Philips Journal of Research最新文献

The characteristic features of direct bonding with respect to its many-sided aspects are briefly enumerated. Nowadays silicon-on-silicon and silicon-on-insulator are the trendsetters. The preparative conditions of direct bonding are compatible with silicon technologies. In addition, in the future, direct bonding may find dedicated applications in the field of hybrid material combinations, micromechanics for precision medical tools, sensors and actuators.

The incorporation of strain is inherent in the manufacture of bond and etchback silicon-on-insulator (BESOI) substrates. In this paper, the principal sources of strain are identified and the magnitude of the strain is estimated. The strain sources discussed include dopant (boron) induced lattice contraction of the etchstop layer, differential thermal expansion, and interfacial microroughness at the time of bonding. Reduction or elimination of SOI layer degradation from some of these strain sources is possible.

The spontaneous formation of a direct bond between materials — a phenomenon sometimes encountered in mechanics and optics — was considered inconvenient at first. It was some time before the advantages of the possibility of realizing direct bonds were realized: direct bonds obviated the need for intermediate adhesive layers. A good deal of research had to be done into the required pretreatment of the material parts and the aftertreatment for bond tightening before direct bonding could be used as a technology.

Geometrical, mechanical, chemical and physical properties of the materials involved all play a part in the formation of a direct bond; they are collectively referred to as the physiognomic properties. This chapter will describe a number of examples demonstrating the wide variety of materials (both inorganic and organic) that can be directly bonded, after which some magnetic, electric and electromagnetic advantages of directly bonded, electromagnetically active materials will be briefly outlined.

Periodically segmented waveguides were fabricated in flux-grown KTP for quasi-phasematched second-harmonic generation (SHG) of a light beam with a wavelength of 425 nm. Diode-pumped violet laser sources are proposed on the basis of these waveguides. We shall show that a pulsed operation of the pump diode laser at a 940 MHz repetition rate enables the construction of sources with a very compact geometry, which are insensitive to temperature fluctuations. These sources may still be considered as quasi-continuous wave (cw) for applications in high-density optical recording.

The most compact type of violet laser source has a size of 1 × 1 × 2 cm³. It contains only the diode pump laser, the KTP waveguide and a miniature lens to couple the pump beam to the waveguide. Time-averaged violet output powers up to 85 μW have been generated for many hours at room temperature without requiring an active temperature control. This output power may be sufficient for reading an optical disc.

By optical feedback of a portion of the transmitted pump beam via an external grating it is possible to generate higher violet powers. In this way, the pump laser is forced to operate in a single spectral mode, the wavelength of which can be tuned to coincide with the phase-matching wavelength of the waveguide. This grating-controlled laser system is shown to generate a 425 nm beam with powers up to 0.5 mW. The total length of the device is about 7 cm.

Progress in long-wavelength strained (compressive and tensile) InGaAs(P) quantum well semiconductor lasers and amplifiers for applications in optical fibre communication systems is reviewed. By the application of grown-in strain, device performance is considerably improved to such an extent that conventional bulk and unstrained quantum well active-layer devices are outperformed, while high reliability, similar to that of unstrained devices, is maintained.

Direct bonding is the result of a complex interaction between chemical, physical and mechanical properties of the surfaces to be bonded and is therefore strongly correlated with the surface state of the materials. Phenomena characteristic of the actual bonding process are (a) the formation of an initial bond area, (b) bond energy, and (c) bond-front velocity. The effects of variations in surface state on these process characteristics have been investigated for silicon, oxidized silicon and fused-silica wafer pairs. The surface bond energy of hydrophilic wafers is in the range of 0.05–0.2 J/m² and is largely determined by the hydrogen bonds formed. The bond energy of hydrophobic wafers is a factor of 10 smaller and is determined by Van der Waals attractive forces. The bond-front velocity is determined by the surface state and the stiffness of the wafer. Both bond energy and bond-front velocity show ageing effects.

Threshold current densities and lasing wavelengths of both ZnSSe/ZnSe/ ZnCdSe and ZnMgSSe/ZnSSe/ZnCdSe lasers under short-pulse (100 ns) operation have been measured as a function of temperature. In the second structure, improved electrical confinement and a lower defect density leads to a better T₀ and a higher maximum lasing temperature. In these lasers a room-temperature pulsed threshold current density of 400 A/cm² has been obtained. Using ZnSe/ZnTe graded electrical contacts, a laser operating voltage of 6.5 V has been realized.

Thermal resistances have been measured in ZnMgSSe/ZnSSe/ZnCdSe lasers. A value of 31 $\text{K}\text{W}$ has been obtained in a 20 μm stripe laser of 600 μm length, mounted substrate-up. Both substrate-up and substrate-down mounted lasers meet the thermal continuous-wave lasing condition at room temperature.

The relationship between stacking fault density and laser performance has been measured. Defect densities higher than 10⁷ cm⁻² significantly increase the lasing threshold.

Characteristics of narrow-stripe gain-guided lasers have been measured. Clear changes are seen between short-pulse (100 ns) and longer pulse (800 ns) operation. A simple model that represents thermal index-guiding is used to explain the behavior. The antiguiding parameter is found to be about −1.1.

Large-vocabulary continuous-speech recognition (CSR) technology is at work. As an application of the technology, we will describe a dictation system (DS). Input to the system is unrestricted spontaneous speech. No adaptation, no special skills are required to use the system. The DS transforms continuous speech into written text. It is essential in this application that the user is free to speak as he or she usually does and should be free to use his or her own wording and formulation. This implies speech recognition for large and open vocabularies, free syntax, continuous speech. The aim of the paper is an attempt to determine what is feasible with today's technology and what will be feasible in the near future. The problems addressed are: what are the limits of today's technology, what is needed to make the next step, i.e. going towards real industrialization of CSR technology.

Patent literature tells its own story of technological innovations. This story is evaluated here in the case of direct bonding. It is concluded that, on a worldwide basis, direct bonding has been approached via three avenues: optical, silicon technology and silicon wafer preparation.

The paper presents the issues and challenges for molecular beam epitaxy (MBE) of the II–VI wide-bandgap semiconductors used for blue/green lasers. Use of reflection high-energy electron diffraction (RHEED) addresses many of these challenges, permitting characterization and control of various aspects of wide-bandgap II–VI MBE growth. The paper describes their use to control composition of Zn_{1 − x}Mg_xSe and ZnS_ySe_{1 − y}, layers, and to measure and control the growth rates of ZnSe, ZnTe and CdSe during migration-enhanced epitaxy (MEE) growth. RHEED oscillations reveal additional information about growth processes during II–VI MBE. The Mg sticking coefficient is found to be independent of substrate temperature, flux ratios, and electron beam excitation. Re-evaporation of Se, but not of Zn, is found to occur during pauses in growth. The effects of an electron beam on growth may be quantitatively determined.