Understanding Smart Sensors - Nomads.usp

MEMS Beyond Sensors 203would not exist without batch processing technology. This chapter discusses afew of the areas that are being explored to indicate the variety and the extent ofMEMS technology. The MEMS field is progressing and expanding very fast.The examples given show the broad coverage of this new field. New actuatordesigns and new MEMS technologies are being developed rapidly. Readersinterested in the most recent developments are referred to the journals, books,and Web sites referenced in this chapter and at the end of the book.9.2 Micromachined ActuatorsActuators micromachined from silicon and other semiconductor materials useelectrostatic, electrothermal, thermopneumatic, electromagnetic, electroosmotic,electrohydrodynamic, shape memory alloy (SMA), thermoresponsivepolymers, and other means to provide motion. Table 9.2 is a comparison of thecapabilities of several actuators [2], ranging from existing products that provideunmatched performance compared to their macroscale counterparts to intriguinglab curiosities that require significant development to become practical.Examples of a silicon microvalve, micromotors, micropump, microdynamometer,microtransmission, and a microsteam engine, as well as actuators in alternativematerials, are discussed in this section.9.2.1 MicrovalvesOne area of MEMS actuators that has achieved production status is microvalves.Figure 9.1 shows one design, a silicon Fluistor (or fluidic transistor)microvalve that is approximately 5.5 mm by 6.5 mm by 2 mm [3]. 1 The bulkmicromachined cavity in the top section is filled with a control liquid. In theunactivated state, gases can flow through the valve. A voltage applied to theheating element on the diaphragm causes sufficient expansion of the liquid todeflect the diaphragm, close the valve seat, and restrict flow. The valve has adynamic range of 100,000 to 1, controlling gas flows from 4 mL per minute to4L per minute at a pressure of 20 psi.9.2.2 MicromotorsMicromotors are among the more interesting demonstrations of the futurepotential of MEMS. Several researchers have fabricated electrostatic and1. Fluistor is a trademark of Redwood Microsystems, Inc.