Z i a i eB i o m e d i c a lM i c r o d e v i c e sL a b o r a t o r y

B i r c k N a n o t e c h n o l o g y C e n t e r1 2 0 5 W S t a t e S t

W e s t L a f a y e t t e , I N 4 7 9 0 7h t t p s : / / e n g i n e e r i n g . p u r d u e . e d u / Z B M L /

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Phase Change Materials for Photonics

ECE 695Chang Keun Yoon

Z i a i eB i o m e d i c a lM i c r o d e v i c e sL a b o r a t o r y

B i r c k N a n o t e c h n o l o g y C e n t e r1 2 0 5 W S t a t e S t

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Contents

Z.Yangetal.,Photonicsjournal,2015.

• WorkingprincipleofPCMinphotonics

• TwoPCMsinphotonicsystem

• TemperaturedependentopticalpropertiesinPCM

• OpticalpropertiesofPCMs

• Applications• Writingofreconfigurablephotonic

devicesinaphase-changefilm

• Ultra-thin perfect absorber

• Non-volatilememory

Z i a i eB i o m e d i c a lM i c r o d e v i c e sL a b o r a t o r y

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Working principle of PCM in photonics• Atomic arrangement of different states

in PCM introduces large change in optical and electrical properties.

• Solid-state phase change systems– Vanadium dioxide (VO2)Electronic transition and structural transition– Chalcogenide (Ge2Sb2Te5)Amorphous and crystalline state transition

• Change of properties in 2 different states

– Dielectric function, 𝜀– Refractive index, n– Carrier density and electrical conductivity

CD-RW technologies, technical forum, northallegheny.org

Z. Yang et al., Photonics Journal, 2015.

𝑛 = 𝜀%& + 𝜀%̃&

� + 𝜀%2

�

𝑤ℎ𝑒𝑟𝑒𝜀%: 𝑟𝑒𝑎𝑙𝑎𝑛𝑑𝜀%̃: imaginary

T. Taubner et al., Nature photonics, 2017

rhombohedraloctahedral-like

Z i a i eB i o m e d i c a lM i c r o d e v i c e sL a b o r a t o r y

B i r c k N a n o t e c h n o l o g y C e n t e r1 2 0 5 W S t a t e S t

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Two recent advanced PCM in Photonics

• VO2 (an oxide system)– Metal to semiconductor

(Monoclinic to tetragonal) transition, vice versa at 70ºC

– Sharp discontinuity in electrical conductivity

N. Yamada et al., Nature Materials, 2007.

• Ge3Sb2Te6 (Chalcogenide system)– Atomicarrangementinamorphousand

crystallinestates– Somebondsstillremainstrongbonds:local

arrangeofatoms– Formscrystalasbeforetransition

M. Kanehira et al., Scientific reports, 2013.

Z i a i eB i o m e d i c a lM i c r o d e v i c e sL a b o r a t o r y

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Temperature dependent optical properties

Parketal.,Thinsolidfilms,2012

• Amorphous (RT) and crystalline (500 ºC) structure grown in different temperatures.

• Crystalline grown Vanadium oxide systems show higher refractive index, n.

• Transmittance in higher temperature show lower transmittance.

• Transmittance of VO2 at 100 ºC (crystalline) is 7.4% less than room temperature (amorphous).

V2O5

VO2

VO2

Amorphous

Crystalline

Crystalline

Z i a i eB i o m e d i c a lM i c r o d e v i c e sL a b o r a t o r y

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OpticalpropertiesofPCMs

• Increaseinrefractiveindex(n),extinctioncoefficient(k),andreflectance(R)aftercrystallization.

• Significantchangesinbondingintroducesdifferenceinopticaldielectricconstant.

Crystallization

Amorphous

T.Taubner etal.,Naturephotonics,2017

Z i a i eB i o m e d i c a lM i c r o d e v i c e sL a b o r a t o r y

B i r c k N a n o t e c h n o l o g y C e n t e r1 2 0 5 W S t a t e S t

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Writing of reconfigurable photonic devices in a PCM film• Fresnel zone-plates

• Structural phase changed from amorphous (n= 3.9) to crystalline (n=4.3).

• Optical pulses of different duration, typically consisting of a few tens of 85 fs pulses.N.I.Zheludev.,Naturephotonics,2015

Z i a i eB i o m e d i c a lM i c r o d e v i c e sL a b o r a t o r y

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Ultra-thin perfect absorber

• Co-existence of phase transition.

• At 343K, the reflectivity drops to ~0.0025 at λ=11.6 µm.

• n >> k, Total reflection is coherence sum of

partial reflection. Phase shift = - 𝜋

• n ~ k,Absorption resonance exists with

thickness of dielectric smaller than λ.F. Capasso et al., Applied physics letter, 2012

Z i a i eB i o m e d i c a lM i c r o d e v i c e sL a b o r a t o r y

B i r c k N a n o t e c h n o l o g y C e n t e r1 2 0 5 W S t a t e S t

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Non-volatilememoryapplications• Large refractive index (~ 2)

change.• High-speed phase transition

10 ~ 100 ns.• Long shelf-life (room temp.).• More than 100,000 cycles.

N. Yamada et al., Nature Materials, 2007.