C. Hysteresis
Tests have also been performed to investigate the hysteresis
behavior of the sensor under normal operating conditions. A
1200 Å-thick device was placed in a humidity chamber at 37
C. The humidity of the chamber was increased from 30% RH
up to 70% RH in increments of 10% RH and then cycled down
back down to 30% RH. Fig. 8 summarizes the results from this
test. The device shows hysteresis of about 1.75% RH. In its original
environment (inside the hermetically sealed silicon–glass
micropackage) the sensor would be initially exposed to moderate
or low humidity levels and once it detects a significant
change the device will be labeled “failed.” As the environment
inside the package is not expected to cycle up/down, this hysteresis
will not adversely affect the performance of the sensor.
However, the data as presented may provide useful for other applications
that require multiple humidity cycling and is useful
to explain other properties of the sensor.