Laboratoire TIMA Micro-Nano-Systems Group 46 Avenue Félix Viallet 38031 Grenoble Cedex. France. Tel: 00 33 4 76 57 43 06 - Fax: 00 33 4 76 57 49 81

Proposition de thèse Durée : 36 mois à partir d’octobre 2015

Micro- capteurs pour des applications en acoustique Laboratoire : TIMA Directeur de thèse : Libor RUFER, [email protected], Tél. : 04 76 57 43 06 Co-encadrant : Skandar BASROUR, [email protected], Tél. : 04 76 57 43 07 Lieu d'exercice : TIMA Laboratory, 46 Avenue Félix Viallet, Grenoble, France, (http://tima.imag.fr)  

MEMS Sensors for Applications in Acoustics Keywords: MEMS, Sensor, Microphone, Acoustics, FEA, Modeling, Piezoelectricity. Introduction: In the last decade, MEMS-based microphones have reached maturity and become a part of many mobile devices. Most of these devices require sensors covering entirely or partially the audible frequency range. Industries such as high-speed train, supersonic aviation and defense demand a development of advanced aero-acoustic microphones with a wide frequency band and a large dynamic range. Such sensors are needed to characterize ultrasonic wave generation, shock waves, and propagation associated with acoustic scaled models used in research and development tasks. Sensors with such advanced properties do not exist today. Recently, TIMA contributed to a development of an acoustic sensor of air-borne sound exceeding considerably a high-frequency limit of standard measuring microphones. Among different transduction approaches applicable to microphones, electrostatic and piezoresistive principles were studied in previous developments. The piezoelectric effect in aluminum nitride (AlN) will be exploited in the frame of this work. Scientific challenges: Microphones are one of the hottest growth areas of MEMS. Prior MEMS microphone implementations in the literature have primarily utilized other transduction mechanisms than the piezoelectric one and the vast majority of developed microphones has targeted consumer audio applications and, thus, has not reached the performance levels necessary for use in aeroacoustic measurements. Until recently, difficulties in fabrication and limited commercial availability of AlN films, despite its attractive properties, resulted in very little attention to this material for use in microfabricated microphones. The main challenge of this work is to take advantage of the current industrial maturity of AlN for the development of a novel device. An important challenge consists in the fact to use a newly available technology process for a novel sensor with advanced specifications.

Tasks: The aim of the project is to develop a piezoelectric (AlN) microphone satisfying the specifications of a large frequency and dynamic range (10 to 600 kHz; 40 to 4 000 Pa). In the first step, the candidate will propose, based on previous works, a microphone design feasible with the resources available to the TIMA Laboratory (CMP – Multi-Project Circuits). The detailed modeling of the device must combine the heterogeneous physical components of the device with coupled-field analysis of the piezoelectric transduction. The second step will be devoted to the sensor fabrication and test. A part of the fabrication will be realized through a multi-project wafer (MPW) processing. Additional fabrication steps will be performed in the CIME Nanotech (Centre Interuniversitaire de Microélectronique et nanotechnologies). A detailed characterization of fabricated structures will be carried out. Different material and structure characteristics as Young's modulus, quality factor, and residual stress will be measured in order to optimize the fabrication process. Later, electro-acoustic performance of the microphone will be verified and the microphone will be validated in a real application. Finally, in the third step, based on an analysis of obtained results, requirements towards a final fabrication process will be gathered. These requirements, including mainly the AlN layer thickness, its orientation, and piezoelectric coefficients values, will be used to focus an AlN process provider for an ultimate design. Other possible development steps include a preamplifier stage design (creating a system on a same chip (SoC) or in a same package (SiP)) or matrix of microphones design (enabling more advanced measurements in complex acoustic fields). Working Context: The proposed project is based on the collaboration with the team of the Acoustic Centre from the LMFA of the Ecole Centrale, Lyon and the Laboratory SIMAP, Grenoble. The PhD student will work at the TIMA Laboratory / MNS Group and will collaborate with members of the SIMAP on the process definition and with members of the LMFA on the validation and the final test of the device. Based on the existing collaboration, the Salento University, Lecce (Italy) will be considered as a back-up technology provider. Prerequisites: (Desired but not required) - Basic knowledge of microelectronic and microsystems technology. - Basic knowledge of mechanical vibrations and elasticity. - Experience with ANSYS or other FEA software.