To investigate the packaging effect on the sensing characteristics of the pressure sensor,
characterization comparisons between unpackaged pressure sensor and packaged pressure sensors
were conducted for both packaging approaches. Due to the different manufacturing lots of the pressure
sensor wafers, the silicon membrane thickness of the pressure sensors are 20 and 30 μm for the damring
and sacrifice-replacement approaches, respectively. Figure 10 shows the signal output comparison
between the unpackaged and packaged pressure sensors under various temperature and pressure loadings. A signal output difference between the packaged and the unpackaged pressure sensors is
observed, as shown in Figure 10(a). Due to the shrinkage characteristics of the molding compound
material during the post-molding curing process, a silicon membrane surface of the pressure sensor has
a compression stress distribution, inducing a signal output shift. Besides, the original resistance of the
four piezoresistors varies from chip to chip. That is one of the possible causes of the signal output shift
of the packaged pressure sensor. However, the packaged pressure sensor has a similar response trend
with that of the unpackaged pressure sensor at room temperature.