Patent GB-1330684-A (GB)
Title: Display means
IPC: H01L31/14
Filed: 1970-10-05
Abstract: 1330684 Electroluminescence MATSUSHITA ELECTRIC INDUSTRIAL CO Ltd 5 Oct 1970 [3 Oct 1969] 47317/70 Heading C4S An image display means for producing a visible image from an incident radiation image (e.g. X-rays, γ-rays, cathode-rays) consists of transparent support 11 and at least the following layers, in order: transparent electrode 12, electroluminescent layer 13, visible light reflecting layer 14, layer 15 opaque to visible light, photoconductive layer 16, radiation permeable electrode 17, and protective layer 18 wherein layers, 13, 14, 15, 16 have respective thickness of d 1 , d 2 , d 3 , d 4  wherein d 2  is in the range 0À1d, to 0À3d 1 , d 3  is in the range 0À1d 1  to 0À3d 1  and d 4  is in the range 3d to 10d. Layers 15 and 14 should be > 10Á. Protective layer 18 has a high resistance to humidity (e.g. silicone rubber or resin wax) and should have a low shrinkage (e.g. 0 to 4%) and retain plasticity after hardening. An A.C. source (19) may apply a field of 800 V/Cm. to the photoconductive layer, may be 50 to 10 kHz, and the source voltage 200 to 1200 V. The display panel may be responsive to 10‹ to 10<SP>4</SP> mn/min., the EL material ZnS based, 25 to 80 Á thick and the reflective layer, which improves the dielectric b/d strength of the EL layer may include barium titanate and be 2À5 to 24 Á thick. The opaque layer may include carbon black and be 2À5 to 24 Á thick, the p.c. layer may contain CdS, and/or CdSe (e.g. 40 to 80% CdSe with 60 to 20% CdS) activated by Cu or Ag and coactivated by Cl or Al and be 75 to 800 Á. The powdered materials are heated in non- oxidizing gas, e.g. nitrogen and argon, at 500 to 800‹ C. CdS alone is not suitable for moving displays. The EL layer may have a dielectric constant of 7 to 40, the reflective layer a constant of 10 to 200 and the opaque layer a specific resistivity of 10<SP>5</SP> to 10<SP>10</SP> #. cm. The transparent support may be lead glass with lead in amount corresponding to an equivalent value of 1 to 10 mm. to protect viewers, and also decreases reflection and refraction. The radiation permeable electrode may be vacuum deposited and of Al or In. Pc layer 16 preferably exhibits a linear relation between dark current and applied alternating voltage up to 800 v./cm. Panel 10 may be prepared by coating, spraying, or screening for example. Layer 12 may be chemically deposited tin oxide and covered by EL paint, e.g. ZnS in urea resin in a solvent, e.g. xylol or butanol. Layer 14 may be 0À5 to 10 Á barium titanate in a binder, e.g. urea resin with xylol or butanol, layer 15 of carbon black powder in a binder such as epoxy resin in a solvent, e.g. butanol or methylethyl ketone. Pc layer 16 may be applied by a squeegee in epoxy resin with butanol or methylethyl ketone. One end of electrode 17 is connected to a Cu electrode for connection to conductor 20. In an example, layer 13 may be 60 Á thick ZnS in a cellulose binder, layer 14, 10 Á thick; layer 14, 10 Á thick barium titanate in urea resin; layer 15, 10 Á carbon powder and epoxy, layer 16, 320 Á activated CdS in epoxy resin with linear relationship of dark current to voltage up to 1900 v./cm. Table I illustrates p.c. properties. Fig. 3 (not shown) illustrates brightness v d 4 /d 1 , Fig. 4 (not shown), dark current v critical electric field, Fig. 5 (not shown), critical electric field v p.c. composition.