DUV Lithography for UHF resonators

The key concept related to the most impressive advancement in terms of technology in the recent past is related to the concept of miniaturization. In fact, scaling down the device dimensions, it is possible to explore many different additional application respect to the macro scale. This possibility has led to the realization of Microelectromechanical systems (MEMS) and Nanoelectromechanical systems (NEMS) which corresponds to devices whose dimensions are, respectively, in the micron or nanometer range. These kind of devices are not only smaller, they often exhibit better performances or allow additional opportunity compared to their bigger counterparts. These reasons explain why MEMS are capturing the research effort in many field such as automotive, medical, communications defense and aerospace. Putting the focus on the communication market, it is in strong development due to growing need of high connectivity, fast exchange and quantity of data. Part of this market is represented by the RF-MEMS based front-end which have been proposed with the aim to target at the same time: low power consumption, small size and a CMOS compatible system so that is possible to have an easy integration with the rest of the circuitry. The central element in the RF-MEMS front-end is represented by piezoelectric MEMS resonators that are mainly employed for the realization for filters and oscillators. In this category, among other researches, contour mode resonators (CMRs) represent a significant field of study since they allow to modify the working frequency by design with a single lithographic step. In this thesis, starting from the work already done by the supervisor Marco Liffredo and the CMRs knowledge present in the ANEMS Lab, the goal is to develop a new generations of CMRs able to reach the 5G frequency range up to 4GHz (the generation already fabricated works around 150MHz). To achieve that result, the impact of the most important design parameters have been investigated. First of all a preliminary set of 2D simulations have been performed to get as much information as possible without a heavy computational cost. Then a further set of 3D simulations have been done to analyze the missing parameters and obtain a model affordable enough to be considered for the development of a new layout. Since to increase the resonance frequency of the devices is required to scale down the critical dimension and because of the purpose of the device itself, which target the batch fabrication for front-end application, the ASML PAS 5500/350C DUV stepper has been selected as lithographic tool. Hence the process flow have been modified to allow the use of that machine and to fulfil the new design requirements. To prove the effectiveness of these changes, some fabrication test where performed and finally, once concluded, the stepper reticle have been written. This last step has been performed in CMi through direct laser writing exploiting the Heidelberg Instruments VPG200 tool.