This is an over view of the filter wafer.
The green color seen in the cavities is an anti reflective coating
on the bottom wafer. The total thickness is 2 millimeters and
the filter wafer consists of two through etched wafers and two
sealing wafers (one silicon and one glass), which are bonded
together.
The photo shows the filter
and IR source as two separate components. Together these form
the integrated IR source and filter seen at the top of the page.
This unit in combination with an IR detector has been developed
as a CO2 sensor for use in anesthesia and ventilator equipment.
This SEM shows a cross section of the CO2
filter. The cavity seen in the SEM is filled with CO2 gas at
two bars of pressure prior to bonding. The cavity is sealed using
anodic bonding trapping the gas and forming the filter.
This SEM of the IR source clearly
shows the etched cavity below the polysilicon filaments. This
cavity acts as thermal isolation form the bulk of the chip.
The finished IR chip has been mounted in a standard
ceramic IC capsule. The photo shows two of the four IR sources
glowing.
Whit a thermal camera we're
able to see the temperature distribution over the IR chip. We
can clearly see that the thin ploysilicon heaters are hottest
in the middle of the hot zone. This temperature is around 650
degrees Celsius.
