High Yield Polymer MEMS Process for CMOS/MEMS Integration (original) (raw)
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Development and applications of a multi-user polymer MEMS technology
This thesis covers the development and characterization of an all polymer micromachining process designed for multiuser applications. This thesis describes the first MEMS process designed to provide multiuser functionality using polymers as structural and sacrificial layers, and offers new fabrication abilities not previously available with silicon micromachining. The structural material for this MEMS process is the negative tone photoresist SU-8, which is excellent for low temperature permanent applications. This work has developed a very reliable method of producing compliant SU-8 microstructures and has characterized it for a new class of structures and actuators. The use of SU-8 offers many advantages with respect to processing, but also introduces many processing challenges that were solved in this work. The polymer MEMS process developed for this work has a multi-thickness structural layer separated from the substrate by a single sacrificial layer. The sacrificial layer includes dimple features to reduce stiction and allow structures in excess of 5000 X 5000 µm 2 to release without problems. The list of working devices fabricated in this process includes low and high aspect ratio compliant mechanisms, micro-optical components, thermal and electrostatic actuators, micro antennas and compliant grippers. The many processing advances introduced through this work include elimination of adhesion failure of polymers during multiple processing steps, alignment of two polymers with similar indices of refraction, development of an anti-stiction substrate with high adhesion anchor areas, characterization of stress gradient in SU-8 with processing conditions, and successful gold wirebonding onto SU-8 devices.
BETTS: bonding, exposing and transferring technique in SU-8 for microsystems fabrication
Journal of Micromechanics and Microengineering, 2010
A novel fabrication process called BETTS (bonding, UV exposing and transferring technique in SU-8) is presented in this paper. SU-8 layers can be transferred and patterned over SU-8 microstructures by means of a removable, flexible and transparent substrate. This substrate is composed of a thin acetate film, which can be also used as a mask, and a cured PDMS layer deposited over it. SU-8 is then spin coated and transferred to the SU-8 structures performing simultaneously the steps of bonding and transferring by UV exposure. Due to the low adhesion between PDMS and SU-8, acetate film removal can be easily performed. BETTS provides easy, irreversible and robust SU-8 to SU-8 bonding, where the absence of oxygen plasma equipment or vacuum systems decreases drastically the fabrication cost and time involved. The reported fabrication process makes it possible to fabricate complex SU-8 three-dimensional structures using a simple and inexpensive procedure and also ensures its compatibility and integration with microfluidic and PCB-MEMS devices. Some specific applications such as multilevel microchannel network, patterned membranes, microchambers and microvalves are reported to demonstrate the potential of the proposed process.
Micro & Nano Letters, 2010
The characterization of the fabrication process to develop free-standing SU-8 structures integrated in PCBMEMS (Printing Circuit Board in Microelectromechanical Systems) technology is presented. SU-8 microcantilevers, microbridges, microchannels and micromembranes have been fabricated following the described procedure. Adherence between FR4 substrate and SU-8 has been studied using the destructive blister method, determining the surface energy. Residual thermal stress has also been analyzed for this integration and compared when using other substrates. Moreover, a study of the copper wet etching with cupric chloride has been performed in order to characterize how this isotropic etching affects the geometry of the copper structures. Finally, stiction has been observed and examined, determining the adhesion energy responsible of this effect. I. INTRODUCTION During the last decade, the fabrication of microstructures employing alternative technologies to silicon and innovative processes has rapidly increased in the field of microelectromechanical systems (MEMS). In this respect, polymer technology has made possible to overcome most of the high costs and restrictions related to traditional silicon manufacturing processes. Specifically, SU-8 is an epoxy-based negative photoresist which can be patterned using standard mask photolithography, offering a simple alternative for rapid prototyping [1]. Another technology that is becoming important in microfabrication area is PCBMEMS, which involves
Novel SU8 based vacuum wafer-level packaging for MEMS devices
Microelectronic Engineering, 2010
This work presents a simple and low-cost SU-8 based wafer-level vacuum packaging method which is CMOS and MEMS compatible. Different approaches have been investigated by taking advantage of the properties of SU-8, such as chemical resistance, optical transparence, mechanical reliability and versatility. A novel technique of wafer level adhesive bonding, which uses SU-8 as structural and adhesive material, has been
Polymer MEMS processing for multi-user applications
Sensors and Actuators A: Physical, 2007
We have developed a new polymer MEMS process that shows enormous flexibility in design parameters. This process uses entirely spin-on layers for structural and sacrificial materials. Further, this process flow is designed for multiple users to fabricate as many devices as possible on the same wafer which up to this point has not been demonstrated with polymer MEMS technologies. In this process, all structural layers are fabricated out of negative tone SU-8 photoresist and all sacrificial and separation layers are defined by a thin film of polystyrene. Using entirely spin-on layers for structural and sacrificial materials provides an easy way to select layer thicknesses without having to significantly alter the materials or processing techniques. A metal thin-film deposition step is also incorporated that allows electrical connection to the microstructures and actuators in this process. To characterize the robustness and flexibility of this technology we have fabricated a variety of in-plane and out-of-plane microstructures including chevron-type thermal actuators and tested their mechanical and electromechanical operation. The entire process sequence is accomplished at temperatures below 200 • C, making this technology compatible for post-processing integration of MEMS on an electronics circuit wafer.
Inkjet printing of SU-8 for polymer-based MEMS a case study for microlenses
2008 IEEE 21st International Conference on Micro Electro Mechanical Systems, 2008
This paper describes a novel method to fabricate polymer MEMS based on the inkjet printing of SU-8, with a special emphasis on integrated micro-optical lens arrays. Inkjet control parameters are optimized in order to enable a stable and reproducible ejection of SU-8 drops in both continuous and drop-on-demand (DOD) modes. Arbitrary patterns of single and multiple polymer drops and arrays of convex microlenses are printed on different substrates. The influence of surface wetting properties on the size and the shape of the printed patterns is investigated. The optical properties of the microlenses are investigated in details. A model for inkjet printing of high-viscous functional materials for polymer MEMS has been used.
Dry Method of Surface Modification of SU-8 for Bio-MEMS
SU-8 has been primarily used for structural elements and microfludics components in MEMS. Microsystems for biological applications require immobilization of biomolecules on the MEMS structures. In order to functionalize SU-8 for such purposes, the surface needs to be modified. In this paper, we report a novel dry method of surface modification of SU-8 which is compatible with standard microfabrication techniques. The surface obtained by spin coating SU-8 (2002) on silicon wafer was modified by grafting amine groups using pyrolytic dissociation of ammonia in a hotwire CVD setup. To demonstrate the presence of amine groups on modified SU-8 surface, the surface characteristic after modification was assessed using Fourier transform infrared spectroscopy. The change in SU-8 surface morphology before and after surface modification was investigated using atomic force microscopy. To show the utility of this process for application in Bio-MEMS, SU-8 microcantilevers were fabricated and subjected to the same surface modification protocol. Following this, the cantilevers were incubated first in a suspension of human immunoglobulin (HIgG) and then in FITC tagged goat anti-human IgG in order to demonstrate the utility of the surface modification performed. The efficacy of the process was assessed by observing the cantilevers under a fluorescence microscope.