A 360 BST Phase Shifter With Moderate Bias Voltage at 30GHz

438 IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 55, NO. 2, FEBRUARY 2007

A 360 BST Phase Shifter WithModerate Bias Voltage at 30 GHz

Gabriel Vélu, Karine Blary, Ludovic Burgnies, Aurélien Marteau, Grégory Houzet, Didier Lippens, andJean-Claude Carru

Abstract—Paraelectric BaSrTiO3 films deposited by sol-gel havebeen investigated from 1 kHz to 40 GHz using coplanar waveg-uides, resonators, and inter-digitated capacitances. At room tem-perature and without bias, the dielectric constant is around 300and the loss tangent is 5 10 2. Tunability is 40% for a 40-Vbias voltage. Analog phase-shifter circuits were subsequently fab-ricated in order to obtain a 360 phase shift in the -band witha moderate bias voltage. The lowest bias value was 17 V at 40 GHz,whereas 40 V were necessary at 30 GHz. For the latter condition,the insertion loss was 6 dB. The best figure-of-merit of the phaseshifters with a loading factor of 1. 4 was 27 /dB. These results showan improvement in terms of voltage-controlled tunability.

Index Terms—Analog phase shifters, dielectric characterization,ferroelectric thin films, interdigitated capacitors, tunability.

I. INTRODUCTION

FERROELECTRIC thin-film materials are good candidatesfor voltage-controlled applications at microwave and mil-

limeter waves. The variations of their complex permittivity (realand imaginary parts) with an applied dc field is used to tunethe operating frequency of passive components such as filters,delay lines, and phase shifters. One of the most mature ferro-electric material is barium titanate doped with strontium (BST).It combines high dielectric constant, moderate loss tangent, andsignificant tunability.

In the current study, we address the dielectric properties ofBa Sr TiO . This material compound is in the paraelectricstate at room temperature with better performance as we re-cently showed [1] by comparing paraelectric and ferroelectric-based phase shifters. BST films (0.3- m thick) have been de-posited by the sol-gel technique [2]. The main interest of thismethod is a good control of the composition all over the sub-strate area along its simplicity. In addition, we choose to de-

Manuscript received April 25, 2006; revised October 13, 2006. This workwas supported in part by the Region Nord-Pas de Calais under the frameworkof Contract CPER/TACT13 between the Region and the French State.

G. Vélu, L. Burgnies, and J.-C. Carru are with the Laboratory of Materialsand Components for Electronics, Université du Littoral-Côte d’Opale, 62228Calais, France (e-mail: [email protected]).

K. Blary, A. Marteau, and D. Lippens are with the Institut d’Electonique,de Microélectronique et de Nanotechnologie–Department of High Frequencyand Semiconductor, Groupe Quantom Opto and Micro Electronics Devices(DOME), Université de Lille 1, 59652 Villeneuve d’Ascq, France (e-mail:[email protected]).

G. Houzet was with the Laboratory of Materials and Components for Elec-tronics, Université du Littoral-Côte d’Opale, 62228 Calais, France. He is nowwith the Institut d’Electronique de Microélectronique et de Nanotechnologie,Université des Sciences et Technologies de Lille, 59652 Lille, France

Color versions of one or more of the figures in this paper are available onlineat http://ieeexplore.ieee.org.

Digital Object Identifier 10.1109/TMTT.2006.889319

velop an inter-digitated capacitance (IDC) technology avoidingseveral masking stages. In counterpart and to preserve a mod-erate tuning voltage, electron beam writing was used for fabrica-tion. From the application side, the key objective was to realizea 360 phase shift at millimeter wavelengths with a few tens ofdc-bias voltage.

Depending on the frequency of operation, the tuning voltageranges from 17 up to 40 V. To our knowledge, this is a sig-nificant improvement while maintaining a high level of perfor-mance with respect to state-of-the-art. The losses at millimeterwaves for unbiased devices is still a problem with a main contri-bution stemming from a mismatch at the access regions. How-ever, the overall losses (dielectric and return losses ) are reducedsignificantly under bias with 6 dB at 40 V and 30 GHz due toa better matching of loaded transmission lines and a decreaseof loss tangent. Another originality of this paper is the widecharacterization frequency range up to 40 GHz for the phaseshifter prototype and for unloaded transmission line integratingthin BST film. This permits us to assess the frequency depen-dence of the relative permittivity of BST with no relaxation ef-fects pointed out in - and -bands paving the way to use thistechnology for key millimeter applications notably at 60 GHz.

This paper is organized as follows. In Section II, we outlinethe material deposition method and the microwave character-izations of BST films in a wide frequency range. Section IIIdeals with the optimization of a phase shifter circuit notably interms of the loading factor and of the dimensions of interdigi-tated capacitors. Characterization of phase shifters is reported inSection IV with special attention on the differential phase shiftand insertion losses up to 40 GHz. Section V is devoted to atransmission line modeling of the phase shifter, assuming loss-less condition and full-wave numerical simulations by means ofa finite-element method.

II. MATERIALS AND CHARACTERIZATIONS

We used BST (50/50), as this material presents moderatelosses at microwaves and also good tunability. BST films weredeposited using a sol-gel technique [2] on the -axis orientedsapphire substrate with 2 2 0.05 cm dimensions. Thedeposition is carried out by spin coating and by repeating thesequence. Typically, we performed 20 repetitions, which per-mits us to obtain 300-nm-thick BST thin films. Crystallizationof film is obtained by heating the sample at 750 C during 1 hin the air.

Crystal quality of epilayers were characterized by X-raydiffraction. The films were polycrystalline, with a perovskitestructure, without secondary phases. Surface morphology was

0018-9480/$25.00 © 2007 IEEE

VÉLU et al.: 360 BST PHASE SHIFTER WITH MODERATE BIAS VOLTAGE AT 30 GHz 439

Fig. 1. SEM of an IDC. Finger width: 1.04 �m, finger spacing: 885 nm, pitch:1.99 �m.

characterized by a scanning electron micrograph (SEM) andatomic force microscopy. The BST surface is usually smooth,fairly uniform, and free of cracks, which are good features inview of the realization of tunable components.

Electrical characterization of films was carried out first ofall by means of a contactless technique in the -band. Inshort, the sample is inserted within a rectangular resonantcavity slightly changing its eigenmodes [3]. Transmission andreflection measurements were also performed by means ofelectrooptic sampling techniques whose results will be reportedelsewhere. In this study, microwave characterizations wereconducted in a wide frequency range, i.e., 1 kHz-40 GHz, usingmainly bare coplanar waveguide (CPW) lines and IDCs.

From the technological side, IDCs were patterned by electronbeam lithography (LECA EBPG 5000). Cr/gold deposition wasperformed by a standard liftoff process, whereas a gold overlaywas deposited by sputtering. Fig. 1 shows an SEM of a typicalIDC used as a discrete device or as a load of transmission line.

It is worth mentioning that discrete devices, as well as phaseshifters are fabricated on the same substrate in order to avoidany dispersion of material characteristic from wafer to wafer.

Fig. 2 shows the variations of the real part ( ) of the com-plex permittivity as a function of frequency measured at roomtemperature. A slight decrease of with frequency is observedfrom approximately 330 at 10 kHz to 290 at 40 GHz. This is inagreement with the empirical Curie–Von Schwindler Law usedin [4]. There is no dielectric relaxation domain in this investi-gated frequency range. Measurements up in the terahertz fre-quency range tends to confirm this trend up to 500 GHz. Theloss tangent is almost constant with frequency with an av-erage value of 5 10 in the frequency range investigated.

Turning now to the tunability, the variations of capacitanceas a function of a dc bias are reported in Fig. 3 from 40 to

40 V at a frequency of 22 GHz. This study has been con-ducted with finger-shaped IDCs having an unbiased capacitance

value around 0.1 pF. The topology is identical to that of ca-pacitance shown in Fig. 1 with a finger width and an interspacingof 1 m. No hysteresis effect is noticed, which gives evidencethat BST film is in a paraelectric state. Quantitatively, the ca-pacitance value decreases by a factor of 2 between the unbiasedcondition and a bias of 40 V. The dielectric permittivity was

Fig. 2. Frequency dependence of the real part of permittivity.

Fig. 3. Capacitance voltage characteristic measured at 22 GHz.

retrieved by means of the formula published in [5]. The voltagecontrol of is roughly the same as the capacitance one.

We have also measured the evolution of the conductanceupon bias. From and , can be determined as afunction of dc bias. As in [6], we found that is divided byapproximately 2 over the voltage range considered in this study:let us mention, however, that the consequence of such a decreasecan be of minor concern since, in a differential mode, we haveto take into account the worst case, i.e., the losses at 0 V. Thistunability was found rather constant (at 40%) from 1 kHz at leastup to 40 GHz. This evolution, independent of the frequency, isquite remarkable and shows that paraelectric BST films can beused as voltage-controlled material in microwaves, as well as inRFs.

III. OPTIMIZATION OF A PHASE SHIFTER

An analog BST phase shifter operating at millimeter waveswas first described by Liu et al. [7]. The circuit consists of aCPW line periodically loaded by interdigitated BST capacitors.Any change of capacitance values under a dc bias changes thecharacteristic impedance so that a taper section is needed at bothends of the CPW. Layout and close-up optical views of the phaseshifter, which illustrate the technology we employed, were dis-played in [1] with the report of a 310 /3.6-dB -band. In thisstudy, the dimension of the CPW lines are: 1) the width of thecentral strip 60 m; 2) the width of the slot: 180 m; and 3) the


Fig. 4. Comparison of tunability at 1 MHz of finger-shaped voltage-controlledcapacitances by varying the finger spacing.

metal thickness: 0.4 m. The length of a typical circuit with 29loading elements is approximately 1.5 cm.

In order to improve the performances of the devices, notablyin terms of phase shift and of insertion loss, we carried out aparametric study by varying: 1) the number of IDC per unitlength; 2) the relevant dimensions of IDCs; 3) the location IDCs;and 4) the shape of the taper. As seen in the following, theresults measured experimentally show overall the same trendsthan those expected by a transmission line model, at least in thelow part of the spectrum.

Of major concern is the maximum phase shift at moderatevoltage, depending mainly on the layout of BST capacitors. Tothis aim we varied the fingers spacing on a typical 1- m scale.In Fig. 4, we show the capacitance variations against voltagemeasured here at 1 MHz (but we saw above the frequency con-stant behavior) for three finger-shaped structures fabricated onthe same BST film. The width between fingers are 0.75, 1, and2 m, respectively, keeping constant the width to spacing ratio.For comparison, the unbiased values of capacitance were nor-malized to unity. It can be shown that micrometer and submi-crometer scale finger-shaped capacitance yields the highest ca-pacitance ratio. Enhanced fringing effects at shorter dimensioncan explain this optimum in the capacitance dimensions.

As a consequence, the phase shifters, which integrate IDCs,were realized using a 1- m technology. Such an issue was re-cently studied in detail [8] by means of a finite-difference time-domain numerical method. In addition, there exists a tradeoffbetween the difficulty of fabrication (notably of compatibilitywith a photolithography setup) and the performances of phaseshifters.

The second figure-of-merit, which is imperative to take intoaccount, is the insertion losses. To this aim, we varied the trans-verse dimensions of the coplanar line and the loading factor ,which is defined as the ratio per unit length between unbiasedIDC and distributed capacitance of the coplanar line. As shownin Fig. 5, the loading factor strongly influences the insertionlosses, which are plotted here at 10 GHz for three values of ,1.4, 2, and 3, respectively. It can be noticed that the losses in-crease drastically with , which has to be chosen close to 1.4for the range investigated here with a minimum insertion loss ofapproximately 5 dB. Let us mention that this value is close tothe one found by Nagra and York [9], which describephase shifters based on GaAs varactors.

Fig. 5. Insertion loss at 10 GHz as a function of loading factor.

Fig. 6. Phase versus frequency of scattering parameter S at 0-V dotted lineand at 40-V continuous line.

IV. PHASE-SHIFTER CHARACTERIZATION

The characterizations of the phase shifters were carried out atmicrowave by means of a vector network analyzer (VNA) fromAgilent Technologies (E8361A: 10 MHz-67 GHz) and coplanarprobes from GGB Industries (40A-GSG-125-DP). The VNAwas calibrated from 10 MHz to 40 GHz using a standard cal-ibration technique.

Fig. 6 shows the frequency dependence of the phase offor unbiased capacitances and with a 40-V bias. It can be seenthat the phase variations at 0 V are steeper than those at 40 Vand that the differential phase shift increases upon frequency.

The magnitude of (insertion loss) as a function of fre-quency is reported in Fig. 7 for 0 and 40 V, respectively. In-sertion losses are below 5 dB for a frequency around 30 GHzfor the latter and around 15 GHz for the former. A rapid rolloffcan be noted above these frequencies, which is explained by thefact that we are approaching Bragg frequency of circuit [9]. Theexplanation for higher insertion losses at 0 V is twofold. Firstof all, the characteristic impedance of the periodically loadedtransmission line is higher than 50 , typically 75 , whereas itis close to 50 with a 40-V bias. Secondly, dielectric losses ofBST at 40 V are less than the one at 0 V.

The variation of the differential phase shift as a function of thebias is reported in Fig. 8 for various frequencies. The objectiveof a 360 value of phase shift is obtained at 30 GHz with a 40-Vbias and at 40 GHz with 17 V only. To the best of our knowledge,this result compares favorably in terms of tuning voltage with


Fig. 7. Magnitude of S as a function of frequency.

Fig. 8. Phase shift versus bias voltage by taking frequency as a parameter.

Fig. 9. Phase shift versus frequency for various bias voltage.

respect to the results published in the literature. For instance, themaximum phase shift obtained by Liu et al. was 310 at 35 GHzwith a 100-V bias for a BST film deposited by sputtering. In thisstudy, the highest phase shift is 600 at 40 GHz with a 40-V bias.

Fig. 9 shows the variation of the differential phase shift as afunction of frequency for different values of the bias voltage.The evolution is linear up to approximately 25 GHz, which ishalf of the Bragg frequency for our phase shifter. The evolutionis then all the more nonlinear as we approach the Bragg fre-quency. A figure-of-merit is usually defined in degrees/deci-bels to take into account both the phase shift and insertion losses.

Fig. 10. K figure-of-merit as a function of frequency.

For the losses, as the phase shift is differential, we consider theworst case, i.e., the losses at 0 V.

The evolution of as a function of frequency is given inFig. 10 for bias ranging from 10 to 40 V. After a steep increase,

shows a slight decrease between 10–40 GHz defining anoperating frequency window. The maximum value range from7 /dB at 10 V to 27 /dB at 40 V.

V. CIRCUIT MODELING AND FULL-WAVE ANALYSIS

Let us now consider the general trends of circuit analysis,which can be conducted by means of a transmission line modelperiodically loaded by discrete capacitance in a parallel config-uration. For the sake of simplicity, we also assumes a losslesscase. The line is described by means of the distributed induc-tance in Henrys/meter and capacitance in Farads/meter.Over a circuit element is defined by (where can bedefined by the pitch of the periodic structure), the cumulatedinductance and capacitance are and

.With these notations, the phase constant of the unloaded

line is

(1)

For the loaded line and unbiased condition, the phase is

(2)

The corresponding phase with a bias is

(3)

The differential phase shift is

(4)

In this expression, is the loading index defined previously:and , and characterizes

the tunability.Expression (4) is valid for frequencies less than Bragg fre-

quency defined without bias by

(5)


Fig. 11. Maximum phase shift calculated by a circuit model and compared toexperiment.

The phase shift achieved by applying a maximum dc voltageis noted and is given by

(6)

with

As aforementioned, various phase shifters were fabricated withdifferent values of loading index ranging between 1–3. Fig. 11shows the experimental values of the phase shift measured at10 GHz and the values calculated with (6). wasobtained from the measurement of the BST capacitance withand without bias. Overall, the agreement between experimentand the circuit modeling is good. Moreover, the plots displayedin Fig. 11 show that the phase shift is almost constant for inexcess to 1.4. We also previously showed experimentally thatthe insertion losses are the lowest for , which appearsas the optimum loading factor, which gives the highest figure ofmerit.

From (6), the phase shift increases linearly with frequency.Fig. 12 thus shows the frequency dependence of up to20 GHz and compares these variations to experiment for a phaseshifter defined by . A good agreement is observed up to15 GHz, however, with a growing discrepancy above.

In conclusion, the circuit model appears relatively correct upto half of the Bragg frequency, whereas above a refined modeltaking into account all the losses appears necessary [9].

At higher frequencies, it become more and more difficultto analyze the phase shifter in a circuit formalism and, as aconsequence, full-wave electromagnetic modeling was carriedout using Ansoft’s commercial software High Frequency Struc-ture Simulator (HFSS) [10]. In a first stage, we performed thenumerical simulations of a coplanar line integrating a 0.3- m-thick BST film without taper and by targeting a characteristicimpedance .

Fig. 13 shows the calculated and variations versusfrequency that were compared with experimental results. Thebest fit was obtained for the following dielectric characteristicsof the BST film and . Let us note that

Fig. 12. Frequency variation of �� with x = 1:4.

Fig. 13. Comparison between full-wave analysis and experiment for a 50-bare CPW fabricated onto a 0.3-�m-thick BST layer.

these values are in rather good agreement with those determinedon IDCs.

In a second stage, we performed simulations of the phaseshifter. When we considered the full circuit, however, some dis-crepancy with the experiment appeared, which was explainedby numerical errors. In order to face such a difficulty, it wasthus decided to simulate one cell by full-wave analysis and touse a chain matrix technique afterwards in order to cascade thevarious elemental cells. The results of these calculations are dis-played in Fig. 14 for 0 and 35 V, respectively. For the latter, theagreement is very good if some discrepancy is apparent above20 GHz for the unbiased condition. As expected, a rapid rolloffof transmission is seen at 0 V due to a Bragg frequency around30 GHz, whereas this limitation is shifted at higher frequencyat 35 V due to the decrease in capacitance [see (5)].

VI. CONCLUSION

We have reported on microwave and millimeter-wave char-acterizations of Ba Sr TiO thin films deposited by sol-gelon a -axis sapphire. These films are in a paraelectric state atroom temperature. The mean value of the real part of the per-mittivity is , and for loss tangent, .The variation of permittivity as a function of a dc bias measuredfrom 40 to 40 V with interdigitated capacitors shows a tun-ability of 40 almost constant as a function of frequency.


Fig. 14. Comparison between full-wave analysis and experiment for a phaseshifter with x = 1:4 and a Bragg frequency of 30 GHz.

It was shown that loss decreases upon bias voltage, the lowestvalue being at 40 V. One way to decrease hasbeen proposed by Tagantsev et al. [11] for BST ceramics. It con-sists of introducing inclusions of dielectric particles with verylow loss, typically MgO. A loss tangent of 0.01 at 10 GHz wasthus demonstrated by the authors. It is believed that such a tech-nique could be adapted to a sol-gel technique in order to deposita BST/MgO film on sapphire. It has also been recently reportedthat small concentrations of acceptor dopants can dramaticallymodify the properties of perovskite oxide thin-film materialssuch as BST. To date, the most notable reduction of loss hasalso been demonstrated in Mg acceptor doped BST thin films[14]–[16].

Analog phase shifters using BST interdigitated capacitors ona micrometer scale periodically loading a high-impedance CPWline were subsequently fabricated. The design was optimized inorder to obtain a high phase shift in the -band. A 600 phaseshift was obtained at 40 GHz with a 40-V bias and 360 with a17-V bias. At 40 GHz, the losses of the circuit without bias arerelatively high, with a figure-of-merit of 22 /dB @ 40 GHzand 40 V. Work is in progress to fabricate left-handed phaseshifters using the same technology, which can also be designedto realize composite left- and right-handed ones. First attemptsto realize such phase shifters were published very recently in[12] and [13].

ACKNOWLEDGMENT

The authors thank P. Mounaix, Centre de Physique Molécu-laire Optique et Hertzienne (CPMOH) Laboratory, BordeauxUniversity, Bordeaux, France, for the terahertz measurementsmade on our BST films between 0.2–1.5 THz.

REFERENCES

[1] G. Vélu, K. Blary, L. Burgnies, J. C. Carru, E. Delos, A. Marteau, andD. Lippens, “A 310 /3.6 dB K-band phase shifter using paraelectricBST thin films,” IEEE Microw. Wireless Compon. Lett., vol. 16, no. 2,pp. 87–99, Feb. 2006.

[2] G. Vélu, J. C. Carru, E. Cattan, D. Remiens, X. Mélique, and D. Lip-pens, “Deposition of ferroelectric BST thin films by sol-gel route inview of electronic applications,” Ferroelectrics, vol. 288, pp. 59–69,2003.

[3] D. C. Dube, M. T. Lanagan, J. H. Kim, and S. J. Jang, “Dielectricmeasurements on substrate materials at microwave frequencies usinga cavity perturbation technique,” J. Appl. Phys., vol. 63, no. 7, pp.2466–2468, Apr. 1988.

[4] T. Hamano, D. J. Towner, and B. W. Wessels, “Relative dielectric con-stant of epitaxial BaTiO thin films in the GHz frequency range,” Appl.Phys. Lett, vol. 83, no. 25, pp. 5274–5276, Dec. 2003.

[5] S. S. Gevorgian, T. Martinsson, P. L. J. Linner, and E. L. Kollberg,“CAD models for multilayered substrate interdigital capacitors,” IEEETrans. Microw. Theory Tech., vol. 44, no. 6, pp. 896–904, Jun. 1996.

[6] G. Vendik, S. P. Zubko, and M. A. Nikol’ski, “Microwave loss factoras a function of temperature, biasing field, barium concentration andfrequency,” J. Appl. Phys., vol. 92, pp. 7448–7452, Dec. 2002.

[7] Y. Liu, S. Nagra, E. Erker, P. Periaswany, T. Taylor, J. Speck, and R.York, “BaSrTiO interdigitated capacitors for distributed phaseshifterapplications,” IEEE Microw. Guided Wave Lett., vol. 10, no. 11, pp.448–450, Nov. 2000.

[8] A. Giere, P. Scheele, C. Damm, and R. Jakoby, “Optimization of uni-planar multilayer structures using non linear tunable dielectrics,” inProc. 35th Eur. Microw. Conf., Paris, France, Oct. 2005, pp. 561–564.

[9] A. S. Nagra and R. A. York, “Distributed analog phase shifters withlow insertion loss,” IEEE Trans. Microw. Theory Tech., vol. 47, no. 9,pp. 1705–1711, Sep. 1999.

[10] HFSS. ver. 9, Ansoft Corporation, Pittsburgh, PA, 2005.[11] A. K. Tagantsev, V. O. Sherman, K. F. Astafiev, J. Venkatesh, and N.

Setter, “Ferroelectric materials for microwave tunable applications,” J.Electroceram., vol. 11, pp. 5–66, 2003.

[12] D. Kuylenstierna, A. Vorobiev, P. Linner, and S. Gevorgian, “Com-posite right/left handed transmission line phase shifter using ferroelec-tric varactors,” IEEE Microw. Wireless Compon. Lett., vol. 16, no. 4,pp. 167–169, Apr. 2006.

[13] J. Perruisseau and A. K. Shrivervik, “Composite right/left handedtransmission line metamaterial phase shifters (MPS) in MMICtechnology,” IEEE Trans. Microw. Theory Tech., vol. 54, no. 4, pp.1582–1589, Apr. 2006.

[14] M. W. Cole, C. Hubbard, E. Ngo, M. Ervin, M. Wood, and R. G.Geyer, “Structure-property relationships in pure and acceptor-dopedBa Sr TiO thin films for tunable microwave device applications,”J. Appl. Phys., vol. 92, pp. 475–483, 2002.

[15] P. C. Joshi and M. W. Cole, “Mg-doped Ba Sr TiO thin filmsfor tunable microwave applications,” Appl. Phys. Lett., vol. 77, pp.289–291, 2000.

[16] M. W. Cole, W. D. Nothwang, C. Hubbard, E. Ngo, and M. Ervin,“Low dielectric loss and enhanced tunability of Ba Sr TiO basedthin films via material compositional design and optimized film pro-cessing methods,” J. Appl. Phys., vol. 93, pp. 9218–9225, 2003.

Gabriel Vélu was born in Béthune, France, in 1969.He received the Ph.D. degree in génie des procédésfrom the Université de Valenciennes et du HainautCambrésis, Valenciennes, France, in 1998.

In 1999, he joined the Université du Littoral-Côted’Opale, Calais, France, where he is currently anAssistant Professor and a member of the Laboratoired’Etudes des Matériaux et des Composants pourL’Electronique (LEMCEL). His research interestsinclude ferroelectric thin-films depositions and theirtunable applications in the microwave field.

Karine Blary was born in Orléans, France, in 1975.She received the Engineer degree with a specialityin material science from the Ecole Universitaire DesIngénieurs de Lille (EUDIL), Lille, France, in 1999,and the Ph.D. degree for her work on opto-electronicswitching devices with the Institut d’Electonique, deMicroélectronique et de Nanotechnologie (IEMN)from the Université de Lille 1, Villeneuve d’Ascq,France, in 2003.

She is currently a Research Engineer in charge ofprocess development with the “open lab” service,

Université de Lille 1, which is concerned with the collaboration between otheracademic research centers in France and with the IEMN. She has recently beeninvolved in electronics, opto-electronics, and microelectromechanical systems(MEMS) projects.


Ludovic Burgnies received the Ph.D. degree inelectronics from the Université de Lille 1, Villeneuved’Ascq, France, in 1997.

From 1994 to 1997, he was focused on transportanalysis in electronic quantum devices. In 1999,he joined the Université du Littoral–Côte d’Opale,Calais, France, where he is currently an AssistantProfessor. His main research is concerned withthe design of agile microwave devices based onferroelectric materials.

Aurélien Marteau was born in Saint Jean d’Angely,France, in 1979. He received the Engineer degreefrom the Ecole Nationale Supérieure d’Ingénieursde Limoges (ENSIL), Limoges, France, in 2003,the Master degree from the University of Limoges(DEA Télécommunications Hautes Fréquences etOptiques), Limoges, France, in and is currentlyworking toward the Ph.D. degree within the DOMEGroup, Institut d’Electronique, de Microélectroniqueet de Nanotechnologie (IEMN), Université des Sci-ences et Technologies de Lille (USTL), Villeneuve

d’Ascq, France.His current interests concern the modeling of complex electromagnetic struc-

tures including double-negative media and their fabrication and characteriza-tion.

Grégory Houzet was born in Cambrai, France,on November 21, 1982. He received the Masterdegree from the Université du Littoral Côte d’Opale(ULCO), Calais, France, in 2006, and is currentlyworking toward the Ph.D. degree at the Institutd’Electronique de Microélectronique et de Nan-otechnologie (IEMN), Université des Sciences etTechnologies de Lille (USTL), Lille, France.

His current interests concern transmission mediumwith metamaterials and negative-refraction devices.

Didier Lippens received the Master of Sciencedegree in electronics engineering, Ph.D. degree, andDoctor ès Sciences degree from the Université desSciences et Technologies de Lille, Lille, France, in1975, 1978, and 1984, respectively.

From 1980 to 1981, he was a Research Engineerwith Thomson CSF, where he led the Quantum andTerahertz Devices Team until 2001. He is currentlythe Head of the Quantum Opto and Micro ElectronicsDevices Group (DOME), Department of High Fre-quency and Semiconductor, Institut d’Electronique

de Microélectronique et de Nanotechnologie (IEMN), Université de Lille 1,Villeneuve d’Ascq, France. He is currently a Professor of electrical engineeringwith the Université de Lille 1, where he is mainly concerned with nanotech-nology and nanosciences. He has been involved with molecular dynamics inliquid crystals and semiconductors physics and is currently more concernedwith nonlinear electronics and opto-electronics along with electromagnetism inartificial media. He has undertaken pioneering research on resonant tunnellingdevices and, more generally, on heterostructure semiconductor devices. Hiscurrent interests are terahertz sources, notably quantum cascade lasers (QCLs),photomixers and heterostructure barrier varactors, photonic bandgaps, andmetamaterials-based passive and active devices.

Jean-Claude Carru is currently a Professor ofelectrical engineering with the University of Lit-toral-Côte d’Opale, Calais, France, where since1992, he has also been the Director of the Labo-ratoire d’Etudes des Matériaux et des Composantspour L’Electronique (LEMCEL), Calais, France. Hehas coauthored over 160 scientific publications. Hiscurrent research interest concerns the characteriza-tion of materials in a large-frequency range fromdc to millimeter waves in view of applications inelectronics.

A 360 BST Phase Shifter With Moderate Bias Voltage at 30GHz

Documents