M.Sc Thesis

M.Sc StudentEkeltchik Daniel
SubjectDesign of A Device for Measuring the Strength of Silicon
DepartmentDepartment of Mechanical Engineering
Supervisor PROF. David Elata
Full Thesis textFull thesis text - English Version


Silicon micro beams are widely used as suspensions in micro electro mechanical systems (MEMS). Micro-beam flexures restrict motion to a preferred direction, and function as springs, which balance actuation forces. Flexures are the structural elements in which deformation is maximal. Though they are often made from single-crystalline silicon, which is theoretically much stronger than the best steel, the micromachining processes that are used to carve beams in wafers, introduce surface micro-defects that dominate their strength.

It is therefore crucial that the strength of micro-beams is measured precisely for individual beam specimens. Furthermore, for many applications it is important to predict the long-term reliability of the beam under various environmental conditions such as physical load, temperature, humidity and radiation.

Numerous macro-scale methods allow testing of different materials and specimens under various conditions, among them methods such as tensile strength testing, three-point bending and four-point bending, all designed to evaluate the strength of the specimen under different physical loads.

In this work, we present a design of a new device, which can subject a micro-beam specimen to predefined mechanical loads, such as pure moment, and maintain this load in order to determine reliability under different environmental conditions. Since the micro actuators used today can generate coupled forces instead of pure torque, it is impossible to apply a moment at the edge of the specimen, and a different approach is needed. The main principle of the device designed in this work is to replicate the edge movement of the specimen, as it would have moved if a pure moment were applied.

Two different actuation methods are proposed, both of which use a voice-coil taken from a 1-inch hard drive. The first method is to attach the voice-coil directly to the flexure. The second method is to use the data-reading arm from the hard drive, and make it slide along the flexure, thus generating the required force.

The masks needed for fabrication are presented, and it is shown that it is possible to manufacture the device using current fabrication techniques.