Albert P. Pisano

Piezoelectric Aluminum Nitride Vibrating Contour-Mode MEMS Resonators

This paper reports theoretical analysis and experimental results on a new class of rectangular plate and ring-shaped contour-mode piezoelectric aluminum nitride radio-frequency microelectromechanical systems resonators that span a frequency range from 19 to 656 MHz showing high-quality factors in air (Qmax=4300 at 229.9 MHz), low motional resistance (ranging from 50 to 700 Omega), and center frequencies that are lithographically defined. These resonators achieve the lowest value of motional resistance ever reported for contour-mode resonators and combine it with high Q factors, therefore enabling the fabrication of arrays of high-performance microresonators with different frequencies on a single chip. Uncompensated temperature coefficients of frequency of approximately -25 ppm/degC were also recorded for these resonators. Initial discussions on mass loading mechanisms induced by metal electrodes and energy loss phenomenon are provided

Modeling and optimal design of piezoelectric cantilever microactuators

A novel model is described for predicting the static behavior of a piezoelectric cantilever actuator with an arbitrary configuration of elastic and piezoelectric layers. The model is compared to deflection measurements obtained from 500-/spl mu/m-long ZnO cantilever actuators fabricated by surface micromachining. Modeled and experimental results demonstrate the utility of the model for optimizing device design. A discussion of design considerations and optimization of device performance is presented.

Microelectromechanical filters for signal processing

Microelectromechanical (MEM) filters based on coupled, lateral microresonators are demonstrated. This class of MEM systems has potential signal-processing applications for filters which require narrow bandwidth (high Q), good signal-to-noise ratio (SNR) and stable temperature and aging characteristics. Both series and parallel filters were fabricated and tested using an off-chip modulation technique. The frequency range of these filters is from approximately 5 kHz to on the order of 1 MHz, for polysilicon microstructures with suspension beams having a 2- mu m-square cross section. A series-coupled resonator pair, designed for operation at atmospheric pressure, has a measured center frequency of 18.7 kHz and a bandwidth of 1.2 kHz.<<ETX>>

Silicon-processed microneedles

A combination of surface- and bulk-micromachining techniques is used to demonstrate the feasibility of fabricating microhypodermic needles. These microneedles, which may be built with on-board fluid pumps, have potential applications in the chemical and biomedical fields for localized chemical analysis, programmable drug-delivery systems, and very small, precise sampling of fluids. The microneedles are fabricated in 1, 3, and 6 mm lengths with fully enclosed channels formed of silicon nitride. The channels are 9 /spl mu/m in height and have one of two widths, 30 or 50 /spl mu/m. Access to the channels is provided at their shank and distal ends through 40-/spl mu/m square apertures in the overlying silicon nitride layer. The microneedles are found to be intact and undamaged following repetitive insertion into and removal from animal-muscle tissue (porterhouse steak).

Silicon-processed overhanging microgripper

A silicon-processed microgripper, suitable for mounting on a micropositioner, has been designed and fabricated by combining surface and bulk micromachining. The microgripper consists of a silicon die (7 mm*5 mm), a 1.5 mm long support cantilever, made from boron-doped silicon substrate material (protruding from the die), and a 400 mu m long polysilicon overhanging gripper extending from the end of the support cantilever. The microgripper is electrostatically driven by flexible, interdigitated comb pairs and has significantly smaller feature sizes than have been reported previously for overhanging microstructures. Problems addressed successfully in the microgripper fabrication include the protection of surface-micromachined fine structures during bulk-silicon etching and rinsing. The microgripper has successfully seized several microscopic objects in laboratory experiments. >

Viscous damping model for laterally oscillating microstructures

Viscous energy loss in oscillating fluid-film dampers that provide frictional shear for laterally-driven planar microstructures is investigated. It is found that Stokes-type fluid motion models viscous damping more accurately than Couette-type flow field. This paper characterizes the damping property of a fluid layer in terms of viscous energy dissipation, then derives analytic damping formulae for practical Q estimation. Theoretical Q-factors are compared to the experimental values, measured from surface-micromachined polysilicon resonators. Data reported by previous investigators are also analyzed and compared. The experimental results indicate that the Stokes-type damping model presents a more general damping treatment with better Q estimation, although discrepancies of 10 to 20% still remain between the estimated and measured Q. >

Parallel microassembly with electrostatic force fields

Microscopic (submillimeter) parts are often fabricated in parallel at high density but must then be assembled into patterns with lower spatial density. We propose a new approach to microassembly using: 1) ultrasonic vibration to eliminate friction and adhesion; and 2) electrostatic forces to position and align parts in parallel. We describe experiments on the dynamic and frictional properties of collections of microscopic parts under these conditions. We first demonstrate that ultrasonic vibration can be used to overcome adhesive forces; we also compare part behavior in air and vacuum. Next, we demonstrate that parts can be positioned and aligned using a combination of vibration and electrostatic forces. Finally, we demonstrate part sorting by size. Our goal is a systematic method for designing implementable planar force fields for microassembly based on part geometry.

Injection molded microfluidic chips featuring integrated interconnects

An injection molding process for the fabrication of disposable plastic microfluidic chips with a cycle time of 2 min has been designed, developed, and implemented. Of the sixteen commercially available grades of cyclo-olefin copolymer (COC) that were screened for autofluorescence and transparency to ultraviolet (UV) light, Topas 8007 x 10 was identified as the most suitable for production. A robust solid metal mold insert defining the microfluidic channels was rapidly microfabricated using a process that significantly reduces the time required for electroplating. No wear of the insert was observed even after over 1000 cycles. The chips were bonded by thermal fusion using different bonding conditions. Each condition was tested and its suitability evaluated by burst pressure measurements. The COC microfluidic chips feature novel, integrated, reversible, standardized, ready-to-use interconnects that enable operation at pressures up to 15.6 MPa, the highest value reported to date. The suitability of these UV transparent, high pressure-resistant, disposable devices was demonstrated by in situ preparation of a high surface area porous polymer monolith within the channels.

Microfabricated Polysilicon Microneedles for Minimally Invasive Biomedical Devices

A two-wafer polysilicon micromolding process has been developed for the fabrication of hollow tubes useful for microfluidic applications. These small tubes can be fabricated with a pointed end, resulting in a micro hypodermic injection needle. Microneedles are desired because they reduce both insertion pain and tissue damage in the patient. Such microneedles may be used for low flow rate, continuous drug delivery, such as the continuous delivery of insulin to a diabetic patient. The needles would be integrated into a short term drug delivery device capable of delivering therapeutics intradermally for about 24 hours. In addition, microneedles can be used for sample collection for biological analysis, delivery of cell or cellular extract based vaccines, and sample handling providing interconnection between the microscopic and macroscopic world.The strength of microneedles was examined analytically, experimentally and by finite element analysis. Metal coatings provide significant increases in the achievable bending moments before failure in the needles. For example, a 10 μ m platinum coating increased the median bending moment of a 160 μ m wide, 110 μ m high microneedle with a 20 μ m wall from 0.25 to 0.43 mNm. In addition, fluid flow in microneedles was studied experimentally. Microneedles 192 μ m wide, 110 μ m high and 7 mm long have flow rates of 0.7 ml/sec under a 138 kPa inlet pressure. This flow capacity exceeds previous microneedle capacities by an order of magnitude.

Single-Chip Multiple-Frequency ALN MEMS Filters Based on Contour-Mode Piezoelectric Resonators

This paper reports experimental results on a new class of single-chip multiple-frequency (up to 236 MHz) filters that are based on low motional resistance contour-mode aluminum nitride piezoelectric micromechanical resonators. Rectangular plates and rings are made out of an aluminum nitride layer sandwiched between a bottom platinum electrode and a top aluminum electrode. For the first time, these devices have been electrically cascaded to yield high performance, low insertion loss (as low as 4 dB at 93MHz), and large rejection (27 dB at 236 MHz) micromechanical bandpass filters. This novel technology could revolutionize wireless communication systems by allowing cofabrication of multiple frequency filters on the same chip, potentially reducing form factors and manufacturing costs. In addition, these filters require terminations (1 kOmega termination is used at 236 MHz) that can be realized with on-chip inductors and capacitors, enabling their direct interface with standard 50-Omega systems