Digital holographic microscopy for the characterization of microelectromechanical systems

Abstract

Digital holography (DH) in microscopy became an important interferometric tool in optical metrology since when camera sensors reached a higher pixel number with smaller size allowing to acquire more defined images and high-speed computers became able to process such data. Consequently, it was possible the investigation of engineered surfaces on microscale, such as microelectromechanical systems (MEMS) that are microdevices composed by mechanical elements, electronics, sensors and actuators built in a small volume, realized using different material layers superimposed in various process steps, usually starting from a silicon substrate. In DH is necessary to perform the reconstruction of the wave field by means of numerical tools. This entails a computational burden but offers the possibility of retrieving not only the intensity of the acquired wavefield, but also the phase distribution. This work describes the principles of DH and shows some interesting numerical tools suitable to process the holographic images in the field of MEMS. The use of different numerical tools is discussed and illustrated with examples taken from the literature.

Thermal Characterization of Dynamic Silicon Cantilever Array Sensors by Digital Holographic Microscopy

“…With regard to the applications of our technique, although the expansion of cantilevers is isotropic, our sensing setup based on stroboscopic reflective-DHM can also be readily applied to study systems composed of different materials which expand non-isotropically upon thermal load. Examples include the effect of thermo-mechanical loads in: (a) the IC-fabrication and optimization process; and (b) the manufacturing and packaging of complex MEMS and micro-components [ 14 , 15 ]. Furthermore, the results also indicate that our technique can be reliably used for future mass sensing applications at elevated temperatures, which is required, for example, for the thermogravimetric analysis of minute amounts of materials.…”

“…Among different groups, two important studied categories with this technique are biological samples [1,3,4,5,6,7] and micro-components [8,9,10,11,14,15]. In all of these studies, the optically-generated holograms are digitally sampled by a charge-coupled device (CCD) camera.…”

“…In recent years, digital holography (DH) has been widely used for phase-contrast sensing applications both on Earth and in space [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 ]. Among different groups, two important studied categories with this technique are biological samples [ 1 , 3 , 4 , 5 , 6 , 7 ] and micro-components [ 8 , 9 , 10 , 11 , 14 , 15 ]. In all of these studies, the optically-generated holograms are digitally sampled by a charge-coupled device (CCD) camera.…”

Single-Shot 3D Topography of Transmissive and Reflective Samples with a Dual-Mode Telecentric-Based Digital Holographic Microscope

“…In addition, QPI-DHM has allowed the identification and characterization of cancer cells and therapies [ 15 , 16 , 17 ]. In material science, the most common applications of DHM are related to the evaluation of MEMS [ 18 , 19 , 20 , 21 ] and the analysis of static and dynamic surface topography [ 22 , 23 , 24 ]. Dynamic DHM imaging has been used to characterize sample changes due to external mechanical and electromagnetic forces and/or thermodynamic variables (e.g., pressure, temperature) [ 25 ].…”

Characterizing microelectromechanical systems with digital holography

“…2,3 In addition, it has previously been demonstrated that digital holography (DH) can be used to investigate engineered surfaces on the microscale level and thus overcome some of the limitations of classical microscopy. 4 In this work, 5 we describe and illustrate the general principles of DH for microscale characterizations. The DH process is based on recording of the interference pattern that exists between object and reference coherence waves, with the use of a digital device (e.g., a CCD or CMOS).…”