Vacuum tubes were integral to the rise of electronics in the 20th century, enabling the development of many core technologies, such as radar, television, radio and audio communications and early computers. However, the invention of the solid-state transistor, and subsequent integrated circuit technology, meant that electronics could be smaller, cheaper, faster and more reliable than vacuum tubes. Because of this, vacuum tubes were ultimately superseded by solid-state devices and thus began the trend of rapid miniaturization of electronics. Interestingly, although solid-state devices supplanted vacuum tubes in most domains, the trend towards miniaturization also enabled the emergence of vacuum microelectronics - a field that uses modern solid-state microfabrication techniques to develop micrometer-scale vacuum-based devices, or field emission devices. The emergence of this field was motivated by the desire to leverage some of the unique performance advantages offered by vacuum-based devices. Indeed, vacuum as an electron conduction medium offers some unique technical advantages over solid-state transport, such as ballistic electron transport, the ability to operate at high frequencies and robustness in harsh conditions, such as extreme temperatures, extreme pressures and high radiation environments. However, in order to leverage these features and enable widespread and practical use of field emission devices in electronics, on-chip ambient operation device architectures directly integrated on Si must be designed.

Here, the design and application of portable field emission devices that can operate in ambient conditions will be presented and discussed. This includes the first demonstration of vacuum-sealed fully integrated diode and triode field emission arrays that are developed in a scalable, BEOL-compatible process directly on Si. The device architectures demonstrate effective vacuum-sealing and gate-modulated field emission, with the ability to block voltages of up to 200 V. High operating voltages and low currents make these devices useful in high voltage drive circuits for MEMS actuators. Then, a novel device architecture for a portable electron source is presented. A fabrication process is developed to integrate graphene as an extraction electrode for field emission arrays on Si. Operation of this device is the first demonstration of a fully integrated field emission array utilizing graphene as both an extraction electrode and electron-transparent vacuum seal, enabling in-air extraction of electrons. The type of on-chip portable electron source developed here presents a unique method for using field emission-based electron sources in non-ideal conditions, unlocking applications ranging from ion thrusters for microrobotics to environmental microscopy.




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