Fabrication technologies related to those which are exploited for the fabrication of integrated circuits can be used to machine mechanical structures with minimum feature sizes in the range of micrometers. The mechanical machining of silicon based on IC-technologies is known as micromachining, and the systems made by micromachining are called MEMS (microelectromechanical systems). The present book describes how to use this technology to fabricate sensors of miniature size for mechanical quantities, such as pressure, force, flow and acceleration. The book includes a chapter with a comprehensive description of the relevant micromachining processes, and an introduction to MEMS, a field much broader than just microsensors. Most of these sensors rely on a deformation of the mechanical construction by an external load, and on a transduction mechanism to convert the deformation into a mechanical signal. The fundamental mechanics and electromechanics required for the understanding and the design of mechanical microsensors are described on a level accessible to engineers of all disciplines. Students in engineering sciences from the third year on should be able to benefit from this description. The most important mechanical sensors are described and discussed in detail with respect to fabrication issues, function and performance. Special emphasis is given to pressure sensors, force sensors, accelerometers, gyroscopes and flow sensors. Electronic interfacing, and a discussion of electronic circuits used for the sensors is also included. Finally the problem of packaging is addressed.

Klappentext

This book on mechanical microsensors is based on a course organized by the Swiss Foundation for Research in Microtechnology (FSRM) in Neuchatel, Swit­ zerland, and developed and taught by the authors. Support by FSRM is herewith gratefully acknowledged. This book attempts to serve two purposes. First it gives an overview on me­ chanical microsensors (sensors for pressure, force, acceleration, angular rate and fluid flow, realized by silicon micromachining). Second, it serves as a textbook for engineers to give them a comprehensive introduction on the basic design issues of these sensors. Engineers active in sensor design are usually educated either in electrical engineering or mechanical engineering. These classical educa­ tional pro grams do not prepare the engineer for the challenging task of sensor design since sensors are instruments typically bridging the disciplines: one needs a rather deep understanding of both mechanics and electronics. Accordingly, the book contains discussion of the basic engineering sciences relevant to mechanical sensors, hopefully in a way that it is accessible for all colours of engineers. Engi­ rd th neering students in their 3 or 4 year should have enough knowledge to be able to follow the arguments presented in this book. In this sense, this book should be useful as textbook for students in courses on mechanical microsensors (as is CUf­ rently being done at the University ofTwente).

Inhalt

1. Introduction.- 2. MEMS.- 2.1 Miniaturisation and Systems.- 2.2 Examples for MEMS.- 2.2.1 Bubble Jet.- 2.2.2 Actuators.- 2.2.3 Micropumps.- 2.3 Small and Large: Scaling.- 2.3.1 Electromagnetic Forces.- 2.3.2 Coulomb Friction.- 2.3.3 Mechanical Strength.- 2.3.4 Dynamic Properties.- 2.4 Available Fabrication Technology.- 2.4.1 Technologies Based on Lithography.- 2.4.1.1 Silicon Micromachining.- 2.4.1.2 LIGA.- 2.4.2 Miniaturisation of Conventional Technologies.- 3. Introduction into Silicon Micromachining.- 3.1 Photolithography.- 3.2 Thin Film Deposition and Doping.- 3.2.1 Silicon Dioxide.- 3.2.2 Chemical Vapour Deposition.- 3.2.3 Evaporation.- 3.2.4 Sputterdeposition.- 3.2.5 Doping.- 3.3 Wet Chemical Etching.- 3.3.1 Isotropic Etching.- 3.3.2 Anisotropic Etching.- 3.3.3 Etch Stop.- 3.4 Waferbonding.- 3.4.1 Anodic Bonding.- 3.4.2 Silicon Fusion Bonding.- 3.5 Plasma Etching.- 3.5.1 Plasma.- 3.5.2 Anisotropic Plasma Etching Modes.- 3.5.3 Configurations.- 3.5.4 Black Silicon Method.- 3.6 Surface Micromachining.- 3.6.1 Thin Film Stress.- 3.6.2 Sticking.- 4. Mechanics of Membranes and Beams.- 4.1 Dynamics of the Mass Spring System.- 4.2 Strings.- 4.3 Beams.- 4.3.1 Stress and Strain.- 4.3.2 Bending Energy.- 4.3.3 Radius of Curvature.- 4.3.4 Lagrange Function of a Flexible Beam.- 4.3.5 Differential Equation for Beams.- 4.3.6 Boundary Conditions for Beams.- 4.3.7 Examples.- 4.3.8 Mechanical Stability.- 4.3.9 Transversal Vibration of Beams.- 4.4 Diaphragms and Membranes.- 4.4.1 Circular Diaphragms.- 4.4.2 Square Membranes.- Appendix 4.1: Buckling of Bridges.- 5. Principles of Measuring Mechanical Quantities: Transduction of Deformation.- 5.1 Metal Strain Gauges.- 5.2 Semiconductor Strain Gauges.- 5.2.1 Piezoresistive Effect in Single Crystalline Silicon.- 5.2.2 Piezoresistive Effect in Polysilicon Thin Films.- 5.2.3 Transduction from Deformation to Resistance.- 5.3 Capacitive Transducers.- 5.3.1 Electromechanics.- 5.3.2 Diaphragm Pressure Sensors.- 6. Force and Pressure Sensors.- 6.1 Force Sensors.- 6.1.1 Load Cells.- 6.2 Pressure Sensors.- 6.2.1 Piezoresistive Pressure Sensors.- 6.2.2 Capacitive Pressure Sensors.- 6.2.3 Force Compensation Pressure Sensors.- 6.2.4 Resonant Pressure Sensors.- 6.2.5 Miniature Microphones.- 6.2.6 Tactile Imaging Arrays.- 7. Acceleration and Angular Rate Sensors.- 7.1 Acceleration Sensors.- 7.1.1 Introduction.- 7.1.2 Bulk Micromachined Accelerometers.- 7.1.3 Surface Micromachined Accelerometers.- 7.1.4 Force Feedback.- 7.2 Angular Rate Sensors.- 8. Flow sensors.- 8.1 The Laminar Boundary Layer.- 8.1.1 The Navier-Stokes Equations.- 8.1.2 Heat Transport.- 8.1.3 Hydrodynamic Boundary Layer.- 8.1.4 Thermal Boundary Layer.- 8.1.5 Skin Friction and Heat Transfer.- 8.2 Heat Transport in the Limit of Very Small Reynolds Numbers.- 8.3 Thermal Flow Sensors.- 8.3.1 Anemometer Type Flow Sensors.- 8.3.2 Two-Wire Anemometers.- 8.3.3 Calorimetric Type Flow Sensors.- 8.3.4 Sound Intensity Sensors - The Microflown.- 8.3.5 Time of Flight Sensors.- 8.4 Skin Friction Sensors.- 8.5 "Dry Fluid Flow" Sensors.- 8.6 "Wet Fluid Flow" Sensors.- 9. Resonant Sensors.- 9.1 Basic Principles and Physics.- 9.1.1 Introduction.- 9.1.2 The Differential Equation of a Prismatic Microbridge.- 9.1.3 Solving the Homogeneous, Undamped Problem using Laplace Transforms.- 9.1.4 Solving the Inhomogeneous Problem by Modal Analysis.- 9.1.5 Response to Axial Loads.- 9.1.6 Quality Factor.- 9.1.7 Nonlinear Large-Amplitude Effects.- 9.2 Excitation and Detection Mechanisms.- 9.2.1 Electrostatic Excitation and Capacitive Detection.- 9.2.2 Magnetic Excitation and Detection.- 9.2.3 Piezoelectric Excitation and Detection.- 9.2.4 Electrothermal Excitation and Piezoresistive Detection.- 9.2.5 Optothermal Excitation and Optical Detection.- 9.2.6 Dielectric Excitation and Detection.- 9.3 Examples and Applications.- 10. Electronic Interfacing.- 10.1 Piezoresistive Sensors.- 10.1.1 Wheatstone Bridge Configurations.- 10.1.2 Amplification of the Bridge Output Voltage.- 10.1.3 Noise and Offset.- 10.1.4 Feedback Control Loops.- 10.1.5 Interfacing with Digital Systems.- 10.1.5.1 Analog-to-Digital Conversion.- 10.1.5.2 Voltage to Frequency Converters.- 10.2 Capacitive Sensors.- 10.2.1 Impedance Bridges.- 10.2.2 Capacitance Controlled Oscillators.- 10.3 Resonant Sensors.- 10.3.1 Frequency Dependent Behavior of Resonant Sensors.- 10.3.2 Realizing an Oscillator.- 10.3.3 One-Port Versus Two-Port Resonators.- 10.3.4 Oscillator Based on One-Port Electrostatically Driven Beam Resonator.- 10.3.5 Oscillator Based on Two-Port Electrodynamically Driven H-shaped Resonator.- 11. Packaging.- 11.1 Packaging Techniques.- 11.1.1 Standard Packages.- 11.1.2 Chip Mounting Methods.- 11.1.2 Wafer Level Packaging.- 11.1.3 Interconnection Techniques.- 11.1.4 Multichip Modules.- 11.1.5 Encapsulation Processes.- 11.2 Stress Reduction.- 11.3 Pressure Sensors.- 11.4 Inertial Sensors.- 11.5 Thermal…