# Junction Temperature Optical Sensing Techniques for Power Switching Semiconductors: A Review
## 3 Junction Temperature Optical Sensing Techniques
### TSOP Sensing Technique
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Year** & **Device** & **I (A)** & \(\lambda\) **(nm)** & **S** & **Err** & \(\Delta\)**T** & **Contribution** & **Ref.** \\ \hline
2022 & SiC M. & 3–18 & 390/510 & - & \(\pm 3\)\({}^{\circ}\)C & 50–130 \({}^{\circ}\)C & Decoupled intensity peaks. & [107] \\
2021 & SiC M. & 14 & 360/420 & - & \(1.5\)\({}^{\circ}\)C & 45–106 \({}^{\circ}\)C & Impact of EL biasing and BTI & [95] \\
2021 & SiC M. & 2–12 & - & - & 2.18 K & 10–120 \({}^{\circ}\)C & Simultaneous device Temperature & [106] \\  & & & & & & and current EL extraction & [106] \\
2020 & SiC M. & 20, 80 & 380/480 & - & - & 30–150 \({}^{\circ}\)C & Peak spectral extraction & [108] \\
2020 & SiC M. & 5,20 & 390/510 & - & \(1.2\)\({}^{\circ}\)C & 10–90 \({}^{\circ}\)C & Multiple photodetection & [96] \\
2020 & SiC M. & 4-11 & 380 & 0.10 mV/\({}^{\circ}\)C & 3.9 \({}^{\circ}\)C & 40–100 \({}^{\circ}\)C & Embeddable detector & [109] \\
2019 & SiC M. & 5 & - & 3.2 mV/K & - & 30–150 \({}^{\circ}\)C & Intensity-temperature model & [105] \\
2019 & SiC M. & 20,25 & 383/485 & 1.53 V/\({}^{\circ}\)C & \(\pm 5\)\({}^{\circ}\)C & 95–135 \({}^{\circ}\)C & Temperature transient & [104] \\
2018 & SiC M. & 5 & 500 & - & - & 30–130 \({}^{\circ}\)C & Photomultiplier for detection & [87] \\
2018 & SiC M. & 5–12 & 387 & - & - & 25–100 \({}^{\circ}\)C & Simple photodetector & [110] \\
2015 & SiC M. & 16 & 420/390 & & 290–800 K & EL—temperature profile & [98] \\
2013 & SiC M. & 9 & 480/390 & & 290–800 K & Diffusion current in SiC structure & [97] \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Advancements in TSOP sensing technique for junction temperature measurement of semiconductor devices. Figure 8: Schematic representation of simultaneous junction temperature and current sensing approach for paralleled SiC MOSFET module Reprinted with permission from Ref. [83], 2023, IEEE. Due to the weak EL signal in the TSOP sensing technique, an integrated operational amplifier was engaged to improve the signal-to-noise ratio (SNR); nevertheless, a slight deviation in measurement accuracy was observed as the junction temperature rose due to the self-heating effect. Moreover, the galvanic isolated sensing method for SiC MOSFET was introduced in [108] based on the variation in light intensity. The extracted EL spectrum exhibited two characteristic peaks around \(\sim\)380 nm and \(-\)480 nm, while a similar approach implemented in [104] has \(\sim\)383 nm and \(\sim\)485 nm for the two peaks, as indicated in Table 4. The two peaks exhibited different temperature coefficients. The major peak had a negative temperature coefficient, while the minor one showed a positive peak. The emission was coupled to the spectrometer via a quartz fiber fixed on the side of the chip for measurement purposes. The former used two independent bandpass filters to extract the peak emissions, and the signal ratio was used to compensate for the EMI due to fast switching transients and optical transmission degradation within a temperature range of 30 to 150 \({}^{\circ}\)C. On the other hand, the latter work displayed a limited temperature range between 90 and 135 \({}^{\circ}\)C, and the sensitivity obtained was \(\sim\)1.53 mV/\({}^{\circ}\)C at a mean error of \(\pm\)5 \({}^{\circ}\)C; the optical measurement, in this case, still required a high bandwidth since the dead time was short. The approach for extracting the forward current and junction temperature from the two peaks simultaneously was implemented by integrating inherent electrical isolation with the EL technique [107]. After establishing a correlation between the current and temperature through an analytical model, a negative gate voltage of \(-\)5 V was applied to the gate of SiC MOSFET to operate in the third quadrant.