Manufacturability of vacuum microtubes

Vacuum microtubes (VMs), a new breed of vacuum tube electronics and solid state technology, are superior in speed, power, radiation hardness and temperature stability than semiconductor-based diodes and transistors. Electrons generated by cold emission, accelerated by an electric field to a velocity of about 6·10⁸ cm/s, travel very short distances of about 1 μm in VMs. With their extremely short transit time, it is possible for VMs to operate at frequencies approaching hundreds of GHz. State of the art studies have demonstrated a few major drawbacks to reliable operation of VMs, namely, unpredictable position of the emitting spot, fluctuating or insufficient emission current, damage to the emitters by excessive electric field, and fundamental problems in producing arrays of emitters with equally sharp apices. In this study we addressed the spreading of technological parameters, such as work function φ, field enhancement factor β´, and emitting area α, and their impact on the operation of a VM. Two designs are discussed. The first design requires low φ on the emitter, and no sharpening or etching (β´=1). The design incorporates low φ regions to localize the emission. We feel that VMs have limited flexibility when designed to operate only by electric field control. Therefore, we propose a second design which operates with a photoemitting cathode for microwave and optoelectronic applications. Using Fowler-Nordheim (F-N) tunneling theory we estimated various manufacturable designs of cold emitter devices and phototubes. Our experimental designs are still not manufacturing prototypes, however; because of their simplicity, they can be produced by almost any semiconductor foundry