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Патент USA US3100334

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Aug. 13, 1963
E. J. SHERMAN
3,100,329
SOLID CAPACITORS
Filed March 24. 1960
¿Fae-cr Pyßa/.Yr/c (Mmes/0N ar »14A/@Maas Mme-4r; »wr/mf
Pfaff ,00,655 ra MAA/64Min,' ax/pf 5r affirm/6 Pfaff 450m'
1 ,sm/arf 4r im "c,
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IN VENTOR.
¿bw/1f@ J.Saw/14AM
di
i l' ' ï
¿stime _. .
j_.frjateaied Aue-13„ ieee
f
»
,
-
f
i
_ -_ __ ..
._
__g-layerqfSince the pellet is,recycledsevenaltimes between",`
f hls‘finvention'reiaies ,to an"`inipmved method ef fab: " ï -the electrolyte and the impregnatins Solutiòmiándis rather»
ating@ solid-_ electrolytic*capacitorv ,1 'More particularly, »_ „_ .porousïinïnalturd it is very diñioult 'toîpreventthe pellet
___rela'tesÍÍto _n._-ïim_pioved methodîofffï?orming dielectric 10 from retaining _some of the electrolyte,_withir`1_._itspores,
msg_çn anòäìzable' d_ectrodè3~
_
‘
» ..
.f
_ „
f
_ I_n ordertoyavoid degr`adat_io__r_1_` of the-finished'_capacitors,
Solid _electrolyticlcapacitors have -been ,"rna‘de:` by elec-` A Í , , _it has been necessary to' utilizevery careful and prolonged 1» ¿ ,
_ _. r_tr`oly_ti_1c_;a_1ly__anodizingfa@bodyoíanlanodizable metalAsuchhl
washing and rinsing ofthe pelletaft'er it¿_i_sïfrer_r_1_ov,_
f _ _
¿the «forming-,bath electrolyte. -,.»_ .In_ . pra'oticeit has been n_'ec
"ress_ary' fto wasll'the pelletvS times 'after eachirrirnersildn‘in Í l
»l'fthe `forming bath, Veach vwashiiigstep being vperformed f_dr
about two minutesin _a separate vat of boilingfdeionized
water. inasmuch es_„the _. cycle of i anodizing, -impregnat- _i
ing, and heatingthepellet usuallyjrepeated five times,
" k“fthe total»timeïspentiinïwashing the wafeìtWenty-ñve times ' ' l l
_.
çendu/Ctive oxide> layëèrscrve `to`reoxidize1and~heali , ~._¿inboilin-g.wat r_.i_s_abou_t one hour. Thujsthe necessityof ,
` yïthe»dielectric film in case offp‘u'ricture ¿ilocal _breakdown
óf the'filmn «_ -'
A
~"
_
__
l
_Inione
method
"
of
"
'
`_g1-,cap
__
_
‘Í ’_
" _Carefully washing the pellet `after _each yimmersion in the
_ ï _
>electrolyte cat__isesfaigconsiderable increase» in the _n_ranui
,-aÍpdwdered'~ , _` Íacturin-g time,
_
_
_
amount oi handling required, and
_
„anodizable
‘ pellet. ‘,„TheInetalL-is
body` or presse
,compact
,_toïform
thus formed
a `porous¿_body
hasy consideri?"
er 25_
~ ' _the
' Another
_Cqst perproblem
.u_nit. in this process
_ _ is that
«_ slmple . immer.
'
' » able surface area but isirathen~frangible~ and mec_:_haniea_11yl~n » sion" of the Vpellet in _the _manganous nitrateg solutiondoes ,_
« ‘_ -` weak
r belo
The` body- is.~_t_her_e`»fore_ sinter’ed at .-alempeuature ï'_
_not _completely_impregnatethe pellet pores with thef solu
he meltingl'ipointßïof thefi" `articular anodizable' ' ’ tion.: For _thisjreason,.'it"has been commonpractice to'
metf__ thereby ÍormingÍapelle't‘Íwhic `_ _has ígood >rn'echani-~3Q _use vacuum or pressure impregnationf‘of vthe manganous
ca_lstrength”andïretfains aÜhifghdeg'ree- ifÍporo‘sity. ' The vnitrate solution." „This practicelrequiresadditional'han
_ _sintered‘miletiisimmersed 1n. afbalthßontainingl a con‘dno- _
>`tivef'electrolyteand janf 'nert'electròdefsuch"as (graphite,
’ dling-` steps,’fas v.well as special equipment such as pumps
”
and valves. .
f
.
,_
,
_
,
f
i
f`lplatinum; andthe like: ,_ _According-to thegprior`_`f`art,"jtlie
_Accordingly,rit is an object of this Yinvention to provide
_ electrolyte,inayïforexample, consist of ¿dilute’phosphorie _35` an improved method of fabricating solid electrolytic ca
` Íor sulfuric acid, .o_rï‘anA aqueousï'solution'~of .a _halogen- '_
lpacitors. '
_‘,Anoth__
substituted acetic acid, »or,asoflil'tio'n‘of~ .ammonium _bor _
f
- `
Y
r object ofr this invention is.. to providey an im#A
ratein afglycolsuch‘as' ethylene glycol. L Fused low-melt-V ‘
.proved method of lforming- dielectric ñlrns on anodizable
ing salts, such ’as _mixtures of potassium nitrate, sodium
electrodes.v
’
`
__ `
f
_
»_
_
nitrat'e`,Íandìthe’like, have‘also‘been‘utilized as the- elec- 40 ¿_ f Another object is to -provide a method of simultane
trolyte." The pellet `is made the anode ’of the bath, and a
__ouslyforming' a ydielectric-film on an anodizableelectrode
current isapiassed'from the pellet through the electrolyte .Q_ _surface and'impre’gnating the electrode with’a _compound `
Vto the inert. electrode, which serves as the bath cathode.'
I _capable _of pyrolytic decomposition into a protective semi
During this step, whichv _isknown as'the forming step, _
,___cenductive oxide.
» ‘_a thin‘dielectric iilm’c‘onsis'tingof the oxide of _thexanodizÁ «4.5
__
_
_v '
f
f, '
These and other objects are accomplished by the instant
able I_,rietalv _is formed-@VGT lthe -sui-«face of the, pelle't,».and-l:__ _invention inthe following manner. A powdered ¿anodiz
_.t_alsoïonfhe_finlternalfsurface‘of the p‘elletifpor'es. There". `ab_l_el«_1net_all iis pressed _into a porous pellet. The pellet
_“ ‘after the pellet is" rer'nfoved _from‘theelectrolyte washedv _ :is vacuum' sintered, _then electrolytically treated in -an `
.-j‘five1`times with boiling «distilled i’ deionizedwatendried,
:aqueous solution of _a compound capable _of-pyrolytic
"I_a__`1_1_d_»_dipp_ed in_asolution of
rn-poundfsuch as man`~ _5,0 conversionîinto'a semiconductive_metalloxide.` Thepellet Y
_ ganous nitratewhich is capable of'p'yrolytie conversion
is thus anodized, and simultaneously thejpellet -pores
to a semiconductive‘ _metal oxideflaye'r. ' The solutionl l lare impregnated -with the compound.’ Subscquently',_, the>
" _impregnates the pelletp‘ores, sothat on subsequent heat~
_ ing a protective layer oi- man-ganese oxide is ,formed over
. wafer is heated -so _as to convert the compound Within the
_ pelletpores'into asemiconductive metal oxide. The steps-
_the pellet and within thepellet pores in' close contact to 55 of _anodiaing _the'pellet and pyrolytically converting the
L _the `dielectric íilml The` pellet issjanodizedagain, yrinsed
' _' _ iivetimes with boiling distilled Tor deionized water, dried,
_ag'ain írnpregnated"_with the manganous'nitrate solution,
:impregnated compound within said pores into the semi-_ f
conductive oxide is usually _repeatedtat least once." How-V
eve1',ïit is no `longer necessary toswash the wafer after
andag'ainheated to convert’ the compound imprcgu'atedr ' _leach "anodization, vsince» _the same compound used as the
_in the pellet pores to the protective manganese foxiïde» »Goßele'ctrolyte _ in the forming- bathV is used to `impregnato
‘laye_r._ This cycle of anodizing tliefpellct, Washingithe " the metal pores and forni azprotective semiconductivela'yer '
. `‘pellet five Itimes _in boiling distilled `¿Ur deionized ,W?ileïs v by pyrolytic action. Another advantage is the reduction
_ ' [drying the pellet, 'irnpregnatíngthe pellet with »a com“ _» in the _number `of handling stepsl and manufacturing time
‘ ~ "pbllildißàpëble `0f @YTOÍYÍÍUCÓDVSISÍOH '£0 a SßlïlîCOIIfïllCI-y
per unit, since anodization and impregnation is combined
«tivernetal5oxidefend heating the waíerto'elîect'the pyl‘o-` 65 „in a single step.' To complete the unit, ia conductive
__lytiç‘convéljSïQnOf 'the ,impl‘êgûáœd COmPOÚÍlíÉÓ PIO; i «coating is deposited uponv the jpellet. Leadvwires are then
Vtective met-al oxide layer, is'usually repeated 4about l4 " rattached _to the pellet' and the conductive coating, and '
or 5 times.
Thereafterl a conductive coating, is l.,alfiplied
the unitis cased by methods known to the art.
f `-
"over the protective metal `oxide layer, leads are v4attached ‘70 ,Y The‘invention and its advantages will‘be- described in
vitothe bulk of the Vpellet* and to the conductive coating, Y.
' ¿M1115 .unit is @Sei - .
'
»
_
'
. ,
greater, detail by the following examples and the accom
panying drawing, in which the single lFIGURE is a ñow y
.
the compound driven into the‘pellet pores by Vthe appliedí`>
¿sheëtfillustrative-of the various‘ste‘ps `in oneï'embodiment‘ j
.of theprocess.
'
‘f
"
f
~
'fvoltageA ' Since injipreg'natio'nv is thus improved, thev number; f
.
of. anodization and Vpyrolysisï> cyclesgfrequired `_ is reduced*
Y
about 30%,.- Still anotherffeature. is that lno‘l harmful'
quantityk ouf‘a powdered anordizlablemetal` is pressed '
into a porousslugorpellet. Thel aniodizable> metal ¿is
residue canbe retained inthe pellet pores',A since onlythe`> , y
solution desired forpyrolytic conversión tothe protective: v ‘ `
layer‘is present withinthe.pelletfpores.”jij. Y
l . 5
` .selected~1from
lium, îcolumbiurn,
the liafnium,
group 'consistingv
tantalum,‘titanium,vtungsten,
of "aluminumyberylf ' `«
The cycle of anodization followed fbypyrolytic 'con
zirconiumfand: the like. inV Vthis’ example, -thejmetal‘'is
version is usually repeated at least' once. In this example,
powdered tantalum, ’and fthe( tantalum particles »have a'
' diameterofjabout ¿2ï to ,4 microns." ,An anode lead 'is
the.V cycle is repeated ifour times.~ -Advzmtageously, -alast
'anodization is performed in _avery ~>dilute,Ymiariga'nbu>
nitrate'solutiomior example 'a solution containing'rabout
' providedbyv embedding in the powder a tantalum .ribbon`
about VÍi'milsv thick, ~25 mils wide, and 1/2 inch long.’ A
I
`
.0l weighti‘percentfor less dissolvedv solute. 1I: Very llittle]- "
gmanganous nitrate is introduced into the 'pelletpores'ïdtl'r;.` '
pres‘sufrelofl abcutjS tons per square inchñis'rused'to press
the powderfinto/'aj` slug or pellet _about 1.8_0’fmils square 15
~ Y
inglthis step,'jsince)`the ,electrolyte‘solution
theunit
is so isiov'en
dilute. fg.
f l0 -milsl thick:
Tliejpressed pelletl is l‘vacuum sintered by heatingfit `for
ZOfmÍIKIutesêîn.ajvacuum‘ furnace kept ‘atll750°,C;_ The A
V applied _ tof theV pellet'V
surface .by dipping it ‘ínfajsuspenls‘ionof finely-dividedV
, , atmospheric pressure in the furnace `is maintained below-
Ílf'mic’ronfHg during this step.` «
gr'apliitel;A TheV graphite-suspension `commercially-avail‘- .»
‘able’ asz'ifäiquada‘gV is suitable for lthisg-:purposefï vTo insur ‘
20
The next Í step " is> knownfas‘` „the` 'forming step. _ The
¿pellet is immersed in‘aiforming iba:
y
l
a goodruniform coating, thepellet-isjoven drieda'ndlthej
_ contains
Y
`an »I ,
electrolyte;` " './äcco'rdingÍ to this iinve'ntion', the electrolyte ' l cycle >of dipping in Va graphite `suspension andf'drying the. .
preferably isfán* aqueous» solution 'of a ‘compound selected-_ wafer is-r'epeated.- v >Aconductivegraphitecoating `is thûstî
`from the -hydroxides, "nitrates, acetates, y‘oxalatesA ' and
«formates 4of lead, nickel, and manganese. Íln‘thi‘s-example,`
formed over the‘pellet’surface.
v
"
' If.
’
y'
_ y» ¿zx
Next_'an _electrically conductive ‘silver-loadedgepoxy'
'
» the electrolyte is an aqueous solutionV of manganese nitrate, ` ‘
`resin''islÍsprayed over thej graphite coating. A cathode»
" .
containingäabout‘58% by we_ightgof the solute.The' ,
>,lead-'is formed by cementing: a-'nickel ribbonl to the con-1 >
Y
electrolyteis"contained in a stainless steel tank,which
, 'ductive `resin layer with'the same epoxy resin.` 'Iîhis`
’ ’ serves as 'theÍ cathode `of thebath. :The pellet is anodized 30' Anickel 'ribbon .formsV an electricalY ‘contact through the’fY Y
bypassing av direct currentffromrthe pellet through the , Y vconductive resin layer‘iand theconductive' graphiteA layer;` ' i
' electrolyte to the steel tank. @The-voltage applied vranges
to the'protective rrianganesey oxide layer whiëh covers `the Y "
from about 10 `to l60 volts,Ídepending- on the thickness
' of the anodized film` desired.l >The/.higher,the voltage»
methods
example
knowntoïthe
of r_another"e‘inbo_Climentofthe
art.Vr _.
„
._ .
invention?Y
. ~
used,'the thicker the resulting film "andï the lower/the 35 ïbyAn
" capacitance of the finished unit. In this example, the - will now be described. _ `Thisjeniboïdifment isgfuseful when.`
~forming voltage is about 60 volts, andA the> pellet is elec
it is desirable. to :utilizepforming»voltages greatlyvv in'exf
trolytically treated in the bath for about 11/2 hours. Dur~
f cess ofV 60 volts.y V'High forming voltages _'a'reÍ preferred ï*
' "
ing this step a thin colored dielectric iilm of tantalum' A for the ,production of units ‘which have lower- ¿capacity
oxide forms over the pellet surface. . The lilrn» may be
'ratings `(le, thicker dielectric iilrns)„` It hasralsoîbeen '
violet, blue, for any of the interference colors depending
' found that Ithe voltage rating 'of iinished capacitor' units
> .upon film thickness, and may vary` in Vthickness from
is directly related to the forming voltage during the fab
>about200 Angstroms to 2000 Angstroms, dependingV on>
theapplied-voltage and the time it is applied. L
Y
rication lof the units, hence capacitors intended to exhibit
>
The 'pellet is -now heatedin air‘for about one minutek v#l5
a high voltage rating are anodized at high voltages.
Example `Il Y
j'at'500" C. Vto eifect the pyrolytic conversionv of the ` l
manganous nitrate within the pellet pores to manganese . "
A quantity of a powdered'anodizablermetal »is formed, l 1
oxide'.> During this step the manganous nitrate Within the
pellet pores decomposes, giving olf fumes ofnitric'oxide. .
>Anon-volatile residue of manganese oxide is left, which
`
`into a- porous pellet about >180 mils square and -10 mills
' thick by fappglying a 'pressurefjof about 450 Ypounds toV H w
so .the
powder. `Inv this example, the> anodizablefmetlalisbß "
closely covers and adheres to the` dielectric 'tantalum " . colfumbium. The pellet isryaeuum'sínteredat 1500?_G„ ’
oxide lilm.
,
f
f
i
for 15 minutes. An Ianode lead is formed by spot-'Weld-VA
‘
The pellet is now ready‘for a repetitionl of the cycle
V. 'ing »to the pellet a columbi-um ribbon> about 3 milsíthick',
K rvof- anodization followed by pyrolytic conversionr of the
25 mils wide, Vand 1A; inch long..v The pellet is i then ‘
55
„.vimpregnated :compound to the protective metal oxide.
Anodiz‘ation is again accomplished in an electrolyte con
resintered at 1500° C. -for 15 minutes.
Y
.
The pellet is now placed in' a forming bath, which in
’ sisting of aqueous manganous nitrate solution. The' bath - ~
`.containing 58% by weight manganous nitrate-solution,
this example contains «an aqueous solution of ' nickel
nitrate >as theelectrolyte. i, rSince it is desired to perform
which was used in‘the tir-str anodization, may be lused in
thefiirst anodization fata high voltage, a dilute> solution ¿i 1
the subsequent anodization steps.Y i However, the voltage 60 of the electrolyte is employed ¿for the first forming step, v "
’applied during all anodizationV steps after Vvthe first step
as concentrated electrolyte solutionstend to break down
is preferably lowerltha’n the voltage appliedfduring‘the t atl high voltages. In this` example, the aqueous electro-`
Íirst forming step, in order _to avoid increasing the thick- l, , .lyte utilized in the Íirstforming step»` contains about .01 f
ness of the rdielectric film. In this example, all the sub- i
Weight'percent nickel nitrate. AsÄin- the previous ex~l
sequent anodization steps are «accomplished by applying
a voltage of about 45 volts for about 45 vminutes to the
pellet in the forming bath.
` ’
»
65
-
ample, the electrolyte is contained Yin- a'> stainless steek.`
tank which serves'fas theV cathode of thejbath‘.` The pellet ‘ '
*is anodized by passinga direct current from `the pellet,`
An important feature of this invention is that the pro- " .1 -thrOugIELfLhe~ electrolyte tothe; steel’> tank. ' In this ex
‘ longed` and careful washing of the pellet required in the
ample, the first anodizationis performedjat 180 volts
prior Vart is not necessary, since a solution ofthe same 70 for 90 minutes. _A dielectric ñlm of. columbium oxidel
compound is used for the various anodization steps and
impregnation‘steps. Another feature is thatV the impreg~
`nation of the electrolyte compound solution within the
pellet poresv is more> thorough than that obtained by
merely immersing the pellet in a solution, since in effect f
»is thereby formed over the pellet.` The nnit is ’now dried
by heating it in air for l5 minutes at 110° C.
Next, the pellet is immersed in af saturated 'aqueous '
solution of nickel nitrate, :andreformed by the applica- ì
tion `of 50 lvolts for 30 minutes. During this step the
-
3,100,329
pellet pores become impregnated with nickel nitrate.
2; The method of fabricating a solid electrolytic ca
pacitor comprising the following steps: pressing -a pow
Theipellet is then heated about one minute at'450o C.
>toeliect the pyrolyticv conversion of the impregnated
nickel nitrate _to a protective layer of nickel oxide which
dered anodizable metal into a porous pellet, said metal
- being selected from the group consisting of aluminum,
k beryllium, columbium, hafnium, tantalurn, tungsten, and
is in close contact with the dielectric columbium oxide
film. y
.
.
zirconium; vacuum sintering rsaid pellet; elcctrolytically
'
The above cycle of reforming the pellet at 5'0‘ volts in
the saturated electrolyte followed by pyrolyzing Áthe im
treating said pellet in ‘a concentrated laqueous s-olution‘of
k :a compound capable of pynolytic conversion into a semi
pregnated nickel nitrate so as to convertit to nickel oxide
conductive metal oxide soasv to simultaneously anodize
is repeated four times. »Advantageouslyg a last anodiza l0 said pellet and impregnate the pellet pores with said com
. tion `is performed for 30` minuts at 50 volts in a dilute
pound; heating said wafer so as to convert said com
nickel nitrate solution. The last anodization may be per
formed in` a solution containing about .01 weight percent
nickel nitrate, such as` that used in the initial forming
pound, which Ihas been thus elec-trolytically introduced,
in said pellet pores into a semiconductive metal oxide;
repeating at> least once the steps of anodizing said pellet»
step. After this last reform the pyrolysis 'step is omitted
and pyrolytically converting the impregnated compound
` and the penal is Oven dried 15 minutes at 110° C. i
within said pores into a semiconductive metal oxide; and
A vconductive coatingY is now» applied to the pellet
surface. The coating may for example consistiof
depositing a conductive coating upon said pellet.
Y3. The method of iorming la solid electrolytic capaci
graphite, applied in the manner» described above in‘Ex
Y ample‘l.
tor'cornprising the `following steps; pressing a powdered
Next, a portion of the wafer adjacent to the
lanodizable metal into a porous pellet; vacuum sintering
anode lead is masked, and the remainder of the pellet
sprayed V_with 60 tin-40 lead solder. A cathode lead is
formed by soldering a gold plated nickel »ribbon to the
solder coated area of the pellet. VThe gold plated ribbon
said pellet; electrolytically treating said pellet in a con
centrated'aqueous solution of a compound rcapable of
pyrolytic conversion into la serniconducti've metal oxide
selected from the group consisting lof lead oxide, nic-kel
-íorms 1an electrical contact through the solder and the 25 oxido, land manganese oxideso as to simultaneously an
conductive graphite to the layer of nickel oxide which
odize said pellet and impregnate thepellet pores with said
covers the dielectric columbium oxide tilm. The unit
' is then cased by methods known to the art.
compound; heating said wafer so as to convert said com
’ Many rntxliûcationsV may be made in the process without
pyrolytically converting Áthe impregnated compound with
pound, which has been electrolytically introduced, in said
It will be understood that the above examples were
pellet pores into »a semiconductive meta-l oxide; repeating
by wayV of illustration only, and not as limitations. 30 at least fonce the steps of anodizing said pellet and
departing from the spirit and scope of the instant inven
in said pores into a semiconductive metal oxide; and de
tion. 'For example, any of the other anodizable metals
may be utilized, such as titanium 'and the like. Other
positing a conductive coating uponsaid pellet.
,4;«The method of fabricating a .solid-electrolytic ca
`serniconduct-ive metal oxides such as'lead oxide may be
utilized for the protective layer over the dielectric film.
pacitlor comprising the following steps: pressing a pow
dered yanodizable metal into a porous pellet; vacuum sin
The electrolyte may be any compound of lead, nickel, l l Ítering said pellet; electrolytically treating said pellet in la
or manganese .whichl is readily vpyrolyzed and leaves a
residue consisting of the oxide oflead, nickel, or man'- »
ganese.
.
What is claimed:
~
`
'
l
'
k
`
Vconcentrated aqueous solution of a compound selected v
yfrom the» group consisting ofthe hydroxides, nitrates,
40
f
>1. 'Ihe method of forming a solid electrfoyltic capacitor>
comprising. the iollowing steps: pressing a powdered
acetates, oxalates, and yñormates of lead, nickel, and man
ganese so `as to simultaneously anodize said pelletand im
pregnate the pellet pores with said compound; heating
. said wafer so as to convert said compound, which has
anodizable metal into a porous pellet; vacuumr sintering
electrolytically introduced, in said pellet pores into
said pellet; electrolytically treating said pellet in a con 45 abeen
semiconductive metal roxide; repeating at least once the
centrated aqueous solution of a compound capable of
steps of «anodizing said pellet and pyrolytically converting
pyrolytic conversion into 4a semiconductive metal oxide so
the impregnated compound with-in said pores into a semi
as ¿to simultaneously -anodize said pellet and impregnato
conductive metal oxide; :and depositing a conductive coat
the pellet pores with ysaid compound; heating said Wafer
`so las to convert said compound,- which has ’been thus
electrolytically introduced, in said pellet pores into a
stmiconductìve metal oxide; repeating at least once the ' '
ing upon said pellet.
'
References Cited in the file of this patent
‘ steps of anodizing said pellet and pyrolyt-ically convert
UNITED STATES PATENTS
ing the impregnated compound vvithin said pores into
55
Gnay et al. __________ _- Oct.
2,299,228
said, semiconductive metal oxide; and depositing acon-`
» ductive coating upon said pelle-t,v ì
.
f.
'
42,936,514
20, 1942
Milland __, __________ „_V May 1,7, 1960
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