Hand rubbing nuclear fusion live in the wilderness

Chapter 409 Graphene wafer with excellent performance
In the live broadcast room, the audience talked about the cracks on the graphene crystal.

Some people feel that the graphene preparation failed this time, while others think that cracks are normal.

After all, the area of ​​the chip is only a little bit big, and cracks will not affect the overall pick-up.

Just like a large crack in a piece of jade weighing two or three tons does not affect it to take a bracelet.

What's more, Won has always succeeded in leaving a deep impression on the audience no matter what he makes.

This makes some viewers feel that a success is inevitable.

Glancing at the barrage on the virtual screen, Han Yuan smiled wryly and replied, "There may indeed be something wrong with this piece of graphene."

"The cracks on it are not as simple as emerald."

"There are cracks in the single crystal of graphene, which are caused by the insufficient release of the overall tensile force of the material. If there are cracks, it means that the crystal shape of the entire material may be deformed."

"And the deformed crystal material cannot be used to cut and make graphene wafers."

After a pause, Han Yuan added:

"Of course, it is only a preliminary judgment now. If there is a specific situation, it needs to be tested by special instruments."

"However, there is a high probability that this graphene single crystal material is useless."

Han Yuan shook his head, put the graphene crystal material in his hand into a special instrument, and then took it to another room in the chemical laboratory.

There are a lot of special testing instruments in the chemical laboratory. Since he got the application knowledge information of intermediate industrial equipment, he has made a comprehensive upgrade of the equipment in the chemical physics laboratory and smelting plant.

Not to mention the various smelting equipment, even the various testing equipment is much more advanced than before.

Equipment such as infrared spectrometers and elemental analyzers all have their own chips and are connected to the central computer.

The data detected by the analysis will be automatically transmitted to the central computer. As long as there is a network, Won can view various data in any corner.

After some tossing, all kinds of test data about this newly prepared graphene single crystal material were finally complete.

Han Yuan flipped through the various data on the screen, shook his head and sighed.

Judging from the data on the infrared spectrometer, there is indeed a problem with this graphene single crystal material.

Along the edge of the Y-shaped crack, the crystal structure of more than half of the whole material is distorted.

This is where the naked eye cannot see it.

Just like a bed sheet that was originally laid flat without any wrinkles, after being rolled, it is full of twisted lines.

Although these twisted lines are invisible to the naked eye, the material is useless for its purpose.

Although graphene wafers do not require a large area, the size of four or five thumbnails is enough, but like silicon wafers, they have quite high requirements for the material itself.

And these twisted lines caused by crack tension will have a great impact on the entire material. These chaotic lines will cause electrons to be strung together in the entire chip, which cannot be used on the chip at all.

Even if there is still a small part of it that has not been distorted, the Korean won dare not use it.

These undistorted places may be intact, but there are still problems with a certain probability, and it is safer to remake a piece.

Of course, before remanufacturing, he had to find out why the graphene single crystal material had cracks and dispose of it to ensure that the next preparation would not happen again.

Won is looking for the cause of the problem with the graphene single crystal material in the laboratory.

Experts from various countries squatting in the live broadcast room are very curious about how the South Korean won will solve this problem.

In particular, Huaguo is an expert in the study of graphene crystals.

Because this problem they also encountered, and to a certain extent did not solve.

As we all know, graphene is a planar structure composed of a single layer of carbon atoms, but when the number of atoms in this planar structure is not enough, the graphene plane will break atomic bonds due to problems such as tension, and then cracks will appear.

This problem exists widely in graphene films.

This is a linear defect produced by the release of compressive stress, which is ubiquitous in graphene films.

It is not so much a problem of cracks as a problem of 'wrinkling' of the graphene crystal.

If the existence of simple cracks does not affect the quality of the graphene material, just avoid the cracks and select wafers.

However, the twisted wrinkles around the cracks will greatly reduce the electrical properties of graphene.

At present, there are three main ways for Huaguo to deal with the "wrinkle" problem that occurs during the growth of graphene crystals:

First, low temperature growth;
Compared with the high-temperature growth environment, the low-temperature growth will greatly weaken the stress problem of the graphene crystal material, and naturally there will be no wrinkles.

Second, select a single crystal substrate with a low thermal expansion coefficient;

Third, weaken the interfacial interaction between graphene and the substrate.

These three methods were developed by Hua Guo after years of research. They can solve the problem of wrinkles on graphene crystals, but they also bring new troubles.

That is, using these three methods to deal with the wrinkle problem of the graphene crystal material will limit the area size of the graphene crystal material growth.

For an insulating substrate with almost no catalytic activity, the nucleation density of graphene will be too high and the growth rate will be too slow. The size of the single crystal domain region is mostly at the level of hundreds of nanometers, and there are few single crystal materials at the micron and millimeter level.

However, graphene single crystal materials with this domain size cannot be used as graphene wafers.

If you want to mass-produce inch-level graphene wafers, it will take a long time, which is not worth the candle.

After all, no matter how excellent the performance of a carbon-based chip is, it still needs a certain area to support the number of transistors inside.

The number of transistors cannot be increased, and the performance of this chip cannot be improved at all.

Therefore, the Huaguo Chinese Academy of Sciences has successfully developed an 8-inch graphene wafer, and the graphene single crystal preparation method used is not chemical vapor deposition.

Instead, another laboratory preparation method is used.

The problem is that the cost of mass production of this laboratory preparation method is very high, and it is not worth the loss to use this method to produce graphene wafers.

The Chinese Academy of Sciences has been looking for ways to manufacture graphene wafers at low cost, and the vapor deposition method is the focus of its research.

But it is a pity that after solving the wrinkle problem, the growth area of ​​graphene single crystal material is limited again, which is very discouraging.

Therefore, Huaguo experts are particularly looking forward to how Won will solve the wrinkle problem on the graphene single crystal material.

In front of the display screen, Han Yuan carefully checked the inspection data of the graphene single crystal material and the records recorded during the manufacturing process.

Checking these things together can basically find the point of the problem.

Just like checking the fragments of parts and black box logs at the scene after a plane crash, through these two things, the scene of the plane crash can basically be restored.

Soon, through the data recorded by the high-temperature smelting furnace and the inspection data of the infrared spectrometer, Han Yuan found out why the cracks appeared in this graphene single crystal material.

In fact, the reason is quite simple, that is, he made a mistake before. The single crystal nickel base material used was too large, resulting in insufficient carbon powder and graphite powder on the single area.

Eventually, after the carbon atoms are heated and restructured to a certain extent, the formed graphene single crystal material has the problem of crystal cracking due to its own tension problem when it is cooled.

For this situation, the solution is not complicated, and it can be solved by increasing the weight according to the corresponding proportion of various materials.

However, according to the amount of materials, various parameters such as the content, pressure, and preparation time of various gases such as methane and ethylene in the high-temperature smelting furnace need to be modified simultaneously.

This is not difficult for Won. After spending some time, Won readjusted various parameter information and started the second graphene preparation.

After finding the problem and the solution, Han Yuan briefly explained the cause of the problem and the solution.

Simply increasing the amount of raw materials according to the corresponding proportions of various materials can solve the wrinkle problem of graphene single crystal materials. Experts from various countries were dumbfounded and could not believe it.

But soon, these experts remembered what Han Yuan said before, and realized what was going on.

In fact, the reason is very simple.

The reason why they and the other party deal with the wrinkles on the graphene single crystal material is very different. The main reason is that the substrate material and crystal nucleus that guide the growth of the graphene single crystal material are different.

For example, in the vapor phase deposition method, the base material used by Huaguo is liquid copper, and the nitrogen-containing molecule 'pyridine' is used as the carbon and nitrogen source.

The catalytic dehydrogenation self-assembly effect of pyridine molecules on the surface of copper foil is used to generate graphene.

The other party used single crystal nickel as the substrate and silicon carbide as the crystal nucleus growth. On this basis, the wrinkle problem of graphene has been solved.

The first production problem was caused by the pure shortage of raw materials, not the thermal effect tension.

After trying to understand what was going on, experts from various countries either shook their heads or showed helpless wry smiles on their faces.

Fortunately, they were still wondering whether the other party did not master the graphene preparation technology. Now it seems that the other party is just not proficient in producing graphene for the first time.

After adjustment, the graphene single crystal material prepared for the second time is thicker than that prepared for the first time, but the cracks are gone.

After a series of inspections, Han Yuan breathed a sigh of relief holding the test data.

The graphene single crystal material prepared for the second time meets the requirements for preparing graphene wafers in terms of various data.

The overall structure is single crystal, no wrinkles overall, ultra-clean overall, and the impurity content is less than 0.0001%.

These are the basic properties. In addition, South Korea also tested a series of things such as the interface thermal conductivity and electrical conductivity of this graphene single crystal material.

Through testing, it can be seen from the data on the display that the carrier mobility of this piece of graphene has reached 160000 cm2·V 1·s 1.

In contrast, the carrier mobility of single crystal silicon is generally between 2500-3500 cm2·V 1·s 1.

Carrier mobility refers to the physical quantity used in solid-state physics to describe how fast the electrons inside a metal or semiconductor move under the action of an electric field.

This is a physical property, and it is not necessary to understand its principle, but it is necessary to know the impact of this physical property on the chip.

First, the carrier mobility and carrier concentration together determine the conductivity (reciprocal of resistivity) of semiconductor materials.

Second, it affects the operating frequency of the device.

Many people should have heard of 'overclocking' chips, especially some PC enthusiasts.

Overclocking refers to the method of increasing the clock speed of an electronic component to operate at a speed higher than that specified by the manufacturer, thereby improving performance.

By overclocking, you can make your computer perform better.

For example, the Core i series CPU of the Intel series can achieve cross-level performance comparison through overclocking.

The i3 processor of the same generation, under overclocking, has a performance comparable to that of the i5 of the same generation, or even surpasses it.

But there is a disadvantage of overclocking. It is just like the long-term high-load labor of the human body, and it is easy to get tired and go to the hospital.

So it has a great impact on the life of the chip.

The superiority of graphene single crystal materials is fully reflected in this aspect.

It is precisely because graphene has such a high carrier mobility that it can be applied to ultra-high frequency devices, making THz possible (no matter how much silicon-based chips are improved, their high frequencies can only reach GHz levels).

For example, in a typical 100 nm channel graphene transistor, the carrier transfer between source and drain only needs 0.1 ps.

In addition, the thermal conductivity of this graphene single crystal material is 3800 W/(m K), which is currently the highest among artificially synthesized electronic devices.

In contrast, the thermal conductivity of monocrystalline silicon is only 250W/(m·K), and the gap between the two can be seen at a glance.

The high thermal conductivity has a significant effect on the interface heat dissipation of high-power devices, after all, the heat can be transferred out in time.

This can improve device efficiency and extend device life, and is expected to be used for thermal management of integrated circuits.

Whether it is high carrier mobility or high thermal conductivity, the excellent performance of graphene single crystal materials can be seen.

This is unmatched by silicon-based chips.

Of course, where there is excellent performance, there will naturally be places where performance is low.

The ultrahigh electron carrier mobility of graphene single crystal material comes from its own lack of inherent band gap.

The lack of an intrinsic bandgap limits the application of graphene in logic circuits.

In fact, this point is quite easy to understand. The electrons running in graphene are like cars running on the highway. The toll booths are the switches of the electrons, which guide each electron to where it goes.

Graphene single crystal material is a highway wider than silicon-based chips, but there are no toll booths on this highway.

This causes the cars driving on it, that is, the electrons, to run around at will.

This is an important problem that must be solved when using graphene materials as wafers in carbon-based chips.

For this problem, the actual practice of various countries is to add a layer of single crystal silicon or silicon carbide crystal material under the graphene wafer.

So as to realize the bandgap function.

However, this method has a big disadvantage, that is, no matter whether single crystal silicon or silicon carbide crystal material is used as the substrate, it will affect the overall operating efficiency of the chip.

Not all materials have such high carrier mobility and thermal conductivity as graphene single crystals.

Even ultra-high-purity silicon carbide crystals are far less efficient in both aspects than graphene single crystals.

In the future, Won will also solve the problem of the band gap of graphene single crystal materials, and the method he uses is also the same.

This path is actually correct, but countries have not found suitable materials.

In other words, they found a suitable material, but they couldn't attach that material as a substrate to a graphene single-crystal wafer.

(End of this chapter)