Vacuum measurement by carbon nanotube field emission

Abstract

A vacuum measurement technology utilizing the carbon nanotube (CNT) field-emission effect has been developed and characterized. The fabricated pressure sensor is a triode type similar to a conventional ionization gauge, but has a planar structure similar to a field-emission display. Owing to the excellent field-emission characteristics of CNTs, it is possible to make a cost effective cold cathode-type ion gauge. The triode-type CNT sensor has been manufactured by a screen-printing method and by a thermal chemical-vapor deposition growth method. A modified structure with an electron filter has also been introduced and characterized so as to improve the performances, such as sensitivity and stability. A glass grid with Cr deposited by e-beam is placed on the cathode. By the voltage applied to the grid, electrons are emitted from the CNTs and they ionize gas molecules in the chamber. Two modes are available to detect the gas density in the chamber, an electron emission mode and an ionization mode. In the electron emission mode, the collector voltage is controlled to be slightly higher than the grid voltage, whereas in the ionization mode it is controlled to be lower than the grid voltage so as to obtain a large ionization ratio. The ionized molecules are gathered at the collector and the electrons return to the grid in the triode structure. The ionization ratio increases as a function of pressure in the electron emission mode. The ionization characteristics are dependent on the gas and the combination of the voltages applied to the grid and the collector. In this article, the various metrological characteristics of the developed pressure sensor utilizing CNTs are introduced.