graphene transistors and two-dimensional electronics

8/11/2019 Graphene transistors and two-dimensional electronics

1/41

Giuseppe Iannaccone University of Pisa

Giuseppe Iannaccone University of Pisa1

Graphene transistors

and

two dimensional electronicsG. Iannaccone, G. Fiori, S. Bruzzone, A. Betti

University of Pisa

Acknowledgments: EC FP7 Project GRADE (n. 317839 )EC FP7 Project GO-NEXTs (n. 309201)

EC FP7 Project GRAND (n. 215752)

EC FP7 NoE Nanosil (n. 216171)

ESF FoNE Project DEWINT CNR

IT PRIN GRANFET (Prot. 2008S2CLJ9)


2/41



Graphene as a material for electronics

High mobility at room

temperature (>104cm2/Vs)

Symmetric properties for

electrons and holes

One-atom thin -> promising

for scaling

Cheap and CMOS compatible

.but .

the zero energy gap is ashowstopper for use in

(digital) electronics .Graphene Band Structure[nanodevice.fmns.rug.nl]


3/41


Rules of the gameIncrease gap, fabricate device, but

keep mobility high, keep reproducibility high3


4/41



Energy gap and the Off state

Small energy gap enablesleakage via interband

tunneling current => high Ioff

EFS

EFD

source channel drain

Poor off state


5/41



Energy gap and the Off state

!Several options to induce a bandgap have beenpursued "manufacturability challenges

Small energy gap enablesinterband leakage => high Ioff

EFS

EFD


EFS

EFD


Poor off state Good off state


6/41


Graphene NanoRibbons

6


7/41



Impressive GNR Experiments

X. Li et al., Science 319, 1229 (2008)

X. Li et al. PRL 100, 206803 (2008)


8/41

Giuseppe Iannaccone University of PisaGiuseppe Iannaccone University of Pisa8

Device modeling tool: NanoTCAD VIDES

!

3D Non-Equilibrium Greens Functions

(NEGF) solver!Fully coherent transport

!Generic 3D structures

CNT and GNR FETs (TB atomistic)

Bilayer graphene FETs (TB atomistic)

Semiconductor NW Transistors (EMA+ TB atomistic)

hBCN

!New version of the code as a pythonmodule all documentation and codeat: http://vides.nanotcad.comand onthe nanohub.org


9/41


Energy gap of graphene nanoribbons

!

Nanoribbons always have a semiconducting gap

!

Huge gap variations for a single-dimer width change

Y.-W. Son et al.PRL 97, 216803

(2006)

(16,0)

(14,0)

(12,0)


10/41


!

DGFET with L = 15 nm, tox = 2 nm

!(12,0) has a width of 1.37 nm

G. Fiori et al., IEEE-EDL 28, 760 (2007)Giuseppe Iannaccone University of Pisa10

GNR-FETs transfer characteristics

(12,0)

(12,0)

(14,0)

(14,0)

(16,0)

(16,0)

(16,0) with edgeroughness


11/41


GNR intrinsic low-field mobility

!

Full band modeling (e- and ph): A. Betti et al. IEDM 2010, APL 2011

! Intrinsic mobility of 1nm GNR ~ 800 cm2/Vs, mainly due to AC phonons.

!10 x smaller

in"1/n2D in graphene


12/41


Option 2: Bilayer graphene

12


13/41


A vertical electric field can open a gap inbilayer graphene

E.McCann, V.I.Fal'ko, PRL. 96, 086805 (2006)

E. McCann, PRB74, 161403(R) (2006)

J.B. Oostinga et al., Nat. Mat. 7, 151 (2008) E. V. Castro et al., PRL, 99, 216802 (2007). T. Ohta et al. Science 313, 951 (2008).

Bilayer Graphene


14/41


Bilayer Graphene Tunnel FET

G. Fiori, G. Iannaccone EDL, Nov. 200914


15/41

TFET principle of operation


16/41


Tunnel Bilayer graphene FET (III)

! Transfer characteristics as a function of gate overlap


17/41

Graphene heterostructures


18/41


Atomic layers of hBN and graphene domains

L. Ci et al.(Rice) Nat. Mat. 9, 430 (2010)Absorption rate of BN "5.68 eV Egap

18


19/41


Lateral

heterostructure FET

19

G. Fiori, G. Iannaccone,IEDM 2011, ACS Nano 2012


20/41


hBCN Bandstructure (from DFT)

20


21/41


LDOS: graphene FET vs BC2N FET

21


22/41


ID-VGSfor different barrier material and length

22

BC2N

tB= 5 nm


23/41


Graphene LHFET - Comparison with ITRS 2012

!Iofffixed at 100 nA/m (as for HP) [Low OP has Ioff5 nA/m]

23


24/41


Graphene LHFET - Comparison with ITRS 2012

24

!Iofffixed at 100 nA/m (as for HP) [Low OP has Ioff5 nA/m]


25/41


Advantages of LH FETs

1. Robust with respectto fabricationtolerances (self

aligned gate)

25


26/41


Advantages of LH FETs

1. Robust with respectto fabricationtolerances (self

aligned gate)

2.

Exploit high mobility

graphene for localinterconnects an S/D

extensions

3.

Several unexplored

options for the high

gap region

26


27/41


Lateral G-BN Heterostructures

27

M.P. LevendorfNature 2012

(Cornell)


28/41


L. Britnell et al.,Science v. 335,

p. 947, 2011

Britnell et al. Nano Letters 2011Britnell et al. Science 2011


29/41


Graphene-base hot electron transistor

29

S. Vaziri et al.(KTH,U. Siegen, IHP)

Nano Letters 2012


30/41


Graphene Barristor

30

K. Yang, Science 2012

(SAIT,Columbia U.,

Samsung)


31/41



32/41


Transfer characteristics

1 layer

not enough

3-5 layers

ON:

thermionic

OFF:

tunnel


33/41


Gate on lead: poor HF performance


34/41


How about analog? fTgold rush

Jan. 09fT=26 GHz

Apr. 09fT=50 GHz

Feb. 10fT=100 GHz

May 10fT=100 GHz

Apr. 11fT=150 GHz


35/41


fTgold rush


36/41


Exploring the design space

Extraction of seriesresistance

Y. Wu et al.,Nature, 472 p. 74, 2011

to be presented at IEDM 2012


37/41


Bilayer Graphene improves performance

!

Optimized structure with tox = 4 nm , tb = 20 nm


38/41


Backgate voltage controls Av0


39/41


fT, fMAX comparable for BGFETs and Si, III-V FETs

to be presented at IEDM 2012


40/41


Graphene in microelectronics: no easy solution

!Nanoribbons require prohibitive fabricationtolerances and are prone to mobility degradation

!Bilayer graphene could be interesting:

#

Digital: only TFETs (experiment under way)

# Analog: FET (focus of the GRADE project: main

challenge is reducing contact resistance)!

Lateral Heterostructure FET

# Most Promising device:Experiments ongoing

!Vertical Heterostructure FET

#

Low on/off ratio, low fT

# Attempts to increase fTwithin GRADE (GBTs)

40


41/41


Thank you

Acknowledgements: EC FP7 Project GRADE (n. 317839 )

EC FP7 GoNexts (n. )

IT PRIN GRANFET (Prot. 2008S2CLJ9)

graphene transistors and two-dimensional electronics

Documents