JPS609280B2 - Optical drive device for thin film EL elements - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for driving a three-layer thin film EL element that exhibits a hysteresis phenomenon in the characteristic of luminance versus applied voltage, and is particularly characterized in writing photographic film images using light. be.

Z added with Mn etc. as an active substance forming a luminescent center
It has been reported that a so-called three-eye structure thin film EL element in which an nS:Mn thin film is sandwiched between insulating films such as Y203 has a hysteresis phenomenon in the applied voltage characteristics of the luminance characteristics.

By utilizing this hysteresis phenomenon, the EL element can be operated as a type of memory function element, and information can be arbitrarily written, memorized, and erased based on the magnitude of the luminance of the element. The present invention relates to a method for driving such a three-layer thin film L element, and is particularly characterized in writing film photographic images using light.

Below, along with an explanation of the hysteresis phenomenon, already proposed driving methods will be described to facilitate understanding of the method of the present invention, which will be described later.

Figure 1 is a cross-sectional view showing the structure of a three-layer structure ZnS:Mn thin film light emitting device, in which 1 is a ZnS thin film layer doped with Mn or the like as an active substance to form a luminescent center, 2 and 3 are transparent layers such as Y203, etc. An insulating thin film, 4 a transparent electrode, 5 a back electrode such as AI, and 6 a glass substrate.

As is clear from this figure, this light emitting element has a structure in which a ZnS thin film layer 1 is sandwiched between transparent insulating thin films 2 and 3, and the material or manufacturing conditions of the Z ship thin film layer 1 or the transparent insulating thin films 2 and 3 are different. By appropriately setting , it is possible to cause a hysteresis phenomenon in the luminance of this element. Figure 2 is a diagram showing the luminance versus applied voltage characteristics of the thin film light emitting device of the above-mentioned Z ship, where the axis represents the amplitude (peak value) V of the applied AC voltage pulse, and the vertical axis represents the luminance B. . As is clear from Fig. 2, the luminance of the device as the voltage of the applied pulse increases (shown by curve A) and the luminance of the device as the voltage decreases (shown as curve B). ), there is a significant hysteresis phenomenon. Therefore, we now select a voltage value Vs (maintenance voltage) at a point where the difference between the minimum luminance Be when the voltage increases and the maximum luminance Bw when the voltage decreases is sufficiently large, and use the AC pulse steering s with this as the amplitude. When driving the element, the element maintains the luminance within the range of luminance Bw depending on the pulse train Ps. That is, when the amplitude of the AC pulse train Ps is instantaneously modulated and a high writing voltage Vw is momentarily applied to the element, the element emits light at the instantaneous brightness Bw', and then emit light at the writing brightness Bw with the next AC sustaining pulse. After settling down, this brightness Bw is maintained by applying the AC sustaining pulse thereafter. On the other hand, if the amplitude of the alternating current sustaining pulse train Ps that maintains the write state in this way is further modulated and a sufficiently low erasing voltage Ve is momentarily applied to the element, the element passes through the instantaneous erasing brightness Be' point and then At the next alternating current sustaining pulse Fs, the brightness settles to the erased brightness Be, and this brightness Be is maintained to perform erasing and memory of the erased state. Further, in the above writing and erasing, if the writing or erasing voltages yw and Ve are arbitrarily selected, an intermediate brightness between the brightness Bw and the skin can be obtained. What has been described above is a method of driving a ZnS thin EL element that has already been proposed, and by doing so, the element can be provided with a kind of memory function.

Furthermore, since such a ZnS thin film light emitting element is sensitive to external irradiation light, a method for optically driving this light emitting element is known.

FIG. 3 is a time chart related to the optical driving method,
Figure A shows the applied voltage waveform applied to the element, and the figure in the figure shows the luminance luminance waveform.

In both figures, the time t on the horizontal axis is shown in correspondence with each other. The optical driving method will be described below with reference to this time chart. As shown in the figure, when an AC pulse train s having an amplitude (peak value) equal to the sustaining voltage Ve and a rest period of the pulse is applied to the element, the period Before T, no writing was performed using voltage or light, and the brightness Be in the erased state was maintained by the AC sustaining pulse blade s.

When this element is irradiated with light from the outside in synchronization with the pulse period of the alternating current sustaining pulse s in period T2, the luminance brightness B increases in response to the incident light energy, and after sufficient light irradiation, it becomes completely white. It settles into a writing state, that is, a state where the brightness is Bw. Even after the light irradiation is stopped, this written state is maintained for the duration of the application period of the maintenance pulse milk fertilizer s. (period t). Next, as shown in period L, when this element is irradiated with light from the outside in synchronization with the rest period of the pulse train Ps, the light emission brightness B decreases in accordance with the incident light energy, and after sufficient light irradiation, it becomes completely It settles into an erased state, that is, a state with brightness Be. Even after the light irradiation is stopped, this erased state is maintained for the application period of the sustain pulse train Ps (period L), so the above operation of performing light irradiation in synchronization with the rest period of the pulse train Ps is an operation for erasing. It can be considered. Furthermore, at the time of this optical writing and optical erasing in periods m2 and T4, the writing and erasing effects correspond to the wavelength of the irradiated light and the amount of incident light, that is, the magnitude of the optical energy. The brightness due to brightness can be changed from brightness Bw to brightness B by appropriately selecting this incident light energy.
It can take any value up to e, and can write and erase halftones.

In this writing and erasing process, the element may be irradiated with light not only during one pulse period and one pause period, but also over several pulse periods and a pause period. It is understood that the optical writing described above is performed by the optical polarization effect of the ZnS layer, and the optical erasing is performed by the optical relaxation effect of the ZnS layer. The present invention is an apparatus for optically writing an optical image recorded on a film onto a thin film EL element by utilizing the optical writing action of the thin film EL element.

FIG. 4 shows a block diagram of an optical drive device according to an embodiment of the present invention, in which 21 is a thin film EL element and has the configuration as described above.

22 houses a light source lamp 23 consisting of a flash lamp, an optical system such as a lens 24, a reflector 25, etc., an electric system such as a flash lamp lighting circuit board 26, a trigger coil 27, a capacitor 28, etc. for lighting the flash lamp, and others. It is a projector consisting of

In view of noise, it is desirable that the electrical system, particularly the board 26, be housed within the projector. Reference numeral 29 denotes a film that can be inserted into and removed from the optical path of the optical system.

30 is the flash lamp lighting circuit board 26 and the thin film E.
This control circuit is connected to the L element drive circuit 31 and creates a trigger signal for a sustain pulse and a charging pulse for lighting the flash lamp.

The drive circuit 31 generates the sustain pulse and applies the sustain pulse between the electrodes of the thin film EL element. This drive circuit also generates a front-fill erase pulse, which is applied to all the poles of the thin film EL element at the same time to erase the entire surface. In other words, the optically written image is erased by voltage. Figure 5 shows a flash lamp lighting circuit, 23 is a flash lamp, C is a large capacity capacitor for lighting the flash lamp, T is a switching transistor for charging, T2 is a control transistor for transistor T, VL is an electrode, M is a trigger coil with a turns ratio of 80:1, T3 is a trigger transistor, C2 is a capacitor, a is a charging pulse input terminal, and b is a trigger input terminal.

In this circuit, the control circuit 30 generates a trigger pulse synchronized with the pulse period of the sustain pulse in response to a signal inputted by a manual switch (not shown), and this trigger pulse turns on the transistor T3 via terminal b to turn on the flash lamp. 23 to emit light.

After the lamp has finished emitting light, the control circuit 30 generates a charging pulse for 1 to 2 seconds, which turns on transistors T and L via terminal a, charging capacitor C in preparation for the next light emission. .

Since the pulse period of the sustain pulse is synchronized with the thin film EL element when the flash lamp emits light, an image magnified three to four times is optically written by the projector 22. The light emitted by the flash lamp is modulated by the negative film 29, and the image of the negative film (i.e., negative) is
is optically written into the thin film EL element. Since the amount of light is controlled by the negative film 29, the optically written image on the thin film EL element is displayed in halftone. In addition, the capacitance of circuit capacitor C in Fig. 5 is 400 French F, the capacitance of capacitor C2 is 0.1 AF,
Voltage VI is 250V.

In addition, in the circuit of FIG. 5, if there is no need to rapidly charge the capacitor C, a large resistor may be used instead of the transistor switch. However, the above embodiment of the present invention uses a xenon flash lamp. However, this is due to the following reasons.

The characteristics of the photosensitivity of the thin film EL element with respect to the wavelength of the irradiated light are as follows.
As shown in curve A in the figure, it has a maximum sensitivity peak at 3500A. Therefore, it can be seen that the optimal light source is one that includes many wavelengths of 3500Δ. As this light source, for example, a tungsten lamp is used because it is easy to drive and easy to handle, and a xenon lamp is an example of a flash lamp. Their emission wavelength characteristics are shown in FIG. From this figure, it can be seen that the xenon lamp containing a larger amount of 3500A is more suitable for optical writing and erasing of EL elements than the tungsten lamp. Furthermore, it is impossible to emit light at the right timing as in the present invention with a slow response lamp such as a tungsten lamp. This is because the sustain driving frequency of the EL element requires 100 days or more, so it is very difficult to turn on and off the tungsten lamp within 1 hsec. On the other hand, xenon flash lamps can emit light for several milliseconds or less, depending on the capacity of the charging capacitor, and it is possible to emit light in time with the maintenance AC pulse as shown in Figure 3. It is. Furthermore, in terms of intensity, a xenon flash lamp is much stronger than a tungsten lamp and is suitable for optical writing and erasing of EL elements. When optically writing a film image onto an EL element, intense light must be instantaneously irradiated while a sustain pulse is being applied. When light is continuously irradiated, optical writing is performed during the pulse period of the sustain pulse, but optical erasing is performed during the pulse rest period. in the end,
Only the optical writing that is the difference between optical writing and optical erasing is performed, and not only is the efficiency of optical writing poor, but also optical writing becomes impossible if the duty of the sustain pulse is small. In addition, in this case, the amount of light is controlled through the film, and the optically written image on the thin film L element displays halftones, so in particular, optical writing based on the difference between light writing and light erasing has a significant negative effect on the halftone display. .

Therefore, in order to perform optical writing efficiently and accurately, a shutter that allows light to pass through for only the duration of the sustain pulse is required, and this shutter must be opened and closed in synchronization with the sustain pulse. As described above, the tungsten lamp is not suitable as a light source for optical writing of thin film EL elements, and requires a mechanical system such as a shutter, which is likely to cause malfunctions.

On the other hand, when using a xenon flash lamp, the above problems do not occur. In the case of optical writing of the present invention, the electrodes 4 and 5 of the thin film EL element are paper-shaped electrodes that are orthogonal to each other, and even if the electrodes 4 and 5 are not formed in a so-called matrix shape, the electrodes 4 and 5 of the thin film EL element are
and 5 may each be an entire surface electrode.

In fact, in the case of electrodes covering the entire surface, there are no gaps between the striped electrodes, so the optically written image becomes more delicate. As shown in Figure 6, this means that the peak of the light receiving sensitivity characteristic of the thin film EL element is 350.
This is because when Mn is used as the active material, yellow light emission occurs with a peak around 6000 A, and the thin film EL element emits yellow light as shown by the curve opening in Figure 6. The effect of expanding the luminous area by receiving its own luminescence,
That is, there is no light seepage. As described above, the present invention synchronizes the lighting timing of the flash lamp with the pulse period of the sustain pulse applied to the thin film EL element, so a shutter is not required.

Further, the duty of the sustain pulse applied to the thin film EL element is not particularly limited and can be arbitrarily selected. The amount of light from the flash lamp can be easily changed by changing the capacity of the lighting capacitor. Furthermore, the use of a flash lamp eliminates the need for a cooling fan, which is normally provided in projectors.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional configuration diagram of the thin film EL device of the present invention, Fig. 2 is a voltage-luminance characteristic diagram of the thin film EL device, Fig. 3A is a diagram explaining the AC pulse train reference s and the timing of light irradiation, Fig. 3 Figure 4 is a diagram showing the relationship between AC pulse train Ps, light irradiation, and luminance, Figure 4 is a configuration diagram of an optical writing device according to the present invention, Figure 5 is a flash lamp lighting circuit diagram constituting the main part of the present invention, and Figure 6 is a diagram showing the relationship between AC pulse train Ps, light irradiation, and luminance. 7 shows the photosensitivity and light emission characteristics of the EL element, and FIG. 7 shows the spectral characteristics of a tungsten lamp and a xenon lamp. 21 is a thin film EL element, 22 is a projector, 23 is a flash lamp, 30 is a control circuit, and 31 is a drive circuit. Key figure 2 figure spear 3 figure gi 4 figure 5 figure 6 figure 7 figure

Claims (1)

[Claims] 1. A thin film EL element that has a hysteresis phenomenon in its applied voltage and luminance characteristics, and an alternating current that has a voltage value at a point where the difference between the minimum luminance when the voltage increases and the maximum luminance when the voltage decreases is sufficiently large. It is characterized by comprising means for applying a pulse train, and means for irradiating the thin film EL element with xenon flash lamp light via a film recording an optical image in synchronization with the pulse period of the alternating current pulse train. Optical drive device for thin film EL elements.