In this study, ZnO film bulk acoustic resonators (FBARs) are proposed to fabricate the mass sensor of high sensitivity. The acoustic cavity is achieved by potassium hydroxide (KOH) etching. The FBAR structures are made of highly C-axis-oriented piezoelectric ZnO thin films using the technique of two-step deposition method. The titanium (Ti) seeding layer, platinum (Pt) bottom electrode, and aluminum (Al) top electrode were deposited by DC sputtering system using a dual gun. Finally, The remnants of silicon and silicon nitride (SiNx) are removed by reactive ion etching (RIE) etching. Furthermore, the two resonant frequencies of longitudinal mode and shear mode had been obtained. From the experimental results of loading effect with titanium and molybdenum, the mass sensitivity of the longitudinal mode and the shear mode are about 3200 Hz cm /ng and 1100 Hz cm /ng respectively, which are larger than those of quartz resonator or other reports. The measurement system was composed of a thermoelectric cooling module to investigate the temperature coefficient of frequency (TCF) of the mass sensor, which is about -70.67 ppm/. Bisides, the positive TCF material, silicon dioxode (SiO2) is deposited on ZnO thin films for the purpose of improving the TCF of FBAR devices. For SiO2/ZnO FBAR devices, the SiO2 reveal the compensation of TCF.

No description available.

Resonant microcantilevers are promising transducers for bacteria detection because of their high sensitivities. Surface stress and mass from adsorbates affect the resonant frequency. We developed a novel method for decoupling the frequency contributions of a change in mass and surface stress on a cantilever sensor validated in theoretical, finite element and experimental framework. Bacteria capture was achieved by several different chemical immobilization of T4 phages. The most successful bacteria capturing surface produced bacterial densities of about 11 bacteria/100^m2. The developed theory is then applied to determine captured bacterial mass on the cantilevers. This provides an estimate of the bacteria mass on the cantilever. Two different functionalizations resulted in predicted bacterial densities of 5 bacteria/100^m2 and 3 bacteria/100^m2. Poor densities relative to surface capture experiments is caused by the boundary effects of the cantilever in solution. / Microelectromechanical Systems and Nanosystems

<div>With an eye towards applications such as the selective sensing of volatile organic compounds (VOCs) or micro-scale thrust generation, inkjet printing was explored as a means to selectively deposit functional materials. The work detailed herein explores a series of fundamental steps to gain expertise related to the piezoelectric inkjet printing of functional materials. The successful printing of nanothermite was demonstrated with two unique printing techniques. Furthermore, the integration of this material with an ignition mechanism was shown to create a fully printed igniter energetic system. These advancements support future work related to the printing of other energetic materials necessary to create tunable reactive systems. This knowledge was then translated into the development of resonant mass sensing devices that are selectively functionalized using inkjet printing. This approach to functionalization allowed for the precise deposition of receptive chemistries on devices resulting in selective, highly-sensitive devices that successfully detected biomarkers secreted after traumatic brain injuries and harmful VOCs. This work implemented oscillator-based sensors to achieve a low-cost, low-power sensor platform with redundant elements. Furthermore, the predictive capabilities of these devices were explored using least squares and linear regression modeling.</div>

An analog controller has been analyzed and built for an electrostatic micro-cantilever beam. The closed loop MEMS device can be used as both actuator and sensor. As an actuator it will have the advantage of large stable travel range up to 90% of the gap. As a sensor the beam is to be driven into chaotic motion which is very sensitive changes in the system parameters. Two versions of the controller have been analyzed and implemented, one for the actuator and one for the sensor. For the actuator, preliminary experiments show good matching with the model. As for the sensor, the dynamic behavior have been studied and the best operating regions have been determined.

An analog controller has been analyzed and built for an electrostatic micro-cantilever beam. The closed loop MEMS device can be used as both actuator and sensor. As an actuator it will have the advantage of large stable travel range up to 90% of the gap. As a sensor the beam is to be driven into chaotic motion which is very sensitive changes in the system parameters. Two versions of the controller have been analyzed and implemented, one for the actuator and one for the sensor. For the actuator, preliminary experiments show good matching with the model. As for the sensor, the dynamic behavior have been studied and the best operating regions have been determined.

abstract: Micro-electro-mechanical systems (MEMS) film bulk acoustic resonator (FBAR) demonstrates label-free biosensing capabilities and is considered to be a promising alternative of quartz crystal microbalance (QCM). FBARs achieve great success in vacuum, or in the air, but find limited applications in liquid media because squeeze damping significantly degrades quality factor (Q) and results in poor frequency resolution. A transmission-line model shows that by confining the liquid in a thickness comparable to the acoustic wavelength of the resonator, Q can be considerably improved. The devices exhibit damped oscillatory patterns of Q as the liquid thickness varies. Q assumes its maxima and minima when the channel thickness is an odd and even multiple of the quarter-wavelength of the resonance, respectively. Microfluidic channels are integrated with longitudinal-mode FBARs (L-FBARs) to realize this design; a tenfold improvement of Q over fully-immersed devices is experimentally verified. Microfluidic integrated FBAR sensors have been demonstrated for detecting protein binding in liquid and monitoring the Vroman effect (the competitive protein adsorption behavior), showing their potential as a promising bio-analytical tool. A contour-mode FBAR (C-FBAR) is developed to further improve Q and to alleviate the need for complex integration of microfluidic channels. The C-FBAR consists of a suspended piezoelectric ring made of aluminum nitride and is excited in the fundamental radial-extensional mode. By replacing the squeeze damping with shear damping, high Qs (189 in water and 77 in human whole blood) are obtained in semi-infinite depth liquids. The C-FBAR sensors are characterized by aptamer - thrombin binding pairs and aqueous glycerine solutions for mass and viscosity sensing schemes, respectively. The C-FBAR sensor demonstrates accurate viscosity measurement from 1 to 10 centipoise, and can be deployed to monitor in-vitro blood coagulation processes in real time. Results show that its resonant frequency decreases as the viscosity of the blood increases during the fibrin generation process after the coagulation cascade. The coagulation time and the start/end of the fibrin generation are quantitatively determined, showing the C-FBAR can be a low-cost, portable yet reliable tool for hemostasis diagnostics. / Dissertation/Thesis / Ph.D. Electrical Engineering 2011

This thesis reports design and implementation of a MEMS based resonant mass sensor for cell detection applications. The main objective of the thesis is the real-time detection of captured cells inside liquid medium and obtaining the detection results by electronic means, without the aid of any external optical instruments. A new resonant mass sensor architecture is presented that has various advantages over its conventional counterparts. The device oscillates in the lateral direction, eliminating squeeze film damping. A thin parylene layer coated on the device prevents liquids from entering the narrow gaps of the device, further improving the quality factor. The resonator is embedded on the floor of a microchannel. A gold film on the proof mass facilitates antibody based cell capture on the device. Theoretical background regarding resonator operation is investigated. Various resonator designs are presented, taking into account design trade-offs, application v considerations, and fabrication limitations. The design procedure is verified with MATLAB Simulink modeling results and finite element simulations. A new process flow has been developed for resonator fabrication, combining SOI, glass, and polymer micromachining. Modifications have been done on the flow for the solution of problems encountered during device fabrication. Each device has a foot print area of 1.5 x 0.5 cm2. The majority of this area is occupied by fluidic connections and reservoirs. Resonance characterization results in air and water have shown that there is significant quality factor enhancement with the parylene coating method. The quality factor decreases to only 170 in water from 610 in air, when the resonator is coated with a thin layer of parylene. Uniformity and linearity tests revealed that the devices have a standard deviation of only 1.9% for different analyte capture sites and an R2 of 0.997 for mass loads as high as 2.7 ng. Detection of Saccharomyces cerevisiae type yeast cells has been done using the resonators. Mass measurement of single yeast cell (13 pg) and yeast clusters (102 pg) have been performed. Antibody and thiol-gold chemistry based Candida Albicans type bacteria capture and detection has also been made in both air and water environments. The mass of several captured bacterial cells in air has been measured as 95pg. Two bacterial cells have been captured on one device inside water and their mass has been measured as 85 pg. It is worthy to note that all mass measurements are consistent with theoretical expectations.

Ces dernières décennies ont vu l'émergence des microsystèmes électromécaniques (MEMS) grâce notamment aux techniques de fabrication employées dans l'élaboration des transistors. L'utilisation de différentes propriétés physiques (électroniques, mécaniques, optiques par exemple) a permis la construction d'un large panel de capteurs miniaturisés. Résultant de la miniaturisation sub-micrométrique des MEMS, les nanosystèmes électromécaniques (NEMS) constituent un tout nouveau type d'objet permettant d'adresser des applications nécessitant un très haut niveau de sensibilité et de résolution, comme la détection de gaz, la spectrométrie de masse ou la reconnaissance de molécules faisant traditionnellement appel à des machines très volumineuses. L'utilisation de ces NEMS requiert cependant un circuit électronique CMOS afin de lire et d'exploiter le signal en sortie de résonateur et servant également à la mise en place d'une boucle oscillante (boucle à verrouillage de phase ou boucle auto oscillante par exemple), architecture idéale pour la détection de masse en temps réel. L'intégration du circuit CMOS avec les résonateurs NEMS constitue un aspect critique quant à la fabrication de capteurs de haute performance. La solution optimale consiste à intégrer de manière monolithique ces deux parties sur la même puce, permettant ainsi de réduire la dimension du capteur et d'améliorer la transmission du signal électrique entre les résonateurs et le circuit CMOS. Cette thèse propose dans un premier temps d'analyser l'intérêt de cette co-intégration du point de vue électrique. Dans un second temps, cette thèse portera sur le développement d'une approche originale visant à co-intégrer de manière monolithique les nano résonateurs au-dessus du circuit CMOS et des interconnexions. La dernière partie portera sur le design d'un détecteur de masse composé d'un réseau compact de NEMS co-intégré CMOS. / During these last decades, Very Large Scale Integration (VLSI) techniques, well developed for transistors, have been used for the Micro ElectroMechanical Systems (MEMS) devices. Thanks to the combination of different physical properties (such as electronic, mechanical, optical etc.) the fabrication of various kinds of miniaturized sensors has been made possible. The sub-µm downscaling of MEMS has allowed the emergence of a new kind of devices called NEMS (for Nano ElectroMechanical Systems) and the possible use of the electromechanical systems in specific applications in which a high level of sensitivity and resolution is necessary, such as gas sensing, mass spectrometry and molecules recognition, to replace traditional bulky machines. Nevertheless, the use of these NEMS requires a CMOS electronic to enhance NEMS resonators readout and to implement closed-loop oscillators (e.g. phase-locked loop or self-oscillating loop) that provide real-time mass measurements. The integration of the electronic circuit with the resonators is a critical aspect for the fabrication of high performance sensors. The best way consists in monolithically processing these two parts on the same die allowing a size reduction of the sensor and an optimal signal transmission between the NEMS resonators and the CMOS circuit. In a first time, this thesis proposes to analyze the interest of this co integration from an electrical point of view. In a second time, this thesis deals with the development of a 3D co integration in which the nano resonators are fabricated above the CMOS circuit and the interconnections. The final part is focused on the layout design considerations for the implementation of a compact mass sensor based on a NEMS array co integrated with a CMOS.

The presented work aims to optimize the performance of piezoresistive cantilevers in cases where the output signal originates either from a static deflection of the cantilever or from the dynamic (resonance) characteristic of the beam. Based on a new stress concentration technique, which utilizes silicon beams and wires embedded in the cantilever, the force sensitivity of the cantilever is increased up to 8 fold with only about a 15% decrease in the cantilever stiffness. Moreover, the developed stress-concentrating cantilevers show almost the same resonance characteristic as conventional cantilevers. The focus of the second part of the present work is to provide guidelines for designing rectangular silicon cantilever beams to achieve maximum quality factors for the fundamental and higher flexural resonance at atmospheric pressure. The applied methodology is based on experimental data acquisition of resonance characteristics of silicon cantilevers, combined with modification of analytical damping models to match the measurement data. To this end, rectangular silicon cantilever beams with thicknesses of 5, 7, 8, 11 and 17 um and lengths and widths ranging from 70 to 1050 um and 80 to 230 um, respectively, have been fabricated and tested. To better describe the experimental data, modified models for air damping have been developed. Moreover, to better understand the damping mechanisms in a resonant cantilever system, analytical models have been developed to describe the cantilever effective mass in any flexural resonance mode. To be able to extract reliable Q-factor data for low signal-to-noise ratios, a new iterative curve fitting technique is developed and implemented. To address the challenge of frequency drift in (mass-sensitive) resonant sensors, and especially cantilever-based devices, the last part of the research deals with a novel compensation technique to cancel the unwanted environmental effects (e.g., temperature and humidity). This technique is based on exploring the resonance frequency difference of two flexural modes. Experimental data show improvements in temperature and humidity coefficients of frequency from -19.5 to 0.2 ppm/˚C and from 0.7 to -0.03 ppm/%RH, respectively. The last part of the work also aims on techniques to enhance or suppress the flexural vibration amplitude in desired overtones.