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Tuesday, March 5, 2013

What is meant by Ovonic Unified Memory?

There is much requirement in the IT industry for a high – speed memory plus that is non–volatile too. A solution to this is provided by the ovonic unified memory
- Ovonic Unified Memory is an approach to such a memory. Further, it offers reduced bit rate and cost. 
- There are some other characteristic features of this memory:
  1. High endurance
  2. Low power consumption
  3. Non – volatile RAM
  4. Readily scaled.
  5. Merged memory/ logic simplified
- Since the ovonic unified memory is readily scaled it is not required to scale the barriers of flash and DRAM memories.
- This represents a new semiconductor technology – a creation of the Energy Conversion Devices, inc. however later it was licensed to the ovonyx inc.
- This technology makes use of a structural phase change that is reversible i.e., from a crystalline phase to the amorphous phase. 
- The material used here is the thin–film chalcogenide alloy. 
- This all constitutes the data storage mechanism of ovonic unified memory (OUM). 
- Each memory cell consists of an active medium in a small volume that acts as the programmable resistor. 
- This resistor switches between the low and high resistance in the dynamic range of greater than 40x. 
- The phase change technology is currently being used in the PD, CD RW, DVD RW and DVD RAM. 
- The basic advantage offered by OUM is in the terms of performance and cost when compared to its conventional counterparts namely the flash and the DRAM memories. 
- OUM has got compatibility with the merged memory/log. 
- A conventional CMOS process is used in the OUM technology along with some additional layers in order to form the memory elements. 
- The OUM products have been commercialized under various licensing agreements. 
- The alloy used in OUM consists of Se and Te elements.
- They exhibit the property of electronic threshold switching phenomenon because of which the OUM memory cells can be programmed at quite low voltages irrespective of which state they are in i.e., whether conductive or resistive. 
- The measurement of the resistance of cell is used to read the information stored. 
- The programming of the OUM devices is done electrically by the alteration of its structure of the alloy. 
- These OUM devices show metallic behavior are independent of the temperature.
- The OUM devices are known for their excellent data retention property in the case of high density array applications. 
- Also, the OUM cells have more than normal life cycle i.e., they can tolerate up to 1013 write and erase cycles without any failure. 
- These devices possess quite a large dynamic range.
- This allows them to be programmed for enabling the multi–state data storage at intermediate resistance values.
- For multi–stage data storage, every cell needs to support multiple–bit storage. 
- The technology behind the ovonic unified memory is the device modeling. 
Here, simple analytical methods show the trends in the properties and size of the material for structures that are spherically equivalent. 
- Other numerical models are inclusive of the mesh evaluation plus the device geometry.
The behavior of the OUM devices can be predicted using the numerical simulation. 
- The behavior of the OUM material depends up on its bulk properties which have a characteristic that they can be quantified. 
- There are 3 considerations of this model:
  1. Phase–change: It includes heat of fusion, crystal growth and nucleation.
  2. Electrical: It includes current density, electric field and percolation conduction.
  3. Thermal: It includes percolation conduction and the heat equations.
Apart from the cost, another advantage of OUM is its near – idle memory qualities such as:
  1. Static
  2. Random accessible
  3. Non – destructive read

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