材料物理材料磁性性質(zhì)

1、材料物理課件材料磁性性質(zhì)第1頁，共36頁，2022年，5月20日，4點23分，星期四I , Magnetization CurvesFig. MPA a) is the curve in the absence of any material: a vacuum. The gradient of the curve is 4.10-7 which corresponds to the fundamental physical constant 0. magnetic flux density : (A/m, Gs) B = 0 (H + M ).M = mHB = H= 0 (1+m)H ,

2、r= / 0 第2頁，共36頁，2022年，5月20日，4點23分，星期四II, Magnetic momentThe concept of magnetic moment is the starting point when discussing the behaviour of magnetic materials within a field. If you place a bar magnet in a field then it will experience a torque or moment tending to align its axis in the direction

3、of the field. A compass needle behaves the same. This torque increases with the strength of the poles and their distance apart. So the value of magnetic moment tells you, in effect, how big a magnet you have. It is also well known that a current carrying loop in a field also experiences a torque (el

4、ectric motors rely on this effect). Here the torque, , increases with the current, i, and the area of the loop, A. is the angle made between the axis of the loop normal to its plane and the field direction. = B i A sin = B m sin 第3頁，共36頁，2022年，5月20日，4點23分，星期四Diamagnetic materials are those whose ato

5、ms have only paired electrons. III, Diamagnetic and paramagnetic materialsParamagnetic materials are those whose atioms have unpaired electrons and has permanent magnetic moments .Although paramagnetic substances like oxygen, tin, aluminium and copper sulphate are attracted to a magnet the effect is

6、 almost as feeble as diamagnetism. The reason is that the permanent moments are continually knocked out of alignment with the field by thermal vibration, at room temperatures anyway (liquid oxygen at -183 C can be pulled about by a strong magnet). 第4頁，共36頁，2022年，5月20日，4點23分，星期四IV, Ferromagnetic mate

7、rialsThe most important class of magnetic materials is the ferromagnets: iron, nickel, cobalt and manganese, or their compounds (and a few more exotic ones as well). The magnetization curve looks very different to that of a diamagnetic or paramagnetic material. 第5頁，共36頁，2022年，5月20日，4點23分，星期四V, Hyste

8、resis loop第6頁，共36頁，2022年，5月20日，4點23分，星期四Memory devices第7頁，共36頁，2022年，5月20日，4點23分，星期四Outline Background Semiconductor Conventional memory technologies Emerging memory technologies第8頁，共36頁，2022年，5月20日，4點23分，星期四1 Magnetic Memory Mechanism: Main applicationsTape Diskette Magnetic drum Magnetic Memory ma

9、terials: -Fe2O3 , CrO2, Fe-Co et alRead/write heads第9頁，共36頁，2022年，5月20日，4點23分，星期四2 Optical MemoryDVD-RWDVDCDApplications:Optical storage materials: PC、PMMA、Epoxy et al.Mechanism:Advantage：low price, high storage density; disadvantagelow access, large box第10頁，共36頁，2022年，5月20日，4點23分，星期四Main applicatio

10、n:3 Semiconductor memoryBased on semiconductor devices；Advantage: fast access, high data storage, low power；Cache memoryStacked memoryFlash memory第11頁，共36頁，2022年，5月20日，4點23分，星期四Comparison of memory technologiesOptical MemoriesMagnetic DisksMagnetic TapesMagnetic Bubble MemoriesSemiconductor RAMsSemi

11、conductor ROMs10010-110-210-310-410-510-610-710-810-910-1010-910-810-710-610-510-410-310-2Access timeCost per bitMain memoryCache第12頁，共36頁，2022年，5月20日，4點23分，星期四Semiconductor memories Cell arrayPeripheral circuitI/O unit circuit 2m+n+k-1第13頁，共36頁，2022年，5月20日，4點23分，星期四Categories of Semiconductor memor

12、ies 第14頁，共36頁，2022年，5月20日，4點23分，星期四Memory technologies Primary categories of electrical memory: RAM, ROM and FlashNonvolatile: after transition from OFF state to ON state, device remained in this state even after turning off the power. Random access memory (RAM) :The charge can be refreshed frequent

13、ly. information is lost when the power removed from the device. (DRAM, SRAM)Read only memory (ROM): Information is not lost when the power is switched off, but the charge stored in chip cant be refreshed.Flash: The charge can be refreshed frequently, and information is not lost when the power is swi

14、tched off. 第15頁，共36頁，2022年，5月20日，4點23分，星期四DRAMThe presence of a charge represents the logical value “1” and its absence the logical value “0”Parasitic capacitance第16頁，共36頁，2022年，5月20日，4點23分，星期四DRAM write and read operationwriteread第17頁，共36頁，2022年，5月20日，4點23分，星期四ROM Mask ROMPROMEPROMEEPROM (Flash)第18

15、頁，共36頁，2022年，5月20日，4點23分，星期四Flash DielectricTunnel oxideMOSFET+Floating GateThreshold shift due to the electric charge第19頁，共36頁，2022年，5月20日，4點23分，星期四MOSFET GDSDSGMetal-oxide-semiconductor field effect transistor第20頁，共36頁，2022年，5月20日，4點23分，星期四Flash write/erase/read operation Apply voltage to control

16、gate (CG)e- tunneling occurs from channel to FGApply voltage to sourcee- transfer occurs from FG to sourceApply voltage to CG.If e- present in FG, no conduction between S and D.If e- is absent, conduction happens.第21頁，共36頁，2022年，5月20日，4點23分，星期四NAND & NOR FlashNAND Flash: erased and programmed block-

17、wise.NOR Flash: erased and programmed byte-wise. 第22頁，共36頁，2022年，5月20日，4點23分，星期四Performance and requirements Fast accessNon-volatilityUnlimited R/W cyclesLow powerWide temperature rangeLow cost第23頁，共36頁，2022年，5月20日，4點23分，星期四Emerging memory FeRAM Organic Memory Nano-Crystal Floating-Gate Flash Memory

18、 Phase Change Memory NRAM第24頁，共36頁，2022年，5月20日，4點23分，星期四Ferroelectric unitHysteresis curveTwo states of polarization under applied field can correspond to a stored “0” or “1”Remnant polarizationCoercive fieldFerroelectric memory (FeRAM)第25頁，共36頁，2022年，5月20日，4點23分，星期四FeRAM (capacitor)Plateline (PL) h

19、as a variable voltage level to enable the switching of the polarization of the ferroelectric capacitor.1T-1C第26頁，共36頁，2022年，5月20日，4點23分，星期四FeRAM operationTo write “1” in the cell, BL is set to VDD and PL is grounded, then a pulse is applied to activate the cell transistor.To write “o” , accomplished

20、 in the same manner but PL and BL are exchanged to reverse the polarization of Ferroelectric capacitor.Read: first BL is grounded, then it is made floating. After the cell is selected by WL, the PL voltage is raised from GND to VDD, raised voltage of BL is dependent of the polarization (data) stored

21、 in FeCAP. 第27頁，共36頁，2022年，5月20日，4點23分，星期四FeFET (polarization)FeFET is in principle a MOSFET transistor whose gate dielectric is ferroelectric.Advantage: reading operation is nondestructive.Disadvantage: retention time is very short to nonvolatile memory.第28頁，共36頁，2022年，5月20日，4點23分，星期四Electrical bis

22、tability:Organic electric bistable devices A phenomenon exhibit two kinds of different stable conductive state by applying appropriate voltage. Typical I-V characteristicsSilicon memory: encode “0” and “1” as the amount of charge stored in device cell Organic memory: store date based on high & low c

23、onductivity response to applied voltage第29頁，共36頁，2022年，5月20日，4點23分，星期四Device structuresCross-BarsShadow mask第30頁，共36頁，2022年，5月20日，4點23分，星期四Device configurationsPolyaniline nanofiberGold nanoparticlesOrganic/nanoparticles systemMetal complex DonorAcceptorDonor-Acceptor system第31頁，共36頁，2022年，5月20日，4點23分，星期四Performance and Characterization ON/OFF current ratioWrite-read-erase cyclesSwitching timeRetention a