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Author: Merlitz, Holger × End date: 2024 × Start date: 2020 × DDC: 500 × Type: Text × Type: article × WGL Institute: IPF ×

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    Non-synchronization of lattice and carrier temperatures in light-emitting diodes
    ([London] : Macmillan Publishers Limited, part of Springer Nature, 2016) Zhang, Jihong; Shih, Tienmo; Lu, Yijun; Merlitz, Holger; Chang, Richard Ru-Gin; Chen, Zhong
    Pulse implementation or switching-off (PISO) of electrical currents has become a common operation in junction-temperature (Tj) measurements for semiconductor devices since 2004. Here we have experimentally discovered a substantial discrepancy between Tj values with and without, PISO (e.g., 36.8 °C versus 76.5 °C above the ambient temperature at 25.0 °C). Our research indicates that methods associated with PISO are flawed due to non-synchronization of lattice temperatures and carrier temperatures in transient states. To scrutinize this discrepancy, we propose a lattice-inertia thermal anchoring mechanism that (1) explains the cause of this discrepancy, (2) helps to develop a remedy to eliminate this discrepancy by identifying three transient phases, (3) has been applied to establishing an original, accurate and noninvasive technique for light-emitting diodes to measure Tj in the absence of PISO. Our finding may pave the foundation for LED communities to further establish reliable junction-temperature measurements based on the identified mechanism.
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    Maximal rectification ratios for idealized bi-segment thermal rectifiers
    ([London] : Macmillan Publishers Limited, part of Springer Nature, 2015) Shih, Tien-Mo; Gao, Zhaojing; Guo, Ziquan; Merlitz, Holger; Pagni, Patrick J.; Chen, Zhong
    Thermal rectifiers whose forward heat fluxes are greater than reverse counterparts have been extensively studied. Here we have discovered, idealized and derived the ultimate limit of such rectification ratios, which are partially validated by numerical simulations, experiments and micro-scale Hamiltonian-oscillator analyses. For rectifiers whose thermal conductivities (κ) are linear with the temperature, this limit is simply a numerical value of 3. For those whose conductivities are nonlinear with temperatures, the maxima equal κmax/κmin, where two extremes denote values of the solid segment materials that can be possibly found or fabricated within a reasonable temperature range. Recommendations for manufacturing high-ratio rectifiers are also given with examples. Under idealized assumptions, these proposed rectification limits cannot be defied by any bi-segment thermal rectifiers.