Advantages and key technologies of graphene in touch screen

On March 24, Beijing time, China Touch Screen News, graphene flexible touch screen opens a new era in the field of electronic consumption

Since the 21st century, with the development of science and technology, great changes have taken place in our lives all the time. From the popularity of computers and mobile phones to the iterative updating of various electronic products, people's needs are also changing. The appearance of touch screen technology makes life, learning and entertainment faster and more convenient.

This article is from: http://www.51touch.com/touchscreen/news/front/202103/03-59437.html

There are many types of modern touch screens: resistive touch screen, capacitive touch screen, infrared technology touch screen, surface acoustic technology touch screen, etc., of which capacitive touch screen and resistive touch screen are the main technologies. However, whether it is capacitive touch screen or resistive touch screen, the ITO conductive layer in the middle is an indispensable core component.

Graphene, with its advantages of high conductivity, high toughness, high strength and high transparency, has become a new material in emerging industries. It has high technology content and broad application prospects. The flexible touch screen made of graphene instead of ITO can achieve the perfect unity of mobile phones and computers, which will bring a new era of change in the consumer electronics field.

ITO conductive layer

Application advantages of graphene material in touch screen

Flexible wrist screen

Graphene is a new two-dimensional material with only one layer of atomic thickness. It has excellent properties in mechanics, heat, optics, electricity and so on. Graphene has obvious application advantages in touch screen, and its main advantages include:

(1) Graphene is almost completely transparent, and the transmittance of single-layer graphene film from ultraviolet, visible to infrared bands is as high as 97.7%, so it will not be color biased;

(2) The contradiction between conductivity and transmittance can be well solved in the graphene transparent electrode. The graphene material is only one carbon atom layer thick, and its carrier mobility is extremely high, so it is the material with the highest conductivity found so far;

(3) Graphene has extremely high mechanical strength and is very soft (even can be folded to a certain extent);

(4) The chemical properties of graphene are stable, and its properties are less affected by the environment;

(5) Graphene is a carbon material with a single atomic layer, which is non-toxic and does not pollute the environment, meeting the requirements of green environmental protection;

(6) The content of carbon element in nature is very rich, so using graphene as the electrode has less restrictions on raw materials.

Key Technologies in Graphene Touch Screen

Large area graphene films are generally grown on copper foil and other metal substrates at high temperatures. For the application of graphene, it is necessary to transfer graphene from the growth substrate to the required substrate surface. The process of graphene touch screen is divided into four processes: graphene transfer, modification, patterning and capacitive screen module preparation, and the focus of research and development at this stage is to improve these four processes.

01 Key technologies of graphene film transfer

There are many transfer methods for graphene films, and there are two kinds of transfer methods most used at present: the transfer method based on PMMA sacrificial layer and the transfer method of pyrolytic tape. The former method: spin coating polymethyl methacrylate (PMMA) on the surface of graphene, etching copper with acid solution, transferring graphene to the target substrate, and finally removing PMMA with acetone. This method is simple and widely used in the laboratory; The latter method: stick the heat release tape with graphene/copper foil, etch copper with acid, then stick the graphene/heat release tape with the target substrate, and finally release graphene through heat transfer. The heat release tape transfer method is convenient for large area use, and it is also convenient to control the shape of the transferred graphene by cutting the tape. Therefore, the heat release tape transfer graphene method is more practical for the graphene touch screen.

02 Key Technology of Graphene Film Modification

According to different application requirements, graphene films also need to be modified and strengthened. For the graphene touch screen, the graphene film needs to further enhance the conductivity of the film while maintaining high light transmittance. In the case of a certain carrier mobility, increasing the carrier concentration of graphene through doping modification is an important way to enhance the conductivity of graphene. The valence band and conduction band of intrinsic graphene are in conical contact at the center of Brillouin zone, so it is a semiconductor or semi metal with zero band gap; Through surface adsorption, lattice vacancy, lattice replacement doping and other ways, the energy band level structure can be changed to form a doping effect similar to that of semiconductors. At present, there are many kinds of graphene doped modifiers, mainly including nitric acid, chloroauric acid, conductive polymer, etc. The modification methods used include immersion, fumigation, in-situ composite and spin coating.

03 Key technologies of graphene film patterning

Graphene is a two-dimensional material composed of carbon atoms, which has good chemical stability. Generally, it is difficult to etch graphene with acid and alkali. Therefore, in the process of realizing capacitive touch screen with graphene, a big problem will be encountered: etching graphene under the existing touch process line conditions. To achieve the etching of graphene, general methods include two aspects: (1) Since graphene is a very thin material with only one atomic layer thickness, unnecessary graphene can be removed by high-energy bombardment; (2) Graphene is composed of carbon atoms, so it can be considered to react with oxygen and other substances under special conditions to remove graphene. Based on this, there are three etching methods for graphene: laser etching, oxygen plasma etching and oxygen ultraviolet etching. Among them, the graphene laser etching method is relatively simple. At the same time, the existing industrial equipment can achieve graphene patterns of 10 micrometers in order to meet the needs of large-scale preparation in the factory.

04 Key technologies of graphene touch module

The manufacturing process of graphene touch module can be divided into the front sensor process and the back bonding process. The purpose of the front bonding process is to realize the sensor of the capacitive touch screen, while the back bonding process is to bond the sensor to the touch chip to form a finished graphene capacitive touch screen. The main process steps include: silk screen printing and etching of silver paste, bonding of graphene sensor and touch chip, bonding of cover plate and defoaming. Among them, graphene sensor and touch chip are electrically connected through flexible printed circuit board (FPC), which requires binding and bonding with ACF adhesive under certain pressure and high temperature conditions.

Summary and outlook

Because of its own characteristics, graphene materials have broad application prospects in the field of touch screens. Leading enterprises at home and abroad have already begun to carry out patent layout in related fields, but there are still many problems to be solved in the mass production of graphene touch screens. Therefore, domestic relevant enterprises still need to increase investment in R&D to have the opportunity to break through the patent blockade of giants, and at the same time, strengthen cooperation with universities or scientific research institutions, actively promote the combination of production, teaching and research, and focus on the transfer, modification, graphitization of graphene and the preparation of capacitive screen modules, so as to accelerate the industrialization process of the application of graphene in the field of touch screens in China.