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Title:Transfer printed mechanical MEMS
Author(s):Elgan, Steven L.
Advisor(s):Ferreira, Placid M.
Department / Program:Mechanical Sci & Engineering
Discipline:Mechanical Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Elastomeric Transfer Printing
Microelectromechanical systems (MEMS) Assembly
Bolometer Assembly
Abstract:Most Microelectromechanical Systems (MEMS) are primarily created using integrated circuit (IC) fabrication techniques and photolithography. These techniques and procedures are time consuming and exhaustive in the amount of steps needed in their creation. Also, fabrication processes often limit the materials, chemicals, and temperatures allowed throughout the extensive creation process in order to ensure cross compatibility with all materials in the device. As such, compromises to optimal design are common in many current commercial MEMS products. Current processes and manufacturing techniques are also very expensive. Elastomeric transfer printing offers solutions to these challenges by introducing the ability to assemble individual modularized components of these devices. Transfer printing frees fabricators to simplify and optimize the creation process by breaking down the devices into unique individual parts. Transfer printing also allows for the use of a wider field of materials as well as the ability to use previously incompatible chemicals, temperatures, and other process parameters in pursuit of perfecting each part individually before final assembly. These parts can then be assembled individually or in an assembly line fashion at potentially a significant decrease in manufacturing cost. This thesis examines three examples of transfer printed MEMS that span the areas of microfluidics, mechatronic, and optical/thermal. The microfluidic example is silicon microfluidic nozzles printed onto PDMS microchannels as a means to create simple modularized micro nozzle arrays. This process vastly cuts down on the steps needed to fabricate traditional MEMS Microfluidic nozzles as well as offers a means to potentially exchange damaged nozzles from existing microfluidics arrays. For the mechatronic area, silicon micro gears are transfer printed onto silicon shafts. These gears then demonstrated interdependent actuation. Transfer printing gears allows MEMS designers new flexibility in micro mechatronic design that was previously limited due to photolithography processes. Lastly, for the optical thermal example, microbolometers are created and transfer printed onto a read-out test bed. Bolometers are a good example of the potential of modularized assembly of 3D MEMS. These devices are resistance-based sensing devices found at the heart of infrared thermal imaging devices. One critical parameter in a microbolometer membrane is the temperature coefficient of resistance (TCR) which is a measure of the bolometer’s sensitivity. Optimally, the TCR should be as negative as possible. Bolometers with a TCR of around -2%/°C are common in industry today and are fabricated directly on the readout integrated circuit (ROIC) which limits the thermal processing that can be done to optimize the bolometer membrane due to the risk of damaging the readout integrated circuit (ROIC). A solution to this problem is to fabricate the bolometer membranes separate from the ROIC, then combine them using transfer printing. Separating the processes allows for the use of high temperature annealing to be performed on the bolometer membrane that would have otherwise damaged the ROIC. This annealing allows the vanadium oxide in the membranes to achieve a much lower TCR of up to -4%/°C. Transfer printing then provides a unique method for assembling the bolometer membrane on the ROIC. Transfer printing is a means for the optimization of MEMS assembly because it removes previous design constraints on MEMS creation and allows manufacturers to modularly and optimally create and assemble MEMS components into enhanced integrated devices.
Issue Date:2011-05-25
Rights Information:Copyright 2011 Steven L Elgan
Date Available in IDEALS:2011-05-25
Date Deposited:2011-05

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