Low-thickness high-quality aluminum nitride films for super high frequency solidly mounted resonators

We investigate the sputter growth of very thin aluminum nitride (AlN) films on iridium electrodes for electroacoustic devices operating in the super high frequency range. Superior crystal quality and low stress films with thicknesses as low as 160 nm are achieved after a radio frequency plasma treatment of the iridium electrode followed by a two-step alternating current reactive magnetron sputtering of an aluminum target, which promotes better conditions for the nucleation of well textured AlN films in the very first stages of growth. Solidly mounted resonators tuned around 8 GHz with effective electromechanical coupling factors of 5.8% and quality factors Q up to 900 are achieved.

Fabricación y caracterización de wolframio nanoestructurado como material de primera pared en reactores de fusión nuclear

El trabajo que se llevará a cabo se basa en el desarrollo de nuevos materiales que sean capaces de resistir las condiciones extremas a las que estarían expuestos en el interior de un reactor de fusión nuclear, como son los altos choques térmicos y los altos flujos iónicos. Actualmente se está investigando en el potencial del wolframio nanoestructurado como material de primera pared (en inglés PFM: Plasma Facing Material). La principal ventaja de éste frente al wolframio masivo radica en su gran densidad de fronteras de grano que hacen que el material sea más resistente a la irradiación. El objetivo de este trabajo será la búsqueda de las condiciones óptimas para la fabricación de recubrimientos de wolframio nanoestructurado mediante la técnica de pulverización catódica ("sputtering") en diferentes configuraciones, continuo ("Direct Current Magnetron Sputtering" o DCMS) y/o pulsado ("High Power Impulse Magnetron Sputtering" o HiPIMS) y caracterizar sus propiedades como PFM mediante perfilometría, microscopía óptica, microscopía electrónica de barrido ("Scanning Electron Microscope" o SEM) y difracción de rayos X ("X-Ray Diffraction" o XRD). A su vez, se realizará un ensayo de implantación con un plasma pulsado de He para analizar los efectos de la irradiación en uno de los recubrimientos. Abstract: The work that will be carried out is based on the development of new materials capable of withstanding the extreme conditions that they will have to face inside a nuclear fusion reactor, such as high thermal loads and high ion fluxes. Currently, nanostructured tungsten potential is being investigated as a plasma facing material (PFM). The main advantage over coarse grain tungsten is its high density of grain boundaries which make the material more resistant to irradiation. The project´s main objective will be the search of the optimal conditions that will allow us to fabricate nanostructured tungsten thin films by using the sputtering technique in different configurations, such as DCMS (Direct Current Magnetron Sputtering) and/or HiPIMS (High Power Impulse Magetron Sputtering) and characterize their properties as a PFM by perfilometry, optical microscopy, SEM (Scanning Electron Microcopy) and XRD (X-Ray Diffracion) analysis. Moreover, an implantation test with a He pulsed plasma will be carried out to analyze the effects of irradiation on one of the coatings.

Hydrogenated amorphous silicon deposited by high pressure sputtering for HIT solar cells

Hydrogenated amorphous silicon thin films were deposited using a high pressure sputtering (HPS) system. In this work, we have studied the composition and optical properties of the films (band-gap, absorption coefficient), and their dependence with the deposition parameters. For films deposited at high pressure (1 mbar), composition measurements show a critical dependence of the purity of the films with the RF power. Films manufactured with RF-power above 80W exhibit good properties for future application, similar to the films deposited by CVD (Chemical Vapor Deposition) for hydrogenated amorphous silicon.

Progresos en sub-sistemas RF y control de la Antena Adaptativa Multihaz GEODA

GEODA project started in 2006 as a complex and ambitious project in the smart antenna field. GEODA is a multiple planar array smart antenna working at 1.7 GHz designed to receive and automatically track several LEO satellite signals simultaneously [1-4]. GEODA evolved to GEODA-GRUA since transmission capabilities were given to the original idea [5-6], so that radiofrequency sub-systems had to be re-designed and digital management subsystem modified accordingly. In this paper, improvements in the reception/transmission (T/R) modules as well as in the Control Subsystem are presented, keeping the original radiating element.

Optically Reconfigurable RF Circuits using Silicon Switches

Mobile and wireless communications systems have become an important part of our everyday lives. These ubiquitous technologies have a profound effect on how we live. People predict bright future to wireless technologies, but it wouldn’t be possible without a hard work of thousands of scientists in the wireless innovation research arena. My Marie Curie project is investigating enabling technologies for future mobile and wireless communications systems

Fabrication process of Mo/Au TES at RT

We report on the fabrication details of TES based on Mo/Au bilayers. The Mo layer is deposited by radio frequency (RF) sputtering and capped with a sputter deposited thin Au protection layer. Afterwards, a second Au layer of suitable (lower) resistivity is deposited ex‐situ by e‐beam evaporation, until completion of the total desired Au thickness. The deposition was performed at room temperature (RT) on LPCVD Si3 N4 membranes. Such a deposition procedure is very reproducible and allow controlling the critical temperature (Tc) and normal electrical resistance (RN ) of the Mo/Au bilayer. The process is optimized to achieve low stress bilayers, thus avoiding the undesirable curvature of the membranes. Bilayers are patterned using photolithographic techniques and wet etching procedures. Mo superconducting paths are used to contact the Mo/Au bilayers, thus ensuring good electrical conductivity and thermal isolation. The entire fabrication process let to stable and reproducible sensors with required and tunable functional properties

Control of the morphology on selective area growth of GaN nanocolumns by rf-plasma-assisted

Selective area growth (SAG) of GaN nanocolumns (NCs), making use of patterned or masked (nanoholes) substrates, yields a periodic, homogeneous distribution of nanostructures, that makes their processing much easier compared with self-assembled ones. In addition, the control on the diameter and density of NCs avoids dispersion in the electrooptical characteristics of the heterostructures based on this type of material (embedded InGaN/GaN quantum disks for example). Selective area growth using a mask with nanohole arrays has been demonstrated by rf-plasma-assisted MBE [1, 2].

Amplificador de envolvente de señales de RF basado en el convertidor buck multifase

En este trabajo se presenta un convertidor DC-DC buck de dos fases de alta velocidad adecuado para emplear en técnicas de linealización de amplificadores como ET (Envelope Tracking) o EER (Envelope Elimination and Restoration). El convertidor ha sido realizado con tecnología LDMOS y la técnica usada para controlarlo ha sido modulación PWM, creada mediante procesado digital y un generador de funciones. La potencia de salida es de hasta 125W de pico, con un rendimiento del 80%, un ancho de banda de hasta 2MHz y en las medidas de linealidad presenta una atenuación a los productos de intermodulación de tercer orden de más de 45 dBc.

Procedimiento De Amplificador De Envolvente De Señales Moduladas En RF Para Técnicas EER Y ET

An envelope amplifier for an EER (Envelope Elimination and Restoration) and ET (Envelope Tracking) techniques is shown in this paper. The amplifier is based on a high speed two phases buck converter and employs RF LDMOS technology for the switching stage. A DPWM (Digital Pulse With Modulation) signal is used to control the amplifier by means of a functions generator. Simulations and measurements on a circuit prototype are presented showing a good agreement. Up to 125W output peak power can be delivered over a 5Ω load resistor. About 80% efficiency has been obtained. And at the two tone test, the third order intermodulation products (IP3) remain below 45dBc over a 2MHz bandwidth.

Monitoring maximum peak power density values as a more reliable marker for measurement procedures to elucidate RF EMF health effects: Leganes project

Considering the measurement procedures recommended by the ICNIRP, this communication is a proposal for a measurement procedure based in the maximum peak values of equivalent plane wave power density. This procedure has been included in a project being developed in Leganés, Spain. The project plans to deploy a real time monitoring system for RF to provide the city with a useful tool to adapt the environmental EM conditions to the new regulations approved. A first stage consisting of 105 measurement points has been finished and all the values are under the threshold of the regulation.

Design methodology in multiphase buck converter based on minimum time control for high efficiency RF amplifiers

This paper proposes an interleaved multiphase buck converter with minimum time control strategy for envelope amplifiers in high efficiency RF power amplifiers. The solution of the envelope amplifier is to combine the proposed converter with a linear regulator in series. High system efficiency can be obtained through modulating the supply voltage of the envelope amplifier with the fast output voltage variation of the converter working with several particular duty cycles that achieve total ripple cancellation. The transient model for minimum time control is explained, and the calculation of transient times that are pre-calculated and inserted into a look-up table is presented. The filter design trade-off that limits capability of envelope modulation is also discussed. The experimental results verify the fast voltage transient obtained with a 4-phase buck prototype.

Design of envelope amplifier based on interleaved multiphase buck converter with minimum time control for RF application

In this paper, an interleaved multiphase buck converter with minimum time control strategy for envelope amplifiers in high efficiency RF power amplifiers is proposed. The solution for the envelope amplifier is to combine the proposed converter with a linear regulator in series. High efficiency of envelope amplifier can be obtained through modulating the supply voltage of the linear regulator. Instead of tracking the envelope, the buck converter has discrete output voltage that corresponding to particular duty cycles which achieve total ripple cancellation. The transient model for minimum time control is explained, and the calculation of transient times that are pre-calculated and inserted into a lookup table is presented. The filter design trade-off that limits capability of envelope modulation is also discussed. The experimental results verify the fast voltage transient obtained with a 4-phase buck prototype.

Multiphase Buck Converter with Minimum Time Control Strategy for RF Envelope Modulation

Power amplifier supplied with constant supply voltage has very low efficiency in the transmitter. A DC-DC converter in series with a linear regulator can be used to obtain voltage modulation. Since this converter should be able to change the output voltage very fast, a multiphase buck converter with a minimum time control strategy is proposed. To modulate supply voltage of the envelope amplifier, the multiphase converter works with some particular duty cycle (i/n, i=1, 2 ... n, n is the number of phase) to generate discrete output voltages, and in these duty cycles the output current ripple can be completely cancelled. The transition times for the minimum time are pre-calculated and inserted in a look-up table. The theoretical background, the system model that is necessary in order to calculate the transition times and the experimental results obtained with a 4-phase buck prototype are given

Optimum Design of an Envelope Tracking Buck Converter for RF PA using GaN HEMTs

In this paper, filter design methodology and application of GaN HEMTs for high efficiency Envelope Amplifier in RF transmitters are proposed. The main objectives of the filter design are generation of the envelope reference with the minimum possible distortion and high efficiency of the amplifier obtained by the optimum trade-off between conduction and switching losses. This optimum point was determined using power losses model for synchronous buck with sinusoidal output voltage and experimental results showed good correspondence with the model and verified the proposed methodology. On the other hand, comparing to Si MOSFETs, GaN HEMTs can provide higher efficiency of the envelope amplifier, due to superior conductivity and switching characteristics. Experimental results verified benefits of GaN devices comparing to the appliance of Si switching devices with very good Figure Of Merit, for this particular application

Series combination of a switched dc-dc converter and a linear regulator for high frequency RF envelope amplifier

Classical linear amplifiers such as A, AB and B offer very good linearity suitable for RF power amplifiers. However, its inherent low efficiency limits its use especially in base-stations that manage tens or hundreds of Watts. The use of linearization techniques such as Envelope Elimination and Restoration (EER) allow an increase of efficiency keeping good linearity. This technique requires a very fast dc-dc power converter to provide variable voltage supply to the power amplifier. In this paper, several alternatives are analyzed to implement the envelope amplifier based on a cascade association of a switched dc-dc converter and a linear regulator. A simplified version of this approach is also suitable to operate with Envelope Tracking technique.