Patent Application
20230081176
This application is based upon and claims priority to Chinese Patent Application No. 202111074604.7, filed on Sep. 14, 2021, the entire contents of which are incorporated herein by reference.
The present disclosure relates to the technical field of preparation methods of epitaxy materials, and in particular to a preparation method of a silicon-based molecular beam heteroepitaxy material, a memristor, and use thereof.
With the advent of the Information Age, the electronic information industry is rapidly developing, and electronic components such as capacitors, diodes, transistors, and complementary metal-oxide semiconductor (CMOS) transistors have become the basic pillars of the electronic information industry. The continuous development of human scientific research promotes the technological upgradation of electronic components, thereby greatly promoting the development of the electronic information industry and improving all aspects of people's lives.
Pulsed laser deposition (PLD), a new epitaxial growth process, shows different characteristics from previous preparation methods in scientific research and production, and has promising application prospects. Since the initial development of the epitaxial growth -technique in the late 1950s and early 1960s, the epitaxial growth technique has become a new research focus in the fields of electronics and communications due to its excellent growth characteristics. The epitaxial growth technique shows wide application potential in the manufacture of high-frequency and high-power devices, the scientific research and exploration of new materials, and the like. In the field of scientific research and exploration of substrates, a new silicon-based molecular beam heteroepitaxy material preparation method can be studied and developed.
It is well known that epitaxial growth refers to the growth of a single crystal layer on a single crystal substrate (the single crystal layer meets specified requirements and has the same crystal phase as the substrate), as if the crystal extends out by a specified length. The quality of epitaxy may vary significantly with different epitaxy methods, and may change considerably with the change in the selected method and specific steps. Epitaxial materials are widely used in integrated circuits, PN junction isolation techniques, and large-scale integrated circuits because the epitaxial materials have a characteristic of improving the material quality. According to this characteristic, a silicon-based molecular beam heteroepitaxy material preparation method can be developed. PLD molecular beam epitaxy (MBE) technique is the latest crystal growth technique, where a substrate is placed inside an ultra-vacuum growth cavity, then a single crystal material to grow is placed on a target sleeve, and when the substrate is heated to a specified temperature, a gas is introduced to achieve a required pressure and a laser is turned on to enable the ejection of a molecular flow, such that a single crystal can grow. PLD involves simple operations and convenient preparation, and has bright prospects in future applications.
In the present disclosure, epitaxial samples that can grow repeatedly are prepared by adjusting preparation conditions such as temperature, oxygen pressure, laser mode, and laser frequency.
The present disclosure is intended to provide a preparation method of a silicon-based molecular beam heteroepitaxy material, a memristor, and use thereof, which solves the problem that the existing method is difficult to control and can generally only produce one layer of epitaxial material.
In order to achieve the objective, the present disclosure adopts the following technical solutions: A preparation method of a silicon-based molecular beam heteroepitaxy material is provided, including the following steps:
a. fixing a cleaned Si substrate on a substrate platform in a cavity of a PLD device, and vacuum-pumping the cavity to 1×10−4 Pa to 5×10−4 Pa;
b. raising a temperature in the cavity to 90° C. to 110° C., and introducing Ar into the cavity to maintain a gas pressure in the cavity at 0.8 Pa to 1.2 Pa; turning on a laser to conduct pre-sputtering of a SrTiO3 target for 1 min to 2 min and then conduct formal sputtering of the SrTiO3 target to form a SrTiO3 film with a thickness of 4 nm to 8 nm; after the sputtering is completed, introducing N2 into the cavity to maintain the pressure in the cavity at 90 Pa to 110 Pa; further raising the temperature in the cavity to 550° C. to 650° C., and pumping out the gas from the cavity to 1×10−4 Pa to 5×10−4 Pa; introducing O2 into the cavity, and adjusting an interface valve to maintain the pressure in the cavity at 0.8 Pa to 1.2 Pa; and raising the temperature in the cavity to 680° C. to 720° C., turning on a laser to conduct the pre-sputtering of a SrTiO3 target for 1 min to 2 min;
c. raising the temperature in the cavity to 740° C. to 760° C., and conducting the formal sputtering of the SrTiO3 target for 10 min to 20 min to form a first layer of SrTiO3 on the Si substrate;
d. adjusting the O2 pressure to 20 Pa to 30 Pa, and conducting the pre-sputtering of a La0.67Sr0.33MnO3 target for 1 min to 2 min and then the formal sputtering of the target for 20 min to 40 min to form a second layer of La0.67Sr0.33MnO3 on the first layer of SrTiO3;
e. adjusting the O2 pressure to 0.8 Pa to 1.2 Pa, and conducting the pre-sputtering of a BTO-CeO2 target for 1 min to 2 min and then the formal sputtering of the target for 10 min to 20 min to form a third layer of BTO-CeO2 on the second layer of La0.67Sr0.33MnO3; and
f. adjusting the O2 pressure to 2×104 Pa to 5×104 Pa, annealing in-situ, and taking a product out after the product is cooled to room temperature.
In step a, the Si substrate may be subjected to ultrasonic cleaning successively in acetone and alcohol, SiO2 removal with a diluted hydrofluoric (HF) acid solution, and ultrasonic cleaning in deionized water, and then taken out and blow-dried with N2.
During the preparation, a temperature procedure may be set as follows:
step 1: raising from 0° C. to 100° C. in 5 min;
step 2: keeping at 100° C. for 3 min;
step 3: raising from 100° C. to 500° C. in 30 min;
step 4: raising from 500° C. to 750° C. in 25 min;
step 5: keeping at 750° C. for 90 min; and
step 6: decreasing from 750° C. to 0° C. in 150 min.
During the preparation, the laser may be set to be in an EGY NGR mode, a frequency of the pre-sputtering may be set to 1 HZ to 3 HZ, and a frequency of the formal sputtering may be set to 3 HZ to 7 HZ.
The first, second, and third layers may have thicknesses of 42 nm, 30 nm, and 40 nm, respectively.
Crystal phases of the first, second, and third layers may be (001)(002); (001)(002); and (001)(002)BTO and (002)(004)CeO2, respectively.
An atomic ratio of BaTiO3 to CeO2 in the third layer may be 0.5:0.5.
A memristor is provided, wherein a structure of the memristor is obtained by allowing a Pd top electrode layer to grow on a silicon-based molecular beam heteroepitaxy material prepared by the method described above.
The Pd top electrode layer may have a thickness of 30 nm to 50 nm and a diameter of 80 μm to 100 μm.
Use of the memristor described above in neuro-imitation devices and ferroelectric devices is provided.
In the preparation method of the present disclosure, the design of a first buffer layer of SrTiO3 on a silicon-based substrate is adjusted and the growth temperature, growth time, oxygen pressure, laser mode, and laser frequency of each layer are adjusted to achieve the growth of a heteroepitaxial material. A general epitaxy method can only provide one epitaxial material growing on a silicon-based substrate, and a buffer layer prepared by a general epitaxy method is only of a few nanometers and is very difficult to control. However, the method provided by the present disclosure can achieve the growth of three types of heterojunction materials, and the design of a buffer layer in the method is very ingenious, which can ensure that the three types of materials are all epitaxial, and results in reliable repeatability and easy preparation. in the present disclosure, P-type silicon is used as a substrate, and different growth conditions are provided to achieve the epitaxial growth of three types of heteroepitaxial materials, and X-ray diffractometry (XRD) and transmission electron microscopy (TEM) tests are conducted to prove that the method is stable and repeatable.
in the present disclosure, epitaxial samples that can grow repeatedly are prepared by adjusting preparation conditions such as temperature, oxygen pressure, laser mode, and laser frequency. In the present disclosure, with a Pd layer as a top electrode and an LSMO layer as a bottom electrode, the I-V and pulse electrical properties of a prepared sample are tested, which are manifested as memristor properties; and the synapse properties and ferroelectric properties are successfully imitated during a pulse modulation process. As we all know, a resistance of a memristor changes with a quantity of electricity flowing through the memristor, and a resistance change experienced by a memristor can be remembered by the memristor, which is very similar to the human brain. In the research of the present disclosure, different pulse parameters are applied to control a resistance of a memristor.
The present disclosure will be further described below in conjunction with examples, but the following examples are only for illustration and do not limit the protection scope of the present disclosure in any way.
As shown in
The preparation method of the present disclosure included the following steps:
1. A suitable substrate was prepared.
P-type Si was adopted as a substrate. The Si substrate was subjected to ultrasonic cleaning in acetone for 10 min and then in alcohol for 10 min, then soaked in a diluted HF acid solution for 90 seconds, taken out by wooden clips and subjected to ultrasonic cleaning in deionized water for 5 min, and finally taken out and blow-dried with N2.
2. The Si substrate was placed in a cavity of a PLD device and the cavity was vacuum-pumped.
As shown in
3. A gas was introduced.
There were four target platforms (e) located directly opposite to the tableting platform (f) (with a thermocouple wire for temperature control) in the cavity, and targets of the first, second, and third epitaxial layers were respectively placed on the target platforms (e) (with an empty one). A laser beam (c) outside the device was irradiated on the target platforms directly facing the tableting platform (f) through a glass window for initiation.
In this step, the thermocouple wire in the tableting platform (f) was heated first, then oxygen in the cavity (a) was pumped out by controlling a gate valve (b); a temperature in the cavity was raised to 100° C., and Ar was introduced to form a pressure of 1 Pa; then SrTiO3 was sputtered for 1 min, and N2 was introduced to maintain a pressure of 100 Pa; the temperature was raised to 600° C., and then the gas in the cavity was pumped out to maintain a pressure of 5×10−4 Pa; O2 was introduced into the cavity at a flow rate of 25 sccm, and the gate valve (b) was adjusted to maintain a pressure in the cavity at 1 Pa; a laser controller was set to be in an EGY NGR mode; and then the pre-sputtering of the SrTiO3 target was conducted for 1 min to 2 min at a pulse frequency of 2 HZ, and the formal sputtering of the target was conducted at a pulse frequency of 5 HZ and a temperature of 700° C.
4. Epitaxy of a first layer of SrTiO3
After the pre-sputtering of SrTiO3, the formal sputtering was conducted for 15 min, and a resulting sample stood for 10 min, such that the first layer of SrTiO3 with a thickness of 42 nm was epitaxially formed on the Si substrate.
5. Epitaxy of a second layer of La0.67Sr0.33MnO3
After the first layer of SrTiO3 was formed, the gate valve (b) was adjusted to maintain the pressure in the cavity at 26 Pa, the pre-sputtering of LaSrMnO3 was conducted for 1 min to 2 min, and then the formal sputtering of the target was conducted for 30 min; and a resulting sample stood for 10 min, such that a second layer of La0.67Sr0.33MnO3 with a thickness of 30 nm was epitaxially formed on the first layer of SrTiO3.
6. Epitaxy of a third layer of (BaTiO3)0.5—(CeO2)0.5
After the second layer of La0.67Sr0.33MnO3 was formed, the gate valve (b) was adjusted to maintain the pressure in the cavity at 1 Pa, the pre-sputtering of (BaTiO3)0.5—(CeO2)0.5 was conducted for 1 min to 2 min, and then the formal sputtering of the target was conducted for 15 min; and a resulting sample stood for 10 min, such that a third layer of BTO-CeO2 with a thickness of 40 nm was epitaxially formed on the second layer of L0.67Sr0.33MnO3. Then the gate valve (b) was adjusted to maintain the pressure in the cavity at 3×104 Pa, and a resulting sample was annealed in-situ, and then taken out after being cooled to room temperature.
A Pd top electrode with a thickness of 40 nm and a diameter of 90 μm was allowed to grow on the sample in a magnetron sputtering device, and an LSMO layer was adopted as a bottom electrode, such as to determine the I-V and pulse electrical properties and ferroelectric properties.
| Number | Date | Country | Kind |
|---|---|---|---|
| 202111074604.7 | Sep 2021 | CN | national |
