Onnik Yaglioglu

Method of characterizing electrical contact properties of carbon nanotube coated surfaces

We present a method for electromechanical characterization of carbon nanotube (CNT) films grown on silicon substrates as potential electrical contacts. The method includes measuring the sheet resistance of a tangled CNT film, measuring the contact resistance between two tangled CNT films, and investigating the dependence on applied force and postgrowth annealing. We also characterize Au-CNT film contact resistance by simultaneous measurement of applied force and resistance. We measure a contact resistance as low as 0.024Ω∕mm2 between two films of tangled single-wall carbon nanotubes grown on a polished silicon substrate and observe an electromechanical behavior very similar to that predicted by classical contact theory.

Design, fabrication, and testing of a piezoelectrically driven high flow rate micro-pump

Towards the development of novel class of miniature transducers with very high specific power, a high frequency and high flow rate hydraulic micro-pump with passive check valves was fabricated and tested. The micro-pump features a small piezoelectric (PZT-5H/PZN-PT) cylinder integrated into micromachined silicon and pyrex chips. The piezoelectric cylinder bonded to a thick circular disk serves as the drive element in the pump chamber, and two axisymmetric silicon membranes with hollow annular bosses serve as system check valves. Using silicone oil as the working fluid, the performance of the micro-pump was tested by varying voltages from 0 to 1600 V and frequencies from 1 kHz to 12 kHz. The micro-pump with PZT-5H element achieved a high flow rate of 2.5 ml/min at 1200 V and 4.5 kHz.

Compliant Carbon Nanotube-Metal Contact Structures

This paper discusses a method to fabricate contact structures using carbon nanotubes (CNTs) and thin film metal deposition which can be used in applications such as electromechanical probes. We discuss the electrical resistance of CNT structures and electrical enhancement schemes using various metal deposition techniques including sputtering and electroless metal plating. Functional CNT-metal composite contact structures are demonstrated and test results, along with failure mechanisms are discussed. We also discuss factors affecting mechanical compliance, electrical resistance and trade offs between them.

Modeling, design, and simulation of a piezoelectrically driven microvalve for high-pressure high-frequency applications

This paper reports the modeling, design, and dynamic simulation of a piezoelectrically-driven microfabricated valve for high frequency regulation of high pressure fluid flows. The enabling concept of the valve is the ability to convert the small displacement of a piezoelectric element into a large valve cap stroke through the use of a hydraulic fluid, while maintaining high force capability. The paper focuses on the development of a sytematic procedure to arrive at a geometric valve design for given performance requirements. Modeling of the non-linear large deflection behavior of the valve membrane and design of this structure to maintain stresses below critical levels are discussed. Design of the piezoelectric material drive portion of the valve to create a stiffness match with the valve membrane and external hydraulic system is detailed. In addition, this paper presents a dynamic simulation of the active valve, including effects such as valve cap dynamics and fluid damping, that allow for understanding and prediction of valve performance under various loading conditions.

Fabrication of a microvalve with piezoelectric actuation

The fabrication of an active MEMS micro valve driven by integrated bulk single crystal piezoelectric actuators is reported. The valve is a nine-layer structure of glass, Si, and silicon on insulator (SOI) assembled by wafer level fusion bonding and anodic bonding, die level anodic bonding and eutectic bonding. Valve head strokes as large as 20/spl mu/m were realized through hydraulic amplification of small strokes of piezoelectric actuators. A flow rate of 0.21ml/s was obtained at 1 kHz. The fabrication, bonding and assembly processes, as well as some test results are described.

Electroless silver plating and in-situ SEM characterization of CNT-metal hybrid contactors

We discuss a metal deposition technique employing electroless silver plating to create hybrid CNT-Metal contact structures which can be used various applications including electromechanical probes. The main purpose of the electroless metal deposition is to enhance the electrical conduction through the contact structures. We discuss different electroless plating formulations and their effect on electrical resistance, as well as their penetration properties into the highly tangled CNT structures. We also present electromechanical characterization of Ag plated CNT structures and in-situ SEM compression results revealing that the Ag particles adhere to the CNTs and do not significantly interfere with the mechanical deformation. Overall, electroless plating presents an attractive alternative to sputtering due to the better penetration properties; however it presents limitations in terms of scalability and manufacturability.