“Ovonic Unified Memory” is the registered name for the non-volatile memory based on the material called chalcogenide.

The term “chalcogen” refers to the Group VI elements of the periodic table. “Chalcogenide” refers to alloys containing at least one of these elements such as the alloy of germanium, antimony, and tellurium discussed here. Energy Conversion Devices, Inc. has used this particular alloy to develop a phase-change memory technology used in commercially available rewriteable CD and DVD disks. This phase change technology uses a thermally activated, rapid, reversible change in the structure of the alloy to store data. Since the binary information is represented by two different phases of the material it is inherently non-volatile, requiring no energy to keep the material in either of its two stable structural states.

The two structural states of the chalcogenide alloy, as shown in Figure 1, are an amorphous state and a polycrystalline state. Relative to the amorphous state, the polycrystalline state shows a dramatic increase in free electron density, similar to a metal. This difference in free electron density gives rise to a difference in reflectivity and resistivity. In the case of the re-writeable CD and DVD disk technology, a laser is used to heat the material to change states. Directing a low-power laser at the material and detecting the difference in reflectivity between the two phases read the state of the memory.


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INTRODUCTION TO OVONIC UNIFIED MEMORY
We are now living in a world driven by various electronic equipments. Semiconductors form the fundamental building blocks
of the modern electronic world providing the brains and the memory
of products all around us from washing machines to super
computers. Semi conductors consist of array of transistors with each transistor being a simple switch between electrical 0 and 1. Now often bundled together in there 10’s of millions they form highly complex, intelligent, reliable semiconductor chips, which are small and cheap enough for proliferation into products all around us. Identification of new materials has been, and still is, the
primary means in the development of next generation
semiconductors.
PRINCIPLE OF OPERATION
Among the above-mentioned non-volatile Memories, Ovonic Unified Memory is the most promising one. “Ovonic Unified Memory” is the registered name for the non-volatile memory based on the material called chalcogenide.
The term “chalcogen” refers to the Group VI elements of the periodic table. “Chalcogenide” refers to alloys containing at least one of these elements such as the alloy of germanium, antimony, and tellurium discussed here. Energy Conversion Devices, Inc. has used this particular alloy to develop a phase-change memory technology used in commercially available rewriteable CD and DVD disks. This phase change technology uses a thermally activated, rapid, reversible change in the structure of the alloy to store data. Since the binary information is represented by two different phases of the material it is inherently non-volatile, requiring no energy to keep the material in either of its two stable structural states. The two structural states of the chalcogenide alloy, as shown in Figure 1, are an amorphous state and a polycrystalline state.
Relative to the amorphous state, the polycrystalline state shows a dramatic increase in free electron density, similar to a metal. This difference in free electron density gives rise to a difference in reflectivity and resistivity. In the case of the re-writeable CD and DVD disk. Technology, a laser is used to heat the material to change states. Directing a low-power laser at the material and detecting the difference in reflectivity between the two phases read the state of the memory.
OUM ATTRIBUTES
• Non volatile in nature
• High density ensures large storage of data within a small area
• Non destructive read:-ensures that the data is not corrupted
• during a read cycle.
• Uses very low voltage and power from a single source.
• Write/erase cycles of 10e12 are demonstrated
• Poly crystalline
• This technology offers the potential of easy addition of non volatile
• memory to a standard CMOS process.
• This is a highly scalable memory. Low cost implementation is expected.
ADVANTAGES
 OUM uses a reversible structural phase change.
 Small active storage medium.
 Simple manufacturing process.
 Simple planar device structure.
 Low voltage single supply.
 Reduced assembly and test costs.
 Highly scalable- performance improves with scaling.
 Multistates are demonstrated.
 High temperature resistance.
 Easy integration with CMOS.
 It makes no effect on measured CMOS transistor parametric.
 Total dose response of the base technology is not affected.

The term “chalcogen” refers to the Group VI elements of the periodic table. “Chalcogenide” refers to alloys containing at least one of these elements such as the alloy of germanium, antimony, and tellurium discussed here. Energy Conversion Devices, Inc. has used this particular alloy to develop a phase-change memory technology used in commercially available rewriteable CD and DVD disks. This phase change technology uses a thermally activated, rapid, reversible change in the structure of the alloy to store data. Since the binary information is represented by two different phases of the material it is inherently non-volatile, requiring no energy to keep the material in either of its two stable structural states.