Recently, Prof. Xie Huikai, Associate Professor Ding Yingtao, and doctoral student Xiao Lei from School of Information and Electronics, BIT, and Dr. Wang Peng from WiO TECH Co., Ltd., proposed a continuously controlled light microshutter based on electrothermal actuation by adopting MEMS technology, which can be effectively applied to the smart lighting of “green buildings”, and they have published an article “Analog-controlled Light Microshutters Based on Electrothermal Actuation for Smart Windows” on Optics Express, one of the top journals in the field of optics (IF:3.669).

Fig. 1. (a) the open state of the electrothermal Microshutter; (b) the closed state of the electrothermal Microshutter; (c) the half-open state of the electrothermal Microshutter; (d) the mixed state of electrothermal microshutter; (e) application scenarios of continuously controlled light Microshutters: smart windows

　　In order to make better use of natural light, smart windows used in “green buildings” have received widespread attention. Microshutter based on MEMS technology is considered to be one of the most promising solutions for smart windows due to its faster switching speed and lower manufacturing cost. However, most Microshutters can only work in two modes (the open state and the closed state), which can not achieve high-precision, dynamic, and multi-gray control of pixels. Electrothermal actuation has unique advantages because of its larger motion range and lower driving voltage, and its actuation displacement can be continuously adjusted and controlled throughout the entire range of actuation, which is exactly what a continuously controlled light microshutter needs. Therefore, a microshutter array based on electrothermal actuation is proposed, and each array is composed of several units (as shown in Fig. 1).

Fig. 2. (a) the SEM of electrothermal Microshutter array (top view); (b) the SEM image of electrothermal microshutter array (front view); (c) the relationship between single pixel light transmission rate and actuation voltage; (d) the relationship between array light transmission rate and actuation voltage; (e) Microshutter deformation diagram with increasing actuation voltage; (f) the open state and the closed state of array; (g) million times of actuation reliability test; (h) long-term power-on reliability test;

　　First, the theoretical model of the electrothermal microshutter is established, and the finite element simulation is carried out to optimize the transmittance and control accuracy of the device. Then, the microshutter device is successfully fabricated by using SOI substrates, combined with bulk micromachining and surface micromachining (as shown in Fig. 2). Besides, a long-term reliability test of the device is also carried out, and the results show that the functions of the device are good and the analog control characteristics are not changed.

　　The device can also be applied in dynamic precision lighting, multi-gray lighting, pattern display, information exchange and astronomical spectrometer, etc..
Paper link: https://doi.org/10.1364/OE.404680