gan power amplifiers for next generation mobile base gan power amplifiers for next generation mobile...

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





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





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





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





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

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