, flux concentration is especially effective and can increase sensitivity up to a factor of 100.

    GMR Electrical Characteristics
    A typical GMR sensor output is shown below:

    GMR Electrical Characteristics

    When a magnetic field produces no further change in resistance, it is deemed saturated. The change in resistance from no field to saturation, usually expressed as a percentage of saturated resistance, is known as magnetoresistance. Hysteresis is the separation between positive- and negative-going curves.

    Although this diagram shows an omnipolar response, meaning it has the same change in resistance for a directionally positive or directionally negative magnetic field, bipolar sensors have recently become available. Bipolar sensors maintain an operate point with the application of a negative (South) magnetic field, and a release point with the application of a positive (North) magnetic field. The part is ideal for use with magnetic encoders that have alternating North/South poles.

  • Hall AMR GMR TMR magnets sensor

    Magnetic sensors are used in vehicle detection, traffic management solutions, and automotive navigation applications.

    Parameter
    Consumption
    ( mA )
    Size ( mm )
    Sensitivity
    ( mV/V/Oe )
    Linearity Range
    ( Oe )
    Operation Temperature
    ( ℃ )
    Hall
    4 – 10
    0.5 x 0.5
    0.05
    0.3 – 1000
    <150
    AMR
    4
    1 x 1
    3
    0.001 – 10
    <150
    GMR
    4
    1 x 1
    2
    2 – 30
    <150
    TMR
    0.002
    0.5 x 0.5
    30
    0.0001 – 100
    <260
  • What is TMR magnetic sensor ?

    A tunnel junction TMR magnetoresistive sensor formed on layers having nitrogen interspersed therein. The nitrogenation of the layers on which the sensor is deposited allows the sensor layers to have very smooth, uniform surfaces.

    The heart of a computer’s long-term memory is an assembly that is referred to as a magnetic disk drive. The magnetic disk drive includes a rotating magnetic disk, write and read heads that are suspended by a suspension arm adjacent to a surface of the rotating magnetic disk and an actuator that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The read and write heads are directly located on a slider that has an air-bearing surface (ABS). The suspension arm biases the slider toward the surface of the disk and when the disk rotates, air adjacent to the surface of the disk moves along with the disk. The slider flies on this moving air at a very low elevation (fly height) over the surface of the disk. This fly height can be on the order of Angstroms. When the slider rides on the air bearing, the write and read heads are employed for writing magnetic transitions to and reading magnetic transitions from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.

    The write head includes a coil layer embedded in first, second and third insulation layers (insulation slack), the insulation stack being sandwiched between first and second pole piece layers. A gap is formed between the first and second pole piece layers by a gap layer at an air-bearing surface (ABS) of the write head and the pole piece layers are connected at a back gap. Current conducted to tire coil layer induces a magnetic flux in the pole pieces which causes a magnetic field to fringe out at a write gap at the ABS for the purpose of writing the aforementioned magnetic impressions in tracks on the moving media, such as in circular tracks on the aforementioned rotating disk.

    In recent read head designs a spin valve sensor, also referred to as a giant magnetoresistive (GMR) sensor, has been employed for sensing magnetic fields from the rotating magnetic disk. This sensor includes a nonmagnetic conductive layer, referred to as a spacer layer, sandwiched between first and second ferromagnetic layers, and hereinafter referred to as a pinned layer and a free layer. First and second leads are connected to the spin valve sensor for conducting a sense current therethrough. The magnetization of the pinned layer is pinned perpendicular to the air-bearing surface (ABS) and the magnetic moment of the free layer is biased parallel to the ABS, but is free to rotate in response to external magnetic fields. The magnetization of the pinned layer is typically pinned by exchange coupling with an antiferromagnetic layer.

    The thickness of the spacer layer is chosen to be less than the mean free path of conduction electrons through the sensor. With this arrangement, a portion of the conduction electrons is scattered by the interfaces of the spacer layer with each of the pinned and free layers. When the magnetizations of the pinned and free layers are parallel with respect to one another, scattering is minimal and when the magnetizations of the pinned and free layer are antiparallel, scattering is maximized. Changes in scattering alter the resistance of the spin valve sensor in proportion to cos Θ, where Θ is the angle between the magnetizations of the pinned and free layer’s. In a read mode, the resistance of the spin valve sensor changes proportionally to the magnitudes of the magnetic fields from the rotating disk. When a sense current is conducted through the spin valve sensor, resistance changes cause potential changes that are detected and processed as read back signals.

    More recently, researchers have focused on the development of magnetic tunnel junction (MTJ) sensors, also referred to as tunneling magnetoresistance (TMR) sensors or tunnel valves. Tunnel valves or MTJ/TMR sensors offer the advantage of providing improved signal amplitude as compared with other GMR sensors. MTJ/TMR sensors operate based on the spin dependent tunneling of electrons through a thin, electrically insulating barrier layer. The structure of the barrier layer is critical to optimal MTJ/TMR sensor performance, and certain manufacturing difficulties such as target poisoning during barrier-layer deposition have limited the effectiveness of such MTJ/TMR sensors. Therefore, there is a strong felt need for a magnetic tunnel junction (MTJ) sensor that can provide optimal MTJ/TMR performance, and also, for a practical method of manufacturing such an optimized MTJ/TMR sensor.

    A Magnetic Tunnel Junction (MTJ) structure is essentially a metal-insulator-metal structure in which the metal electrodes are composed for ferromagnetic alloys.  This structure is called an MTJ because a potential applied between the ferromagnetic electrodes induces a tunnel current that is dependent on the relative orientation of the magnetization of the ferromagnetic electrodes on opposite sides of the insulating tunnel barrier.  Thus in effect, it shows a magnetoresistance effect, in which the value of the tunneling magnetoresistance (TMR) is dependent on the relative orientation of the magnetization between the ferromagnetic electrode layers.  In order to take advantage of the TMR effect for sensing purposes, the ferromagnetic electrodes on opposite of the insulating barrier are designed to respond differently to magnetic field so that their differing response produces a large change in resistance in response to an applied magnetic field.  Generally, one layer, called the Pinned Layer (PL) is designed so that its magnetization does not respond to a magnetic field, and the other layer, the Free Layer (FL) is designed so that its magnetization orientation changes readily in response to a magnetic field.   This type of structure using a PL and FL is often called a spin valve.  It can be sued for linear magnetic field sensing, detecting the angle of an applied magnetic field, and for magnetic switching and proximity sensing applications.