Martin L. Green

Aluminum films prepared by metal-organic low pressure chemical vapor deposition

Abstract In this study, we have chemically vapor deposited aluminum films by the pyrolysis of triisobutylaluminum, an aluminum alkyl, at temperatures of 220–300 °C onto silicon, SiO2 and device wafer substrates. The step coverage of our films is good, as demonstrated by our ability to deposit films conformally in the 2.5 μm windows of a typical device. The optical reflectivity of the films is low because of surface roughness of the order of 1000–1500 A, which also renders them frosty in appearance. The films are highly pure aluminum with resistivities ranging between 2.8 and 3.5 μΩ cm. Transmission electron microscopy examination of the films shows them to be composed of columnar grains 1–3 μm in width, whcch may either be strongly oriented with a 〈111〉 fiber texture or be randomly poriented, depending on the surface activation treatment. Chemically vapor-deposited aluminum films have potential as metallizations for future generations of very-large-scale integrated devices.

Pseudotwinning and pseudoelasticity in β Fe-Be alloys

Pseudoelasticity in β Fe-Be has been observed and rationalized in terms of pseudotwinning. a type of stress-assisted martensitic transformation which arises from the interaction of long-range order and twinning in this alloy. The ordered structure, which gives rise to a chemical contribution for the reversion of the pseudotwin upon release of the stress, is not homogeneous DO3 as was previously reported, but a decomposed α + B2 microstructure. A crystallographic model predicts that the pseudotwinning process is describable by the stress-assisted martensitic phase transformation Pm3m (B2) → Cmmm. The electron diffraction evidence presented here to confirm this prediction is believed to be the first experimental proof of long-standing theories regarding the interaction of order and twinning. n nThe macroscopic mechanical behavior of β Fe-Be has been investigated in compression at room temperature. Maximum pseudoelasticity is observed for specimens water-cooled and aged at 325–425°C. which gives rise to a modulated α + B2 microstructure. Aging at higher temperatures causes a sharp drop-off in pseudoelasticity and the disappearance of the modulated microstructure. In addition, pseudotwins in specimens exhibiting little pseudoelasticity always have accommodation dislocations associated with them. It is concluded that the modulated microstructure promotes pseudoelasticity by strengthening the parent matrix, thereby enabling it to accommodate the pseudotwins in an elastic manner.

Hardness anisotropy of SrF2, BaF2, NaCl and AgCl crystals

The value of Knoop microhardness was obtained for crystals of SrF2, BaF2, NaCl and AgCl by indentation in various directions on several crystallographic planes. In all cases, the hardness is essentially dependent on the crystallographic direction along the long axis of the indentor and independent of the plane of indentation, as first reported by Garfinkle and Garlick for other cubic crystals. In addition, although the absolute value of hardness varies from one crystal to another, the hardness anisotropy was quite similar for all crystals. Since the primary slip mode is different among the crystals tested, it is concluded that hardness anisotropy cannot be used to determine the primary slip mode.

Directional solidification of Co-Cu-R permanent-magnet alloys

Co-Fe-Cu-Ce permanent-magnet alloys have been prepared by directional solidification using a modified Bridgman technique. Samples melted at low superheat temperatures ( DeltaT sim 20deg C above the melting point of about 1100°C) and solidified at moderate rates (∼2.3 cm/h) resulted in a reasonably homogeneous columnar grain structure with a preferred crystallographic orientation. The c axis is generally aligned within 15° of the growth axis. Increasing the speed of solidification led to a fine-grained structure with no texture, while decreasing the speed led to coarse columnar grains with erratic orientation. A large superheat temperature ( DeltaT sim 300-400deg C resulted in a reaction of the liquid with the alumina crucible wall and led to the formation of face-centered cubic Co-rich dendrites. With the modified Bridgman technique, oriented samples 8 cm long and 2.54 cm in diameter have been prepared with good magnetic properties. After annealing at 1000°C followed by aging at 400°C, a Co 3.5 Fe 0.5 CuCe alloy exhibited values of i H c = 7000 Oe, B r = 6100 G, and (BH)_{max} = 9.2 MG.Oe. A Co 3.6 Fe 0.5 Cu 0.9 Ce alloy exhibited values of i H c = 6000 Oe, B_{r} = 6250 G, aud (BH)_{max} = 9.5 MG.Oe after similar treatment.

High gain SiGe heterojunction bipolar transistors grown by rapid thermal chemical vapor deposition

Abstract Rapid thermal chemical vapor deposition (RTCVD) is a processing technique that results from the combination of radiant heating lamps and a CVD chamber. It is the ultimate cold-wall CVD reactor and allows one to clean wafers in situ and immediately thereafter to deposit epitaxial layers. Very thin layers (less than 100 A) can be deposited by either gas or lamp power switching. We report here the growth of high-quality silicon layers, both intrinsic and in situ doped, and devices that were processed from multilayer structures. Heterojunction bipolar transistors (HJBTs) containing 30% Ge in the base layer have been grown, and current gains as high as 300 have been observed. These HJBTs show great promise as microwave transistors. RTCVD processing is a production-worthy technology that will play an important role in the manufacture of future heterostructural devices.

Low cobalt CrCoFe and CrCoFe-X permanent magnet alloys

CrCoFe alloys containing 3-10 w/o Co and CrCoFe-X alloys containing 2-5 w/o Co and 0.1-3.0 w/o of B, C, Ti, Ge or Hf were prepared and magnetically hardened by slow cooling in a magnetic field at rates varying from 0.4-6.2°C/h. The extent of magnetic hardening, as indicated by the coercive force, has been explained in terms of the spinodal decomposition temperature of the alloy. It has been found that the higher the spinodal decomposition temperature of the alloy, the faster is the cooling rate at which maximum magnetic hardening is observed. Quaternary additions were not found to be beneficial in that they did not enhance the kinetics of spinodal decomposition, and magnetically diluted the ternary alloys. Energy products as high as 5.3 MGOe, with B r = 13.4kG and H c = 528 Oe, have been observed for the 5Co-30Cr-65Fe alloy.

Low cobalt Cr‐Co‐Fe permanent magnet alloys (invited)

This paper reviews the results of studies in our laboratory in the 2 to 12% Co range of Cr‐Co‐Fe permanent magnet alloys. Our salient results are as follows: (1) Isotropic ternay alloys, typified by 10.5Co‐28Cr‐Fe (Chromindur II) with values of Br = 9800, Hc = 400 Oe and (BH)max = 1.8 MGOe. This alloy is now in volume production for telephone receiver applications. (2) Anisotropic ternary alloys prepared by a newly developed ’’deformation‐aging’’ process, with values of (BH)max ranging from 2.3 MGOe for a 5Co‐33Cr‐Fe alloys to 5.5 MGOe for an 11.5Co‐33Cr‐Fe alloy. Adding 2% Cu raises the value of (BH)max by 0.5–1.0 MGOe. (3) Anisotropic alloys prepared by magnetic‐field aging, with values of (BH)max ranging from 4.2 MGOe for a 2.5Co‐32Cr‐Fe alloy to 6.2 MGOe for a 9Co‐27Cr‐Fe alloy. (4) Sintered magnets typified by the 5Co‐31Cr‐Fe alloy with (BH)max∼4.4 MGOe.

Intrinsic Magnetic Properties and Mechanism of Magnetization of Co‐Fe‐Cu‐R Permanent Magnets

The anisotropy constant Ku and the intrinsic coercive force MHc were determined in the temperature range 4.2° to 297°K on a single crystal of Co3.5Fe.5CuCe1.09. Also, a magnetization curve was obtained on a thermally demagnetized sample of this composition in which domain walls were present. It was necessary for the applied field to reach the value of the coercive force to substantially change the magnetization. As a result of these magnetic measurements and the direct observation of the precipitate particles by Leamy and Green using transmission electron microscopy, it appears that the magnetization process is governed by domain wall pinning.

Preparation and properties of sintered CoCuFeCe permanent magnets

Abstract Sintered directional permanent magnets of Co 3.8 Cu 0.9 Fe 0.5 Ce have been prepared with an energy product of 9.3 × 10 6 GOe, and intrinsic coercive force of 7000 Oe. Relatively low alignment fields, compacting pressures, sintering temperatures, and magnetizing fields were used. The magnets have a fine equiaxed microstructure, are crack free and mechanically strong.

The physical metallurgy and electrical contact resistance of mechanically alloyed CuRu composites

Abstract Mechanical alloying (high energy attrition milling) has been used to create a novel type of electrical contact material, a Cu-15vol.%Ru composite consisting of a fine (micron-scale) distribution of ruthenium in copper. Because these elements are mutually insoluble, mechanical alloying is one of the only ways of creating such a non-equilibrium microstructure. Consolidation of the composite powders into strip was carried out by warm and cold rolling, to preserve the metastable microstructure. The removal of surface copper from the consolidated strip gives rise to a “sandpaper” structure in which the hard, refractory and conductive ruthenium particles, now protruding from the surface, serve as the electrical contacts, whereas the copper matrix supports these particles and provides electrical continuity. The fact that this is so is borne out by the observation that in contact resistance versus exposure time tests, the Cu-15vol.%Ru composite behaves much more like pure ruthenium than like pure copper. Thus, we have developed a procedure for producing a base metal-ruthenium composite with electrical contact properties similar to those of ruthenium, without the difficulties (i.e. hot forging) or expense of working with pure ruthenium. This processing is applicable to an unlimited number of alloy systems.