Digital life has become a feature of the information age, which has changed all aspects of human life. Behind this, there are great feats of new materials, which are the "behind-the-scenes heroes" of digital life.
Computer is an important equipment in digital life. The core components of computer are central processing unit (CPU) and memory (RAM), which are built on the basis of large-scale integrated circuits, and these integrated circuits are made of semiconductor materials. Si wafers are the first generation of semiconductor materials, and the Si wafers used in integrated circuits must have large diameter, high crystal integrity, high geometric accuracy and high cleanliness. In order to make integrated circuits have high efficiency, low energy consumption and high speed, the second generation semiconductor single crystal materials such as GaAs and InP have been developed one after another. The third generation wide band gap semiconductor materials such as SiC, GaN, ZnSe, diamond, new silicon-based materials such as SiGe/Si and SOI(Silicon On Insulator), and superlattice quantum well materials can be used to make high temperature (3~5°C), high frequency, high power, radiation resistance, blue-green light and ultraviolet light emitting devices and detectors, thus greatly improving the performance of the original silicon integrated circuits, and are future semiconductor materials.
In human-computer communication, it is often necessary to display various forms of information, such as words, data, graphics, images and moving images. The most commonly used display means of static information, such as printers, copiers, fax machines and scanners, are generally called information output and input devices. In order to improve the resolution and the speed of input and output, it is necessary to develop high-sensitivity and stable photosensitive materials, such as photosensitive drum materials on laser printers and copiers. At present, inorganic selenium alloys and organic phthalocyanine dyes are used. The main component for displaying moving image information is cathode ray tube (CRT), which is widely used in computer terminal displays and flat-panel televisions. At present, the electroluminescent materials used in CRT mostly use inorganic materials such as sulfide (ZnS, CdS, etc.) and oxide (Y2O3, YAlO3) doped with rare earth (Tb3+, Sn3+, Eu3+, etc.) and transition element (Mn2+).
in order to reduce the huge volume of CRT, the trend of information display is high resolution, large display capacity, flat, thin and large. For this reason, flat panel display technologies such as liquid crystal display technology (LCD), field emission display technology (FED), plasma display technology (PDP) and light emitting diode display technology (LED) are mainly adopted. Widely used in high definition television (HDTV), video phone, computer (desktop or mobile) display, automobile and personal digital terminal display, CRT is no longer a unique show, but forms a situation of blooming with various flat panel displays.
liquid crystal materials used in liquid crystal display technology have been used in watches, calculators, notebook computers and video cameras for a long time. nematic and chiral materials such as phenylcyclohexane, cyclohexylcyclohexane and pyridine were used as liquid crystal materials earlier, and then ferroelectric (FE) liquid crystals were developed. The response time is in the microsecond level, but the stability of ferroelectric liquid crystals is poor and can only be improved by side-chain method. At present, antiferroelectric liquid crystals tend to be developed because of their high stability.
LCD materials have some difficulties in large-screen display. At present, the main candidates for large-screen display are plasma display panel (PDP) and light-emitting diode (LED). The phosphor used in PDP is barium aluminum oxide doped with rare earth. The development of field emission display (FED) is promoted by using diamond-like carbon materials as cold cathode and rare earth ion doped oxides as luminescent materials. Semiconductor materials for manufacturing high-brightness light-emitting diodes are mainly red, orange and yellow GaAs-based and GaP-based epitaxial materials, blue-emitting GaN-based and ZnSe-based epitaxial materials, etc.
due to the rapid development of internet and multimedia technology, human beings have to process, transmit and store terabytes (112bits) with ultra-high information capacity, and the ultra-high-speed information flow reaches terabytes per second (Tb/s). It can be said that human beings have entered the era of terabytes information. Modern information storage methods are various. Taking computer system storage as an example, the storage methods are divided into random internal storage, offline storage, offline external storage and offline storage. Random Access Memory (RAM) requires high integration and fast data access. Therefore, semiconductor dynamic random access memory (DRAM), which is based on large-scale integrated microelectronics technology, has more than 2 million transistors. External storage mostly adopts magnetic recording, and the main forms of magnetic storage media are magnetic tape, bubble, floppy disk and hard disk. The improvement of magnetic storage density mainly depends on the improvement of magnetic medium materials, such as magnetic oxides (such as g-Fe2O3, CrO2, metal magnetic powder, etc.), ferrite series, ultrafine magnetic oxide powder, electroless plating of Co-Ni alloy or vacuum sputtering deposition of Co-based alloy continuous magnetic thin film media, etc., and the information storage capacity of magnetic storage has been greatly improved. Solid-state (flash memory is a nonvolatile erasable memory, which is an integrated circuit based on semiconductor diodes. It is compact and sturdy, and can be inserted between internal memory and external memory. Generally, soft magnetic materials with high saturation magnetic induction are used as the core materials of recording heads, such as 8Ni-2Fe, Co-Zr-Nb, Fe-Ta-C, 45Ni-55Fe, Fe-Ni-N, Fe-Si-Ni, 67Co-1Ni-23Fe, etc. Giant magnetoresistance (GMR) materials developed in recent years have a sharp decrease in resistance under a certain magnetic field, which is generally more than 1 times higher than that of ordinary magnetic metals and alloys. GMR generally consists of free layer/conductive layer/pinned layer/antiferromagnetic layer, in which the free layer can be made of strong magnet materials such as Ni-Fe, Ni-Fe/Co, Co-Fe, and permanent magnet films such as Co-Cr-Pt are arranged at both ends, the conductive layer is a copper film with several nm, the pinned layer is a soft magnetic Co alloy with several nm, and the magnetization fixed layer is made of Ni-O and Co-Fe with 5 ~ 4 nm. The read head with GMR effect increases the recording density of the disk by nearly 2 times at once, so the study of giant magnetoresistance effect is of great significance to the development of magnetic storage.
The rise of CD and CD player in the audio-visual field benefits from the great development of optical storage technology. Optical disc storage records information in the form of light spots by modulating laser beams. Compared with magnetic storage technology, optical disk storage technology has large storage capacity and long storage life; Non-contact reading/writing and erasing, the optical head will not wear or scratch the disk surface, so the optical disk system is reliable and can be replaced freely; The carrier-to-noise ratio (CNR) does not decrease after repeated reading and writing. In the process of optical disc storage technology developing from CD(Compact Disk (CD) DVD(Digital Versatile Disk (DVD) to future high-density DVD(HD-DVD) and ultra-high-density DVD(SHD-DVD), the storage medium material is the key, and the optical disc material written once is ablative (Tc alloy thin film, Se-Tc amorphous film, etc.) and phase change type (Te-Ge-Sb amorphous film, AgInTeSb series film, doped ZnO film, push-pull azo dye, phthalocyanine dye) are the main materials of erasable and rewritable optical discs (GdCo, TeFe amorphous film, BiMnSiAl film, rare earth doped garnet series YIG, Co-Pt multilayer film). The storage density of optical disc depends on the wavelength of laser tube. When InGaAlP red laser tube (wavelength 65nm) is used for DVD disc, each side of disc with a diameter of 12cm can be stored as 4.7 gigabytes (GB), while when ZnSe (wavelength 515nm) is used, it can reach 12GB, and when GaN laser tube (wavelength 41nm) is used in the future, the storage density can reach 18GB. In order to read and write the information in the CD, a high-power semiconductor laser must be used, and the laser diode used is made of compound semiconductors such as GaAs and GaN.
besides being used in optical disk storage, lasers also play a well-known role in optical communication. With the semiconductor laser with low threshold, low power consumption, long life and fast response, optical fiber communication has become a reality. Optical communication means that the electric signal is changed into an optical signal by a semiconductor laser, then transmitted for a long distance by optical fiber, and finally changed from an optical signal into an electric signal for people to receive. Optical signals transmitted by optical fibers are emitted by lasers, and semiconductor lasers are commonly used, and the materials used are GaAs, GaAlAs, GaInAsP, InGaAlP, GaSb, etc. The photodetector used at the receiving end is also made of semiconductor material. Without optical fiber, optical communication can only be "an armchair strategist". Low-loss optical fiber is the key material of optical fiber communication. At present, the optical fiber sensing materials mainly include low-loss Shi Ying glass, fluoride glass, sulfide glass based on Ga2S3 and plastic optical fiber. One kilogram of Shi Ying-based optical fiber can replace tons of copper-aluminum cables. The emergence of optical fiber communication is a revolution in information transmission, which has the advantages of large information capacity, light weight, small occupied space, anti-electromagnetic interference, less crosstalk and strong confidentiality. The rapid development of optical fiber communication has played a vital role in the construction and opening of modern information superhighway.
in addition to wired communication, information is also transmitted wirelessly. The most striking development in wireless communication is the mobile phone. The more users there are in mobile phones, the higher the frequency they use. Now, they are transitioning to gigacycles. The microwave transmission and reception of telephones are also realized by semiconductor transistors, some of which are being replaced by GaAs transistors. Piezoelectric materials in high-frequency surface acoustic wave (SAW) and bulk surface acoustic wave (BAW) devices widely used in mobile phones are piezoelectric crystals such as a-SiO2, LiNbO3, LiTaO3, Li2B4O7, KNbO3, La3Ga5SiO14 and ZnO/ Al2O3 and SiO2/ZnO/DLC/Si are high sonic thin film materials, and the microwave dielectric ceramic materials used are concentrated in BaO-TiO2 _ 2 system, Bao-LN _ 2O _ 3-TiO _ 2 (ln = La, PR, Nd, SM, EU, GD) system and composite perovskite A (B1/3B ~ 2/3) O3 system (A). B=Mg,Zn,Co,Ni,Mn； B = Nb, Ta) and lead-based composite perovskite system.
with the increasing demand of intelligent instruments for high-precision thermistors, as well as the rapid popularization of hand-held telephones, PDA's, notebook computers and other portable information and communication devices, there is a great demand for temperature sensors and thermistors. Negative temperature coefficient (NTC) thermistors are sintered by mixing metal oxides such as Co, Mn, Ni, Cu, Fe, Al, etc., and their resistance decreases exponentially with the increase of temperature, and the resistance value is-. Positive temperature coefficient (PTC) thermistors are generally made of BaTiO3 material with a small amount of rare earth elements and sintered at high temperature. When the temperature of this material rises to Curie temperature, its resistance will suddenly increase exponentially, and the resistance-temperature change rate is usually between 2% and 4%. The former is widely used in the rapid charging of Ni-Cd, Ni-MH and lithium batteries, the adjustment of image contrast of liquid crystal display (LCD), and the temperature compensation crystal oscillator widely used in cellular phones and mobile communication systems to compensate the temperature to ensure the stability of device performance. In addition, it is also found in micro-motors in computers, camera lens focusing motors, print heads of printers, servo controllers of floppy disks and drivers of pocket players. The latter can be used for over-current protection, degaussing of heaters, color TVs and monitors, starting delay of pocket compressor motors, and preventing thermal breakdown of constant effect transistor (FET) of notebook computers.
In order to ensure the smooth operation of information, there are many materials making contributions silently. For example, the materials used to make green batteries include MH alloy and Ni(OH)2 for the anode and cathode of Ni-MH battery, LiCoO2, LiMn2O4 and MCMB carbon for the anode and cathode of Li-ion battery, etc. Materials used for tantalum capacitors in mobile phones, PCs and digital audio/video devices such as digital cameras, MD players/recorders, DVD devices and game machines; Modern permanent magnet material Fe14Nd2B is very important in manufacturing permanent magnet electrodes, magnetic bearings, earphones and microwave devices. Printed circuit board (PCB) and ultra-thin new copper clad laminate (CCL) with high and low dielectric loss; Epoxy molding compound, alumina and aluminum nitride ceramics are packaging materials for semiconductors and integrated circuit chips; The key structures and process auxiliary materials for integrated circuits (high purity reagents, special gases, plastic packaging materials, lead frame materials, etc.) are endless. These new materials, which are brilliant in the vast material world, are playing an indispensable role in digital life.
With the development of science and technology, large-scale integrated circuits will usher in the era of deep sub-micron (.1mm) silicon microelectronics technology. Lines smaller than .1mm belong to the nanometer category, and its line width is close to the De Broglie number of electrons, and the transport and scattering of electrons inside the device will also show quantization characteristics. Therefore, the design of the device will face a series of thorny problems from the working principle and process technology of the device, which leads to the "limit" of silicon microelectronics technology. Because the speed of photons is much faster than that of electrons, and the frequency of light is much higher than that of radio, it is an inevitable trend for the carrier of information to change from electrons to photons in order to improve the transmission speed and carrier density. At present, many kinds of laser crystals and optoelectronic materials have been developed, such as N.