Characterization of two Field- Plated GaN HEMT Structures Hongtao Xu, Christopher Sanabria,...
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Transcript of Characterization of two Field- Plated GaN HEMT Structures Hongtao Xu, Christopher Sanabria,...
Characterization of two Field-Plated GaN HEMT Structures
Hongtao Xu, Christopher Sanabria, Alessandro Chini, Yun Wei, Sten Heikman, Stacia Keller, Umesh K. Mishra and
Robert A. York
Electrical and Computer EngineeringUniversity of California at Santa Barbara
Supported by ONR
Outline
Motivation Introduce two field-plated device
structures and their analysis DC and Small-signal measurements Power characterization Noise characterization Conclusion
Optimize GaN HEMT performance from the device structure level.
Use field-plated GaN HEMT structure for high power microwave circuits.
Further improve the power capacity, PAE and breakdown.
GaN HEMT for low noise applications.
Motivation
Field-plated device structures (I)
GaN2DEG
DrainSourceGate
SiNField Plate
Field-plate is connected to the gate through the common path of the gate and gate feeder in the extrinsic device region.
GaN HEMT devices of 32 W/mm was reported with this structure. Most commonly used structure.
Field-plate length
AlGaN
Field-plated device structures (II)
GaN
DrainSource
Gate & Field Plate
2DEG
SiN
Field-plate length
Gate and field-plate are intimately connected. RIE etching of SiN may damage the AlGaN surface.
AlGaN
Field-plate length
GaN
AlGaN
2DEG
DrainSource
SiNx
Gate Field-plate
Field-plated device structure
Field-plate length
DrainSource
SiNx
Gate Field-plate
Normal FP GaN HEMTs Intimately connected FP GaN HEMTs
Possible affected parameters: Rg, Cgd
Gate resistance Rg
1
3g g
WR R
L
j g
First order approximation:
Rg modeling
∆Rg
∆Rfp
Simulated by EM model:Rg = 1.6 Ω for normal FP structure.Rg = 1.33 Ω for intimately connected FP structure.
Rfp
RgSimplified Model
Distributed EM Model
Simulation on a 75 µm gate finger with 0.7 µm field-plate length.
EM simulation at 4 GHz
Field-plate
Gate finger
Field-plate
Gate finger
Normal FP device Intimately connected FP device
Simulation on a 75 µm gate finger.
0.7 µm field-plate length.
DC measurement
0 5 10 15 20
0.0
0.2
0.4
0.6
0.8
1.0
1.2
intimately connected field-plated device normal field-plated device
Vds
(V)
Cur
rent
Den
sity
(A
/mm
)
Intimately connected FP device has higher pinch-off voltage.
Both devices have similar Idss at Vgs=0 V.
200 ns pulsed I-V curves of two field-plated GaN HEMTs
Specifications:
Lg = 0.7 µm; Wg = 2x75 µm;Field-plate length = 0.7 µm;2000 Å SiN passivation layern0 = 9.96x1012 cm-2;Hall mobility ~1450 cm2/Vs
SP measurement (ft, fmax)
1 10 1000
10
20
30
40
50
h21,
U (
dB)
Frequency (GHz)
h21 of intimately connected field-plate device U of intimately connected field-plate device h21 of normal Field-plate device U of normal Field-plate device
Small-signal characterization of two field-plated GaN HEMTs
ft = 20 GHzfmax = 40 GHz
ft = 21 GHzfmax = 51 GHz
Normal FP device
Intimately connected FP device
Small signal model and simulation
Lg
Ls
LdRd
Rs
Rg Rgd
Cgs
Cds
Ri
Rds
gmVe-jωτ
+
V
-
Cgd
Gate Drain
Source
-0.5 0.0 0.5-1.0 1.0
S12
S21
S11
S22
Freq. (50 MHz to 30 GHz)
Measurement vs. Simulation
ADS-based parameter extraction routines. Models incorporate dominant parasitics and losses.
Intrinsic small signal parameters
Ri(Ω) Rds(Ω) Rgd(Ω) Cgd(fF) Cds(fF)
Normal FP device 7.178 1297.6 22.882 45.497 14.842
Intimately connected FP device 8.276 960.0 15.374 70.885 16.340
Cgs(fF) gm(S) Rs(Ω) Rg(Ω) Rd(Ω)
Normal FP device 270.7 0.040 6.531 0.924 5.503
Intimately connected FP device 246.0 0.040 4.830 0.782 5.423
Power Characterization
0 5 10 15 2010
20
30
40
50
Peak PAE=70.9%
PSAT
=10.1W/mm
Po
ut(d
Bm
),G
t(dB
)
Pin(dBm)
10
20
30
40
50
60
70
80
PA
E(%
)
0 5 10 15 20 25
10
20
30
40
50
Peak PAE=60%
PSAT
=12.9 W/mm
Pou
t(dB
m),
Gt(
dB)
Pin(dBm)
10
20
30
40
50
60
70
PA
E(%
)
Normal FP device Intimately connected FP device
Single-tone class B power measurement at 4 GHz with Vds=40 V
Noise characterization (I)
Noise performance of non-field-plated devices, normal field-plated devices and Intimately connected field-plated devices.
4 6 8 10 12
0.8
1.2
1.6
2.0
2.4
2.8
3.2
3.6N
Fm
in (
dB)
Frequency (GHz)
non-FP device normal FP device intimately connected FP device
-15
-10
-5
0
5
10
15
20G
a (dB)
NFmin and Ga were found by sweeping Ids and Vds.
Noise characterization (II)
0.5 0.6 0.7 0.8 0.9 1.0 1.10
3
6
9
12
15
5 GHz
12 GHz
Ga
(dB
)Field-plate length (m)
0.5 0.6 0.7 0.8 0.9 1.0 1.10.4
0.8
1.2
1.6
2.0
2.4
12 GHz
5 GHz
NF
min (
dB)
Field-plate length (m)
Noise performance of field-plate devices with different field-plate lengths.
Rg decreases as field-plate length increases. (NFmin decreases.)
Cgd increases as field-plate length increases. (NFmin increases.)
Conclusion
Two field-plated device structures were characterized and analyzed.
The structure with intimately connected field-plate helps to reduce the gate resistance, but the larger Cgd reduces the gain and efficiency.
The noise performance of field-plated device is better than non-field-plated device.