Flexible Electronics: Materials, Circuits, and Design...
Transcript of Flexible Electronics: Materials, Circuits, and Design...
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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
www.umn.edu/~chriskim/
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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)
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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
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Flexible Electronics: Today
Display Solar cell
Battery
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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
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Holst Centre / IMEC
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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
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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
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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
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One Strategy: Stretchable Silicon Electronics
John Rogers, UIUC
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Another Strategy: Printing Circuits
Roll-to-Roll
(dynamic, high-volume)
Sheet-to-Sheet
(static, low-volume,
high precision)
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Sheet-to-Sheet Printing Methods
Each method has advantages/disadvantages and specific ink requirements
Ink Filament
Printing
Aerosol Jet
Printing
Inkjet
Printing
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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
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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
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-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
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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
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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
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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
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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
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2 mm
VDD
D
CLK
GND
VDD
Q
Q
Reset
NAND Gate Inverter Crossover
D Flip-Flop Circuit (= 1 bit memory)
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-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
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D Flip-Flop Circuit (= 1 bit memory)
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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
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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
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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
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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
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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
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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
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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
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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
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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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