MlCR SERV Toshiki H m o . Long-Sheng Fan, Wen Y. Lee, Tetsuo Semba, John Hong*, Suiya Pattanaik', Patrick Webb, Wen-Han Juan, ad Susanna Chan IBM Corp., Almaden Research Center, 650 Harry Road, San Jose, CA95120 'IBM Corp., Storage Systems Division 1. lotlwludion A micm-actuator which can dramatically increase the recordmg density of a harddisk drive W D ) is presented"). This mim-actuator is located between suspension and slider (Fig. l), allowing the slider (and the magnetic head) to move with very high kquency and accuracy. This enables a fmer data track pitch. resulting m a higher areal recording density. The target of our project is more than IO GbiVinch2 recording density by more than 25 kilo track-per-inch(TP1) hack pitch, which requires higher LMb-ac tua to r Desieo Fig. 2 shows a design of a micm-achutor, which is an electrostatically driven rotary actwdor. cent^ of rotation" is fixed on the substrate, and the "suspended part" is the place where slider is attached, and this part is suspmded by "Flexun hems" which allow only rotational motion to the suspended pait. Many electrostatic elecmdes are attached on the "ann", and they are tilted to generate pure torque according to the center of the rotation. "Suspended Pads" are the parts where the magnetic head's bonding pads are connectal. The head signal is led to "Fixed pads" through flexible spring struefure. This structure is necessary to connect head (moving part) to the outside circuit. 3. F a b r i d This micm-actuator was fabricuted by using high aspect ratio polymer etching and electroplating. These technologies enable 40 pn-thick structure with 2 pm resolution (aspect ratio 201) I*! Advantages of high aspect ratio are (1) high Zinplane stiffness ratio (propor tional to the square of the aspect ratio), and (2) high eleckostatic force (proportional to the aspect ratio). Fig. 3 shows SEM photographs of a micro-actuator. whose size is 1.7 mm by 2.6 mm. Fig. 4 (a) shows the microactuator assembled with pia-slider and suspension. Fig. 4@) shows the magnified view of the connection of the head to the micro-actuator. Slider pads are connected by solder balls. 4. Exnerimeot This micro-actuator assembly was placed in a HDD (IBM Ulbnstarm 2ES), and a servo e x p i ment was Wried out. First, servo patterns were Written on the disk, then the bead position was detected by the a magnetic head, processed by an analogue controller, and fed back to the micrc-actuator. We 6x4 the VCM to test the micro-actuator's performance only. Fig. 5 shows the open-loop transfer hction of the micro-actuator and the controller. The 0 dFl croswver hyuency (servo bandwidth) is 6.4 kHz with gain margin of 16.8 dB and phase margin of 5 5 O . Thii is the highest bandwidth demonsbated so far by any of the second stage actuator mothcds. Fig. 6 shows the step response. The response time is less than 0.2 mS, and this is much faster than VCM. Acknowledgement: This I.csearch w parlly supported by DARPA contracl #DABT63-95-C0026. 2 kHz tracking servo bandwidth.