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the magnetic properties also depend upon the thickness). Having emphasized the magnetic properties
of the Ni x% Fe 100−x% thin films, let us perform the comparison. It was reported in the literature that [11]:

Ni 79% Fe 17% Mo 4% thin films have the flux density 0.7 T, coercivity 5 A/m, and permeability 3400,
Ni 85% Fe 14% Mo 1% thin films have the flux density 1–1.1 T, coercivity 8–300 A/m, and permeability
3000–20000, Ni 50% Co 50% thin films have the flux density 0.95–1.1 T, coercivity 1200–1500 A/m, and
permeability 100−150 (Ni 79% Co 21% thin films have the permeability 20).

In general, high flux density, low coercivity, and high permeability lead to high-performance MEMS.
However, other issues (affordability, compliance, integrity, operating envelope, fabrication, etc.) must be
also addressed while making the final choice. It must be emphasized that the magnetic characteristics,
in addition to the film thickness, are significantly influenced by the fabrication processes and chemicals
(materials) used.
The magnetic core in microstructures and microtransducers must be made. Two major challenges in
fabrication of high-performance microstructures and microtransducers are to make electroplated mag-
netic thin films with good magnetic properties as well as planarize the stationary and movable members.
Electroplating and micromolding techniques and processes are used to deposit NiFe, NiFeMo, and NiCo
thin films. In particular, the Ni 80% Fe 20% , NiFeMo, and NiCo (deposited at 25°C) electroplating solutions
are:

• Ni 80% Fe 20% : NiSO 4 –6H 2 O (200 g/l), FeSO 4 –7H 2 O (9 g/l), NiCl 2 –6H 2 O (5 g/l), H 3 BO 3 (27 g/l), and
2
saccharine (3 g/l). The current density is 10–25 mA/cm (nickel foil is used as the anode);
• NiFeMo: NiSO 4 –6H 2 O (60 g/l/), FeSO 4 –7H 2 O (4 g/l), Na 2 MoO 4 –2H 2 O (2 g/l), NaCl (10 g/l), citric
2
acid (66 g/l), and saccharine (3 g/l). The current density is 10–30 mA/cm (nickel foil is used as
the anode);
• Ni 50% Co 50% : NiSO 4 –6H 2 O (300 g/l/), NiCl 2 –6H 2 O (50 g/l), CoSO 4 –7H 2 O (30 g/l), H 3 BO 3 (30 g/l),
sodium lauryl sulfate (0.1 g/l), and saccharine (1.5 g/l). The current density is 10–25 mA/cm 2
(nickel or cobal can be used as the anode).
The most important feature is that the Ni x% Fe 100−x% –NiFeMo–NiCo thin films (multiplayer nanocom-
posites) can be fabricated shaping the magnetic properties of the resulting materials to attain the desired
performance characteristics through design and fabrication processes.

Micromachined Polymer Permanent Magnets
Electromagnetic microactuators can be deviced and fabricated using micromachined permanent magnet
thin films including polymer magnets (magnetically hard ceramic ferrite powder imbedded in epoxy resin).
Different forms and geometry of polymer magnets are available. Thin-film disks and plates are uniquely
suitable for microactuator applications. For example, to actuate the mirrors in optical devices and optical
MEMS, permanent magnets are used in rotational and translational (linear) microtransducers, microsen-
sors, microswitches, etc. These polymer magnets have thickness ranging from hundreds of micrometers
to several millimeters. Excellent magnetic properties can be achieved. For example, the micromachined
polymer permanent-magnet disk with 80% strontium ferrite concentration (4 mm diameter and 90 µm
thickness), magnetized normal to the thin-film plane (in the thickness direction), has the intrinsic coer-
civity H ci = 320,000 A/m and a residual induction B r = 0.06 T [12]. Permanent-magnet polymer magnets
with thickness up to several millimeters can be fabricated by the low-temperature processes. To make the
permanent magnets, the Hoosier Magnetics Co. strontium ferrite powder (1.1–1.5 µm grain size) and Shell
epoxy resin (cured at 80°C for 2 h) can be used [12]. The polymer matrix contain a bisphenol-A-based
epoxy resin diluted with cresylglycidyl ether and the aliphatic amidoamine is used as for curing. To prepare
the polymer magnet composites, the strontium ferrite powder is mixed with the epoxy resin in the ball-
mill rotating system (0.5 rad/s for many hours). After the aliphatic amidoamine is added, the epoxy is
deposited and patterned using screen-printing. Then, the magnet is cured at 80°C for 2 h and magnetized
in the desired direction.

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