Development of a Oxygen Sensor for Marine ... - DTU Nanotech

4.3. TEMPERATURE SENSOR 35
a Pt300, and a Pt600 (where the number is the resistance of the sensor.
Figure 4.9: Close up of the l-edit design for the Pt300
Of these 3, the Pt50 is the safest design. The reason for this is that the
The Pt300 and Pt600 have a width of 10 µm, while the Pt50 have a width
of 20 µm. Hence if some error occurs during the metallization part of the
process for the sensor, and you end up with a width of 9 µm instead, which is
merely 1 µm off. It would translate into a 10% shift in the resistance, while it
would merely be 5% with the Pt50. Hence having a reasonably wide resistor
can minimize a potential error, unfortunately however the higher the width,
the lower the resistance is as well. So once again it is a matter of balancing
one advantage against another disadvantage.
Figure 4.10: Close up of the l-edit design for the Pt600, it is basically the
Pt300 done twice.
Why the 4 contacts, instead of merely 2? Well consider if there was only
2, each serving as a contact for both current and voltage, the total resistance
between the two can then be calculated from:
R = V
I = 2Rc + 2Rsp + Rs
(4.2)
Where Rc is the contact resistance between the chip and the equipment
connected to it, Rsp the spreading resistance, and Rs the chip resistance (and