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Trend on Silicon Technologies for Millimetre Wave Applications up to 220 GHz

Microwave andchnologiesfrom Photonic Bandgap Devices to Antenna and Applicationsalternative to classical Ill-v technologies to address millimetre-wave applicationsGe hbt devices with cutoff frequenz(Kuhnnd 300 GHz(Rieh et al, 2004)respectivelmentation ofwave system-on-chip (SoC) such as 60 GHz WLAN(Floyd et al, 2006),(Doan40/80/160 Gb/s optic-fiber transceivers (Perndl et al, 2004)or 24/77 GHoweverhigh performances pakey issue in1esupport for active function development, passive functions being implemented on siliconusing specific technologies such as membrane technologies (Vu et al, 2008)hin film0),(Wolf et al, 2005) Nevertheless, if such techneoved their efficacy fefunctions, theirdifficult since they need complex technological process, Recent work(Gianesello et al, 2006)have demonstrated thatto adapplications up to G-band (140-220 GHz) if high resistivity(HR) silicon-on-standard technology has been demonstrated(Montusclaal, 2005) and HR SOltechnology has proved its efficacy to improve the overall performances of integratedantennas However, in millimeter frequency range the bea, the required selectivity levels,appears as one of the most critical point

Hence, in vied,faced with problems in relation to control design, ie modellingaccuracy, as well as the high insertionels inherent in such deviceslow electrical lengths involved in millimetre-wave, the technological dispersion has to be asion of tecanctions in millimetre-wave frequency range Ill-V technologies that are behind themillimetre- microwave functionsobtained in Ill-v technology for wide- andband filters reported herewill be the reference for comparison with other technologies Several technological processdicated to silicon technologies were then studied membrane and thin film microstriptechnologies Finally, millimetre-wave electrical perff deviceonents and active circuits achieved in sT-Microelectrordvanced cMOSHR SOI technoloas to investigate for the suitability of that technology to addresmillimetre-wave Systems on Chip (SOC)up to 220 GHz and beyond Classical stub-basedplemented in coplanar waveguide technology were first designed so asetitive withtechnologies, Then, the design of coupled-lineswand filtersthe vat 60 GHz These concepts were validated througcomparison with experiments performed up to 220 GHzntechopen

rend on Silicon Technologies for Millimetre-Wave Applications up to 220 GHzrealized on a 400-um-thick silicon substrate9, tand=0018) The technologicalprocess is composed of five main steps as depicted in Figdeposited on the front side Next, the elaboration of metal level is performed by first themould After the suppression of photoresist mould, the seed layer is suppressed in the slotThe third step is to realize air bridges a photoresist mould is used to fill up coplanar slotsen depositedbridges, a gold seedevaporated and then 3-Hm-thick gold is electroplated Theremoving silicon substrate in the back side SiDeep Reactive lon Etching(DRIE)technion brane breaking during DRIE process, the waferrough a thick photoresist mould Moreis bondedupport one in the front side

Finally, the structures are released from thebath followed by co2 drvinf dielectric, the membrane possesses a mechanical stiffness strong enough to absorbthe stresses induced by various technological processes while retaining effective permittivityFig 8 Membrane technological process32 Wide-band bandpass filter Desigts in millimetre bandrming the required level of technologicalacy While membrane technologies offerterest in the reductionlectric losses, a permittivity close to l severelyin terms of achievable impedances Indeed, when meeting the conditions described bHeinrich(Section 22)so as to limit both the dispersion of the transmission lines and losses,for a relative permittivity of 18, the ground-to-ground dimension (a)isIz Within these conditions, the strip width should be set in an interval between 65 umand 140 um, which makes the achievement of 50 Q2 transmission line impossible Hedispersive than the lll-V technology, the constraintsterval betweenm and 199 um, this lead to achievable characteristiQ to 138Q aGHz Despite the degree of freedom isble in the synthesis(Matthaei et al, 1980) whichts to adjust impedance values, the limitation of the achievable impedance range forntechopen

Microwave andfrom Photonic Bandgap Devices to Antenna and Applicationsmembrane technologies does not allow us to reach bandwidth less than 55%, Nevertheless,he use of topology with dual stubsThe layout of a 4th-order filter with dual short-ended stubs at 94 GHz is displayed in Fig 9(a) An insertiondb for a relative bandwidth ofobtained by electrolsimulation HFSS( Fig 9-(b) Experimental results were made from 60 GHz to 110 GHzFig 9 4th-ordre classical shunt-stubs bandpass filter Photograph (a), Simulated andperimental magnitude responses(Based on the previous filter topology, we have developed a 4th-order filter with folded stubspling betweennon-adjacenttors

Thus, it creates a transmissionthe nature of the coupling created For electrical coupling (capache band is due to the presence of a transmission zero at low frequency Thus, it is possiblereduced insertion loss In comparison with experimental results, we can notice that there is4 GHz frequency shift In regards to the complexity of such a topology, the results(b)Fig 10 Filter with folded stubs Photograph(a), Simulated and experimental magnitudentechopen

rend on Silicon Technologies for Millimetre-Wave Applications up to 220 GHz33 Narrow-band bandpass filter Designappropriate for achieving broHowever the difficumet in the dof bandpass filters are tougher for achiefilter with narrow bandwidth(5% 3-dB bandwith), With the use of classical coupled-lineter at 4 GHz weTechnological constraints impose line- and slot-widths to be greater than 10 um Interarge, which yields a difficulty toggHnd bridges Moreover, in considering the low permittivity and electrical lengths afced with coupled lirdth to length ratio is too large(Vu et al008) Therefore, the topology we developed is a pseudo-elliptic filter with ring resonatoruch a filter is characterized by the presence of two separate propagating modes, whicensured by the introduction of dises in the ring Inpled-linesdeveloped by M K Mohd SallehMohd salleh et2008) This 2nd-order ring-based filter at 94 GHz has a relativebandwidth of 5% It consists of two quarter wavelength lines excited by two identicalade the design ease andmited the tuning steps

The electromagneticFig 11)show a 53% bandr4 GHz E646loss better than 20 dBform maior drawbacks that limitfor the filterthe fistthe limitedachievable impedance range; the secondms the low permittivity which, whileteresting to limit the dispersion of the line, limits its use to relatively low frequency rangedry way using Deep Reactive lon Etching is difficult to control Therefore, one hasdevelop new technologies to implement passive functions in millimeter frequency range11 2nd-order ringtor filter(a) Photograph(b)Simulated and experimenntechopen

Microwave andfrom Photonic Bandgap Devices to Antenna and Applicationsm Microstrip (TFMs)Technologies4ted hereafter can be eitit is particularly well suitedbenefits of silicon technology are undisputable in the dedevices Neverthelessdifficult because of the high insertion-loss levels As our purpose was to keep the siliconsubstrate for implementation of active functions, an alternative consisted in the use of silicbeing insulated via a ground plane The prof this ground plane allows avoidingdielectric-loss effects related to theed librarih various models are available for such a technology, microstrip by natureThe first step of the technological process(Fig 12 ) is ground plane achithin-tungsten and gold-based adhesion films(200 A/ 300 Afirst deposited byaporation Due to poor adhesion between BCB and gold, a 300-A-thin film of titaniumThe dielectric we used was the photosensitive BCB 4026-26 from Dow Chemical, Midland,tand=210-3) It allows a 10-um-thick layerincluding pre-bakedspeed,ere obtained A soft baking (up to 210C) of this first dielectricresistance to subsequent processing operations

The second 10-um-thick BCB film polymerfilm was then spin coated and patterned (photolithography: UV light exposure and DS2100way as the first layer Then a final hard baking for polymerizationas performed from in stage annealing up to 230C The signal transmission linesas the coplanar accesses were fabricated at the same time The coplanar accesses on the topconnected to the ground plane through the sides of the dielectric In order tobtain metallization using gold electroplating,hotoresist layer is used to protect other devices After theating of the photoresistd tht, transmissiolines andith wider dimensions(3 um)were made A thin conductor filmA/200 A) for electroplatind, and thenotoprocessed to define the exact dimensions of the transmline and coplanar accesser electroplating of 3 um of gold, theeloper stage The thin conductor film was removed with wet-etching, and thephotoresist was finally diluted with a remover The transmission line structure obtained isntechopen

rend on Silicon Technologies for Millimetre-Wave Applications up to 220 GHzphotoresistFig 12 Technological process for BCB-based transmission lineCoplanar arks have shown that the BCB layer thickness is a parameter that most influencehe losses(Six et al, 2005),(Leung et al, 2002),(Prigent et al, 2004-a) Investigations werearried out so as to reduce these insertion losses As shown in Fig 14, the transmission lineyer can be considered as the optimum dielectric thickness

Beyond 20-Hm-thick,noobtained Within such a topologywere performed through a broad frequency range from 05 GHz to 220 GHzTransmission line with 50-Q2 mpedaas calibrated out this was achieved by means ofhru-reflection line calibration method (TRL) The calibration standards and transmissionfabricated on theP 8510 XF and anrits4/C network anere used in the(45 MHz-120 GHz) and(140 GHz-220 GHz) frequSimulated results andntttenuation nd for a 50- transmission line at 220 GHz is of the order of 0 6 db/nlines for different bcb thickness csimulation and experimental resultsntechopen

Microwaveiesfrom Photonic Bandgap Devices to Antenna and ApplicationsFig 15 Comparison between simulation(ADSmeasurement results of a 50-Q TEMS-ne with 20-um BCB thickness up to 220 GHz42 BandSo as to illustrate the Si-BCB based thin film microstrip technology, the filter to be designedroughly corresponds to a U-band filter, the 3-dB passband is 49-51 GHz, the rejection levelin the 41 15-46 15-GHz frequency band is 35 dB, and no specification for the upper bandis requiredCoupled-line topologies are basically well suited for narrow bandpass filters Neverthelf the desired insertioses and rejection levels, such topologies becetable with the above filter specifications Indeed, the closeness of the passband andhigh rejection levels Hence, the filter order has to be increased,which significantly degrades global insertion losses These considerations have led us tow filter topology based on dual behavior resonators(DBRs), which means bothstopband and passband (Rizzi, 1988) Such a resonator results from two different opennded stubs set in parallel Each stub brings a transmission zero on either side of theobal synthesis enabledndependently control thebandwidth, the upper and lower frequency bands, as well as the different transmissiofrequencies of an nth-order filter, ie

, composed of DBRs(Quendo et al, 2003) Let us apn alike development to the design of a 4th-order filter that meets the desired specificationsIt resultsfour transmission zerrequenciested or joined thisdepends on the electrical length of the four resonators: theydiffer or be identical (Fig16) For the sake of simplicity, the electrical characteristics of the upper frequency stubs, ieLla Zla),(L2a, Z2a),(L3a, Z3apper transmission zeros were joined Similarly, the lower frequencyfilter was designed based on the joint use of the synthesis(Quendo03)and thebased dmethod that allowsd coral,2003-a)(Prigent et al, 2003-b),(Tagushi, 1987),(Prigent et al, 2002) As depicted in Fig 17, the filterelectrical response obtained with this design method was in a very good agreement with thesimulations results (ADS-Momentumntechopen

rend on Silicon Technologies for Millimetre-Wave Applications up to 220 GHzesponse with differentimpedance and length) or with four identical resonatorswof the 4th-order DBR filter in U-band (b) comparison of electromagneticemulationexperiment, in wide frequency range up to 75 GHz(c)43 AppliAccording to the quality of the experimental results observed at 94 GHz, one has attemptedto transpose our concepts to upper frequency domain in G-band (140-220 GHz) In thisitivity and design accuracyhe electrical lengths thatLet us consider the design of a 4th-oder classical shunt-stubs filter with 10% 3-dB-bandwidthAccording to classical synthesis(Matthaei et al, 1980), while designing filter with suchecifications, we are faced to technical impossibilities

Indeed, at this frequency level,ng Hence, the electromagneticulation resultsmoreover, the filter dimensions made the electrical response correctiondifficult, indeed impossible, So as to overcome such a difficulty, the solution we haveterest,not the fundamental freqThus, the filter to be designed is a 4th-order filterth 60 GHz central frequency In this way, one can reach the filter specifications whileeping a correct shape factor for the stubs(Fig 18)ment results10 GHz and 140-220 GHz bands Despite a slight insertion losses improvement, themeasurement results are in a complete accordan

ce with the desired specificationsntechopen

rend on Silicon Technologies for Millimetre-Wave Applications up to 220 GHzwe present is the(either GaAs or InP)techonductorsubstrate allows taking adt properties of charge inherent in thisalactive functions implementation(transistor for instance)(Dambrine et al, 1999) Thusuch a technology offers the possibility to realize millimetre-wave monolithic integratedircuits (MWMICs) for which passive and active components are madeuced by the surface mounting and the wiring of theponents are reduced, as well as the cost of productiontechnology is based on the deposit ofmetalts goodvell as its high resistance to oxidation, metal widely used fortechnologies is gold In millimetre frequency range, gold thicknesortantparameter, generally 3-um-thick, so as to reduce propagationSeveral techniquesachieve this metallic dplatinghen the metal thickness exceeds the micron thatly, in order to minimize costs, the filing of metallizationbriefly describe the steps needed to implement components in Ill-V technology, nametechnology of electroplating and lithography combined, as well as the masks topologyThe basic principle of the technology studied hereafter is the deposit of successive layers oftched and eliminated after dilution ontodefined throuptical masks used in the phases of the sacrificial layer insulation In the describedre used: the first whose dimensions are higher (3 um) thanthe second having the exact dimensions The use of suchws, if there is no overlap between the two sacrifito avoid bulgesthe edhe patterns dSo a thin metal layer(few hundred angstroms) is deposited either by vacuum evaporationcathode spraying This last technique is preferred to the firstof the sacrificial layers, and therefore the protected patterns

Moreover, it allows a greatergidity of the metallic layer In conventional Ill-V technologies, this thin metal layer isaayer to ensure a good adhesion folin air, it is virtually impossible to achieve electrolysis directly on the titanitroplating performed the adhesion layer is chemically etched Neverthelesthe etching of the device, both adhesion layer and gold deposit are etched Moreover, fordimensions, it is necessary to insist in the etching process, this has the effectthe deposit One should also remark that, most of the time, during the etching pretheregold to prevent the tiletchinpatterns For this reasons, the proposed technology uses a nickel deposit that satisfies all therequirements: a good substrate adhesion, a good gold-growth and ease in etching processntechopen

Microwave andchnologiesfrom Photonic Bandgap Devices to Antenna and ApplicationsThe third step consists in electroplating itself, once achieved patterns definition and thinetal layer deposit phases An electric current flotdouble cyanide of gold and potassium(KAu(CN)))creates a chemical reaction neelectrodes Gold ions being positive, the sample foached to the cathode it follohenomenon of transfer of charges called electroplating This basic principle is relativelymple; however this operation must still be undertaken with some caution Indeed, ohmicf a transmission line depend not only on the resistivity of the metal, but also totherefopplydensity relatively low Hif very low currendensity yields a very low roughness, it also increases theechanical strength of the sacrificial laWe must therefore finpromise betweenroughness and mechanical strength3 um Gold electroplatingn line realization: a- Lithography process, b- Tranes aftercrificial layer removing and thin metal layer etchingIn the millimetre and sub-millimetre frequency range coplanar waveguides are moret al, 1998),( Papapolymerou et al 1999)

Many studies have, indeed, shown that coplanarwaveguides can be considered as a good alternative to microstrip lines in this frequencyrange(Houdard, 1976),(Hirota Ogawa, 1987),(Ogawa Minagawa, 1987),(Brauchler etplane, the ground connections through via-holes are eliminated and no revertly reduces cost, becbetween the different elements of a coplanar system, global size reduction may be obtainedas well Another advantage of the coplanar technology is flexibility in the design of theIndeed a lline with givd bydefining the ratio between thedesifaced with twehen they deal with coplanar technologyis the lack of mature equivalentcircuit models like those available for microstrip lines, The second one concerns themetrical coplanarle bends or tn of such perturbing modes is achieved by inserting bridges over the centreconductor, so that the potentials on either side of the lateral ground planes are identicalet al, 1989),(Beilenhoff et al, 1991) Consequently, additional stepsThere are two types of air-bridges: classical inter-ground and inter-conductor bridges, theirto force a similar voltage on either side of the central conductor Whatever the bridgntechopen

rend on Silicon Technologies for Millimetre-Wave Applications up to 220 GHzgethe high-resolution technology, one of the advathis technological process is thecontrol of the shape of the air-bridge Indeed in hybrid technology, air-bridgesrocess the shape of tht to control involving a problem of reprfirst and in the other hand proused allows good control of the fixture of these bridges as illustrate in Fig 2Fig 2 Air-bridge realization: (a)- Lithography process, (b)- Airbridges realized with IEMNtechnological procesn order to minimize the parasitic influence of the bridge on the electrical characteristic oheight, 10 um width, 80 um length (d=70 um 10 um minimum spacing between slot bordernd bridge), and 3-um metal thickness Moreover, to give it a good mechanical stability, amaximum length must be defined for a given width: for example, 10 um and 20 um widthallowm lengths of 100 and 180 um, respectively Although the bridge introduces ancess capacitance, this does not conproblem for the bridge widths here as long asdimensions, no compensation techniques, such as using sections of high-impedance line, areequired(Rius et al, 2000-a), (Weller et al

, 1999)So as to determine the optimum sizing of coplanar transstatic approach The RLCG equivalentdetermined fronons derived from a global analysis These values depend for electrical andgeometrical parameter of the transmission lines as well as the frequency C and G elementsas the skin effect modifies the currentplemented in GaAs technology (1=400 um, t=3 um, ar=119, tand=2x10-, o=4 1x107 Sm)line- and slot-width of W 26 um, S-22]m, respectively Fig 3 illustrates the evolutionthe R and L parameter for transmission line model as a function of thentechopen

Microwave andchnologiesfrom Photonic Bandgap Devices to Antenna and Applicationswith knowledge of RlCG parameters, onesily determine the parameters offunction of its geometrical parameters: line- and slot-widthswell as ground-to-ground distance, The inter-ground distance (d=w+2xS)is an importanttic modes thisdistance d has to be low compared to the wavelength; the commonly used constraintd sA/10 An increase of this constraint (as2x/20=dmex)alneglecting the radiationlosses Moreover, it limits extend of radiating waves, and therefore the problelied tording to Fig, 4-(a), the attenuation also depends on the groundground distance It is, in fact, inversely proportional to the distance d

It follows that interthe inter-ground distance chosdimensions of the line-width and inter-ground distance This ration W/d is predominant inthe attenuation, it is preferable to set W in the interval betweenhe ground plane width (Wg)and the substrate thickness (hs)are chosen to make a trade-offweend low dispersion up to the w-frequency bandfollowing conditions are then chosen to realize our dev2(W+25)4)Fig 3 Evolution of R and L parameters as a function of the frequencyntechopen

rend on Silicon Technologies for Millimetre-Wave Applications up to 220 GHzfunction of :(a) ground-to-ground distance (b) Lineration23 Wide-band bandpass filter designe first investigated on the design of quarter-wavelength shunt-stub filters Such topologybandwidth is in close relatith the impedance level of these,so as to respect optimal sizing described above the impedance range extends from 30Q2to 70 Q2 Thus, the available 3-db bandwidth will be approximately bounded by 100% andFor bandwidths below 36%, very low impedance levels are needed Thus, shape factorsbecome too large for corredfrom the device with regard to both the parasiticand modelling difficulties So, other topologies suchdeal with 58% and 36%0,3-dB-bandwidth 3rd-order filterson 827 GHz

According to synthesis, the first example with 58% 3-dB-bandwidthresults in a 25 Q2 impedance for the resonators when inverters are kept to 51 Q2 Twenty-fiveevel of inlosses, the standard geometry was chosen as follows: 26 um for thestrip widths and 22 urthe slot widths The 36% bandwidth was reacimpedances of 56 Q2 and 15 Q2 for inverters and resonators, respectively As before, 15 Q2obtained with two double 30@ stubs Itds to the lowest bandwidth thatedance range bounded by 30 Q2 and 70rthe inverters, strips andum forperimental and simulated results agree over a broad g5-(b)Asfirst prototype,ntechopen

Microwave andfrom Photonic Bandgap Devices to Antenna and ApplicationsFig 5 Layout, simulated, and experimental associated magnitude responses of the 82 7-GHzcentral-frequency, (a)58%3-dB-bandwidth and (b)36% 3-dB-bandwidth filtersAs shelossesh filter selectivity: 096, and 181 dbbtained for 58%, and 36% bandwidth filters, respectively These values are in compling expression(Matthaei et al 1980),(Cohn, 195eIs, n the filter order w itsunloaded quality factor, which is close to 25 for the standard 50 22 transmission line used5 Narrow-band bandpass fint when the selectivity of the filter is increased, Thehich is directly in relation to the level of selectivityIn order to illustrate this, we present the results obtainebupled-linesthird-order bandpass filters

The first one is at a center frequency of 65 GHz, 22% 3-dBlayouts of these filters, For such topologies, according to well-known synthesis(Matthaer980), the bandwidth and the coupling coefficient level of the coupled -lines sectioin close relation Indeed, narrow selective bandwidths are obtained with low cotground plane between the coupled strips This leads to low coupling levels on a reducedto the finite conductivity of the metal (41x107 Sm for gold metallization) and to thefactor of the GaAs substrate(tand 2xry high insertion losses arepected when designing such narrow-band filters These insertion losroughly from (5) For instance, for a third-order, 22% 3-dB-bandwidth coupled-line filterdesigned with 26-um strip widths, insertion losses between 195 dB and 295 db areobtained However if the bandwidth is decreased to 5%, insertionreach a criticalntechopen

rend on Silicon Technologies for Millimetre-Wave Applications up to 220 GHzlevel between 87 and 13 dB These values were calculated with the unloaded quality factorproving this critical point is tothe striphs, but thiseveral problems The first problem cethe bridge topology: a largebecause of mechanical stability constraintsfabricate an inter-strip bridge as shown in Figs 6 and7 By doing So, the ground connections used for filtering the coupled-slotline modes arewith a tiny strip on the first metallization layncerns modelling Obviously, as the strips are wider, the conditionsSection 22ssarily still valid mothedityconditions of the analytical quasi-TEM models used are not always met Finally, thedimensions of the discontinuities increase with the strip widths and, consequently, strongparasitic effects appear Modelling them accurately is quite difficult and it allows onlyn optimization procedure is needed to adjust all theharacteristics of the filttechnique(Prigent, et aL, 2004-b) As sheFig

6 for the 22% 3-dB-bandwidth prototypegood agreement is observed betsimulated andtal results This agreemenwide frequency band from 500 MHz to 110 GHz and, as expected, correctfrom 66 to 110 GHz for the second prototype Theental results7 and give a 4-dB insertion loss and 10-dB return loss for a centre frefreguency of915 GHz Compared to the expected resubroadening In this case, this problem is only due to the reverse side of the substrate Indeed,the frequency response Post-simulrried out to checby taking into account correct conditions on the substrate backside This post-simulationrrect bandwidthand return loss are necessary to assess the insertion loss accgrounded CPW linesa very convenient solution, three-dimensional technologicalin-or thick-film microstrip transmission lines appear to beell suited (Rius et aL, 2000-b),(Six et al, 2001),(Aftanasar et al, 2001),(Warns etal, 1998), (Schnieder Heinrich, 2001ntechopen

Microwave andfrom Photonic Bandgap Devices to Antenna and ApplicationsFig 6 Layout, Simulated andsults65-GHz central-frequency, 22%dB-bandwidth, coupled-line filterLayout, Simulated and experimental resuslts of a 65-GHz central-freq5%3-dB-ittle series, technologies on silicon offer an interest with respectreductiontaining their interest in the integration of active functions Nevertheless theirdrawback is that levels of dielectric losses are not compatible with the specificationsequired for the passive functions

An alternative consists in the use oftransparent for functions in microwave Thus, the electrical characteristics of this supporttch withm, the ideal dielectric On the other hand, membrane technolots to minimize phenomena of dispersion, as well as the removal of cavity modesThe technological process developed hereas the one developed in Ill-Vhe silicon The membrane technology developed at the LAAs laboratory (Toulntechopen