MEMS: Invention to Market

1. MEMS: Invention to Market • Invention->Market • Creation of a new market is slow. • Market->Invention (easier) • What is the existing competition? • Impact – will it take over the market? • Manufacturing • Sales • Modeling as in this course: Analysis of options, performance, price. Planning of R+D, business plan.

2. Device Categories • Technology Demonstrations • Test device concept • Test fabrication technology • Small # of devices/low yield ok • Research Tools • Small # of devices, often custom. • Commercial Products • Large # of devices, high yield, low cost, packaging all critical.

3. Transducers, Sensors, and Actuators • Transducers: Generally convert one form of energy to another. (Not generally conserving energy.) • Could be a sensor or an actuator. • Sensors measure something and provide an output signal. Usually electrical, but sometimes optical or mechanical. • Actuators move something. (But what would an LED be?)

4. Domains • Thermal (temperature, heat, heat flow) • Mechanical (force, pressure, velocity, acceleration, position) • Chemical (concentration, composition, reaction rate) • Magnetic (magnetic field intensity, magnetization) • Radient (intensity, wavelength, polarization, phase) • Electrical (voltage, current, charge, resistance)

5. Examples of Sensors and Actuators • Position Sensors • Resistive strain sensor. (dimensions change, R=rl/A) • Piezoresistive strain sensor. (dimensions and r change) Sensitivity measured by the gauge factor GF=relative resistance change/strain=(DR/R)/(DL/L)=DR/eR GF=~2 for metals (mostly geometry, some piezoresistance) GF=~100 for semiconductors (piezoresistive)

6. Piezoelectric materials (Curies, 1880) • Electric field <-> strain (deformation) • Polarization <-> stress • Sensor/Actuator • In your watch, Quartz (but this is changing!! (Si Time)) • Also pyroelectric materials have temperature<->polarization.

12. Magnetostrictive Actuators • Materials expand/contract with magnetic field • Similar to piezoelectric effect • Terfenol-D Tb0.27Dy0.73Fe1.9 -> strain of 2X10-3 or 0.2%. • Permanent magnetic materials • Micromirror, microrelay, micromotor N S N S B

13. RF MEMS – Switching or changing capacitance or building micromachined RF components.

14. Also ink jets!

16. Biological Actuators – Future, nano, research stage. • Biomedical Sensors and Actuators • Neural probes • Artificial retinas • Hearing prosthetics (in use) • Living cells as sensors (chips for culturing and measuring cell properties (see Kovaks, for example) • Chemical Actuators – Electrochemical actuators using polypyrrole.

17. Chemical Sensors – many types! • Chemireisistors (organic and inorganic) • Chemicapacitors • Micromachined Calorimeter (combustible gasses or explosive particles) • Micro hot plate (R(T) for several materials. • Chem FETs • Can do the same thing with many ion sensitive membranes. Pd – Sensitive to hydrogen at 10 ppm Problem: Drift

18. Pumps • Mechanical • Electrophoretic/Electroosmotic, used in separations of DNA and protein fragments. V Neutrals dragged along by mobile ions. Flow nearly constant velocity across channel. mobile +ions + + + + + + + - - - - - - - - - immobile -ions

19. Optical Transducers • MANY types! • Overlap between commercial electronics and MEMS. • Thermal (Bolometers) • Light heats element, causes resistance change. • Fabry Perot etalon type devices (interference) for changing reflection. Like microspectrometer shown previously. • E-ink displays (MEMS?) • Thermocouple • Golay cell • Light -> heat -> expanding gas -> moves something -> signal. • Spectrometers • Diffractive sensors. - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

20. Preview of a case study (or project).Capacitive Accelerometer, p. 497, Senturia. • Fabrication Technology – sets limits on structures. • Lumped element modeling in different domains. • Capacitive transducer/actuator • Elasticity, contact mechanics, stiction • Structures – springs/beams. • Fluids – squeeze film damping • Electronics, feedback • System dynamics • Noise