Sung Q. Lee

Design and performance of a self-sensing, self-actuating piezoelectric monomorph with interdigitated electrodes

A smart cantilever structure using single-crystal relaxor ferroelectric material is presented. The smart cantilever possesses both sensing and actuation capabilities, embedded in a monomorph and resulting in a smart structure. Single crystal relaxor ferroelectric materials (1-x)Pb(Zn1/3Nb2/3)O3-xPbTiO3 (PZN-PT) and (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-PT) are ideal for actuator and sensor applications since they exhibit very high piezoelectric coefficients. We separately pattern interdigitated electrodes on the top and bottom surfaces of a single crystal cantilever beam. The interdigitated electrode design results in an electric field- gradient that after poling not only induces flapping actuation but also, simultaneously, allows us to detect internally or externally induced stresses. As a monolithic actuator integrated with a sensor, it has potential applications in various Micro-Electro-Mechanical Systems (MEMS), Scanning Probe Microscopy (SPM) and Near-field Scanning Optical Microscopy (NSOM). We fabricate monomorph prototypes and characterize their performance in terms of actuation displacement and sensing capabilities, respectively. Finally, an active vibration control experiment was successfully conducted by using the smart cantilever structure.

Fabrication of a piezoelectric biosensor based on a PZN-PT/PMN-PT single crystal thin film

In this paper, novel piezoelectric microbalance biosensors using single crystal lead zinc niobate-lead titanate (PZN-PT) and lead magnesium niobate-lead titanate (PMN-PT) are presented. The PZN-PT/ PMN-PT materials exhibit extremely high piezoelectric coefficients and other desirable properties for biosensors, supposed to be a superior substitution for the conventional quartz crystal with the improved performance. . These biosensors provide rapid and minute quantitative target detection by monitoring the change in resonance frequency of the crystal probe. With the geometrical variations, various prototypes are compared with conventional quartz crystal microbalances (QCM). The superiority of the materials over conventional quartz crystal is demonstrated experimentally in terms of sensitivity. In addition, we examine the feasibility of ultra miniaturization of the PZN-PT based biosensor by fabricating freestanding single crystal films of the PZN-PT and patterning micro-scale biosensors with ion milling and argon-ion laser-induced etching technique. A fabricated prototype sensor utilizing the material in a thin film form has a size of 300x100x7um3.

MEMS acoustic sensor using PMN-PT single-crystal diaphragm

The MEMS (micro-electro-mechanical systems) microphone enables the manufacturing of small mechanical components on the surface of a silicon wafer. The MEMS microphones are less susceptible to vibration because of the smaller diaphragm mass and an excellent candidate for chip-scale packaging. The PMN-PT materials itself exhibit extremely high piezoelectric coefficients and other desirable properties for an acoustic sensor. In this paper, we present a piezoelectric MEMS microphone based on PMN-PT single crystal diaphragm. The fabrication process including dry etching conditions and scale-factored prototype is presented. In particular, this paper introduces the design of a PMN-PT single crystal diaphragm with interdigitated electrode.

Development of a nanoindenter using a piezoelectric actuator

In this paper, we report an innovative depth-sensing nanoindenter using a lead zirconium titanate (PZT) stack actuator. The conventional nanoindenter requires two sensors and closed-loop controls for precise loading or positioning due to inherent high hysteresis and creep characteristics of the PZT actuators. On the other hand, we have shown that an open-loop positioning control scheme using a single displacement sensor can be used for nanoindentation. The developed control scheme compensates for the hysteresis and creep errors of PZT actuators. By adopting the single-sensor open-loop control, the overall system structure can be simplified and a robust control environment can be achieved. In addition, a high positioning repeatability was achieved by using a flexure type mainframe with a high preload applied to the PZT actuator. To verify the system performance, we conducted the standard indentation tests on a fused quartz sample, and the results were compared with those from a commercial nanoindenter. Besides the basic nanoindentation functions, the developed system also has the capability for surface imaging through a scanning function. The pre-indentation scanning capability proved to be a very useful method for positioning the tip in the desired indentation location. Similarly, post-indentation scanning allows for visualization of the indentation marks after the tests.

PMN-PT piezoelectric near field optical probe for data storage

This paper presents the fabrication process of a novel aperture which allows near field optical data storage. We use PMN-PT ((1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3) single crystal material - a new generation oxide material known as relaxor ferroelectrics that exhibits extraordinary piezoelectric properties - to fabricate microlenes using photolithography and dry etching techniques. In this paper, we describe the fabrication processes of a PMN-PT single crystal material microlens prototype with a miniature aperture for near field optical data storage. PMN-PT has the merits of transparency for optical usage and also has a high dielectric coefficient that is suitable for actuator and sensor applications. It provides an advantage of manufacturing both aperture and actuator/sensor with the same material. The thermal reflow technique is used to fabricate photoresist microlenses on a freestanding single crystal PMN-PT film as a mask. The PMN-PT lenses are fabricated by a chemically assisted ion beam etching (CAIBE) technique. Finally the focused ion beam (FIB) machining process is used to place a miniature aperture at the apex of the microlens. We were able to successfully fabricate the 10μm PMN-PT microlenses with less than 100nm apertures. From the experimental measurement, we were able to obtain the optical throughput of 1.83x10-7 from a 50nm aperture.

Design of a compact atomic force microscope to enhance scanning speed

A novel design of an atomic force microscope (AFM) with a (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-PT) single crystal scanner and a self-sensing cantilever is presented in this paper. The piezoelectric scanner and the self-sensing cantilever are integrated into a small-sized all-in-one structure with a microscope objective focused on the tip. The Z-scanner consists of two parallel PMN-PT unimorphs. This design can minimize the rotation and the sideways deflection at the sensing tip. The XY-scanner consists of two perpendicular small rods of PMN-PT. In this design, each PMN-PT rod serves as an actuator as well as a flexure because of the elastic property of the single crystal material. Under this configuration, the XY scanner can guarantee a fully decoupled planar scanning motion without positioning sensors and a sophisticated closed-loop control mechanism which is required for a XY scanner with conventional piezoelectric tubes. Furthermore, by adopting a self-sensing MEMS cantilever, the AFM design is simplified by discarding various optical sensing components. The attached objective offers fast visible inspection and rough positioning of the tip for measurement setups. We used a digital signal processor (DSP) based control scheme to achieve fast control speeds of the AFM. We also used LABVIEW for a flexible programming environment. We conducted finite-element analyses to characterize the dynamic performance of the AFM system. The system showed a high frequency band due to the small inertia of the moving part with relatively rigid structure. In addition, various scanning tests were performed to demonstrate that the system is capable of providing near video images.

A single-crystal piezoelectric scanner for scanning probe microscopy

In this paper, a small size monolithic XY scanner was designed and fabricated. The scanner has a flat triangular shape and consists of two 0.5mm-thick and 5mm-long lead-zinc-niobate-lead-titanate ((1x)Pb(ZnNb)O3 - xPbTiO3) or PZN-PT rods. The use of this material is critical to the reduction of the scanner size. The mechanical resonance characteristics for the PZN-PT rods and the assembled scanner were tested. The fabricated scanner provides a high resonance frequency and assured parallelism between the scanner and the sample surface. It enables a fast open loop control capability that naturally lends itself to use in scanning probe microscopy. The scanner and a self-sensing cantilever were integrated into a small-size atomic force microscope (AFM) design. A commercially available self-sensing cantilever and an additional actuator were used for contact scanning of a HOPG (Highly Ordered Pyrolytic Graphite) sample surface. The scanning performance of the scanner was verified by obtaining atomically resolved image of the HOPG surface.