Design and Fabrication of PZT-Actuated Silicon Suspensions for Hard Disk Drives

Piezoelectrically actuated suspensions are currently being considered by the magneticrecording industry, as a means of achieving dual-stage actuation in magnetic Hard Disk Drives. In most designs, piezoelectric actuators are placed behind the suspension, and only the position-error-signal obtained from the magnetic head, is utilized as the feedback signal to construct the dual-stage servo. In general, this approach achieves a relatively low operating voltage for piezoelectric actuation and low frequency runout attenuation. However, it may be susceptible to instabilities due to the excitation of suspension resonance modes.
In this dissertation, a silicon suspension, suitable for use in a piezoelectrically actuated dual-stage servo system for magnetic Hard Disk Drives, has been designed, fabricated and tested. The new suspension design incorporates a piezoresistive sensor that measures the position of magnetic head relative to the voice coil motor. The availability of this position signal enables a more compliant suspension design and allows the piezoelectric actuators to be placed closer to the magnetic head. This arrangement not only achieves similar driving voltage and runout attenuation to other piezoelectrically actuated suspensions but, in addition, it is able to measure and attenuate runout induced by suspension vibration.
An integrated-gimbal structure is another unique feature for this silicon suspension. This gimbal design features two adjacent flexures as the torsion bar, which differs from previous gimbal designs. This new torsion bar design successfully produces the necessary gimbal pitch and roll flexibility, while providing very high in-plane and out-of-plane bending stiffness in a very limited design parameter space. Other features of the silicon suspension design presented in this dissertation, which enable piezoelectric actuation, include: a stretch area, a leverage mechanism aid electrical interconnects. All these features were implemented on a single piece of single crystal silicon.
A simple and reliable SOI-like process has been developed to fabricate this new silicon suspension. The most challenging aspect of this process is the lithography that takes place after the deep-reactive-ion-etch (DRIE). By fabricating the proposed silicon suspension, we demonstrated that this newly developed process is capable of making structures with an aspect-ratio of 20 and 3 um lithography precision on the topography of post DRIE.
A fabricated silicon suspension was tested on a rotating disk. The experimental results indicate that this silicon suspension has a dynamic performance that is compatible with current metal suspensions found in the commercial products.
Tsung-Lin Chen
Roberto Horowitz
Publication date: 
December 31, 2001
Publication type: 
Ph.D. Dissertation
Chen, T. (2001). Design and Fabrication of PZT-actuated Silicon Suspensions for Hard Disk Drives. United States: University of California, Berkeley.

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