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We will discuss our work to build, characterize, and scale- up a metallized plastic muscle-like actuator called a Spiral Wound Transducer (SWT). Prototype SWTs have been built using microelectronics fabrication methods. The prototypes have demonstrated large amplitude motion and analog response. The prototypes, though small, have demonstrated forces equivalent to 12 grams for compressions of more than 15 percent at 30 Hz. The size of the SWTs is essentially unrestricted. Our work with commercially available metallized Mylar films to produce much larger, more powerful, and lower cost SWT devices will also be discussed.

I . The University of North Carolina at CharlotteDepartment of Electrical and Computer EngineeringCharlotte, NC 282232. Duke UniversityDepartment of Biomedical EngineeringDurham, NC 277063. MCNC, Electronic Technologies DivisionResearch Triangle Park, NC 277094. The University of North Carolina at CharlotteDepartment of ChemistryCharlotte, NC 282235. The University of North Carolina at CharlotteDepartment of Mechanical EngineeringCharlotte, NC 282236. Integrated Electronic Innovations Inc.Cary, NC 27513ABSTRACTA miniature ultrasound scanner has been constructed using a MEMS actuatorcalled an Integrated Force Array (IFA).1'2'3'4'5 A second type of actuator called aSpiral Wound Transducer (SWT) is under development and shows significantpromise for this application. Both the scanner and SWT will be discussed.1. MINIATURE ULTRASOUND SCANNERWe have previously discussed the miniature ultrasound scanner6 shown inFigure 1.

Vapor‐deposited amorphous silicon films of 4000 A thickness have been epitaxially crystallized on (100) silicon substrates by pulsed Nd : YAG laser radiation of 125‐nsec duration at power levels of 90–120 MW/cm2. The epitaxial layers were found to be defect free when examined by transmission electron microscopy and Rutherford backscattering. Patterned arrays of epitaxial crystal were produced by overlapping individual 39‐μm laser pulse spots.

135 nsec pulses ofλ = 1.06μm light from a Nd: YAG laser have been used to form Schottky barriers by irradiation of a 500A thick metal film on n-type silicon. Large area barriers were fabricated by over-lapping individual 30μ diameter laser pulses of from 4 to 12 J/cm2. The barrier height was 0.73 ± 0.03 V, independent of the laser power. The barrier quality, as assessed by measurement of the forward current characteristic, decreased with laser power to a value of n = 1.5 at 12 J/cm2.

Lasers have long established a permanent position in manufacturing.1–5 They are used to cut hard and brittle materials, to weld metallic objects rapidly and efficiently, to harden locally surfaces of metals, and to drill microscopic holes in materials as diverse as rubber and steel. High power electron beams are routinely used for spot welding and to a lesser extent for cutting and drilling.

Data are reported for n-MOSFET's fabricated in laser crystallized poly-Si on amorphous insulating substrates. The dependence of electrical characteristics on the effective channel length in the range of 100 to 0.3 µm and on channel width from 120 to 20 µm is presented. The electron surface mobility is found to increase as the channel length is reduced, approaching that of devices in single-crystalline silicon. The source-to-drain leakage current, negligible for long channels, rapidly increases for channels shorter than ≃ 3 µm. This excessive current results from grain boundary diffusion of As from source and drain during high temperature fabrication steps.

The charge collected within the SiO 2 layer of an MOS capacitor during bombardment with kilovolt electrons is approximately proportional to the field in the oxide. We have used this proportionality to form SEM images of the field distribution in MOSFET channels.

Polycrystalline silicon films on SiO2 and Si3N4 may be processed by tightly focused, overlapping laser pulses to yield large‐grained (1–5μm) material. In individual nonoverlapping spots the large grains are arranged in concentric rings whose origin is clarified in this letter.

Extensive seeded epitaxial growth of crystalline Si over SiO2 was achieved by an oscillatory regrowth method applied to rectangular Si pads recessed into a thick SiO2 film. Narrow (≃5 μm) via holes linked the pads with the bulk (100) Si substrate. Oriented single crystals propagated as far as 500 μm from the seeding area, following the long term advance of a scanned focused laser beam.

Parallel secondary electron and charge collection images of a CdS/Au Schottky barrier show that photoetching of the CdS improves the charge collection efficiency. This is explained in terms of preferential removal of (near) surface recombination centers by the photoetching. Evidence is given that lack of photoetching of specific areas of the surface is due to the fact that such areas are photoelectrochemically inactive, possibly because of poor electrical contact with underlying CdS, and combined photoetching and scanning electron microscopy investigation is suggested as a way to check semiconductors for inactive regions.

The redistribution of antimony impurity atoms implanted in (111) and (100) substrates was studied as a function of the power density of Q-switched YAG laser radiation (λ = 0.53μm) used to recrystallize 4700Å films of amorphous silicon vapor deposited over blanket and patterned Sb buried layer structures. Results for fully crystallized layers show impurity profiles ranging from a sharp interface displaced outward slightly relative to the as-grown interface, to complete redistribution of antimony into the deposited layer. Studies of patterned buried layer structures indicate that epitaxial crystallization can be achieved on (111) and (100) substrates without serious damage to the surface topography necessary for subsequent mask alignment.

The fabrication of silicon-on-insulator structures was examined utilizing epitaxial growth of Si films on porous silicon and subsequent enhanced oxidation of the porous substrate. Porous silicon films have been formed by local anodic dissolution of silicon wafers in HF, while retaining the single crystalline structure. Low temperature liquid phase epitaxy (LPE) from saturated Ga solutions as well as molecular beam epitaxy (MBE) and laser induced epitaxy have been studied. Transmission electron microscopy (TEM) has demonstrated that all three techniques can achieve crystalline Si film growth on porous silicon. Surface smoothness and crystal perfection of the resulting epitaxial layers varies considerably with each technique.

Beam processing can be applied to thin, polycrystalline silicon films on amorphous substrates to: a( increase grain size, b( produce single, isolated crystals, and c( to produce oriented single crystals. Specific methods for these tasks are outlined. Crystal growth and heat flow consideration appropriate to each are presented.

We have grown high quality epitaxial Si films from amorphous deposited layers using pulsed and CW Nd:YAG lasers. Pulsed irradiation produced epitaxial growth by melting and resolidification. The regrowth is relatively insensitive to interfacial and incorporated impurities of C, O, and Ar. Gallium dopants in the amorhous film redistribute within the melt and are zone refined towards the surface during solidification. Gallium left within the regrown layer exceeds the maximum equilibrium solid solubility by an order of magnitude. Continuous wave irradiation can produce epitaxial regrowth in the solid phase providing that the silicon is deposited on an atomically clean substrate. No Ge dopant redistributed has been observed in this regime.

Silicon crystals that have been annealed by both Cw and pulsed laser irradiation have been examined by scanning, charge collection microscopy. In this technique, the short circuit current across a laser annealed diode is employed as the video signal in a scanning electron microscope, which provides a source of focused carrier injection. Repetitively pulsed, overlapping spot arrays show excellent uniformity on a scale large compared to the laser spot size, but exhibit inhomogeneity in the 1 to 10 μm range. Specifically, 1 μm ripple is observed in diodes annealed at laser powers near the surface melting of the sample surface. In well‐annealed material, the periphery of each laser spot is the region of best charge collection. Measurement of collection efficiency vs. injection depth yields estimates of carrier lifetime in the laser melted an resolidified layer. These are always small, of order 1 nsec. Finally, we have observed conversion of p‐type silicon surfaces to n‐type following CW laser annealing.

Laser induced melting and resolidification of single crystal silicon introduces electrically active point defects. The electrical properties of laser processed silicon were monitored by capacitance transient spectroscopy (DLTS) and thermally stimulated capacitance (TSCAP) measurements. Removal of residual defects by thermal annealing occurs between 500°C and 700°C. More importantly, the defects are passivated by reaction with atomic hydrogen in the temperature range of 100–300°C.

125 nsec pulses of λ = 1.06 μm light from a Nd:YAG laser have been used to convert amorphous, vapor deposited layers of Ge and Ge + Si on (100) Si substrates to epitaxial heterostructures. Pulse energy densities in the range from 4 to 12 J/cm 2 melt the deposited layers, which regrow epitaxially. A cellular defect structure is formed in the resolidified material via a cellular crystal growth mechanism.

The growth of device-worthy silicon crystals on insulating substrates would have a revolutionary impact upon microelectronics, and is consequently the object of intense effort. This article reviews recent progress in the application of laser and electron beams and incoherent light to this end. In every case, radiant energy is employed to melt a precursor material, from which device-worthy layers are produced during resolidification. Techniques include seeded and unseeded growth, partial and complete encapsulation of the liquid layer, and oscillation of the solid-liquid interface. Considerations of liquid zone stability, temperature gradient control, and interface morphological stability are central to each technique. Progress in this field has been rapid and several techniques have been successfully demonstrated.

Seeded epitaxial growth of Si over SiO2 is demonstrated in two types of structures. In the first case, rectangular pads of deposited Si were recessed into a thick SiO2 film. Narrow (≃ 5μm) via holes in SiO2 linked the pads with the bulk Si substrates. In the second embodiment, SiO2 patterns were recessed into the Si wafers which were then covered with a continuous 0.5μm poly-Si layer. In both cases, nearly planar geometries were maintained by use of local oxidation and etching techniques. Silicon was recrystallized with a focused Ar+ laser beam. Depending on the scanning conditions and the Si pattern geometry, single crystal growth propagated between 30 and >500μm. The factors influencing the extent and quality of the crystallized regions are discussed.

Contrast from domain walls in materials with cubic magnetic anisotropy has been observed in scanning electron microscope (SEM) images. This contrast, which is visible in both the backscattered and absorbed current images, with normal electron beam incidence arises from the interaction of the convergent incident electron beam with the domains on either side of the wall.

Laser melting of crystalline silicon introduces electrically active defects which are observed by capacitance transient spectroscopy. The electrical activity of these point defects is neutralized by reaction with atomic hydrogen at 200 °C.

We have recently examined the microscopic electrical inhomogeneities present in dislocation free, floating zone, Si crystals grown under various conditions by conductivity mode scanning electron microscopy. Schottky barriers produced by evaporation of thin Au-Pd (on N type) or Ti (on P type) electrodes were employed in order to eliminate possible changes in defect structure or electrical activity during production of a diffused junction.Doped and undoped crystals, as well as crystals subjected to special treatments, such as melt quenching were examined in this study. Prior to SEM analysis, each crystal was characterized by preferential etching, Cu or Li decoration, and x-ray topography. All of the defects detected by these methods, save C impurity striations detected via their dilatation of the Si lattice in x-ray topographs, were observed in the SEM experiments. For example, “swirl” defects of both type “A” (large) and type “B” (small) were readily revealed via the enhanced recombination rate of electron beam injected carriers in their vicinity (see Figs. 1 and 2).