Fundamental of driving methods for OLED

1
Fundamental of driving methods for OLED

• Reiji Hattori (??? ???)
• ??????? ??????????
• ?????????? ???
• ???(E-mail)hattori_at_ed.kyushu-u.ac.jp

2
Basic pixel circuit of AM-OLED
PowerSourceline
Scanning line
Scanning line
DrivingTFT
Switching TFT
Switching TFT
Data line
Data line
OLED
OLED
Cathode
Cathode
(a) 1-TFT
(b) 2-TFT
What is wrong with this circuit?
Can you imagine how to apply the voltages to
data, scan, and source lines?
3
Basic pixel circuit of AM-OLED
VDD
VD
VD
Vth
VG
Von
Von
VG
0
0
(a) 1-TFT
(b) 2-TFT

• Small duty ratio
• High current
• Short life time

• Large duty ratio
• Low current
• Long life time

4
2TFT Pixel circuits
Source follower connectionSince VGVDATA-VOLED,
VG varies by VOLED that increases with OLED
degradation.
Constant current connectionSince VGVDATA, VG
doesnt change by VOLED, if the driving TFT works
in a saturation region.
Select line
Select line
VG
Source line
Source line
S
D
G
G
Data line
Data line
Common Cathode
S
D
VDATA
VDATA
VG
VEL
VEL
Cathode
Cathode
Anode
Anode
Select line
Select line
VG
VEL
VEL
S
D
Common Anode
G
G
Data line
Data line
D
S
VDATA
VDATA
VG
Source line
Source line
5
OLED lifetime dependent on driving method
Voltage
Voltage
Current
3
3
Voltage
Current
Luminescence
Current
Luminescence
Luminescence
Lifetime
Lifetime
Lifetime
time
time
time
(a) Constant voltage driving
(b) Constant current driving
(c) Constant luminous driving
Digital driving
PM driving Analog driving
Optical feedback
6
OLED structures

-

-
Metal cathode Electron Transport Layer Hole
Transport Layer Transparent conductor (ITO) Glass
substrate
Metal cathode Polymer Layer Hole injection
Layer Transparent conductor (ITO) Glass substrate
Small molecule OLED
Polymer OLED
7
Common anode structures
Light emission
Light emission

-
TFT
Transparent conductor (ITO) Organic layer Metal
cathode Glass substrate
Transparent conductor (ITO) Organic layer Metal
cathode Glass substrate Bank layer
Inverted Structure (NOVALED)
Contact hole Structure
http//www.novaled.com/sites/technology/fields.php
8
RURA issue of LTPS TFT AM-OLED

• LTPS TFT has large mobility and threshold voltage
  variations caused by a grain boundary.
• The variations directly generate a intensity
  variation because OLED is driven by a current in
  contrast that LCD is driven by a voltage.
• Improving the process and device structure can
  not solve the problem perfectly.
• Compensation by circuit and driving method is
  necessary.

Intensity variation of LTPS 2TFT pixel circuit
AM-OLED caused by threshold voltage variation
(Intensity variation 16) Sarnoff Co. (1997)
9
Sticking issue of a-Si TFT AM-OLED
40
40 Intensity degradation

• Serious sticking image problem
• Human eyes can recognize the 1 deference of
  structured pattern and 3 deference of random
  pattern.
• Fixed image should be avoided.

10
Appearance of RURA Sticking image
?? ??
LTPS TFT
a-Si TFT
11
Classification of AM-OLED driving
Area Ratio Grayscale
EPSON
Current Copier
Digital
NEC, Matsushita Casio
Time Ratio Grayscale
SEL
Current Program
Compensation Circuit
Current Mirror
Voltage Program
Current Modulation
Sony
Simple 2TFT
Toshiba IDTech Samsung
Analog

SKD AU Opt
Time Modulation
Hitachi
12
Classification of AM-OLED driving II
Constant Voltage Driving
Constant Current Driving
Area ratio
Digital
Current program
Analog
Epson
TMD LG Philips
Casio
Time ratio
SEL
Voltage program
Kyocera Samsung Electronics
Samsung SDI TPO
Time modulation
Hitachi
a-Si
LTPS
13
LTPS TFT AM-OLED circuit

• ????
• ????

14
Area ratio grayscale driving method
Supply line
Signal lines
Dr-TFT
O-LED
Cs
Sw-TFT
Scan line
(Seiko-Epson, IDW99)
15
Area ratio grayscale driving method 1
PS line
ES line
Sw1
Storagecapacitor
Dr
OLED
Video data line
OLED voltageSupply line
Cathode
Display-Period-Separated (SEL, SID00)
Simultaneous-Erasing-Scan (SEL, SID00)
16
Area ratio grayscale driving method 2
2.9?s/line
AddressingPeriod (AP)
Emitting Period (EP)
1 2 ? ? ? 480
1.4ms
T
1SF
2SF
3SF
4SF
5SF
6SF
Display-Period-Separated
1T
2T
4T
8T
16T
32T
1 frame (16.7ms)
60Hz
17
Area ratio grayscale driving method 3
1 ??????
???1
Display-Period-Separated?
???n
????
??????
???????????????????????????????
1 ??????
???1
Simultaneous-Erasing-Scan?
???n
?????
1 ??????
???1
Multiple Addressing Sequence?
???n
18
Area ratio grayscale driving method 4
Multiple Addressing Sequence?
19
Why we can get luminous uniformity?
TFT Vgsconst.
Vdd
Vth shift
VTFT
VEL
OEL
Vdd
VOEL
VTFT
20
Voltage programming
Data
VDD
Select
C2
MN2
MN1
C1
MN3
Data AZ AZB Select
?Vdata
AZ
AZB
MN4
OLED
12345678
(a)
(b)
(Sarnoff Co. SID98)
21
Voltage programming 2
??
????1
????2
Vth???
Vth???
Vdata???
Vdata????
Vdata????
22
Voltage programming 3
VOLED -Vdd
V
t
W/L4,µ100cm2/Vs,C1pF ? A/C0.5µsec
23
Voltage programming 4
Vdd
C2
Vdata ? Vdata?Vdata
4 ? 5
Vth ? Vg
C1
Cg
24
Advance Detection Self Compensation
???m
???n-1
???n
???n
???n-1
?????n
?????n
??? ??
??? ??
?? ??
Vth?? ??
25
Point Scanning
???????????
1
176
?????????????IC
1R 1G 1B
8R 8G 8B
?????????
8RGB
??????????????
????????
26
Current programming 1
Idata
Vdd
Select line 1
Vselect1
Select line 2
Vselect2
T4
Source line
Data line
T2
T3
T1
CS
ID
Kyushu Univ. Univ. of Michigan
OLED
27
Current programming 2
Idata
Vdd
Frame time
Select time
Select time
Select line 1
Vselect1
Select line 2
Vselect2
Vselect1
T4
VT4
Source line
Data line
T2
Vselect2
VT2
T3
VDS
T1
VGS
Idata
ID
CS
VOLED
OLED
ID
28
Current programming 3
A Writing
B Emitting
29
Current programming 4
Idata
Vdd
Frame time
Select time
Select time
Scanning line 1
Vselect1
Scanning line 2
Vselect2
CS
Vselect1
T3
T1
Source line
Data line
Vselect2
T2
Idata
T4
Idata
ID
OLED
ID
30
Current programming 5
Scanning line 1
Scanning line 1
Scanning line 1
Scanning line 1
Scanning line 2
Scanning line 2
T4
T4
T4
T4
T2
T2
T2
T2
T3
T3
T3
T3
T1
T1
T1
T1
(a)
(b)
(c)
(d)
31
Current programming 6
T4
T4
T4
T2
T2
T2
CS
T3
T3
T1
T1
T3
T1
CS
CS
OLED
OLED
OLED
(a)
(b)
(c)
32
Current programming 7
33
Current programming 8
Philips Research Lab. IDW00
Kyushu Univ Univ. of Michigan IEICE
Transactions 2000
Sarnoff Co. IEDM98
Sony SID01
Matsushita SID03
NEC EuroDisplay02
34
Current programming 9
VDD
???n
??? ??????? ?????
Cst
P2
P1
P3
???m ???????m ?????m
Cboost
P4
????? ??
?? ??
IOLED
Idata
Vcathode
35
Current programming 10
?Vselectlt0
?Vselectgt0
Cp
Cp
Idata
Idata
TDrive
TDrive
TSwitch
TSwitch
Cs
Cs
?Vglt0
?Vggt0
IOLED
IOLED
IOLED
?Vggt0
?Vglt0
0
Idata
36
?????????

• ?????????????????
• T2???????????????????????????????
• T4?T2???????????????????????
• T2?T4?L????W?T4??????????
• ????????????????????
• T2?T4??????????????????????

data
write scan
idata
T4
T1
T3
erase scan
(Sony 2001)
37
???????????PWM??
Signal voltage
Sweep voltage
Input line
OLED luminous period
T1
Inverter
C1
OLED
Signal voltage
Signal range
Sweep voltage
T3
T2
Sweep gate line
Reset line
Frame period
Data line
Sweep line
Hitachi (SID02)

• DLP (Digital light processing)??????
• ???????OLED?????????????

38
3TFT ???????????PWM??
Hitachi (SID04)
39
a-Si TFT AM-OLED circuit

• ????
• ????

40
TFT ??????
Luminance100 cd/m2 Display Size11 inch Display
TypeVGA Color Pixel Size116?350 mm Channel
Length6 mm
a-Si (µ0.4 cm2/Vs)
poly-Si (µ10 cm2/Vs)
41
????????
?? 100 cd/m2 ????? 314 lm/m2 (??)X3.14 ?????_at_540 6
49 lm/W ????? 0.48 W/m2 (?????)/
(?????) ???? 1.32E14 1/scm2 (?????)/(???????) ????
?? 3 ???? 70 mA/cm2 (????)X(???)/(??????) ??????
116 um x 349 um ??/???? 0.29 uA (????)X(??????) T
FT???(u) 0.4 cm2/Vs ????(L) 6 um ?????(Vg) 15
V ????(Vth) 5 V ????(d) 300 nm ??????(er) 7.0 ???
? 4.15 um Id0.5(W/L)u(er?e0/d) (Vg-Vth)2
42
????????2
?? 100 cd/m2 ???? 14.2 cd/A ?3_at_540nm ???? 0.70
mA/cm2 (??)/(????) ?????? 116 um x 349
um ??/???? 0.29 uA (????)X(??????) TFT???(u) 0.4
cm2/Vs ????(L) 6 um ?????(Vg) 15 V ????(Vth) 5
V ????(d) 300 nm ??????(er) 7.0 ???? 4.15
um Id0.5(W/L)u(er?e0/d) (Vg-Vth)2
43
a-Si TFT?????????

• ?????
• ??????????????
• ????????????
• ?????????????
• TFT?????????????????
• ????????IC???

44
IBM?????????
SID03 IDTech, IBM, Chi Mei
45
IBM?????????
????
D
D
D
D
Vdata
G
G
G
G
S
S
S
S
VGSgtVth
VGSVth
VGSVthVdata
VGSVthVdata
VS-Vth
VS0
VS-Vth
VS-18VOLED
Vca10V
Vca0
Vca0
Vca-18V
(2) Vth???
(1) ????
(3) Vdata???
(4) ??
46
IBM?????????
Vdata
VG
CS
VC
VS
COLED
Vca
47
IBM?????????
48
IBM????????(2TFT)
???
???
???
???
T2
????
????
T2
T3
T1
T1
CS
CS
????
????
?????????????????(???????????????)?????TFT?????
49
??????????? (IDW03)
????????
IDW03 IDTech
50
??????????? (IDW03)
CsltltCOLED
-VDATA
c
c
c
c
a
b
a
b
a
b
a
b
VthVDATA
0
0
-VDD
Vp
(1) Preparation
(2) Program Vth
(3) Write Vdata
(4) Emission
VaVth Vb0 VcVth
VaVtha Vb-VDATA VcVth
Va -VDD Vth VDATA Vb -VDD Vclt0
VaVpVthVDATA VbVp VcVp

• ?????????????OLED???????????????
• TFT????????????????????

51
??????????? (SID06)
52
0
VdH
Vth sense
Vth
VdH-Vth
0
0
0
Not Writing
-VdHVth
VdH-Vth
0
0
-Vp
-Vp
Vd
Writing
Vd
Reset OLED
Vd-VdHVth
Vd-VdHVth
VdH-Vth
VdH-Vth
0
-Vp
53
Tth(On) Tth(Off)
54
(No Transcript)
55
KAIST????????
VDD
VDTVth
VDT
(1)
(2)
Emission
KAIST IEEE Electron Device Letters, Vol.24, No.9,
(2003)
56
KAIST ???????? (SID04)
(1)
(2)
(3)
VDD
DT
TNO
Sw3
C2
SLTn-1
TNO
SLTn-1
Sw2
Sw1
C1
DTFT
SLTn
SLTn
OLED
DT
VCC
n-1thVinput
nthVinput
SID04 KAIST Kyung Hee Univ.
57
SNU???????? (IMID05)
Seoul National University, IMID05
58
SEC ????????
Development of a 14.1 inch Full Color AMOLED
Display with Top Emission Structure J. H. Jung,
J. C. Goh, B. R. Choi, C. C. Chai, H. Kim, S. P.
Lee, U. C. Sung, C. S. Ko, N. D. Kim, and K.
Chung LCD RD Center, Samsung Electronics Co.,
Ltd., Kyunggi-do, Korea
59
???????a-Si TFT??OLED

• ??????
• ??????????
• Vth?????????
• ????????????????Vth?????
• ????????LSI
• ??????????????
• ?????????????????????
• Vth????
• ????????????Vth?????????

60
CASIO?? ?????????
Select
Frame
Select
IData
V1
Scanning line
V1
Source line
V2
V2
T1
0
T3
VG
Data line
IData
CS
Vm
T2
OLED
IOLED
0
IOLED
VOLED
0
3-TFT,1-C, 3-Busline
61
CASIO?? ?????????
???????????
10
Vs0V
Vs18V
VGVD
OEL
8
T3
T3
CS
CS
6
µA
D
I
4
VGConst.
IEL
IEL
2
(2)?????
(1)?????
0
0
10
20
V
V
D
62
CASIO?? ?????????
63
CASIO?? ?????????
Select
Frame
Select
IData
V1
Scanning line
V1
Source line
V2
CS
V2
0
T3
T1
IData
Data line
T2
IOLED
IOLED
OLED
0
VOLED
0
64
CASIO?? ????????V
Wring
Holding
IData
Selecting
VSelect
Source line
VSource
Select line
VSelect
VSource
T1
VReset
Data Line
T3
IT3
IData
CS
T2
IT3
IOLED
IOLED
VReset
?????????
65
CASIO?? ?????????
CASIO KYUSHU UNIV. IDW 2004
66
CASIO?? ?????????
???????????

• Each pixel column has two data-lines.
• The programming time is doubled.
• The number of selecting source driver outputs
  are reduced by a half.
• Using CL and de-MPX, increase of data driver
  outputs can be avoid.

67
CASIO?? ?????????
??????? ????DeMUX
68
CASIO?? ?????????
??????????
Current Programming
Current Mirror
69
CASIO?? ?????????
?????????????DeMUX
70
???????a-Si TFT??OLED

• ??????
• OLED?????????????????
• ???????????????
• ??????????????????
• ???????????LSI
• ?????????????????
• MOS????????????????????
• ??????????????
• ????
• ???????????????????
• ?????????????

71
???????
Idata
ID
VGSVDS
C
C Cp Cline
???????????? ??TFT??????????? ??????
72
????
Cpd 8pF, VGA 11inch, Wdata10µm
Cathode
10µm
xc
Scan line
xs
Data line
16cm