Improvement of Light Extraction/Rel of Deep UV LED Using ...

Hao-chung Kuo, Bob Lin (Picosun)

[email protected]

(IEEE, IET, SPIE and OSA Fellow)Department of Photonics and Institute of Electro-optical Engineering, NCTU

Improvement of Light Extraction/Rel of Deep UV

LED Using Novel Package (ALD)

Special Thanks : Everlight, Epistar-Lextar, PW, Picosun, ITRI

Outline

• Introduction

• Motivation

• Liquid Packaging Design

• Optical Optimization

• Conclusion

2

The World We Live in Today (Covid 19)

3

Imagine a World Where You Can…

4

Limitations of Existing UV Bulb Technology

5

UVC-LED深紫外消毒優勢照射後細菌和病毒DNA斷裂，並經多次照射後瓦解

消毒方式高溫水煮酒精擦拭傳統汞燈紫外燈 LED紫外線消毒

簡易程度麻煩麻煩麻煩簡單

消毒時間 15-20分鐘擦拭時間決定 15-30分鐘 10秒

副作用對物品有損害刺激皮膚汞有毒，產生臭氧無

可消滅的細菌種類多There Are Many Types of Bacteria That Can Be Eliminated

蟎蟲幽門螺旋桿菌

寄生蟲金黃色葡萄球菌病毒(COVID 19) 沙門氏菌

黴菌細菌

8

那些需要大空間潔淨地方的人(如醫院房間或飛機艙) ，使用耗電量大的汞燈來產生紫外線，因此世界各地的公司都在努力提高UVC-LED產能，用以產生一種更緊湊、更高效的替代品。

本月初時，Seoul Viosys 宣布 Violeds UV LED技術成功在30秒內殺死99.9%的新型冠狀病毒(COVID-19)。

UV LEDs 對病毒和細菌都是致命的，因為100-280nm波長的UVC

波段會粉碎遺傳物質。

UV-LED Structure and Challenges

9

•Defect density cause low IQE:Enhance IQE by epitaxy•Low EQE:Enhance IQE and LEE (by chip process or package)•Flip-chip structure:•Sapphire heating dissipation:Move to vertical process•AlN transparency:Remove substrate (vertical process)•AlN buffer quality and thickness:Nano PSS/ELO•p-GaN absorption:p-AlGaN contact (Vf will be higher)•Contact electrode absorption:Reflective contact

Bottleneck of UVC-LED

10

Bottleneck of UVC-LED performance

Performance comparison

UVC LED Power (EQE) still need to be improved

11⚫ Environmental Science: Water Research & Technology. 2017;3(2):188-202.⚫ Nature Photonics. 2019 Apr;13(4):233-44.

Record : Max EQE ~20% for UVC LED for Production EQE <7% especially Large Chip

Benchmark

12

UVC AlGaN with Al0.5GaN (Al easy to degrade)

State-of-the-art: achieve 60% IQE by novel epi structure design

Publication: Zhang, Z.-H.; Huang Chen, S.-W.; Zhang, Y.; Li, L.; Wang, S.-W.; Tian, K.; Chu, C.; Fang, M.; Kuo, H.-C.; Bi, W., ACS Photonics 2017, 4 (7), 1846-1850.Zhang, Z. H.; Huang Chen, S. W.; Chu, C.; Tian, K.; Fang, M.; Zhang, Y.; Bi, W.; Kuo, H. C.,. Nanoscale Res Lett 2018, 13 (1), 122

• NPSS planarization technology：→ AlN TDD = 1.5107 cm-2

• Sputter AlN & SLs, realize 76% transparent

Low droop EBL design：→ Droop< 4%

0 2 4 6 8 10 12 14 160

10

20

30

40

50

60

70

IQE

(%

)

Excitation Power (mW)

IQE_NCTU, 2017

IQE_NCTU, 2018

AlN on

npss

TDD

(cm-2)

AFM Ra

(nm)

2017 3.6107 0.9

2018 1.5107 0.5

Intensity enhanced 2.6 X

Droop <4%

IQE up to 60%

13

Co-work with Prof. Miyake and NYCU/ITRI

Everything start from high-quality AlN template

14

External quantum efficiency of 7.6% for the 275 nm DUV LED structure is obtained (Flip Chip type).

EQE 7.6% mid-size (20*20mil) UVC LED with HEBUT

Reduce efficiency droop by a novel EBL design

Wafer-level Thin-Film Flip-Chip UVA and UVC-LEDs

15

16

HUST/NCTU paper related to LEE (x2 improvement)

Novel graphene material were used to enhance LEEACS Appl. Mater. Interfaces 2018, 10, 8238-8244

17UCSB 2003 patent

NCTU 2003 paper JF Chu et al.

Everlight & Epileds beat Seoul Semi

Conventional Structure of UVC LED Package (Air Type) LEE shall be improvement

18Air Type -> Total Internal Reflection to Reduce Light Extraction

Ref : LEDinside

Several methods to improve UVC LED light extraction

Ref Year Device structureOutput performance of

device

Light extraction

improvement (%)

[1] 2018Flip chip + aluminum reflector with 60 degree

tilt angle

5.28 mw at 100 ma

EQE ~ 1 % / 285 nm 18.38 %

[2] 2019 Flip chip + silicone oil + hemisphere lens14.25 mw at 60 ma

EQE 5.39% / 281 nm70.7 %

[3] 2018Flip chip + aluminum reflector with 60 degree

tilt angle12.74 mw at 350 ma /280 nm 43.8 %

[4] 2017 Flip chip + hemisphere resin 44.2 mw at 50 ma

EQE 20.3% / 275 nm26 %

[5] 2017Flip chip + AlN-nanoparticle doped

fluoropolymer25.1 mw at 120 ma / 280 nm 20.5 %

[6] 2018Flip chip + graphene oxide-based

fluoropolymer + lens structureNot available / 280 nm 15.0 %

[7] 2019 Flip chip + flexible fluoropolymer film 23 mw at 400 ma / 275 nm 30.0 %

[8] 2019

Flip chip + PDMS fluid + hemisphere lens +

SiO2 nanoparticle + aluminum reflector with

60 degree tilt angle

77.4 mw at 200 ma / 275 nm 81.45 %

How to improve light extraction to >20%?

1. Crystals 2018, 8, 4202. Crystals 2019, 9, 2033. Applied Optics 2018, 57,254. Appl. Phys. Express 10, 031002 (2017)5. IEEE Photonics Technology Letters, 29, 14, 20176. ACS Appl. Mater. Interfaces 2018, 10, 8238−82447. ACS Appl. Mater. Interfaces 2019, 11, 19623−196308. Nanoscale Research Letters (2019) 14:236

Liquid Packaging Design (70% LEE Enhancement)

20

Liquid Packaging Design

21

Use silicone oil -> Liquid Packaging Structure ->Total Internal Reflection Reduction ->Light Extraction Enhancement

Crystals 2019, 9, 203.

Air Type

Liquid packaging


22

Crystals 2019, 9, 203.

Transmission Spectra

1. the transmittance of the silicone oil is over than 82 % from 260 nm to 350 nm.2. For 281 nm, transmittance of silicone oil is about 94 %.3. The structure of silicone oil is very simple. It is composed of Si-O and Si-CH3 functional groups. The main

chain of silicone oil is bonded by Si-O which has high bonding energy 108 Kcal/mol. It is not easily brokenby UVC and UVB, since UVC and UVB energy is 102 Kcal/mol and 91 Kcal/mol, respectively. Thischaracteristic makes silicone oil transparent from 260 to 350 nm.


23Crystals 2019, 9, 203.

Test Result

27.2% increaseflat type @ 281nm

70.7% increaselens type @ 281nm


24Crystals 2019, 9, 203.


25

• Heat Transf. Res. 2019, 50, 349-360 (Note : UVA not UVC)• Nanoscale Research Letters (2019) 14:236 (Note : later than our research)

Thermal Resistance Improvement – Similar Result from other papers

UVA liquid package UVC liquid package

26

Crystals 2019, 9, 203.

Test environment is under room temperature 25 °C and driving current is 60 mA. The result showsthat the average light maintenance of liquid packaging DUV-LED and conventional DUV-LED is98.5 % and 96.6 %, respectively. The light maintenance of both structures are in the same level andthe liquid packaging PT-V DUV-LED is even better than conventional one.


Why ALD for LED passivation?

28

• ALD process could achieve 100% conformal coating on the

mesa or the deep trench sidewall.

• The dense dielectric film is very important for the material

with high Al composition (e.g. AlxGa1-xN QW for UVC-LED) that

PECVD ALD

Film formationthickness (nm)

> 10 1-3

Aspect ratio Low Ultra high

Quality Low High

Uniformity Low High

Device reliability Low High

UVC-LED performance improvement

• UVC-LED achieved high power and high reliability by introduced ALD

passivation technology

40 mil @10A/cm2

波長 276 nm

Vf 6.82 V

輸出功率 119.9 mW

EQE 7.62 %

30

ALD Coating on package without cap

Conclusion

1. We have proposed a liquid packaging structure with silicone oil and hemispherelens for DUV-LED device.

2. With this kind of design, the light output can be enhanced by 70.7% and thethermal resistance can be reduced by 30.3% compared to the conventionalpackage structure.

3. After the reliability test, the light output maintenance of liquid packaging DUV-LEDs for 200 hours can still keep above 98 %. (now pass 500hr)

4. Combine with high LEE chip + hemisphere lens EQE>7% 120mW was achieved(life pass 500hr power keep @ 90%)

5. UVC-LEDs performance were significantly improved by ALD passivationtechnology. (pass 500hr)

6. Mini Micro UVC LED, Novel package material , are under investigated

𝝀 𝜼𝒆𝒙𝒕 𝜼𝒊𝒏𝒕 𝜼𝒊𝒏𝒋 𝜼𝒆𝒙𝒕

276 nm 7% = 50% ×70-

80%(?)× >18%

80% 30%20%

33

eVIO通過使用先進技術,在保持紫外線原有的病毒抑

制和殺菌能力的同時,抑制對身體和動物體的影響

• 在有人的環境中也可以用紫外線對空間和物體表面進行消毒

✓ 空間殺菌:可以在不影響人體的情況對整個空間進行消毒

✓ 物體表面殺菌:對物體表面的消毒很有效

◆ 會議室◆ 電梯◆ 醫療場

所

200 210 220 230 240 250 260 270 2800.0

0.2

0.4

0.6

0.8

1.0人體有害的領域

Inte

nsi

ty (

a.u

.)

Wavelength (nm)

一般的254 nm

準分子燈

人體安全區域

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✓ 222nm light

source

✓ 對人體影響小:蛋白質和角蛋白的吸收係數在 222 nm 紫外線和常規紫外線波長之間有所不同

222 nm的波長極為有用因為它保留了殺

菌作用又不影響人體。eVIO使用獨家技

術將Excimer燈去除有害的波長留下只對

人體溫和的222 nm波長紫外線進行殺菌

，且對皮膚和眼球無害。

eVio照射波長

常規紫外線常規紫外線

吸收率差~10倍透過率低於 0.01%

透過率 30% 10%

35

✓ Coating technology

• 光集成有害紫外線阻擋塗層• 高效內反射塗層• 世界上第一項可以用單一光線照射波長

為222 nm的紫外線的技術

✓ Sensor technology

Wavelength TLV 相對分光有害作用

222 nm 22 mJ/cm2 27%

254 nm 6 mJ/cm2 100 %

36

殺菌力能力空間/空氣能否常時間維持

殺菌用藥劑/漂白水

75% 酒精

一般殺菌用紫外線

新型態光殺菌(222nm)

. 空間限制

. 對人體有害

. 殺菌能力受限

Issue:

• 254 nm UV light• 222 nm UV light

. 不受限時間和空間

. 對人體無害

. 低能量損耗 ( ~50% )

. 可以跟一般照明系統共存

. 可以有效使99% COVID-19

病毒不活化

Improve:

對人體無害程度

物體表面殺菌

Thank you for your attention.

Improvement of Light Extraction/Rel of Deep UV LED Using ...

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