JP3044319B2 - Field emission type magnetic sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic sensor utilizing the fact that the trajectory of electrons emitted by field emission is bent by a magnetic field in a measurement environment.

[0002]

2. Description of the Related Art Conventionally, a solid-state Hall element has been known as a magnetic sensor. A solid-state Hall element is an element utilizing a Hall effect in a semiconductor. When a current and a magnetic field are applied to the element, an electromotive force proportional to the product thereof is generated.
Since a differential amplifier is required to detect the Hall voltage generated from the solid-state Hall element, a Hall IC in which the solid-state Hall element and the amplifying means are integrated has been developed.
The Hall IC is a monolithically integrated signal processing circuit including a sensor and an amplifying element, and an amplifying circuit and a sensor for improving the sensitivity of the sensor are monolithically integrated on a silicon substrate.
C has been put to practical use.

[0003] The silicon Hall IC is used as various sensors such as a Gauss meter and a displacement converter, and its maximum operating temperature is at most about 100 degrees Celsius. As another magnetic sensor, there is an element called a superconducting quantum interference element (SQUID). This SQUI
D is an electronic element that can measure the strength of the magnetic field in the smallest unit (quantum) using the Josephson effect. By measuring the direct current that can flow through the parallel connected Josephson junctions, D is a geomagnetic sensor. Measurement of a small amount of magnetism, such as detection of magnetism due to changes in the heart or movement of the heart. SQUIDs have high sensitivity, but use superconducting elements, so that utility equipment such as a cooling device becomes large. Furthermore, since it is difficult to handle, it is difficult to be portable, and it is expensive.

Recently, magnetic sensors have been used for encoders of robots and manipulators. However, even if the use environment of the three-dimensional magnetic sensor is to take measures against heat resistance of the sensor section, the heat generated by the motor may cause the magnetic sensor to generate heat.
It is an environment that exceeds the degree. Therefore, even if an attempt is made to use the Hall element as a magnetic sensor, the Hall IC cannot be used as a magnetic sensor because the maximum use temperature of the Hall IC is low as described above. Further, even if it can be used after taking measures such as cooling, there is a problem that the sensitivity of the Hall IC is insufficient.

[0005] Further, as the magnetic sensor, a highly sensitive S
Although a QUID can be used, it is not practical to use the SQUID as the magnetic sensor because the SQUID is difficult to handle, as described above, and is far from being small and inexpensive. Therefore, a field emission type magnetic sensor has been proposed that measures the strength and direction of a magnetic field by emitting electrons by field emission in a magnetic field and utilizing the Lorentz force of the electrons emitted in the magnetic field. ing.

By the way, when the electric field applied to the surface of a metal or semiconductor is set to about 10 ⁹ [V / m], electrons pass through a barrier and emit electrons in a vacuum even at room temperature due to a tunnel effect. This phenomenon is called field emission (Field Emis
sion), which has been known for a long time, uses a field emission cathode (Fiel
d Emission Cathode).

FIG. 5 shows a field emission (FE) magnetic sensor using a field emission array (FEA) in which an array is formed by providing a large number of field emission cathodes. In this figure, the FEA is an emitter having a saw-toothed tip. (Emitter) 101, and a gate (Gate) 102 elongated in the form of a plate along the emitter 101, and a triangular anode (Anode1) 105-1 divided into two opposing the FEA. , Anode (Anode2) 10
5-2 are arranged. These FEA and anodes 105-1 and 105-2 are formed in a micron size by making full use of semiconductor fine processing technology.

[0008] In the FE magnetic sensor having such a flat shape, a gate 102 and an emitter 101 are formed by depositing niobium or the like on a substrate such as a quartz plate. Since the distance between the tip of the sawtooth-shaped emitter 101 and the gate 102 is made to be submicron, the emitter-gate voltage V _eg of only several tens of volts is applied so that the distance from the emitter 101 is reduced. Electrons can be field-emitted.

The field-emitted electrons fly as shown by a solid line in the figure and fly to the anodes 105-1 and 105-1 provided on the substrate.
Reached at 05-2 and collected. As a result, the anode currents I ₁ and I ₂ flow, and the anode currents I ₁ and I ₂ flow.
The magnitudes of ₁ and I ₂ are detected by detectors 106-1 and 106-2, respectively. In this case, when the FE magnetic sensor is not placed in the magnetic field, the anode current I
The magnitudes of ₁ and I ₂ are substantially equal. Incidentally, the anode voltage V _a is applied to the anode 105-1 and 105-2. In such a flat FE magnetic sensor, electrons emitted from the emitter 101 are emitted in a direction parallel to the surface of the substrate.

Next, consider the case where the magnetic flux B is applied to such an FE magnetic sensor. As shown
When the magnetic flux B is applied to the FE magnetic sensor in a direction from top to bottom as shown in the figure, the magnetic flux B is emitted from the emitter 101 and becomes an electron flying toward the anodes 105-1 and 105-2. The Lorentz force acts, and the electron trajectory is bent forward by the magnetic flux B as shown in the figure.

Then, since the anodes 105-1 and 105-2 for collecting the field-emitted electrons are divided into two, one of the anodes positioned in the direction of the electron whose orbit is bent by the applied magnetic field B. with current I ₂ of the anode 105-2 is increased, a current I ₁ of the other anode 105-2 is decreased. Since the increasing rate or decreasing rate of the anode currents I ₁ and I ₂ changes according to the direction and strength of the applied magnetic field, the two anodes 105-1 and 105-1,
105-2, the difference between the anode currents I ₁ and I ₂ (I
By detecting ₁₋ I ₂ ), the direction and intensity of the applied magnetic field can be detected.

[0012] Next, showing an I-V characteristic of FEA in FIG. 6, the gate 102 to ground the emitter 101 as shown in FIG. 5, the level of the voltage V _OP as an emitter-gate voltage V _eg Is applied, a point on the illustrated IV characteristic curve is set as an operating point, and an emission current I _OP flows through the emitter 101.

[0013]

However, the emission current _Ie of the field emission array changes irregularly (fluctuations) with the passage of time. Assuming that the fluctuation of the emission current _Ie is ± ΔI, the emission current _{Ie
Since e} becomes (I _OP ± ΔI), the emission current I _e
As shown in FIG. 6, the effect of the fluctuation of the operating point equivalently appears as a change in the operating point up and down. That is,
This appears as a change in the anode currents I ₁ and I ₂ flowing through the anodes 105-1 and 105-2. Moreover, the emitter 10
1 does not fluctuate uniformly over the length direction, but fluctuates differently at each tip, so that the anode current I ₁ and the anode current I ₂ change differently, and the emission current I _e Fluctuation is S / N of FE magnetic sensor
There is a problem that it worsens.

Further, the emission current and the noise frequency have a relationship as shown in FIG. 8, which is so-called 1 / f noise. In particular, arrays for such field emission
Is manufactured by semiconductor manufacturing technology,
Forming micro emitters and gates on the order of several μm using engineering technology
When released due to slight changes in the manufacturing process
The characteristics of the electrons are very different. Therefore, the difference between the currents flowing through the two anodes 105-1 and 105-2 detected by the FE magnetic sensor (I ₁ −
I ₂ ) has a variation, and since it is detected as a direct current component, there is a problem that the S / N is also reduced by 1 / f noise.

Therefore, the present invention relates to such a field emission device.
When forming a magnetic sensor using
It is an object of the present invention to provide a highly sensitive field emission type magnetic sensor having a high N.

[0016]

In order to achieve the above object, a field emission type magnetic sensor according to the present invention has a sharp tip.
An emitter formed at the top of the
A gate disposed close to the tip, and the gate
Emitted from the tip of the emitter by the voltage applied to
Are spaced apart from each other to capture electrons
At least two anodes, and the two anodes
And a comparing means for detecting the difference of the current flowing through the de, before
A DC biased periodic signal is applied between the emitter and the gate as a field emission power supply,
Detection means for extracting only the periodic signal component are connected to the two anodes, and the anode currents are respectively extracted from the detection means .
Noise included in the emission current of the emitter to vary and
The offset component is removed.

Further, in the field emission type magnetic sensor of the present invention, an AC signal is used as the periodic signal. In this case, as the detecting means, a filter that passes only the frequency of the AC signal, Alternatively, a phase detecting means for extracting only a component synchronized in phase with the AC signal is used. Also,
The field emission type magnetic sensor of the present invention uses a pattern signal that repeats a predetermined pattern every cycle as the periodic signal, and in this case, the detecting unit has the same pattern as the pattern signal. In addition, a phase detecting means for obtaining a correlation with a reference pattern signal whose phase is synchronized is used. Note that a lock-in amplifier may be used as the phase detecting means.

[0018]

According to the present invention, it is possible to reduce the temporal fluctuation of the emission current and the deterioration of the S / N ratio due to 1 / f noise, which are characteristics of the field emission array, and to reduce the influence of noise. A sensitive field emission type magnetic sensor can be realized. Further, by extracting only the component that is phase-synchronized with the periodic signal that modulates the emission current, it is possible to remove the noise component included in the same frequency as the modulated signal. Furthermore, a sensor output that is stable over time can be obtained.

[0019]

FIG. 1 shows a first embodiment of a field emission (FE) magnetic sensor according to the present invention. In this figure, a field emission array (FEA) has a sawtooth-shaped emitter (Em).
1) and a gate (Gate) 2 formed in an elongated plate along the emitter 1. A triangular anode (Anode1) 5 is divided into two parts facing the FEA.
-1, an anode (Anode2) 5-2 are arranged. These FEA and anodes 5-1 and 5-2 are manufactured in a micron size by making full use of semiconductor fine processing technology.

In the FE magnetic sensor having such a flat shape, a gate 2, an emitter 1, and anodes 5-1 and 5-2 are formed by depositing niobium or the like on a substrate such as a quartz plate. Since the distance between the tip of the saw-toothed emitter 1 and the gate 2 is made to be submicron, the emitter-gate voltage V _eg of only several tens of volts is applied, so that the distance from the emitter 1 is reduced. Electrons can be field-emitted.

The field-emitted electrons fly as shown by the solid lines in the drawing and are anodes 5-1 and 5-2 provided on the substrate.
Reached and collected. Thereby, the anode current I
₁ and I ₂ flow, respectively, and the anode currents I ₁ and I ₂
Is detected by the detectors 6-1 and 6-2, respectively. In this case, when the FE magnetic sensor is not placed in a magnetic field, the magnitudes of the anode currents I ₁ and I ₂ are substantially equal. The anodes 5-1 and 5-
The anode voltage V _a is applied to the 2. In such a flat FE magnetic sensor, electrons emitted from the emitter 1 are emitted in a direction parallel to the surface of the substrate.

[0022] While the I-V characteristic of the FEA is the characteristic shown in FIG. 6 described above, the gate 2 and ground the emitter 1 as shown in FIG. 1, as an emitter-gate voltage V _eg, the V _OP An AC signal (V
_ac ) 4 is superimposed and applied. Therefore, the operating point on the IV characteristic curve is periodically moved up and down by the AC signal (V _ac ) 4, and the emitter 1 has an emission that changes according to the AC signal (V _ac ) 4. The current I _OP flows.

Therefore, by the electrons emitted from the emitter 1 and reaching the anodes 5-1 and 5-2 and collected,
Anode currents I ₁ , I flowing through anodes 5-1 and 5-2
₂ also changes according to the AC signal 4. The anode currents I ₁ and I ₂ are supplied to the band-pass filter 6-
1, and 6-2 are passed to the detectors 7-1 and 7-2. The band-pass filters 6-1 and 6-2 have frequency characteristics that pass only the same frequency components as the AC signal 4. Therefore, only the components of the AC signal 4 are given to the detectors 7-1 and 7-2. The detectors 7-1 and 7-
2, the magnitude of the anode currents I ₁ and I ₂ is substantially equal in a state where the FE magnetic sensor is not placed in the magnetic field, and Since they are changed in the same direction, the difference between the anode current I ₁ and the anode current I ₂ (I ₁ −I
₂ ) is almost zero.

In this case, the frequency of the AC signal 4 modulating the emission current is set to several tens kHz or more, and the fluctuation frequency is generally a low frequency component. If only the component of the AC signal 4 is extracted by -2, the noise component added to the anode currents I ₁ and I ₂ due to the fluctuation can be removed. Furthermore, several tens of kHz
At the above frequencies, the level of 1 / f noise is also small, so that it is hardly affected by 1 / f noise.

Next, consider the case where the magnetic flux B is applied to such an FE magnetic sensor. As shown
When the magnetic flux B is applied to the FE magnetic sensor in a direction from top to bottom as shown in the figure, the magnetic flux B is emitted from the emitter 1 to the electrons flying toward the anodes 5-1 and 5-2. The Lorentz force acts, and the electron trajectory is bent forward by the magnetic flux B as shown in the figure.

Then, since the anodes 5-1 and 5-2 for collecting the field-emitted electrons are divided into two, one of the ones located in the direction of the electrons whose trajectory is bent by the applied magnetic field B. with current I ₂ of the anode 5-2 is increased, the current I ₁ of the other anode 5-2 is decreased. Since the rate of increase or decrease of the anode currents I ₁ and I ₂ changes according to the direction and strength of the applied magnetic field, the anode currents I ₁ and I ₂ flowing through the two anodes 5-1 and 5-2, respectively. (I ₁ -I ₂ ) of the detectors 7-1 and 7- through the band-pass filters 6-1 and 6-2.
2, the direction and intensity of the applied magnetic field can be detected. In this case, it is not affected by the fluctuation of the emission current and the 1 / f noise as described above.

Next, a second embodiment of the FE magnetic sensor according to the present invention is shown in FIG. In this figure, the FE magnetic sensor 1
The anode currents I ₁ and I ₂ output from 0 are input to a lock-in amplifier (Lock-in AMP) 11. A reference signal is output from the lock-in amplifier 11 and supplied to the modulation signal source 13. That is, the modulation signal output from the modulation signal source 13 is superimposed on the DC bias (V _OP ) and applied to the gate in the FE magnetic sensor 10. As a result, the anode currents I ₁ and I ₂ change in the same manner as the modulation signal output from the modulation signal source 13.

The anode currents I ₁ and I ₂ are inputted to the lock-in amplifier 11 and compared with the reference signal, which is the same signal as the modulation signal, so that the anode currents I ₁ and I ₂ change the same as the modulation signal. , Only the component whose phase matches the modulation signal is extracted. Therefore, noise included in the same frequency as the modulation signal can be removed. Further, the frequency of the modulated signal is
If the frequency is set to kHz, the influence of the fluctuation of the emission current and the influence of the 1 / f noise are of course the same as described above.

FIG. 3 is a block diagram of a generally used lock-in amplifier, and the outline of the lock-in amplifier will be described with reference to FIG. In FIG. 3, the lock-in amplifier is composed of two blocks, a signal system and a reference system.
The weak signal input to 41 is connected to preamplifiers 20 and 2
1. The signal is amplified to a required voltage level together with noise by the attenuator 22 and the middle amplifiers 23 and 25.
Next, a noise component is removed from the input signal by passing through a band-pass filter 26, and the signal is input to a phase-sensitive detector (PSD) 27.

On the other hand, the reference signal (REF) having the same frequency as the measurement signal input to the reference system is supplied to the REF IN 43
Is input to a phase locked loop (PLL) 32 via a buffer 31, and the PLL 32 reproduces a reference signal whose phase is synchronized at the same frequency as that of the reference signal. The phase of the reference signal reproduced by the PLL 32 is adjusted by the phase shifter 33, and the reference signal is supplied to the PSD 27 via the buffer 34 as a drive signal of the PSD 27. The PSD 27 detects the amplitude of the input signal based on the phase of the drive signal. Although the configuration shown in FIG. 3 is configured to receive a reference signal from the outside, the configuration is such that the reference signal is output to the outside from the PLL 32 so that the reference signal is supplied to the sensor side. Can also.

Next, FIG. 4 shows the configuration of a lock-in amplifier that can be used in the present invention based on such a lock-in amplifier. In this figure, anode currents I ₁ and I ₂ output from the FE magnetic sensor 10 are supplied to a first input terminal 5.
5-1 and a second input terminal 55-2, respectively, and are amplified by a first amplifier 51-1 and a second amplifier 51-2 to a predetermined voltage level together with a noise component. 52-1, second synchronization detector 52-2
Is input to The reference signal generated from the reference signal generator 54 is supplied to each of the first synchronization detector 52-1 and the second synchronization detector 52-2, and is synchronized with the reference signal at the same frequency. Is detected from the anode currents I ₁ and I ₂ and output. That is, noise components such as fluctuations included in the anode currents I ₁ and I ₂ can be removed, and the signals of the anode currents I ₁ and I ₂ from which the noise components have been removed are supplied to the differentiator 53 to obtain the difference. The signal (I ₁ −I ₂ ) is calculated, and the sense output terminal 5
7 is output.

The reference signal output from the reference signal generator 54 is output from the reference signal output terminal 56 and supplied to the modulation signal source 13 shown in FIG.
Generates a reference signal having the same phase as the reference signal generated from the reference signal generator 54,
FE magnetic sensor 10 superimposed on _OP as field emission power supply
Is applied to the gates. The synchronization detectors 52-1, 5
2-2 may be a PSD as described above, or may be a correlator composed of a multiplier for multiplying the input signal and the reference signal and an accumulator for accumulating the multiplied output of the multiplier. Furthermore, the reference signal generated from the reference signal generator 54 is not limited to a signal that changes in a sine wave shape, but may be a pattern signal that repeats at a predetermined cycle, for example, an M-sequence code or a PN signal. Further, the amplifiers 51-1 and 51-2 may be provided with a band-pass filter for removing noise.

As described above, in the FE magnetic sensor according to the second embodiment of the present invention, the noise component contained in the same frequency as the reference signal can be removed by comparing the phase with the reference signal. , The S / N ratio becomes better, and a highly sensitive FE magnetic sensor can be obtained.

[0034]

As described above, the magnetic sensor of the present invention is
A few μm is placed through a micro vacuum space.
Between the emitter of the
Pressure is applied, at which time it is released from the tip of the emitter
Detect that electrons change their trajectories due to external magnetic fields
Because it is emitted, extremely as a magnetic sensor
There is an advantage that a small one can be configured.
Further, in such a magnetic sensor, unstable fluctuation in emission current and is a characteristic of electric field emission array,
The deterioration of the S / N ratio due to 1 / f noise can be reduced, and a high-sensitivity magnetic sensor that is less affected by noise can be realized. Furthermore, by extracting only the components that are synchronized with the modulation signal that modulates the emission current, it is possible to remove noise components contained in the same frequency and obtain a sensor output that is stable over time. Can also.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a first embodiment of an FE magnetic sensor according to the present invention.

FIG. 2 is a diagram showing a configuration of a second embodiment of the FE magnetic sensor according to the present invention.

FIG. 3 is a diagram illustrating a general example of a lock-in amplifier.

FIG. 4 is a diagram showing a lock-in amplifier used in a second embodiment of the FE magnetic sensor of the present invention.

FIG. 5 is a principle diagram of the proposed FE magnetic sensor.

FIG. 6 is an IV characteristic diagram of FEA.

FIG. 7 is a diagram showing a change in an operating point due to noise.

FIG. 8 is a diagram showing a relationship between an emission current and a noise frequency.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 FEA 2 Gate 3, 12 DC bias 4 AC signal 5-1, 5-2 Anode 6-1, 6-2 Bandpass filter 7-1, 7-2 Current detector 8 Anode voltage 10 FE magnetic sensor 11 Lock-in Amplifier 13 Modulation signal source 14, 57 Sense output terminal 51-1, 51-2 Amplifier 52-1, 52-2 Synchronization detector 53 Difference device 54 Reference signal generator 55-1, 55-2 Input terminal 56 Reference signal output Terminal

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-62-272169 (JP, A) JP-A-60-127480 (JP, A) JP-A-7-283459 (JP, A) JP-A-7-27 159501 (JP, A) JP-A-6-347525 (JP, A) JP-A-6-308207 (JP, A) JP-A-4-194690 (JP, A) JP-A-58-111767 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G01R 33/028

Claims (7)

(57) [Claims] (1) a tip formed at a sharp vertex;
A mitter and a gate arranged close to the tip of the emitter
And the voltage applied to the gate causes the tip of the emitter to
Separated from each other to capture electrons emitted from the edge
At least two anodes arranged in parallel with each other, and comparing means for detecting a difference between currents flowing through the two anodes, and a DC-biased periodic signal between the emitter and the gate is supplied to a field emission power supply. and it applies as a detection means for taking out only the periodic signal components to the two anodes connected respectively, by retrieving the anode current from each of the detecting means, due to changes in the magnetic field
Noise and noise included in the emission current of the emitter
Field emission type magnetic sensor that removes DC and DC components . 2. The field emission type magnetic sensor according to claim 1, wherein an AC signal is used as the periodic signal. 3. The field emission type magnetic sensor according to claim 2, wherein a filter that passes only the frequency of the AC signal is used as the detection unit. 4. A field emission type magnetic sensor according to claim 2, wherein said detecting means uses a phase detecting means for extracting only a component synchronized in phase with said AC signal. 5. A field emission type magnetic sensor according to claim 1, wherein a pattern signal which repeats a predetermined pattern every period is used as said periodic signal. 6. A phase detector according to claim 5, wherein said detector has the same pattern as said pattern signal, and uses a phase detector for obtaining a correlation with a reference pattern signal whose phase is synchronized. Field emission type magnetic sensor. 7. A field emission type magnetic sensor according to claim 4, wherein a lock-in amplifier is used as said phase detecting means.