| Graphene is a kind of two-dimensional nano-film material with excellent mechanical and electrical properties,allowing it to be applied to pressure sensors as a sensitive unit.At present,some achievements have been made in the research of graphene pressure sensors,but most of them are oriented to low temperature and range,because graphene is easy to pollute and oxidize under high temperature and aerobic environment,therefore,the protection of graphene has become a key technology in the fabrication of graphene MEMS pressure sensors.Based on this,a novel fabrication method of graphene MEMS pressure sensor using Si Nx film to protect graphene and dual bonding to keep graphene in oxygen-free and hermeticity environment is proposed.Firstly,The anaerobic packaging graphene pressure sensor chip is designed.The whole structure of the sensor is determined by the energy band theory of graphene,the chip is divided into three parts,each part is interconnected by metal bonding,and bonding structure and metal layer are designed in detail,then the process flow of the sensor are designed,and the corresponding photolithographic plate is drawn by the software.Finally,two kinds of packaging are designed to meet the different temperature environment.Then,the process technology of graphene pressure sensor chip based is explored.The preparation technology of silicon elastic diaphragm,wet transfer and patterning of graphene nanofilms,sealing ring and bonding bump,and the etching technology of cross beam structure are discussed in detail,the metal bonding process is used to realize the oxygen-free package interconnection of each part of the sensor chip,the chip is welded to the package shell by nano-silver,and the wire leads to complete the whole sensor processing.Finally,the samples of the sensor were tested and characterized.The transfer quality,bonding quality and sensor properties of graphene were characterized.No obvious defects were observed on the surface of the graphene by optical microscopy,and electrical measurements showed no change in the resistance of the graphene after bonding,the results of graphene temperature experiments show the necessity of oxygen-free encapsulation of graphene at high temperatures.The excellent bonding quality was demonstrated by interface analysis,shear strength test,hermetic test and high temperature store test.It was proved that dual bonding can keep graphene in oxygen-free state for a long time at high temperature.The average shear strength of dual bonding is 14.3 MPa,and the leakage rate is up to 1.72×10-4Pa·cm3/s.After 350℃high temperature stored（HTS）for 10 h,the shear strength and the leakage rate of the device remain almost unchanged.The average sensitivity of the sensor is found at 0 to 100 MPa is 3.11Ω/MPa by static test,and the sensor has high repeatability,which shows that the dual bonding is suitable for packaging the graphene pressure sensor and it is an effective solution to realize practical graphene and improve the stability of devices. |
