CN103954898A - Testing method for OLED product service life - Google Patents

Abstract

The invention discloses a testing method for an OLED product service life. The method includes the following steps: through welding a tested OLED white-light device on an experiment board, enabling the OLED white-light device to emit light normally and applying a set accelerating current stress I1 to the experiment board so as to light on the OLED white-light device and carry out a life-service invalidation test and recording a time t1 when the luminance of the OLED white-light device is decayed to 50% of the original luminance; then applying a set accelerating current stress Ii to the experiment board and repeating the step 1 and recording a corresponding service life time ti; and then according to the accelerating current stresses (I1, I2...Ii) and corresponding (ti, ti...ti), obtaining an average life service Mu0<-> and a neutral-position service life t0.5 of the OLED white-light device under a condition of a normal current stress I0. The OLED product service life detected by the testing method is high in precision and the consumed time is shorter.

Description

A kind of method of testing of OLED life of product

Technical field

The present invention relates to a kind of method of testing of life of product, be specifically related to a kind of method of testing of OLED life of product.

Background technology

Domestic enterprise still carries out life test according to conventional method to its research and development OLED product at present, not only expend the plenty of time, and very easily lag behind the speed of model change, life test has lost meaning like this, in the time carrying out OLED life tests, general the spent time is all long, and cost is high simultaneously, serious waste manpower and materials, the ratio of precision in the life-span simultaneously detecting is poor.

Summary of the invention

The object of the invention is to overcome the shortcoming of above-mentioned prior art, a kind of method of testing of OLED life of product is provided, the precision of the OLED life of product that the method detects is high, and the time of cost is short.

For achieving the above object, the method for testing of described OLED life of product comprises the following steps:

1) tested OLED white light parts is welded on brassboard and makes OLED white light parts normally luminous, apply to described brassboard and set acceleration current stress I ₁, light described OLED white light parts and carry out life failure test, when the brightness decay of described OLED white light parts is to starting 50% of brightness, writing time t ₁;

2) apply the acceleration current stress I of setting to described breadboard _i, repeating step 1), record corresponding life time t _i;

3) according to accelerating current stress (I ₁, I ₂... I _i) and corresponding (t _i, t _i... t _i) obtain described OLED white light parts at usual current stress I ₀condition under mean lifetime and median life t _0.5.

Described step 3) comprise the following steps:

1) according to described acceleration current stress (I ₁, I ₂... I _i) and with corresponding (t ₁, t ₂... t _i) utilize least square method to obtain accelerated aging equation:

u＝α-β lnI (1)

Wherein, α and β known constant, I is for accelerating electric current pressure, and u is life time;

2) obtain according to weighted mean formula, Reverse index formula and Nelson theorem:

${\mathrm{\&tau;}}_{\mathrm{ji}}=\frac{t_j}{t_i}={\left(\frac{I_j}{I_i}\right)}^{\mathrm{\&beta;}}---\left(2\right)$

Wherein, accelerator coefficient τ _ji=t _j/ t _i, β is the slope in life-span accelerate equation, can utilize thus I _icurrent stress under test period t _icalculate current stress I _junder test period t _j;

3) make j=0, can obtain OLED at normal working stress I ₀under with respect to accelerating stress I _ithe expression formula of lower life-span accelerator coefficient is:

${\mathrm{\&tau;}}_i={\mathrm{\&tau;}}_{0i}=t_0/t_i={\left(\frac{I_0}{I_i}\right)}^{\mathrm{\&beta;}}---\left(3\right)$

Wherein, β is the slope in formula (1);

4), due to described OLED life-span obeys logarithm normal distribution, accelerate stress I _iunder mean lifetime with median life t ⁱ _0.5be respectively

${\stackrel{\&OverBar;}{\mathrm{\&mu;}}}_i=e^{({\mathrm{\&mu;}}_i+\frac{1}{2}{\mathrm{\&sigma;}}^2)},{t^i}_{0.5}=e^{{\mathrm{\&mu;}}_i}---\left(4\right)$

5) convolution (3) and (4), just can calculate OLED at I ₀under mean lifetime with median life t _0.5be respectively:

${\stackrel{\&OverBar;}{\mathrm{\&mu;}}}_0={\mathrm{\&tau;}}_i\&CenterDot;{\stackrel{\&OverBar;}{\mathrm{\&mu;}}}_i,t_{0.5}={\mathrm{\&tau;}}_i\&CenterDot;{t^i}_{0.5}---\left(5\right)$

Then OLED is subject to obtaining current stress I under normal circumstances ₀and the numerical value of β is brought in formula (3) and (4), recycling formula (5) draws I ₀under condition, OLED mean lifetime is and median life is t _0.5.

Compared with prior art, the present invention has following beneficial effect:

The method of testing of OLED life of product of the present invention is by applying different acceleration current stress I on OLED _i, and be recorded in acceleration current stress I _icondition under the life-span t of described OLED _i, and according to described different acceleration current stress I _iand t _iobtain the mean lifetime of described OLED described OLED under the condition that applies normal current stress, the degree of accuracy of the mean lifetime of simple to operate, the OLED that obtains is high, can provide at short notice that white light OLED is produced and the reliable life information of new product development.

Brief description of the drawings

Fig. 1 is the statistic curve of three groups of constant stresss in embodiment mono-;

Fig. 2 is I in embodiment mono- ₁, I ₂, I ₃life characteristics figure.

Embodiment

Below in conjunction with embodiment, the present invention is described in further detail, following embodiment is only for the present invention is described, but the practical range being not intended to limit the present invention.

The method of testing of OLED life of product of the present invention, comprises the following steps:

1) tested OLED white light parts is welded on brassboard and makes OLED white light parts normally luminous, apply to described brassboard and set acceleration current stress I ₁, light described OLED white light parts and carry out life failure test, when the brightness decay of described OLED white light parts is to starting 50% of brightness, writing time t ₁;

2) apply the acceleration current stress I of setting to described breadboard _i, repeating step 1), record corresponding life time t _i;

3) according to accelerating current stress (I ₁, I ₂... I _i) and corresponding (t _i, t _i... t _i) obtain described OLED white light parts at usual current stress I ₀condition under mean lifetime and median life t _0.5.

Wherein, described according to accelerating current stress (I ₁, I ₂... I _i) and with corresponding (t _i, t _i... t _i) obtain described OLED white light parts at usual current stress I ₀condition under mean lifetime and median life t _0.5.Comprise the following steps:

1) according to described acceleration current stress (I ₁, I ₂... I _i) and with corresponding (t ₁, t ₂... t _i) utilize least square method to obtain accelerated aging equation:

u＝α－β lnI (1)

Wherein, α and β known constant, I is for accelerating electric current pressure, and u is life time;

2) obtain according to weighted mean formula, Reverse index formula and Nelson theorem:

${\mathrm{\&tau;}}_{\mathrm{ji}}=\frac{t_j}{t_i}={\left(\frac{I_j}{I_i}\right)}^{\mathrm{\&beta;}}---\left(2\right)$

Wherein, accelerator coefficient τ _ji=t _j/ t _i, β is the slope in life-span accelerate equation, can utilize thus I _icurrent stress under test period t _icalculate current stress I _junder test time ask t _j;

3) make j=0, can obtain OLED at normal working stress I ₀under with respect to accelerating stress I _ithe expression formula of lower life-span accelerator coefficient is:

${\mathrm{\&tau;}}_i={\mathrm{\&tau;}}_{0i}=t_0/t_i={\left(\frac{I_0}{I_i}\right)}^{\mathrm{\&beta;}}---\left(3\right)$

Wherein, β is the slope in formula (1);

4), due to described OLED life-span obeys logarithm normal distribution, accelerate stress I _iunder mean lifetime with median life t ⁱ _0.5be respectively

${\stackrel{\&OverBar;}{\mathrm{\&mu;}}}_i=e^{({\mathrm{\&mu;}}_1+\frac{1}{2}{\mathrm{\&sigma;}}^2)},{t^i}_{0.5}=e^{{\mathrm{\&mu;}}_i}---\left(4\right)$

5) convolution (3) and (4), just can calculate OLED at I ₀under mean lifetime with median life t _0.5be respectively:

${\stackrel{\&OverBar;}{\mathrm{\&mu;}}}_0={\mathrm{\&tau;}}_i\&CenterDot;{\stackrel{\&OverBar;}{\mathrm{\&mu;}}}_i,t_{0.5}={\mathrm{\&tau;}}_i\&CenterDot;{t^i}_{0.5}---\left(5\right)$

Then OLED is subject to obtaining current stress I under normal circumstances ₀and the numerical value of β is brought in formula (3) and (4), recycling formula (5) draws I ₀under condition, OLED mean lifetime is and median life is t _0.5.

Embodiment mono-

1) data statistics

The data of hypothetical record are as described in Table 1:

Table 1

2) process test figure, calculate test findings

Suppose 1: under current stress I, white light OLED life-span obeys logarithm normal distribution, its distribution function is

$F\left(t\right)=\mathrm{\&Phi;}\left(z\right)={\&Integral;}_{\&infin;}^z\frac{1}{\sqrt{2\mathrm{\&pi;}}}\exp [-\frac{z^2}{2}]\mathrm{dz}---\left(6\right)$

In formula, z=(lnt-μ)/σ, μ is logarithm average, σ is called logarithm standard deviation.

Suppose 2: at normal working stress I ₀with each acceleration stress I _iunder (i=1,2,3), the mechanism of white light OLED is constant, gets weighted mean:

$\mathrm{\&sigma;}=\underset{i=1}{\overset{3}{\&Sum;}}{n}_i{\mathrm{\&sigma;}}_i/\underset{i=1}{\overset{3}{\&Sum;}}{n}_i---\left(7\right)$

Suppose 3: for white light OLED, acceleration model meets Reverse index formula, the horizontal I of average μ and electric stress meets following relational expression:

μ＝α+βlnI (8)

In formula: α, β is acceleration parameter to be estimated.

Suppose 4: failure probability meets Nelson theorem.Nelson has proposed sample residue storage life in 1980 only with cumulative failure part and stress level was relevant at that time at that time, and irrelevant with accumulation mode.Be that OLED is at stress I _iunder, time t has worked _ithe failure probability of accumulation is F _i(t _i), be equivalent to this product at stress I _junder, time t has worked _jthe failure probability F accumulating _j(t _j), be

F _i(t _i)＝F _j(t _j) (9)

Statistical study stress accelerated life test data

Pair distribution function formula (1) 6 is done with down conversion

${\mathrm{\&Phi;}}^{-1}\left(F\left(t\right)\right)=\frac{1}{\mathrm{\&sigma;}}1\mathrm{nt}-\frac{\mathrm{\&mu;}}{\mathrm{\&sigma;}}---\left(10\right)$

Order

$x=\ln t,y={\mathrm{\&Phi;}}^{-1}\left(F\left(t\right)\right)---\left(11\right)$

$a=1/\mathrm{\&sigma;},b=-\mathrm{\&mu;}/\mathrm{\&sigma;}---\left(12\right)$

Obtain following linear relation:

y＝ax+b (13)

Out-of-service time is sorted from small to large, each t _icorresponding cumulative failure probability F (t _i) adopt meta order formula to calculate:

$F\left(t_j\right)=\frac{j-0.3}{n_i+0.4},j=\mathrm{1,2},\&CenterDot;\&CenterDot;\&CenterDot;,n_i---\left(14\right)$

So just obtain battery of tests data

$(t_j,F\left(t_j\right)),j=\mathrm{1,2},\&CenterDot;\&CenterDot;\&CenterDot;,n_i---\left(15\right)$

Adopt least square method to estimate the parameter of lognormal distribution.Be converted into according to formula (11) wushu (15)

Lognormal distribution linear model adopts least square method to return as straight line, and its coefficient expression formula is as follows

$a=\frac{\underset{j=1}{\overset{n_i}{\&Sum;}}{x}_j{y}_j-\left(\underset{j=1}{\overset{n_i}{\&Sum;}}{x}_j\underset{j=1}{\overset{n_i}{\&Sum;}}{y}_j\right)/n_i}{\underset{j=1}{\overset{n_i}{\&Sum;}}{x^2}_j-{\left(\underset{j=1}{\overset{n_i}{\&Sum;}}{x}_j\right)}^2/n_i}$ $b=\underset{j=1}{\overset{n_i}{\&Sum;}}{y}_j/n_i-a\underset{j-1}{\overset{n_i}{\&Sum;}}{x}_j/n_i---\left(17\right)$

Can be obtained by formula (13):

σ＝1/a,μ＝-b/a (18)

The related coefficient expression formula of xj and yj is

$R^2=\frac{{(\underset{j=1}{\overset{n_i}{\&Sum;}}{x}_i{y}_j-\left(\underset{j=1}{\overset{n_i}{\&Sum;}}{x}_j\underset{j=1}{\overset{n_i}{\&Sum;}}{y}_j\right)/n_i)}^2}{(\underset{j=1}{\overset{n_i}{\&Sum;}}{x^2}_j-{\left(\underset{j=1}{\overset{n_i}{\&Sum;}}{x}_j\right)}^2/n_i)(\underset{j=1}{\overset{n_i}{\&Sum;}}{y^2}_j-{\left(\underset{j=1}{\overset{n_i}{\&Sum;}}{y}_j\right)}^2/n_i)}---\left(19\right)$

Here the x in formula (18) and (19), _jand y _jcalculate by test figure and formula (17), the absolute value of R more approaches 1, illustrates that the degree of linear dependence between two variablees is higher.

Convolution (6), (11) and (15) three groups of constant stress data in can his-and-hers watches 1 are processed, and its statistic curve is shown in Fig. 1, and the straight line in this figure adopts least square method to carry out matching.Concrete data are listed in table 2.

Lognormal distribution parameter under the each stress of table 2 is as shown in table 2:

Table 2

3) calculate accelerated aging equation

By I ₁=13mA, I ₂=16mA, I ₃μ under tri-groups of constant stresss of=19mA ₁=7.0926, μ ₂=6.7269 and μ ₃=6.5939, utilize least square method to solve and obtain α=11.6094, β=-1.7609, accelerated aging equation is

u＝11.6094-1.7609lnI (20)

Accelerated aging curve is OLED life characteristics figure, as shown in Figure 2.Fig. 2 is actually life characteristics figure, its coefficient of determination R ²=0.9783, close to 1, illustrate that fitting degree is very good, this confirms that the acceleration model of white light OLED meets the supposition of Reverse index formula completely.

4) according to theory hypothesis, the OLED life-span is carried out to prediction and calculation

Note accelerator coefficient τ _ji=t _j/ t _i,, convolution (7), (8), (9) can obtain

${\mathrm{\&tau;}}_{\mathrm{ji}}=\frac{t_j}{t_i}={\left(\frac{I_j}{I_i}\right)}^{\mathrm{\&beta;}}---\left(21\right)$

In formula: β is the slope in accelerated aging equation (8), is acceleration parameter.Can be obtained by formula (21)

t _j＝τ _jit _i (22)

According to formula (21), utilize at I _itest period t under stress _i, just can obtain and be equivalent at stress I _junder test period t _j.

Press the definition of accelerator coefficient, in formula (21), make j=0, can obtain product at normal working stress I ₀under with respect to accelerating stress I _ithe expression formula of (i=1,2,3) accelerator coefficient of lower life-span

${\mathrm{\&tau;}}_i={\mathrm{\&tau;}}_{0i}=t_0/t_i={\left(\frac{I_0}{I_i}\right)}^{\mathrm{\&beta;}}---\left(23\right)$

In the time of OLED life-span obeys logarithm normal distribution, accelerate stress I _iunder mean lifetime with median life t ⁱ _0.5be respectively

${\stackrel{\&OverBar;}{\mathrm{\&mu;}}}_i=e^{({\mathrm{\&mu;}}_1+{\frac{1}{2}}^{{\mathrm{\&sigma;}}^2})},{t^i}_{0.5}=e^{{\mathrm{\&mu;}}_i}---\left(24\right)$

Like this, convolution (23) and (24), just can calculate OLED at I ₀under mean lifetime with median life t _0.5be respectively

${\stackrel{\&OverBar;}{\mathrm{\&mu;}}}_0={\mathrm{\&tau;}}_i\&CenterDot;{\stackrel{\&OverBar;}{\mathrm{\&mu;}}}_i,t_{0.5}={\mathrm{\&tau;}}_i\&CenterDot;{t^i}_{0.5}---\left(25\right)$

By I ₀=8.50mA substitution accelerated aging equation (20), can obtain the logarithm average μ of OLED under running current ₀=7.8409;

Again β=-1.7609 substitution formula (18) is tried to achieve respectively to OLED at three stress I _iaccelerator coefficient under (i=1,2,3): τ ₁=2.0915, τ ₂=3.0158, τ ₃=3.4552.According to formula (7), and utilize each stress I in table 2 _ithe estimation values sigma of lower logarithm standard deviation _i(i=1,2,3) can obtain σ=0.0818.Logarithm average μ in convolution (24) and table 2 _i, try to achieve I _iunder mean lifetime be respectively: ${\stackrel{\&OverBar;}{\mathrm{\&mu;}}}_1=1207.1h,$ ${\stackrel{\&OverBar;}{\mathrm{\&mu;}}}_2=837.1h,$ ${\stackrel{\&OverBar;}{\mathrm{\&mu;}}}_3=730.6h.$

Therefore, utilize formula (25) just can calculate I ₀under OLED mean lifetime be ${\stackrel{\&OverBar;}{\mathrm{\&mu;}}}_0={\stackrel{\&OverBar;}{\mathrm{\&mu;}}}_1\&CenterDot;{\mathrm{\&tau;}}_1={\stackrel{\&OverBar;}{\mathrm{\&mu;}}}_2\&CenterDot;{\mathrm{\&tau;}}_2={\stackrel{\&OverBar;}{\mathrm{\&mu;}}}_3\&CenterDot;{\mathrm{\&tau;}}_3:=2524.6h.$ In addition, adopt and use the same method that can to obtain median life be t _0.５＝2516.2h。

Claims (2)

1. a method of testing for OLED life of product, is characterized in that, comprises the following steps:

1) tested OLED white light parts is welded on brassboard and makes OLED white light parts normally luminous, apply to described brassboard and set acceleration current stress I ₁, light described OLED white light parts and carry out life failure test, when the brightness decay of described OLED white light parts is to starting 50% of brightness, writing time t ₁;

2) apply the acceleration current stress I of setting to described breadboard _i, repeating step 1), record corresponding life time t _i;

3) according to accelerating current stress (I ₁, I ₂... I _i) and corresponding (t _i, t _i... t _i) obtain described OLED white light parts at usual current stress I ₀condition under mean lifetime and median life t _0.5.

2. the method for testing of OLED life of product according to claim 1, is characterized in that, described step 3) comprise the following steps:

1) according to described acceleration current stress (I ₁, I ₂... I _i) and with corresponding (t ₁, t ₂... t _i) utilize least square method to obtain accelerated aging equation:

u＝α－β lnI (1)

Wherein, α and β known constant, I is for accelerating electric current pressure, and u is life time;

2) obtain according to weighted mean formula, Reverse index formula and Nelson theorem:

${\mathrm{\&tau;}}_{\mathrm{ji}}=\frac{t_j}{t_j}={\left(\frac{I_j}{I_i}\right)}^{\mathrm{\&beta;}}---\left(2\right)$

Wherein, accelerator coefficient τ _ji=t _j/ t _i, β is the slope in life-span accelerate equation, can utilize thus I _icurrent stress under test time ask t _icalculate current stress I _junder test period t _j;

3) make j=0, can obtain OLED at normal working stress I ₀under with respect to accelerating stress I _ithe expression formula of lower life-span accelerator coefficient is:

${\mathrm{\&tau;}}_i={\mathrm{\&tau;}}_{0i}=t_0/t_i={\left(\frac{I_0}{I_i}\right)}^{\mathrm{\&beta;}}---\left(3\right)$

Wherein, β is the slope in formula (1);

4), due to described OLED life-span obeys logarithm normal distribution, accelerate stress I _iunder mean lifetime with median life t ⁱ _0.5be respectively

${\stackrel{\&OverBar;}{\mathrm{\&mu;}}}_i=e^{({\mathrm{\&mu;}}_1+\frac{1}{2}{\mathrm{\&sigma;}}^2)},{t^i}_{0.5}=e^{{\mathrm{\&mu;}}_i}---\left(4\right)$

5) convolution (3) and (4), just can calculate OLED at I ₀under mean lifetime with median life t _0.5be respectively:

${\stackrel{\&OverBar;}{\mathrm{\&mu;}}}_0={\mathrm{\&tau;}}_i\&CenterDot;{\stackrel{\&OverBar;}{\mathrm{\&mu;}}}_i,t_{0.5}={\mathrm{\&tau;}}_i\&CenterDot;{t^i}_{0.5}---\left(5\right)$

Then OLED is subject to obtaining current stress I under normal circumstances ₀and the numerical value of β is brought in formula (3) and (4), recycling formula (5) draws I ₀under condition, OLED mean lifetime is and median life is t _0.5.