Transcript GaN HEMTs with Novel integrated Passive Components

Characterization of two FieldPlated 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 Engineering
University 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
Motivation




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.
Field-plated device structures (I)
Field Plate
SiN
AlGaN
Source
Gate
Drain
2DEG
GaN
Field-plate length



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-plated device structures (II)
Gate & Field Plate
SiN
AlGaN
Drain
Source
2DEG
GaN
Field-plate length


Gate and field-plate are intimately connected.
RIE etching of SiN may damage the AlGaN surface.
Field-plated device structure
Intimately connected FP
GaN HEMTs
Normal FP GaN HEMTs
Gate
Field-plate
Gate
SiNx
Field-plate
SiNx
Drain
Source
Field-plate length
AlGaN
2DEG
GaN

Drain
Source
Possible affected parameters: Rg, Cgd
Field-plate length
Gate resistance Rg
First order approximation:
1
W
Rg  Rg
3
L
Rg modeling
Rfp
Simplified
Model
Distributed
EM Model
Rg
Simulated by EM model:
Rg = 1.6 Ω for normal FP
structure.
Rg = 1.33 Ω for intimately
connected FP structure.
Simulation on a
75 µm gate finger
with 0.7 µm fieldplate length.
∆Rfp
∆Rg
EM simulation at 4 GHz
Normal FP device
Intimately connected
FP device
Field-plate
Field-plate
Gate finger
Gate finger
Simulation on a
75 µm gate finger.
0.7 µm field-plate
length.
DC measurement
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 layer
n0 = 9.96x1012 cm-2;
Hall mobility ~1450 cm2/Vs
intimately connected field-plated device
normal field-plated device
Current Density (A/mm)
1.2
1.0
0.8
0.6

0.4
0.2
0.0
0
5
10
Vds (V)
15
20

Intimately connected FP
device has higher pinch-off
voltage.
Both devices have similar Idss
at Vgs=0 V.
SP measurement (ft, fmax)
Small-signal characterization
of two field-plated GaN HEMTs
50
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
h21, U (dB)
40
30
Normal FP device
ft = 21 GHz
fmax = 51 GHz
Intimately connected
FP device
20
10
ft = 20 GHz
fmax = 40 GHz
0
1
10
Frequency (GHz)
100
Small signal model and
simulation
Lg
Rg
Gate
+
V
Rgd
Ri
Rd
Cgd
Drain
gmVe-jωτ
Rds
Cgs
-
Measurement vs. Simulation
Ld
S11
S12
Cds
-1.0
Rs
-0.5
0.0
Ls
Source
S21
S22
ADS-based parameter extraction
routines. Models incorporate
dominant parasitics and losses.
Freq. (50 MHz to 30 GHz)
0.5
1.0
Intrinsic small signal parameters
Ri(Ω)
Normal FP device
Intimately connected
FP device
Rds(Ω)
Rgd(Ω)
Cgd(fF)
7.178 1297.6
22.882
45.497 14.842
8.276
15.374
70.885 16.340
Rs(Ω)
Rg(Ω)
Cgs(fF)
960.0
gm(S)
Cds(fF)
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
Single-tone class B power measurement at 4 GHz with Vds=40 V
Intimately connected FP
device
Normal FP device
50
Gt(dB)
80
Peak PAE=70.9%
70
40
Peak PAE=60%
60
40
50
40
PSAT=10.1W/mm
20
30
20
10
0
5
10
Pin(dBm)
15
10
20
PAE(%)
30
30
40
PSAT=12.9 W/mm
20
30
20
10
10
0
5
10
15
Pin(dBm)
20
25
PAE(%)
50
Pout(dBm),
70
60
Pout(dBm),
Gt(dB)
50
Noise characterization (I)
Noise performance of non-field-plated devices, normal
field-plated devices and Intimately connected field-plated
devices.
20
3.6
non-FP device
normal FP device
15
intimately connected FP device
10
2.8
2.4
5
2.0
0
1.6
-5
1.2
Ga (dB)
NFmin (dB)
3.2
-10
0.8
-15
4
6
8
10
12
Frequency (GHz)
NFmin and Ga were found by sweeping Ids and Vds.
Noise characterization (II)
2.4
15
2.0
12
5 GHz
12 GHz
1.6
Ga (dB)
NFmin (dB)
Noise performance of field-plate devices
with different field-plate lengths.
1.2
0.8
5 GHz
0.4
9
6
12 GHz
3
0
0.5
0.6
0.7
0.8
0.9
1.0
Field-plate length (m)


1.1
0.5
0.6
0.7
0.8
0.9
1.0
Field-plate length (m)
Rg decreases as field-plate length increases. (NFmin decreases.)
Cgd increases as field-plate length increases. (NFmin increases.)
1.1
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.