TriQuint Semiconductor, Inc. Increased channel temperature: the next challenge limiting RF performance on GaN on SiC FET technology and strategies to reduce it. Sep 3, 2013 TriQuint Semiconductor, Inc.

TriQuint Semiconductor, Inc. Outline Introduction The thermal limitation Approaches The obvious approach: A Diamond substrate The not so obvious approach: A new circuit design approach Summary TriQuint Semiconductor, Inc.

TriQuint Semiconductor, Inc. Disclosures This is not a talk on Semiconductor Hetero-structures, but a talk on the limitations of one of such structures as a product. This is not a talk with great detailed results, but a talk about an idea. This is a talk on thermal improvements at the chip level. There is a parallel world on thermal improvements at the package level that I will not cover here. Part of the work presented here is supported by TriQuint’s DARPA NJTT Program, Contract #W31P4Q-12-C-0067 TriQuint Semiconductor, Inc.

TriQuint Semiconductor, Inc. Outline Introduction The thermal limitation Approaches The obvious approach: A Diamond substrate The not so obvious approach: A new circuit design approach Summary TriQuint Semiconductor, Inc.

Barrier Discontinuity Substrate Thermal Conductivity Introduction 2008 TriQuint’s Technology Roadmap GaN: A high power density, high voltage technology CREE demonstrates 40 W/mm on GaN on SiC Nitronex demonstrates 10 W/mm on GaN on Si TriQuint releases a 40V technology TriQuint releases a 48V technology GaAs GaN on SiC Band Gap 1.42 eV 3.50 eV VSat 1.2 107 cm/s 2.5 107 cm/s Barrier Discontinuity ~0.2 eV 0.5 eV Substrate Thermal Conductivity 51.5 W/mC 400 W/mC TriQuint Semiconductor Inc,

TriQuint Semiconductor Inc, Introduction 2013 TriQuint’s Technology Reality GaN: A high power density, high voltage technology GaAs GaN Products In spite of good reliability, GaN on SiC is being used well below its performance potential WHY? TriQuint Semiconductor Inc,

THE NEW LIMITING FACTOR ON RF POWER DEVICES Introduction NOT SURPRISING !!!! The typical heat flux at the GaN-SiC interface is ~ 100 times larger than the heat flux at the surface of the sun The typical heat flux at the GaN on SiC – package is similar to the heat flux at the surface of the sun HEAT DISSIPATION : THE NEW LIMITING FACTOR ON RF POWER DEVICES TriQuint Semiconductor, Inc.

TriQuint Semiconductor, Inc. Introduction Traditional chip level approaches to thermal management at the chip level Thermal Vias Thinning Substrates In GaN on SiC, none of those approaches is effective Thermal vias have lower thermal conductivity than SiC and do not spread the heat Thinning substrates is only effective if the thermal conductivity of the package is higher than that of the substrate, which is not the case in GaN on SiC TriQuint Semiconductor, Inc.

TriQuint Semiconductor, Inc. Outline Introduction The thermal limitation Approaches The obvious approach: A Diamond substrate The not so obvious approach: A new circuit design approach Summary TriQuint Semiconductor, Inc.

The obvious approach: RF Power limited by the substrate NOT by the FET The Diamond Substrate Gedanken Experiment. “The role of the substrate” Performance-Reliability Space GaN on GaAs GaN on Si GaN on SiC Channel Temperature (C) Dissipated Power (W/mm) RF Power limited by the substrate NOT by the FET TriQuint Semiconductor, Inc.

The obvious approach: Diamond will allow GaN to operate up to 8 W/mm The Diamond Substrate Gedanken Experiment. “The role of the substrate” Performance-Reliability Space GaN on GaAs GaN on Si GaN on SiC GaN on Diamond Channel Temperature (C) Dissipated Power (W/mm) Diamond will allow GaN to operate up to 8 W/mm TriQuint Semiconductor, Inc.

The obvious approach: GaN on Diamond process approach The Diamond Substrate GaN on Diamond process approach Si (111) GaN Protection GaN GaN Protection GaN Protection Si (111) Epoxy Si (111) Epoxy Handle Wafer Handle Wafer Deposit Protective layer GaN/Si(111) Attach temporary support Remove Si(111) substrate Transition Diamond Protection Diamond Transition GaN GaN Transition GaN Protection GaN Transition Epoxy Protection Diamond Handle Wafer Epoxy Handle wafer Handle Wafer Deposit Transition Layer Diamond Remove handle wafer Remove protective layer TriQuint Semiconductor, Inc.

TriQuint Semiconductor, Inc. The obvious approach: The Diamond Substrate Critical properties and dimensions Protection Layer Removal should not damage the GaN surface It should robust against temperature budget It should withstand chemistry budget Transition Layer Thin to minimize thermal penalty Mechanically strong to survive temperature cycling Diamond High Thermal conductivity Protection GaN Transition Diamond TriQuint Semiconductor, Inc.

TriQuint Semiconductor, Inc. The obvious approach: The Diamond Substrate Promising initial Results (Dumka et al.) Electrical Results (GaN on Diamond) DC I-V 40V 10Ghz Load Pull Thermal Results GaN on Diamond (50nm TL) GaN on SiC 50 100 150 200 0.8 1.6 2.4 3.2 P [W] ΔT [K] Peak T 50 100 150 200 250 300 0.8 1.6 2.4 3.2 P [W] ΔT [K] Peak T DARPA’s NJTT Contract #W31P4Q-12-C-0067 TriQuint Semiconductor, Inc.

The obvious approach: The Diamond Substrate Summary GaN on Diamond has already demonstrated its potential By achieving similar RF power densities as GaN on SiC on equivalent geometries in spite of more challenging surface process By lowering the temperature rise under the same power consumption However, GaN on Diamond is an emerging technology with several tough engineering problems still to solve TriQuint Semiconductor, Inc.

TriQuint Semiconductor, Inc. Outline Introduction. The thermal limitation Approaches The obvious approach: A Diamond substrate The not so obvious approach: A new circuit design approach Summary TriQuint Semiconductor, Inc.

The not so obvious approach: A new circuit design approach 2005 TriQuint’s Technology Roadmap GaN: A high power density, high voltage technology TriQuint Semiconductor, Inc

TriQuint Semiconductor, Inc. The not so obvious approach: A new circuit design approach Examples of GaN Products Product Features • Frequency: DC to 3.5 GHz • Linear Gain: >15 dB at 3.5 GHz • Operating Voltage: 28 V • Output Power (P3dB): 55 W at 3.5 GHz •Lead-free and RoHS compliant Product Features Frequency: DC to 6 GHz Output Power (P3dB): 18 W at 6 GHz Linear Gain: >10 dB at 6 GHz Operating Voltage: 28 V Low thermal resistance package Lead-free and RoHS compliant If all we care about is power ….. Why is power density important? TriQuint Semiconductor, Inc.

TriQuint Semiconductor, Inc. The not so obvious approach: A new circuit design approach Why is power density so important? Chip Size Cost Reduce Combining Losses Bandwidth Really??? TriQuint Semiconductor, Inc.

The not so obvious approach: A new circuit design approach Traditional Circuit design approach Choose Unit Cell Electrical Amplifier Design Channel Temperature Finish Change Unit Cell Increase Gate to Gate Spacing Reduce Finger Width The device is used at its full power density potential Yes No TriQuint Semiconductor, Inc.

The not so obvious approach: Instead of increasing Gate to Gate pitch We reduce Gate to Gate pitch A new circuit design approach What if: ARE YOU CRAZY!!! NO I AM NOT!!! TriQuint Semiconductor, Inc.

The not so obvious approach: A new circuit design approach Instead of increasing gate to gate pitch Reduce Gate to Gate pitch … but keep the power density per area constant Geometry: 4x100um. GtoG: 50um PDissip: 5.0W/mm =2W TBase: 25C. TPeak:80.62C Geometry: 8x100um. GtoG: 25um PDissip: 2.5W/mm =2W TBase: 25C. TPeak:58.74C That’s a 40% reduction of thermal resistance without increasing the chip . TriQuint Semiconductor, Inc.

The not so obvious approach: Instead of decreasing the finger width Increase the finger width … but keep the power density per area constant A new circuit design approach Geometry: 4x100um. GtoG: 50um PDissip: 5.0W/mm =2W TBase: 25C. TPeak:80.62C Geometry: 4x200um. GtoG: 50um PDissip: 2.5W/mm =2W TBase: 25C. TPeak:54.02C That’s a 48% reduction of thermal resistance without increasing the chip size. TriQuint Semiconductor, Inc.

The not so obvious approach: A new circuit design approach What kind of channel temperature reduction can we expect? 2W 4x100um device equivalent Depending on the bandwidth we are willing to sacrifice, the temperature increase can be limited by half. TriQuint Semiconductor, Inc.

The not so obvious approach: A new circuit design approach What do we trade? Chip Size (Cost) No But can be engineered even without touching the semiconductor Smaller Gate Length Individual source Vias Bandwidth Yes Losses (Gain/Power) No TriQuint Semiconductor, Inc

The not so obvious approach: A new circuit design approach AND THAT’S NOT ALL!!! TriQuint Semiconductor, Inc.

The not so obvious approach: A new circuit design approach Relation between Power density and Mean Time to Failure Normalized Power Density 0.85 0.9 0.95 1 1.05 1.1 1.15 100 40 10 4 0.4 0.1 0.04 0.01 Normalized Time to Failure Lower Power Density Lower Al in the Barrier Lower Inverse Piezoelectric effect Better Reliability TriQuint Semiconductor, Inc.

The not so obvious approach: A new circuit design approach A circuit quoted to have a MTTF of 1Million hours at 85C base temperature using the old design strategy, will be able to be quoted to have a MTTF of 1Billion hours at the same 85C base temperature. TriQuint Semiconductor, Inc.

TriQuint Semiconductor, Inc. Outline Introduction The thermal limitation Approaches The obvious approach: A Diamond substrate The not so obvious approach: A new circuit design approach Summary TriQuint Semiconductor, Inc.

TriQuint Semiconductor, Inc. Summary Today, RF power devices are limited by the substrate and not by the intrinsic capabilities of the GaN semiconductor. The development of new hetero-substrates (GaN on diamond) or thick substrate circuitry and not the development of new barrier-channel configurations will push the technology to higher power densities. In the meantime, we should use smarter design approaches and develop “less sexy support technologies” (e.g ISVs) to minimize the effect of temperature. TriQuint Semiconductor, Inc.

TriQuint Semiconductor, Inc. Engineering is about using science to solve the problems that really matter TriQuint Semiconductor, Inc.