150

S. Palleboina and K. Pallela

process is more suitable to design the wings of MAV structures in different dimen-

sions based on the material proposed as MEMS technology also supports the

biological implantations.

Bulk Micromachining (BMM) Process

This method allows the substrate to be used in three sides of its dimensions. Single

Crystalline Silicon is used due to its electrical and mechanical properties. Generally

wet etching and dry etching methods are used to design MEMS. Anisotropic etchants

such as KOH and TMAH are used for performing the web etching. However, TMAH

etchants are highly compatible with CMOS process as these etchants are alkaline ion

free.

Practical Considerations of Designing MAVs Using MEMS

Design of an MAV demands various aerodynamic considerations along with its body

parts and power sources connected to it at various sections. Silicon is the dominant

material used in MEMS for most of the device fabrications and recently soft material

like polymers are designed using natural materials. These hybrid systems are biocom-

patible and for example, parylene is used to fabricate variety of valves and pumps

for fluidic applications at micro levels. Ho et al. [3] suggested parylene based MAV

wing membrane with a typical thickness. The same material can also be used for

electrostatically activated check-valves. Considering the above two reasons MEMS

devices can be integrated on the wing, which forms a complete unit.

Ho et al. [3] reported a successful operation of independent actuators at a voltage

of 50 V. Fully integrated actuators on these wings are even working up to a voltage of

300 V due to the increase in the gap (d) between electrodes at the time of integration.

The general equation for electrostatic force (Fe) is given by

Fe = ^{εo AV 2}

2d

(11.1)

where A is the area of two conductive plates.

d is the gap between plates.

V is the applied voltage.

εo is the permittivity of free space.

A careful note must be considered at low voltages that the fabrication needs to be

done carefully to reduce the electrode gap at the time of integration. Otherwise, the

electrostatic forces proportional to demand a voltage rise by its square for maintaining

same force when the gap size is increasing.