JP2006032840A - Inspecting method and device of tunnel magnetoresistive effect element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inspecting method and a device of TMR element capable of definitely confirming reliability in TMR element without breaking the element in a short time. <P>SOLUTION: Whether a pulse noise is generated or not is detected by applying a higher voltage than that normally used to the TMR element to evaluate the TMR element in response to the existence or non-existence of the generation. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method and apparatus for inspecting a TMR element such as a head element or a magnetoresistive memory (MRAM) using the tunnel magnetoresistive effect (TMR).

  After manufacturing a magnetic head having a TMR head element or during its manufacture, it is usually performed to evaluate whether it is a good product or a defective product. As one of the evaluations, it is required to confirm reliability that can withstand long-term use depending on whether or not the breakdown voltage is sufficiently large.

  In Patent Document 1, as an inspection method for confirming reliability without damaging or destroying the TMR head element, a resistance value is measured by passing a set initial current value through the TMR head element and measuring the resistance value. The test current value is obtained using the value, or the correction current value is obtained several times based on the resistance value and the voltage value which is a measurement standard of the element, and the final corrected current value is supplied to the TMR head element. A method is disclosed in which a resistance value is measured, an inspection current value is obtained using the final resistance value, and a characteristic inspection such as an electromagnetic conversion characteristic of the TMR head element is conducted using the inspection current value thus obtained. ing.

JP 2001-23131 A

  However, the inspection method described in Patent Document 1 needs to finally perform a characteristic inspection such as an electromagnetic conversion characteristic of the TMR head element, and it takes a lot of labor and a very long time to confirm the reliability. Has a big problem.

  Accordingly, an object of the present invention is to provide a method and apparatus for inspecting a TMR element that can confirm the reliability of the TMR element in a short time, easily and reliably.

  According to the present invention, there is provided a method for inspecting a TMR element in which a voltage higher than that during normal use is applied to the TMR element to detect the occurrence of pulse noise, and the TMR element is evaluated according to the presence or absence of the occurrence. .

  Whether or not pulse noise is output is detected by applying a higher voltage than in normal use. For this reason, it is possible to evaluate the quality of the TMR element very easily and in a short time. In addition, in this case, since the quality evaluation can be performed without causing element destruction, it is possible to select the quality of the TMR elements. In particular, in the present invention, since a voltage higher than the normal working voltage is applied to the TMR element, the reliability of the TMR element can be confirmed in a very short time, which is very effective for mass production.

  The applied voltage is preferably a DC voltage of 250 mV or more.

  It is also preferable that the applied voltage is lower than the voltage that damages the TMR element.

  The detection of the presence or absence of occurrence of pulse noise is to compare the output of the TMR element with a predetermined threshold value, and it is preferable to evaluate that the TMR element is defective when the output of the TMR element exceeds this threshold value.

  It is also preferable that the predetermined threshold value is 1.2 times the peak value of the normal output of the TMR element.

  It is also preferable that detection of occurrence of pulse noise is performed in a state where a DC external magnetic field in a predetermined direction is applied to the TMR element. As a result, the influence of Barkhausen noise (BHN) can be removed.

  According to the present invention, means for applying a higher voltage to the TMR element than in normal use, means for detecting the presence or absence of generation of pulse noise from the TMR element in a state where this voltage is applied, There is provided an inspection apparatus for a TMR element comprising means for evaluating the TMR element.

  As described above, it is detected whether pulse noise is output by applying a voltage higher than that in normal use. For this reason, it is possible to evaluate the quality of the TMR element very easily and in a short time. In addition, in this case, since the quality evaluation can be performed without causing element destruction, it is possible to select the quality of the TMR elements. In particular, in the present invention, since a voltage higher than the normal working voltage is applied to the TMR element, the reliability of the TMR element can be confirmed in a very short time, which is very effective for mass production.

  The means for applying the voltage is preferably means for applying a DC voltage of 250 mV or more to the TMR element.

  It is also preferable that the means for applying the voltage is a means for applying a voltage lower than the voltage that damages the TMR element.

  The means for detecting is a means for comparing the output of the TMR element with a predetermined threshold, and the means for evaluating is a means for evaluating that the TMR element is defective when the output of the TMR element exceeds the threshold. Preferably there is.

  It is also preferable that the predetermined threshold value is 1.2 times the peak value of the normal output of the TMR element.

  It is also preferable to further include means for applying a DC external magnetic field in a predetermined direction to the TMR element when detecting whether or not pulse noise is generated. As a result, the influence of BHN can be removed.

  It is also preferable that the TMR element is a TMR head element or an MRAM.

  According to the present invention, the quality of a TMR element can be evaluated very easily and in a short time, and the quality can be evaluated without causing element breakdown. In particular, in the present invention, since a voltage higher than the normal working voltage is applied to the TMR element, the reliability of the TMR element can be confirmed in a very short time, which is very effective for mass production.

  FIG. 1 is a diagram schematically illustrating a configuration for inspecting a TMR head element as one embodiment of the present invention.

  In the figure, reference numeral 10 denotes a bar member in which a plurality of TMR heads are connected to each other and arranged in a row, and 11 denotes a TMR head element inspection apparatus.

  The bar member 10 is in a state in which MR height processing is performed after a wafer formed by forming a large number of TMR heads in a matrix is cut and separated into individual bar members. Each TMR head 10a of the bar member 10 is electrically connected to a TMR read head element, an inductive write head element, a pair of terminal pads 10b electrically connected to the TMR read head element, and the inductive write head element. And a pair of terminal pads 10c connected to each other.

  The inspection device 11 is a device that can measure a wide band up to several tens of MHz, for example, up to 80 MHz. Specifically, a pair of probes 11a that can be electrically contacted with a pair of terminal pads 10b for a TMR read head element, and are electrically connected to the pair of probes 11a. A constant voltage circuit 11b that supplies a high constant voltage, a wide-band current measurement circuit 11c that is electrically connected to a pair of probes 11a and measures the value of a current flowing through the TMR head element, and a current measurement circuit 11c A wide-band A / D converter 11d for converting the analog output of the current measurement circuit 11c representing the measured current value into a digital signal, and an A / D converter 11d. The digital signal is continuously input to determine the output voltage of the TMR head element and compared with a threshold value to determine whether the TMR head element is good and And a digital computer 11e for controlling the operation of the pressure circuit 11b and the A / D converter 11d.

  FIG. 2 is a flowchart for explaining the processing operation of the inspection apparatus 11 in the present embodiment.

  First, a pair of probes 11a are brought into electrical contact with a terminal pad 10b of a TMR head element that evaluates the quality of the bar member 10, and in this state, the constant voltage circuit 11b performs TMR in an environment where the magnetic disk device is used. Application of a constant voltage to the TMR head element that is higher than the normal operating voltage applied to the element, for example, 250 mV or more, and lower than a voltage that damages the TMR head element, for example, 400 mV is started (step S1). In this case, in order to suppress the influence of the magnetic field generated by the sense current flowing through the TMR head element, it is desirable that a DC external magnetic field is applied in the magnetization direction of the free layer of the TMR head element so that BHN is not generated.

  Next, the current measurement circuit 11c measures the value of the current flowing through the TMR head element, and inputs the value to the computer 11e to calculate the output voltage value of the TMR head element (step S2). The output voltage value can be easily calculated from the resistance value of the TMR head element and the measured current.

  The calculated output voltage value is compared with a predetermined threshold value (step S3). As the threshold value in this case, for example, a value about 1.2 times the peak value of the baseline output in which no pulse noise exists is used. However, the numerical value of 1.2 is merely an example, and other numerical values may of course be used. Further, a value that does not depend on the peak value of the normal baseline output may be used as the threshold value.

  If the output voltage value is greater than or equal to the threshold value, it is determined that pulse noise has occurred, and the TMR head element is evaluated to be defective (step S5). On the other hand, if the output voltage value is less than the threshold value, the process proceeds to the next step S4, where it is determined whether or not a predetermined time has elapsed since the start of this inspection. The predetermined time in this case is a considerably short time of about 5 seconds, for example.

  If the predetermined time has not elapsed, the measurement and calculation process in step S2 and the comparison determination process in step S3 are repeated. If the predetermined time has elapsed, the process proceeds to the next step S6, and it is evaluated that the TMR head element is a non-defective product (step S6).

  Next, the same evaluation is sequentially performed on the other TMR head elements of the bar member 10.

  FIG. 3 is a sectional view of an example of the structure of the TMR read head element to be evaluated as seen from a direction orthogonal to the air bearing surface (ABS), and FIG. 4 is a view of the TMR read head element from the ABS direction. It is sectional drawing.

  As shown in these drawings, the TMR layer portion of the TMR read head element includes an antiferromagnetic layer (PtMn150Å) 32, a pinned layer on a lower shield layer (NiFe) 30 via a buffer layer (Ta / NiFe) 31. (CoFe20Å / Ru8Å / CoFe30Å) 33, barrier layer (Al5.75Å-Ox) 34, free layer (CoFe20Å / NiFe30Å) 35, and cap layer (Ta) 36 are sequentially laminated. An upper shield layer 38 is laminated via a metal gap layer 37. A bias layer 39 is formed in the track width direction of the TMR layer portion. The order of stacking the TMR layers may be reversed.

  Next, the reason why the TMR head element can be evaluated for quality by the processing operation shown in FIG. 2 will be described.

  5 to 7 are graphs respectively showing the results of measuring output voltages of different TMR head elements with a wide-band measuring instrument in a state where a magnetic field from a recording medium or an external AC magnetic field is not applied. The horizontal axis represents time (μsec), and the vertical axis represents the output voltage (mV) after amplifying the TMR head element output by the amplifier. In this case, the voltage applied to the TMR head element is 300 mV, which is higher than 150 mV, which is a normal use voltage applied to the TMR head element in the usage environment of the magnetic disk device.

  In this way, a voltage higher than the normal operating voltage is applied, and an external DC magnetic field in the magnetization direction of the free layer is applied, but no other external magnetic field is applied, and measurement is possible up to a band of several tens of MHz. When the output of the TMR head element is measured by a wide-band measuring device, a substantially constant baseline output is observed in the TMR head element of FIG. On the other hand, in the TMR head element of FIG. 6, pulse noise is sometimes generated even in a very short period of 5 μsec. In the TMR head element of FIG. There is a lot of noise.

  In order to actually determine whether or not the TMR head element generates pulse noise, whether or not the measured absolute value of the output voltage of the TMR head element is equal to or greater than a predetermined threshold, for example, the peak of the output voltage in FIG. If the voltage is Vp, for example, it is determined whether or not the threshold is 1.2 Vp or more.

  For these TMR head elements, when the withstand voltage test is performed by gradually increasing the applied voltage, the breakdown voltage of the TMR head element of FIG. 5 is as high as about 700 mV, whereas the TMR head elements of FIG. 6 and FIG. The breakdown voltage was as low as about 400 mV. Therefore, the TMR head element of FIG. 5 in which no pulse noise is generated can be evaluated as a good product with a normal barrier layer and high reliability. The TMR head element in FIG. 6 and FIG. Since a pinhole would have occurred in the layer, it could be evaluated as a defective product with low reliability.

  When the same withstand voltage test is performed on a plurality of TMR head elements, the distribution is divided into two groups, group A and group B, as shown in FIG. In FIG. 8, the horizontal axis represents the head element resistance value, and the vertical axis represents the breakdown voltage.

The TMR head elements A _{1 to} A ₅ included in the group A are evaluated as highly reliable products because their breakdown voltages are about 700 mV, and the TMR head elements B _{1 to} B ₅ included in the group B are rated as breakdown voltages. Is evaluated as a defective product with low reliability since it is as low as about 400 mV.

  As described above, according to the present embodiment, it is possible to examine the reliability of the TMR head element and evaluate the quality thereof very easily and in a short time. In addition, in this case, since the reliability can be evaluated without causing element destruction, it is possible to select whether the TMR head element is good or bad. In particular, in this embodiment, since a voltage higher than the normal use voltage is applied to the TMR head element, the reliability of the TMR head element can be confirmed in a very short time, which is very effective for mass production.

  In the embodiment described above, 300 mV is applied to the TMR head element as a voltage higher than the normal use voltage, but it was confirmed how much voltage can be applied to evaluate the reliability of the TMR head element in a short time. . Table 1 shows the presence or absence of pulse noise generation for 5 seconds when the applied voltage is set to 150 mV, 200 mV, 250 mV, 300 mV, and 350 mV for 44 TMR head element samples. It shows the result of further increasing the withstand voltage test. However, the sample with the withstand voltage characteristic “low” has an element breakdown voltage of about 400 mV, and the sample with “high” has an element breakdown voltage of about 700 mV.

  A sample in which pulse noise occurs at any applied voltage has low withstand voltage characteristics, which is a TMR head element having a pinhole in the barrier layer. Even samples that do not generate pulse noise when the applied voltage is 150 mV or 200 mV, have low withstand voltage characteristics. However, the withstand voltage characteristics are always high in samples with an applied voltage of 250 mV or more and no pulse noise. Therefore, when the applied voltage is 250 mV or more, preferably about 300 mV, the reliability of the TMR head element can be evaluated in a short time and reliably.

  FIG. 9 summarizes the contents of Table 1 and shows the frequency of samples with and without the occurrence of pulse noise.

  As can be seen from the figure, when the applied voltage is 150 mV and 200 mV, the frequency of the samples without pulse noise generation exceeds the frequency of the samples with high withstand voltage characteristics. Indicates that it contains low ones. If the applied voltage is 250 mV or higher, the frequency of samples without pulse noise coincides with the frequency of samples with high withstand voltage characteristics, and the presence or absence of pulse noise enables almost complete selection of pinholes. You can see that

  FIG. 10 is a diagram schematically illustrating a part of a configuration for inspecting a TMR head element according to another embodiment of the present invention.

  In the embodiment of FIG. 1, the TMR head element is inspected in the state of the bar member after the MR height processing, but in this embodiment, the magnetic head slider 100 is separated from the bar member. Then, the pair of terminal pads 100b of the TMR head element is electrically contacted with the pair of probes 101a to perform the inspection. Other configurations, operations, and effects of the inspection apparatus are the same as those in the embodiment of FIG.

  FIG. 11 is a diagram schematically illustrating a part of a configuration for inspecting a TMR head element according to still another embodiment of the present invention.

  In the present embodiment, a pair of probes 111a are electrically connected to connection pads 112a that are electrically connected to the TMR head element in a head gimbal assembly (HGA) in which a magnetic head slider 110 is mounted on a suspension 112. Contact and test. Other configurations, operations, and effects of the inspection apparatus are the same as those in the embodiment of FIG.

  In the above-described embodiment, the case of inspecting the TMR head element has been described. However, it is obvious that the present invention can be similarly applied to the case of inspecting the MRAM.

  All the embodiments described above are illustrative of the present invention and are not intended to be limiting, and the present invention can be implemented in other various modifications and changes. Therefore, the scope of the present invention is defined only by the claims and their equivalents.

It is a figure which illustrates schematically the structure which test | inspects a TMR head element as one Embodiment of this invention. It is a flowchart explaining the processing operation of the test | inspection apparatus in embodiment of FIG. FIG. 2 is a cross-sectional view of an example of the structure of each TMR read head element in the embodiment of FIG. 1 as viewed from a direction orthogonal to ABS. FIG. 4 is a cross-sectional view of the TMR read head element of FIG. 3 as viewed from the ABS direction. It is a graph showing the result of having measured the output voltage of the TMR head element with the broadband measuring device in the state which has not applied the magnetic field from a recording medium, or an external alternating current magnetic field. It is a graph showing the result of having measured the output voltage of the TMR head element with the broadband measuring device in the state which has not applied the magnetic field from a recording medium, or an external alternating current magnetic field. It is a graph showing the result of having measured the output voltage of the TMR head element with the broadband measuring device in the state which has not applied the magnetic field from a recording medium, or an external alternating current magnetic field. It is a graph showing the result of having withstand a voltage test about a plurality of TMR head elements. It is the figure which summarized the content of Table 1 and represented the frequency of the sample with and without pulse noise generation | occurrence | production. It is a figure which illustrates schematically a part of structure which test | inspects the TMR head element in other embodiment of this invention. It is a figure which illustrates roughly a part of structure which test | inspects the TMR head element in other embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Bar member 10a TMR head 10b, 10c, 100b One pair of terminal pad 11 Inspection apparatus 11a, 101a, 111a One pair of probe 11b Constant voltage circuit 11c Current measurement circuit 11d A / D converter 11e Digital computer 100, 110 Magnetic head Slider 112 Suspension 112a A pair of connection pads

Claims (16)

  A tunnel magnetoresistive element characterized by applying a voltage higher than that during normal use to a tunnel magnetoresistive element to detect the presence of pulse noise and evaluating the tunnel magnetoresistive element according to the occurrence of the noise Effect element inspection method.   The method according to claim 1, wherein the applied voltage is a DC voltage of 250 mV or more.   3. The method according to claim 1, wherein the applied voltage is lower than a voltage that damages the tunnel magnetoresistive element.   The detection of the presence or absence of the occurrence of pulse noise compares the output of the tunnel magnetoresistive element with a predetermined threshold, and the tunnel magnetoresistive element when the output of the tunnel magnetoresistive element exceeds the threshold The method according to claim 1, wherein the method is evaluated as a defective product.   5. The method according to claim 4, wherein the predetermined threshold is a value that is 1.2 times a peak value of a normal output of the tunnel magnetoresistive element.   6. The method according to claim 1, wherein the presence / absence of the pulse noise is detected in a state in which a DC external magnetic field in a predetermined direction is applied to the tunnel magnetoresistive effect element.   The method according to claim 1, wherein the tunnel magnetoresistive element is a tunnel magnetoresistive head element.   The method according to any one of claims 1 to 6, wherein the tunnel magnetoresistive element is a magnetoresistive memory.   Means for applying a higher voltage to the tunnel magnetoresistive effect element than in normal use, means for detecting the presence or absence of pulse noise from the tunnel magnetoresistive effect element in the state in which the voltage is applied, and depending on the presence or absence of the occurrence An inspection apparatus for a tunnel magnetoresistive effect element, comprising: means for evaluating the tunnel magnetoresistive effect element.   10. The apparatus according to claim 9, wherein the means for applying the voltage is a means for applying a DC voltage of 250 mV or more to the tunnel magnetoresistive element.   11. The apparatus according to claim 9 or 10, wherein the means for applying the voltage is means for applying a voltage lower than a voltage damaging the tunnel magnetoresistive element.   The means for detecting is a means for comparing the output of the tunnel magnetoresistive element with a predetermined threshold, and the means for performing the evaluation is the tunnel magnetoresistive element when the output of the tunnel magnetoresistive element exceeds the threshold. 12. The apparatus according to claim 9, wherein the magnetoresistive element is a means for evaluating that the magnetoresistive element is defective.   13. The apparatus according to claim 12, wherein the predetermined threshold value is a value that is 1.2 times the peak value of the normal output of the tunnel magnetoresistive element.   The apparatus according to any one of claims 9 to 13, further comprising means for applying a DC external magnetic field in a predetermined direction to the tunnel magnetoresistive effect element when detecting whether or not the pulse noise is generated. .   The device according to claim 9, wherein the tunnel magnetoresistive element is a tunnel magnetoresistive head element. The apparatus according to claim 9, wherein the tunnel magnetoresistive element is a magnetoresistive memory.

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