JPS5842473B2 - Hakumaku EL Soshino Kudohouhou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical image memory panel that is improved so that an optical image with an amount of incident light below a threshold can be read out as a light emission output.

Emit light with hysteresis phenomenon in response to applied AC voltage,
When driving an optical image memory panel in which a polarized latent image of an optical image is formed by applying voltage and irradiating light, the voltage component necessary to maintain light emission is applied to the panel on which the latent image is formed at the peak value. By applying an AC pulse train with
A method for driving an optical image memory panel that reads out a written polarization latent image as a light emission output and maintains the light emission is disclosed in Japanese Patent Application No. 49-65249 (Japanese Patent Application Laid-open No. 50-1
57085)).

This prior invention will be explained in detail below.

Figure 1 is a cross-sectional view of an EL element, where 21 is a ZnS thin film doped with Mn etc., 22.23 is a transparent insulating layer such as Y2O3, etc.
24 is a metal back electrode, 25 is a transparent electrode, and 26 is a glass substrate.

As a property of the sandwich type element in which the EL light emitting layer is sandwiched between dielectric layers, it has a hysteresis characteristic in the relationship between the AC applied voltage and the luminance depending on the insulating layer material, manufacturing conditions, etc.

FIG. 2 is a diagram for explaining the method of driving this EL element, and shows a case where only the optical polarization effect is utilized in writing the optical image.

The panel described below is a panel composed of an EL element exhibiting the above-mentioned optical polarization effect and hysteresis phenomenon, and is referred to as an optical image memory panel.

The solid line in Figure 2A is the voltage waveform applied to the optical image memory panel, and the dashed line a, broken line b, and thin line C indicate the amount of internal polarization in different regions of the panel by the external electric field υ.
It is expressed by converting it into a, υb, and υC.

The same port also illustrates the light emitting output of the panel.

In this driving method, a polarization latent image of an optical image is formed only by optical polarization. Therefore, as shown in Figure A, pattern light is irradiated simultaneously with the application of DC voltage υ0 for polarization formation, and the panel A latent image of the light image is formed on the surface as the magnitude of the polarization amount.

In the ZnS thin film EL element, this polarization latent image is maintained as it is for several hours to several tens of hours in a dark room after voltage application and pattern light irradiation are stopped.

Next, the optical image stored in the memory as described above is read out as a light emission output using an alternating current pulse train whose peak value is VS, and the light emission is maintained during the application of the pulse.

The peak value VS of the pulse Ps is as follows.

That is, Fig. 3 is a diagram showing the luminance versus applied voltage characteristics of the EL elements that make up this panel.As mentioned above, this element emits light with a hysteresis phenomenon, and on this hysteresis loop, the maximum Select a voltage value Vs with a sufficiently large difference between the luminance brightness Bw and the minimum luminance Bs, and set this value V8.
is taken as the peak value of the above panel Ps.

The readout of the polarization latent image when the pulse Ps is applied will be explained with reference to Fig. 3.The panel now stores the amount of polarization charge corresponding to the optical image, and in Fig. 2A, this The amount of polarization is shown converted to external voltage in each area on the panel.

When an AC pulse Ps whose application direction of the first pulse Ps' is opposite in polarity to the DC voltage pulse for polarization formation is applied to the panel in this state, the internal polarization electric fields Va, Vb
, Vc is superimposed on the electric field Vs caused by the pulse Ps', so this panel effectively receives an external voltage (Vs +Va
), (Vs +Vb), and (Vs +Vc) are applied.

Therefore, as shown in FIG. 3, depending on the pulse Ps,
The panel momentarily displays brightness Bwa' corresponding to each voltage,
It emits light at Bwb' and Bwc' and can display an optical image.

The light emission output waveform at this time is shown on the same page.

On the other hand, when the next AC pulse train Ps is continuously applied to this panel, due to the hysteresis phenomenon of the element, each light emitting point becomes stable as shown in FIG.
Light emission of wb and Bwc is performed.

This light emission is continued during the application period of the AC pulse train Ps, and the normal image of the written optical image is displayed.

Therefore, this AC pulse train Pa can be called a sustain pulse.

If the direction of application of the first pulse Ps' of the sustain pulse train Ps is made to have the same polarity as the applied pulse for polarization formation, light is emitted only by the next reversed pulse.

Further, the duty of the sustain pulse train Ps may be arbitrary.

FIG. 4 is a diagram showing another driving method. In this embodiment, a constant DC voltage υ0 is applied and uniform light is irradiated to the entire memory panel to form a uniform optical polarization electric field, and then the voltage The application of υ0 is stopped, and the panel is irradiated with pattern light to optically relax the polarization, thereby forming a latent image corresponding to the irradiation pattern.

That is, the internal polarized charge formed by the photopolarization effect is
The image written on the panel is the inverse of the optical image because it is relaxed and reduced in proportion to the amount of light irradiated.

That is, the area indicated by curve a/ has the least amount of light irradiation, followed by curves b' and ♂, but when read out in the opposite direction, the area indicated by curve a/ emits the strongest light.

This latent image is also retained on the panel in a dark room for several to several tens of hours.

In this case, as in the case described above, the display is sustained by applying the alternating current sustaining pulse train Ps to the panel.

The same part shows the light emission output waveform due to this pulse train Ps.

In this example, since the written latent image is an inverted image of the optical image, the image read out by application of the first pulse Ps of opposite polarity to the polarization voltage is an inverted image.

By the way, with the driving method described above, a light image with an amount of incident light below the threshold cannot be read out as a light emission output.

That is, in FIG. 2A, a polarization latent image is formed by irradiating a light image for t hours with a DC bias voltage of 40 volts,
When reading out an optical image by applying a pulse train Ps-voltage Vs=190V, duty 50%, and repetition I KHz later, it is not possible to read out an image with an incident light amount of less than (140) as shown in FIG.

FIG. 5 shows the relationship between the amount of incident light and the luminance of the emitted light output using the DC bias voltage as a parameter.

This existence of a threshold in the amount of incident light is the main cause of AC hysteresis memory, ZnS (Mn).
This is due to the deep trap level at the interface between the and the insulating layer.

In view of the above points, it is an object of the present invention to provide a driving method that makes it possible to read out an optical image with an amount of incident light below the threshold as a light emission output. Based on method.

That is, the present invention makes it possible to read out optical images with a light intensity of 440 volts or less by irradiating light with a certain intensity as bias light together with the optical image while applying a DC bias voltage (40 volts). .

FIG. 6 shows a schematic configuration diagram of an embodiment of the present invention.

1 is a reflecting mirror, 2 is a pattern irradiation light source, 3 is a variable irradiation intensity power supply, 4 is a bias light source, 5 is a bias light intensity variable power supply, 6 is a condenser lens, 7 is a transmission pattern, 8 is a light diffusion plate, 9 1 is an imaging lens, 10 is a glass substrate, 11 is a transparent electrode SnO2, 12 is an insulating layer Y2O3, and 13 is ZnS (Mn
) EL layer, 14 is an AI back electrode, 15 is a DC bias variable power supply, 16 is an AC sustaining pulse Ps power supply, SWl, SW
2 is a switch.

Therefore, short-circuit switch SW1 for 80 minutes, switch SW1
2 is short-circuited between de, that is, a DC bias voltage is applied between the electrodes, the light source 2 irradiates the transmission pattern 7 through the condensing lens b, and the pattern image 7 is focused on the EL layer 13 by the imaging lens 9.

At the same time, the light diffuser plate 8 is irradiated from the light source 4 through the condensing lens 6, and the EL layer 13 is irradiated with diffused light through the condensing lens 6.

The intensity I40 of this bias light is set to l4 (1 inch).

of After irradiation, switch SW1 is short-circuited between AB.

The switch SW2 continues to short-circuit de.

In this state, the polarization latent image is retained, that is, stored.

Next, switch SW2 is used to read out the EL light emission output.
and df and apply an AC sustaining pulse P8.

As described above, the present invention has discovered that there is a threshold in the amount of incident light when irradiating pattern light, and is intended to read out light images that are irradiated below this threshold. It also irradiates light at the same time and cancels out the light intensity threshold, making it possible to write and read out low-intensity light images that were previously impossible, or even light images irradiated by a light source with a light intensity below the threshold.

In addition, if the bias light intensity is appropriately selected, unnecessary ambient light can be removed to output a clear optical image.

Moreover, by selecting the DC bias voltage, it is possible to vary the range of the amount of incident light and the value of the threshold amount of light.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional configuration diagram of a ZnS thin film EL element, Figure 2 is a diagram explaining the driving method of the prior invention, and Figure 3 is a diagram of a ZnS thin film EL element.
A characteristic diagram of the applied voltage versus luminance of the L element, FIG. 4 is a diagram explaining the driving method of another embodiment of the prior invention, and FIG. 5 is a diagram of the ZnS
Relationship diagram between the amount of incident light and the output luminance of a thin film EL element, No. 6
The figure is a diagram explaining the driving method according to the present invention. Ps is a sustain pulse, Vs is a voltage value of the sustain pulse, 7 is an optical image pattern, 4 is a bias light source, 12 is an insulating layer, 13
is a ZnS (Mn) layer.

Claims (1)

[Claims] 1. A thin film EL element which forms a polarized latent image of an optical image by irradiating light onto a thin film EL element having a hysteresis characteristic between an applied alternating current voltage and luminance, and displays the polarized latent image by emitting light by applying an alternating current pulse. In the driving method, polarization is achieved by irradiating the thin film EL element with bias light having an amount of light approximately equal to the minimum amount of light required for forming the polarization latent image, and irradiating the light image with light during a voltage application period. A method for driving a thin film EL element, characterized by forming a latent image.