Online proceedings - EDA Publishing Association

I
OLED
7-9 October 2009, Leuven, Belgium
b U
b U
(1)
LOW
mLOW m HIGH
HIGH
Current [A]
1,E-02
1,E-03
1,E-04
1,E-05
LEP = 60 nm
y = 2,144E-08x 6,729E+00
R 2 = 1,000E+00
LEP = 80 nm
y = 2,350E-08x 6,194E+00
R 2 = 1,000E+00
LEP = 100 nm
y = 2,464E-08x 5,287E+00
R 2 = 9,999E-01
1 10
Voltage [V]
Fig. 3. The effect of the LEP thickness; forward I-V characteristics at 25 o C
and the fitted power functions
In our case above 4 V the HIGH range power function is
effective. For simplicity we deal with the only HIGH range
and we leave HIGH subscript. We use it as follow (2):
I
OLED
mT
, d
T
, d bT
, d U
LEP
LEP
where T is the temperature and d LEP is the thickness of the
LEP.
We have fixed the glass substrate to a cold-plate. In the
case of power dissipation the temperature of the LEP could
be a bit higher than that of the cold-plate. In other words, the
tail of the I-V curve may show a certain degree of selfheating.
We measured this temperature error by an infrared
camera. This error is less than 1 C at the tail of curve.
IV.
LEP
PARAMETER FITTING
We carried out the fitting of power function, and we have
tried to determinate m and b parameters on each curve. Fig. 4
shows the changing of m parameter. If the LEP thickness or
the temperature increases, then the exponent decreases.
Similarly we plotted the b parameter (Fig. 5). If the LEP
thickness or the temperature increases, then the factor
increases.
m as exponent
8
7
6
5
4
3
2
1
0
0 20 40 60 80 100
Thickness of LEP [nm]
Temperature
Fig. 4. The effect of the LEP thickness and temperature for the m exponent
(Temperature range is between 5 and 50 C)
(2)
b as factor
10
8
6
4
2
*1E-8
Temperature
0
0 20 40 60 80 100
Thickness of LEP [nm]
5. The effect of the LEP thickness and temperature for the b factor
(Temperature range is between 5 and 50 C)
These parameters vs. LEP thickness able to change
polynomial way. The temperature dependence of m and b
act as polynomial. That’s why we suggest matrixes for m and
b.
V. MODEL
The problem is similar in the case of two parameters. We
use x instead of m and b (3):
x
T
d
LEP
T X d
LEP
, (3)
where T is a temperature row matrix, d LEP is the thickness
column matrix, X is the parameter matrix. If the temperature
and the LEP thickness is known, then the x(T , d LEP ) matrix
product will give only a number.
As follows we show matrixes when the polynomials are
quadratic (4):
0
x
11
x12
x13
d
LEP
0 1 2
1
x T,
d
LEP
T T T
x21
x22
x23
d
LEP (4)
2
x
31
x32
x33
d
LEP
Where the upper index means power exponent.
We determined the M and B matrixes (5), these are:
5.76E
5
M
3.30E
6
3.21E
8
2.21E
3
B
2.49E
5
6.98E
8
VI.
2.26E
2 6.68E
0
2.05E
4 4.03E
2
,
2.64E
8
5.05E
4
3.42E
2 3.14E
1
3.59E
4 4.26E
3
4.73E
6 3.28E
5
CONCLUSION
We have constructed the electro-thermal model for
different LEP-thickness white OLEDs. The model uses
power function to approximate the forward bias above 4 V.
(5)
©EDA Publishing/THERMINIC 2009 122
ISBN: 978-2-35500-010-2