JPS6152681A - Display panel and driving thereof - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a display panel using image display elements such as liquid crystal elements and LED (light emitting diode) elements, and a method for driving the same. This relates to a driving method. [Prior Art] First, the optical modulating substance according to the present invention will be described. The optical modulating substance used in the display panel and driving method thereof of the present invention takes either a first optically stable state or a second optically stable state depending on the applied electric field. That is, a substance having a bistable state with respect to an electric field, particularly a liquid crystal having such a property, is used. As the liquid crystal having bistability that can be used in the driving method of the present invention, chiral smectic liquid crystal having ferroelectricity is most preferable, and chiral smectic C phase (SmO2) or H phase (Sm) I liquid crystal is the most preferable. Are suitable. Regarding this ferroelectric liquid crystal, please refer to “LE JOU”
RNAL DE PHYSIQUELETTERS”
3B (L-69) 1975. rFerroe
electricLiquid Cr7stals J
``Applied Physics 'Le
tters” 31B (11) 1980. r
submicro 5econd'B15table
Electrooptic Switching in
LiquidCrystal+J; “Solid State Physics” 113 (141) 1981. ferroelectric liquid crystals disclosed in these documents can be used in the present invention. More specifically, as an example of the ferroelectric liquid crystal compound used in the method of the present invention, decyloxybenzylidene=p'-amino-2-methylbutylcinnamate (DOBAMBC
), hexyloxybenzylidene-P'-amino-2
-Chloropropyl cinnamate (HOBACPC: )
and 4-o-(2-methyl)-butylresorsilitin-4'-octylaniline (FIBRA8). When constructing an element using these materials, the liquid crystal compound is Smi! In order to maintain the temperature in such a state that it becomes a phase or a SmO2 phase, the element can be supported by a copper block or the like in which a heater is embedded, if necessary. FIG. 2 schematically depicts an example of a ferroelectric liquid crystal cell. 24 and 24' are In2O3, Sr+02 or I
A substrate (glass plate) coated with a transparent electrode such as TO (Indium-Tin Oxide), between which a liquid crystal molecular layer 25 is oriented perpendicularly to the glass surface.
1t phase liquid crystal is sealed. A thick line 26 represents a liquid crystal molecule, and this liquid crystal molecule 26 has a dipole moment (P) 27 in a direction perpendicular to the molecule. When a voltage higher than a certain threshold is applied between the electrodes on the substrates 24 and 24', the helical structure of the liquid crystal molecules 26 is unraveled, and the liquid crystal molecules 26 are aligned so that all dipole moments (P) 27 are directed in the direction of the electric field. You can change direction. The liquid crystal molecules 26 have an elongated shape and exhibit refractive index anisotropy in the long axis direction and the short axis direction. Therefore, for example, if polarizers are placed above and below the glass surface in a crossed nicol positional relationship, It is easily understood that this becomes a liquid crystal optical modulation element whose optical characteristics change depending on the polarity of applied voltage. Furthermore, if the thickness of the liquid crystal cell is made sufficiently thin (
For example, in 11L), the helical structure of the liquid crystal unravels even when no electric field is applied, as shown in Figure 3, and its dipole moment) P or P' is either upward (27a) or downward (27b). takes the state of When an electric field E or E' with a different polarity above a certain threshold value is applied to such a cell as shown in FIG. 3, the dipole moment electric field E or E'
is upward 27a or downward 2 according to the electric field vector.
7b', and accordingly the liquid crystal molecules are either in the first stable state 28 or the second stable state 28'.
Orient towards. ' There are two advantages to using such a ferroelectric liquid crystal as an optical modulation element. Firstly, the response speed is extremely fast, and secondly, the alignment of liquid crystal molecules has bistability. To explain the second point with reference to FIG. 2, for example, when the electric field E is applied, the liquid crystal molecules are oriented in a first stable state 28, and this state remains stable even when the electric field is turned off. Moreover, when an electric field E' in the opposite direction is applied, the liquid crystal molecules are oriented to the second stable state 28' and the orientation of the molecules is changed.
It remains in this state even if the electric field is turned off. Further, as long as the applied electric field E does not exceed a certain threshold value, each orientation fB is maintained. In order to effectively realize such fast response speed and bistability, it is preferable for the cell to be as thin as possible, and generally, the thickness is 0.5
IJL to 5JL is suitable, especially IJL to 5JL. A liquid crystal-electro-optical device having a matrix electrode structure using ferroelectric liquid crystals of this kind has been proposed, for example, by Clark and Ragabal in US Pat. No. 4,367,924. Next, a case in which an image is actually displayed will be described below. The principle of matrix type display, which is one of the liquid crystal display methods, is that a scanning electrode group and a signal electrode group are configured in a Madrisk shape, and a liquid crystal compound is filled between the electrodes to form a large number of pixels to display images or information. However, with this method, increasing the image density or increasing the screen size requires a huge number of scanning electrodes and display electrodes, which slows down the response speed of the liquid crystal. , voltage is also distributed to pixels other than display pixels. This causes harmful effects due to so-called crosstalk. In order to improve this point, voltage averaging drive method, dual frequency drive method, 1-division matrix method, multiple matrix method, etc. have already been proposed, but all of these methods require a larger display element screen and a higher To cope with the increase in the number of scanning lines due to density increase,
was difficult. Recently, active matrix displays (Active Matrix D), in which switching elements such as FETs (field effect transistors) are arranged in a matrix for each pixel to directly drive the liquid crystal, have been developed.
isplay) system has been considered and put into practical use. [Problems to be Solved by the Invention] However, although the active matrix method solves the problem of crosstalk, the method using conventional liquid crystal (nematic) elements has a limit in speeding up display. Large-screen display was also constrained by the number of repeated river waves. In addition, when a ferroelectric liquid crystal is used as a liquid crystal element, the drawbacks of the nematic liquid crystal described above are improved, but there is still room for further improvement in terms of simplifying the circuit configuration as the density of display images increases. there were. The present invention was made to solve these conventional problems, and by improving the circuit configuration of display electrodes using an active matrix, the number of signal lines can be significantly reduced, thereby simplifying the circuit. The purpose is to [Means] Figure TfIJ1 is a circuit configuration diagram showing the basic concept of the present invention,
As is clear from the figure, a pixel electrode is provided at the first terminal functioning as the source or drain of the FET element, a plurality of counter electrodes are connected corresponding to the pixel electrode, and a scanning signal is applied to the source of the FET element. Alternatively, the voltage is applied to a scanning signal line leading to a second terminal functioning as a drain, and a plurality of counter electrodes arranged parallel to the scanning signal line, and a gate line (FET's first terminal 3 terminals)). Generally, in a display of n pixels, JiXZ leader lines are required, but in the present invention, 3r'n×3 leader lines are required. Note that if the cube of N does not exist as a natural number, it is necessary to increase the number of lead lines slightly. [Function] As is clear from the circuit diagram of FIG. 1, the present invention selects a write line by using two of the three signal line groups as scanning signal lines, and selects the remaining one line group. An image is displayed by inputting a display signal to a signal line. Specifically, FET which is a driving element
A signal voltage is applied so that the gate of the field effect transistor (field effect transistor) is turned on, and in synchronization with this, the FET
By forming an electric field between the source terminal and the drain terminal, which are terminals other than the gate, and changing the polarity, two display states, a first orientation state and a second orientation state, are controlled. . Therefore, the ferroelectric liquid crystal used in the present invention is a material that takes either the first optically stable state or the second optically stable state depending on the polarity of the electric field, that is, a bistable state with respect to the electric field. A substance having the following properties is used. In addition, in an FET that is a driving element, whether it is P type or N type, which terminal other than the gate acts as the source and which acts as the drain depends on the direction of voltage application. Determined. That is, for N type, the lower voltage side acts as a source, and for P type, the higher voltage side acts as a source. Note that the voltage level at each signal electrode can be set to any value without being limited to the embodiments described below, as long as the potential difference between each signal is maintained relatively. [Example 1] A first specific example of image display using the liquid crystal display device of the present invention is described below.
The explanation will be made based on the drawings and FIGS. 4 to 7. In the circuit configuration shown in Figure 1, an N-type FET is used as a driving element.
Preferably, a TPT (thin film transistor) and a ferroelectric liquid crystal are used as the liquid crystal element, and each voltage value for writing the predetermined display pattern shown in FIG. 5 is set to a desired value that satisfies the following conditions. be done.

[11 m=a in scanning signal line ■, m=b in scanning signal line ■,
When writing "bright" in the position of sentence = C on the display signal line. ~/- [2] When selecting m=a on scanning line ■, m=b on scanning line ■, and writing "dark" on display signal line ζC. However, each symbol represents the following items. VLII:: Absolute value of threshold voltage of ferroelectric liquid crystal vP Gate threshold voltage of FET constituting the near-active matrix ■ sn: Scanning signal voltage ■ vc, ,: Scanning signal voltage ■ VGI: Higher than display signal voltage The electrical signal waveforms of each signal voltage at phases t1 to t8 are shown in FIG. 6. In FIG. 6, the horizontal axis represents time and the vertical axis represents voltage. The write operation to each pixel when such an electric signal is given is fJrV.
In the @fJS7 diagram shown in the figure, the horizontal axis represents time, and the vertical axis represents each display state of upper ON (dark) and lower OFF (bright). That is, it represents whether each pixel is in a "dark" or "bright" state at each phase time. Note that it is assumed that QN-1 in the figure maintains the signal state as it was when it was scanned last time. Further, the coordinates of each pixel in FIG. 7 are 0 or more and the phase shown in FIG. 4, and the desired display pattern shown in FIG. 5 is completed by each operation from 1 to t8. In this example, Vp=0 in FIG. 6, but if Vp#0, it is sufficient to shift VC (gate voltage) by Vp. When DOBAMBC is used as (7), the specific values are: V LC = 1 to 20 (V), the operating temperature is 75° C. to 85° C., and the time required to write one pixel is approximately 50 gg. Since the circuit configuration of the present invention is the same as forming a passive matrix on one pixel of a normal active matrix, crosstalk is inevitable as in the case of a conventional passive matrix. The optimal conditions considering the following are described below. In FIG. 8, when the counter electrode is used as a scanning signal line, if another scanning line selects a pixel on the active matrix, the counter electrode from 1 to n in FIG. operate independently and do not affect the voltage applied to the light control material (for example, LC) sandwiched between the active matrix electrode and the counter electrode in pixels separated by the counter electrode. However, when the pixel electrode on the active matrix is not selected, the gate is turned OFF and the pixels separated by the opposing electrodes 1 to n are connected through the pixel electrode on the active matrix as shown in Figure (b). This results in a short circuit, and the voltage when one of the opposing electrodes 1 to n is selected is distributed through the pixel electrodes on the active matrix. Assuming that the scanning signal voltage applied to the counter electrode is ■, and the voltage of the other unselected counter electrodes is 0, more precisely, the selected scanning signal voltage is VON, and the scanning signal voltage when not selected is VOF
When F is defined as V=(VON-VOFF)6
゜Then, when V is applied to one selected scanning line m (1≦m≦n), the voltage appearing on the other scanning lines, in other words, the voltage applied between the electrodes of other pixels is v ′=v -! − It can be expressed as Also, the voltage appearing in the scanning signal iJim is. It is expressed as v″=vLx.Here, even if VON may exceed the threshold value of the material used (for example, LC), vOFF will never be exceeded.
Therefore, the above-mentioned 3'lli pressure values v', v''. V OFF is required to be smaller than the absolute value of the threshold value of the material used. Therefore, if VOFF = a VON is defined, the above-mentioned 3
Since all of the voltage values are a function of WON, it is necessary to satisfy the following conditions. In other words, wax (V'
, V″, VOFF) <Vo, ,,,, ■Here, V
Q is the threshold value of the material used. ■Rewriting the equation, max (V?'(1-a), Li11-Mo
N (1-a), aVON) < VO---
In formula 00, if n#1, -HVoH (1-a)≦"-n" ON (1-a)
In order to determine the optimal value for a, it is necessary to finish with n lol 1 (
1-a) = a 'VON, then ・→old ...■ By applying aVB (a is a constant expressed by the formula 0, and n is the number of scanning signal lines) to the selected scanning signal line, the OFF pixel is The lighting problem is resolved. In reality, some ferroelectric liquid crystals reverse their memory state if a low electric field is applied for a long period of time, so it is desirable to keep the VOR as low as possible, and the scanning time Therefore, n is also subject to constraints. f, Figure 9 shows F in the TFT used in the present invention.
FIG. 10 is a cross-sectional view of a ferroelectric liquid crystal cell using TPT, FIG. 11 is a perspective view of a TPT substrate, FIG. 12 is a plan view of the TPT substrate, and FIG. 13 is a cross-sectional view showing the configuration of ET. 12
A partial sectional view taken along line A-A' in the figure, Figure 14 is
FIG. 2 is a partial sectional view taken along line BB' in FIG. 2, and each of the above figures shows one embodiment of the present invention. FIG. 10 shows one specific example of a liquid crystal element that can be used in the method of the invention. A gate voltage g! is placed on the substrate 14 made of glass, plastic, etc. 18. A semiconductor film 10 (amorphous silicon doped with hydrogen atoms) formed via an insulator 11 (such as a silicon nitride film doped with hydrogen atoms), and two terminals 1 and 5 in contact with the semiconductor film 10. and a pixel electrode 5 (ITO; Indnium Tin) connected to the terminal 4 of the TFT.
Oxide) is formed. Furthermore, an insulating layer 7 (polyimide, polyamide,
Polyvinyl alcohol, borinolaxylylene, SiO
, 5i02) and a light shielding film 2 made of aluminum, chromium, or the like. A counter electrode 15 (IT
Indium Tin Oxide) and an insulating film 1G are formed. Between the substrates 14 and 14', the ferroelectric liquid crystal 1 described above is provided.
7 is being held. Also, the substrates 14 and 14'
□A sealing material 19 for sealing the ferroelectric liquid crystal 17 is provided around the periphery. Polarizers 13 and 13' in a cross-collar state are arranged on both sides of the liquid crystal element having such a cell structure, and the observer A is able to observe the incident light beam. A reflector plate 12 (diffuse reflective aluminum sheet or plate) is provided behind the polarizer 13' so that the display state can be seen by the reflected light weight 1. Further, in each of the above figures, the terms "source electrode" and "drain electrode" are used only when current flows from the drain to the source. In the function of an FET, it is also possible for the source to function as a drain. [Effects] As is clear from the above explanation, the present invention can significantly reduce the number of signal lines compared to the conventional circuit configuration. Therefore, a significant improvement can be expected in terms of circuit simplification.

[Brief explanation of the drawing]

Fig. 1 is a circuit configuration diagram showing the basic concept of the present invention, Figs. 2 and 3 are perspective views schematically showing the ferroelectric liquid crystal used in the method of the present invention, and Fig. fjS4 shows the coordinates of the corresponding pixels. tJS5 is an explanatory diagram showing an example of the display pattern of the corresponding pixel, FIG. 6 is an explanatory diagram showing the electric signal waveform applied to the scanning electrode and display electrode, and FIG. 157 is an explanatory diagram showing the write operation to each pixel. 8 is a pixel configuration diagram in one display electrode of an active matrix, FIG. 9 is a cross-sectional view showing the structure of an FET in a TFT, and FIG. 10 is a cross-sectional view of a ferroelectric liquid crystal cell using a TFT. FIG. 11 is an At view of the TPT substrate, FIG. 12 is a plan view of the TPT substrate, FIG. 13 is a partial cross-sectional view taken along the line A-A', and FIG. 14 is a partial cross-sectional view taken along the line B-B'. 1; Source electrode (drain electrode) 2; Light-shielding metal or light absorption layer 3; N4 layer 4; Drain electrode (source electrode) 5; Pixel electrode 6; First insulating layer 7; Second insulating layer 8; TFT substrate 9; Gate section 10 having a light shielding effect directly under the semiconductor; Semiconductor 11, transparent electrode 12 in the gate wiring section. Reflector plate 13.13'; Polarizing plate 14.14''; Transparent substrate 15 made of glass, plastic, etc.
Counter electrode 16; Insulation 11 17; Ferroelectric liquid crystal layer 18; Gate electrode 18; Sealing material 20; Small film semiconductor 21, gate wiring 22; Panel substrate 23; Gate portions 24, 24' having a light blocking effect; Substrate 25 coated with a transparent electrode; Liquid crystal molecule layer 26; Liquid crystal molecules 27; Dipole moment (P) 27a; Upward dipole moment 27b; Downward dipole moment 28; First stable state 28'; Second stable state 28'; steady state

Claims (1)

[Scope of Claims] 1) A display panel characterized in that a plurality of counter electrodes are provided corresponding to image display electrodes connected to a first terminal which is a terminal other than the gate of a field effect transistor constituting an active matrix substrate. 2) The display panel according to claim 1, wherein the field effect transistor is a thin film transistor. 3) a signal line connected to a second terminal functioning as a source or a drain of the field effect transistor and a plurality of counter electrodes arranged in parallel, and a gate line connected to a third terminal functioning as a gate of the thin film transistor; The display panel according to claim 1, wherein the signal line and the plurality of counter electrodes are arranged orthogonally. 4) The display panel according to claim 1, wherein a liquid crystal capacitor is electrically connected to the image display electrode. 5) Claim 4, wherein the liquid crystal is a ferroelectric liquid crystal.
Display panel as described in section. 6) The display panel according to claim 5, wherein the ferroelectric liquid crystal is a chiral smectic liquid crystal. 7) Corresponds to the gate line tangential to the third terminal functioning as the gate, the signal line tangential to the second terminal functioning as the source or drain, and the image display electrode connected to the first terminal of the thin film transistor constituting the active matrix substrate. Of the three types of signal lines consisting of multiple counter electrode lines,
A method for driving a display panel, characterized in that a scanning signal is applied to two types of signal lines, and a display signal is applied to the remaining one type of signal line. 8) A signal line connected to a second terminal functioning as a source or a drain of the field effect transistor and a plurality of counter electrode lines are arranged in parallel and connected to a third terminal functioning as a gate of the field effect transistor. 8. The display panel driving method according to claim 7, wherein the gate line, the signal line, and the plurality of counter electrodes are arranged orthogonally. 9) The display panel driving method according to claim 7, wherein the display signal is applied to a gate line connected to a third terminal functioning as a gate of a field effect transistor. 10) The method for driving a display panel according to claim 7, wherein a liquid crystal capacitor is electrically connected to the image display electrode. 11) The method for driving a display panel according to claim 10, wherein the liquid crystal is a ferroelectric liquid crystal. 12) The method for driving a display panel according to claim 11, wherein the ferroelectric liquid crystal is a chiral smectic liquid crystal.