The design and fabrication of MEMS Inertial Sensors (both accelerometers and gyroscopes) made of Aluminum Nitride (AlN) is described in this dissertation.

The goal of this work is to design and fabricate inertial sensors based on c-axis oriented AlN polycrystalline thin films.

AlN is a post-CMOS compatible piezoelectric material widely used for acoustic resonators, such Bulk Acoustic Wave (BAW) and Lamb Wave Resonators (LWR). In this work we develop the design techniques necessary to obtain inertial sensors with AlN thin film technology. Being able to use AlN as structural material for both acoustic wave resonator and sensing elements is key to achieve the three level integration of RF-MEMS components, sensing elements and CMOS in the same chip.

Using AlN as integration platform is particularly suitable for large consumer emerging markets where production costs are the major factor that determine a product success.

In order to achieve a platform integration, the first part of this work focuses on the fabrication process: starting from the fabrication technology used for LWR devices, this work shows that by slightly modifying some of the fabrication steps it is possible to obtain MEMS accelerometers and gyroscopes with the same structural layers used for LWR.

In the second part of this work, an extensive analysis, performed with analytical and Finite Element Models (FEM), is developed for beam and ring based structures. These models are of great importance as they provide tools to understand the physics of lateral piezoelectric beam actuation and the major limitations of this technology.

Based on the models developed for beam based resonators, we propose two designs for Double Ended Tuning Fork (DETF) based accelerometers.

In the last part of the dissertation, we show the experimental results and the measurements performed on actual devices.

As this work shows analytically and experimentally, there are some fundamental constraints that limit the ultimate sensitivity of piezoelectric sensors based on resonating beam structures.

Although the limitations of the structures here considered cannot achieve tactical grade sensitivities, this research proves that it is possible to achieve performances close to those required by large consumer electronics. This work proves that AlN based platforms can be a great opportunity for future developments in IMU and in general for MEMS integrated solutions.

There is a rising demand for harsh-environment integrated circuits and sensors for a wide variety of applications, ranging from structure health monitoring and process control to space navigation. The ability to continually obtain information in situ in high temperature environment such as a jet engine or a deep oil well can potentially save millions of dollars and even human lives. It also opens doors to space missions to locations with extreme conditions such as Venus, where devices would be required to operate around 500 °C. Wide bandgap materials are well suited for these applications due to their superior electrical and mechanical properties compared to the silicon incumbents. 4H-SiC, a polytype of silicon carbide (SiC), for instance, has a bandgap (3.2 eV) that is almost 3 times of that of silicon (1.12 eV). The wider bandgap results in a much lower intrinsic carrier concentration compared to that of silicon, which makes it an ideal candidate for high temperature (> 300°C) applications. These high temperature capabilities will be the main subject of investigation in this thesis. The overarching objective of the thesis is to develop 4H-SiC technologies for both transistor and sensor devices. Specifically, we investigate and develop the design, simulation, fabrication and characterization of 4H- SiC bipolar junction transistor (BJT) that is capable of operating at elevated temperatures up to 400°C. In addition, a high-performance temperature sensor based on 4H-SiC pn diode which can stably operate in a temperature range from 20°C to 600°C is demonstrated. This type of temperature sensor can be integrated with supporting circuitries to create a sensing module that is capable of working at extremely high temperatures.

Complex engineering systems ranging from automobile engines to geothermal wells require specialized sensors to monitor conditions such as pressure, acceleration and temperature in order to improve efficiency and monitor component lifetime in what may be high temperature, corrosive, harsh environments. Microelectromechanical systems (MEMS) have demonstrated their ability to precisely and accurately take measurements under such conditions. The systems being monitored are typically made from metals, such as steel, while the MEMS sensors used for monitoring are commonly fabricated from silicon, silicon carbide and aluminum nitride, and so there is a sizable thermal expansion mismatch between the two. For these engineering applications the direct bonding of MEMS sensors to the components being monitored is often required. This introduces several challenges, namely the development of a bond that is capable of surviving high temperature harsh environments while mitigating the thermally induced strains produced during bonding.

This project investigates the development of a robust packaging and bonding process, using the gold-tin metal system and the solid-liquid interdiffusion (SLID) bonding process, to join silicon carbide substrates directly to type-316 stainless steel. The SLID process enables bonding at lower temperatures while producing a bond capable of surviving higher temperatures. Finite element analysis was performed to model the thermally induced strains generated in the bond and to understand the optimal way to design the bond. The cross-sectional composition of the bonds has been analyzed and the bond strength has been investigated using die shear testing. The effects of high temperature aging on the bond's strength and the metallurgy of the bond were studied. Additionally, loading of the bond was performed at temperatures over 415 °C, more than 100 °C, above the temperature used for bonding, with full survival of the bond, thus demonstrating the benefit of SLID bonding for high temperature applications.

Lastly, this dissertation provides recommendations for improving the strength and durability of the bond at temperatures of 400 °C and provides the framework for future work in the area of high temperature harsh environment MEMS packaging that would take directly bonded MEMS to temperatures of 600 °C and beyond.

The explosive development of wireless and mobile communication systems has continuously driven rapid technology innovation in component performance and system integration. In order to obtain faster signal processing and reduce integration complexity, the miniaturized and Complementary metal–oxide–semiconductor (CMOS) compatible micro-electromechanical system (MEMS) resonators are likely to be the driving core of a new generation of devices such as radio frequency (RF) filters and oscillators which are the main building blocks in the RF front-end. Thus, a high-performance MEMS resonator technology is highly in demand as the fundamental components in the RF front-end for an advanced wireless communication system.

Among various microelectromechanical resonator technologies, aluminum nitride (AlN) Lamb wave resonators (LWRs) have attracted great attention since it combines the advantages of surface acoustic wave (SAW) and bulk acoustic wave (BAW): the ability of high resonance frequency (fs) and multi-frequency on a single chip. The AlN-based structure provides for CMOS compatibility, and the lowest order symmetric (S0) Lamb wave mode exhibits high phase velocity up to 10000 m/s, weak phase velocity dispersion, small temperature coefficient of frequency (TCF), high quality factor (Q), and moderate electromechanical coupling coefficient (k2). However, the performance parameters needs to be further improved to enable the low-loss filters and stable oscillators. This dissertation addresses a number of issues and demonstrated the high-performance (high-fs., large-k2, high-Q, low-TCF, and low-resonance impedance (Zmin)) piezoelectric AlN LWRs to fulfill the technical requests for the RF front-end.

The k2 and fs optimization of the AlN LWR using the S0 Lamb wave mode is achieved by choosing electrode materials and thicknesses for specific electrode configurations. This study adopts the finite element analysis (FEA) to investigate the influence of electrodes on the dispersive characteristics of the S0 mode propagating in the multi-membranes. From the theoretical study, it is found that the phase velocity is directly related to the density (ρ) and equivalent phase velocity in the metal, while the coupling coefficients depend on ρ and acoustic impedance (Z) of the metal. Large-Z material is preferred for the IDT and light material is favored for the bottom electrode to optimize the k2. Thicker metal for the IDT loads the k2 more when AlN is thin and enhance k2 more when AlN is relatively thick.

In order to boost the Q, a new class of the AlN LWRs using butterfly-shaped plates is introduced in this dissertation for the first time. The butterfly-shape plates can effectively suppress the vibration in the tether location and reduce anchor loss. The 59˚ butterfly-shaped resonator enables an unloaded Q up to 4,758, showing a 1.42× enhancement over the conventional resonator. The experimental results are in good agreement with the simulated predictions by the 3D perfectly matched layer (PML)-based FEA model, confirming that the butterfly-shaped AlN thin plate can efficiently eliminate the anchor dissipation. What’s more, by employing the butterfly-shape AlN plates with rounded tether-to-plate transition which has smaller tether-to-plate angle, the suppression in the anchor loss and enhancement in the Q is even more effective, which is also demonstrate by the simulations. The fabricated butterfly-shaped resonator with 45˚ beveled tether-to-plate transition yields a Q of 1,979 which upwards 30% over a conventional rectangular resonator; while another AlN LWR on the butterfly-shaped plate with rounded tether-to-plate transition yields a Q of 2,531, representing a 67% improvement. In addition, the butterfly-shaped plate didn’t introduce spurious modes on a wide spectrum, compared to other Q increase techniques.

The TCF reduction along with the k2 and fs optimization is demonstrated by introducing the symmetrical SiO2/AlN/SiO2 sandwiched structure to replace the conventional temperature compensation structure AlN/SiO2. The symmetrical SiO2/AlN/SiO2 sandwiched plate experiences the less temperature-induced bending deformation than the conventional AlN/SiO2 bilayer plate when the operation temperature arises from room temperature to 600°C. The symmetrical SiO2/AlN/SiO2 sandwiched plate also enables the pure S0 mode which shows the higher vp and larger k2 than the QS0 mode in the AlN/SiO2 bilayer plate. In the SiO2/AlN/SiO2 sandwiched membrane, the single IDT with the bottom electrode configuration offers a simple process flow and a large k2 at the relatively thin hAlN region (hAlN = 0.1λ). The double-sided IDTs configuration provides a large k2 up to 4% at the relatively thick hAlN region (hAlN/λ = 0.4λ) even when the thick SiO2 layers are employed for thermal compensation at high temperatures. Based on the correct choices of the AlN and SiO2 thicknesses in the symmetrical SiO2/AlN/SiO2 sandwiched membrane, the LWRs can be thermally stable and retain a large k2 at high temperatures.

The low-Zmin and high-fs AlN LWR is studied by utilizing the first order symmetric (S1) mode propagating in a specific thickness of AlN. In order to achieve the larger electromechanical coupling coefficient and high phase velocity as well as avoid the negative group velocity in the S1 Lamb wave mode, the 4-μm-thick AlN layer and 3-μm-wide finger electrodes are employed in the Lamb wave resonator design. The experimental results show the S1 mode presents a Zmin of 94 Ω at 1.34 GHz, lower than the Zmin equal to 224 Ω of the S0 mode at 878.3 MHz.

The three-dimensional thermal ground plane was developed in response to the needs of high-power density electronics applications in which heat must be removed as close to the chip surface as possible. The novel design for this planar cooling device was proposed with three key innovations in the evaporator, wick, and reservoir layer, which provided enhanced and reliable cooling performance without wick dryout and back flows. For the evaporator and reservoir layer, a combination of a tapered channel and a triple-spike microstructure was designed to break up the pinned meniscus at the end of the vapor and liquid channels. The overall microstructure had three spikes where the main liquid meniscus was separated by a middle spike and then continued to flow between the tapered walls of the middle and side spikes. For the wick layer, a nanowire-integrated microporous silicon membrane was developed to overcome dryout by driving the coolant out of the channels and spreading the coolant on top of the wick surface with the assistance of extended capillary action. This innovative design used nanowires to extend and enhance capillary force, especially at the end of the pores where the coolant was pinned and unable to overflow out of the pores. The chronic dryout problem in micro cooling devices could be solved by these innovative designs.

To analyze the thermal-fluid system, fluid dynamic and phase-change models were used to calculate thermodynamic and fluidic properties, such as operating temperature, pressure, vapor-liquid interface radius of curvature, and rate of bubble formation. The microscale heat conduction theory derived from traditional Fourier's law with classical size effect and effective medium theory were used to calculate the thermal conductivities of nanowires and porous silicon wick in the cross-plane direction, respectively. The theoretical results of porous silicon showed good agreement with the experimental results measured by the 3ù technique, demonstrating the reduction of thermal conductivity from bulk silicon. Cooling performance of the developed device was demonstrated experimentally with a micro ceramic heater, thermocouple modules, and microfabrication techniques, including photoelectrochemical etching to create porous silicon, deep reactive-ion etching to form a thin wick membrane, and hydrothermal synthesis to grow nanowires on top of the wick membrane. This study shows the feasibility of reliable, continuous, and high-performance micro cooling devices using enhanced capillary forces to address the increasing requirements of thermal management for chip-level electronics.

In this thesis, a new piezoelectric valve system with bi-chevron aluminum nitride (AlN) actuator is described. The intended application of the new piezoelectric valve is for the advanced printing technology with supercritical carbon dioxide as the solvent. With supercritical carbon dioxide as the solvent, the ink dissolved will start to nucleate with a micronozzle and generate extremely small and uniform ink particles due to rapid expansion of supercritical solution (RESS). Therefore, the resolution of the printing can be improved and induce a much better printing quality.

To successfully operate this new printing technology, the operation pressure of this valve system should be as high as 30 MPa. This operation pressure is much higher than what the current piezoelectric MEMS valve can offer. Aluminum nitride is chosen as the piezoelectric material over lead zirconate titanate (PZT) because the depolarization of PZT due to compressive stresses limits the operating pressure to less than 5 MPa. In order to meet high pressure requirements, thin-film AlN is selected because it doesn't experience compressive stress depolarization and is IC compatible. The piezoelectric valve system is designed with bi-chevron shape not only to amplify the generated stroke but also to reduce undesired out-of-plane motion. This amplification mechanism is achieved by the cantilever beam structure without increasing the size of the valve system significantly. In the bi-chevron, the use of piezoelectrics with matched sets of actuator arms enables a push-pull actuation in both directions and also reduces out-of-plane buckling.

To verify the working function of the bi-chevron actuator, a pre-prototype device is introduced and fabricated. And the result from the static testing of the pre-prototype device is compared with the finite element simulation and the theoretical analysis. The result shows a good fitting between finite element simulation and the pre-prototype device measurement (maximum error is about 17%). However, the error between the theoretical analysis and finite element simulation is significant due to the particle top/bottom electrode coverage. This is because partial-coverage results in a nonuniform electrical field along the width of the AlN beam and simultaneously reduces the generated stroke and the generated force. For the dynamic performance, an alternating current (AC) is used to actuate the pre-prototype device rather than direct current (DC). It is because AC actuating voltage gives the dynamic response of the pre-prototype device and then indicates the resonant frequency of the pre-prototype devices which corresponds to the operation speed while DC actuating voltage has no effect on the dynamic performance at all. The result of the dynamic performance shows that the prototype device will give 1.5 micron in-plane generated stroke with acceptable out-of-plane generated stroke when the device is actuated in 60 kHz with 10 V actuating voltage. The pre-prototype device has 1100 micron long, 10 micron wide, and 2° angle AlN beams.

In addition to the pre-prototype device, the prototype device is fabricated for the supercritical carbon dioxide valve system. The difference between prototype devices and supercritical carbon dioxide devices is that supercritical carbon dioxide devices have been sealed with a cap. That means the prototype devices can become goal devices, supercritical carbon dioxide valves, after sealing the device with a cap. This prototype device uses a SOI wafer with bi-chevron AlN actuator to control the flow of the supercritical carbon dioxide valve. This is prototype device is also evaluated and the result verify that this fabrication process is correct.

Polymer Nanocomposite Materials with High Dielectric Permittivity and Low Dielectric Loss Properties

by

Anju Toor

Doctor of Philosophy in Mechanical Engineering

University of California, Berkeley

Professor Tarek Zohdi, Co-chair

Professor Albert P. Pisano, Co-chair

Materials with high dielectric permittivity have drawn increasing interests in recent years

for their important applications in capacitors, actuators, and high energy density pulsed power.

Particularly, polymer-based dielectrics are excellent candidates, owing to their properties

such as high breakdown strength, low dielectric loss, flexibility and easy processing. To

enhance the dielectric permittivity of polymer materials, typically, high dielectric constant

filler materials are added to the polymer. Previously, ferroelectric and conductive fillers have

been mainly used. However, such systems suffered from various limitations. For example,

composites based on ferroelectric materials like barium titanate, exhibited high dielectric

loss, and poor saturation voltages. Conductive fillers are used in the form of powder

aggregates, and they may show 10-100 times enhancement in dielectric constant, however

these nanoparticle aggregates cause the dielectric loss to be significant. Also, agglomerates

limit the volume fraction of fillers in polymer and hence, the ability to achieve superior

dielectric constants. Thus, the aggregation of nanoparticles is a significant challenge to their

use to improve the dielectric permittivity.

We propose the use of ligand-coated metal nanoparticle fillers to enhance the dielectric

properties of the host polymer while minimizing dielectric loss by preventing nanoparticle

agglomeration. The focus is on obtaining uniform dispersion of nanoparticles with no

agglomeration by utilizing appropriate ligands/surface functionalizations on the gold

nanoparticle surface. Use of ligand coated metal nanoparticles will enhance the dielectric

constant while minimizing dielectric loss, even with the particles closely packed in the polymer

matrix. Novel combinations of materials, which use 5 nm diameter metal nanoparticles

embedded inside high breakdown strength polymer materials are evaluated. High breakdown

strength polymer materials are chosen to allow further exploration of these materials for

energy storage applications.

In summary, two novel nanocomposite materials are designed and synthesized, one involving

polyvinylidene fluoride (PVDF) as the host polymer for potential applications in

energy storage and the other with SU-8 for microelectronic applications. Scanning elec-

tron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray

spectroscopy and ultramicrotoming techniques were used for the material characterization

of the nanocomposite materials. A homogeneous dispersion of gold nanoparticles with low

particle agglomeration has been achieved. Fabricated nanoparticle polymer composite films

showed the absence of voids and cracks. Also, no evidence of macro-phase separation of

nanoparticles from the polymer phase was observed. This is important because nanoparticle

agglomeration and phase separation from the polymer usually results in poor processability

of films and a high defect density. Dielectric characterization of the nanocomposite materials

showed enhancement in the dielectric constant over the base polymer values and low

dielectric loss values were observed.

A harsh environment can be defined by one or more of the following: High temperature, high shock, high radiation, erosive flow, and corrosive media. Among all the harsh environment applications, high temperature applications have drawn lots of attention due to the emerging activity in automotive, turbine engine, space exploration and deep-well drilling telemetry. Silicon carbide has become the candidate for these harsh environment applications because of its wide bandgap, excellent chemical and thermal stability, and high breakdown electric field strength. This dissertation details the two building blocks of high-temperature UV sensing chip, namely Ultraviolet sensor and transistors. High temperature performance of silicon carbide metal-semiconductor-metal UV sensor is characterized at high temperatures for the first time. The sensor exhibits high photo-to-dark current ratio and fast rise and fall time even at high temperatures. Complementary SiC junction field-effect transistors of different gate configurations are proposed, fabricated and characterized from room temperature to 600 °C for the first time. High intrinsic gains at high temperatures suggest that complementary junction field-effect transistors are suitable devices for high temperature operational amplifier.

The explosive development of wireless and mobile communication systems has lead to rapid technology innovation in component performance, complementary metal-oxide semiconductor (CMOS) compatible fabrication techniques, and system improvement to satisfy requirements for faster signal processing, cost efficiency, chip miniaturization, and low power consumption. The demands for the high-performance communication systems whose fundamentals are precise timing and frequency control have driven the current research interests to develop advanced reference oscillators and radio frequency (RF) bandpass filters. In turn a promising microelectromechanical systems (MEMS) resonator technology is required to achieve the ultimate goal. That is, micromechanical vibrating resonators with high quality factor (Q) and good frequency-temperature stability at high series resonance frequency (fs) are the required fundamental components for a high-performance wireless communication system.

Recently, Lamb wave mode propagating in piezoelectric thin plates has attracted great attention for designs of the electroacoustic resonators since it combines the advantages of bulk acoustic wave (BAW) and surface acoustic wave (SAW): high phase velocity and multiple frequency excitation by an interdigital transducer (IDT). More specifically, the Lamb wave resonator (LWR) based on an aluminum nitride (AlN) thin film has attracted many attentions because it can offer the high resonance frequency, small temperature-induced frequency drift, low motional resistance, and CMOS compatibility. The lowest-order symmetric (S0) Lamb wave mode propagation in the AlN thin plate is particularly preferred because it exhibits a phase velocity close to 10,000 m/s, a low dispersive phase velocity characteristic, and a moderate electromechanical coupling coefficient. However, the uncompensated AlN LWR shows a first-order temperature coefficient of frequency (TCF) of approximately -25 ppm/C. This level of the temperature stability is unsuitable for any timing application. In addition, the Q of the AlN LWR is degraded to several hundred while the IDT finger width is downscaled to a nanometer scale to raise the resonance frequency up to a few GHz.

This dissertation presents comprehensive analytical and experimental results on a new class of temperature-compensated and high-Q piezoelectric AlN LWRs. The temperature compensation of the AlN LWR using the S0 Lamb wave mode is achieved by adding a layer of silicon dioxide (SiO2) with an appropriate thickness ratio to the AlN thin film, and the AlN/SiO2 LWRs can achieve a low first-order TCF at room temperature. Based on the multilayer plate composed of a 1-um-thick AlN film and a 0.83-um-thick SiO2 layer, a temperature-compensated LWR operating at a series resonance frequency of 711 MHz exhibits a zero first-order TCF and a small second-order TCF of -21.5 ppb/C^2 at its turnover temperature, 18.05 C. The temperature dependence of fractional frequency variation is less than 250 parts per million (ppm) over a wide temperature range from -55 to 125 C. In addition to the temperature compensation at room temperature, the thermal compensation of the AlN LWRs is experimentally demonstrated at high temperatures. By varying the normalized AlN and SiO2 thicknesses to the wavelength, the turnover temperature can be designed at high temperatures and the AlN LWRs are temperature-compensated at 214, 430, and 542 C, respectively. The temperature-compensated AlN/SiO2 LWRs are promising for a lot of applications including thermally stable oscillators, bandpass filters, and sensors at room temperature as well as high temperatures.

The influences of the bottom electrode upon the characteristics of the LWRs utilizing the S0 Lamb wave mode in the AlN thin plate are theoretically and experimentally studied. Employment of a floating bottom electrode for the LWR reduces the static capacitance in the AlN membrane and accordingly enhances the effective coupling coefficient. The floating bottom electrode simultaneously offers a large coupling coefficient and a simple fabrication process than the grounded bottom electrode but the transduction efficiency is not sacrificed. In contrast to those with the bottom electrode, an AlN LWR with no bottom electrode shows a high Q of around 3,000 since it gets rid of the electrical loss in the metal-to-resonator interface. In addition, it exhibits better power handling capacity than those with the bottom electrode since less thermal nonlinearity induced by the self-heating exists in the resonators.

In order to boost the Q, a new class of the AlN LWRs using suspended convex edges is introduced in this dissertation for the first time. The suspended convex edges can efficiently reflect the Lamb waves back towards the transducer as well as confine the mechanical energy in the resonant body. Accordingly the mechanical energy dissipation through the support tethers is significantly minimized and the Q can be markedly enhanced. More specifically, the measured frequency response of a 491.8-MHz LWR with suspended biconvex edges yields a Q of 3,280 which represents a 2.6x enhancement in Q over a 517.9-MHz LWR based on the same AlN thin plate but with the suspended flat edges. The suspended convex edges can efficiently confine mechanical energy in the LWR and reduce the energy dissipation through the support tethers without increasing the motional impedance of the resonator. In addition, the radius of curvature of the suspended convex edges and the AlN thickness normalized to the wavelength can be further optimized to simultaneously obtain high Q, low motional impedance, and large effective coupling coefficient.

To further enhance the Q of the LWR, a composite plate including an AlN thin film and an epitaxial cubic silicon carbide (3C-SiC) layer is introduced to enable high-Q and high-frequency micromechanical resonators utilizing high-order Lamb wave modes. The use of the epitaxial 3C-SiC layer is attractive as SiC crystals have been theoretically proven to have an exceptionally large fs and Q product due to its low acoustic loss characteristic at microwave frequencies. In addition, AlN and 3C-SiC have well-matched mechanical and electrical properties, making them a suitable material stack for the electroacoustic resonators. The epitaxial 3C-SiC layer not only provides the micromechanical resonators with a low acoustic loss layer to boost their Q but also enhances the electromechanical coupling coefficients of some high-order Lamb waves in the AlN/3C-SiC composite plate. A micromachined electroacoustic resonator utilizing the third quasi-symmetric (QS3) Lamb wave mode in the AlN/3C-SiC composite plate exhibits a Q of 5,510 at 2.92 GHz, resulting in the highest fs and Q product, 1.61x10^13 Hz, among suspended piezoelectric thin film resonators to date.

Despite commercial availability since the 1950's, silicon strain sensors have not experienced the same success as other microdevices, such as accelerometers, pressure sensors, and inkjet heads. Strain sensors measure mechanical deformation and could be used in many structural components, improving safety, controls, and manufacturing tolerances. This thesis examines major strain sensing techniques and highlights both advantages and disadvantages of each. MEMS resonant strain gauges are identified to have superior performance over many traditional strain gauges in terms of sensitivity, resolution, stability, and size. To use these gauges, additional issues such as harsh environment survivability, strain transfer, temperature stability, and encapsulation must be solved, as detailed in this thesis.

Concerning harsh environment survivability, this work presents a MEMS resonant strain gauge fabricated from silicon carbide, which operates at 600°C, and has been tested to 64,000 G, while still resolving 0.01 microstrain in a 10 kHz bandwidth. Specific details on how to create harsh environment testing equipment are presented. Additionally, this original work identifies a unique temperature stability method based on purposely mismatched device and substrate layers. Full analytical equations are presented, and experimental confirmation of the scheme shows that temperature stability is improved from 23 ppm/°C to 3.6 ppm/°C.

All MEMS devices are created on flat substrates, which are useful when integrating electronics, but can be difficult to use when measuring strain in structural components, especially round objects. Furthermore, no work has been presented for gauges operating at high strain. To address this issue, this thesis contains the first demonstration of a MEMS resonant strain gauge operating at 1000 microstrain on a static automobile halfshaft. Details on joining the substrate to the circular halfshaft are presented, as well as how to treat the issue of strain transfer.

To protect the device, encapsulation is designed specifically to not change the strain sensitivity of the gauge. The encapsulation utilizes directional ion beam sputtering, which is experimentally shown to deposit spatially confined, extremely thin material through the release holes. Typical depositions were nanometers in thickness (<0.5% of deposited material) and on the order of tens to hundreds of femtograms.