The Application of Parylene in microelectromechanical technology

Parylene is a new type of polymer coating material launched by United Carbon Corporation in the 1960s. It is the common name for paraxylene polymere. At present, according to the different molecular structures, Parylene materials can be divided into various types such as Parylene N, Parylene C, Parylene D, Parylene F, Parylene HT, etc. Parylene C is mainly used as a high-purity passivation layer and dielectric layer in microelectronics and semiconductors. It can also be used as passivation, protection, lubrication and other coatings in microelectronics; In addition, it can also be used as isolation, solidification, and reinforcement materials in biomedical anti-corrosion and cultural relic protection.
Application of Parylene
Currently, most needle shaped electrodes are prepared using MEMS microsystem processing technology on a silicon substrate. The substrate is a flat hard substrate, which is not suitable for attaching to curved structures such as the cerebral cortex and cylindrical nerve bundle surfaces, and is particularly unsuitable for attaching to large-scale biological tissue surfaces. However, electrodes with flexible substrates typically have flat thin films with a certain height as their electrode contacts, without forming a needle tip structure. When used, they can only adhere to the surface of the cortex or nerve bundle, without the effect of needle tip penetration into biological tissue, and cannot achieve deep contact with biological tissue. The collected signal quality or stimulation effect is poor. Therefore, the existing microneedles have the problem of not being able to balance the flexible adhesion performance and needle tip penetration performance. In response to existing problems, the CN116965825A patent provides a flexible needle tip electrode and its preparation method. The specific preparation method is as follows:
(1) Provide SOI substrate;
(2) Etching the top silicon layer of the SOI substrate to form a silicon needle tip;
(3) Produce a flexible substrate layer, a conductive layer, and an insulation layer on the surface of the SOI substrate in sequence. Both the flexible substrate layer and the insulation layer can be made of flexible insulation materials. Flexible insulation materials can use any one of Parylene, Polyimide (PI), Ethylene terephthalate, etc. Among them, Perrin includes Parylene C, Parylene D, Parylene N, Parylene HT, etc.
(4) Release the buried oxygen layer on the SOI substrate to obtain a flexible needle tip electrode.
The flexible needle tip electrode prepared by this preparation method integrates the advantages of a hard needle tip and a flexible substrate, which can better adhere to the surface of the cerebral cortex or nerve bundle. At the same time, it can also make the needle tip electrode deeply contact with biological tissues, ensuring the quality of collected signals and stimulation effects; Moreover, the overall integrity of the silicon needle tip and flexible substrate in this patented technology is good, and it is not easy for the silicon needle tip to fall off. Moreover, the size of the silicon needle tip can reach micrometers or even nanometers, making it easy to achieve industrial batch production.

References
CN116965825A A flexible needle tip electrode and its preparation method.