1. MEMS Fabrication
S.APPA RAO

2. Overview
What are MEMS?
MEMS: Micro-Electro-Mechanical Systems => ‘smalltech’
MEMS Applications
MEMS fabrication process
Future of MEMS technology

4. MEMS Overview Micro Electro Mechanical Systems
Micron level mechanical parts
Made from transistor materials and metals
Van Der Waals forces
Intermolecular bonding
Plays an important part in design

5. What are MEMS?
Combination of mechanical functions (sensing, moving, heating) and electrical functions (switching ,deciding) on the same chip using micro fabrication technology
Lab on a Chip (LOC)
System on a Chip
Micro-sensors / micro-actuators
Small silicon cantilevers (AFM tips) etc

6. The Role of MEMS
While the functional elements of MEMS are miniaturized structures, sensors, actuators, and microelectronics, the most notable (and perhaps most interesting) elements are the microsensors and microactuators. Microsensors and microactuators are appropriately categorized as “transducers”, which are defined as devices that convert energy from one form to another. In the case of microsensors, the device typically converts a measured mechanical signal into an electrical signal. Micro-Electro-Mechanical Systems, or MEMS, is a technology that in its most general form can be defined as miniaturized mechanical and electro-mechanical elements (i.e., devices and structures) that are made using the techniques of microfabrication. The critical physical dimensions of MEMS devices can vary from well below one micron on the lower end of the dimensional spectrum, all the way to several millimeters.
Michael Huff, Michael Huff is at the MEMS Exchange, Corporation for National Research Initiatives, 1895 Preston White Drive, Suite 100, Reston, Virginia , USA

7. MEMS Ratchet http://www.memx.com/
Imagine a machine so small that it is imperceptible to the human eye.  Imagine working machines no bigger than a grain of pollen.  Imagine thousands of these machines batch fabricated on a single piece of silicon, for just a few pennies each.  Imagine a world where gravity and inertia are no longer important, but atomic forces and surface science dominate. Imagine a silicon chip with thousands of microscopic mirrors working in unison, enabling the all optical network and removing the bottlenecks from the global telecommunications infrastructure. You are now entering the micro-domain, a world occupied by an explosive technology known as MEMS.  A world of challenge and opportunity, where  traditional engineering concepts are turned upside down, and the realm of the "possible" is totally redefined.

8. MEMS Applications
Accelerometers in consumer electronics devices such as game controllers
Automotive applications (20 per vehicle)
Communications (telecom)
Biotechnology (Lab on a Chip)
System on a Chip

9. MEMS Architecture

11. MEMS Accelerometer
MEMS are quietly changing the way you live, in ways that you might never imagine.  The device that senses your car has been in an accident, and fires the airbag is a MEMS device.  Most new cars have over a dozen MEMS devices, making your car safer, more energy efficient, and more environmentally friendly. MEMS are finding their way into a variety of medical devices, and everyday consumer products. (From MEMX )

12. MEMS Advantages
Significantly lower manufacturing costs (semiconductor process)
Small inertial mass
Particularly realized in the area of:
– sensors
– signal switching

13. Materials for MEMS
Materials are the foundation required to develop microsensors. MEMS are made of:
Metals
Polymers
Ceramic materials
Semiconductors
Composite materials

14. MEMS Process
Same as the process steps used for making conventional electronic circuits

15. Fabrication Process

16. Fabrication Process

17. Fabrication Process

18. Fabrication Techniques
Mask Lithography
Injection molding
Microstereolithography
Silicon Surface Micromachining
Silicon Bulk Micromachining

19. Mask Lithography Use of photo resist Multiple layers – Multiple steps
Positive
Dissolves under light
Negative
Hardens under light
Both get covered with desired material, then photo resist is dissolved by a solvent
Multiple layers – Multiple steps

20. Mask Lithography

21. Thin Film Deposition Deposition techniques: Chemical Deposition
Chemical Vapor Deposition
Physical Vapor Deposition
DC magnetron sputtering

22. Lithography Application of photo resist
Optical exposure to print an image of the mask onto the resist
Immersion in an aqueous developer solution to dissolve the exposed resist

23. MEMS Accelerometer Made of bulky and heavy metal parts
Require high operating voltage/current
Needs careful maintenance
Highly expensive not throwaway type
CONVENTIONAL ACCELEROMETER SENSOR

24. Piezoresistive Accelerometer

25. Masks used for Accelerometer

26. Layout of the Resistor

27. Injection Molding Starts with mask lithography
Metal poured over resist
Resist gets dissolved
Metal form is left for plastic injection molding

28. Injection Molding

29. Microstereolithography
Similar principal to mask lithography, but for 3D pieces
Uses an “active mask”
Not a physical mask
Utilizes a photo-reactive acrylic resin
Each layer image projected through a DMD(digital mirror device)
Projected into the resin
Uses lenses
Resin that is illuminated, Cross-links and hardens
Piece is then covered in a hardened layer

30. Microstereolithography
Dimensional capabilities
Lateral and Vertical resolution: 10μm
Maximum field size: 10.24mm x 7.68mm
Structural height: up to 5mm

31. Microstereolithography

32. Microstereolithography

33. Micromachining Technology
The three characteristic features of MEMS fabrication technologies are miniaturization, multiplicity, and microelectronics. Miniaturization is clearly an important part of MEMS, since materials and components that are relatively small and light enable compact and quick-response devices. Multiplicity refers to the batch fabrication inherent in semiconductor processing. Consequently, it is feasible to fabricate thousands or millions of components as easily and concurrently as one component, thereby ensuring low unit component cost. Furthermore, multiplicity provides flexibility in solving mechanical problems by enabling the possibility of a distributed approach through use of (coupled) arrays of micromechanical devices. Finally, microelectronics provides the intelligence to MEMS and allows the monolithic merger of sensors, actuators, and logic to build closed-loop feedback components and systems.

34. Types of Micromachining
BULK micromachining:
SURFACE micromachining:
LIGA process:

35. Silicon Surface Micromachining
Uses the same process as IC fabrication
Needs multiple layers to create structures
Cheapest form of Micromachining
Similar to lithography
Sacrificial material
Structural material
When sacrificial material is removed, only whole structures are left

36. Silicon Surface Micromachining

37. Silicon Surface Micromachining

38. Silicon Surface Micromachining

39. Silicon Bulk Micromachining
Done with Crystalline silicon
Constructed using etch stop planes
Chemical process
Anisotropic Etching
Speed dependent – Directional
etch in different crystallographic directions at different rates
Slower directions create and etch stop plane

40. Wet Etching and Plasma Dry Etching
Wet etching where the material is dissolved when immersed in a chemical solution Dry etching where the material is sputtered or dissolved using reactive ions or a vapor phase etchant

41. Deep Reactive Ion Etching (DRIE)
Uses photo resist and a mask to create structures

42. Sapphire Etching
Metal Mask, 100µm etch depth, .28µm/min etch rate, Chlorine etching

43. Pressure Sensor Etching
Used on silicon, Metal mask, .81µm etch depth, Utilizes Fluorine,

44. High-Speed Etching Silicon material, 1µm/min etch rate, W-Si Mask

45. MEMS Technical Limitations
Imprecise fabrication methods
Expensive and complex packaging
CAD Design tool inaccuracies
Limits to miniaturization
Material process limitations
Functional engineering limits

46. Future of MEMS
As with all emerging technologies, the MEMS industry had been predicted to revolutionize technology and our lives.
MEMS may be incorporated in biological structures, linked by wireless networks
It has the potential to change our daily lives as much as computers / networks
Computation, communication and actuation

47. Summary MEMS – Micro Electro Mechanical Systems
Fabricated using silicon fabrication tools
Lithography, mask/etc, deposit/etch etc
MEMS can be fabricated out of a number of materials: polymers, ceramics, metals, etc
Fabless ICs are used by many MEMS designers
Polymeric and ceramic MEMS are also made

48. References http://home.earthlink.net/~trimmerw/mems/tour.html
“Micromachining for Optical and Optoelectronic Systems”. MING C. WU