Automatic recognition of unique characteristics of an object can provide a powerful solution to verify its authenticity and safety. It can mitigate the growth of one of the largest underground industries—that of counterfeit goods–flowing through the global supply chain. In this article, we propose the novel concept of material biometrics, in which the intrinsic chemical properties of structural materials are used to generate unique identifiers for authenticating individual products. For this purpose, the objects to be protected are modified via programmable additive manufacturing of built-in chemical “tags” that generate signatures depending on their chemical composition, quantity, and location. We report a material biometrics-enabled manufacturing flow in which plastic objects are protected using spatially-distributed tags that are optically invisible and difficult to clone. The resulting multi-bit signatures have high entropy and can be non-invasively detected for product authentication using $$^{35}$$ 35 Cl nuclear quadrupole resonance (NQR) spectroscopy.
The Global Positioning System (GPS) is the primary means of Positioning, Navigation, and Timing (PNT) for most civilian and military systems and applications. The rapid growth in autonomous systems has created a widespread interest in self-contained Inertial Navigation System (INS) for precise navigation and guidance in the absence of GPS. The microscale PNT systems need both specialized and low cost fabrication technologies to cost effectively bring these technologies to market. We describe an ultra-clean (low leak rate) wafer-level vacuum encapsulation microfabrication process of Micro-Electro-Mechanical Systems (MEMS) based sensors and devices. Using this process we have fabricated inertial sensors, frequency reference resonators, and pressure sensors. In addition to providing excellent resistance to shock and vibration, this combined microfabrication and packaging method would allow the use of high volume low cost plastic packaging at the device level. The microfabrication process is an 8” wafer process based on high aspect ratio bulk micromachining of a 30 μm thick single-crystal silicon device layer that is vacuum encapsulated at 10 mTorr between two silicon wafers with the demonstrated leak rate of only 6.5 × 10−18 atm cm3/s.
In this thesis, a low-voltage 32 kHz silicon tuning fork MicroElectroMechanical Systems (MEMS)-based resonator design with a high Quality factor of over 73,000 is presented with a Complementary Metal-Oxide Semiconductor (CMOS) sustaining amplifier towards a low power oscillator. The resonator is designed using MEMS Integrated Design for Inertial Sensors (MIDIS) process developed by Teledyne DALSA Semiconductor Inc. (TDSI). MIDIS offers wafer-level vacuum encapsulation with ultra-low leak rate. Ultra-low polarization voltage, as low as 10mV, is needed to excite the resonator by using a transduction gap reduction technique based on electrostatic deflection of movable electrodes and subsequent localized melting of welding pads for permanent position locking. Further, the technique helps to minimize unexpected electrostatic stiffness induced by time-varying capacitance across transduction gaps to just-0.6 N/m. The motional resistance drops down to about 2kΩ as a result of a small gap size and the technique helps to improve the Quality Factor (Q). A sustaining amplifier using a transimpedance operational amplifier configuration is system-integrated with the tuning fork resonator to establish continuous oscillation with low damping losses. An average power consumption of around 600µW is measured on the oscillator, which is suitable for mobile electronic systems. v Dedicated to my parents vi ACKNOWLEDGEMENTS My special thanks to Dr. Vamsy Chodavarapu, my advisor, for giving me guidance all through my research work as well as unlimited access to the software and other resources necessary for completing the design of this work. I would also like to appreciate everyone who has offered me assistance in this work. This includes George Xereas, who spared some of his valuable time to teach me with patience how to use the CoventorWare software for MEMS-based resonator design; Balaadithya Uppalapati, who gave me the basic tutorials on how Silvaco EDA tools should be used for oscillator circuit design; and Dr. Weisong Wang, for imparting knowledge of MEMS fundamentals to me through lectures in class. I also deeply appreciate Dr. Guru Subramanyam, who provided me with several useful points on which parts I should improve regarding the work in the future. vii
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