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Semiconductor pressure sensors have better characteristics
than conventional pressure sensors, such as high sensitivity,
high accuracy, no hysteresis, small size and on-chip, to
recommend their useful in a wide field. Ongoing advances in IC
fabrication technology, semiconductor pressure sensors have
become to the major objective of manufacture already. The
sensitivity of a silicon pressure sensor is influenced by the
geometry structure of thin diaphragm, piezoresistor layout and
piezorestive coefficients.Therefore, the semiconductor pressure
sensors which the diaphragm has a uniform, smooth, well-
controlled thickness dimension and low resistivity of the
piezoresistors are helpful to promote the performance of the
sensors. Recently, there are many reports about improving the
sensitivity and other important parameter of the silicon
pressure sensors by utilizing special geometry structure. From
this point of view, the objective of the paper focus on the
fabrication and characterization of JFET pressure sensors,which
replace four resistors by JFET in the form of a Wheatston
bridge, its voltage-variable-resistance effect can improve the
performance of the sensor. In this experiment, the process
design, precision control of diaphragm thickness, the parameters
which may influence the output voltage (sensitivity and Voffset)
of sensors including the diaphragm thickness,piezoresistors
layout, dopant concentration and pn junction of JFET etc. are
discussed. On the precision control of diaphragm
thickness, we use 85C、45%wt、KOH etchant which has different
etch rate for Si and SiO2 to make a thin square diaphragm (1mm
length and 15um thickness) and alignment window simultaneously,
then JFET can be diffused on the correct position of diaphragm
and crystallographic line. On the measurement of
sensitivity, it can be increased (Normalize Sensitivity from 1
to 1.08) by increasing gate voltage (Vgs from 0V to 2V) or it
can be increased(Normalize Sensitivity from 1 to 1.03) by
increasing input voltage (Vin from 1V to 5V). On the
measurement of zero-pressure offset voe (Voffset), it can be
compensated for adjusting the gate voltage or increasing input
voltage.
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