Key Engineering Materials Vols. 295-296

Abstract: This paper presents a high precision AFM for nanometrology of large area micro-structured surfaces. A PZT with a stroke of 100 microns is used as the Z-directional actuator for the AFM cantilever. Two capacitance-type displacement probes are aligned at two sides of the PZT along the movement direction. The displacement as well as the tilt motion of the PZT can be accurately measured and compensated for based on the probe outputs. It was confirmed that the tilt motion of the PZT was approximately 32 arcseconds over the 100 micron stroke. The sample is moved by two linear stages for scanning in the X- and Y-directions over an area of 50 mm x 40 mm. The angular error motions of the stages that influence the AFM accuracy are measured by an autocollimator for compensation. A piezo-resistive cantilever, which can output the atomic force signal by itself, was employed instead of the conventional optical force sensing device for compactness of the AFM structure. A large area sinusoidal metrology surface has been successfully measured by the developed high-precision AFM.

Abstract: The primary purpose of this research is to adopt a commercially available DVD pickup head and modify it to become a high-speed scanning nano-measurement probe. With the principle of astigmatism the probe can execute the autofocusing motion by an imbedded voice coil motor (VCM) following the height change of the tested object in the vertical Z-direction. Given high precision triangular current signal with appropriate frequency to the input ports of tracking, the same VCM can be moved along the lateral X-direction for profile scanning. Firstly this paper presents the structure of DVD pickup head, the theory of autofocusing and auto scanning, and the developed controller. Then experimental setups and accuracy calibration will be introduced. In order to achieve a bi-directional precision measurement in autofocusing and scanning, this study has developed a hysteresis error compensation scheme by a DSP-32 integrated system. In association with a high precision linear stage in Y-direction, this high precision micro/nano optical probe can measure the 3D profile of the miniature object successfully at fast speed.

Abstract: This investigation presents a fibre-optic Fabry-Perot interferometer as a displacement sensor in an atomic force microsope (AFM). A simple model of light wave transmission between two fibres with the same core diameter is proposed to determine the theoretical equation of light intensity of interference fringes from the fibre-optic Fabry-Perot interferometer. By replacing an AFM cantilever with a movable reflective mirror, the variations of relative light intensity of the interference fringes with the spacing between the fibre and the mirror were recorded. The theoretical equation for the light intensity of interference fringes was close to those obtained experimentally. Finally, a fibre-optic Fabry-Perot interferometer was operated in an AFM to image a two-dimensional phase array with a pitch of 4 µm and a depth of 150 nm.

Abstract: Mechanical properties of DNA, for example the elastic modulus, are of vital importance for its biological function. Previously, the modulus is mainly obtained by bending, stretching and twisting DNA using various techniques and tools. By applying vibrating mode scanning polarization force microscopy (VPSFM), deformations of DNA under ultra-small indentation forces can be measured and so the radial modulus can be computed. In this paper, modeling of the VPSFM measuring system is presented. The system is modeled as a spring-mass-damper oscillator under various force fields, such as van der Waals force, attractive electrical force and repulsive interactions between the tip and sample. The electrical polarization force is described by using uniformly charged line model and the DNA is considered to be a simple elastic rod. By numerically integrating the equation of tip motion, the contact force and the radial modulus of DNA under different deformation can be calculated. We found that in measuring radial modulus of DNA, the existence of substrate cannot be neglected, especially when the relative large deformation is reached.

Abstract: A prototype all-coil electromagnetic force balance has been designed and built. This measurement system compares the mechanical force to an SI realization of electromagnetic force, which is driven from interaction of currents in radial coil set and levitation coil. The preliminary measurement results demonstrate that the magnetic field distribution and magnetic force output are consistent with the results by simulation.

Abstract: The design of mechanical structures depends upon characterizing the stress/strain state in these devices under the combined influence of both loading and residual stresses. The performance of the dynamic structures is strongly influenced by residual stresses. Understanding of the behavior of gyroscopes in presence of residual stresses and ability to relieve the stresses are essential for improving the performance. In this paper, we briefly analyze the cause of residual stresses. The effect of residual stresses on natural frequencies of the drive mode and sense mode is theoretically analyzed. The FE model of the z-axis gyroscope is built to investigate the relation between the frequencies and the residual stress by model analysis. Methods for residual stress relief are presented. The results of the simulation demonstrate that the performance of the gyroscopes with serpentine beams and stress relief slots can be improved significantly.

Abstract: A precision 6-degree-of-freedom measurement system has been developed for simultaneous on-line measurements of imprint lithography stage. To successfully accomplish nanometer-scale pattern transfer from mold to resist film on the wafer, two types of positioning methods, static and dynamic, are used in this system. Two laser interferometers, two optical reflection mirrors and special structure on the stage with 3 elastic tracks are employed in this system to detect the positions and rotations of the stage. Through an algorithm, measurements of pitch, yaw and roll motions can be achieved. This system can realize on-line position detecting. Based on adjusting of PZTs, the detecting precision can reach 10nm and ±3 milli-arcsec, respectively. The measuring range can reach 100mm and ±10 arcsec, respectively.

Abstract: The principle of operation of double-ended resonant tuning forks (DETF) is described in this paper. A new kind of DETF used in the resonant gyroscope is proposed. Considering the feasibility of fabrication, the dimensions are optimized. The variation of the natural frequency against the force applied to one end of the DETF is discussed. The relation between the driving modal frequency of resonant gyroscope and the driving modal frequency of DETF is analyzed.

Abstract: Long range scanning stages with very small positioning errors are the key elements in the nano-CMM that is used to determine the sizes and coordinates of micromachines and parts in three dimensions to realize MEMS/nano technology. A transmission stage needs six degree-of-freedom precision motion controls. A compact critical angle sensor (CAS) can be mounted on the base or frame to be used to monitor the orientation parameters of the scanning/transmission stage along the 3 axes and feedback the error signal of the sensor output to maintain the stage moving performance. By calibration with an autocollimator, the resolution is better than 0.1 arcsec with a measurement range above 600 arcsec.