Edwin Jan Klein - Universiteit Twente

Chapter 6
Next, the heater was heated directly, by connecting it to an adjustable power supply.
The dissipation in and resistance of the heater were determined by measuring the
current through and voltage across the heater. Figure 6.12a shows the measurement
results of several measurement runs performed on the same omega shaped heater with
a radius of 50 µm. As was the case for the indirect heating, the resistivity increases
between the first and the second run due to passivation of the heaters but is then stable
for the subsequent third and fourth runs. In the fourth run the power dissipation in the
heater was increased beyond 300 mW (equivalent to ≈1 mW/µm heater length) at
which a further passivation effect was observed, this time decreasing the resistance as
shown by the fifth measurement run.
Resistance (W)
260
240
220
200
180
run 1
run 2
run 3
run 4
run 5
0 200 400 600 800
Dissipated power (mW)
a)
b)
Figure 6.12. Measured a) and normalized b) heater resistance as a function of the heater
dissipation.
In the fifth run the limits of the heater were tested by increasing the applied voltage
until heater breakdown. Until a dissipation of 500 mW (≈0.63 mW/µm) the heater
showed no signs of breaking down. Beyond this value, however, the resistance was
seen to decrease, resulting in a runaway increase of the heater dissipation until the
heater finally broke down at 870 mW in this case.
Point of failure
142
Normalized heater resistance
1.20
1.15
1.10
1.05
1.00
0.95
0 100 200 300 400 500 600
Dissipated power (mW)
Heating pattern shows
that the current flows
along the edges
a) b)
Figure 6.13. Microscope images of a broken down omega a) and circular b) heater showing
the heat distribution and the points of failure.
All breakdowns in the heaters were the result of single point failures as shown in
Figure 6.13a and 6.13b for the omega and circular heater respectively. These pictures