Benzocyclobutene-based Electric Micromachines Supported on Microball Bearings: Design, Fabrication, and Characterization

This dissertation summarizes the research activities that led to the development of the first microball-bearing-supported linear electrostatic micromotor with benzocyclobutene (BCB) low-k polymer insulating layers. The primary application of this device is long-range, high-speed linear micropositioning. The future generations of this device include rotary electrostatic micromotors and microgenerators. The development of the first generation of microball-bearing-supported micromachines, including device theory, design, and modeling, material characterization, process development, device fabrication, and device test and characterization is presented. The first generation of these devices is based on a 6-phase, bottom-drive, linear, variable-capacitance micromotor (B-LVCM). The design of the electrical and mechanical components of the micromotor, lumped-circuit modeling of the device and electromechanical characteristics, including variable capacitance, force, power, and speed are presented. Electrical characterization of BCB polymers, characterization of BCB chemical mechanical planarization (CMP), development of embedded BCB in silicon (EBiS) process, and integration of device components using microfabrication techniques are also presented. The micromotor consists of a silicon stator, a silicon slider, and four stainless-steel microballs. The aligning force profile of the micromotor was extracted from simulated and measured capacitances of all phases. An average total aligning force of 0.27 mN with a maximum of 0.41 mN, assuming a 100 V peak-to-peak square-wave voltage, was measured. The operation of the micromotor was verified by applying square-wave voltages and characterizing the slider motion. An average slider speed of 7.32 mm/s when excited by a 40 Hz, 120 V square-wave voltage was reached without losing the synchronization. This research has a pivotal impact in the field of power microelectromechanical systems (MEMS). It establishes the foundation for the development of more reliable, efficient electrostatic micromachines with variety of applications such as micropropulsion, high-speed micropumping, microfluid delivery, and microsystem power generation

Characterization of Dynamic Friction in MEMS-Based Microball Bearings

Rolling element bearing is a well-known concept in macroscale machinery applications. They are prospective candidates for friction reduction in microelectromechanical system (MEMS), as well as for providing stable, robust support for moving micromechanisms. The characteristics of rolling element bearings need to be investigated to facilitate their applications in MEMS. It is well understood that the measured data on the macroscale cannot be directly applied to the microscale. This paper presents an in-situ noncontact experimental system to characterize the friction behavior of microball bearings on the microscale. The methodology presented in this paper provides a useful template to study the dynamical behavior of linear microball bearings with a variety of materials, geometries, and surface qualities. The system, actuated by a motor, affords wide ranges of motion for the determination of the coefficient of friction (COF) without any interference due to the measurement system. With careful optimization, the error in measurement has been reduced to 2%. Different designs of microball bearings demonstrated an average static COF of 0.01 and an average dynamic COF of 0.007 between stainless-steel and silicon-micromachined contacting surfaces at 27﯃ and 40% relative humidity

Vision-Based Microtribological Characterization of Linear Microball Bearings

Microball bearings can potentially provide robust and low friction support in micromachines such as micromotors and microgenerators. Their microtribological behavior needs to be investigated for design and control of such micromachines. In this paper a vision-based, non-intrusive measurement method is presented for characterization of friction in linear microball bearings. Infrared imaging is used to directly observe the dynamics of microballs and track the motion of bearing components. It is verified that microballs roll most of the time with occasional sliding or bumping resulting from fabrication nonuniformity. The friction-velocity curve demonstrates evident hysteresis. The dependence of frictional behavior on several factors is studied

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Dynamic characterization of a linear electrostatic micromotor supporte