printed electronics: devices, circuits and hybrid system...

Printed Electronics: Devices, Circuits and Hybrid System Integration

Donald Lupo, Petri Heljo, Marika Janka, Santtu Koskinen, Miao Li, Matti Mäntysalo, Juha Niittynen, Sampo Tuukkanen

Department of ElectronicsTampere University of Technology

Tampere, Finland

Outline

• TUT Introduction– Town, university and Dept. of Electronics– Organic and printed electronics

• Gravure printed thin film diodes and circuits– Devices and interfaces– RF rectification: rectifier, charge pump, energy harvesting– Self-aligned passivation

• Printed electronics for system integration• Optimisation of printing parameters• Printed multilayer interconnects for System in Package• Adaptive printing

D. Lupo, Plastic Electronics 2012 2

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8.10.2012

Tampere: “Manchester of the North”

• Founded as a market town in 1775, now third largest city in Finland (213,000 inhabitants)

• Major growth during industrial revolution (thanks partly to Tammerkoski rapids)

• Situated between 2 large lakes, Näsijärvi and Pyhäjärvi

• Industry includes paper, mining machinery, glass manufacturing equipment – and mobile phones!


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8.10.2012

Tampere University of Technology (TUT)

• Established in 1965• 11,600 students (2009)• Strong tradition of university/industry cooperation


Printed Electronics at TUT

• electronic system integration and manufacturing concepts utilizing printing processes

• interconnections, systems, reliability and performance analysis

• electronic devices and circuits utilizing solution processable materials and printing processes

• diodes, transistors, sensors, supercapacitors

•Printable Electronics Group•Head of group: Dr. Matti Mäntysalo

•Organic Electronics Group•Head of group: Prof. Donald Lupo•Senior scientist: Dr. Sampo Tuukkanen

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Over 250 m2 dedicated lab space, incl. dust-free processing laboratory of 60 m2 (non certified but close to ISO 14644-1 class 5)

Printing equipments: Ink-jet (2x iTi MDS 2.0, Dimatix DMP-2831), Gravure (NSM Labratester), Flexo (RK Flexiproof 100), Screen (DEK)

Variety of other deposition and processing tools and equipments for characterisation of material properties and electrical performance (spin coater, fibrelaser, drop watcher, semiconductor parameter analyser, profilometer, etc.)

Environmental test equipments (thermal chambers for shock and cycling, vibration, salt tests, drop tests, etc.)

Variety of analysis tools in University (profilometers, SEMS, AFM, etc.)

PR

INT

LA

B

Professor Donald Lupo


Outline





Organic thin film diodes

• Most organic thin film diodes (TFDs) are Schottky diodes

– Metal/semiconductor contacts areOhmic in one bias and blocking in theother

– In forward bias, charges are injectedand current can flow

– In reverse bias, the charge injectionbarrier is high

– High rectification ratio• Current flow is vertical• Lower requirements for charge carrier

mobility and resolution/registrationthan TFTs

• Fewer issues for printing

Semiconductor

Cathode

Anode

Cebrite, patent application WO04/66410 (2004).


Diode fabrication

Simple three-layer vertical diode structureHigh-throughput printing process manufacturing

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SilverPTAAAl/CuPET

OhmicContact

Rectifyingcontact

Wet etched aluminium/copper (screen printed etch resist)PTAA and silver gravure printedDiodes fabricated and characterised in ambient conditionsNo fine patterning or in-line vacuum processes


Printed diodes: the expectation

Organic Schottky diodes• P-type semiconductor

Semiconductor mobility• PTAA 0.002 cm2 / Vs

Electrodes• PTAA HOMO at 5.1 eV• Cathode: calcium,

aluminium…• Anode: platinum, gold…

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PTAAHOMO5.1 eV

High w.f. Anode

Low w.f. CathodeEnergy in

eV

p-type semiccathode

+-

p-typesemiccathode

I

+ -

p-type semiccathode

IX


Printed diodes– the reality

Some surprises in actual diode performance

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1E-12

1E-11

1E-10

1E-9

1E-8

1E-7

1E-6

1E-5

1E-4

1E-3

1E-2

-6 -4 -2 0 2 4 6

Cur

rent

Den

sity

[A/c

m2 ]

Voltage [V]

500 nm, Cu700 nm, Cu1200 nm, Cu1200 nm, Al

Cu and Al give almost the same rectification ratio and forward currentBut threshold voltage of 700 mV with Al, absent in CuGood rectification with Ag top contact (stability issues with PEDOT-PSS)Long-term stability of diode performance in ambient air without encapsulation


Interfaces in printed organic diodes

• Good results for Cu/PTAA/Ag diodes• The i-V curve shows clearly that Cu is the cathode and Ag is

the anode• But according to the literature, the work function of Ag is 4.3 –

4.7 and Cu‘s is ca 4.7• >>> in principle, this shouldn‘t work!• Plus, the rectification ratio is 100,000 with sputtered Cu and

1000 with evaporated Cu• So, something else was happening


Interfaces in printed organic diodes– experimental studies

• Kelvin probe indicated that printed Ag actedessentially as Ag2O (WF 5.2 eV) but did not account for Cu cathodic behaviour (K. Lilja et al., ACS Applied Materials and Interfaces 3, 7 (2011))

• log plots of i-V curves for sputtered and evaporated Cu indicated different onset ofspace charge limited current (SCLC)• XPS measurements indicated difference in overlayers on sputtered and evaporated Cu

– Sputtered Cu showed strong C signals atsurface compared to evaporated

– Ar sputtering to Cu signals indicated an organic layer of ca. 5-10 nm on sputtered Cu

•Impedance spectra at low V indicate strong interfacial phenomena

K. Lilja et al., ACS Applied Materials an Interfaces 3, 7 (2011)

K. Lilja et al, J. Phys. D. 44, 295301 (2011)


Interfaces in printed organic diodes –what might be happening

• Based on impedance and XPS data, a model can be proposed• Effective Schottky barrier is increased beyondmeasured value when semiconductor and metal (+ Cu2O and organic) are brought intocontact.

• pinning of Fermi level in organic semiconductordue to tailing of wave function from metal• change in pinning due to intermediate dielectric• orientation of dipole potential between twointerlayers has further effect

• Dual dielectric layer present in bothevaporated and sputtered Cu >> can explainthe fact that rectification is seen in both cases. Thicker layers in sputtered Cu enhance theeffect• In forward bias, field is high enough to assisttunnelling >> identical forward currents atsufficiently high bias

Simplified model for the diode Schottky contact. Source: K. Lilja et al, J. Phys. D. 44, 295301 (2011)


Voltages up to 7.4 V 5.4 Voutput at 1 MHz

2.7 V output at 10 MHz

Printed organic diodes: halfwaverectifier

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• In a half-wave rectifier circuit with an input AC zero-to-peak signal of 10 V:

• Voltages up to 7.4 V• 5.4 V stable DC current at 1 MHz• Rectification up to 10 MHz

• 3 dB point above 20 MHz throughoptimisation

C = 47 nF R = 1 M

K.E. Lilja, T.G. Bäcklund, D. Lupo, T. Hassinen, and T. Joutsenoja, Gravure printed organic rectifying diodes operating at high frequencies, Organic Electronics 10: 1011 (2009) 0

1

2

3

4

5

6

7

8

1E+4 1E+5 1E+6 1E+7 1E+8

DC O

ut [V

]

Frequency [Hz]

450 nm3 V at13.56 MHz

K. Lilja, P. Heljo et al, PRODI workshop 2010


Printed organic diodes: Charge pump circuit

• DC output from half-wave rectifiers not sufficient– Full-wave rectifier provides less ripple (P. Heljo

et al., in prep.) but less voltage (drop over diodes)

– Higher DC output voltages required for manyapplications

– Use of a charge pump circuit could providehigh enough voltages to drive OFET

• Printed 2-stage charge pump (4 diodes & 4 capacitors) was fabricated

• VDC~18,6 V @ 100 kHz (input 10 VAC)• VDC~10,4 V @ 13,56 MHz• Multiple stages could be used to further increase the

output voltage

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Commonly used charge pump structure for RFID tags[Shiho KIM et al. A Full wave voltage multiblier for RFID Transponders. IEIEC Trans. Commun. 91 (2008)]

0

2

4

6

8

10

12

14

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1,0E+03 1,0E+04 1,0E+05 1,0E+06 1,0E+07 1,0E+08

Out

put v

olta

ge [V

]

Frequency [Hz]

Voltage doubler

Half-wave with diode 1

Half-wave with diode 2

Petri Heljo et al, LOPE-C 2011 Conference Proceedings


RF Energy Harvesting

• Potential application of RF rectification: energy harvesting for distributed sensors

• Running project: universal autonomous power source for distributed electronics (Autovolt)

• Hybrid integration project together with Aalto University funded by Academy of Finland

• Printed energy harvesters to drive ultra-low power distributed sensors (chip developed by Aalto Univ.)

• Fully printed RF harvester based on ink jet printed optimised Ag antenna and capacitor and gravure printed diode

• Effective use of inductive coupling to deliver power to load comparable to sensor chip

• Improvement of dc output voltage by further thinning of diode and optimisation of processing

• Work in progress: charging supercapacitor with rectifier output, coupling to sensor chip

M. Li et al., Proc. LOPEC 2012


Self-aligned curing by Joule heating

• Dielectric deposition for some applicationse.g. passivation or gate dielectrics shouldbe as well registered as possible to theelectrode – can be a challenge withprinting

• Joule heating approach: deposit a thermally cross-linkable dielectric (PVP with suberoyl chloride) then pass currentthrough the electrode

• Dielectric is crosslinked around electrodeand can be removed elsewhere

• Contact pads can be kept free due to lowercurrent density

• Currently investigating for gate dielectricsand passivation of conductors

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M. Janka, S. Tuukkanen, T. Joutsenoja, D. Lupo, Thin Solid Films 519, 6587 (2011)


Outline





Printable electronics for heterogenous system integration

• Complex functions still frequently require someuse of Si components

• Here printing technology can enable new manufacturing platforms and product concepts

• We have especially explored ink jet printing for system integration

• digital process allows rapid prototyping and customized products

• small stand by time.• contact-free manufacturing method• no specific tools, flexibility • variety of different substrates• patterning on 3D surfaces and over steps possible• Versatility – One machine, many materials• Controlled amount of material accurately placed.• ”All in one” –process• Throughput increasing

Antenna

Direct IC connection

Integrated system

Direct contact on 3D

Component attachment


Effects of printing parameters• Proper drop formation is critical to good printing and depends on velocity, surface tension etc.

Critical to have well-formed drop before impact on substrate• Key parameters affecting velocity are waveform amplitude and printhead temperature (pulse width has minor

effect on velicity and mainly affects drop size)• Parameter optimisation needed to reduce deviation in printing from printheads across substrate

• Resolution (drop spacing) is critical to get continuous lines without shorts• Resolution too low >> porous structure• Resolution too high >> bulging lines• Flash dry process >> “stacked coin” structures• Optimal resolution may depend on geometry and application

30 µs 45 µs 75 µs 110 µs 150 µs

Drop ejection Tail break-off Tail merge

Formed drop500 µm

250 µm

Ville Pekkanen, doctoral thesis, 2011)


Connecting bare ICs• Today wire-bonding is still the dominant technology• It is a flexible technology due to point-to-point

connections, providing cheap and reliable interconnections that obviate chip-specific tools.

• Inkjet technology can be used to connect chips to package or directly to printed circuit boards.

• It has the same flexibility than wire-bonding has, but all connections can be made simultaneously.

• The greatest challenge of replacing wirebonds with inkjetted first level interconnections is the massive and advanced infrastructure of wire-bonding technology.

• Requirements for bare die interconnections are much greater in line accuracy than in case of packed device.

• A daisy-chain test pattern was printed on top of the IC. The chain is one pixel (ca. 40 m) wide.

• The spacing of the pads is about 70 µm.

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Interconnections and tracks

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Substrate

Chemical treatment

Printhead

Ink

1. Surface treatment

2. Printing conductor

3. Sintering Heat

4. Printing dielectric

5. CuringUV+Heat

6 to N repeating steps


Sensor-box

• Joint work with Royal Institute of Technology (KTH)

• The package measures the relative room humidity and shows to the user through LEDs.

• The structure contains MCU,LEDs, printed battery, integrated using inkjet and nano-silver

A binary Xaar126 printhead with 50 pl A DMC-11610 printhead with 10 pl Sensor-boxSpray-coated f-MWCNTs


Bio-sensing

• Joint work with Royal Institute of Technology (KTH), iPack center

• Wearable bio-sensing node– ECG, EMG, EEG

• Highly integrated SoC integrated with printed electronics


Cospas-Sarsat Antennas

• Electronic integration into life-vest• Manufacturing antenna with printed

electronics• Electrical RF characterization

– Measurement and analysis• Environmental tests

– Humidity (JESD22-A101B)– Salt fog (JESD22-A107B)– Adhesion test (ASTM D3359)

• Succesful field tests– Cospat-Sarsat satellite system


RF System (partially inkjetted)RF System-in-Package

Number of discrete passives 21 0201 (mainly) Size of discrete components also some bigger components

Number of active components 1 Conductive layers 4 + 2 (by

printing) Number of IC pads 102 Pad size 65 m Pitch 130 µm IC size 4.0 mm x 4.0 mm Substrate material Polyimide Module size 9.0 mm x 9.0 mm

The key milestones:1. Printing the patterns with required accuracy,2. Printing the interconnections to IC chip and board,3. Printing the second layer.


Integration of GSM BB

• Joint project with Nokia• Integrating GSM BB with inkjet

technology– 4 IC, Over 50 passive components– 6 conductive layers printed with

inkjet technology– 17 mm x 17 mm x 1 mm.

Adaptive printingIC3 IC3IC3

Detect the component locations for each module

Correct the print image accordingto measured locations


Summary and outlook• Gravure printed Schottky diodes can work quite well – even when they

shouldn‘t• Change in interfacial properties with process is critical

• HF rectifier diodes can be printed using a fully air stable amorphoushole conductor polymer and no fine patterning steps• Optimisation of architecture can drive frequency up to > 20 MHz• Diodes can be integrated into rectifier circuits and energy harvesters• Voltage drop still an issue; better materials needed

• Printing is a useful tool for electronics manufacturing when Si isinvolved• Efficient process and system integration• Optimisation of a variety of printing parameters is critical• Multilayer direct printing of interconnects and vias enable efficient SiP

manufacturing• Adaptive printing can correct for placement errors


Acknowledgements29

Kaisa Lilja Dr. Ville PekkanenEsa KunnariDr. T. Joutsenoja, presently at VTTDr. T. G. Bäcklund, presently at Merck Chemicals Ltd.Dr. H. S. Majumdar and Prof. R. Österbacka from Åbo Akademi UniversityDr. T. Kololuoma and T. Hassinen from VTTOrganic Electronics and Printable Electronics Groups at TUT

FundingUPM-Kymmene Corporation, Tekes (the Finnish Funding Agency for Technology and Innovation), Academy of Finland, European Space Agency


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