Smart Piezoelectric PZT Microcantilevers with Inherent Sensing and Actuating Abilities for AFM and LFM
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laser diode and a 4 segment photo detector, via separating the reflected laser light signals into lever bending and torsion. Again, the necessity of optical components brings the same problems as in the case of the AFM. Several force sensing cantilevers have been proposed and developed to get rid of the problems caused by the optical sensing components [6-8]. Among the sensing mechanisms of force sensing cantilevers, the piezoelectric scheme shows superiority in the operation of dynamic mode AFM, because a piezoelectric cantilever can be excited by an applied ac voltage without any disturbance of the sensing action [9]. This excellent characteristic also makes for simple operation of dynamic AFM in liquid [10] and vacuum [11]. Moreover, AFMs equipped with a cantilever array show potential applications in both nanolithography and imaging on large scales and high speed. These are important for applications in high density data storage and wafer inspection [4, 12-14]. Conventional AFMs use a single probe that can only scan an area of less than 10' gm'. The separate control of each cantilever in an array is needed, because 1) the resonance frequency of each cantilever will be slightly different due to the deviation of geometric structure in the microfabrication process, 2) the original tip-sample spacing of each cantilevers will be different, and 3) the different traces of each cantilever must be individually feedback controlled. This paper describes a smart structure, PZT (Lead zirconate titanate) microcantilever with the inherent ability of force sensing and feedback-actuation. Based on this structure, the individual feedback control of each cantilever in a piezoelectric cantilever array for multiprobe AFM becomes possible. In addition a smart cantilever, which is a free standing SiO 2 beam integrated with two parallel PZT beams on one side, is proposed to measure the torsion due to the friction force for the LFM application. FABRICATION Fabrication starts from sol-gel deposition of the Pb(Zr0 .53Ti0.47)03 layer on a Pt/Ti/SiO/Si substrate. Then a micromachining process is used to sculpt the free standing cantilever structure. The details of the fabrication procedure are similar to a previously reported process [15]. Fig. I shows a schematic drawing and an SEM micrograph of a smart structure for AFM. This structure includes a 125 gi. long and 50 jtm wide cantilever integrated with a PZT layer of 100 grm length, and a PZT reference pattern of the same surface area. The smart force sensing cantilever for LFM is shown in Fig. 2 (a). The tip on the end of cantilever shown in Fig. 2 (a) is fixed by glue via a micro-manipulator. Two structures were made, one contains a PZT layer with separated surface electrodes (Fig. 2 b), the other was integrated with two parallel beams of PZT/surface electrode
Fig. l(a) SEM photo of the PZT smart structure for AFM application.
Fig. 1(b) Schematic drawing of the PZT smart structure shown in (a). 36
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