JP2008059655A - Method of evaluating characteristic of thin film magnetic head - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To precisely select a thin film magnetic head whose recording and reproducing performance deteriorates at a low temperature. <P>SOLUTION: After applying a first effective recording current to a writing element to record the signal on a recording medium, the signal recorded on the recording medium is read by a reading element to obtain a recording and reproducing characteristic value to the first effective recording current (S1). A second effective recording current lower than the first effective recording current is applied to the writing element to record the signal on the recording medium and thereafter, the signal recorded on the recording medium is read by a reading element to obtain a recording and reproducing characteristic value to the second effective recording current (S2). The absolute value of the difference between the first recording and reproducing characteristic value and the second recording and reproducing characteristic value is obtained (S3). When the second recording and reproducing characteristic value does not satisfy a second reference value and the absolute value of the difference is not smaller than a third reference value, the thin film magnetic head is determined to be a defective. In the other cases, the thin film magnetic head is determined to be a nondefective (S4). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for evaluating characteristics of a thin film magnetic head. The present invention relates to a method for discriminating a thin film magnetic head whose recording / reproducing characteristics deteriorate particularly at low temperatures.

  Conventionally, hard disk drives have been mainly used in personal computers and servers as devices capable of recording large amounts of data, but in recent years their use has expanded, for example to be installed in car navigation systems and portable terminals. It has become to. Along with this, hard disks are required to operate even in harsh temperature environments than before. Recently, the problem at low temperature is particularly problematic. When the temperature is lowered, the holding force of the magnetic recording medium is increased and recording becomes difficult, so that the recording / reproducing characteristics are deteriorated. In order to compensate for the deterioration, for example, in Patent Document 1, the hard disk is provided with a temperature sensor, and the recording / reproduction characteristics are optimized by adjusting the effective write current at a low temperature. In Patent Document 2, the error rate degradation at low temperatures is compensated by adjusting the current flowing through the reading element to optimize the recording / reproducing characteristics. Here, the error rate is an index indicating how much error is included in data read after predetermined data is written, and is usually defined as follows.

Error rate = Log10 (number of error data / data population)
In this way, the hard disk drive optimizes the recording / reproduction characteristics at low temperatures. However, even a thin film magnetic head before being incorporated into the hard disk drive can be efficiently There is a need to screen for evaluation.

  Unlike the case of a hard disk drive, when evaluating the recording / reproduction characteristics of a thin film magnetic head at a low temperature, it is desirable to keep the entire evaluation apparatus at a low temperature, and a large-scale cooling device is required for that purpose. In addition, since it takes a considerable time to change the temperature of the entire evaluation apparatus having a large heat capacity, it is not easy to measure a thin film magnetic head at a low temperature.

Patent Document 3 discloses a method for evaluating in a hard disk drive the recording / reproducing characteristics of a thin film magnetic head whose characteristics deteriorate at low temperatures. In this method, the error rate is measured for two types of track densities, and if the difference between the error rates is smaller than a certain reference value, it is determined that the recording / reproducing characteristics are deteriorated at a low temperature.
JP 2004-5952 A JP 2005-116166 A JP 2006-172638 A

  The error rate difference disclosed in Patent Document 3 means the amount of error rate degradation caused by the leakage magnetic field from the write element. This evaluation method is based on the premise that if the amount of deterioration is small, the leakage magnetic field from the recording element is small, and a head with a small leakage magnetic field is generally weak in recording ability itself, and as a result, the recording ability will be insufficient at low temperatures. Yes. In practice, however, thin-film magnetic heads with strong recording ability but small leakage magnetic field from the recording element are judged to be heads that are erroneously deteriorated at low temperature by this method. There is a problem that a large thin film magnetic head is mistakenly determined to be a normal product.

  An object of the present invention is to provide a method for more accurately selecting a thin film magnetic head whose recording / reproduction characteristics deteriorate at low temperatures.

  In order to solve the above problems, the method for evaluating the recording / reproducing characteristics of the thin film magnetic head according to the present invention recorded the signal on the recording medium after applying the first effective recording current to the writing element and recording the signal on the recording medium. A first step of obtaining a predetermined recording / reproduction characteristic value for the first effective recording current by reading the signal with the reading element, and a second effective recording current lower than the first effective recording current to the writing element A second step of obtaining a predetermined recording / reproduction characteristic value with respect to the second effective recording current by reading the signal recorded on the recording medium with a reading element after applying the signal to the recording medium and applying the first step; A third step of obtaining an absolute value of a difference between the predetermined recording / reproducing characteristic value for the effective recording current and the predetermined recording / reproducing characteristic value for the second effective recording current;

  By using a second effective recording current that is lower than the first effective recording current, the recording capability of the thin film magnetic head decreases, so the retention of the magnetic recording medium increases at low temperatures and the recording characteristics deteriorate. The situation can be simulated. Another cause of deterioration in recording / reproduction characteristics at low temperatures is that the magnetic distance between the recording medium and each element of the thin film magnetic head increases due to shrinkage of the writing and reading elements of the thin film magnetic head at low temperatures. Can be mentioned. In magnetic recording, the recording / reproduction characteristics deteriorate at a low temperature because the recording / reproduction characteristics deteriorate as the magnetic distance increases. In the present invention, utilizing the difference between the expansion amount generated in the write element and the read element of the thin film magnetic head by heat generated by the first effective recording current and the expansion amount generated by heat generated by the second effective recording current, Changes in the magnetic distance between the recording medium and each element of the thin film magnetic head due to temperature can be simulated.

  If the specified recording / reproduction characteristic value for the first effective recording current does not satisfy the first reference value and the absolute value of the difference is greater than or equal to the third reference value, the thin film magnetic head is determined to be defective. In this case, it is possible to use a determination method for determining that the product is non-defective. If the predetermined recording / reproduction characteristic value for the second execution recording current does not satisfy the second reference value and the absolute value of the difference is equal to or greater than the third reference value, the thin film magnetic head is determined to be defective. In other cases, it is also possible to use a determination method for determining a non-defective product.

  As described above, according to the present invention, it is possible to simulate the environment in which the thin film magnetic head actually operates at room temperature and low temperature, and the thin film magnetic head whose recording / reproducing characteristics deteriorate at low temperature is obtained. More efficient sorting is possible. Since the present invention measures the influence of the recording magnetic field itself, not the leakage magnetic field, the possibility of erroneously determining a normal head and a head that deteriorates at a low temperature, which was a problem in the prior art, is reduced. A thin film magnetic head whose recording / reproducing characteristics deteriorate at low temperatures can be selected.

  Embodiments of the present invention will be described below with reference to the drawings. First, an example of a spin stand which is an evaluation apparatus for carrying out the present invention is shown in FIG. The spin stand 1 includes a base 2 as a support for the apparatus. The recording medium 3 that is a magnetic disk is rotated at an arbitrary number of rotations by a spindle motor (not shown) provided on the base 2. The spinstand 1 also includes a thin film magnetic head 4 that records and reproduces magnetic information on a recording medium. The thin film magnetic head 4 has a writing element 4a and a reading element 4b. The thin film magnetic head 4 is supported by a carriage 5, and the rotary stage 6 on which the carriage 5 is mounted rotates to scan the recording medium 3 in a direction across the width of a predetermined measurement track. The rotary stage 6 is mounted on a linear stage 7 that moves in parallel, and the distance between the rotation center of the recording medium 3 and the rotation center of the carriage 5 can be changed. The thin film magnetic head 4 is connected to a preamplifier 8 for adjusting a read output and changing a recording state. The preamplifier 8 is connected to a processing device 9 equipped with a CPU (Central Processing Unit), a memory, a display, and the like. Connected. A read channel 10 for measuring the error rate is built in the processing device 9. The arithmetic circuit 11 is a circuit for selecting a non-defective product and a defective product of the thin film magnetic head by calculating a difference between the two error rates after measuring the error rate with two types of effective recording currents.

  Next, a method for evaluating a thin film magnetic head using the present invention will be described. FIG. 2 is a flowchart of a method for evaluating recording / reproduction characteristics of a thin film magnetic head described below.

  (Step 1) First, a recording current that can saturate magnetically record the recording medium is applied to the writing element 4a of the thin film magnetic head 4, the data recorded on the recording medium is read by the reading element 4b, and the read channel 10 is used. Measure the error rate. The current applied at this time is the first effective recording current, and the obtained error rate is a predetermined recording / reproducing characteristic value for the first recording current. After measurement, the error rate value is stored in the memory. FIG. 3 is a diagram showing the relationship between the error rate measured with the first effective recording current and the effective recording width. Here, the effective recording width is the width of the write element 4a of the thin film magnetic head, and the error rate is easily influenced by the effective recording width. . These thin-film magnetic heads 4 are the same type of heads, and are judged as good or defective in advance in an environmental test. Here, the environmental test is a hard disk drive test performed at various environmental temperatures, and the test is usually performed not only at a normal temperature but also at a low temperature. For this reason, products that are good in this environmental test are judged to operate normally at low temperatures as well as normal temperatures, and conversely, those that are defective in this environmental test usually have problems operating at low temperatures. It is thought that there was.

  As shown in FIG. 3, in the measurement of the error rate under the condition of the first effective recording current, it is not possible to clearly select the thin film magnetic heads that are judged as good or defective in the environmental test. If the first reference value does not satisfy the error rate (the error rate is lower than the first reference value) is selected as a defective product, four of nine thin-film magnetic heads that are judged to be good in the environmental test are rejected. Since it sorts as a non-defective product, it is not an efficient sorting method. Here, the first reference value is to select a good environmental test as a defective product when sorting thin film magnetic heads that have been judged pass / fail in an environmental test in advance using the error rate at the first effective recording current. The number to be set is set to be as small as possible.

  (Step 2) Next, a second effective recording current lower than the effective recording current used in Step 1 is applied, and the error rate is measured. The error rate obtained at this time is a predetermined recording / reproduction characteristic value for the second effective recording current, and this value is also stored in the memory. Even if the set value of the recording current is the same, the effective recording current varies greatly depending on the parameter setting of the preamplifier 8. For example, overshoot and duration of the preamplifier 8 are set. The overshoot is the magnitude of the current rise when a current exceeding the original write current is passed to the position where the magnetization changes, and the duration is the time during which the overshoot is applied. The reason for using a low effective recording current here is that, as described above, the retention force of the recording medium increases at a low temperature, and the effective distance between the recording medium and each element is reduced due to the contraction of each element of the thin film magnetic head. This is to reproduce the state in which the recording / reproduction characteristics deteriorate due to an increase in size.

  FIG. 4 is a graph showing the relationship between the error rate measured with the second effective recording current lower than the first effective recording current and the effective recording width. Compared with the error rate measured with the first effective recording current (FIG. 3), the judgment result of the non-defective product and the defective product in the environmental test and the more consistent evaluation result were obtained. When an error rate that does not satisfy the second reference value (which is worse than the second reference value) is selected as a defective product, three out of nine thin-film magnetic heads determined to be non-defective in environmental tests are selected as defective products. Sorting can be performed with higher accuracy than when sorting with one effective recording current (4 out of 9). Here, the second reference value is to select a non-defective environmental test as a defective product when a thin film magnetic head that has been judged pass / fail in an environmental test in advance is selected by a method using the error rate at the second effective recording current. The number to be set is set to be as small as possible.

  (Step 3) Next, the absolute value of the difference between the predetermined recording / reproduction characteristic value for the first effective recording current obtained in Step 1 and the predetermined recording / reproduction characteristic value for the second effective recording current obtained in Step 2 is calculated. Ask. Here, the increase in the absolute value suggests that the characteristics of the thin film magnetic head greatly differ depending on the temperature change, and such a thin film magnetic head has a high possibility of becoming a problem not only at a low temperature but also at a high temperature.

  (Step 4) FIG. 5 shows the relationship between the absolute value of the error rate difference obtained in Step 3 and the error rate obtained in Step 2. Here, the error rate value which is a predetermined recording / reproduction characteristic with respect to the second effective recording current does not satisfy the second reference value (is worse than the second reference value), and the difference between the error rates obtained in step 3 If the absolute value is greater than or equal to the third reference value, the thin film magnetic head is determined to be defective, and otherwise it is determined to be good. Here, the third reference value is the number of screening environmentally acceptable products as defective when the thin film magnetic heads that have been judged to be good or bad by environmental testing in advance are sorted by the absolute value of the error rate difference obtained in step 3. It is set to be as small as possible.

  If the error rate obtained in step 1 does not satisfy the first reference value and the absolute value of the error rate difference obtained in step 3 is greater than or equal to the third reference value, the thin film magnetic head is determined to be defective. In other cases, it may be judged as a good product. Here, the error rate is used as the predetermined recording / reproduction characteristic value. However, SNR (ratio of signal to noise), overwrite, or the like may be used instead. Since the error rate is an index used to directly evaluate the performance of the hard disk drive, it is desirable to use the error rate also when evaluating the recording / reproducing characteristics of the thin film magnetic head. In order to reproduce a state closer to an actual hard disk drive, it is desirable to measure the error rate after recording background noise on the recording medium before recording the data signal.

(Example)
3 to 5 show an embodiment of the present invention. As a tester for this measurement, a single arm tester manufactured by GUJIC was used. The preamplifier used was TI 1970 made by Text Instruments. The measurement was performed on the outer periphery of the recording medium (radius 44.14 mm, skew angle 16 degrees), and the rotational speed of the medium was 7200. The data transfer rate for measuring the error rate was 810 Mbps. In the first effective recording current, the set current value of the preamplifier was 43 mA, and the overshoot and duration settings were 4 and 1, respectively. In the second effective recording current, the set current value of the preamplifier was 30 mA, and both the overshoot and duration settings were 0. As described above, FIG. 3 shows the error rate when the first effective recording current is applied, and the first reference value (the error rate is −2.5) is used to judge the quality of the thin film magnetic head. FIG. 4 shows the error rate when the second effective recording current is applied, and the second reference value (error rate is −1.5) was used to determine the quality of the thin film magnetic head. FIG. 5 shows the relationship between the absolute value of the error rate difference measured at each recording current and the error rate at the second effective recording current. The third reference value (error rate difference 0. 8) was used. When a thin film magnetic head that shows an error rate that does not meet the second standard value (which is worse than the second standard value) and a thin film magnetic head that is equal to or greater than the third standard value are selected as defective products, they are judged as non-defective products in environmental tests. Two of the nine thin-film magnetic heads are selected as defective products, and can be selected with higher accuracy than when selecting with the first effective recording current (four out of nine). When measuring with different thin film magnetic heads or recording media, the reference value naturally changes.

  Table 1 shows the results of actually selecting a thin film magnetic head by three methods. Here, the overkill rate is an index indicating the ratio that is judged as a non-defective product from the error rate measurement at the thin-film magnetic head level, although it is judged as a non-defective product in the environmental test with the hard disk drive. As shown in FIG. 3, the method 1 is a case where the judgment is made based on the error rate measured with the first effective recording current, and the method 2 is the second lower than the first effective recording current as shown in FIG. This is a case where the judgment is made based on the error rate measured with the second effective recording current, and method 3 judges the quality of the thin film magnetic head using the present invention as shown in FIG. As shown in the table, the method 3 using the present invention has a lower overkill rate than the conventional method 1, and can efficiently classify non-defective products and defective products in the environmental test. In other words, the present invention can accurately select thin film magnetic heads whose characteristics deteriorate at low temperatures.

It is a conceptual diagram which shows an example of the evaluation apparatus used by this invention. It is a flowchart explaining the characteristic evaluation method of this invention. It is the figure which showed the error rate and effective recording width which were measured with the 1st effective recording current. It is the figure which showed the error rate and effective recording width which were measured by the 2nd effective recording current lower than the 1st effective recording current. It is the figure which showed the error rate measured with the absolute value of the difference of the error rate of this invention, and the 2nd effective recording current.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Spinstand 2 Base 3 Recording medium 4 Thin film magnetic head 4a Writing element 4b Reading element 5 Carriage 6 Rotation stage 7 Linear stage 8 Preamplifier 9 Processing apparatus 10 Read channel 11 Arithmetic circuit

Claims (5)

In a method for evaluating the recording / reproducing characteristics of a thin film magnetic head,
The first effective recording current is applied to the writing element to record the signal on the recording medium, and then the signal recorded on the recording medium is read by the reading element, thereby performing a predetermined recording / reproduction with respect to the first effective recording current. A first step to determine the characteristic value;
A second effective recording current lower than the first effective recording current is applied to the writing element to record the signal on the recording medium, and then the signal recorded on the recording medium is read by the reading element. A second step of obtaining the predetermined recording / reproducing characteristic value for the second effective recording current,
A third step of obtaining an absolute value of a difference between the predetermined recording / reproducing characteristic value for the first effective recording current and the predetermined recording / reproducing characteristic value for the second effective recording current;
A method for evaluating recording / reproducing characteristics of a thin film magnetic head, comprising:   If the predetermined recording / reproducing characteristic value for the first effective recording current does not satisfy the first reference value and the absolute value of the difference is not less than the third reference value, the thin film magnetic head is determined to be defective. The evaluation method according to claim 1, further comprising a determination step of determining that the product is non-defective in other cases.   If the predetermined recording / reproduction characteristic value for the second effective recording current does not satisfy the second reference value and the absolute value of the difference is equal to or greater than the third reference value, the thin film magnetic head is determined to be defective. The evaluation method according to claim 1, further comprising a determination step of determining that the product is non-defective in other cases.   4. The evaluation method according to claim 1, wherein an error rate is used as the predetermined recording / reproducing characteristic value.   5. The method according to claim 4, wherein at least one of the first step and the second step includes recording background noise on the recording medium before recording the signal. Evaluation method described in 1.

Images