vertical power electronic devices based on bulk gan...

Vertical Power Electronic Devices Based on Bulk GaN Substrates

Dr. Isik C. Kizilyalli, CTO and Founder

Avogy, Inc.

677 River Oaks Parkway, San Jose, CA 95134

Partially funded by ARPA-E SWITCHES (Dr. T. Heidel)ONR-N00014-14-C-0087 (Dr. P. Maki)

Avogy (San Jose, CA): Advancing Energy Efficiency

Vision and Mission for Vertical GaN Devices

Power Supplies*

Solar EV WindMotorDrive

UPS/Grid/Rail/Ship

Voltage (V) 600-1200 600 - 1200 600 - 1200 1200 - 3300 600 - 1200 1200 - 3300

Current (A) 0.5 – 20A 1 – 75A 50 – 200A 100 – 200A 2 – 100A 100 – 400A

Devices in Systems

Today

Si MOSFETSi PN

SiC SBD

Si MOSFETSi IGBTSi PN

SiC SBD

Si IGBTSi PN

Si IGBTSi PN

Si IGBTSi PN

Si IGBTSi Thyristor

Si PIN

Vision:Every power system in the world will utilize a vertical GaN device, circuit, technology, or science developed by 2030

Mission:The most efficient and compact power systems in the world are enabled by vertical GaN technologies

*Smart homes, LED drivers, laptops, mobile devices, data centers

Power Device Figure of Merit Curve

4

4BV2/Ron,sp=εμnEC3

1. Ron,sp= WD/qμnND

2. WD=2BV/EC

3. BV=εEC2/2qND

GaN-on-GaN means less chip areaFor a given on-resistance (Ron) of 10mΩ:

500mΩ, 50 chips 40mΩ, 4 chips 10mΩ, 1 chip

GaN-on-GaNSiC

GaN-on-SiSi-MOSFET

GaN-on-GaN lowers die costwhile improving Ron ×Coff

switching characteristic

5

Schematic of a Boost Converter

Switch frequency increases → Optimum L and C Decreases

Vi is boosted to Vo

Volume ≈ 4 in3

Weight = 5 oz.Efficiency 92%

World’s Smallest 85W Adapter

Volume ≈ 10 in3

Weight = 9 oz.Efficiency 90%

Volume 2.5 in3

Weight 4 oz.Efficiency 95%

Avogy Proof of Concept – 4in3Apple 85W Adapter Target

Limited by magnetics (inductors, transformers, capacitors) and thermal issues

DEVELOP THE ECOSYSTEM

Data Center OCIWind inverterAC-DC converterSolar inverter

Wide band gap semiconductors benefits power systems

Dramatically smaller, cheaper magnetics

Higher efficiency = 67% less heat dissipated

Higher reliability = Can operate at higher temperature (175oC)

Power switching frequency increases from kilohertz to megahertz

10u compute + 3u power

12u compute + 1u power

Power

93 ft3

43 ft3

10kW, 4213 in3,, 78 lbs

10kW, 528 in3,, 25 lbs

100 in3

25 in3

WOCSEMMAD 2015

Bulk GaN vs. GaN-on-Si/SiCAttributes GaN on Si GaN on SiC GaN on Bulk-GaN

Defect Density (cm-2) 109 5x108 103 to 106

Lattice Mismatch, % 17 3.5 0

CTE Mismatch, % 54 25 0

Layer Thickness (µm) < 5 < 10 > 50

Breakdown Voltage (V) < 1000 < 2000 > 5000

Avalanche Capability No No Yes

Device Types Lateral Lateral Vertical and Lateral

Microscopy and Growth

Vertical FET Advantages over Lateral HEMTs

• Grow thick GaN layers: Drift region BV >> 1200V• Reduced number of defects: Improved Reliability, Large EC

• Breakdown occurs in bulk and not surface, avalanche capability• Current flow vertical and not parallel to surface• Realize high current (>> 20A) devices, Normally-off operation• For the same Rdson , a VFET is smaller than a HEMT

Drift Region Design

TCAD Simulations using Ec = 3.3 MV/cm and μ n = 1100 cm2/V-s

Maximize breakdown voltage and minimize on-resistance

Edge Termination Design• Junction Termination Extension (JTE): Novel Avogy design*

• TCAD simulations guided the design for 600V to 5kV device

• 5kV Final design is 25 guard rings

• Spreading the potential over a wide area outside the edge

• Use ion implantation to implement the structure

• Field plates using dielectrics is not as effective

2D-Electrostatic Potential (-5000V=Anode) 2D-Electric Field

*US Patents: 8,716,716 and 8,741,707

N+ GaN

N- GaN Drift Region (6-40μm)

P+ GaNIsolation Isolation

Cathode (+)

Anode (-)

P-N Diode Topology

2600V PN Diode with Rsp=2.0 mΩ-cm2

0

0.005

0.01

0.015

0.02

0.025

0 1000 2000 3000

Cu

rren

t (A

)

Reverse Bias (V)

Avalanche Capability

0.0

2.0

4.0

6.0

8.0

10.0

0 2 4 6 8 10

Forw

ard

Cu

rren

t (A

)

Forward Voltage (V)

Epi and Device Fabrication at Avogy

0

2

4

6

8

10

12

14

0

20

40

60

80

100

120

140

0 500 1000

Cap

acit

ive

Ch

arge

(n

C)

Cap

acit

ance

(p

F)

Reverse Voltage (V)

Avalanche capability

• GaN devices do have avalanche capability

• PN diodes with 1700V epi design in TO-220 packages

• Current pulse width of 30ms, up to 15mA

• Avalanche energy in each pulse > 900mJ

0

2

4

6

8

10

12

14

16

0 500 1000 1500 2000 2500

IR (

mA

)

VR (V)

Temperature Dependence of Breakdown Voltage

16

𝐵𝑉 𝑇 ≈ 𝐵𝑉25°𝐶 1 + 𝛼∆𝑇 where 𝛼 ≈ 6 × 10−4 °𝐾−1

Inductive (100μH) load testing: 1.5A at 1200V (0.7mm2)*

Scope traces showing the diode current (pink) and DUT voltage (yellow) *Survive 10A at 1200V (8mH)

DUT

Schottkydiode

InductorCPower Supply

PulseGenerator

DUT diode avalanching to 1.5A from a 10 mH inductor

DUT diode avalanching to 10A from a 0.1 mH inductor.

UIL circuit diagram

Inductive Load Avalanche testing of GaN diodes

PD45-1

Imax L (H) Pmax (W) E (mJ) V @ Imax V @ Imax/2

0.5 1.00E-03 622 0.125 1244 1264

1 1.00E-03 1244 0.5 1244 1320

2 1.00E-03 2530 2 1265 1445

0.5 1.00E-02 632.5 1.25 1265 1365

1 1.00E-02 1280 5 1280 1500

2 1.00E-02 2560 20 1280 Breaks at 1780V-1.5A

0.1 1.00E-01 128.4 0.5 1284 1300

0.2 1.00E-01 260 2 1300 1365

0.5 1.00E-01 650 12.5 1300 1465

50k pulses at 1kHz with heat sinking Measurements at the last pulse

Imax L (H) Pmax (W) E (mJ) V @ Imax V @ Imax/2

0.2 1.00E-01 256 2 1280 1350

1 1.00E-02 1260 5 1260 1520

Vertical GaN Diodes: Reverse Recovery

19

ID (5A/div)

Fast Si

Diode

Vertical GaN

Diode

Double Pulse Test results at VR=600V, If=5A

Comparing AVD05A120A with STTH512

Vertical GaN Diodes: Customer Testing

Diode turn-off 800V 15A and 25°C

10.3μJ Loss for Avogy Diode

40.6μJ Loss for SiC Diode

20

Temperature Dependent Leakage Current

3.7kV Diode with Rsp=2.95mW-cm2

• ND ≈ 5x1015 cm-3 (measured by C-V)• Drift layer thickness is 40μm• Edge termination designed for 5kV• Next ND ≈ 2-3x1015 cm-3 and 50μm

Measured Forward I-V PN-Diode Drift Region= 40μm

mn =1760(TL/300)-3/2 cm2/V-sElectron mobility in low-defect GaN > 1700 cm2/V-s

Diode Area ≈ 0.12 mm2

Minority Carrier Lifetime (τp ≈ 2ns)

I=400A for BV=700V PN Diodes

Agilent high power network analyzer

(Pulsed at 100μs)

J=2.5kA/cm2Demo 100A DC and BV=1400V

Bulk GaN wafers: Question of Availability

• 2” and 4” bulk GaN wafers are available

• Roadmap to 6” wafers

• Demand driven by optoelectronics

• Prices decreasing and quality improving

• Gave us a 3 year and 100 (42 issued) patent lead over the competition

Excerpt from ISPSD 2012 tutorialExcerpt from ISPSD 2011 plenary talk

26

Bulk GaN Suppliers

Supplier Method Size TDD (cm-2)

SEIHVPE 2", 4", 6" 104 - 106

Lift-Off 2", 4", 6" 104 - 106

MCC HVPE 2", 4", 6" 5x106

Soraa SCORA/AT 2", 4" << 5x106

Lumilog HVPE 2" 1x107

HCI HVPE 2", 3", 4" 3x106

FKK HVPE 2", 4" 3x106

Kyma HVPE 18x18mm < 5x106

Ammono AT* 1x1 cm, 1", 1.5" < 104

NGK 2", 4" 1x107

Bulk GaN Supply

1200-1700V PN Diode Trend Charts

# of diodes ≈ 40000

Avogy Inc. | Confidential under NDA | 4/19/2015 30

Test Lot Qty 168hr 500hr 1000hr Notes

HTRB(150˚C, 960V)

PD59 77 0/77 0/77 0/77 HTRB device qualification completeFailure mechanism identified and solved Substrate specification patented

PD66 77 0/77 0/77 0/77

PD67 77 0/77 0/77 0/77

THB(85˚C, 85%RH, 80V)

PD59 77 0/77 0/77 0/77 THB device qualification complete

PD60 77 0/77 0/77 0/77

PD66 77 0/77 0/77 0/77

PD77 77 0/77 0/77 0/77

HTOL

PD67/68 77 0/77 0/77 0/77 Working with substrate vendors/specs1. Pass HTOL with Substrate Vendor A,B2. Fail HTOL with Substrate Vendor C, D• No change in BV, Imax, or Ron• Shift in leakage current

PD77 77

PD77 77

PD77 77

TCT(-65˚C to 150˚C,

100/500/1000cyc)

PD68 77 0/77 0/77 0/77 TCT device qualification completePD77 77 0/77 0/77 0/77

PD77 77 0/77 0/77 0/77

PD78 77 0/77 0/77 0/77

PD76 77 0/77 0/77 0/77

1200V PN Diode Qualification/Reliability

Can you guess which die will yield and be reliable

• Devices in the top row consistently have:• Lower reverse currents at VR > 500V • Pass HTRB tests (-980V or -1360V at 150-175°C)

• Surface morphology good predictor of yield and reliability

Comparison between prediction with test data

Correlation valid for all substrate vendors, MOCVD tools

Device High Temperature Operating Life (HTOL)

Diode Forward Current HTOL Test• Superior material quality• Tjn = 275°C with ID=20kA/cm2

0 500 1000 1500 2000

Stre

ss V

olt

age

(V

) 1

V/d

iv

Time (Sec)

Constant Current Aging: I = 20kA/cm2

33

GaN p-n diodes on SCORA wafers

No JTE Device BV = 500-680VSub-threshold ideality n=25 substrates 13x13 mm2

Device Area = 0.11mm2

SCORA Substrates as Received

Diodes at Test

Parameter Extraction: Measurement versus Simulation

Forward current: Best fit obtained with τp = 1 ns and μn = 900-1000 cm2/V-s

Sensitivity Analysis: τp

WOCSEMMAD 2015

Substrates from Na-flux method

WOCSEMMAD 2015

Vertical GaN FET Devices: Keep the Structures Simple

Bardeen-Brattain Transistor, Bell Labs 1947

2D Simulation of Current Flow

39

Vertical FET Structure

40

FET Layout and Process

Source

Gate

Pad

Buried p-layerGate

channel channel

FET Total Area

0.17mm2

FET Active Area

0.13mm2

41

Multiple MOCVD Growths for Transistor

42

1.5kV 2.2mΩ-cm2 ‘Normally-Off’ Vertical GaN FET

43

Performance Gap Between FET and P-N Diode

44Need to Improve the BV and RDS,ON for the FET

Vertical FET Structure II

45

47

Smart 3-in-1 Charging

Power your laptop

and two mobile

devices -

simultaneously.

Zolt also powers your

GoPro, portable

speakers, camera

and more.

© Copyright 2015 Avogy Inc. | Introduction for Investors | Proprietary & Confidential

Compatible w/ 90%+ of

Laptops

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