AVS 51st International Symposium
    MEMS and NEMS Monday Sessions
       Session MN-MoA

Paper MN-MoA4
BCB-Based Linear Micromotor Supported on Microball Bearings: Design Concepts, Characterization, and Fabrication Development

Monday, November 15, 2004, 3:00 pm, Room 213C

Session: Micro and Nano Fabrication Techniques for MEMS and NEMS
Presenter: A. Modafe, University of Maryland, College Park
Authors: A. Modafe, University of Maryland, College Park
N. Ghalichechian, University of Maryland, College Park
R. Ghodssi, University of Maryland, College Park
Correspondent: Click to Email
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.