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The application of microelectromechanical systems (MEMS) to medicine is described. Three types of biomedical devices are considered, including diagnostic microsystems, surgical microsystems, and therapeutic microsystems. The opportunities of MEMS miniaturization in these emerging disciplines are considered, with emphasis placed on the importance of the technology in providing a better outcome for the patient and a lower overall health care cost. Several case examples in each of these areas are described. Key aspects of MEMS technology as it is applied to these three areas are described, along with some of the fabrication challenges.

The fabrication and structural characterization of a surface micromachined, resonant frequency, Pb(Zr, Ti)O 3 (PZT) microcantilever will be presented. The PZT microcantilever was fabricated using surface micromachining techniques, and used a low-stress silicon nitride thin film as the base material for the microcantilever onto which a PZT thin film was incorporated. The PZT thin film is used as both the microsensor and the microactuator. A unique fabrication procedure was developed in order to eliminate the step of encapsulating the PZT during the removal of the spacer layer. The encapsulation step was avoided because of the difficulty in finding a suitable material, which would protect the PZT during the removal of the spacer layer yet not affect its material properties. This predicament was resolved by removing the spacer layer prior to the deposition of the PZT. The microcantilevers were characterized extensively using an atomic force microscope in an unusual manner. The atomic force microscope was modified in such a fashion that the deflection at the tip of the microcantilever could be measured as the frequency of an electrical signal applied to the PZT thin film was varied. In addition, an impedance analyzer was used to characterize the microcantilevers. Simple thin-film, laminated plate theory was used to obtain a closed-form solution for the modal response of the microcantilever, while ANSYS was used to obtain modal and harmonic simulation results. It will be shown that the experimental, numerical, and theoretical modal results are within ±10% of one another. The experimental and numerical harmonic results differ by an order of magnitude; however, the numerical model is currently being modified to more accurately represent the PZT microcantilever. From the information gathered during the structural characterization of the PZT microcantilever, it will be shown that certain higher-order resonant frequency modes have very large mechanical responses. These higher-order resonant frequency modes give designers another parameter to adjust when trying to optimize the design of their resonant frequency device.

Novel piezoelectric cantilever beams for micro sensors and actuators based on PZT thin films have been batch fabricated by surface micromachining. Lead zirconate titanate (PZT) thin film is formed by metalorganic deposition (MOD) on Pt/Ti/SiO 2 /Si (1 0 0) substrates and Pt/Ti/LTO/Si 3 N 4 cantilever beams and then annealed at 700°C in air. The PZT thin film is 0.5 lm thick and has dielectric permittivity of 1698, remanent polarization of 13.66 lC/cm 2 , and coercive field of 44.5 kV/cm. The influence of deposition temperatures on PZT thin film stress has been investigated. When continuously controlling the deposition temperatures, the stress of the thin film is reduced from 0.313 · 10 8 to 0.269 · 10 8 N/m, that is 16.4% decrease. With the total 120 designed devices on 4-inch wafers, the number of functional devices is increased from 82 to 97, that is 12.47%. IntroductionPZT thin films have been intensively investigated since they offered promising piezoelectric and ferroelectric properties that can be applied to microelectronic, optoelectronic, and micromechanical devices [1,2]. Recently the PZT thin film has attracted more attention to its applications to microelectromechanical systems (MEMS) due to its desirable properties such as spontaneous polarization, high piezoelectric constant, and pyroelectricity [3][4][5]. There are several methods to deposit PZT thin films such as sol-gel process which was employed to fabricate ultrasonic micromotors [6], hydrothermally synthesized PZT films which were deposited on metal to form bimorph cantilever [7], screen printing PZT for dynamic micropumps [8], sputtering [9], laser ablation [10], electron beam deposition [11], ion beam deposition [12], metalorganic chemical vapor deposition (MOCVD) [13,14], and metalorganic decomposition (MOD) [15]. Here MOD is defined as a metalorganic deposition method to spin-coat a PZT solution on substrates, then to cure and anneal the PZT thin films by heating the substrates. The precursors of MOD PZT are metalorganic materials different from that of sol-gel. The precursors of MOD PZT are less harmful compared to that of sol-gel PZT. Among all the techniques, the MOD method appear to be most promising in the area of MEMS because it offers the advantages of simplified apparatus, excellent film uniformity, good composition control, high film density, high deposition rate, excellent step coverage, and amenability to large scale processing. However, currently very few reports are available on MOD PZT films for MEMS applications. At present cracking of the MOD PZT film is the most serious problem to delay the applications of MOD PZT thin films to micro devices. In contrast, the unique aspects of this research are the following: (1) Novel MOD procedures to fabricate MOD PZT thin films on Pt/Ti/SiO 2 /Si (1 0 0) substrates and Pt/Ti/LTO/Si 3 N 4 cantilever beams, (2) Measurement of curvature change to characterize the stress of PZT thin films, and (3) Demonstration of functional piezoelectric cantilever beams based on MOD PZT thin films to veri...

A silicon-based piezoelectric linear stepper motor has been designed and fabricated. The motor is based on an inertial drive concept derived from sequential electrostatic clamping and unclamping of a piezoelectric bar measuring 38.1 x 6.36 x 0.787 mm. The piezoeIectric micromotor has been constructed and tested for precision surgical applications. The measured performance is dependent on the operating conditions selected. Representative performance i s a speed of 1.2 "/s against a 3.0 N load. The motor is limited in its travel by approximately the diameter of the silicon wafer used to fabricated it. The resolution of the motor is less than 100 nm in its most precise actuation mode.