PhD Thesis

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« Microsystem design and integration on a cylinder for strain measurement: application to a medical instrument ».

Author: W. Yang
Advisor: S. Basrour
thesis reviewer(s): Ch. Malhaire ,
These de Doctorat Université de Grenoble
Speciality: Micro et Nano Electronique
Defense: November 24 2011
ISBN: 978-2-84813-179-9


This thesis aims at developing an instrumented cylinder that allows measuring its deflection status during medical interventions. Two types of material are used to fabricate the cylinder: the stainless steel and the NiTi. The microgauges located along the cylinder enable the real-time measurement of the strain distribution, thus allowing the guidance of the cylinder to its planned target in surgical operations. Upon presentation and comparison of several approaches of strain measurement, the method using semiconductor piezoresistive strain microgauges integrated on the cylinder appears to be the optimal solution, in terms of measurement sensitivity, bio-compatibility and microfabrication facility. The theoretical analysis and finite element method analysis are carried out to analyze the mechanical characteristics of the cylinder in deflection. These analyses also serve to determine the positioning and the dimensions of the piezoresistive strain microgauges on the cylinder. A primary prototype has been implemented and characterized in order to verify the functionality of the system. The microgauges are implemented on thin cylinders by microfabrication in the cleanroom. Germanium works as the piezoresistive material for the microgauges. Due to the topological particularities of the cylinders as the substrate for microfabrication, several adjustment measures are taken into the fabrication process on curved metal substrates, in regard to the standard process of material deposition and surface micromachining. The fabrication result is presented, and the potential improvements of the current process are discussed.

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