Thermal conditions that allow for fast crystallization should not be too similar to standby conditions, e. Phasechange memory controller architecture for low. Abbreviated as pcm, phase change memory is a type of nonvolatile memory that is much faster than the common flash memory, and it also uses up to onehalf the power. The combination of quick heating and cooling results in the amorphous phase, and this operation is referred to as a reset operation. We studied the temperature dependence of the resistance levels in both a projected memory. We have found that, if data is stored in pcm devices, the physical attributes of those devices can be exploited to achieve inplace computation. Tominaga 1 phase change memory technology relies on the electrical and optical properties of certain materials changing substantially when the atomic structure of the material is altered by heating 1 or some other excitation process 2. Phase change memory pcm is a nonvolatile memory composed of 1 transistor and 1 resistor. The phase change material is in the crystalline phase in an asfabricated device.
The fundamental mechanism for phasechange memory was invented in the 1960s by. This kind of memory will replace current well known flash memory. Thermal energy storage with phase change material lavinia gabriela socaciu 76 introduction thermal energy storage tes is defined as the temporary holding of thermal energy in the form of hot or cold substances for later utilization 1. Introduction the spice model is developed for the write operation of pillarshaped phase change memory based on physics and geometry of pcm.
Phase change memory is susceptible to a fundamental tradeoff of unintended vs. This stems primarily from the fact that phase change is a thermally driven process rather than an electronic process. Phase change materials and phase change memory mrs bulletin. This interval means that phasechange materials can be transformed from 0 to 1 by a picosecond excitation, and implies that emerging technology could store data many times faster than silicon random access memory ram for tasks that require memory and processors to. According to its proponents, pcm technology has the potential to provide inexpensive, highspeed, highdensity, highvolume nonvolatile storage on an unprecedented scale. Prams exploit the unique behaviour of chalcogenide glass. Phasechange memory pcm is a form of computer randomaccess memory ram that stores data by altering the state of the matter from which the device is fabricated. Phase change memory joint project pcm mobile platform memory system transformation mobile ram nand pcm code storage, xip code execution, web browsing, swapping, boot, email, multitaskingram photo pictures, movies, rom in place code execution, high performance, long battery life, instant on and play, low cost single chip solution. Phasechange memory alloys have been used since the 1990s in rewritable optical disks such as compact disks cd, and later also in digital versatile disks dvd and bluray disks bd. For information storage, a phase change memory device uses a large contrast either in electrical resistance between the amorphous phase high. Energy demands vary on daily, weekly and seasonal bases.
An overview of phase change memory device physics to cite this article. Lastras 2, alvaro padilla1, bipin rajendran, simone raoux2, and rohit s. The structure of these disks is essentially the same and is shown in fig. Pcm, about 1,000 times faster than ram, is one such effort thats being extensively developed by researchers and tech giants. Rethinking database algorithms for phase change memory. Phase change memory technology phase change chalcogenides exhibit a reversible phase change phenomenon when changed from the amorphous phase to the crystalline phase. Evaluating phase change memory for enterprise storage systems. Pdf on oct 1, 2016, hongsik jeong published high density pcmphase change memory technology find, read and cite all the research. We survey the current state of phase change memory pcm, a nonvolatile solidstate. Ibm press room ibm scientists have created randomly spiking neurons using phasechange materials to store and process data. As shown in figure 1, in the amorphous phase, the material is highly disordered there is an absence of regular order to the crystalline lattice.
Phase change materials and phase change memory simone raoux, feng xiong, matthias wuttig, and eric pop phase change memory pcm is an emerging technology that combines the unique properties of phase change materials with the potential for novel memory devices, which can help lead to new computer architectures. Extending the writeerase lifetime of phase change memory. This interval means that phasechange materials can be transformed from 0 to 1 by a picosecond excitation, and implies that emerging technology could store data many times faster than silicon random access memory ram for tasks that require memory and processors to work together to perform computations. It first calculates the heat generation of the heater, then gets the temperature of the phase. Nonresistancebased cellstate metric for phasechange memory. Breitwisch 2, michele franceschini, davide garetto, kailash gopalakrishnan 1, bryan jackson, bulen t kurdi, chung lam2, luis a. Multilevel cell mlc pcm storing multiple bits in a single cell o. The storage element is a phase change memory pcm cell 1 and the selector is an ovonic threshold switch ots 2.
What varies is the thickness of individual layers, which is determined by the. Based on the temperature, it simulates the phase changing of pcm. Aug 15, 2016 new discoveries about phase change memory show it can switch at picosecond scales theoretically opening the door to a dram replacement thousands of times faster than our current memory technology. Because no electrical power is required to maintain either phase of the material, so phase change memory is nonvolatile. Phase change materials have a large electrical contrast. Phase change materials are tecontaining alloys, typically lying along the getesb 2 te 3 quasibinary tie line. Current crowding at the heater to phase change material contact results in a programmed. Tominaga1 phasechange memory technology relies on the electrical and optical properties of certain materials changing substantially when the atomic structure of the material is altered by heating1 or some other excitation process25. Aug 16, 2016 the researchers are working hard to create new means to store data. Phase change memory pcm is an emerging technology that combines the unique properties of phase change materials with the potential for novel memory devices, which can help lead to new computer architectures. Pcm can be built at higher chip densities than dram, which is expectedto translate into highercapacities and lower cost per gb. A novel scalable and stackable nonvolatile memory technology suitable for building fast and dense memory devices is discussed. Architecting phase change memory as a scalable dram.
This demonstration marks a significant step forward in the development of energyefficient, ultradense integrated neuromorphic technologies for applications in. The electrical current passes through the phase change material between the top electrode and heater. It works by using a semiconductor alloy that can be changed rapidly between an ordered, crystalline phase having lower electrical resistance to a disordered, amorphous phase with. Candidates for nonvolatile memory and neuroinspired computing devices include phasechange materials pcms, resistiveswitching oxides.
Request pdf overview of phasechange chalcogenide nonvolatile memory technology phasechange nonvolatile semiconductor memory technology is. Phase change memory pcm provides a nonvolatile storage mechanism amenable to process scaling. This is the first of a new lineup of memory guy posts by ron neale. Phase change memory pcm is a form of computer randomaccess memory ram that stores data by altering the state of the matter from which the device is fabricated. In a projected memory device, the essential idea is to design the device in such a way that the physical mechanism of information storage is decoupled from the informationretrieval process18.
One of the leading prototypical memories that is being investigated is phase change memory. These new memory technologies exhibit a combination of characteristics that make them at least partially suitable for both main memory and storage applications. Designing crystallization in phasechange materials for universal memory and neuroinspired computing. Architecting phase change memory as a scalable dram alternative. Phase change memory uses a semiconductor alloy that can be changed rapidly between an ordered, crystalline phase having lower electrical resistance to a disordered, amorphous phase with much higher electrical resistance. Phase amount in the double phase region the lever rule at the point b. Everything from passive components like resistors, capacitors and the like through devices like diodes, and onto other electronic components like transistors, fets and even. Chalcogenide phasechange materials pcms are leading candidates for such.
In the older generation of pcm, heat produced by the passage of an electric current through a heating element generally made of tin was used to either quickly heat. A phasechange material is one that exists in at least two phases with remarkably di. We address the challenges facing this technology, including the design of pcm. The electrical and thermal properties of phase change materials are surveyed with a focus on the scalability of the materials and their impact on device design. Invited paper phasechangememory stanford university. The chapter starts with the discovery of a one way resistance transformation phenomenon in a chalcogenide, namely molybdenite mos 2.
In pcm technology, high heat over 600 c is applied to a storage cell to change the phase to store data. Ibm press room ibm scientists have created randomly spiking neurons using phase change materials to store and process data. Phase change materials exist in an amorphous and one or sometimes several crystalline phases, and. Because electrical transport in amorphous phasechange materials is thermally activated e a is typically in the range of 0. Phase change memory technology phase change memory pcm is a term used to describe a class of nonvolatile memory devices that employ a reversible phase change in materials to store information. We survey the current state of phase change memory pcm, a nonvolatile solid state. Set and reset state of pcm refers to low and highresistance state, respectively. Phase change memory pcm is a nonvolatile solidstate memory technology based on the large resistivity contrast between the amorphous and crystalline states in phase change materials. Phasechange memory also known as pcm, pcme, pram, pcram, oum ovonic unified memory and cram or cram chalcogenide ram is a type of nonvolatile randomaccess memory. Pdf designing crystallization in phasechange materials for. Reliability enhancement of phase change memory for. Much ado about memory, dram and nand flash are the most common technologies currently in use for fast main memory and slower storageclass memory, respectively. To meet increasing performance requirements including improvements to memory speed, capacity, power usage, and. Phase composition the ni composition of the liquid phase is c l the ni composition of the solid.
Overview of phasechange chalcogenide nonvolatile memory. Shenoy1 1 ibm almaden research center, 650 harry road, san jose, california 95120. Projected phasechange memory devices nature communications. We call such a memory unit computational memory, where resistive memory devices, in particular phasechange memory pcm devices, could play an important role as building blocks. In a memory array, the pcm devices are typically placed in. Phase change memory pcm is an emerging class of nonvolatile memory technologies that offers an attractive combination of features, making it a likely replacement for dram. Evaluating phase change memory for enterprise storage. Electronic components are at the core of electronics technology. First flexible phasechange random access memory developed. Phase change materials and phase change memory mrs. Ibm scientists imitate the functionality of neurons with a. Current crowding at the heater to phase change material contact results in. Phase change materials and phase change memory eric pop. During writes, an access transistor injects current into the storage material and thermally induces phase change, which is detected during reads.
University of pittsburgh, 2014 phase change memory pcm recently has emerged as a promising technology to meet the fast growing demand for large capacity main memory in modern computing systems. Revisiting hash table design for phase change memory. It first calculates the heat generation of the heater, then gets the temperature of the phase change material. Architectural techniques for multilevel cell phase change memory based main memory lei jiang, ph. This model includes both the heater and the phase change material. Jan 29, 2016 phase change memory phase change memory also known as pcm, pcme, pram, pcram, ovonic unified memory, chalcogenide ram and cram is a type of nonvolatile randomaccess memory. According to the size of amorphous phase and crystalline phase, the resistance of pcm in read operation is calculated. Designing crystallization in phasechange materials for. Then the evolution of the understanding of the underlying physics governing the phase change characteristics by various investigators is. As fabricated, the phase change material is in the crystalline, lowresistance state because the processing temperature of the beol metal interconnect layers is sufficient to crystallize the. In phasechange memory pcm, lowfield electrical resistance is typically used to quantify the programmed cell state. The memory cell is built by layering a storage element and a selector. There is a huge variety of different components that are available with a variety of different functions. Ibm in memory computing with 1 million phase change memory.
The projected memory device or cell comprises a carefully designed segment consisting of a noninsulating material projection segment that is parallel to the phasechange. Their ability to switch, reversibly and extremely quickly, between the crystalline and amorphous phases, combined with the high stability of both phases, makes them ideally suitable for memory applications. Phase change memory pcm is a type of nonvolatile ram that stores data by changing the state of the material used, meaning it changes back and forth between amorphous and crystalline states on a microscopic level. Candidates for non volatile memory and neuro inspired computing devices include phase change materials pcms1619, resistive switching. Phasechange materials possess a unique combination of properties that make them promising candidates for the memory material in phasechange ram pcram devices. Pcm is 500 to 1,000 times faster than normal flash memory. Matter can exist in various phases such as solid, liquid, gas, condensate and plasma. Modeling the phasechange memory material, ge2sb2te5, with a. Designing crystallization in phasechange materials for universal.
Phasechange memory controller architecture for lowlatency. Braininspired computing using phasechange memory devices featured. Pcm devices as a memory device is that writes are too slow. Phase change memory pcm recently has emerged as a promising technology to meet the fast growing demand for large capacity main memory in modern computing systems. For example, a pcm cell with four distinct resistance levels can store two bits. Communications of advanced materials, volume 30, issue 9, march 1, 2018 selfhealing of a confined phase change memory device with a metallic surfactant layer, xie et al which has cast some new light. Phase change memory stanford nanoheat stanford university. This demonstration marks a significant step forward in the development of energyefficient, ultradense integrated neuromorphic technologies for applications in cognitive computing. Pcm, relying on analog current and thermal e ects, does not require control over discrete electrons. Because no electrical power is required to maintain either phase of the material, so phasechange memory is nonvolatile. With the large current and slow switching, phase change memory was not competitive with eprom, and the semiconductor memory industry lost interest optical memory application of laserinitiated reversible phasechange in chalcogenide alloy films was reported in 1971.
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