VM-TEST: Mechanical property measurement using electrostatically actuated vertical MEMS test structures fabricated in thick metal layers

An efficient method is presented to determine the mechanical properties of thick metal layers using the pull-in voltage of electrostatically actuated structures. To fabricate these high aspect ratio beams without severe deformations, additional features were added, which made existing pull-in voltage equations inaccurate and therefore corrections were necessary. ANSYS Multiphysics was used to analyze the differences between ideal beams and the fabricated beams. To demonstrate the proposed approach, both nickel and gold devices were fabricated. To extract the material property values, a sum of least squares fitting scheme was used. A Young’s modulus of 186.2 and 60.8 GPa was obtained for nickel and gold structures respectively. Both values are significantly smaller than values reported for bulk material, but fall within the range of values reported in the literature.     

Deep sub micron high aspect ratio polymer structures produced by hard X-ray lithography

Microfabrication using X-ray lithography is a well established process in many laboratories worldwide. Radiation spectra, mask technology and process conditions are optimized for patterning resist thicknesses of several hundred micrometers with lateral dimensions of a few microns. This article provides first results as to how far these technologies can be extended to form structures with sub-micrometer lateral dimensions in resist layers of a few micrometers thickness. Available equipment and processes of the 2.5 GeV electron storage ring ANKA and the process technology of the Institut für Mikrostrukturtechnik (IMT) in Karlsruhe, Germany, have been applied. An X-ray mask with a 2.7 m Ti-membrane and 20 m thick Au-absorbers is used to expose 1.6 m PMMA resist on silicon wafers. As the smallest features on the mask are 2 m, a double exposure with an intermediate deliberate relative movement between mask and resist generated sub-micron resist test structures. Smallest feature sizes are between 300 and 400 nm. They are not yet limited by diffraction, but by different process conditions that lead to adhesion loss, resist cracking and surface rounding. It has been shown that an intermediate layer of 1.2 m thick polyimide between resist and substrate significantly enhances adhesion and reduces resist cracking. Reducing the beam power impinging onto the sample from typically 21 to 0.4 W leads to a 50% reduction of the surface rounding at the top of the microstructures. To demonstrate the capability to pattern thicker resist layers, first samples with an increased resist thickness of 4.1 m and an aspect ratio of up to 8 were processed. Finally, a metal mesh with 2 m thick Au-absorbers and 900 nm hexagonal holes was applied to pattern showpieces of sub micron features using a reduced electron energy of 1.3 GeV.The high resolution metal mesh was provided by R. Fettig of IMT.     

Fabrication and preliminary testing of X-ray lenses in thick SU-8 resist layers

Deep X-ray lithography processing of SU-8 negative resist layers with thicknesses of up to 1 mm and physical-chemical properties of SU-8 polymer structures were investigated to find the optimum conditions for the fabrication of X-ray refractive lenses. The exposure was carried out at the ANKA storage ring in Karlsuhe, Germany. Experimental tests of the lenses were performed at the ESRF in Grenoble, France. First lenses showed a gain in the range of 20, a full width at half maximum of the focal spot intensity of approximately 2 m to 3 m and unique radiation stability of the optical characteristics.     

Boundary-integral equation method for elastodynamic scattering by a compact inhomogeneity

The set of singular integral equations which relates unknown fields on the surface of the scatterer to a time-harmonic incident wave is solved by the boundary element method. The general method of solution is discussed in some detail for scattering by an inclusion. Results are presented for a spherical cavity, and for a soft and a stiff spherical inclusion. Fields on the surface of the scatterer are compared with previous results obtained by different methods. Back-scattered and forward-scattered displacement fields are presented, both as a function of position at fixed frequency, and as a function of frequency at fixed position. The quasi-static approximation is briefly discussed.     

Sizing of disbonds at a thin-layer substrate interface from spectral peaks

An ultrasonic through transmission technique is used to inspect the interface of a thin layer and a substrate. An experiment is performed using a specimen constructed of a 0.040 inch (1.02 mm) polycarbonate layer bonded by an adhesive film to an aluminum plate. Circular flaws are induced with paper placed between the adhesive film and the polycarbonate layer to create disbonds. The flaws range in size from 0.5 inches (12.7 mm) to 0.067 inches (1.70 mm) in diameter. A through transmission ultrasonic inspection technique, which uses a flat transducer as a transmitter and a focused transducer as a receiver, is employed. Time signals from the receiving transducer are recorded for each flaw, transformed to the frequency domain by use of a fast Fourier transform (FFT), and are linearly deconvolved with the FFT of the time signals of the aluminum plate alone. The peaks of the resulting frequency response functions for each flaw predict the resonant frequencies of the flaws. The area of the thin layer above a disbond is modeled as a thin plate which is excited by the incident ultrasonic wave motion at its edges. The resonance peaks at the center of the plate are related to the size of the flaw. The principal result of the paper is that, based on the theory presented here, the size of the disbond can be obtained from measurements of the resonance peaks.     

A simple scheme for self-focusing of an array

A self-focusing technique and its application to a linear array system are presented in this paper. By application of the technique the system is capable of both sonification and reception focusing. The array is first excited as an unfocused array. Next a cross-correlation technique is used to determine time delays of reception of the largest amplitude backscattered signals at the elements of the array. The original transducer signal is then reemitted with the appropriate time delays to achieve sonification focusing on the scatterer producing the largest signal. This process is repeated in an iterative mode to focus energy on the strongest scatterer. Once insonification focusing has been achieved the last time-delay calculations are used once more for reception focusing, i.e., to correct the signals received by the individual elements for differences in arrival times. A low cost linear array has been constructed to implement the self-focusing technique. Examples demonstrate the capability of the technique to focus on the largest hole of sets of three holes in an aluminum specimen.     

Effects of near-tip inhomogeneities on scattering of ultrasonic waves by cracks

The efficacy of ultrasonic methods to detect and characterize a crack depends on topographical features of the crack faces, the presence of inhomogeneities in the crack's environment, and the mechanical properties in the near-crack region. In this paper, the effects on the scattered ultrasonic field of various features of fatigue and stress corrosion cracks such as partial crack closure, the presence of microcracks and microvoids, and near-tip zones of different mechanical properties have been investigated. A representation integral for the scattered field has been used to formulate the ultrasonic scattering problem. Numerical results have been obtained for some canonical configurations. For the configurations examined in this paper, crack closure has the most significant effect on far-field scattering.     

Numerical analysis of the acoustic signature of a surface-breaking crack

The boundary element method is used to calculate the acoustic signature, produced by a line focus scanning acoustic microscope, of an elastic object containing a surface-breaking crack. The acoustic signature has a vertical (z) and horizontal (x) dependence. A model of the microscope developed earlier is used and extended to take account of the crack. The mathematical formulation of the scattering problem for the cracked object leads to hypersingular integral equations. A suitable technique is employed to solve such equations by the boundary element method. An electromechanical reciprocity identity is used to relate the received voltage to the acoustic wavefields collected by the lens. The acoustic wavefield scattered from the cracked object is investigated, and curves are presented that display the acoustic signature, as functions of (x ,z), for cracks of various depths and orientations. A method to measure the depth of a surface-breaking crack using the acoustic signature is suggested.     

The teacher version of the Child Behavior Profile: I. Boys aged 6–11.

Reports the development and standardization of the teacher version of the Child Behavior Profile for boys aged 6–11 yrs. The teacher profile is scored from the Teacher's Report Form (TRF). Factor analysis of TRFs completed on 450 clinically referred boys yielded 8 behavior problem syndromes: anxious, social withdrawal, unpopular, self-destructive, obsessive-compulsive, inattentive, nervous-overactive, and aggressive. Norms were constructed from a sample of 300 randomly selected nonreferred boys. Compared to normal Ss, disturbed Ss scored significantly higher on all behavior problem scales and significantly lower on teacher-reported school performance and adaptive functioning. One-week test–retest reliability averaged .89 for the behavior problem scales, whereas 2- and 4-mo stability averaged .77 and .64, respectively. Computer- and hand-scored versions of the new teacher profile are described. (24 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)