Mumbai University > Electronics Engineering > Sem 8 > MEMS Technology

Marks: 5M

Silicon

Ideal substrate material used in MEMS because of the following reasons:

i. It is mechanically stable & easy to integrate with mechanical parts

ii. It has same thermal expansion coefficient as that of steel (215 GPa) , but it is as light as Al with d = 2.3 g/cm3

iii. Melting Point = 14000C (2*Al) = makes dimensionally stable

iv. Thermal expansion coefficient, 8 times smaller than steel & 10 times Al

v. Naturally ,no mechanical hysteresis therefore , ideal for actuators

Silicon compounds:

• Si dioxide (SiO2)

• Si Carbide (SiC)

• Si Nitride (Si3N4)

1) Silicon dioxide (SiO2)

• Least expensive

• Good thermal & electrical isolation

• Used as masking & sacrificial materials in surface micro-machining technique

• Easy to produce

o Dry heating Si , Si + O2 ----> SiO2

o Wet oxidation Si + 2H2O ----> sio2 + 2H2

2) Silicon Carbide (SiC)

• High Melting Point

• Masking

• Superior dimensional stability

3) Silicon Nitride (Si3N4)

• Ultra strong Resistance to oxidation

• High strength Electrical insulator

• Masking for deep etching

4) GaAs

• Compound semi-conductor with equal no. of Ga & As atoms

• Excellent material for nanolithography photonic devices

• Therefore GaAs compound is not easy to produce

• High electron mobility (7 * Si)

• Good thermal insulator

5) Quartz

• Used in sensor , excellent structural stability

• High Melting Point

• Used as piezoelectric material

• Good insulator

6) Polymer

• Used as masking in photolithographic technique

• Used as organic substrate

• Electric insulator & dielectric substances in micro transistor

• Used as packing material