WO2005085890A2 - Detecteur de champ magnetique - Google Patents

Detecteur de champ magnetique Download PDF

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Publication number
WO2005085890A2
WO2005085890A2 PCT/GB2005/000741 GB2005000741W WO2005085890A2 WO 2005085890 A2 WO2005085890 A2 WO 2005085890A2 GB 2005000741 W GB2005000741 W GB 2005000741W WO 2005085890 A2 WO2005085890 A2 WO 2005085890A2
Authority
WO
WIPO (PCT)
Prior art keywords
elements
magnetic field
sensing structure
field sensing
network
Prior art date
Application number
PCT/GB2005/000741
Other languages
English (en)
Other versions
WO2005085890A3 (fr
Inventor
Peter Littlewood
Meera Parish
Original Assignee
Cambridge University Technical Services Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from US10/791,090 external-priority patent/US20050190507A1/en
Priority claimed from GB0407920A external-priority patent/GB0407920D0/en
Application filed by Cambridge University Technical Services Limited filed Critical Cambridge University Technical Services Limited
Publication of WO2005085890A2 publication Critical patent/WO2005085890A2/fr
Publication of WO2005085890A3 publication Critical patent/WO2005085890A3/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/02—Measuring direction or magnitude of magnetic fields or magnetic flux
    • G01R33/06—Measuring direction or magnitude of magnetic fields or magnetic flux using galvano-magnetic devices
    • G01R33/09—Magnetoresistive devices

Definitions

  • the invention relates to magnetic field sensors and particularly although not exclusively to low-field sensors. Some embodiments also relate to high-field sensors.
  • the silver chalcogenides are narrow-gap semiconductors, so conventional theories predict that the magnetoresistance should saturate at large fields, unlike what is observed. Moreover, the silver chalcogenides possess no magnetic moments, therefore the magnetoresistance cannot be spin-mediated like the colossal magnetoresistance of the manganites. Polycrystalline metals may also exhibit a linear magnetoresistance, but this behaviour requires the presence of open Fermi surfaces which is not the case here.
  • US6353317 describes a magnetic field sensor comprising special semiconductor/metal nano-composite structures produced using island lithography.
  • WO01/21414 also discloses sensor structures comprising a combination of semiconducting and conducting materials.
  • the invention provides a magnetic field sensor which allows fine control of the magnetoresistive response and is easy to manufacture. Typical embodiments are expected to show a large, substantially linear, magnetoresistive response.
  • a magnetic field sensing structure comprising a first electrode and a second electrode, the first and second electrodes being electrically coupled via a network comprising a plurality of discrete semiconducting elements providing a plurality of possible current paths between the electrodes. It is expected that commercial embodiments of the invention may achieve a ten percent effect at 100 gauss, that is of the same order as current read heads for hard disk drives, but with much reduced manufacturing costs. Furthermore, sensors according to embodiments of the invention typically show a linear non- saturating response would thus also be suitable for high field applications, or applications where a graded or quantitative output is necessary.
  • the absence of any metallic parts in some embodiments of the invention allow the sensor to be used in conditions where ferromagnetic materials must be excluded, e.g. high field applications such as in medical scanners.
  • Figure 1 is a schematic illustration of a first embodiment
  • Figure 2a and b are schematic illustrations of different implementations of the first embodiments
  • Figure 3a to e are schematic illustrations of a second embodiment
  • Figure 4 is a schematic illustration of a third embodiment
  • Figure 5 is schematic illustration of a sensor or read head embodying a sensing structure according to the first, second or third embodiments.
  • Figure 6 is a schematic illustration of a fourth embodiment of the invention.
  • a sensor incorporating a manufactured sensing structure as described in the several embodiments below provides a low cost, high sensitivity magnetic field sensor, which is particularly suitable to detect low intensity fields. However, given the potential for a sensor which does not saturate at high magnetic fields, such a sensor would be equally suitable for high field applications.
  • a first embodiment shown in figure 1, comprises a rectangular 4x4 sensing structure or array 10 of discrete disk-shaped semiconductor elements 12, which are disposed on a substrate (not shown).
  • the elements 12 overlap to a small extent to form connections 14 between elements 12.
  • Electrodes 16, 18 apply a voltage across the array. These electrodes are of metal or some other substance which forms a good ohmic contact with the elements 12.
  • the electrodes connect to each of the disks on opposing sides of the array, as shown, but in an alternative arrangement (not shown) the electrodes may connect only to some but not all of the opposing elements.
  • a potential difference is established between the electrodes 16, 18 and the overall resistance of the structure determined in any convenient way, for example by measuring the current that flows for a given potential difference and calculating the resistance using Ohm's law.
  • One of the electrodes may, but need not, be grounded.
  • it is not essential to use the value of the potential difference which has been established between the electrodes. Instead, separate voltage probes (not shown) applied to two or more individual elements may be used; such an arrangement avoids the problem of contact potentials.
  • the applicant has discovered, surprisingly, that the measured resistance across the array varies substantially linearly with the strength of a magnetic field applied to the array, and furthermore that this linearity does not appear to saturate even when extremely high magnetic fields are applied. Further numerical experimentation has shown that the magnetoresistive response does not saturate when the number of columns between the electrodes is even, but that the response does saturate when the number is odd.
  • the resistance changes with applied field as a result of the current taking a variety of differing paths between the electrodes.
  • the current might preferentially take a first path 100 as shown in figure 1, but at high fields this might become less advantageous because of differing individual element responses to the applied field, and a second path 102 may then be preferred.
  • the preferred path may change depending upon how (if at all) each of the individual elements reacts in the presence of the field, and in particular the extent to which each element manifests a Hall effect voltage.
  • the elements 12 need not be disk-shaped, nor does their interconnectivity have to be as shown in figure 1.
  • the elements may be identical or alternatively they may differ in at least one electrical property such as resistance or mean free path.
  • each element will of course have four contacts with adjacent elements.
  • Such an embodiment could, of course, equally well have different numbers of elements along pe ⁇ endicular edges (e.g. 4x3) as well as the equal numbers (4x4) shown in figure 1.
  • 4x3 the equal numbers shown in figure 1.
  • disk shaped elements are arranged on a hexagonal grid, each element will then have six contacts with adjacent elements.
  • different numbers of connections can be achieved.
  • the number of elements involved may potentially be quite small. So, for example, where a rectangular grid arrangement is employed, grids as small as 1x2, 2x2 or 1x3 may be envisaged (the first figure in each case representing the number of rows between the electrodes).
  • the elements 22 in figure 2a use a diamond shape with four equal sides, and provides an arrangement in which each element 22 has four connections 24 with adjacent elements.
  • a connection scheme with three connections per element can be established in a rectangular grid as shown in figure 2b. This is achieved by an arrangement where the long sides 28b point in alternating directions from one row of the grid to the next.
  • the elements are not restricted to being the same size or shape and thus any desirable pattern of connectivity is achievable by selecting the shapes of the elements accordingly.
  • the elements are formed on the substrate using standard semiconductor technology, such as lithography.
  • the size of the elements is preferably less than l ⁇ m, for example 0.1 ⁇ m. Smaller feature sizes of 10 to 20nm could be achieved using self-assembling quantum dot arrays.
  • the size of each element is preferably larger than the mean free paths of charge carriers.
  • Any suitable semiconductor material of high carrier mobility can be used, e.g. indium antimonide, gallium arsenide, or even silicon.
  • the sensing structure could even be formed by constructing the elements from a metal layer, although metal may be a less desirable material due to its small Hall effect.
  • Each individual element may be homogenous in its physical properties, or alternatively each element could, in itself, be inhomogeneous.
  • the physical properties of the elements may differ one from another or alternatively the properties of each of the elements may be substantially the same.
  • one of the particular benefits of the invention lies in the ability to tune the magnetoresistive response during manufacture by selecting appropriate physical properties of the elements in order to achieve a particular desired magnetoresistive response.
  • Appropriate physical properties to be selected include (but are not limited to) material, resistance, carrier mobility, size, shape and so on.
  • the thickness i.e. the dimension at the elements 12 perpendicular to the substrate
  • radius or other geometric factor of each element can be tuned or selected by using different lithographic designs, or the carrier mobility of the elements can be tuned by doping of the elements.
  • Each of these manipulations will affect the magnetoresistive of the individual elements and can thus be used to tune the overall response curve.
  • the magnetoresistive response can be tuned by selecting the number of elements and their interconnection topology. By increasing the number of elements in the sensing structure 10, linearity at low fields of the magnetoresistance response is typically increased.
  • the characteristic field at which the response switches from a quadratic response at low fields to a linear response at higher fields
  • the characteristic field at which the response switches from a quadratic response at low fields to a linear response at higher fields
  • the spread of the mobility distribution (e.g. a Gaussian distribution) is larger than the average of the mobility distribution, simulations have shown that the characteristic field is given by the inverse of the spread of the mobility distribution rather than by the average mobility.
  • "Spread" here, may refer to any width characteristic of the distribution e.g. the standard deviation or any multiplicative factor thereof, or to the difference between the greatest value of an element within the network and the least.
  • the magnetoresistive response of the sensing structure 10 can be tuned by selecting characteristics of the elements 12, and by selecting the number, arrangement and connection patterns of elements 12.
  • An infinite number of arrangements and connection patterns is clearly possible, subject only to the constraint that there must exist current paths between the electrodes 16 and 18 that allow current components that are both parallel and pe ⁇ endicular to the electrodes. There must, thus, be at least two elements in parallel, but implementations with four elements, between 5 to 100 elements, or even with more than 100 elements can also be envisaged. In other arrangements (not shown) there may be more than two electrodes 16, 18 and/or these may be positioned other than as shown in figure 1. For example, four electrodes may be provided, along the respective edges of the structure; this allows more flexibility in the application of different voltages to the device.
  • Figures 3a to 3e show a variety of second embodiments.
  • the elements 12 do not overlap, but instead form separate islands.
  • the elements are thus spaced apart and connected by bridges 32 (as shown in figure 3a) of conducting material.
  • bridges 32 may consist of for example wires or tracks of metal or of some suitably doped semiconductor materials.
  • the second embodiment is, in its functioning to a large extent equivalent to the first embodiment and the same considerations regarding the tuning of the magnetoresistive response still apply.
  • the looser arrangement of elements 12 and the independence of the connection scheme from the geometrical shape of the elements allows for a more flexible design of connection patterns.
  • Figures 3a to c show connection patterns with respectively 4,3 and 6 connections per element; these could of course also be achieved by overlapping elements that are disk shaped or diamond shaped.
  • the connection pattern in figure 3d (two connections per element) and the connection pattern in figure 3e (variable number of connections per element) would be impossible to achieve with overlapping elements unless different element shapes are used.
  • a controllable element 40 (shown in figure 4) is used in conjunction with the structures of the first, second or fourth embodiments.
  • the element 40 comprises an element 12, as described above, and, additionally a a control 42 (for example a control electrode) associated with the element 12.
  • the control 42 may allow electrons to be injected or extracted from element 12 thus providing real-time tuning of the carrier density of the element 40.
  • controllable elements 40 of this type By providing a structure that has one or more controllable elements 40 of this type (or even providing a structure that is wholly made up of such elements), and by altering the physical properties of the element(s) in real time, one can control and adjust the overall magnetoresistive response of the sensing structure wlrier the sensor is in use.
  • the controls 42 could be used to adjust carrier mobility and/or to apply a variable voltage to individual elements.
  • the respective controls 42 of the elements 40 may be addressed in any conventional manner, for example by means of a metallic or non-metallic control grid (not shown) which overlies or otherwise connects to the individual elements.
  • the controls 42 comprise individually addressable gating structures which apply controllable gate voltages. Such structures may be created by any convenient means - for example using a surface metal pad with a separately controlled voltage bias across an oxide or insulating barrier.
  • the controls 42 could comprise optically-gated structures.
  • Other possibilities include epitaxially grown structures - by MBE, CVD, MOVPD etc., two-dimensional electron gas structures, MOS capacitor structures and MIS structures.
  • a sensor inco ⁇ orating a sensing structure according to the first or second embodiment is shown in figure 5.
  • the sensor 50 comprises a measuring arrangement 52 connected by lead 54 to the electrodes 16 and 18 (not shown in figure 5) of sensing structure 10.
  • the sensor 50 further comprises a mobility controller 56 which is connected by leads 58 to a control grid (not shown) which is coupled to the mobility control connections 42 of the elements of the sensing structure 10.
  • Mobility controller 56 is used to tune the magnetoresistive response of the sensor in real time and, potentially, in use by injecting or extracting electrons from the elements 12 of the structure 10.
  • a sensor as described above may be used in a magnetic read-head, for example in a hard-disk drive.
  • the first, second and third embodiments all provide two-dimensional sensing structures.
  • a three-dimensional sensing structure may be provided.
  • such a sensing structure is provided by means of a three-dimensional stacking 60 of three-dimensional elements 62, as shown in figure 6.
  • Such elements may be in the shape of a sphere or octahedron and the stacking may be for example, a simple cubic stacking.
  • Figure 6 shows a simple cubic stacking 60 in which elements 62 are overlapping in six locations, thus providing six contacts per element.
  • other element shapes, configurations and connection topologies may be envisaged.

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  • Physics & Mathematics (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Hall/Mr Elements (AREA)
  • Measuring Magnetic Variables (AREA)
  • Magnetic Heads (AREA)

Abstract

L'invention concerne une structure de détection de champ magnétique utilisant la magnétorésistance comme signal. Cette structure comprend un réseau non homogène d'éléments semi-conducteurs interconnectés pouvant présenter différentes formes. Le réglage ou la sélection des propriétés physiques des éléments permet d'ajuster l'ensemble de la réponse magnétorésistive de sorte qu'elle soit importante et sensiblement linéaire sur une plage donnée de champs magnétiques. Ces structures de détection peuvent être utilisées, par exemple, dans des têtes de lecture de disques durs. D'autres modes de réalisation peuvent trouver une application dans la détection de champs de niveau bas ou élevé, certains de ces modes de réalisation présentant un intérêt particulier lorsque la stabilité thermique constitue un facteur important.
PCT/GB2005/000741 2004-03-01 2005-02-28 Detecteur de champ magnetique WO2005085890A2 (fr)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
US10/791,090 2004-03-01
US10/791,090 US20050190507A1 (en) 2004-03-01 2004-03-01 Magnetic field sensor
GB0407920.8 2004-04-07
GB0407920A GB0407920D0 (en) 2004-04-07 2004-04-07 Magnetic field sensor

Publications (2)

Publication Number Publication Date
WO2005085890A2 true WO2005085890A2 (fr) 2005-09-15
WO2005085890A3 WO2005085890A3 (fr) 2005-12-01

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PCT/GB2005/000741 WO2005085890A2 (fr) 2004-03-01 2005-02-28 Detecteur de champ magnetique

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3731007A (en) * 1971-04-19 1973-05-01 Denki Onkyo Co Ltd Magnetic head having a magneto-resistive bridge circuit
EP0375107A2 (fr) * 1988-12-23 1990-06-27 General Motors Corporation Magnétorésistance
EP1052520A1 (fr) * 1999-05-10 2000-11-15 Hitachi Europe Limited Dispositif magnétoélectrique

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3731007A (en) * 1971-04-19 1973-05-01 Denki Onkyo Co Ltd Magnetic head having a magneto-resistive bridge circuit
EP0375107A2 (fr) * 1988-12-23 1990-06-27 General Motors Corporation Magnétorésistance
EP1052520A1 (fr) * 1999-05-10 2000-11-15 Hitachi Europe Limited Dispositif magnétoélectrique

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
PARISH M M ET AL: "Non-saturating magnetoresistance in heavily disordered semiconductors" NATURE NATURE PUBLISHING GROUP UK, vol. 426, no. 6963, 13 November 2003 (2003-11-13), pages 162-165, XP002330399 ISSN: 0028-0836 *

Also Published As

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