JPS6217360B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention utilizes EL (Electro
This relates to a heat treatment method for stabilizing the physical characteristics, dielectric breakdown characteristics, etc. of thin film EL devices that emit light (luminescence).

Conventionally, for AC-operated thin-film EL devices, a high electric field (about 10 ⁶ V/cm) is regularly applied to the light-emitting layer to improve dielectric strength, luminous efficiency, operation stability, etc. % Mn (or Cu,
_A three- _{layer structure} ZnS:Mn ( _{or ZnSe} :
Mn) EL devices have been developed, and improvements in various light-emitting properties have been confirmed. This thin film EL element emits high-intensity light when an alternating current electric field of several KHz is applied, and has a long lifespan. Also, this thin film
It has been discovered that the light emission of EL elements has hysteresis characteristics, such that the luminance of light differs for the same applied voltage in the process of increasing the applied voltage and in the process of decreasing the voltage from the high voltage side. In the process of increasing the voltage applied to a thin film EL element with hysteresis characteristics, when light, electric field, heat, etc. are applied, the thin film EI element is excited to a state of luminance corresponding to the intensity, and emits light. The so-called memory phenomenon, in which the luminance remains high even after the electric field, heat, etc. are removed and the original state is restored, has opened up a new field of application for display technology.

FIG. 1 shows the basic structure of a ZnS:Mn thin film EL device as an example of a thin film EL device.

The structure of the thin film EL device will be explained in detail based on the attached drawings. A transparent electrode 2 made of In ₂ O ₃ , SnO ₂ , etc. is placed on a glass substrate 1, and Y ₂ O ₃ , etc. is further laminated thereon.
A first dielectric layer 3 made of TiO ₂ , Al ₂ O ₃ , Si ₃ N ₄ , SiO ₂ or the like is formed in an overlapping manner by sputtering or electron beam evaporation. A ZnS light emitting layer 4 is formed on the first dielectric layer 3 by electron beam evaporation of ZnS:Mn sintered pellets. At this time, the ZnS:Mn sintered pellets used for deposition are pellets in which the concentration of Mn, which is an active substance, is set to suit the purpose. A second dielectric layer 5 made of the same material as the first dielectric layer 3 is laminated on the ZnS light emitting layer 4, and a back electrode 6 made of Al or the like is further deposited thereon. The transparent electrode 2 and the back electrode 6 are connected to an AC power source 7, and the thin film
The EL element is driven.

When an AC voltage is applied between the electrodes 2 and 6, the above AC voltage is induced between the dielectric layers 3 and 5 on both sides of the ZnS luminescent layer 4, and therefore the electric field generated within the ZnS luminescent layer 4 Therefore, electrons excited and accelerated into the conduction band that have obtained enough energy can directly
The Mn luminescent center is excited by collision, and when the excited Mn luminescent center returns to the ground state, it emits yellow-orange light. In other words, electrons accelerated by a high electric field entered the Zn site, which is a luminescent sensor, in the ZnS luminescent layer 4.
When the electron of Mn atom is excited and falls to the ground state,
It emits strong light in a wide wavelength range with a peak of approximately 5850 Å. When a rare earth fluoride other than Mn is used as an active substance, green and other luminescent colors characteristic of this rare earth element can be obtained.

The thin film EL device having the above configuration needs to be aged for a certain period of time after each thin film is fabricated in order to stabilize changes in luminance and the like over time and to remove defective elements due to early failures. Aging generally requires a heat treatment time of ten or more hours to several tens of hours, and the above objective is achieved within this period. By performing aging efficiently, physical characteristics such as luminance of light emission are stabilized, and the occurrence of other defective elements other than initial failures is prevented. Furthermore, the lifetime of wire breakage can be predicted from the minute fracture points that occur during aging. However, conventional thin film
The aging method for EL devices involves heat treatment while applying a constant AC voltage, which takes a long time and also reduces the luminance of the thin film EL device during the aging process.
Since the applied voltage characteristics (hereinafter referred to as B-V characteristics) change, if the voltage applied through the transparent electrode 2 and the back electrode 6 is set to a constant value and heat-treated, the aging efficiency will decrease over time. was. Figure 2 shows the B-V characteristics of the thin film EL device 1, 3, and 5 hours after the start of aging, where the curve _l1 is the B-V characteristic curve before the start of aging, and the curve _l2 is the B-V characteristic curve after the start of aging. B-V characteristic curve over time,
Curve l ₃ is the B-V characteristic curve after the same 3 hours have passed,
Curve _l4 is the BV characteristic curve after the same 5 hours have elapsed. Therefore, if the applied voltage value during aging is kept constant at VD, the actual operating point on the BV curve will move with the passage of time. In order to perform aging efficiently, it is necessary that the voltage value is above a certain level and that the operating point on the BV curve is approximately constant.

FIG. 3 is an explanatory diagram showing changes in luminance over time during aging when aging is performed at a constant voltage. Further, FIG. 4 is an explanatory diagram showing the change over time of the light emission start voltage value (voltage value that provides 1 foot lambert of brightness) V _th during aging. In order to carry out aging effectively in a short time, special requests should be made to
55-85705, it is desirable to apply an alternating current pulse having sufficient luminance and a suitable voltage, e.g., at least (V _th +20) volts and at most (V _th +60) volts. However, in the aging process set at a constant voltage, as shown in Figures 3 and 4, B-
The V characteristics and V _th change, resulting in insufficient luminance and voltage values. If the initial set voltage is increased to compensate for this luminance and voltage drop, more defective elements than necessary will be produced due to dielectric breakdown.

In view of the above problems, it is an object of the present invention to provide a new and useful aging method for a thin film EL element that can efficiently obtain an aging effect in a short time by making full use of technical means.

Hereinafter, the present invention will be explained in detail according to embodiments with reference to the drawings.

FIG. 5 is an explanatory diagram showing a change in the rectangular wave alternating current pulse applied voltage (peak value) during aging to explain an embodiment of the present invention.

During the aging process, the light emission starting voltage value V _th of the thin film EL element changes as shown in FIG. Therefore, in this example, the aging voltage applied to the thin film EL element during aging is adjusted to V _{th +}
The voltage is applied while controlling the voltage to be V _C (V _C : constant). In addition, the value of V _c is preferably about 15V to 80V.
Set to a constant value within the range of 20V to 50V.
By controlling the aging voltage in accordance with the variation of V _th in this way, a sufficient voltage is always applied to the thin film EL element during the aging process, and the aging effect is improved.

For example, the system measures the light emission starting voltage value V _th for 5 seconds at 10 minute intervals, and then
Aging is performed by adding a constant voltage V _C to the measured V _th for a minute. Note that the light emission starting voltage value V _th is
For example, it can be applied with an applied voltage that gives a luminance of 1 foot Lambert.

An example of the system configuration is shown in FIG. 10 is the power supply section, 11 is the EL driver, 12 is the EL panel,
13 is a light sensor. In addition, T of the power supply section 10
_r11 and T _r12 constitute a constant voltage power supply circuit. When measuring the light emission starting voltage, the signal Sigl turns off the transistor T _r13 connected in parallel to the Zener diode ZD (constant voltage characteristic of 30 V), and the signal
Sig2 enables the operation of the base voltage setting circuit (with hold function) SB of transistor T _r12 . The operational amplifier OP ₁ converts the light-receiving current into a voltage, which is compared with the voltage corresponding to the brightness of 1 foot Lambert using the next stage operational amplifier OP ₂ .
By forming the feedback circuit as described above,
The base voltage setting circuit SB is set so that the EL panel 12 can output a luminance of 1 foot Lambert. That is, by this feedback control, the voltage at point A applied to the EL driver 11 through the Zener diode ZD is set to _Vth .

Next, the operation of the base voltage setting circuit SB is stopped by the signal Sig2, and the set value of the base voltage at the time of the measurement is held. At the same time, the signal Sig1 turns on the transistor T _r13 . This results in a voltage that is the sum of the constant voltage of the Zener diode ZD, that is, V _th
A voltage of +V _C is applied to point A to drive the EL panel 12. After 10 minutes, a change in V _th is expected and the measurements described above are performed again.

Aging can be performed by repeating the above operation and applying an applied voltage according to fluctuations in V _th .

As explained in detail above, according to the present invention, sufficient luminance can be obtained from the thin film EL element during aging treatment,
Since an appropriate voltage is applied, aging processing can be performed efficiently in a short time.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the basic structure of a thin film EL element. Figure 2 shows the thin film EL after the start of aging.
It is a BV characteristic diagram of an element. FIG. 3 is an explanatory diagram showing the change in luminance of the thin film EL element during aging. FIG. 4 is an explanatory diagram showing the change over time in the light emission start voltage V _th of the thin film EL element during aging.
FIG. 5 is an explanatory diagram showing changes in applied voltage during aging to explain one embodiment of the present invention. 6th
The figure is a block diagram showing an example of the configuration of an aging system. 2...Transparent electrode, 4...ZnS light emitting layer, 6...Back electrode, 7...AC power supply.

Claims (1)

[Claims] 1. A thin film EL element consisting of a light emitting layer that emits EL light in response to the application of an electric field is interposed between a pair of electrodes, and a predetermined voltage value (V _th ) is applied to the light emission starting voltage value (V th ).
The heat treatment is performed while applying an aging voltage having a voltage value (V _th +V _C ) that is the sum of the voltage value (V th +V C ), and the voltage value ₍ V _th ) of the aging voltage is V _th +V
_C ) A method for aging a thin film EL device, which is characterized by controlling and compensating.