Design et fabrication d'un senseur de pression sans fil implantable

The aim of this project is to design and fabricate a wireless implantable pressure sensor. This device is conceived to be part of a complete system to allow urologists to conduct their urodynamic tests wirelessly through the implantation of the sensor into the patient bladder. Actually, urodynamic tests are via catheters which are uncomfortable for the patient and can induce a bias in the result by obstructing the urethra. The pressure sensor is the centrepiece of a whole wireless urodynamic system developed to address these problems.; There are different types of pressure sensors but a capacitive pressure sensor in contact mode has been chosen for this application because its characteristics are perfect for this project. Once the sensor type is chosen, we need a way to predict its behaviour under pressure. An analytical model has been programmed in Matlab language to simulate the sensor response. This simulation furnishes all the information necessary to determine the optimum dimensions for the sensor to insure maximum sensibility. The results of this model are then compared to the results from a finite element analysis program specialized in micro electromechanical systems design and simulation, the Coventor suite. The correlation between the two models is fine, but it mainly illustrates the limits of finite elements analysis as the computer used did not have enough memory to verify the convergence of its solutions. The mesh size needed to confirm the results from the finite element analysis was too fine for the computer available, a recent and powerful personal computer.; The sensors dimensions are chosen with the help of the two simulations and the masks are fabricated in the laboratory using a photographic process. Due to the fact that the Poly-Grames laboratory is a microwave lab and not a microfabrication one, a modular approach was chosen. The different parts of the sensors are fabricated separately and then assembled using a pick and place tool. The parts are batch-produced using the following microfabrication techniques: photolithography, wet etching, plasma assisted chemical vapour deposition, sputtering, evaporation and electroplating.; Numerous techniques have been developed to seal the cavity under vacuum. It is important to seal the cavity with minimum pressure because of the dampening effect introduced by the presence of air when it is compressed by the sagging membrane. Two eutectic soldering techniques were tried without success. However, the manual assembly of the parts using conductive and non-conductive epoxy was successful and allowed the fabrication of many sensors with a free moving membrane. All the attempts to seal the sensor under vacuum were unsuccessful.; It is however possible to measure the behaviour of the sensor exactly as it would be if the cavity was vacuum sealed by piercing a hole that connects the cavity with the exterior and by applying different pressure on the two sides of the sensor. Measures have shown that some force is preventing the membrane to touch the bottom of the sensor under air pressure, but the membrane has been observed to sag. Moreover, the membrane touches the bottom and a measurement can be done when the pressure is exerted mechanically. This phenomenon indicates the presence of pinholes in the membrane that can allow the air to pass into the cavity. The air is evacuated through the hole, but its presence in the cavity creates an air cushion that prevents the membrane from touching the bottom of the sensor. Limited time did not allow us to resolve this problem, but the solutions are simple but costly, like the fabrication of the membrane using only sputtering or evaporation.