P. D. Grant

A Comparison between RF MEMS Switches and Semiconductor Switches

This paper addresses the fundamentals of RF switches providing a comparison between semiconductor and RF MEMS switches. The basis of comparison is introduced by defining a figure of merit that is a function of the off-state capacitance and the on-state resistance. A simple transmission line model is presented to illustrate the impact of the switch off-state capacitance on the switch isolation and frequency range of operation. The figure of merit analysis given in this paper demonstrates that RF MEMS switches have superior insertion loss and isolation performance in comparison to MESFET and p-i-n diode switches. The paper also addresses several other design considerations beside insertion loss and isolation for selecting the right RF switch. A discussion is given on the potential use of RF MEMS switches in satellite and wireless applications.

An L-band monolithic InAs/InP quantum dot mode-locked laser with femtosecond pulses

We have developed an InAs/InP quantum dot (QD) gain material using a double cap growth procedure and GaP sublayer to tune QDs into the L-band. By using it, a passive L-band mode-locked laser with pulse duration of 445 fs at the repetition rate of 46 GHz was demonstrated. The 3-dB linewidth of the RF spectrum is less than 100 KHz. The lasing threshold injection current is 24 mA with an external differential quantum efficiency of 22% and an average output power of 27 mW. The relationship between pulse duration and 3-dB spectral bandwidth as a function of injection current was investigated.

Optically induced fast wavelength modulation in a quantum cascade laser

An optically induced fast wavelength shift is demonstrated in a standard middle infrared (MIR) quantum cascade laser (QCL) by illuminating the front facet with a femtosecond (fs) near infrared (NIR) laser, allowing fast optical frequency modulation (FM) for free space optical communication (FSOC) and FM spectroscopy. Using an etalon as a narrow band-pass wavelength filter, the wavelength modulation (WM) was clearly observed at frequencies up to 1.67 GHz. This approach can also be used for wavelength conversion and might be extended to QCLs operating in different wavelength regions.

Characterization of diamond-like carbon by Raman spectroscopy, XPS and optical constants

Crystalline diamond coatings and, increasingly, diamond-like amorphous carbon (DLC) films are used for tribological and protective layers for their hardness and chemical inertness. They are also under investigation for their electron emitting properties, with possible applications in field emission displays. In this study, hydrogen-free DLC films were deposited by laser ablation using a KrF excimer laser and fluences between 0.5 and 2 J/cm(2). Information about the disorder and short range order in the films was gained via Raman spectra. As the ratio of graphitic and diamond bonds (sp(2) and sp(3)) is often hidden in these measurements, other analytical methods have to be included. XPS spectra exhibit for certain films the presence of sp(3) bonds or graphitic growth. For a better determination of the sp(3)-content, a correlation with optical properties in the near TR to near UV region was established. These values depended strongly on the substrate temperature and the laser fluence. DLC formation with large sp(3) contents could be demonstrated without substrate heating. Vickers hardness values and measurements on the electron emissivity of the films are strongly correlated to the sp(3) content and the preparation method of the films

High-speed all-optical modulation of a standard quantum cascade laser by front facet illumination

A simple experimental scheme to control intersubband lasing transition by optically induced nonresonant interband transition is presented, allowing for high-speed all-optical modulation of mid-infrared (MIR) quantum cascade laser (QCL). Illuminating the QCL front facet with 100 fs Ti:sapphire laser pulse, a fast modulation of a cw-MIR emission is observed with an estimated transient time of less than 81 ps, limited by instrument bandwidth, and a modulation depth of 18%. It has a great potential for high-speed modulation of high power QCL at room temperature.

Electron field emission from diamond-like carbon, a correlation with surface modifications

We report a series of experiments characterizing the emission obtained from near-amorphous carbon deposited by excimer laser ablation. We found that vacuum arc discharge and material transfer are responsible for morphology modifications that greatly enhance emission. When the morphology of the materials are well controlled, we find that our carbon has a work function one half that of silicon.

Room-Temperature Heterodyne Detection up to 110 GHz With a Quantum-Well Infrared Photodetector

A measurement of the photoresponse of a quantum-well infrared photodetector is presented. The detector response was measured from 80 K to 300 K. At 300 K, the high-frequency photocurrent response was measured up to 110 GHz and demonstrated a 1/omega decay

Effects of heat treatment on a MgOSi structure: a possible buffer layer structure for high-Tc superconductors

Abstract Thin films of MgO with a thickness of 0.1 μm were deposited by reactive rf sputtering on monocrystalline p-type Si substrates as a diffusion barrier for high- T c superconductor/semiconductor hybrid devices. After a heat treatment at temperatures from 700 to 1000°C in oxygen, the MgO Si samples were investigated by Auger electron spectroscopy (AES) for elemental distribution and differential capacitance measurements for surface electrical properties. The AES results showed the formation of a mixed MgO SiO x layer with a thickness of about 500 A after a treatment at 900°C for 1 h. The differential capacitance results showed a decrease of the minority carrier lifetime in Si after the treatment at temperatures above 800°C. The interface state density estimated from the preliminary capacitance results was about 10 11 cm −2 eV −1 .

Double-gated microtip emitters for brighter field-emission displays

Reducing the aperture of the beams emitted by microtips is important to increase the luminance of field-emission displays. Double-gated microtip emitters have been fabricated where the second gate is used to focus the beam emitted by the tip under the action of the attracting field produced by the first gate. The first gate is designed in a volcano shape to shield the apex of the tip from the second gate that is recessed under the level of the first one. This is rendered possible by using a thin rf sputtered SiO2 layer with very good dielectric properties between the two gates. The beam aperture is reduced from 25° to 7° when the second gate is biased at a voltage 15 V lower than the tip. No reduction in emitted current is observed when the second gate is biased at that voltage, which results in an eightfold increase in current density. Reducing the aperture of the beams emitted by microtips is important to increase the luminance of field-emission displays. Double-gated microtip emitters have been fabricated where the second gate is used to focus the beam emitted by the tip under the action of the attracting field produced by the first gate. The first gate is designed in a volcano shape to shield the apex of the tip from the second gate that is recessed under the level of the first one. This is rendered possible by using a thin rf sputtered SiO2 layer with very good dielectric properties between the two gates. The beam aperture is reduced from 25° to 7° when the second gate is biased at a voltage 15 V lower than the tip. No reduction in emitted current is observed when the second gate is biased at that voltage, which results in an eightfold increase in current density.

Effects of annealing on TlBaCaCuO thin films

We have studied the effects of high‐temperature anneals on sequentially deposited TlBaCaCu films in an environment containing O2 and TlOx . From Auger electron spectroscopy depth profiles, it was found that Tl was quite volatile and can be easily eliminated from the thin films after a short treatment at 830 °C. However, the Tl can be incorporated in the films after appropriate treatment.