Why do we put the micro in microelectronics?

Why Micro? 1.Lower Energy and Resources for Fabrication 2.Large Arrays 3.Minimally Invasive 4.Disposable 5.Smaller Time Scales 6.Lower Cost What about the Physics?

Scaling at the Microscale Not all properties scale in the same way! Volume Forces Gravity Inertia Mass Surface Forces Surface Tension Viscosity Heat Loss

Animal Kingdom Larger Animals Limited number Limited environments Slow Gravity limited Small Animals Heat loss size 2 Heat generation size 3 Large energy intake (food)

Why can’t I walk on water? weight scales as l 3 surface tension scales as l As animals become smaller, weight decreases more rapidly than surface tension.

Why can’t I lift a car? weight scales as l 3 strength scales as l 2 ants can carry 50 time their weight a human shrunk to ant size could carry 300 times his/her own weight an ant increased to human size will not be able to support it’s own weight

The Industrial Revolution

Example: Digital Mirrors Digital Light Processing (DPL)

Digital Light Processing: A New MEMS-Based Technology By Larry Hornbeck

Systron Donner Inertial Division

Accelerometer: Analog Devices Inc. Commercially available two-axis accelerometer Mass Acceleration direction Anchor Displacement sensor Support Arms

A Polysilicon Accelerometer (2 Microns Thick) Mass Support Arms Sensing Electrodes Support arms are 2 microns square and ~ 100 microns long From John Yasaitis, Analog Devices Inc

Closeup of ADI Accelerometer From John Yasaitis, Analog Devices Inc

Accelerometer

From John Yasaitis, Analog Devices Inc

Why silicon?

Silicon Crystalline Materials Regular arrangement of atoms with long range order Many Properties Depend on Atomic Structure

22 Silicon Si semiconductor 5 silicon atoms in a unit cell Diamond lattice Covalent bonds 14 electrons 4 valence electrons Silicon molecules: nm0.235 nm Si electronsholes

Integrated Circuits in 1958 Jack Kilby at Texas Instruments

Integrated Circuits in 1962 RTL Logic (Noyce and Hoerni)

Integrated Circuits in 1965 Operational Amplifier, Fairchild ua 709

Integrated Circuits in 1991 Power PC, AIM (Apple-IBM-Motorola Alliance)

Today’s Microelectronics & MEMS Analog Devices, Accelerometers and Gyroscopes

Decrease in Minimum Feature Size with Time (Moore’s law)

Clean Room Classification English system: Numerical designation of the class is maximum allowable number of particles that are 0.5  m and larger per cubic foot of air. Metric system: Numerical designation of the class is taken from the Logarithm (base 10) of the maximum allowable number of particles that are 0.5  m and larger per cubic foot of air IC is very sensitive to particles. It usually requires Class 10 or better MEMS is more robust to particulates

Microfabrication Silicon Oxidation Photoresist Deposition Masking and Exposure Figures from May and Sze

Photoresist Development Si02 etching Photoresist Cleaning Doping Metallization Patterning Figures from May and Sze

Dry Oxidization : Si (solid) + O 2 (gas)  SiO 2 (solid) Wet Oxidization: Si (solid) + 2H 2 O (gas)  SiO 2 (solid) + 2H 2 (gas) Thermal Oxidization

Photolithography: Pattern Transfer The remaining image after pattern transfer can be used as a mask for subsequent process such as etching, ion implantation, and deposition.

Doped Silicon N- doped P- doped Silicon molecules: Si P B free electrons bound electrons holes

Diffusion Constant source – High surface concentrations, shallow, "deposition“ Limited source – Low surface concentrations, deep, "drive-in"

Ion-implantation

Thermal Evaporator Pump down to 1  torr ( 1 torr = 1 mmHg) Place wafers upside down to reduce particles Heat sources until white hot Low pressure = long mean-free- path (i.e., directional deposition) Use shutter for better timing Thin Film Deposition

LIGA: electroplating nickel