MOS capacitor sensor array for hydrogen gas measurement

195 Pages·2005·5.33 MB·English

by  Qu, Xi Dong

MOS CAPACITOR SENSOR ARRAY
FOR HYDROGEN GAS MEASUREMENT
Xi Dong Qu
B. Sc., Fudan University, 1989
THESIS SUBMITTED IN PARTIAL FULFILLMENT OF
THE REQUIREMENTS FOR THE DEGREE OF
MASTER OF APPLIED SCIENCE
In the
School
of
Engineering Science
O Xi Dong Qu 2005
SIMON FRASER UNIVERSITY
Summer 2005
All rights reserved. This work may not be
reproduced in whole or in part, by photocopy
or other means, without permission of the author.
Approval
Name: Xi Dong Qu
Degree: Master of Applied Science
Title of Thesis: MOS Capacitor Sensor Array for Hydrogen Gas
Measurement
Examining Committee:
Chair: Dr. John Dill
Professor of Engineering Science
Dr. Glenn Chapman
Senior Supervisor
Professor of Engineering Science
Dr. Jonathan Wu
Supervisor
Associate Professor of Department of Electrical and
Computer Engineering, University of Windsor
Dr. Ash Parameswaran
Internal Examiner
Professor of Engineering Science
Date DefendedJApproved: Wednesday, June 29,2005
SIMON FRASER UNIVERSITY
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Abstract
Palladium-MOS hydrogen sensors have wide applications in the industries. This
thesis presents a novel design and development of a hydrogen sensor and sensor array
based on MOS capacitor structure. The primary target of the device is the applications
in the fuel cell system. In total, three generations of MOS capacitor structures have been
designed, fabricated and tested. An empirical model for sensors' response to hydrogen
concentrations is established and validated. Experimental results demonstrate that the
sensor is highly sensitive to hydrogen gas, and the sensor array, which is based on the
third generation structure, is capable of not only hydrogen leaks detection, but leaks
location, and gas distribution monitoring. A gas test station and a sensor data
acquisition system for the characterization and calibration of sensor array are also
devised and implemented. A method and apparatus for gas leaks detection, location and
distribution monitoring is provided as well.
Dedication
This thesis is dedicated to my wife, Tong Zou, for her unwavering love and
support, and to my parents, Jida Qu and Quhua Xi, who taught me the joy of education
and the value of perseverance.
Acknowledgements
The author would like to thank Dr. Glenn Chapman for his supervision and
guidance, Dr. Jonathan Wu and Dr. Cheng Hu for their motivation and support, and
Mrs. Eva Czyzewska and Mr. Bill Woods for their assistance in preparing the samples.
This work was sponsored by the National Research Council Canada.
Table of Contents
..
...........................................................................................................................
Approval
11
...
...........................................................................................................................
Abstract
111
..........................................................................................................................
Dedication iv
............................................................................................................
Acknowledgements v
..............................................................................................................
Table of Contents vi
...................................................................................................................
List of Figures ix
...................................................................................................................
List of Tables xiv
..................................................................................................
Chapter 1: Introduction 1
Background .................................................................................................... 1
Existing Hydrogen Microsensors .................................................................... 3
Metal-Oxide-Semiconductor (MOS) Sensors ................................................. 4
Semiconducting Metal Oxide Sensors ............................................................ 7
Catalytic Combustion Sensors ........................................................................ 9
Electrochemical Sensors .............................................................................. 1 1
Thermal Conductivity Sensors ...................................................................... 12
Piezoelectric Sensors ..................................................................................... 13
Surface Acoustic Wave (SAW) Sensors ....................................................... 13
Pyroelectric Sensors ...................................................................................... 13
Fiber Optic Sensors ....................................................................................... 14
Summary ................................................................................................. 14
Objective ...................................................................................................... 1 6
Outline ........................................................................................................... 17
................................................................................
Chapter 2: Principles of Operation 19
Introduction ................................................................................................... 19
MOS Device Physics ..................................................................................... 19
Hydrogen Sensing Mechanism ...................................................................... 28
Existing Pd-MOS Capacitors ........................................................................ 34
Summary ....................................................................................................... 35
.........................................................
Chapter 3: MOS Sensor Design and Fabrication 37
3.1 Introduction ................................................................................................... 37
3.2 First Generation Pd-MOS Capacitor ............................................................. 38
3.2.1 Fabrication Procedures of First Generation Pd-MOS Capacitor ................... 39
3.2.2 SiOz Fabrication ............................................................................................ 40
Palladium Deposition .................................................................................... 43
Palladium Patterning ..................................................................................... 45
Substrate Type ............................................................................................... 47
Second Generation Pd-MOS Capacitor ......................................................... 48
Sensor Dimensions ........................................................................................ 49
Fabrication Procedures of Second Generation Pd-MOS Capacitor .............. 50
Field Oxide Fabrication ................................................................................. 51
Capacitor Oxide Fabrication ......................................................................... 53
Palladium Pad (Level 1 Pd) Fabrication ....................................................... 54
Palladium Contact (Level 2 Pd) Fabrication ................................................. 55
Third Generation Pd-MOS Capacitor ........................................................... 56
MOS Sensor Structure Modification to Eliminate Crosstalk ........................ 56
Fabrication Procedures of Third Generation Pd-MOS Capacitor ................. 57
Summary ....................................................................................................... 65
......................................................................................
Chapter 4: Experimental Setup 67
Introduction ................................................................................................... 67
Three Ways for Sensor Characterization. ...................................................... 67
Gas Test System Setup .................................................................................. 68
Gas Delivery and Control .............................................................................. 69
Calibration Chamber ..................................................................................... 71
mgh Vacuum Chamber ................................................................................ -74
Gas Nozzle .................................................................................................... 75
Sensor Measurement System Setup .............................................................. 76
C-V Measurement ......................................................................................... 79
Sensor Array Measurement ........................................................................... 83
Summary ...................................................................................................... -93
.................................................................................
Chapter 5: Experimental Methods 95
Introduction .................................................................................................. -95
Experiments with Individual MOS Sensors .................................................. 95
Sensor Response to Hydrogen Concentration ............................................... 96
Sensor Response to Hydrogen Leakage ........................................................ 98
Sensor Response in High Vacuum ................................................................ 99
Experiments with MOS Sensor Array ......................................................... 100
Scheme for Hydrogen Distribution Monitoring ......................................... 100
Scheme for Detecting and Locating Hydrogen Leaks ................................. 103
Summary ..................................................................................................... 106
.................................................................................
Chapter 6: Experimental Results 107
6.1 Introduction ................................................................................................. 107
6.2 Individual MOS Sensor Behaviours ............................................................ 108
6.2.1 Sensitivity to Hydrogen Concentration ....................................................... 108
6.2.2 Sensitivity to Hydrogen Leakage ................................................................ 110
6.2.3 Sensitivity in High Vacuum ........................................................................ 112
6.2.4 Transient Response ................................................................................... 1 14
6.2.5 Preliminary Results of Gas Distribution ..................................................... 116
vii
Response Equation ...................................................................................... 118
Temperature Property .................................................................................. 132
Comprehensive Transfer Function ............................................................. 137
Other Properties ........................................................................................... 144
Sensor Array Data Analysis ........................................................................ 146
Sensor Array Calibration ............................................................................. 146
Gas Distribution Monitoring ...................................................................... 147
Gas Leak Detection and Location ............................................................... 152
Summary ..................................................................................................... 157
..................................................................
Chapter 7: Conclusions and Future Work 158
7.1 Conclusions ............................................................................................... 1 5 8
7.2 Future Work ............................................................................................... 163
............
Appendix: Method and Apparatus for Detecting and Locating Gas Leaks 167
A . 1 Method .......................................................................................................1 67
A.2 Apparatus ................................................................................................... 169
A.3 Examples ..................................................................................................... 171
.................................................................................................................
Reference List 178
...
Vlll
List of Figures
Figure 1-1 Schematic representations of (a) a Pd-MOS transistor and (b) its
current-voltage characteristics demonstrating the effects of the
hydrogen dipole layer at the interface. Here D = drain, G = gate,
Hai = hydrogen concentration at the Pd-oxide interface, based on
Lundstrom et a1 [7]. ........................................................................................ 5
Figure 1-2 Schematic representations of (a) a Pd-MOS capacitor and (b) its C-
V curves demonstrating the effects of the hydrogen dipole layer: a
negative flat-band voltage shift (AV). Here Hai = hydrogen
concentration at the Pd-oxide interface, based on Lundstrom et a1
[7]. ................................................................................................................. .7
Figure 1-3 Model of inter-grain potential barrier (a) without hydrogen and (b)
with hydrogen, based on G. W. Hunter [3]. ................................................... 8
Figure 1-4 Illustration of pellistor calorimeter showing catalyst on alumina
bead (the inner coil is Pt wire), based on G. W. Hunter [3] ......................... 10
Figure 1-5 Schematic representations of (a) a potentiometric hydrogen sensor
and (b) an amperometric current-limiting sensor, based on G. W.
Hunter [3]. .................................................................................................. 1 2
Figure 2-1 Schematic illustration of a classical capacitor ............................................. 20
Figure 2-2 Schematic representation of a MOS capacitor ............................................. 21
Figure 2-3 Schematic illustration of an n-type MOS capacitor in the regions
of (a) accumulation, (b) depletion and (c) inversion, as modified
from W. S. Ruska [27]. ................................................................................ 22
Figure 2-4 Equivalent circuit of a MOS capacitor ......................................................... 23
Figure 2-5 Capacitance-voltage (C-V) characteristic of an n-type MOS
capacitor in the regions of accumulation, depletion and inversion,
as modified from W. S. Ruska [27]. ............................................................ 24
Figure 2-6 Schematic illustration of oxide trapped charges, based on S. Wolf
[28] .............................................................................................................. .26
Figure 2-7 Capacitance-voltage (C-V) characteristic of an n-type MOS
capacitor in a non-ideal case (VFB> O), the dashed line showing the
ideal case (VFB= 0), as modified from W. S. Ruska [27]. ........................... 27
Figure 2-8 Schematic comparison of the solubility of hydrogen in Pd, Ni, and
Pt as a function of temperature at a pressure of 1 atm, as modified
from F. A. Lewis [29]. ................................................................................. 28