MACHINE LEARNING AUGMENTATION MICRO-SENSORS FOR SMART DEVICE APPLICATIONS

Novel smart technologies such as wearable devices and unconventional robotics have been enabled by advancements in semiconductor technologies, which have miniaturized the sizes of transistors and sensors. These technologies promise great improvements to public health. However, current computational paradigms are ill-suited for use in novel smart technologies as they fail to meet their strict power and size requirements. In this dissertation, we present two bio-inspired colocalized sensing-and-computing schemes performed at the sensor level: continuous-time recurrent neural networks (CTRNNs) and reservoir computers (RCs). These schemes arise from the nonlinear dynamics of micro-electro-mechanical systems (MEMS), which facilitates computing, and the inherent ability of MEMS devices for sensing. Furthermore, this dissertation addresses the high-voltage requirements in electrostatically actuated MEMS devices using a passive amplification scheme. The CTRNN architecture is emulated using a network of bistable MEMS devices. This bistable behavior is shown in the pull-in, the snapthrough, and the feedback regimes, when excited around the electrical resonance frequency. In these regimes, MEMS devices exhibit key behaviors found in biological neuronal populations. When coupled, networks of MEMS are shown to be successful at classification and control tasks. Moreover, MEMS accelerometers are shown to be successful at acceleration waveform classification without the need for external processors. MEMS devices are additionally shown to perform computing by utilizing the RC architecture. Here, a delay-based RC scheme is studied, which uses one MEMS device to simulate the behavior of a large neural network through input modulation. We introduce a modulation scheme that enables colocalized sensing-and-computing by modulating the bias signal. The MEMS RC is tested to successfully perform pure computation and colocalized sensing-and-computing for both classification and regression tasks, even in noisy environments. Finally, we address the high-voltage requirements of electrostatically actuated MEMS devices by proposing a passive amplification scheme utilizing the mechanical and electrical resonances of MEMS devices simultaneously. Using this scheme, an order-of-magnitude of amplification is reported. Moreover, when only electrical resonance is used, we show that the MEMS device exhibits a computationally useful bistable response. Adviser: Dr. Fadi Alsalee

Nanoelectromechanical Sensors based on Suspended 2D Materials

The unique properties and atomic thickness of two-dimensional (2D) materials enable smaller and better nanoelectromechanical sensors with novel functionalities. During the last decade, many studies have successfully shown the feasibility of using suspended membranes of 2D materials in pressure sensors, microphones, accelerometers, and mass and gas sensors. In this review, we explain the different sensing concepts and give an overview of the relevant material properties, fabrication routes, and device operation principles. Finally, we discuss sensor readout and integration methods and provide comparisons against the state of the art to show both the challenges and promises of 2D material-based nanoelectromechanical sensing.Comment: Review pape

The integration of active silicon components in polymer microfluidic devices

Early microfluidic devices borrowed technology from established CMOS microfabrication, and were therefore structurally similar to silicon computer chips. In the late 1990s, George Whitesides' group pioneered a cheaper, mass producible polymer device fabrication technique called 'soft lithography' that revolutionized modern microfluidics. This dissertative work has been focused on re-introducing silicon as a common material in microfluidic devices, but as an active component instead of a structural one. These active components exploit the optical properties, electronic properties, and optoelectronic properties of silicon. The optical properties of silicon are utilized in the integration of silicon nanophotonic ring resonators as refractive index sensors embedded in microfluidic channels. The electronic properties of silicon are utilized in the fabrication of an ultra-thin Schottky diode for use as a transmission radiation particle detector for focused ion-beams. Finally, the optoelectronic properties of silicon are used as a photoconductive layer in light-induced dielectrophoretic manipulation of cells. These three projects are combined to investigate optofluidic sensing and manipulation, with potential radiobiological applications

Statics and dynamics of electrothermal micromirrors

Adaptive and smart systems are growing in popularity as we shift toward personalization as a culture. With progressive demands on energy efficiency, it is increasingly important to focus on the utilization of energy in a novel way. This thesis investigates a microelectromechanical system (MEMS) mirror with the express intent to provide flexibility in solid state lighting (SSL). By coupling the micromirror to an optical source, the reflected light may be reshaped and directed so as to optimize the overall illumination profile. In addition, the light may be redirected in order to provide improved signal strength in visible light communications (VLC) with negligible impact on energy demands. With flexibility and full analog control in mind, the design of a fully integrated tip-tilt-piston micromirror with an additional variable focus degree of freedom is outlined. Electrothermal actuators are used to both steer the light and tune the focal length. A detailed discussion of the underlying physics behind composite beams and thermal actuators is addressed. This leads directly into an overview of the two main mirror components, namely the segmented mirror and the deflection actuators. An in-depth characterization of the dynamics of the mirror is discussed including the linearity of the thermal response. Frequency domain analysis of such a system provides insight into tunable mechanical properties such as the resonant frequency and quality factor. The degenerate resonant modes can be separated significantly. It is shown that the frequency response may be tuned by straining specific actuators and that it follows a predictable pattern. As a result, the system can be scanned at increasingly large angles. In other words, coupled mechanical modes allow variable damping and amplification. A means to determine the level of coupling is examined and the mode shape variations are tracked as a function of the tuning parameters. Finally, the applications of such a device are explored and tested. Such applications include reliable signal-to-noise ratio (SNR) enhancements in VLC of 30 dB and color tunable steerable lights using laser diodes. A brief discussion of the implications of dynamic illumination and tunable systems is juxtaposed with an explanation behind the integration of an electrothermal micromirror and an all digital driver

Indium Phosphide Based Optical Waveguide MEMS for Communications and Sensing

Indium phosphide (InP) is extensively used for integrated waveguide and photonic devices due to its suitability as a substrate for direct bandgap materials (e.g. In1-XGaXAsYP1-Y) operating at the lambda=1550 nm communications wavelength. However, little work has been reported on InP optical waveguide micro-electro-mechanical systems (MEMS). In this work, InP cantilever and doubly-clamped beams were micromachined on an In0.53Ga0.47As "sacrificial layer" on (100) InP substrates. Young's modulus was measured using nanoindentation and microbeam-bending. Intrinsic stress and material uniformity (stress gradient) were obtained by measuring the profile of doubly-clamped and cantilever beams using confocal microscopy. The study resulted in a Young's modulus of 80.4-106.5 GPa (crystal orientation-dependent). Although InP was grown lattice-matched to the substrate, arsenic from the underlying In0.53Ga0.47As sacrificial layer resulted in intrinsic compressive stress. Adding trace amounts of gallium to the InP layer during epitaxial growth induced tensile stress to offset the effect of arsenic. The materials characterization was extended to develop optical waveguide switches and sensors. In the first device, two parallel waveguides were actuated to vary the spacing between them. By modulating the gap using electrostatic pull-in actuation, the optical coupling strength was controlled via the evanescent field. Low voltage switching (<10 V), high speed (4 us), low crosstalk (-47 dB), and low-loss (<10 %) were achieved. Variable coupling over a 17.4 dB dynamic range was also demonstrated. The second device utilized a single movable input waveguide, which was actuated via electrostatic comb-drives to end-couple with one of several output waveguides. Low voltage switching (<7 V), 140 us switching speed (2 ms settling time), low crosstalk (-26 dB), and low-loss (<3.2 dB) were demonstrated. Sensing techniques based on mass-loading were developed using end-coupled cantilever waveguides. Here, the mechanical resonance frequency was measured by actuating the cantilever and measuring the end-coupled optical power at the output waveguide. A proof-of-concept experiment utilized a focused-ion-beam to mill the cantilever tip and resulted in a measurable resonance shift with mass-sensitivity delta_m/delta_f=5.1 fg/Hz. The cantilever waveguide devices and measurement techniques enable accurate resonance detection in mass-based cantilever sensors and also enable single-chip sensors with on-chip optical detection to be realized