Application of borate crystals as gate dielectric layer material

Abstract

The application relates to application of borate crystal as a gate dielectric layer material and belongs to the technical field of semiconductor devices. The borate crystal can obtain a two-dimensional sheet through exfoliation and the internal structure of the crystal is not damaged after exfoliation; due to the inert surface of the borate crystal, the surface of the prepared two-dimensional sheet is free of dangling bonds; the van der Waals dielectric material of the borate crystal can be used as a gate dielectric layer of a two-dimensional material electronic device through a transfer method; the band gap of the selected borate crystals KBe2BO3F2 and NH4Be2BO3F2 is greater than 8eV, and the borate crystals have good insulation properties; the sheet after exfoliation can be used as a van der Waals dielectric material and can be used for preparation of a high-performance two-dimensional material electronic device.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of semiconductor devices, and more particularly relates to a method for using borate crystals as gate dielectric layer materials. BACKGROUND

[0002] Further development of integrated circuits requires the basic component unit field effect transistor (FET) to be continuously reduced in size while improving performance. In the past few decades, silicon-based FETs have been continuously miniaturized along Moore's Law and have approached their physical limits. Two-dimensional semiconductors, due to their atomic thickness and high carrier mobility, have become ideal channel materials for building the next generation of FETs. However, the integration of high-quality gate dielectric layers in two-dimensional FETs faces major challenges. Amorphous oxide dielectric materials, such as SiO2, Al2O3, and HfO2, which perform well in silicon technology, cannot form a uniform and clear interface with two-dimensional materials due to their long-range disorder characteristics, thus having difficulties in eliminating charge scattering and traps, resulting in high gate leakage current, high interface state density, and low breakdown field strength, which cannot meet the requirements of the International Roadmap for Devices and Systems. In addition, due to the non-pendulum bond surface of two-dimensional materials, it is still challenging to deposit a thin layer of oxide without damaging the surface layer. Therefore, FET devices based on two-dimensional materials cannot achieve the full potential predicted by theory.

[0003] Compared with amorphous oxides, two-dimensional crystalline dielectric materials, such as hexagonal boron nitride (hBN), calcium fluoride (CaF2), and strontium titanate (SrTiO3), have atomically flat surfaces and can be well combined with two-dimensional semiconductors to form smoother dielectric / two-dimensional material interfaces. In theory, the use of two-dimensional dielectric materials can overcome the problems of interface quality and defect levels. However, due to the relatively narrow band gap and low dielectric constant, hBN with an ultra-thin physical thickness exhibits extremely high leakage current (J>10 3 A cm -2 ). The application of CaF2 and SrTiO3 is mostly limited to back-gate FETs, although top-gate two-dimensional FETs are required for large-scale integrated circuits. Therefore, it is necessary to develop two-dimensional crystalline dielectric materials with a wide band gap, high breakdown strength, high dielectric constant, and compatibility with two-dimensional electronic devices. SUMMARY

[0004] The present application solves the problem of poor interface quality when using amorphous dielectric materials for two-dimensional transistor gate dielectric layers and small dielectric constant and band gap when using crystalline dielectric materials in the prior art, which affects device performance. The present application provides the application of borate crystals as gate dielectric layer materials, which have a high dielectric constant and a large band gap, a large breakdown field strength when used as a transistor gate dielectric layer, a small leakage current, can form a van der Waals interface with two-dimensional materials and are easy to integrate, thereby obtaining excellent transistor performance.

[0005] According to the purposes of the present application, the borate crystal is provided as the application of the gate dielectric layer material.

[0006] Preferably, the borate crystal is KBe2BO3F2, NH4Be2BO3F2, K3Ba3Li2Al4B6O 20 F or β-BaB2O4.

[0007] Preferably, the dielectric constant of the borate crystal is greater than 10.

[0008] Preferably, the band gap of the borate crystal is greater than 5eV.

[0009] Preferably, the application is specifically: the borate crystal is obtained by exfoliation into a two-dimensional sheet, and then transferred to the transistor channel material; the thickness of the two-dimensional sheet is 1-160nm.

[0010] Preferably, the exfoliation is mechanical exfoliation or liquid phase exfoliation.

[0011] Preferably, the thickness of the two-dimensional sheet is 1-20nm.

[0012] Preferably, the surface of the two-dimensional sheet is free of dangling bonds.

[0013] Overall, compared with the prior art, the above technical solutions conceived by the present application mainly have the following technical advantages:

[0014] (1) The borate crystal of the present application has a high dielectric constant, a large band gap, and a surface free of dangling bonds, can form a high-quality interface with a two-dimensional semiconductor, so that the transistor device has excellent performance, and has the effects of improving the performance of the transistor, reducing the power consumption, scaling up the preparation, and reducing the size.

[0015] (2) The borate crystal of the present application can be used as a dielectric layer of a two-dimensional material electronic device, can significantly reduce the carrier scattering source in the two-dimensional channel material, so as to ensure that the two-dimensional material has high mobility and low hysteresis.

[0016] (3) The borate crystal used in the present application has a surface free of dangling bonds, can form a van der Waals contact with the channel material, and will not cause damage to the surface of the channel material.

[0017] (4) The borate crystal used in the present application can be exfoliated into a two-dimensional sheet and integrated with a two-dimensional semiconductor to prepare a high-performance two-dimensional transistor.

[0018] (5) The borate crystal of the present application can be used in combination with commonly used high-dielectric-constant dielectric materials (Al2O3, HfO2 or Sb2O3) to achieve better device properties. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the preparation of borate crystal van der Waals dielectric materials in Examples 1-4.

[0020] Figure 2 This is an optical microscope image of the KBe2BO3F2 sheet prepared by mechanical peeling in Example 1.

[0021] Figure 3 This is an atomic force microscope image of the KBe2BO3F2 sheet in Example 1 and its thickness.

[0022] Figure 4 This is the X-ray diffraction pattern of the KBe2BO3F2 thin film in Example 1.

[0023] Figure 5 This is a band structure diagram of the KBe2BO3F2 sheet in Example 2.

[0024] Figure 6 It is the dielectric constant of the KBe2BO3F2 sheets of different thicknesses in Example 3.

[0025] Figure 7 This is an optical microscope image of the MoS2 field-effect transistor with KBe2BO3F2 as the gate dielectric layer in Example 4.

[0026] Figure 8 This is the transfer characteristic curve of the MoS2 field-effect transistor in Example 4.

[0027] Figure 9 This is the output characteristic curve of the MoS2 field-effect transistor in Example 4.

[0028] Figure 10 This is an optical microscope image of the NH4Be2BO3F2 sheet prepared by mechanical peeling in Example 5.

[0029] Figure 11 This is an atomic force microscope image of the NH4Be2BO3F2 sheet in Example 5 and its thickness.

[0030] Figure 12 It is the dielectric constant of NH4Be2BO3F2 sheets of different thicknesses in Example 6.

[0031] Figure 13 This is an optical microscope image of the MoS2 field-effect transistor with NH4Be2BO3F2 as the gate dielectric layer in Example 7.

[0032] Figure 14 This is the transfer characteristic curve of the MoS2 field-effect transistor in Example 7.

[0033] Figure 15 is the output characteristic curve of the MoS2 field effect transistor in Example 7. DETAILED DESCRIPTION

[0034] In order to make the objects, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and not intended to limit the present application. In addition, the technical features involved in the various embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0035] The borate crystal van der Waals dielectric material in the present application is prepared by exfoliation of borate crystal two-dimensional sheet, which can be transferred to the surface of other materials as a gate dielectric layer for preparing high-performance transistor devices.

[0036] The borate crystal van der Waals dielectric material has high dielectric constant, large band gap and excellent dielectric performance. At the same time, its surface has no dangling bond, which can significantly reduce the carrier scattering source in the two-dimensional channel material, thereby ensuring that the two-dimensional material has high mobility and low hysteresis.

[0037] In some embodiments, the transistor is a top-gate field effect transistor.

[0038] In some embodiments, the borate crystal van der Waals dielectric material is KBe2BO3F2, NH4Be2BO3F2, K3Ba3Li2Al4B6O 20 F or β-BaB2O4, all of which can be prepared into two-dimensional sheets by exfoliation.

[0039] In some embodiments, the thickness of the borate crystal van der Waals dielectric material is 1-160 nanometers, preferably 1-20 nanometers.

[0040] As a preferred, the borate crystal van der Waals dielectric material is selected as KBe2BO3F2, which can be prepared by mechanical exfoliation and has adjustable thickness.

[0041] When the borate crystal van der Waals dielectric material in the present application is used in a field effect transistor, the sub-threshold swing value can be less than 100 mV / dec, and the hysteresis can be less than 70 mV.

[0042] The following are specific examples

[0043] Example 1

[0044] The borate crystal van der Waals dielectric material and the preparation method thereof involved in the present application include the following steps:

[0045] (1) A small amount of KBe2BO3F2 crystal is placed on the adhesive tape and repeatedly mechanically exfoliated. During the exfoliation process, the KBe2BO3F2 on the adhesive tape will be continuously thinned, and after about ten times of exfoliation, a relatively thin KBe2BO3F2 can be obtained.

[0046] (2) The KBe2BO3F2 sheet obtained by mechanical exfoliation is observed by optical microscope.

[0047] (3) The KBe2BO3F2 sheet is characterized by atomic force microscope and X-ray diffraction.

[0048] Example 2

[0049] The operation steps are the same as those of Example 1, except that the band gap width of the KBe2BO3F2 sheet is obtained by theoretical calculation.

[0050] Example 3

[0051] The operation steps are the same as those of Example 1, except that a SiO2 / Si sheet with Au surface evaporation is selected as the substrate, and the KBe2BO3F2 sheet with different thicknesses after exfoliation is transferred to the Au surface. An Au electrode is prepared on the KBe2BO3F2 sheet, and a parallel-plate capacitor is constructed together with the substrate for testing the dielectric constant of the KBe2BO3F2 sheet.

[0052] Example 4

[0053] MoS2 is prepared on a SiO2 / Si substrate by mechanical exfoliation method, and then the KBe2BO3F2 sheet is transferred to the MoS2 surface to prepare a field effect transistor, and its performance is tested.

[0054] Example 5

[0055] The operation steps are the same as those of Example 1, except that the crystal for exfoliation is NH4Be2BO3F2.

[0056] Example 6

[0057] The operation steps are the same as those of Example 3, except that the crystal for testing is NH4Be2BO3F2.

[0058] Example 7

[0059] The operation steps are the same as those of Example 4, except that NH4Be2BO3F2 is selected as the dielectric layer.

[0060] Results and analysis

[0061] Figure 1 is a schematic diagram of the preparation of borate crystal van der Waals dielectric material by exfoliation in the present application.

[0062] Figure 2 is an optical microscope photo of KBe2B03F2 flakes prepared by mechanical exfoliation in Example 1. The results show that KBe2B03F2 crystals can be prepared into flakes with different sizes by mechanical exfoliation.

[0063] Figure 3 is an atomic force microscope photo and thickness curve of KBe2B03F2 flakes in Example 1. The results show that the exfoliated KBe2B03F2 flakes have smooth surface and uniform thickness.

[0064] Figure 4 is an X-ray diffraction spectrum of KBe2B03F2 flakes in Example 1. The results show that the tested sample has strong diffraction peaks, which are attributed to the (00-3) and (00-6) crystal planes of KBe2B03F2, indicating that the prepared sample is KBe2B03F2.

[0065] Figure 5 is a band diagram of KBe2B03F2 in Example 2. The results show that KBe2B03F2 has a large band gap of 8.03 eV, which is conducive to the application of dielectric layer.

[0066] Figure 6 is the dielectric constant of KBe2B03F2 with different thicknesses in Example 3. The results show that as the thickness decreases, the dielectric constant of KBe2B03F2 will decrease to a certain extent, but all above 20.

[0067] Figure 7 is an optical microscope photo of the field effect transistor prepared by mechanical exfoliation of MoS2 and transfer of KBe2B03F2 in Example 4, and Bi / Au is used as the source-drain-gate electrode.

[0068] Figure 8 is the transfer characteristic curve of the field effect transistor in Example 4. The results show that the transistor has a small sub-threshold swing of 100 mV / dec, a small hysteresis of 70 mV, a high on-off ratio of 10 8 and a small gate leakage current of 10 -14 A.

[0069] Figure 9 is the output characteristic curve of the field effect transistor in Example 4. The linear output characteristic curve at different gate voltages shows that the source-drain electrode is ohmic contact.

[0070] Figure 10 is an optical microscope photo of NH4Be2B03F2 flakes prepared by mechanical exfoliation in Example 5. The results show that NH4Be2B03F2 crystals can be prepared into flakes with different sizes by mechanical exfoliation.

[0071] Figure 11is an atomic force microscope image and thickness curve of NH4Be2B03F2 flakes in Example 5. The results show that the exfoliated NH4Be2B03F2 flakes have smooth surfaces and uniform thicknesses.

[0072] Figure 12 is the dielectric constant of NH4Be2B03F2 with different thicknesses in Example 6. The results show that the dielectric constant of NH4Be2B03F2 decreases to some extent as the thickness decreases, but is all above 15.

[0073] Figure 13 is an optical microscope image of a field effect transistor prepared by mechanical exfoliation of MoS2 and transfer of NH4Be2B03F2 in Example 7. Bi / Au is used as the source-drain-gate electrode.

[0074] Figure 14 is the transfer characteristic curve of the field effect transistor in Example 7. The results show that the transistor has a small sub-threshold swing of 77 mV / dec, a small hysteresis of 22 mV, a high on-off ratio of 10 8 -14 and a small gate leakage current of 10

[0075] Figure 15 is the output characteristic curve of the field effect transistor in Example 7. The linear output characteristic curve at different gate voltages shows that the source-drain electrode is ohmic contact.

[0076] Those skilled in the art will easily understand that the above description is only the preferred embodiment of the present application, and is not intended to limit the present application. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.​

Claims

1. Use of borate crystals as a gate dielectric layer material, characterized in that, The borate crystals are KBe₂BO₃F₂, NH₄Be₂BO₃F₂, and K₃Ba₃Li₂Al₄B₆O. 20 F or β -BaB2O4; The specific application is as follows: a two-dimensional sheet of borate crystal is obtained by peeling, and then transferred to a transistor channel material, wherein the channel material is a two-dimensional material.

2. Use according to claim 1, wherein The borate crystal has a dielectric constant greater than 10.

3. Use according to claim 1, characterized in that, The borate crystal has a band gap greater than 5 eV.

4. Use according to claim 1, characterized in that, The two-dimensional sheet has a thickness of 1-160 nm.

5. The use according to claim 4, wherein the compound is ###0002### The exfoliation is mechanical exfoliation or liquid phase exfoliation.

6. Use according to claim 4, characterized in that, The two-dimensional sheet has a thickness of 1-20 nm.

7. The use according to claim 4, wherein the compound is ###0002### The two-dimensional sheet surface is free of dangling bonds. The two-dimensional sheet has a thickness of 1-160 nm. The exfoliation is mechanical exfoliation or liquid phase exfoliation. The two-dimensional sheet has a thickness of 1-20 nm. The two-dimensional sheet surface is free of dangling bonds.

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