Cold Electron Sources for Low Size Weight and Power Mass Spectrometers

Electron emitters are key components of many instruments with scientific, industrial, or medical applications. The first stage of mass spectrometers involve ionizing the sample by electron impact at high energy. Presently, the default source of electrons in most cases are hot filament cathodes. Hot filaments have a number of drawbacks, including high power draw, heating, high vacuum requirements, gradual burn-out, and a wide range of emitted electron energies. For space-based applications, they are not replaceable. Long lifetime cold cathodes have been a goal for decades. Field emitters such as Spindt and CNT emitters are the most prominent. They rely on a sharp tip to enhance electric fields to eject electrons. However they also eject their tip material and have short lifetimes. Metal-Insulator-Metal tunneling cathodes impart the energy to escape into vacuum by accelerating electrons as they tunnel across an insulator towards a thin top metal exposed to vacuum. We are designing and fabricating a similar structure involving a semiconductor, insulator, and a 2D material top electrode. The insulator is designed for stability, low defect density, and high tunneling current. The top electrode creates a tunneling potential across the insulator without the need for scattering metal films that can damage the insulator. The top of the insulator will be in contact with the 2D material, which is very stable and will not diffuse into the insulator, which is the biggest contributor to this type of device degradation and failure. In addition to these desirable properties, our device is fabricated on-chip using semiconductor processing methods. Importantly, they will take less than 15 volts to operate. This is extremely low power, as the tunneling current is 10 mA/cm2, so operating the device takes 150 of milliwatts/cm2 in contrast to a hot filament, which uses 5 or more watts/cm2, and the field emitters, which require extremely high voltages.