Mass spectrometry has long been used as a scientific tool in a wide variety of applications. A portable mass spectrometer would make many of these applications faster and more efficient. One of the key components of a mass spectrometer is its ion detection system; to make a mass spectrometer portable, this system must be small and involve as few components as possible. Single ion detection has been achieved through several methods, nearly all of which are well-known and understood. These methods, however, often require bulky vacuum and/or cooling systems in order to achieve high sensitivity. An ion detection system that can achieve high sensitivity under atmospheric pressure and normal temperature conditions would make portable mass spectrometry much more feasible. This thesis introduces a new method of detecting ions which does not require a vacuum or cold temperatures to operate: the solid-state ion detector, or SSID. Although ion detection using solid-state devices has been investigated previously, this work introduces metal-oxide-semiconductor field-effect transistors (MOSFETs) in a cascode configuration which acts as the primary detector when combined with a Faraday cup and mechanical switch. This detector is followed by a second amplifying stage which features RC-filters to help reduce noise and improve the detector's overall sensitivity. The detector is placed on a printed circuit board that was designed to fit a pre-determined system. Additional power circuitry for the mechanical switch was also designed and added to the detector circuitry. The SSID will be most sensitive when the input capacitance is made as small as possible. With this in mind, MOSFETs with a very low (< 1pF) gate capacitance were fabricated at BYU for use in the SSID. The performance of these MOSFETs was compared to a commercially available device in the same configuration. When tested, both MOSFETs had a sensitivity of hundreds of electrons when integrated in the complete SSID circuit. The commercial MOSFET demonstrated an estimated sensitivity of 150 electrons. The SSID shows much promise, and suggestions are made for further improving it to achieve even higher sensitivity levels. If made more sensitive, the next step would be to create an array of SSID detectors to be used in a portable mass spectrometer.
College and Department
Ira A. Fulton College of Engineering and Technology; Electrical and Computer Engineering
BYU ScholarsArchive Citation
Sabbah, Sadek Salman, "A Solid-State Ion Detector for Use in Portable Mass Spectrometry" (2014). All Theses and Dissertations. 5825.
Sadek Sabbah, mass spectrometry, ion detectors, solid-state devices, MOSFETs