Digital Holographic Microscopy for Mechanical Characterization of MEMS Membrane Resonator

By AZoNano

Table of Contents

Introduction
Experiment
Conclusion
About Imina Technologies

Introduction

Microelectromechanical Systems (MEMS) are very small devices comprising micrometer-sized components with a broad range of capabilities. The size of these devices is continuously decreasing, while their complexity and adoption are significantly growing. These factors, in turn, increase the requirement for precise and rapid mechanical and electrical interactions for testing and characterization of MEMS devices.

This article discusses the application of two miBot micromanipulators from Imina Technologies in the dynamic characterization of an MEMS membrane resonator by digital holographic microscopy (DHM).

Experiment

The MEMS resonator comprises a 1-µm-thickness circular silicon membrane, a resonating cavity, electrothermal actuators, and electrical contacts with 200 µm side lengths. In this experiment, the device is to be characterized with DHM to identify its resonant frequencies and capture the images of membrane deformation.

By utilizing real-time digital reconstructions of phase information, DHM technology provides nanometer-scale vertical resolution and intensity images, as in traditional optical microscopy.

It is necessary to perform testing and characterization by directly contacting the electrical pads to ensure that the measurements taken are independent of the other devices and components of the system.

The two miBot micromanipulators were used to tackle the difficulties in approaching and contacting the electrical pads without damaging the wire bonds. The nanometer positioning resolution over their four degrees of freedom was suitable for this operation as it reduced most of the risk associated with incorrect maneuvers.

Moreover, the extremely short length of the miBot arm ((<2 cm) eliminates the vibration of probes at this scale.

A DHM R2100 Digital Holographic Microscope from Lyncee Tec was used to perform the imaging and dynamic characterizing of the MEMS device. The two miBot micromanipulators equipped with tungsten probes were mounted on a miBase from Imina Technologies and fitted to a DHM stroboscopic module, as shown in Figure 1.

Figure 1. Experimental setup of the miBots and miBase mounted on a manual X-Y positioning stage under the DHM.

The miBase from Imina Technologies was mounted on the DHM manual X-Y positioning stage and the miBot manipulators were allowed to slid into coarse position manually, as shown in Figure 2.

Figure 2. The miBot micromanipulators in contact with the MEMS resonator

The built-in intuitive miBot Remote Control (MRC) software operated the micromanipulators utilizing a control pad to make accurate contact with the electrical pads within seconds, as depicted in Figure 3.

Figure 3. The miBot probes in contact with the electrical pads of the MEMS resonator

A 10 Vpeak sinusoidal signal was swept from 1 to 200 kHz and phase data was monitored to identify the frequencies at which the largest membrane displacements are taken place, as depicted in Figure 4.

Figure 4. DHM 3D phase plot of the actuating MEMS resonator at 60 kHz. Displayed units are in micrometers

Now, the miBot manipulator was shifted from electrical pad and mounted on the membrane to monitor the deformation caused by an applied force on the silicon membrane. The probe was gradually lowered onto the membrane by adjusting the step size and speed of the miBot arm to characterize the out-of-plane deformation with DHM, as demonstrated in Figure 5.

Figure 5. 3D phase plot of a miBot probe mechanically deforming the silicon membrane. The “ripples" are an interference effect of partial refection off the back of the cavity due to the transparency of the silicon membrane

Conclusion

Imina Technologies miBot micromanipulators enabled the precise and flexible positioning of the probes, which was essential for this MEMS application. Moreover, together with the miBase, they delivered a portable and user-friendly microprobing solution, which can be incorporated into almost any setup and ready to use within 10 min.

The freedom to move the miBots proved to be a key advantage during the experiment as it enabled the modification of one of the miBots’ function from injecting an electrical signal to applying a mechanical deformation on the MEMS membrane, thus saving time by eliminating the need to change the setup.

About Imina Technologies

Imina Technologies is a privately held company founded in 2009 to exploit more than ten years of research in high precision robotics at the Swiss Federal Institute of Technology in Lausanne, Switzerland (EPFL).

With many years of experience in precision engineering, micro-robotics and nanomanipulation, Imina's interdisciplinary team is geared up for the needs of the most demanding users. Their unique combination of know-how enables them to propose complete solutions for even the most specific applications.

This information has been sourced, reviewed and adapted from materials provided by Imina Technologies.

For more information on this source, please visit Imina Technologies.

Date Added: Mar 12, 2013 | Updated: Jun 11, 2013
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