1. Summary of Introduction
MEMS (U.S.) Sometimes Microsystems in Europe.
MEMS=MicroElectroMechanical Systems
Very broad definition in practice: Mechanical, Electrical, Optical, Thermal, Fluidic, Chemical, Magnetic.
Generally systems created using microfabrication that are not integrated circuits. Many (but not all) of the microfabrication techniques were borrowed from the IC industry.
Market is smaller than IC market, but more diverse and growing faster.

2. Some Examples Accelerometer mTAS or Micro Total Analysis System TI DLP
Electrical/Mechanical
mTAS or Micro Total Analysis System
Purifies, amplifies, and detects DNA, for example.
Fluids/Biochemistry/Optical/Electrical
TI DLP
Optical/Mechanical/Electrical/Surface Science
Microrelay
Mechanical/Electrical/Surface Science
Microplasma Source
Electrical/Electromagnetic/Plasma
What do you need to know for MEMS?
Everything???!!!
Truly an interdisciplinary field.

3. What are we going to do?
Learn a useful subset of techniques needed for designing MEMS devices. Not all!!
We will design MEMS devices.
Project teaming survey is due Friday – see web site.
Project assignment is on the web site.
We will discuss examples of MEMS devics and use the techniques we have developed.
First we will look at microfabrication and process integration.
Other notes:
First homework is due today. (Some flexibility here – students joining class, thurn-in mechanism …)
Second homework is due on Tuesday.

4. Microfabrication: Types of Micromachining for MEMS
Bulk Micromachining
Etch away large parts of the silicon wafer.
Traditionally, KOH or other chemical etch.
Recently DRIE (Deep Reactive Ion Etch), an anisotropic plasma etch.
Surface micromachining
On surface of wafer/substrate
Sometimes can be a post-process on top of CMOS wafer for process integration with electronics.
Typically much thinner structures than bulk micromachining, but metal structures can be fairly thick.
LIGA
X-ray lithographie, galvanoformung, abformtechnik (or lithography, electrodeposition, and molding).
A special type of surface micromachining, not much used in its original form.
Now sometimes refers to using very thick photoresist to make thick electroplated structures.

5. Packaging
Ideally, part of fabrication process, then just use a cheap plastic package.
Often, a surface micromachined device is bonded to a bulk micromachined package (the cavity to contain the device is etched from the wafer using bulk micromachining).
Sometimes the package is the most expensive part of the device (pressure sensors, microfluidics). Especially true when the device interacts with the outside environment.

6. References: Text (brief), Campbell or other IC fabrication text (generally good, but incomplete for MEMS), Madou (specific to MEMS).

8. Silicon wafer fabrication
Taken from

9. Silicon wafer fabrication – slicing and polishing
Taken from

14. LPCVD Systems
Taken from

33. Electrodeposition/Electroplating
Drain
Source
Gate
Beam
Surface Micromachined
Post-Process Integration with CMOS
V Electrostatic Actuation
~100 Micron Size
Drain
Gate
Source
Beam
SEM of NEU microswitch

34. IBM 7-Level Cu Metallization (Electroplated)

39. Packaging
Ideally, part of fabrication process, then just use a cheap plastic package.
Often, a surface micromachined device is bonded to a bulk micromachined package (the cavity to contain the device is etched from the wafer using bulk micromachining).
Sometimes the package is the most expensive part of the device (pressure sensors, microfluidics). Especially true when the device interacts with the outside environment.

43. Micromachining Ink Jet Nozzles
Microtechnology group, TU Berlin

44. Bulk micromachined cavities
Taken from
Anisotropic KOH etch (Upperleft)
Isotropic plasma etch (upper right)
Isotropic BrF3 etch with compressive oxide still showing (lower right)

45. Surface Micromachining
Taken from
Deposit sacrificial layer
Pattern contacts
Deposit/pattern structural layer
Etch sacrificial layer

46. NUMEM Microrelay Process

47. NUMEM Microrelay Process

48. Residual stress gradients
Taken from
More tensile on top
More compressive on top
Just right! The bottom line: anneal poly between oxides with similar phosphorous content. ~1000C for ~60 seconds is enough.

49. Residual stress gradients
Taken from
A bad day at MCNC (1996).

50. DRIE structures Increased capacitance for actuation and sensing
Taken from
Increased capacitance for actuation and sensing
Low-stress structures
single-crystal Si only structural material
Highly stiff in vertical direction
isolation of motion to wafer plane
flat, robust structures
Thermal Actuator
Comb-drive Actuator
2DoF Electrostatic actuator

52. Scalloping and Footing issues of DRIE
<100 nm silicon nanowire over >10 micron gap
1 µm
microgrid
Footing at the bottom of
device layer
Milanovic et al, IEEE TED, Jan

53. Sub-Micron Stereo Lithography
New Micro Stereo Lithography for Freely Movable 3D Micro Structure
-Super IH Process with Submicron Resolution-
Koji Ikuta, Shoji Maruo, and Syunsuke Kojima
Department of Micro System Engineering, school of Engineering, Nagoya University
Furocho, Chikusa-ku, Nagonya , Japan
Tel: , Fax:
Fig. 6 Schematic diagram of the super IH process
Fig. 1 Schematic diagram of IH Process
Fig. 5 Process to make movable gear and shaft
(a) conventional micro stereo lithography needs base layer
(b) new super IH process needs no base
Micro Electro Mechanical Systems
Jan., 1998 Heidelberg, Germany

54. Sub-Micron Stereo Lithography
New Micro Stereo Lithography for Freely Movable 3D Micro Structure
-Super IH Process with Submicron Resolution-
Koji Ikuta, Shoji Maruo, and Syunsuke Kojima
Department of Micro System Engineering, school of Engineering, Nagoya University
Furocho, Chikusa-ku, Nagonya , Japan
Tel: , Fax:
Fig. 10 Micro gear and shaft make of solidified polymer
(b) side view of the gear of four teeth
(d) side view of the gear of eight teeth
Micro Electro Mechanical Systems
Jan., 1998 Heidelberg, Germany

55. Taken from: http://www. imm-mainz. de/english/sk_a_tec/basic_te/liga

56. Simple Carbon Nanotube Switch
Diameter: 1.2 nm
Elastic Modulus: 1 TPa
Electrostatic Gap: 2 nm
Binding Energy to Substrate: 8.7x10-20 J/nm
Length at which adhesion = restoring force: 16 nm
Actuation Voltage at 16 nm = 2 V
Resonant frequency at 16 nm = 25 GHz
Electric Field = 109 V/m or 107 V/cm + Geom.
(F-N tunneling at > 107 V/cm)
Stored Mechanical Energy (1/2 k x2 ) = 4 x J = 2.5 eV