JP2000329818A - Esd resistance evaluation method for electronic element, esd resistance testing device and esd resistance evaluation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain physical quantity unable to obtain by a conventional method by using a plurality of test currents in ESD(static electricity discharge) resistance evaluation. SOLUTION: This evaluation method evaluates ESD resistance of an electronic element using an ESD test current having a waveform whose current value is specified by a function of time including two or more physical constants. A plurality of physical constant sets of a current changing a predetermined steady physical characteristic value of the element by a predetermined amount by applying the test current to the electronic element are obtained by an experiment. In a system in which two or more desired physical quantities among the physical quantities obtained by converting the physical quantities expressed by each physical constant and each physical constant set are expressed in a coordinate axis, an approximate curve equation passing the vicinity of a plurality of points shown by each physical constant set is obtained, this approximate curve equation includes variables of physical quantities expressed by each coordinate axis and calculated, constants, and the calculated constants of the approximate curve equation are used as a standard for evaluation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin-film magnetic head element (especially a magnetoresistive element used for an MR head for reproduction), an ESD (electrostatic discharge) of an electronic element such as a transistor, an IC and an LSI. E, a new ESD evaluation method for evaluating resistance to
The present invention relates to an SD test device and an ESD evaluation device.

[0002]

2. Description of the Related Art During the handling of various electronic devices (for example, thin film magnetic heads and semiconductor ICs), an electrostatic discharge (electrostatic discharge) occurs.
ostatic discharge: referred to herein as "ESD"). Static electricity accumulates for various reasons, and when applied to an electronic circuit element, the element is destroyed. Knowing the ESD durability of the device by testing in advance is necessary to determine the caution of handling during the manufacturing process and when assembling to a circuit board, etc., and to determine the circuit configuration and device configuration of a device having electronic circuit elements. is important. Further, the ESD resistance test of the device is indispensable for the development of a device having good ESD durability.

[0003] ESD stress models for testing ESD immunity are based on the reproduction of typical discharge pulses that can be exposed during device fabrication and handling. Conventionally, as such a model, a human body model (Human Body Mod
el: HBM), machine model (Machine Model: MM),
Charged Device Model (CDM) 3
Two Standard Models have been developed.

[0004] The human body model is a US military standard MIL-STD-883E.
(METHOD 3015.7), Electronic Industries Association Standard EIA / JESD 22-A11
4 and standardized by the ESD Association standard ESD STM 5.1-1998. This human body model models an electrostatic stress generated in an element when a person carrying an electrostatic charge contacts a lead terminal of the element. The mechanical model is described in the Electronic Industries Association Standard EIA / JESD 22-A115-A, etc., and this model generates static electricity generated in the element when the electrostatically charged mechanical device contacts the lead terminals of the element. It models electric stress. The charging device model is described in the Electronic Industries Association Standard JESD22-C101 and the like.
7 describes an SD current pulse.

FIG. 6 shows a basic configuration of a conventional test apparatus for evaluating the ESD resistance of an electronic device against an ESD current caused by an HBM. The test apparatus includes a charging circuit formed by connecting a variable voltage DC power supply 21, a charging resistor 22, and a capacitor 23 in series, and a discharging circuit formed by connecting a capacitor 23, a discharge resistor 24, and an electronic element 25 to be evaluated in series. One of the circuits and the switch 26
Is configured to be selectively closed. In this test apparatus, a capacitor 23 is charged with a charge by a voltage source 21 through a charging resistor 22. By switching the switch 26, the electric charge stored in the capacitor 23 is discharged through the discharge resistor 24 to an electronic device under test (Device Under Testing: DUT). The resistance value R _C of the charging resistor 22, the resistance value Rd of the discharging resistor 24, and the capacitance C of the capacitor 23 are each 1
It is defined as MΩ, 1.5 kΩ, and 100 pF. The electronic element 25 is configured to be detachably mounted on the socket.
5 is connected in series to the discharge circuit. Further, as the switch 26, a mercury relay switch is usually used so as not to cause separation or disappearance of the discharge current.

Next, a procedure of a conventional method for evaluating the ESD resistance of an electronic device using the above-described test apparatus will be described. First,
The charging voltage V by the voltage source 21 is set, the switch 26 is set so as to close the charging circuit side, and the capacitor 23 is charged. Next, the switch 26 is switched to the discharge circuit side, the ESD test current is discharged to the electronic element 25, and the subsequent deterioration of the characteristics of the electronic element 25 is examined. Such an electronic element 2
The characteristic of the element 5 is, for example, the resistance value r _{0 of the} electronic element 25.
There is.

FIG. 7 shows an example of an electronic element to be evaluated.
This is an evaluation example when a thin film magnetic head is used. The resistance value of the magnetic head after the test current discharge was measured for each voltage while gradually increasing the charging voltage V from 0 to 5 V steps.
Here, assuming that the resistance value r of the element is increased by 1 ohm or more from the initial value as a condition for judging element destruction, the initial value is about 35 ohm as shown in FIG.
Up to V, there is almost no change in the resistance value r, and the charging voltage is 5
The breakdown voltage is about 35.5 ohm at 5 V and 60 V, and rapidly rises to about 39 ohm at 65 V, so the breakdown voltage is found to be 65 V. Total energy E dissipated in the device when the device breakdown occurs, the energy stored in the capacitor 23 (CV ^2/2) is consumed at a rate proportional to their resistance value in the discharge resistor 24 and the element 25 Because

(Equation 8) Is obtained. As described above, according to the conventional method, the ESD resistance of a device at a test current having a specific time constant can be quantitatively evaluated by obtaining the breakdown energy E according to the above-described method.

[0008]

However, the inventor of the present application has found that when the time constant of the test pulse current increases, the apparent breakdown energy calculated by the conventional method increases. It is considered that such a phenomenon is due to the fact that among the energy supplied to the element, the energy that diffuses outside the element as thermal energy is not taken into account. That is, according to the conventional method, it is not possible to obtain the true destructive energy (energy actually stored in the element at the time of the element destruction) that destroys the element. Furthermore, the energy supplied to the element is
How much delay time will diffuse outside the device,
It cannot be known by conventional methods. It is considered that such a thermal diffusion delay time depends on the structure of the element, but conventionally, since a method for obtaining the delay time has not been developed, it is a factor that delays the development of an element having good heat dissipation characteristics. Has also become.

The present invention has been made in view of the above circumstances, and relates to device destruction due to ESD. New destruction such as true destruction energy and thermal diffusion delay time until the ESD energy is diffused out of the device as heat. The purpose is to determine a physical quantity that is a reference for ESD resistance evaluation.

[0010]

Means for Solving the Problems The present inventor has devised a new model described below with respect to device destruction due to ESD, and uses a plurality of test currents having different time constants to realize a true device destruction. It has been proved that the breaking energy and the thermal diffusion delay time can be determined. Note that these physical quantities cannot be obtained by the conventional method.

FIG. 1 shows the energy consumption P ₀ (t) of the ESD pulse test current consumed by the device and the diffusion energy P _d (t) of the energy stored in the device which diffuses as heat outside the device. This is a model showing each time change. Note that the current value I of the test current in this model is

(Equation 9) It is assumed that it exhibits an attenuated pulse waveform represented by
Here, I ₀ is an initial value (maximum value) of the pulse current, t is an elapsed time, and τ _d is a time constant. In this case, assuming that the resistance value of the element is r ₀ , according to Joule's law,

(Equation 10) It is expressed as Also, the total energy E _Th consumed by the device due to the test current is

[Equation 11] Is represented by

In the model shown in FIG. 1, the diffusion energy P
_It is assumed that _d is obtained by shifting the current energy P ₀ consumed by the element by a fixed delay time Δt _td . Note that such an assumption is only one of the simplest models of the present invention, and a model based on an appropriate assumption can be constructed without departing from the scope of the invention disclosed in this specification.

In the model shown in FIG. 1, the energy E _s (t) actually stored in the element is

(Equation 12) Can be represented by FIG. 2 is a graph showing the time change of E _s (t). As is apparent from FIG.
At t _td , the stored energy takes the maximum value Es _max . The maximum value of the stored energy in this element is

(Equation 13) It is expressed as When this Es _max becomes equal to or more than the critical energy (true breaking energy) E _C required for device breakdown, device breakdown occurs. Here, from the above equations (3) and (5),

[Equation 14] Is obtained. Here, since E _C and Δt _td are physical constants depending on the structure and the like of the device, it has been found that the apparent device breakdown energy E _Th is a function of the time constant τ _d of the test current.

Therefore, for a plurality of test currents having different time constants, the apparent breakdown energies that cause the device to break down are obtained, and these time constant τ _d and apparent breakdown energy E _Th are applied to the above equation (6). It is possible to calculate the true breaking energy E _C and the thermal diffusion delay time Δt _td by a conventionally known appropriate approximation method such as the nonlinear least square method by the differential correction method or the nonlinear least square method by the quasi-Newton method. . The ESD resistance evaluation based on these calculated constants E _C and Δt _td is an absolute evaluation independent of the time constant of the test current, so that an absolute evaluation that is not classified into HBM, MM, or the like can be performed, and an element having good heat radiation characteristics can be obtained.
This also causes the development of a device having a high true breaking energy, which makes it possible to further develop a high-performance electronic device.

[0015] Through the above findings, the present inventor, in the method for evaluating the ESD resistance of an electronic element, has determined from the test results using a plurality of test currents a physical quantity that cannot be obtained by a test using a single test current. I found what I could ask for. Therefore, even in a device for evaluating the ESD resistance of an element, a test current generating device for generating a plurality of test currents and an operation having software and hardware for obtaining a physical quantity that cannot be obtained by a single test current from these test results With the provision of the device, it is possible to obtain a new physical quantity serving as a reference for the evaluation of ESD resistance.

The present invention is not limited to a test current having a specific waveform, a specific physical quantity, a specific element, and the like, and can be appropriately changed within the scope of the invention disclosed in this specification. .

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is a method for evaluating the ESD resistance of an electronic device using an ESD test current having a waveform whose current value is specified by a function of time including two or more physical constants. Applying a current to an electronic element to change a predetermined steady-state physical property value of the element by a predetermined amount. A plurality of the physical constant sets of the current are obtained by experiments or the like, a physical quantity represented by each physical constant, and each physical constant set. In a system in which two or more desired physical quantities among the physical quantities obtained by converting the coordinate axes are used, an approximate curve equation passing near a plurality of points indicated by each physical constant set is obtained. A variable of the physical quantity represented by the coordinate axis and a calculation constant (preferably 2
The above-described calculation constant) is used as a reference for evaluation, and the evaluation constant of the approximate curve equation is used as an evaluation standard.

As the physical constant for specifying the current value, an appropriate physical quantity such as a current initial value, a time constant, a frequency, and an attenuation factor can be used. It is also possible to use capacitance or the like. The predetermined steady-state physical characteristic value of the element is an appropriate physical characteristic value such as an electric resistance, a response characteristic, and a magnitude of an output of the element, and indicates a substantially constant value when the environment in which the element is placed is constant. Can be used. To change the steady physical property value by a predetermined amount means, for example, that the steady physical property value fluctuates to such an extent that the element is considered to be destroyed.
Usually, the electric resistance value of the element is a certain amount (or a certain ratio)
It is defined as rising. The system can be a two-dimensional space or a multi-dimensional space of three or more dimensions. Further, the physical quantities serving as the coordinate axes of the system may all be physical constants themselves for specifying the test current,
All of them may be physical quantities converted from the physical constants specifying the test current, or they may be mixed. The approximate curve equation can be calculated using a conventionally known appropriate method such as a nonlinear least squares method based on a differential correction method or a nonlinear least squares method based on a quasi-Newton method.

In the above evaluation method, an ESD test current generated by an RC series discharge circuit can be used. In this case, each test current I _n which is obtained by experiments,

(Equation 15) Where Q _n is the amount of charge stored in the capacitor at the start of discharge, and
_n is the electric resistance value of the discharge circuit, C _n is the capacitance of the capacitor, and these electric resistance values R _n , capacitance C _n and charge amount Q _n constitute each physical constant set. It can be. Note that the discharge circuit resistance R _n is defined as R _n = R ₂ + r ₀ when a resistor having a resistance value R ₂ and an electronic element having a resistance value r ₀ are connected in series. That is, in the present invention, the “discharge circuit resistance” can be defined as a value that takes into account not only the resistance value of the discharge resistor but also the electric resistance value of the element. If the resistance value of the element is smaller than the resistance value of the discharge resistor to an error level, the resistance value of the discharge resistor can be used as it is as the discharge circuit resistance.

According to this, the time constant τ of each test current
_dIs τd = C_nR_n (8) In the above experiment, in other words, this time constant τ
_dTest currents of different
It seeks multiple time constants that change the characteristics to the same extent.
You. The smaller the time constant, the more rapidly the test current attenuates.
The effect of thermal energy diffusion outside the device is small.
And apparent element breakdown energy E _ThIs a true break
Breaking energy E_CApproach. Therefore, the choice of the time constant
(Ie, the discharge resistance R_nAnd charging capacity C_nHow to choose)
The time constants so that the logarithms of the time constants are evenly spaced.
For example, in the region where the time constant is small, the measured value is
You can see how close to Lugie is.

When the test current represented by the above equation (7) is used, the change over time Es (t) of the energy stored in the element is:
Referring also to the above equation (4), when t ≦ Δt _d

(Equation 16) When t> Δt _d

[Equation 17] It is represented by Here, I ₀ is the initial value of the test current (t = 0
, R ₀ is the resistance value of the element (here, the resistance value before application of the test current). From equation (7), the initial value I ₀
Is expressed as I ₀ = Q _n / (C _n R _n ).

The ESD tolerance test element is generally to take steps such as gradually increased charging voltage V _ch to the charging capacitor C _n, the maximum value Es _max true element fracture energy E of Es (t) _{When it} exceeds _C , the element is destroyed. As described above in the section of the solution, Es (t) is t
= Δt _td takes the maximum value Es _max . At this time, the total energy consumed by the element, that is, the apparent element breakdown energy E _Th is

(Equation 18) It is expressed as Here, V _Th is the charging voltage V _ch when the element is destroyed.

Therefore,

[Equation 19] Becomes

As described above, the approximate curve equation of the present invention can be expressed by using the apparent element breakdown energy E _Th and the time constant τ _d of the decay pulse test current. That is, the form of the above approximate curve equation is

(Equation 20) Where E _C and Δt _td are calculation constants,
_Th and τ _d are variables of physical quantities serving as coordinate axes, and the coordinates (τ _dn ,
E _Thn )

(Equation 21) Where r ₀ can be an electrical resistance value of the element (eg, a resistance value before application of a test current, a resistance value during application of a current, or a resistance value immediately after application of a current).
According to this, the calculated constant E _C represents the true destructive energy that causes the element to be destroyed, and Δt _td represents the time from when the energy is supplied to the element to when the energy is diffused outside the element as heat. Since it represents the thermal diffusion delay time, it is possible to evaluate the absolute ESD resistance of the device using these.

Further, the discharge resistance R _n and the capacitance C _n can be selected so that the ratio between the discharge resistance R _n and the capacitance C _n constituting each of the above physical constant sets is constant. According to this, if the charging voltage V _ch is constant, the apparent element breakdown energy E _Th (total energy supplied to the element by discharging the test current) is also constant. This is, E _Th, of the energy _{(1/2) · C n · V} ch stored in the capacitor at discharge start, only the ratio of the element resistance r ₀ with respect to the discharge resistance R _n is consumed by the element Because it ’s energy,

(Equation 22) Where V _ch , (C _n / R _n ) and r
It is clear from the condition setting that ₀ is constant.
According to this, for example, the apparent element breakdown energy E _Th for destroying the element can be obtained by gradually decreasing the time constant τ _d (= CR) with the charging voltage V _ch fixed. it can. And a plurality of charging voltages V
_For the case of _ch , E is obtained by changing the time constant.
_{If Th} is obtained, a plurality of time constants CR at the time when the element is inevitably destroyed can be obtained. In other words, when the discharge resistor R and charging the capacitor C can be arbitrarily set independently, sometimes constant .tau.d _n when a plurality of apparent fracture energy E _Thn or test current obtained experimentally overlap obtained, The experimental efficiency may be reduced, but according to the present invention, this can be avoided.

If the capacitance C _n constituting each set of physical constants is constant, the charge Q stored in the capacitor is constant when the charging voltage V (= Q / C) to the capacitor is equal. Become. According to this, it is effective for a test under the condition that the electric charge contributing to ESD is constant like CDM.

As described above, the present invention provides an electronic device having an E
It is a method for evaluating SD resistance, and as a criterion for evaluation,
Energy E _C which elements by the ESD current flows is accumulated in reality within the element at the time that led to the destruction
Is used. Further, in addition, as a point of reference, it is also possible to use a heat radiation characteristics Delta] t _td element.

The above-described evaluation method of the present invention can be implemented using the following test equipment and evaluation equipment. Such a test apparatus of the present invention comprises a variable voltage DC power supply, a charging circuit in which a charging resistor and a charging unit are connected in series, and a discharging circuit in which the charging unit, a discharging resistor and an electronic element are connected in series. An ESD resistance test apparatus configured to selectively close any one of the circuits, wherein a charge capacity adjustment unit that adjusts a charge capacity of the charging unit; and an electric resistance value of the discharge resistor. And a discharge resistance adjusting means for adjusting the discharge resistance. Note that a capacitor can be used as the charging unit, and in this case, the charging capacity is the capacitance of the capacitor. The electronic element is
By being detachably attached to the socket, it can be connected to the discharge circuit.

The charge capacity adjusting means and the discharge resistance adjusting means can be linked so that the ratio between the charge capacity of the charging section and the electric resistance of the discharge circuit becomes substantially constant.

The charging section may be a conventionally known variable capacitance capacitor or may be composed of a plurality of capacitors having different capacitances connected in parallel so as to be switched by a charging capacity changeover switch. The charge capacity adjusting means can be constituted by the rotation axis for adjusting the capacity of the variable capacitor or the charge capacity changeover switch.

The discharging resistor is a conventionally known variable resistor (volume) or a plurality of resistors having different electric resistances connected in parallel so as to be switched by a resistance changeover switch. The discharge resistance adjusting means can be constituted by the resistance adjusting rotary shaft of the variable resistor or the resistance changeover switch.

The physical quantities that specify the plurality of test currents obtained by the test apparatus directly or indirectly represent the physical properties of the electronic device to be evaluated. Also,
By converting these physical quantities according to the laws of physics, it is possible to obtain a wide variety of physical quantities. An apparatus for evaluating ESD resistance using these physical quantities can be configured as follows.

That is, the ESD resistance evaluation apparatus of the present invention
A storage means for storing a plurality of combinations of two or more predetermined physical quantities representing physical properties of an electronic element to be evaluated for SD resistance, and each physical quantity set indicates in a system in which each physical quantity stored in the storage means is used as a coordinate axis. Calculating means for calculating an approximate curve equation passing near a plurality of points, wherein the approximate curve equation includes variables of the respective physical quantities and a calculation constant, and the calculation means calculates the calculation constant. And
An evaluation means for evaluating the ESD resistance of the electronic element based on the calculated constant is provided. Examples of the physical quantity stored in the storage unit include a physical quantity that specifies each test current obtained by an experiment in the above-described evaluation method and a physical quantity obtained by converting the test current (for example, an apparent element breakdown energy). be able to.

Such an evaluation device can be constituted by, for example, a computer having a CPU, a main storage memory, and an auxiliary storage device. For example, the above evaluation can be performed by a process executed on such a computer. In this case, a main storage memory or an auxiliary storage device (such as a hard disk) of a computer can be used as the storage unit of the present invention, and the calculation unit and the evaluation unit include a CPU of the computer and a software program executed by the CPU. And can be configured by: Such a software program can be configured to apply, for example, an appropriate least squares method to the physical quantities stored in the storage means.

Further, the above-described evaluation device may be configured as an integral unit with the above-mentioned ESD test device. For example,
After discharging to the electronic element, the electric resistance value of the element is appropriately measured, and this resistance value and a physical quantity specifying the discharge current at this time are set in the storage means, and whether or not the element has been destroyed is determined. And it is possible to store an appropriate physical quantity in the storage means when it is determined that it has been destroyed.

As the evaluation means in the evaluation device, the calculation result is displayed as a numerical value on a display device, and the display method (color, font, etc.) is changed according to a condition set according to the magnitude of the calculation result. Or it can be configured to evaluate whether or not the obtained physical quantity exceeds a certain reference value, and other appropriate configurations can be adopted.

In the above evaluation apparatus, the ES of the waveform whose current value is specified by a function of time including two or more physical constants
A plurality of sets of the above-described physical constants of a test current which is a D test current and changes a predetermined steady-state physical characteristic value of the element by a predetermined amount by being applied to the electronic element, and the storage means,
Physical quantity represented by each physical constant or at least 2 of physical quantities obtained by converting each physical constant set
A plurality of combinations of the above physical quantities can be stored. This combination can be stored, for example, in the form of array variables handled by a computer program.

Further, the ESD test current is RC series.
The test current I generated by the discharge circuit.
Is I = (Q / CR) .e^{-t / CR}  Where Q is the discharge open current.
The amount of charge stored in the capacitor at the beginning, R is
Is the electrical resistance of the circuit, C is the capacitance,
From the electrical resistance R, the capacitance C and the charge Q,
Of the test current that changes the predetermined steady-state physical characteristic value of
The above set of physical constants is constructed and calculated by the arithmetic means.
The form of the approximate curve equation used is E_Th= E_C/ (1-exp (-2 · Δt)_td/ Τ_d)) Where E_CAnd Δt_tdIs a calculated constant, and E
_ThAnd τ_dIs a physical quantity stored in the storage means.
These are variables that are also used as coordinate axes.
Conversion to a combination of physical quantities stored in storage means
Is E_Th= (Q²/ 2C) · r₀/ R (r₀Is the electricity of the element
Resistance) τ_d = Be configured to be performed by CR
Can be.

[0039]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a thin-film magnetic head element will be described below. 2. Description of the Related Art A thin-film magnetic head used in a high-density, large-capacity hard disk in recent years includes an MR element (GMR element) as a reproducing element. In particular, recent GMR elements (such as spin valve elements) have a thickness of several tens to several hundreds of mm, and are liable to be destroyed by electrostatic discharge applied to the elements during manufacturing or operation of the device. It has been known. That is, if the amount of energy exceeds the allowable energy amount, the magnetoresistance effect rate is greatly deteriorated due to melting, electromigration, diffusion, and the like of the metal constituting the element. Such deterioration of the MR ratio appears in the form of an increase in the electric resistance value of the element.

Therefore, the purpose of this embodiment is to evaluate the ESD resistance of the spin valve element.
A case will be described in which a plurality of ESD test currents having decay pulse waveforms having different time constants are used.

FIG. 3 shows a plurality of ESs having different time constants.
This is an ESD test apparatus for generating a D pulse test current and applying it to an MR element. The device comprises a variable voltage DC power supply 1
1. A charging circuit in which a charging resistor 12 and a charging unit 13 having a resistance value _RC are connected in series, and a discharging circuit in which a charging unit 13, a discharging resistor device 14, and an electronic element 1 are connected in series. One of the circuits is configured to be selectively closed. Such circuit switching is performed by a switch 15 similar to the conventional one. Also, the electronic element 1
Is configured to be connected to a discharge circuit by being removably mounted on a socket, so that a test can be performed while sequentially removing and replacing a plurality of test elements.
Note that the charging resistance _RC is 1 MΩ.

The charging unit 13 includes a charging capacity changeover switch 16
_M are connected in parallel so as to be switched by a plurality of capacitors C _{1... M} having different capacitances. That is, by switching the switch 16, one of the plurality of capacitors can be selectively connected to the charging circuit or the discharging circuit. The switch 16 serves as a charging capacity adjusting means.

The discharge resistor device 14 is composed of a plurality of resistors Rd _{1... M having} different electric resistance values connected in parallel so as to be switched by a resistance changeover switch 17.
That is, by switching the switch 17, one of the plurality of resistors can be selectively connected to the discharge circuit. Incidentally, all of the discharge resistor R in the discharge circuit is represented by the sum of the electric resistance value r ₀ of the resistance value Rd _n and the element of the selected resistor (Rd _n + r _0). Switch 17
Are discharge resistance adjusting means.

The number of capacitors is equal to the number of discharge resistors, and the ones with the same suffix in the figure correspond one to one. Each capacitance and resistance values such that the ratio is substantially constant and the capacitance of a pair of capacitors C _n and the discharge circuit resistance _{R (= Rd n + r 0} ) is selected. In this embodiment, an example of RC set (Rd ₁ , C ₁ ) = (739 Ω, 50 pF) τd ₁ = 37.0 nsec (Rd ₂ , C ₂ ) = (1.08 kΩ, 73.3 pF) τd ₂ = 79.2 nsec ( Rd ₃ , C ₃ ) = (1.48 kΩ, 100 pF) τd ₃ = 148 nsec (Rd ₄ , C ₄ ) = (2.2 kΩ, 150 pF) τd ₄ = 330 nsec (Rd ₅ , C ₅ ) = (2.96 kΩ) , 200 pF) τd ₅ = 592 nsec :: Incidentally, was appended also constant .tau.d _n when the test current in the case of each combination.

[0045] the charging capacitance switch 16, the discharge resistor switch 17, the charge capacity C _n of the charging unit 13, the ratio between the resistance value Rd _n of the discharge resistor 14 is linked to be constant . Such a configuration can be realized, for example, by configuring the switches 16 and 17 with a common multi-contact switch, and can be realized by another appropriate method.

FIG. 4 shows a spin valve element 1 to be evaluated for ESD resistance according to the present embodiment. The element 1 functions as a reproducing element of a thin-film magnetic head for a hard disk, and has a giant magnetoresistance effect element (GMR: Gian).
t MagnetoResistive).

The illustrated spin valve element 1 is called a top spin valve in which an antiferromagnetic film is formed on the upper side, and NiFe (70 °) ＼C is arranged in order from the lower side.
oFe (10Å) ＼Cu (35Å) ＼CoFe (30
Å) A multilayer film represented by 膜 PtMn (400Å). The values in parentheses indicate the thickness of each film. Each membrane is
For example, a film can be formed by a conventionally known appropriate vacuum thin film forming method such as a sputtering method. NiFe film at bottom and C
The oFe film constitutes the free magnetic layer 2, the Cu film constitutes the nonmagnetic conductive layer 3, and the C film on the Cu film
The oFe film constitutes the pinned magnetic layer 4 and is made of PtM
The n film constitutes the antiferromagnetic layer 5. The magnetization direction of the pinned magnetic layer 4 is fixed by the exchange coupling magnetic field of the antiferromagnetic layer 5, while the magnetization direction of the free magnetic layer 2 is freely rotated by applying a magnetic field from the magnetic disk. This element 1 reads magnetic information recorded on a magnetic disk by detecting a resistance change caused by the magnetization rotation of the free magnetic layer 2.

On both sides of the element 1, a magnetic domain control layer 6 for applying a bias magnetic field to the free magnetic layer 2 to make it a single magnetic domain.
Is formed. This layer 6 is generally called a hard bias layer since a paramagnetic material (magnet) is generally used. On both sides of the element 1, lead films 7 for applying a sense current to the element 1 are formed, and the leads 7 are formed on the magnetic domain control layer 6. The spin valve element 1 is provided between upper and lower magnetic shield layers 8a and 8b via half gap layers 9a and 9b. The overall structure of a magnetic head having such a spin valve element 1 is well known in the art, and can be easily manufactured by those skilled in the art based on the disclosure of the present specification. Usually, the spin valve element 1 is provided on the surface of the slider facing the magnetic disk (ABS surface).
And read magnetic information by contact start / stop (CSS). The slider is provided with an electrode electrically connected to the lead 7 of the element 1. In this embodiment, a test current is discharged to the spin valve element 1 via this electrode.

In the spin-valve element 1 having the above-described structure, when an excessive ESD stress is applied, Cu constituting the conductive layer 3 may be melted and the element may be destroyed. Further, the spin valve element 1 uses exchange coupling at the atomic level.
Atomic diffusion may occur due to the stress, and the reproduction output may be significantly reduced.

In order to evaluate the ESD resistance of the spin-valve element 1, a plurality of magnetic heads having the same structure and having the above-described spin-valve element 1 are prepared for the test according to the present embodiment, and the test apparatus is used. Te, for each time constant .tau.d _n, experimentally determined power supply voltage V _Thn at which the electric resistance value r ₀ of the element 1 is increased more than 1ohm. Charge capacity C _n of each time constant .tau.d _n is determined, since (the Q _n the amount of charge stored in the capacitor at the start discharge) V _{Thn =} Q _n / C _n is, at each time constant, element The charge amount Q _n at the time of destruction,
The charge capacity C _n and the discharge resistance R _n are obtained. The set of these physical constants Q, C, and R allows the test current to be expressed as a function of time using equation (7). Of course, V _Thn may be used as a physical constant for specifying the test current. Further, the breaking energy E apparent in each time constant .tau.d _n
Th is obtained by applying the above physical constant set to the above equation (11) and performing conversion. 5, the element fracture energy E _Th apparent obtained as described above on the vertical axis, in a system which constant tau _d and horizontal axis when the test current, constant .tau.d _n and the apparent time of each test current The relationship between the breaking energies E _Thn is plotted with x marks.

The data of these five points is input to an ESD evaluation device constituted by a computer or the like, and an approximate curve equation passing near these five points is calculated by using an appropriate approximation method. This approximate curve equation is expressed in the form of the above equation (12), and has a time constant τd and an apparent fracture energy E
_Th is a variable, and the true element breakdown energy Ec and the thermal diffusion delay time Δt _td are constants. In this embodiment, the true destructive energy E _{C is} calculated by the evaluation device.
Was 2.5 nJ, and the thermal diffusion delay time Δt _td was 80 nsec. The curve plotted by (•) in FIG. 5 represents this approximate curve.

[0052]

According to the present invention, by using a plurality of test currents, it is possible to obtain a physical quantity that cannot be obtained by the conventional method, and to evaluate the ESD resistance of the electronic element based on the physical quantity. For example, since the true destructive energy of the electronic element and the heat diffusion delay time until the energy supplied to the element diffuses out of the element can be obtained, the element having high ESD resistance and good heat radiation characteristics can be obtained. Can do development. Further, since an absolute value that is not affected by the time constant of the test current can be obtained as the evaluation value (that is, the calculation constant of the approximate curve equation) obtained by the present invention, it is necessary to distinguish between HBM and MM. In addition, it is possible to evaluate resistance to a wide range of ESD stress.

[Brief description of the drawings]

FIG. 1 is a model of an ESD evaluation method of the present invention,
5 is a definition graph of a simple model for determining the thermal diffusion of ESD energy.

FIG. 2 is a graph of the true energy stored in the device obtained based on the model.

FIG. 3 is a simplified circuit diagram showing one embodiment of the ESD resistance test apparatus of the present invention.

FIG. 4 is an enlarged view of a main part of a magnetic head used in an embodiment of the present invention.

FIG. 5 is a graph showing an evaluation method of the example.

FIG. 6 is a simplified circuit diagram of a conventional ESD resistance test apparatus.

FIG. 7 is a graph showing an example of a conventional ESD resistance evaluation.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Electronic element (spin valve element) 11 Variable voltage DC power supply 12 Filling resistor 13 Charging part 14 Discharge resistance device 15 Circuit changeover switch 16 Charge capacity changeover switch (charge capacity adjustment means) 17 Discharge resistance changeover switch (discharge resistance adjustment) means)

Claims (13)

[Claims] 1. A method for evaluating the ESD resistance of an electronic device using an ESD test current having a waveform whose current value is specified by a function of time including two or more physical constants, wherein the test current is applied to the electronic device. A plurality of the physical constant sets of the current that change the predetermined steady-state physical characteristic value of the element by a predetermined amount, calculate the physical quantities represented by the respective physical constants, and the physical quantities obtained by converting the respective physical constant sets. In a system in which the desired two or more physical quantities are used as coordinate axes, an approximate curve equation that passes through a plurality of points indicated by each physical constant set is obtained, and the approximate curve equation is a physical quantity variable represented by each coordinate axis,
Wherein the calculated constant of the approximate curve expression is used as a criterion for evaluation.
Resistance evaluation method. 2. The ESD test current is generated by an RC series discharge circuit, and each test current In obtained by an experiment is _expressed by the following equation. Where Q _n is the amount of charge stored in the capacitor at the start of discharge, and
_n is an electrical resistance value of the discharge circuit, C _n is a capacitance of the capacitor, according to claim these electric resistance R _n, by an electrostatic capacitance C _n and the charge amount Q _n physical constants set constituted 2. The method for evaluating ESD resistance of an electronic device according to item 1. 3. ESD test current, there is generated by RC series discharge circuit, each test current I _n which is determined by experiments, Equation 2] Where Q _n is the amount of charge stored in the capacitor at the start of discharge, and
_n is the electric resistance of the discharge circuit, C _n is the capacitance of the capacitor, and these electric resistance R _n , capacitance C _n and electric charge Q _n form a set of physical constants. The form of the equation is Where E _C and Δt _td are calculation constants,
_Th and tau _d is a variable of a physical quantity serving as coordinate axes, the coordinates of the points indicated by each physical constants set in the coordinate system (tau
_dn , E _Thn ) is 2. The method according to claim 1, wherein r ₀ is an electric resistance value of the device. 4. A discharge resistor R constituting each set of physical constants.
ESD robustness evaluation method for electronic devices according to claim 2 or 3 ratio of _n and the capacitance C _n is constant. 5. A capacitance C constituting each set of physical constants.
4. The electronic device according to claim 2, wherein _n is constant.
D tolerance evaluation method. 6. A method for evaluating the ESD resistance of an electronic element, wherein the amount of energy actually stored in the element at the time when the element is destroyed by the flow of an ESD current is evaluated as a criterion for evaluation. A method for evaluating the ESD resistance of an electronic element, which is used. 7. A method for evaluating the ESD resistance of an electronic device, the evaluation being based on the amount of energy actually stored in the device when the device is destroyed by the flow of an ESD current. A method for evaluating the ESD resistance of an electronic device, comprising using the heat dissipation characteristics of the device. 8. A charging circuit comprising a variable voltage DC power supply, a charging resistor and a charging section connected in series, and a discharging circuit comprising a series connection of the charging section, a discharging resistor and an electronic element. An ESD tolerance test device configured to selectively close one of the circuits, a charge capacity adjustment unit that adjusts a charge capacity of the charging unit,
And a discharge resistance adjusting means for adjusting an electric resistance value of the discharge resistance device. 9. The charging capacity adjusting means and the discharging resistance adjusting means are linked so that the ratio between the charging capacity of the charging section and the electric resistance of the discharging circuit becomes substantially constant. Item 10. An ESD resistance test apparatus for an electronic element according to item 8. 10. The charging unit is a variable capacitor or a plurality of capacitors having different capacitances connected in parallel so as to be switched by a charging capacity switch, and the capacity adjusting rotation of the variable capacitor is performed. A charge capacity adjusting means is constituted by a shaft or the charge capacity changeover switch, and the discharge resistor device is a variable resistor or a plurality of resistors having different electric resistance values connected in parallel so as to be switched by a resistance changeover switch. Consisting of resistors
The ESD resistance test apparatus for an electronic element according to claim 8, wherein a discharge resistance adjusting unit is configured by a resistance adjustment rotation axis of the variable resistor or the resistance changeover switch. 11. A storage means for storing a plurality of sets of two or more predetermined physical quantities representing physical properties of an electronic element to be evaluated for ESD resistance, and a system using each physical quantity stored in the storage means as a coordinate axis, Calculating means for obtaining an approximate curve equation passing near a plurality of points indicated by each physical quantity set, wherein the approximate curve equation includes a variable of each of the physical quantities and a calculation constant, and the arithmetic means includes The calculated constant is determined, and the ESD of the electronic element is calculated based on the calculated constant.
An apparatus for evaluating the ESD resistance of an electronic device, comprising an evaluation unit for evaluating the resistance. 12. An ESD test current having a waveform whose current value is specified by a function of time including two or more physical constants, and which is applied to an electronic element to change a predetermined steady-state physical characteristic value of the element by a predetermined amount. There are a plurality of sets of the above-described physical constants of the test current to be applied, and the storage means stores a physical quantity represented by each physical constant or a combination of at least two or more physical quantities obtained by converting each physical constant set. Are stored in plural sets.
3. The device for evaluating ESD resistance of an electronic element according to claim 1. 13. The ESD test current is generated by an RC series discharge circuit, and the test current I is expressed by the following equation. Where Q is the amount of charge stored in the capacitor at the start of discharge, R is the electrical resistance of the circuit, C is the capacitance of the capacitor, These electric resistance value R, capacitance C and charge amount Q
A set of the above-mentioned physical constants of the test current for changing the predetermined steady-state physical characteristic value of the element by a predetermined amount is formed. The form of the approximate curve expression obtained by the calculating means is: Where E _C and Δt _td are calculation constants,
_Th and τ _d are variables that are both physical quantities stored in the storage means and coordinate axes. The conversion from the above set of physical constants to a combination of physical quantities stored in the storage means is expressed as follows: The apparatus according to claim 12, wherein r ₀ is an electric resistance value of the element.