A critical requirement for the success of autonomous remote systems is the realization of miniature power sources with long lifetimes, especially for sensor networks working in harsh, inaccessible environments where battery replacement would be expensive or impossible. Applications include environmental monitoring, civil infrastructure health monitoring, and implantable medical devices such as pacemakers and intra cranial implants. To achieve high-energy long-lifetime miniature power sources, we need to use fuels with high energy density that can perform reliably in harsh environments. Low energy beta radioisotopes such as Nickel-63, Promethium-147 have energy density several orders of magnitude higher than electrochemical, lithium-ion, and hydrocarbon fuels, and their emitted electrons can be easily shielded with low radiation and chemical risks. Furthermore, the radiation process is independent of the surrounding environment, which makes it a great candidate to power device working in harsh environments. The choice of the radioisotope depends on the application requirements. In this dissertation, since we are focused on long term sensing applications, we will focus our studies on Nickel-63, which has a half life of 100.2 years. For remote wireless sensing and communication applications, continuous signal transmission is often not required with data acquisition once every minute or over longer durations is sufficient. However, RF power ranging from 1mW to hundreds of mW is required for signal transmission to reach receiver that maybe located at distant places. Furthermore, we need to use minimum amount of Nickel-63 for both cost and safety reasons. To achieve both requirements, a pulsed power generating system is designed and implemented. In the system, inside a vacuum chamber, a conducting cantilever is placed above a Nickel-63 radioactive source. As the emitted electrons are collected on the cantilever charging it with negative charge, the Nickel-63 source gets positively charged. As the voltage across the gap increases,the cantilever is pulled toward the source. Electrostatic discharge occurs when the electric field across the gap exceed the break down limit. Although the cantilever pull down process can take several minutes, the discharge process occurs in nanoseconds. A pulsed power amplification is thus achieved. With 1.5mCi input, output RF signal with hundreds of milliwatts have been demonstrated. The pulsed RF power generator is further characterized both theoretically and experimental to achieve the application-determined output RF frequency and power. The RF frequency is found to be determined with the equivalent capacitance and inductance of the system. A capacitive humidity sensor is integrated with system, and a fully self-powered wireless humidity sensor node with decades of life time was demonstrated with ambient humidity level coded in the output RF signal. To have a high quality factor RF signal with well-defined frequency for long distance wireless RF communication, a surface acoustic wave (SAW) resonator is integrated into the system as a frequency selector, and RF output signal with equivalent quality factor over 1000 have been demonstrated. For applications that requires decades of continuous power, this dissertation also reports on an 11.2% ultra-high efficiency 50um-thick thinned-down silicon carbide betavoltaics under (Nickel-63 irradiation. The efficiency can be further increased to 23.6%, while the device thickness can be decreased to below 30um. Comparing to the best SiC betavoltaics reported so far, our devices have an efficiency improvement of 3-4X, with a fuel fill factor improvement of 8-10X, which will lead to an overall power density improvement of 30-40X. Comparing to the best available planar silicon betavoltaics, our devices have power density improvements of 100X (6X in efficiency, and 16X improvement in fuel fill factor.)
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