材料物理课件 (8)材料磁性性质共37页文档

IV, Ferromagnetic materials
The 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.
4π.10-7 which corresponds to the fundamental
physical constant μ0.
P
magnetic flux density :
M
m
V
(A/m, Gs)
B = μ0 (H + M ). M = χ mH B = μH= μ0 (1+χm)H ,
μ r= μ/ μ0
Magnetic Memory materials: -Fe2O3 , CrO2, Fe-Co et
al
Read/write heads
Mechanism:
Main applications Diskette
Tape
Magnetic drum
2 Optical Memory Optical storage materials: PC、PMMA、Epoxy et al. Mechanism:
write read
ROM
Mask ROM
EPROM
PROM EEPROM (Flash)
Flash
MOSFET + Floating Gate
Dielectric Tunnel oxide
Threshold shift due to the electric charge
MOSFET
Metal-oxidesemiconductor field effect transistor
To 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 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 in FeCAP.
FeRAM (capacitor)
1T-1C Plateline (PL) has a variable voltage level to enable the switching of the polarization of the ferroelectric capacitor.
FeRAM operation
II, Magnetic moment
The 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 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 (electric motors rely on this effect). Here the torque, τ, increases with the current, i, and the area of the loop, A. θ is the angle made between the axis of the loop normal to its plane and the field direction.
source
Apply voltage to CG. If e- present in FG, no conduction between S
and D. If e- is absent, conduction happens.
NAND & NOR Flash
NAND Flash: erased and programmed block-wise. NOR Flash: erased and programmed byte-wise.
Semiconductor memories
2m+n+k-1
Cell array
I/O unit circuit
Peripheral circuit
Categories of Semiconductor memories
Memory technologies
Primary categories of electrical memory: RAM, ROM and Flash
Nonvolatile: 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 frequently. 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 can’t be refreshed. Flash: The charge can be refreshed frequently, and information is not lost when the power is switched off.
Paramagnetic 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 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).
V, Hysteresis loop
Memory devices
Outline
Background Semiconductor
Conventional memory technologies Emerging memory technologies
1 MagnS
G
G
Flash write/erase/read operation
Apply voltage to control gate (CG) e- tunneling occurs from channel to FG
Apply voltage to source e- transfer occurs from FG to
Magnetic Properties of Materials
I , Magnetization Curves
Fig. MPA a) is the curve in the absence of any
material: a vacuum. The gradient of the curve is
Main application: