JP3007976B2 - Magnetic sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method in which electrons emitted from an emitter in a vacuum are
The present invention relates to a magnetic sensor which is bent by Lorentz force and is collected by one of a pair of collectors.

[Prior Art] In a conventional magnetic sensor, a semiconductor bipolar transistor forms a pair of collectors, and electrons emitted from an emitter are bent by a magnetic field to be detected while traveling through a base. There is a magnetic sensor that allows a large amount of electrons to flow into one of them. Further, an electron microscope having a field emission type electron gun is provided with an emitter for emitting electrons in a vacuum, a grid for extracting electrons, and a collector as an anode, and a Lorentz force by an external magnetic field. There is a technology to deflect.

[Problems to be solved by the invention]

In a conventional bipolar transistor-type magnetic center having two collectors, electrons emitted from an n-type emitter are injected as minority carriers into a p-type base, and are deflected by Lorentz force due to a magnetic field to be detected. Many are collected in the collector, and the two collector currents are differentially amplified to detect the magnetic field, but the minority carrier electrons traveling in the base region are not largely deflected due to scattering, Since the emitter junction area is generally larger than the base width, it is difficult to increase the difference between the two collector currents, so that the detection sensitivity cannot be increased. In electron field emission type electron guns, the distance between the electron emitter and the grid is large, and the applied voltage here must be as large as several KV in order to emit electrons.

According to the present invention, the distance between the emitter and the grid is set to, for example, about several thousand angstroms through an insulating thin film, electrons can be emitted at a low voltage between the emitter and the grid, and the two electrodes are very close to each other between the insulating films. It is an object of the present invention to provide a small-voltage, high-sensitivity, ultra-small magnetic sensor in which a collector is provided at a distance of about several micrometers from an emitter to collect electrons from the emitter in a vacuum.

[Means for solving the problem]

In order to achieve the above object, in the magnetic sensor of the present invention, a micro vacuum chamber is formed by utilizing a semiconductor fine processing technique, and an emitter separated by an insulating film and a grid and an insulating film are separated here. The two collectors are arranged, the thickness of the insulating film is several thousand angstroms, and the distance between the emitter and the two collectors is as small as several micrometers. By connecting substantially the same resistors R ₁ and R ₂ in series to the _two collectors, a change in the collector current flowing through these can be detected as a change in voltage. When the detected magnetic field B is not applied, the series-connected resistors R ₁ and R ₁ based on the currents flowing through the respective collectors
It is preferable to adjust the resistance values of these resistors R ₁ and R ₂ so that the voltage drops of ₂ become equal. It is necessary to dispose the emitter, the collector, and the like relatively to the magnetic field so that the electron beam traveling from the emitter to the collector is deflected by Lorentz force and collected by one of the collectors. If a material having a small work function is coated on the surface of the emitter, or if the emitter is formed of the material, it is convenient because electrons can be easily emitted. Further, light can be emitted to the emitter to facilitate electron emission, and electrons can be emitted into vacuum by the photoelectric effect.
In addition, since the emission of electrons often becomes difficult when an adsorbed gas is present on the surface of the emitter, the emitter may be heated to about 100 ° C. in order to promote outgassing and facilitate electron emission.
In this case, in order to reduce the heat capacity and the power consumption of the heater, it is better to form an emitter and a grid on the micro air bridge and heat the micro air bridge. The electrode of this micro heater can be used as an emitter.

[Action]

For example, if a DC voltage is applied between the emitter of the magnetic sensor configured as described above and the two collectors 3a and 3b, and a DC voltage is applied between the emitter and the grid, electrons are emitted from the emitter into a vacuum, The electron beam reaches the two collectors, and approximately the same current flows through the two collectors 3a and 3b. The voltage drop at the resistors R ₁ and R ₂ connected in series to the respective collectors 3a and 3b is differentially amplified, and when the external magnetic field is zero, the resistors R ₁ and R ₂ are set so that the differential output becomes zero. If adjusted, there is an external magnetic field, and by allowing the electron beam to be deflected to either collector side by Lorentz force, the collector current on the deflected side increases, so the collector side on the collector side The voltage drop increases, the differential output changes, and the direction and magnitude of the magnetic field can be detected. At this time, the direction of the magnetic field is determined based on which collector has a larger voltage drop, and the magnitude of the magnetic field can be determined from the voltage drop, that is, the magnitude of the collector current.

〔Example〕

Embodiments will be described with reference to the drawings. FIG. 1 is a schematic plan view when a magnetic sensor of the present invention is formed on a silicon (Si) chip, and FIG. 2 is XX 'of FIG.
It is a cross-sectional schematic view as seen from line, FIG. 3 is a DC power supply E _1, E
FIG. 3 is a schematic diagram of a measurement circuit of the magnetic sensor of the present invention, which also shows the circuit configuration of resistors R ₁ and R ₂ connected in series to the collector ₂ and the collectors 3a and 3b. The magnetic sensor according to the present embodiment can be manufactured by the following steps. First, a thermally oxidized SiO ₂ film 11 is coated on a Si substrate 10 by 0.2 μm.
m thickness. On top of this, Al (0.05 μm thickness), Mg (0.05 μm thickness), Mo
(0.1 μm thickness) and Al (0.05 μm thickness) are formed by sputtering with Al and Mo to form a four-layer structure, and Mg is vacuum deposited. The upper and lower Al are used to improve the adhesion to the SiO ₂ film, and Mo is used to withstand an HF-based etchant. Mg is used because both metals and oxides have a small work relationship and easily emit electrons. These electrodes are etched with a phosphoric acid-based Al etchant by photolithography. In this etchant, Mo and Mg are also soluble, and the emitter electrode 1 'and one collector electrode 3a' can be patterned into the shapes shown in FIGS. At this time, since the hollow region to be the vacuum chamber 15 is formed in a later step, the emitter electrode 1 'and one collector electrode are formed when this electrode pattern is formed.
3a 'is a continuous pattern without being separated. Thereafter, the SiO ₃ film 12 is formed by sputtering to a thickness of about 0.2 μm. Further, Al (0.05 μm) which is an electrode metal to be the grid electrode 2 ′ and the other collector electrode 3 b ′
(Thickness), Mo (0.1 μm thickness) and Al (0.05 μm thickness) by sputtering, and pattern formation is continued as in the formation of the emitter electrode 1 ′ and one collector electrode 3 a ′. . Next, a low-melting glass film 13 is formed by sputtering to a thickness of about 1.5 μm. Next, the formation of the vacuum chamber 15 and the formation of the lead wire extraction holes 16a, 16b, 16c and 16d on the pad portions of the respective electrodes are performed by etching using photolithography. Thereafter, the lid 14 of the transparent glass plate is placed on the vacuum chamber 15 in a vacuum, heated to a temperature higher than the melting point of the low-melting glass 13 (for example, 450 ° C.), and vacuum-sealed. The portions where the emitter electrode 1 ', the grid electrode 2', and the collector electrodes 3a ', 3b' face the vacuum chamber 15 are the emitter 1, the grid 2, and the collector.
3a and 3b are supported. As shown in FIG. 3, a lead wire is taken from each electrode pad of the magnetic sensor element thus formed, and between the emitter electrode 1 'and the grid electrode 2', the grid side is positive. for example connecting a 10V DC power source E _2, and the one collector electrode 3a ', 1 M.OMEGA
Variable resistance R ₁ and the other collector electrode 3b '1 MΩ
Connect a fixed resistor R _2, furthermore, the side opposite to these collector of the variable resistor R ₁ and the fixed resistor R ₂ and a common point G, and the common point G, so that the emitter 1 is a negative 30V Power supply E
To connect the _1. With such a circuit configuration, the electrons extracted from the emitter 1 into the vacuum chamber 15 flow into the two collectors 3a and 3b almost equally, and the two collectors 3a and 3b respectively receive I ₁ , The current becomes I ₂ . A voltage drop V _1, V ₂ at each by the currents I _1, I ₂ resistors R _1, R _2, when the external magnetic field B is zero, to be equal, advance to adjust the variable resistor R ₁ . Therefore, when an external magnetic field B = 0 will voltage drop V ₁ and the differential amplifier output is also zero V ₂ between each resistor R ₁ and R _2. However, if it is applied in a direction such that the electron beam from the application direction the emitter 1 of the external magnetic field B is much flows toward the collector 3a, current I ₁ is increased through the resistor R _1, the voltage drop V ₁ since but greater than V _2, so that these differential amplifier output increases. In this way, the direction of application of the magnetic field B can be determined based on which of the collectors the current flows into, and the magnitude of the magnetic field B can be determined from the magnitude of the current. Thus, the magnetic sensor of the present invention is configured and operates. In the above embodiment, a separate electrode is provided as the grid electrode 2 '. However, the electric field between the emitter electrode 1' and the grid electrode 2 'is very large, and dielectric breakdown is likely to occur. Since the thermal oxide film of Si has an extremely large dielectric strength, the thermally oxidized SiO ₂ film 11 in FIG.
It can also be used as an insulating film between the electrode and the grid electrode 2 '. In this case, a Si substrate 10 is used as the grid electrode 2 '.
It is preferable to remove the thermally oxidized SiO ₂ film 11 under the vacuum chamber 15 and diffuse the phosphorus to a high concentration by exposing the exposed surface of the Si substrate 10 to an extremely small low resistance of the depletion layer. good. In the above embodiment, the lid 14 of the transparent glass plate was
However, the photoelectric effect can also be used by irradiating the surface of the emitter 1 with light from outside the lid 14 of the transparent glass plate. When this magnetic sensor is used for reading data from a magnetic memory, a soft magnetic thin film having high magnetic permeability and good high-frequency characteristics is formed by sputtering or the like in order to guide the magnetism in this extremely small area to the vacuum chamber 15. By patterning, the outside and the vacuum chamber 15 can be connected.

〔The invention's effect〕

The present invention is configured as described above, and has the following effects. First, since the semiconductor fine processing technology can be used, the emitter electrode 1 ', the grid electrode 2', and the pair of collector electrodes 3a ', 3 having a thin film thickness of about 0.1 .mu.m are used.
b ', the formation and patterning of an insulating film are possible, and a very small vacuum chamber 15 can be formed, so that the applied voltage between the emitter 1 and the collectors 3a and 3b and between the emitter 1 and the grid 2 can be reduced. . Further, since the distance between the pair of collectors 3a and 3b can be made extremely small and the electron beam is deflected in a vacuum, the two collector currents I ₁ and I ₂
Change can be detected, and high-speed operation can be performed. Thus, the magnetic sensor of the present invention can be a small, high-sensitivity, high-speed response magnetic sensor.

[Brief description of the drawings]

FIG. 1 is a schematic plan view of a magnetic sensor of the present invention, FIG. 2 is a schematic sectional view taken along line XX 'of FIG. 1, and FIG. 3 shows a measurement circuit configuration of the magnetic sensor. It is a schematic diagram. 1 Emitter, 1 'Emitter electrode, 2 Grid
2 '... grid electrode, 3a, 3b ... collector, 3a', 3b '...
... collector electrode, 10 ... Si substrate, 11,12 ... SiO ₂ film, 13 ...
Low melting point glass, 14 ... Lid, 15 ... Vacuum chamber, 16a, 16b, 16c, 1
6d …… Lead wire outlet hole

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-57-177573 (JP, A) JP-A-59-222969 (JP, A) JP-A-7-159501 (JP, A) JP-A-62 272169 (JP, A) JP-A-2-285272 (JP, A) JP-A-58-111767 (JP, A) JP-A-6-21530 (JP, A) JP-A-54-144890 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G01R 33/00-33/18

Claims (1)

(57) [Claims] An emitter for emitting electrons;
A pair of collectors 3a and 3b opposed to each other in a vacuum with the grid 2 and the emitter 1 arranged with an insulating film interposed therebetween, and the electron beam emitted from the emitter 1 depends on the magnetic field to be detected. A pair of collectors by Lorentz force
Of 3a, 3b, it is configured to be collected by one side,
A magnetic sensor configured to detect a magnetic field from a change in current flowing through the collectors 3a and 3b.