Papers

AVS1996 Session MM+MS-MoA: Issues in Manufacturing and Design

Monday, October 14, 1996 1:30 PM in Room 204B

Monday Afternoon

Start	Invited?	Item
1:30 PM		MM+MS-MoA-1 Commercialization of MEMS K. Petersen (Cepheid) Technologies and devices generally classified as MEMS span a very broad spectrum of markets and applications. Today, MEMS products in the pressure measurement markets, low-end inertial measurement markets, and in the projection display markets are generally micromechanical structures integrated with electronics and fabricated in a conventional IC wafer fab. These successful devices dominate commercial micromachining production. In general, products which can be developed, manufactured, tested and packaged in a format similar to an integrated circuit are prime candidates for commercialization by medium to large IC companies. However, emerging new MEMS products in the areas of micro-instrumentation, micro-fluidics, data storage, high-end inertial instruments, relays and others are not so suitable to conventional IC wafer fabs. Many of these types of new products may have vastly different requirements from the integrated circuit related to development, testing, manufacturing and packaging. This presentation will present a number of these emerging "unconventional" applications and will discuss development and manufacturing issues.
2:10 PM		MM+MS-MoA-3 Similarities and Differences Surface Micromachined MEMS and IC's R. Payne (Analog Devices Inc.) Surface MicroMachined MEMS have gotten off to a fast production start in the form of accelerometers for AirBag deployment. This paper will review the similarities and differences between the manufacturing technology requirements for MEMS and IC's. There are three basic ways to integrate surface structures into an IC flow. They are the insertion of MEMS structures in the beginning, the middle or at the end of the flow. An example of the first is the MICS process from the University of California at Berkeley. The second method has been popularized by Analog Devices through their use of mid process applied polysilicon to fabricate monolithic AirBag accelerometers. The third choice of process architecture is for polysilicon MEMS devices imbedded in the substrate first in the process. Standard CMOS can then be run on the pre-MEM'd wafer as has been demonstrated by Sandia National Labs. Finished wafers offer a series of interesting manufacturing challenges to the MEMS manufacturer that go beyond IC's. The moving structures either require a wafer level sealing step or special precautions in handling the wafer and the die in the separation step. Successful examples of each approach will be shown. The packages for die with an unsealed moving element are naturally hermetic. Standard IC packages are usable with standard die attach and sealing methods. The stress needs to be managed more carefully for MicroMachined chips. A class of devices that require distinctly non-standard techniques are resonant devices requiring vacuum encapsulation.The very small volumes of typical IC packages present a unique challenge of residual gas management to say the least. Surface MicroMachined MEMS devices can be built largely on the infrastructural back of the IC industry and the capital equipment built to manufacture IC's. Special needs must be recognized and accommodated for the successful manufacturing of "Silicon That Moves".
2:50 PM		MM+MS-MoA-5 Electrostatically Actuated Test Structures for MEMS Process Monitoring S. Senturia, P. Osterberg, R. Gupta (Massachusetts Institute of Technology) As the MEMS field matures, there is an increasing need for methods of monitoring manfucturing processes to assure uniformity and repeatability, and for test structures from which critical performance parameters can be routinely extracted. This paper examines one very useful method: the measurement of the pull- in voltage of electrostatically actuated cantilevers, beams, and diaphragms. The test structures are fabricated using the selected MEMS process (e.g. surface micromachining, bulk micromachining, LIGA, etc.), and are probed at the wafer level using standard electrical test equipment in conjunction with a microscope. The pull-in voltage by itself is an excellent probe of uniformity and repeatability, because it depends both on material properties and geometry. The extraction of material properties from the pull-in data requires additional geometric measurements in conjunction with models developed using the MIT MEMCAD system. Generally, the method is applicable to test structures which have a conductor-containing moveable part suspended over a fixed electrode or ground plane. Examples drawn from wafer-bonded and surface-micromachined technologies will be presented.
3:30 PM		MM+MS-MoA-7 Out-of-Plane Microstructures using Stress Engineering of Thin Films C. Tsai, A. Henning (Dartmouth College) +++++++++++++++++++++++++++++++++++++++++++++
3:50 PM		MM+MS-MoA-8 Molding of High Aspect Ratio Microstructures K. Kelly, J. Collier, J. Rogers, M. Despa (Louisiana State University); C. Khan-Malek (Center for Microstructures and Devices); C. Marque (Louisiana State University) Members of the Mechanical and Chemical Engineering Departments at Louisiana State University, as well as personnel at the Center for Micromachining and Devices, are developing the capability to mold sheets covered with high aspect ratio microstructures using the LIGA process. A variety of uses are envisioned for the micro structure-covered sheet (heat transfer applications, acoustics applications, composite material applications).A variety of electroplated mold inserts which can be used ot mold high aspect ratio microstructures will be presented. Experimental results from molding experiments using these mold inserts will also be presented. The manufacturing methods associated with mold insert manufacture and molding will be described in detail.
4:10 PM		MM+MS-MoA-9 Simulation of Rarefied Flows in MEMS Device C. Wong, M. Hudson, T. Bartel, J. Payne (Sandia National Laboratories) Advances in micromachining technology enable fabrication of microfluidic devices that include valves, pumps, heat exchangers, and gas turbines. Gaseous flows through micro devices may be rarefied because the size of the Micro-Electro-Mechanical Systems (MEMS) features are comparable to the mean free path of gas molecules. At this length scale, traditional Navier-Stokes continuum analyses are not applicable, even with slip velocity and temperature jump boundary conditions. The Direct Simulation Monte Carlo (DSMC) particle technique is the likely candidate methodology for these problems. The DSMC technique models the fluid as particles, computes the trajectories of these particles, and calculates macroscopic properties. The place and time of collisions are determined by means of a statistical consideration. We have compared DSMC results and continuum predictions (with and without slip boundary conditions) with experimental data for gaseous flow through micron-sized channels. These channels are 3 mm long, 1.2 \mu\m high, and 5 \mu\m wide. Recently published gaseous flow data shows that there exists nonlinear behavior of the pressure distribution a long these microchannels for varying flow conditions (P\sub inlet\ = 5 to 25 psig). This unexpected behavior can be explained with DSMC predictions. A reliable simulation tool like DSMC that accurately models the rarefied phenomena for MEMS devices can help optimize design and operation, thus saving time, materials, and cost. Our DSMC code runs on massively parallel computers enabling conceptual design simulations to be run in a timely fashion. This work was supported by the US DOE under contract DE-AC04-94AL8500.