An MFS storage structure, its preparation method and applications

Abstract

The present invention discloses an MFS storage structure, a preparation method thereof and an application. The MFS storage structure includes a substrate, a ZnO low-temperature buffer layer, a ZnO thin film, a Zn 1‑x M x O thin film and a Zn 1‑y M y O ferroelectric thin film, which are sequentially stacked; wherein, M is selected from at least one of Mg, V, Sb, Y or Gd; wherein, 0 < x ≤ 0.4 and 0.3 ≤ y ≤ 0.6. The MFS storage structure constructs a quasi-homogeneous epitaxial integration system, thereby reducing thin film interface defects, improving the quality of the ferroelectric thin film, enhancing the on / off efficiency of the ferroelectric gate to regulate the channel current, and realizing high-performance ferroelectric storage.

Description

Technical Field

[0001] The present invention relates to the technical fields of semiconductor thin film growth and ferroelectric field effect transistors, and particularly relates to a MFS storage structure, a preparation method thereof, and an application thereof. Background Art

[0002] In early research, for the preparation of a metal-ferroelectric-semiconductor (MFS) storage structure, a ferroelectric thin film was directly prepared on a Si substrate, so that the SiO2 insulating layer in a traditional MOSFET (metal-oxide-semiconductor field effect transistor) was replaced by a ferroelectric layer, and the switching of the channel current was controlled by the reversal of ferroelectric polarization. However, the ferroelectric material directly prepared on the semiconductor belongs to heteroepitaxial growth, and many defects will be formed at the interface, resulting in very poor charge retention, which seriously restricts the further improvement of its performance.

[0003] Therefore, there is an urgent need for a new type of metal-ferroelectric-semiconductor (MFS) storage structure to solve the problems of excessive defect formation at the interface and poor charge retention. Summary of the Invention

[0004] The first technical problem to be solved by the present invention is:

[0005] To provide a MFS storage structure. The MFS storage structure constructs a quasi-homogeneous epitaxial integration system, thereby reducing thin film interface defects, improving the quality of the ferroelectric thin film, improving the efficiency of the ferroelectric gate to control the on / off of the channel current, and realizing high-performance ferroelectric storage.

[0006] The second technical problem to be solved by the present invention is:

[0007] To provide a preparation method of the MFS storage structure.

[0008] The third technical problem to be solved by the present invention is:

[0009] The application of the MFS storage structure.

[0010] To solve the first technical problem, the technical solution adopted by the present invention is:

[0011] A MFS storage structure includes a substrate, a ZnO low-temperature buffer layer, a ZnO thin film, a Zn 1-x M x O thin film, and a Zn 1-y M y O ferroelectric thin film, which are sequentially stacked.

[0012] Wherein, M is selected from at least one of Mg, V, Sb, Y, or Gd;

[0013] Among them, 0 < x ≤ 0.4 and 0.3 ≤ y ≤ 0.6.

[0014] As a II-VI wide-bandgap semiconductor, ZnO has advantages such as higher electron saturation drift velocity and stronger anti-irradiation ability than GaAs and GaN.

[0015] The low-temperature buffer layer has a relatively low growth temperature, below 400 degrees.

[0016] Growing a low-temperature ZnO buffer layer on the substrate in the present invention can effectively reduce the lattice mismatch between the ZnO thin film and the substrate and the lattice distortion caused by different thermal expansion coefficients.

[0017] Furthermore, in the present invention, a ZnO thin film and a Zn 1-x M x O thin film are sequentially grown on the ZnO low-temperature buffer layer to construct a heterojunction. The heterojunction has characteristics such as small lattice mismatch, small thermal mismatch, few defects, and large band offset. A high-concentration two-dimensional electron gas will be formed at the ZnO / Zn 1-x M x O heterojunction interface. Further, in the present invention, a Zn 1-x M x O ferroelectric thin film is grown on the ZnO / Zn 1- y M y O ferroelectric thin film to construct a quasi-homogeneous epitaxial integration system, thereby reducing film interface defects, improving the quality of the ferroelectric thin film, and realizing high-performance ferroelectric storage. No two-dimensional electron gas will be formed at the interface of the Zn 1-y M y O ferroelectric thin film.

[0018] According to an embodiment of the present invention, M is doped in the ZnO thin film to modify the ZnO thin film. M is selected from at least one of Mg, V, Sb, Y, or Gd. At a suitable Zn / M doping ratio, doping with a single element or co-doping with multiple elements can make the ZnO thin film exhibit ferroelectricity.

[0019] According to an embodiment of the present invention, doping Mg in the ZnO thin film can exhibit better ferroelectricity.

[0020] Furthermore, the present invention can adjust the ZnO / Zn 1-x M x O heterojunction and Zn 1-y M yThe values of x and y in the O ferroelectric film are used to adjust the ferroelectricity of the two. If the value of x is not within the range: 0<x≤0.4, it will cause defects in the crystal structure, resulting in phase separation, thus affecting the formation of the interface two-dimensional electron gas. The value of y must be within the range: 0.3≤y≤0.6, so that Zn 1-y M y O film has strong ferroelectricity. If the value of y is less than 0.3, Zn 1-y M y O film will not undergo polarization reversal, Zn 1-y M y O film does not have ferroelectricity and cannot act as a ferroelectric film gate.

[0021] According to one embodiment of the present invention, 0.3≤y≤0.37. Only when y≥0.3, Zn 1-y M y O thin film can show ferroelectricity, but the larger the y value is, the lower the film quality will be. When it exceeds 0.4, phase separation will begin to occur. 1-y M y The value of y in the ferroelectric film is 0.3≤y≤0.37, which enables the ferroelectric film to be field-reversibly polarized. 1-y M y O ferroelectric film has a high dielectric constant and high ferroelectricity, and its remanent polarization strength exceeds 100μC / cm 2 .

[0022] According to one embodiment of the present invention, the Zn 1-x M x The thickness of the O film is 30 to 60 nm. The reason for choosing a thinner thickness is to form an interface two-dimensional electron gas at the heterojunction.

[0023] According to one embodiment of the present invention, the Zn 1-y M y The thickness of the ZnO ferroelectric film is 100-400 nm. 1- y M y O ferroelectric film thickness needs to be greater than that of the Zn 1-x M x O film thickness to maximize the Zn 1-y M y Remanent polarization and field-induced strain in O ferroelectric films.

[0024] According to an embodiment of the present invention, the substrate includes at least one of sapphire, mica, and quartz substrates. Preferably, the substrate is sapphire, which has better stability and mechanical strength. Further, there are lattice mismatch and thermal mismatch between the sapphire substrate and the commonly used semiconductor material GaN, which will generate defects in the epitaxial layer and affect the uniformity of the grown crystal. The present invention grows a ZnO low-temperature buffer layer on the sapphire substrate to avoid the above-mentioned defects.

[0025] To solve the second technical problem, the technical solution adopted by the present invention is:

[0026] A method for preparing the MFS storage structure includes the following steps:

[0027] Grow a ZnO low-temperature buffer layer, a ZnO thin film, Zn 1-x M x O thin film, and Zn 1-y M y O ferroelectric thin film on the substrate in sequence.

[0028] According to an embodiment of the present invention, a method for preparing the MFS storage structure includes the following steps:

[0029] S1, grow a 10 - 30 nm ZnO low-temperature buffer layer on the substrate at 100 - 900 °C; heat the substrate to 600 - 700 °C and anneal for 10 - 30 minutes;

[0030] S2, cool the substrate to 200 - 700 °C and grow a ZnO thin film with a thickness of 400 - 600 nm; heat the substrate to 600 - 700 °C and anneal for 10 - 30 minutes;

[0031] S3, cool the substrate to 300 - 500 °C and use Zn 1-x M x O target material to grow a 30 - 60 nm thick Zn 1-x M x O thin film; heat the substrate to 600 - 700 °C and anneal for 10 - 30 minutes;

[0032] S4, through Zn 1-y M y O target material, epitaxially grow a 100 - 400 nm thick Zn 1-x M x O ferroelectric thin film on the ZnO / Zn 1-y M y O heterojunction.

[0033] According to an embodiment of the present invention, before the substrate is used in step S1 of the method, pretreatment is required. First, the substrate is ultrasonically cleaned with analytical pure acetone and alcohol twice respectively, for 5-10 minutes each time, and finally rinsed with deionized water and air-dried naturally.

[0034] According to an embodiment of the present invention, the purity of the Zn 1-x M x O target material is 99.999%; the purity of the Zn 1-y M y O target material is 99.999%.

[0035] According to an embodiment of the present invention, the growth process used is selected from MBE (Molecular Beam Epitaxy), PLD (Pulsed Laser Deposition), and MOCVD (Metal-Organic Chemical Vapor Deposition).

[0036] Another aspect of the present invention also relates to the application of the MFS storage structure in a field-effect transistor. It includes the MFS storage structure as described in the embodiments of the first aspect above. Since the field-effect transistor adopts all the technical solutions of the MFS storage structure of the above embodiments, it has at least all the beneficial effects brought by the technical solutions of the above embodiments.

[0037] Another aspect of the present invention also provides an application of the MFS storage structure in a semiconductor memory. It includes the MFS storage structure as described in the embodiments of the first aspect above. Since the semiconductor memory adopts all the technical solutions of the MFS storage structure of the above embodiments, it has at least all the beneficial effects brought by the technical solutions of the above embodiments.

[0038] One of the technical solutions in the above technical solutions has at least one of the following advantages or beneficial effects:

[0039] In the present invention, growing a low-temperature ZnO buffer layer on the substrate can effectively reduce the lattice mismatch between the ZnO thin film and the substrate and the lattice distortion caused by different thermal expansion coefficients. Further, in the present invention, a ZnO thin film and a Zn 1-x M x O thin film are sequentially grown on the ZnO low-temperature buffer layer to construct a heterojunction. The heterojunction has the characteristics of small lattice mismatch, small thermal mismatch, few defects, and large band offset, and a high-concentration interfacial two-dimensional electron gas can be formed near its interface. Further, in the present invention, a Zn 1-x M x O heterojunction is grown on the ZnO / Zn 1-y M yO ferroelectric thin films to construct a quasi - homoepitaxial integration system, thereby reducing film interface defects, improving the quality of ferroelectric thin films, achieving high - performance ferroelectric storage, constructing a new MFS structure, realizing ferroelectric non - volatile storage functions, and improving the on - off efficiency of ferroelectric gate - controlled channel current.

[0040] This invention adjusts the ZnO / Zn 1-x M x O hetero - junction and the values of x and y in the Zn 1-y M y O ferroelectric thin films to adjust the ferroelectricity of both. Among them, if the value of x is not within the range: 0 < x ≤ 0.4, it will lead to crystal structure defects, resulting in phase separation, thus affecting the formation of the two - dimensional electron gas at the interface. Among them, the value of y needs to be within the range: 0.3 ≤ y ≤ 0.6, so that the Zn 1-y M y O thin film has ferroelectricity to achieve high - performance ferroelectric storage applications.

[0041] Other features and advantages of this invention will be described in the subsequent specification, and, in part, will be obvious from the specification or understood by implementing this invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The above - mentioned and / or additional aspects and advantages of this invention will become obvious and easy to understand from the description of the embodiments in conjunction with the following drawings, where:

[0043] Figure 1 It is a flowchart of the preparation method of the MFS storage structure for Examples 1 - 8.

[0044] Figure 2 It is a schematic diagram of the MFS storage structure for Examples 1 - 8.

[0045] Figure 3 It is the X - ray diffraction θ - 2θ scanning spectrum of Example 1. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0046] The embodiments of this invention are described in detail below. The examples of the embodiments are shown in the drawings, where the same or similar reference numerals represent the same or similar elements or elements with the same or similar functions from beginning to end. The embodiments described below by referring to the drawings are exemplary and are only used to explain this invention and cannot be understood as a limitation of this invention.

[0047] The technical solutions in the embodiments of this invention will be described clearly and completely below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only a part of the embodiments of this invention, rather than all the embodiments. Based on the embodiments of this invention, all other embodiments obtained by those of ordinary skill in the art without creative work belong to the scope of this invention.

[0048] Example 1

[0049] A method for preparing an MFS storage structure, as Figure 1 shown, specifically includes the following steps:

[0050] S1 First, ultrasonically clean the sapphire substrate with analytical pure acetone and alcohol twice respectively, for 10 minutes each time, and finally rinse it with deionized water and air-dry it naturally.

[0051] S2 ① At 250 °C, grow a ZnO low-temperature buffer layer with a thickness of 20 nm on the substrate by MBE technology;

[0052] ② Raise the temperature of the substrate to 650 °C and anneal for 20 minutes;

[0053] ③ Lower the temperature of the substrate to 500 °C and grow a ZnO thin film with a thickness of 400 nm by MBE technology;

[0054] ④ Raise the temperature of the substrate to 650 °C and anneal for 20 minutes;

[0055] ⑤ Lower the temperature of the substrate to 400 °C and grow a ZnMgO thin film with a thickness of 40 nm by MBE technology using a Zn 0.83 Mg 0.17 O target material;

[0056] ⑥ Raise the temperature of the substrate to 650 °C and anneal for 20 minutes.

[0057] (3) Epitaxially grow a ZnMgO top layer structure on the ZnO / Zn 0.83 Mg 0.17 O heterojunction. By radio frequency magnetron sputtering technology, use a Zn 0.66 Mg 0.34 O target material to grow a Zn 0.66 Mg 0.34 O ferroelectric thin film to obtain the MFS storage structure of Example 1, as Figure 2 shown. Among them, the growth temperature of the Zn 0.66 Mg 0.34 O ceramic target is 200 °C.

[0058] The purity of the above ZnO, Zn 0.83 Mg 0.17 O, Zn 0.66 Mg 0.34 O is 99.999%.

[0059] Example 2

[0060] The difference between Example 2 and Example 1 is only that: the Zn 0.83 Mg0.17 Replace the O target material with Zn 0.83 V 0.17 O target material, and replace the Zn in Example 1 with 0.66 Mg 0.34 Replace the O target material with Zn 0.66 V 0.34 O target material.

[0061] Example 3

[0062] The difference between Example 3 and Example 1 is only that: replace the Zn in Example 1 with 0.83 Mg 0.17 Replace the O target material with Zn 0.83 Sb 0.17 O target material, and replace the Zn in Example 1 with 0.66 Mg 0.34 Replace the O target material with Zn 0.66 Sb 0.34 O target material.

[0063] Example 4

[0064] The difference between Example 4 and Example 1 is only that: replace the Zn in Example 1 with 0.83 Mg 0.17 Replace the O target material with Zn 0.83 Y 0.17 O target material, and replace the Zn in Example 1 with 0.66 Mg 0.34 Replace the O target material with Zn 0.66 Y 0.34 O target material.

[0065] Example 5

[0066] The difference between Example 5 and Example 1 is only that: replace the Zn in Example 1 with 0.83 Mg 0.17 Replace the O target material with Zn 0.83 Gd 0.17 O target material, and replace the Zn in Example 1 with 0.66 Mg 0.34 Replace the O target material with Zn 0.66 Gd 0.34 O target material.

[0067] Example 6

[0068] The difference between Example 6 and Example 1 is only that: replace the Zn in Example 1 with 0.83 Mg 0.17 Replace the O target material with Zn 0.6 Mg 0.4 O target material, and replace the Zn in Example 1 with 0.66 Mg 0.34Replace the O target material with Zn 0.7 Mg 0.3 O target material.

[0069] Example 7

[0070] The difference between Example 7 and Example 1 is only that: replace the Zn 0.83 Mg 0.17 O target material with Zn 0.8 Mg 0.2 O target material, replace the Zn 0.66 Mg 0.34 O target material with Zn 0.4 Mg 0.6 O target material.

[0071] Example 8

[0072] The difference between Example 8 and Example 1 is only that: replace the Zn 0.66 Mg 0.34 O target material with Zn 0.63 Mg 0.37 O.

[0073] Performance test:

[0074] Take the MFS storage structures of Examples 1 to 8 for X-ray diffraction testing to further verify the feasibility of quasi-homogeneous epitaxial growth of ZnMgO ferroelectric thin films on ZnMgO / ZnO heterojunctions. Among them, the test results of Example 1 are as Figure 3 shown. It can be seen from the X-ray diffraction θ-2θ scan spectrum that the ZnO(002) diffraction peak and the Al2O3(006) substrate diffraction peak. This result shows that high-quality c-axis oriented ZnO thin films have been epitaxially grown on c-plane Al2O3, and at the same time, the single crystal property of the ZnO thin film has been verified. This means that quasi-homogeneous epitaxial growth of ZnMgO ferroelectric thin films on ZnMgO / ZnO heterojunctions is practically feasible. The results of Examples 2 to 5 are similar to those of Example 1, and are not shown one by one to avoid redundancy.

[0075] The above are only the embodiments of the present invention, and do not limit the patent scope of the present invention accordingly. All equivalent transformations made using the content of the specification of the present invention, or directly or indirectly applied in the relevant technical fields, are equally included in the patent protection scope of the present invention.

Claims

1. An MFS storage structure, characterized in that: Including a substrate, a ZnO low-temperature buffer layer, a ZnO thin film, Zn 1-x M x O thin film, and Zn 1-y M y O ferroelectric thin film; wherein, M includes at least one of Mg, V, Sb, Y, and Gd; wherein, 0 < x ≤ 0.4, 0.3 ≤ y ≤ 0.

37.

2. The MFS storage structure according to claim 1, wherein: The Zn 1-x M x O thin film has a thickness of 30 to 60 nm.

3. A MFS storage structure according to claim 1, wherein: The Zn 1-y M y O ferroelectric thin film has a thickness of 100 to 400 nm.

4. A MFS storage structure according to claim 1, characterized in that: The substrate includes at least one of sapphire, mica, and quartz substrates.

5. A method for preparing an MFS storage structure according to any one of claims 1 to 4, characterized in that: Comprising the following steps: Grow a ZnO low-temperature buffer layer, a ZnO thin film, Zn 1-x M x O thin film, and Zn 1-y M y O ferroelectric thin film on the substrate in sequence.

6. The method according to claim 5, wherein: The process used for growth is selected from at least one of MBE, PLD, and MOCVD.

7. Application of an MFS storage structure according to any one of claims 1 to 4 in a field effect transistor.

8. Application of an MFS storage structure according to any one of claims 1 to 4 in a semiconductor memory.

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