Lawrence A. Hornak

A Torque-Sensitive Tactile Array for Robotics

We introduce a new tactile sensor and show its advantages for robotic applications. The tactile array elements are composed of magnetic dipoles (in an elastic medium) whose position and orientation are detected by magnetoresistive sensors. We show that, unlike the existing tactile sensor designs, this device is sensitive to torque as well as to normal and tangential forces. We demonstrate experimentally the fabrication, sensitivity, and repeatability of the tactile elements.

Communication network issues and high-density interconnects in large-scale distributed computing systems

The authors discuss the impact of the physical interconnection environment through which the concurrent processes among locally distinct computing nodes of large-scale multicomputer systems are coupled. The communication capabilities implied for massively parallel computing systems by fine-grain task partitioning and by fine-grained communications are discussed in detail. Wafer-scale and hybrid wafer-scale system technologies which would support such communications are described. >

Polyalkylsilyne photodefined thin-film optical waveguides

Polysilynes, a new class of amorphous alkyl silicon network polymers, undergo a novel photo-oxidative crosslinking reaction associated with up to a 15% decrease in refractive index related to the loss of SiSi bonding. We describe the fabrication and initial measurements of waveguides formed with this index imaging technique in poly(cyclohexylsilyne) films on both SiO2 and poly(methyl methacrylate)-coated silicon wafers. Measurements of multimode guides show typical propagation losses of 0.68 dB/cm at 633 nm. Results indicate the polyalkylsilynes show promise as self-developing, planar optical waveguide media.

Dynamic Sensing for Robots: An Analysis and Implementation

Dynamic sensing is discussed in detail. We have initiated a systematics of robotic sensor design by formulating the general problems and addressing the specific question of how to arrange the sensing elements. We have derived a general relationship between the number and speed of the sensing elements as a function of their response and processing times. We have thus constructed afiber-optic sensor for the fingers of a Unimation Puma 500 robot. The sensor consists of three linear arrays ( each with 12 sensing elements), attached to the edges of the robot fingers in a U shape. The elements are composed of parallel, equally spaced, collimated light beams that pass from finger to finger. Each linear array can be scanned dynamically to provide a 12 X 18 = 256-pixel cov erage of a 2 X 3-cm area.

Fresnel phase plate lenses for through-wafer optical interconnections

While the advantages of optical over electrical interconnects for conventional 2-D VLSI and wafer-scaleintegrated (WSI) circuits have not been clearly demonstrated, for 3-D interconnection structures such as those necessary for stacked wafer and similar architectures, the trade-off between using optical or electrical methods for vertical links is not straightforward. Current work on fabricating a through-wafer optical interconnect within a hybrid-WSI environment is motivated by the need to obtain experimental data on the overall performance of an optical interconnect so that this trade-off can be clarified inthe case of hybrid-WSI and in the general case at least more well defined. This paper details the design and fabrication of SiO(2) Fresnel phase plate lens arrays for use in the experimental 1.3-microm wavelength through-wafer optical interconnects to be constructed. These 0.8-N.A. lenses have submicron minimum linewidths and are VLSI process compatible. Preliminary results are presented indicating that, with the use of these lens arrays, vertical optical interconnect densities comparable with that of on chip bonding pads ( approximately 250-microm pitch) are obtainable within these architectures.

Advanced interconnection technologies and system-level communications functions

Drawing on advanced packaging and interconnection schemes along with advances in VLSI technologies, the authors consider some examples of novel interconnection technologies. Novel polymer waveguides requiring only exposure to deep UV to fabricate a waveguide are emphasized as a potentially important material compatible with overlaying complex VLSI circuitry. Superconducting microstrip interconnections are considered. These examples suggest that conventional VLSI silicon technologies will evolve to become the support for the selective introduction of advanced interconnection technologies, yielding within the smaller system volumes of wafer-level systems the heterogeneous mixture of technologies seen in, or being introduced into, conventional, complex systems. It is pointed out that the specific examples used are microfabricated structures on substrates appropriate for achieving narrow features.<<ETX>>

The impact of high-T/sub c/ superconductivity on system communications

Reviews simple models for understanding the intrinsic behavior of superconducting striplines for frequencies much less than the gap frequency omega /sub g/, and low reduced temperatures. The effects of extrinsic factors such as nonideal stripline geometries and dielectrics are also examined. It is concluded that although based upon classical theory, these models are useful in providing performance estimates so that preliminary observations can be made regarding the application of high-T/sub c/ superconducting lines within digital computer systems. Finally, possible applications as well as performance questions regarding the use of high-T/sub c/ superconductors within contemporary and future digital systems are discussed. >

Wafer-level optical interconnection network layout

Two important issues will greatly influence the success of mapping optical interconnections into future waferlevel distributed computing systems: (1), the scalability of active optical devices with cointegration along side ULSI components, and (2), the scalability of optical networks and components to the wafer level. If these criteria can be met, planar integrated and free-space optics can potentially provide a very high performance communication network within the multi-wafer environment. With the predominantly planar geometry and processing of waferlevel circuits, process compatible integrated planar optical interconnections are especially attractive for providing network passive connectivity. As with their electrical counterparts, spatial, as well as time division multiplexing of optical interconnections is desirable, given that layout and area constraints are not too severe. Therefore here, emphasis is shifted away from the individual behavior of traditional long distance lightwave single mode waveguides towards the collective system behaviour (i.e. density, coupling, layout, etc.) of large dense arrays of multimode optical waveguides. In this paper, initial experimental optical coupling results are presented for arrays of multimode polysilyne polymer waveguides, both for straight configurations and for arrays with radial right angle bend layouts.

Future Physical Environments and Concurrent Computation

Using graph-based representations of computation problems [1]–[3], the communication function of a “pseudo-general purpose,” massively parallel computing environment is discussed to help define technology-focussed realizations of that communication function. Compatible computation problems are neither constrained to highly regular structures (such as systolic arrays and their generalizations [4]) nor extended to the globally non-deterministic behavior of many general purpose problems [5]. A fully distributed [6], data driven [7] computing environment is assumed, emphasizing the impact of communications on algorithm execution [8]. Evolution of such massively concurrent computing environments is necessary to sustain the growth of computing power as device technologies approach fundamental limits on dimensional scaling and higher device performance [9],[10].

Cointegration of optoelectronics and silicon ULSI for scaled, high-performance distributed computing systems

The evolution of silicon submicron technologies will yield very powerful single chip U LSI processors (possibly processor arrays) and high performance advanced packaging technologies, providing significant opportunities to realize very compact, distributed computing systems. However, exploiting that opportunity will require development of very high performance communication networks, scaled to the much smaller size and more monolithic realization of such future distributed systems. Optical communication is presently being applied to larger scale versions of such networks which, if scalable to the smaller, more monolithic world of future system structures, may help overcome several physical limits of scaled electrical networks. We review general system-level limits of scaled optical networks, assuming cointegration of Si CMOS logic, GaAs-based optoelectronics and waveguides within a common monolithic technology. The system limits suggest that a number of performance limits remain. Resolving such limits will be critical in exploiting the considerable advantages of scaled, optical interconnections for such future, highly integrated systems.