A Design Method and System for a Heating Platform for uCVD Graphene Preparation

Abstract

The present invention discloses a design method for a heating platform for preparing uCVD graphene, which relates to the technical field of graphene preparation and solves the technical problem of low design efficiency of the heating platform. The method includes: constructing a basic heating microchip structure based on an SOI wafer, where the basic heating microchip structure includes a Cu layer, an SiO2 layer, and an Si layer connected in sequence from top to bottom; inputting current to the Si layer of the basic heating microchip structure, solving the heating curve, analyzing the influence of the resistivity of the Si layer on heating according to the heating curve, and determining an appropriate resistivity of the Si layer, and determining the doping of the Si layer according to the determined resistivity of the Si layer; on the premise that the thicknesses of each layer of the basic heating microchip structure are fixed, respectively change the length and width, and solve the corresponding heating curves, and determine the length and width of the basic heating microchip structure according to the two heating curves; perform thermoelectric simulation on the basic heating microchip structure using finite element analysis software to verify whether it meets the requirements.

Description

Technical Field

[0001] The present invention relates to the technical field of graphene preparation, and more specifically, it relates to a design method and system for a heating platform for uCVD graphene preparation. Background Art

[0002] The uCVD preparation system was first proposed by relevant researchers at the University of California, Berkeley in 2009 and is an improved method of chemical vapor deposition. In addition to having various advantages of the CVD method, it also avoids the disadvantages of long CVD reaction time, low growth efficiency, long repeated experiment cycle, high experimental cost, etc., and has characteristics such as program control, miniaturization, and rapid preparation. In the uCVD method, the micro-core heating platform used to heat the catalyst and grow graphene on the surface is the core component of the preparation system and is also the most critical component affecting the growth quality of graphene.

[0003] Currently, the heating platform is first made into a physical object according to the design requirements, and then its heating performance is actually verified to see if it meets the requirements. If it does not meet the requirements, the physical object needs to be repeatedly modified and verified, resulting in a long production cycle and high cost. Summary of the Invention

[0004] The technical problem to be solved by the present invention is in view of the above-mentioned deficiencies of the prior art. The object of the present invention is to provide a design method and system for a heating platform for uCVD graphene preparation, which can shorten the production cycle of the heating platform and reduce the cost.

[0005] The present invention provides a design method for a heating platform for uCVD graphene preparation, including:

[0006] Step S1. Construct a basic heating microchip structure based on an SOI wafer, where the basic heating microchip structure includes a Cu layer, a SiO2 layer, and an Si layer connected in sequence from top to bottom;

[0007] Step S2. Input current into the Si layer of the basic heating microchip structure, solve the heating curve, analyze the influence of the resistivity of the Si layer on heating according to the heating curve, determine the appropriate resistivity of the Si layer, and determine the doping of the Si layer according to the determined resistivity of the Si layer;

[0008] Step S3. On the premise that the thicknesses of each layer of the basic heating microchip structure are fixed, change the length and width respectively, and solve the corresponding heating curves, and determine the length and width of the basic heating microchip structure according to the two heating curves;

[0009] Step S4. Perform thermoelectric simulation on the basic heating microchip structure obtained in step S3 using finite element analysis software to verify whether it meets the requirements.

[0010] As a further improvement, in step S1, the basic heating microchip structure is constructed by UG or PRO / E or SolidWorks or CATIA.

[0011] Further, in step S2, the basic heating microchip structure is placed in a sealed cavity and powered on for heating. According to Joule's law, the energy generated by the basic heating microchip structure is:

[0012] Q = I 2 Rt (1)

[0013] where I is the input current, t is the heating duration, R is the resistance of the Si layer,

[0014]

[0015] ρ is the resistivity of the Si layer, L is the length of the basic heating microchip structure, and S is the effective cross-sectional area for current input;

[0016] In the early stage of vacuum annealing, according to the laws of thermodynamics, the heat energy generated by electrification, in addition to being absorbed by the basic heating microchip structure itself to increase the internal energy, there is also a part lost due to thermal radiation and thermal convection.

[0017] Q = Q A +Q R +Q C (2)

[0018] Q A is the increased internal energy, Q R 、Q C are the energies lost due to thermal radiation and thermal convection respectively; due to the small volume of the basic heating microchip structure, the thermal conductivities of the materials used are relatively high, and the layers are in close contact with each other, so it can be approximately considered that the overall temperature of the basic heating microchip structure is uniform. The increase in internal energy is:

[0019] Q A =∑c i m i ΔT(t) i = 1, 2, 3 (3)

[0020] where c i 、m i are the specific heat capacity and mass of each layer of material, ΔT(t) is the temperature difference before and after heating, and thermal radiation and thermal convection can be described by the following formula:

[0021]

[0022]

[0023] σ is the Stefan-Boltzmann constant, ε i, A i are the emissivity and outer surface area of the i-th layer material respectively, h is the heat convection coefficient, T S , T ∞ are the temperatures of the inner wall of the cavity and the gas in the cavity respectively.

[0024] Furthermore, a numerical iterative method is used to approximately solve the heating curve. Taking the time interval as Δt, formula (2) can be approximated as:

[0025]

[0026] Thus, the temperature formula for heating is as follows:

[0027]

[0028] In the formula, T n-1 , T n are the initial temperature and the final temperature of the n-th heating time period respectively, T0 = T S = T ∞ = 25 °C.

[0029] Furthermore, in step S4, a thermoelectric simulation is performed on the basic heating microchip structure by using ANSYS finite element analysis software.

[0030] The present invention provides a uCVD graphene preparation heating platform system, which includes a sealed main box body. A basic heating microchip structure is arranged in the main box body. One end of the main box body is provided with a three-way joint. One end of the three-way joint is connected with a methane pipe, and a first flowmeter and a first control valve are arranged on the methane pipe. The other end of the three-way joint is connected with a hydrogen pipe, and a second flowmeter and a second control valve are arranged on the hydrogen pipe. The other end of the main box body is provided with an exhaust pipe and a recovery pipe. A pressure gauge, a third control valve and a vacuum pump are arranged on the exhaust pipe. The recovery pipe is connected with a recovery tank. A controller is arranged on the outer side of the main box body, and the controller is electrically connected with the basic heating microchip structure, the first flowmeter, the first control valve, the second flowmeter, the second control valve, the pressure gauge, the third control valve and the vacuum pump.

[0031] As a further improvement, the basic heating microchip structure includes a Cu layer, a SiO2 layer and a Si layer which are connected in sequence from top to bottom. Cantilevers are respectively arranged at both ends of the Si layer, and the controller is electrically connected with the cantilevers.

[0032] Furthermore, the Si layer is a boron-doped N-type silicon layer with a resistivity of 0.2 Ω·cm.

[0033] Furthermore, a heavily doped thin layer with a resistivity of 0.004 Ω·cm is formed on the surface layer of the cantilever and its input end through a photolithography and diffusion process.

[0034] Further, a bracket is provided at the bottom of the cantilever. The bracket includes an Si bottom plate, and the top of the Si bottom plate is connected to the cantilever through SiO2 struts.

[0035] Advantages

[0036] Compared with the prior art, the present invention has the following advantages:

[0037] Through relevant heat transfer theory research and 3D finite element simulation of ANSYS, it can be known that the heating performance of the microchip heating platform is greatly affected by the resistivity of the energized silicon layer and the width of the current input cross-section, but its surface temperature has good consistency. In particular, the improved suspended multi-cantilever heating platform adopting selective doping technology not only has good temperature uniformity and maintains a small temperature difference on the growth surface, but also has the advantages of being convenient, stable and reliable, and can better meet the requirements of the uCVD system. The present invention can shorten the production cycle of the heating platform and reduce costs. Description of the Drawings

[0038] Figure 1 is a structural schematic diagram of the present invention;

[0039] Figure 2 is a structural schematic diagram of the basic heating microchip based on the SOI wafer;

[0040] Figure 3 is a heating temperature curve graph under different silicon layer resistivities;

[0041] Figure 4 is a heating temperature curve graph under different lengths;

[0042] Figure 5 is a heating temperature curve graph under different widths;

[0043] Figure 6 is a thermoelectric simulation diagram of the basic heating microchip structure based on the SOI wafer;

[0044] Figure 7 is a schematic diagram of the basic heating microchip structure in the present invention;

[0045] Figure 8 is a thermoelectric simulation diagram of the basic heating microchip structure in the present invention.

[0046] Wherein: 1 - main box body, 2 - basic heating microchip structure, 3 - three-way joint, 4 - methane pipe, 5 - first flowmeter, 6 - first control valve, 7 - hydrogen pipe, 8 - second flowmeter, 9 - second control valve, 10 - exhaust pipe, 11 - recovery pipe, 12 - pressure gauge, 13 - third control valve, 14 - vacuum pump, 15 - receiving trough, 16 - controller, 17 - Cu layer, 18 - SiO2 layer, 19 - Si layer, 20 - cantilever, 21 - Si base plate, 22 - SiO2 pillar. Detailed implementation manners

[0047] The present invention will be further described below with reference to specific embodiments in the accompanying drawings.

[0048] Refer to Figures 1 to 8 , a design method for a heating platform for preparing uCVD graphene, comprising:

[0049] Step S1. Construct a basic heating microchip structure based on an SOI wafer, and the basic heating microchip structure includes a Cu layer, an SiO2 layer, and an Si layer that are sequentially connected from top to bottom, as Figure 2 shown;

[0050] Step S2. Input a current to the Si layer of the basic heating microchip structure, solve the heating curve, analyze the influence of the resistivity of the Si layer on heating according to the heating curve, and determine the appropriate resistivity of the Si layer, and determine the doping of the Si layer according to the determined resistivity of the Si layer;

[0051] Step S3. On the premise that the thicknesses of the layers of the basic heating microchip structure are fixed, change the length and width respectively, and solve the corresponding heating curves, and determine the length and width of the basic heating microchip structure according to the two heating curves;

[0052] Step S4. Perform a thermoelectric simulation on the basic heating microchip structure obtained in Step S3 on finite element analysis software to verify whether it meets the requirements.

[0053] In Step S1, the basic heating microchip structure is constructed by UG or PRO / E or SolidWorks or CATIA.

[0054] In Step S2, the basic heating microchip structure is placed in a sealed cavity and powered on for heating. According to Joule's law, the energy generated by the basic heating microchip structure is:

[0055] Q = I 2 Rt (1)

[0056] wherein, I is the input current, t is the heating duration, and R is the resistance of the Si layer,

[0057]

[0058] ρ is the resistivity of the Si layer, L is the length of the basic heating microchip structure, and S is the effective cross-sectional area for current input;

[0059] In the early stage of vacuum annealing, according to the laws of thermodynamics, the heat energy generated by energization, in addition to being absorbed by the basic heating microchip structure itself to increase the internal energy, there is also a part lost due to thermal radiation and heat convection.

[0060] Q = Q A + Q R + Q C (2)

[0061] Q A is the increased internal energy, Q R , Q C are the energies lost due to thermal radiation and heat convection respectively; due to the small volume of the basic heating microchip structure, the thermal conductivities of the materials used are relatively high, and the layers are in close contact with each other, so it can be approximately considered that the overall temperature of the basic heating microchip structure is uniform, and the increase in internal energy is:

[0062] Q A = ∑c i m i ΔT(t) i = 1, 2, 3 (3)

[0063] where c i , m i are the specific heat capacity and mass of each layer of material, ΔT(t) is the temperature difference before and after heating, and thermal radiation and heat convection can be described by the following formula:

[0064]

[0065]

[0066] σ is the Stefan-Boltzmann constant, ε i , A i are the emissivity and outer surface area of the i-th layer of material respectively, h is the heat convection coefficient, T S , T ∞ are the temperatures of the inner wall of the cavity and the gas in the cavity respectively.

[0067] By using a numerical iterative method to approximately solve the heating curve, taking the time interval as Δt, then formula 2 can be approximated as:

[0068]

[0069] From this, the following temperature formula for heating can be obtained:

[0070]

[0071] In the formula, Tn-1 and T n are the initial temperature and the final temperature of the nth heating period respectively, and T0 = T S = T ∞ = 25 °C. The simulated heating temperature curves at different resistivities are as Figure 3 shown. I = 1.1 A; L = 5 mm, W = 5 mm; the thicknesses of the Si layer, SiO2 layer, and Cu layer are: H1 = 500 μm, H2 = 1 μm, H3 = 25 μm respectively.

[0072] As can be seen from Figure 3 , the higher the resistivity of the energized Si layer, the steeper the temperature rise curve, and the shorter the time to heat to the predetermined temperature. When the resistivity is too large, the chip is damaged because the heating temperature exceeds the melting point of Cu, and at the same time, the control circuit is made more difficult due to the too short heating time. However, if the resistivity is too low, it may not be possible to heat to the expected temperature value. Therefore, combined with the structural parameters of the chip, doping appropriately to obtain an appropriate resistivity is a key point in the design of the heating chip.

[0073] The thicknesses of each layer of the basic heating microchip structure based on the SOI structure are often fixed. Therefore, the change in the size of the basic heating microchip structure is mainly based on the length and width of the bottom layer, that is, the length and width of the Si layer. When other parameters remain unchanged, the relationship between the heating temperature and the length and width dimensions of the bottom layer is as Figure 4 and 5 shown.

[0074] As can be seen from Figure 4 and 5 , when the length of the chip increases, the heating rate does not increase significantly. The maximum temperature that can be reached increases due to the increase in the chip resistance. However, when the length increases by a certain length, the increase in the maximum temperature is no longer obvious. Therefore, the length of the chip can be appropriately increased according to needs to synthesize longer graphene without worrying about the chip temperature exceeding the melting point of Cu and being damaged. Compared with the length of the chip, the width of the current input cross-section has a more obvious effect on heating. The reduction of the chip width makes the heating resistance increase rapidly, the heating rate increase rapidly, and it is possible that the surface temperature exceeds the melting point of Cu.

[0075] In step S4, the thermoelectric simulation of the basic heating microchip structure is carried out by using ANSYS finite element analysis software. To verify the temperature characteristics of the basic heating microchip structure described above, with the same parameters, the resistivity of the Si layer is taken as 0.2 Ω·cm, and the thermoelectric simulation is carried out on the finite element analysis software ANSYS, and the results are as follows Figure 6 shown.

[0076] From Figure 6It can be seen that the temperature obtained by heating is about 1000 °C, which is highly consistent with the results proved in the previous section. In addition, the temperature distribution on the top Cu surface is uniform. Although the temperature in the center is higher and the temperature around is lower, the temperature difference across the entire surface is only about 1 °C, greatly improving the consistency of graphene synthesis.

[0077] A uCVD graphene preparation heating platform system includes a sealed main box body 1. Inside the main box body 1, there is a basic heating microchip structure 2. At one end of the main box body 1, there is a three-way joint 3. One end of the three-way joint 3 is connected to a methane pipe 4. On the methane pipe 4, there are a first flowmeter 5 and a first control valve 6. The other end of the three-way joint 3 is connected to a hydrogen pipe 7. On the hydrogen pipe 7, there are a second flowmeter 8 and a second control valve 9. At the other end of the main box body 1, there are an exhaust pipe 10 and a recovery pipe 11. On the exhaust pipe 10, there are a pressure gauge 12, a third control valve 13, and a vacuum pump 14. The recovery pipe 11 is connected to a recovery tank 15. Outside the main box body 1, there is a controller 16. The controller 16 is electrically connected to the basic heating microchip structure 2, the first flowmeter 5, the first control valve 6, the second flowmeter 8, the second control valve 9, the pressure gauge 12, the third control valve 13, and the vacuum pump 14.

[0078] As the heating chip of the core component of the system, the basic heating microchip structure 2, in addition to completing the growth processes of high-temperature annealing (in an H2 environment, 1000 °C, 20 minutes), constant-temperature growth maintenance (in a CH4 and H2 mixed environment, 1000 °C, 5 minutes), and rapid cooling (the time for cooling from 1000 °C to room temperature is controlled within 1 minute), also requires that the temperature difference on the chip surface be as small as possible to synthesize high-quality graphene. Therefore, the heating chip should have the characteristics of miniaturization, high resistivity, and low thermal expansion.

[0079] As Figure 7 shown, the basic heating microchip structure 2 includes a Cu layer 17, an SiO2 layer 18, and an Si layer 19 connected in sequence from top to bottom. At both ends of the Si layer 19, there are cantilevers 20 respectively. The controller 16 is electrically connected to the cantilevers 20. At the bottom of the cantilevers 20, there are brackets. The brackets include an Si bottom plate 21. The top of the Si bottom plate 21 is connected to the cantilevers 20 through SiO2 pillars 22, making the heating microchip suspended on the brackets. The suspended heating structure enables each surface to have the same convective heat transfer environment, improving the temperature consistency of the heating chip and accelerating the cooling rate during the cooling stage.

[0080] The Si layer 19 is a boron-doped N-type silicon layer with a resistivity of 0.2 Ω·cm. A heavily doped thin layer with a resistivity of 0.004 Ω·cm is formed on the surface layer of the cantilever 20 and its input end through photolithography and diffusion processes. This enables the cantilever to conduct a relatively large current and allows the heat generated by the chip to be mainly concentrated on the middle heating platform, thus avoiding the cantilever fracture situation often encountered in experiments due to excessive cantilever temperature. The thermoelectric simulation results of the micro-core heating platform are as follows Figure 8 shown. From Figure 8 the simulation results, it can be seen that the suspended multi-cantilever micro-core heating structure using the selective doping process not only improves the temperature distribution and uniformity of the top layer, accelerates the heating speed, maintains better temperature consistency, reduces the temperature difference on the synthesis surface, but also reduces the temperature of the cantilever, making the heating platform more convenient, stable and reliable, meeting the harsh requirements of the graphene growth process.

[0081] The above is only the preferred embodiment of the present invention. It should be pointed out that for those skilled in the art, without departing from the structure of the present invention, several deformations and improvements can be made, which will not affect the implementation effect of the present invention and the practicality of the patent.

Claims

1. A design method for a heating platform in the preparation of uCVD graphene, characterized in that, Including: Step S1. Construct a basic heating microchip structure based on an SOI wafer, where the basic heating microchip structure includes a Cu layer, an SiO2 layer, and an Si layer connected in sequence from top to bottom; Step S2. Input an electric current to the Si layer of the basic heating microchip structure, solve the heating curve, analyze the influence of the resistivity of the Si layer on heating according to the heating curve, determine the appropriate resistivity of the Si layer, and determine the doping of the Si layer according to the determined resistivity of the Si layer; Step S3. On the premise that the thicknesses of each layer of the basic heating microchip structure are fixed, change the length and width respectively, solve the corresponding heating curves, and determine the length and width of the basic heating microchip structure according to the two heating curves; Step S4. Perform a thermoelectric simulation on the basic heating microchip structure obtained in Step S3 using finite element analysis software to verify whether it meets the requirements; In Step S2, place the basic heating microchip structure in a sealed cavity and apply electricity for heating. According to Joule's law, the energy generated by the basic heating microchip structure is: Q = I 2 Rt (1) where I is the applied current, t is the heating duration, R is the resistance of the Si layer, ρ is the resistivity of the Si layer, L is the length of the basic heating microchip structure, and S is the effective cross-sectional area for current input; In the early stage of vacuum annealing, according to the laws of thermodynamics, the thermal energy generated by the applied electricity, in addition to being absorbed by the basic heating microchip structure itself to increase the internal energy, there is also a part lost due to thermal radiation and thermal convection. Q = Q A +Q R +Q C (2) Q A is the increased internal energy, Q R , Q C are the energies lost by thermal radiation and thermal convection respectively; due to the small volume of the basic heating microchip structure, the thermal conductivities of the materials used are relatively high, and the layers are in close contact with each other. Therefore, it is considered that the overall temperature of the basic heating microchip structure is uniform, and the increase in internal energy is: Q A = Σc i m i ΔT(t) i = 1, 2, 3 (3) where c i and m i are the specific heat capacity and mass of each layer of material, and ΔT(t) is the temperature difference before and after heating. Heat radiation and heat convection can be described by the following formula: σ is the Stefan-Boltzmann constant, ε i , A i are the emissivity and outer surface area of the i-th layer material respectively, h is the heat convection coefficient, T S , T ∞ are the temperatures of the inner wall of the cavity and the gas in the cavity respectively; Use a numerical iterative method to approximately solve the heating curve. Taking the time interval as Δt, formula (2) can be approximated as: From this, the following temperature formula for heating can be obtained: where, T n-1 and T n are respectively the initial temperature and the final temperature of the nth heating period, T0 = T S = T ∞ = 25 °C.

2. The design method of a heating platform for preparing uCVD graphene according to claim 1, characterized in that, In Step S1, construct the basic heating microchip structure using UG or PRO / E or SolidWorks or CATIA.

3. A design method for a heating platform for preparing uCVD graphene according to claim 1, characterized in that, In Step S4, perform a thermoelectric simulation on the basic heating microchip structure using ANSYS finite element analysis software.

4. A heating platform system for preparing uCVD graphene, characterized in that, Including a sealed main box body (1), a basic heating microchip structure (2) is provided inside the main box body (1). One end of the main box body (1) is provided with a three-way joint (3). One end of the three-way joint (3) is connected to a methane pipe (4). A first flowmeter (5) and a first control valve (6) are provided on the methane pipe (4). The other end of the three-way joint (3) is connected to a hydrogen pipe (7). A second flowmeter (8) and a second control valve (9) are provided on the hydrogen pipe (7). The other end of the main box body (1) is provided with an exhaust pipe (10) and a recovery pipe (11). A pressure gauge (12), a third control valve (13), and a vacuum pump (14) are provided on the exhaust pipe (10). The recovery pipe (11) is connected to a recovery tank (15). A controller (16) is provided outside the main box body (1). The controller (16) is electrically connected to the basic heating microchip structure (2), the first flowmeter (5), the first control valve (6), the second flowmeter (8), the second control valve (9), the pressure gauge (12), the third control valve (13), and the vacuum pump (14).

5. The uCVD graphene preparation heating platform system according to claim 4, characterized in that, The described basic heating microchip structure (2) includes a Cu layer (17), a SiO2 layer (18), and a Si layer (19) connected in sequence from top to bottom. Cantilevers (20) are provided at both ends of the Si layer (19), and the controller (16) is electrically connected to the cantilevers (20).

6. The uCVD graphene preparation heating platform system according to claim 5, characterized in that The Si layer (19) is a boron-doped N-type silicon layer with a resistivity of 0.2 Ω·cm.

7. The uCVD graphene preparation heating platform system according to claim 5, characterized in that, A heavily doped thin layer with a resistivity of 0.004 Ω·cm is formed on the surface layer of the cantilever (20) and its input end through photolithography and diffusion processes.

8. The uCVD graphene preparation heating platform system according to claim 5, characterized in that, A bracket is provided at the bottom of the cantilever (20). The bracket includes a Si base plate (21), and the top of the Si base plate (21) is connected to the cantilever (20) through a SiO2 pillar (22).

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