IMPROVED ELECTRICALLY CONDUCTIVE MATERIALS FOR DEVICES

Abstract: An electrically conductive photoresist electrode is formed by a combination of a photoresist and conductive black powder. This conductive photoresist has the properties of being photosensitive, electrically conductive, and black to avoid reflectivity by the electrode structure, as occurs in display devices.

Description: Improved electrically conductive materials for devices. The present invention is directed to an improvement in structures utilizing conductive photoresist electrodes. In particular, electrophoretic imaging display (EPID) devices are described using a blackened control electrode, but the use of conductive photoresists, blackened or otherwise, may be provided in numerous structures for electrodes. Electrophoretic display devices with control electrodes may be seen, for example, in U.S. patent no. 4,203,106 to Dalisa et.al. This reference provides the background to the type of device for which the present invention is particularly useful. In such EPID devices, materials used for control electrodes are often either an evaporated aluminium film or an evaporated indium oxide (In203) film. These electrode materials have certain disadvantages. In particular, an aluminium conductive film is highly reflective, Further, these materials have questionable adhesion to insulating materials such as used in EPID devices. Conductor cracking and possible flaking causes open or short circuits in these devices. Also, these materials must be patterned with a photoresist-etching procedure in order to be properly formed. Of these disadvantages, the itost serious are high reflectivity and poor adhesion of the electrode material. In a control grid EPID device this causes the device to resemble a mirror at nost viewing angles and reduces the contrast and readability of the device to unacceptable levels. Short circuits render the display unusable. The present invention seeks to provide electrically conductive photoresists, such as can be used as control grid electrodes in an EPID, device which will obviate the above difficulties. In particular, the formation of a control electrode in an EPID device having the properties of being photosensitive when required, electrically conductive, and black solves the foregoing difficulties. The arrangements of the presently clained invention may be seen more clearly by reference to the drawing figure ailich illustrates without limitation an ento#int#nt of the present invention, and wherein Figure 1 illustrates an expanded view of the electrode structure in an EPID device, and Figure 2 illustrates a structure for the control electrode in such device. An electrophoretic device with a control grid is constructed generally as seen in Figure 1. In such a structure, a substrate panel 10 is provided on its surface with a plurality of parallel transparent conduc- tive strips adherent to a surface of the substrate, which strips serve as column electrodes 11. Such electrodes may typically be fared of indium oxide applied to the panel ty means of a sputtering technique, for example. The substrate 10 and electrodes 11 are then covered with an insulating layer 13 ccmçosed of a photoresist or other dielectric which might be applied by a process of dip coating, for example. A plurality of row electrodes 14 are then adherently applied to the surface of the insulating layer 13 in the form of parallel strips extending transversely to the column electrodes. These row electrodes 14, as well as the underlying insulating layer 13, are then patterned with minute pockets or boles 18 which are shown in an enlarged portion in Figure 2. The holes 18 are not shown in Figure 1 in order to avoid cluttering of the drawing. The row electrodes 14 may act as a control electrode for the EPID device. A second substrate panel 17 is then provided parallel to the first panel 10 with a plane major surface facing the first panel 10. This surface is coated with an electrode layer 16 which is a continuous transparent electrode layer of indium oxide, for example. An electrophcr retic solution (not shown) is placed between the two panels and elec troves. In such an arrangement for an EPID structure, the present invention enables the control electrode 14 to be formed in a manner to avoid high reflectivity so as to avoid the control electrode frcan resembling a mirror. This occurs, for example, by constructing the electrode 14 from a mixture of one part of carbon powder, such as lamp black powder, to two parts of a photoresist material by volume. This catibired form is mixed and a conductive photcresist is obtained which is photosensitive, is electrically conductive, and has a black color. The photoresist material may be a ccooercial photoresist such as Shipley AZ 1350B. Other examples are AZ 4110 and AZ 1450 of the Azoplate division of American Hoechst Corp.; Kodak 809 and 820 of Kodak Corp.; and Selectilux P of EM Chemicals; all of which are positive type photoresist materials. Negative type photoresists, such as Kodak 747 and Selectilux N, can also be used. Using such materials as the control electrode in an EPID device such as that of Figure 1, will achieve conduction as required, as well as provide a non-reflective surface. Moreover, this material of the present invention has an excellent adhesion to the insulating layer 13. Since it is a photoresist, it can be easily patterned in the form of the patterned electrode of Figure 2. The formation of the electrically ccnductive photoresist could also be achieved with other conducting materials, such as silver, for ex, ple. The amount of conductive material loadings could be varied to change the conductivity. It is highly likely that such a material would be extremely useful for thick film resistors where high Curing tan#ratures, normally used with thick film pastes, are prohibitive. As an example, conductive contacts for materials, such as triglycinesulface or TGS, may provide a good thick film of material according to the invention for infrared radiation detectors. While one example to the present invention has been illustrated and described, the present invention includes all variations and features which may be evident from the claims.

Claims: 1. A conductive layer comprising a combination of a photoresist and a conductive material. 2. A conductive layer according to claim 1, wherein said conductive material is black powder. 3. A conductive layer according to claim 2, wherein said black powder is carbon powder. 4. A conductive layer according to claim 1, wherein said conduc- tive material is silver powder. 5. In a display device comprising a solution sandwiched between substrates, and electrically conductive pcrtions facing said solution fared on said substrates, the improvement comprising at least one of said electrically conductive portions being a photosensitive blackened photoresist. 6. The zmprcseIrentofofclaim 5, where said blackened photoresist includes one part carbon powder and two parts photoresist. 7. A display device according to claim 5, wherein said solution is an electrophoretic solution. 8. A display according to claim 7, wherein said at least one electrically conductive portion includes a control electrode at one side of said electropretic solution. 9. A display device according to claim 8, wherein said control electrode includes one part carbon and two parts photoresist.

Inventors: WHITE, ROGER PAUL
Applicants: N.V. PHILIPS' GLOEILAMPENFABRIEKEN
Application year: 1984
Main classification: H01B1
IPC codes: G09F9, G03F7, H01B1, G02F1