Papers

AVS2004 Session MN-MoA: Micro and Nano Fabrication Techniques for MEMS and NEMS

Monday, November 15, 2004 2:00 PM in Room 213C

Monday Afternoon

Start	Invited?	Item
2:00 PM		MN-MoA-1 Parylene and Its MEMS Applications Y.-C. Tai (California Institute of Technology) Parylene is the generic name for members of a unique family of thermoplastic polymers that are deposited by using the dimer of para-xylyene (di-para-xylylene, or DPXN). It is first commercialized by the Union Carbide Corporation as early as in 1956, but even today its use has been mainly limited to protective coatings of electronic components, medical instruments. Recently, however, parylene has become an emerging polymer MEMS material for various applications. This paper then reviews the related parylene MEMS technologies, material properties, and applications that were done in our Caltech lab. First, parylene is widely available through a unique room-temperature, pinhole-free, and conformal CVD deposition method, originally developed by William F. Gorham in 1950s. This benign parylene preparation process makes it a suitable technology for post-CMOS integration. Material wise, parylene has rather low melting temperature around 300 C, but it is rather inert and biocompatible. More importantly, we have shown that it is straightforward to make parylene thin film with a tensile intrinsic stress by controlling the last thermal steps. This feature allows free-standing parylene MEMS structures in many designs. As a result, we have successfully developed a multi-layer parylene MEMS technology including buried metal layers. For the last few years, we then have demonstrated various parylene MEMS applications including microstructures, micro sensors and actuators. In this paper, we will discuss parylene-based filters, neurocages, flow sensors, pressure sensors, accelerometers, bolometers, valves, pumps, etc. However, it is our belief that the brightest future of parylene MEMS is for fully integrated systems that can perform complex functions such as our on-going projects like retinal implants and labs on-a-chip.
2:40 PM		MN-MoA-3 Fabrication of Ferroelectric Nanomechanical Resonators K. Son, T. George (Jet Propulsion Laboratory); R.W. Fathauer, S. Bhaskar, W. Cao, S. Dey, L. Wang, S.M. Phillips (Arizona State University); B. Lambert, D.P. Weitekamp (California Institute of Technology); B.H. Houston, J.F. Vignola, J.E. Butler (Naval Research Laboratory); J. Yang, M.A. Khan (University of South Carolina) Due to their ultra-small volumes, high sensitivity, and high operating frequencies, nano-mechanical resonators are promising for a variety of applications, including the detection of chemical or biological molecules and RF communications. A major challenge in this technology is efficient coupling to the resonator motion, particularly for applications that preclude low temperatures and/or bulky hardware. We report on our unique approach to this problem, namely the use of a ferroelectric on the resonator. Torsional geometries are used because they are amenable to our coupling technique, whereby an RF voltage applied to metal plates flanking the resonator exerts a torque on the ferroelectric. Due to its large spontaneous polarization, we are using lead zirconate titanate (PZT) as the ferroelectric. PZT is grown on both nanocrystalline diamond and single-crystal GaN resonators using the sol-gel method or MOCVD. Bare Si resonators are also being studied to provide a baseline. Novel double-paddle designs have been developed in which the paddles are supported at nodes of the motion to minimize losses through the supporting members. Their performance is compared to more conventional single-paddle designs. For resonance frequencies in the range of 0.1 to 1.0 GHz, we are examining structures with support-beam cross sections of 200 nm x 200 nm. Resonators are fabricated using electron beam lithography followed by various reactive ion etching methods specifically developed for each material. The sacrificial layers are silicon oxide for both Si and diamond resonators. For GaN, a p-type layer is used for the resonator and an n-type layer for the sacrificial layer. This allows release of the resonators using photoelectrochemical etching. Evaluation of resonators is carried out using scanning laser Doppler vibrometry, and compared to numerical simulations of resonator performance developed using finite element-based structural dynamics codes.
3:00 PM		MN-MoA-4 BCB-Based Linear Micromotor Supported on Microball Bearings: Design Concepts, Characterization, and Fabrication Development A. Modafe, N. Ghalichechian, R. Ghodssi (University of Maryland, College Park) We report on design, characterization, and fabrication development of a linear variable-capacitance micromotor (VCM) supported on microball bearings for micropositioning. Microball bearings provide robustness, stability, uniform air gap, and low friction. The stator of the VCM integrates benzocyclobutene (BCB) low-k polymer as the insulating layer with silicon micromachined V-grooves as the microballs housing. BCB polymers enable the development of MEMS-based electric machines with minimal electrical energy loss for low-temperature (<350°C) applications. We have performed an extensive characterization of electrical properties of BCB and developed a fabrication method for integration of silicon microball bearings etched in potassium hydroxide (KOH) solution with BCB insulating dielectric films. The VCM is designed to provide an aligning force of over 1 mN when driven by a 100 V square-wave excitation voltage. The electrical performance of the VCM is directly affected by the properties of BCB film. We have shown that the parasitic capacitance of the stator can be reduced by 40 % when using BCB instead of conventional oxide dielectrics. Furthermore, our capacitance tests show that the low dielectric constant of BCB does not change appreciably despite the moisture absorption in BCB; however, the current-voltage tests confirm that the breakdown strength of BCB reduces to less than half and the leakage current is doubled after moisture absorption, suggesting an upper limit for the excitation voltage. A novel fabrication process is developed to fabricate the stator V-grooves in KOH solution following the fabrication of the active area. A combination of surface treatment and cure management of BCB was used to improve the adhesion of BCB and thin film chromium/gold etch mask. Deep V-grooves as long as 20 mm were successfully fabricated in presence of BCB film. We will present the design and preliminary results of fabrication and characterization of the device.
3:20 PM		MN-MoA-5 Dielectrophoretic Assembly and Integration of Functional Nanodevices with VLSI Circuitry S. Evoy, Y. Dan (The University of Pennsylvania); A. Narayanan, S. Raman (Virginia Tech) The bottom-up synthesis and integration of nanoscale structures open new opportunities for the development of functional integrated systems with respect to reduced size, power consumption, and increased range of materials and functionalities that can be accessed. We present a novel platform for the development and deployment of nanosensors in integrated systems. The nanosensor technology is based on cylindrical structures grown using porous membranes as templates.¹ These nanostructures are manipulated using dielectrophoretic forces, allowing their individual assembly and characterization. The assembly and electromechanical characterization of Rh rods and carbon nanopipes (MWNT) was performed. In addition, these segmented growth technologies have already allowed the development of striped nanowires consisting of a central functional segment terminated by two metallic extremities. ² Further development of such gold-terminated structures would allow assembly of sensing devices in which the metal/metal contact point would represent a negligible contribution compared to the chemresistive response of the central segment. We also report on the successful integration of nanodevices with mixed mode circuitry fabricated in a 0.18 um BiCMOS process. We were successfully able to assemble Rh nanorods of approximately 5 um in length onto prefabricated a CMOS Wheatsone bridge circuitry. We report on the designs of such mixed mode systems whose layouts integrate dielectrophoretic assembly sites with a resistance read-out, signal processing, and wireless communication circuitries. ¹ S. Evoy, B. Hailer, M. Duemling, W. Barnhart, S. Raman, B. R. Martin, T E. Mallouk, I Kratochvilova, and T. S. Mayer, MRS Symp. Proc., 687, 63-68 (2002). ² S. Evoy, et al , "Dielectrophoretic assembly and integration of functional nanostructures with CMOS operating circuitry", Micro. Eng. (in press).
3:40 PM		MN-MoA-6 Nanoscale Synthesis of Particles and Vesicles in Microfluidic Devices A.P. Lee (University of California at Irvine) This presentation will focus on the development of microscale and nanoscale platform technologies for the interrogation and manipulation of biological and physiological activities. One platform we are developing can generate micro and nanoscale droplets/particles/vesicles by controlling amphiphilic interfaces in microfluidic devices. In contrast to what has currently been done, we devise new techniques and platforms for forming each individual vesicle with complete nanoscale control of parameters in order to “program” its size, shape, compositional structure, and ultimately its functions and properties. This control is enabled by nanoscale control of interfacial forces through the development of novel microfluidic technology to manipulate oil-water interfaces. These self-assembly forces are ubiquitous in nature and are responsible for the complex nanoscale structures in biological components. Through the design of microfluidic channel networks, droplet arrays present a novel method for controlling biochemistry and self-assembly at picoliter to femtoliter volumes, approaching the level of cellular activities. Nanoscale features can be designed into these vesicles that mimic biological functions such as molecular recognition, protein synthesis, and molecular transport. Based on the materials delivered, droplets can then form polymer nanoparticles (e.g. photopolymerization), lipid bilayer vesicles, and multilayer drug particles. Applications that we are pursuing include smart vesicles for targeted imaging and therapeutics for cardiovascular diseases, synthetic antibodies by molecular imprint polymer nanoparticles, protein crystallization, quantum dot synthesis in droplet microreactors, combinatorial cell-based assays, and cell-encapsulation for combinatorial assays and tissue engineering.
4:20 PM		MN-MoA-8 Layered Nanofabrication (lnf) As a Tool for NEMS and Bio-NEMS B.E. Koel, A.A.G. Requicha, M.E. Thompson (University of Southern California) We have proposed a new rapid prototyping technique at the nanoscale, called Layered Nanofabrication (LNF)¹. A nanometer-sized, three-dimensional (3-D) object can be build by successive fabrication of layers in which nanoparticles are first deposited and then manipulated by using atomic force microscopy (AFM). Each layer is then planarized by adding a molecular sacrificial layer whose top surface serves as a support for the next processing step. The sacrificial layers, or conversely the nanoparticles, are removed in a final step. Achieving suitable planarization for LNF requires extreme constraints on the approach used for this process. We have focused thus far on pushing the efficiency and control in deposition of films from self-assembled monolayers (SAMS). Improvements in permanently bonding or linking nanoscale components are also required. Our progress to date will be reviewed, including discussion of various siloxane and other SAMS, and chemical linking of and electrochemical deposition on Au nanoparticles. ¹A. A. G. Requicha, S. Meltzer, R. Resch, D. Lewis, B. E. Koel, and M. E. Thompson, Layered nanoassembly of three-dimensional structures, Proc. IEEE International Conf. on Robotics & Automation, Seoul, S. Korea, pp. 3408-3411, May 21-26, 2001.
4:40 PM		MN-MoA-9 Ultrafast Fabrication of 3D Microstructures for MEMS Applications H. Yu, B. Li, X. Zhang (Boston University) Recently, the interest in three-dimensional (3D) microstructures with mechanical, electrical, optical, and biological functionalities has increased dramatically. These microstructures promise to be of great importance for numerous applications including those for the coming biotechnology revolution. This paper introduces an innovative 3D fabrication method by using a laser scanning system, which allows for rapid processing of freeform multi-layered microstructures, and more importantly enables fast development of microdevices with a low cost. In particular, by using this method, we can create a variety of 3D microstructures including: oblique micropillar arrays, micro T-plugs, embedded microchannels, and freestanding microcantilevers. Compared to the existing manufacturing techniques, our direct UV laser writing method greatly simplifies fabrication processes, potentially reducing the design-to-fabrication time to a few hours. Furthermore, the process can be set up in a conventional manufacturing environment without the need for clean room facilities. The ultrafast and low cost characteristics allow our method to be extremely beneficial during the product development stages. The initial process validation has been presented by using SU-8 material. This technique is expected to be able to process a broad range of materials, including polymers, metals, and semiconductors by using ultrafast lasers. The results presented in this paper serve as the first crucial step towards the rapid manufacturing of microdevices with mechanical, optical, and/or biological functionalities for enormous applications.
5:00 PM		MN-MoA-10 Micro-fabricated Charge-sensing Resistive Probe H. Park, J. Jung, D.-K. Min, C. Park, K. Baeck, S. Kim, H. Ko, S. Hong (Samsung Advanced Institute of Technology, Korea) We fabricated a scanning probe microscopy (SPM) probe that can image surface charges of ferroelectric domains at high speed without an additional signal modulation system like a lock-in amplifier. The probe detects electric field by field-induced resistance change in a semiconductor resistive region formed at the apex of the tip; the majority carriers in the resistive region are depleted or accumulated by the electric field. To minimize the size of the resistive region and align it at the apex of the tip, we developed a self-aligning process, which is designed to etch Silicon for tip formation with the same masking material as that used in the preceding ion implant process forming the resistive region. We simulated tip fabrication process using SUPREM IV and confirmed that only low-doped n-type resistive region of 150 nm size existed at the tip apex as designed. In order to measure the field sensitivity, we contacted the fabricated resistive probe on a thermally oxidized silicon sample and measured 0.5 % resistance change per voltage applied to the sample. The response time to the external field was about 10 nsec. We obtained domain images of triglycine sulfate (TGS) single crystal with the probe in contact mode. The operating voltage of the probe was 2 V and the scan rate was 2 Hz. We controlled the polarization of Pb(Zr_0.4Ti_0.6)O₃ (PZT) by applying voltage between the resistive tip and the bottom electrode of PZT, and acquired the domain images with the same probe at 2 Hz scan rate. The diameter of detected domain was 500 nm and the transition width between opposite domain images was about 120 nm. By controlling and detecting the ferroelectric domains without an additional signal modulating system, we verified that the resistive probe could be used for a high speed SPM mapping surface charges and be applied to the probe-based data storage system in which a fast read/write head of simple structure and process is essential.