The operation of the MOIS transistor
can be viewed as the voltage control current source, similar
to that of the conventional MOS transistors. The MOIS transistor
has lower electron and hole mobility. Therefore the applications
of the MOIS transistor are not so good in the current mode circuit.
The oscillator circuit is one of the application that MOIS operates
in the voltage mode. When the air pressure is applied to the
transistor on the silicon substrate, the transconductance of
the transistor is changed and the frequency of the circuit is
changed more than the oscillator circuit which is used MOS transistors.
This is because the mobility is changed according to the present
of gold atom in devices substrate. This structure of transistors
is suitable to be made as a pressure control oscillator. In
this thesis, MOIS transistor Ring Oscillators are investigated.
The circuits consist of odd stages of the inverter chain. The
designed MOIS devices are fabricated on the Si substrate,n (100)
oriented with the thickness of 400 mm. The wafer resistivity
is 8-12 ohm-cm. This wafer are etched using EPD anisotropic
etchant to form thin square diaphragm on the backside of the
transistor with the thickness of 20 mm. It is found that The
change of output frequency of the circuit depends on the change
of transconductance of the transistors as the air pressure is
applied to diaphragm. Different device types, PMOIS and NMOIS,
are studied and compared. And from the experimental it is found
that the change of frequency are depended on the direction of
drain current via edge of diaphragm. And the highest sensitivity
can be produced from 3-stage ring oscillator with NMOIS in the
diaphragm that determined the current flow paralleled with the
diaphragm edge.
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