Application of borate crystal as gate dielectric layer material

Abstract

The invention relates to application of a borate crystal as a gate dielectric layer material, and belongs to the technical field of semiconductor devices. According to the borate crystal, the two-dimensional sheet can be obtained through stripping, the internal structure of the crystal cannot be damaged after stripping, and due to the inert surface of the borate crystal, the surface of the prepared two-dimensional sheet is free of dangling bonds; the borate crystal Van der Waals dielectric material can be used for a gate dielectric layer of a two-dimensional material electronic device through a transfer method; the forbidden bandwidths of the selected borate crystals KBe2BO3F2 and NH4Be2BO3F2 are both larger than 8 eV, the borate crystals have the good insulating property, and the peeled sheets serve as Van der Waals dielectric materials and can be used for preparing high-performance two-dimensional material electronic devices.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor devices, and more specifically, relates to a method of using borate crystals as gate dielectric layer materials. Background Art

[0002] The further development of integrated circuits requires that the size of its basic building block, the field effect transistor (FET), continues to decrease while the performance continues to increase. In the past few decades, silicon-based FETs have been continuously miniaturized along Moore's Law and have reached their physical limits. Two-dimensional semiconductors have become ideal channel materials for building next-generation FETs due to their atomic-level thickness and high carrier mobility. However, the integration of high-quality gate dielectric layers in two-dimensional FETs faces major challenges. Amorphous oxide dielectric materials that perform well in silicon technology, such as SiO2, Al2O3, and HfO2, cannot form a uniform and clear interface with two-dimensional materials due to their long-range disordered properties, so they have 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 device and system roadmap. In addition, due to the dangling bond-free surface of two-dimensional materials, it is still challenging to deposit a thin layer of oxide without destroying 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 that can be well integrated with two-dimensional semiconductors to form a smoother dielectric / two-dimensional material interface. In theory, the use of two-dimensional dielectric materials can overcome the problems of interface quality and defect energy levels. However, due to the relatively narrow band gap and low dielectric constant, hBN with ultra-thin physical thickness exhibits extremely high leakage current (J>10 3 A cm -2 ). The applications of CaF2 and SrTiO3 are mostly limited to back-gate FETs, although top-gate 2D FETs are required for large-scale integrated circuits. Therefore, it is necessary to develop 2D crystalline dielectric materials with wide bandgap, large breakdown strength, high dielectric constant, small leakage current, and compatible with 2D electronic devices. Summary of the invention

[0004] The present invention solves the problem in the prior art that the interface quality is poor when amorphous dielectric materials are used for the gate dielectric layer of a two-dimensional transistor, and the dielectric constant and band gap are small when crystalline dielectric materials are used, thereby affecting the performance of the device. The present invention provides the use of borate crystals as gate dielectric layer materials. The dielectric material has a high dielectric constant and a large band gap. When used as a gate dielectric layer of a transistor, the breakdown field is strong and the leakage current is small. It can form a van der Waals interface with a two-dimensional material and is easy to integrate, thereby obtaining excellent transistor performance.

[0005] According to the purpose of the present invention, there is provided a use of borate crystals as a gate dielectric layer material.

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

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

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

[0009] Preferably, the application is as follows: borate crystals are peeled off to obtain two-dimensional flakes, which are then transferred to transistor channel materials; the thickness of the two-dimensional flakes is 1-160 nm.

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

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

[0012] Preferably, the two-dimensional sheet has no dangling bonds on its surface.

[0013] In general, the above technical solution conceived by the present invention has the following technical advantages compared with the prior art:

[0014] (1) The borate crystal van der Waals dielectric material of the present invention has a high dielectric constant, a large band gap, and no dangling bonds on the surface, and can form a high-quality interface with a two-dimensional semiconductor, thereby making the transistor device have excellent performance, and has the effect of improving the performance of the transistor, reducing power consumption, scalable preparation, and reducing size.

[0015] (2) The borate crystals of the present invention can be used as dielectric layers of two-dimensional material electronic devices, which can significantly reduce the carrier scattering sources in the two-dimensional channel material, thereby ensuring that the two-dimensional material has high mobility and low hysteresis.

[0016] (3) The borate crystal van der Waals dielectric material used in the present invention has no dangling bonds on its surface and can form van der Waals contact with the channel material without causing damage to the surface of the channel material.

[0017] (4) The borate crystal van der Waals dielectric material used in the present invention can be peeled off into two-dimensional thin sheets and integrated with two-dimensional semiconductors to prepare high-performance two-dimensional transistors.

[0018] (5) The borate crystals of the present invention can be used in combination with commonly used high dielectric constant dielectric materials (Al2O3, HfO2 or Sb2O3) to achieve better device properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 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 photograph of the KBe2BO3F2 flakes prepared by mechanical exfoliation in Example 1.

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

[0022] Figure 4 This is the X-ray diffraction spectrum of the KBe2BO3F2 flake in Example 1.

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

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

[0025] Figure 7 This is an optical microscope photograph 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] Fig. 9 This is the output characteristic curve of the MoS2 field effect transistor in Example 4.

[0028] Fig.10 This is an optical microscope photograph of the NH4Be2BO3F2 flakes prepared by mechanical exfoliation in Example 5.

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

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

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

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

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

[0034] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention 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 of the present invention is prepared by peeling off a two-dimensional borate crystal sheet, which can be transferred to the surface of other materials as a gate dielectric layer to prepare high-performance transistor devices.

[0036] The borate crystal van der Waals dielectric material has a high dielectric constant, a large band gap, and excellent dielectric properties. At the same time, it has no dangling bonds on its surface, 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 can be prepared into two-dimensional flakes by exfoliation.

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

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

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

[0042] The following are specific embodiments

[0043] Example 1

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

[0045] (1) Place a small amount of KBe2BO3F2 crystals on a tape and tear it repeatedly for mechanical peeling. During the tearing process, the KBe2BO3F2 on the tape will become thinner. After about ten times of tearing, a thinner KBe2BO3F2 can be obtained.

[0046] (2) Use an optical microscope to search for KBe2BO3F2 flakes obtained after mechanical exfoliation.

[0047] (3) Atomic force microscopy and X-ray diffraction characterization of KBe2BO3F2 thin films.

[0048] Example 2

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

[0050] Example 3

[0051] The operation steps are the same as those in Example 1, except that a SiO2 / Si sheet with Au evaporated on the surface is selected as the substrate, the peeled KBe2BO3F2 sheets of different thicknesses are transferred to the Au surface, and Au electrodes are further prepared on the KBe2BO3F2 sheets to form a parallel plate capacitor together with the substrate for testing the dielectric constant of the KBe2BO3F2 sheets.

[0052] Example 4

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

[0054] Example 5

[0055] The operation steps are the same as those in Example 1, except that the crystal to be stripped is NH4Be2BO3F2.

[0056] Example 6

[0057] The operating steps are the same as those in Example 3, except that the crystal tested is NH4Be2BO3F2.

[0058] Example 7

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

[0060] Results and Analysis

[0061] Figure 1 Schematic diagram of preparing borate crystal van der Waals dielectric material by exfoliation in the present invention.

[0062] Figure 2 is an optical microscope photograph of the KBe2BO3F2 flakes prepared by mechanical exfoliation in Example 1. The results show that KBe2BO3F2 crystals can be prepared into flakes of different sizes by mechanical exfoliation.

[0063] Figure 3 The following are the atomic force microscope photos and thickness curves of the KBe2BO3F2 flakes in Example 1. The results show that the surface of the peeled KBe2BO3F2 flakes is flat and the thickness is uniform.

[0064] Figure 4 This is the X-ray diffraction spectrum of the KBe2BO3F2 flake in Example 1. The results show that the tested sample has very strong diffraction peaks, which are attributed to the (00-3) and (00-6) crystal planes of KBe2BO3F2, indicating that the prepared sample is KBe2BO3F2.

[0065] Figure 5 is the energy band diagram of KBe2BO3F2 in Example 2. The results show that KBe2BO3F2 has a large band gap of 8.03 eV, which is beneficial to the application of dielectric layers.

[0066] Figure 6 is the dielectric constant of KBe2BO3F2 with different thicknesses in Example 3. The results show that as the thickness decreases, the dielectric constant of KBe2BO3F2 decreases to a certain extent, but is always above 20.

[0067] Figure 7 This is an optical microscope photograph of a field effect transistor prepared by mechanically peeling off MoS2 and transferring KBe2BO3F2 in Example 4, in which Bi / Au is used as the source, drain and gate electrodes.

[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 subthreshold swing of 100mV / dec, a small hysteresis of 70mV, and a 8 The high on / off ratio and 10 -14 A small gate leakage current.

[0069] Fig. 9 1 is an output characteristic curve of the field effect transistor in Example 4. The linear output characteristic curve under different gate voltages shows that the source-drain electrode is an ohmic contact.

[0070] Fig.10 is an optical microscope photograph of NH4Be2BO3F2 flakes prepared by mechanical exfoliation in Example 5. The results show that NH4Be2BO3F2 crystals can be prepared into flakes of different sizes by mechanical exfoliation.

[0071] Fig.11The following are the atomic force microscope photos and thickness curves of the NH4Be2BO3F2 flakes in Example 5. The results show that the surface of the exfoliated NH4Be2BO3F2 flakes is flat and the thickness is uniform.

[0072] Fig.12 is the dielectric constant of NH4Be2BO3F2 with different thicknesses in Example 6. The results show that as the thickness decreases, the dielectric constant of NH4Be2BO3F2 decreases to a certain extent, but is always above 15.

[0073] Fig.13 This is an optical microscope photograph of the field effect transistor prepared by mechanically peeling off MoS2 and transferring NH4Be2BO3F2 in Example 7, and Bi / Au is used as the source, drain and gate electrodes.

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

[0075] Fig.15 1 is an output characteristic curve of the field effect transistor in Example 7. The linear output characteristic curve under different gate voltages shows that the source-drain electrode is an ohmic contact.

[0076] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. Application of borate crystals as gate dielectric layer materials.

2. The use according to claim 1, characterized in that The borate crystals are KBe2BO3F2, NH4Be2BO3F2, K3Ba3Li2Al4B6O 20 F or β-BaB2O4.

3. The use according to claim 1, characterized in that The dielectric constant of the borate crystals is greater than 10.

4. The use according to claim 1, characterized in that The band gap of the borate crystals is greater than 5 eV.

5. The use according to claim 1, characterized in that The application is specifically as follows: a two-dimensional sheet is obtained by exfoliation of borate crystals, and then transferred to a transistor channel material; the thickness of the two-dimensional sheet is 1-160 nm.

6. The use according to claim 5, characterized in that The peeling is mechanical peeling or liquid phase peeling.

7. The use according to claim 5, characterized in that The thickness of the two-dimensional sheet is 1-20 nm.

8. The use according to claim 5, characterized in that The two-dimensional sheet has no dangling bonds on its surface.

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