Study, design and characterization of a CMOS vibration and dynamic strain sensing microsystem

Details

Supervisors

Flandre, Denis

Faculty

Ecole polytechnique de Louvain

Degree label

Master [120] : ingénieur civil électricien, à finalité spécialisée

Abstract

Structural Health Monitoring is one of the most important tools for maintaining the safety and integrity of structures, such as in the fields of civil engineering or aerospace. Because the consequences of inadequate structural integrity monitoring leading to failure can be devastating, it is important to be able to detect the smallest defect in a structure as quickly as possible. An increasing number of powerful technologies are emerging in the field of structural monitoring. This work is based on the study and dynamic characterization of strain sensor exploiting the piezoresistive effects of silicon in CMOS technology. Silicon is a semiconductor material with a high sensitivity to deformation, mainly due to its intrinsic piezoresistive properties, which derive from its crystalline structure and the modulation of charge carrier mobility under stress. The combination of these properties with the ease of integration of silicon into electronic systems makes it an ideal candidate for use in strain sensors. The two main objectives and results of this work are: firstly, to develop a model based on an experimental setup consisting in a vibration generator, which is simulated by a piezoelectric actuator, and a strain sensor. An initial model has been established using a simple silicon strain gauge as a sensor with a gauge factor of 150. The model has been studied, simulated, tested and validated in the WELCOME laboratories at UCLouvain. Secondly, the strain gauge has been substituted with a CMOS strain sensor developed and patented at UCLouvain. This is a self-biased current reference circuit with a high supply rejection based on a $\beta$-multiplier configuration. Two distinct topologies have been analysed. The first involves eight transistors and a resistor, while the second is a full-transistor configuration. These devices demonstrate a gauge factor of over 300 in a previous work. The frequency responses of the two topologies have been extracted over a wide frequency range while subjected to excitations, ranging from a few hertz to hundreds of kilohertz. An additional static operation study at high temperatures, up to 80°C, and a differential analysis before and after bonding the sensor have been carried out.