Integrated gradiometer
First Claim
1. An integrated gradiometer for measuring a magnetic field gradient associated with a magnetic field, comprising:
- a semiconducting substrate;
a first sensor, fabricated on the semiconducting substrate and responsive to the presence of the magnetic field, for producing a first electrical signal proportional to a first magnetic field strength of the magnetic field;
a second sensor, fabricated on the semiconducting substrate and responsive to the presence of the magnetic field, for producing a second electrical signal proportional to a second magnetic field strength of the magnetic field;
said first and second sensors being spaced apart at a distance effective for measuring a magnetic field gradient having a spatial scale of up to about 10 μ
m; and
a comparator, for receiving and comparing said first and second electrical signals, and for producing an output representing a magnitude of the magnetic field gradient applied across said sensors.
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Accused Products
Abstract
Magnetic field sensors, each generating an electrical output signal in proportion to the local magnetic field, are lithographically fabricated on a semiconductor substrate with a small spatial separation. The lateral dimension of the sensors and the separation length are the order of the minimum lithographic feature size. Comparing the electrical signals of the sensors results in a measurement of the local magnetic field gradient. Large field gradients, that vary on a small spatial scale, may be associated small magnetic structures such as microscopic magnetic particles. Detection of a field gradient can be used to infer the presence of a magnetic particle.
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Citations
30 Claims
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1. An integrated gradiometer for measuring a magnetic field gradient associated with a magnetic field, comprising:
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a semiconducting substrate;
a first sensor, fabricated on the semiconducting substrate and responsive to the presence of the magnetic field, for producing a first electrical signal proportional to a first magnetic field strength of the magnetic field;
a second sensor, fabricated on the semiconducting substrate and responsive to the presence of the magnetic field, for producing a second electrical signal proportional to a second magnetic field strength of the magnetic field;
said first and second sensors being spaced apart at a distance effective for measuring a magnetic field gradient having a spatial scale of up to about 10 μ
m; and
a comparator, for receiving and comparing said first and second electrical signals, and for producing an output representing a magnitude of the magnetic field gradient applied across said sensors. - View Dependent Claims (3, 4, 5, 6, 7, 8, 9)
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- 10. The gradiometer of claim 1, wherein said substrate is fixed to a scanning probe head and apparatus.
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10-1. A method of measuring magnetic field gradients on a small spatial scale, comprising the steps of:
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providing lithographically fabricated first and second magnetic field sensors with lateral spatial scales of up to about 10 microns and with a separation of up to about 10 microns to thereby form a gradiometer;
introducing a source of local magnetic field to the proximity of the substrate;
applying a magnetic field across the sensors to produce in the first sensor a first electrical signal proportional to a first magnetic field strength of the magnetic field at the first sensor and in the second sensor a second electrical signal proportional to a second magnetic field strength of the magnetic field at the second sensor; and
comparing the first and second electrical signals to obtain an output representative of a magnitude of a magnetic field gradient across the sensors.
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11-2. The method of claim 10, wherein the local magnetic field is produced by a microscopic magnetic particle and the relative value is proportional to the local field gradient of the field produced by the magnetic particle.
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15. A method of detecting biological agents that are bound to magnetic particles, comprising the steps of:
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providing lithographically fabricated first and second magnetic field sensors with lateral spatial scales of up to about 10 microns and with a separation of up to about 10 microns to thereby form a gradiometer;
functionalizing each of a plurality of microscopic magnetic particles with a first species;
functionalizing a surface of the integrated gradiometer with a second species;
positioning the functionalized magnetic particles near the sensors to allow a selective reaction binding the magnetic particle to the surface, thereby exposing each sensor to a magnetic field produced by the functionalized magnetic particles and generating a first electrical signal proportional to a first magnetic field strength of the magnetic field at the first sensor and a second electrical signal proportional to a second magnetic field strength of the magnetic field at the second sensor; and
comparing the first and second electrical signals to identify the existence of a magnetic field gradient across the sensors indicative of the presence of a target agent. - View Dependent Claims (16, 17, 18, 19)
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20. An array of integrated gradiometers, comprising:
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an array of cells, wherein each cell comprises;
a semiconducting substrate;
a first sensor, fabricated on the semiconducting substrate and responsive to the presence of the magnetic field, for producing a first electrical signal proportional to a first magnetic field strength of the magnetic field;
a second sensor, fabricated on the semiconducting substrate and responsive to the presence of the magnetic field, for producing a second electrical signal proportional to a second magnetic field strength of the magnetic field;
said first and second sensors being spaced apart at a distance effective for measuring a magnetic field gradient having a spatial scale of up to about 10 μ
m;
a comparator, for receiving and comparing said first and second electrical signals, and for producing an output representing a magnitude of the magnetic field gradient applied across said sensors;
a first conductor for transmitting current bias to the cell;
a second conductor for transmitting a sensed voltage from the cell to a sense amplifier; and
an isolation element for electrically isolated the cell from the bias and signal wires and from other cells in the array. - View Dependent Claims (21, 22, 23, 25)
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27. An integrated gradiometer, comprising:
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a first magnetic field sensor fabricated on a semiconducting substrate as a Hall plate using a first conducting layer, fabricated with lateral dimensions of up to about 10 microns, and capable of producing a first electrical signal in proportion to the local magnetic field at the position of said first sensor;
a second magnetic field sensor fabricated on the semiconducting substrate as a Hall plate using a second conducting layer, fabricated with lateral dimensions of up to about 10 microns, and capable of producing a second electrical signal in proportion to the local magnetic field at the position of said second sensor, and spatially separated from the first magnetic field sensor by a distance of up to about 10 microns; and
a comparator, for receiving and comparing said first and second electrical signals, and for producing an output representing a magnitude of a magnetic field gradient applied across said sensors. - View Dependent Claims (28, 29)
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30. An integrated gradiometer, comprising:
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a first magnetic field sensor fabricated on a semiconducting substrate as a Hall plate using the bottom quantum well of a double quantum well heterostructure, fabricated with lateral dimensions of up to about 10 microns, and capable of producing a first electrical signal in proportion to the local magnetic field at the position of said first sensor;
a second magnetic field sensor fabricated on the semiconducting substrate as a Hall plate using the top quantum well of a double quantum well heterostructure, fabricated with lateral dimensions of up to about 10 microns, and capable of producing a second electrical signal in proportion to the local magnetic field at the position of said second sensor, and spatially separated from the first magnetic field sensor by a distance of up to about 10 microns; and
a comparator, for receiving and comparing said first and second electrical signals, and for producing an output representing a magnitude of a magnetic field gradient applied across said sensors.
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Specification