Showing papers by "Goksen G. Yaralioglu published in 2000"

High-speed tapping mode imaging with active Q control for atomic force microscopy

Abstract: The speed of tapping mode imaging with the atomic force microscope (AFM) has been increased by over an order of magnitude. The enhanced operation is achieved by (1) increasing the instrument’s mechanical bandwidth and (2) actively controlling the cantilever’s dynamics. The instrument’s mechanical bandwidth is increased by an order of magnitude by replacing the piezotube z-axis actuator with an integrated zinc oxide (ZnO) piezoelectric cantilever. The cantilever’s dynamics are optimized for high-speed operation by actively damping the quality factor (Q) of the cantilever. Active damping allows the amplitude of the oscillating cantilever to respond to topography changes more quickly. With these two advancements, 80μm×80 μm high-speed tapping mode images have been obtained with a scan frequency of 15 Hz. This corresponds to a tip velocity of 2.4 mm/s.

Contact stiffness of layered materials for ultrasonic atomic force microscopy

Abstract: A method to calculate the contact stiffness between a layered material and an ultrasonic atomic force microscope (UAFM) tip is proposed. The radiation impedance method is used to determine the ratio of the applied force to the average displacement within the contact area. This information is used in an iterative algorithm based on Hertzian theory to obtain the contact stiffness. The algorithm converges into a couple of iterations and does not suffer from numerical convergence difficulties as does finite element analysis (FEA). In the ultrasonic frequency range, comparisons with Hertzian theory and FEA show the validity of the results in a quasistatic case. Definitions of the minimum detectable layer thickness and the penetration depth of the UAFM are given and evaluated for several thin film–substrate pairs. These results also show the potential of the method for modeling defects and power loss due to radiation in layered materials.

Thin film characterization by atomic force microscopy at ultrasonic frequencies

Abstract: We present a technique in which atomic force microscopy at ultrasonic frequencies is used to determine the thickness of thin films. In this technique, the resonance frequency of a flexural mode of an atomic force microscope cantilever is used to determine the tip-sample contact stiffness. This allows the film thickness to be determined, provided that the tip and sample elastic moduli and radii of curvature are known. We report experimental results for thin metal and polymer films deposited on silicon substrates and compare them with the predictions of a theoretical model.

Integration of through-wafer interconnects with a two-dimensional cantilever array

Abstract: High-density through-wafer interconnects are incorporated in a two-dimensional (2D) micromachined cantilever array. The design addresses alignment and density issues associated with 2D arrays. Each cantilever has piezoresistive deflection sensors and high-aspect ratio silicon tips. The fabrication process and array operation are described. The integration of cantilevers, tips, and interconnects enables operation of a high-density 2D scanning probe array over large areas.

Finite element method and normal mode modeling of capacitive micromachined SAW and Lamb wave transducers

Abstract: Surface wave and Lamb wave devices without piezoelectricity are the latest breakthrough applications of the capacitive micromachined ultrasonic transducers (CMUTs). CMUTs were introduced for airborne and immersion applications. However, experiments showed that those devices couple energy not only to the medium but also to the substrate they are built on. By placing the CMUTs on a substrate in an interdigitated configuration, it is possible to couple energy to Lamb wave or Rayleigh wave modes with very high efficiency without a need for any piezoelectric material. In this study, we calculate the acoustic field distribution in a silicon substrate as well as the acoustic impedance of the CMUT membrane, which includes the power coupled to the substrate. We apply the normal mode theory to find the distribution of the acoustic power among different Lamb wave modes. For low frequency (1 MHz) devices, we find that the lowest order antisymmetric (A/sub 0/) mode Lamb wave is the dominant mode in the substrate, and 95% of the power propagates through this mode. For high frequency devices (100 MHz), interdigital CMUTs excite Rayleigh waves with efficiencies comparable to piezoelectric surface acoustic wave (SAW) devices.

A first experimental verification of micromachined capacitive Lamb wave transducers

Abstract: Capacitive Micromachined Ultrasonic Transducers (cMUTs) are generally used to transmit and receive ultrasound in both air and water. These devices can be made on silicon and manufactured using standard CMOS processing techniques. When cMUTs are used in this way, significant effort is made to minimize energy loss into the substrate. If this loss is instead exploited so that the devices are optimized to couple energy into the silicon bulk, Lamb waves and Rayleigh waves are generated with high efficiency. These waves can then be detected using a similar device structure. With this method it is possible to fabricate Lamb wave devices on silicon using conventional integrated circuit processing techniques. This paper discusses the manufacturing and characterization of the first of these devices: a 1 MHz Lamb wave transducer that is fundamentally based on cMUT technology. The characterization of this device demonstrates that the energy coupled into the substrate results in a Lamb Wave where the lowest order anti-symmetric mode (A/sub 0/) is dominant. The insertion loss of this device in air is 43.06 dB.