ELSEVIER Microelectronie Engineering 30 (1996) 531-534 MICROELE~O~C ENGINEERING INITIAL FABRICATION OF A MICRO-INDUCTION GYROSCOPE C.B. Williams t, C. Shearwood~, P.H. Mellor 1, A.D. Mattingley2, M.R.J. Gibbs 2, and R.B. Yates l 1MEMS Unit, Department of Electronic & Electrical Engineering, Mappin Street, University of Sheffield, Sheffield, S1 3JD, United Kingdom 2Sheffield Centre for Advanced Magnetic Materials & Devices, Department of Physics, University of Sheffield, Sheffield, $3 7RH, United Kingdom A planar coil design capable of levitating an aluminium rotor by electromagnetic induction is described. The coil is fabricated from Au onto a Si(001) substrate with a footprint size of 700 pro, and coil thickness and typical width of 1.3 pm and 50 ~un respectively. The rotors are made from AI with a thickness of 12 I.tm and diameter of 400 pm. A maximum levitation height of 10 pm is measured with a coil excitation current of 800 mApk. This height is increased to 25 pm by the incorporation of a high permeability amorphous magnetic backing plane below the planar coils. Excellent quantitative agreement is observed between the predictions of modelling and experimental measurements of levitation height versus coil excitation current. The application of this levitated rotor to a wide range of applications, including a micromachined rotating gyroscope is described. 1. INTRODUCTION There is a growing demand for small gyroscopic sensors for automotive and aerospace applications. In the last few years there has been a great deal of research into micromachined gyroscopes. The vast majority of these use a vibrating structure to measure rate of rotation using the coriolis effect [1]. These gyroscopes are small and cheap but have modest performance and as yet do not meet the exacting requirements of the automotive sector. ~ ~""---- rotor mmm Fig. 1. Schematic diagram of the electromagnetic induction levitated rotor. As an alternative to vibrating gyroscopes, a novel rotating micro-gyroscope is being investigated [2,3]. Like conventional rotating gyroscopes, in this device rate of rotation is determined by measuring the precession of a spinning rotor. Figure 1 shows a cross-sectional diagram of the gyroscope. The rotor is levitated above the substrate using electromagnetic induction. Levitation is necessary to give the rotor the degree of freedom required to operate as a gyroscope sensor. It also has the advantage of frictionless rotation which leads to increased lifespan. The device described so far can only be operated at a few tens of degrees above the horizontal, otherwise the rotor would fall off. However, operation can be extended to any orientation with the use of a counterbalancing electrostatic force between the rotor and coils operated in closed loop feedback. The resolution required for an automotive grade gyroscope for active suspension - defined in the PROMETHEUS [4] yaw rate sensor specification - is 0.1 °/s at a bandwidth of 20 Hz. Initial studies indicate that the proposed rotating gyroscope will exceed these specifications. The device can also be used as an ultra-high speed micro-motor. The viscous drag forces on the rotor are extremely low, and so operational speeds in excess of one million rpm are feasible. This paper describes the results of the first stage of the gyroscope project: the levitation of a micro-rotor using electromagnetic induction. 0167-9317/96/$15.00 © 1996 - Elsevier Science B.V. All rights reserved. SSDI 0167-9317(95)00302-9