Because no electrical power is required to maintain either phase of the material, so phasechange memory is nonvolatile. Ibm press room ibm scientists have created randomly spiking neurons using phasechange materials to store and process data. Breitwisch 2, michele franceschini, davide garetto, kailash gopalakrishnan 1, bryan jackson, bulen t kurdi, chung lam2, luis a. Nonresistancebased cellstate metric for phasechange memory. 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. In a memory array, the pcm devices are typically placed in. An overview of phase change memory device physics to cite this article. 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 this 4part series ron takes a look at the recentlypublished analysis by a team from ibm and yale university wiley. Introduction the spice model is developed for the write operation of pillarshaped phase change memory based on physics and geometry of pcm. Prams exploit the unique behaviour of chalcogenide glass. Rethinking database algorithms for phase change memory. Modeling the phasechange memory material, ge2sb2te5, with a.
Phasechange memory controller architecture for lowlatency. The combination of quick heating and cooling results in the amorphous phase, and this operation is referred to as a reset operation. Phase change memory technology phase change chalcogenides exhibit a reversible phase change phenomenon when changed from the amorphous phase to the crystalline phase. During writes, an access transistor injects current into the storage material and thermally induces phase change, which is detected during reads. Designing crystallization in phasechange materials for universal.
The projected memory device or cell comprises a carefully designed segment consisting of a noninsulating material projection segment that is parallel to the phasechange. 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. 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. According to its proponents, pcm technology has the potential to provide inexpensive, highspeed, highdensity, highvolume nonvolatile storage on an unprecedented scale. In pcm technology, high heat over 600 c is applied to a storage cell to change the phase to store data. Because electrical transport in amorphous phasechange materials is thermally activated e a is typically in the range of 0. Evaluating phase change memory for enterprise storage systems. 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. The structure of these disks is essentially the same and is shown in fig. To meet increasing performance requirements including improvements to memory speed, capacity, power usage, and. Pdf designing crystallization in phasechange materials for. 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. The electrical current passes through the phase change material between the top electrode and heater.
Phase change memory stanford nanoheat stanford university. For information storage, a phase change memory device uses a large contrast either in electrical resistance between the amorphous phase high. 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. We studied the temperature dependence of the resistance levels in both a projected memory. One of the leading prototypical memories that is being investigated is phase change memory. Pcm can be built at higher chip densities than dram, which is expectedto translate into highercapacities and lower cost per gb. Current crowding at the heater to phase change material contact results in a programmed.
This demonstration marks a significant step forward in the development of energyefficient, ultradense integrated neuromorphic technologies for applications in cognitive computing. Pcm, about 1,000 times faster than ram, is one such effort thats being extensively developed by researchers and tech giants. Phasechange materials possess a unique combination of properties that make them promising candidates for the memory material in phasechange ram pcram devices. Architecting phase change memory as a scalable dram. 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. This demonstration marks a significant step forward in the development of energyefficient, ultradense integrated neuromorphic technologies for applications in. Phase change materials and phase change memory mrs. 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.
According to the size of amorphous phase and crystalline phase, the resistance of pcm in read operation is calculated. The phase change material is in the crystalline phase in an asfabricated device. Current crowding at the heater to phase change material contact results in. For example, a pcm cell with four distinct resistance levels can store two bits. Based on the temperature, it simulates the phase changing 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.
Overview of phasechange chalcogenide nonvolatile memory. There is a huge variety of different components that are available with a variety of different functions. 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. Phase change materials have a large electrical contrast. Extending the writeerase lifetime of phase change memory. 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. Revisiting hash table design for phase change memory. This stems primarily from the fact that phase change is a thermally driven process rather than an electronic process. Braininspired computing using phasechange memory devices featured. We survey the current state of phase change memory pcm, a nonvolatile solid state. Chalcogenide phasechange materials pcms are leading candidates for such. Energy demands vary on daily, weekly and seasonal bases. Lastras 2, alvaro padilla1, bipin rajendran, simone raoux2, and rohit s. 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.
Everything from passive components like resistors, capacitors and the like through devices like diodes, and onto other electronic components like transistors, fets and even. 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. Architectural techniques for multilevel cell phase change memory based main memory lei jiang, ph. We have found that, if data is stored in pcm devices, the physical attributes of those devices can be exploited to achieve inplace computation. Then the evolution of the understanding of the underlying physics governing the phase change characteristics by various investigators is. Phase change materials and phase change memory mrs bulletin. Ibm press room ibm scientists have created randomly spiking neurons using phase change materials to store and process data. Phasechange memory controller architecture for low. 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. Ibm in memory computing with 1 million phase change memory.
It first calculates the heat generation of the heater, then gets the temperature of the phase. This kind of memory will replace current well known flash memory. Phase change memory is susceptible to a fundamental tradeoff of unintended vs. We address the challenges facing this technology, including the design of pcm. Phase change memory pcm is a nonvolatile memory composed of 1 transistor and 1 resistor. 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. A novel scalable and stackable nonvolatile memory technology suitable for building fast and dense memory devices is discussed. 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. Pcm devices as a memory device is that writes are too slow. 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.
Ibm scientists imitate the functionality of neurons with a. Pcm, relying on analog current and thermal e ects, does not require control over discrete electrons. The fundamental mechanism for phasechange memory was invented in the 1960s by. Phase change materials exist in an amorphous and one or sometimes several crystalline phases, and. Aug 16, 2016 the researchers are working hard to create new means to store data. 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. Set and reset state of pcm refers to low and highresistance state, respectively. The storage element is a phase change memory pcm cell 1 and the selector is an ovonic threshold switch ots 2. Request pdf overview of phasechange chalcogenide nonvolatile memory technology phasechange nonvolatile semiconductor memory technology is. In phasechange memory pcm, lowfield electrical resistance is typically used to quantify the programmed cell state.
We present the physics behind this large resistivity contrast and describe how it is being exploited to create high density pcm. Phase composition the ni composition of the liquid phase is c l the ni composition of the solid. 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. 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. Designing crystallization in phasechange materials for. Thermal conditions that allow for fast crystallization should not be too similar to standby conditions, e. 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. 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. Candidates for non volatile memory and neuro inspired computing devices include phase change materials pcms1619, resistive switching.
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. Phase change materials are tecontaining alloys, typically lying along the getesb 2 te 3 quasibinary tie line. Candidates for nonvolatile memory and neuroinspired computing devices include phasechange materials pcms, resistiveswitching oxides. 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. Electronic components are at the core of electronics technology. 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. Multilevel cell mlc pcm storing multiple bits in a single cell o. Phase change memory key attributes 10 5 10 6 200200 ns 30 kbs flash easy no smallbyte n. Invited paper phasechangememory stanford university. Projected phasechange memory devices nature communications.
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. Phase amount in the double phase region the lever rule at the point b. 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. First flexible phasechange random access memory developed. Evaluating phase change memory for enterprise storage. Shenoy1 1 ibm almaden research center, 650 harry road, san jose, california 95120. 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.
Because no electrical power is required to maintain either phase of the material, so phase change memory is nonvolatile. The memory cell is built by layering a storage element and a selector. We survey the current state of phase change memory pcm, a nonvolatile solidstate. Pdf on oct 1, 2016, hongsik jeong published high density pcmphase change memory technology find, read and cite all the research. 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. A phasechange material is one that exists in at least two phases with remarkably di. These new memory technologies exhibit a combination of characteristics that make them at least partially suitable for both main memory and storage applications. Architecting phase change memory as a scalable dram alternative. 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 change material.
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. The chapter starts with the discovery of a one way resistance transformation phenomenon in a chalcogenide, namely molybdenite mos 2. Phase change materials and phase change memory eric pop. 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. 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.
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