A thermal analysis of the operation of microscale, inorganic light-emitting diodes

Abstract

An analytical model is developed to study the thermal properties of microscale, inorganic light-emitting diodes (m-ILEDs) with ultra-thin geometries and layouts. The predicted surface and m-ILED temperatures agree well with experiments and finite-element simulations. A simple scaling law is obtained for the normalized m-ILED temperature versus the normalized m-ILED size. This study provides a theory to guide the design of layouts that minimize adverse thermal effects on the performance of m-ILEDs not only for solid-state lighting but also for applications integrating m-ILED devices on complex/soft substrate as are currently of interest in optogenetics and other emerging areas in biology.

Temperature- and size-dependent characteristics in ultrathin inorganic light-emitting diodes assembled by transfer printing

“…2(b) shows the temperature change, DT, in the l-ILEDs determined by the finite element method (FEM) 22 as a function of the injection power, for the case of steady-state behavior in devices with various sizes. The temperature distribution across the l-ILED is approximately uniform 23,24 because its thermal conductivity, 160 W/m/K, 24 is orders of magnitude larger than that of the other associated materials, BCB (0.3 W/m/K 14 ), PET (0.15 W/m/K 14 ), PDMS (0.15 W/m/K 25 ), and glass (1.4 W/m/K 26 ). The model assumes that the bottom surface of the glass is at ambient temperature and that the top surface of the BCB undergoes natural heat convection with a convection coefficient of 25 W/m 2 /K.…”

Recent Advances on Thermal Management of Flexible Inorganic Electronics

“…In addition to the 3D thermal model for rectangular heat sources, Lu et al [55] established an analytical axisymmetric model to study the thermal properties of square µ-ILEDs with an effective radius of r 0 = L/ √ π, with L as the length of the µ-ILED, which compares well with FEA and experiments. Yin et al [56] studied the thermal properties of different shaped serpentine metal heater devices analytically, which can be used to evaluate the heating effects of complex shaped flexible heaters.…”

Heterogeneously Integrated Optoelectronic Devices Enabled by Micro‐Transfer Printing

“…In all cases of μ‐ILEDs, the ultra‐small, thin device geometries together with the high thermal conductivity of the metal interconnects yield advantages in thermal management. The rates of passive heat spreading scale favorably with device size, which is enabling for their reliable operation on substrates with low to moderate thermal conductivities such as plastics or biological tissues ( Figure ) . Moreover, the metal lines serve dual roles as electrical interconnects as well as efficient heat sinks due to their high thermal mass, compared to the μ‐ILEDs, and thermal conductivities .…”