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Stefanescu A.,IMT Bucharest | Neculoiu D.,IMT Bucharest | Konstantinidis G.,FORTH IESL MRG Heraklion | Cismaru A.,IMT Bucharest | And 3 more authors.
Proceedings of the International Semiconductor Conference, CAS | Year: 2010

Analytical and finite element models of submicron Film Bulk Acoustic Resonator (FBAR) based on GaN are reported. The analytical modelling is based on Mason's model for three composite layer 257-260 FBAR structure. The numerical modelling shows good agreement with theoretical and experimental results previously obtained on FBAR operating around 6 GHz. © 2010 IEEE.


Stefanescu A.,IMT Bucharest | Muller A.,IMT Bucharest | Konstantinidis G.,FORTH IESL MRG Heraklion | Buiculescu V.,IMT Bucharest | And 4 more authors.
Proceedings of the International Semiconductor Conference, CAS | Year: 2012

We report on new models developed for surface acoustic wave resonators (SAW) on GaN/Si substrate working on frequencies above 5 GHz. The devices are composed of interdigital transducers (IDT) with finger and interdigit spacings 200nm wide. Different examples of modeling these devices, from 1D equivalent circuit to 3D FEM model are presented. The simulations are validated with experimental results for one port SAW and for a two port resonator SAW devicse. © 2012 IEEE.


Muller A.,IMT Bucharest | Stavrinidis A.,FORTH IESL MRG Heraklion | Giangu I.,IMT Bucharest | Giangu I.,Polytechnic University of Bucharest | And 6 more authors.
IEEE MTT-S International Microwave Symposium Digest | Year: 2016

Two different novel SAW type pressure sensing structures were manufactured using micromachining and nanolihographic processes: SAW supported on a GaN/Si (1.2 μm/ 10 μm) membrane for the first type structure and SAW supported on a 1.2 μm thin GaN membrane for the second type. The two resonance peaks observed for both structures were identified, using wave shape simulations, as Rayleigh mode and symmetric Lamb mode, respectively. The resonance frequency shift vs. pressure (measured in the 1-5 Bar range), as well as the pressure sensitivity and its sign have been analyzed for both structures and both peaks. High absolute values of the sensitivity (in the range 346... 2680 kHz/Bar) and of the pressure coefficient of frequency (in the range 66... 278 ppm/Bar) have been obtained. It was demonstrated that the second type structures and the Lamb mode are more pressure sensitive. © 2016 IEEE.


Bunea A.-C.,IMT Bucharest | Neculoiu D.,IMT Bucharest | Dragoman M.,IMT Bucharest | Konstantinidis G.,FORTH IESL MRG Heraklion | Deligeorgis G.,FORTH IESL MRG Heraklion
European Microwave Week 2015: "Freedom Through Microwaves", EuMW 2015 - Conference Proceedings; 2015 45th European Microwave Conference Proceedings, EuMC | Year: 2015

In this paper we present, for the first time, a X band slot antenna with a shorted graphene patch. The graphene patch is biased through the signal and ground of the coplanar waveguide feed. The change in the electric field determines a change of the impedance of the graphene sheet, leading to tuning of the antenna behavior. The 3D electromagnetic design and simulation will be presented. The structures were fabricated on high-resistivity silicon with a 0.3 μm thick silicon oxide layer and a single layer graphene sheet deposited by Graphenea. The experimental results are in good agreement with the simulations and show a tunability of over 20 dB in the minimum of the reflection losses and a 7.5 MHz frequency shift. The measured operating bandwidth (|S11| <-10 dB) is between 9.3-10.435 GHz. © 2015 EuMA.


Muller A.,IMT Bucharest | Konstantinidis G.,FORTH IESL MRG Heraklion | Dinescu A.,IMT Bucharest | Buiculescu V.,IMT Bucharest | And 6 more authors.
THERMINIC 2013 - 19th International Workshop on Thermal Investigations of ICs and Systems, Proceedings | Year: 2013

Microwave integrated circuits based on GaN are able to work at high temperatures. In the same time, the temperature in GaN based MMICs has to be carefully monitored. A reliable method to measure the temperature for Silicon integrated circuits is based on the change of the I-V characteristic of a p-n junction. This type of measurement cannot be applied on GaN based circuits. A possible way to measure the temperature in GaN MMICs can be based on a SAW resonator. The SAW resonator changes its resonance frequency when temperature changes. A lot of research and industrial developments have already used SAW based delay lines, based on quartz, or LiNbO3, for temperature measurements. The SAW based sensors offer the possibility to monitor the temperature wireless [1], [2], but, some applications require wired temperature reading. © 2013 IEEE.


Muller A.,IMT Bucharest | Neculoiu D.,Polytechnic University of Bucharest | Konstantinidis G.,FORTH IESL MRG Heraklion | Vaha-Heikila T.,VTT Technical Research Center of Finland
NATO Science for Peace and Security Series B: Physics and Biophysics | Year: 2010

A review of recent developments of membrane supported millimeter wave circuits based on GaAs micromachining, performed in authors' labs. is presented. Coupled line band pass filters for 35 GHz, Yagi-Uda antennae for 60 GHz having as support a 2 μm thin GaAs membrane are presented. Also the manufacturing direct, video-type receiver module having the Yagi-Uda antenna and Schottky diode monolithic integrated on the same GaAs membrane is presented. The very good results obtained on the measurements of these circuits have demonstrated the high capabilities of GaAs micromachining in manufacturing of high performances millimeter wave circuits and the potential advantage of these technologies for the sub-millimeter wave frequency range were other solutions are not available. © 2010 Springer Science+Business Media B.V.


Muller A.,IMT Bucharest | Konstantinidis G.,FORTH IESL MRG Heraklion | Giangu I.,IMT Bucharest | Buiculescu V.,IMT Bucharest | And 5 more authors.
IEEE MTT-S International Microwave Symposium Digest | Year: 2014

The paper presents the manufacturing of GaN based single SAW resonator temperature sensing structures, having IDTs with fingers/interdigit spacing width within 200-120 nm range. 'On wafer' hot plate resonance frequency vs. temperature measurements were performed in the 20-150°C temperature range. Further measurements have been performed in the -268-+150°C temperature range, using a cryostat setup. The sensitivities obtained demonstrate the advantage of GaN SAW resonators as temperature sensors. © 2014 IEEE.


Stefanescu A.,IMT Bucharest | Neculoiu D.,IMT Bucharest | Muller A.,IMT Bucharest | Dinescu A.,IMT Bucharest | And 2 more authors.
Romanian Journal of Information Science and Technology | Year: 2011

This paper proposes an analysis of two types of Surface Acoustic Wave (SAW) resonators composed of interdigital transducers (IDT) of 200 nm wide on GaN/Si devoted for GHz applications. Two finite element (FEM) models for basic periodic cells are given to demonstrate de characteristics of the resonators at different resonance frequencies. E-beam lithographical techniques have been used for the IDT fingers. Experimental measurements of the S parameters have shown a good agreement with the simulation results regarding the resonance frequency.


Stefanescu A.,IMT Bucharest | Muller A.,IMT Bucharest | Dinescu A.,IMT Bucharest | Konstantinidis G.,FORTH IESL MRG Heraklion | And 3 more authors.
Proceedings of the International Semiconductor Conference, CAS | Year: 2011

For the integration of surface acoustic wave (SAW) devices with nanostructures, numerical simulations must be employed. This paper describes finite element (FEM) models for a basic periodic cell of two types of SAW devices on GaN/Si devoted for GHz applications. E-beam lithographical techniques have been used for IDT fingers of 200nm wide. On wafer measurements of S parameters have shown a good agreement with the simulation results regarding the operation frequency. © 2011 IEEE.


Muller A.,IMT Bucharest | Konstantinidis G.,FORTH IESL MRG Heraklion | Buiculescu V.,IMT Bucharest | Dinescu A.,IMT Bucharest | And 6 more authors.
Sensors and Actuators, A: Physical | Year: 2014

The paper presents the manufacturing and characterization of GaN based SAW (surface acoustic wave) type temperature sensors. In contrast with most SAW sensor structures, manufactured on classical piezoelectric materials where delay lines or two port resonators have been used, in this paper, the resonance frequency shift vs. temperature for a single resonator structure was used for temperature measurements. It is demonstrated that the single resonator SAW structures ensure better performances in terms of sensitivity and losses compared with two port resonator structures. The sensor structure was manufactured using deep submicron e-beam nano-lithographic process on GaN/Si (finger width and interdigit spacing of 200 nm) and resonance frequencies higher than 5 GHz have been obtained at room temperature. The high resonance frequency ensures an increase of the sensitivity of the sensor structure. The sensor was characterized by "on wafer" resonance frequency shift and sensitivity measurements in the 23-150 C temperature range using S11 reflection parameter. The resonance frequency shift vs. temperature and the sensitivity for the sensor structures assembled on a special ceramic carrier, were measured, in a cryostat, in the -268-+150 C temperature range. Sensitivities higher than 300 kHz/ C, (corresponding to values higher than 50 ppm/ C) have been obtained. © 2014 Elsevier B.V.

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