G. Sensor Tests on the Actual Packaging Substrate
Our future aim has been to integrate the RH sensor to the silicon
substrate fabrication process to facilitate assembly procedure
and hence reduce the associated costs and labor. However,
we also expected that the leads (sometimes called feedthroughs)
that connect any elements inside the package to the external
world has specific capacitance and resistance that are associated
with them complicating the measurement of capacitance
especially at the measurement frequency (1 MHz). To further
investigate this, one of the 300-Å-thick relative humidity sensors
(with the highest sensitivity thus minimal intrusion to measurement
due to lead parasitics) was mounted on the silicon substrate
and the two ends of the sensor is wire-bonded to the pads
inside the Glass-silicon package. Then the leads of the sensor
is connected to the PCB board utilizing the feedthrough leads
embedded in the silicon substrate as shown in Fig. 12. This is
the actual testing setup had the sensor been integrated into the
silicon substrate fabrication process. The initial measurements
at 1 MHz was not satisfactory due to dominating parasitics at
this frequency. Hence other frequencies has been utilized as an