KR20230079974A - Driving method for thin film magneto resistance sensor - Google Patents

Abstract

One embodiment of the present invention is a method of driving a thin film magnetoresistive sensor including a plurality of magnetoresistive bodies formed on a substrate, a first step of applying a bias voltage to a bridge circuit to which the plurality of magnetoresistance bodies are connected, from the bridge circuit A method for driving a thin film magnetoresistive sensor comprising a second step of sensing an output voltage and a third step of measuring a change in a magnetic field by analyzing a change in the output voltage, wherein the bias voltage is in the form of a pulse, Measurement errors caused by resistance heat generated when current flows through the magnetoresistive material can be eliminated.

Description

Driving method for thin film magneto resistance sensor {Driving method for thin film magneto resistance sensor}

The present invention relates to a method for driving a thin film magnetoresistive sensor.

The thin-film magnetoresistive sensor can measure a magnetic field using a change in resistance caused by Planar Hall Resistance (PHR) and Anisotropic Magneto-Resistance (AMR). The thin-film magnetoresistive sensor depends on the direction of current flowing through the ferromagnetic thin film, the direction of magnetization of the ferromagnetic thin film, and the direction of an external magnetic field. The thin film magnetoresistance sensor may measure a magnetic field by arranging four magnetoresistive elements formed of ferromagnetic thin films in a Wheatstone bridge structure and measuring a change in output voltage. It is difficult to form the four magnetoresistive bodies exactly the same, and an offset voltage may be output. In addition, resistance heating (Joule heating) may occur in the process of measuring the magnetic field by applying a current to the magnetoresistive material. Resistance heating can change the resistance of the magnetoresistive body, causing a change in output voltage, which can cause an error in the thin film magnetoresistive sensor.

KR 10-1891413 B1

An object according to an embodiment of the present invention is to provide a method for driving a thin film magnetoresistive sensor in which a bias voltage in the form of a pulse is applied to four magnetoresistive elements arranged in a Wheatstone bridge structure.

An object according to an embodiment of the present invention is to provide a method for driving a thin film magnetoresistive sensor for correcting drift of an output signal due to resistance heating using an output signal due to resistance heating measured in the absence of an external magnetic field. it is for

A method of driving a thin film magnetoresistance sensor according to an embodiment of the present invention is a method of driving a thin film magnetoresistance sensor including a plurality of magnetoresistance elements formed on a substrate, wherein a bias voltage is applied to a bridge circuit to which the plurality of magnetoresistance elements are connected. It may include a first step of applying, a second step of sensing an output voltage from the bridge circuit, and a third step of measuring a change in a magnetic field by analyzing a change in the output voltage. In this case, the bias voltage may be in the form of a pulse.

In addition, the on time of the pulse may be determined as a minimum time for the magnetoresistive element to generate a resistance change due to a magnetic field.

In addition, the off time of the pulse may be determined as a minimum time for the temperature of the magnetoresistive body to recover to an original temperature before the pulse is applied.

In addition, before performing the first step, a preparation step of sensing and storing an output voltage when a bias voltage is applied to the bridge circuit in the absence of the magnetic field may be further performed. At this time, in the third step, the output voltage stored in the preparation step is subtracted from the output voltage sensed in the second step to obtain a change in output voltage due to the magnetic field, and the change in the magnetic field can be measured by analysis.

Features and advantages of the present invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings.

Prior to this, the terms or words used in this specification and claims should not be interpreted in a conventional and dictionary sense, and the inventor may appropriately define the concept of the term in order to explain his or her invention in the best way. It should be interpreted as a meaning and concept consistent with the technical idea of the present invention based on the principle that there is.

According to an embodiment of the present invention, by applying a bias voltage in the form of a pulse to four magnetoresistive elements arranged in a Wheatstone bridge structure, resistance heating can be minimized and drift of an output signal caused by resistance heating can be quickly stabilized.

An object according to an embodiment of the present invention is to correct an output signal drift due to resistance heating, so that an accurate measurement value can be obtained even if a magnetic field is measured at high speed before a warm-up time for the output signal drift to be stabilized.

1 is a diagram showing a Wheatstone bridge circuit of a thin film magnetoresistive sensor according to an embodiment of the present invention.
2 is a graph showing an output voltage drift that occurs when a DC bias voltage is applied.
3 is a flowchart showing each step of a method of driving a thin film magnetoresistive sensor according to an embodiment of the present invention.
4 is a graph showing output voltage drift due to self-heating when a bias voltage in the form of a pulse is applied.
5 is a view showing a comparison between a waveform of an output signal when there is no external magnetic field and a waveform of an output signal when there is an external magnetic field.

Objects, advantages, and features of one embodiment of the present invention will become more apparent from the following description of one embodiment in conjunction with the accompanying drawings. In adding reference numerals to components of each drawing in this specification, it should be noted that the same components have the same numbers as much as possible, even if they are displayed on different drawings. In addition, terms such as "one side", "other side", "first", and "second" are used to distinguish one component from another, and the components are not limited by the above terms. no. Hereinafter, in describing an embodiment of the present invention, a detailed description of related known technologies that may unnecessarily obscure the subject matter of an embodiment of the present invention will be omitted.

In addition, it should be noted that the terms used in the present invention are only used to describe specific embodiments and are not intended to limit the present invention, and singular expressions include plural expressions unless otherwise specified in context.

Hereinafter, with reference to the accompanying drawings, an embodiment of the present invention will be described in detail.

1 is a diagram showing a Wheatstone bridge circuit of a thin film magnetoresistive sensor 1 according to an embodiment of the present invention.

The thin film magnetoresistive sensor 1 may include a plurality of magnetoresistive elements 13 . A plurality of magnetoresistive bodies 13 may be connected in a Wheatstone bridge structure. A plurality of magnetoresistive elements 13 may be connected by a line 12 that transmits an electrical signal. Line 12 may be formed of an electrically conductive material. The line 12 may be formed of a wire or an electrode pattern formed on a substrate. The thin film magnetoresistive sensor 1 may be formed on a substrate. The substrate may be formed of various materials such as silicon (Si), PCB, glass, and the like. The magnetoresistive body 13 may be formed of a material having ferromagnetism. For example, the magnetoresistive body 13 may be formed of a metal such as Ni or Fe or an alloy including the same. The magnetoresistive body 13 may be formed in a thin film shape on the substrate. The magnetoresistive body 13 may be formed in various patterns such as a rectangle and a serpentine. The first to fourth magnetoresistive bodies 13a, 13b, 13c, and 13d may have the same shape and size and have the same resistance.

In the magnetoresistive body 13, the first to fourth magnetoresistive bodies 13a, 13b, 13c, and 13d may be spaced apart from each other and connected in a Wheatstone bridge structure. The first magnetoresistive body 13a and the second magnetoresistive body 13b may be connected in series, and the third magnetoresistive body 13c and the fourth magnetoresistive body 13d may be connected in series. The first magnetoresistive body 13a and the third magnetoresistive body 13c may be connected in parallel, and the second magnetoresistive body 13b and the fourth magnetoresistive body 13d may be connected in parallel. The connection point between the first magnetoresistive body 13a and the third magnetoresistive body 13c (first point P1) and the connection point between the second magnetoresistive body 13b and the fourth magnetoresistive body 13d (second point P2) ) is applied with a bias voltage (V _B ), and the connection point (third point P3) of the first magnetoresistive body 13a and the second magnetoresistive body 13b and the third magnetoresistive body 13c and the fourth magnetoresistive body The voltage between the connection points (the fourth point P4) of (13d) may be the output voltage Vo.

The power supply unit 11 is connected between the first point P1 and the second point P2 to apply a bias voltage V _B to the magnetoresistive body 13 . The measurement unit 14 may be connected between the third point P3 and the fourth point P4 to obtain the output voltage Vo. The measurement unit 14 may perform an information processing function of recognizing and analyzing the voltage between the third point P3 and the fourth point P4 to calculate the strength of the external magnetic field.

When the resistances of the first to fourth magnetoresistive bodies 13a, 13b, 13c, and 13d connected by the Wheatstone bridge structure are the same (R1=R2=R3=R4) and no external magnetic field is applied, the output voltage ( Vo) becomes 0V. The output voltage Vo can be calculated as in Equation 1.

(V+): voltage of the third point (P3), (V-): voltage of the fourth point (P4), V _B : bias voltage (V _B ), R1: resistance of the first magnetoresistive body (13a), R2 : Resistance of the second magnetoresistive body 13b, R3: Resistance of the third magnetoresistive body 13c, R4: Resistance of the fourth magnetoresistive body 13d, Vo: Output voltage (Vo)

It is an ideal case that the first to fourth magnetoresistive bodies 13a, 13b, 13c, and 13d have the same resistance. Actually, the resistance of the first to fourth magnetoresistive bodies 13a, 13b, 13c, and 13d is different due to variations in manufacturing or various other causes (R1≠R2≠R3≠R4). Therefore, even if an external magnetic field is not applied, the output voltage Vo exists, and this is called an offset voltage. Offset voltage may be caused by various causes.

Since the first to fourth magnetoresistive elements 13a, 13b, 13c, and 13d are not perfectly identical physically, an offset voltage may be generated due to a difference in resistance. The resistance of the magnetoresistive body 13 may vary even if the shape is slightly different. The offset voltage generated by the shape mismatch of the magnetoresistive body 13 can be corrected by adding or subtracting from the output voltage Vo.

Resistance of the magnetoresistive body 13 may change according to temperature change. Depending on the material constituting the magnetoresistive body 13, the resistance change is different according to the temperature change. The change in resistance according to the temperature change can be expressed using the temperature coefficient (α). The temperature coefficient (α) can be expressed as in Equation 2 below.

α: temperature coefficient, R: current resistance, Ra: resistance before temperature change, △T: changed temperature

The current resistance can be expressed as Equation 3 below.

α: temperature coefficient, R: current resistance, Ra: resistance before temperature change, △T: changed temperature

The same temperature change may occur throughout the first to fourth magnetoresistive bodies 13a, 13b, 13c, and 13d. For example, the ambient temperature of the thin film magnetoresistive sensor 1 may increase due to an increase in air temperature, and the temperature of the entirety of the first to fourth magnetoresistive elements 13a, 13b, 13c, and 13d may equally rise. In this case, the voltage (V+) _ΔT of the third point P3 and the voltage (V−) _ΔT of the fourth point P4 may be obtained as shown in Equation 4 below.

(V+) _△T : voltage of the third point (P3) after temperature change, (V-) _△T : voltage of fourth point (P4) after temperature change, V _B : bias voltage (VB), R1: first Resistance of magnetoresistive body 13a, R2: resistance of second magnetoresistive body 13b, R3: resistance of third magnetoresistive body 13c, R4: resistance of fourth magnetoresistive body 13d, α: temperature coefficient

Referring to Equations 1 and 4, the voltage ((V+) _ΔT ) of the third point P3 after temperature change is equal to the voltage V+ of the third point P3 when there is no temperature change, It can be confirmed that the voltage ((V-) _ΔT ) of the fourth point P4 after the temperature change is the same as the voltage (V-) of the fourth point P4 when there is no temperature change. Therefore, the offset voltage generated by the shape difference between the first to fourth magnetoresistive bodies 13a, 13b, 13c, and 13d remains as it is, but no additional offset voltage is generated due to temperature change. That is, when the temperatures of the first to fourth magnetoresistive bodies 13a, 13b, 13c, and 13d change equally with the overall change in ambient temperature, no offset voltage is generated in the output voltage Vo.

Materials with resistance generate joule heating when current flows through them. The amount of heat generated by resistance is different depending on the resistance of each of the first to fourth magnetoresistive bodies 13a, 13b, 13c, and 13d. The temperature change (ΔT) of the magnetoresistive body 13 due to resistance heating is proportional to the power consumption (P=I ² R). The same current flows through the first magnetoresistive body 13a and the second magnetoresistive body 13b connected in series. Since the first magnetoresistive body 13a and the second magnetoresistive body 13b have different resistances (R1≠R2), resistance heating is also different. The voltage ((V+) _I ) of the third point P3 due to resistance heating can be calculated as in Equation 5 below.

(V+) _I : voltage at the third point (P3) due to resistance heating, V _B : bias voltage (VB), R1: resistance of the first magnetoresistive body 13a, R2: resistance of the second magnetoresistive body 13b , α: temperature coefficient, I: current, (V+): voltage of the third point (P3)

In Equation 5, if the resistance R1 of the first magnetoresistive body 13a and the resistance R2 of the second magnetoresistive body 13b are the same, the voltage at the third point P3 due to resistance heating ((V+) _I ) is equal to the voltage (V+) of the third point (P3) of Equation 1. However, in reality, the resistance R1 of the first magnetoresistive body 13a and the resistance R2 of the second magnetoresistive body 13b are not equal (R1≠R2). The ratio of the resistance R1 of the first magnetoresistive body 13a and the resistance R2 of the second magnetoresistive body 13b (R1=kR2) can be expressed as k. In a practical case, the voltage ((V+) _I ) of the third point P3 due to resistance heating can be calculated as in Equation 6 below.

(V+) _I : voltage at the third point (P3) due to resistance heating, V _B : _{bias voltage (VB)} , R1: resistance of the first magnetoresistive body 13a, R2: resistance of the second magnetoresistive body 13b , α: temperature coefficient, I: current, (V+): voltage at the third point (P3), k: resistance (R1) of the first magnetoresistive body (13a) and resistance (R2) of the second magnetoresistive body (13b) rain of

In Equation 6, the voltage ((V+) _I ) of the third point P3 due to resistance heating is different from the voltage V+ of the third point P3 of Equation 1. Since the resistance R3 of the third magnetoresistive body 13c and the resistance R4 of the fourth magnetoresistive body 13d are different, this phenomenon occurs in the same way at the voltage V- of the fourth point P4. That is, the difference in resistance of the first to fourth magnetoresistive bodies 13a, 13b, 13c, and 13d causes a difference in resistance heating when current is applied. The difference in resistance heating of the first to fourth magnetoresistive bodies 13a, 13b, 13c, and 13d causes a resistance change according to a temperature change. The difference between resistance changes of the first to fourth magnetoresistive bodies 13a, 13b, 13c, and 13d changes the voltage at the third point P3 and the voltage at the fourth point P4 to generate an offset voltage. The overall temperature change does not cancel each other out and does not affect the output voltage, but the offset voltage generated by resistance heating does not cancel each other out and affects the output voltage. Therefore, it is necessary to minimize the effect of the offset voltage due to resistance heating on the measurement of the magnetic field.

2 is a graph showing an output voltage drift (Vo drift) that occurs when a DC bias voltage (VB) is applied.

FIG. 2 is a result of measuring the output voltage Vo at 30-second intervals after applying a DC bias voltage VB to the bridge circuit shown in FIG. 1 for 5 minutes in the absence of an external magnetic field. It can be seen that the output voltage Vo continues to move every 30 seconds. When the bias voltage VB is direct current (DC), current continues to flow through the magnetoresistive body 13, so resistance heating continues. If resistance heating continues, the resistance of the magnetoresistive body 13 continues to change, and the output voltage Vo also continues to move. This phenomenon is referred to herein as output voltage drift (Vo drift) due to resistance heating.

If an external magnetic field is measured during this output voltage drift (Vo drift), measurement accuracy is lowered. This is because the output voltage (Vo) varies at each measurement point in the same external magnetic field environment. Therefore, in this case, a stabilization process is required in which the bias voltage VB is applied until there is almost no voltage drift. After a sufficient time for stabilization has passed, the output voltage drift (Vo drift) caused by resistance heating disappears, and from this time, the change in the external magnetic field can be accurately measured.

However, a sufficient period for the output voltage drift (Vo drift) to be stabilized may vary, and a time point at which a change in an external magnetic field should be measured may vary. Depending on the development of technology, multiple measurements may be required in a short period of time, or measurements may be required immediately upon system startup. Therefore, waiting for a stabilization period is not a solution.

3 is a flowchart showing each step of a method of driving the thin film magnetoresistive sensor 1 according to one embodiment of the present invention.

A method of driving a thin film magnetoresistive sensor 1 according to an embodiment of the present invention relates to a method of driving a thin film magnetoresistive sensor 1 including a plurality of magnetoresistive elements 13 formed on a substrate. The driving method of the thin film magnetoresistive sensor 1 may include a preparation step and a measurement step. The measuring step may include a first step, a second step, and a third step. The driving method of the thin film magnetoresistive sensor 1 includes a first step (S21) of applying a bias voltage (VB) to a bridge circuit to which a plurality of magnetoresistive elements (13) are connected, and sensing an output voltage (Vo) from the bridge circuit. It may include a second step (S22), and a third step (S22) of measuring the change in the magnetic field by analyzing the change in the output voltage (Vo). In this case, the bias voltage VB may have a pulse form.

The first step is to apply a bias voltage (VB) in the form of a pulse to the bridge circuit. When the bias voltage VB in the form of a pulse is applied in the first step, the output voltage Vo can be measured during the on-time Ton of the pulse. After sensing the output voltage Vo in the second step, the change in the magnetic field can be measured by analyzing the change in the output voltage Vo in the third step.

As shown in FIG. 1, a pulse includes an on time (Ton) and an off time (Toff) in one period (TP). When the bias voltage VB in the form of a pulse is applied, there is an off time Toff in which no current flows through the magnetoresistive body 13, and resistance heating does not occur during that time. Therefore, the amount of offset voltage generated by resistance heating can be reduced.

4 is a graph showing output voltage drift (Vo drift) due to self-heating when a bias voltage (VB) in the form of a pulse is applied. 4 is a result of measuring the output voltage (Vo) every 30 seconds when the bias voltage (VB) is DC (100%) and the on-time (Ton) of the pulse is 80%, 60%, 40%, and 20% indicates

It can be seen that the most output voltage drift (Vo drift) occurs when the bias voltage (VB) in the form of direct current is applied. It can be seen that the smallest output voltage drift (Vo drift) occurs when the ratio of the on-time (Ton) of the pulse is 20%. That is, the smaller the on-time (Ton) of the pulse, the smaller the output voltage drift (Vo drift) occurs.

In the case of applying the bias voltage (VB) in the form of direct current, the output voltage drift (Vo drift) increases even after 5 minutes. When the on-time (Ton) of the pulse is 60%, it can be seen that the output voltage drift (Vo drift) does not increase any longer and is stabilized after about 3 minutes and 30 seconds. When the on-time (Ton) of the pulse is 20%, it can be confirmed that the output voltage drift (Vo drift) does not increase any more and is stabilized after about 1 minute and 30 seconds. That is, it can be seen that the shorter the on-time (Ton) of the pulse is, the shorter the time for the output voltage drift (Vo drift) to be stabilized becomes.

The shorter the on-time (Ton) of the pulse, the smaller the output voltage drift (Vo drift) and the shorter the stabilization time. Therefore, the shorter the on-time (Ton) of the pulse, the higher speed measurement is possible. Table 1 below shows the degree of drift of the output voltage (Vo) and the resolution limit when the ratio of the on-time (Ton) of the pulse is different.

On-time (Ton) rate of pulse Magnitude of output voltage drift (Vo drift) after 5 minutes When sensor sensitivity is 2V/T
Minimum measurement resolution limit 100% 30mV > 15mT 80% 21 mV > 10.5mT 60% 10 mV > 5mT 40% 6mV > 3mT 20% 2.4 mV > 1.2mT One% ~10 ㎶ > ~5 μT

In Table 1, when the pulse on time (Ton) ratio is 100%, 80%, 60%, 40%, and 20%, it is the data derived from the experiment, and when it is 1%, it is 100% and 80% , 60%, 40%, and 20% are obtained by calculating according to the trend of the values. In Table 1, it can be seen that the lower the ratio of the on-time (Ton) of the pulse, the smaller the output voltage drift (Vo drift) after 5 minutes. In addition, it can be seen that the lower the pulse on-time (Ton) ratio is, the lower the minimum measurement resolution limit is. The driving method of the thin film magnetoresistive sensor 1 according to an embodiment of the present invention uses a bias voltage (VB) in the form of a pulse, but may use a pulse having a minimum on-time ratio (Ton). At this time, the minimum time possible as the on-time (Ton) of the pulse may be determined as the minimum time for the magnetoresistive body 13 to generate resistance fluctuations due to the magnetic field. In other words, the minimum time possible as the on-time (Ton) of the pulse is the minimum time in which a change due to an external magnetic field appears as a change in magnetoresistance when a current is applied to the magnetoresistive body 13 during the on-time (Ton) of the pulse. am. Since one embodiment of the present invention uses a pulse having a minimum on-time (Ton), the thin film magnetoresistive sensor 1 is quickly stabilized, has a high resolution, and can perform a large number of measurements within a fixed time. there is.

Meanwhile, resolution higher than 5 μT, which is the minimum resolution limit when the sensor sensitivity is 2 V/T and the on-time (Ton) of the pulse is 1%, may be required. Measurements may be required before the stabilization time has elapsed. In the driving method of the thin film magnetoresistive sensor 1 according to an embodiment of the present invention, when high-speed measurement is required, the difference between the output voltage Vo when the bias voltage VB is turned on or off A differential method of subtraction is applied, but correction can be performed by purely measuring the output voltage drift (Vo drift) in the absence of an external magnetic field and subtracting it from the output voltage (Vo).

In the driving method of the thin film magnetoresistive sensor 1 according to an embodiment of the present invention, before performing the first step, the output voltage (Vo) when the bias voltage (VB) is applied to the bridge circuit in the absence of a magnetic field. ), a preparation step of sensing and remembering may be further performed. At this time, the third step subtracts the output voltage (Vo) stored in the preparation step from the output voltage (Vo) sensed in the second step to obtain a change in the output voltage (Vo) due to the magnetic field, and analyzes the change in the magnetic field. can be measured

The preparation step may be performed before the first step. After performing the preparation step once, the measurement step can be repeatedly performed. The preparation step is performed in the absence of an external magnetic field. The preparation step is to perform the first step and the second step in the absence of an external magnetic field and memorize the output voltage (Vo) measured in the second step. In detail, a bias voltage (VB) in the form of a pulse is applied to the bridge circuit in the absence of an external magnetic field. That is, the first step is performed in the absence of an external magnetic field. And measure the output voltage (Vo). That is, the second step is performed. At this time, the output voltage (Vo) is shown in FIG.

5 is a diagram showing a comparison between a waveform of an output signal when there is no external magnetic field and a waveform of an output signal when there is an external magnetic field. A graph showing the temperature change of the magnetoresistive body 13, a graph showing the output voltage Vo, and a graph showing the bias voltage VB are displayed together.

Referring to FIG. 5, a case without an external magnetic field is referred to. When the pulse is on, the output voltage (Vo) rises, while the pulse is on, drift of the output voltage (Vo) occurs due to resistance heating, and when the pulse is off, the output voltage (Vo) becomes 0. At the same time, when the pulse is on, the temperature of the magnetoresistive body 13 starts to rise, while the pulse is on, the temperature of the magnetoresistive body 13 rises, and when the pulse is turned off, the temperature of the magnetoresistive body 13 starts to rise. starts to decrease The temperature of the magnetoresistive body 13 can be restored to its original state after a sufficient period of time.

In the preparation step, in FIG. 5 , the output voltage Vox when there is no external magnetic field may be stored. After the preparation phase, the measurement phase is performed. The measuring step may have an external magnetic field.

In FIG. 5, refer to the case where there is an external magnetic field. When the pulse is on, the output voltage (Vo) rises, while the pulse is on, drift of the output voltage (Vo) occurs due to resistance heating, and when the pulse is off, the output voltage (Vo) becomes 0.

Here, since an external magnetic field exists, the drift of the output voltage Vo occurs in a state where resistance change due to the external magnetic field exists. Therefore, the output voltage Voy in the presence of an external magnetic field is different from the output voltage Vox in the absence of an external magnetic field. The third step subtracts the output voltage (Vox) when there is no external magnetic field stored in the preparation step from the output voltage (Voy) when there is an external magnetic field sensed in the second step, and the output voltage (Voz) changed by the magnetic field. ) can be acquired and analyzed to measure the change in the magnetic field.

The time point at which the difference (Voz) between the output voltage (Voy) in the presence of an external magnetic field and the output voltage (Vox) in the absence of an external magnetic field is obtained may be the last time (t2) of the on-time (Ton) of the pulse. . That is, at the point t2 in FIG. 5, the output voltage difference (Voz) can be obtained. This is because current flows through the magnetoresistive body 13 during the on-time (Ton) of the pulse, so that time is required to generate a change in magnetoresistance due to an external magnetic field.

In the driving method of the thin film magnetoresistive sensor 1 according to an embodiment of the present invention, the off time (Toff) of the pulse is the minimum time at which the temperature of the magnetoresistive element 13 recovers to the original temperature before the pulse is applied. can be determined by the time of As shown in FIG. 5, the turn-off time (Toff) of the pulse is longer than the period from the time point (t2) when the pulse is turned off to the time point (t3) when the temperature of the magnetoresistive body 13 recovers to the original temperature before the application of the pulse (t3). can be set longer.

If the temperature rise of the magnetoresistive body 13 due to resistance heating does not recover to the original temperature before the pulse is applied and the pulse flows again, the resistance heating may continue to accumulate. In this case, even if the output voltage Vox stored in the preparation step when there is no external magnetic field is subtracted in the third step, an error due to resistance heating still exists in the output voltage Vo. Therefore, it is preferable that the off-time (Toff) of the pulse is set longer than the time for the temperature of the magnetoresistive body 13 to recover to its original temperature.

As described above, in the driving method of the thin film magnetoresistive sensor 1 according to an embodiment of the present invention, in the absence of an external magnetic field, the output voltage Vox reflecting the effect of resistance heating by current is stored, and the external The difference from the output voltage (Voy) in the presence of a magnetic field can be calculated, and the difference can be recognized as the effect of an external magnetic field. Therefore, the effect of output voltage drift (Vo drift) caused by resistance heating can be removed, and the external magnetic field can be accurately measured.

Although the present invention has been described in detail through specific examples, this is for explaining the present invention in detail, the present invention is not limited thereto, and within the technical spirit of the present invention, by those skilled in the art It will be clear that the modification or improvement is possible.

All simple modifications or changes of the present invention fall within the scope of the present invention, and the specific protection scope of the present invention will be clarified by the appended claims.

1: thin film magnetoresistive sensor
10: bridge circuit
11: power supply
12: line
13: magnetoresistive body
14: measuring part

Claims (4)

A method of driving a thin film magnetoresistive sensor including a plurality of magnetoresistive bodies formed on a substrate,
a first step of applying a bias voltage to a bridge circuit to which the plurality of magnetoresistive bodies are connected;
a second step of sensing an output voltage from the bridge circuit; and
A third step of measuring a change in a magnetic field by analyzing a change in the output voltage;
The bias voltage is in the form of a pulse, a method of driving a thin film magnetoresistive sensor. The method of claim 1,
The on time of the pulse is
A method of driving a thin film magnetoresistive sensor, wherein the magnetoresistive element is determined as a minimum time for generating a resistance change by a magnetic field. The method of claim 1,
The off time of the pulse is
A method of driving a thin film magnetoresistive sensor, wherein the temperature of the magnetoresistive body is determined by a minimum time for recovering to an original temperature before a pulse is applied. The method of claim 1,
Before performing the first step, a preparation step of sensing and storing an output voltage when a bias voltage is applied to the bridge circuit in the absence of the magnetic field is further performed,
The third step is
A method for driving a thin film magnetoresistive sensor, wherein the change in output voltage due to a magnetic field is obtained by subtracting the output voltage stored in the preparation step from the output voltage sensed in the second step, and the change in the magnetic field is measured by analysis.

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