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Flexible electronics is a technology that attaches inorganic/organic devices to flexible substrates to form circuits. Compared with traditional silicon electronics, flexible electronics refers to thin-film electronic devices that can be bent, folded, twisted, compressed, stretched, and even deformed into any shape but still maintain high-efficiency optoelectronic performance, reliability, and integration.
Countries such as the United States, Japan, South Korea and other countries have strategically deployed flexible electronics projects, and they will maintain a high-speed growth trend in high-precision fields for a long time. This is also a historical opportunity that my country should try to seize.
What are the commonly used materials for flexible electronics in FPC factories?
01 flexible substrate
In order to meet the requirements of flexible electronic devices, properties such as lightness, transparency, flexibility and stretchability, and insulation and corrosion resistance have become key indicators of flexible substrates.
Common flexible materials include: polyvinyl alcohol (PVA), polyester (PET), polyimide (PI), polyethylene naphthalate (PEN), paper sheets, textile materials, etc.
Polyimide material has the advantages of high temperature resistance, low temperature resistance, chemical resistance and good electrical characteristics. It is the most potential material for flexible electronics. Only in the selection of flexible substrates, in addition to the high temperature resistance characteristics, the flexible substrate Light transmittance, surface roughness and material cost are all factors to be considered when choosing.
Polydimethylsiloxane (PDMS) is also a widely recognized flexible material. Its advantages include convenience and easy availability, stable chemical properties, transparency and good thermal stability. Especially under ultraviolet light, the distinguishing characteristics of adhesion and non-adhesion make the surface easy to adhere to electronic materials.
Although PET has a low conversion temperature, between 70 and 80°C, PET is inexpensive and has good light penetration. It is a highly cost-effective material for transparent conductive films.
02 Metal Material
Metal materials are generally conductive materials such as gold, silver and copper, which are mainly used for electrodes and wires. For modern printing processes, conductive nano-inks are mostly used as conductive materials, including nanoparticles and nanowires. In addition to good electrical conductivity, metal nanoparticles can also be sintered into thin films or wires
03Organic Materials
Large-scale pressure sensor arrays are very important for the development of wearable sensors in the future. Pressure sensors based on piezoresistive and capacitive signal mechanisms have signal crosstalk, resulting in inaccurate measurements. This problem has become one of the biggest challenges in the development of wearable sensors.
Due to the perfect signal conversion and amplification performance of the transistor, the use of the transistor makes it possible to reduce signal crosstalk. Therefore, a lot of research in the field of wearable sensors and artificial intelligence is centered on how to obtain large-scale flexible pressure-sensitive transistors.
The p-type polymer materials traditionally used in field-effect transistor research are mainly thiophene polymers, and the most successful example is the poly(3-hexylthiophene) (P3HT) system. Naphthalenetetraimide and perylenetetraimide show good n-type field effect performance, and are the most widely studied n-type semiconductor materials, and are widely used in small molecule n-type field effect transistors.
04Inorganic semiconductor materials
Inorganic semiconductor materials represented by ZnO and ZnS have shown broad application prospects in the field of wearable flexible electronic sensors due to their excellent piezoelectric properties.
For example, a flexible pressure sensor based on directly converting mechanical energy into optical signals has been developed. This matrix takes advantage of the photoluminescence properties of ZnS:Mn particles.
The core of Lizhi Luminescence is photon emission caused by piezoelectric effect.
The electronic energy band of piezoelectric ZnS produces a squeeze effect under pressure to produce a tilt, which can promote the excitation of manganese ions, and the subsequent de-excitation process emits yellow light.
05Carbon material
Carbon materials commonly used in flexible wearable electronic sensors include carbon nanotubes and graphene. Carbon nanotubes have the characteristics of high crystallinity, good electrical conductivity, large specific surface area, micropore size can be controlled by the synthesis process, and the specific surface utilization rate can reach 100%.
Graphene has the characteristics of light, thin, transparent, and good electrical and thermal conductivity. It has extremely important and broad application prospects in sensor technology, mobile communication, information technology and electric vehicles;
In the application of carbon nanotubes, the conductive polymer sensor obtained by the composite of multi-armed carbon nanotubes and silver and obtained by printing, under 140% stretching, the conductivity is still as high as 20S/cm.
When carbon nanotubes and graphene are used in combination, highly stretched transparent field effect transistors can be prepared. It combines graphene/single-wall carbon nanotube electrodes and single-walled carbon nanotube grid channels with a corrugated inorganic dielectric layer. Due to the presence of the corrugated aluminum oxide dielectric layer, there is no change in the drain current under more than 1,000 stretch-diastolic cycles of 20% amplitude, showing good sustainability
Application areas of flexible electronics
01flexible electronic display
The flexible electronic display is a brand-new product developed on the flexible electronic technology platform. It is a variable and bendable display device made of soft materials. At present, flexible display modes (electronic paper technology, LCD, OLED, etc.) can be realized on display devices made on flexible substrates, such as writable e-books, U disk capacity display, etc.
02 Flexible energy storage
Flexible energy storage is an emerging energy storage technology that makes organic/inorganic material electronic devices on flexible/ductile plastic or thin metal substrates. With its unique flexibility/ductility and high-efficiency and low-cost manufacturing process, it is used in information, energy, Medical, national defense and other fields have broad application prospects, and have been successfully used in flexible electronic displays, organic light-emitting diodes OLED, printed RFID, thin-film solar panels, and electronic surface bonding.
For example, a foldable 210 mAh/hour battery made by Samsung is used in wearable devices. The thickness of the battery itself can be 0.3 mm thick, which can be bent and folded 50,000 times on a person’s wrist. There is no failure.
03Flexible Medical Electronics
The basic feature of flexible medical electronics is to integrate various electronic components on a flexible substrate to form a skin-like flexible circuit board, which has high flexibility and elasticity like skin.
Flexible medical electronics can be naturally integrated with human tissues for a long time, can accurately measure medical indicators, such as body temperature, respiration, blood pressure, ECG, etc., and provide real-time basic data for big data medical treatment.
04 flexible circuit board
Flexible Printed Circuit (FPC) is a highly reliable and excellent flexible printed circuit boardmade of polyimide or polyester film. It has the characteristics of high wiring density, light weight, thin thickness and good bendability, which perfectly fits the development theme of lightness, thinness and miniaturization.
The FPC industry is dominated by Japan, the United States and South Korea. In recent years, the increase in production costs has prompted the FPC industry to gradually shift its focus to domestic soft board factories.
At present, Japanese-funded enterprises occupy a leading position in the upper reaches of the industrial chain with first-mover advantages. They started late in China and are relatively weak.
In recent years, the flexible electronics market has expanded rapidly and has become a pillar industry in some countries, with broad application prospects in the fields of information, energy, medical care, and national defense. Shenlian Circuit FPCB Factory has been focusing on the production of FPC and Rigid-flex PCB for 19 years. It is the unanimous choice of well-known customers.
