研究目的
To measure the junction temperature and estimate the health of gallium nitride light-emitting diodes (LEDs) using dynamic impedance and optical output measurements.
研究成果
The study demonstrated new indicators of GaN LED temperature, health, and imminent failures through electrical and optical small-signal modulation responses. It found highly sensitive GaN LED temperature predictors and established a foundation for in-field health monitoring techniques using smart drivers and optical wireless communication infrastructure.
研究不足
The study acknowledges that the accuracy of high-frequency measurements may be deteriorated due to the impact of parasitic inductance, making measurements at certain Zim and f values impractical. Additionally, the study suggests that further research is needed to correlate the active region defects presence with the impedance response for current bias.
1：Experimental Design and Method Selection:
The study used a vector network analyzer (VNA) to characterize the dynamic optical and electrical responses of LED packages. The one-port reflection method was employed to measure the small-signal impedance dependence on bias current and temperature. A photodiode connected to the second port enabled simultaneous optical response detection.
2：Sample Selection and Data Sources:
Two commercially available white CSP GaN LEDs were tested. The phosphor light-conversion layers were removed to leave bare chips.
3：List of Experimental Equipment and Materials:
Vector network analyzer (VNA), photodiode, thermostat for temperature control, microwave probe, ceramic substrates with silver solder.
4：Experimental Procedures and Operational Workflow:
The junction temperature was controlled by a thermostat, and preliminary junction-to-case thermal resistance characterization was done with a thermal transient testing method. The small-signal impedance and optical responses were measured across a range of temperatures and bias currents.
5：Data Analysis Methods:
The data was analyzed to reveal temperature-sensitive parameters of the electrical and optical responses, and to demonstrate a correlation between the non-radiative current and the small-signal impedance.
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