It is interesting to note that the Planar method was conceived
in 1959 by Fairchild, based in the company expertise as a manfucturer
of photo cameras and related materials.
Basically, the manufacture technique consists to use a photo-sensistive
material layer that polimerizes when exposed to the ultraviolet
light known as PHOTORESIST.
The Silicon matrix treated previously with PHOTORESIST layer that
is then exposed to the ultra violet light through a photographic
mask on which are the areas to be etched. The exposed parts of of
the lacquer harden, and the unexposed parts are rinsed off.
Afterwards the Silicon matrix with the printed layout was etched.
Due to the stringent requirements of the photographic reproduction
techniques it was possible to obtein a high quality printing, in
such way every detail of the semiconductor layout like: holes, images,
small planes and so on could be reproduced precisely. Such so accurate
image reproduction never could be achieved with the early mechanical
masks used in the manufacturer of the Mesa TRANSISTOR.
The engineers called it as Planar TRANSISTOR, because as suggested,
all the regions in the matrix appeared in the same plane.
As the earlier TRANSISTOR technologies seen, the Planar method nevertheless
had a drawback due to its inability to produce power TRANSISTORS,
because of the high resistance of the collector material. In June
1960 Bell Laboratories, where the first solid-state amplier was
invented, announced a new, epitaxial method of fabricating TRANSISTOR.
Basically it consists in the growing of a thin Silicon layer on
a single-crystal substrate.
Since the resistivity of the layer could differ from that of the
substrate, the process allowed the formation of TRANSISTORS within
the epitaxial layer whose characterisitcs were independent of the
That means it was possible to built a TRANSISTOR on a strong and
thick substrate with a thin base capable to operate in high frequency
and due to the low collector resistivity it could supply more power.
Around 1960, the commercial production of the bipolar TRANSISTOR
had achieved a significative technological stage. Therefore the
researches laboratories were with an eye in the future and starting
from the advancements introduced by the Planar method developed
a new concept of solid-state amplifer, the FIELD-EFFECT TRANSISTOR.