ICMCTF2002 Session H3-2: Materials and Processes for MEMS

Wednesday, April 24, 2002 1:30 PM in Room Royal Palm 4-6

Wednesday Afternoon

Start	Invited?	Item
1:30 PM	Invited	H3-2-1 Micro Rapid Prototyping of 3D Heterogeneous MEMS X.C. Li (University of Wisconsin-Madison) Similarities between silicon-based micro-electro-mechanical-systems (MEMS) and Shape Deposition Manufacturing (SDM) processes are obvious: both integrate additive and subtractive processes and use part and sacrificial materials to obtain functional structures. These MEMS techniques are two-dimensional (2D) processes for a limited number of materials while SDM enables the building of parts that have traditionally been impossible to fabricate because of their complex shapes or of their variety in materials. This study adapts SDM methodology to MEMS fabrication. By incorporating laser microdeposition and micromachining, the micro manufacturing system takes computer-aided design (CAD) output from a computer to reproduce heterogeneous micro components. To precisely deposit submicron/nano powders, an ultrasonic-based micro-feeding mechanism is developed. This additive/subtractive micro manufacturing technology provides a solid foundation for a seamless integration from CAD to the realization of complex 3D heterogeneous MEMS in a wide selection of materials.
2:30 PM	Invited	H3-2-4 Characterization of Symmetrical and Asymmetrical Polysilicon Surface Micromachined Electrothermal Actuators E.S. Kolesar, W.E. Odom, M.D. Ruff, S.Y. Ko, J.T. Howard, P.B. Allen, J.M. Wilken, N.C. Boydston, J.E. Bosch, A.J. Jayachandran (Texas Christian University) Several microactuator technologies have been investigated for positioning individual elements in large-scale microelectromechanical systems (MEMS). Electrostatic, magnetostatic, piezoelectric and thermal expansion represent the most common modes of microactuator operation. This research focuses on the design and comparative performance evaluation of symmetrical and asymmetrical electrothermal actuators. The motivation is to present a unified description of the behavior of the electrothermal actuator so that it can be adapted to a variety of microsensor and microactuator applications. The MEMS polysilicon surface micromachined electrothermal actuator uses resistive (Joule) heating to generate thermal expansion and movement. This investigation reports on a new symmetrical bi-directional polysilicon electrothermal actuator. In the traditional asymmetrical electrothermal actuator design, the single-hot arm is narrower than the cold arm, and thus, the electrical resistance of the hot arm is greater. When an electrical current passes through the device (both the hot and cold arms), the hot arm is heated to a higher temperature than the cold arm. This temperature differential causes the hot arm to expand along its length, thus forcing the tip of the device to rotate about the flexure. Another variant of the asymmetrical design features a double-hot arm arrangement that eliminates the parasitic electrical resistance of the cold arm. Furthermore, the second hot arm improves electromechanical efficiency by providing a return current conductor that is also mechanically-active. In this design, the rotating cold arm can have a narrower flexure compared to the flexure in the traditional single-hot arm device because it no longer needs to conduct an electrical current. The narrower flexure results in an improvement in mechanical efficiency. Recently, bi-directional deflections have been achieved with a new electrothermal actuator design. When hot arms are positioned on adjacent sides of the cold arm and flexure, the independent excitation of either hot arm results in deflections that are bi-directional. This research compares the tip deflection performance of the asymmetrical single- and double-hot arm electrothermal actuator designs along with that of the bi-directional variant. Deflection measurements of both actuator designs as a function of arm length and applied electrical power are presented. The electrothermal actuator and microengine designs were accomplished with the L-Edit software program, and they were fabricated using the JDS Uniphase Integrated Microsystems Multi-User Microelectromechanical Systems (MEMS) Process(MUMPs) foundry.
3:10 PM		H3-2-6 High Sensitivity Chlorine Gas Sensors using Cu-Phthalocyanine Thin Films T. Miyata, S. Kawaguchi, M. Ishii, T. Minami (Kanazawa Institute of Technology, Japan) In regard to pollution in human environments, low-cost techniques for sensing the presence of chlorine (Cl₂) gases have become urgently required. In addition, these gases with their very strong sterilizing effects have come to be widely used in many fields, such as food hygiene, sewage treatment and various industrial processes. In this paper, we introduce newly developed chlorine gas sensors using Cu-phthalocyanine thin films. The Cu-phthalocyanine thin films (thickness of 250 nm) were evaporated onto substrates; Au thin films were deposited as electrodes. The deposition temperature was varied from 120 to 170°C. The current flowing through the electrodes of sensors in the atmosphere was under the limit of detection at an applied voltage of 5 V. The sensor resistances decreased when exposed to chlorine gas. It was found that the current through the sensors increased with increasing chlorine gas concentration. The characteristics of Cu-phthalocyanine thin film sensors were strongly dependent on the preparation conditions of the thin films and the operating temperatures of the gas sensors. For example, the current flowing through sensors increased as the deposition temperature of the Cu-phthalocyanine thin films was increased upto 170°C; i.e., maximum current was obtained in a sensor with a Cu-phthalocyanine thin film deposited at 170°C. At an operating temperature of RT, the current through this sensor varied from 0.015 to 3.85µmA when exposed to chlorine gas with a concentration ranging from 0.18 to 35 ppm; the current exhibited good linearity relative to gas concentrations in this range.
3:30 PM		H3-2-7 Crystallization Behaviors and Compositional Control of TiNi-based SMA Thin Films P.Y. HSU (National Cheng Kung University, Tainan, Taiwan, ROC); J.M. Ting (National Cheng Kung University, Taiwan, ROC) TiNi-based alloys are known as shape memory alloys (SMA) due to their shape memory effect and superelasticity. TiNi-based thin film recently attracts intensive attention due to its applications in microelectromechanical system (MEMS) technology. Deposition of TiNi-based thin films is normally performed using sputter deposition techniques. However, as-deposited TiNi-based thin films are usually amorphous. Post-deposition heat treatment is therefore required for the crystallization of the films. Although the crystallization behaviors of bulk TiNi-based alloys have been examined in general, a number of reports have clear shows the differences in crystallization behaviors between bulk materials and thin film materials of Ti-Ni SMA. As a result, this study was to investigate the crystallization behaviors of a series of two TiNi-based SMA thin films, namely, Ti-Ni and Ti-Ni-Cu thin films. An dc sputter deposition techniques was used for the growth of SMA thin films under various pressures and electrode distances. The compositions of resulting thin films were analyzed using electron probe for micro analysis (EPMA). A Tencor alpha-step 500 was used to determine the film thickness. Surface morphologies were examined using scanning electron microscopy (SEM). X-ray diffractormetry was employed to determine the crystalline structure. Crystallization behaviors were investigated using a differential scanning calorimeter (DSC). The Kissinger method were used to determine the activation energies. Crystallization of these TiNi-based thin films were found to depend on film composition and thickness. Activation energies were also found to differ from that of the respective bulk materials.