CNT–based Field Ionization Micro Vacuum Pumps
- Category: Energy, Medical Electronics, Nanotechnology
- Tags: Akintunde Akinwande, Daniel Jang, Luis Velásquez-García
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Download as PDFThis project aims to develop the technology for field-enabled low-power portable vacuum sources that can be made cheaply and reliably, opening the doors to exciting applications such as portable mass spectrometers and high-performance sensors for inertial navigation. Our micropump uses arrays of isolated vertically aligned carbon nanotubes (VA-CNTs) to field-ionize the background gas, that is, to quantum tunnel electrons from the outer shell of neutral gas molecules due to the presence of a very high electrostatic field near the VA-CNT tip (Figure 1). Field strength of at least 108V/cm is needed to field-ionize gases [1] . The ions are then implanted in a non-evaporative getter structure biased at a high negative voltage, hence obtaining vacuum. The field ionization micropump that we are developing is designed to work at pressures as high as 30 Torr. Our fabricated field ionizer, shown in Figure 2, is composed of arrays of VA-CNTs surrounded by a ring of VA-CNTs. The central VA-CNT of each unit enhances the electric field to achieve field ionization, while the high-transparency ring increases the flux of neutral molecules to the ionization region. VA-CNTs are ideal for field ionization because of their high aspect ratio, which enables low-voltage field ionization and their inherent chemical and mechanical robustness. Unlike electron impact ionizers [2] , the field enhancer of a field ionizer is biased at a higher voltage than the gate. Therefore, the ions it creates do not stream back to the field enhancers, which results in enhanced reliability. The getter will be biased at a lower potential with respect to the gate to attract and implant the positive ions. Current research efforts include optimization of the fabrication of the devices and experimental characterization as ionizers and pumps.
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- Figure 1: The potential well the tip and surrounding gas in field ionization. The high electric field will raise the gas’s potential well to allow for electrons to tunnel to the tip, thereby ionizing the gas molecules.
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- Figure 2: SEM of a fabricated array of field ionizers. The device is composed of an array of isolated vertical CNTs, each surrounded by a high-transparency electrode ring, i.e., gate.
