Micro-fabrication of bio-MEMS based force sensor to measure the force response of living cells

Understanding how a living cell behaves has become a very important topic in today’s research field. Hence, different sensors and testing devices have been designed to test the mechanical properties of these living cells. This thesis presents a method of micro-fabricating a bio-MEMS based force sensor which is used to measure the force response of living cells. Initially, the basic concepts of MEMS have been discussed and the different micro-fabrication techniques used to manufacture various MEMS devices have been described. There have been many MEMS based devices manufactured and employed for testing many nano-materials and bio-materials. Each of the MEMS based devices described in this thesis use a novel concept of testing the specimens. The different specimens tested are nano-tubes, nano-wires, thin film membranes and biological living cells. Hence, these different devices used for material testing and cell mechanics have been explained. The micro-fabrication techniques used to fabricate this force sensor has been described and the experiments preformed to successfully characterize each step in the fabrication have been explained. The fabrication of this force sensor is based on the facilities available at Michigan Technological University. There are some interesting and uncommon concepts in MEMS which have been observed during this fabrication. These concepts in MEMS which have been observed are shown in multiple SEM images

Characterization of Mechanical Properties at the Micro/Nano Scale: Stiction Failure of MEMS, High-Frequency Michelson Interferometry and Carbon NanoFibers

Different forces scale differently with decreasing length scales. Van der Waals and surface tension are generally ignored at the macro scale, but can become dominant at the micro and nano scales. This fact, combined with the considerable compliance and large surface areas of micro and nano devices, can leads to adhesion in MicroElectroMechanical Systems (MEMS) and NanoElectroMechanical Systems (NEMS) - a.k.a. stiction-failure. The adhesive forces between MEMS devices leading to stiction failure are characterized in this dissertation analytically and experimentally. Specifically, the adhesion energy of poly-Si μcantilevers are determined experimentally through Mode II and mixed Mode I&II crack propagation experiments. Furthermore, the description of a high-frequency Michelson Interferometer is discussed for imaging of crack propagation of the μcantilevers with their substrate at the nano-scale and harmonic imaging of MEMS/NEMS. Van der Waals forces are also responsible for the adhesion in nonwoven carbon nanofiber networks. Experimental and modeling results are presented for the mechanical and electrical properties of nonwoven (random entanglements) of carbon nanofibers under relatively low and high-loads, both in tensions and compression. It was also observed that the structural integrity of these networks is controlled by mechanical entanglement and flexural rigidity of individual fibers as well as Hertzian forces at the fiber/fiber interface

Electrostatic zipping actuators and their applications to MEMS

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2004.Includes bibliographical references (p. 161-168).Electrostatic actuation is the most common and well-developed method of generating motion on the micro scale. To overcome the challenge of providing both high force and large displacement, electrostatic zipping actuators have been developed and applied to various devices. As device thicknesses increase, however, conventional laterally- moving zipping actuators become less practical due to their high pull-in voltages caused by their minimum achievable electrode gaps. This thesis presents a fundamental improvement of the laterally-moving electrostatic zipping actuator. Its major contributions are: 1) a compliant starting zone is introduced into the fixed electrode to significantly reduce the pull-in voltage of the zipping electrode; 2) numerical and analytical methods are developed to solve general zipping actuator problems; 3) optimization is performed to minimize the effort required to actuate the zipping electrode and its load; and 4) the improved zipping actuators are designed into a relay to illustrate their use and performance. To design a cross-bar micro relay, two zipping actuators are combined with a curved bistable switch beam and two contacts.(cont.) The micro relay is monolithically fabricated in silicon using deep reactive ion etching to move laterally in the wafer plane. Both actuators provided up to 10 mN of actuation force over their 80 [mu]m of stroke at 140 V, and toggle the bistable relay at a maximum rate of 160 Hz. Pullin voltage, actuation voltage and force-displacement measurements of the actuators and switch beam confirm theoretical expectations based on numerical, analytical and finite element analyses, after accounting for fabrication variations. The shortest pulse required to switch the relay is 400 [mu]s, and the time taken for the actuator to close the relay was approximately 3 ms. The relay was operated at 100 Hz for over 120 hours through more than 40 million cycles without any observed stiction or fracture fatigue. To achieve low contact resistance for a laterally-moving micro relay, wet anisotropically etched silicon [111] planes are developed to form relay contact surfaces that offer flat wiping surfaces and ease of thick metalization. Experimental contacts are fabricated and their average contact resistance is measured to be [approx.] 50 m[omega].(cont.) A process plan is also proposed to combine the [111] plane contacts with the prior zipping actuators and the switch beam to build a micro relay with low contact resistance for power protection applications. The compliant starting zone concept can also be applied to vertically-moving MEMS devices. A MEMS valve is also designed using a zipping actuator having com- pliant starting zones. As another application of the zipping mechanism, a nonlinear spring is also presented and analyzed.by Jian Li.Ph.D

Design and control of a multi-axis micro-electro-mechanical system array for coordinated micro-manipulation

Micro-electro-mechanical system design and implementation is a field that has received much attention over the past few decades. These robotic systems with features on the micro-scale have an unparalleled opportunity to change the way scientists interact with and understand micro and nano-scale phenomenon. Their capabilities allow experimentation that cannot be achieved with standard macro-scale equipment. Potential applications range from observing biological processes in living cells, to smart materials that automatically detect microcracks. So far, however, only a few truly successful applications have been realized. One of the most elusive goals in MEMS design is creating a system capable of coordinated motion tasks. This task requires an innovative approach to mechanism design and control. In this work a novel micro-positioning stage is presented that is intended to be implemented in a very large scale array. The stages are actuated by custom optimized electro-thermal-compliant micro-actuators intended for high force applications. These actuators, in combination with mechanical amplification, enable a high degree of mobility which allows a large work area. Furthermore the stage itself has a small foot print to allow a high density of actuators to interact in the common workspace. Control of the stages is realized using vision feedback with Kalman Filtering for high-speed intersample estimation. An iterative learning controller is then used for high precision tracking. This approach gives a high degree of accuracy that is nearly as good as the resolution of the measurement system, and at frequencies that approach the bandwidth of the system --Abstract, page iii