MEMS integrated submount alignment for optoelectronics

One of the most expensive and time-consuming production processes for single-mode fiber-optic components is the alignment of the photonic chip or waveguide to the fiber. The alignment equipment is capital intensive and usually requires trained technicians to achieve desired results. Current technology requires active alignment since tolerances are only /spl sim/0.2/spl mu/m or less for a typical laser diode. This is accomplished using piezoelectric actuated stages and active optical feedback. Joining technologies such as soldering, epoxy bonding, or laser welding may contribute significant postbond shift, and final coupling efficiencies are often less than 80%. This paper presents a method of adaptive optical alignment to freeze in place directly on an optical submount using a microelectromechanical system (MEMS) shape memory alloy (SMA) actuation technology. Postbond shift is eliminated since the phase change is the alignment actuation. This technology is not limited to optical alignment but can be applied to a variety of MEMS actuations, including nano-actuation and nano-alignment for biomedical applications. Experimental proof-of-concept results are discussed, and a simple analytical model is proposed to predict the stress strain behavior of the optical submount. Optical coupling efficiencies and alignment times are compared with traditional processes. The feasibility of this technique in high-volume production is discussed.     

Telecommunications applications of integrated optics and optoelectronics

Integrated optics and optoelectronics will play key roles in the evolution of the telecommunications network. We briefly review the available and developing technologies for integrated optical and optoelectronic devices, and summarize their characteristics and their natural areas of application in telecommunications. We then describe the trends and developments in fiber communication systems, services, and architectures, and how they can benefit from these devices. Major areas in which these devices are expected to contribute are: lowering the costs of high-speed network termination equipment to aid in providing inexpensive wide-band services to the subscriber; increasing the fraction of the fiber's natural bandwidth that can be made available for network usage; and increasing the network flexibility to facilitate multiservice integration.     

GaAs in GaSb: Strained nanostructures for mid-infrared optoelectronics

Molecular beam epitaxy was used for the first time to grow novel GaAs/GaSb heterostructures with ultrathin (0.8–3 monolayers) GaAs layers embedded in GaSb. These structures were studied by X-ray diffraction, transmission electron microscopy, and photoluminescence. By contrast to known structures with self-assembled quantum dots, GaAs layers in GaAs/GaSb structures are subject to elastic tensile stresses due to 7% lattice mismatch. The structures exhibit intense photoluminescence in the 2 μm region at low temperatures. Quantum-dimensional islands are formed in the structure at a nominal GaAs layer thickness exceeding 1.5 monolayers. The band alignment of the structures is of type II. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 36, No. 7, 2002, pp. 869–873. Original Russian Text Copyright ? 2002 by Solov’ev, Toropov, Meltser, Terent’ev, Kyutt, Sitnikova, Semenov, Ivanov, Motlan, Goldys, Kop’ev.     

Fabrication of MnGa/GaAs contacts for optoelectronics and spintronics applications

The crystal structure, composition, and magnetic, and electric-transport properties of Mn_xGa_y layers deposited onto a GaAs surface by pulsed laser deposition in a hydrogen atmosphere, pulsed laser deposition in vacuum, and electron-beam evaporation in vacuum are investigated. It is shown that the features of each technique affect the composition and crystal structure of the formed layers, and the degree of abruptness and crystalline quality of the heterointerface. Apparently, the composition and crystal structure are responsible for modification of the ferromagnetic properties. The defects in the heterointerface affect the properties of the Mn_xGa_y/GaAs diode structure, in particular, the height of the Schottky diode potential barrier.     

Making GaAs integrated circuits

Digital gallium arsenide (GaAs) integrated circuits offer prospects for high-performance electronics, particularly for increased speed and radiation hardness. Prototype GaAs devices fabricated in technologies ranging from ion-implanted metal semiconductor field-effect transistors (MESFETs) and junction field-effect transistors (JFETs) to epitaxial heterostructures, such as high-electron-mobility transistors (HEMTs) and heterojunction bipolar transistors (HBTs), have demonstrated these advantages. While these GaAs technologies share many common fabrication features, the unique characteristics of each and GaAs materials present significant manufacturing challenges. It is argues that to produce real integrated circuits (ICs) for system applications, the disciplines and rigors of a production environment as well as the innovations of research and development are required     

GaAs integrated microwave circuits

GaAs has many desirable features that make it most useful for microwave and millimeter-wave integrated circuits. The process of selective epitaxial depositions of high purity single-crystal GaAs with various doping concentrations into semi-insulating GaAs substrates has been developed. These high-resistivity substrates (>10⁶ohm.cm) provide the electrical isolation between devices, eliminating the difficulties and deficiencies normally encountered in trying to obtain isolation with dielectrics, back-etching, p-n junctions, etc. This monolithic approach to integrated-circuits thus allows for improved microwave pedormance from the devices since parasitics are reduced to a minimum. Planar Gunn oscillators and Schottky barrier diodes have been fabricated for use in a completely monolithic integrated millimeter wave (94 GHz) receiving front end. The Gunn oscillators are made in a sandwich-type structure of three selective deposits whose carrier concentrations are approximately 10¹⁸-10¹⁵-10¹⁸cm^-3. The Schottky diodes consist of two deposits with concentrations of 10¹⁸and 10¹⁷cm^-3. The Schottky contact is formed by evaporating Mo-Au onto the 10¹⁷cm^-3deposits; all ohmic contacts are on the surface and are alloyed to the N⁺regions.     

A novel pseudomorphic (GaAs1−xSbx-InyGa1−yAs)/GaAs bilayer-quantum-well structure lattice-matched to GaAs for long-wavelength optoelectronics

Two types of quantum well (QW) structures grown lattice matched on (100) GaAs have been studied. The first type of structure consists of pseudomorphic GaAs_xSb_1-x/GaAs (x≤0.3) SQWs which show emission wavelengths longer than those reported for pseudomorphic In_yGa_1−yAs/GaAs QWs. However, the attractive emission wavelength of 1.3 μm has not been achieved. To reach this goal, a novel type of bilayer QW (BQW) has been grown consisting of a stack of two adjacent pseudomorphic layers of GaAs_xSb_1−x and In Ga_1-y As embedded between GaAs confinement layers. In this BQW, a type-II heterojunction is formed between GaAs_xSb_1−x and In_yGa_1−yAs, resulting in a spatially indirect radiative recombination of electrons and holes at emission wavelengths longer than those achieved in the GaAs_xSb_1−x/GaAs and Ii_yGa_1−yAs/GaAs SQWs. The longest 300K emission wavelength observed so far was 1.332 μm.     

High-density GaAs integrated circuit manufacturing

The essential items in the development of a high-density high-yield volume manufacturing process for GaAs integrated circuits are presented. The critical issues and decisions for creating the high-density GaAs (HGaAs) enhancement and depletion mode Schottky gate MESFET process are reviewed. The authors describe the process steps, fabrication equipment, and materials used to fabricate self-aligned, refractory gate, enhancement/depletion (E/D) MESFET multilevel metal GaAs integrated circuits. Representative device and circuit results are included.     

Planar GaAs MOSFET integrated logic

Selective and multiple ion implantations directly into a semi-insulating GaAs substrate were utilized to fabricate planar integrated circuits with deep-depletion plasma-grown native oxide gate GaAs MOSFET's. 1.2-µm gate 27-stage enhancement/depletion (E/D) type ring oscillators, with the circuit optimized to reduce parasitic capacitance, were fabricated (using conventional photolithography) to assess the speed-power performance in digital applications. A minimum propagation delay of 72 ps with a power-delay product of 139 fJ was obtained, making these devices the fastest among current GaAs and Si logic fabricated by conventional photolithography. A minimum power-delay product of 36 fJ with a propagation delay of 157 ps was obtained. The power-delay product is comparable with that of 1.2-µm gate GaAs E-MESFET logic, and the speed is more than twice as great. This paper includes a comparison of the theoretical cut off frequency of MESFET and MOSFET logic devices operating in depletion mode. Results indicate that MOSFET logic has superior potential for high-speed operation.     

GaAs IGFET digital integrated circuits

A technique to utilize GaAs insulated gate field effect transistors (IGFEI's) with large surface state densities in digital integrated circuits is described. In this technique, the threshold voltage is electrically set to obtain enhancement-mode characteristics of the IGFET's. Due to change in surface charge with time, these circuits will not function at very low frequencies. Several advantages of this IGFET technology over other enhancement-mode GaAs technologies are presented.     

High speed GaAs integrated circuits

Much interest has been expressed in the use of GaAs MESFET's for high speed digital integrated circuits (IC's). Propagation delays in the 60- to 90-ps/gate range have been demonstrated by several laboratories on SSI and MSI logic circuits. Recently, large scale digital IC's with over 1000 gates have been demonstrated in GaAs. In this review paper, the device, circuit, and processing approaches presently being explored for high speed GaAs digital circuits are presented. The present performance status of high speed circuits and LSI circuits is reviewed.     

GaAs monolithic integrated optical preamplifier

A GaAs monolithic integrated optical preamplifier has been developed based on the transimpedance principle. By associating the amplifier with an external p-i-n diode, a sensitivity of -38 dBm was measured at 140 Mbits/s and 10^-9error rate with a signal wavelength of 1.3 μm. A TiWSiN-integrated technology was used to realize larger than 100-kω feedback resistors and gate leakage could be minimized by improving Schottky contact deposition and employing selective implantation. The optimization details of the FET and resistor elements, as well as the design techniques for integrated transimpedance amplifiers are presented.     

GaAs optoelectronic integrated light sources

A comprehensive discussion on key technology needed to realize GaAs optoelectronic integrated circuits (OEIC's) is given, including heat dissipation, reflector formation, controlled diffusion, surface steps, high density electronic circuits, and structures for integration. Examples of horizontal-type integration as well as vertical type are compared, with some details of optical and electronic performance.     

Formation of microgratings for III-V semiconductor integrated optoelectronics by high-voltage electron-beam lithography

The importance of low-order Bragg reflection gratings in semiconductor integrated optoelectronics is discussed and the advantages of direct-write electron-beam lithography for defining such gratings are described. We present the results of a theoretical and experimental study of this technique on bulk III-V semiconductor substrates. The use of 60-keV electron beams is shown to give improved edge resolution and relaxed tolerance on dosage compared with conventional (15-30 keV) beam energies. This enables fine patterns with high aspect ratios to be defined on thick (0.3-0.5 μm) resist films. Gratings having 0.23-μm period and 1:1 mark/space ratio have been defined on thick PMMA resist over InP substrates. Initial results for formation of gratings on GaInAsP/InP heterostructure substrates are presented.     

High-speed integrated logic with GaAs MESFET's

The feasibility of using GaAs metal-semiconductor field-effect transistors (GaAs MESFET's) in fast switching and high-speed digital integrated circuit applications is demonstrated. GaAs MESFET's with 1-/spl mu/m gate length are shown to have a current-gain-bandwidth product f/SUB T/ equal to 15 GHz. These devices exhibit a 15 ps internal delay in a large-signal switching test. A simple logic circuit consisting of MESFET's and Schottky diodes was monolithically integrated on a semiinsulating GaAs substrate. This logic circuit exhibits a propagation delay of 60 ps with no output load, and 105 ps when its output is loaded by three similar logic gates. A useful bandwidth of approximately 3 GHz is observed.     

用于光通信的GaAs集成电路

介绍了用于 1 0 Gb/s光传输系统前端模块的超细栅 Ga As FET器件的制作技术以及制作的数 /模 IC芯片组     

GaAs HBT's for microwave integrated circuits

The status of the microwave GaAs heterojunction bipolar transistor (HBT) technology is reviewed. Microwave circuits for advanced military and commercial systems continue to increase their dependence on the performance, functionality, and cost of active components fabricated using solid-state technology. The performance advantages provided by GaAs HBT's, for several critical circuit applications, have stimulated a worldwide development activity. Progress in HBT device technology and microwave circuit applications has been extremely rapid because of the broad availability of III-V compound semiconductor epitaxial materials and prior experience with GaAs field-effect transistors (FET's) and monolithic microwave integrated circuits (MMIC's). The great flexibility of HBT's in microwave circuits makes them prime candidates for applications in complex multifunctional microwave/digital IC's in next-generation systems     

Proton isolation for GaAs integrated circuits

Significant improvement in the electrical isolation of closely spaced GaAs integrated circuit (IC) devices has been achieved with proton implantation. Isolation voltages have been increased by a factor of four in comparison to a selective implant process. In addition, the tendency of negatively biased ohmic contacts to reduce the current flow in neighboring MESFET's (backgating) has been reduced by at least a factor of three. The GaAs IC compatible process includes implantation of protons through the SiO2field oxide and a three-layered dielectric-Au mask which is definable to 3-µm linewidths and is easily removed. High temperature storage tests have demonstrated that proton isolation, with lifetimes on the order of 10⁶h at 290°C, is not a lifetime limiting component in a GaAs IC process.     

Ion implantation of GaAs integrated circuits

The conditions required for the fabrication of low pinch-off voltage MESFETs by ion implantation have been established. Calculation of the device characteristics from measured carrier concentration profiles has shown that of Vp of -1.5V is best achieved using low implant energies together with ion doses of 2 × 10¹² cm^?2. Characterisation of the implant and annealing conditions has enabled the implanted dose to be corrected for the activation after annealing. Measurement of the processed devices has shown the variation in saturation current to be as low as 3 mA over 75% of the wafer area, showing suitability for use in logic circuit fabrication.     

Silicon-based optoelectronics

The decade of the 1990's is an opportune time for scientists and engineers to create cost-effective silicon “superchips” that merge silicon photonics with advanced silicon electronics on a silicon substrate. We can expect significant electrooptical devices from Column IV materials (Si, Ge, C and Sn) for a host of applications. The best devices will use strained-layer epitaxy, doped heterostructures, and bandgap engineering of quantum-confined structures. This paper reviews Si-based photonic components and optoelectronic integration techniques, both hybrid and monolithic