CN1177802A - Mn-Bi-Al magneto-optic material with high recording density and preparation method therefor - Google Patents
Mn-Bi-Al magneto-optic material with high recording density and preparation method therefor Download PDFInfo
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- CN1177802A CN1177802A CN 96109334 CN96109334A CN1177802A CN 1177802 A CN1177802 A CN 1177802A CN 96109334 CN96109334 CN 96109334 CN 96109334 A CN96109334 A CN 96109334A CN 1177802 A CN1177802 A CN 1177802A
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Abstract
The present invention it relates to a magnetooptical memory medium and its preparation method. Said invention is aimed at providing a high-property low-cost magnetooptical memory material formed of Mn, Bi and Al. Its preparation method includes the following steps: under the vacuum condition of that its vacuity is better than 8 X 10(-5) torr, Bi, Al and Mn are deposited on a transparent substrate in turn to form random film layer, then the film layer is passed through such processes of constant-temp. treatment at 100-550 deg. C and vacuum annealing treatment to obtain the invented alloy film material whose chemical composition is MnBixAly, where X = 0.20=0.70, Y = 0.05-0.15. The magnetooptical spectrum of said material has two characteristic peaks near by 696nm and 375 nm, and its peack remanent polar angles are respectively up to 3.49 deg and 3.69 deg.
Description
The invention belongs to the information storage material field, particularly relate to a kind of magnetic-optical storage medium and preparation method thereof.
Magneto-optic memory when putting goods on the market in 91 years, and the dish capacity just reaches 665Mb, was increased to 1.4Gb in 95 years.According to statistics, the annual sales amount of magneto-optic memory just increases year by year by index.Recently studies show that adopt the template substrate, magnetooptic recording density can reach 10Gb/in
2, this can compare with the hard disc that adopts the giant magnetoresistance reading head; Adopt the near-field scan method, magnetooptic recording density can reach 45Gb/in
2Adopt nanoimprinting technology, recording density can increase to 0.25Tb/in
2This shows that in today that infotech is advanced by leaps and bounds, the magneto-optic storage has boundless development prospect.
Yet, the development of super-high density magnetic optical information memory technology, one of its gordian technique will be the development and the exploitation of novel Magnetooptic recording medium.For magneto-optic information stores pattern, signal read the utmost point that signal to noise ratio (S/N ratio) is proportional to material to kerr rotational angle; Again, Wei Lai ultrahigh density storage will adopt blue-green Laser.Therefore, storage develops to the super-high density direction crucial effects is arranged for magneto-optic to the material of Kerr effect to find to have the big utmost point the short wavelength.Principal character of the present invention promptly is to provide a kind of novel magnetooptical memory material that satisfies the superior performance of above-mentioned condition.
With regard to magneto-optic memory technique, at present the most promising material system of generally acknowledging has amorphous tb-fe-co class, platinum/cobalt multilayer film, manganese bismuth or mix the Mn-Bi-Al silicon alloy film etc. of aluminium silicon.Discuss respectively with regard to the relative merits of above-mentioned material respectively below.
(1) tb-fe-co (TbFeCo) class noncrystal membrane is present commercialization magneto-optic disk material.The advantage of this material is not have the crystal boundary noise, but because amorphous state is a metastable structure, material is heated and can takes place to wear out, and therefore exists the instability of long-term use.In addition, not only costliness but also easily oxidation such as used rare earth material terbium.Particularly, this non-crystalline material magneto-optical kerr angle is less.Its Ke Er angle is about 0.4 degree when the 860nm wavelength that commercial optical discs is used.And near short wavelength 400nm, the Ke Er angle drops to about 0.3 degree.The signal to noise ratio (S/N ratio) of this moment is low to being not enough to tell useful signal.Therefore, this class material will be used to do the super-high density magnetic optical storage a lot of difficulties.
(2) platinum/cobalt (Pt/Co) multilayer film is that Recent study gets a material system often.Compare with the TbFeCo film, the Pt/Co artificial material is big than the long wavelength on the contrary at short wavelength's Ke Er angle.Such as, near the 400nm, the Ke Er angle of this material has 0.45 degree approximately.But metal Pt is very valuable, and the magnetic performance and the dynamic read write attribute of material will change when thickness in monolayer changes several dust.These all bring very big difficulty for practical application and technology preparation.
(3) compare with preceding two material systems, manganese bismuth (MnBi) or Mn-Bi-Al silicon (MnBiAlSi) magneto-optic thin film have very large Ke Er angle.
(a) for pure MnBi material, according to up-to-date bibliographical information: by regulating the chemistry ratio of Mn and Bi, its Ke Er angle maximum can reach 1.79 degree; Also there are 1.5 degree [1] at the Ke Er angle near short wavelength 400nm.But this material exists structural phase transition near Curie temperature, and this phase transition temperature just in time is positioned at writing of information and wipes temperature range.The incomplete reversibility of phase transformation makes the magneto-optical property of material descend significantly.On the other hand, the crystallite dimension of pure MnBi alloy (several micron) is bigger.Thereby the signal to noise ratio (S/N ratio) of reading of material is dropped to about 40 decibels, and dynamically write and wipe number of times and can only maintain about thousands of times.These factors make that pure MnBi film almost can not be practical.[1]G.Q.Diand?S.Uchiyama，Phys.Rev.B?53，3327(1996)
(b) according to Chinese patent CN1037797A (12/89) number: by in MnBi, adding alloy element Al and Si, formed MnBi
XAl
YSi
Z, X=0.7 → 1.0 wherein, Y=0.2 → 0.5, Z=0.5 → 0.2, the magneto-optical property and the thermal stability of film all improve significantly.Such as, magneto-optical kerr angle maximum can reach 2.04 degree, the Ke Er angle reaches 1.6 degree near the 400nm, reflectivity is 40% to the maximum, and crystallite dimension is less than 0.06 micron, and phase transition temperature rises and reversibility increases, from 380 ℃ of quenchings during to room temperature, the Ke Er angle of material, coercive force, saturation magnetization is preceding the same with quenching.Dynamically but read-write number of times superelevation is 200 ten thousand times.On the preparation method, this patent is added in alloy element Al outside the Mn/Bi layer, even prior to the Bi deposition, or deposits after the Mn layer, will cause Al to be difficult for carrying out alloying reaction with Mn and Bi like this, thereby make the magneto-optical property of film can not get improving significantly.On rate of sedimentation, this patent does not relate in addition, and TEXTURE STATE is changeable in the time of will causing thin film deposition like this, thereby repeatability or yield rate greatly reduce.On physical property, although after adding Al and Si, the thermal stability of MnBi sill and dynamic read write attribute have greatly improved, but kerr rotational angle and the pure MnBi material of this material when the short wavelength is very nearly the same, add the noise that the polycrystalline crystal boundary causes, make this material still be difficult to be useful for the information stores of super-high density.
The shortcoming that the objective of the invention is to overcome existing material and technology is with not enough, by implementing new material prescription and technology, provides a kind of magnetooptical memory material of being made up of Mn-Bi-Al of high-performance and low-cost.The magneto-optic spectrum of this material has two characteristic peaks near 696nm and 375nm, peak value residue Ke Er angle is respectively up to 3.49 degree and 3.69 degree.When 420nm, greater than 3.25 degree, reflectivity is up to 50% to the Ke Er angle for the material utmost point.The crystallite dimension of this material is between 10nm to 50nm.This magneto-optic memory technique has very high signal to noise ratio (S/N ratio) at short-wave band.
The object of the present invention is achieved like this,
The first, adopt the transparent substrate of high-temperature insulation, such as quartz glass, or polymethyl methacrylate plastics etc. are made substrate.The waviness of substrate surface should be below 100 dusts.Substrate will carry out conventional washing before use, with dust and the greasy dirt that removes substrate surface, thereby obtains the substrate surface with mirror features of cleaning.
The second, adopt physical gas-phase deposite method in high-vacuum apparatus, to prepare the Mn-Bi-Al membraneous material.High-vacuum apparatus comprises: multi-source thermal evaporation coating machine, many crucibles electron gun coating machine, many targets radio frequency or magnetic control film coating machine, many targets laser or ion beam deposition machine etc.
The 3rd, directly adopt manganese, bismuth, aluminium elemental metals raw material are as evaporation source or target material, and its purity should be more than chemical pure (comprising chemical pure).Manganese, bismuth, aluminium starting material will carry out conventional prevapourising or pre-sputter before deposition, to remove the oxide on surface.Directly adopting simple metal to come the benefit of plated film as raw material is that the crystal structure and the chemical constitution of film is controlled easily.Starting material carry out plated film successively by following atomic ratio, can obtain having the magneto-optic memory technique MnBi of high record density
XAl
Y, X=0.20 → 0.70 wherein, Y=0.05 → 0.15.Above-mentioned stoicheiometry can be respectively according to raw material weight in different film plating process, thicknesses of layers, or monitoring such as plated film time realizes.
Thicknesses of layers can be monitored with the quartz crystal shaker.Compare MnBiXAl at the known materials atom chemistry
YUnder the situation of overall film thickness D, can pass through following formula,
d
Mn＝D/(1+X/A+Y/B)
d
Bi＝X/A*d
Mn
d
Al＝Y/B*d
Mn
A=0.34674, B=0.7399 calculate the gross thickness of every kind of material in film, take this as a foundation to carry out the predetermined chemical that plated film just can obtain material and compare MnBi
XAl
Y. for reducing oxygen content, the base vacuum degree is better than 5 * 10 in the chamber, plated film initial vacuum
-5Torr.
The 4th, according to Bi, Al, Mn be deposition three layers or random layer metal film on substrate successively.Gross thickness is selected between 100 → 1000 dusts.Plating is during Bi, and rate of sedimentation is low more good more, is controlled at 2 dusts/below second, can make (001) crystal face of Bi be parallel to substrate surface so usually, thereby is easy to acquisition [001] TEXTURE STATE.The rate of sedimentation of Al has no special requirements, usually in that the 2-5 dust/between second, the rate of sedimentation of Mn can reduce the oxidized degree of Mn like this greater than 5 dust/seconds.Adopt Bi, Al, the Mn deposition order can form stronger [001] texture on the one hand, can promote Al to participate in Mn on the other hand, and the alloying process of Bi is beneficial to the formation of MnBiAl alloy phase.Vacuum tightness during plated film is better than 8 * 10 in the electron gun evaporation system
-5Torr is better than 3 * 10 in radio frequency or magnetic control sputtering system
-2Torr.
The 5th, rete splashes down during for anti-oxidation and annealing, after having plated alloy film, adds the plating layer protecting film with same film plating process immediately.Diaphragm can be selected SiO, SiO for use
2, materials such as SiN, the controllable thickness of protective seam is between 200 dust to 2000 dusts.Vacuum tightness during plated film is better than 8 * 10 in the electron gun evaporation system
-5Torr is better than 3 * 10 in radio frequency or magnetic control sputtering system
-2Torr.
The 6th, in vacuum chamber, laminar film is carried out diffusion-alloying and handle.Alloying Treatment can original position be carried out, and also can carry out in another vacuum chamber.Vacuum tightness is high more good more, is generally selected in 5 * 10
-5Torr to 1 * 10
-7Between the torr.On technology, can adopt cycle annealing, temperature range is generally 150 → 550 ℃.Annealing time can be between half an hour to 6 hour.
Vacuum annealing also can be adopted the pulse temperature annealing way, and referring to accompanying drawing-1. pulse height can be controlled between 100 ℃ to 550 ℃, the temperature retention time in each cycle can be controlled between 2 minutes to 15 minutes, and total annealing time should be between half an hour to 6 hour.
Novelty of the present invention and creativeness show, courageously use the new material prescription.MnBi with existing patent
XAl
YSi
Z, X=0.7 → 1.0 wherein, Y=0.2 → 0.5, Z=0.05 → 0.2, material is compared, the prescription of MnBiAl alloy film material of the present invention, or the chemical constitution proportioning is different fully, promptly adopts prescription to be MnBi
XAl
Y, X=0.20 → 0.70 wherein, Y=0.05 → 0.15, alloy.
Novelty of the present invention and creativeness also show, adopt new preparation technology.It is characterized in that comprising following content:
(1) Al is positioned in the middle of Mn layer and the Bi layer, so that Bi, Al, Mn carry out alloying simultaneously, thereby improve the physical property of material.And the rate of sedimentation of Bi is low, generally at 2 dusts/below second.
(2) adopt the measures such as high evaporation speed of Mn, its speed is usually greater than 5 dust/seconds, thereby avoids the oxidation of metal M n, so that reduction thermal annealing temperature.
(3) to adopt the pulse annealing mode that material is carried out Alloying Treatment be to enter the MnBi lattice in order to help the Al atomic energy in the present invention.After the Al atom enters the MnBi lattice, partly substitute large-sized Bi atom and occupy the brilliant position of lattice point, thereby form the superior MnBiAl alloy phase of new magneto-optical property.Compare with former MnBi material, the lattice of new alloy phase shrinks at the C direction of principal axis.We find: for this alloy system of MnBi (Al), the lattice amount of contraction is big more, and it is good more that magneto-optical property will become.Under optimum process condition, the magneto-optical kerr corner of MnBiAl film can increase to about theoretical value 4.5 degree.Therefore, we propose from principle: promote that the lattice contraction of MnBi or MnBiAl alloy phase is the important channel of improving the material magneto-optical property.
The alloy firm that adopts above-mentioned steps to prepare has the surface characteristics of bright luster.Amplify 500 times and observe under polarizing microscope, magnetic domain should present very tiny list structure.Behind the saturated magnetization, magnetic domain then has the contrast of uniformity.When the X-photo structure was analyzed, film should have very strong (002) texture, sees shown in the accompanying drawing-2.The vertical face magnetic anisotropic that magneto-optic thin film is very strong makes the magneto-optical kerr magnetic hysteresis loop of material have extraordinary rectangle degree, sees shown in the accompanying drawing-3.The coercive force of material can be regulated by appropriate change stoicheiometry and annealing schedule according to actual needs, and range of adjustment can be from 1000 → 5000 oersteds.
Superiority of the present invention: the MnBiAl alloy film material according to the method for the invention and step preparation has excellent magneto-optical property.The typical magneto-optical property of material, referring to accompanying drawing-3 to shown in the accompanying drawing-5.Near short wavelength 400nm, the utmost point is easy to accomplish that to kerr rotational angle more than 3.3 degree (accompanying drawing-4), the ellipse inclined to one side rate of Ke Er also has 1 degree many (accompanying drawings-5).So huge Kerr magnetooptical effect is more than 2 times of common MnBi or MnBiAlSi film, and will exceed an order of magnitude than Pt/Co multilayer film.Up to the present normal temperature and pressure huge linear Ke Er enhancement effect down like this does not also see any patent and bibliographical information.Moreover, this material also has very high reflectivity.Reflectivity during the He-Ne Lasers wavelength is up to 55.2%, during 400nm greater than 35%.
The present invention be advantageous in that used starting material Mn, Bi, Al's is cheap, and the preparation method of alloy firm is simple, thereby is applicable to large-scale industrial production.
To the present invention be advantageous in that in order being easy to form high performance MnBiAl alloy phase, will to plate Bi earlier during plated film, plate Al again, plating Mn. then is that Al will be in the middle of Mn and Bi layer, so that the Al atom diffusion enters the MnBi lattice.And the rate of sedimentation of Bi is low more good more, thereby makes (001) crystal face of Bi film be parallel to substrate surface.Such as, rate controlled 2 dusts/below second.The film growth pattern of control rate of sedimentation can improve the repeatability and the percentage of A-class goods effectively.
The present invention be advantageous in that and use highly purified Mn and high vacuum coating equipment, thereby can avoid the oxidation of metal M n, reduce the temperature of vacuum annealing.In addition, lower thickness of monolayer, can shortening heat diffusion time.Such as, can make annealing temperature be reduced to 150 ℃, the time shortens to 1 hour.
Below in conjunction with embodiment and accompanying drawing the present invention is described in detail.
Accompanying drawing-the 1st, the synoptic diagram accompanying drawing-the 2nd of the pulse temperature annealing process in the material preparation process of the present invention, the x-ray diffraction synoptic diagram of material crystals structure of the present invention, Q=2* π/d, d: interplanar distance.Accompanying drawing-the 3rd, the magneto-optical kerr magnetic hysteresis loop synoptic diagram of material of the present invention, when lambda1-wavelength was 420 nanometers, the utmost point was 3.25 degree to kerr rotational angle.Accompanying drawing-the 4th, the typical magneto-optical kerr spectrum of material of the present invention synoptic diagram, when photon energy was 1.78 electron-volts, the utmost point was 3.49 degree to kerr rotational angle; And when photon energy was 3.30 electron-volts, the utmost point was 3.69 degree to kerr rotational angle.Accompanying drawing-the 5th, the ellipse inclined to one side rate synoptic diagram of the typical magneto-optical kerr of material of the present invention.Near short wavelength 400nm, the ellipse inclined to one side rate of Ke Er is greater than 1 degree.
Embodiment one:
The preparation stoicheiometry is 1: 0.47: 0.15 MnBi in high vacuum four crucible electron gun evaporation systems
0.47Al
0.15Alloy firm 1) prepare analytically pure Bi, Al, Mn, and SiO material ingot, and be fused to respectively in four crucibles.2) adopting transparent thickness is that the thick optical glass of 0.1mm is as substrate material.This material places the top of evaporation source through after conventional cleaning and drying, and the distance of source and substrate is 25cm.3) reach 5 * 10 when vacuum tightness
-3During Torr, can carry out the ion bombardment, with further clean substrate surface, bombardment time is about 15 minutes, about 100 milliamperes of bombarding current.Treat that vacuum tightness is better than 1 * 10
-6During Torr, just can carry out vacuum coating.4) metal-coated membrane.Successively depositing Bi on the substrate, Al and Mn metal material according to following order.Adopt the quartz crystal shaker to make the thickness of each individual layer be controlled at 45nm respectively, 7nm and 33nm, the evaporation time was respectively 250 seconds, 18 seconds and 55 seconds.During evaporation, the rate of sedimentation of bismuth will be controlled at below the 0.2nm/s, and the speed of manganese was higher than for 5 dust/seconds.5) protective film coating.In position the Bi/Al/Mn multilayer film that has prepared is added plating one deck SiO diaphragm.Plated film speed about 15 dust/seconds, the plated film time is 100 seconds, and thicknesses of layers is 157nm.6) anneal in the pulse temperature of in the vacuum chamber sample being carried out shown in accompanying drawing-1, make Mn, Bi, the Al metal carries out diffusion-alloying.Vacuum tightness will be higher than 1 * 10
-6Torr, annealing temperature is between 150 → 550 ℃, and annealing time is between 1 hour to 6 hours.7) stoicheiometry of preparing out by said procedure is 1: 0.47: 0.15 a MnBiAl alloy firm, has very excellent structure, optics, magnetics and magneto-optical property, referring to accompanying drawing-2 to accompanying drawing-5. near 400nm, its utmost point can be greater than 3.3 degree to kerr rotational angle, the ellipse inclined to one side rate of Ke Er then is higher than 1 degree.So huge Kerr magnetooptical effect is more than 2 times of common MnBi or MnBiAlSi film, and exceeds an order of magnitude than Pt/Co multilayer film.Moreover, this material also has very high reflectivity.Reflectivity during the He-Ne Lasers wavelength is up to 55.2%, during 400nm greater than 35%.Embodiment two:
The preparation chemistry is than the MnBi that is 1: 0.49: 0.18 in high vacuum four target sputtering systems
0.49Al
0.1818 alloy firms 1) prepare analytically pure Bi, Al, Mn, and SiO target, and place magnetic control target respectively, or on the radio frequency target.2) adopting transparent thickness is that the thick quartz glass of 0.1mm is as baseplate material.This material places vacuum chamber through after strict cleaning and drying.3) treat that the base vacuum degree is better than 1 * 10
-6During Torr, pour argon gas and carry out pre-sputter, Ar air pressure can be 1 * 10
-2Torr to 1 * 10
-4Between the Torr, sputtering time is between 10--＞20 minute.4) successively on substrate, alternately deposit Bi according to following order, Al, each 20 layers of Mn group element materials.Rate of sedimentation is between 0.05nm--＞0.5nm.Individual layer is controlled at Bi (2.3nm) respectively, Al (0.4nm), Mn (1.7nm).5) annealing makes Mn in vacuum chamber, Bi, and the Al metal carries out diffusion-alloying.Vacuum tightness will be higher than 1 * 10
-6Torr, annealing temperature is between 150 → 550 ℃, and annealing time is more than 3 hours.
Like this, just, the MnBiAl alloy firm that available can be good.Material physical property referring to accompanying drawing-2 to the embodiment three of accompanying drawing-5.:
The preparation chemistry is than the MnBi that is 1: 0.4: 0.1 in the high vacuum four target sputtering systems that in-situ annealing is arranged
0.4Al
0.1Alloy firm 1) with embodiment two.2) with embodiment two.3) with embodiment two.4) add in-place hot substrate makes its temperature between 150 → 500 ℃.5) simultaneously, successively on substrate, alternately deposit Bi, Al, each 10 layers of Mn group element materials according to following order.Rate of sedimentation is between 0.05nm--＞0.5nm.Individual layer is controlled at Bi (2nm) respectively, Al (0.22nm), Mn (1.65nm).
Thereby, the MnBiAl alloy firm that available can be good.Performance referring to accompanying drawing-2 to accompanying drawing-5.
Claims (4)
1. Mn-Bi-Al magneto-optic memory technique with high record density is characterized in that:
This material consists of MnBi
XAl
Y, X=0.20 → 0.70 wherein, Y=0.05 → 0.15;
This material has near the residue utmost point of 3.69 degree short wavelength 400nm to kerr rotational angle.
2. one kind prepares the described method with Mn-Bi-Al magneto-optic memory technique of high record density of claim 1, is included in and carries out vacuum coating on the transparent substrate, handles through vacuum annealing, and it is characterized in that: vacuum moulding machine is better than 5 * 10 at the base vacuum degree
-5Under the condition of torr, press Bi, Al, the Mn order deposits the random layer gross thickness successively on substrate be the film of 100-1000 dust; Control starting material growth rate and relative thickness obtain material predetermined chemistry ratio and specific TEXTURE STATE.The speed of deposition Bi was lower than for 2 dust/seconds; The rate of sedimentation of Al is 2-5 dust/second, and the rate of sedimentation of Mn is 5-10 dust/second; Perhaps also comprise the deposition layer protecting film.Then, in vacuum chamber laminar film is carried out Alloying Treatment, condition is that vacuum tightness is 5 * 10
-5Torr to 1 * 10
-7Between the torr, constant temperature was annealed 0.5 hour to 6 hours between 150 ℃-550 ℃.
3. have the method for the Mn-Bi-Al magneto-optic memory technique of high record density by the described preparation of claim 2, it is characterized in that: described diaphragm is SiO, SiO
2, materials such as SiN, the thickness of protective seam are the 200-2000 dust.Vacuum tightness during plated film is better than 8 * 10 in the electron gun evaporation system
-5Torr is better than 3 * 10 in radio frequency or magnetic control sputtering system
-2Torr.
4. the method that has the Mn-Bi-Al magneto-optic memory technique of high record density by the described preparation of claim 2, it is characterized in that: the described Alloying Treatment of carrying out comprises with pulse temperature and annealing, its condition is that pulse height is between 100 ℃ to 550 ℃, the temperature retention time in each cycle is 2 minutes to 15 minutes, and total annealing time is between half an hour to 6 hour.
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101544473B (en) * | 2009-03-06 | 2011-11-23 | 湖州金泰科技股份有限公司 | Method for plating glasses to a large area without pollution |
| CN102610346A (en) * | 2011-12-01 | 2012-07-25 | 中国计量学院 | Novel rare-earth-free nanometer composite permanent magnet material and preparation method thereof |
| CN111721993A (en) * | 2020-06-19 | 2020-09-29 | 贵州江源电力建设有限公司 | High-sensitivity miniaturized current detection system |
-
1996
- 1996-09-20 CN CN 96109334 patent/CN1079565C/en not_active Expired - Fee Related
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101544473B (en) * | 2009-03-06 | 2011-11-23 | 湖州金泰科技股份有限公司 | Method for plating glasses to a large area without pollution |
| CN102610346A (en) * | 2011-12-01 | 2012-07-25 | 中国计量学院 | Novel rare-earth-free nanometer composite permanent magnet material and preparation method thereof |
| CN102610346B (en) * | 2011-12-01 | 2015-10-28 | 中国计量学院 | A kind of Novel rare-earth-free nanometer composite permanent magnet material and preparation method thereof |
| CN111721993A (en) * | 2020-06-19 | 2020-09-29 | 贵州江源电力建设有限公司 | High-sensitivity miniaturized current detection system |
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| CN1079565C (en) | 2002-02-20 |
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