Patent Application: US-88850104-A

Abstract:
the present invention relates to switchable components for high - frequency technology , in particular microwave technology , which use liquid - crystalline dielectrics , to the liquid - crystal materials , to the use thereof , and to a process for the production of the components , for their operation and for improving their characteristics .

Description:
preferred components are phase shifters , varactors , radio wave antenna arrays and others . in the present application , unless expressly stated otherwise , the term compounds denotes both one compound and a plurality of compounds . the liquid - crystal media according to the invention preferably have nematic phases of in each case at least from − 20 ° c . to 80 ° c ., preferably from − 30 ° c . to 85 ° c . and very particularly preferably from − 40 ° c . to 100 ° c . the phase particularly preferably extends up to 120 ° c . or more , preferably up to 140 ° c . or more and very particularly preferably up to 180 ° c . or more . the term “ have a nematic phase ” here means firstly that no smectic phase and no crystallisation are observed at the corresponding temperature at low temperatures and secondly that no clearing occurs on heating from the nematic phase . the investigation at low temperatures is carried out in a flow viscometer at the corresponding temperature and checked by storage in test cells , with a layer thickness of 5 μm , for at least 100 hours . at high temperatures , the clearing point is measured by conventional methods in capillaries . furthermore , the liquid - crystal media according to the invention are characterised by high optical anisotropies in the visible range . the birefringence at 589 nm is preferably 0 . 20 or more , particularly preferably 0 . 25 or more , particularly preferably 0 . 30 or more , particularly preferably 0 . 40 or more and very particularly preferably 0 . 45 or more . in addition , the birefringence is preferably 0 . 80 or less . the liquid - crystal media according to the invention are furthermore characterosed by high optical anisotropies in the microwave range . the birefringence is , for example at about 8 . 3 ghz , preferably 0 . 14 or more , particularly preferably 0 . 15 or more , particularly preferably 0 . 20 or more , particularly preferably 0 . 25 or more and very particularly preferably 0 . 30 or more . in addition , the birefringence is preferably 0 . 80 or less . the preferred liquid - crystal materials have phase shifter qualities of 15 °/ db or more , preferably 20 °/ db or more , preferably 30 °/ db or more , preferably 40 °/ db or more , preferably 50 °/ db or more , particularly preferably 80 °/ db or more and very particularly preferably 100 °/ db or more . the material quality δn ( microwaves )/ tan ( δ ) of the preferred liquid - crystal materials is 3 or more , preferably 4 or more , preferably 5 or more , preferably 10 or more , preferably 15 or more , preferably 17 or more , particularly preferably 20 or more and very particularly preferably 25 or more . the liquid crystals employed preferably have a positive dielectric anisotropy . this is preferably 5 or greater , preferably 10 or greater , particularly preferably 20 or greater and very particularly preferably 30 or greater . in some embodiments , however , it is also possible advantageously to use liquid crystals having a negative dielectric anisotropy . the liquid crystals employed are individual substances or mixtures . they preferably have a nematic phase . the individual liquid - crystal compounds are essentially selected from the known compounds or are obtainable analogously to known compounds . preference is given to the use of compounds or mixtures of compounds , where the compounds generally contain two , three or four polycyclic , preferably pentaor hexacyclic , particularly preferably hexacyclic , rings . however , the compounds may also contain polycyclic rings and / or fused rings , preferably divalent naphthalenes or phenanthrenes . particular preference is given to compounds which contain rings , preferably 1 , 4 - phenylene rings , which are optionally mono - or polysubstituted . the rings are preferably laterally substituted by halogen ( particularly f or cl ), but also by pseudohalides . the aromatic rings may optionally be heterocyclic , in particular n - heterocyclic rings , preferably divalent pyridine or pyrimidine . it is also possible to use compounds containing divalent cyclohexyl , dioxane , tetrahydropyran , thiazole , thiadiazole , oxazole and / or oxadiazole rings . at least in some compounds present in the mixtures used , a polar end group , which preferably denotes ncs , cn , scn , nco , halogen , preferably f or cl , a pseudohalide , a partially or fully fluorinated alkyl , alkoxy , alkenyl or alkenyloxy group , in which , in addition , one or more , preferably generally non - adjacent , ch 2 groups may be replaced by o , s and / or c ═ o , preferably ocf 3 , cf 3 , and also sf 5 or so 2 cf 3 , is located in at least one of the terminal positions . the other terminal position may likewise contain a substituent from the last - mentioned group of dielectrically positive substituents , but may be a dielectrically neutral group , such as , for example and preferably , alkyl , alkenyl , alkoxy , alkenyloxy or oxaalkyl , and this is also preferred . if liquid - crystalline mixtures are used , these generally also comprise dielectrically neutral compounds , in which both ends of the molecule preferably , independently of one another , carry one of the last - mentioned dielectrically neutral groups . the generally divalent rings of the molecules may be bonded directly to one another . however , they may also be linked by bridges . the compounds preferably contain zero , one or two , particularly preferably zero or one , bridging group . they preferably contain a bridge having an even number of bridging atoms , preferably — c ═ ch —, — c ≡ c —, — co — o —, — o — co —, — cf 2 o — or — o — cf 2 —. the term “ alkyl ” preferably covers straight - chain and branched alkyl groups having from 1 to 7 carbon atoms , in particular the straight - chain groups methyl , ethyl , propyl , butyl , pentyl , hexyl and heptyl . groups having from 2 to 5 carbon atoms are generally preferred . the term “ alkenyl ” preferably covers straight - chain and branched alkenyl groups having from 2 to 7 carbon atoms , in particular the straight - chain groups . particularly preferred alkenyl groups are c 2 — to c 7 - 1e - alkenyl , c 4 — to c 7 - 3e - alkenyl , c 5 — to c 7 - 4 - alkenyl , c 6 — to c 7 - 5 - alkenyl and c 7 - 6 - alkenyl , in particular c 2 — to c 7 - 1e - alkenyl , c 4 — to c 7 - 3e - alkenyl and c 5 — to c 7 - 4 - alkenyl . examples of further preferred alkenyl groups are vinyl , 1e - propenyl , 1e - butenyl , 1e - pentenyl , 1e - hexenyl , 1e - heptenyl , 3 - butenyl , 3e - pentenyl , 3e - hexenyl , 3e - heptenyl , 4 - pentenyl , 4z - hexenyl , 4e - hexenyl , 4z - heptenyl , 5 - hexenyl , 6 - heptenyl and the like . groups having up to 5 carbon atoms are generally preferred . the term “ fluoroalkyl ” preferably covers straight - chain groups having a terminal fluorine , i . e . fluoromethyl , 2 - fluoroethyl , 3 - fluoropropyl , 4 - fluorobutyl , 5 - fluoropentyl , 6 - fluorohexyl and 7 - fluoroheptyl . however , other positions of the fluorine are not excluded . the term “ oxaalkyl ” or “ alkoxyalkyl ” preferably covers straight - chain radicals of the formula c n h 2n + 1 — o —( ch 2 ) m , in which n and m are each , independently of one another , from 1 to 6 . n is preferably 1 and m is preferably from 1 to 6 . compounds containing a vinyl end group and compounds containing a methyl end group have low rotational viscosity . in the present application , the term dielectrically positive compounds means compounds having a δε of & gt ; 1 . 5 , dielectrically neutral compounds means those in which − 1 . 5 ≦ δε ≦ 1 . 5 , and dielectrically negative compounds means those having a δε of & lt ;− 1 . 5 . the dielectric anisotropy of the compounds is determined here by dissolving 10 % of the compounds in a liquid - crystalline host and determining the capacitance of this mixture at 1 khz in at least one test cell with a layer thickness of about 20 μm having a homeotropic surface alignment and at least one test cell with a layer thickness of about 20 μm having a homogeneous surface alignment . the measurement voltage is typically from 0 . 5 v to 1 . 0 v , but is always less than the capacitive threshold of the respective liquid - crystal mixture . the host mixture used for determining the applicationally relevant physical parameters is zli - 4792 from merck kgaa , germany . as an exception , the determination of the dielectric anisotropy of dielectrically negative compounds is carried out using zli - 2857 , likewise from merck kgaa , germany . the values for the respective compound to be investigated are obtained from the change in the properties , for example the dielectric constants , of the host mixture after addition of the compound to be investigated and extrapolation to 100 % of the compound employed . the compound to be investigated is employed in a concentration of 10 %. if the solubility of the compound to be investigated is inadequate for this purpose , the concentration employed is , by way of exception , halved , i . e . reduced to 5 %, 2 . 5 %, etc ., until the concentration is below the solubility limit . in the present application , high - frequency technology and ultrahigh - frequency technology denote applications with frequencies in the range from 1 mhz to 1 thz , preferably from 0 . 1 ghz to 500 ghz , preferably from 2 ghz to 300 ghz , particularly preferably from about 5 to 150 ghz . all concentrations in this application , unless explicitly stated otherwise , are given in per cent by weight and relate to the corresponding mixture as a whole . all physical properties are and have been determined in accordance with “ merck liquid crystals , physical properties of liquid crystals ”, status november 1997 , merck kgaa , germany , and apply to a temperature of 20 ° c ., unless explicitly stated otherwise . δn is determined at 589 nm and δε at 1 khz . in the case of the liquid - crystal media of negative dielectric anisotropy , the threshold voltage was determined as the capacitive threshold v 0 in cells with a liquid - crystal layer aligned homeotropically by means of lecithin . the liquid - crystal media according to the invention may , if desired , also comprise further additives and optionally also chiral dopants in the conventional amounts . the amount of these additives employed is in total from 0 % to 10 %, based on the amount of the mixture as a whole , preferably from 0 . 1 % to 6 %. the concentrations of the individual compounds employed are in each case preferably from 0 . 1 to 3 %. the concentration of these and similar additives is not taken into account when indicating the concentrations and the concentration ranges of the liquid - crystal compounds in the liquid - crystal media . the compositions consist of a plurality of compounds , preferably from 3 to 30 , particularly preferably from 6 to 20 and very particularly preferably from 10 to 16 , compounds , which are mixed in a conventional manner . in general , the desired amount of the components used in lesser amount is dissolved in the components making up the principal constituent , advantageously at elevated temperature . if the selected temperature is above the clearing point of the principal constituent , the completion of the dissolution process is particularly easy to observe . however , it is also possible to prepare the liquid - crystal mixtures in other conventional ways , for example using premixes or from a so - called “ multibottle ” system . the examples below serve to illustrate the invention without representing a restriction . in the examples , the melting point t ( c , n ), the transition from the smectic ( s ) phase to the nematic ( n ) phase t ( s , n ) and the clearing point t ( n , i ) of a liquid - crystal substance are indicated in degrees celsius . the various smectic phases are characterised by corresponding suffixes . the percentages above and below are , unless explicitly noted otherwise , per cent by weight , and the physical properties are the values at 20 ° c ., unless explicitly stated otherwise . all the temperature values indicated in this application are ° c ., and all temperature differences are correspondingly differential degrees , unless explicitly stated otherwise . in the present application and in the examples below , the structures of the liquid - crystal compounds are indicated by means of abbreviations , also referred to as acronyms , the transformation into chemical formulae taking place in accordance with tables a and b below . all radicals c n h 2 + 1 and c m h 2m + 1 are straight - chain alkyl radicals having n and m carbon atoms respectively . the coding in table b is self - evident . in table a , only the acronym for the parent structure is indicated . in individual cases , the acronym for the parent structure is followed , separated by a hyphen , by a code for the substituents r 1 , r 2 , l 1 , l 2 and l 3 : table a code for r 1 , r 2 , l 1 , l 2 , l 3 r 1 r 2 l 1 l 2 l 3 nm c n h 2n + 1 c m h 2m + 1 h h h nom c n h 2n + 1 oc m h 2m + 1 h h h no . m oc n h 2n + 1 c m h 2m + 1 h h h nmff c n h 2n + 1 c m h 2m + 1 f h f nomff c n h 2n + 1 oc m h 2m + 1 f h f no . mff oc n h 2n + 1 c m h 2m + 1 f h f no . omff oc n h 2n + 1 oc m h 2m + 1 f h f n c n h 2n + 1 cn h h h nn . f c n h 2n + 1 cn f h h nn . f . f c n h 2n + 1 cn f f h nf c n h 2n + 1 f h h h nf . f c n h 2n + 1 f f h h nf . f . f c n h 2n + 1 f f f h ncl c n h 2n + 1 cl h h h ncl . f c n h 2n + 1 cl f h h ncl . f . f c n h 2n + 1 cl f f h nmf c n h 2n + 1 c m h 2m + 1 f h h ncf 3 c n h 2n + 1 cf 3 h h h nocf 3 c n h 2n + 1 ocf 3 h h h nocf 3 . f c n h 2n + 1 ocf 3 f h h nocf 3 . f . f c n h 2n + 1 ocf 3 f f h nocf 2 c n h 2n + 1 ochf 2 h h h nocf 2 . f . f c n h 2n + 1 ochf 2 f f h ns c n h 2n + 1 ncs h h h rvsn c r h 2r + 1 — ch ═ ch — cn h h h c s h 2s — nesn c r h 2r + 1 — o — c s h 2s — cn h h h nam c n h 2n + 1 cooc m h 2m + 1 h h h nf . cl c n h 2n + 1 f cl h h ns c n h 2n + 1 ncs h h h ns . f c n h 2n + 1 ncs f h h ns . f . f c n h 2n + 1 ncs f f h table c shows possible dopants which are generally added to the mixtures according to the invention . table d c 15 cb 15 cm 21 r / s - 811 cm 44 cm 45 cm 47 cn r / s - 1011 r / s - 2011 r / s - 3011 r / s - 4011 stabilisers which can be added , for example , to the mixtures according to the invention are shown below . the following examples are intended to explain the invention without limiting it . above and below , percentages are per cent by weight . all temperatures are indicated in degrees celsius . m . p . denotes melting point , cl . p . denotes clearing point . furthermore , c = crystalline state , n = nematic phase , s = smectic phase and i = isotropic phase . the data between these symbols represent the transition temperatures . δn denotes optical anisotropy ( 589 nm , 20 ° c .). k15 was investigated at 27 . 5 ° c . with respect to its microwave properties , as described in the interfering - body measurement method section . dielectric properties of the liquid crystal were determined both parallel and perpendicular to the microwave measurement field on alignment of the director of the lc with a magnetic field up to 0 . 15 t . the data are shown in the table after example 5 . a binary mixture comprising 10 % of pvpu - 3 - s and 90 % of k15 ( referred to as mixture a - 1 below ) was investigated as described in comparative example 1 , at 26 . 5 ° c . a binary mixture comprising 20 % of pptu - 4 - s and 80 % of k15 ( referred to as mixture a - 2 below ) was investigated as described in comparative example 1 , at 26 . 5 ° c . the mixtures of examples 3 to 5 ( m1 to m3 ) were investigated at a temperature of 27 . 5 ° c . the results are shown in the following table . table of results example : c1 1 2 3 4 5 lc a - 0 ( k5 ) a - 1 a - 2 m1 m2 m3 c ( k15 )/% 100 90 80 none t /° c . 27 . 5 26 . 5 +/− 0 . 5 27 . 5 +/− 1 . 0 δn ( 589 nm ) 0 . 4083 0 . 3907 0 . 3934 freq ./ ghz 8 . 3 . . . 8 . 75 ε ( 0 = v ) 2 . 8291 2 . 8035 2 . 8493 3 . 2190 3 . 0966 3 . 4547 tan ( δ )( 0 ) 0 . 0355 0 . 0252 0 . 0251 0 . 0158 0 . 0137 0 . 0116 ε ∥ 2 . 9301 3 . 0501 3 . 0267 3 . 6832 3 . 6614 3 . 6855 tan ( δ ) ∥ 0 . 0243 0 . 0178 0 . 0198 0 . 0089 0 . 0070 0 . 0085 ε ⊥ 2 . 5028 2 . 5331 2 . 5440 2 . 5597 2 . 5993 2 . 5866 tan ( δ ) ⊥ 0 . 0777 0 . 0433 0 . 0584 0 . 0261 0 . 0215 0 . 0276 δn μw 0 . 1297 0 . 1549 0 . 1447 0 . 3193 0 . 3012 0 . 3115 tan ( δ ) av . 0 . 051 0 . 03055 0 . 0391 0 . 0175 0 . 01425 0 . 01805 ε av . 2 . 6452 2 . 7054 2 . 7049 2 . 9342 2 . 9533 2 . 9529 ε av . / tan ( δ ) av . 2 . 54 5 . 07 3 . 70 18 . 24 21 . 14 17 . 26 dielectric constant ε r , dielectric loss factor tan δ , calculated anisotropy in the microwave range δn μw = |{ square root } ε r par − { square root } ε r perp |, optical anisotropy δn opt , average of tan δ and ε r , material quality factor δn μw / tan δ av . . it can clearly be seen that the high optical anisotropy of the novel lc mixtures , in contrast to k15 , was also successfully transferable to the lower microwave range . the anisotropy values δn opt of mixtures m1 , m2 and m3 clearly exceed the value for k15 and the highest value known hitherto for the microwave anisotropy of a liquid crystal , δn mw = 0 . 22 at 30 ghz [ lim1 ], [ lim2 ]. the anisotropy of mixture m2 is already extraordinarily high and almost as great as the anisotropy at λ = 589 nm . the anisotropy δn mw appears to converge with the optical anisotropy value δn opt as early as the lower millimetre wave range . the material quality achieved here is approximately eight times as great as for k15 used hitherto in microwave circuits . this mixture is suitable for increasing the quality of lc - based microwave phase shifters to well above 50 °/ db , which would make these competitive with technologically complex circuits based on high - purity thin films on monocrystalline substrates and even clearly exceed the results of phase shifters having thick ferroelectric layers . in addition , the ε r average is in the same order of magnitude as for standard substrate materials for microwave circuits [ rog1 ], making complex adaptation of conductor geometries , as , for example , in the case of thick ferroelectric layers ( ε r ≈ 200 . . . 450 ), superfluous . a phase shifter in inverted microstrip technology was produced using liquid - crystal mixture m1 . for comparison , the same phase shifter was produced using k15 . lc k15 m1 freq ./ ghz 10 20 10 20 volt ./ v diff . phase shift /° 0 0 0 0 0 5 28 58 75 210 10 30 62 123 241 30 35 62 132 270 the entire disclosures of all applications , patents and publications , cited herein and of corresponding german application no . 10331722 . 8 , filed jul . 11 , 2003 are incorporated by reference herein . the preceding examples can be repeated with similar success by substituting the generically or specifically described reactants and / or operating conditions of this invention for those used in the preceding examples . from the foregoing description , one skilled in the art can easily ascertain the essential characteristics of this invention and , without departing from the spirit and scope thereof , can make various changes and modifications of the invention to adapt it to various usages and conditions . table of references : [ aci1 ] b . acikel , y . liu , a . s . nagra , t . r . taylor , p . j . hansen , j . s . speck and r . a . york : phase shifters using ( ba , sr ) tio 3 thin films on sapphire and glass substrates . ieee mtt - 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