Research On Key Technology Of Process Design And Processing Of Graphene Pressure Sensor

Graphene is a two-dimensional honeycomb material with hexagonal symmetry.It has excellent electrical and mechanical properties,ultra-high electron mobility and large specific surface area,so graphene is widely used in the field of sensors.Because graphene is composed of carbon monoatomic layer,compared with other kinds of sensors,there are some problems,such as small measurement range,easy to adsorb impurities in surrounding environment and denaturation,small application range of devices,poor consistency and can not be used for a long time,and so on.Graphene application is one of the most urgent problems to be solved.In this paper,a large range graphene pressure sensor is proposed.Based on the transmission medium of silicon nitride elastic diaphragm,the process of nano-film is optimized for the problems of unstable performance and poor consistency of graphene devices at present.The methods of BN/graphene/BN heterostructure and Cu-Sn-Cu solid-liquid eutectic bonding are proposed to protect graphene.In this paper,the design of the sensor scheme,the matching design between the sensor chip and the package substrate,the fabrication of the sensor chip and the package substrate,the sensor package and the evaluation of the quality of the sensor package are completed.The main research contents and achievements are as follows:?1?The whole scheme of a large number of range pressure sensors is proposed.According to the matching design,the process design of sensor chip and packaging substrate is completed.Based on the structure of sensor chip,the embedded electrode is corroded by wet method.The fabrication process planning and mask design of the sensor chip were completed by the process design of nano-film transfer and the preparation of sealing ring and bonding bump.Based on the structure of sensor packaging substrate,the etching process of pressure cavity,the fabrication of buried electrode,the preparation of insulating layer and the preparation of seal ring and bond bump are designed.The preparation process planning and mask design of sensor packaging substrate are completed.?2?The fabrication of sensor chip is completed.The process of buried electrode was studied and the transfer process of graphene was optimized.On the basis of the conventional process,the cleaning process was added to remove metal ions and other impurities,and the optical microscope was used to remove the impurities.The quality of graphene nanothin films was characterized by electrical measurements and Raman spectra.The results showed that the quality of heterojunction was improved obviously after optimizing the sensor structure and the transfer process of nano-films,and the impurities and folds were obviously reduced.?3?The bonding and packaging of the sensor are realized.The bonding quality was evaluated by interface analysis,electrical properties test,shear strength test and gas tightness test.The results show that there are only three layers of metal in the bonding interface,pure Sn and intermediate metal compounds are completely depleted,and the average shear strength is50.6 MPa.The resistance measurement results of Kelvin structure are similar to the theoretical estimates.The leakage rate is up to 2.64×10^-4Pa·cm³/s and has very good air tightness.?4?Study on the stability of graphene.By comparing the electrical properties of graphene before and after bonding,the results showed that the bonding and process did not cause damage to graphene.The results of further high temperature harsh environment?300°C,10 h?showed that the graphene resistance of the unfinished package changed by 54.9%,and the performance change of the completed package of graphene sensitive element was only 2.94%.Cu/Sn/Cu bonding is suitable for graphene pressure sensor.It is an effective solution to realize graphene practicality and improve device stability.