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Flexible Electronics: Materials, Circuits, and Design Methodology Chris H. Kim Dept. of Electrical and Computer Engineering University of Minnesota, Minneapolis, MN [email protected] www.umn.edu/~chriskim/
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Flexible Electronics: Materials, Circuits, and Design ...people.ece.umn.edu/groups/VLSIresearch/papers/2012/DMD12_Flextronics.pdf · Flexible Electronics: Materials, Circuits, and

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Page 1: Flexible Electronics: Materials, Circuits, and Design ...people.ece.umn.edu/groups/VLSIresearch/papers/2012/DMD12_Flextronics.pdf · Flexible Electronics: Materials, Circuits, and

Flexible Electronics: Materials,

Circuits, and Design Methodology

Chris H. Kim

Dept. of Electrical and Computer Engineering

University of Minnesota, Minneapolis, MN

[email protected]

www.umn.edu/~chriskim/

Page 2: Flexible Electronics: Materials, Circuits, and Design ...people.ece.umn.edu/groups/VLSIresearch/papers/2012/DMD12_Flextronics.pdf · Flexible Electronics: Materials, Circuits, and

Presentation Outline

• Motivation and Applications

• Fabrication Methods and Transistor

Characteristics

• Design Methodology and Circuit Examples

• Case Study: Flexible Dynamic Random

Access Memory (DRAM) Array

• Closing Remarks

Acknowledgements Collaborator: Prof. C. Dan Frisbie, Chemical Engineering Dept., Univ. of Minnesota Students and post-docs: Wei Zhang, Mingjing Ha, Daniele Braga

Funding: National Science Foundation (NSF), Office of Naval Research (ONR)

2

Page 3: Flexible Electronics: Materials, Circuits, and Design ...people.ece.umn.edu/groups/VLSIresearch/papers/2012/DMD12_Flextronics.pdf · Flexible Electronics: Materials, Circuits, and

Large Area Flexible Electronics

• Devices: Transistors, LEDs, batteries, sensors

• Flexible, large area, low temperature processing, low

cost, printable

• Applications: Flexible displays, e-paper, RFID, solar

cells, sensor sheets/tapes, lighting, …

• Market size: $9.4B in ‘12, projected to top $63B by ‘22

Flexible circuit E-paper Solar Cell

3

Page 4: Flexible Electronics: Materials, Circuits, and Design ...people.ece.umn.edu/groups/VLSIresearch/papers/2012/DMD12_Flextronics.pdf · Flexible Electronics: Materials, Circuits, and

Flexible Electronics: Today

Display Solar cell

Battery

4

Page 5: Flexible Electronics: Materials, Circuits, and Design ...people.ece.umn.edu/groups/VLSIresearch/papers/2012/DMD12_Flextronics.pdf · Flexible Electronics: Materials, Circuits, and

Next Generation Flexible Electronics

Problem: Traumatic brain injury for

soldiers exposed to repeated blasts.

Goal: To create a low cost, flexible blast

dosimeter to monitor pressure,

acceleration, sound and light. Non-

volatile memory will record data for one

week

DARPA Funded Project, PARC

5

Holst Centre / IMEC

Page 6: Flexible Electronics: Materials, Circuits, and Design ...people.ece.umn.edu/groups/VLSIresearch/papers/2012/DMD12_Flextronics.pdf · Flexible Electronics: Materials, Circuits, and

Digital signal

processing

Memory

Ele

ctro

de

Amp ADC

Large area MxN sensor array

Battery

CPU and

wireless

transmitter

(silicon chip)

Power

management

+

-

Flexible electronics

(this work)Silicon electronics

(conventional)

control

Existing EEG system Proposed EEG system

Electrode sheet

Flexible electronics

...... ...

Next Generation Flexible Electronics

6 MURI/ONR funded project, Minnesota

Page 7: Flexible Electronics: Materials, Circuits, and Design ...people.ece.umn.edu/groups/VLSIresearch/papers/2012/DMD12_Flextronics.pdf · Flexible Electronics: Materials, Circuits, and

3V, 6-bit analog-to-digital

converter (Stanford)

15V, delta-sigma analog-to-digital

converter (IMEC)

15V 8-bit microprocessor

(IMEC)

20V, 64b RFID tag

(IMEC)

Challenge: Complex System Integration

7

Page 8: Flexible Electronics: Materials, Circuits, and Design ...people.ece.umn.edu/groups/VLSIresearch/papers/2012/DMD12_Flextronics.pdf · Flexible Electronics: Materials, Circuits, and

Presentation Outline

• Motivation and Applications

• Fabrication Methods and Transistor

Characteristics

• Design Methodology and Circuit Examples

• Case Study: Flexible Dynamic Random

Access Memory (DRAM) Array

• Closing Remarks

8

Page 9: Flexible Electronics: Materials, Circuits, and Design ...people.ece.umn.edu/groups/VLSIresearch/papers/2012/DMD12_Flextronics.pdf · Flexible Electronics: Materials, Circuits, and

One Strategy: Stretchable Silicon Electronics

John Rogers, UIUC

9

Page 10: Flexible Electronics: Materials, Circuits, and Design ...people.ece.umn.edu/groups/VLSIresearch/papers/2012/DMD12_Flextronics.pdf · Flexible Electronics: Materials, Circuits, and

Another Strategy: Printing Circuits

Roll-to-Roll

(dynamic, high-volume)

Sheet-to-Sheet

(static, low-volume,

high precision)

10

Page 11: Flexible Electronics: Materials, Circuits, and Design ...people.ece.umn.edu/groups/VLSIresearch/papers/2012/DMD12_Flextronics.pdf · Flexible Electronics: Materials, Circuits, and

Sheet-to-Sheet Printing Methods

Each method has advantages/disadvantages and specific ink requirements

Ink Filament

Printing

Aerosol Jet

Printing

Inkjet

Printing

11

Page 12: Flexible Electronics: Materials, Circuits, and Design ...people.ece.umn.edu/groups/VLSIresearch/papers/2012/DMD12_Flextronics.pdf · Flexible Electronics: Materials, Circuits, and

Ion-Gel Top-Gated OTFT

Gate

Ion-gel

Channel

S D

Substrate

Gate contact: PEDOT:PSS in water

(Baytron P)

Dielectric: 90 wt% ethyl acetate

8 wt% [EMIM][TFSI]

(Solvent Innovation)

2 wt% PS-PMMA-PS

S/D Contacts: Au

Substrate: Kapton or PEN (Dupont)

or Silicon

Semiconductor: 2 mg/ml P3HT(Merck)

90 vol% Chloroform

10 vol% Terpineol

12

Page 13: Flexible Electronics: Materials, Circuits, and Design ...people.ece.umn.edu/groups/VLSIresearch/papers/2012/DMD12_Flextronics.pdf · Flexible Electronics: Materials, Circuits, and

I-V of Ion-Gel Top-Gated OTFT

• High gate capacitance

– Low voltage operation

- 1 . 0 - 0 . 5 0 . 0 0 . 5 1 . 01 0

- 1 1

1 0- 1 0

1 0- 9

1 0- 8

1 0- 7

1 0- 6

1 0- 5

1 0- 4

1 0- 3

I (A

)

VG

( V )

VD

= - 0 . 1 V

VD

= - 1 . 0 V

0.0 0.5-0.5-1.0

1E-10

1E-9

1E-8

1E-7

1E-6

1E-5

1E-4

1E-3

1E-11

VDS = -1.0V

VDS = -0.1V

VGS (V)

|I D

S|

(A)

1.0

~0.4mA drain current

@ Vdd=1.0V

Substrate

PEDOT:PSS

Ion GelP3HT

Au Au

13

Page 14: Flexible Electronics: Materials, Circuits, and Design ...people.ece.umn.edu/groups/VLSIresearch/papers/2012/DMD12_Flextronics.pdf · Flexible Electronics: Materials, Circuits, and

-1.0

-0.5

0.0

0.5

1.0

-1.5

-1.0

-0.5

0.0

VA (100Hz)

VB (200Hz)

VOUT VDD = -1V

0 5 10 15 20

Time (ms)

Input V

oltage (

V)

Outp

ut

Voltage

(V

)

25 30

NAND Logic Gate

VDD

GND

VA VB

VOUT

Transistors

Resistor

500 um

VA VB VOUT

0 0 1

1 0 1

0 1 1

1 1 0 VDD

GND

VA VB

VOUT

14

Page 15: Flexible Electronics: Materials, Circuits, and Design ...people.ece.umn.edu/groups/VLSIresearch/papers/2012/DMD12_Flextronics.pdf · Flexible Electronics: Materials, Circuits, and

Ring Oscillator with Tunable Load

0 10 20 30 40 50-2

-1

0

VDD

TL6

TD6

Vout

TL5

TD5

TL4

TD4

TL3

TD3

TL2

TD2

TL1

TD1

VBIAS

VDD = -2V VBIAS = -2.25V f ~ 150 Hz

Time (ms)

VO

UT (

V)

1mm

VBIAS

GND

VDD

VOUT

15

Page 16: Flexible Electronics: Materials, Circuits, and Design ...people.ece.umn.edu/groups/VLSIresearch/papers/2012/DMD12_Flextronics.pdf · Flexible Electronics: Materials, Circuits, and

Presentation Outline

• Motivation and Applications

• Fabrication Methods and Transistor

Characteristics

• Design Methodology and Circuit Examples

• Case Study: Flexible Dynamic Random

Access Memory (DRAM) Array

• Closing Remarks

16

Page 17: Flexible Electronics: Materials, Circuits, and Design ...people.ece.umn.edu/groups/VLSIresearch/papers/2012/DMD12_Flextronics.pdf · Flexible Electronics: Materials, Circuits, and

Process Design Kit (PDK): Taking a Page Out of

Silicon’s Playbook

Tool vendors, $5B (2010)

Fabless semiconductor

companies, $75B (2010)

IP companies, $3B

(2010)

Foundry, $25B

(2010)

PDK environment

17

Page 18: Flexible Electronics: Materials, Circuits, and Design ...people.ece.umn.edu/groups/VLSIresearch/papers/2012/DMD12_Flextronics.pdf · Flexible Electronics: Materials, Circuits, and

Systematic Design Flow Based on a PDK

Basic cell

layout

Basic cell

schematic

-1.0 -0.50

-1

-2

-3

0.0

Cu

rre

nt

(mA

)

Voltage

Single device

measurementsRing oscillator

measurements

Array

circuit

layout

Array

circuit

schematic

Circuit

simulation

Automated

script-based

printing

Measurements

and testing

De

sig

n

itera

tion

G

D

SDevice

compact

model

Circuit

simulation

using HSPICE

Layout Versus

Schematic (LVS)

check

De

sig

n

itera

tion

Printing

Input File

Aerosol-Jet®

printing system

(Optomec, Inc.)

Design Rule

Check (DRC)

Ref: opdk.umn.edu 18

Page 19: Flexible Electronics: Materials, Circuits, and Design ...people.ece.umn.edu/groups/VLSIresearch/papers/2012/DMD12_Flextronics.pdf · Flexible Electronics: Materials, Circuits, and

2 mm

VDD

D

CLK

GND

VDD

Q

Q

Reset

NAND Gate Inverter Crossover

D Flip-Flop Circuit (= 1 bit memory)

19

Page 20: Flexible Electronics: Materials, Circuits, and Design ...people.ece.umn.edu/groups/VLSIresearch/papers/2012/DMD12_Flextronics.pdf · Flexible Electronics: Materials, Circuits, and

-1.5

-1.0

-0.5

0.0

-1.5

-1.0

-0.5

0.0

CLK (5Hz) Data (2.5Hz)

Q VDD = -1.5V

0 0.2 0.4 0.6

Time (s)

Input V

oltage (

V)

Ou

tput

Voltage (

V)

0.8

VDD

D

CLK

GND

VDD

Q

Q

1

Timing

Parameter

Output Data Pattern

“0” to “1” “1” to “0”

TC-Q 35ms 48ms

TSETUP 10ms 40ms

D flip-flop with Reset function

8 NAND gates + 3 Inverters

20

D Flip-Flop Circuit (= 1 bit memory)

Page 21: Flexible Electronics: Materials, Circuits, and Design ...people.ece.umn.edu/groups/VLSIresearch/papers/2012/DMD12_Flextronics.pdf · Flexible Electronics: Materials, Circuits, and

Presentation Outline

• Motivation and Applications

• Fabrication Methods and Transistor

Characteristics

• Design Methodology and Circuit Examples

• Case Study: Flexible Dynamic Random

Access Memory (DRAM) Array

• Closing Remarks

21

Page 22: Flexible Electronics: Materials, Circuits, and Design ...people.ece.umn.edu/groups/VLSIresearch/papers/2012/DMD12_Flextronics.pdf · Flexible Electronics: Materials, Circuits, and

General Purpose DRAM Array for

Display/Sensor Applications

• Low voltage, low

power

• Random access

• Compatible with

existing OTFT

logic circuits*

ONON OFF ...

...

FlexibleBattery VDD

GND

INV, NAND,

ROSC, etc.

RBL’s

*Y. Xia, et al., Adv. F

unc. Mater., 2010

22

Page 23: Flexible Electronics: Materials, Circuits, and Design ...people.ece.umn.edu/groups/VLSIresearch/papers/2012/DMD12_Flextronics.pdf · Flexible Electronics: Materials, Circuits, and

Previous Organic Memory Reseach

• Non-volatile memory

– Floating-gate structure

– Ferroelectric materials

• Volatile memory

– Write-only SRAM (JSSC07)

• Braille sheet display

• Static power problem

– No previous work on

general purpose DRAM BIAS

VDD VDD

WL

BL

VSSVSS

M. Takamiya, JSSC 2007

Floating Gate

Control Gate

T. Sekitani, Science 2009

23

Page 24: Flexible Electronics: Materials, Circuits, and Design ...people.ece.umn.edu/groups/VLSIresearch/papers/2012/DMD12_Flextronics.pdf · Flexible Electronics: Materials, Circuits, and

Electrolyte Gated OTFT with an

Unusually High Gate Capacitance

• Polarized ions enable Cgate=10~100µF/cm2 *

– High gate capacitance ideal for DRAM cells

– 65nm LP CMOS: Cgate~1.4µF/cm2

*Y. Xia, et al., Adv. Func. Mater., 2010

Gate

Source Drain

Substrate

Channel

--

-

--

---

--

+

~5µm

R

S

S S

R R

R

S

S

R

Transistor OFF

Gate

Source Drain

Substrate

Channel

- - - - - - - - - -R

S

S S

R R

R

S

S

R

+ + ++ +

Transistor ON

24

Page 25: Flexible Electronics: Materials, Circuits, and Design ...people.ece.umn.edu/groups/VLSIresearch/papers/2012/DMD12_Flextronics.pdf · Flexible Electronics: Materials, Circuits, and

P-type Only 3T DRAM Gain Cell

• Ideal memory cell for electrolyte gated OTFTs

– Long retention time (> 1 minute), compared to 65nm

CMOS (~100µs [4])

– P-type only implementation possible, no static power

RWL = VDD

WWL=0

VDDWBL =

VDD / 0

RBL

= 0

0

VDDVDD / 0 RBL

VDD

VDD+ΔV

VDDVDD / 0 0

Leakage

for ‘0’

Write mode Hold mode Read mode

VDD+ΔV

[4] K. Chun, et al., VLSI symp., 2009

25

Page 26: Flexible Electronics: Materials, Circuits, and Design ...people.ece.umn.edu/groups/VLSIresearch/papers/2012/DMD12_Flextronics.pdf · Flexible Electronics: Materials, Circuits, and

8x8 Printed Organic DRAM Array

24 mm

Process

Channel

Array size

TRETENTION

PSTANDBY

Ion-gel organic TFT

Poly(3-Hexylthiophene)

64 bits (8 WLs, 8 BLs)

> 60sec @ 1.30V WWL

5.5 nW/bit

Read delay < 12 msec

Write delay < 20 msec

Array dim 24 x 25 mm2

Supply 0.8V - 1.2V

PACTIVE 8 µW/bit

TR dim. W/L = 500µm / 25µm

Photograph of Printed

Organic DRAM Array

ISSCC 2011, EE Times, MIT Tech Review

26

Page 27: Flexible Electronics: Materials, Circuits, and Design ...people.ece.umn.edu/groups/VLSIresearch/papers/2012/DMD12_Flextronics.pdf · Flexible Electronics: Materials, Circuits, and

Array Retention Time Measurements

• Worst case retention time: 30 sec for WWL=1.25V

• Retention time over 1 minute for WWL=1.30V

WWL = 1.25V

WWL = 1.30V

30 40 50 60

0%

10%

20%

30%

Retention time (sec)%

of

failin

g c

ells

201 2 3 4 5 6 7

8

1

2

3

4

5

6

7

Wo

rdlin

e #

Bitline #

> 60

50

40

308

1 2 3 4 5 6 7 8 9

1

2

3

4

5

6

7

8

9

-60

-55

-50

-45

-40

-35

-30

(sec)1 2 3 4 5 6 7 8 9

1

2

3

4

5

6

7

8

9

-60

-55

-50

-45

-40

-35

-30

27

Page 28: Flexible Electronics: Materials, Circuits, and Design ...people.ece.umn.edu/groups/VLSIresearch/papers/2012/DMD12_Flextronics.pdf · Flexible Electronics: Materials, Circuits, and

Power Consumption Comparison

• 12X+ power savings in active mode

• < 10nW/bit refresh power in retention mode

1000 4T+2R SRAM

100

10

1

0.1

0.01

0.001

98µW

8µW 8µW

Po

we

r c

on

su

mp

tio

n (

µW

/bit

)

11nW 5.5nWWW

L=

1.2

5V

SRAM

(Pstatic only)

DRAM

(active)

DRAM

(active)

DRAM

(stdby)

DRAM

(stdby)

WW

L=

1.3

0V

WW

L=

1.2

5V

WW

L=

1.3

0V

IDC

1/12

1/17,818

‘1’ ‘0’

BL BLB

WL WL

RWL

WBL RBL

3T DRAM

WWL

28

Page 29: Flexible Electronics: Materials, Circuits, and Design ...people.ece.umn.edu/groups/VLSIresearch/papers/2012/DMD12_Flextronics.pdf · Flexible Electronics: Materials, Circuits, and

Closing Remarks • Flexible electronic products are already here

– Displays, solar cells, batteries

• Next generation flexible electronics systems

– Multi-functional electronic sheets for sensing,

detection, processing, storage, and communication

– Complex integration of various circuit components

• Multi-disciplinary effort key to success

– Ink and material development

– Transistors and interconnect design

– Fabrication methods (R2R, sheet based)

– Circuit design and computer-aided-design tools

– Application and systems

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