Carbon-based Electronics: Graphene

Transcription

1 Carbon-based Electronics: Graphene 1 st NANO-TEC Workshop European Commission ICT Theme Jeong-Sun Moon HRL Laboratories, LLC Team Members: Deanna Curtis, Steven Bui, Ming Hu, Dana Wheeler, Danny Wong, Dustin Le, Andrey Kiselev, Chaoyin Zhou, Richard Ross, Chuck McGuire, Bin Shi (HRL), Kurt Gaskill, Joe Tedesco, Paul Campbell, Glenn Jernigan (NRL), Josh Robinson, Mark Fanton (EOC), Ying Liu (PSU), Peter Asbeck (UCSD), Ki-wook Kim, M. Nardelli (NCSU), and Amy Liu (IQE) Partially Supported by DARPA CERA program, monitored by Dr. John Albrecht. The views, opinions, and/or findings contained in this article/presentation are those of the author/presentor and should not be interpreted as representing the official views or policies, either expressed or implied, of the Defense Advanced Research Projects Agency or the Department of Defense."

2 Content 1. A brief introduction of graphene 2. Unique properties of graphene 3. From the unique properties to future applications Q: Would graphene impact future systems? 4. Recent progress in graphene 5. Challenges and Future outlook

3 Graphene Graphene = a single layer of carbon atoms in honeycomb lattice 2D structure instead of 1D nanowires or carbon nanowires Recent study of graphene was initiated by Prof. Geim s group and Prof. deheer s group A single layer of sp2 carbon Graphite Novoselov et al., Science, p.666, 2004 Epitaxial graphene Berger et al., J. of Phys. Chemistry, p.11912, 2004

4 Graphene Band structure A single layer of graphene AB P. R. Wallace, Phys. Rev, 1947 A. H. Castro Neto, Rev. of Modern Physics, 2009 Band structure: Zero bandgap Zero effective mass Linear dispersion hole electron E vs k graphene InSb Zero bandgap Ambipolar (n, p) characteristics

5 Bandgap Engineering A bilayer graphene Bottom layer more doped Equally doped Top layer more doped Ohta, Bostwick, Seyller, Horn and Rotenberg. Science 313, 951 (2006) A bilayer graphene offers a bandgap of ~0.25 ev ( ~10 k B T room ).

6 Graphene: Vsat and Critical field Saturation Velocity (4.7x10 7 cm/sec) Graphene (electrons and holes) Source Injection Velocity (6.4x10 7 cm/sec) <vx>=2/ V F ky Si Higher saturation velocity can be achieved at reduced electric field from graphene. Offer highly-scaled ballistic transistors.

7 Ballistic Graphene FET Characteristics 2D model with full electrostatics Initial calculation: ignores tunneling from valence band I_b allis tic (m A /u m ) VG Vt=0.1~0.9V Step of 0.2V Lg=60 nm EOT=2 nm VDS(V) Ft (THz) Channel charge-limited ft VG-Vt=0.3V VG-Vt=0.7V VDS (V) Effective transit time Ttr=1/2 ft For ft=1.7 THz, Ttr=94 fsec For Lg=60nm, veff~6e7 cm/sec

8 How does Graphene Compared with? Merit Si Graphene GaAs In 0.53 Ga As InAs InSb Mobility (cm 2 /vs) 1000 (n) 300 (p) 15000~ ~ Vsat (cm/sec) 8e6 ~ 5e7 1.2e7 2.7e7 4e7 5e7 Bandgap (ev) ~0.2max Carrier density (cm2) 5e12 ~1e13 2~2.5 e12 1.3e12 1e12 MOS Scaling High Si CMOS compatibility High Low Low Low Low

9 Properties of Graphene Zero-band gap with bandgap engineering possibility Fermi Velocity = 10 8 cm/sec (10x better than Si) Saturation velocity = 5x10 7 cm/sec (~2x faster than InP) Mobility (room temp) ~ cm 2 /vs (~10x better than III-V) Current density = 10 9 A/cm 2 Highest quality material on flexible substrates (~ x better than any other flexible electronics materials known) Highest optical transparency Thermal conductivity ~48 W/(cm K) (~2x better than diamond) Young s modulus = 500 GPa (~better than SiC, 1.2 TPa diamond) Lowest mass and high surface-to-volume ratio Thermoelectric energy conversion A single molecule sensing

10 Potential Applications of Graphene LCD Stanford Univ, 2010 Samsung, , Univ. of Manchester Stretchable Si Univ. of Illinois Flexible graphene HRL, 2009 Graphene Samsung, 2010 Interconnect GIT, 2009 UT Dallas, 2008

11 A Path for ultimate Scaling of MOSFET - Self-aligned (n, p) MOSFET - Advantage for device scaling Metal Gate High-K dielectric EOT = 1nm Non-alloyed ohmic preferred Low ohmic contact Resistance S Substrate D Graphene: 0.3 nm thick maintain high (n,p) mobility high channel velocity high phonon energy high thermal conductivity (lower Tj) High drive current

12 Graphene Transistor Development Phase Rapid Growth of Graphene S&T: A world s first 2 graphene MOSFET A world s first 3 graphene-on-si MOSFETs (HRL, 2009) Graphene-on-SiC Graphene-on-Si 2010 HRL/NRL lot7_gr0806n_b_505042_iv3 Novoselov et al., Science, 2004 Graphite 2004 Gm= 1.4 ms/mm Wu et al., Epitaxial graphene Berger et al., CERA June, 2008 Gate Source Graphene Drain Source A world s first Epitaxial graphene RF-FET (HRL, Dec, 2008) Lemme et al., EDL, 2007 Ion/Ioff < 3 FET mobility ~530 cm 2 /Vs Ids ( A/ m) Vds (V) 75mm graphene-on- SiC wafer (NRL/HRL) Epitaxial graphene RF- FET gm = 770 ms/mm, Ion/Ioff = 33 FET mobility~ 6000 cm2/vs (HRL, 2009)

13 75mm Wafer-scale Graphene Epitaxial Graphene layers were grown on 50 and 75 mm diameter 6H-SiC wafers 50 mm Epitaxial Graphene wafer Sheet resistance map 75 mm Epitaxial Graphene wafer Sheet resistance map World s first Graphene MOSFETs on 75 mm diameter wafer % /sq World s first Graphene MOSFETs on 50 mm diameter wafer % /sq

14 Graphene Layer Using spectral Raman, sites were analyzed. The ngl was determined by fitting the 2D spectra. The findings were correlated with transmission electron microscopy (TEM). Map of 2D Raman spectrum position Analysis of 2D Raman peaks TEM Analysis of graphene ngl =1 ngl =2 Wafer 817 Raman spectral analysis shows single and bilayer graphene on an entire 2 wafer.

15 Self-aligned Graphene MOSFETs - Self-aligned MOSFET - Gate dielectric and metal gate Source Metal Gate SiC Substrate Gate dielectric Drain graphene Source Graphene Drain GR822_5151_243 Wg =2x5.6 m, Lg = 3 m Vgs =3 V, step= -0.5 V 771 A/ m Lot8_GR0808NA_495043mos_iv_ A/ m Gate Source Ids ( A/ m) 1000 Ids ( A/ m) Wafer Vds (V) Vds (V) Vds = 1V: Ion = 770 A/ m Vds = 1V: Ion = 520 A/ m

16 Ion/Ioff at Vds = 1 V Graphene MOSFETs show an maximum Ion/Ioff of 26 at Vds = 1 V. Transfer curves at Vds = 1 V Wafer = 822 Transfer curves at Vds = 1 V Wafer = 819 Ids (ma) Vds = 1 V Lg = 3 m Wg = 2x6 m FETs Ids (ma) Vds = 1 V Lg = 3 m Wg = 2x6 m FETs 2 pfet nfet 2 pfet nfet Wafer Vgs (V) Vds = 1 V Max. Ion/Ioff = 18 Wafer Vgs (V) Vds = 1 V Max. Ion/Ioff = 26

17 Graphene RF N-MOSFET & P-MOSFET GR0804A_5050_80_6ummesa P-FET Vgs = -5 V, step = 0.5 V N-FET Vgs = 5 V, step = -0.5 V Ids (A) Vds (V) Graphene p-mosfet and n-mosfet are demonstrated

18 Graphene (n,p) MOSFET FET Mobility Graphene MOSFETs show a record peak FET mobility of 9100 cm 2 /Vs. FET = (L/W) (gm/c g ) (1/Vd) MOSFET Transfer Curves Wafer 822, Graphene p-mosfet CERA Wafers FET Mobility Graphene n-mosfet Ids (A) Vds = 50 mv Vg (V) FET Mobility (cm 2 /Vs) 1000 Si n-mosfet Si 100 p-mosfet Effective Electric Field (MV/cm) FETmob_819 FETmob_822 FETmob_822_2 FETmob_818 Si Univ Mob FETmob_806 p-fet mob_806 p-fet mob_804 FETmob_804 gm (50 mv) = 9-13 S/ m Demonstrated 10X better FET mobility than that of Si CMOS

19 4. Carrier FET Mobility ( 5000 cm 2 /Vs) Long-channel (L g = 3 m) Graphene MOSFETs show a record transconductance of 770 ms/mm at Vds = 4 V. 800 GR822_242_gm 770 ms/mm gm_ext (ms/mm) Vds = 1.5 V Vds = 2.5 V Long-channel graphene MOSFET: L g = 3 m W g = 2x6 m Peak gm = 770 ms/mm at Vds = 4 V Vgs (V) A long-channel graphene MOSFET with a record gm/cgs was demonstrated.

20 Graphene-on-SiC MOSFETs (2008) Demonstrated wafer-scale graphene RF transistors operating in GHz domain. 20 Graphene RF FETs: Wafer = GR0801A Ft = 4GHz Fmax = 14 GHz Ft (GHz), Fmax (GHz) Fmax = 14 GHz Graphene FET #2 Ft = 4GHz Ft Fmax(U) Graphene FET #1 Vds = 6 V, Vgs = -2.5 V Devices

21 Graphene-on-Si Technology Development Graphene-on-Si technology offer a path toward very largescale of graphene synthesis Graphene-on-Si graphene A world s first 2 graphene-on-si MOSFET 3C-SiC FZ Si (111) (a) (b) 3C-SiC 20 nm A world s first 3 graphene-on-si MOSFET Si 3 nm HRL/EOC, 2009

22 Ambipolar Graphene-on-Si MOSFETs EM09087_525078_gm 1.1 P-type Vds = 1 V N-type Ids (ma) Vg (V) First demonstration of ambipolar (e & h) behaviors from graphene-on-si

23 Semiconductor Comparison for Receiver Graphene MOSFET Si MOSFET GaAs PHEMT InAs 2DEG(1/cm 2 ) 1-10e12 2e12 1.3e12 Idss (A/mm) Hall Mobility (cm 2 /vs) > Vsat (cm/sec) 4.9e7* 8e6 2e7 3.5e7 Gm (ms/mm) K(W/cm-K) (InP) Ft, fmax 300, 300 (goal) 350, 120, , 270 LNA MMICs GHz 77 GHz 94 GHz Receiver-on-chip w/ integration density Grapheneon-Si approach SiGe 77GHz Radar Need baseband processing Need baseband processing * Based on gm/cg

24 Technology Needs for Ultra-Low-power & Linear Receiver LNA Technology Vds (V) DC power/stage 2.8 AlP 0.18 um CMOS 1-2 ~9 mw Energy Gap (ev) GaP Si GaAs AlAs InGaAs InP GaSb AlSb 0.13 um CMOS ~2-10 mw InP 1.5 ~11-15 mw MHEMT 1.4 ~5 mw AlSb/InAs mw 0.4 Ge InAs InSb Graphene tbd Lattice constant (A) Lower bandgap devices offer low-power LNA operation.

25 Device F min, Bandwidth, vs. Saturation Velocity F min = 1 + k f C g [(R s + R g )/gm] 1/2, f T ~gm/c g ~V sat /(2 L g ), bandwidth: Rn (noise resistance) ~ [1+(2 f*cg*rg) 2 ]/gm 2 Technology Vsat (cm/s) Bandgap (ev) Si 8x GaAs 2.2x In 0.53 Ga 0.47 A s/inalas/inp 2.7x InSb ~5x Graphene ~5x Minimum NF (db) NFmin vs. Semiconductors Si nmosfet GaAs phemt InP HEMT RF CMOS Si n-mos Frequency (GHz) High-performance LNA requires high Vsat. Graphene and ABCS HEMT offer the highest Vsat. Reduced Rn wider bandwidth Provide low-noise performance over wider bandwidth 90nm RF CMOS GaAs PHEMT InP HEMT Graphene?

26 CERA and Linear LNA Figure of Merit LNA FOM = gain*bw/[(nf-1)*p dc ] Linearity FOM = OIP3/P dc OIP3 3 gm G gm" p Noise Figure (db) CERA program is designed to demonstrate W-band LNA SiGe GaAs InP InP ABCS GaAs SiGe Graphene ABCS Efficiency (db/mw) W-band LNAs CERA goal (ft/fmax = 500/500 GHz at Vds = 0.25V) NF (db) of LNA Wideband LNA (covering up to 10 GHz) SiGe HBT ABCS HEMT 90nm CMOS InP HEMT OIP3/Pdc of LNA MESFET Linear FET goal: NF and DC power of ABCS HEMT & Linearity of MESFET Question: Would graphene be high-performance linear FET?

27 Nonlinear RF: Clean & Efficient Signal Generation Phase/Amplitude modulation in Digital Radio, Comm & spread spectrum: Requirement of phase noise (QPSK)= -90 dbc/hz at 100 khz Device: Ft, fmax, 1/f noise Multiplier (xn): 10LogN Frequency multipliers Ids Phase noise RF_out Vgate Time RF_in Edmar Camargo, Artech House, 1998 Spectral control Ft, fmax, 1/f noise Phase noise Conversion efficiency Bandwidth

28 Ultra wideband Spectrally-pure RF Signal Generation RF systems need spectrally-pure ultra-wide band RF/MW/mmW signal generation. Until now, there are no clear technical implementation approaches. 100 MMIC Freq Doubler Effi vs BW 100 MMIC Spectral Purity vs BW MMIC Efficiency (%) 10 1 SiGe HBT 0.15um phemt 0.15 mhemt 0.14um InP HEMT InGaP HBT HRL x2 doubler 14% bandwidth Fundamental Rejection (db) Graphene MMIC HRL Graphene FET Bandwidth (%) Bandwidth (%) Graphene shows a feasibility and path for the desired signal generation.

29 Graphene for high-efficient & linear Mixer I (gm) V2 (square-law device) Ids High gm Mixer efficiency: E sys 3um long-channel graphene FET Phase noise = -110 dbc/hz at 10kHz offset Carrier-to-noise in 2x = 6 db (ideal) IP3 ( dbm) LO( dbm) 10 Unwanted reciprocal mixing phenomena Vgate RF_in Higher gm near the ambipolar point would offer mixer operation with reduced LO power and LO phase noise consequently. Improve mixer efficiency Reduce unwanted reciprocal mixing in electronic warfare environments Improve phase-noise limited mixer dynamic range

30 Graphene Frequency Multiplication 12 Graphene MOSFET_w818_2x25um_1V 10 Ids (ma) Vgs (V)

31 Graphene Frequency Mixing Ids I V 2 Vgate Potentially offer high dynamic range in mixing RF_in Signal Amplitude (dbm) LO-RF -80 LO-RF GR_802Cd44_2x6um_2Vds_3.3mA-3.5V_10MHz_mix LO RF Vds = 2 V, Ids = 3.7mA Away from the Dirac point 2LO LO+RF Frequency (MHz) 3LO Signal Amplitude (dbm) GR_802Cd44_2x6um_2Vds_2mA-7.5V_10MHz_mix Near Dirac point No 2f2-f1 present -40 LO 2LO LO-RF RF LO+RF -70 3LO Frequency (MHz)

32 Graphene NEMS: Fast & Linear RF Switches Insertion loss FET or PIN MEMS Graphene > 1dB <0.2 db <0.2 db Isolation < 25dB >30 db >30 db Linearity Nonlinear Linear Linear Speed ~10nS ~usec ~5nS Operation voltage RF systems such as phased-array-radars need signal routing with fast, linear and low-loss capability. Vp Vp m V V k a few V 30-70V 1-5V Reliability High Medium (due to sticking) tbd Switching Time (usec) s Graphene Membrane RF Switch HRL s Graphene design1 Air gap = 0.5um Area = 50x50um 2 k= 0.7 N/m HRL s design3 Air gap = 0.1um Pull-down Voltage (V) Offer a fastest (GHz) RF switch with low (1V) actuation voltage. Enable integration with CMOS, III-V ICs. Offer an integrated electronic-nems. s 0.5um Al 0.8um Au HRL s Graphene design2 Air gap = 2.5um Area = 100x100 um 2 k = 0.7 N/m 7um Au Analog Device

33 Very-large Scale Active Flexible Electronics Key metrics for active flexible electronics Electronic mobility Flex graphene HRL, 2009 Thermal management Flexibility & Largescale Material Table 1. Flexible Electronic Material comparison Field-effect Mobility (cm 2 /Vs) Thermal Conductivity (W/mK) a-si:h <1 < 5 High-speed Cost performance Pentacene good good a-in-ga-zn-o 6-9 <1 Si nano-membrane poor poor Graphene inch good

34 Very Large Scale Active Flexible Electronics Rx Fundamental physical limit: Strain = thickness/(2*radius of curvature) LNA Stretchable Si Univ. of Illinois HRL s sensor RF tag on PCB Tx Graphene Samsung, 2010 Electronic mobility (cm 2 /Vs) Monolayer-thick graphene can be only material form with 4-5 order-ofmagnitude higher flexibility while maintaining high material quality, in principle. III-V Si Flex Electronic Material Comparison Ultra-thin Si (ft*lg = 3GHz*um) Organic film (ft*lg <3 MHZ*um) /radius of curvature (1/mm) graphene

35 Potential Applications of Graphene Some other applications EMI Non-volatile memory Cooling Harsh environment THz Thermoelectric Chem sensors Bioelectronics EMI Rejection (db) Transparent and EMI shielding Graphene EMI Rejection at Ku-band SiC_dB Graphene_dB Frequency (GHz)

36 Graphene as Emerging Material 2008 Source Graphene Gate Drain Source A world s first Epitaxial graphene RF-FET (HRL, Dec, 2008) A world s first 2 graphene MOSFET (HRL) Ids (A) SOA Graphene FET: gm = 770 ms/mm, Ion/Ioff = 33 FET mobility~ 6000 cm2/vs (HRL, 2009) GR0804A_5050_80_6ummesa P-FET Vds (V) N-FET 2009 lot7_gr0806n_b_505042_iv Ids ( A/ m) Vds (V) A world s first 3 graphene-on-si MOSFETs (HRL, 2009) 75mm graphene-on- SiC wafer (HRL) UT Dallas, 2008 Flexible graphene HRL, 2009 Samsung, 2010 Interconnect GIT, 2009