low frequency noise in gan-based advanced electronic devices a dissertation for doctor of philosophy...
TRANSCRIPT
Low Frequency Noise in GaN-Based Advanced Electronic Devices
A Dissertation for
Doctor of Philosophy
By
Nezih Pala
Thesis Advisors:
Dr. Michael Shur
Dr. Remis Gaska
2
Talk outline
• Motivation• Introduction to low frequency noise• Devices under study• Possible noise sources in FETs• Determination of noise sources in HFETs and MESFETs
• New model for 1/f noise in HFETs• Conclusions and Key Contributions
3
Motivation
•Low frequency noise is a figure of merit and limiting factor for high frequency Field Effect Transistors including HFETs and MESFETs.
•Low frequency noise is upconverted to high frequencies limiting the performance of the transistors in the microwave range[1]. Especially when these devices are used as oscillators or mixers, low frequency noise limits the phase noise characteristics and degenerates the performance of the electronic system.
•Low frequency noise analysis is a powerful tool for examining compound semiconductors and yielding information about crystal defects and interfaces [2].
[1] M. N. Tutt, D. Pavlidis, A. Khatibzadeh, B. Bayraktaroglu, IEEE Trans. Microwave Theory and Tech. 43, 1461-1471, (1995)[2]L. K. J. Vandamme, IEEE Trans. Elec. Devices, 41, 2176, (1994)
4
Types of Low Frequency Noise in FETs
•Thermal Noise SV = 4kTR
SI =4kT / R
•Generation- Recombination noise.
•1/f Noise
fNV
fS
I
fS VI
22 )(
)(
)(
)(Hooge Parameter fN
I
S I2
ec 111
222 1
14
FF
nV
N
I
S
olume
TI
100 101 102 103
10-22
10-21
10-20
10-19
10-18
Lorentzian
1/f Noise
G-R contribution
HFETR= 100
Frequency (Hz)
SI (
f)
(A
2 /Hz)
Nyquisit (thermal) noise(S
I = 4kT/R)
5
Low Frequency Noise Measurement Setup
• Main instrument: FFT Spectrum Analyzer SR770, Stanford Research Systems• Measurement range: 1 mHz – 100 kHz• Measurement sensitive to vibrations air suspended table (optical table)• Measurement sensitive to electromagnetic fields and light shielded
enclosure• Use of batteries less disturbances of power system frequencies and
harmonics
6
Devices Under Study
MOS-HFET HFET
30 nm Si:Al0.2Ga0.8N 2x1018
50 nm AlN
7-13 nm SiO2
SiC/Sapphire
1 m i-GaN50-70 nm Si:GaN (2-5)x1017
HD-MOSFET HD-MESFET
2m GaN
AlN
7-13 nm SiO2
Sapphire
50-70 nm Si:GaN (0.5-1.5) x 1018
7
GaN Research Cycle
Epilayer growth by MOCVDUSC
Layout design by L-EditRPI
Mask and Device FabricationRPI,USC
Characterization:DC, RFLow Frequency NoiseRPI, USC
2D SimulationRPI
8
Fabrication of GaN Based FETs I
•Source/Drain ohmic metal deposition• e-beam evaporation, •Ti/Al/Ti/Au (100Å/300Å/200Å/1000Å) • Annealing at 850 oC for 60 sec. in N2 ambient
•Ion implantation for isolation •He+, 40 keV, 2x1014 cm-2
•Provides planar geometry
9
Fabrication of GaN Based FETs II
•SiO2 deposition for MOS-HFET and MOSFET
type devices• Plasma Enhanced Chemical Vapor Deposition (PECVD)
•SiO2 patterning and removal•BOE Etch
10
Fabrication of GaN Based FETs III
•Contact pad metal deposition•e-beam evaporation, •Ti/Au (200Å/5000Å)
•Gate metal deposition•e-beam evaporation,•Ni/Au (300Å/500Å)
11
DC Characteristics of AlGaN/GaN HFET and MOS-HFET
•Several orders of of magnitude reduction in gate leakage current in MOS-HFET•Comparable Drain saturation current about 720 mA/mm.•Larger gate voltage swing for MOS-HFET.•Higher linearity in transconductance of MOS-HFET.•Decreased transconductance for MOS-HFET due to decreased gate capacitance
-16 -12 -8 -4 0 4 8 12
10-1210-1110-1010-910-810-710-610-510-4 HFET
MOS-HFET
Gat
e Le
akag
e C
urre
nt
I G
(A
)
Gate Bias VGS
(V)-20 -15 -10 -5 0 5
0.0
0.2
0.4
0.6
0.8
0
20
40
60
80
100
120
140
Dra
in S
atur
atio
n C
urre
nt
I DS
at
(A
/mm
)
Gate Bias VGS
(V)
HFET MOS-HFET
Tra
nsco
nduc
tanc
e G
(m
S/m
m)
12
DC Characteristics of GaN HD-MESFET
Lg= 1.5 m =100 cm2/Vs Ne=1.5x1018 cm-3
•High saturation current density.•RC 0.3 mm ( C ~ 1x10-6 cm2 ).•Low gate leakage current (<10 nA) indicates the quality of Schottky contacts.•Good agreement with the simulation results is encouraging for submicron devices.
-10 -8 -6 -4 -2 00
50
100
150
200
250
300
350
0
15
30
45
60
75
Tra
nsco
nduc
tanc
e (m
S/m
m)
Dra
in S
atur
atio
n C
urre
nt I D
sat (
mA
/mm
)
Gate Bias VGS
(V)
0.0 0.5 1.0 1.5 2.0 2.5 3.0
0
200
400
600
800
1000
=100 cm2V/s
=400 cm2V/s
=1200 cm2V/s
Dra
in S
atur
atio
n C
urre
nt I D
sat (
mA
/mm
)
Gate Length (m)
HFET
MESFET
13
DC Characteristics of GaN HD-MESFET
Lg= 1.5 m =100 cm2/Vs Ne=1.5x1018 cm-3
•High saturation current density.•RC 0.3 mm ( C ~ 1x10-6 cm2 ).•Low gate leakage current (<10 nA) indicates the quality of Schottky contacts.
-6 -5 -4 -3 -2 -1 0
10-11
10-10
10-9
10-8
VD=12 V
VD=0.05 V
Gat
e Le
akag
e C
urre
nt
I G
Gate Bias VGS
(V)0 2 4 6 8
0
50
100
150
200
250
300
VG=-5V
VG=-4V
VG=-3V
VG=-2V
VG=-1V
VG=0V
Dra
in c
urr
en
t
I d
(m
A/m
m)
Drain voltage Vd (V)
14
Noise spectra for HFETs and MESFETs
The noise spectra SId/Id2 have the form of 1/f noise with close to unity
(= 1.0-1.15) for both types of devices.
fNI
S
d
I 2
310)32(
1 10 100 1000
-150
-140
-130
-120
-110
-100
-90
-80HD-MESFET, V
G=0V
1/f
HFET, VG=0V
MOS-HFET, VG=0V
SN
D
SI /
I2 (d
B/H
z)
Frequency (Hz)
35 1010
MESFET
HFET
15
Possible Noise Sources in FETs
•1/f noise•Contact Noise •Gate Leakage Current•Surface Noise•Channel (under the gate and source-gate, gate-drain regions) Noise•Fluctuations of the Schottky barrier space charge region (SCR) in MESFETs
•Generation-Recombination Noise
RGaN=RS1+RCh+RS2
Lg
Source Gate
RS1RCh RS2
Drain
RCRC
L
16
Contribution of Contact Noise Sources TLM Measurements
1 10- 135
- 130
- 125
- 120
1/L 2
1/L
S I /
I2,
dB
/Hz
Spacing L , um
22GaN
RRcI
R
SS
I
SGaN
222
1
LR
S
I
S
GaN
RcI
LR
S
I
S
GaN
RI GaN1
22
•SRc>>SGaN
•SRc<<SGaN
Contact noise
Channel or Surface noise
Noise form the channel is dominant.
(RC<<RGaN)
tW
LRGaN
NfR
SR 2
2
2
22
2
222 )()( GaNC
GaN
GaN
R
GaNC
C
C
RcRI
RR
R
R
S
RR
R
R
S
R
S
I
SGaN
L
W
t
17
Calculation of Current Noise Density for Series Resistors
)( SC RRIV )()(0 SCSC RRIRRIV
)()( SCSC RRIRRI 22 )}({)}({ SCSC RRIRRI
)()( 22
sC RRSCI SSIRRS
2
2
22
2
22 )()( CS
S
S
R
SC
C
C
RI
RR
R
R
S
RR
R
R
S
I
SsC
RC RS
V
0CS RR
18
The contribution of the gate leakage current fluctuations to the output drain current noise of AlGaN/GaN HFETs was studied by three different methods:
1. The low frequency noise in the AlGaN/GaN HFETs and Metal-Oxide-Semiconductor Heterostructure Field Effect Transistors (MOS-HFETs) have been compared.
2. The gate current fluctuations were measured directly, in AlGaN/GaN HFETs.
3. The correlation between the gate and drain current fluctuations was measured and analyzed.
Contribution of the Gate Current Fluctuations
19
Contribution of the Gate Current Fluctuations
222dg
Vg
d
Id
IR
S
I
S dominant
contribution
10-4 10-3 10-2-160
-140
-120
-100
-80
=10-3
=0.1
SId/I d2 , d
B/H
z
Drain Current Id, A
10-3 2x10-3 3x10-3 4x10-3
-135
-130
-125
-120
-115
=10-4
=0.6-0.8
SId/I d2 , d
B/H
zDrain Current I
d, A
■Measured ●Calculated from measured gate noise
20
100 1000 100000.0
0.2
0.4
0.6
0.8
1.0f=200Hz
low noise-samples
high noise-samples
Co
rre
latio
n
Gate Series Resistance Rg, W
Correlation Between Drain and Gate Current Fluctuations
IgGate
Vg
Rg
SVg
Vd
Drain
Rd
SVd
Source
4diffsum
gd
SSS
VgVd
gd
SS
S
fVVS dgsum /)( 2
fVVS dgdiff /)( 2 }22
2
gRrR
rRSS g
d
dIgVd
21
Location of the Noise Sources in MESFETs
1x10-5 1x10-4 1x10-3-140
-130
-120
-110
-100
-90
-80
Vd=0.5 V
f=200Hz
S Id
/ I d2
(d
B/H
z)
Drain Current Id, A
IRR
R
R
S
I
S
ChS
S
S
RI S
2
2
22 )(
22
2
2 )( dChS
Ch
d
Id
IRR
BdR
I
S
Channel Noise = 10-3
Space charge region fluctuations
noise from surface and channel out of the gate:
2
2
2
2
2 )()( chS
S
SchS
ch
chd
Id
RR
R
fNRR
R
fNI
S
22
10-6 10-5 10-4 10-3 10-2-140
-130
-120
-110
-100
-90
-80
Id
- 1
SI/I
2 , dB
/Hz
Drain current Id, A
2
2
2
2
2 )()( SCh
S
SSCh
Ch
Chd
Id
tot
Rtot
d
Vd
RR
R
fNRR
R
fNI
S
R
S
V
S
Location of the 1/f Noise Sources in HFETs
sCh RR
112
dChd
Id IRI
S
channel noise
noise from surface and channel out of the gate:
2
2
22 )( chs
s
s
Rs
d
Id
RR
R
R
S
I
S
n
ch
I IRI
S
22
1
No fit indicates the concentration dependence of .
23
-8 -6 -4 -2 0 2 4
0.0
0.5
1.0
1.5
2.0
2.5
VT = - 5.6 V
107 C
G (
F/c
m2 )
Gate Voltage, VG (V)
Estimation of Electron Concentration and Mobility
ChCh
gn WRqn
L gV
Vg gCh CdVq
n1
1
0 2x1012 4x1012 6x1012 8x10120
200
400
600
800
1000
Mob
ility
, mn,
cm
2 /Vs
Concentration nCh
, cm-2
24
Hooge Parameter as a Function of 2D Electron Concentration
fAnI
S
ChCh
I
2Chn
1
22
1
Ch
I
nI
S
)1()( 2 FFn
(Typical for tunneling[1,2])
1.L. K. J. Vandamme, X. Li, and D. Rigaud, “1/f noise in MOS devices, mobility or number fluctuations?”, IEEE Transaction Electron Devices 41 (1994) 1936–1945
2. A. L. McWhorter, “1/f noise and germanium surface properties”, in Semiconductor Surface Physics, R.H. Kingston, ed., Philadelphia PA, Univ. of Pennsylvania Press (1957) 207-228
1012 1013
10-3
10-2
HFET MOS-HFET
1/nCh
Concentration ns, cm-2
25
New Model for 1/f Noise in Doped Channel HFETs
•Tunneling into donor states in GaN•Phonon assisted tunneling•Longer jumps correspond to lower frequency noise
AlGaN GaN
C
F
D
1
2
x0
-e
q
x
26
Equations for the Tunneling Model
)()()( ddc fxx
,)2(
212
2
pd
fm
p
c
x
dxxp0
)(2
exp'
mFxxmxp c 2)(2)(
2/3
'
Fxx
e
3/2
24
3
mF
xF
2
1
0
0
':
':
d
d
e
e
d
d
2/30 )/exp( Fc xx
: 2D tunneling cross-section
: capture rate due to tunneling
: electron momentum in 2 DEG
Where :
27
Equations for the Tunneling Model
dxx
Fxffx
An
N
n
xSd ddddSn22
020 ))((1
)/()1()(4)(
d dd
dddddFdSn d
An
ffxN
n
S
)1())/(ln(3
)](1)[(823/12
020
This is 1/f noise
kTTN
Ng
ggkT dc
c
DdF
exp)(42
ln(2
fn
TC
n
Sn20
20
)(~
0
F
dd Fx
exp0
kT
ddFd
ge
f
1
1)(
28
0 50 100 150 200 250 30010-14
10-13
10-12
10-11
100 Hz
SId/I d2 ,1
/Hz
Temperature T, K
Comparison With the Experiment
•Very good agreement of the noise maximum amplitude and position
•But the shapes of the dependencies are different
•And the temperature dependence of the 1/f noise has to be checked in undoped HFETs
Experiment
Theory
29
Temperature Dependencies of Noise Density in HFETs and MOS-HFETs
300 350 400 450 500 550-150
-145
-140
-135
-130
-125
-120
3200Hz1600Hz
800Hz400Hz200Hz
100Hz
Vg= 0 VVd=0.5 V
SiO2/AlGaN/GaN MOS-HFET
SI /
I2 (
dB/H
z)
Temperature (K)300 350 400 450 500 550
-150
-145
-140
-135
-130
-125
-120
Smax
Tmax
3200Hz
400Hz
1600Hz800Hz
200Hz
110Hz
Vg=0 VVd=0.5 V
AlGaN/GaN HFET
SI /
I2 (
dB/H
z)
Temperature (K)
Such S(T) dependencies are typical for the noise from local levels
Ea= 0.8 - 1.0 eV,
30
What is the Origin of the G-R Noise?
22
22 1
14
FF
LWn
N
I
S C
s
tsI
Fsc vn /1
[*]
[*] Copeland J. A., IEEE Trans. Elect. Dev. 18, 50, 1971
mv FF /2
)/exp(0 kTt FCn vN /10 t
F
C
Al0.2Ga0.8N
GaN
SurfaceChannel
d
1
t
3
2
1) G-R Process by a level in the channel
310-18 cm : To small to be true!Nts1026 cm-2 : To large to be true!
2) Electrons can be captured via tunneling. Might lead 1/f noise not GR noise.
3) G-R Process by a level in AlGaN barrier layer
Et = 0.8 - 1.0 eV, n (10-12 - 10-13)cm2,
Nt1016 cm-3 : All reasonable values.
where
222 1
14
FF
LWn
dN
I
S
s
tI
31
Temperature Dependencies of Noise in HD-MESFETs and HD-MOSFETs
300 350 400 450 500 550-140
-135
-130
-125
-120
HD-MESFET
3000Hz
1500Hz
800Hz
400Hz
200Hz
100Hz
SI /
I2 (
dB/H
z)
Temperature (oK)300 350 400 450 500 550
-140
-135
-130
-125
-120
HD-MOSFET
3000Hz
800Hz
400Hz
1500Hz
200Hz
100Hz
SI /
I2 (
dB/H
z)Temperature (oK)
Temperature dependence of noise in HD-MESFETs and HD-MOSFETs is weaker than the one in HFETs. Contribution of GR noise is weaker in HD-MESFETs compared to 1/f noise.
32
Comparison of Hooge Parameters
1.E-07
1.E-06
1.E-05
1.E-04
1.E-03
1.E-02
1.E-01
1.E+00
1.E+0110
1
10-1
10-2
10-3
10-4
10-5
10-6
10-7
GaN[7,13]
Si[1,2]
GaAs[1,2]
SiC[3,4]
GaN HFETon sapphire[8,9]
GaAs HEMT[5]
GaN HFETon SiC[8,11]
GaN MESFET [7]
GaN MOSHFET[10]
GaAs MESFET[12]
Si NMOS[6]
33
Comparison of Hooge Parameters References
1. R.H.,Clevers, Physica B 154, 214, (1989)2. F.N. Hooge, M. Tacano, Physica B 190, 145, (1993) 3. M. Levinshtein, S. Rumyantsev, J. Plamour, D. Slater, J. Appl. Phys. 81, 1758, (1997) 4. M. Tacano and Y. Sugiyama, Solid State Elect., Vol. 34. No 10, pp.1049-53, 1991. 5. D. Fleetwood, T.L. Meisenheimer, J. Scofield, IEEE Trans. Elct. Dev. Vol. 41, No 11, p. 19366. L.K. J Vandamme, X. Li, D. Rigaud, IEEE Trans. Elct. Dev. Vol. 41, No:11, p. 1936, Nov. 1994 7. Present Work8. A. Balandin, S. Morozov, G. Wijeratne, C. Cai, L. Wang, C. Viswanathan, Appl. Phys. Lett., 75, No. 14, p.2064, (1999)9. S. Rumyantsev, M.E.Levinshtein, R. Gaska, M. S. Shur, J. W. Jang, and M. A. Khan, J. Appl. Phys. 87, N4 pp.1849-1854, (2000)10. N. Pala, R. Gaska, S. Rumyantsev, M. S. Shur M. Asif Khan, X. Hu, G. Simin, and J. Yang, Electronics Letters, vol. 36, No. 3, p. 268, Feb. 2000.11. S. L. Rumyantsev, N. Pala, M. S. Shur, R. Gaska, M. E. Levinshtein, M. Asif Khan, G. Simin, X. Hu, and J. Yang, Electronics Letters, Submitted12. M. E. Levinshtein and S. L. Rumyantsev, Techn. Phys. Lett. vol. 19, no. 7-8, pp. 55-59, 199313. N.V. Dyakonova, M.E. Levinshtein, S. Contreras, W. Knap, B. Beaumont, P. Gibart.,"Low-frequency noise in GaN" Semiconductors. v.32, N 3, pp.257-260,(1998), March
34
Conclusions (HFETs)• Hooge parameter = 10-3 - 10-5 for both HFETs and MOS-HFETs. SiO2 deposited on AlGaN in MOS-HFETs does not contribute much to noise.
• In the devices with low gate leakage current the contribution of the gate leakage current to the low frequency noise of drain current is fully masked by other noise mechanisms.
•In the transistors with no contribution of the gate leakage current to the output noise the noise sources are located in the channel.
•Hooge parameter a is inversely proportional to the channel concentration in GaN/AlGaN HFETs – typical for tunneling mechanism. The model based on this mechanism is in qualitative agreement with our experimental data but the agreement must be checked further for undoped HFETs.
•Generation-recombination noise with activation energy of Ea ~ 0.8 - 1.0 eV has been found in both HFETs and MOS-HFETs. The analysis shows that the trap responsible for the observed generation-recombination noise can be located in the AlGaN barrier layer.
35
Conclusions (MESFETs)
• The noise properties of MESFETs and MOSFETs are similar. Hooge parameter = (2-3)10-3 for both devices. • This value is about one order of magnitude smaller than the value of reported for bulk n-type GaN.
• Drain and source contacts do not contribute much to the low frequency noise.
• The noise originates from the bulk of GaN in the channel and in the source to gate and drain to gate regions.
• The temperature dependence of noise shows a weak contribution of generation-recombination noise at elevated temperatures.
36
Key Contributions
•Design and fabrication of MOS-HFET with SiO2 as gate dielectric:
•Reduction in gate leakage current six orders of magnitude,
•Design and fabrication of HD-MESFET :
•Comparable output characteristics with HFETs with the advantages of simpler epilayer structure.
•Systematic measurement and analysis of low frequency noise to determine:
•Effect of gate leakage current ,
•Location of trap level causing GR noise,
•Origin of 1/f noise,
•Concentration dependence of 1/f noise.
•Development of a new model to explain 1/f noise in doped channel HFETs.