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WO2001027592A1 - Detecteur de perles magnetisables - Google Patents

Detecteur de perles magnetisables Download PDF

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Publication number
WO2001027592A1
WO2001027592A1 PCT/US2000/028469 US0028469W WO0127592A1 WO 2001027592 A1 WO2001027592 A1 WO 2001027592A1 US 0028469 W US0028469 W US 0028469W WO 0127592 A1 WO0127592 A1 WO 0127592A1
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WO
WIPO (PCT)
Prior art keywords
magnetic field
magnetoresistors
bead
field sensor
layer
Prior art date
Application number
PCT/US2000/028469
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English (en)
Inventor
Mark C. Tondra
John M. Anderson
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Nve Corporation
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Publication date
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Publication of WO2001027592A1 publication Critical patent/WO2001027592A1/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/72—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables
    • G01N27/74—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables of fluids
    • G01N27/745—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables of fluids for detecting magnetic beads used in biochemical assays
    • 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 present invention relates to the detection of magnetizable beads and, more particularly, to detection of magnetizable beads in connection with biological and chemical assays.
  • binding assays which are based on use of certain binding molecules to capture through specific chemical bondings the molecules selected for detection.
  • specific bondings include polynucleic acid bondings or hybidizations involving DNA and RNA, antibody to antigen bondings, and various ligand to various receptor bondings.
  • the detection of the selected molecules may be of primary interest in its own right, but may instead be of primary interest in indicating the presence of some other analyte molecule, species or organism.
  • One arrangement for implementing such a detection scheme is to provide a sensor in which the binding molecules are relatively strongly attached to a solid substrate.
  • An assay is begun by applying a sample solution containing various kinds of molecules possibly including the molecules selected for detection to the sensor along with label molecules attached to label beads (or particles) also present in the sample solution or in a supplemental solution concurrently also applied.
  • the binding molecules through specific bondings, or recognition events, capture the selected molecules or the label molecules attached to label beads, or both, and thereafter hold them at the corresponding capture sites, i.e. the sites of the binding molecules undergoing such a bonding.
  • Label molecules on label beads are needed so that the occurrence of a recognition event leads to some measurable signal to indicate that a selected molecule was found present.
  • One kind of label bead for doing this is a paramagnetic material bead having magnetizations that depend on externally applied magnetic fields. Application of such an externally applied field forcefully draws away any unbound label beads leaving the bound label beads at the capture sites while also magnetizing those bound label beads. Magnetic field detectors at the capture sites must sense the anomalies introduced into the externally applied field by the presence of bound label beads to produce the desired signals indicating the number of, and possibly the location of, such bound label beads. From this information the number of selected molecules, and kinds thereof, in the sample solution can be determined.
  • Such label beads can range in magnetic material composition from pure ferromagnetic material (e.g. permalloy) to small percentages of paramagnetic material encapsulated in plastic or ceramic spheres.
  • label beads are typically coated with a chemical or biological species that selectively binds to the selected molecules in an analyte of interest including DNA, RNA, viruses, bacteria, microorganisms, proteins, etc. to define the assay function, or the kind of recognition events, to be associated with that bead.
  • the label beads must typically be very small, that is, on the order of a few to tens of nanometers (nm) up to maybe a hundred or so or even up to a few microns in some instances. As a result the anomalies in an externally applied field will be very small. Thus, there is a desire for suitable magnetic field detectors for use with such beads.
  • the present invention provides a ferromagnetic thin-film based magnetic field detection system used for detecting the presence of selected molecular species.
  • the system has a magnetic field sensor supported on a substrate with a binding molecule layer positioned on a side thereof capable of selectively binding to the selected molecular species.
  • the magnetic field sensor is substantially covered by an electrical insulating layer which in some embodiments has a recess therein adjacent to the sensor in which the binding molecule layer is provided.
  • An electrical interconnection conductor is supported on the substrate at least in part between the sensor and the substrate in some embodiments, and is electrically connected to the sensor.
  • the magnetic field sensor can be provided in a bridge circuit, and can be formed by a number of interconnected individual sensors located adjacent to the binding molecule layer.
  • Figure 1 shows a coordinate definition schematic diagram
  • Figure 2 shows a magnetizable sphere based magnetic response field schematic over a structure
  • Figure 3 shows a direction lines schematic for a magnetizable sphere in a uniform externally applied field
  • Figure 4 shows field magnitude value bands for the field of Figure 3 at a selected plane
  • Figure 5 shows an alternative magnetizable sphere based magnetic response field schematic over a structure
  • Figure 6 shows a detector device portion embodying the present invention
  • Figure 7 shows an electrical schematic diagram providing a representation of Figure 6
  • FIGS. 8 and 9 show layer diagrams of a detector device portion embodying the present invention
  • Figure 10 shows a detector device portion embodying the present invention
  • Figure 11 shows a layer diagram of a detector device portion embodying the present invention
  • Figure 12 shows a graph having a plot representing performance of a component used with the present invention
  • Figures 13, 14 and 15 show detector device portions embodying the present invention
  • Figures 16 and 17 show layer diagrams of a detector device portion embodying the present invention
  • FIGS 18, 19 and 20 show detector device portions embodying the present invention. DETAILED DESCRIPTION
  • the need for a very sensitive magnetic field detector follows from the smallness of the label beads and that the field anomalies caused thereby in an otherwise more or less uniform externally applied magnetic field are very localized in roughly decaying as 1/r 3 , where r is the magnitude of the distance from the center of a bead. Because of this highly localized field, only the sensor structure within about one bead diameter sees an appreciable magnetic field effect. Yet, of course, the largest signal possible from a given label bead is desired without suffering nonlinear effects due to bead to bead interactions.
  • the applied field disruption from a label bead that is detected by a sensor is proportional to the magnetization of that bead.
  • paramagnetic beads have either a small, or are entirely devoid of, remnant magnetization (i.e., the magnetization remaining in the bead after an externally applied magnetic field is removed). Consequently, a magnetic detector arrangement requires an additional externally applied magnetic field to magnetize the beads used in any assay.
  • the detector design must be such that detection can take place in an externally applied magnetic field optimal for detection, but not have the detection sensor response saturated, and not mask the field anomaly provided by the presence of a label bead.
  • ⁇ m is the dimensionless magnetic susceptibility.
  • the entities "magnetizable beads" is defined in terms of the susceptibility ⁇ m . While ⁇ m can be measured for any material, only some materials have values substantially different from zero ( ⁇ m of empty space is zero).
  • a paramagnetic material has a single-valued ⁇ m just greater than zero, typically -0.001
  • a ferromagnetic material has a multivalued ⁇ m (due to hysteresis) that is much larger than zero (typically - 1 ).
  • larger values for ⁇ m lead to larger signals at the detector.
  • ferromagnetic particles have a tendency to agglomerate because of magnetic attraction to one another (which potentially ruins an assay) and the multivalued nature of ⁇ m for such material leads to difficulties in quantification of surface coverage. Consequently, the typical assay employs a paramagnetic material magnetizable bead with as large a ⁇ m as possible without causing agglomeration.
  • this dipole field will have no azimuthal angular dependence and can be represented by just two vector components. These two components of the dipole field at
  • H r X m H app (8 ⁇ /3)_(a 3 /r 3 ) cos( ⁇ ), and
  • H ⁇ ⁇ m H app (4 ⁇ /3)_(a 3 /r 3 ) sin( ⁇ )
  • H tota H app [1 - ⁇ m ( ⁇ /6)].
  • a practical superparamagnetic bead (having a magnetization in a magnetic field much greater than ordinary paramagnetic material) has a value for ⁇ m around 0.05, so the total field at magnetic field detector structure 11 would be on the order of
  • H tota . H app [1 - 0.05( ⁇ /6)] * (0.97)H app .
  • the effect of bead 10 is thus to provide an anomaly in the externally applied field that has the effect of attenuating the total applied field at magnetic field detector structure 11 by about 3%, a change in field value from the value of the externally applied field within the range of detectability of the sensors to be described below.
  • a suitable arrangement for magnetic field detector structure 11 can be advantageouslyfabricated using ferromagnetic thin- film materials based on magnetoresistive sensing of magnetic states, or magnetic conditions, thereabout.
  • Such devices may be provided on a surface of a monolithic integrated circuit to provide convenient electrical interconnections between the device and the operating circuitry therefor in the integrated circuit chip.
  • operating external magnetic fields can be used to vary the angle of the magnetization vector in such a film portion with respect to the easy axis of that film portion which comes about because of an anisotropy therein typically resulting from depositing the film in the presence of a fabrication external magnetic field oriented in the plane of the film along the direction desired for the easy axis in the resulting film.
  • operating external magnetic fields can vary the angle to such an extent as to cause switching of the film magnetization vector between two stable states which occur as magnetizations oriented in opposite directions along that easy axis.
  • the state of the magnetization vector in such a film portion can be measured, or sensed, by the change in resistance encountered by current directed through this film portion.
  • the resistance in the plane of a ferromagnetic thin-film is isotropic with respect to the giant magnetoresistive effect, rather than depending on the direction of a sensing current therethrough as for the anisotropic magnetoresistive effect, depends on the cosine of the angle between magnetizations in the two ferromagnetic thin-films on either side of an intermediate layer.
  • the electrical resistance through the "sandwich" or superlattice is lower if the magnetizations in the two separated ferromagnetic thin-films are parallel than it is if these magnetizations are antiparallel, i.e. directed in opposing directions.
  • the also present anisotropic magnetoresistive effect in very thin- films is considerably reduced from the bulk values therefor in thicker films due to surface scattering, whereas very thin-films are a fundamental requirement to obtain a significant giant magnetoresistive effect.
  • the giant magnetoresistive effect can be increased by adding further alternate intermediate and ferromagnetic thin-film layers to extend the "sandwich" or superiattice structure.
  • the giant magnetoresistive effect is sometimes called the "spin valve effect" in view of the explanation that a larger fraction of conduction electrons are allowed to move more freely from one ferromagnetic thin-film layer to another if the magnetizations in these layers are parallel than if they are antiparallel with the result that the magnetization states of the layers act as sort of a valve.
  • These magnetizations results often come about because of magnetic exchange coupling between the ferromagnetic thin-films separated by the intermediate layers, these intermediate layers typically formed from a nonferromagnetic transition metal.
  • the effect of the exchange coupling between the ferromagnetic thin-film layers is determined to a substantial degree by the thickness of such an intermediate layer therebetween.
  • the layer coupling can be of zero value between extremes of such oscillations.
  • Exhibiting the giant magnetoresistive effect in a superiattice structure, or in an abbreviated superiattice structure formed by a three layer "sandwich" structure, requires that there be arrangements in connection therewith that permit the establishment alternatively of both parallel and antiparallel orientations of the magnetizations in the alternate ferromagnetic thin-film layers therein.
  • One such arrangement is to have the separated ferromagnetic thin-films in the multilayer structure be antiferromagnetically coupled but to a sufficiently small degree so that the coupling field can be overcome by an external magnetic field.
  • Another arrangement is to form the ferromagnetic thin-film layers with alternating high and low coercivity materials so that the magnetization of the low coercivity material layers can be reversed without reversing the magnetizations of the others.
  • a further alternative arrangement is to provide "soft" ferromagnetic thin-films and exchange couple every other one of them with an adjacent magnetically hard layer (forming a ferromagnetic thin-film double layer) so that the ferromagnetic double layer will be relatively unaffected by externally applied magnetic fields even though the magnetizations of the other ferromagnetic thin-film layers will be subject to being controlled by such an external field.
  • One further alternative arrangement, related to the first, is to provide such a multilayer structure that is, however, etched into strips such that demagnetizing effects and currents in such a strip can be used to orient the magnetizations antiparallel, and so that externally applied magnetic fields can orient the magnetizations parallel.
  • parallel and antiparallel magnetizations can be established in the ferromagnetic thin-films of the structure as desired in a particular use.
  • Such a structure must be fabricated so that any ferromagnetic or antiferromagnetic coupling between separated ferromagnetic films is not too strong so as to prevent such establishments of film magnetizations using practical interconnection arrangements.
  • a magnetic field sensor suited for fabrication with dimensions of a few microns or less can be fabricated that provides a suitable response to the presence of very small external magnetic fields and low power dissipation by substituting an electrical insulator for a conductor in the nonmagnetic layer.
  • This sensor can be fabricated using ferromagnetic thin-film materials of similar or different kinds in each of the outer magnetic films provided in a "sandwich" structure on either side of an intermediate nonmagnetic layer which ferromagnetic films may be composite films, but this insulating intermediate nonmagnetic layer permits electrical current to effectively pass therethrough based primarily on a quantum electrodynamic effect "tunneling" current.
  • This "tunneling" current has a magnitude dependence on the angle between the magnetization vectors in each of the ferromagnetic layers on either side of the intermediate layer due to the transmission barrier provided by this intermediate layer depending on the degree of matching of the spin polarizations of the electrons tunneling therethrough with the spin polarizations of the conduction electrons in the ferromagnetic layers, the latter being set by the layer magnetization directions to provide a "magnetic valve effect".
  • Such an effect results in an effective resistance, or conductance, characterizing this intermediate layer with respect to the "tunneling" current therethrough.
  • a sandwich type e.g. 35A NiFeCo / 15 CoFe / Cu 35 / 15 CoFe / 35 NiFeCo
  • a pinned sandwich e.g. 35A NiFeCo / 15 CoFe / Cu 35 / 40 CoFe / 100 IrMn, also called a spin valve
  • AMR Anisotropic Magnetoresistive
  • the key for all of these will be to get the beads close to the sensitive layer or layers, and to magnetically bias the magnetoresistors such that they give maximum sensitivity to the presence of the beads.
  • Another enhancement to the sensing material is to give it "hard edges" by oxidizing the edges, pinning them with some antiferromagnetic material, or constructing them so that the two magnetic layers contact each other at the edge of the resistor stripe. Resistors prepared this way will have lower hysteresis in the range of magnetic field magnitudes relevant for the assay.
  • the GMR magnetoresistors typically used here are formed of a succession of thin, alternating magnetic and nonmagnetic metallic layers having aan electrical resistance that is a function of an external magnetic field.
  • This resistance varies with the angle ⁇ between the magnetizations of adjacent magnetic layers with a sin ⁇ dependance, and a typical change from a minimum (i.e., magnetic layers are aligned in parallel) to maximum (i.e., when magnetic layers are aligned antiparallel) resistance is ⁇ 10% of the minimum value.
  • the thin succession of layers is fashioned into sensors as long, thin, rectangular structures but with pointed ends. The observed resistance is then proportional to the length and inversely proportional to the width.
  • a typical sheet resistance is 10 ohms/D.
  • a 1 ⁇ m x 1 ⁇ m GMR detector is positioned directly beneath paramagnetic label bead 10 so that this bead is situated above the upper surface of structure 11 in the z direction.
  • Such a detector would typically have a current therethrough of 5 mA, and a 10 ⁇ to 11 ⁇ resistance change corresponding to H app ranging from 200 Oe to 0 Oe. This represents the 10% resistance change over 200 Oe as indicated in Figure J.
  • the detector voltage then, changes at a rate of 25 ⁇ V / Oe.
  • the maximum H app possible without saturating the sensor is 200 Oe.
  • the field attenuation from the bead modeled above is, on average, 0.05 times the H app .
  • the noise of the detector has two main components: thermal noise and current dependent 1/f noise.
  • the thermal (Johnson) noise for a 10 ⁇ resistor is 0.4 nV / N RZ " .
  • the detector' s intrinsic 1/f noise will typically be two orders of magnitude higher than the thermal noise at 1 Hz, and have a corner frequency at 10 kHz.
  • the relative positional arrangement in Figure 2 of bead 10 and GMR magnetic field detector structure 11 , and the relative orientation of the externally applied magnetic field, can be varied.
  • One variation of the externally applied magnetic field relative orientation is to apply such a field normal to the plane of GMR detector structure 11 as shown in Figure 5.
  • GMR detector structure 11 is about 1000 times more difficult to magnetize in the direction normal to its major surface than in a direction parallel thereto, and so a much larger magnetizing field can be applied to bead 10 and that structure without saturating the GMR magnetoresistors therein.
  • magnetic field detector structure 11 rather being shown by itself with bead 10 directly thereover, is shown over a space between that structure and a another GMR magnetic field detector structure, 11 '.
  • GMR magnetic field detector 11 permits measurement circuit advantages including use of a differential detection, e.g. a bridge circuit detector, arrangement.
  • a bead detection site can be provided with only one magnetoresistor as shown in Figure 2
  • a bridge circuit having two or more magnetoresistors therein offers several benefits including rejection of common mode noise, and provision of first order temperature compensation.
  • one or more of several GMR magnetoresistors provided therein are exposed to possible magnetic field anomalies due the possible presence of bead 10 while the remaining magnetoresistors are not so exposed, or are instead exposed to fields in the opposite direction.
  • Site 10 is provided so that one pair (active) of magnetoresistors, that is, 13 and 14, are in opposite legs of the bridge circuit and subject to the field anomaly introduced by the presence of bead 10 while the other pair (reference) formed of magnetoresistors 15 and 16 is not so subjected even they are also subjected to the externally applied field.
  • the signal developed across the bridge circuit is provided between two metal interconnections signal terminals, 21 and 22, and provided to the signal inputs of a differential amplifier, 23, providing a corresponding differential output signal at its output, 24.
  • magnetoresistors distinguishable as active magnetic field anomaly sensing magnetoresistors and reference magnetic field sensing magnetoresistors during an assay can be accomplished using one or another of several techniques.
  • the simplest way is to provide a covering of a suitable kind such that no bead ever reaches a position sufficiently close to the reference magnetoresistors to magnetically affect them.
  • the detection site can be fabricated, or subsequently modified, so that few or no particles will able to adhere to a surface of, or a surface near, the reference magnetoresistors.
  • a passivation layer over the detector surface can be kept thick over the reference magnetoresistors as in the layer diagram of Figure 8 to substantially separate bead 10 therefrom but kept thin over the active magnetoresistors (the upper or final two layers removed over structure 11 with binding molecule coating 12 there) as shown in the layer diagram of Figure 9 to allow bead 10 to approach closely.
  • Flux concentrators 19 and 20 in the form of permeable material masses can be incorporated into a bridge circuit detection arrangement to concentrate externally applied magnetic fields in and about the active magnetoresistors, as shown in Figures 6 and 9, or a flux concentrator, 25, can be provided to increase and guide magnetic fields developed in the detector itself through providing current through a conductor coil, 26, formed thereabout as shown in Figure 10.
  • both the active pair and the reference pair of magnetoresistors are shown positioned in the gap between two such concentrating flux concentrators, or in the gap between the two ends of an enhancing and guiding flux concentrator, so that they all will be immersed in substantially the same concentrated externally applied magnetic field.
  • the flux concentrator or concentrators are simply acting as a multiplier of the externally applied magnetic field.
  • the multiplication factor is approximately [concentrator length] / [concentrator separation gap].
  • the reference magnetoresistors can be positioned underneath the flux concentrators. They will in such a position experience a much smaller net field (they are substantially shielded from the applied field) than the active magnetoresistors positioned in the concentrator gap (the common mode field rejection is then lost) but they will require no space to be provided for them in the gap.
  • a Si based wafer, 30, which may have monolithic integrated circuitry therein, has a 200 nm layer of substrate Si 3 N 4 , 31 , supported thereon, on which a 1.5 ⁇ m layer of Al is first deposited.
  • This Al layer is patterned using standard photolithography and a reactive ion etch (RIE) to form what will become the interconnections, 32, for the magnetic field detector, or assay, circuit.
  • RIE reactive ion etch
  • a 2.5 ⁇ m (must be at least as thick as the previous Al layer) thick layer of Si 3 N 4 is deposited over the patterned Al. Then, the resulting surface is planarized using chemical mechanical polishing (CMP). The Al interconnections are exposed during the CMP, so that the resulting surface of the wafer has both Al and a Si 3 N 4 base, 33, in it. Both materials are smooth. The GMR magnetic field detector structure material is then deposited.
  • CMP chemical mechanical polishing
  • the succession of alternating magnetic and nonmagnetic metallic thin-film layers in the GMR magnetic field detector structure is formed in a vacuum deposition system using rf diode sputtering.
  • the succession thickness is 10 nm to 40 nm, depending upon the particular structure chosen for use.
  • the thicknesses of individual layers within the succession are controlled to tenths of nanometers.
  • the GMR succession is followed by providing thereon a 10 nm CrSi etch stop layer on which is further provided a 40 nm Si 3 N 4 mask layer.
  • the Si 3 N 4 mask layer is patterned using standard photolithography and an RIE etch.
  • the GMR magnetic field detector structure + etch stop succession is then etched through the resulting Si 3 N 4 mask using an ion mill to leave the GMR magnetic field detector structure 11 magnetoresistors, 34. Most or all of the Si 3 N 4 mask is etched away in the ion mill, and at least some or all of the CrSi layer, 35, below this mask remains on these magnetoresistors. At this point, the GMR magnetic field detector structure 11 magnetoresistors and Al interconnections are complete and can be tested. The GMR magnetoresistors and the Al interconnections are then passivated by providing thereover a thin layer of Si 3 N 4 as a passivation layer, 36.
  • this passivation layer depends upon two things, the step height of the GMR magnetoresistors above the base layer therebelow, and the standoff voltage required between the GMR elements and the bead samples that will be present above the passivation. If some passivation is required and the voltage requirements are minimal, though non-zero ( ⁇ 10 Volts), the passivation layer minimum thickness limitation will be the first requirement for topological coverage of the GMR step edge. A rule of thumb is to use a passivation layer thickness equal to that of the step being covered, although less is possible. A passivation layer thickness of 10 nm is typically sufficient.
  • Such a passivation layer provides a nominal standoff voltage of about 1000 Volts / ⁇ m, so a 10 nm passivation will nominally provide 10 V.
  • the resulting detector is shown in Figure 11 with binding molecule coating 12 thereon over GMR magnetic field detector structure 11 magnetoresistors 34.
  • the interconnection metal is to be provided below the GMR magnetic field detector structure, on the other hand, the structures of the layer diagrams in either of Figures 8 and 9 can be fabricated.
  • the succession of alternating magnetic and nonmagnetic metallic thin-film layers in the GMR magnetic field detector structure is deposited directly upon substrate Si 3 N 4 layer 31 on Si wafer 30 as above.
  • An 10 nm CrSi etch stop layer plus a Si 3 N 4 masking layer of 40 nm thickness is deposited, and then photolithography and RIE are used to pattern the Si 3 N 4 to form an etching mask, followed again by use of an ion mill to etch the GMR magnetic field detector structure + etch stop succession thereby leaving the GMR magneticfield detector structure 11 magnetoresistors.
  • Thin Si 3 N 4 passivation layer 36 is then deposited serving here as an inner passivation layer, and passageways, or vias, to the GMR magnetic field detector structure 11 magnetoresistors are etched in inner passivation layer 36 using RIE.
  • a relatively thick Al ( ⁇ 1 ⁇ m) layer is next deposited and patterned using photolithography and RIE, so that interconnections, 37, are made for the GMR magnetic field detector structure 11 magnetoresistors.
  • the Al needs to be thick so that the lead resistance is low compared to the resistance of these magnetoresistors.
  • Exposed surfaces of aluminum interconnections 37 and Si 3 N 4 passivation layer 36 then have deposited thereon a 10 nm aluminum nitride (AIN) layer, 38, for its adhesion properties followed by a 1.5 ⁇ m Si 3 N 4 layer, 39, which together form the outer passivation for the device.
  • Figure 8 shows a layer diagram of the resulting structure at this point of the fabrication process which leaves an outer passivation layer so thick that bead 10 thereon over GMR magnetic field detector structure 11 magnetoresistors would have little magnetic effect on those reference magnetoresistors.
  • Flux concentrators 19 and 20 can be added at this point for amplifying externally applied fields, or coil 26 and flux concentrator 25 can be added at this point for guiding on-chip fields.
  • a photoresist plating mold is formed, and permalloy is electroplated into the mold to a thickness of about 15 ⁇ m to form flux concentrators 19 and 20.
  • Figure 9 shows the structure resulting to this point in the fabrication process if binding molecule coating 12 is again ignored.
  • binding molecule coating 12 There are many methods to provide binding molecule coating 12, i.e. of preparing the assay probe region, the particulars of which depend upon the intended purpose of the assay.
  • One method to create probes for a DNA hybridization assay is described in the following.
  • the resulting structure after the flux concentrators are completed is coated with gold using a lift-off mask that leaves gold over large portions of the chip, but such that it does not short different magnetoresistor interconnections together.
  • spots of reagents containing thiolated DNA o gomers are dispensed over the intended assay probe region using a Sapphire-tipped Rapidograph pen.
  • the chip surface is also treated with thiolated PEG (O-(2-mercaptoethyl)-o'-methyl-polyethylene glycol 5000.
  • thiolated PEG O-(2-mercaptoethyl)-o'-methyl-polyethylene glycol 5000.
  • the response of a typical GMR magnetic field detector structure magnetoresistorto an external magneticfield is unipolar, linear, and saturates in fields ranging from tens of Oe to a few hundreds of Oe, depending upon the particular magnetic design.
  • a plot of the observed resistance vs. externally applied magnetic field strength for a typical multilayer GMR magnetic field detector structure magnetoresistor is shown in Figure 12. The presence of a bead 10 is then detected by observing a change in the resistance due to the external field experienced by the magnetoresistor
  • Detecting a single magnetizable bead with GMR magnetic field detector structure magnetoresistors at a binding molecule coated assay surface is typically insufficient in view of the overall assay signal-to-noise ratio being proportional to the number of capture sites at the assay surface, i.e. proportional to the square root of the assay surface area over which such sites are provided, assuming a random areal distribution of "noise events".
  • Assay "noise events” include situations like beads sticking where they are not supposed to be sticking in the detection scheme (non assay-specific adhesion, leading to artificially high magnetic signal) and other kinds of particles (other than beads) sticking to detection sites in place of beads (contaminants, for instance, leading to artificially low magnetic signal).
  • assay surfaces that are much larger than a typical bead, say a 50 ⁇ m sided square, lead to a desire to measure the surface concentration of beads across the entire surface, or detection site, as accurately as possible.
  • a GMR magnetic field detector structure magnetoresistor arrangement having multiple effective individual detectors can be provided across such a assay surface, or detection site, by having several individual GMR magnetic field detector structure magnetoresistors electrically connected together in series.
  • Figure 13 shows a top view of such a detector arrangement in a portion of a device formed on an integrated circuit under a square binding molecule coating forming detection site 12 in which the individual GMR magnetic field detector structure magnetoresistors are each approximately 4 ⁇ m wide, separated by 2 ⁇ m, and connected together using Al metal interconnections 37 formed over the top of the series connected magnetoresistors. Passivation layers and any flux concentrators used are omitted from this view for clarity.
  • These magnetoresistors are individual sensors like the magnetoresistors in Figure 6 and so designated 13, 13', 13", 13'", 13"", 13 v , 13 v ⁇ and 13 v " in representing an active group of magnetoresistors.
  • the "active region", or detection site 12 is a square 50 ⁇ m on a side that is effectively defined by the existence of the binding molecule coating "assay surface” and possibly other construction features such as thinned sensor passivation, etc.
  • the same assay surface can be monitored by two series connected, interleaved GMR magnetic field detector structure magnetoresistor groups connected as shown in Figure 14 for again a portion of a detector device formed on an integrated circuit with some layers omitted for clarity.
  • These groups are again taken as like the magnetoresistors in Figure 6 and so designated 13, 13', 13" and 13'" for one group of active resistors, and designated 14, 14', 14" and 14'" for the other group of active resistors.
  • the gap between two adjacent magnetoresistors is ideally as small as possible to maximize surface coverage, but is limited in coverage by practical lithographical spacing considerations.
  • each of the magnetoresistors can vary over a wide range, from the narrowest that can be fabricated ( ⁇ 0.5 ⁇ m) in the best resolution fabrication process to as wide as the entire assay site if only one or two magnetoresistors are to be used.
  • the length-to-width ratio of each of the magnetoresistors is to be such that the resistance total of the groups satisfies detection circuit criteria. For example, some preamplifiers operate best with a source impedance of about 1 k ⁇ which requires 100 squares of 10 ⁇ /square material.
  • the width of an individual magnetoresistor is also important because the most sensitive region of such a magnetoresistor is in the interior thereof because the edges thereof are magnetically relatively stiff in resistor rotation of the magnetization in those regions. Wider resistors, in so having a proportionally larger sensitive region, will thus be more sensitive. On the other hand, wider resistors require more current to generate the same voltage signal because of reduced resistance. Too much current can generate excess heat which may disturb or destroy the coating forming the assay surface or affect the test in other ways.
  • the system sensitivity to a single bead is enhanced by using multiple GMR magnetic field detector structure magnetoresistors with respect to such a bead so that more than one of those magnetoresistors is affected by the magnetic field anomaly introduced by the presence of a bead.
  • the bead would instead be directed to a position between two adjacent magnetoresistors, or even in the area between four such magnetoresistors.
  • a channel can be provided between each member of a pair of magnetoresistors, or a hole could be provided in the area between four magnetoresistors, in which the beads would be more likely to be captured, and in which the binding molecule coating forming the assay surface would be placed.
  • FIG. 15 Such an arrangement is shown in Figure 15 in which a bridge circuit is shown formed in a portion of the detector arrangement provided on a monolithic integrated circuit having detection site 12 located between active magnetoresistors 13 and 14 where each will experience the magnetic field anomaly introduced by the presence of a bead 10 bound to site 12 while more remotely located reference magnetoresistors 15 and 16 will not.
  • the depth of these channels or holes,40, should be such that the center of the bead is level with the magnetoresistors in the vertical direction as is shown in Figure 16 which is a portion of a layer diagram of the device portion shown in Figure 15 and an enhancement of the structure shown in Figure 9.
  • Word lines can be used to generate such externally applied fields on-chip that either supplement or eliminate off -chip magnetic field generating.
  • Permeable mass flux keepers can be used to direct the flux from the lines and from the beads. Use of a buried word line would allow the beads to be close to the magnetoresistors as does the use of buried connectors as shown in Figure 11. Alternatively, the externally applied excitation magnetic fields could be directed perpendicularly to the major surfaces of the magnetoresistors but then off-chip magnetic field generating is likely to be needed.
  • the other magnetoresistor in the bridge circuit previously described as also being active in other arrangements has been redesignated 14' here. If the excitation orientation is parallel, the beads should come to be positioned on the magnetoresistors or between two magnetoresistors as in Figures 15, 16 and 17. Of course, the binding molecule coating material to which the beads come to stick to in a position must thin with respect to the thickness of detection devices layers ( ⁇ 1 ⁇ m). If the coating is instead tens of ⁇ m thick, then any magnetoresistor arrangement will be insensitive.
  • the magnetic field anomaly arising from the presence of a micron sized magnetizable bead is, in actuality, often very non-uniform and can be best detected in a differential mode using a gradiometer magnetic field measurement arrangement.
  • a bridge sensor can be made to use this property by putting two magnetoresistors in a gap between flux concentrators I where beads are allowed, or even promoted, to stick while putting two identical magnetoresistors resistors in an otherwise identical gap between flux concentrators where beads are not allowed or promoted to stick.
  • the externally applied magnetic field could be generated by on- chip current conductors located under the flux concentrators.
  • Beads near current conductors will redistribute magnetic flux generated by the current as well. If the beads are on the same side of the conductors as a magnetoresistor, the current generated magnetic field at the magnetoresistor due to current in the conductor will be reduced. If the beads are on the opposite side of the conductor from the magnetoresistor, the current generated magnetic field will be increased. In the former situation, the beads form a higher magnetic permeability path and concentrate flux away from the magnetoresistor. In the latter case, the lower permeability of the beads permits a larger amount of flux to go around the conductor for a given amount of current therethrough.
  • Typical magnetizable beads for assays require magnetic fields of several hundred to over a thousand Oe for saturation.
  • the gap for beads would be much narrower than the gap for the magnetoresistors. So while the same flux would pass across both gaps, the flux density would be much lower at the active magnetoresistor gap than at the bead gap.
  • the flux loop permeable mass would ideally has coil 26 wound therearound for current to generate the externally applied field. Alternatively, that field could be generated by an underlying planar coil.

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Abstract

L'invention concerne un système de détection de champ magnétique à couche mince ferromagnétique (Figs. 6-20), qu'on utilise pour détecter la présence d'une espèce moléculaire choisie. Un détecteur de champ magnétique (11, 13, 14) disposé sur un substrat (30, 31, 33) présente une couche de molécules de liaison (12) placée sur un côté dudit substrat et pouvant se lier sélectivement à ladite espèce moléculaire choisie. Le détecteur de champ magnétique (11, 13, 14) peut être sensiblement recouverte d'une couche isolante comportant un évidement (38, 39, 40) adjacent au détecteur (11, 13, 14), dans lequel la couche de molécules de liaison (12) est disposée. Un conducteur d'interconnexion électrique (32) peut être disposé sur le substrat (30, 31, 33), au moins partiellement, entre le détecteur (11, 13, 14) et le substrat (30, 31, 33), et raccordé électriquement au détecteur (11, 13, 14). Le détecteur de champ magnétique (11, 13, 14) peut être installé dans un montage en pont (Fig. 7) et comporter plusieurs détecteurs individuels interconnectés (13, 13', 13', 13''', 13'''', 13?v, 13vi, 13vii¿; 14, 14', 14', 14''').
PCT/US2000/028469 1999-10-13 2000-10-13 Detecteur de perles magnetisables WO2001027592A1 (fr)

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EP1293792A2 (fr) * 2001-09-17 2003-03-19 Canon Denshi Kabushiki Kaisha Elément de détection magnétique utilisant l'effet de magnéto-impédance, procédé de fabrication de cet élément, et équipement portable utilisant cet élément
EP1469311A1 (fr) * 2002-01-29 2004-10-20 Asahi Kasei Kabushiki Kaisha Biocapteur, procede de mesure de molecules magnetiques et procede de mesure de l'objet mesure
EP1525447A2 (fr) * 2002-05-31 2005-04-27 The Regents Of The University Of California Procede et appareil de detection de substances d'interet
WO2009068598A1 (fr) * 2007-11-30 2009-06-04 Siemens Aktiengesellschaft Dispositif de détection magnétique de particules individuelles dans un canal microfluidique
CN109283228A (zh) * 2018-11-19 2019-01-29 江苏多维科技有限公司 一种基于磁阻元件的氢气传感器及其检测氢气的方法

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EP1293792A2 (fr) * 2001-09-17 2003-03-19 Canon Denshi Kabushiki Kaisha Elément de détection magnétique utilisant l'effet de magnéto-impédance, procédé de fabrication de cet élément, et équipement portable utilisant cet élément
EP1293792A3 (fr) * 2001-09-17 2004-01-14 Canon Denshi Kabushiki Kaisha Elément de détection magnétique utilisant l'effet de magnéto-impédance, procédé de fabrication de cet élément, et équipement portable utilisant cet élément
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EP1469311A1 (fr) * 2002-01-29 2004-10-20 Asahi Kasei Kabushiki Kaisha Biocapteur, procede de mesure de molecules magnetiques et procede de mesure de l'objet mesure
EP1469311A4 (fr) * 2002-01-29 2005-08-31 Asahi Chemical Ind Biocapteur, procede de mesure de molecules magnetiques et procede de mesure de l'objet mesure
EP1525447A2 (fr) * 2002-05-31 2005-04-27 The Regents Of The University Of California Procede et appareil de detection de substances d'interet
EP1525447A4 (fr) * 2002-05-31 2006-12-06 Univ California Procede et appareil de detection de substances d'interet
WO2009068598A1 (fr) * 2007-11-30 2009-06-04 Siemens Aktiengesellschaft Dispositif de détection magnétique de particules individuelles dans un canal microfluidique
US8641974B2 (en) 2007-11-30 2014-02-04 Siemens Aktiengesellschaft Device for magnetic detection of individual particles in a microfluid channel
CN109283228A (zh) * 2018-11-19 2019-01-29 江苏多维科技有限公司 一种基于磁阻元件的氢气传感器及其检测氢气的方法
EP3885759A4 (fr) * 2018-11-19 2022-08-17 MultiDimension Technology Co., Ltd. Capteur d'hydrogène fondé sur un élément de magnétorésistance et procédé de détection d'hydrogène correspondant
CN109283228B (zh) * 2018-11-19 2024-07-23 江苏多维科技有限公司 一种基于磁阻元件的氢气传感器及其检测氢气的方法

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