When a high-power radio frequency (RF) metal oxide semiconductor field effect transistor (MOSFET) works in low-efficiency situations, considerable power is dissipated into heat, resulting in an excessive junction temperature and a likely failure. In this study, an optical fiber Bragg grating (FBG) sensor is installed on the die of a high-power RF MOSFET. The temperature change of RF MOSFET with the change of input signal is obtained by using the temperature frequency shift characteristic of the FBG reflected signal. Furthermore, the fast and repetitive capture of junction temperature by FBG reveals details of the temperature variation within each RF pulse, which is correctly correlated with input signals. The results show that besides monitoring the temperature accumulation of the chip for a long time, the FBG can also capture junction temperature details of the chip within each pulse period. Finally, a Cauer-type thermal model of the RF MOSFET was constructed based on the temperature information captured by the FBG.

The localized overheat is detrimental for the performance and lifetime of devices, especially in high-power, wide-bandgap semiconductor devices. But highly precise thermal characterization methods of the micro-nano regions within electronic devices remain challenging because of limitations in spatial resolution, electromagnetic interference and other factors. To address this challenge, we present a fluorescence thermometry utilizing a near-field fiber optic probe with quantum dots. Temperature-sensitive quantum dots modified on the probe tip as the nano-sensors provide excellent fluorescence stability and superior electromagnetic compatibility. The probe exchanges heat with the micro-nano scale hot spot on the sample surface and achieves thermal imaging based on the operating principle of scanning probe microscopy. The effective sensing area is minimized to nanoscale because of an aperture on the probe tip, achieving high detection spatial resolution. Using the probe with a sensitivity of 0.11 nm/°C, we investigated temperature difference of different-sized hot spots. The probe also effectively characterized the in-situ temperature distribution of an Au bonding wires with current flow inside, demonstrating its real-time monitoring capability for electronic devices. This innovative tool provides significant promise for performance assessment and failure analysis in electronic devices.

Quantum dots (QDs) exhibit photoluminescence that is highly sensitive to temperature, but their stability degrades rapidly in high-temperature environments. This study introduces an innovative sensor preparation method: CdSe/ZnS QDs are encapsulated in the optical fiber by the precision fusion splicing of concave fiber. This method provides robust protection, enabling the QDs to retain nearly 100% fluorescence after 30 min of continuous laser irradiation, compared with unprotected QDs, which lose 95% of their fluorescence. The sensor exhibits a linear temperature response up to $105~^{\circ }$ C, with repeated measurements showing deviations of less than $0.5~^{\circ }$ C. By comparison, unprotected QDs showed a $6.7~^{\circ }$ C fluctuation during three measurements at a sample temperature of $80~^{\circ }$ C. Furthermore, in situ testing on a device with a 100 s operating period and a 50% duty cycle revealed that the device’s temperature increased by up to $33.6~^{\circ }$ C within 50 s, with temperature changes correlating closely to the operating cycle. These findings highlight the sensor’s durability in high-temperature environments and suggest its broader industrial application potential.

In microdevices, local temperature serves as a crucial indicator of device performance. Traditional measurements often struggle to capture transient thermal events due to the small and short-lived nature of the heat generation region within the device. In this study, we use scanning probe microscopy with a fiber Bragg grating (FBG) near-field probe to identify hot spot locations precisely. We employ the time-stretched dispersive Fourier transform (TS-DFT) technique to enhance the demodulation rate, facilitating the mapping of the probe signal from the frequency domain to the time domain. Through numerical calculations of the optical pulse propagation process in a dispersive medium and conjunction with near-field temperature calibration experiments, we validate the capability of this technique to achieve the demodulation rate of 51.43 MHz. In practice, our measurements show that when subjected to an electrical excitation signal of 2 ms, the microheater leads a thermal impulse response of about 6°C, and the measurement process does not affect its regular operation.