CN102509768B - Fe3O4/p-Si structure and preparation method with current-regulated magnetoresistance effect - Google Patents

Abstract

The present invention relates to a Fe ₃ 0 ₄ /p-Si structure with current-regulated magnetoresistance effect and a preparation method thereof. The structure is that Fe ₃ 0 ₄ is grown on a p-type Si single crystal substrate; the heterostructure is grown at 100K temperature, Under the magnetic field of 50kOe, within the current range of 1mA, the maximum magnetoresistance value can reach 40%. The three-target adjustable ultra-high vacuum magnetron sputtering coating machine produced by the Shenyang Scientific Instrument Development Center of the Chinese Academy of Sciences is used. A Fe target with a purity of 99.99% is installed on the strong magnetic target head. The thickness of the target is 2mm and the diameter is 60mm; The distance between the substrate holders is 10cm; the p-type Si single crystal substrate is installed on the substrate holder above the target head; by controlling the vacuum, sputtering gas, current, voltage, sputtering time and other conditions, the p-type Si _Fe3O4 samples _grown on Si single crystal substrates. Compared with the performance of other Fe ₃ O ₄ /Si structures: the heterostructure prepared by the present invention has a larger magnetoresistance effect under a small current; the method adopted is the reactive magnetron sputtering method, which is simple and practical, and is beneficial to Promotion in industrial production.

Description

Fe3O4/p-Si structure and preparation method with current-regulated magnetoresistance effect

technical field

The present invention relates to a Fe ₃ O ₄ /p-Si structure and preparation method with current-regulated magnetoresistance effect, more specifically, a Fe ₃ O ₄ /p-Si heterogeneous structure capable of regulating magnetoresistance effect through current intensity. texture and preparation method.

Background technique

In recent years, spintronic materials have attracted much attention due to their great application prospects in magnetic information storage and reading. The 2007 Nobel Prize in Physics was awarded to two pioneers of spintronics, Professors Albert Fert and Peter Grünberg. Now, how to combine materials with high spin polarizability and semiconductor materials to produce a larger magnetoresistance effect is a problem to be solved. the

First-principle calculations show that the energy band structures of Fe ₃ O ₄ , La _1-x A _x MnO ₃ (LAMO, where A is alkaline earth elements Ca, Sr and Ba, etc.), CrO ₂ , and NiMnSb are between those of metals and insulators. Between them, they are called semi-metallic materials. For one spin direction, the energy band structure of semi-metallic materials has metallic characteristics, and has a certain density of states near the Fermi surface; for the other spin direction, its energy band structure has insulator characteristics, and the density of states near the Fermi surface is zero or electrons are localized. Therefore, theoretically, half-metallic materials should have 100% spin polarizability. The Curie temperatures of LAMO and CrO ₂ materials are relatively low, which cannot meet the requirements of practical applications. The structure of the Heusler alloy is relatively complex, the price is relatively expensive, it is not easy to prepare, and it is not conducive to actual production. Fe ₃ O ₄ material has the characteristics of high Curie temperature, resistivity matching with semiconductor, etc. Therefore, combining Fe ₃ O ₄ with semiconductor as ferromagnetic layer will obtain a composite material with magnetoresistance effect.

At present, among the experimental reports at home and abroad, only Chinese Wang et al. reported on APPLIED PHYSICS LETTERS 92, 012122 (2008) that the Fe 3 O 4 layer was grown on n-type Si by laser molecular beam epitaxy, and the Fe ₃ O ₄ layer was grown at 50kOe The maximum magnetoresistance value measured under a magnetic field is 6%. Mi et al. reported in JOURNAL OF APPLIED PHYSICS 107, 103922 (2010) that a Fe ₃ O ₄ layer was prepared on a p-type Si substrate with a resistivity of 2Ωcm by using magnetron sputtering without heating the substrate. A magnetoresistance value of 30% was observed at a magnetic field of 90 kOe and a current of 100 mA.

The magnetoresistance effect reported by Mi et al. in JOURNAL OF APPLIED PHYSICS 107, 103922 (2010) is that the current flows longitudinally through the structure, that is, the current flows from Fe ₃ O ₄ to Si. In addition, low currents are mostly used in practical applications, which can save energy; and high magnetoresistance values are required to improve the sensitivity of devices, so the research results mentioned above cannot meet the requirements of practical applications.

Contents of the invention

From the perspective of industrial production, it is necessary to use the sputtering method to prepare samples; from the practical application, the samples that need to be prepared have a high magnetoresistance effect, and the current that needs to produce the magnetoresistance effect is small, which is conducive to energy saving. Proceeding from the above two purposes, the present invention develops a Fe ₃ O ₄ /p-Si structure with a current-regulated magnetoresistance effect, and observes a larger magnetoresistance effect at a lower current, and the magnetoresistance effect is a surface The internal magnetoresistance effect, that is, the current flows within the Fe ₃ O ₄ layer rather than longitudinally through the structure.

A kind of Fe ₃ O ₄ /p-Si structure with current control magnetoresistance effect of the present invention is to grow Fe ₃ O ₄ on p-type Si single crystal substrate; the heterogeneous structure is under 100K temperature, 50kOe magnetic field, In the current range of 1mA, the maximum magnetic resistance value can reach 40%. A magnetoresistance value of 30% was observed at a magnetic field of 90kOe and a current of 100mA, which was higher than the magnetic field used in the present invention and the current intensity was higher, but the magnetoresistance value was lower than the result of the present invention.

The Fe ₃ O ₄ /p-Si structure with current-regulating magnetoresistance effect of the present invention uses a base material that is a p-type Si(100) single wafer with a resistivity of 0.02Ωcm. The p-type Si(100) used here The resistivity of the single wafer is 2 orders of magnitude lower than that of the p-type Si (100) single wafer used by Mi et al. in JOURNAL OF APPLIED PHYSICS 107, 103922 (2010), and the substrate was heated during the preparation process, Thus, the degree of crystallization of Fe ₃ O ₄ becomes better.

Specific steps are as follows:

1) The three-target adjustable ultra-high vacuum magnetron sputtering coating machine produced by the Shenyang Scientific Instrument Research and Development Center of the Chinese Academy of Sciences is used. An Fe target with a purity of 99.99% is installed on the strong magnetic target head. The thickness of the target material is 2mm and the diameter is 60mm; the distance between the target and the substrate holder is 10cm;

2) After the p-type Si single crystal substrate material is cleaned of surface impurities by means of ultrasonic waves, the p-type Si single crystal substrate is installed on the substrate holder above the target head;

3) Turn on the three-target adjustable ultra-high vacuum magnetron sputtering coating machine, start the first-level mechanical pump and the second-level molecular pump to vacuumize, until the vacuum degree of the back and bottom of the sputtering chamber is better than 8×10 ^-6 Pa;

4) When the vacuum degree of the back of the sputtering chamber is better than 8×10 ^-6 Pa, feed the mixed gas of Ar and O ₂ with a purity of 99.999% into the vacuum chamber, wherein the flow rate of Ar gas is 100 sccm, O ₂ gas The flow rate is 2.4sccm, and the vacuum degree is kept at 1Pa;

5) Raise the temperature of the p-type Si single crystal substrate to 500°C at a rate of 10°C/s;

6) After the substrate temperature reaches 500°C and stabilizes, turn on the stepper motor that controls the rotation of the substrate holder, so that the substrate holder and the p-type Si single crystal substrate installed on the substrate holder rotate at a speed of 2 revolutions per minute;

7) Turn on the sputtering power supply, apply a current of 0.2A and a DC voltage of 350V on the Fe target, pre-sputter for 10 minutes, and wait for the sputtering current and voltage to stabilize;

8) Open the baffle under the substrate holder to start sputtering. During the sputtering process, the p-type Si single crystal substrate is kept at 500°C and rotates at a speed of 2 revolutions per second;

9) After 15 minutes of sputtering, close the baffle plate under the substrate holder, then turn off the sputtering power supply, stop feeding the sputtering gas Ar and O ₂ , fully open the gate valve, continue vacuuming, and turn off the control substrate A rotating stepper motor was installed, and the temperature of the p-type Si single crystal substrate was lowered to room temperature at a cooling rate of 5°C/min, and then the vacuum system was turned off; after the system cooled down, the vacuum chamber was filled with nitrogen gas with a purity of 99.999%. Until the air pressure in the sputtering chamber reaches a standard atmospheric pressure, stop feeding nitrogen, open the vacuum chamber, and take out the Fe ₃ O ₄ sample grown on the p-type Si single crystal substrate.

The Fe ₃ O ₄ /p-Si structure with current-regulating magnetoresistance effect involved in the present invention has application value in spin electronics devices, and can replace existing magnetic metal materials as spin injection source materials.

Compared with the properties and preparation methods of other Fe ₃ O ₄ /Si structures: the heterostructure prepared by the present invention has a large magnetoresistance effect under low current; the method adopted is the reactive magnetron sputtering method, which is simple and practical , which is conducive to the promotion in industrial production. Compared with existing technology:

1, because the main method adopted in industrialized production at present is the sputtering method, the reactive sputtering method adopted in the present invention is similar to the adoption of the laser molecular beam epitaxy method reported on APPLIED PHYSICS LETTERS 92, 012122 (2008) by Wang et al. Compared with, it has obvious advantages in industrial production;

2. The present invention measures 40% of the in-plane magnetoresistance value under a magnetic field of 50kOe and a current lower than 1mA, which is higher than the longitudinal magnetic resistance at 100mA reported by Mi et al. in JOURNAL OF APPLIED PHYSICS 107, 103922 (2010). The resistance effect has more practical application value and is more energy-saving in the application process. the

Description of drawings

Fig. 1 shows the X-ray diffraction spectrum of the Fe ₃ O ₄ /p-Si structure prepared in the present invention.

Fig. 2 shows the photoelectron spectrum of Fe 2p in the Fe ₃ O ₄ /p-Si structure prepared in the present invention.

Fig. 3 shows the zero-field cooling curve and the plus-field cooling curve of the Fe ₃ O ₄ /p-Si structure prepared by the present invention.

Fig. 4 shows the relation curve of the magnetoresistance versus the applied current of the Fe ₃ O ₄ /p-Si structure prepared by the present invention at a temperature of 100K and a magnetic field of 50kOe.

Fig. 5 shows a schematic diagram of the electrical transport characteristic measurement of the Fe ₃ O ₄ /p-Si structure of the present invention.

Detailed ways

According to our analysis of the structure and properties of the samples prepared in the present invention, the best implementation of the Fe ₃ O ₄ /p-Si structure with the current-regulating magnetoresistance effect will be described in detail below: the method of the electrode is to allow the current Flowing through the Fe ₃ O ₄ plane, that is, there are four electrodes on the Fe ₃ O ₄ layer:

1. The three-target adjustable ultra-high vacuum magnetron sputtering coating machine produced by the Shenyang Scientific Instrument Development Center of the Chinese Academy of Sciences is used. An Fe target with a purity of 99.99% is installed on the strong magnetic target head. The thickness of the target is 2mm and the diameter is 60mm; the distance between the target and the substrate holder is 10cm;

2. After the p-type Si single crystal substrate material is cleaned of surface impurities by means of ultrasonic waves, the p-type Si single crystal substrate is installed on the substrate holder above the target head; 

3. Turn on the three-target adjustable ultra-high vacuum magnetron sputtering coating machine, start the first-level mechanical pump and the second-level molecular pump to vacuumize, until the vacuum degree of the back and bottom of the sputtering chamber is better than 8×10 ^-6 Pa;

4. When the vacuum degree of the background of the sputtering chamber is better than 8×10 ^-6 Pa, pass a mixed gas of Ar and O ₂ with a purity of 99.999% into the vacuum chamber to keep the vacuum degree at 1 Pa, wherein the Ar gas The flow rate is 100sccm, and the flow rate of _O2 gas is 2.4sccm; until the sample preparation is completed and the sputtering is stopped, the introduction of the mixed gas of Ar and _O2 into the sputtering chamber can be stopped;

5. After completing step 4), raise the temperature of the p-type Si single crystal substrate to 500°C at a rate of 10°C/s;

6. After the substrate temperature reaches 500°C and stabilizes, turn on the stepper motor that controls the rotation of the substrate holder, so that the substrate holder and the p-type Si single crystal substrate installed on the substrate holder rotate at a speed of 2 revolutions per minute; The rotation of the substrate holder cannot be stopped until the sample preparation is completed;

7. Turn on the sputtering power supply, apply a current of 0.2A and a DC voltage of 350V on the Fe target, pre-sputter for 10 minutes, and wait for the sputtering current and voltage to stabilize;

8. Open the baffle under the substrate holder to start sputtering. During the sputtering process, the p-type Si single crystal substrate is kept at 500°C and rotates at a speed of 2 revolutions per second;

9. After 15 minutes of sputtering, close the baffle plate under the substrate holder, then turn off the sputtering power supply, stop feeding the sputtering gas Ar and O ₂ , fully open the gate valve, continue vacuuming, and turn off the control substrate A rotating stepper motor was installed, and the temperature of the p-type Si single crystal substrate was lowered to room temperature at a cooling rate of 5°C/min, and then the vacuum system was turned off; after the system cooled down, the vacuum chamber was filled with nitrogen gas with a purity of 99.999%. Until the air pressure in the sputtering chamber reaches a standard atmospheric pressure, stop feeding nitrogen, open the vacuum chamber, and take out the Fe ₃ O ₄ sample grown on the p-type Si single crystal substrate.

We measured the as-prepared samples by X-ray diffraction, X-ray photoelectron spectroscopy, magnetic properties and electrical transport properties. the

Figure 1 shows the X-ray diffraction spectrum of the prepared Fe ₃ O ₄ /p-Si structure. It can be seen from the figure that the diffraction peaks all come from Fe ₃ O ₄ and Si(400), indicating that the prepared sample is a polycrystalline Fe ₃ O ₄ film without orientation growth.

Figure 2 shows the photoelectron spectrum of Fe 2p in the prepared Fe ₃ O ₄ /p-Si structure. It can be seen from the figure that the characteristic peaks of Fe ²⁺ are located at 709 and 723eV, causing the broadening of Fe 2p ^1/2 and Fe 2p ^3/2 peaks, and the characteristic satellite peak of Fe ³⁺ at 719eV, these two characteristics further Explain that we prepared Fe ₃ O ₄ samples.

Fig. 3 shows the zero-field cooling curve and the plus-field cooling curve of the prepared Fe ₃ O ₄ /p-Si structure under a 300Oe magnetic field. It can be seen from the figure that the magnetization of the sample changes significantly around 116K, indicating that the Verwey transition temperature of the sample we prepared is 116K, which further proves that the sample we prepared is a Fe ₃ O ₄ sample close to stoichiometry.

Fig. 4 shows the relationship curve of the magnetoresistance of the prepared Fe ₃ O ₄ /p-Si structure under the temperature of 100K and the magnetic field of 50kOe as a function of the applied current. It can be seen from the figure that the maximum magnetoresistance value of the heterostructure can reach 40% at a temperature of 100K, a magnetic field of 50kOe, and a current range of 1mA.

Fig. 5 shows a schematic diagram of measuring electrical transport characteristics of the Fe ₃ O ₄ /p-Si structure. This figure shows that the electrode connection method for measuring the magnetoresistance effect in the present invention is the standard four-terminal method, and the electrode is Ag.

Claims (1)

1. one kind has the Fe that electric current is regulated and control magneto-resistance effect ₃O ₄/ p-Si structure is characterized in that in resistivity be the p-type Si single crystal substrates of the 0.02 Ω cm Fe that grows ₃O ₄This structure is under the 100K temperature, under the 50kOe magnetic field, in the current range of 1mA, and the maximum magnetic flux resistance value can reach 40%; The preparation method is as follows:

1) the adjustable superhigh vacuum magnetron sputtering film-plating machine of three targets that adopts scientific instrument development center, Chinese Academy of Sciences Shenyang to produce, at ferromagnetism target head a purity being installed is 99.99% Fe target, and the thickness of target is 2mm, and diameter is 60mm; Distance between target and the substrate frame is 10cm;

2) p-type Si single crystal substrates material is removed surface impurity by hyperacoustic mode after, p-type Si single crystal substrates is installed on the substrate frame that is positioned at target head top;

3) the adjustable superhigh vacuum magnetron sputtering film-plating machine of unlatching three targets successively starts the one-level mechanical pump and the secondary molecular pump vacuumizes, until the back end vacuum degree of sputtering chamber is better than 8 * 10 ^{– 6}Pa;

4) the back end vacuum degree when sputtering chamber is better than 8 * 10 ^{– 6}During Pa, passing into purity to vacuum chamber is 99.999% Ar and O ₂Mist, wherein the flow of Ar gas is 100sccm, O ₂The flow of gas is 2.4sccm, with vacuum keep at 1Pa;

5) p-type Si single crystal substrates temperature is risen to 500 ℃ with 10 ℃/second speed;

6) until base reservoir temperature reach 500 ℃ and stable after, open the stepping motor of control substrate frame rotation, make substrate frame and be installed in p-type Si single crystal substrates on the substrate frame with the rotational speed of per minute 2 circles;

7) open shielding power supply, apply the electric current of 0.2A and the direct voltage of 350V at the Fe target, pre-sputter 10 minutes waits sputtering current and voltage stabilization;

8) plate washer of opening substrate frame below begins sputter, and in the sputter procedure, p-type Si single crystal substrates remains on 500 ℃ and always with the rotational speed of 2 circles each second;

9) sputter was closed the plate washer of substrate frame below after 15 minutes, then closed shielding power supply, stopped to pass into sputter gas Ar and O ₂, open slide valve fully, continue to vacuumize, turn off the stepping motor of control substrate frame rotation, and p-type Si single crystal substrates temperature is down to room temperature with the rate of temperature fall of 5 ℃/min, then close vacuum system; After system cools, being filled with purity to vacuum chamber is 99.999% nitrogen, until the air pressure in the sputtering chamber reaches a standard atmospheric pressure, stops to pass into nitrogen, opens vacuum chamber, takes out the Fe that grows on the p-type Si single crystal substrates ₃O ₄Sample.

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