Modelado y desarrollo de microcantilevers resonantes para sensores

Esta tesis está enfocada en el diseño, simulación, fabricación y caracterización de sensores de masa basados en microcantilevers de silicio. Los cantilevers con forma de T son diseñados como estructuras formadas por 3 vigas unidas en su extremo por medio de una masa rectangular extra. Los cantilevers son excitados para alcanzar su resonancia mecánica, en modo flexión perpendicular al sustrato, con un piezoactuador PZT pegado en la parte posterior del sustrato y la frecuencia de resonancia es monitoreada por cuatro piezoresistencias configuradas en un puente de Wheastone. Diversos cantilever son fabricados variando su proceso de fabricación, dimensiones y geometrías, su operación es verificada y su desempeño mecánico y eléctrico evaluado. El desempeño del dispositivo es comparado con los valores obtenidos del modelo analítico y de las simulaciones con ANSYS, obteniendo buena concordancia. Se seleccionan las dos estructuras con los mayores valores de frecuencia de resonancia y factor de calidad. Para el primer cantilever, de 400μm de largo, 300μm ancho y 15μm de espesor, la frecuencia de resonancia, del primer y segundo modo de vibración, se encuentra en 97kHz y 690kHz respectivamente, ambos con un factor de calidad de ~800. Para el segundo cantilever, de 200μm de largo, 150μm ancho y 15μm de espesor, la frecuencia de resonancia fundamental se encuentra en 400kHz con un factor de calidad de ~900. Los dispositivos son caracterizados como sensores de masa al adherir microesferas de poliestireno a la superficie del cantilever y medir los cambios en la frecuencia. Para el primer cantilever, los valores de sensibilidad de masa son: 12,4pg/Hz y 3,1pg/Hz para el primer y el segundo modo respectivamente y 0,8pg/Hz para el segundo cantilever. Además, los cantilevers son caracterizados como sensores de gas al recubrir su superficie con PDMS, exponerlos a vapor de etanol y medir los cambios en la frecuencia. Para la primera y segunda estructura, el valor de sensibilidad al etanol es de 13,2ppm/Hz y 0,6ppm/Hz respectivamente. Estos resultados ilustran el alto potencial para utilizar estas sencillas estructuras como plataforma en aplicaciones sensitivas.This work has been focused on the design, simulation, fabrication and characterization of silicon microcantilevers based mass sensors. The T-shape cantilever was designed as a structure formed by 3 cantilevers that are hold together by means of an extra rectangular mass. Cantilevers were driven at their mechanical resonance in flexural mode perpendicular to the substrate by a ceramic-insulated multilayer piezoactuator PZT glued at the backside and the resonance frequency was monitored by reading the signal generated by four piezoresistors in a Wheatstone bridge configuration. Several cantilevers structures have been fabricated with different process, dimensions and geometries, its operation verified and their mechanical and electrical performance evaluated. Device performance was compared with analytical model and simulation predictions obtained using ANSYS achieving good agreement. Two different structures were selected based on the high resonance frequency and quality factor values. For the first cantilever of 400μm long, 300μm wide and 15μm thick, the fundamental and second resonance frequency in air were 97kHz and 690kHz respectively, both with a quality factor of ~800. And for the second cantilever of 200μm long, 150μm wide, 15μm thick the fundamental resonance frequency in air was 400kHz with a quality factor of ~900. The devices were characterized as mass sensor attaching microspheres of polystyrene to the cantilever’s surface tip and measuring resonance frequency changes. For the first cantilever mass sensitivity values of 12,4pg/Hz and 3,1pg/Hz for the fundamental and second mode respectively were achieved and 0,8pg/Hz for the second cantilever. Also the cantilevers were characterized as gas sensor, covering the cantilever’s surface tip with PDMS, exposing it to ethanol vapor and measuring resonance frequency changes. For the first cantilever ethanol sensitivity values of 13,2ppm/Hz were achieved and 0,6ppm/Hz for the second cantilever. These results show the great potential for high sensitive sensor of this simple device

Modelado y desarrollo de microcantilevers resonantes para sensores

Descripció del recurs: el 13 setembre 2011Esta tesis está enfocada en el diseño, simulación, fabricación y caracterización de sensores de masa basados en microcantilevers de silicio. Los cantilevers con forma de T son diseñados como estructuras formadas por 3 vigas unidas en su extremo por medio de una masa rectangular extra. Los cantilevers son excitados para alcanzar su resonancia mecánica, en modo flexión perpendicular al sustrato, con un piezoactuador PZT pegado en la parte posterior del sustrato y la frecuencia de resonancia es monitoreada por cuatro piezoresistencias configuradas en un puente de Wheastone. Diversos cantilever son fabricados variando su proceso de fabricación, dimensiones y geometrías, su operación es verificada y su desempeño mecánico y eléctrico evaluado. El desempeño del dispositivo es comparado con los valores obtenidos del modelo analítico y de las simulaciones con ANSYS, obteniendo buena concordancia. Se seleccionan las dos estructuras con los mayores valores de frecuencia de resonancia y factor de calidad. Para el primer cantilever, de 400μm de largo, 300μm ancho y 15μm de espesor, la frecuencia de resonancia, del primer y segundo modo de vibración, se encuentra en 97kHz y 690kHz respectivamente, ambos con un factor de calidad de ~800. Para el segundo cantilever, de 200μm de largo, 150μm ancho y 15μm de espesor, la frecuencia de resonancia fundamental se encuentra en 400kHz con un factor de calidad de ~900. Los dispositivos son caracterizados como sensores de masa al adherir microesferas de poliestireno a la superficie del cantilever y medir los cambios en la frecuencia. Para el primer cantilever, los valores de sensibilidad de masa son: 12,4pg/Hz y 3,1pg/Hz para el primer y el segundo modo respectivamente y 0,8pg/Hz para el segundo cantilever. Además, los cantilevers son caracterizados como sensores de gas al recubrir su superficie con PDMS, exponerlos a vapor de etanol y medir los cambios en la frecuencia. Para la primera y segunda estructura, el valor de sensibilidad al etanol es de 13,2ppm/Hz y 0,6ppm/Hz respectivamente. Estos resultados ilustran el alto potencial para utilizar estas sencillas estructuras como plataforma en aplicaciones sensitivas.This work has been focused on the design, simulation, fabrication and characterization of silicon microcantilevers based mass sensors. The T-shape cantilever was designed as a structure formed by 3 cantilevers that are hold together by means of an extra rectangular mass. Cantilevers were driven at their mechanical resonance in flexural mode perpendicular to the substrate by a ceramic-insulated multilayer piezoactuator PZT glued at the backside and the resonance frequency was monitored by reading the signal generated by four piezoresistors in a Wheatstone bridge configuration. Several cantilevers structures have been fabricated with different process, dimensions and geometries, its operation verified and their mechanical and electrical performance evaluated. Device performance was compared with analytical model and simulation predictions obtained using ANSYS achieving good agreement. Two different structures were selected based on the high resonance frequency and quality factor values. For the first cantilever of 400μm long, 300μm wide and 15μm thick, the fundamental and second resonance frequency in air were 97kHz and 690kHz respectively, both with a quality factor of ~800. And for the second cantilever of 200μm long, 150μm wide, 15μm thick the fundamental resonance frequency in air was 400kHz with a quality factor of ~900. The devices were characterized as mass sensor attaching microspheres of polystyrene to the cantilever's surface tip and measuring resonance frequency changes. For the first cantilever mass sensitivity values of 12,4pg/Hz and 3,1pg/Hz for the fundamental and second mode respectively were achieved and 0,8pg/Hz for the second cantilever. Also the cantilevers were characterized as gas sensor, covering the cantilever's surface tip with PDMS, exposing it to ethanol vapor and measuring resonance frequency changes. For the first cantilever ethanol sensitivity values of 13,2ppm/Hz were achieved and 0,6ppm/Hz for the second cantilever. These results show the great potential for high sensitive sensor of this simple device

CMOS-MEMS capacitive sensors for intra-cranial pressure monitoring : sensor fabrication & system design

Low-frequency variation of intracranial pressure (ICP) is a key indicator determining the successful outcome of a patient, subjected to traumatic brain injury (TBI). Post-trauma ICP increase can lead to fatal secondary injuries and hence continuous ICP monitoring would be an essential modality required in a neuro-monitoring system. This paper discusses the system design considerations of an integrated CMOS-MEMS sensor system for monitoring ICP in patients subjected to TBI. Design and fabrication steps of the on-chip CMOS-MEMS sensor are presented first. Interface circuit design challenges introduced by the low, not-well-controlled MEMS sensitivity and large offset due to the fabrication tolerance are discussed next. A review and comparison of the reported capacitive sensors and their interface circuits follows. The paper concludes discussing the biocompatible packaging of the system for in-vivo testing

pH measurement IoT system for precision agriculture applications

This paper presents the design and validation of a pH measurement IoT system for Precision Agriculture applications. The system is based on an IoT architecture which consist on: data acquisition and processing, information, centralization and access to users. The design process of each module is reported as well as its experimental validation process. With a -0.058V slope for pH measurement and RMSE of 0.037 for the calibration model, we demonstrated the capability of the system to perform measurements at multiple points in large areas

A Monolithically Integrated Pressure/Oxygen/Temperature Sensing SoC for Multimodality Intracranial Neuromonitoring

A fully integrated SoC for multimodality intracranial neuromonitoring is presented in this paper. Three sensors including a capacitive MEMS pressure sensor, an electrochemical oxygen sensor and a solid-state temperature sensor are integrated together in a single chip with their respective interface circuits. Chopper stabilization and dynamic element matching techniques are applied in sensor interface circuits to reduce circuit noise and offset. On-chip calibration is implemented for each sensor to compensate process variations. Measured sensitivity of the pressure, oxygen, and temperature sensors are 18.6 aF/mmHg, 194 pA/mmHg, and 2 mV/°C, respectively. Implemented in 0.18 m CMOS, the SoC occupies an area of 1.4 mm × 4 mm and consumes 166 μW DC power. A prototype catheter for intracranial pressure (ICP) monitoring has been implemented and the performance has been verified with ex vivo experiment.ASTAR (Agency for Sci., Tech. and Research, S’pore