CN115666209B - A packaging method and packaging structure for improving the stability of graphene carrier concentration - Google Patents

Abstract

The invention discloses a packaging method and a packaging structure for improving the concentration stability of graphene carriers, comprising the following steps: manufacturing a graphene chip; carrying out secondary spin coating on the graphene chip substrate by adopting PMMA solution and mixed doping agent, and baking; wherein the mixed dopant is PMMA doped with F4 TCNQ; packaging the graphene chip subjected to secondary spin in a glove box; and regulating and controlling the packaged graphene chip. The packaging method disclosed by the invention not only effectively isolates the surface of the regulated graphene chip from air and reduces the influence of water and oxygen in the air on the carrier concentration stability of the graphene chip, but also reduces the carrier concentration of the graphene. And the obtained graphene chip packaging structure is smaller, the transportation and measurement of the graphene chip packaging structure are not affected basically, the graphene chip packaging structure is not required to be placed in a glove box for storage, and the storage of the chip is greatly facilitated. In addition, the packaging method has the advantages of simple operation process, less time consumption and cheap raw materials, so that the packaging method is suitable for popularization.

Description

A packaging method and packaging structure for improving the stability of graphene carrier concentration

technical field

The invention belongs to the technical field of graphene device packaging, in particular to a packaging method and a packaging structure for improving the stability of graphene carrier concentration.

Background technique

In a low temperature and strong magnetic field environment, due to the pinning effect, the single-layer graphene grown on the SiC (0001) surface exhibits a quantum Hall platform in a very wide magnetic field range, and the corresponding fill factor is 2. However, graphene is heavily n-doped, and its carrier concentration is usually 10 ¹² ~10 ¹³ cm ^-2 , so the quantum Hall platform corresponding to the fill factor of 2 cannot be achieved at a relatively low magnetic field. A variety of methods for regulating the carrier concentration of graphene have been studied, among which the more common method is to use F4TCNQ (2,3,5,6-tetrafluoro-7,7',8,8'-tetracyanodimethyl-p-benzoquinone), such as Document 1 (Form doping of grapheneclose to the Dirac point by polymer-assisted assembly of molecular dopants. Nat. Commun. 9, 3956 (2 018)) records that using F4TCNQ as an electron acceptor, heating the chip at 160 °C, the carrier concentration changes with the increase of heating time, and the carrier concentration can be reduced from 1×10 ¹³ cm ^-2 to near the Dirac point (0 cm ^-2 ). However, for chips with low initial carrier concentration, the control rate is too fast to achieve stable control of carriers. When the five-layer structure is adopted, the stability of the carriers is better, but each layer of glue needs to be heated, and the uniform five-layer glue greatly increases the difficulty of regulation; and ZEP520A (the main component is ZEP glue, ZEP glue is a styrene methacrylate-based electron beam positive glue), such as literature 2 (Lara-Avila, S.et al.Non-volatile photochemical gating of an epitaxial graphene/polymer heterostructure. Ad It is recorded in v.Mater. 23, 878-882 (2011) that ZEP 520A can produce a large amount of chlorine free radicals by ultraviolet light irradiation, realize the quantity that chlorine free radicals form by controlling the metering of ultraviolet light irradiation, thereby realize the control of carrier concentration.Although the above-mentioned control method can effectively reduce its carrier concentration, the graphene after the regulation all has the unstable problem of carrier concentration in atmospheric environment.Need to place it in nitrogen, argon gas or vacuum and just can effectively improve graphene chip carrying current The stability of sub-concentration greatly limits its practical application.

Contents of the invention

In view of the above-mentioned problems in the prior art, the present invention provides a packaging method and a packaging structure for improving the stability of graphene carrier concentration.

First aspect of the present invention provides a kind of encapsulation method that improves graphene carrier concentration stability, comprises the following steps:

S1, making graphene chips;

S2, performing secondary leveling on the graphene chip substrate: firstly, using PMMA solution to perform the first leveling and baking on the graphene chip base; then using a mixed dopant to perform a second leveling on the graphene chip after the first leveling, wherein the mixed dopant is PMMA doped with F4TCNQ (2,3,5,6-tetrafluoro-7,7',8,8'-tetracyanodimethyl-p-benzoquinone);

S3. In the glove box, the graphene chip after the second glue leveling is packaged;

S4. Regulating the packaged graphene chip to reduce the graphene carrier concentration.

Preferably, in step S2, the baking temperature is 160-180°C, and the baking time is 3-6 min.

Preferably, in step S2, the solvent used in the PMMA solution is anisole, the molecular weight of the PMMA is 920000-980000; the mass percentage of F4TCNQ in the mixed dopant is 4-7wt%.

Preferably, in step S3, the following three ways can be used to package the graphene chip after the secondary glue leveling:

(1) Encapsulation with hot-melt adhesive, the specific steps are: in the glove box, use hot-melt adhesive to wrap the graphene chip after secondary uniform glue, then heat the hot-melt adhesive to melt it, then cover the glass slide with the hot-melt adhesive, and remove the encapsulated graphene chip as a whole; wherein, the heating temperature is 90-100°C, and the heating time is 1-5 min; the packaging process is carried out under protective gas or vacuum conditions in the glove box, and the protective gas is argon or nitrogen.

(2) When the size of the test bench is significantly larger than the size of the graphene chip after the second glue leveling, the following method is used for packaging. The specific steps are: glue the printed circuit board on the test bench with low-temperature glue, and glue the graphene chip after the second glue leveling on the top of the printed circuit board with low-temperature glue, and connect the graphene chip after the second glue leveling with the printed circuit board. The cover encapsulates the graphene chip after the second glue leveling and the lead, and connects the printed circuit board to the test bench with the lead wire, so as to realize the connection between the graphene chip after the second glue leveling and the test bench.

(3) When the airtightness of the test bench is high, use the following method for packaging. The specific steps are: in the glove box, use low-temperature glue to fix the test bench and the graphene chip after the second glue leveling.

Preferably, in step S4, the control method is: heating the packaged graphene chip, the heating temperature is 90-95 °C, and the heating time is 2-5 min. Since the heating operation can deform PMMA, the electron acceptor F4TCNQ can reach the surface of graphene to reduce the carrier concentration of graphene.

Preferably, the second glue leveling can be realized in the following manner instead: use PMMA/MMA to carry out the first glue leveling and the first baking on the graphene chip substrate, and then use ZEP520A to carry out the second glue leveling and the second baking on the graphene chip after the first leveling.

Preferably, the first baking temperature is 160-180°C, and the baking time is 3-6 minutes; the second baking temperature is 160-180°C, and the baking time is 3-6 minutes.

Preferably, in step S4, the control method is to irradiate the packaged graphene chip with an ultraviolet lamp, the wavelength of the ultraviolet light is 248-260 nm, and the irradiation time is 2-5 min. Since ultraviolet light irradiation can induce the formation of a large number of chlorine free radicals, chlorine free radicals, as electron acceptors, can effectively reduce the carrier concentration of graphene.

The second aspect of the present invention provides the graphene chip packaging structure obtained by the above packaging method.

Preferably, the graphene chip packaging structure includes: a test platform stacked in sequence, a printed circuit board, a graphene chip after secondary gluing, and a glass cover; wherein, a protective gas or a vacuum environment is filled between the glass cover and the graphene chip after the secondary gluing, and the graphene chip after the secondary gluing is connected to the printed circuit board by a lead, and the printed circuit board and the test bench are connected by a lead.

Preferably, between the test bench and the printed circuit board, as well as between the printed circuit board and the graphene chip after secondary glue leveling, the fixation is realized by low-temperature glue, and the bottom of the glass cover is fixed with the printed circuit board and sealed inside the glass cover by low-temperature glue.

Preferably, the graphene chip packaging structure comprises: a test bench stacked in sequence, a graphene chip after the secondary glue leveling, and a glass cover; wherein, a protective gas or a vacuum environment is filled between the glass cover and the graphene chip after the second glue leveling, and the graphene chip after the second glue leveling and the test bench are connected by wires.

Preferably, the low-temperature glue is used to fix the test platform and the graphene chip after the second glue leveling, and the bottom of the glass cover is fixed to the test platform and sealed inside the glass cover with low-temperature glue.

The present invention has following beneficial effects:

(1) The present invention provides a packaging method and packaging structure for improving the stability of graphene carrier concentration. The packaging method can not only effectively isolate the surface of the regulated graphene chip from the air, reduce the influence of water and oxygen in the air on the stability of graphene carrier concentration, but also reduce the graphene carrier concentration (it can be reduced to 1×10 ¹⁰ ~10 ¹¹ cm ^-2 ).

(2) The packaging structure of the graphene chip obtained in the present invention is small, basically does not affect the transportation and measurement of the chip, and can provide corresponding and relatively convenient packaging methods for different situations, providing multiple ideas for chip packaging. The encapsulated graphene chip does not need to be stored in a glove box, which greatly facilitates the storage of the chip, and at the same time avoids the impact of the difference between the internal and external environments of the glove box on the chip, making the transportation of the chip more convenient.

(3) In the present invention, the two control technologies adopted can achieve uniform doping of graphene, and the operation is relatively simple, and the state before the control can be restored after removing the dopant, that is, it is reversible.

(4) The packaging method of the present invention has simple operation process, less time consumption, and cheap raw materials, and can greatly improve the stability of the graphene (chip) carrier concentration and the convenience of use, so it is suitable for promotion.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the accompanying drawings used in the embodiments. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other accompanying drawings can also be obtained based on these drawings without creative work.

Fig. 1 is a flow chart of a packaging method that improves the stability of graphene carrier concentration provided by the present invention;

Fig. 2 is the optical microscope picture of the graphene chip in embodiment 1;

Fig. 3 is the schematic diagram of the cut surface of the graphene chip after secondary homogenization in embodiment 1;

Fig. 4 is the schematic diagram of the graphene chip encapsulation structure that obtains when test bench size is obviously greater than the graphene chip size after secondary even glue in embodiment 1;

Fig. 5 is the schematic diagram of the graphene chip encapsulation structure that obtains when test platform airtightness is higher in embodiment 2;

Fig. 6 is the schematic cross-sectional view of the graphene chip encapsulation structure that hot-melt adhesive encapsulation obtains in embodiment 3;

Fig. 7 is the change diagram of the Hall resistance of the graphene chip with the magnetic field in detecting the carrier concentration;

Fig. 8 is the graph of the change with the magnetic field after the Hall resistance of the graphene chip in the detection carrier concentration is antisymmetrically processed in a low field;

Among them, 1. Test bench; 2. Printed circuit board; 3. Graphene chip after secondary uniform glue; 4. Glass cover.

Detailed ways

In the following description, specific details such as specific system structures and technologies are presented for the purpose of illustration rather than limitation, so as to thoroughly understand the embodiments of the present invention. It will be apparent, however, to one skilled in the art that the invention may be practiced in other embodiments without these specific details.

Example 1

With reference to Fig. 1, a kind of packaging method that improves the stability of graphene carrier concentration comprises the following steps:

S1. Making a graphene chip; here it is made by a conventional method in this field, as shown in Fig. 2 is the optical microscope image of the prepared graphene chip, and the white dotted line is the graphene boundary: (1) Growth of graphene on the outer edge of silicon carbide: in an atmosphere of argon gas at an atmospheric pressure, the temperature is rapidly raised to 2000 ° C for 5 minutes for annealing. Since silicon has a higher vapor pressure at high temperature, the sublimation rate is faster than that of carbon, so that part of the carbon remains on the surface of SiC to form graphene, that is, graphene on the outer edge of silicon carbide is obtained; Graphene Hall strips are made by beam lithography, and then graphene chips are obtained by electron beam exposure and electron beam evaporation of metal electrodes;

S2. Perform secondary homogenization on the obtained graphene chip substrate: (1) use PMMA to perform the first homogenization on the graphene chip substrate, the speed of homogenization is 6000 rpm, the thickness is about 240 nm, and bake at 160 °C for 5 min; (2) The graphene chip after the first homogenization is performed with a mixed dopant, the speed of homogenization is 6000 rpm, and the thickness is about 235 nm; the graphene chip after the second homogenization is obtained. Figure 3;

Among them, the mixed dopant is obtained by mixing 5 mg of F4TCNQ with a volume of 1.8 ml of PMMA A4 (4% mass fraction), and the mass fraction of F4TCNQ in the mixed dopant is 7%.

S3. When the size of the test bench 1 is significantly larger than the size of the graphene chip 3 after the second gluing, the graphene chip 3 after the second gluing is packaged in the following manner. The specific steps are: the printed circuit board 2 is glued on the test bench 1, and the graphene chip 3 after the second gluing is glued on the top of the printed circuit board 2 with a low-temperature glue (VGE-7031 varnish, varnish is varnish), and the graphene chip 3 after the second gluing is connected to the printed circuit board 2 with a lead wire Then put the graphene chip 3 and the test bench 1 of the graphene chip 3 and the printed circuit board 2 after the second glue leveling, the low-temperature glue and the glass cover 4 into the glove box, and use the low-temperature glue and the glass cover 4 to package the graphene chip 3 and the lead after the second glue leveling, and connect the printed circuit board 2 to the test bench 1 with the lead wires, so as to realize the connection between the graphene chip 3 and the test bench 1 after the second glue leveling. Obtain the packaging structure shown in Figure 4 (A is a top view, B is a side view), as shown in Figure 4B, stacked sequentially from bottom to top: test bench 1, printed circuit board 2, graphene chip 3 after secondary glue leveling, glass cover 4. Between the test bench 1 and the printed circuit board 2 and between the printed circuit board 2 and the graphene chip 3 after the secondary glue leveling, realize fixing with low-temperature glue; the bottom of the glass cover 4 realizes the fixing between the printed circuit board 2 and the sealing inside the glass cover 4 with low-temperature glue; Realize the connection between the graphene chip 3 and the test bench 1 after the second glue leveling. This method is less difficult than hot melt adhesive packaging, and can achieve a larger packaging area, reducing the difficulty of packaging.

S4. Regulate the carrier concentration of the packaged graphene chip by heating at 90°C (heating for 3 min).

Example 2

S1. Preparation of graphene chip; Here, the conventional method in this field is used to make: (1) Growth of graphene on the outer edge of silicon carbide: in an atmosphere of argon gas at atmospheric pressure, the temperature is rapidly raised to 2000 ° C for 5 minutes, and silicon has a higher vapor pressure at high temperature, and the sublimation rate is faster than that of carbon, so that part of the carbon remains on the surface of SiC to form graphene, that is, a graphene chip on the outer edge of silicon carbide is obtained; Plating metal electrodes to obtain graphene chips;

S2. Perform secondary coating on the obtained graphene chip substrate: (1) use PMMA/MMA (8.5% by mass of MMA, MAA) to perform the first coating on the graphene chip, the speed of coating is 5000 rpm, the thickness is 320 nm, and bake at 160 °C for 5 minutes; (2) Use ZEP520A to perform the second coating on the graphene chip after the first coating, the speed of coating is 6000 rpm, and the thickness is 30 0 nm and baked at 170 °C for 5 min.

S3, when the airtightness of the test bench 1 is high, adopt the following method to package the graphene chip 3 after the second glue leveling. This method is less difficult than the hot melt adhesive packaging operation. The specific steps are: use low-temperature glue to fix the test bench 1 and the graphene chip 3 after the second glue leveling. The chip 3 and the test bench 1 are connected by wires. Obtain the encapsulation structure shown in Figure 5 (A is a top view, B is a side view), as shown in Figure 5B, stacked successively from bottom to top: test bench 1, graphene chip 3 and glass cover 4 after the second glue leveling; low-temperature glue is used to fix between the test bench 1 and the graphene chip 3 after the second glue leveling; The graphene chips 3 after uniform glue are connected to the test bench 1 through wires. This method is less difficult than hot melt adhesive packaging operation;

S4. Control the carrier concentration of the packaged graphene chip by means of ultraviolet light irradiation (248 nm).

Example 3

S1. Preparation of graphene chip; Here, the conventional method in this field is used to make: (1) Growth of graphene on the outer edge of silicon carbide: in an atmosphere of argon gas at atmospheric pressure, the temperature is rapidly raised to 2000 ° C for 5 minutes, and silicon has a higher vapor pressure at high temperature, and the sublimation rate is faster than that of carbon, so that part of the carbon remains on the surface of SiC to form graphene, that is, a graphene chip on the outer edge of silicon carbide is obtained; Plating metal electrodes to obtain graphene chips;

S2. Perform secondary coating on the obtained graphene chip substrate: (1) use PMMA/MMA (8.5% by mass of MMA, MAA) to perform the first coating on the graphene chip substrate, the speed of coating is 5000 rpm, the thickness is 320 nm, and bake at 160 ℃ for 5 min; 300 nm and baked at 170 °C for 5 min.

S3. In the glove box, use hot-melt adhesive to package the graphene chip after the secondary leveling. The specific steps are: put the graphene chip after the second leveling, hot-melt adhesive, and a glass slide cut into a suitable size into the glove box, wrap the graphene chip after the second leveling with hot-melt adhesive, then heat the hot-melt adhesive to melt it, cover the glass slide with the hot-melt adhesive, and remove the packaged graphene chip as a whole. The resulting graphene chip packaging structure is shown in Figure 6 (leads and test benches are not shown here), which are stacked sequentially from bottom to top: the graphene chip after the second glue leveling, protective gas or vacuum, and the glass slide; the edge of the glass slide is sealed with hot melt adhesive, and the gap between the glass slide and the graphene chip after the second glue leveling is filled with protective gas or in a vacuum environment.

S4. Control the carrier concentration of the packaged graphene chip by means of ultraviolet light irradiation (248 nm).

Detection of carrier concentration

测试室温下实施例1制备的一个石墨烯芯片的纵向电阻率，得到纵向电阻率为5.47 kΩ，由于当芯片纵向电阻率处于5~6 kΩ范围时，其5K时对应的载流子浓度大致在1~2×10 ¹¹ cm ^-2 ，此时芯片的霍尔电阻可以在较低的磁场：小于4 T进入平台，然后将芯片放入低温腔中，降至5 K且保持稳定，给样品通入电流（这里依次通入了1 μA、20 μA、30 μA、40 μA、50 μA），然后给芯片施加连续变化的磁场，磁场范围为-9 T到9 T，测试芯片霍尔电压随磁场的变化，结果如图7所示。 It can be seen from the results in Figure 7 that the chip has entered the platform at 2.5 T, and the Hall resistance (ratio) is obtained by dividing the Hall voltage by the input current, and then taking the change of the Hall resistance with the magnetic field from -0.5 T to 0.5 T. At this time, the Hall resistance changes linearly with the magnetic field, and the data is desymmetricalized (see Figure 8). The carrier concentration of a graphene chip is 1.95×10 ¹¹ ~1.98× ^{10 11 cm -2} (the carrier concentration of the graphene chip will increase slightly with the increase of the current). After completing all the tests, the carrier concentration of the packaged graphene chip prepared in Example 1 was 1×10 ¹⁰ ~2×10 ¹¹ cm ^-2 , and the carrier concentration of the packaged graphene chip prepared in Example 2 was 1×10 ¹¹ ~3×10 ¹¹ cm ^-2 . From the above test results, it can be seen that this packaging method can not only improve the stability of the chip, but also effectively reduce the carrier concentration of the chip.

The present invention is not limited to the above-mentioned specific implementation manners, and various transformations made by those skilled in the art starting from the above-mentioned ideas without creative work all fall within the scope of protection of the present invention.

Claims (8)

1. a packaging method improving the stability of graphene carrier concentration, is characterized in that, comprises the following steps: S1, making graphene chips; S2, carrying out secondary leveling to the graphene chip base: adopting PMMA solution to carry out the first time leveling and baking of the graphene chip base; then using a mixed dopant to carry out the second time leveling of the graphene chip after the first leveling, wherein the mixed dopant is PMMA mixed with F4TCNQ; S3. In the glove box, the graphene chip after the second glue leveling is packaged; S4. Regulate the graphene chip that has been packaged to reduce the carrier concentration of graphene; In step S3, the graphene chip after the second glue leveling is packaged with hot melt adhesive. The specific steps are: in the glove box, wrap the graphene chip after the second glue leveling with hot melt adhesive, then heat the hot melt glue to melt it, then cover the glass slide with the hot melt glue, and remove the packaged graphene chip as a whole; wherein, the packaging process is carried out under protective gas or vacuum conditions in the glove box, the edge of the glass slide is sealed with hot melt glue, and a protective layer is filled between the glass slide and the graphene chip after the second glue leveling. Inert gas or vacuum environment. 2. a kind of encapsulation method that improves graphene carrier concentration stability according to claim 1, it is characterized in that, in step S2, described baking temperature is 160～180 ℃, and baking time is 3～6 min; The used solvent of described PMMA solution is anisole, and the molecular weight of described PMMA is 920000～980000; The mass percentage content of the F4TCNQ in described mixed dopant is 4～7wt%. 3. A packaging method for improving the stability of graphene carrier concentration according to claim 1, wherein the heating temperature is 90-100° C., and the heating time is 1-5 min; the protective gas is argon or nitrogen. 4. A kind of encapsulation method that improves graphene carrier concentration stability according to claim 1, is characterized in that, in step S4, described control mode is: the graphene chip that completes encapsulation is heated, and heating temperature is 90～95 ℃, and heating time is 2～5min. 5. a kind of encapsulation method that improves graphene carrier concentration stability according to claim 1, it is characterized in that, described secondary even glue adopts following mode to replace and realize; Adopt PMMA/MMA to carry out glue evenly for the first time and bake for the first time to graphene chip substrate, then adopt ZEP520A to carry out glue evenly for the first time and bake for the second time to the graphene chip after the first time even glue. 6. a kind of encapsulation method that improves graphene carrier concentration stability according to claim 5, is characterized in that, described baking temperature for the first time is 160～180 ℃, and baking time is 3～6min; Described second baking temperature is 160～180 ℃, and baking time is 3～6min. 7. A kind of encapsulation method that improves graphene carrier concentration stability according to claim 1, is characterized in that, in step S4, described control mode is to use ultraviolet lamp to irradiate the graphene chip that completes encapsulation, and the wavelength of described ultraviolet lamp is 248～260nm, and irradiation time is 2～5min. 8. A graphene chip encapsulation structure made by the encapsulation method improving the stability of graphene carrier concentration according to any one of claims 1-7.