Polycrystalline silicon-germanium films for integrated microsystems

Two approaches were demonstrated for fabricating microstructures after completion of CMOS circuits with aluminum metallization. The first approach employed n-type poly-Ge deposited at 400/spl deg/C as a structural material with an SiO/sub 2/ sacrificial layer and an HF release. The CMOS circuits were protected from the release etchant with an amorphous Si layer. Clamped-clamped lateral resonator test structures had quality factors in vacuum as high as /spl sim/30000. Following a 500/spl deg/C, 30 s RTA the poly-Ge stress was 200 MPa (tensile) and the resistivity was 5.3 m/spl Omega/-cm. In the second integration approach, p-type poly-Si/sub 0.35/Ge/sub 0.65/ deposited at 450/spl deg/C was the structural material with poly-Ge as the sacrificial material and H/sub 2/O/sub 2/ as the release etchant. The H/sub 2/O/sub 2/ did not significantly etch the p-type poly-SiGe structural layer and no protection of the underlying CMOS layers was needed. For the first time, the fabrication of LPCVD surface microstructures directly on top of standard electronics was demonstrated, providing dramatic reductions in both MEMS-CMOS interconnect parasitics and device area. A folded flexure lateral resonator had a quality factor in vacuum as high as /spl sim/15000. No stress or dopant-activation anneal was needed, since the in situ boron-doped poly-SiGe was found to have an as-deposited stress of only -10 MPa (compressive) and a resistivity of only 1.8 m/spl Omega/-cm.     

Test Case Generation as an AI Planning Problem

While Artificial Intelligence techniques have been applied to a variety of software engineering applications, the area of automated software testing remains largely unexplored. Yet, test cases for certain types of systems (e.g., those with command language interfaces and transaction based systems) are similar to plans. We have exploited this similarity by constructing an automated test case generator with an AI planning system at its core. We compared the functionality and output of two systems, one based on Software Engineering techniques and the other on planning, for a real application: the StorageTek robot tape library command language. From this, we showed that AI planning is a viable technique for test case generation and that the two approaches are complementary in their capabilities.     

Comparison of contact sensor localization abilities during manipulation

This paper presents an experimental comparison of tactile array versus force-torque sensing for localizing contact during manipulation. The manipulation tasks involved rotating objects and translating objects using a planar two fingered manipulator. A pin and a box were selected as limiting cases of point and line contact against a cylindrical robot finger tip. Practical implementations of the two sensor types are compared theoretically and experimentally, and three different localization algorithms for the tactile array sensor are considered. Force-torque contact sensing results suffered from difficulties in calibration, transient forces, and low grasp force. Tactile array sensing was immune to these problems and the effect of shear loading was only noticeable for a simple centroid algorithm. The results show that with care, both of these sensing schemes can determine the contact location within a millimeter during real manipulation tasks.     

High-aspect-ratio, molded microstructures with electrical isolation and embedded interconnects

 A thin film molding process was developed to enable the fabrication of monolithic micromechanical structures with built-in electrical isolation and embedded interconnects. High-aspect-ratio composite structures were created from undoped polysilicon, low stress nitride and doped polysilicon, in a dual micromolding process. These monolithic electro-mechanical microstructures are more resistant to thermal effects and misalignment errors compared to microsystems assembled from discrete elements. In addition, the microstructures are molded in a re-usable mold providing an economical advantage. A gimballed electrostatic microactuator was successfully fabricated using this process. Electrical isolation was achieved with a combination of low stress nitride and undoped polycrystalline silicon. Various isolation geometries were investigated. Current leakages of less than 1 nA at 30 V were measured for isolation structures 40 μm long and 80 μm tall. Received: 13 November 2000/Accepted: 16 November 2000     

Microgimbal torsion beam design using open, thin-walled crosssections

A thin-film micromolding process enabled the construction of microtorsional springs with unique cross-sectional designs by combining high-aspect-ratio beams with horizontal surface features. Cross sections such as T-bars, pi sections, and channels were utilized in creating torsional springs with low torsional stiffnesses and high in- and out-of-plane bending stiffnesses. Experimental modal analysis was used to determine torsional stiffnesses as low as 0.13 μN·m/deg with T-bar springs 45 μm tall, 50 μm wide, and 100 μm long. Springs of the same outer dimensions but with solid rectangular cross sections were calculated to have torsional stiffnesses of at least two orders of magnitude greater. Several microgimbals were constructed using the thin-film micromolding process with various torsional spring designs. Modal analysis was used to experimentally determine pitch and roll natural frequencies. Torsional stiffness models for open, thin-walled sections that included warping effects were developed and used to analytically predict the torsional natural frequencies of tested spring designs to within 20%     

Microstructure to substrate self-assembly using capillary forces

We have demonstrated the fluidic self-assembly of micromachined silicon parts onto silicon and quartz substrates in a preconfigured pattern with submicrometer positioning precision. Self-assembly is accomplished using photolithographically defined part and substrate binding sites that are complementary shapes of hydrophobic self-assembled monolayers. The patterned substrate is passed through a film of hydrophobic adhesive on water, causing the adhesive to selectively coat the binding sites. Next, the microscopic parts, fabricated from silicon-on-insulator wafers and ranging in size from 150×150×15 μm³ to 400×400×50 μm ³, are directed toward the substrate surface under water using a pipette. Once the hydrophobic pattern on a part comes into contact with an adhesive-coated substrate binding site, shape matching occurs spontaneously due to interfacial free energy minimization. In water, capillary forces of the adhesive hold the parts in place with an alignment precision of less than 0.2 μm. Permanent bonding of the parts onto quartz and silicon is accomplished by activating the adhesive with heat or ultraviolet light. The resulting rotational misalignment is within ~0.3°. Using square sites, 98-part arrays have been assembled in less than 1 min with 100% yield. The general microassembly approach described here may be applied to parts ranging in size from the nano- to milliscale, and part and substrate materials including semiconductors, glass, plastics, and metals     

Boundary evaluation using inner and outer sets: the ISOS method

A boundary-evaluation algorithm for constructive solid geometry is presented for representations in which the primitives can be bounded by complex surfaces (such as splines) as well as by simpler polynomial surfaces. A fundamental part of the algorithm is the spatial decomposition of each primitive in a way that yields three planar bounded volumes, one containing the primitive (outer set), one contained within the primitive (inner set), and the third being the set difference of the first two, containing the boundary of the primitive. A positive feature of this approach is that the geometric coverage can be extended to any family of solid primitives for which an initial inner-solid-outer-solid segmentation and a subdivision procedure can be devices. Satisfying these two requirements ensures that the resulting primitive definitions are in the canonical form necessary for evaluation. Therefore the cost in terms of software development of adding primitive types does not depend on the number or type of existing primitives     

Creep deformation cracking of polyethylene in methanol

Compression-moulded high-density polyethylene with a large spherulite size was deformed in methanol, an environment cracking agent. The mechanical test involved constant load creep in tension. At smaller loads corresponding to longer lifetimes, the final failure consisted of a macroscopic crack oriented perpendicular to the tensile axis. Deformed specimens were etched in permanganic acid and the spherulitic and lamellar structures near the macroscopic crack were examined using optical, scanning electron and transmission electron microscopy. The large-scale fracture was the result of crack nucleation in the interlamellar regions and subsequent sub-critical crack growth with micro-cracks joining up to form larger cracks.