News on March 24th, Beijing time, graphene flexible touch screen opens a new era in consumer electronics
Since the 21st century, with the development of science and technology, our lives have undergone tremendous changes all the time. From the popularization of computers and mobile phones to the iterative update of various electronic products, people's needs are also changing. The emergence of touch screen technology makes life, learning, and entertainment faster and more convenient.
There are many types of modern touch screens: resistive touch screens, capacitive touch screens, infrared technology touch screens, surface acoustic wave technology touch screens, etc. The dominant technologies are capacitive touch screens and resistive touch screens. However, whether it is a capacitive touch screen or a resistive touch screen, an indispensable core component is the ITO conductive layer in the middle.
Graphene has become an emerging material in emerging industries due to its high conductivity, high toughness, high strength, high transparency and other advantages. It has high technical content and wide application prospects. The flexible touch screen made of graphene instead of ITO can realize mobile phone and The perfect unity of computers will bring about a new era of changes in the field of consumer electronics.
ITO conductive layer
Application advantages of graphene materials in touch screens
Flexible screen wrist machine
Graphene is a new two-dimensional material with only one layer of atomic thickness, and has excellent properties in mechanics, heat, optics, and electricity. Graphene has obvious application advantages in touch screens, and its main advantages include:
(1) Graphene is almost completely transparent, and the light transmittance of single-layer graphene film from ultraviolet, visible to infrared bands is as high as 97.7%, so there is no color cast;
(2) The contradiction between electrical conductivity and light transmittance can be well resolved in the graphene transparent electrode. The graphene material is only one carbon atom layer thick, and its carrier mobility is extremely high, which is the conductivity found so far. Highest material
(3) Graphene has extremely high mechanical strength and is very soft (it can even be folded to a certain extent);
(4) Graphene has stable chemical properties, and its performance is less affected by the environment;
(5) Graphene is a monoatomic layer of carbon material, which is non-toxic, non-polluting to the environment, and meets the requirements of green and environmental protection;
(6) The content of carbon elements in nature is very rich, so the use of graphene as an electrode has less restriction on raw materials.
Key technologies in graphene touch screens
Large-area graphene films are generally grown on the surface of metal substrates such as copper foil at high temperatures. For graphene applications, it is necessary to transfer graphene from the growth substrate to the desired substrate surface. The process of graphene touch screens is divided into four processes: graphene transfer, modification, patterning and the preparation of capacitive screen modules, and the current research and development focus is also on improving these four processes.
01Key Technology of Graphene Film Transfer
There are many transfer methods for graphene films, and currently there are two types that are most used: PMMA sacrificial layer-based transfer methods and pyro-release tape transfer methods. The former method: spin-coated polymethyl methacrylate (PMMA) on the surface of graphene, etch the copper with acid, then transfer the graphene to the target substrate, and finally remove PMMA with acetone. This method is simple to operate. Used extensively in the laboratory; the latter method: Laminate the pyro-release tape with graphene/copper foil, etch the copper with acid solution, then attach the graphene/pyro-release tape to the target substrate, and finally pass the pyro-release tape through Heat transfer to release graphene. The heat-release tape transfer method is convenient for large-area use, and at the same time, it is convenient to control the shape of the transferred graphene through the cutting of the tape. Therefore, for the graphene touch screen, the heat-release tape transfer graphene method is more practical.
02Key Technologies of Graphene Film Modification
According to different application requirements, the graphene film also needs to be modified and enhanced. For graphene touch screens, 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 by 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 in the center of the Brillouin zone, so it is a zero-band gap semiconductor or semi-metal; it can be changed by surface adsorption, lattice vacancy, lattice replacement doping, etc. Band energy level structure, forming doping effect similar to semiconductor. At present, there are many types of graphene doping modifiers, mainly nitric acid, chloroauric acid, conductive polymer, etc. The modification methods used include soaking, fumigation, in-situ compounding, and spin coating.
03Key technologies for graphene film patterning
Graphene is a two-dimensional material composed of carbon atoms and has good chemical stability. Generally, it is difficult to corrode graphene with acid and alkali. Therefore, in the process of implementing capacitive touch screen with graphene, a big problem will be encountered: the etching of graphene can be achieved under the existing touch process line conditions. . To achieve the etching of graphene, the general method includes two aspects: (1) Since graphene is a very thin material with only one atomic layer thickness, high-energy bombardment can be used to remove unwanted graphite (2) Graphene is composed of carbon atoms, so it can be considered to chemically 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 has a relatively simple processing method. At the same time, the existing industrialized equipment can realize graphene patterns on the order of 10 microns, which meets the demand for large-scale production in factories.
04Key Technologies of Graphene Touch Module
The graphene touch module manufacturing process can be divided into a front-end sensor process and a back-end bonding process. The purpose of the front-end process is to realize the sensor of a capacitive touch screen, and the back-end process is to bond the sensor to the touch chip to form a graphene capacitor. Finished touch screen. The main process steps include: silk screen and etching of silver paste, bonding of graphene sensor and touch chip, cover bonding and defoaming. Among them, the graphene sensor and the touch chip are electrically connected through a flexible printed circuit board (FPC), which needs to be bound and bonded with ACF glue through certain pressure and high temperature conditions.
Summary and outlook
Graphene materials have broad application prospects in the field of touch screens due to their own characteristics. Leading companies at home and abroad have already begun to carry out patent layouts in related fields, but there are still many problems to be solved in the mass production of graphene touch screens. . Therefore, domestic related companies still have to increase R&D investment 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, and actively promote the integration of industry, education and research, focusing on the transfer, modification, and graphics of graphene. In order to speed up the industrialization process of graphene in the touch screen field in my country, it is necessary to seek meaningful improvements in the preparation process of chemical and capacitive screen module preparation.
