Preface ........................................................ xi
1 Introduction ................................................. 1
1.1 A Fabrication Perspective ............................... 3
1.2 Scaling Laws and Fluid Phenomena ........................ 5
1.2.1 Viscous Flow ..................................... 7
1.2.2 Surface Tension .................................. 9
1.2.3 Diffusion ....................................... 10
1.3 Microfluidic Functions ................................. 11
1.3.1 Flow Control .................................... 12
1.3.2 Particle Manipulation ........................... 12
1.3.3 Fluid Ejection .................................. 13
1.4 Semantics .............................................. 13
1.5 Categorizing Fabrication Processes ..................... 15
1.5.1 Bulk Micromachining Versus Surface
Micromachining .................................. 15
1.5.2 Serial Versus Parallel Fabrication Processes .... 16
1.5.3 Major Fabrication Process Categories ............ 16
1.6 Organization of this Book .............................. 17
References ............................................. 19
2 Geometric Features .......................................... 25
2.1 Common Types of Features ............................... 28
2.1.1 Cavities and Orifices ........................... 28
2.1.2 Microchannels ................................... 30
2.1.3 Membranes ....................................... 34
2.2 Geometric Characteristics .............................. 36
2.2.1 Profile ......................................... 36
2.2.2 Feature Resolution .............................. 40
2.2.3 Aspect Ratio .................................... 41
2.2.4 Degrees of Freedom .............................. 41
2.2.5 Surface Roughness ............................... 47
References ............................................. 50
3 Materials for Microfluidic Devices .......................... 55
3.1 Types of Materials ..................................... 56
3.1.1 Polymers ........................................ 56
3.1.2 Silicon ......................................... 59
3.1.3 Glass ........................................... 61
3.1.4 Metals .......................................... 62
3.1.5 Other Materials ................................. 63
3.2 Material Properties .................................... 64
3.2.1 Mechanical Properties ........................... 65
3.2.2 Thermal Properties .............................. 69
3.2.3 Electrical Properties ........................... 73
3.2.4 Optical Properties .............................. 77
3.2.5 Magnetic Properties ............................. 79
3.2.6 Other Physical Properties and Characteristics ... 80
3.2.7 Chemical Resistance ............................. 82
3.3 Surface Conditions ..................................... 83
References ............................................. 87
4 Photolithography ............................................ 99
4.1 Introduction ........................................... 99
4.1.1 Photoresist .................................... 100
4.1.2 Photomasks ..................................... 100
4.2 Process Basics ........................................ 101
4.2.1 Coating ........................................ 102
4.2.2 Baking ......................................... 103
4.2.3 Alignment ...................................... 103
4.2.4 Exposure ....................................... 105
4.2.5 Developing ..................................... 108
References ............................................ 108
5 Solidification Processes and Soft Lithography .............. 111
5.1 Radiation-Selective Polymerization .................... 112
5.1.1 Ultraviolet Polymerization ..................... 113
5.1.2 Alternative Radiation Sources .................. 114
5.1.3 Multilevel Features and 3D Profiles ............ 115
5.2 Casting and Molding ................................... 122
5.2.1 Primary Casting ................................ 124
5.2.2 Replica Molding ................................ 126
5.2.3 Microinjection Molding ......................... 128
5.2.4 Compression Molding ............................ 129
5.3 Thermoplastic Reshaping ............................... 129
5.3.1 Hot Embossing .................................. 130
5.3.2 Nanoimprint Lithography ........................ 131
5.3.3 Thermoforming .................................. 132
5.4 Tabulated Examples of Solidification Processes ........ 132
References ............................................ 134
6 Subtractive Processes ...................................... 141
6.1 Wet Etching ........................................... 144
6.1.1 Isotropic Wet Etching .......................... 145
6.1.2 Anisotropic Wet Etching ........................ 147
6.2 Dry Etching ........................................... 150
6.2.1 Ion Etching .................................... 152
6.2.2 Vapor Phase Etching ............................ 153
6.2.3 Reactive Ion Etching ........................... 154
6.2.4 Deep Reactive Ion Etching ...................... 157
6.3 Directed Beam Subtractive Processes ................... 158
6.3.1 Laser Ablation ................................. 159
6.3.2 Focused Ion Beam Milling ....................... 161
6.4 Mechanical Subtractive Processes ...................... 161
6.4.1 Precision Machining ............................ 162
6.4.2 Abrasive Jet Milling ........................... 162
6.4.3 Chemical-Mechanical Polishing .................. 163
6.5 Tabulated Examples of Subtractive Processes .......... 164
References ............................................ 166
7 Additive Processes ......................................... 173
7.1 Physical Vapor Deposition ............................. 175
7.1.1 Evaporation .................................... 178
7.1.2 Sputtering ..................................... 178
7.1.3 Pulsed Laser Deposition ........................ 179
7.2 Oxidation ............................................. 179
7.3 Chemical Vapor Deposition ............................. 180
7.4 Electroplating ........................................ 183
7.5 Printing and Coating Techniques ....................... 186
7.5.1 Spin-on-Glass .................................. 187
7.5.2 Screen Printing and Blade Leveling ............. 188
7.5.3 Micro Contact Printing ......................... 188
7.5.4 Ink-Jet Printing and Direct-Write Material
Deposition ..................................... 189
7.5.5 Dip-Pen Nanolithography ........................ 190
7.6 Tabulated Examples of Additive Processes .............. 192
References ............................................ 193
8 Fugitive and Sacrificial Release Processes ................. 199
8.1 Reasons for Fugitive and Sacrificial Release
Processes ............................................. 201
8.2 Approaches to Fugitive and Sacrificial Release
Processes ............................................. 201
8.2.1 Examples of Approaches to Fugitive Processes ... 202
8.2.2 Examples of Approaches to Sacrificial Release
Processes ...................................... 206
8.3 Tabulated Examples of Fugitive and Sacrificial
Release Processes ..................................... 209
References ............................................ 210
9 Substrate Bonding and Fluidic Interfacing .................. 213
9.1 Reasons for Substrate Bonding ......................... 213
9.2 Process Issues and Selection Criteria for Substrate
Bonding ............................................... 214
9.3 Approaches to Substrate Bonding ....................... 216
9.3.1 Polymer Substrate Bonding ...................... 217
9.3.2 Glass Substrate Bonding ........................ 219
9.3.3 Silicon Substrate Bonding ...................... 220
9.3.4 Other Substrate Materials and Bonding Methods .. 221
9.4 Tabulated Examples of Bonding Processes ............... 222
9.5 Practical Issues and Selection Criteria for Fluidic
Interfacing ........................................... 223
9.6 Approaches to Fluidic Interfacing ..................... 226
References ............................................ 230
10 Functional Domains and System Integration .................. 237
10.1 Perspectives on Microfluidic Functionality ............ 237
10.2 Energy Transduction ................................... 239
10.2.1 Electrokinetic Transduction and Electrical
Measurements ................................... 240
10.2.2 Electromechanical, Electromagnetic, and
Electroacoustic Transduction ................... 241
10.2.3 Electrothermal, Thermopneumatic, and
Thermomechanical Transduction .................. 241
10.2.4 Electrochemical and Chemomechanical
Transduction ................................... 242
10.2.5 Optical Interfacing ............................ 243
10.3 Microfluidic System Integration ....................... 244
References ............................................ 246
List of Acronyms and Abbreviations ............................ 253
About the Authors ............................................. 257
Index ......................................................... 259
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