MINI-VACUUM CHAMBER

By March 24, 2019Project ReI12

Research on microelectromechanical systems (MEMS) involves experimentally evaluating microstructures’ performance both in air and in vacuum. Moving microstructures usually exhibit different performance whether they are functioning in air or vacuum. The damping effect due to the presence of air has significant effect on moving microstructure especially when the microstructure is in resonance. Accordingly, the possibility for comparing the performance of MEMS in air and vacuum is very helpful to characterize these microstructures. Furthermore, for MEMS devices that are producing electrical signal for their motions, the detection of these signals is much easier in vacuum than in air for the decrease of damping and more strength of the electrical signal. The size of microstructures requires microscopes to observe them, and the need for electrical inputs or outputs demands proper electrical connections in air and vacuum. Use of laser vibrometer allows for characterizing MEMS devices in air and vacuum. Such measurements in vacuum require the object under investigation be seen through an optical window for the laser beam to illuminate the object and the reflected back light be detectable by the optical sensor. However, a piece of equipment is needed to provide all these requirements: be useable under microscope, be equipped with an optically transparent window for laser beam transmission, and accommodates electrical connections to function in vacuum. 

 

In using the mini-vacuum chamber, one needs to prepare the MEMS device for the test, insert the MEMS device inside the chamber and provide electrical connections, and run the experiment after preparing and proper positioning of the chamber. The released MEMS device is fixed on the test fixture especially fabricated for using with the mini-vacuum chamber (included). Depending on the type of MEMS device some electrical connections are needed. For those MEMS designs whose inputs are force or velocity and the purpose of the experiment is to measure output motions, there might not be a need for electrical connections. However, for most MEMS designs, some electrical connections are required. To provide electrical connections, the MEMS designs are connected to the test fixtures using wire bonder. By turning the main cap, part 5, about the axis, part 6, for 180 degrees, the inside of the mini-vacuum chamber becomes fully accessible. Then, the test fixture is inserted inside the mini-vacuum chamber on the two leading screws, which function as the guide and allows for the position of the test fixture to be adjusted. This adjustment enables one to position the MEMS design at a proper distance with the objective lenses of the microscope. By fixing the test fixture at the adjusted position, the electrical connections from the test fixture to the chamber internal sides of standard electrical ports are provided. Finally, the main cap is turned back and by rotating the handle knob, part 16, the part 17 will slides beneath part 8 and seals off the mini-vacuum chamber. By removing part 1, which is to protect the optical glass, part 3, from being physically touched, the mini-vacuum chamber can be positioned under a microscope. For the very thin height of the chamber in this invention, the mini-vacuum chamber is easily fitted under most standard microscopes. By connecting the air way, part 9, to a vacuum pump through a vacuum valve and in series with a vacuum gauge as displayed in figures II, III, IV, V, and VI, the setup is usable for experiments in air and in vacuum.

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