Heat reduction in wearable devices by integrating radiative photonic structure and thin metal film

Abstract

The advanced small electronic devices such as flexible/stretchable elec Abstract tronics Introduction with multi-functionalities and next-generation optoelectronics have been widely spread due to their applicabilities. However, although the size of these wearable devices has been decreased considerably, their power densities have remarkably increased. Hence, the self-heat generation has been concerned because it results in thermal damage to our skin and the deterioration of the device functionalities in terms of operation speed, working time, and battery life. Moreover, the strong solar irradiance in daytime is one of strong heat source to these advanced wearable electronics, however, the conventional heat reduction method for electronics is generally optimized in housing or indoor environments. Thus, a new cooling approach under strong solar irradiance has been required for these small electronics . Thus, we propose the photonic-based cooling strategy of thin-film geometrical layouts that consist of thin metal layer and engineered photonic structures selectively emitting the thermal infrared wave in atmospheric window (i.e., 8 – 13μm). Therefore, this system can effectively reduce the heat dissipation compared to the conventional conduction/convection-based cooling methods. In this study, aluminum was selected as the candidate of metallic layer for heat sink, with 30 μm-thick thickness allowing flexibility. The selective emitter (SE), which is photonic structure emitting thermal infrared wave, was formed on the metal film and composed of SiNx, SiO2, and polydimethylsiloxane (PDMS). The simulated and measured emissivities were over 70% on average value in the wavelength of 8 – 13 μm. The detailed characterization results will be discussed in our study .