Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
2002-11-08
2004-12-21
Abraham, Fetsum (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S004000, C257S005000, C257S347000, C257S359000, C438S048000
Reexamination Certificate
active
06833593
ABSTRACT:
The present invention concerns an electrode means comprising first and second thin-film electrode layers with electrodes in the form of parallel strip-like electrical conductors in each layer, wherein the electrodes of the second electrode layer are oriented crosswise or substantially orthogonally to the electrodes of the first layer, wherein at least one of the electrode layers is provided on an insulating surface of a substrate or backplane, and wherein the electrode layers are provided in parallel spaced-apart planes contacting a globally provided layer of a functional medium therebetween; as well as a method for manufacturing an electrode means of this kind.
The present invention further concerns an apparatus comprising at least one electrode means comprising first and second thin-film electrode layers with electrodes in the form of parallel strip-like electrical conductors in each layer, wherein the electrodes of the second electrode layer are oriented crosswise or substantially orthogonally to the electrodes of the first layer, wherein at least one of the electrode layers is provided on an insulating surface of a substrate or backplane, and wherein the electrode layers are provided in parallel spaced-apart planes contacting a globally provided layer of a functional medium therebetween, wherein functional elements are formed in volumes of the functional medium defined at respective overlaps between electrodes of the first electrode layer and the electrodes of the second electrode layer to provide a matrix-addressable array, wherein a functional element can be activated by applying a voltage to the crossing electrodes defining the functional element such that a potential is generated across the latter, whereby the physical state of a functional element may be temporarily or permanently changed or a switching between discernible physical states take place, said voltage application essentially corresponding to an addressing of the functional element for write or read operations thereto, and wherein the functional elements according to the properties of a selected functional material can be made to operate as at least one of the following, viz. switchable logic elements of a data processing apparatus, memory cells in a data storage apparatus, or pixels in an information displaying apparatus, whereby the addressing of said elements, cells or pixels in any case takes place in a matrix-addressing scheme.
Finally, the present invention also concerns uses of the electrode means according to the invention in the apparatus according to the invention.
The present invention particularly concerns electrode means for use in apparatuses and devices comprising functional elements in a planar array, wherein the functional elements are addressed via respectively a first electrode means with parallel strip-like electrodes arranged in contact with the functional elements on one side thereof and another electrode means with similar electrodes, but oriented perpendicular to the electrodes of the first electrode means and provided in contact with the opposite side of the functional elements. This constitutes what is called a matrix-addressable device. Such matrix-addressable devices can comprise e.g. functional elements in the form of logic cells, or in the form of memory cells. The functional elements may include one or more active switching means, in which case the matrix-addressable device is termed an active matrix-addressable device, or the functional elements may consist of passive means only, e.g. resistive or capacitive means in which case the matrix-addressable device is termed a passive matrix-addressable device.
The latter is regarded as providing a most efficient way of addressing, for instance in case of memory devices, as no switching elements, viz. transistors are required in a memory cell. It is then desirable to achieve as high storage density as possible, but present design rules which set a lower limit to the cell, also limit the fill factor thereof, i.e. the area of the memory material of the matrix-addressable memory device that actually can be used for storage purposes.
A prior art passive matrix-addressable device is shown in
FIG. 1
a
and comprises an essentially planar global layer
3
of functional material in sandwich between a first electrode means comprising parallel strip-like electrodes
1
of width w and spaced apart by a distance d and a similar second electrode means comprising parallel strip-like electrodes
2
of the same width w, but with the electrodes
2
arranged perpendicular to the electrodes
1
. In the global layer
3
of functional material the overlap between the electrodes
1
,
2
of the respective electrode means defines a functional element
5
in the functional material of the global layer
3
. By applying voltage to the electrodes crossing at this location, a physical state of the functional element which e.g. can be a logic cell, or a memory cell, may be changed or switched.
FIG. 1
b
shows the prior art device of
FIG. 1
a
in a section taken along the line X—X making the layout of the electrodes
1
,
2
and the global layer of the sandwiched functional material
3
as well as the location of the functional element
5
apparent. The functional material of the global layer
3
usually has properties such that an application of the voltage to crossing electrodes
1
,
2
only will affect the functional element
5
at the crossing thereof and not neighbouring functional elements or cells at the electrodes crossings in the vicinity of the former. If the functional material of the global layer e.g. is electrically conducting, this can be achieved by providing it with anisotropic conducting property, such that conduction only can take place in a vertical direction to the functional material and between the overlapping electrodes, with no current flowing through the global layer to the other functional elements. However, for a large number of applications the functional material of the global layer can be non-conducting, i.e. dielectric, and the functional element can be regarded as highly resistive or a pure dielectric such that it will be behave like a capacitor. The dielectric material may be a polarizable inorganic or organic material and capable of exhibiting hysteresis. Such materials include both ferroelectric and electret materials and their capability of becoming polarized and exhibiting hysteresis are exploited in e.g. ferroelectric matrix memories or electret matrix memories with a device configuration similar to that shown in
FIG. 1
a
. In such devices the polarization state in a memory cell, i.e. the functional element
5
, may be set by a proper application of voltages to the electrodes defining the memory cell
5
at their overlap and the polarization can be switched or the cell can be restored to an initial state by operations which shall conform to write and read operations to the memory cell. The functionality of such matrix devices is, of course, not only dependent on the functional material selected, but also on architectural and structural constraints of the memory device. The storage capacity in the memory medium in this global layer
3
depends on the size and density of the memory cells
5
and these will in their turn depend on the minimum process-constrained feature that can be created in the manufacturing process. Such features are e.g. when electrodes are laid down as metallization which afterwards is patterned in a photomicrolithographic process resorting to photolithographic masks and e.g. etching, dependent on the smallest process-constrained feature f that can be defined by the mask and its value will in its turn depend on the wavelength of the light used. In other words, this feature f will usually within the scope of today's technology be limited to say 0.15-0.2 &mgr;m, and hence the width w of the electrodes
1
,
2
and the spacings therebetween will be of about this magnitude.
In that connection it should be noted that the value 2f usually is termed the pitch and that the maximum number of lines per unit le
Gudesen Hans Gude
Leistad Geirr I.
Abraham Fetsum
Thin Film Electronics ASA
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