Multi-level polysilicon surface-micromachining technology: Applications and issues

Polysilicon surface micromachining is a technology for manufacturing Micro-Electro-Mechanical Systems (MEMS) which has, as its basis, the manufacturing methods and tool sets used to manufacture the integrated electronic circuit. This paper describes a three-level mechanical-polysilicon surface-micromachining technology and includes a discussion of the advantages of this level of process complexity along with issues which affect device fabrication and performance. Historically, the primary obstacles to multi-level polysilicon fabrication were related to the severe wafer topography generated by the repetition of film depositions and etching. The introduction of Chemical Mechanical Polishing (CMP) to surface micromachining has largely removed these issues and opened significant avenues for device complexity. Several examples of three-level devices with the benefits of CMP are presented. Of primary hindrance to the widespread use of polysilicon surface micromachining, and in particular microactuation mechanisms, are issues related to the device surfaces. The closing discussion examines the potential of several latter and post-fabrication processes to circumvent or to directly alleviate the surface problems

Manufacturing microsystems-on-a-chip with 5-level surface micromachining technology

An agile microsystem manufacturing technology has been developed that provides unprecedented 5 levels of independent polysilicon surface-micromachine films for the designer. Typical surface-micromachining processes offer a maximum of 3 levels, making this the most complex surface-micromachining process technology developed to date. Leveraged from the extensive infrastructure present in the microelectronics industry, the manufacturing method of polysilicon surface-micromachining offers similar advantages of high-volume, high-reliability, and batch-fabrication to microelectromechanical systems (MEMS) as has been accomplished with integrated circuits (ICs). These systems, comprised of microscopic-sized mechanical elements, are laying the foundation for a rapidly expanding, multi-billion dollar industry 2 which impacts the automotive, consumer product, and medical industries to name only a few

Microfabricated microengine for use as a mechanical drive and power source in the microdomain and fabrication process

A microengine uses two synchronized linear actuators as a power source and converts oscillatory motion from the actuators into rotational motion via direct linkage connection to an output gear or wheel. The microengine provides output in the form of a continuously rotating output gear that is capable of delivering drive torque to a micromechanism. The microengine can be operated at varying speeds and its motion can be reversed. Linear actuators are synchronized in order to provide linear oscillatory motion to the linkage means in the X and Y directions according to a desired position, rotational direction and speed of said mechanical output means. The output gear has gear teeth on its outer perimeter for directly contacting a micromechanism requiring mechanical power. The gear is retained by a retaining means which allows said gear to rotate freely. The microengine is microfabricated of polysilicon on one wafer using surface micromachining batch fabrication

Microfabricated actuators and their application to optics

Several authors have given overviews of microelectromechanical systems, including microactuators. In our presentation we will review some of these results, and provide a brief description of the basic principles of operation, fabrication, and application, of a few selected microactuators (electrostatic and surface tension driven). We present a description of a three-level mechanical polysilicon surface-micromachining technology with a discussion of the advantages of this level of process complexity. This technology, is capable of forming complex, batch-fabricated, interconnected, and interactive, microactuated micromechanisms which include optical elements. The inclusion of a third deposited layer of mechanical polysilicon greatly extends the degree of complexity available for micromechanism design. Two examples of microactuators fabricated using this process are provided to illustrate the capabilities and usefulness of the technology. The first actuator is an example of a novel actuation mechanism based on the effect of surface tension at these micro-scale dimensions and of a microstructure within a microstructure. The second is a comb-drive-based microengine which has direct application as a drive and power source for micro optical elements, specifically, micro mirrors and micro shutters. This design converts linear oscillatory motion from electrostatic comb drive actuators into rotational motion via a direct linkage connection. The microengine provides output in the form of a continuously rotating output gear that is capable of delivering drive torque to a micromechanism

Micromachined sensor systems on a chip: The integration of MEMS with CMOS and its applications

The monolithic integration of micromechanical devices with their controlling electronics offers potential increases in performance as well as decreased cost for these devices. Analog Devices has demonstrated the commercial viability of this integration by interleaving micromechanical fabrication steps with microelectronic fabrication steps to produce a single-axis accelerometer on a chip. A next-generation integrated technology developed at Sandia National Laboratories eliminates many of the constraints associated with Analog`s process. This new technology enables the manufacture of complex micromachined sensor systems on a chip. An overview of Sandia`s micromachined system-on-a-chip technology along with application of the technology to inertial sensor systems designed by researchers at U.C. Berkeley will be given

Friction in surface micromachined microengines

Understanding the frictional properties of advanced Micro-Electro- Mechanical Systems (MEMS) is essential in order to develop optimized designs and fabrication processes, as well as to qualify devices for commercial applications. We develop and demonstrate a method to experimentally measure the forces associated with sliding friction of devices rotating on a hub. The method is demonstrated on the rotating output gear of the microengine recently developed at Sandia National Laboratories. In-situ measurements of an engine running at 18300 rpm give a coefficient of friction of 0.5 for radial (normal) forces less than 4 {mu}N. For larger forces the effective coefficient of friction abruptly increases, suggesting a fundamental change in the basic nature of the interaction between the gear and hub. The experimental approach we have developed to measure the frictional forces associated with the microengine is generically applicable to other MEMS devices

Performance tradeoffs for a surface micromachined microengine

An electromechanical model of Sandia`s microengine is developed and applied to quantify critical performance tradeoffs. This is done by determining how forces impact the mechanical response of the engine to different electrical drive signals. To validate the theoretical results, model-based drive signals are used to operate actual engines, where controlled operation is achieved for the following cases: (1) spring forces are dominant, (2) frictional forces are dominant, (3) linear inertial forces are dominant, (4) viscous damping forces are dominant, and (5) inertial load forces are dominant. Significant improvements in engine performance are experimentally demonstrated in the following areas: positional control, start/stop endurance, constant speed endurance, friction load reduction, and rapid actuation of inertial loads

The Error and Repair Catastrophes: A Two-Dimensional Phase Diagram in the Quasispecies Model

This paper develops a two gene, single fitness peak model for determining the equilibrium distribution of genotypes in a unicellular population which is capable of genetic damage repair. The first gene, denoted by $\sigma_{via}$, yields a viable organism with first order growth rate constant $k > 1$ if it is equal to some target ``master'' sequence $\sigma_{via, 0}$. The second gene, denoted by $\sigma_{rep}$, yields an organism capable of genetic repair if it is equal to some target ``master'' sequence $\sigma_{rep, 0}$. This model is analytically solvable in the limit of infinite sequence length, and gives an equilibrium distribution which depends on \mu \equiv L\eps , the product of sequence length and per base pair replication error probability, and \eps_r , the probability of repair failure per base pair. The equilibrium distribution is shown to exist in one of three possible ``phases.'' In the first phase, the population is localized about the viability and repairing master sequences. As \eps_r exceeds the fraction of deleterious mutations, the population undergoes a ``repair'' catastrophe, in which the equilibrium distribution is still localized about the viability master sequence, but is spread ergodically over the sequence subspace defined by the repair gene. Below the repair catastrophe, the distribution undergoes the error catastrophe when $\mu$ exceeds \ln k/\eps_r , while above the repair catastrophe, the distribution undergoes the error catastrophe when $\mu$ exceeds $\ln k/f_{del}$, where $f_{del}$ denotes the fraction of deleterious mutations.Comment: 14 pages, 3 figures. Submitted to Physical Review

Multi-Level Micromachined Systems-on-a-Chip: Technology and Applications

Researchers at Sandia have recently designed and built several research prototypes, which demonstrate that truly complex mechanical systems can now be realized in a surface micromachined technology. These MicroElectro- Mechanical Systems (MEMS) include advanced actuators, torque multiplying gear tmins, rack and pinion assemblies, positionable mirrors, and mechanical discriminators. All of tile mechanical components are batch fabricated on a single chip of silicon using the infrastructure origimdly developed to support today's highly reliabk; and robust microelectronics industry. Sand ia is also developing the technology 10 integrate microelectronic circuits onto the s,ime piece of silicon that is used to fabricate the MEMS devices. This significantly increases sensitivity and reliability, while fhrther reducing package size and fabrication costs. A review of the MEMS technology and capabilities available at Sandia National Laboratories is presented

Micromachined sensor and actuator research at the Microelectronics Development Laboratory

An overview of the major sensor and actuator projects using the micromachining capabilities of the Microelectronics Development Laboratory at Sandia National Laboratories is presented. Development efforts are underway for a variety of micromechanical devices and control electronics for those devices. Surface micromachining is the predominant technology under development. Pressure sensors based on silicon nitride diaphragms have been developed. Hot polysilicon filaments for calorimetric gas sensing have been developed. Accelerometers based upon high-aspect ratio surface micromachining are under development. Actuation mechanisms employing either electrostatic or steam power are being combined with a three-level active (plus an additional passive level) polysilicon surface micromachining process to couple these actuators to external devices. Results of efforts toward integration of micromechanics with the driving electronics for actuators or the amplification/signal processing electronics for sensors is also described. This effort includes a tungsten metallization process to allow the CMOS electronics to withstand high-temperature micromechanical processing