Since the sensor is not accessible for calibration after it is
sealed inside the glass–silicon micropackage, it is important that
it shows little or no drift. A 1200 Å-thick polyimide sensor was
tested at 37 C for 48 h at 50% RH, and re-tested at 37 C
for 48 h at 80% RH; the results from both of these tests are
shown in Fig. 6. The relatively higher drift as seen in Fig. 6
is a known characteristic of polyimide humidity sensors and
agrees well with published results [5]. The maximum drift was
approximately 0.4% RH at 50% RH conditions and was about
11.4% RH at 80% RH conditions.