CN108962539B - A kind of metal/oxide three-layer heterojunction film and preparation method thereof - Google Patents

Abstract

The invention discloses a metal/oxide three-layer heterojunction film and a preparation method thereof, wherein the preparation method comprises the following steps: on a monocrystalline silicon or gadolinium gallium garnet substrate, a platinum film, an yttrium iron garnet film and a cobalt oxide film are sequentially arranged from bottom to top, a three-layer heterojunction structure is formed by covering through an antiferromagnetic oxide CoO, the traditional platinum film/yttrium iron garnet film double-layer heterojunction structure is improved, the spin thermoelectric voltage can be improved by 100% under the same thermal gradient condition, the spin transmission rate is greatly improved, and the thermal stability of a device is enhanced.

Description

A kind of metal/oxide three-layer heterojunction film and preparation method thereof

technical field

The invention belongs to the technical field of magnetic ultra-thin film materials, and in particular relates to a metal/oxide three-layer heterojunction film which can improve the size of spin thermoelectric effect and a preparation method thereof.

Background technique

Spintronics is an emerging science of data transmission, processing and storage by manipulating electron spins. The spin thermoelectric effect refers to the phenomenon that in a ferromagnetic/heterojunction, when a thermal gradient is established perpendicular to the normal direction of the sample and the magnetic moment of the sample is arranged longitudinally in the plane, a voltage difference is established laterally in the sample plane. Spintronics has potential application value and is expected to recycle Joule heat in processors to realize spintronic devices with high energy efficiency. Most of the traditional heterojunction structure materials are based on silicon substrate or gadolinium gallium garnet substrate, from bottom to top, it is a double-layer heterojunction of yttrium iron garnet film and platinum film, and the spin thermoelectric voltage and spin transport rate are different. high.

SUMMARY OF THE INVENTION

In order to overcome the above-mentioned defects of the prior art, the object of the present invention is to provide a metal/oxide three-layer heterojunction thin film and a preparation method thereof. For platinum film (Pt), yttrium iron garnet film (YIG) and cobalt oxide film (CoO), the traditional platinum film/yttrium iron garnet film double-layer heterojunction structure was improved by antiferromagnetic oxide CoO Covering to form a three-layer heterojunction structure, under the same thermal gradient conditions, the spin thermoelectric voltage is increased by up to 100%, the spin transfer rate is improved, and the thermal stability of the device is enhanced.

The above-mentioned purpose of the present invention is achieved through the following technical solutions:

A metal/oxide three-layer heterojunction thin film, using single crystal silicon or gadolinium gallium garnet as a substrate, on the substrate from inside to outside in order: platinum film, yttrium iron garnet film and cobalt oxide membrane; wherein,

The thickness of the platinum film is 3-9 nm;

The thickness of the yttrium iron garnet film is 15-90 nm;

The thickness of the cobalt oxide film is 1.5-6 nm.

Further, the thickness of the platinum film is 4-8 nm, preferably 6 nm.

Further, the thickness of the yttrium iron garnet film is 30-75 nm, preferably 50 nm.

Further, the thickness of the cobalt oxide film is 3.0-4.5 nm, preferably 4.0 nm.

In the second aspect, the preparation method of the above-mentioned metal/oxide three-layer heterojunction film, specifically, includes the following steps:

S1: Place the cleaned substrate in the sputtering chamber of the magnetron sputtering equipment, evacuate to a degree of vacuum ^of 2.0×10 ^-5 Pa, pass argon gas, and maintain the argon gas pressure at 1-3 mtorr; DC magnetron sputtering Pt target under the condition of power of 50-70W and current of 100mA to obtain Pt film; wherein, the sputtering rate is

S2: After the Pt film is grown, let it stand for 1 hour, take out the sample, and place it in the cavity of the pulsed laser deposition equipment, evacuate to a degree of vacuum of 2.0×10 ^-6 Pa, and the temperature of the substrate in the cavity rises to 400°C , pass oxygen, and maintain the oxygen pressure at 1.0-5.0Pa; under the condition of power of 70-90mW and voltage of 18.5-20.5kV, pulse laser strikes the YIG target to obtain YIG film; among them, the laser repetition frequency is 1-8Hz;

S3: After the laser strike is completed, the temperature in the cavity will naturally drop to normal temperature, then take out the sample, and rapidly anneal it in an annealing furnace with a temperature of 800-850 °C for 5-10 minutes;

S4: Place the annealed material in a magnetron sputtering chamber, evacuate to a degree of vacuum of 2.0×10 ^-5 Pa, and pass argon gas to maintain the argon gas pressure at 1-3 mtorr; when the power is 40-60W, Under the condition of the current of 175mA, the Co target was sputtered by DC magnetron to obtain a Co film; among them, the sputtering rate was

S5: After the Co film is grown, stand for 1 hour, take out the sample, and place it in an annealing furnace with a temperature of 350-450° C. for rapid annealing in an oxygen atmosphere for 5-10 minutes, and the Co film is oxidized to form a CoO film.

Further, the sputtering rate of the DC magnetron sputtering Pt target in step S1 is:

Further, the laser repetition frequency of the pulsed laser striking the YIG target in step S2 is 3-5 Hz.

Further, the sputtering rate of the DC magnetron sputtering Co target in step S4 is:

Compared with the prior art, the beneficial effects of the present invention are:

1. Most of the traditional thermoelectric materials are based on silicon substrates or gadolinium gallium garnet substrates, and from bottom to top are double-layer heterojunctions of yttrium iron garnet films and platinum films. The present invention is based on single crystal silicon or gadolinium gallium garnet On the substrate, from bottom to top are platinum film (Pt), yttrium iron garnet film (YIG) and cobalt oxide film (CoO). The spin transfer rate is enhanced and the thermal stability of the device is enhanced.

2. The reversed platinum film/yttrium iron garnet film of the present invention adopts the form of high-speed annealing, which not only ensures the formation of the yttrium iron garnet film, but also ensures that the performance of the platinum film is not lost after short-time high temperature treatment.

3. The present invention forms a three-layer heterojunction structure by covering the antiferromagnetic oxide CoO, which better prevents the surface oxidation of the sample, improves its thermal stability, and reduces the cost compared with the traditional covering gold film.

Description of drawings

FIG. 1 is a comparison diagram of the V _SSE voltage of the metal/oxide three-layer heterojunction film in the present invention and the conventional platinum film/yttrium iron garnet film double-layer heterojunction film.

Detailed ways

The technical solutions of the present invention will be described in detail below with reference to the accompanying drawings, but the protection scope of the present invention is not limited to the following embodiments.

The samples of GGG/Pt/YIG/CoO thin films and GGG/Pt/YIG thin films were prepared by using a computer-controlled multifunctional magnetron sputtering equipment AJA and a pulsed laser deposition equipment PLD with gadolinium gallium garnet (GGG) as the substrate. as follows:

生长完静置1h后，形成厚度为3～9nm的铂膜，取出样品。Put the cleaned substrate into the sputtering chamber, evacuate, and when the background vacuum of the chamber drops to 2.0×10 ^-5 Pa, argon gas is passed through, and the argon gas pressure is maintained at 1-3 mtorr; a magnetron is used. The method of sputtering is DC sputtering of Pt target, the power is 50-70W, the current is 100mA, and the sputtering rate is

After standing for 1 h after the growth, a platinum film with a thickness of 3-9 nm was formed, and the sample was taken out.

Put it into the PLD chamber of the pulsed laser deposition equipment, evacuate it, and when the background vacuum of the chamber drops to 2.0×10 ^-6 Pa, the temperature in the chamber is raised to 400°C, oxygen is supplied, and the oxygen pressure is maintained at 1.0-5.0Pa ; Using pulsed laser to strike the YIG target, the power is 70~90mW, the voltage is 18.5~20.5kV, and the laser repetition frequency is 1~8Hz. After the laser strikes, a yttrium iron garnet film with a thickness of 15~90nm is formed. The sample was taken out after the internal temperature naturally dropped to normal temperature.

Anneal at 800-850℃ for 5-10min in a rapid annealing furnace.

生长完静置1h后，取出样品。After the annealing is completed, the sample is put into the magnetron sputtering chamber again, and the vacuum is drawn. When the background vacuum of the chamber is reduced to 2.0×10 ^-5 Pa, the argon gas is passed through, and the argon gas pressure is maintained at 1-3 mtorr; The magnetron sputtering method was used to sputter the Co target with a power of 40-60W and a current of 175mA. The sputtering rate was

After growing for 1 h, the samples were taken out.

The samples were put into a rapid annealing furnace at 350-450°C for 5-10 min, and the Co was oxidized to form a cobalt oxide film with a thickness of 1.5-6 nm to obtain a GGG/Pt/YIG/CoO sample.

Example 1

生长完静置1h后，形成厚度为3nm的铂膜，取出样品。Put the cleaned substrate gadolinium gallium garnet (GGG) into the sputtering chamber, evacuate, and when the background vacuum of the chamber drops to 2.0×10 ^-5 Pa, pass argon gas, and the argon gas pressure is maintained at 1～3mtorr; DC sputtering Pt target by magnetron sputtering, the power is 50W, the current is 100mA, and the sputtering rate is

After standing for 1 h after the growth, a platinum film with a thickness of 3 nm was formed, and the sample was taken out.

Put it into the PLD chamber of the pulsed laser deposition equipment, evacuate it, and when the background vacuum of the chamber drops to 2.0×10 ^-6 Pa, the temperature in the chamber is raised to 400°C, oxygen is supplied, and the oxygen pressure is maintained at 1.0-5.0Pa ; Using pulsed laser to strike the YIG target, the power is 700mW, the voltage is 18.5kV, and the laser repetition frequency is 1Hz. After the laser strikes, a yttrium iron garnet film with a thickness of 15nm is formed, and the temperature in the cavity is naturally lowered to room temperature. sample.

生长完静置1h后，取出样品。Anneal at 800℃ for 5min in a rapid annealing furnace. After the annealing is completed, put the sample into the magnetron sputtering chamber again, evacuate, and when the background vacuum of the chamber drops to 2.0×10 ^-5 Pa, pass argon gas, The argon gas pressure was maintained at 1-3 mtorr; the magnetron sputtering method was used to sputter the Co target with a DC power of 40W and a current of 175mA. The sputtering rate was

After growing for 1 h, the samples were taken out.

The samples were placed in a rapid annealing furnace at 350 °C for 5 min, and the Co was oxidized to form a cobalt oxide film with a thickness of 1.5 nm to obtain a GGG/Pt/YIG/CoO sample.

Example 2

生长完静置1h后，形成厚度为9nm的铂膜，取出样品。Put the cleaned substrate gadolinium gallium garnet into the sputtering chamber, vacuumize, and when the background vacuum of the chamber drops to 2.0×10 ^-5 Pa, pass argon gas, and the argon gas pressure is maintained at 1～3mtorr ; DC sputtering Pt target by magnetron sputtering, the power is 70W, the current is 100mA, and the sputtering rate is

After standing for 1 h after the growth, a platinum film with a thickness of 9 nm was formed, and the sample was taken out.

Put it into the PLD chamber of the pulsed laser deposition equipment, evacuate it, and when the background vacuum of the chamber drops to 2.0×10 ^-6 Pa, the temperature in the chamber is raised to 400°C, oxygen is supplied, and the oxygen pressure is maintained at 1.0-5.0Pa ; Using pulsed laser to strike the YIG target, the power is 90mW, the voltage is 20.5kV, and the laser repetition frequency is 8Hz. After the laser strikes, a yttrium iron garnet film with a thickness of 90nm is formed, which is taken out after the temperature in the cavity naturally drops to room temperature. sample.

生长完静置1h后，取出样品。Anneal at 850℃ for 10min in a rapid annealing furnace. After the annealing is completed, put the sample into the magnetron sputtering chamber again, and pump the vacuum. When the background vacuum of the chamber is reduced to 2.0×10 ^-5 Pa, the argon gas is passed through. , the argon gas pressure is maintained at 1 ~ 3mtorr; the magnetron sputtering method is used to sputter the Co target, the power is 60W, the current is 175mA, and the sputtering rate is

After growing for 1 h, the samples were taken out.

The sample was placed in a rapid annealing furnace at 450 °C for 10 min, and Co was oxidized to form a cobalt oxide film with a thickness of 6 nm to obtain a GGG/Pt/YIG/CoO sample.

Example 3

生长完静置1h后，形成厚度为6nm的铂膜，取出样品。Put the cleaned substrate gadolinium gallium garnet into the sputtering chamber, vacuumize, and when the background vacuum of the chamber drops to 2.0×10 ^-5 Pa, pass argon gas, and the argon gas pressure is maintained at 1～3mtorr ; DC sputtering Pt target by magnetron sputtering, the power is 65W, the current is 100mA, and the sputtering rate is

After standing for 1 h after the growth, a platinum film with a thickness of 6 nm was formed, and the sample was taken out.

Put it into the PLD chamber of the pulsed laser deposition equipment, evacuate it, and when the background vacuum of the chamber drops to 2.0×10 ^-6 Pa, the temperature in the chamber is raised to 400°C, oxygen is supplied, and the oxygen pressure is maintained at 1.0-5.0Pa ; Using pulsed laser to strike the YIG target, the power is 80mW, the voltage is 19.5kV, and the laser repetition frequency is 5Hz. After the laser strikes, a yttrium iron garnet film with a thickness of 50nm is formed, which is taken out after the temperature in the cavity naturally drops to room temperature sample.

生长完静置1h后，取出样品。Annealed at 800℃ for 8min in a rapid annealing furnace; after the annealing, put the sample into the magnetron sputtering chamber again, and pumped the vacuum. When the background vacuum of the chamber dropped to 2.0×10 ^-5 Pa, argon was passed through. , the argon gas pressure is maintained at 1 ~ 3mtorr; the magnetron sputtering method is used to sputter the Co target, the power is 50W, the current is 175mA, and the sputtering rate is

After growing for 1 h, the samples were taken out.

The sample was placed in a rapid annealing furnace at 400 °C for 8 min, and Co was oxidized to form a cobalt oxide film with a thickness of 4 nm to obtain a GGG/Pt/YIG/CoO sample.

The same process as in Example 3 is adopted, except that the steps of DC sputtering Co target and high temperature annealing of Co film are not used, and the obtained sample is GGG/Pt/YIG.

The above-mentioned GGG/Pt/YIG/CoO and GGG/Pt/YIG samples were subjected to glue spin, photolithography, and development to obtain a standard Hall pattern, which was etched in a multi-functional magnetron sputtering equipment AJA to obtain the Hall pattern, respectively Atomic layer deposition equipment and magnetron sputtering equipment were used to grow alumina and Cr (for generating thermal gradients), take out the sample, overcut into I-beams, and measure the GGG/Pt/YIG and GGG/Pt/YIG and As shown in Figure 1, it can be seen that the V _SSE voltage of the GGG/Pt/YIG/CoO sample of the present invention _is obvious at the same temperature It is larger than the GGG/Pt/YIG sample that is not covered with CoO, indicating that the three-layer heterojunction structure formed by the antiferromagnetic oxide CoO covered by the present invention improves the spin transport rate and enhances the thermal stability of the device.

The above descriptions are only preferred embodiments of the present invention, but the present invention should not be limited to the contents disclosed in the embodiments. Therefore, all equivalents or modifications accomplished without departing from the disclosed spirit of the present invention fall into the protection scope of the present invention.

Claims (6)

1. A metal/oxide three-layer heterojunction film takes monocrystalline silicon or gadolinium gallium garnet as a substrate, and is characterized in that the substrate sequentially comprises from inside to outside: a platinum film with the thickness of 3-9 nm, an yttrium iron garnet film with the thickness of 15-90 nm and a cobalt oxide film with the thickness of 1.5-6 nm;

the preparation method of the metal/oxide three-layer heterojunction film comprises the following steps:

s1: the cleaned substrate is placed in a sputtering cavity of a magnetron sputtering device and is vacuumized until the vacuum degree is 2.0 multiplied by 10^-5Introducing argon gas when the pressure is Pa, and maintaining the pressure of the argon gas to be 1-3 mtorr; under the conditions that the power is 50-70W, the current is 100mA and the sputtering rate is

Carrying out direct current magnetron sputtering on a Pt target under the condition to obtain a Pt film, standing for 1h after the Pt film grows, and taking out a sample;

s2: placing the sample in a cavity of a pulsed laser deposition device, and vacuumizing until the vacuum degree is 2.0 multiplied by 10^-6Pa, raising the temperature in the cavity to 400 ℃, introducing oxygen, and maintaining the oxygen pressure at 1.0-5.0 Pa; striking a YIG target by pulse laser under the conditions that the power is 70-90 mW, the voltage is 18.5-20.5 kV and the laser repetition frequency is 1-8 Hz to obtain a YIG film, naturally cooling the temperature in the cavity to normal temperature after the laser striking is finished, and taking out a sample;

s3: rapidly annealing the sample in the step S2 in an annealing furnace at the temperature of 800-850 ℃ for 5-10 min;

s4: placing the annealed material in a magnetron sputtering cavity, and vacuumizing until the vacuum degree is 2.0 multiplied by 10^-5When Pa, introducing argon, and maintaining the pressure of the argon at 1-3 mtorr; under the conditions that the power is 40-60W, the current is 175mA and the sputtering rate is

Performing direct current magnetron sputtering on a Co target under the condition to obtain a Co film, standing for 1h after the Co film grows, and taking out a sample;

s5: and (5) placing the sample in the step S4 in an annealing furnace with the temperature of 350-450 ℃ for rapid annealing for 5-10 min, and oxidizing the Co film to form a CoO film.

2. The metal/oxide three-layer heterojunction thin film according to claim 1, wherein the thickness of the platinum film is 4 to 8nm, the thickness of the yttrium iron garnet film is 30 to 75nm, and the thickness of the cobalt oxide film is 3.0 to 4.5 nm.

3. The metal/oxide triple-layer heterojunction thin film according to claim 1 or 2, wherein the thickness of said platinum film is 6nm, the thickness of said yttrium iron garnet film is 50nm, and the thickness of said cobalt oxide film is 4.0 nm.

4. The metal/oxide triple-layer heterojunction thin film as claimed in claim 1, wherein in step S1, the sputtering rate of said dc magnetron sputtering Pt target is

5. The metal/oxide triple-layer heterojunction thin film according to claim 1, wherein in the step S2, the laser repetition frequency of the pulsed laser hitting the YIG target is 3 to 5 Hz.

6. The metal/oxide triple-layer heterojunction thin film as claimed in claim 1, wherein in step S4, the sputtering rate of said dc magnetron sputtering Co target is

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