3.1.2 Applications of Thin Films

Applications Outside Semiconductor Technology

Let's first look at applications of thin films outside of semiconductor technology - so we know and then can forget it for the time being. What we have, very briefly and not exhaustively, is

Application Field	Examples
Optics	Antireflection coating; on lenses or solar cells, .. Reflection coatings for mirrors. Coatings to produce decorations (color, luster, ...), Interference filters. CD's, DVD's and upcoming D's. Waveguides. Photosenistive coating of "analog" film for old cameray
Chemistry	Diffusion barriers. Protection agains corrosion / oxidation. Sensors for liquid / gaseous chemicals.
Mechanics	"Hard" layers (e.g. on drill bits). Adhesion providers. Friction reduction.
Magnetics	"Hard" discs. Video / Audio tape. "SQUIDS"
Electricity (without semiconductors)	Insulating / conducting films; e.g. for resistors, capacitors. Piezoelectric devices

You should know some of this stuff from experience (do your glasses have an antireflection treatment? an antiscratch layer?) or from your studies.

For some other applications you may easily guess where thin films come in (remember the formula for the capacity of two plates with a dielectric in between? The thickness or better thinness of the dielectric does play a crucial role, after all).

Some others may be totally unknown, but no matter: Thin films do play an important role in many branches of Materials Science and Engineering, and a lot of what we learn in this course can be directly transferred to those applications.

Illustrations of Applications in Semiconductor Technology

Let's just look at a few pictures of thin films in semiconductor technology to get a first flavor of what we are up to. Nothing more needs to be said.

The blue line shows the conduction band of a modern Semiconductor Laser. It is what you want for superior perfomance. It follows from the sequence of >25 thin films deposited on top of each other, starting from the 1,5 µm GaAs, as shown.
SEM cross section through a 64 Mbit DRAM (1996 or so). The "holes" (idiotically called "trenches") contain the capacitor.	TEM picture of a cut through a "trench" containing one capacitor and 6 thin layers . "ONO" = Oxide-Nitride-Oxide layer sequence; about 3 nm per layer.