MTL Annual Report

This project looks 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 analytical instruments.  Our micropump uses arrays of isolated vertically aligned carbon nanotubes (VA-CNTs) to field-ionize gas particles, i.e., to quantum tunnel electrons from the outer shell of neutral gas molecules due to the presence of a local very high electrostatic field (Figure 1). A field strength of at least 10⁸ V/cm is needed to field-ionize gases ^[1].  The ions that are created by the field ionizers are implanted in a getter structure biased at a high negative voltage to obtain vacuum. The field ionization micropump that we are developing will work at pressures as high as 30 Torr.  Our proposed structure, shown in Figure 2, is composed of a central VA-CNT surrounded by a ring of VA-CNTs. The central VA-CNT 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 because of 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.

1. R. Gomer, Field Emissions and Field Ionization.  American Institute of Physics, 1992. [↩]
2. L.-Y. Chen and A. I. Akinwande, “Aperture-collimated double-gated silicon field emitter arrays,” IEEE Transactions on Electron Devices, vol. 54,  pp. 601-8, 2007. [↩]