Thermoreflectance
Operating Principle[edit]
Basic Operation[edit]
Calibration[edit]
Measurement Procedure[edit]
- Position device on stage, place thermocouple on top of device
- Hook LED array up to DC current source
- Current less than 1000mA for NIR, 1600mA for blue and green
- Hook TEC to Agilent power supply, apply 200mA current (or other depending on application) (<1V). Keep temperature below 60C.
- Agilent power supply must have GPIB address 6
- This is a bug, it should be fixed in future software
- Microsanj pulse generator should not be on during calibration
- Agilent power supply must have GPIB address 6
- Wait for temperature to reach steady state, record T (again, <60C). ~5 degrees C change is ideal for this.
- Turn power supply off. Wait for temperature to reach steady state. Record time and temperature
- Turn on Microsanj transient imaging module
- Open ThermoVIEW (not cal) and check image to make sure it is in focus and CCD is not saturated.
- Close ThermoVIEW. If ThermoVIEW does not close properly, calibration software will not work (restarting computer solves this problem)
- Open ThermoCAL. Input image average (default OK), temperature change recorded from steps 4-5
- If device is heated when the TEC is on, the sign should be positive
- Input thermal time constant. Make this number larger than the number recorded in steps 4-5
- Input current you went up to in step 3 (right-hand side of window)
- Custom string does work if you’d rather use a different power supply, but it has to have address 6
- Turn image shift on and make sure the ROI is somewhere with a lot of clear edges. This solves some issues relating to vertical shifting during heating/cooling.
- Start calibration by hitting “start acquisition” button
- It takes a couple cycles for minimum and maximum temperatures to reach actual values. Keep track of thermocouple read-out and only take data from points where this is consistent. Change in temperature box can be updated while measurement is going on.
- When image is converged, enter file name and click “save image.” This will save the image from exactly one heating/cooling cycle.
- Inspect image in ThermoView for the following:
- Calibration coefficient on the order of 1e-4. 1e-3 is indicative of shifting during calibration
- Calibration coefficient is the same for the same material everywhere. It need not be identical pixel-by-pixel, but an averaged region on the top of the image should give you the same value as an averaged region at the bottom.
- Calibration coefficient on already-calibrated materials matches already-calibrated values.
- If you believe the results, record Cth values in log book (on desktop of thermal imaging computer)
- Turn off LED, CCD, and TEC
Tips[edit]
There seem to be two issues with calibration:
- Slow room drift
- Sample moves relative to objective in z and in the x-y plane
- For slow room drift:
- Use a small TEC and small temperature changes. Try to get it to converge as quickly as possible - save a lot of intermediate images.
- Turning room lights off can help as well
- For x-y shift:
- Try de-focusing - x-y shift tends to multiply the effect of spatial inhomogeneities because adjacent pixels get divided by each other. Blurring the image diminishes these inhomogeneities
- Obviously, this only works if you have a fairly clean sample, otherwise dirty spots that should be ignored just get bigger.
- For z shift:
- De-focusing tends to work for this as well. Not sure why.
- Try to get the chip really level.
- Try cooling instead of heating.
- For materials covered by thin transparent films, try using the white LED. Fabry-Perot effects can dominate the calibration because the sample moves up and down relative to the objective, but these can be avoided by using a more broadband source.
Low Frequency[edit]
Transient[edit]
Measurement Procedure[edit]
Position device on stage and probe it Turn on Microsanj Transient imaging module and high-speed signal generator
- Hook up the LED:
- Attach Trigger:LED on the transient imaging module to TRIG IN on the high-speed pulse source
- Attach PULSE OUT from the 300V pulse source (on the right of the module) on the high-speed pulse source to the LED
- Hook up the device:
- Attach Trigger:DEV on the transient imaging module to the input trigger of the Stanford Research synthesized function generator
Either:
- Attach the function:out from the function generator to the input of your device pulse source
- Attach your device pulse source to the device (check polarity on the ILX current sources)
OR attach your device directly to the function generator
- Make sure camera is attached to CCD power on the transient imaging module
- Open the ThermoVIEW software and in the Project Manager, make the following changes:
- Image type: Transient
- Use Pulse Gn. Checked (GPIB 6)
- Use Fn Gn checked (GPIB 19) if using SRS pulse generator
- Workspace path: choose something appropriate
- Adjust LED current, etc. until historgram looks good – when the “good illumination” light turns green )lower right-hand corner), click “Get Image”
- Check Voltage and Delay fields on the left hand side of the screen.
- If you are using the SRS function generator, you must change the voltage and click “update V” in order for the change to take effect
- Delay corresponds the falling edge of the LED pulse – to take an image of your device at the end of the heating cycle, set delay to the device pulse width
- Begin averaging when signals have all checked out
- Save image at the bottom of the screen when it looks converged
- Turn off LED, CCD, and TEC
Pulse setups[edit]
Current pulsing[edit]
See the ILX LDP 3811 page if you are using the ILX pulsed current source to get the correct wiring diagram.
Optical input pulsing[edit]
Manual and Guides[edit]
User Manual[edit]
- NT200t Reference Manual (PDF - 4/7/2011)
Documentation[edit]
- Thermoreflectance Imaging Guide by Xi Wang (PDF)
FAQ[edit]
If there are issues with your measurement or the tool, check whether a solution is posted below first. If you still are experiencing problems, contact Ben Curtin at [bcurtin@ece.ucsb.edu] or 773-592-9568.
Bug Tracker[edit]
List bugs/issues that haven't been resolved with this setup below. If you have a temporary fix, please include it in the "description" field. Issues will be crossed off the list once they are resolved or documentation has been updated to address them.
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Minor Issues[edit]
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Suggestions[edit]
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