Note: Descriptions are shown in the official language in which they were submitted.
l ! THE INV~NTION
This inventlon is concerned with eleetrolumine~cent deviees for
display purpos~. Such devices comprise an ol~etrol~mineseent (EL) layer
between t~o electrode layers, ono of tb~ eloctrodes beln~ traDJparent to
penmit viewabllit~ of the ~-L layer. It is knoun to provldo a d rk layer
behind the EL layer in order to im~prove tho contraJt ratio of tho doviee,
that i9 to say~ to provide visibility of the EL layer even under a~bient
conditions of high brightness. Such a dark layer is diseloset in U. S.
patent 3,560,784, the material for tho dark layer compri6ing arsenic
sulfide, arsenie selenide, ~r~enic sulfoselenide or mixtures thereof.
Ho~ever, said arsenic eompounds either do not prov*te a satisfactory dark
color or they cba~go color during u~o.
An EL displa~ device often compriJes seven electrode segments in
the shape of a sub~eantiall~ rect~nguLar figure eight. An~ dig~t from
O to 9 can be repr-sented b~ illu~inating appropriate portions of the EL
m~terial overla~ins said se~ent~. Said portions c n be illuminat~d by
applying a volt ge betwoen a transparent overlnJing electrode and the ;
appropriate segmentea eleetrode, with onl~ that port~on of tho EL layer
direetl1 between saia two olietrodes being ene~glzed to luminescence. If
EL materi-l outsido tho bound of said portion l~nrsces, haloing can
¦occur, whieh is undodrable. If an excessive amount of additional EL
¦materi~l luminesces, eondition known as "cross talk" ean occur, whieh
~ the und-~ir 1l 111 ln tlon of ~ r p-rt of n dditlon l -g~ant. ¦ ~ ;
31~
~4~Z65
D-20,109 I The us~ of a dark layer can cauY~ a probl~m in that it :increa~es the
tendency for haloing or cross t~lk to occur.
I We have Eound th~t the probl~n of haloing can b~ controlled by
Il proper control of the dark layer material. Spacifically, the dark layer ¦
¦I material should l~ve a resi~tivity of ~bout 10 to 10 ohtl~-c~n~imeter~. I
Preferably, the dark layer material should comprise predominantly a c~m- I
pound of elements from ~roups IIB ~ VIA of the periodic table.
In the drawing, Fig. 1 i9 a schematic sectional view of the layer~
of an EL device in accordance with this invention. Fig. 2 shows the
configuration of electrode segments of an EL device used for numerical
display, wlth the shape of the other layera sho~m in phantom.
An EL devics in one embodiment in accordarlce with this invention, as
shown in Fig. 1, comprised a dark field layer 1 and an EL layer 2 between
two electrodes 3 and 4. There was a dielectric layer 5 between dark laye~ .
1 and electrode 3. There was another dielectric layer 6 between EL layer
2 and electrode 4. Layers 4 and 6 were transparent to light emitted by
EL layer 2. Electrode 3 was a metallic electrode and e}ectrode 4 was ~
a tranoparent electrode. The layers were all mounted on a gla~ substrat ~.
7.
Fig. 2 shows a configuration of seven electrodes 3 with th-ir exten-
~ions for electrical connection. The contour of el~ctrode 4 is shown in
phantom; outline 8, al~o in phantom, shows the ~hape for dielectric
layers 5 and 6, EL layer 2/ The co ~ gYuration of electrode~ 3 can be
used to represent any digit including zero. For example, if it is desired :
~25 to present the numeral nine, an electrical potential would be established
between electrodle 4 and él~ctrodes 3a,3b,3c,3d and 3e. The EL material --
directly between those regions of electrodes 3a,3b,3c,3d and 3e that
mated with e ~ctrode 4 would be energiz d to luminescence and the numeral
nine would be presented in illuminatet form. If, howev~r, the resistivity
of dark layer 1 i5 low., the appearance o~ said numeral would be fuzzy,
that is to say, haloing would occur, becsuse ~L material in layer 2 that
. laterally extended outside the mating regions of the electrodes would
lu=lnesce. D u the reslstlvlty of dark hyer 1 shou-d be hlgh ~nouch
4~Z6S
D-20,109 ~ to prevent ~c'h haloing. Said resi~tivity will be dep~nd~nt on the thick-¦
ness of dark layer 1 but, generally, it should be grea~er ~han about 10
ohm-c~ntimeter~
ll However, if the resistivity of dark layer 1 is too high, it will not
¦I be able to withs~and the electrical field stre-lses between electrodes 3
and 4 without breakdown because of ~oule heating in said layer. Thus,
¦ the resistivi~y of dark layer l should be low enough to prevent such
~oule heating. Said re~istivity will be dependent on the thickness of
dark layer 1 but, generally, it should be less than about 106 ohm-
- centimeters.
In order to provid~ a dark layer 1 that wlll have adequate light
absorption in a reasonable layer thirkness and that will provide the
desired resistivity in a reasonable layer thic~ness, the dark'layer
material should comprise predomin&ntly a compound of elements from groups
IIB-VIA of the periodic table. It may also be desirable to provida ¦
elements or compounds from groups IVA and VIIA of the'periodic table in ~ ;
the dark layer material.
In one example, glass sub~trate 7 wa~ coa~ed with tin oxide by ¦
chemical vapor deposition to orm elec~rode 4, which was then acid etched
to provide the contour for electrode 4 shown in Fig. 2. Next, yttrium
oxite wa~ ther~ally vapor dopo~ited in vacuum through a mask to provide
dLelectric layer 6 in the shape of outline 8 s'hown in Fig. 2. EL layer
2 WaJ similarly deposited in the same outline 8, as was dark layer 1,
the material for which was a fused, homogeneous mixture of 9C~. cadmium
telluride ant lC~ lead telluride. 'The resistivity of said material wa~
about 1.5 x 105 ohm-centimeters. Dielectric layer 5 was then deposited
in the same manner as dielectric layer 6. Aluminum was thermally vapor
depo~ited through a mask to provide segmented elactrode 3 on layer 5.
When the device was e~ectrically energized, a 10 foot lambert
' segment in the presence of 100 foot candl3 light at a 30 angle of
'incidence was read with a contra~t ratio of 2.4 for the lit versus
¦ background contra-~t.
_ 3 _
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Il
D-20,109 ¦l In this example, dark layer 1 is shown between EL layer 2 and
!1~ dielectric Layer 5. Dark layer 1 may also be placed, instead, between
I jl electrode 3 and dielectric layer 5.
ll Another suitable dark layer material could be 8~/~ cadmium telluride
¦' 2~/, tin telluride, which has a resistivity of about 5 x 10 ohm-centi-
meters. The nddition of 1% of tin chloride to said material would
. j provide a resistivity of about 2.9 x 10 ohm-centimeters. Another
material could be 69~/o zinc telluride - 3o~ tin telluride - 1% tin
¦I cbloride, the slsti~lty of ~hich ls ab~ut 2.6 x 1~ . ¦
