Guided by Miss. Shahida Submitted by, Sajas K.K.

Roll no: 18 S5 EC

Introduction

What is transparent electronics?

 In transparent electronics the usual opaque semiconductor materials forming the basis for electronic device fabrication is replaced with transparent materials.

 There are two technologies which preceded and underlie transparent electronics: 1.

Transparent Conducting Oxides (TCOs) 2.

Thin Film Transistors (TFTs)

Transparent Conducting Oxides TCOs)

 TCOs constitute an unusual class of materials possessing two physical properties (generally considered mutually exclusive): 1.

High optical transparency. ( Eg>3.1eV) 2.

High electrical conductivity.

Transparent electronic devices

Transparent Passive devices Transparent Active devices

Transparent Passive devices



Transparent Thin Film Resistors



Transparent Thin Film Capacitors



Transparent Thin Film Inductors

Transparent Thin Film Resistors

 Resistive material: ITO (Indium Tin Oxide)  Typical sheet resistance ~ 10 10 5  Conductivity of TCO’s depends on number of oxygen vacancies ( 𝑉 𝑂 ) and metal atoms occupying interstitial sites.

Transparent Thin Film Capacitors

 Most insulators are transparent.

 Contact layer is made of highly conducting TCOs (ITO).

 𝐶 = 𝜀 𝑖 𝐴 .

𝑑

Transparent Thin Film Inductors

 Hard to realize due to poor conductivity of TCO’s compared to metals. 𝑄 = 2𝜋𝑓𝐿/𝑅 𝐿  High L requires larger number of turns which in turn results in increased parasitic resistance.

Schottky Barriers

 Formed from metal (anode)-semiconductor (cathode) junction.

 Space charge region (depletion region) and potential barrier formation due to difference in work function of metal and semiconductor.

 Schottky barrier height , where 𝜙 𝐵𝑛 ∅ 𝐵𝑛 = ∅ 𝑀 − 𝜒 𝑆 → Schottky barrier height ∅ 𝑀 → work function of metal 𝜒 𝑆 → Electron affinity of semiconductor

Energy band in a Schottky barrier

Transparent Thin Film Transistors

 Constitutes the heart of transparent electronics  Channel is formed from highly insulating, wide band gap transparent semiconductor(ZnO).

 Source, drain and gate contacts are made from highly conductive TCO (ITO).

 Two possible configurations are: a) Bottom gate b) Top gate

Possible structure, (a) Bottom gate, and (b) Top gate.

Operation of a bottom gate TFT

Strengths and Weaknesses Strengths

Visible transparency Large area Low cost (solution based deposition and printing) Low temperature processing Free real estate Passive availability (R & C) Robust stable inorganic materials Safe, nontoxic materials

Weaknesses

High resistance of TCO’s Lack of complementary devices Low frequency of operation.(KHz f to few MHz).

T = 𝜇(𝑉 𝐺𝑆 − 𝑉 𝑇 )/2𝜋𝐿 2 Technological immaturity

Applications

 Active Matrix LCD (AMLCD).

 Active Matrix Organic Light Emitting Device display backplane (AMOLED).

 Value added glass.

 Transparent electronics on opaque substrates.

 UV detectors and arrays • Transparent solar cells • UV detectors for spectrally resolved imaging.

• Security applications: Invisible cameras and Invisible RFID’s

Conclusion

• Started as a mere electrical device technology during world war 2, transparent electronics now holds the key for many future advancements in security, entertainment efficient utilization of energy.

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Reference

‘Transparent Electronics ’, Springer publications, J.F.Wager, D. A. Keszler, R. E. Presley.

• ‘Transparent electronics: from synthesis to applications’, Wiley publications: Antonio Facchetti, Tobin J. Marks