  This work introduces the design analysis simulation and a standard MEMS
fabrication process for a three dimensional microcoil with a magnetic core and
a digital switch configuration using a completely integrated fully MEMS
compatible process to achieve a digitally controlled inductance. The proposed
design can also be utilized as a micro transformer. The proposed design
consists of five identical 3D coils and their corresponding MEMS switches.
These coils are digitally controlled to achieve a variable inductor ranging
from one fifth of the coil inductance up to five times the coil inductance. A
standard five layer Polymumps process is proposed to fabricate the microcoils
and the integrated switches. Each micro coil is anchored directly on chip
connected to the input signal from one side and the other is connected to the
switch. The Ni based magnetic core improves the coil response by confining and
guiding the magnetic field in the magnetic device compared to Si core based by
more than five times. The presented coil has the number of windings limited by
the designed length and the minimum spacing that can be realized by standard
optical lithography. The coil diameter is also restricted by the limits defined
by optical lithography whereas the maximum height realizable by the Polymumps
process limits the height of the magnetic core and accordingly results in lower
inductor performance. Based on this technique we present coils ranging from 100
um in length and ten winding up to 1000 um in length and 100 windings. The new
monolithically integrated MEMS switches act as selectors to achieve a variable
inductance with digital control to allow the selection among n inductance steps
where n is the number of coils.
