Improved magnetoresistors

Claim 2

A sensor providing electrical output changes in response to changes in an applied magnetic field, said sensor comprising: a substrate and a thin film of monocrystalline semi-conductive material disposed on said substrate, said thin film having inner and outer surfaces, said monocrystalline semi-conductive thin film including a substantially rectangular sensing area for sensing a magnetic field applied perpendicularly to said film surfaces, said sensing area being defined as the entire area of said film disposed between the shorter, if they are not of equal length, of two parallel highly conductive portions in low electrical resistance contact with film portions adjacent the film outer surface, characterised in that said electrical output changes are of the order of one volt even when the sensor is exposed to temperatures up to over 220°C; said substrate comprises a substantially electrically-­insulating monocrystalline substrate having a thermal expansion characteristic close to that of indium arsenide; the sensor includes a material forming the surface of said substrate that has a crystal lattice constant close to that of said semi-conductive material to be deposited onto said surface as said monocrystalline thin film; said monocrystalline thin film is of a semi-conductive material having only a moderate average current carrier density and moderate average current carrier mobility, and a band gap of at least 0.35 electron volts; said rectangular sensing area has two long edges of substantially equal length and two short edges of substantially equal length, and one of said two parallel conductors extends along the length of each long edge; and there is an accumulation layer in said thin film extending across said sensing area and disposed adjacent a surface of said thin film, where said current carriers can preferentially flow between said highly conductive portions contacting opposed edges of said sensing area, which accumulation layer is effective to provide an apparent increase in carrier mobility and concentration in said semi-conductive material, an apparent reduction in thickness of said film, and an actual improvement in the magnetic sensitivity of said film and in the temperature insensitivity of the magnetic sensitivity of said film.

Claim 3

A sensor according to claim 1, characterised in that the length of the short edges is about 30% - 50% of the length of the long edges

Claim 4

A sensor according to claim 1 or 2, characterised in that said substrate includes a plurality of said thin film sensing areas, and said plurality of sensing areas are connected electrically in series with one another.

Claim 5

A sensor according to claim 1 or 2, characterised in that said monocrystalline semi-conductive thin film has an elongated portion, the elongated portion comprises a plurality of successive sensing areas, each successive sensing area extends across the width of the elongated portion, the sensing areas are electrically connected in series with one another, and a conductive coating extends completely across said elongated portion between adjacent ones of said successive sensing areas, so that power consumption of said sensor is significantly reduced but sensor size is not significantly increased.

Claim 6

A magnetoresistive sensor providing electrical output changes in response to changes in an applied magnetic field, said sensor comprising: a substrate and a thin film of monocrystalline semi-conductive material disposed on said substrate, said thin film having inner and outer surfaces, said monocrystalline semi-conductive thin film including a substantially rectangular sensing area for sensing a magnetic field applied perpendicularly to said film surfaces, said sensing area being defined as the entire area of said film disposed between the shorter, if they are not of equal length, of two parallel highly conductive portions in low electrical resistance contact with film portions adjacent the film outer surface, characterised in that the sensor provides significant unamplified electrical output changes in response to changes in applied magnetic field over a temperature range of from below 0°C to over 300°C; said substrate has a thermal expansion characteristic close to that of said monocrystalline film of said semi-conductive material disclosed on said substrate; there is a surface on said substrate that is substantially electrically insulating and monocrystalline, and which contains few crystal defects and has a crystal lattice constant close to that of said semi-conductive material; said substantially rectangular sensing area has a dimension along its short edges that is about 30% - 50% that of its long edges; there is a first electrical conductor on said film extending along the length of one of the long edges of the rectangular sensing area; there is a second electrical conductor on said film extending along the length of the other of the long edges of the rectangular sensing area; said film of semi-conductive material is less than 5 micrometres thick and is nominally undoped, and has a given average electron density and a given average electron mobility; there is an electron accumulation layer adjacent the outer surface of said semi-conductive film which extends entirely across the sensing area between the conductors contacting its long edges, which accumulation layer has an electron density at least an order of magnitude higher than said given average electron density and an electron mobility that is significantly greater than said given average electron mobility, and which is effective to provide a magnetic sensitivity and range of operating temperature as if the semi-conductive thin film were apparently much thinner and had a much higher electron density and electron mobility; and there are means adjacent the surface of said semi-conductive thin film for inducing said accumulation layer in said semi-conductive thin film.

Claim 7

A magnetoresistive sensor providing electrical output changes in response to changes in an applied magnetic field, said sensor comprising: a substrate and a thin film of monocrystalline semi-conductive material disposed on said substrate, said thin film having inner and outer surfaces, said monocrystalline semi-conductive thin film including a substantially rectangular sensing area for sensing a magnetic field applied perpendicularly to said film surfaces, said sensing area being defined as the entire area of said film disposed between the shorter, if they are not of equal length, of two parallel highly conductive portions in low electrical resistance contact with film portions adjacent the film outer surface, characterised in that the sensor provides significant unamplified electrical output changes in response to changes in applied magnetic field over a temperature range of from below 0°C to over 300°C; said substrate has a thermal expansion characteristic close to that of said monocrystalline film of said semi-conductive material disclosed on said substrate; there is a surface on said substrate that is substantially electrically insulating and monocrystalline, and which contains few crystal defects and has a crystal lattice constant close to that of said semi-conductive material; said substantially rectangular sensing area has a dimension along its short edges that is about 30% - 50% that of its long edges; there is a first electrical conductor on said film extending along the length of one of the long edges of the rectangular sensing area; there is a second electrical conductor on said film extending along the length of the other of the long edges of the rectangular sensing area; said film of semi-conductive material is less than 5 micrometres thick and is nominally undoped, and has a given average electron density and a given average electron mobility; there is an electron accumulation layer adjacent the outer surface of said semi-conductive film which extends entirely across the sensing area between the conductors contacting its long edges, which accumulation layer has an electron density at least an order of magnitude higher than said given average electron density and an electron mobility that is significantly greater than said given average electron mobility, and which is effective to provide a magnetic sensitivity and range of operating temperature as if the semi-conductive thin film were apparently much thinner and had a much higher electron density and electron mobility; and there are means adjacent the surface of said semi-conductive thin film for inducing said accumulation layer in said semi-conductive thin film.

Claim 8

A magnetoresistive sensor according to claim 5, characterised in that said monocrystalline thin film of semi-conductive material has an elongated portion, the elongated portion comprises a plurality of successive sensing areas, each successive sensing area extends across the width of the elongated portion, the sensing areas are electrically connected in series with one another, and a conductive coating extends completely across said elongated portion between adjacent ones of said successive sensing areas, so that power consumption of said sensor is significantly reduced but sensor size is not significantly increased.

Claim 9

A magnetoresistive sensor according to claim 6, characterised in that the plurality of sensing areas is a plurality of over 10, and the conductive coating over the sensing area is a metal gate electrode disposed on a dielectric layer.

Claim 10

A magnetoresistive sensor according to claim 5, characterised in that said monocrystalline film of semi-conductive material is about 1 - 3 micrometres thick and is nominally undoped, and has a band gap of at least 0.35 electron volt, a moderate average electron density and moderate average electron mobility; and there is a coating means on the exposed sensing area of said film surface for inducing and maintaining said accumulation layer in said thin film.

Claim 11

A magnetoresistive sensor according to claim 8, characterised in that said means for inducing said accumulation layer in said thin film is a coating on said film surface, which coating includes a discrete portion of a metal layer over said sensing area.

Claim 12

A magnetoresistive sensor according to claim 9, characterised in that said substrate includes a plurality of said thin film sensing areas, said sensing areas are electrically in series with one another, and said coating induces said accumulation layer in said film without application of a voltage from an electrical contact to said sensor in addition to respective electrical contacts made to said sensing area conductors.

Claim 13

A magnetoresistive sensor according to claim 10, characterised in that said film has an elongated portion, each end of which has an electrical contact for electrically biasing said sensing areas in series with one another, said substrate includes a resistor network, and said resistor network is interconnected with said discrete portions of said metal layer and said electrical contacts to concurrently electrically bias said metal layer portions with respect to their respective sensing areas of said film when said sensing areas are biased, so as to concurrently induce or enhance said accumulation layer in said film.

Claim 14

A magnetoresistive sensor according to claim 8, characterised in that said coating means for inducing said accumulation layer in said thin film includes an electrode layer, the electrode layer is disposed over said sensing area, and said electrode layer is electrically biased when an electrical potential is applied to one of said conductors contacting the long edges of said sensing area.

Claim 15

A magnetoresistive sensor according to claim 8, characterised in that said monocrystalline film of semi-conductive material has an elongated portion, the elongated portion comprises a plurality of successive sensing areas, each successive sensing area extends across the width of the elongated portion, the sensing areas are electrically connected in series with one another, and a conductive coating extends completely across said elongated portion between adjacent ones of said successive sensing areas, so that power consumption of said sensor is significantly reduced but sensor size is not significantly increased.

Claim 18

A method of making a magnetoresistive sensor according to claim 14, in which the substantially lattice-matching semi-conductive material is deposited onto said substrate to a thickness of less than 3 micrometres, said sem-conductive material has a band gap of at least about 0.35 electron volt and a given average carrier concentration and given average electron mobility; and said sensing area is coated with at least one layer for inducing or enhancing said accumulation layer in said sensing area of said film.