Frequently Asked Questions¶
The following questions reflect the kinds of technical questions customers commonly ask about pulse/TR-mode and IR-mode measurement on Microsanj NanoTherm (NT220-series) systems.
Q: In TR (thermoreflectance) mode, pulsed excitation of the device under test is required. For a device with both gate and drain terminals, which terminal is pulsed? A: Either terminal can be pulsed, or both. Biasing is sometimes simplified by modulating only the drain voltage, but typical pulsed I-V (PIV) measurements pulse both the gate and drain terminals together.
Q: Can the system measure thermal data with the device held at a stable, continuously biased condition — i.e., no pulsed excitation? A: Yes. The system can measure at steady state for extended periods, up to approximately 200 seconds.
Q: How does IR mode work, and what does "IR mode" mean on these systems? A: In IR mode, the system captures thermal images at a rate limited by the IR camera's frame rate (60 Hz, i.e., roughly 17 ms per frame). Images can be captured either as a movie sequence or at steady state.
Q: Can the system measure devices that run hotter than typical thermoreflectance calibration ranges — for example, a device under test that operates above 300°C on a heated chuck or probe station? A: Yes. Measurements have been verified up to 600°C, and higher measured temperatures are possible. Thermoreflectance is typically calibrated up to 120–150°C to confirm the linearity of the thermoreflectance coefficient over that range. Higher-temperature calibrations, performed with a custom high-temperature stage, have verified coefficient linearity out to 300°C. [chart/image in source — not reproduced here]
Q: Does high-temperature measurement capability apply to both TR and IR modes? A: Yes.
Q: TR mode has a transient resolution of 50 ns. What is the best achievable transient resolution in IR mode? A: 17 ms, corresponding to the IR camera's 60 Hz frame rate.
Q: What is the best spatial resolution achievable in IR mode? A: At 3x magnification, the IR camera's effective pixel size is approximately 4 µm (the underlying microbolometer sensor has a native pixel pitch around 12 µm). The diffraction-limited spatial resolution in the 7–14 µm wavelength band is approximately 5–10 µm, depending on the IR lens used. In practice, the IR camera is best suited to general, macroscopic thermal distributions at low magnification rather than fine spatial detail.
Q: The datasheet lists NETD (noise-equivalent temperature difference, typical with 5-minute averaging) as 250 mK. Does that number apply to both TR and IR mode, or is there a different figure for each? A: TR mode typically achieves an NETD of 250 mK with 5-minute averaging. IR mode typically achieves an NETD below 15 mK with 5-minute averaging. In general, IR mode is more sensitive to small temperature changes, though TR mode can offer better sensitivity under certain specific conditions.