Highly enantioselective oxidations of ketene dithioacetals leading to trans bis-sulfoxides

Ketene dithioacetals undergo a Sharpless-type asymmetric oxidation using (+)-DET, Ti(O(i)()Pr)(4), and cumene hydroperoxide to give the trans bis-sulfoxides 4a-f with essentially complete control of enantioselectivity and diastereoselectivity. The high enantioselectivity is a consequence of carrying out two asymmetric processes on the same substrate. However, this should lead to the formation of a small amount of the meso isomer but none was isolated. From monitoring the enantioselectivity of the monoxide over time, it was concluded that small amounts of the meso isomer must be formed. The inability to isolate this compound could be because it acted as a ligand on titanium and remained tightly bound even upon workup.     

Improved breakdown for SOI MOSFETs fabricated in electron-beamrecrystallized polysilicon

The breakdown mechanism for SOI (silicon-on-insulator) n-type MOSFETs is discussed. It is proposed that by reducing the channel lateral electric field at the drain that breakdown can be increased. A two-dimensional finite-element modeling program was used to design a treble diffused drain-sources (TDD) implant profile which would increase the breakdown voltage. The modeling showed that a linearly graded structure would lower the electric field in the channel and would subsequently increase drain-source breakdown voltage by over 20%. Transistors fabricated in e-beam recrystallized material verified these predictions     

Process and device performance of a high-speed double poly-Sibipolar technology using borosenic-poly process with coupling-baseimplant

Use of boron and arsenic diffusions through an emitter polysilicon film (borosenic-poly emitter-base process) produces a transistor base width of less than 100nm with an emitter junction depth of 50 nm and an emitter-to-base reverse leakage current of approximately 70 pA. The borosenic-poly process resolves both the channeling and shadowing effects of a sidewall-oxided spacer during the base boron implantation. The process also minimizes crystal defects generated during the emitter and base implantations. The coupling-base boron implant significantly improves a wide variation in the emitter-to-collector periphery punchthrough voltage without degrading the emitter-to-base breakdown voltage current gain, cutoff frequency, or ECL gate delay time. A deep trench isolation with 4-μm depth and 1.2-μm width reduces the collector-to-substrate capacitance to 9 fF, while maintaining a transistor-to-transistor isolation voltage of greater than 25 V. The application of self-aligned titanium silicide technology to form polysilicon resistors without holes and to reduce the sheet resistance of the emitter and collector polysilicon electrodes to 1 Ω/square is discussed     

Low-Pressure chemical vapour deposition of tantalum pentoxide films for ulsi devices using tantalum pentaethoxide as precursor

A laminar flow low-pressure chemical vapour deposition (LPCVD) system (LAM Integrity^TM) has been used to deposit tantalum pentoxide (Ta₂O₅) from Ta(OEt)₅ films in the presence of oxygen (O₂) at 470 °C at a typical deposition rate of 4 nm min^?1. Uniformities of <1.5% (SD 1σ) over a 150 mm silicon substrate were obtained. The layers were annealed under different conditions. It was discovered that the films did not change their stoichiometry as determined by Rutherford backscattering (RBS). The as-deposited films were amorphous but became crystalline (β-Ta₂O₅) at temperatures > 700 °C. The transmission electron microscopy (TEM) results on crystallisation behaviour were supported by X-ray diffraction data. The electrical properties of the Ta₂O₅ films have been characterised using MIS (metal/insulator/silicon) capacitor structures. Leakage values of <10^?6 A cm^?2 at 6 MV cm^?1 equivalent applied electric field and breakdown strengths of >7 MV cm^?1 at 1.6 μA were obtained for annealed layers. Compound dielectric constants (native silicon oxide thickness of about 2.5 nm plus Ta₂O₅ of various thicknesses) between 14 and >30 have been measured. The electrical properties reveal the potential use of Ta₂O₅ as a storage capacitor dielectric in 64 and 256 Mbit DRAM (dynamic random access memory) devices.     

Integrated-circuit digital logic families III?ECL and MOS devices

This final installment of a three-part article is devoted to emitter-coupled logic (ECL) devices as well as to metal oxide semiconductor (MOS) logic devices of the p-channel (P-MOS) and complementary (CMOS) types. The concluding portion presents a summary chart comparing the major parameters of the various IC digital families discussed in the three installments, plus a useful check list of available functions.     

Spacetimes with killing tensors

For Einstein-Maxwell fields for which the Weyl spinor is of type {2, 2}, and the electromagnetic field spinor is of type {1, 1} with its principal null directions coaligned with those of the Weyl spinor, the integrability conditions for the existence of a certain valence two Killing tensor are shown to reduce to a simple criterion involving the ratio of the amplitude of the Weyl spinor to the amplitude of a certain test solution of the spin two zero restmass field equations. The charged Kerr solution provides an example of a spacetime for which the criterion is satisfied; the chargedC-metric provides an example for which it is not.This piece of work was completed, in part, during the authors' summer 1972 stays at The University of Texas at Dallas, Division of Mathematics and Mathematical Physics, the Max-Planck-Institut für Physik und Astrophysik in München, and the Black Hole session of the Ecole d'été de Physique Théorique in Les Houches; supported, in part, by the National Science Foundation, Grants GP-8868, GP-3463 9X, GP-20023, and GU-1598; the Air Force Office of Scientific Research, Grant 903-67; the National Aeronautics and Space Administration, Grant 44-004-001; the Westinghouse Corporation; the Clark Foundation; and the Rhodes Trust.     

Growth reactions and mechanisms in chemical beam epitaxy (CBE)

The rapidly increasing interest in chemical beam epitaxy (CBE) and related ultra-high vacuum (UHV)-based epitaxial growth techniques has arisen primarily as a result of their expected technological advantages compared to either the conventional molecular beam epitaxy (MBE) or metalorganic vapour phase epitaxy (MOVPE) processes. The CBE-related techniques do, however, provide the additional important advantage, compared to MOVPE, that the UHV environmental allows in-vacuo analytical techniques to be used to provide in-situ characterization regarding the composition and crystallography of the growing layers, and also vital information regarding the growth mechanisms involved. The present paper reviews the current understanding relating to III–V CBE reaction mechanisms, and highlights specific topics which require further investigation.