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

MICROFLEX S Beeby, J Tudor, University of Southampton 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.

MICROFLEX S Beeby, J Tudor, University of Southampton Scales and Dimensions - MEMS Human hair (   m) Silicon die (5 x 5 mm) MEMS Pollen

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

MICROFLEX S Beeby, J Tudor, University of Southampton Example 2: Optical MEMS - DLP Texas Instruments Digital Light Processors 1.3 million mirrors, 13  m Wide, used in projectors.

MICROFLEX S Beeby, J Tudor, University of Southampton 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

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

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

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

MICROFLEX S Beeby, J Tudor, University of Southampton 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 Denso Corporation Micromachining

MICROFLEX S Beeby, J Tudor, University of Southampton 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)

MICROFLEX S Beeby, J Tudor, University of Southampton 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 Substrate Structure

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

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