The objective of this thesis was to develop a fast-response multifunctional MEMS (Micro Electro Mechanical Systems) sensor for the simultaneous measurement of in-cylinder pressure and temperature in an internal combustion (IC) engine. In a representative IC engine, the pressure and temperature can reach up to about 1.6 MPa and 580 °C, respectively, at the time of injection during the compression stroke. At the peak of the combustion process, the pressure and temperature near the cylinder wall can go beyond 6 MPa and 1000 °C, respectively. Failure of current membrane-based MEMS pressure sensors operating at high temperatures is mainly caused by cross-sensitivity to temperature, which affects the pressure readout. In addition, the slow thermal response of temperature sensors used for such a dynamic application makes real-time sensing within a combustion engine very challenging. While numerous approaches have been taken to address these issues, no MEMS sensor has yet been reported that can carry out real-time measurements of in-cylinder pressure and temperature. The operation of the sensor proposed in this Thesis is based on a new non-planar and flexible multifunctional membrane, which responds to both pressure and temperature variations at the same time. The new design draws from standard membrane-based pressure and thermostatic-based temperature MEMS sensing principles to output two capacitance values. A numerical processing scheme uses these values to create a characteristic sensing plot which then serves to decouple the effects of pressure and temperature variations. This sensing scheme eliminates the effect of cross-sensitivity at high temperatures, while providing a short thermal response time. Thermal, mechanical and electrical aspects of the sensor performance were modeled. First, a semi-analytical thermo-mechanical model, based on classic beam theory, was tailored to the shape of the multifunctional membrane to determine the sensor’s response to pressure and temperature loading. ANSYS® software was used to verify this semi-analytical model against finite element simulations. Then the model was then used to calculate the capacitive outputs of the multifunctional MEMS sensor subjected to in-cylinder pressure and temperature loading during a complete cycle of operation of a typical IC engine as well as to optimize the sensor specifications. Several prototypes of the new sensing mechanism fabricated using the PolyMUMPs® foundry process were tested to verify its thermal behavior up to 125 °C. The experiments were performed using a ceramic heater mounted on a probe station with the device connected to a precision LCR-meter for capacitive readouts. Experimental results show good agreement of the temperature response of the sensor with the ANSYS® finite element simulations. Further simulations of the pressure and temperature response of different configurations of the multifunctional MEMS sensor were carried out. The simulations were performed on an array of 4200 multifunctional devices, each featuring a 0.5 µm thick silicon carbide membrane with an area of 25×25 µm2, connected in parallel shows that the optimized sensor system can provide an average sensitivity to pressure of up to 1.55 fF/KPa (over a pressure range of 0.1-6 MPa) and an average sensitivity to temperature of about 4.62 fF/°C (over a temperature range of 160-1000 °C) with a chip area of approximately 4.5 mm2. Assuming that the accompanying electronics can meaningfully measure a minimum capacitance change of 1 fF, this optimized sensor configuration has the potential to sense a minimum pressure change of less than 1 KPa and a minimum temperature change of less than 0.35 °C over the entire working range of the representative IC engine indicated above. In summary, the new developed multifunctional MEMS sensor is capable of measuring temperature and pressure simultaneously. The unique design of the membrane of the sensor minimizes the effect of cross-sensitivity to temperature of current MEMS pressure sensors and promises a short thermal response time. When materials such as silicon carbide are used for its fabrication, the new sensor may be used for real-time measurement of in-cylinder pressure and temperature in IC engines. Furthermore, a systematic optimization process is utilized to arrive at an optimum sensor design based on both geometry and properties of the sensor fabrication materials. This optimization process can also be used to accommodate other sensor configurations depending on the pressure and temperature ranges being targeted.

The objective of this thesis was to develop a fast-response multifunctional MEMS (Micro Electro Mechanical Systems) sensor for the simultaneous measurement of in-cylinder pressure and temperature in an internal combustion (IC) engine. In a representative IC engine, the pressure and temperature can reach up to about 1.6 MPa and 580 °C, respectively, at the time of injection during the compression stroke. At the peak of the combustion process, the pressure and temperature near the cylinder wall can go beyond 6 MPa and 1000 °C, respectively. Failure of current membrane-based MEMS pressure sensors operating at high temperatures is mainly caused by cross-sensitivity to temperature, which affects the pressure readout. In addition, the slow thermal response of temperature sensors used for such a dynamic application makes real-time sensing within a combustion engine very challenging. While numerous approaches have been taken to address these issues, no MEMS sensor has yet been reported that can carry out real-time measurements of in-cylinder pressure and temperature. The operation of the sensor proposed in this Thesis is based on a new non-planar and flexible multifunctional membrane, which responds to both pressure and temperature variations at the same time. The new design draws from standard membrane-based pressure and thermostatic-based temperature MEMS sensing principles to output two capacitance values. A numerical processing scheme uses these values to create a characteristic sensing plot which then serves to decouple the effects of pressure and temperature variations. This sensing scheme eliminates the effect of cross-sensitivity at high temperatures, while providing a short thermal response time. Thermal, mechanical and electrical aspects of the sensor performance were modeled. First, a semi-analytical thermo-mechanical model, based on classic beam theory, was tailored to the shape of the multifunctional membrane to determine the sensor’s response to pressure and temperature loading. ANSYS® software was used to verify this semi-analytical model against finite element simulations. Then the model was then used to calculate the capacitive outputs of the multifunctional MEMS sensor subjected to in-cylinder pressure and temperature loading during a complete cycle of operation of a typical IC engine as well as to optimize the sensor specifications. Several prototypes of the new sensing mechanism fabricated using the PolyMUMPs® foundry process were tested to verify its thermal behavior up to 125 °C. The experiments were performed using a ceramic heater mounted on a probe station with the device connected to a precision LCR-meter for capacitive readouts. Experimental results show good agreement of the temperature response of the sensor with the ANSYS® finite element simulations. Further simulations of the pressure and temperature response of different configurations of the multifunctional MEMS sensor were carried out. The simulations were performed on an array of 4200 multifunctional devices, each featuring a 0.5 µm thick silicon carbide membrane with an area of 25×25 µm2, connected in parallel shows that the optimized sensor system can provide an average sensitivity to pressure of up to 1.55 fF/KPa (over a pressure range of 0.1-6 MPa) and an average sensitivity to temperature of about 4.62 fF/°C (over a temperature range of 160-1000 °C) with a chip area of approximately 4.5 mm2. Assuming that the accompanying electronics can meaningfully measure a minimum capacitance change of 1 fF, this optimized sensor configuration has the potential to sense a minimum pressure change of less than 1 KPa and a minimum temperature change of less than 0.35 °C over the entire working range of the representative IC engine indicated above. In summary, the new developed multifunctional MEMS sensor is capable of measuring temperature and pressure simultaneously. The unique design of the membrane of the sensor minimizes the effect of cross-sensitivity to temperature of current MEMS pressure sensors and promises a short thermal response time. When materials such as silicon carbide are used for its fabrication, the new sensor may be used for real-time measurement of in-cylinder pressure and temperature in IC engines. Furthermore, a systematic optimization process is utilized to arrive at an optimum sensor design based on both geometry and properties of the sensor fabrication materials. This optimization process can also be used to accommodate other sensor configurations depending on the pressure and temperature ranges being targeted.

Compliant electronics are an emerging class of electronics which offer physical flexibility in their structure. Such mechanical flexibility opens up opportunities for wide ranging applications. Nonetheless, compliant electronics which can be functional in unusual environments are yet to be explored. Unusual environment can constitute a harsh environment where temperature and/or pressure is much higher or lower than the usual room temperature and/or pressure. Unusual environment can be an aquatic environment, such as ocean/sea/river/pond, industrial processing related liquid and bodily fluid environment, external or internal for implantable electronics. Finally, unusual environment can also be conditions when extreme physical deformation is anomalously applied to compliant electronics in order to understand their performance and reliability under such extraordinary mechanical deformations. Therefore, in this thesis, three different aspects of compliant electronics are thoroughly studied, addressing challenges of material selection/optimization for unusual environment applications, focusing on electrical performance and mechanical flexible behavior. In the first part, performance of silicon-based high-performance complementary metal oxide semiconductor (CMOS) devices are studied under severe mechanical deformation. Next, a high-volume manufacturing compatible solution is offered to reduce the usage of toxic chemicals in semiconductor device fabrication. To accomplish this, Germanium Dioxide (GeO2) is simultaneously used as transient material and dielectric layer to realize a dissolvable/bioresorbable transient electronic system which can be potentially used for implantable electronics. Finally, wide bandgap semiconductor Gallium Nitride is studied to understand its mechanical flexibility under high temperature conditions. In summary, this research contributes to the advancement of material selection, optimization and process development towards achieving compliant and transient devices for novel applications in unusual environments.

No description available.

Previous studies on very high-cycle fatigue behavior of thin silicon films suggest a strong environmental dependence of the degradation mechanism, the precise nature of which is still subject to debate. In the present study, 2-micron-thick polycrystalline Si notched cantilever beam structures were used to investigate fatigue degradation in a high-temperature (80°C), high-humidity (90%RH) environment. The specimens were subjected to fully reversed sinusoidal loading at resonance (~40kHz) with stress amplitudes ranging from 1.46 to 1.6GPa, resulting in life-spans between 10⁶ and 10⁹ cycles. Comparison to a reference set of S-N data obtained at moderate environmental conditions (30°C and 50%RH) reveals a strong tendency for faster degradation with increasing temperature and humidity. The obtained damage accumulation rates in the 80°C, 90%RH environment exceed the reference by two orders of magnitude. Transmission electron microscopy (TEM) on vertical through-thickness slices reveals oxide thickening after cycling. The influence of ~20nm Al[subscript2]O₃ deposited on the surface of the fatigue specimens using Atomic Layer Deposition (ALD) technique was also studied. The presence of the alumina coating results in a higher fatigue resistance at 30°C and 50%RH, as well as a drastically different frequency evolution behavior. No oxide thickening was observed in the TEM for coated run-out specimens. A model is proposed to explain the different degradation behavior of the ALD-alumina coated samples. Thickened oxides after cycling appear consistent with the reaction-layer fatigue mechanism. Finite element modal analysis incorporating surface oxide layers and cracking was employed to relate the damage observed in TEM to the experimentally measured changes in resonant frequency. In conclusion, the reaction-layer mechanism seems capable of describing micron-scale polysilicon fatigue, even though the critical processes such as room-temperature, stress-assisted oxidation remain elusive.

This thesis concerns with the development of a dual-parameter sensor based on fiber Bragg grating (FBG) and a packaging design for high pressure sensing in harsh environment. This thesis starts by introducing a novel design of a partially coated FBG, using a metallic insert and a thermal curing epoxy. An analytical opto-mechanical model, based on couple mode theory, was developed and presented. The experimental and modelling result of the optical response of the partially coated FBG were compared and shown to be in excellent agreement. The experiments were executed on a custom-built fiber optic calibration station. The coated FBG sensor has a temperature sensitivity of 26.9 ± 0.3 pm/°C, which is 2.7 times higher than a bare fiber; and a force sensitivity of 0.104 nm/N, which is 13 times smaller than a bare fiber. The zero reference of the sensor has a drift of a maximum of 70 pm but the sensor is shown to settle within ±5 pm after 3 thermal cycles and 10 tensile loading cycles. A low profile packaging design is presented for a maximum pressure of 20.68 MPa (3000 psi) for harsh environment applications. A detailed study with FEM analysis revealed the optimal design for the package’s sleeve thickness is 0.5 mm. The temperature sensitivity is in close agreement with the unpackaged coated sensor with 10% difference. Compared to the modelling, the equivalent force sensitivity is 27% lower due to prototype dimensional uncertainties and modelling uncertainties with the material properties. The lack of pre-tension of the FBG sensor in the package also attributed to lower force sensitivity at pressure level lower than 4.13 MPa (600 psi).

Certains domaines d'applications tels que l'aérospatial, l'automobile ou le forage de haute profondeur peuvent nécessiter la visualisation de certains paramètres physiques dans des environnements hostiles. Les capteurs microélectroniques basés sur le silicium y atteignent souvent leurs limites, qui sont qualifiées de conditions « sévères ». Ce travail se base principalement sur l'étude de solutions de capteurs mécaniques fonctionnant en conditions sévères. Le principe de ces capteurs repose sur l'exploitation de transistors de mesures HEMT à base de nitrures III-V (III-N), à la fois piézoélectriques et semiconducteurs, qui reste stable en conditions sévères. La compréhension des interactions entre physique des semiconducteurs et physique des matériaux ainsi que la caractérisation de structures possibles pour la détection mécanique représentent les principaux enjeux de ce sujet de thèse. La modélisation mécanique analytique et numérique des structures étudiées a permis d'appréhender le comportement de structures piézoélectriques multicouches. Le couplage de ce modèle électromécanique avec un modèle électronique du capteur a permis d'établir la faisabilité du principe de détection ainsi que la linéarité de la réponse du capteur. La caractérisation des prototypes réalisés en cours de thèse ont corroboré la linéarité du capteur tout en faisant apparaître l'influence de nombreux effets parasites réduisant sa sensibilité à savoir les effets de résistance parasites et de piézorésistances variables. / Some industrial areas as oil, automotive and aerospace industries, require electromechanical systems working in harsh environments. An elegant solution is to use III–V materials alloys having semiconductor, piezoelectric and pyroelectric properties. These materials, particularly nitrides such as GaN or AlN, enable design of advanced devices suitable for harsh environment. By using free-standing structure coupled with sensing HEMT transistors that are stable at high temperatures, it is possible to obtain mechanical sensors suitable for harsh environments. This PhD thesis focuses on a cantilever-based strain sensor and a drumskin-based pressure sensor. Analytical models of both sensors have been developed and establish the feasibility of the sensing principle as well as its response linearity. The characterization tests of fabricated prototypes validate the possibility of measuring external mechanical load with both sensors. The linearity of the response has also been confirmed by experimental measurements. The experimental sensitivity is smaller than the theoretical one due to several parasitic effects not included in the model such as parasitic resistance and variable piezoresisitive effects.

In this study, gas sensing systems that are based on piezoelectric smart material and structures are proposed, designed, developed, and tested, which are mainly aimed to address the temperature dependent CO2 gas sensing in a real environment. The state-of-the-art of gas sensing technologies are firstly reviewed and discussed for their pros and cons. The adsorption mechanisms including physisorption and chemisorption are subsequently investigated to characterize and provide solutions to various gas sensors. Particularly, a QCM based gas sensor and a C-axis inclined zigzag ZnO FBAR gas sensor are designed and analyzed for their performance on room temperature CO2 gas sensing, which fall into the scope of physisorption. In contrast, a Langasite (LGS) surface acoustic wave (SAW) based acetone vapor sensor is designed, developed, and tested, which is based on the chemisorption analysis of the LGS substrate. Moreover, solid state gas sensors are characterized and analyzed for chemisorption-based sensitive sensing thin film development, which can be further applied to piezoelectric-based gas sensors (i.e. Ca doped ZnO LGS SAW gas sensors) for performance enhanced CO2 gas sensing. Additionally, an innovative MEMS micro cantilever beam is proposed based on the LGS nanofabrication, which can be potentially applied for gas sensing, when combined with ZnO nanorods deposition. Principal component analysis (PCA) is employed for cross-sensitivity analysis, by which high temperature gas sensing in a real environment can be achieved. The proposed gas sensing systems are designated to work in a high temperature environment by taking advantage of the high temperature stability of the piezoelectric substrates.

No description available.

Fiber optic temperature sensing has become a well-defined field in the past few decades [1] through the use of Fiber Bragg Gratings, Fabry-Perot interferometry, and pyrometry, to list several techniques in use today.  The use of fiber optics offers significant advantages over electronic sensing in terms of size and insensitivity to harsh conditions such as extreme temperatures and corrosive environments.  The availability of optical sapphire materials, including fibers, has allowed the creation of fiber optic sensing elements able to continuously operate at temperatures of 1600"C [2] or more, thus outstripping the abilities of many commonly used thermocouples (excluding platinum types R, S, and B) [3] which will also exhibit a sensitivity to electromagnetic fields. In addition to the aforementioned benefits, fiber optic sensing techniques provide a great deal of accuracy in temperature measurement over the entire working range of the sensor. The work documented in this thesis consists of efforts to minimize the overall footprint of a sapphire based extrinsic Fabry-Perot interferometry (EFPI) temperature sensing element, as well as strides made in multiplexing the same element and reducing the error potential from cross sensitivity of the thermometer with applied strain.  This work has been variously funded by Pratt & Whitney and the Department of Energy. / Master of Science