GB2213267A

GB2213267A - Hall effect magnetometer

Info

Publication number: GB2213267A
Application number: GB8822361A
Authority: GB
Inventors: Roger Edward Jones; Dawn Anita Jackson; Piers James Geoffrey Dawe; Bruce Dunnett
Original assignee: STC PLC
Current assignee: STC PLC
Priority date: 1987-12-05
Filing date: 1988-09-22
Publication date: 1989-08-09
Anticipated expiration: 2008-09-22
Also published as: GB2213267B; GB8728496D0; GB8822361D0

Abstract

A Hall effect magnetometer comprises a semiconductor Hall element (32) mounted on a ceramic substrate (31). A high temperature superconductive pattern (33) applied to the substrate provides a flux transformer or concentrator for the Hall element (32). The small loop (33a) of the flux transformer (33) may comprise a multi-turn coil. Loop (33a) may be screened from external magnetic fields by a housing. The smaller loop of the transformer (33) may be deposited on the surface of the Hall element. <IMAGE>

Description

SUPERCONDUCTIVE DEVICES This invention relates to devices incorporating high temperature (e.g. liquid nitrogen temperature) superconductive materials. and in particular to magnetometer devices.

Superconductive magnetometers have been proposed in which a superconductive flux concentrator is provided with a superconductive magnetic sensor, typically a superconductive quantum device (SQUID) e.g.

a Josephson junction device. Such magnetometers employ conventional metallic alloy superconductors and operate at a few degrees above absolute zero. They require liquid helium cooling and are thus costly in operation.

Recently the so called high temperature superconductors have been introduced. These are ceramic materials and exhibit superconductive properties at temperatures above the boiling point of liquid nitrogen. Cooling of these materials is thus a relatively simple matter. However, as the materials are ceramics, they are somewhat intractable and are not readily amenable to the formation of SQUID device structures.

The object of the invention is to minimise or to overcome this disadvantage.

According to the invention there is provided a Hall effect magnetometer, including a non-conductive non-magnetic substrate, a semiconductor element mounted on a substrate and provided with electrodes whereby measurement of Hall voltages responsive to applied magnetic flux may be effected and a flux transformer associated with the semiconductor element whereby to provide a local concentration of magnetic flux through the semiconductor element, and wherein the flux transformer is provided as a pattern of a superconductive material applied to the substrate.

- We have found that the the use of a semiconductor Hall element overcomes the problems involved on manufacturing superconductive devices from ceramic materials. The arrangement has the further advantage that, by operating the Hall element at liquid nitrogen temperature, a significant increase in carrier mobility and a decrease in electrical noise are achieved. This results in increased effective sensitivity of the Hall element to a magnetic field applied thereto.

Further applications of superconductive flux transformers are described in our co-pending application No88 Serial No ) No........) (R E Jones 27-4-1X) which claims priority from application No. 8728497 (R E Jones 27-4).

Embodiments of the invention will now be described with reference to the accompanying drawings in which : Figures 1 and 2 illustrate the preparation of a superconductive device; Figures 3 and 4 are respectively plan and sectional views of a Hall effect magnetometer employing the superconductive device of Figures 1 and 2.

Figure 5 illustrates a magnetometer device in which one loop of the flux transformer comprises a multiturn coil; Figure 6 shows a magnetometer in which one loop of the flux transformer is disposed directly on the Hall element; and Figure 6a is a part sectional view of the Hall element portion of the sensor of Figure 6.

Referring to Figures 1 and 2, the superconductive device is disposed on a non-magnetic, non-conductive substrate 11, e.g. of a ceramic material.

For this purpose we prefer to employ zirconia stabilised with yttric or magnesia. A superconductive material is applied to the substrate in the form of a paste 12 comprising particles of the material and liquid binder.

Typically the paste 12 is applied to the substrate 11 via a silk screen 13 (figure 1) provided with a mask pattern 14 whereby a desired pattern of superconductive material is defined. The silk screen is removed and the substrate together with the deposited pattern is fired to drive off the binder and form the desired crystalline form of the superconductor 15 (Figure 2). Preferably the superconductor comprises a high temperature superconductor, i.e. a material that exhibits superconductive properties at temperatures around the boiling point of liquid nitrogen. Typically the superconductor comprises a Yttrium/Barium/Copper mixed oxide (Y Ba2 Cu3 7-x) which has superconductive properties at the temperature of liquid nitrogen. This material is superconductive at 770K and has a transition temperature of 92 deg. K.The oxygen content of its material, i.e. the value of x, is chosen between zero and unity to provide its desired superconductive properties. The precise value of x will depend on the particular process conditions that are employed to form this material. The manner in which oxygen content is determined will be apparent to those skilled in the art.

The device structures of Figures 1 and 2 may be used in -a variety of applications. An example of such an application is described below with reference to Figures 3 and 4 of the accompanying drawings.

As shown in Figures 3 and 4, a magnetometer includes a ceramic substrate 31 on which a semiconductor Hall element or chip 32 is mounted. Typically the Hall element comprises gallium arsenide as this material has a high carrier mobility and thus displays a high sensitivity to applied magnetic fields. Advantageously the carrier mobility of the semiconductor element is enhanced by modulation doping to form a surface heterostructure or by the provision of a thin surface doped layer (8 doping). In a further embodiment the Hall element 32 comprises an indium phosphide (InP) substrate on which a high mobility indium gallium arsenide (InGaAs) surface layer is disposed. In an alternative embodiment, the substrate may comprise indium antimomide (InSb) or a layer of indium antimomide disposed on a gallium arsenide substrate.When the semiconductor element is cooled to the temperature of liquid nitrogen, the carrier mobility is significantly increased whilst the background noise is decreased. This provides a significant increase in the sensitivity of response of the Hall element to an applied magnetic field.

Concentration of magnetic flux through the semiconductor Hall element 32 is provided by a superconductive flux transformer 33 provided as a pattern of superconductive material applied to the substrate 31, e.g. by the process described above. The transformer 33 comprises a relatively small loop 33a, in register with the semiconductor element 32, and a relatively large loop 33b. The two loops are coupled by substantially parallel closely spaced linear members 33c so as to define a closed loop arrangement. Connection to the semiconductor element 32 is effected via current contact pads 34 and voltage contact pads 36 to which flying leads (not shown) are connected. In some arrangements the small loop may comprise a multiturn coil to provide further concentration of the flux thus enhancing the sensitivity of the device. The smaller loop 33a is screened from external magnetic fields by a magnetically permeable housing (not shown).

When the magnetometer is cooled to liquid nitrogen temperatures the flux transformer 33 becomes superconductive. The net magnetic flux through the closed loop arrangement has a fixed and quantised value which is an integer multiple of h/2e where h is Planck's constant and e the electronic charge. The net magnetic flux through the transformer thus remains at a constant value determined by a constant current flowing around the closed loop. In the presence of an external magnetic field, the additional flux through the larger loop results in a corresponding flux through the smaller loop which is screened from external magnetic fields, but in the opposite sense such that the total net flux through the loops remains unchanged. As the flux through the small loop 33b is restricted to the area of that loop it is significantly more concentrated than that through the larger loop 33a.This provides a concentration of flux through the semiconductor element 32 thus increasing the sensitivity of the magnetometer.

Figure 5 shows an alternative structure in which the smaller loop of the flux transformer comprises a multiturn coil 51. The Hall element 52 is placed at the centre of the coil. This structure may be formed by a two-stage screen printing process. First, the multiturn coil 51 is printed on the substrate 53. An insulator layer (not shown) is applied to the coil and is patterned to expose the inner and outer ends of the coil. A second screen printing then provides the larger loop 54 and connects that larger loop to the coil 51.

Figure 6 shows in schematic form a further structure in which the smaller loop 61 of the flux transformer is deposited on the surface of the Hall element 62. Typically the Hall element is located in a recess 63 formed on the substrate 64 (Figure 6a) such that the upper surface of the Hall element is flush with substrate surface, The superconductive material providing the flux transformer is applied simultaneously to the substrate 64 and to the Hall element 62.

The Hall effect magnetometer described above may be used in various applications, but is of particular advantage in surveying applications e.g. for minimal prospecting and/or geological surveying.

Claims

1. A Hall effect magnetometer, including a non-magnetic substrate, a semiconductor element mounted on the substrate and provided with electrodes whereby measurement of Hall voltages responsive to applied magnetic flux may be effected and a flux transformer associated with the semiconductor element whereby to provide a local concentration of magnetic flux through the semiconductor element, and wherein the flux transformer is provided as a pattern of a superconductive material applied to the substrate.

2. A Hall effect magnetometer as claimed in claim 1, wherein the flux transformer comprises a Yttrium/Barium/Copper oxide ( Y Ba2 Cu3 07

3. A Hall effect magnetometer as claimed in claim 2, wherein the flux transformer comprises a screen printed pattern on the substrate.

4. A Hall effect magnetometer as claimed in claim 1, 2 or 3, wherein the semiconductor Hall element comprises gallium arsenide.

5. A Hall effect magnetometer as claimed in claim 4, wherein the semiconductor Hall element is modulation doped or provided with a doped surface layer whereby the carrier mobility is enhanced.

6. A Hall effect magnetometer as claimed in cliam 1, 2 or 3, wherein the Hall element comprises an indium phosphide (InP) substrate on which an indium gallium arsenide (lnGaAs) surface layer is disposed.

7. A Hall effect magnetometer as claimed in any one of claims 1 to 6, wherein a portion of the flux transformer is disposed on the Hall element.

8. A Hall effect magnetometer substantially as described herein with reference to and as shown in Figures 3 and 4 , or Figure 5 or Figures 6 and 6a of the accompanying drawings.

9. Surveying applications incorporating a Hall effect mangetometer is claimed in any one of the proceding claims.