In the open literature many efforts have been described which are focussed on the
conversion of the electrodes as described in the previous section to more rigid devices
by applying the glass membranes in a more solid state performance: leafing out the
inner solution and replace it by a solid state contact. For instance sputtering the glass
directly onto a metal electrode. This idea is a mistake, because the basic recipe should
always be to create a cell where all interfaces are thermodynamically well defined and
the Nernst equation can be obeyed. In terms of solid state physics: Fermi levels of
charged species should be able to become equal throughout the whole system. It is
remarkable that solutions to this problem did not come from chemical engineers, but
from electrical engineers and physicists, who are most probably more familiar with
thermodynamic equilibria, as for instance occurring in electronic components with
doped semiconductors, contact potentials etc. Especially the knowledge how to create
a stable interface between silicon and silicon dioxide, as in the case of a MOSFET
device, is of importance. It couples in a stable way an electric field, penetrating the
oxide, to the “electronic world”. In case the outer surface of the oxide is in
equilibrium with an ionic solution in contact with the oxide, the resulting interfacial
potential will modulate the electric field and thus a perfect and stable contact is
provided between the “ionic world” and the “electronic world”. This idea was the first
new concept investigated by the author and received the name ISFET technology.