Design Of FBAR Micro-accelerometer

FBAR micro accelerometer is a novel electro-acoustic resonant micro accelerometer, which crossed the micro-inertial technology and RF MEMS technology. It has the potential to meet the comprehensive requirements for micro accelerometer used in critical applications, including high performance, reliability, stability and manufacturability. This paper aims to solve four crucial and foundamental problems: the force sensing mechanism, the structure design, the temperature compensation design and integrated manufacturing process of sensor head, Which has laid a solid theoretical foundation for future development of practical devices.Due to the current shortages for understand force sensing mechanism of FBAR micro accelerometer, this paper analyze the resonance frequency shifting under stress by starting from the First-principles calculation of elastic constants-stress characteristics of the wurtzite AlN and put forward a FBAR differential-synthetic method to establish the multiple dimensioned computing models for force sensing characteristics of FBAR.A novel FBAR-on-diaphragm structure of FBAR micro accelerometer sensor head is presented to avoid the manufacturability disadvantages of the existing two kinds of FBAR micro accelerometer sensor head structure. The integration of two-level transducer successfully is implemented by this structure, which transform the inertial force to the stress on the diaphragm and this stress are converted into the resonance frequency shifting of FBAR. A case of FBAR micro accelerometer with FBAR-on-diaphragm structure has been designed, its sensitivity is about several KHz/g.Considering the FBAR resonance frequency drift caused by the temperature variation, the method of element level which is added the temperature compensated layer and the method of system level which is set reference FBAR have been put forward to enhance the temperature stability of sensor head with FBAR-on-diaphragm structure.According to structure parameters of sensor head and MEMS silicon micromachining technology constraints, the process flow have been designed. The via-hole type AlN FBAR has been fabricated and measured. The design of FBAR-on-diaphragm structure and the feasibility of the process for the sensor head have been verified.