Microrobots for wafer scale microfactory: design fabrication integration and control.

Future assembly technologies will involve higher automation levels, in order to satisfy increased micro scale or nano scale precision requirements. Traditionally, assembly using a top-down robotic approach has been well-studied and applied to micro-electronics and MEMS industries, but less so in nanotechnology. With the bloom of nanotechnology ever since the 1990s, newly designed products with new materials, coatings and nanoparticles are gradually entering everyone’s life, while the industry has grown into a billion-dollar volume worldwide. Traditionally, nanotechnology products are assembled using bottom-up methods, such as self-assembly, rather than with top-down robotic assembly. This is due to considerations of volume handling of large quantities of components, and the high cost associated to top-down manipulation with the required precision. However, the bottom-up manufacturing methods have certain limitations, such as components need to have pre-define shapes and surface coatings, and the number of assembly components is limited to very few. For example, in the case of self-assembly of nano-cubes with origami design, post-assembly manipulation of cubes in large quantities and cost-efficiency is still challenging. In this thesis, we envision a new paradigm for nano scale assembly, realized with the help of a wafer-scale microfactory containing large numbers of MEMS microrobots. These robots will work together to enhance the throughput of the factory, while their cost will be reduced when compared to conventional nano positioners. To fulfill the microfactory vision, numerous challenges related to design, power, control and nanoscale task completion by these microrobots must be overcome. In this work, we study three types of microrobots for the microfactory: a world’s first laser-driven micrometer-size locomotor called ChevBot，a stationary millimeter-size robotic arm, called Solid Articulated Four Axes Microrobot (sAFAM), and a light-powered centimeter-size crawler microrobot called SolarPede. The ChevBot can perform autonomous navigation and positioning on a dry surface with the guidance of a laser beam. The sAFAM has been designed to perform nano positioning in four degrees of freedom, and nanoscale tasks such as indentation, and manipulation. And the SolarPede serves as a mobile workspace or transporter in the microfactory environment

A reconfigurable tactile display based on polymer MEMS technology

This research focuses on the development of polymer microfabrication technologies for the realization of two major components of a pneumatic tactile display: a microactuator array and a complementary microvalve (control) array. The concept, fabrication, and characterization of a kinematically-stabilized polymeric microbubble actuator (¡°endoskeletal microbubble actuator¡±) were presented. A systematic design and modeling procedure was carried out to generate an optimized geometry of the corrugated diaphragm to satisfy membrane deflection, force, and stability requirements set forth by the tactile display goals. A refreshable Braille cell as a tactile display prototype has been developed based on a 2x3 endoskeletal microbubble array and an array of commercial valves. The prototype can provide both a static display (which meets the displacement and force requirement of a Braille display) and vibratory tactile sensations. Along with the above capabilities, the device was designed to meet the criteria of lightness and compactness to permit portable operation. The design is scalable with respect to the number of tactile actuators while still being simple to fabricate. In order to further reduce the size and cost of the tactile display, a microvalve array can be integrated into the tactile display system to control the pneumatic fluid that actuates the microbubble actuator. A piezoelectrically-driven and hydraulically-amplified polymer microvalve has been designed, fabricated, and tested. An incompressible elastomer was used as a solid hydraulic medium to convert the small axial displacement of a piezoelectric actuator into a large valve head stroke while maintaining a large blocking force. The function of the microvalve as an on-off switch for a pneumatic microbubble tactile actuator was demonstrated. To further reduce the cost of the microvalve, a laterally-stacked multilayer PZT actuator has been fabricated using diced PZT multilayer, high aspect ratio SU-8 photolithography, and molding of electrically conductive polymer composite electrodes.Ph.D.Committee Chair: Allen,Mark; Committee Member: Bucknall,David; Committee Member: Book,Wayne; Committee Member: Griffin,Anselm; Committee Member: Yao,Donggan

Advanced Segmented Silicon Space Telescope (ASSiST)

We propose thin silicon wafers as the building blocks of highly segmented space telescope primary mirrors. Using embedded MEMS actuators operating at high bandwidth control, this technology can achieve diffraction-limited image quality in the 3-300 micron wavelength range. The use of silicon wafers as cryogenic mirror segments is carried forward considering a point design of a future FAIR-class NASA ORIGINS mission. We recognize four major economic factors that justify a massive paradigm shift in the fabrication of ultralightweight space telescopes: The precise process control and repeatability of silicon wafer manufacturing dramatically reduces the huge labor investment in mirror figuring experienced with Hubble Space Telescope. Once developed, the incremental cost of additional space telescopes based upon proven silicon manufacturing techniques can be very small. We estimate the marginal cost of a 30m mirror when deploying a constellation can be as low as 36 million (Year 2002 dollars). Federal R&D funding in the area of microelectromechanical devices and advanced 3-D silicon processing is certain to have far greater economic return than similar investments in other technologies, such as optical membrane technology. The 300B per year silicon processing industry will continue to drive increased MEMS functionality, higher product yields, and lower cost. These advances will continue for decades. The intention here is to present the case for the economic advantage of silicon as a highly functional optical substrate that can be fabricated using unparalleled industry experience with precision process control. We maintain that many architectures superior to the ASSiST concept presented here are possible, and hope that this effort prompts future thinking of the silicon wafer telescope paradigm

Silicon and Polymer Components for Microrobots

This dissertation presents the characterization and implementation of the first microfabrication process to incorporate high aspect ratio compliant polymer structures in-plane with traditional silicon microelectromechanical systems (MEMS). This discussion begins with in situ mechanical characterization of microscale polymer springs using silicon-on-insulator-MEMS (SOI-MEMS). The analysis compares microscale samples that were tested on-chip with macroscale samples tested using a dynamic mechanical analyzer. The results describe the effect of the processing steps on the polymer during fabrication and help to guide the design of mechanisms using polymers. Characterization of the dielectric breakdown of polymer thin films with thicknesses from 2 to 14 μm between silicon electrodes was also performed. The results demonstrate that there is a strong dependence of the breakdown field on both the electrode gap and shape. The breakdown fields ranged from 250 V/μm to 635 V/μm, depending on the electrode geometry and gap, approaching 10x the breakdown fields for air gaps of the same size. These materials were then used to create compliant all-polymer thermal and electrostatic microactuators. All-polymer thermal actuators demonstrated displacements as large at 100 μm and forces as high as 55 μN. A 1 mm long electrostatic dielectric elastomer actuator demonstrated a tip displacement as high as 350 μm at 1.1 kV with a electrical power consumption of 11μW. The actuators are fabricated with elastomeric materials, so they are very robust and can undergo large strains in both tension and bending and still operate once released. Finally, the compliant polymer and silicon actuators were combined in an actuated bio-inspired system. Small insects and other animals use a multitude of materials to realize specific functions, including locomotion. By incorporating compliant elastomer structures in-plane with traditional silicon actuators, compact energy storage systems based on elastomer springs for small jumping robots were demonstrated. Results include a 4 mm x 4 mm jumping mechanism that has reached heights of 32 cm, 80x its own height, and an on-chip actuated mechanism that has been used to propel a 1.4mg projectile over 7 cm

Integration of shape memory alloy for microactuation

Shape memory alloy (SMA) actuators in microelectromechanical system (MEMS) have a broad range of applications. The alloy material has unique properties underlying its high working density, simple structures, large displacement and excellent biocompatibility. These features have led to its commercialization in several applications such as micro-robotics and biomedical areas. However, full utilization of SMA is yet to be exploited as it faces various practical issues. In the area of microactuators in particular, fabricated devices suffer from low degrees of freedom (DoF), complex fabrication processes, larger sizes and limited displacement range. This thesis presents novel techniques of developing bulk-micromachined SMA microdevices by applying integration of multiple SMA microactuators, and monolithic methods using standard and unconventional MEMS fabrication processes. The thermomechanical behavior of the developed bimorph SMA microactuator is analyzed by studying the parameters such as thickness of SMA sheet, type and thickness of stress layer and the deposition temperature that affect the displacement. The microactuators are then integrated to form a novel SMA micromanipulator that consists of two links and a gripper at its end to provide three-DoF manipulation of small objects with overall actuation x- and y- axes displacement of 7.1 mm and 5.2 mm, respectively. To simplify the fabrication and improve the structure robustness, a monolithic approach was utilized in the development of a micro-positioning stage using bulk-micromachined SMA sheet that was fabricated in a single machining step. The design consisted of six spring actuators that provided large stage displacement range of 1.2 mm and 1.6 mm in x- and y-axes, respectively, and a rotation of 20° around the z-axis. To embed a self-sensing functionality in SMA microactuators, a novel wireless displacement sensing method based on integration of an SMA spiral-coil actuator in a resonant circuit is developed. These devices have the potential to promote the application of bulk-micromachined SMA actuator in MEMS area

Workshop on "Robotic assembly of 3D MEMS".

Proceedings of a workshop proposed in IEEE IROS'2007.The increase of MEMS' functionalities often requires the integration of various technologies used for mechanical, optical and electronic subsystems in order to achieve a unique system. These different technologies have usually process incompatibilities and the whole microsystem can not be obtained monolithically and then requires microassembly steps. Microassembly of MEMS based on micrometric components is one of the most promising approaches to achieve high-performance MEMS. Moreover, microassembly also permits to develop suitable MEMS packaging as well as 3D components although microfabrication technologies are usually able to create 2D and "2.5D" components. The study of microassembly methods is consequently a high stake for MEMS technologies growth. Two approaches are currently developped for microassembly: self-assembly and robotic microassembly. In the first one, the assembly is highly parallel but the efficiency and the flexibility still stay low. The robotic approach has the potential to reach precise and reliable assembly with high flexibility. The proposed workshop focuses on this second approach and will take a bearing of the corresponding microrobotic issues. Beyond the microfabrication technologies, performing MEMS microassembly requires, micromanipulation strategies, microworld dynamics and attachment technologies. The design and the fabrication of the microrobot end-effectors as well as the assembled micro-parts require the use of microfabrication technologies. Moreover new micromanipulation strategies are necessary to handle and position micro-parts with sufficiently high accuracy during assembly. The dynamic behaviour of micrometric objects has also to be studied and controlled. Finally, after positioning the micro-part, attachment technologies are necessary

Enabling Capillary Self-Assembly for Microsystem Integration

Efficient and precise assembly of very-large quantities of sub-millimeter-sized devices onto pre-processed substrates is presently a key frontier for microelectronics, in its aspiration to large-scale mass production of devices with new functionalities and applications (e.g. thin dies embedded into flexible substrates, 3D microsystem integration). In this perspective, on the one hand established pick&place assembly techniques may be unsuitable, due to a trade-off between throughput and placement accuracy and to difficulties in predictably handling very-small devices. On the other hand, self-assembly processes are massively parallel, may run unsupervised and allow contactless manipulation of objects. The convergence between robotic assembly and self-assembly, epitomized by capillarity-enhanced flip-chip assembly, can therefore enable an ideal technology meeting short-to-medium-term electronic packaging and assembly needs. The objective of this thesis is bridging the gap between academic proofs-of- concept of capillary self-assembly and its industrial application. Our work solves several issues relevant to capillary self-assembly of thin dies onto preprocessed substrates. Very-different phenomena and aspects of both scientific and technological interest coexist in such a broad context. They were tackled both experimentally and theoretically. After a critical review of the state-of-the-art in microsystem integration, a complete quasi-static study of lateral capillary meniscus forces is presented. Our experimental setup enables also a novel method to measure the contact angle of liquids. Recessed binding sites are introduced to obtain perfectly-conformal fluid dip-coating of patterned surfaces, which enables the effective and robust coding of geometrical information into binding sites to direct the assembly of parts. A general procedure to establish solder-mediated electro-mechanical interconnections between parts and substrate is validated. Smart surface chemistries are invoked to solve the issue of mutual adhesion between parts during the capillary self-assembly process. Two chemical kinetic-inspired analytic models of fluidic self-assembly are presented and criticized to introduce a novel agent-based model of the process. The latter approach allows realistic simulations by taking into account spatial factors and collision dynamics. Concluding speculations propose envisioned solutions to residual open issues and further perspectives for this field of rapidly-growing importance

Improvements to Micro-Contact Performance and Reliability

Microelectromechanical Systems (MEMS) based devices, and specifically microswitches, continue to offer many advantages over competing technologies. To realize the benefits of micro-switches, improvements must be made to address performance and reliability shortfalls which have long been an issue with this application. To improve the performance of these devices, the micro-contacts used in this technology must be understood to allow for design improvements, and offer a means for testing to validate this technology and determine when such improvements are ready for operational environments. To build devices which are more robust and capable of continued operation after billions of cycles requires that improved fabrication techniques be identified and perfected to allow for more sophisticated designs to be tested