Low-voltage gradient zinc oxide varistor ceramic, preparation method and application thereof

Abstract

The application relates to low-voltage gradient zinc oxide pressure-sensitive ceramic and a preparation method and application thereof. By adjusting sintering pressure and content of a second phase, the pressure-sensitive voltage of undoped and doped pressure-sensitive ceramic can be effectively controlled, low-voltage gradient ZnO pressure-sensitive ceramic is obtained, and the problem that the existing zinc oxide pressure-sensitive ceramic cannot realize the low-voltage gradient characteristic is solved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of functional materials, and particularly relates to a low-voltage gradient zinc oxide pressure-sensitive ceramic and a preparation method and application thereof. BACKGROUND

[0002] Due to the rapid development of integrated circuits and semiconductor electronics, the demand for low-voltage pressure-sensitive resistors has been increasing in recent years. In order to greatly reduce the pressure-sensitive voltage in the pressure-sensitive resistor, it is usually necessary to manufacture the ceramic with exaggerated growth grains as thin as possible. However, the thin layer design of zinc oxide ceramic not only leads to an increase in sensitivity to microstructure because of the few grain boundaries along the electric field, but also increases the risk of mechanical failure as the thickness decreases.

[0003] Therefore, people hope to find an alternative strategy to design the potential barrier in low-voltage pressure-sensitive resistors. In addition to the contribution of dopants, it has long been recognized that the piezoelectric effect also plays an important role due to the non-centrosymmetric wurtzite structure of zinc oxide. However, due to the small internal stress generated by high-temperature sintering, this effect is usually negligible for most zinc oxide-based pressure-sensitive resistors. In contrast, experiments on zinc oxide-based bicrystals with predetermined polarization vectors show that a larger external compressive stress can greatly reduce the potential barrier height along the c-axis from the head to the heat direction, while increasing the potential barrier height from the tail to the tail direction. Although these findings indicate the potential of piezoelectric devices, it is more desirable to adjust the potential barrier through internal stress in practice, because pressure-sensitive resistors are rarely subjected to large external mechanical loads. In fact, early studies have shown that internal thermal stress affects the distribution of potential barrier height, but the change in current-voltage response is very limited compared to the response under external load.

[0004] Therefore, a simple and efficient strategy is provided to adjust the internal stress in zinc oxide (including doped and undoped) ceramics to achieve a significant nonlinear current-voltage response at low voltage, which is very important for pressure-sensitive ceramic materials. SUMMARY

[0005] The technical problem to be solved by the present application is to provide a low-voltage gradient zinc oxide pressure-sensitive ceramic and a preparation method and application thereof.

[0006] The present application provides a zinc oxide pressure-sensitive ceramic, wherein the components of the zinc oxide pressure-sensitive ceramic include 90-100 parts by weight of zinc oxide and 0-6 parts by weight of a second phase material.

[0007] Preferably, the components of the zinc oxide pressure-sensitive ceramic include 94-98 parts by weight of zinc oxide and 2-6 parts by weight of a second phase material.

[0008] Preferably, the zinc oxide is undoped zinc oxide or doped zinc oxide, and the doped zinc oxide includes one or more of Co, Al, Mn, Cr, etc.

[0009] Further preferably, the zinc oxide is a nanomaterial.

[0010] The second phase material is a hard second phase material, and the elastic modulus is 300 GPa or more.

[0011] Preferably, the second phase material includes at least one of nanodiamond, alpha phase aluminum oxide, cubic boron nitride, and other second phases with an elastic modulus higher than 300 GPa.

[0012] Further, the nanodiamond is an unmodified nanodiamond or an acid-modified nanodiamond.

[0013] The acid-modified nanodiamond is a nanodiamond modified by a mixed acid of concentrated sulfuric acid (H2SO4) and concentrated nitric acid (HNO3).

[0014] The preparation includes mixing nanodiamond, concentrated sulfuric acid (H2SO4), and concentrated nitric acid (HNO3), and then obtaining by ultrasonic, water bath stirring reaction for 2-10 h.

[0015] The zinc oxide pressure-sensitive ceramic is obtained by cold sintering from raw materials containing zinc oxide and second phase materials.

[0016] The zinc oxide pressure-sensitive ceramic is a low voltage gradient zinc oxide pressure-sensitive ceramic, and the pressure-sensitive voltage is 100 V / mm or less, and further 10 V / mm-50 V / mm.

[0017] The present application provides a preparation method of a zinc oxide pressure-sensitive ceramic, comprising:

[0018] The components are weighed, and a mixture containing zinc oxide and second phase materials is sintered to obtain a zinc oxide pressure-sensitive ceramic.

[0019] The zinc oxide includes but is not limited to zinc oxide powder; and the second phase material includes but is not limited to hard second phase powder.

[0020] Preferably, the preparation of the mixture containing zinc oxide and second phase materials includes method 1 or method 2.

[0021] The method 1 is mixing zinc oxide and water, then mixing with a second phase material solution, filtering and collecting the precipitate, and drying to obtain a mixture.

[0022] The method 2 is mixing zinc oxide, second phase material, and solvent, ball milling, and drying to obtain a mixture.

[0023] Further, the method 1, the zinc oxide and water are mixed, stirred, and ultrasonically treated to form a stable ZnO colloidal solution, the second phase material is dispersed in water, and the well-dispersed ZnO colloidal solution is dropped into the second phase material under magnetic stirring, the second phase material and the zinc oxide powder are rapidly self-assembled and precipitated to the bottom, and the precipitated second phase material / zinc oxide mixture is collected by vacuum filtration and dried.

[0024] Preferably, in the method 1, the zinc oxide and water are mixed and stirred for 0.5-1.5h after mixing;

[0025] In the method 1, the concentration of the zinc oxide and water after mixing is 5-20mg / mL;

[0026] In the method 1, the concentration of the second phase material solution is 0.5-2mg / mL, and the solvent of the second phase material solution is water;

[0027] In the method 1, the drying is vacuum drying, the temperature is 60-100℃, and the time is 12-24h.

[0028] Preferably, in the method 2, the solvent is ethanol; the ball milling parameters include: the ball-to-material ratio of ball milling is 40-60:1, the rotation speed of ball milling is 100-200r / min, and the ball milling time is 3-8h; the drying temperature is 80-120℃, and the drying time is 4-8h.

[0029] The mixture containing zinc oxide and the second phase material is uniformly mixed, wherein the uniform mixing method is grinding.

[0030] Further, the grinding of the mixture containing zinc oxide and the second phase material is: the mixture of zinc oxide and the second phase material is mixed with acetic acid and then ground; wherein the concentration of acetic acid is 0.6M-2M; and the mass ratio of acetic acid to the mixture is 15-20:100.

[0031] Preferably, the grinding time is 3-10h.

[0032] Preferably, the sintering is cold sintering, and the cold sintering process parameters are: uniaxial pressure 50-300MPa, heating rate 10-30℃ / min, sintering temperature 100-400℃, and time 0.5-6h.

[0033] The cold sintering is performed in a stainless steel mold with uniaxial pressure applied.

[0034] The application provides an application of the low-voltage gradient zinc oxide pressure-sensitive ceramic prepared by the method in the field of integrated circuits, semiconductor electronics, automotive electronics, communication equipment, etc., which has a protection circuit, improves stability, prevents overvoltage, and keeps the system running normally.

[0035] The present application introduces superhard nanosecond phase particles by cold sintering process, which can produce large local residual stress in ZnO matrix. The built-in stress-induced piezoelectric polarization is used to adjust the grain boundary barrier of ZnO-based low-voltage varistor. In addition, by adjusting the sintering pressure and the content of the second phase, the present application can effectively control the varistor voltage of undoped and doped varistor ceramics, and obtain low voltage gradient ZnO varistor ceramics.

[0036] Beneficial effects

[0037] The present application uses zinc oxide and second phase for compounding, and uses the effective strategy of built-in stress-induced piezoelectric polarization to adjust the barrier of ZnO-based low-voltage varistor. The superhard second phase is introduced by sintering process, which can produce local residual stress up to ~1GPa in ZnO matrix. Therefore, the superhard second phase / zinc oxide composite material shows significant nonlinear current-voltage response at low varistor voltage, which is due to the significant influence of positive and negative polarization on the grain boundary barrier, resulting in the reduction of barrier height.

[0038] The present application provides low voltage gradient ZnO varistor ceramics, which can effectively control the varistor voltage of undoped and doped varistor ceramics by adjusting the sintering pressure and the content of the second phase, and obtain different low voltage gradient ZnO varistor ceramics.

[0039] For example, the content of the second phase is adjusted in the comparison between Example 1 and Example 3, and different low voltage gradient ZnO varistor ceramics are obtained.

[0040] For example, the sintering pressure is adjusted in the comparison between Example 3 and Example 5, and different low voltage gradient ZnO varistor ceramics are obtained.

[0041] The low voltage gradient ZnO varistor ceramic provided by the present application has a varistor voltage of 100V / mm (10V / mm-50V / mm) or less, and a nonlinear coefficient of 4-40. BRIEF DESCRIPTION OF DRAWINGS

[0042] Figure 1 It is a scanning electron microscope image of the cross section of the zinc oxide block prepared in the present application comparative example 1;

[0043] Figure 2 It is a scanning electron microscope image of the cross section of the diamond / zinc oxide composite material block prepared in the present application example 1;

[0044] Figure 3 It is a transmission electron microscope image of the nanodiamond / zinc oxide composite material block prepared in the present application example 1;

[0045] Figure 4 It is a Raman spectrum of the samples of the present application example 1 and comparative example 2, andFigure 4 b is the X-ray diffraction pattern of the sample of Example 1 and Comparative Example 2 of the present application;

[0046] Figure 5 is the plot of electric field E and current density J for the samples of the present application and comparative examples. DETAILED DESCRIPTION

[0047] The present application is further described in connection with the following specific examples. It will be understood, however, that these examples are included merely for purposes of illustration and that no limitations of the scope of the present application are intended by inclusion of them. In addition, it should be understood that those skilled in the art will be able to utilize the present application in its broadest aspects and thus the application should not be limited to the specific examples that follow.

[0048] I. Materials Table 1 shows the specifications and sources of the raw materials or reagents used in the examples of the present application.

[0049] Material name Specification (purity) Producer (place of production) Nano-zinc oxide 99.99％ Shanghai Maikelin Biochemical Technology Co., Ltd. Co-doped nano-zinc oxide 99.99％ China National Pharmaceutical Group Shanghai Chemical Reagent Co., Ltd. Zinc oxide ZnO (only Example 2) ≥99.0％ China National Pharmaceutical Group Shanghai Chemical Reagent Co., Ltd. Nano-diamond (elastic modulus 980 GPa) 99.99％ Henan Yuxing Carbon Material Co., Ltd. C 60 (elastic modulus 36 GPa) 99.99％ Shanghai Maikelin Biochemical Technology Co., Ltd. Anhydrous ethanol 99.9％ China National Pharmaceutical Group Shanghai Chemical Reagent Co., Ltd. Commercial alpha-phase aluminum oxide powder (elastic modulus 400 GPa) 99.99％ Daiming Industrial Co., Ltd., Japan Nitric acid 63～65％ China National Pharmaceutical Group Shanghai Chemical Reagent Co., Ltd. Sulfuric acid 95～98％ China National Pharmaceutical Group Shanghai Chemical Reagent Co., Ltd.

[0050] In the examples and comparative examples, the samples were both sides sprayed with gold, and the nonlinear performance test was carried out using a pressure sensitive resistor tester. The test method was as follows: the voltage values of the samples at given 0.01 mA / mm 2 and 0.1 mA / mm 2 current were measured by the pressure sensitive resistor tester and the voltage values were recorded as the pressure sensitive voltage, and then the nonlinear coefficient a was calculated by formula 1: and

[0051]

[0052] Example 1

[0053] (1) Self-made acid treated nanodiamonds: 1 g of nanodiamond particles were placed in a three-necked flask and mixed with 100 ml of concentrated acid solution of 98% sulfuric acid (H2SO4) and 68% nitric acid (HNO3) with a volume ratio of 3:1, respectively. The mixture was placed in an ultrasonic bath for 30 minutes, and then stirred vigorously in a water bath at 80°C for 4 hours. After cooling to room temperature, 200 ml of deionized water was added to dilute the mixture. The obtained diamond particles were repeatedly washed by vacuum filtration with a large amount of deionized water until the pH value became neutral. Finally, the nanodiamond particles were dried at 80°C for 12 hours. Acid treated diamond was obtained.

[0054] ​​(2) First, the nano-zinc oxide powder was poured into deionized water and stirred for half an hour, then ultrasonically treated for 1 hour to form a stable zinc oxide colloidal solution. Next, acid-treated nanodiamonds were dispersed in deionized water (0.5 mg / ml), and the well-dispersed zinc oxide colloidal solution was added dropwise under magnetic stirring. The nanodiamonds and zinc oxide powder rapidly self-assembled and precipitated to the bottom. The precipitated nanodiamond and zinc oxide mixture was collected by vacuum filtration and dried in a vacuum oven at 60°C for 24 hours to obtain a mixed powder (ZnO and nanodiamonds in a mass ratio of 96:4).

[0055] (3) Mix the powder with 20% of its total mass of 0.6 mol L. -1 An aqueous acetic acid mixture was prepared and ground for 6 minutes using a mortar and pestle. The wet powder was then placed into a stainless steel mold and a uniaxial pressure of 150 MPa was applied. A heating mantle integrated with the mold provided a heating rate of 15 °C / min, which was maintained at 300 °C for 60 minutes. After sintering, the block was allowed to cool naturally to room temperature. Its varistor voltage was 25.7 V / mm, and its nonlinearity coefficient was 8.1.

[0056] like Figure 2 The image shows a scanning electron microscope (SEM) image of the cross-section of the diamond / zinc oxide composite material block prepared in Example 1 of this invention, in which bright diamonds are distributed in the zinc oxide matrix.

[0057] like Figure 3 The image shows a transmission electron microscope (TEM) image of the cross-section of the diamond / zinc oxide composite material block prepared in Example 1 of this invention, indicating that diamond is distributed in the zinc oxide matrix.

[0058] like Figure 4 a and Figure 4 Figure b shows the Raman spectra of the samples from Example 1 and Comparative Example 2 of the present invention. In Example 1, the diamond did not undergo a phase transition, while in Comparative Example 2, the diamond underwent a phase transition.

[0059] like Figure 5 The diagram shows the electric field E and current density J of the embodiments and comparative examples of the present invention. By adding an ultra-hard second phase, the varistor voltage of embodiments 1, 2, and 3 of the present invention is reduced compared to the zinc oxide matrix of comparative example 1.

[0060] Example 2

[0061] (1) ZnO and α-phase Al2O3 with a mass ratio of 96:4 were mixed and anhydrous ethanol was added to obtain a slurry. The slurry was placed in a ball mill and ball milled at a speed of 150 r / min for 5 h with a ball-to-material ratio of 50:1. Then it was dried at 80℃ for 8 h to obtain a mixture.

[0062] (2) Mix the powder with 20% of its total mass of 0.6 mol L-1 An aqueous acetic acid solution was mixed and ground in a mortar for 6 minutes. The wet powder was then loaded into a stainless steel mold and a uniaxial pressure of 150 MPa was applied. A heating mantle integrated with the mold provided a heating rate of 15 °C / min, and the temperature was maintained at 300 °C for 60 minutes. After sintering, the block was allowed to cool naturally to room temperature. Its piezoresistive strength is 35.4 V / mm, and its nonlinearity coefficient is 4.9.

[0063] Example 3

[0064] According to Example 1, step (1) in this example is the same as step (2) in Example 1 (ZnO and nanodiamond with a mass ratio of 98:2).

[0065] (2) Mix the powder with 20% of its total mass of 0.6 mol L -1 The acetic acid aqueous solution was mixed and ground in a mortar for 6 minutes. The wet powder was then loaded into a stainless steel mold and a uniaxial pressure of 150 MPa was applied. A heating mantle integrated with the mold provided a heating rate of 15 °C / min. -1 The sample was sintered at 300°C for 60 minutes. After sintering, the block was allowed to cool naturally to room temperature. Its varistor voltage is 15.7 V / mm, and its nonlinear coefficient is 5.4.

[0066] like Figure 5 The diagrams show the electric field E and current density J of the embodiments and comparative examples of the present invention. By adjusting the content of the second phase, different low voltage gradient ZnO varistors were obtained in Examples 1 and 3.

[0067] Example 4

[0068] According to Example 1, step (1) in this example is the same as step (2) in Example 1 (co-doped zinc oxide and nanodiamond in a mass ratio of 97:3).

[0069] (2) Mix the powder with 18% of its total mass of 1 mol L -1 An aqueous acetic acid mixture was prepared and ground for 6 minutes using a mortar and pestle. The wet powder was then placed into a stainless steel mold and a uniaxial pressure of 150 MPa was applied. A heating mantle integrated with the mold provided a heating rate of 15 °C / min, and the temperature was maintained at 300 °C for 60 minutes. After sintering, the block was allowed to cool naturally to room temperature. Its varistor voltage was 19.2 V / mm, and its nonlinear coefficient was 12.4.

[0070] Example 5

[0071] According to Example 1, step (2) of this example is the same as that of Example 1 (ZnO and nanodiamond with a mass ratio of 98:2).

[0072] (2) mixed with 20% of 0.6 mol L -1 aqueous acetic acid solution and ground in a mortar for 6 minutes. Subsequently, the wet powder was loaded into a stainless steel die and a uniaxial pressure of 100 MPa was applied. The heating rate given by a heating jacket integrated with the die was 15°C / min -1 and kept at 300°C for 60 minutes. After sintering, the bulk was cooled to room temperature naturally. Its piezoresistive voltage was 20.3 V / mm and the nonlinearity coefficient was 5.1.

[0073] Comparative Example 1

[0074] The nano-zinc oxide and 20% of 0.6 mol L -1 aqueous acetic acid solution were mixed and ground in a mortar for 6 minutes. Subsequently, the wet powder was loaded into a stainless steel die and a uniaxial pressure of 150 MPa was applied. The heating rate given by a heating jacket integrated with the die was 15°C / min -1 and kept at 300°C for 60 minutes. The piezoresistive voltage was 102.3 V / mm and the nonlinearity coefficient was 1.2.

[0075] As Figure 1 shown in the scanning electron microscope image of the cross section of the zinc oxide bulk prepared in the comparative example 1 of the present application, the grains are larger than those in the example 1. It can be compared Figure 2 that the bright diamond particles are shown in Figure 2

[0076] Comparative Example 2

[0077] The mixed powder of example 1, the only difference is that the spark plasma sintering process parameters are as follows: the sintering temperature is 950°C, the heating rate is 100°C / min, the holding time is 8 min, and the die is graphite die. The piezoresistive voltage is 140 V / mm and the nonlinearity coefficient is 1.1.

[0078] Comparative Example 3

[0079] The nano-zinc oxide and C 60 (elastic modulus is about 36 GPa) mixed powder with a mass ratio of 96:4 were sintered according to the step (3) in example 1, and its piezoresistive voltage was 1400 V / mm and the nonlinearity coefficient was 6.2.

[0080] In the example 1 of the present application, a superhard second phase diamond (980 GPa>300 GPa) is added to the zinc oxide powder and sintered into a bulk, and in the comparative example 3, a soft second phase C 60 ​(36 GPa < 300 GPa) sintered into a bulk. These two are in sharp contrast, the piezoresistive voltage of Example 1 is 25.7 V / mm, while the piezoresistive voltage in Comparative Example 3 is as high as 1400 V / mm, in sharp contrast, embodying the introduction of the superhard second phase by the sintering process, generating a local residual stress as high as ~1 GPa in the ZnO matrix. Causing piezoelectric polarization of zinc oxide, thereby making the barrier height lower. Therefore, the superhard second phase / zinc oxide composite material exhibits a significant nonlinear current-voltage response at a low piezoresistive voltage.

Claims

1. A zinc oxide varistor ceramic, characterized by, The zinc oxide pressure-sensitive ceramic component comprises 94-98 parts by weight of zinc oxide and 2-6 parts by weight of a second phase material; the second phase material comprises at least one of nano-diamond, alpha phase aluminum oxide and cubic boron nitride; The preparation method of the zinc oxide pressure-sensitive ceramic comprises: weighing each component by weight fraction, sintering a mixture containing zinc oxide and a second phase material to obtain the zinc oxide pressure-sensitive ceramic; the sintering is cold sintering; the cold sintering process parameters are: uniaxial pressure of 50-300 MPa, heating rate of 10-30 ℃ / min, sintering temperature of 100-400 ℃, and time of 0.5-6 h.

2. The zinc oxide varistor ceramic of claim 1, wherein The second phase material is a hard second phase material, and the elastic modulus is 300 GPa or more; The zinc oxide is undoped zinc oxide or doped zinc oxide.

3. The zinc oxide varistor ceramic of claim 2, wherein The doped zinc oxide comprises one or more of Co, Al, Mn and Cr doped zinc oxide.

4. A preparation method of the zinc oxide pressure-sensitive ceramic of claim 1, comprising: weighing each component by weight fraction, sintering a mixture containing zinc oxide and a second phase material to obtain the zinc oxide pressure-sensitive ceramic; The sintering is cold sintering; the cold sintering process parameters are: uniaxial pressure of 50-300 MPa, heating rate of 10-30 ℃ / min, sintering temperature of 100-400 ℃, and time of 0.5-6 h.

5. The preparation method according to claim 4, characterized in that, The preparation of the mixture containing zinc oxide and a second phase material comprises method 1 or method 2; The method 1: mixing zinc oxide and water, then mixing with a second phase material solution, filtering and collecting the precipitate, and drying to obtain the mixture; The method 2: mixing zinc oxide, a second phase material and a solvent, ball milling, and drying to obtain the mixture.

6. The preparation method according to claim 5, characterized in that, In the method 1, the zinc oxide and water are stirred after mixing and are subjected to ultrasonic treatment for 0.5-1.5 h; In the method 1, the concentration of the zinc oxide and water after mixing is 5-20 mg / mL; In the method 1, the concentration of the second phase material solution is 0.5-2 mg / mL; the solvent of the second phase material solution is water; In the method 1, the drying is vacuum drying, the temperature is 60-100 ℃, and the time is 12-24 h.

7. The preparation method according to claim 5, characterized in that, In the method 2, the solvent is ethanol; In the method 2, the ball milling parameters include: ball-to-material ratio of 40-60:1, rotation speed of 100-200 r / min, and ball milling time of 3-8 h; the drying temperature is 80-120 ℃, and the drying time is 4-8 h.

8. The preparation method according to claim 4, characterized in that, The grinding of the mixture containing zinc oxide and a second phase material comprises: grinding the mixture of zinc oxide and a second phase material after mixing with acetic acid; the concentration of the acetic acid is 0.6 M-2 M; the mass ratio of the acetic acid to the mixture is 15-20:100; The grinding time is 3-10 h.

9. Application of the zinc oxide pressure-sensitive ceramic of claim 1 or the zinc oxide pressure-sensitive ceramic prepared by the method of claim 4 in the fields of integrated circuits, semiconductor electronics, automotive electronics and communication equipment.

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