Micro-electromechanical systems or abbreviated to MEMS, are small systems in silicon substrates that are composed of electronic and mechanical components. All components of a MEMS are put on a substrate with lithographic techniques. The MEMS resonator at NXP (formerly the semiconductor division of Philips) are made with “micromachining” processes, which use technologies that are also used for the production of Integrated Circuits (ICs). Wafers with MEMS structure undergo several steps during the production of ICs. Each step entails a variation of the product to a greater or lesser extent. All these variations were simulated and a revealed a thorough understanding of the stable functioning of the MEMS.
Assess the variations of the production process on a MEMS resonator, with various FEM calculations, such as vibrations, stress, mechanical damping, acoustic losses and electrical capacitance.
In close conjunction with a few departments of NXP, the specifications were identified. On the basis of these a proposal was made as to what parts of the MEMS could be simulated. The simulation contained:
- Vibration calculations, natural frequencies, transfer functions
- Electrical capacitance
- Mechanical stress calculations as a consequence of some thermal process phases.
- Damping calculations of the vacuum and the resonator part
- Acoustic losses from the anchor of the resonator
A set of design criteria was composed on the basis of the simulations. This way the jitter and stable functioning could be guaranteed for a lifetime of more than 30 years.
Apart from these requirements the specifications also have to be recorded because of the manufacturability. Therefore, simulations were done to assess the stability of the oscillation frequency. The dimensions of the oscillator were also varied to analyse the stability of the production process. The influence of temperature and vacuum pressure were taken into account. The complex multi physics simulations resulted in a set of specifications for the production environment to lower the rate of defects.
In depth presentation of this project on COMSOL conference 2012 in Milan click here