AFM-Based Characterization Method of Capacitive MEMS Pressure Sensors for Cardiological Applications

Abstract

Current CMOS-micro-electro-mechanical systems (MEMS) fabrication technologies permit cardiological implantable devices with sensing capabilities, such as the iStents, to be developed in such a way that MEMS sensors can be monolithically integrated together with a powering/transmitting CMOS circuitry. This system on chip fabrication allows the devices to meet the crucial requirements of accuracy, reliability, low-power, and reduced size that any life-sustaining medical application imposes. In this regard, the characterization of stand-alone prototype sensors in an efficient but affordable way to verify sensor performance and to better recognize further areas of improvement is highly advisable. This work proposes a novel characterization method based on an atomic force microscope (AFM) in contact mode that permits to calculate the maximum deflection of the flexible top plate of a capacitive MEMS pressure sensor without coating, under a concentrated load applied to its center. The experimental measurements obtained with this method have allowed to verify the bending behavior of the sensor as predicted by simulation of analytical and finite element (FE) models. This validation process has been carried out on two sensor prototypes with circular and square geometries that were designed using a computer-aided design tool specially-developed for capacitive MEMS pressure sensors.

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“…It has a capacitive sensing mechanism in which a silicon wafer is used as a diaphragm that bends due to external pressure. A cardiological implantable device is also reported in [131] with the combination of CMOS circuitry and monolithically fabricated MEMS pressure sensor. The reported sensor is a capacitive MEMS pressure sensor that works by measuring the deflection of the flexible top plate.…”

Performance evaluation of CCOs for the optimization of low-power pressure-based implantable wireless systems

“…Intelligent stents (iStents), or stents with sensing and communication capabilities, have been lately proposed as economic and innocuous alternatives for monitoring ISR [14][15][16][17][18][19][20][21][22][23]; although the aforesaid HF condition can also be monitored effectively if the pulmonary artery pressure is periodically measured by the use of an iStent, as theoretically proposed in [22]. Besides that, the V-LAP™ device, based on a self-expandable double umbrella as anchoring element, has been proposed to measure and transmit left atrial pressure (LAP) for HF follow-up [24].…”

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“…However, further work is still required to test biocompatibility and functional behavior of these designed devices under in vivo situations. Other important engineering problems found in the practical application of implanted intelligent stents, such as requirements of accuracy, reliability, low power, and reduced size, were described in [ 49 ] and will have to be addressed in each specific medical or clinical application. Artificial intelligence algorithms for real-time monitoring 3D-printed electrical impedance tomography (EIT) sensors have been recently presented, applied to the monitoring of lung deformation [ 50 ].…”