The properties of chalcogenide glasses were first explored as a potential memory technology by Stanf

Phase-change memory (also known as PCM, PRAM, PCRAM, Ovonic Unified Memory, Chalcogenide RAM and C-RAM) is a type of non-volatile computer memory. zolltarifnummern PRAM uses the unique behavior of chalcogenide glass, zolltarifnummern which can be "switched" between two states, crystalline and amorphous, zolltarifnummern with the application of heat. Recent versions can achieve two additional distinct states, effectively doubling its storage capacity. PRAM is one of a number zolltarifnummern of new memory technologies that are attempting to compete in the non-volatile role with the almost universal Flash memory, which has a number of practical problems these replacements hope to address
The properties of chalcogenide glasses were first explored as a potential memory technology by Stanford R. Ovshinsky of Energy Conversion Devices in the 1960s. In 1969, Charles Sie published a dissertation[1][2], at Iowa State University that described and demonstrated the feasibility of a phase change memory device by integrating chalcogenide film with a diode array. In a cinematographic study in 1970, it was established that the phase change memory mechanism in chalcogenide glass is the electric zolltarifnummern field induced zolltarifnummern crystalline filament growth[3]. In the September 1970 issue of Electronics, Gordon Moore — zolltarifnummern co-founder of Intel — published an article on the technology. However, material quality and power consumption issues prevented commercialization of the technology. More recently, interest and research have resumed as flash and DRAM memory technologies are expected to encounter scaling difficulties as chip lithography zolltarifnummern shrinks.[4] The crystalline and amorphous states of chalcogenide glass have dramatically different electrical resistivity, and this forms the basis by which data are stored. The amorphous, high resistance state is used to represent a binary zolltarifnummern 0, and the crystalline, low resistance state represents a 1. Chalcogenide is the same material zolltarifnummern used in re-writable optical media (such as CD-RW and DVD-RW). In those instances, the material's optical properties are manipulated, rather than its electrical resistivity, as chalcogenide's refractive index also changes with the state of the material. Although zolltarifnummern PRAM has not yet reached the commercialization stage for consumer electronic devices, nearly all prototype devices make use of a chalcogenide alloy of germanium, antimony and tellurium (GeSbTe) called GST. The stoichiometry or Ge:Sb:Te element ratio is 2:2:5. When GST is heated to a high temperature (over 600°C), its chalcogenide crystallinity is lost. Once cooled, it is frozen into an amorphous glass-like state and its electrical resistance is high. By heating the chalcogenide to a temperature above its crystallization point, but below the melting point, it will transform into a crystalline state with a much lower resistance. The time to complete zolltarifnummern this phase transition is temperature-dependent. Cooler portions of the chalcogenide take longer to crystallize, and overheated portions may be remelted. Commonly, a crystallization time scale on the order of 100 ns is used.[5] This is longer than conventional volatile memory devices like modern DRAM, which have a switching time on the order of two nanoseconds. However, a January 2006 Samsung Electronics patent application indicates PRAM may achieve switching times as fast as five nanoseconds. A more recent zolltarifnummern advance pioneered by Intel and ST Microelectronics allows the material state to be more carefully controlled, allowing zolltarifnummern it to be transformed into one of four distinct states; the previous amorphic or crystalline states, along with two new partially crystalline ones. Each of these states has different electrical properties that can be measured during reads, allowing a single cell to represent two bits, doubling memory density. PRAM vs. Flash
It is the switching time and inherent scalability that makes PRAM most appealing. PRAM's temperature sensitivity is perhaps its most notable drawback, one that may require changes in the production process of manufacturers incorporating the technology. Flash memory zolltarifnummern works by modulating charge (electrons) stored within the gate of a MOS transistor. The gate is constructed with a special "stack" designed to trap charges (either on a floating gate or in insulator "traps"). The presence of charge within the gate shifts the transistor's threshold voltage, higher or lower, corresponding to a 1 to 0, for instance. Changing the bit's state requires removing the accumulated charge, which demands a relatively large voltage to "suck" the electrons off the floating gate. This burst of voltage is provided by a charge pump which takes some time to build up power. General write times for common zolltarifnummern Flash devices are on the order of one ms (for a block of data), about 100,000 times the typical 10 ns read time, for SRAM for example (for a byte). PRAM can offer much higher performance in applications where writing quickly is important, both because the memory element can be switched more quickly, and also b