CNT-based gas ionizers with integrated MEMS gate for portable mass spectrometry applications

We report the fabrication and experimental characterization of a novel low-cost carbon nanotube (CNT)-based electron impact ionizer (EII) with integrated gate for portable mass spectrometry applications. The device achieves low-voltage ionization using sparse forests of plasma-enhanced chemical vapor deposited (PECVD) CNTs field emitter tips, and a proximal gate with open apertures to facilitate electron transmission. The gate is integrated using a deep reactive ion etched (DRIE) spring-based high-voltage MEMS packaging technology. The device also includes a high aspect-ratio silicon structure (mufoam) that facilitates sparse CNT growth and limits the electron current per emitter. The devices were tested as field emitters in high vacuum (10^-8 Torr). Electron emission starts at a gate voltage of 110 V, and reaches a current of 9 uA at 250 V (2.25 mW) with more than 55% of the electrons transmitted through the gate apertures. The devices were also tested as electron impact ionizers using argon. The experimental data demonstrates that the CNT-EIIs can operate at mtorr-level pressures while delivering 60 nA of ion current at 250 V with about 1% ionization efficiency.