Ph.D Thesis

Ph.D StudentHirshberg Arnon
SubjectAdvanced Motion Conversion Structures and Interconnect
Method for MEMS
DepartmentDepartment of Mechanical Engineering
Supervisor PROF. David Elata
Full Thesis textFull thesis text - English Version


This work presents a new method for fabricating MEMS devices that perform out-of-plane motion from in-plane actuation. In micromachining, out-of-plane motion is often achieved by multiple assemblies or complex fabrication processes. The resulting out-of-plane response is often non-linear and has a limited range of stability. However, bulk micromachining technology enables the production of electrostatic comb-drive actuators, which can be designed to have a linear in-plane response with a large stability range. I developed new mechanical motion conversion structures that enable harnessing the stable linear in-plane motion of electrostatic comb-drives to achieve a stable and linear out-of-plane motion. The principal idea is to use flexures with a slanted cross section. When a slanted cross section flexure is displaced in the in-plane direction it deforms in the out-of-plane direction as well. Previous attempts by others to fabricate such conversion structures proved to be incompatible with parallel mass fabrication techniques. This work describes the mistrials I made to construct slanted cross section flexures while utilizing the natural crystal structure of the silicon. After failing to do this, I have devised a simpler original design which is more suitable for mass fabrication. The simpler design replicates the moment of inertia of a slanted flexure using standard bulk fabrication process. In order to test the motion-conversion structures, the flexures were embedded in a micro machined device. The detailed designs and their fabrication process are explained and demonstrated.    

To further simplify integration of these devices, I developed a new and original method to bond gold and aluminum wires directly onto silicon substrates without requiring metal bond pads. The new method was measured for mechanical strength and electric conduction. Results show compatibility with mil-spec and demonstrate controllable conductance.