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Advances in LIGA-Based Post-Mold Fabrication

Description: The establishment of a process to allow planarization of deep x-ray lithography based microfabncated metal components via diamond lapping has enabled examination of three additional microfabrication issues. The areas of improvement that are discussed include materials, microassembly and packaging, and multilevel fabrication. New materials work has centered on magnetic materials including precision micromagnets and surface treatments of electrodeposited materials. Assembly and packaging has been aided by deep silicon etch processing and the use of conventional precision milling equipment combined with press-tit assembly. Diffhsion bonding is shown to be a particularly important approach to achieving multilevel metal mechanisms and furthermore shows promise for achieving batch assembled and packaged high aspect-ratio metal micromechanics,
Date: October 21, 1998
Creator: Christenson, T.R.
Partner: UNT Libraries Government Documents Department

Parallel Assembly of LIGA Components

Description: In this paper, a prototype robotic workcell for the parallel assembly of LIGA components is described. A Cartesian robot is used to press 386 and 485 micron diameter pins into a LIGA substrate and then place a 3-inch diameter wafer with LIGA gears onto the pins. Upward and downward looking microscopes are used to locate holes in the LIGA substrate, pins to be pressed in the holes, and gears to be placed on the pins. This vision system can locate parts within 3 microns, while the Cartesian manipulator can place the parts within 0.4 microns.
Date: March 4, 1999
Creator: Christenson, T.R. & Feddema, J.T.
Partner: UNT Libraries Government Documents Department

A Batch Wafer Scale LIGA Assembly and Packaging Technique vai Diffusion Bonding

Description: A technique using diffusion bonding (or solid-state welding) has been used to achieve batch fabrication of two- level nickel LIGA structures. Interlayer alignment accuracy of less than 1 micron is achieved using press-fit gauge pins. A mini-scale torsion tester was built to measure the diffusion bond strength of LIGA formed specimens that has shown successful bonding at temperatures of 450"C at 7 ksi pressure with bond strength greater than 100 Mpa. Extensions to this basic process to allow for additional layers and thereby more complex assemblies as well as commensurate packaging are discussed.
Date: January 27, 1999
Creator: Christenson, T.R. & Schmale, D.T.
Partner: UNT Libraries Government Documents Department

Fabrication of MEMS Devices by Powder-Filling into DXRL-Formed Molds

Description: We have developed a variety of processes for fabricating components for micro devices based on deep x-ray lithography (DXRL). Although the techniques are applicable to many materials, we have demonstrated them using hard (Nd{sub 2}Fe{sub 14}B) and soft (Ni-Zn ferrite) magnetic materials because of the importance of these materials in magnetic micro-actuators and other devices and because of the difficulty fabricating them by other means. The simplest technique involves pressing a mixture of magnetic powder and a binder into a DXRL-formed mold. In the second technique, powder is pressed into the mold and then sintered to densify. The other two processes involve pressing at high temperature either powder or a dense bulk material into a ceramic mold that was previously made using a DXRL mold. These techniques allow arbitrary 2-dimensional shapes to be made 10 to 1000 micrometers thick with in-plane dimensions as small as 50 micrometers and dimensional tolerances in the micron range. Bonded isotropic Nd{sub 2}Fe{sub 14}B micromagnets made by these processes had an energy product of 7 MGOe.
Date: January 7, 1999
Creator: Christenson, T.; Garino, T.J. & Venturini, E.
Partner: UNT Libraries Government Documents Department

Deep x-ray lithography based processing for micromechanics

Description: Deep x-ray lithography based fabrication provides a means to fabricate microactuators with useful output forces. High energy x-ray exposure provides a tool for fabrication of the next generation of precision engineered components. Device characterization, materials science, an metrology continue to pose challenges at this scale.
Date: October 1995
Creator: Christenson, T. R.
Partner: UNT Libraries Government Documents Department

Understanding and Tailoring the Mechanical Properties of LIGA Fabricated Materials

Description: LIGA fabricated materials and components exhibit several processing issues affecting their metallurgical and mechanical properties, potentially limiting their usefulness for MEMS applications. For example, LIGA processing by metal electrodeposition is very sensitive to deposition conditions which causes significant processing lot variations of mechanical and metallurgical properties. Furthermore, the process produces a material with a highly textured lenticular rnicrostructural morphology suggesting an anisotropic material response. Understanding and controlling out-of-plane anisotropy is desirable for LIGA components designed for out-of-plane flexures. Previous work by the current authors focused on results from a miniature servo-hydraulic mechanical test frame constructed for characterizing LIGA materials. Those results demonstrated microstructural and mechanical properties dependencies with plating bath current density in LIGA fabricated nickel (LIGA Ni). This presentation builds on that work and fosters a methodology for controlling the properties of LIGA fabricated materials through processing. New results include measurement of mechanical properties of LIGA fabricated copper (LIGA Cu), out-of-plane and localized mechanical property measurements using compression testing and nanoindentation of LIGA Ni and LIGA Cu.
Date: January 25, 1999
Creator: Buchheit, T.E.; Christenson, T.R.; Lavan, D.A. & Schmale, D.T.
Partner: UNT Libraries Government Documents Department

Design and fabrication of a LIGA milliengine

Description: This paper reports on the design and fabrication of a new milliscale magnetic actuator that is ideally suited for LIGA processing. LIGA processing permits the fabrication of millisized machine elements that cannot be fabricated by conventional miniature machining techniques because of their small feature sizes. The Milliengine is a magnetically driven device that utilizes a unique design to extend the 2-dimensional fabrication capability of LIGA to create 3-dimensional machinery.
Date: April 1, 1997
Creator: Garcia, E.J.; Christenson, T.R.; Polosky, M.A. & Jojola, A.A.
Partner: UNT Libraries Government Documents Department

Torsion Testing of Diffusion Bonded LIGA Formed Nickel

Description: A test technique has been devised which is suitable for the testing of the bond strength of batch diffusion bonded LIGA or DXRL defined structures. The method uses a torsion tester constructed with the aid of LIGA fabrication and distributed torsion specimens which also make use of the high aspect ratio nature of DXRL based processing. Measurements reveal achieved bond strengths of 130MPa between electroplated nickel with a bond temperature of 450 C at 7 ksi pressure which is a sufficiently low temperature to avoid mechanical strength degradation.
Date: January 27, 1999
Creator: Buchheit, T.E.; Christenson, T.R. & Schmale, D.T.
Partner: UNT Libraries Government Documents Department

Deep X-Ray Lithography Based Fabrication of Rare-Earth Based Permanent Magnets and their Applications to Microactuators

Description: Precision high aspect-ratio micro molds constructed by deep x-ray lithography have been used to batch fabricate accurately shaped bonded rare-earth based permanent magnets with features as small as 5 microns and thicknesses up to 500 microns. Maximum energy products of up to 8 MGOe have been achieved with a 20%/vol. epoxy bonded melt-spun isotropic Nd2Fe14b powder composite. Using individually processed sub- millimeter permanent sections multipole rotors have been assembled. Despite the fact that these permanent magnet structures are small, their magnetic field producing capability remains the same as at any scale. Combining permanent magnet structures with soft magnetic materials and micro-coils makes possible new and more efficient magnetic microdevices.
Date: January 27, 1999
Creator: Christenson, T.R.; Garino, T.J. & Venturini, E.L.
Partner: UNT Libraries Government Documents Department

Ultra-Precise Assembly of Micro-Electromechanical Systems (MEMS) Components

Description: This report summarizes a three year effort to develop an automated microassembly workcell for the assembly of LIGA (Lithography Galvonoforming Abforming) parts. Over the last several years, Sandia has developed processes for producing surface machined silicon and LIGA parts for use in weapons surety devices. Some of these parts have outside dimensions as small as 100 micron, and most all have submicron tolerances. Parts this small and precise are extremely difficult to assembly by hand. Therefore, in this project, we investigated the technologies required to develop a robotic workcell to assembly these parts. In particular, we concentrated on micro-grippers, visual servoing, micro-assembly planning, and parallel assembly. Three different micro-grippers were tested: a pneumatic probe, a thermally actuated polysilicon tweezer, and a LIGA fabricated tweezer. Visual servoing was used to accuracy position two parts relative to one another. Fourier optics methods were used to generate synthetic microscope images from CAD drawings. These synthetic images are used off-line to test image processing routines under varying magnifications and depths of field. They also provide reference image features which are used to visually servo the part to the desired position. We also investigated a new aspect of fine motion planning for the micro-domain. As parts approach 1-10 {micro}m or less in outside dimensions, interactive forces such as van der Waals and electrostatic forces become major factors which greatly change the assembly sequence and path plans. We developed the mathematics required to determine the goal regions for pick up, holding, and release of a micro-sphere being handled by a rectangular tool. Finally, we implemented and tested the ability to assemble an array of LIGA parts attached to two 3 inch diameter wafers. In this way, hundreds of parts can be assembled in parallel rather than assembling each part individually.
Date: April 1, 1999
Creator: Feddema, J.T.; Simon, R.; Polosky, M. & Christenson, T.
Partner: UNT Libraries Government Documents Department

Mechanical and metallographic characterization of LIGA fabricated nickel and 80%Ni-20%Fe Permalloy

Description: A table top servohydraulic load frame equipped with a laser displacement measurement system was constructed for the mechanical characterization of LIGA fabricated electroforms. A drop in tensile specimen geometry which includes a pattern to identify gauge length via laser scanning has proven to provide a convenient means to monitor and characterize mechanical property variations arising during processing. In addition to tensile properties, hardness and metallurgical data were obtained for nickel deposit specimens of current density varying between 20 and 80 mA/cm{sup 2} from a sulfamate based bath. Data from 80/20 nickel-iron deposits is also presented for comparison. As expected, substantial mechanical property differences from bulk metal properties are observed as well as a dependence of material strength on current density which is supported by grain size variation. While elastic modulus values of the nickel electrodeposit are near 160 GPa, yield stress values vary by over 60%. A strong orientation in the metal electrodeposits as well as variations in nucleating and growth morphology present a concern for anisotropic and geometry dependent mechanical properties within and between different LIGA components.
Date: April 13, 1998
Creator: Christenson, T. R.; Buchheit, T. E.; Schmale, D. T. & Bourcier, R. J.
Partner: UNT Libraries Government Documents Department

Micro-grippers for assembly of LIGA parts

Description: This paper describes ongoing testing of two microgrippers for assembly of LIGA (Lithographie Galvanoformung Abformung) parts. The goal is to place 100 micron outside diameter (OD) LIGA gears with a 50 micron inner diameter hole onto pins ranging from 35 to 49 microns. The first micro gripper is a vacuum gripper made of a 100 micron OD stainless steel tube. The second micro gripper is a set of tweezers fabricated using the LIGA process. Nickel, Permalloy, and copper materials are tested. The tweezers are actuated by a collet mechanism which is closed by a DC linear motor.
Date: December 31, 1997
Creator: Feddema, J.; Polosky, M.; Christenson, T.; Spletzer, B. & Simon, R.
Partner: UNT Libraries Government Documents Department

Optical measurement of LIGA milliengine performance

Description: Understanding the parameters that affect the performance of milliscale and microscale actuators is essential to the development of optimized designs and fabrication processes, as well as the qualification of devices for commercial applications. This paper discusses the development of optical techniques for motion measurements of LIGA fabricated milliengines. LIGA processing permits the fabrication of precision millimeter-sized machine elements that cannot be fabricated by conventional miniature machining techniques because of their small feature sizes. In addition, tolerances of 1 part in 10{sup 3} to 10{sup 4} may be maintained in millimeter sized components with this processing technique. Optical techniques offer a convenient means for measuring long term statistical performance data and transient responses needed to optimize designs and manufacturing techniques. Optical techniques can also be used to provide feedback signals needed for control and sensing of the state of the machine. Optical probe concepts and experimental data obtained using a milliengine developed at Sandia National Laboratories are presented.
Date: December 31, 1997
Creator: Dickey, F.M.; Holswade, S.C.; Christenson, T.R.; Garcia, E.J. & Polosky, M.A.
Partner: UNT Libraries Government Documents Department

Silicon microfabrication technologies for nano-satellite applications

Description: Silicon (Si) has a strength to density ratio of 3.0({sigma}{sub y}/{delta}=(6.8GPa/2.3g/cc)), an order-of-magnitude higher than titanium, aluminum, or stainless steel. Silicon also demonstrates favorable thermal, optical, and electrical properties making it ideal for use as a structural foundation for autonomous, mesoscopic systems such as nanosatellites. Using Si substrates, a structure that can simultaneously act as a thermal management system, a radiation shield, an optical material, a package, and a semiconductor substrate can be realized.
Date: December 9, 1999
Creator: Shul, R.J.; Kravitz, S.H.; Christenson, T.R.; Willison, C.L. & Zipperian, T.E.
Partner: UNT Libraries Government Documents Department

Deep x-ray lithography for micromechanics

Description: Extensions of the German LIGA process have brought about fabrication capability suitable for cost effective production of precision engineered components. The process attributes allow fabrication of mechanical components which are not capable of being made via conventional subtractive machining methods. Two process improvements have been responsible for this extended capability which involve the areas of thick photoresist application and planarization via precision lapping. Application of low-stress x-ray photoresist has been achieved using room temperature solvent bonding of a preformed photoresist sheet. Precision diamond lapping and polishing has provided a flexible process for the planarization of a wide variety of electroplated metals in the presence of photoresist. Exposure results from the 2.5 GeV National Synchrotron Light Source storage ring at Brookhaven National Laboratory have shown that structural heights of several millimeter and above are possible. The process capabilities are also well suited for microactuator fabrication. Linear and rotational magnetic microactuators have been constructed which use coil winding technology with LIGA fabricated coil forms. Actuator output forces of 1 milliNewton have been obtained with power dissipation on the order of milliWatts. A rotational microdynamometer system which is capable of measuring torque-speed data is also discussed.
Date: August 1995
Creator: Christenson, T. R. & Guckel, H.
Partner: UNT Libraries Government Documents Department

Control of thin film processing behavior through precursor structural modifications

Description: In the sol-gel processing of ceramic thin films it has been frequently noted that the processing behavior, microstructure and properties of the films are dependent on the nature of the coating solution. In an attempt to understand such thin film processing-property relationships, the authors have systematically investigated the effects of varying the precursor nature on thin film densification and crystallization for ZrO{sub 2} and TiO{sub 2} films. Metal alkoxide starting compounds, e.g., zirconium n-butoxide{center_dot}n-butanol and titanium i-propoxide, were reacted with acetic acid and 2,4-pentanedione to prepare coating solutions for thin film deposition. The use of these chelating ligands resulted in solution oligomeric species of different nature. Studies of thin film processing indicated that film processing characteristics, i.e., consolidation, densification and crystallization, were strongly dependent on solution precursor nature. Ligand steric size, pyrolysis behavior, extent of chelation, and precursor reactivity were found to be key variables in controlling film processing characteristics.
Date: February 1, 1995
Creator: Schwartz, R. W.; Voigt, J. A.; Boyle, T. J.; Christenson, T. A. & Buchheit, C. D.
Partner: UNT Libraries Government Documents Department

High G MEMS integrated accelerometer

Description: This paper describes the design and implementation of a surface micromachined accelerometer for measuring very high levels of acceleration (up to 50,000 G). Both the mechanical and electronic portions of the sensor were integrated on a single substrate using a process developed at Sandia National Laboratories. In this process, the mechanical components of the sensor were first fabricated at the bottom of a trench etched into the water substrate. The trench was then filled with oxide and sealed to protect the mechanical components during subsequent microelectronics processing. The wafer surface was then planarized in preparation for CMOS processing using Chemical Mechanical Polishing (CMP). Next, the CMOS electronics were fabricated on areas of the wafer adjacent to the embedded structures. Finally, the mechanical structures were released and the sensor tested. The mechanical structure of the sensor consisted of two polysilicon plate masses suspended by multiple springs (cantilevered beam structures) over corresponding polysilicon plates fixed to the substrate to form two parallel plate capacitors. The first polysilicon plate mass was suspended using compliant springs (cantilever beams) and acted as a variable capacitor during sensor acceleration. The second polysilicon plate mass was suspended using very stiff springs and acted as a fixed capacitor during acceleration. Acceleration was measured by comparing the capacitance of the variable capacitor (compliant suspension) with the fixed capacitance (stiff suspension).
Date: December 31, 1996
Creator: Davies, B.R.; Barron, C.C.; Montague, S.; Smith, J.H.; Murray, J.R.; Christenson, T.R. et al.
Partner: UNT Libraries Government Documents Department

Microstructure of bulk and electro-formed Ni implanted with Ti and C

Description: The microstructure of high-purity Ni implanted with overlapping concentration profiles of Ti and C was examined with transmission electron microscopy. An amorphous phase forms at concentrations of 15--18 at.% Ti and 22 at.% C, while a two-phase alloy (amorphous + fcc Ni) forms for {le} 16 at.% C. Electroformed layers with sub-micron fcc grains of Ni or Ni{sub 80}Fe{sub 20} were also found to be amorphized by Ti + C implantation, a key requirement for applying this treatment to Ni-based micro-electromechanical systems to reduce their friction and wear.
Date: October 13, 1997
Creator: Follstaedt, D.M.; Myers, S.M.; Knapp, J.A.; Dugger, M.T. & Christenson, T.A.
Partner: UNT Libraries Government Documents Department

Strength and tribology of bulk and electroformed nickel amorphized by implantation of titanium and carbon

Description: Dual ion implantation of titanium and carbon was shown to produce an amorphous layer of exceptional strength within annealed bulk Ni and electroformed Ni and Ni{sub 80}Fe{sub 20} materials used in micro-electromechanical systems. The intrinsic elastic and plastic mechanical properties of the implanted region were quantified using nanoindentation testing in conjunction with finite-element modeling, and the results were interpreted in the light of microstructures observed by electron microscopy. The implantation treatment was found to produce substantial reductions in unlubricated friction and wear.
Date: October 1, 1997
Creator: Myers, S.M.; Knapp, J.A.; Follstaedt, D.M.; Dugger, M.T. & Christenson, T.R.
Partner: UNT Libraries Government Documents Department

Performance of Ultra Hard Carbon Wear Coatings on Microgears Fabricated by Liga

Description: Stiction and friction are of concern for the reliable, long-term application of Ni-alloy micromachines. We have found that the application of a 30-70 nm hard carbon coating produces a significant reduction in the friction coefficient and wear rate of electroformed Ni substrates in reciprocating sliding contact under simulated MEMS operating conditions. To evaluate the performance of coated components, a series of 70-pm-thick microgears ranging in diameter from 0.2 to 2.2 mm were fabricated from electroformed Ni via standard LIGA processes and fixtured on posts in preparation for the coating procedure. A pulsed vacuum- arc deposition process was used to deposit a carbon coating on the gears with the plasma incident at a shallow angle to the gears' top surface. A sample bias of -2 keV was used in order to produce a coating with relatively low stress and good adhesion while maintaining high hardness. This coating process is known to be somewhat comformal to the component surfaces. The coating uniformity, particularly in the high-aspect-ratio areas between the gear teeth, was evaluated with micro-Raman spectroscopy. It is shown that the coating can be applied uniformly on the top gear surface. Between the gear teeth the coating was the same thickness as on top of the gear down to a point 50 ~m below the top surface. Below that point (i.e. between 50 and 70 Lm), the coating thickness is somewhat thinner, but is still present. These results demonstrate that it is possible to a deposit hard carbon coating on microgears to reduce friction and wear in micromachines.
Date: December 18, 1998
Creator: Ager III, J.W.; Brown, I.G.; Christenson, T.R.; Dugger, M.T.; Follstaedt, D.M.; Knapp, J.A. et al.
Partner: UNT Libraries Government Documents Department

Energetic Particle Synthesis of Metastable Layers for Superior Mechanical Properties

Description: Energetic particle methods have been used to synthesize two metastable layers with superior mechanical properties: amorphous Ni implanted with overlapping Ti and C, and amorphous diamond-like carbon (DLC) formed by vacuum-arc deposition or pulsed laser deposition. Elastic modulus, yield stress and hardness were reliably determined for both materials by fitting finite-element simulations to the observed layer/substrate responses during nanoindentation. Both materials show exceptional properties, i.e., the yield stress of amorphous Ni(Ti,C) exceeds that of hardened steels and other metallic glasses, and the hardness of DLC (up to 88 GPa) approaches that of crystalline diamond (approx. 100 GPa). Tribological performance of the layers during unlubricated sliding contact appears favorable for treating Ni-based micro-electromechanical systems: stick-slip adhesion to Ni is eliminated, giving a low coefficient of friction (approx. 0.3-0.2) and greatly reduced wear. We discuss how energetic particle synthesis is critical to forming these phases and manipulating their properties for optimum performance.
Date: January 1, 1998
Creator: Follstaedt, D.M.; Knapp, J.A.; Myers, S.M.; Dugger, M.T.; Friedmann, T.A.; Sullivan, J.P. et al.
Partner: UNT Libraries Government Documents Department

High-G accelerometer for earth-penetrator weapons applications. LDRD final report

Description: Micromachining technologies, or Micro-Electro-Mechanical Systems (MEMS), enable the develop of low-cost devices capable of sensing motion in a reliable and accurate manner. Sandia has developed a MEMS fabrication process for integrating both the micromechanical structures and microelectronics circuitry of surface micromachined sensors, such as silicon accelerometers, on the same chip. Integration of the micromechanical sensor elements with microelectronics provides substantial performance and reliability advantages for MEMS accelerometers. A design team at Sandia was assembled to develop a micromachined silicon accelerometer capable of surviving and measuring very high accelerations (up to 50,000 times the acceleration due to gravity). The Sandia integrated surface micromachining process was selected for fabrication of the sensor due to the extreme measurement sensitivity potential associated with integrated microelectronics. Very fine measurement sensitivity was required due to the very small accelerometer proof mass (< 200 {times} 10{sup {minus}9} gram) obtainable with this surface micromachining process. The small proof mass corresponded to small sensor deflections which required very sensitive electronics to enable accurate acceleration measurement over a range of 1,000 to 50,000 times the acceleration due to gravity. Several prototype sensors, based on a suspended plate mass configuration, were developed and the details of the design, modeling, fabrication and validation of the device will be presented in this paper. The device was analyzed using both conventional lumped parameter modeling techniques and finite element analysis tools. The device was tested and performed well over its design range (the device was tested over a range of a few thousand G to 46,000 G, where 1 G equals the acceleration due to gravity).
Date: March 1, 1998
Creator: Davies, B.R.; Montague, S.; Bateman, V.I.; Brown, F.A.; Chanchani, R.; Christenson, T. et al.
Partner: UNT Libraries Government Documents Department

Design and testing of planar magnetic micromotors fabricated by deep x-ray lithography and electroplating

Description: The successful design and testing of a three-phase planar integrated magnetic micromotor is presented. Fabrication is based on a modified deep X-ray lithography and electroplating or LIGA process. Maximum rotational speeds of 33,000 rpm are obtained in air with a rotor diameter of 285 {mu}m and do not change when operated in vacuum. Real time rotor response is obtained with an integrated shaft encoder. Long lifetime is evidenced by testing to over 5(10){sup 7} ration cycles without changes in performance. Projected speeds of the present motor configuration are in the vicinity of 100 krpm and are limited by torque ripple. Higher speeds, which are attractive for sensor applications. require constant torque characteristic excitation as is evidenced by ultracentrifuge and gyroscope design. Further understanding of electroplated magnetic material properties will drive these performance improvements.
Date: May 1, 1993
Creator: Guckel, H.; Christenson, T. R.; Skrobis, K. J.; Klein, J. & Karnowsky, M.
Partner: UNT Libraries Government Documents Department