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GaN Power Amplifiers for Next
Generation Mobile Base-Station
张乃千 Naiqian Zhang March 17th, 2016
2
Requirements for PAs in mobile base-stations
GaN performance in 4G+ to 5G communications
Short introduction to Dynax Semiconductor
Technology challenges to further improve GaN
Summary
3 5G: Connecting Everything
Wireless world research forum, 2014
4 Scenarios of Connectivity
5G Connectivity Scenarios and Challenges
Scenarios Challenges
Seamless Wide-Area Coverage
√ Anywhere anytime data rate: 100 Mbps
High-Capacity Hot-Spot
√ User data rate: 1 Gbps √ Peak data rate: 10s of Gbps √ Traffic volume density: 10s of Tbps/km²
Low-Power Massive-Connection
√ Connection density:106/km² √ Ultra-low power consumption and Ultra-low cost
Low-Latency High-Reliability
√ Air interface latency: 1 ms √ End-to-end latency: 1 ms √ Reliability: nearly 100%
5 Cell Size and Transmitted Power
Macro-cells provide basic coverage for all. (< 1 Gb/month data plan)
Small Cells handle coverage complain and hotspot data. (3-5 Gb/month data plan)
Wifi cover indoor (with limited outdoor) hotspots.
Base Station Category
Power for Base Stations
Power from Amplifiers
Femtocell < 0.25 W < 2 W
Picocell 0.25-0.5 W > 2 W
Microcell 1-5 W > 10 W
Metrocell 5-10 W > 40W
Macrocell > 10 W > 100 W Huawei MBB insight fellow voice, 2014
6 Spectrum and Cell Size
2300-6000 MHz
200 Mbps speed
Metro- and Micro- Cells
55-85 GHz
2 Gbps speed
Pico- and Femto- Cells
20-50 GHz
1 Gbps speed
Micro- and Pico- Cells
700-2300 MHz
100 Mbps speed
Macro- and Metro- Cells
Huawei MBB insight fellow voice, 2014
7 Requirements for Power Amplifier
Many available bands from 700 MHz up to 85 GHz.
Software defined radio architecture for base-station.
Higher frequency-power product. Up to 6 GHz for primary bands, and 85 GHz for complimentary bands.
Wider band-width. 400 MHz for primary bands, and 5 GHz for complimentary bands.
Higher efficiency. 60% for primary bands.
8 Base Station Power Consumption
Only 15% total energy consumption of wireless network converted into transmitted information.
Power amplifiers use about 65% energy of a base-station.
If the PA efficiency increases from 50% to 60%, about 6.7 TWh energy will be saved.
Nokia Networks, 2012
9
Requirements for PAs in mobile base-stations
GaN performance in 4G+ to 5G communications
Short introduction to Dynax Semiconductor
Technology challenges to further improve GaN
Summary
10 Three Generations of Semiconductor
High Efficiency
High Power Density
Low Capacitance
Wide Band-Width
Small Size
Property Si GaAs GaN
Energy Gap(eV) 1.11 1.43 3.4
Critical Electric Field
(MV/cm) 0.6 0.5 3.5
Charge Desity
(1x1013/cm2) 0.3 0.3 1
Saturation Velocity
(1x107 cm/s) 1 1.3 2.7
Mobility (cm2/V·s) 1300 6000 1500
Thermal Conductivity
(W/cm·K) 1.5 0.5
1.5
(3.4)
High Voltage
High Current
High Frequency
High Junction Temperature
GaN is the ideal semiconductor for high efficiency, wide-band RF power amplifiers.
Compound & Advanced Si, vol. 9, 2014
11 Efficiency Comparison: Si, GaAs, GaN
At 1.8GHz and 7dB output PAR, LDMOS efficiency is 32% and GaN is 37%, while that of GaAs is only 14%.
With low thermal conductivity, GaAs total output power is also not high.
GaAs: Fujitsu
Silicon LDMOS: NXP A2T18S160W31SR3
GaN: NXP A2G22S160-01SR3
12 GaN for 4G: Higher Efficiency
GaN’s advantage of higher efficiency over LDMOS is more prominent for higher frequency.
Freq (MHz)
Gain (dB)
Pout (dBm)
Adj_L (dbc)
Adj_U (dBc)
Eff (%)
2530 14.7 47.4 -29.6 -30.1 51.9
2580 14.6 47.4 -30.2 -31.4 52.6
2630 14.4 47.4 -30.5 -31.1 52.4
Efficiency improvement: 8%
Asymmetric Doherty PA, Pout=55W 3*20MHz LTE, PAR=7.5 dB
NXP LDMOS: AFT26H250W03SR6
GaN: DX1H2527240F DX1H2527170F
13 GaN for 4G+: Wide Band
To achieve 100 Mbps data rate, carrier aggregation technology is used to combine several 20 MHz (or wider) signals into a 400 MHz band signal.
For tens of watts average power, needs at least 4 LDMOS amplifiers to cover from 1800 to 2200 MHz, while only one GaN device will do the same job.
CREE GaN: CGHV22200 NXP LDMOS: A2T18S162W31SR3
14 Wide-band GaN PA and MMIC
Wide-band Class-BJ PA
1.7 - 2.8 GHz
Psat : > 20 W
PAE: > 52%
Gain : 10 dB
High Power MMIC
2.7 - 3.5 GHz
Pout: > 60 W
PAE: > 42 %
Gain: 25 dB
CETC 13th Inst., 2014
E. Ture, Proc. 44th European MW Conf., 2014
15 Wide-band GaN Doherty Amplifiers
RWTH Aachen: 10 W Doherty, 2.0 – 2.7 GHz
Efficiency = 55% at PAR = 7.5 dB from 2.0 to 2.4 GHz.
Alctel: 20W Doherty, 2.0 – 2.8 GHz
Efficiency = 50% at PAR = 7 dB from 2.1 to 2.6 GHz.
16 4G+: 3.4 – 3.8 GHz Applications
Present 4G uses 2.5 – 2.7 GHz band, but under heavy pressure for wider band-width.
For higher frequency and wider band-width, GaN starts to show overwhelming advantages comparing to LDMOS.
Freescale LDMOS: MRF7S38075 Qrovo GaN: QPD3601
The efficiency of a 150W GaN device is 53%, while that of a 100W LDMOS is only 40%.
And more: bandwidth and linearity.
17 4G+: Video Bandwidth
Aside from signal bandwidth, wider VBW helps Digital Pre-Distortion (DPD) to improve system linearity, especially for wide-band signal.
VBW of a GaN device is 100 to 400 MHz, while LDMOS is less than 40 MHz.
Freescale GaN: A2G22S160
Freescale LDMOS: MRF7S38075
40 42 44 46 48 50 528
10
12
14
16
18 Gain
Drain Efficiency
Pout(dBm)
Ga
in(d
B)
10
20
30
40
50
60
Dra
in E
fficie
ncy
(%)
GaN: DX1H3438120F
VBW = 400 MHz
18 Si, GaAs, GaN in Millimeter Wave PA
In millimeter wave, Si CMOS hardly achieves 0.1 W power and 10% efficiency.
GaAs may obtain 2 W power and 16% efficiency.
GaN can output over 5 W power and 28% efficiency.
2004, A. Betti-Berutto etc.
2015, IEEE, Yuanliang etc.
Freq. (GHz) TriQuint GaN MMIC
19 GaN: Integrates the Front End
GaN is suitable for every component in a RF front system (millimeter wave or 5G):
Wide-band, high efficiency PA
High power, wide-band SWITCH
Low noice, high power VCO
High reliability, wide-band LNA
GaN SoC
20 GaN RF Device Market Forecast
GaN market share might surpass LDMOS by 2020.
GaN price will drop steadily with increasing deployment volume.
Yole Development, 2014
LDMOS price forecast ABI, 2013
21 GaN MMIC Market
In WRC-15, available bands for 5G spread from 20 to 90 GHz. GaN draws attention in base-station applications.
“Engalco Research Resource” forecasts:
GaN gains share in power MMIC.
SiGe expands in handheld terminals.
GaAs remains dominant, but being squeezed by above two.
Engalco Research Resource, 2013
22
Requirements for PAs in mobile base-stations
GaN performance in 4G+ to 5G communications
Short introduction to Dynax Semiconductor
Technology challenges to further improve GaN
Summary
23 Introduction to Dynax
Established since 2007, Dynax is dedicated to GaN RF power devices.
From epitaxial growth, wafer fabrication, to device packaging.
Started volume shipment from Q4 2015.
24 Products for Mobile Communications
Operating Voltage: 48V. Test Condition: 100us, 10% Duty Cycle Pulse
Frequency Output Power Power Gain Drain Efficiency
3.4-3.6 GHz 140 W 16 dB @ 3.5 GHz 63% @ 3.5 GHz
3.4-3.6 GHz 100 W 17 dB @ 3.5 GHz 65% @ 3.5 GHz
2.5-2.7 GHz 240 W 18 dB @ 2.6 GHz 67% @ 2.6 GHz
2.5-2.7 GHz 170 W 19 dB @ 2.6 GHz 71% @ 2.6 GHz
2.5-2.7 GHz 120 W 19.5 dB @ 2.6 GHz 72% @ 2.6 GHz
1.88-2.025 GHz 240 W 20 dB @ 1.88 GHz 70% @ 1.88 GHz
1.88-2.025 GHz 170 W 21 dB @ 1.88 GHz 74% @ 1.88 GHz
1.88-2.025 GHz 120 W 21.5 dB @ 1.88 GHz 75% @ 1.88 GHz
0.7-2.7 GHz 50 W 18 dB @ 2.6 GHz 72% @ 2.6 GHz
0.7-2.7 GHz 30 W 18 dB @ 2.6 GHz 72% @ 2.6 GHz
0.7-2.7 GHz 10 W 18 dB @ 2.6 GHz 72% @ 2.6 GHz
25 Development of Power Switches
Power devices are fabricated on GaN-on-Si substrates.
Samples are available upon request for industry partners.
Device leakage and dynamic Ron are under well control.
Part Number Substrate Vds (V) Ids (A) Description
GP2000D01T Sapphire 2000 1 GaN HEMT, Normally-on
GP200D25T Si 200 30 GaN HEMT, Normally-on
GP600D10T Si 600 10 GaN HEMT, Normally-on
GP600E10T Si 600 10 GaN HEMT, Normally-off
GP600S10D Si 600 10 GaN Diode
26
Requirements for PAs in mobile base-stations
GaN performance in 4G+ to 5G communications
Short introduction to Dynax Semiconductor
Technology challenges to further improve GaN
Summary
27 Challenge I: Thermal Management
28 GaN on CVD Diamond
Flip-bond GaN epitaxial to a temporary carrier substrate.
Remove the original growth substrate.
CVD deposit Diamond to the back of GaN epi.
Detach the temporary carrier and obtain GaN_on_Diamond.
Element 6: F. Ejeckam et al., LEC 2014
29 GaN_on_Diamond Performance
With half of the thermal resistance compared to GaN_on_SiC, the allowed power density is nearly doubled for GaN_on_Diamond.
TriQuint: D.C.Dumka et al., ITHERM Conf. 2014
30 AlN Passivation
AlN passivation layer clearly reduces thermal resistance of a GaN HEMT over SiN or SiO2 passivation.
Simulated thermal resistance of GaN-based HEMT with SiO2/SiN passivation layer
Simulated improvement of thermal resistance of GaN-based HEMT with AlN passivation layer
measured thermoreflectance mapping of GaN HEMT at 1.25 W/mm dissipated power (SiO2/SiN coated)
measured thermoreflectance mapping of GaN HEMT at 1.25 W/mm dissipated power (AlN coated).
III-V Lab: R.Aubry et al., LEC 2014
31 Phase-Changing Material
PCM is sealed in a cavity underneath device active region by Indium foil.
MIT/ACT: D. Piedra et al., SEMI-THERM Sympo. 2012
32 C/C Composit Package
NEC: Y. Han et al., TCPMT. 2012
GaN-FET model for finite element thermal simulation (unit finger).
IR microscopy temperature distributions in the active regions for GaNFETs. (a) Temperature distribution of device assembled in C/C composite based package. (b) Assembled in CuMo-based package.
Volume model of GaN-FET assembled in the C/C composite-based package for finite element thermal simulation.
33 Integrated Thermal Array Plate
ITAP improves thermal conductivity by 55%, compared to AuSn die attach.
HRL: A. Margomenos et al., ITHERM Conf. 2014
34 Challenge II: Freq. & Power Response
Power devices not only pursue small signal frequency response, but pay more attention to output power level, efficiency, gain and even bias voltage.
With traps in GaN material structure, and strong polarization effect, special measures are taken to improve above parameters.
Freq = 3.5 GHz
Vd = 50 V
Psat : 50.2 dBm
Eff(d) : 68%
Gain : 18 dB
Mitsubishi: Akira Inoue, IWS 2015
35 Thin AlN Barrier
Thin AlN barrier improves gate aspect ratio, and helps high frequency response.
50% efficiency at 18 GHz.
Schematic cross section of the AlN/GaN DHFET on SiC substrate(right) and SEM picture of the gate foot (left)
Measured PAE versus power density at 10 and 18 GHz from a 0.15×50 μm2 AlN/GaN
DHFET on SiC substrate
CW power sweep tuned for PAE at 10 GHz and VDS = 15 V of a 0.15×50
μm2 AlN/GaN DHFET on SiC substrate
CW power sweep tuned for PAE at 18 GHz and VDS = 25 V of a 0.15×50
μm2 AlN/GaN DHFET on SiC substrate
IEMN/Padova: F. Medjdoub et al., ESSDERC 2014
36 AlInN Barrier with GaN Passivation
GaN cap layer above AlInN reduces current collapse (dispersion), thus increase power density by 22% at 10 GHz, compared to using AlN cap.
Less dispersion also enables higher biasing voltage, further increasing power density by 27% at 40 GHz.
Large-signal measurements at 10 GHz for HEMTs having LSD =4 μm and LG = 200 nm fabricated on AlN- (a) and GaN-capped (b) epilayers.
Large-signal measurements at 40 GHz for AlN-capped HEMTs having LG = 200 nm and LSD = 4 μm biased at (VGS, VDS) = (−4.7, 20) V.
Large-signal measurements at 40 GHz for a GaN-capped HEMTs having LG = 200 nm and LSD = 4 μm, biased at (VGS, VDS) = (−2.6, 35) V.
(ETH-Zürich) S. Tirelli et al., TED 2013
37 InGaN Back Barrier
InGaN back barrier improves channel charge confinement, reducing output conductance, thus increases efficiency at high frequency.
Pout = 20 dBm at 90 GHz.
Fujitsu: K. Makiyama et al., LEC 2014
38 Self-Aligned Gate
Self-aligned gate to reduce gate-drain distance.
Re-grown n+ GaN ohmic to reduce contact resistance.
Ft/fmax = 310/364 GHz for 20 nm gate length.
Highly-scalable self-aligned gate (SAG) GaN DH-HEMT technology with n+GaN re-grown ohmic contacts.
Vertically-scaled DH-HEMT epitaxial structures (a) for D-mode operation and (b) for E-mode operation
HRL: K. Shinohara et al., IEDM 2011
39 Air-bridged Field-Plate
Air-bridged field-plate reduces Cgs, thus improves frequency response.
Air-bridged field-plate also helps temperature stability of breakdown voltage.
Zhejiang Univ.: Xie Gang et al., Chin. Phys. 2013
40 Challenge III: Reliability
G Meneghesso, et al, JMWT 2010
41 Improve Material Quality
Traps in epitaxial layers result in instability of Vth.
Optimization of material growth reduces traps, and lowers Vth shift to as low as 0.14 V.
TSMC: K.Wong et al., ISPSD 2014
42 Surface Treatment Before Passivation
Due to strong polarization, deep level traps exist on GaN surface.
Proper passivation with selected dielectrics can reduce the surface traps or make them shallower.
Dedicated surface treatments will further reduce dielectric/GaN interface traps, improving device reliability.
TSMC: Y. Lin et al., ISPSD 2014
43 Gate and Passivation Dielectric
HfO2/Al2O3 double layer Gate dielectric.
H2O2 surface treat-ment to Gate area.
(a) IDS and gm, max, and (b) IGD degradation characteristics of the studied devices biased at VGS = 5 V and VDS = 15 V for 48 hours.
NCKU: B. Chou et al., ISEEE 2014
44 Field-Plate Optimization
Field-plate mitigates electric field peak at the drain-side gate edge, improving reliability and reducing current dispersion.
Multiple field-plates.
Slant field-plate.
Recessed field-plate.
HRL: S.G. Khalil et al., RPS 2014
45
Requirements for PAs in mobile base-stations
GaN performance in 4G+ to 5G communications
Short introduction to Dynax Semiconductor
Technology challenges to further improve GaN
Summary
46 Summary
Nowaday and future mobile communications ask for higher frequency, wider bandwidth, higher efficiency power amplifiers for base-stations.
Due to outstanding physical properties, GaN RF devices show prominent characteristics used in power amplifiers, especially as the frequency starts to expand to 3.5 GHz.
GaN industry is ready to support power amplifier evolving in mobile base-stations in volume.
There are (a lot of) things to do to make GaN better!
47
苏州能讯高能半导体有限公司 江苏省苏州昆山国家高新区晨丰路18号 邮编:215300 电话: 0512-36886888
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