Microengineered sensor devices with field emission electron sources

This dissertation describes the design, simulation, fabrication, and characterization of a microengineered pressure sensor device and a microengineered mass spectrometer device, both of which use field emission cathode tip arrays as electron sources. VLSI and MEMS process techniques are used to scale down the dimensions from existing vacuum pressure sensors and mass spectrometers. The microengineered pressure sensor device is fabricated on a silicon substrate approximately 1cm by 1cm. It consists of an electron source in the form of cathode tip array structure, an electron accelerating space which includes a gas ionization volume, and an ion collection electrode. The electrons emitted from the cathode are accelerated to energies high enough to ionize neutral gas molecules in the ionization volume. The ions are then collected by a negatively biased electrode located at center of the device. This pressure sensor device further utilizes a magnetic field created by a permanent magnet to lengthen the electron trajectory. It is the first report of a magnetic ionizing type pressure (vacuum) sensor with a field emission electron source on a chip. The test results show that the ion current is a linear function of pressure and is consistent with the theoretical modeling and simulation. The microengineered mass spectrometer device is fabricated using two silicon substrates approximately 1cm by 1cm, where one is a cathode electron source and the other is the ion collector. A field emission cathode tip array is used as an electron source to ionize the input gas molecules. The ions are extracted by an electric field and follow a curved trajectory that is determined by the ion mass, charge state and the crossed combination of static electric and magnetic fields. The separated ions are then collected at different locations on the parallel planar electrodes. A number of different structures were design and simulated. The optimized geometry of this device was fabricated and tested. Fowler-Nordheim field emission behaviors were investigated. This device is the first miniature mass spectrometer using a field emission electron source