class notes ww10

The Applications of The Applications of Nano MaterialsNano Materials

Department of Chemical and Department of Chemical and Materials EngineeringMaterials Engineering

San Jose State UniversitySan Jose State University

Zhen Guo, Ph. D.

Session Session 1010, Slide , Slide 22Instructor: Dr. Zhen GuoMatE 297, Spring 2006

How to study NanomaterialsHow to study Nanomaterials

Microstructure PropertiesMaterials ApplicationsProcessing

Basic Materials Science Principles

Part I -- Done

Part II – Done Part III – This one


The Applications of Nano MaterialsThe Applications of Nano Materials

Nano MaterialsApplications

Electronics Magnetic Device

Optics

MEMSBio Device

Structure

Daily Lifeconsumable

Renewable Energy


Applications of Nano MaterialsWeek 903/22

Application (I) – Nano grained structural materials and Nano Composite

Quiz #4Quiz #4

1st Draft Due (3 copies)1st Draft Due (3 copies)

Week 1004/06

Application (II) – Nano Electric Materials: Quantum Computing Logic Device and memory

Blue Sheet #4Peer review comment Due

Week 1104/13

Application (III) – Nano Materials and Renewable Energy source

Prof. David MitlinUniversity of Alberta

Week 1204/20

Application (IV) – Nano Magnetic Materials

Prof. Jiangyu LiUniversity of Washington

Week 1304/27

Application (V) – Nano materials applications on Aerospace

Dr. Geetha DholakiaNASA AMES Research Center

Week 1405/04

Applications (VI) -- Biochemical Properties of Nano Materials

Dr. Sun LeiDigital Health, Intel Corp.

Week 1505/11

Application (VII) – Nano Materials and Optical Device

Dr. Danielle Chamberlin, Agilent Corp (Term paper due)


Session X – Nano Electric Materials

-- Single Electron Transistor-- Other Novel Transistor-- Nano Crystal Memory -- Phase Change Memory


MOSFET PrinciplesMOSFET Principles

• Review MOSFET principles – accumulations, depletion, and inversion. Vt, Vg, Ids, Idsat, etc.• Just remember that Electrons are like water, source / drain like two bottles, channel is a pipe in between and gate is like a valve to open / close the pipe...


Single Electron BoxSingle Electron BoxSingle Electron BoxSingle Electron Box One Quantum Dot One Quantum Dot Two ElectrodesTwo Electrodes Tunneling JunctionTunneling Junction Control Gate CapacitorControl Gate Capacitor

Electrons are injected/ejected Electrons are injected/ejected into / from quantum dots thru into / from quantum dots thru tunneling junctions.tunneling junctions.

Extra electrons injected into Extra electrons injected into quantum dots will lead to quantum dots will lead to excessive charging energyexcessive charging energy Courtesy from Rainer Waser: Nano-

electronics and Information technology PP427-445


Coulomb BlockadeCoulomb BlockadeCoulomb Blockade is caused by excessive charging energy Wc Coulomb Blockade is caused by excessive charging energy Wc which increase as the size of quantum dot decreasewhich increase as the size of quantum dot decrease

With adding extra electron into QD

rCr

QV sp 0

0

44

http://www.plus2physics.com/capacitors/study_material.asp

Wc=e2/2Cspr => Csp => Wc

When Wc >> kT, thermal energy is no longer sufficient to overcome excessive charging energy => Coulomb Blockade

Quantum Effect of Coulomb Blockade – Quantum confinement Quantum Effect of Coulomb Blockade – Quantum confinement cause energy level split => next electrons may need to occupy cause energy level split => next electrons may need to occupy higher energy levelhigher energy level

Wc = e2/2Csp + E (n)


Bias Condition for Coulomb Blockade Bias Condition for Coulomb Blockade When gate voltage is zero, the charge at quantum dot is zero.When gate voltage is zero, the charge at quantum dot is zero.

As gate voltage increases to a certain value, electrons are As gate voltage increases to a certain value, electrons are attracted to quantum dot, making 1e net charge of dot attracted to quantum dot, making 1e net charge of dot

Further increase gate voltage will increase electron number.Further increase gate voltage will increase electron number.

gg

g

t

t

gt

c

VC

Q

C

Q

neQQ

nAnWnF

)()()(

)(2

2)(

)()(

)(222)(

222

2

22222

gt

ggtgg

gt

ggtgggg

gt

ggt

g

g

t

tc

CC

VCCVenCnenF

CC

VCCVenCQVnA

CC

VCCne

C

Q

C

QnW


Bias Condition for Coulomb BlockadeBias Condition for Coulomb BlockadeTo maintain the electron number in quantum dots, we haveTo maintain the electron number in quantum dots, we have

rCsp 04

Courtesy from Rainer Waser: Nano-electronics and Information technology

To substitute the equations in previous slide, we obtainedTo substitute the equations in previous slide, we obtained

gg

g C

enV

C

en )

2

1()

2

1(

)1()( nFnF

)(2

)1(2)1()1(

)(2

2)(

222222

gt

ggtgg

gt

ggtgg

CC

VCCVCnenenF

CC

VCCVenCnenF

gggg VCneneVenCne )1(2)1(2 2222

gggg C

enVneVeC )

2

1()12(2 2

When Consider both sides, we have

gt

tct CC

CeQQ

2or


Single Electron Transistor (SET)Single Electron Transistor (SET)SET – three terminal switching deviceSET – three terminal switching device that can that can transfer electron one by one from source to drain transfer electron one by one from source to drain

dgdg

ddgg

dg CC

en

CC

VCVC

CC

en

)2

1()

2

1(


-- can be considered -- can be considered as two independent as two independent tunneling junctionstunneling junctions-- Each will have to -- Each will have to satisfy Coulomb satisfy Coulomb Blockade conditionsBlockade conditions

gg

g C

enV

C

en )

2

1()

2

1(

sgd

sg

gg

sg CC

enV

CC

VC

CC

en

)

2

1()

2

1(


Single Electron Transistor (SET)Single Electron Transistor (SET)Con’d: Two Equations can be reduced to

)2

(1

)2

(1

ggd

dggd

VCe

neC

VVCe

neC

sg

gg

dsg

gg

CC

eneVC

VCC

eneVC

22

SourceBlue Line

DrainRed Line

• In grey area, both source and drain satisfy coulomb blockade condition for same n value=>Fixed # electrons.

• In green area, source and drain satisfy different value. -- In Area A, for source junction, it satisfy n=1 so one

electron will tunnel from source to QD -- Once electron at QD, it found that drain junction is

favor n=0 so this electron will further tunnel to drain -- Current Flow from source to drain-- Giving a small Vds, Ids will vary with Vg periodically-- Vg can behave as a switch. Vg=0, need Vds greater

than threshold, Vg=e/2Cg, linear Ids verse Vds


Fabrication of SET (I)Fabrication of SET (I)• PADOX – Pattern Dependent Oxidization

-- 1-D Si Nano Wire connected with 2-D Si layers at both ends-- Oxidization process forms tunneling barriers at both ends.-- Can be either width or thickness modulated.-- For Vertical PADOX, it is possible to form 2 tiny islands


Fabrication of SET (II)Fabrication of SET (II)• Surface-Treated SOI Channel

-- 1-D SOI channel intentionally undulated with alkaline based solutions -- The nano scaled undulation results in potential fluctuation due to the difference of quantum confinement effect from one part to another.-- The channel effectively splits into several quantum dots.-- Process is completely compatible with current CMOS fabrications


Advantage and DisadvantagesAdvantage and Disadvantages

Advantages:Advantages: Lower power assumptionLower power assumption Good scalabilityGood scalability

DisadvantagesDisadvantages Operated usually at low temperatureOperated usually at low temperature High output impedance due to tunnelingHigh output impedance due to tunneling Vds has to be less than Vg to have gate fully Vds has to be less than Vg to have gate fully

control the switch. control the switch.


Other Novel Logic TransistorOther Novel Logic Transistor Ferro-Electric Field Effect Transistor (FeFET)Ferro-Electric Field Effect Transistor (FeFET)


-- On state: for positive gate voltage, the polarization vector P is directed towards Channel. -- Cohesive voltage Vc keep remanent polarization Pr large enough to invert channel and keep current flow even when Vg=0 (non-volatile operation)-- Off State: negative gate voltage will bring Pr direct opposite to channel and + charge are accumulated in the channel region. Channel resistance is high and no current flow


Other Novel Logic TransistorOther Novel Logic Transistor Spintronic transistor – based on the effect of spin Spintronic transistor – based on the effect of spin orientation on electron’s transportation propertiesorientation on electron’s transportation properties-- Source and drain are both ferro-magnetic materials with identical magnetization direction-- Channel is a hetero-junction of semiconductor compound with a highly mobile 2-D electron gas. -- Source will inject a spin-polarized current into channel. Without gate voltage, spin will remain unchanged so electron travel to drain on a very high velocity (1% of speed of light)-- When applied gate voltage, spin direction will be rotated by magnetic field so the spin is no longer aligned with drain side => More scattering, higher resistance, lower velocity.


Other Novel Logic TransistorOther Novel Logic Transistor Molecular transistor – Single Molecular acting Molecular transistor – Single Molecular acting as electronic switch and storage elements as electronic switch and storage elements


Nano Crystal Memory Nano Crystal Memory IntroductionIntroductionWhy Nano Crystal MemoryWhy Nano Crystal MemoryNew Development on Nano Crystal MemoryNew Development on Nano Crystal Memory

Nano Crystal Flash MemoryTraditional Floating Gate Memory

Floating GateUsually Poly Si


Recent Trend in Non-volatile Memory

• Current flash memory is continuing to follow Moore’s Law at 90 / 65 / 45nm Nodes

-- 18 years for 9 generations

• ETOX and NAND will still be the mainstream flash memory in next 5 years.

• There is no clear roadmap to continuously scale flash memory beyond 32nm node.


ITRS Roadmap for Emerging Memory Device (2003)

63


Nano-crystal Memory for Nano-crystal Memory for Technology GapTechnology Gap

S. J. Baik et al, IDEM, 2003


Principle of Nano Crystal MemoryPrinciple of Nano Crystal Memory

Nano Crystal Flash MemoryTraditional Floating Gate Memory

Floating GateUsually Poly Si

Improvement of Data Retention and SILT.


Nano Crystal as Storing BitNano Crystal as Storing Bit Nano Crystal Technology has been studied Nano Crystal Technology has been studied extensively to replace traditional floating gate as extensively to replace traditional floating gate as charge storage mediacharge storage media.. Advantages:Advantages: Scalability with Channel Tunneling and EraseScalability with Channel Tunneling and Erase Compatible with Traditional CMOS PlatformCompatible with Traditional CMOS Platform Improved Charge Retention and EnduranceImproved Charge Retention and Endurance Potential Multi Bit usagePotential Multi Bit usage

Challenges:Challenges: Strictly control the size and distribution of nano crystalsStrictly control the size and distribution of nano crystals Still Litho node limitedStill Litho node limited Much work to be done for a integrated reliable and high Much work to be done for a integrated reliable and high

yield process yield process


Silicon Nano Crystal as Storing MediaSilicon Nano Crystal as Storing Media

R. Muralidhar et al. IDEM, 2003

• Reduce SILC and thus improve data retention and endurance• Decrease gate coupling and thus improve leakage and erase saturation• Possible multi-bit storage as particle size goes down to discrete energy state of electrons


Metal Dots as Storage MediaMetal Dots as Storage Media

• Metal dots can be Co, W or Au• Suppose to be better than Si as work function is higher (more attractive to electrons)• Multilayer can improve retention and endurance

C. Lee, et al, IDEM, 2003

M. Takata, et al, IDEM, 2003


Silicon Nano Crystals Produced by Silicon Nano Crystals Produced by CVD Methods (I)CVD Methods (I)

• A Si-rich SiOx thin film is deposited on Si surface by PECVD method. The non-stoichemetry are controlled by gas flow ratios.

• An furnace annealing were performed on this film at 1000C in N2 atmosphere to precipitate Si Nano crystals out of supersaturated film.

-- U.S. Pattern Pending


Si – SiOSi – SiO22 Binary Phase Diagram Binary Phase Diagram -- Si has no solubility in SiO2 at equilibrium state-- Si has no solubility in SiO2 at equilibrium state


Silicon Nano Crystals Produced by Silicon Nano Crystals Produced by CVD Methods (II)CVD Methods (II)

-- U.S. Pattern Pending

• Thermal Decomposition of SiH4 precursor on Silicon surface for Si Nano crystals .

• No Anneal Step is required.

• Most compatible with current CMOS technology.

• Challenge is how to control location and size distribution.


Other Ideas of Synthesis Nano CrystalsOther Ideas of Synthesis Nano Crystals

Controllable Nucleation and Growth Controllable Nucleation and Growth

VolmerVolmer-Weber Growth (3-D Island Growth) on Thi-Weber Growth (3-D Island Growth) on Thin Filmn Film

In-Situ Phase Segregation (In-Situ Phase Segregation (SpinodalSpinodal Decomposition Decomposition))

Pre-patterned Growth (Pre-patterned Growth (Polymer Precursor Self-assemblyPolymer Precursor Self-assembly))


SummarySummary

Nano storing bit can and must meet Si Nano storing bit can and must meet Si technology in 5 years.technology in 5 years.

Nano crystal memory is the most promising Nano crystal memory is the most promising one to be compatible with CMOS platformone to be compatible with CMOS platform

Many challenges still exist ranging from Many challenges still exist ranging from manufacturing nano particles to integration manufacturing nano particles to integration into traditional process flowinto traditional process flow

Materials scientist can definitely help!Materials scientist can definitely help!


Phase Transformation MemoryPhase Transformation Memory

Phase Transformation Memory• Same principle as DVD• Using transformation between amorphous and crystalline phase based on cooling speed.• Different phases has different optical and electrical properties.• Easy to be integrated and scalable.

Session Session 1010, Slide , Slide 3434Instructor: Dr. Zhen GuoMatE 297, Spring 2006Stephen Lai, Intel, December 2003.


Basic Architecture of Nano Crystal Memory

Floating nano crystals can be -- Silicon nano crystals (multiple or single) -- Silicon nano wires-- Metal nano dots (single or Multi layers)

S. Tiwari et al. Appl, Phy lett, 1996R. Muralidhar et al. IDEM, 2003


Nucleation and Growth ControlNucleation and Growth Control• Nano particles need strong nucleation and slow growth

• Low temperature (high T) promote nucleation and slow down growth

• The distance among nucleation sites has to be bigger than diffusion length

• Nucleus size should be controlled around critical radius


Volmer-Weber Growth Volmer-Weber Growth

• 3-D island growth

• Neither complete wetting nor complete non-wetting surface

• Island size and distribution controlled by heterogeneous nucleation sites

sfisf


Spinodal DecompositionSpinodal Decomposition

Spontaneous transformation Spontaneous transformation due to instabilitydue to instability

No nucleation barriers-only No nucleation barriers-only require local compositional require local compositional fluctuationsfluctuations

Wave length (or particle size) Wave length (or particle size) is a function of undercoolingis a function of undercooling

Misfit strain will also play a Misfit strain will also play a key role in particle size key role in particle size (barriers for growth)(barriers for growth)


Self-Assembly PatterningSelf-Assembly Patterning

K. W. Guarini et. al. IDEM, 2003

class notes ww10

Documents

v nano magnetic materials

nanoelectric materials

structural materials

quantum dots

source drain

nano composite week

nano crystal memory

electron number