A lot of researches are going on about new memorymaterials.In this paper we explore electronic,optical and magneticproperties of graphene and graphene nanoribbons forsemiconductor memory applications.Graphene is having highmobility,good scaling properties.Also it shows Ferromagnetic andanti ferromagnetic properties.Measurable Optical properties areappeared in literature. All these properties are tunable with bandgap .These factors point outs that graphene is a suitable candidatefor making memories like flash,optical storage devices,MagneticRAM etc.The bandgap of the graphene is a considerable designproblem when making electronic devices.
But nanoribbons cansolve this issue and can provide enough band gap suitablefor memory devices.Short channel effects scattering,ambipolarconduction is another point that need attentionKeywords—Graphene,AGNR,ZGNR,Bandgap,Spin Polarisation.I. INTRODUCTIONAccording to ITRS, Memory technology is always thedrivers of moore’s law.But DRAM and flash memory arereaching its limit and by 2024 it will saturate .This indicatesthe need for new materials and methods.3D architecture isproposed as an alternative technology for scaling, but still thisfaces reliability issues like cell to cell interference, enduranceand retention.
ECC schemes, wear leveling ,memory scrubbingetc were used to overcome this issues but all these againleads to higher area conception. Hewlett Packard is doingresearch on a memory device that uses nanowires coatedwith titanium dioxide to form memoristor.And also they areworking with Hynix Semiconductor to develop ResistiveRandom Access Memory (ReRAM).Researchers at IBM havedeveloped race track memory by magnetizing sections ofnanowires. Researchers at Rice University have found thatthey can use silicon dioxidenanowires sand witched betweentwo electrodes to create memory devices.
Another method hasbeen developed to increase the density of memory devices isto store information on magnetic nanoparticles. Researchersat North Carolina State University were found growingarrays of magnetic nanoparticles, called nanodots, which areabout 6 nm in diameter. Intel and Micron have announced3D XPoint, which is 1,000 times quicker and 1,000 timesmore durable than existing NAND flash. It also offers a 10ximprovement in density. It uses bulk material property change.Graphene has drawn attention of researchers because of itselectronic properties and hence One of the candidate for postsilicon era.In this paper we like to present graphene and itsvariants for different kinds of storage device solutions.SectionII discuss the graphene prospectus.
SectionIII presents GNRFETbased memory.Section IV presents magnetic memoryusing graphene.Section V describe about optical properties ofgraphene for optical memories. Section VI discusses Resistivememory the graphene.
II. GRAPHENE PROSPECTUSA paper published on 2004 2, 3 about graphene openeda lot of discussion about its electronics properties.Earlier discussionswas about the mobility of graphene 2the measuredrecord mobility’s in graphene will be more than 100 000cm2/Vs at room temperature and 1 000 000 cm2/Vs at 4 K 4,5.
Since high mobilities leads to high performance devices,this opened the thought of device engineers.The main category of graphene are a)large area grapheneb)Bilayer graphene c)Graphene nanoribbons.Among this largearea graphene and bilayer graphene are having bandgapproblems and showing ambipolar conduction.But graphenenanoribbon showing excellent tunable bandgaps.There is twovariants of graphene nanoribbon Zigzag and Armchair .
Inthis Zigzag graphene nanoribbon(ZGNR) is metallic in naturewhere as Armchair graphene(AGNR0 shows enough band gapsas shown in figure 1All these observations lead to the idea of bandgap engineeringin graphene.Raman spectroscopy studies reveal that by controllingwidth,dopping,strain bandgap can be improved6.Graphene oxide,because of its flexibility draws attention formaking flexible devices.Later it was proved that GO ishaving good electronics properties.The same way quantumdots of graphene can be used for improving electronicsperformance.?III.
TRANSISTOR BASED MEMORYGraphene can be used as channel material for normal FETin order to improve the performance.In memory applicationsthe main scenario is ON/OFF ratio.The second one is subthresholdconduction.
scaling and short channel effects.With theinherent properties of graphene,all these can be improved.when studying the bandgap ,it is already observed that bilayersuitable for memory application.Experimentally proved thatat least 300 to 400mev band gap is required for memoryFig.
1. Graphene transistor classifications adapted from1Fig. 2. Simulated bandgaps using DFT methods a)Graphene b)armchairgraphene nanoribbon b)Zigzag graphene nanoribbonapplications.
Simulated band gap for graphene,ZGNR,AGNRusing DFT method is shown in figure2. AGNR can providesuch required bandgaps.The band gap can be varied usinga)axial strain b)dopping ?? II .
Again bandgap is reducing withincrease in width.It is observed that double gate geometries offer highFig. 3.
Band gap versus uniaxial strain for an AGNR, N = 23, 24, 25.Adapted from 9Fig. 4. Conduction band profile along the channel position for (a) conventionalGNRFET(b) dopped-GNRFET.Adapted from 22ON/OFF ratio and less sub threshold conduction.
Then lightdopping can suppress ambipolar effects.The highest ON/OFFratio observed is 1010 using GNRtunneling FET. So it canbe concluded that this device is best suitable for memoryapplications9.
The required structure is as shown in figureIII.The characteristics of shottky barrier FET(SBFET),idealFig. 5. IDVG characteristics of (a) an ideal SBFET and (b) an ideal MOSFET.Adapted from 9Fig. 6.
(a) The log(ID) vs. VG characteristics of the GNR tunneling FETs.Adapted from 9MOSFET,GNR tunneling FET is as shown in Fig IIII forcomparison purposeFig. 7. Tunneling GNRFET 9IV. MAGNETIC MEMORYzigzag GNRs are having a magnetic insulating groundstate with ferromagnetic ordering at each zigzag edge, andanti parallel spin orientation between the two edges . Fromthe spin-density it can be predicted that spin moments aremainly distributed at the edge carbon atoms.When comparingnonspin-polarized solutions, and spin-polarized edgestates are more favoured, and the total energy differencebetween these states increases with the width of GNRs.
The spin-polarized states are further stabilized by ferromagneticcoupling at the edge, while antiferromagnetic couplingbetween the two edges. The energy difference betweenferromagnetic and antiferromagnetic coupling is verysmall, and decreases with the width of ribbon. These magneticeffects can be used for making MRAM or spinRAMlike structures.
10.Magnetic tunnel junctions,Nanospintronicslogic gates are already reported111213.Graphene ferroelectricmemory also reported in14.A magnetoresistive RAMis as shown in Fig. IVFig. 8.
The device consists of a ferromagnetic cobalt electrode and a platinumelectrode deposited on top of the GO-NP nanocomposite.Adapted from21Fig. 9. Average magnetic moments calculated for the zigzag nanoribbons.Image taken from 20V. OPTICAL MEMORYGraphene properties are very much sensitive to its atomicstructure. Optical graphene properties are depends on the directinterband electron transitions.Reflectance from the monolayeris determined for infra-red region by the intraband DrudeBoltzmannconductivity and for higher frequencies by the interbandabsorption.
15.Sensitizing graphene-based field-effectdevices to optical excitation can have a strong impact ontechnologies.Graphene-Mos2 optical detector are proposed in16.The structure is as shown in Fig.V.These type of architecturescan be used for optical memories.The same way graphenequantum dots also exhibiting optical properties17VI. GRAPHENE RESISTIVE MEMORYResistive memories reported mainly are based on grapheneoxide.
The switching operation of graphene oxide resistiveswitching memory (RRAM) is governed by two mechanism.That is oxygen migration and Al diffusion. The Al diffusioninto the graphene oxide is the main factor to determine theswitching endurance property which limits the long term lifetimeof the device 18.The electrical switching and enduranceproperties of graphene oxide resistive memory is as shown inFig.VI.
Fully transparent resistive memory is developed in ?.Itused graphene as transparent stable resistive material.Fig.
10. Transmittance and reflectance at normal incidence for the multilayergrapheneFig. 11. Schematic of device architecture.Fig. 12.
(a) The electrical switching and (b) endurance properties of grapheneoxide RRAM consisted of Al=GO(30 nm thickness) structure.VII. CONCLUSIONThe electronics,optic,magnetic properties of graphene wasstudied towards the semiconductor application.Graphene issuitable for making all type like transistor,Magnetic,Opticmemories.This strongly recommends intensified research intographene based memories.ACKNOWLEDGMENTThe authors would like to thank the department of Electricaltechnology ,Karunya Institute of science Technology,Coimbatoreand the Department of Electronics and CommunicationEngineering of Sahrdaya College of EngineeringTechnology, Kodakara, Kerala, India for the timely help andsupport for carrying out this work