Publications

A mesoscale dimensional artifact based on silicon bulk micromachining fabrication has been developed with the intention of evaluating the artifact both on a high precision Coordinate Measuring Machine (CMM), and on a video-probe based measuring system. A high accuracy touch-probe based CMM can achieve accuracies that are as good as the 2-D repeatability of video-probe systems. While video-probe based systems are commonly used to inspect mesoscale mechanical components, a video-probe system's certified accuracy is generally much worse than its repeatability. By using a hybrid artifact where the same features can be extracted by both a touch-probe and a video-probe, the accuracy of video-probe systems can be improved. In order to use the micromachined device as a calibration artifact, it is important to understand the uncertainty present in the touch-probe measurements. An uncertainty analysis is presented to show the potential accuracy of the measurement of these artifacts on a high precision CMM.

Abstract not provided.

Microsystems using electrothermal bent-beam microactuators have been demonstrated for a variety of applications including optical attenuators, RF switches, and micro positioners, thus creating a need for information on the longevity of these devices. This paper reports on the dc and pulse mode lifetime testing of this class of actuators constructed using polysilicon p++ doped and single crystal silicon. The relative temperature profile along the top surface of an actuator is experimentally verified by scanning probe microscopy. Displacement measurements are used to explore links between aging behavior and the design variables and operating conditions. At low power levels (which result in average operating temperatures of 300-400 ° C) both polysilicon and p++ Si devices provide continuous dc operation for >1400 min. in air without change in amplitude. While some types of p++Si devices show monotonic loss of amplitude in pulse tests, others have been operated up to 30 million cycles without degradation. The displacement for polysilicon actuators can either increase or decrease depending on the geometry of the device and operating conditions, both of which are related to temperature and stress of the structural members. Polysilicon grain ransformations are observed over extended operation at high temperatures. Performance changes are correlated to material properties using SEM and TEM images. © 2006 IEEE.

Abstract not provided.

Abstract not provided.

This work is the result of a Sandia National Laboratories LDRD funded fellowship at the University of Michigan. Although, guidance and suggestions were offered by Sandia, the work contained here is primarily the work of Brian H. Stark, and his advisor, Professor Khalil Najafi. Junseok Chae, Andrew Kuo, and their coworkers at the University of Michigan helped to record some of the data. The following is an abstract of their work. We have developed a vacuum packaging technology using a thick nickel film to seal MEMS structures at the wafer level. The package is fabricated in a three-mask process by electroplating a 40 micro-meter thick nickel film over an 8 micro-meter sacrificial photoresist that is removed prior to package sealing. Implementation of electrical feedthroughs in this process requires no planarization. The large release channel enables an 800x800 micro-meter package to be released in less than three hours. Several mechanisms, based upon localized melting and lead/tin solder bumping, for sealing the release channel have been investigated. We have also developed Pirani gauges, integrated with this package, which can be used to establish the hermeticity of the different sealing technologies. They have measured a sealing pressure of approximately 1.5 Torr. Our work differs from previous Pirani gauges in that we utilize a novel doubly anchored structure that stiffens the structural membrane while not substantially degrading performance in order to measure fine leak rates.

We describe a post release die separation process for polysilicon surface micromachines using a combination of diamond scribing and breaking. The process resulted in yields above 80% for two types of electrostatic actuators. The paper describes the experimental apparatus and optimization of the process using a four parameter design of experiments. We determined that the two key parameters in the scribe-and-break process are the scribe force and the scribe angle. We also examined the theory of crack creation during the scribing process and determined experimentally that the crack depth in silicon is consistent with the theory developed for the scribing of glass. Copyright © 2004 by ASME.

Many microfabrication techniques are being developed for applications in microelectronics, microsensors, and micro-optics. Since the advent of microcomponents, designers have been forced to modify their designs to include limitations of current technology, such as the inability to make three-dimensional structures and the need for piece-part assembly. Many groups have successfully transferred a wide variety of patterns to both two-dimensional and three-dimensional substrates using microcontact printing. Microcontact printing is a technique in which a self-assembled monolayer (SAM) is patterned onto a substrate by transfer printing. The patterned layer can act as an etch resist or a foundation upon which to build new types of microstructures. We created a gold pattern with features as small as 1.2 {micro}m using microcontact printing and subsequent processing. This approach looks promising for constructing single-level structures such as microelectrode arrays and sensors. It can be a viable technique for creating three-dimensional structures such as microcoils and microsprings if the right equipment is available to achieve proper alignment, and if a means is available to connect the final parts to other components in subsequent assembly operations. Microcontact printing provides a wide variety of new opportunities in the fabrication of microcomponents, and increases the options of designers.

This paper reports on the use of bent-beam electrothermal actuators for the purpose of generating rotary and long-throw rectilinear displacements. The rotary displacements are achieved by orthogonally arranged pairs of cascaded actuators that are used to rotate a gear. Devices were fabricated using electroplated Ni, p ++ Si, and polysilicon as structural materials. Displacements of 20-30 μm with loading forces > 150 μN at actuation voltages < 12 V and power dissipation < 300 mW could be achieved in the orthogonally arranged actuator pairs. A design that occupies < 1 mm 2 area is presented. Long-throw rectilinear displacements were achieved by inchworm mechanisms in which pairs of opposing actuators grip and shift a central shank that is cantilevered on a flexible suspension. A passive lock holds the displaced shank between pushes and when the power is off. This arrangement permits large output forces to be developed at large displacements, and requires zero standby power. Several designs were fabricated using electroplated Ni as the structural material. Forces > 200 μN at displacements > 100 μm were measured.

This paper reports on the design, simulation, and preliminary testing of a three phase variable reluctance stepping motor. This motor is pancake-shaped with an overall outside diameter of 8 mm and a height of 3 mm. The outside diameter of the rotor is 4.7 mm. The rotor and stators occupy 2 mm of the height with the remaining 1 mm reserved for a 6:1 planetary gear reductor. The rotor and stators were constructed of Hyperco 50 using conventional miniature machining. The reductor was assembled using copper and PMMA (polymethylmethacrylate) components that were constructed using the LIGA (Lithographic Galvanoformung Abformung) microfabrication process. The maximum measured stall torque of the motor without the reductor is 0.47mNm at 4W and the maximum speed is 2,400 rpm.

A completely foundry compatible chip-scale package for surface micromachines has been successfully demonstrated. A pyrex (Corning 7740) glass cover is placed over the released surface micromachined die and anodically bonded to a planarized polysilicon bonding ring. Electrical feedthroughs for the surface micromachine pass underneath the polysilicon sealing ring. The package has been found to be hermetic with a leak rate of less than 5 x 10{sup {minus}8} atm cm{sup {minus}3}/s. This technology has applications in the areas of hermetic encapsulation and wafer level release and die separation.