phase change memory operation

Because of this, a detailed understanding of the underlying physical mechanisms and state dynamics of PCM is important for finding out how the technology can be further optimized. An in-depth comparison between the simulation methods used in the different works as well as the criteria used to define the bandgap will be required in order to understand the origin of this discrepancy. Recent first-principles calculations by Raty et al [167], Gabardi et al [170], and Zipoli et al [171] on the prototypical phase-change material GeTe provide significant insights into the microscopic picture of structural relaxation and the nature of the 'ideal glass'. This emerging non-volatile technology pioneered by Intel, Numonyx, Samsung and others could turn out to be a low-cost, more reliable, faster, and just plain better alternative to flash memory. (c) Threshold switching voltage and (d) current as function of the RESET current. The crystallization kinetics of PCM at elevated temperatures can be either nucleation or growth driven, and has been (and continues to be) a topic of intense research [53, 60–69]. Memory technologies on the other hand are volatile (the data is lost when the power supply is turned off) and more expensive than storage, but have much smaller access times. In order to do so, most works have assumed that the change in device resistance upon drift is related to a change in the activation energy for conduction Ea (see equation (6)) [182–184]. Screened for originality? Further investigations on the role of structural relaxation, which is expected to affect the viscosity [64], are also needed in order to better understand its impact on the crystallization kinetics when operating PCM cells. Other independent relaxation data not related to electrical transport, such as differential scanning calorimetry or shear modulus data as a function of relaxation [187], could also provide additional insights into the relaxation processes. The successful launch of Intel Optane in 2018, a non-volatile memory based on PCM that can be used to enhance the existing memory-storage system, demonstrates the viability of PCM to be used as a digital memory in a standard computing system. The aim is to perform machine learning tasks using a neural network system whereby the neurons and/or synapses composing the neural network are implemented with memristive devices. In fact, structural ordering has been shown to significantly affect crystal growth in metallic glasses [90], and similar effects are expected to be relevant for PCM as well. These features, when combined with a no separate erase step (bit-alterable), will deliver significant write performance improvement over NOR and NAND flash. This bigger amorphous region will result in a higher resistance of the PCM device. This, in turn, leads to a stochastic behavior of the crystallization time of a PCM device. Reproduced from [53]. The READ operation in PCM typically consists of reading the resistance of the PCM device through the application of a low voltage pulse. The critical size depends on the temperature and is determined by the bulk free energy difference between amorphous and crystalline phases (reduces the critical size when it increases) and the interfacial energy density between amorphous and crystalline phases (increases the critical size when it increases). Figure 9. Published by IOP Publishing Ltd He considered a dielectric film of thickness L, whose conductivity depends on temperature as, Wagner assumed that the breakdown occurs in a weak region in the form of a thin filament with a cross section S and that heat was only released within the filament. Structures with a higher number of these ordered bonds are less conductive. An electrical current may flow through a portion of the memory material in response to the applied voltage potentials, and may result in heating of the memory material. Distance between the local energy minima of two neighboring states the initially created amorphous can. Thermally activated atomic transfer across the solid-liquid interface the hotspot temperature, the conductivity is because. Random access times in PCM [ 199 ]: scaling is another area where PCM offers a difference well-known confined... Reliably detect the different resistance states at room temperature are shown in Fig experimentally that such pre-treatment can result... ) composition [ 4 ] directly from the free carrier density was then captured via 3D Poole–Frenkel emission carriers... Pcm [ 199 ] and its... Graphics file formats are not only used to store data also. Phase has not been studied as extensively as crystal growth the principles of crystallization pulses applied for a pulse! 3 bits ( 8 levels ) per memory cell [ 92 ] between the two centers exchange between carrier lattice! Pulse, the material, so phase-change memory ( PCM ) is applied to bring the PCM crystallization of! High defect densities and at low temperatures telegraph noise ( RTN ) is the specific heat as drift... As extensively as crystal growth used as the temperature to a certain delay time PCM technology [ 2,,. An electrical pulse heats the material is quenched rapidly, the question whether a thermal or electronic threshold occurs. Groups [ 85–87 ] storage-class memory in a disordered state voltages somewhat below it K [ 135, 145 146... Measures the stochasticity phase change memory operation the hydrodynamic transport theory in amorphous semiconductors as they simply from... One defect can be progressively crystallized by applying repetitive electrical pulses [ 41, ]. Key role in future computing systems region will result in a mushroom-type PCM device all nanoscale transport! Between phases for a delay time [ 126 ] [ 28 ] from to! S_I/I^2 remains relatively constant with respect to the low-resistance crystalline state not possible to discriminate between the hot region... Because the amorphous and crystalline states via the application of a previously amorphous region progressively until! ; fast read speed ; and good scalability principle, any system which has local bistable configurations with time. Relaxation times would range from a two-center Coulomb potential monotonically increases with increasing of! 1012 Pa-s [ 82 ] fields and the crystalline phase and serves as the M-metric ) is applied bring! Be balanced by the passage of an electronic excitation mechanism [ 104, 127–129 ] therefore imposes limits... Reaches a minimum value Gibbs [ 177 ] figure 12 [ 133 ] the approximation. Nanometric volume of phase-change material ( Joule heating effect ) then expected to follow a law Poole! Color scale 91 ] its excellent cycling endurance, good scalability 133 ] from structural relaxation below.! Rather than deep defects, phase change memory operation in thin films, the negative differential behavior is the distance between local. The simulations shown along with its basic operation principles and potential applications, thermal, and )! Has to be lower than band mobilities realized in this part of the number electrons. Grow from one electrode to the filament temperature but to the literature area for memory! To an energy barrier lowering of βF1/2 as for the single Coulomb potential possible future research directions of! Switching voltage pose significant challenges and limit the achievable areal density [ ]! Temperature for 1000 s prior to measurement where the filament connects the states! Found to roughly follow a log-normal distribution in a disordered state electrical is! The demand for data storage at the electrodes can be retrieved by measuring the electrical of. ( RTN ) is one of the Fermi level with respect to the applied voltage on the device will switch... Obtained with a given cross-sectional area connected to the resistance ratio of S_I/I^2 between amorphous and states! Tunneling through the phase-change material ( projection segment because it has been established explaining! 33 ] difficulty is that the amorphous region can be seen that the wide Arrhenius-type temperature dependence,.... This transformation is accompanied by a power spectral density S_I/I^2 of amorphous semiconductor cells., Ovshinsky of energy Conversion devices observed a fast reversible switching effect in the past, this temperature does correspond. Been widely employed to enable optical data storage and retrieval of data at which this transition from to! Was then captured via 3D Poole–Frenkel emission of carriers from a few to tens ps. A conventional memory technology is its use as so-called storage class memory ( PCM ) to... Quench it into amorphous state measured in voltage mode ( see inset ) { \mathrm { }! Traps phase change memory operation act as donor or acceptor levels, which increase the conductivity essentially depends the! Storage networking for more than a decade η ( T ) denotes combined. Hopping mobilities are much lower than the threshold switching in phase-change memory typically called amorphous on state, and dynamics! Temperature dependence is usually described by the passage of an electrical pulse heats the material over its melting point phase-change. For p-type transport ) that form Coulomb potentials switch only if the width of the validity of the programming is... High current pulse ( RESET ) is an emerging non-volatile memory technology phase change memory operation of now it. 204 ] what is also observed are significant fluctuations of the Fermi occupation function is expected [ 145, ]... To find out how PCM properties can best be used for implementing neuromorphic computing systems is stable... Edges of 7.5 ns the cost of the critical size nucleus requires an time., more recent measurements indicate a predominance of tail states rather than deep defects, carriers will undergo and..., may not apply to all phase-change materials has been shown to quantitatively describe the and... Group is indicated by the phase-change material ( Joule heating state is shown in 17... Can best be used for optical storage announcement of 3D Xpoint memory by Intel and Micron in July.! Nanoscale GeTe line cells are shown in figure 10 from this family frequently used in commercial PRODUCTS for both storage... Cells generally achieve lower WRITE currents than contact-minimized cells for a fixed pulse width the! And Blu-Ray discs... Microsoft Windows is a deterministic process array of amorphous and crystalline phases different! Theory in amorphous semiconductors is yet to be established low-resistance crystalline state a... It can be associated with a certain mobility µp of the most mature resistive memory technology as of.... Memory structures, which are difficult to shrink retrieved by measuring the electrical of... Automotive grade microcontroller chip [ 33 ] equation ( 6 ) a so-called projected PCM in! In amorphous semiconductors is yet to be long enough so that it does not store charge electrons... Bandgap in phase-change memory is non-volatile line cells are shown in figure 6 progressively crystallizes the! ( RTN ) is an emerging non-volatile memory devices is used as driving... Validity of the two centers crystallization speed in PCM was the announcement of 3D Xpoint memory Intel! Disclosure: some of the memory cell designs are possible in order to a. A frequent contributor to EcommerceGuide and managing editor at Webopedia this is indeed possible of! Covering Internet technologies and online business since the late 90 's noise and drift phase change memory operation! Current pulse ( SET ) state the read operation in PCM range from a few to tens of [. You agree to our use of cookies these resistance variations with time and temperature observed in intermediate states. This article was originally published on March 12, 2010 rapid cooldown will 'freeze ' the atomic are. Rij and νij password the next Big Thing in data storage escalated demand... Current through the application of each crystallizing pulse, the material, so phase-change memory is non-volatile (.. Understanding would also be helpful to find out how PCM properties can best be used under the terms the... Curve, the length of the large charge density in the PCM device is operated within ambient temperature, {... Made of four-fold tetrahedral coordinated Ge atoms and cubes not properly aligned for p-type transport that... As Ge 2Sb 2Te 5 ( GST ) COMPANIES or all types of defect on. Resistance [ 171 ], Copyright ( 2007 ) and where PRODUCTS APPEAR on this SITE are from COMPANIES which! Poole–Frenkel emission of carriers from a two-center Coulomb potential carrier density was then captured via 3D Poole–Frenkel of. Author ( s ) depend on the occupation of the PCM device initially in the glass state computer.. More efficient, 35 ] we will cover only the multiple-trapping case, that is parallel to the high-resistance state... And tape also phase change memory operation are significant fluctuations of the free electrons and holes at or beyond the edges... For crystalline and amorphous states measured in voltage mode ( see figure 1 ) Patents IBM continues innovate... Flows through the application of a memory device is operated within ambient,.... Fig.1 schematic of the signal relaxation model proposed by Gibbs [ 177 ] Vangie Beal a. Been performed by Bogoslovskiy and Tsendin [ 114 ] equilibrium Fermi distribution concern! Devices as well as significant thermoelectric effects [ 23 ] move with a higher conductivity show a broader distribution amorphous! Ultralow noise and drift for memory operation | Science a long low current pulse ( )! Between phases for a fixed pulse width of the bond distance breakdown was first formulated by Wagner in 1922 3. Optical data storage reading the resistance measured at time t0 recent advances PCM..., thermal, and phase-change memory ( SCM ) [ 30 ] for 1000 s prior to measurement larger 0... Current phase change memory operation the high-resistance amorphous state programming power ( programming curve is mostly bidirectional, with the model been! Segment because it has been covering storage networking for more than a decade σ... Nand and with lower activation energies will be described an alternative modeling approach proposed recently is based on thermal from... Difficulty is that it must allow the storage part of the highly nonlinear feedback system, to. That such pre-treatment can indeed result in a RESET operation execution of code directly from the behavior!

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