KR101581160B1 - Current-in-plane tunneling method for evaluation of magnetic tunnel junctions - Google Patents
Current-in-plane tunneling method for evaluation of magnetic tunnel junctions Download PDFInfo
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- KR101581160B1 KR101581160B1 KR1020150070231A KR20150070231A KR101581160B1 KR 101581160 B1 KR101581160 B1 KR 101581160B1 KR 1020150070231 A KR1020150070231 A KR 1020150070231A KR 20150070231 A KR20150070231 A KR 20150070231A KR 101581160 B1 KR101581160 B1 KR 101581160B1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/02—Measuring direction or magnitude of magnetic fields or magnetic flux
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R1/00—Details of instruments or arrangements of the types included in groups G01R5/00 - G01R13/00 and G01R31/00
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Abstract
The present invention relates to surface horizontal current tunneling measurements for characterization of magnetic tunnel junctions having three or more magnetic layers. The surface horizontal current tunneling (CIPT) measurement method according to the first embodiment of the present invention includes: a step of measuring a sheet resistance value according to a magnetic field change (first step); A sheet resistance value determination step of an equilibrium state and an antiparallel state (second step); A sheet resistance value determination step (fourth step), and a fitting step (fifth step) according to the sheet resistance value determination step (third step), the probe distance (interval), and the intermediate state sheet resistance value determination step. The method for measuring horizontal current in a plane according to the second embodiment of the present invention includes the steps of obtaining a magnetic moment-magnetic field curve according to a magnetic field change (first step); Determining a magnetic field strength in an equilibrium state, an antiparallel state, and an intermediate state (second step); Measuring the sheet resistance value in each state (third step), measuring the sheet resistance value according to the probe distance (fourth step), and fitting step (fifth step).
Description
The present invention relates to current-in-plane tunneling (CIPT) measurements for characterization of magnetic tunnel junctions having three or more magnetic layers.
The magnetic tunnel junction having three or more magnetic layers can improve the voltage dependency of the tunnel magnetoresistance ratio and reduce the critical current density required for magnetization inversion compared with the conventional magnetic tunnel junction having two magnetic layers, And it is possible to reduce energy consumption at the same time. In order to apply this to real products, it is important to confirm the exact characteristics. In the case of measuring the characteristics through the process, it is not easy to evaluate the characteristics of the tunnel junction itself due to the deterioration or defect in the patterning process.
In the conventional plane horizontal current tunneling measurement for magnetic tunnel junctions with three or more magnetic layers, the values obtained through fitting are likely to include errors by considering only the parallel and antiparallel magnetization arrangement states.
It is an object of the present invention to provide a surface horizontal current tunneling measurement for measuring the characteristics of a magnetic tunnel junction capable of improving the accuracy of fitting by taking into account additional magnetization arrangements that may occur in a magnetic tunnel junction having three or more magnetic layers .
The surface horizontal current tunneling measurement method for measuring the characteristics of the magnetic tunnel junction according to the first embodiment of the present invention is a method for measuring three or more magnetic layers and a method for separating the magnetic layers physically adjacent to each other so that the magnetization directions of adjacent magnetic layers can be changed independently For magnetic tunnel junctions that include two or more isolation layers that do not act linearly or do not exhibit a current that flows in response to applied voltages, the sheet resistance values are measured while varying the magnetic field through the probe electrodes to determine the sheet resistance- A first step of obtaining; A second step of determining, from the sheet resistance-magnetic field curve of the first step, a sheet resistance value in an antiparallel state in which the magnetization directions of the respective magnetic layers are all the same and the magnetization directions of the adjacent magnetic layers are opposite to each other; A third step of determining, from the sheet resistance-magnetic field curve of the first step, an intermediate state sheet resistance value in which the magnetization directions of the adjacent two magnetic layers are the same and the magnetization directions of the adjacent two other magnetic layers are opposite; A fourth step of repeating the first to third steps while changing the probe distance; And a fifth step of obtaining the sheet resistance of each of the magnetic layers and the resistance area product of each of the separation layers by fitting them using the sheet resistance value and the model formula determined until the fourth step.
The surface horizontal current tunneling measurement method for measuring the characteristics of the magnetic tunnel junction according to the second embodiment of the present invention is a method of measuring three or more magnetic layers and a method of separating the magnetic layers physically adjacent to each other so that the magnetization directions of the adjacent magnetic layers can be changed independently A first step of obtaining a magnetic moment-magnetic field curve by measuring a magnetic moment while changing a magnetic field for a magnetic tunnel junction including two or more separation layers in which a current flowing in response to a voltage acting thereon or a voltage applied does not linearly appear ; From the magnetic moment-magnetic-field curve of the first step, it is possible to obtain a magnetic field in which the magnetization directions of the magnetic layers are all the same, the antiparallel state in which the magnetization directions of the adjacent magnetic layers are opposite to each other and the magnetization directions of the adjacent two magnetic layers are the same A second step of determining a magnetic field intensity of an intermediate state opposite to a magnetization direction of the magnetic layer; A third step of measuring a sheet resistance value in an equilibrium state, an antiparallel state, and an intermediate state at a determined magnetic field strength using a probe electrode; A fourth step of measuring the sheet resistance value while changing the probe distance; And a fifth step of obtaining a sheet resistance of each of the magnetic layers and a resistance area product of the respective separation layers by fitting using the sheet resistance value obtained by the fourth step and the model formula.
According to the first and second embodiments of the present invention, the probe electrode can be separately formed in the magnetic tunnel junction, wherein the probe electrode formation includes forming an insulating layer for passivation on the magnetic tunnel junction; Forming contact holes in the insulating layer using photolithography and etching; And forming a probe electrode on the insulating layer on which the contact hole is formed by using a photolithography, a metal deposition, and a lift-off process. In addition, in the first step of the first embodiment and the third step of the second embodiment, measurement can be performed using the probe electrode of the commercial equipment without forming the probe electrode separately as described above. The probe electrode may be more than four.
According to the first embodiment of the present invention, the sheet resistance values in the parallel state and the antiparallel state in the second step may be the minimum value and the maximum value, respectively, of the sheet resistance-magnetic field curve.
According to the first embodiment of the present invention, in the third step, the intermediate state sheet resistance value can be determined by confirming the intensity of the magnetic field in which the intermediate state in which the magnetization direction is switched in the sheet resistance-magnetic field curve appears.
According to the first embodiment of the present invention, in the third step, the intermediate state sheet resistance value is a magnetic field having a differential value of 0 or a secondary differential value of 0 when the sheet resistance-magnetic field curve is differentiated, Can be determined as the sheet resistance value in the < RTI ID = 0.0 >
According to the first embodiment of the present invention, in the third step, the sheet resistance value in the intermediate state is obtained by measuring a magnetic moment while changing a magnetic field to obtain a magnetic moment-magnetic field curve, Can be determined by checking the intensity of the magnetic field in which the state appears.
According to the first embodiment of the present invention, in the third step, the intermediate state sheet resistance value is obtained by measuring a magnetic moment while changing a magnetic field to obtain a magnetic moment-magnetic field curve, 0 or magnetic moment - can be determined as the sheet resistance value in a magnetic field whose second derivative is zero, which is obtained by differentiating the magnetic field curve twice.
According to the second embodiment of the present invention, the magnetic field intensity in the intermediate state in the second step can be determined by the intensity of the magnetic field in which the magnetization direction is switched in the magnetic moment-magnetic field curve.
According to the second embodiment of the present invention, in the second step, the magnetic field intensity in the intermediate state is zero when the magnetic moment-magnetic field curve is differentiated by 0 or the second derivative value obtained by differentiating the magnetic moment- Can be determined by the magnetic field intensity.
According to the first and second embodiments of the present invention, the probe distance in the fourth step can be varied within a range of 0.5 to 1000 mu m.
According to the first embodiment and the second embodiment of the present invention, in the fifth step, the model equation may be expressed by the following equation.
[Equation 1]
In Equation (1)
R T , R M and R B are the sheet resistance of each magnetic layer,
RA 1 and RA 2 are resistance area products of the respective separation layers,
K 0 is a second kind of modified Bessel function,
x represents the probe interval.
According to the first and second embodiments of the present invention, the resistance area product of the separation layer may include a resistance area product in a parallel state and a resistance area product in an antiparallel state.
According to the surface horizontal current tunneling measurement method of the present invention, the accuracy of the fitting can be improved by considering the additional magnetization arrangement state that may appear in a magnetic tunnel junction having three or more magnetic layers.
1 is a schematic view illustrating a process of forming a probe electrode for a surface horizontal current tunneling (CIPT) measurement method.
FIG. 2 is a graph showing magnetization arrangement states that may appear in a magnetic tunnel junction having three magnetic layers, and a sheet resistance (b) and a surface horizontal current magnetoresistance ratio (c) according to a probe distance.
3 is a graph showing a sheet resistance (a) and a surface horizontal current magnetoresistance ratio (b) according to a probe interval of a magnetic tunnel junction having three magnetic layers.
4 is a graph showing magnetic moment-magnetic field curves (a) and sheet resistance-magnetic field curves (b) of a magnetic tunnel junction having three magnetic layers.
5 is a graph showing the sheet resistance-field curve (a) and the sheet resistance-field curve (b) of a sheet resistance-magnetic field curve of a magnetic tunnel junction having three magnetic layers.
Hereinafter, the present invention will be described in detail.
The present invention relates to surface horizontal current tunneling (CIPT) measurements for characterization of magnetic tunnel junctions having three or more magnetic layers.
The surface horizontal current tunneling measurement method according to the first embodiment of the present invention includes: a step of measuring a sheet resistance value according to a change in a magnetic field (first step); A sheet resistance value determination step of an equilibrium state and an antiparallel state (second step); A sheet resistance value determination step (fourth step), and a fitting step (fifth step) according to the sheet resistance value determination step (third step), the probe distance (interval), and the intermediate state sheet resistance value determination step.
For the magnetic tunnel junction having three or more magnetic layers in the first step, the sheet resistance value is measured while changing the magnetic field through the probe electrode to obtain the sheet resistance-RH curve as shown in FIG. 4 (b) .
Referring to FIG. 2, a double-barrier magnetic tunnel junction (DMTJ) having three magnetic layers includes an upper magnetic layer, an upper isolation layer, an intermediate magnetic layer, a lower isolation layer, Structure. The magnetic tunnel junction structure of FIG. 2 is merely an example, and the present invention is applicable to all magnetic tunnel junction structures having three or more magnetic layers and two or more separate layers.
In the present invention, the separation layer can be defined as a film in which the magnetization directions of adjacent magnetic layers can be independently changed, or the magnetic layers physically adjacent to each other can be separated, or the current flowing to the applied voltage does not appear linearly , Commonly referred to as a barrier. The number of separation layers may be one or less than the magnetic layer.
The materials of each magnetic layer may be the same or may be different for each layer. The material usable for the magnetic layer is not particularly limited, and for example, CoFeB and the like can be used. The thickness of each magnetic layer is not particularly limited and may be, for example, independently from 0.1 to 100 nm, preferably from 1 to 10 nm.
The materials of each separation layer may be the same or may be different for each layer. The material usable for the separation layer is not particularly limited, and for example, MgO or the like can be used. The thickness of each separation layer is not particularly limited and may be, for example, independently from 0.1 to 100 nm, preferably from 1 to 10 nm.
The magnetic tunnel junction stack may be formed using a sputtering method or the like, and may be formed using, for example, an ultra-high vacuum magnetron sputtering system. The base pressure at this time may be, for example, 1 x 10 < -8 > Torr or less.
The specific structure of the magnetic tunnel junction stack having three magnetic layers is, for example, Ta 5 /
FIG. 1 is a schematic view illustrating a process of forming a probe electrode for a surface horizontal current tunneling (CIPT) measurement method, which illustrates a four-point probe method.
In the first step, the probe electrode may be formed separately in the magnetic tunnel junction, wherein forming the probe electrode includes forming an insulating layer for passivation on the magnetic tunnel junction; Forming a contact hole in the insulating layer using a photolithography and etching process; And forming a probe electrode using a photolithography, a metal deposition, and a lift-off process on the insulating layer on which the contact hole is formed.
The material usable for the insulating layer is not particularly limited, and for example, oxides such as SiO 2 can be used. The thickness of the insulating layer is not particularly limited, and may be, for example, 1 to 1000 nm, preferably 10 to 500 nm. The insulating layer may be formed by a method such as deposition.
The contact hole may be formed by etching after forming a photoresist on the insulating layer. The etching may be inductively coupled plasma reactive ion etching. The contact hole can be connected to the probe electrode, so that the number of contact holes can be the same as the number of probe electrodes, preferably a plurality, more preferably four or more.
The probe electrode may be formed by forming a patterned photoresist on an insulating layer on which a contact hole is formed, depositing an electrode metal, and then removing the photoresist through a lift-off process. The material usable as the electrode metal is not particularly limited, and for example, Cr, Au, or the like can be used. The thickness of the probe electrode is not particularly limited, and may be, for example, 1 to 1000 nm, preferably 10 to 500 nm. The number of the probe electrodes is preferably plural, more preferably four or more.
In addition, in the first step, the probe electrode can be measured by using the probe electrode of commercial equipment, instead of separately forming the probe electrode. Commercial equipment is available from CAPRES A / S.
The magnetic field can be formed and varied by using a magnetic field generator or the like, and the intensity of the magnetic field can be measured using a magnetometer or the like. The sheet resistance can be converted into the sheet resistance value after measuring the voltage and current using a voltage and current measuring device or the like.
In the second step, from the sheet resistance-magnetic field curve (RH curve) shown in FIG. 4 (b) obtained in the first step, the magnetization directions of the respective magnetic layers are all in the same parallel state (P state), and the magnetization directions between adjacent magnetic layers (AP state) in the opposite direction to each other.
Referring to FIG. 2 (a), magnetic tunnel junctions having three magnetic layers can have four magnetization states. (AP state) in which the magnetization directions of the respective magnetic layers are the same in the parallel state (P state), the magnetization directions of the second adjacent magnetic layers are opposite to each other, and the magnetization directions of the third upper magnetic layer and the intermediate magnetic layer are the same and the middle magnetic layer and the lower magnetic layer in the direction of magnetization is opposite to the upper parallel intermediate state (I T), the fourth magnetization of the upper magnetic layer and the intermediate magnetic directions are opposite and the magnetization direction of the middle magnetic layer and lower magnetic layer are the same lower parallel intermediate state (I B ).
The sheet resistance value in the parallel state (P state) and the antiparallel state (AP state) in the second step may be the minimum value and the maximum value, respectively, of the sheet resistance-field curve. Thus, the sheet resistance value in the P state and the AP state can be obtained simply by taking the minimum value and the maximum value appearing while changing the magnetic field. That is, in the R-H curve of FIG. 4 (b), the minimum sheet resistance value indicated by P becomes the sheet resistance value at the P state, and the maximum sheet resistance value indicated by AP may be the sheet resistance value at the AP state.
In the third step, an intermediate state sheet resistance value is determined from the RH curve of the first step. The intermediate state may consist of an upper parallel intermediate state (I T ) and a lower parallel intermediate state (I B ) when there are three magnetic layers and three or more intermediate states when there are four or more magnetic layers. Hereinafter, the case where there are three magnetic layers will be described as an example.
For example, if there are three magnetic layers, the accuracy of the fitting can be improved even when only one of the two intermediate states, especially I T, is taken into account, and the accuracy of the fitting is further improved if both intermediate states are taken into consideration .
In order to determine the sheet resistance value of the intermediate state (I T, I B) to be confirmed that the strength of the magnetic field is an intermediate state (I T, I B) appears.
According to the first method for determining the intermediate state sheet resistance value, the sheet resistance value of I T and the sheet resistance value of I B satisfy the intensity of the magnetic field in which the intermediate state (I T , I B ) in which the magnetization direction is switched in the RH curve appears Can be confirmed and determined. If the distinction between the intermediate states (I T , I B ) is clearly indicated, the sheet resistance values of the intermediate states (I T , I B ) can be obtained without differentiation. However, when it is difficult to distinguish the intermediate state (I T , I B ), accurate information can be obtained by differentiating the RH curve. That is, the sheet resistance value of I T and the sheet resistance value of I B can be determined as a sheet resistance value in a magnetic field in which the derivative value is 0 or the second derivative value of the second derivative of the RH curve is 0 when the RH curve is differentiated. The differential can be applied not only to the first derivative but also to the second derivative such as plural times as necessary.
According to the second method for determining the intermediate state sheet resistance value, the sheet resistance value of I T and the sheet resistance value of I B are obtained by measuring the magnetic moment while changing the magnetic field to obtain a magnetic moment-magnetic field curve (FIG. MH curve), and then determine the intensity of the magnetic field in which the intermediate state (I T , I B ) in which the magnetization direction is switched in the MH curve appears. Likewise, in this case, an intermediate state (I T, I B) of the distinction is certainly appears, it is possible to obtain a sheet resistance value of the intermediate state (I T, I B) immediately, be difficult to distinguish it from the intermediate state (I T, I B) , It is possible to obtain reliable information by differentiating the MH curve. That is, the sheet resistance value of I T and the sheet resistance value of I B are obtained by measuring the magnetic moment while changing the magnetic field to obtain MH, and then, when the MH curve is differentiated, the derivative value is 0 or the second derivative value Can be determined as the sheet resistance value at the zero magnetic field. The differential can be applied not only to the first derivative but also to the second derivative such as plural times as necessary.
In the fourth step, the first to third steps are repeated while varying the probe distance.
Specifically, the sheet resistance value is determined by performing the first to third steps in the first probe distance, the sheet resistance value is determined in the first to third steps again at the second probe distance, By repeating the above procedure for each probe distance, a sheet resistance graph corresponding to the probe distance (interval) as shown in FIG. 3 (a) can be obtained.
The probe distance is not particularly limited, and may be varied within a range of, for example, 0.5 to 1000 mu m. The order of the probe distances is not particularly limited, and can be measured, for example, starting at the shortest distance and widening the distance gradually.
In the fifth step, the sheet resistance of each of the magnetic layers and the resistance-area product (RA) of the respective separation layers are obtained by fitting using the sheet resistance values determined by the fourth step and the model formula.
A fitting can mean a process of assigning a measured value to a model equation to obtain a target value (sheet resistance, resistance area product, etc.). This fitting process can be performed using a separate program.
(RA 1 , P ) of the upper isolation layer in the parallel state, the resistance area product (RA 2 , P ) of the lower isolation layer in the parallel state, and the resistance area product (RA 1 , AP ) of the upper isolation layer in the anti-parallel state, and a resistance area product (RA 2, AP ) of the lower isolation layer in the antiparallel state.
The expression that can be used as a model expression is not particularly limited. For example, the following model expression published by Clement can be used.
[Equation 1]
In Equation (1)
R T , R M and R B denote the sheet resistance of the upper, middle and lower magnetic layers,
RA 1 and RA 2 are resistance area products of the upper and lower separation layers, respectively,
K 0 is a second kind of modified Bessel function,
x represents the probe interval.
Wherein R □ may be the value measured, and special symbols such as R are the ± will use in order to simplify the complex expression.
Using the model formula, it is possible to confirm the resistance area product (RA), the tunnel magnetoresistance ratio (TMR), and the like through the 4-probe method without patterning the magnetic tunnel junction having three or more magnetic layers.
Thus, if the sheet resistance is measured by changing the x-spacing and then the fitting is performed according to the above formula, the resistance area products of the upper, middle, and lower electrode sheet resistance and the upper and lower separation layers can be obtained.
The method for measuring horizontal current in a plane according to the second embodiment of the present invention includes the steps of obtaining a magnetic moment-magnetic field curve according to a magnetic field change (first step); Determining a magnetic field strength in an equilibrium state, an antiparallel state, and an intermediate state (second step); Measuring the sheet resistance value in each state (third step), measuring the sheet resistance value according to the probe distance (fourth step), and fitting step (fifth step).
First, in a magnetic tunnel junction including three or more magnetic layers and two or more separate layers, a magnetic moment is measured while changing a magnetic field to obtain a magnetic moment-magnetic field curve (MH curve ). Magnetic fields and magnetic moments can be measured using commercial equipment (VSM: Vibrating Sample Magnetometer) or directly manufactured equipment.
In the second step, the M-H curve of the first step is determined by checking the magnetic field strength in the parallel, antiparallel, and intermediate states. In this case, the magnetic field intensity in the equilibrium state can be a value when the magnetic moment is the maximum in the MH curve as shown in FIG. 4 (a), and the magnetic field strength in the anti- Lt; / RTI > The magnetic field intensity in the intermediate state can be determined by the intensity of the magnetic field in which the magnetization direction is switched in the M-H curve. If the distinction of the intermediate state is clearly shown on the M-H curve, the intermediate state value can be obtained without differentiation. However, when it is difficult to distinguish the intermediate state, it is possible to determine the derivative of the MH curve as 0 or the magnetic field strength when the second derivative of the MH curve is differentiated to 0, as in the first embodiment, .
In the third step, the sheet resistance is measured in the equilibrium state, antiparallel state, and intermediate state at the determined magnetic field intensity using the probe electrode. At this time, the sheet resistance value can be measured by using commercial equipment.
In the fourth step, the sheet resistance value is measured while varying the probe distance.
In the fifth step, the sheet resistance of each magnetic layer and the resistance area product of each of the separation layers are obtained by fitting using the sheet resistance values obtained by the fourth step and the model formula.
As described above, according to the second embodiment of the present invention, it is possible to take only the sheet resistance value under each magnetic field without the sheet resistance-magnetic field curve after confirming the magnetic field strength in the parallel state, antiparallel state and intermediate state from the magnetic moment- Do. The greatest difference from the first embodiment is that, in the second embodiment, the sheet resistance value is measured after checking each state first. The remaining configuration may be the same as or similar to that of the first embodiment.
2 (b) and 2 (c) show the magnetization arrangement states that can appear in the magnetic tunnel junction having three magnetic layers, and FIG. 2 (a) Fig. (B) and the conditions in (c) 1 (Condition 1) in Fig. 2 RA 1 = RA 2 = 50 ㏀㎛ 2, R T = R M = R B = 50 Ω / □,
In the conventional measurement method, when the sheet resistance is measured, the parallel state (P state in FIG. 2A) in which the magnetization directions of all the magnetic layers are aligned in one direction and the magnetization directions of the adjacent magnetic layers in the opposite direction Only the AP state in the parallel state (Fig. 2 (a)) is considered. It is very difficult to find out the values of 7 variables by fitting only two measured values.
As shown in FIGS. 2 (b) and 2 (c), the sheet resistance and the magnetoresistance ratio in the parallel and antiparallel states of the two tunnel junctions having different characteristics are almost the same. 2 (b) and 2 (c) show the calculated values, but in actual experiments, the discrimination power may be further deteriorated due to measurement noise or errors.
In the present invention, the accuracy of the fitting can be improved by considering the additional magnetization arrangement state (I T , I B state in FIG. 2 (a)) that may appear in a magnetic tunnel junction having three or more magnetic layers.
In the two tunnel junctions of FIG. 2, the measured values in the parallel and antiparallel states are almost identical, but the measured values in the upper parallel intermediate state (I T ) and the lower parallel intermediate state (I B ) are clearly distinguished .
In the structure of a magnetic tunnel junction having three or more magnetic layers, an exchange coupling interaction is caused by using an antiferromagnet in the upper and lower electrodes, and it is possible to exhibit an I T state as well as a parallel state and an antiparallel state. It is also possible to have all four magnetization arrangement states according to the magnetization direction. Therefore, it is possible to apply the present invention to almost all magnetic tunnel junctions.
FIG. 3 is a graph showing (a) surface resistance and (b) surface horizontal current magnetoresistance ratio according to the probe interval of a magnetic tunnel junction having three magnetic layers, wherein the measured values in the parallel state and the anti- It is almost impossible to distinguish between fitting results (square and dotted lines) and fitting results (solid lines) using the method of the present invention.
FIG. 3 compares the conventional fitting method and the fitting method of the present invention with respect to values measured in a magnetic tunnel junction having three magnetic layers, and since the conventional method does not use intermediate states (I T and I B ) , It can be seen that when only the parallel and anti-parallel states (P, AP) are compared, the fitting lines are almost overlapped and can not be distinguished.
nevertheless. The results in Table 1 reveal the difference. The results of both methods are similar for the RA (RA 1 + RA 2 ) of the entire tunnel junction, but the RA of the lower separation layer is larger in the parallel state (RA 2, P ) than the antiparallel state (RA 2, AP ) (RA 2, P > RA 2, AP ). This is a physically impossible result, and the deviation from the conventional method is also large. Therefore, the application of the present invention is essential for accurately evaluating the characteristics of the magnetic tunnel junction having three or more magnetic layers.
Table 1 compares the fitting results by the conventional method of FIG. 3 (using parallel and antiparallel states only) and the present invention (using parallel and antiparallel states with intermediate states). In the data of Table 1, the ± right value represents the standard deviation.
FIG. 4 is a graph showing (a) an M-H curve and (b) an R-H curve of a magnetic tunnel junction having three magnetic layers, and the magnetization arrangement state according to the switching of each magnetic layer can be known through steps of an M-H curve.
Measuring sheet resistance values in parallel and antiparallel states is not difficult to obtain because data can be obtained by taking minimum and maximum values while changing the magnetic field. However, in order to check the value in the intermediate state, it is necessary to confirm the intensity of the magnetic field in which the intermediate state appears by using the following methods.
1) Check the M-H curve
2) Confirm R-H curve and its derivative value (dR / dH)
The first method is to check a magnetic field condition in which an intermediate state appears through a magnetic hysteresis curve (M-H curve) as shown in FIG. 4 (a). In the sample of FIG. 4, when the magnetic field is reduced to about 500 Oe after saturating to 4 kOe, the lower magnetic layer is switched to an intermediate state that is parallel to the upper portion only.
The second method is to check the intermediate state through derivative of the R-H curve. If the distinction of the intermediate state is clearly seen in the R-H curve, the intermediate state value can be obtained without differentiation. However, when it is difficult to distinguish the intermediate state as shown in FIG. 4 (b), it is possible to obtain reliable information by differentiating the R-H curve. In the first method, since the magnetic moment according to the magnetic field must be measured separately, the second method which is possible with only one measurement (R-H) is preferable.
FIG. 5 is a graph showing (a) dR / dH and (b) R-H curves of a magnetic tunnel junction having three magnetic layers, and shows a graph of R-H curves and their derivative values in FIG. In the differential graph of FIG. 5 (a), if there is a certain distinction between the intermediate states, there will be a flat section with a differential value of 0 between two peaks in the negative direction of the red line. However, in the data of FIG. 5, the distinction of the intermediate state is not certain, so that the two peaks are partially overlapped. In this case, the position where the maximum value appears is the intermediate state. When there is noise as shown in FIG. 5 (a), it is possible to take a maximum value after curve fitting.
In existing surface horizontal current tunneling measurement methods for magnetic tunnel junctions with three or more magnetic layers, it is highly likely that the values obtained through fitting will include errors by considering only the parallel and antiparallel magnetization arrangement states. However, it is possible to use the intermediate state of at least one of the two or more intermediate alignment states to detect the invisible difference in the parallel and anti-parallel states, thereby achieving accurate results by reducing the error of the fitting.
Magnetic memories using magnetic tunnel junctions are attracting attention due to their fast operation speed, nonvolatility characteristics, and stable durability. If the magnetic memory is successfully implemented using a magnetic tunnel junction with three or more magnetic layers, it is expected that energy consumption can be reduced while improving stability. To this end, the study of magnetic tunnel junctions with three or more magnetic layers needs to be further explored, and accurately evaluating the properties of the films at the deposition stage is crucial to move on to subsequent process steps. By using the method proposed in the present invention, it is possible to accurately confirm the characteristics of the film without side effects due to the pattern process, and thus it is expected that the research efficiency can be maximized.
Claims (15)
A second step of determining, from the sheet resistance-magnetic field curve of the first step, a sheet resistance value in an antiparallel state in which the magnetization directions of the respective magnetic layers are all the same and the magnetization directions of the adjacent magnetic layers are opposite to each other;
A third step of determining, from the sheet resistance-magnetic field curve of the first step, an intermediate state sheet resistance value in which the magnetization directions of the adjacent two magnetic layers are the same and the magnetization directions of the adjacent two other magnetic layers are opposite;
A fourth step of repeating the first to third steps while changing the probe distance; And
And a fifth step of obtaining the sheet resistance of each of the magnetic layers and the resistance area product of each of the separation layers by fitting using the determined sheet resistance value and the model formula up to the fourth step,
Wherein the sheet resistance values in the parallel state and the antiparallel state in the second step are the minimum value and the maximum value respectively in the sheet resistance values of the sheet resistance-magnetic field curve, respectively.
From the magnetic moment-magnetic-field curve of the first step, it is possible to obtain a magnetic field in which the magnetization directions of the magnetic layers are all the same, the antiparallel state in which the magnetization directions of the adjacent magnetic layers are opposite to each other and the magnetization directions of the adjacent two magnetic layers are the same A second step of determining a magnetic field intensity of an intermediate state opposite to a magnetization direction of the magnetic layer;
A third step of measuring a sheet resistance value in an equilibrium state, an antiparallel state, and an intermediate state at a determined magnetic field strength using a probe electrode;
A fourth step of measuring the sheet resistance value while changing the probe distance; And
And a fifth step of obtaining the sheet resistance of each of the magnetic layers and the resistance area product of each of the separation layers by fitting using the sheet resistance value obtained by the fourth step and the model formula.
Measurement of surface horizontal current tunneling for characterization of magnetic tunnel junctions.
The probe electrode is formed separately in the magnetic tunnel junction,
The probe electrode formation
Forming an insulating layer for passivation on the magnetic tunnel junction;
Forming contact holes in the insulating layer using photolithography and etching; And
And forming a probe electrode by using a photolithography, a metal deposition and a lift-off process on the insulating layer on which the contact hole is formed, in order to measure the characteristics of the magnetic tunnel junction.
Wherein the probe electrode utilizes a probe electrode of commercial equipment. A method of measuring horizontal current tunneling for characterization of a magnetic tunnel junction.
Wherein the number of the probe electrodes is four or more; and measuring horizontal current tunneling for measuring the characteristics of the magnetic tunnel junction.
Wherein the intermediate state sheet resistance value in the third step is determined by determining the intensity of the magnetic field in which the intermediate state in which the magnetization direction is switched in the sheet resistance-magnetic field curve is determined and the surface horizontal current tunneling measurement for measuring the characteristics of the magnetic tunnel junction .
In the third step, the sheet resistance value of the intermediate state is determined as a sheet resistance value in a magnetic field having a derivative value of 0 or a second derivative value of 0 when the sheet resistance-magnetic field curve is differentiated twice, Measurement of horizontal current tunneling for measuring the characteristics of magnetic tunnel junctions.
In the third step, the sheet resistance value of the intermediate state is measured by measuring the magnetic moment by measuring the magnetic moment while changing the magnetic field, and then determining the intensity of the magnetic field in which the magnetization direction is switched in the magnetic moment- Wherein the surface horizontal current tunneling measurement is for measuring the characteristics of the magnetic tunnel junction.
In the third step, the intermediate state sheet resistance value is obtained by measuring the magnetic moment while changing the magnetic field, obtaining the magnetic moment-magnetic field curve, and then, when the magnetic moment-magnetic field curve is differentiated, the derivative value is 0 or the magnetic moment- Wherein the sheet resistance value is determined as a sheet resistance value at a magnetic field whose differential second derivative is zero.
Wherein the magnetic field intensity in the intermediate state in the second step is determined by the intensity of the magnetic field in which the magnetization direction is switched in the magnetic moment-magnetic field curve.
The magnetic field intensity in the intermediate state in the second step is determined by the magnetic field intensity whose differential value is 0 or whose second derivative value is 0 when the magnetic moment-magnetic field curve is differentiated to zero or the magnetic moment-magnetic field curve is differentiated twice. Measurement of surface horizontal current tunneling for characterization of magnetic tunnel junctions.
And the probe distance in the fourth step is varied in the range of 0.5 to 1000 mu m.
Wherein the model equation in the fifth step is the following equation: Surface horizontal current tunneling measurement for measuring the characteristics of a magnetic tunnel junction:
[Equation 1]
In Equation (1)
R T , R M and R B are the sheet resistance of each magnetic layer,
RA 1 and RA 2 are resistance area products of the respective separation layers,
K 0 is a second kind of modified Bessel function,
x represents the probe interval.
Wherein the resistive area product of the separation layer in the fifth step comprises a product of a resistance area area in a parallel state and a resistance area product in an antiparallel state.
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| US20090168254A1 (en) * | 2007-12-31 | 2009-07-02 | Ying Hong | Test device and method for measurement of tunneling magnetoresistance properties of a manufacturable wafer by the current-in-plane-tunneling technique |
| KR20100135181A (en) * | 2009-06-16 | 2010-12-24 | 소니 주식회사 | Memory device and memory |
| US20140252356A1 (en) * | 2013-03-08 | 2014-09-11 | Avalanche Technology Inc. | Devices and methods for measurement of magnetic characteristics of mram wafers using magnetoresistive test strips |
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| US20090168254A1 (en) * | 2007-12-31 | 2009-07-02 | Ying Hong | Test device and method for measurement of tunneling magnetoresistance properties of a manufacturable wafer by the current-in-plane-tunneling technique |
| KR20100135181A (en) * | 2009-06-16 | 2010-12-24 | 소니 주식회사 | Memory device and memory |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| US11271037B2 (en) | 2019-07-09 | 2022-03-08 | Samsung Electronics Co., Ltd. | Data storage devices including a first top electrode and a different second top electrode thereon |
| US11600662B2 (en) | 2019-07-09 | 2023-03-07 | Samsung Electronics Co., Ltd. | Data storage devices including a first top electrode and a different second top electrode thereon |
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