The Tunability in Mechanical Properties and Fracture Toughness of Sputtered Silicon Oxynitride Thin Films for MEMS-based
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1222-DD02-20
The Tunability in Mechanical Properties and Fracture Toughness of Sputtered Silicon Oxynitride Thin Films for MEMS-based Infrared Detectors I-Kuan Lin1, Ping-Hsin Wu2, Kuang-Shun Ou2, Kuo-Shen Chen2 and Xin Zhang1 1 Department of Mechanical Engineering, Boston University, Boston, MA 02215, USA 2 Department of Mechanical Engineering, National Cheng Kung University, 70101, Taiwan ABSTRACT This paper presents the mechanical characterization of the elastic modulus, hardness and fracture toughness of silicon oxynitride films (SiON) with different oxygen and nitrogen content, subjected to thermal annealing processed at 400 °C and 800 °C. The Fourier-transform infrared (FT-IR) spectroscopy was employed to characterize the SiON films with respect to the absorbance peak in the infrared spectrum. The nanoindentation testing showed that both the elastic modulus and hardness slightly increased after thermal annealing. Finally, the fracture toughness of the SiON films were estimated using Vickers micro-indentation tests and the result revealed that the fracture toughness decreased with increasing rapid thermal annealing (RTA) temperature and nitrogen content. We believe these results benefit microelectromechanical systems (MEMS) in regards to maintaining the structural integrity and improving reliability performance. INTRODUCTION Silicon oxynitride (SiON) has been under extensive investigation for over a decade as a promising material system for the development of optical, photonic and microelectronic applications, including waveguide devices, nonvolatile memories and gate dielectrics [1,2]. It demonstrates a unique tunability in optical, electronic and mechanical properties by changing the chemical composition of oxygen and nitrogen, from silicon dioxide (SiO2) to silicon nitride (Si3N4) [3-5]. 50μm Al
SiNx
IR Pt/Ti
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Figure 1. (a) A SEM image of a bimaterial Si3N4/Al IR detector array and (b) the schematic view of the bending of a pixel of IR detectors during sensing operation. One of the potential applications of SiON films are uncooled microcantilever-based infrared (IR) focal plane arrays (FPAs). The function of this kind of IR detector is based on the bending of bimaterial microcantilevers upon absorption of IR radiation by the absorber, such as Si3N4. Subsequently, the deformation can be readily determined by using piezoresistive, optical, or capacitive methods [6]. As shown in Figure 1, each pixel of the microcantilever-based IR
FPAs is comprised of a thin Si3N4 top layer deposited on a thin Al bottom layer. However, in the IR spectrum the absorbance peak of Si3N4 is about 840 cm-1 which means the Si3N4 could easily detect the target whose wave number is about 840 cm-1[3]. Therefore, SiON films, which have unique tunability in their absorbance peak, could become an ideal candidate for IR detectors, in order to detect the target which has specific IR radiation. Thermal annealing is an important and common technique in modern semiconductor and MEMS fabrication. However, the thermal annealing pro
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