Design and prototyping of beol-embedded cmos-mems accelerometers
- Autores: Piotr Jozef Michalik
- Directores de la Tesis: Jordi Madrenas Boadas (dir. tes.), Daniel Fernández Martínez (codir. tes.)
- Lectura: En la Universitat Politècnica de Catalunya (UPC) ( España ) en 2015
- Idioma: español
- Tribunal Calificador de la Tesis: Maria Aranzazu Uranga del Monte (presid.), Joan Pons Nin (secret.), Josep Montanyá i Silvestre (voc.)
- Programa de doctorado: Programa Oficial de Doctorado en Ingeniería Electrónica
- Materias:
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- Resumen
In the last two decades, MicroElectroMechanical Systems (MEMS) accelerometers and other inertial sensors have demonstrated a steady trend of miniaturization as well as price and power consumption reduction, while maintaining other performance parameters. This triggered their ubiquitous use in high-volume consumer electronics devices like smart phones, tablets, video game consoles or wearables to name a few.
Currently one of the bottlenecks to maintain the price and size reduction trends is a necessity of using a custom MEMS fabrication process. The commercial MEMS accelerometers and gyroscopes are either multi-chip modules (MEMS chip plus electronics chips), or a separate MEMS process is applied to the same wafer in order to deploy the sensor next to the electronics. CMOS micromachining, where standard CMOS back-end of line (BEOL) interconnection layers are used as MEMS structural and sacrificial materials could be a possible breakthrough. An approach based on reactive ion etching of full interconnection stack followed by a substrate etching is currently the most-popular CMOS-MEMS integration method, however due to its limitations it has not reached significant success outside academia. More recently with the advent of RF-oriented microelectronic technologies significant effort has been made to develop RF-MEMS devices like switches or resonators by using simple isotropic etching of inter-metal dielectric (IMD) of the CMOS BEOL. In this thesis it is demonstrated that thanks to the appearance of thick metal and via layers used normally in these technologies for inductors and power routing, this method can be also applied to integrate on-chip accelerometers. The main advantage of the pursued approach is its technological simplicity, that results in potentially ultra-low production cost and feasibility (not demonstrated yet though) of deploying a sensor above electronics (as no substrate etching is required). Such devices could become new IP cores ready-to-integrate in more complex systems on a chip (SoC).
This dissertation presents the design and prototyping process of CMOS monolithic acceleration sensors obtained using simple isotropic IMD etching of CMOS BEOL interconnection stack without any substrate etching steps. To the best of the author¿s knowledge such devices had not been reported before this work. The developments start from the MEMS post-CMOS process experiments and characterization that lead to first working accelerometer prototypes, which are further integrated on one chip with the sensing electronics. The final integrated devices are capable of 3-axis sensing, exhibit acceleration noise below 80 µG/vHz at 1.38 mW power consumption per axis and show a room for further improvement.
