A survey of nanonewton force calibration techniques suitable for micro-electromechanical systems (MEMS) is presented. The reviewed techniques include: mass-derived force, pendulums, calibrated master springs, resonance and electromagnetic techniques. Considerable background material is provided to support the hypothesis that virtual power methods, such as those employed on the NIST watt balance are applicable to the MEMS force calibration problem. A review of progress at NIST on two prototype nanowatt balances designed for MEMS calibrations is given.

Micromaterial's parameters, such as stiffness constants, critical values and fatigue limits are determined with mechanical tests on microfabricated samples. Single crystal silicon, nickel or nickel-iron alloys are investigated using newly developed testing devices. In the microsample tensile test, force and elongations are measured independently with high accuracy. 10^-5 N is the resolution of the force measurement with a precise balance, Elongations down to 10 nm are resolved by analyzing light optical microscope images of the testing region with the least square template matching algorithm. The stiffness constants obtained from the tensile test are in excellent agreement with the results of the vibration tests. In addition, Q-factor measurements are performed, using a phase-locked loop for precise frequency stabilization. The same technique is applied for fatigue experiments, in which rack growth is measured with a resolution of 15 nm. Using a new apparatus, torsion tests are performed: a microfabricated sensor is used to quantify the applied torque and the twist angle is determined from the reflection of a laser beam, measured with a photodiode. The theoretical analysis presented in this paper concerns two typical problems of microstructure design: the stress concentration at sharp notches in single crystal silicon microstructures and the process induced anisotropy in LIGA structures.

An optical metrology station has been developed for measuring static and dynamic displacements of a forced balance vibration micromachined sensor. The station uses tow fiber optic Fabry-Perot interferometers along with homodyne demodulation for generating real time displacement measurements having nanometer range resolution. The MEMS electro-optical interferometry test station is fully automated through the use of motorized x-y-z linear stages for fiber positioning and through the use of a PC running a LabView software user interface for data acquisition control and signal demodulation. The station has been given extensive graphic capabilities for simplified operation and data interpretation. Although the MEMS optical interferometry test station has been implemented to assist in the characterization of InterScience's wideband accelerometers, the concept of homodyne demodulation can be easily extended for performing metrology in a wide variety of MEMS structures for both, static and dynamic analyses. In this paper we report the design and construction. We also discus its potential for complete automation and the intended operation of the system in a pressure controlled environment. The operation of the system under rough or better vacuum conditions has been considered in the presented design through the use of vacuum compatible components. It is anticipated that vacuum operation will be incorporated in future upgrades of the present station since viscous damping is a factor of critical importance in microscopic vibrating structures.

Resonator structures offer a unique mechanism for characterizing MEMS materials, but measuring the resonant frequency of microstructures is challenging. In this effort a network analyzer system was used to electrically characterize surface-micromachined resonator structures in a carefully controlled pressure and temperature environment.A microscope laser interferometer was used to confirm actual device deflections.Cantilever, comb, and piston resonators fabricated in the DARPA-sponsored MUMPs process were extensively tested. Measured resonator frequency results show reasonable agreement with analytic predictions computed using manufacturer measured film thickness and residual material stress. Alternatively the measured resonant frequency data can be used to extract materials data. Tuning of resonant frequency with DC bias was also investigated. Because the tested devices vary widely in complexity, form a simple cantilever beam to a comb resonator, the data collected is especially well suited for validation testing of MEMS modeling codes.

A stroboscopic phase-shift interferometry is applied to visualize the high-frequency microvibration of a surface acoustic wave (SAW) devices quantitatively. The Fizeau-type interferometry is realized with a multi-mode semiconductor laser diode and an optical isolator. With the laser light illuminating stroboscopically, observed interference intensity gives information about average displacements of the vibrations. Distribution of the 50 MHz SAW propagation along the propagation path has been observed. The measured amplitude of the vibration is 3 nm. Repetition accuracy evaluated with the root mean square method is 1.2500 of the laser wavelength. This method is useful for estimating and improving performances of microdevices.

This paper compares measured to modeled stress-induced curvature of simple piston micromirrors. Two similar flexure-beam micromirror designs were fabricate using the 11th DARPA-supported multi-user MEMS processes (MUMPs) run. The test devices vary only in the MUMPs layers used for fabrication. In one case the mirror plate is the 1.5 micrometers thick Poly2 layer. The other mirror design employs stacked Poly1 and Poly2 layers for a total thickness of 3.5 micrometers . Both mirror structures are covered with the standard MUMPs metallization of approximately 200 angstrom of chromium and 0.5 micrometers of gold. Curvature of these devices was measured to within +/- 5 nm with a computer controlled microscope laser interferometer system. As intended, the increased thickness of the stacked polysilicon layers reduces the mirror curvature by a factor of 4. The two micromirror designs were modeled using IntelliCAD, a commercial CAD system for MEMS. The basis of analysis was the finite element method. Simulated results using MUMPs 11 film parameters showed qualitative agreement with measured data, but obvious quantitative differences. Subsequent remeasurement of the metal stress and use of the new value significantly improved model agreement with the measured data. The paper explores the effect of several film parameters on the modeled structures. Implications for MEMS film metrology, and test structures are considered.

Low scanning speed as well as hysteresis nonlinearities have been fundamental limitations of scanning probe based micro/nano-fabrication techniques. Scanning speeds are typically limited to about 1/10th the fundamental vibrational mode of the piezo-positioning system while hysteresis nonlinearities cause significant errors in large- range positioning applications. This paper presents a method to achieve higher scan rates by using inversion of the piezo-actuator dynamics as well as by compensating for the hysteresis nonlinearities. The approach decouples the inversion into (a) inversion of the hysteresis nonlinearities and (b) inversion of the structural dynamics, to find an input voltage profile that achieves precision tracking of a desired scan trajectory. The results show that an order of magnitude increase in scanning speed is achieved, while maintaining precision tracking of the desired scan path.

In this paper, we report on the recent advances in building an integrated environment for the design and simulation of microsystems based on commercially available CAD tools. The environment allows a continuous design flow from front-end to back-end for both monolithic and hybrid microsystems. Based on the FEM simulation results in a pre-design phase, simulation models of available standard components are developed in a system level and coupled to layout generators. A multi-level, mixed-mode, multi-technology simulation is ensured and a schematic driven layout is generated. Tools for anisotropic etching simulation are integrated in order to predict the etching procedure of full-custom microstructures.

In thick photoresist applications, commercially available acrylic sheets are bonded to a substrate as an alternative to the casting and in-situ polymerization of PMMA. The factors affecting the adhesion of a thick acrylic sheet to different substrates have been studied. In case of copper and titanium substrates and bond-strength can be improved by roughening the surface through chemical oxidation which then provides a mechanical interlocking between the resist and substrate surfaces. Annealing of PMMA sheet before gluing and use of adhesion promoter such as organosilane further improves the bond strength at the resist-substrate interface. The resist adhesion to various substrates is evaluated by measuring the debonded length of the acrylic sheet during a mechanical cleaving test.

The potentials afforded by the incorporation of a commercial proximal probe microscope (PPM) into a high resolution field emission scanning electron microscope (SEM) are substantial for MEMS inspection and metrology. An instrument of this type is currently being tested at the National Institute of Standards and TEchnology. This instrument will be used in the development of NIST traceable standards for dimensional metrology at the nanometer level. The combination of the two microscopic techniques facilitates: high precision probe placement, the capability of measuring and monitoring the probe geometry, monitoring the scanning of the probe across the feature of interest and an ability for comparative microscopy. The integration of the commercial instrument is the first step in the development of a custom NIST integrated SEM/SxM metrology instrument. This paper presents early results regarding the integration of the two instruments and the application of these instruments to the development of SRM 2090 and the prototype SEM sharpness standard.

A low-cost mask fabrication process for deep x-ray lithography is described. The mask consists of Kapton films stretched on a ring with absorber structures formed by optical lithography using NFR015 resist and gold electroplating, similar to the masks from the 'early x-ray lithography age'. Such masks proved easy to fabricate and are presently being evaluated for deep x-ray lithography applications. First experiments indicate that they exhibit sufficient radiation resistance and limited variational dimensional changes during exposure at 1.3-1.5 GeV on the XRLM3 beamline at CAMD.

An entirely new class of micromachined 3D microwave and millimeter-wave integrated circuits and antennas are being developed at the University of Wisconsin-Madison using a subset o the LIGA micromachining process. The deep x-ray lithography and metal plating portions of the LIGA process are used to precisely form tall metal structures on semiconductor and dielectric substrates. This micromachining process allows metal height to be included as a parameter in the design of integrated circuits, which will permit several important advancements in high frequency waveguiding circuits and integrated antennas. With appropriate thick- metal cross-sectional geometry, transmission line losses and dispersion may both be reduced on a given substrate. Vertical-walled metal structures allow increased control over element-to-element coupling for integrated coupled-line filters and couplers and result in very significant reductions in ohmic loss. It will be demonstrated that the first single-level coupled-line 3dB coupler can be fabricated using the LIGA process. In addition, the mechanical properties of the thick metal structures will be utilized in the fabrication of integrated antennas and transmission lines that are unsupported by a dielectric substrate. The elimination of the substrate beneath antennas reduces losses to substrate modes, and the elimination o the substrate beneath transmission line filters is necessary for extremely high Q integrated filters. This paper will present simulated loss results that demonstrate the advantages of thick metal transmission lines, measured results of a coupled-line bandpass filter, and a recently fabricated thick-metal tapered slotline antenna which extends nearly a centimeter off of the edge of a GaAs wafer.

Subject of this investigation is a one-step rapid machining process to create miniaturized 3D parts, using the original sample material. An experimental setup where metal powder is fed to the laser beam-material interaction region has been built. The powder is melted and forms planar, 2D geometries as the substrate is moved under the laser beam in XY- direction. After completing the geometry in the plane, the substrate is displaced in Z-direction, and a new layer of material is placed on top of the just completed deposit. By continuous repetition of this process, 3D parts wee created. In particular, the impact of the focal spot size of the high power laser beam on the smallest achievable structures was investigated. At a translation speed of 51 mm/s a minimum material thickness of 590 micrometers was achieved. Also, it was shown that a small Z-displacement has a negligible influence on the continuity of the material deposition over this power range. A high power CO₂ laser was used as energy source, the material powder under investigation was stainless steel SS304L. Helium was used as shield gas at a flow rate of 15 1/min. The incident CO₂ laser beam power was varied between 300 W and 400 W, with the laser beam intensity distribute in a donut mode. The laser beam was focused to a focal diameter of 600 (Mu) m.

This paper describes experimental results of using various microlithography techniques to fabricate a range of microactuator devices from NiTi shape memory alloys. The range of products includes: planar double-beams form rolled foils etched form both sides; tapered double-beams; planar double beams from sputter-deposited films etched rom one side; a tubular test piece. Such photofabrication in not easily achieved and problems discussed in this paper include: achieving acceptable edge profiles through the thickness of the materials while maintaining high etch factors; tapering foil microactuators by means of chemical micro milling; coating NiTi tubes with electrophoretic photoresist; imaging a curved surface with a small radius of curvature; control of etching parameters for a constant rate of etch; the influence of NiTi oxide coatings on etching and; technical comparisons with other potential manufacturing processes.