Introduction to MEMS

1. Introduction to MEMS • What is MEMS? • What do MEMS devices look like? • What can they do? • How do we make them on textiles? S Beeby, J Tudor, University of Southampton

2. What are MEMS? MEMS – MicroElectroMechanical Systems Systems that combine mechanical and electrical functionality fabricated in dimensions that range from microns to millimetre Typically use silicon as the substrate due to its semiconducting characteristics and excellent mechanical properties. S Beeby, J Tudor, University of Southampton

3. 10-1 10-1 10-6 10-5 10-4 10-3 10-2 10-0 Scales and Dimensions - MEMS MEMS S Beeby, J Tudor, University of Southampton Human hair (f 80-100mm) Silicon die (5 x 5 mm) Pollen

4. Example 1 - Inertial MEMS Mechanical component S Beeby, J Tudor, University of Southampton Signal Processing Integrated electronics Silicon substrate Integrated mechanical and electrical components Smart microsensor systems

5. Example 2: Optical MEMS - DLP Texas Instruments Digital Light Processors 1.3 million mirrors, 13mm Wide, used in projectors. S Beeby, J Tudor, University of Southampton http://www.dlp.com/includes/demo_flash.aspx

6. Factors to Consider • MEMS requires a mechanical structure specifically designed for the application • The fabrication process must be considered at the outset since this defines dimensional limits and material properties • MEMS are typically sensors or actuators - requires a microscale transducer • Most MEMS use silicon but plastics, ceramics and glasses can be used S Beeby, J Tudor, University of Southampton

7. Example 3: Pressure Sensors Pressure sensors utilise an thin membrane formed on or in the silicon chip. S Beeby, J Tudor, University of Southampton Photo from GE Novasensor – Catheter pressure sensors Pressure Sensing mechanism detects the movement of the diaphragm. Signal conditioning electronics integrated on the same die.

8. Microfluidics MEMS designed to handle or process minute quantities of liquids. Devices include micro-pumps, micro-mixers, flow channels, reaction chambers, micro-filters. S Beeby, J Tudor, University of Southampton Example micro-pump

9. S Beeby, J Tudor, University of Southampton Sensors & Transducers Magazine (S&T e-Digest), Vol.66, Issue 4, April 2006, pp.521-525

10. Micromachining This is the process of fabricating mechanical components in the micron to millimetre size range. • Typically based upon silicon IC fabrication processes (see next slide). Especially true for micron scale devices. • Also includes ‘traditional’ approaches (precision CNC machining, electroplating, molding) • Variety of materials S Beeby, J Tudor, University of Southampton Denso Corporation

11. Silicon Micromachining Processes • Typically based upon IC fabrication processes which enable: • Simultaneous device processing on each wafer • Batch fabrication (many wafers simultaneously) • Low cost in high volumes • Inherently small size (nanometres to millimetres) • But Beware! • High cost of infrastructure (both initial and running) • High cost of equipment • Specialist processes often required • (poor standardisation) S Beeby, J Tudor, University of Southampton

12. Structure Substrate Surface Micromachining Mechanical structures formed on the surface of a substrate. Formed from materials deposited on the substrate. Most common method of surface micromachining is known as Sacrificial Layer Technology. Additive process growing / depositing layers of materials, patterning and selectively removing them S Beeby, J Tudor, University of Southampton

13. Poly Si Dry etch Dry etch Surface Micromachining (2) Example on silicon: Silicon S Beeby, J Tudor, University of Southampton Silicon Nitride Silicon Dioxide Wet etch

14. Recommended Reading! MEMS Mechanical Sensors by Steve P. Beeby, Graham Ensell, Michael Kraft and Neil White £62 on Amazon S Beeby, J Tudor, University of Southampton