Open AccessEvaluation of the porous silicon capacitor as a moisture sensor for vacuum applications
Author(s) -
Kevin R. Zavadil,
G.T. Cordes,
Michael J. Kelly,
T.R. Guilinger
Publication year - 1996
Language(s) - English
Resource type - Reports
DOI - 10.2172/399681
Subject(s) - moisture , microelectronics , calibration , capacitor , materials science , vacuum level , process engineering , porosity , water content , environmental science , optoelectronics , electrical engineering , engineering , composite material , voltage , physics , geotechnical engineering , quantum mechanics
A growing demand exists for inexpensive and reliable sensors for moisture detection in reduced pressure processing environments. Sandia`s Porous Silicon Capacitor (PSC) sensor appears to be an ideal candidate for this application. This sensor is a solid state device that detects moisture through changes in dielectric constant with water adsorption. Standard microelectronic fabrication techniques are used in its production affording low cost production and ready integration into complex sensor and electronic arrays. This sensor has previously been investigated for moisture detection in fluid streams, however, little effort has been placed on its behavior in a vacuum environment. Sandia`s Sensors in Vacuum (SIV) test facility has been employed to evaluate the performance characteristics of this sensor in vacuum. In addition, a vacuum-based study allows for a more controlled environment in which the intrinsic lower limit for moisture detection and response times to moisture changes can be easily determined quantitatively. This report describes the performance characteristics of a series of sensors from a single production lot. Calibration of these sensors to moisture levels from part per billion to part per hundred concentrations has been performed. The concentration-dependent sensitivity of these sensors is documented. The response time and drift characteristics of these sensors are also discussed. The investigation of a preliminary method for increasing the recovery time of the sensor after moisture exposure is presented. The role of hydrocarbon contamination, a potential problem in some vacuum schemes, is also evaluated. Specific recommendations are made on how to implement this sensor for vacuum applications