JPH04225329A - Active matrix liquid crystal display device - Google Patents

Abstract

PURPOSE:To display good images free from 'flickering', etc., by impressing sufficient electric fields to the liquid crystals between picture element electrodes and counter electrodes even at the time of non-selection when active circuits attain a shut-off state. CONSTITUTION:The capacity compensation capacitors Cs which accumulate the charges of the signals impressed to the picture element electrodes when the active circuits A1, A2 attain a conducting state are connected in parallel to the respective picture element electrodes and the capacity of the liquid crystal capacitors CLCs formed of the picture element electrodes and the counter electrodes as well as the liquid crystals between these electrodes is compensated by the above-mentioned capacity compensation capacitors Cs. In addition, each of the capacity compensation capacitors Cs is formed by connecting two pieces of thin-film diodes D11, D12 having the large capacity per unit area in series reverse from each other.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active matrix liquid crystal display device using thin film diodes as active elements for selecting pixel electrodes.

0002

2. Description of the Related Art There is an active matrix liquid crystal display device that uses a thin film diode as an active element for selecting a pixel electrode.・
There is something called a to-back (BTB) structure.

6 and 7 are partial circuit diagrams of a conventional active matrix liquid crystal display device, with FIG. 6 showing a diode ring structure and FIG. 7 showing a back-to-back structure.

This active matrix liquid crystal display device has a plurality of striped counter electrodes (transparent electrodes) 1 formed parallel to each other at close intervals on one side of a pair of transparent substrates facing each other with a liquid crystal layer in between. On the other substrate, a large number of signal lines 2 perpendicular to the length direction of the counter electrode 1 are wired in parallel with each other at intervals slightly wider than the area of the display pixels, and are arranged along each of the signal lines 2. A large number of pixel electrodes (transparent electrodes) 3 facing each of the above-mentioned counter electrodes 1 are formed in an array, and each of the above-mentioned signal lines 2 and each pixel electrode 3 along this signal line 2 is connected to a thin film diode (hereinafter simply referred to as a thin-film diode). They are connected via an active circuit consisting of a diode (also called a diode).

As shown in FIG. 6, the liquid crystal display device with the diode ring structure has a pair of active circuits A1 each having a plurality of (two in the figure) diodes connected in series at both ends of the pixel electrode 3. , A2, and the diode of one active circuit A1 connected to one end of the pixel electrode 3, and the diode of the active circuit A2 connected to the other end of the pixel electrode 3. The directions of the diodes are opposite to each other.

In this liquid crystal display device with a diode ring structure, each of the active circuits A1 and A2 connecting the signal line 2 and both ends of the pixel electrode 3 is constructed by connecting a plurality of diodes in series. This is to increase the ON voltage for displaying pixels.

That is, each of the above active circuits A1 and A2
If the active circuits A1 and A2 were constructed with only one thin film diode, the threshold voltage at which the active circuits A1 and A2 become conductive with respect to forward currents would be too low, and voltage due to noise etc. would be applied to the signal line 2. This voltage will still be applied to the pixel electrode 3 even if the active circuits A1 and A2 are connected in series, but if each active circuit A1 and A2 is configured with a plurality of thin film diodes connected in series, the threshold voltage of the active circuits A1 and A2 will be becomes high, and when a signal with a voltage higher than this threshold value is applied to the signal line 2, the display drive voltage is applied to the pixel electrode 3. Therefore, by increasing the difference between the ON voltage and the OFF voltage, noise is reduced. Display driving that is not affected by voltage or the like can be performed.

This liquid crystal display device is driven for display by sequentially applying a scanning signal to each opposing electrode 1 and applying an image data signal to each signal line 2 in synchronization with this. Note that the scanning signal and the image data signal are both signals whose polarities are inverted at the same period, and the polarities of the scanning signal and the image data signal are opposite to each other.

To explain the display operation of this liquid crystal display device, suppose that a data signal with a positive voltage (+Vc) higher than the thresholds of the active circuits A1 and A2 is applied to the signal line 2. The liquid crystal capacitor consisting of the electrode 1, the pixel electrode 3, and the liquid crystal between them can be considered to be transiently conductive, whereas the active circuits A1 and A2 consisting of thin film diodes have high resistance.
At the moment the data signal is applied, the voltage +Vc of the data signal is applied across the active circuits A1 and A2.

Since the voltage +Vc of this data signal is higher than the threshold of the active circuits A1 and A2, an active circuit (connected to the upper end of the pixel electrode 3 in the figure) consisting of a diode in the forward direction from the signal line 2 A current flows to the pixel electrode 3 through the active circuit A1.

[0011] Also, at this time, since a scanning signal of negative voltage, which is opposite in polarity to the data signal applied to the pixel electrode 3, is applied to the counter electrode 1, there is a gap between the pixel electrode 3 and the counter electrode 1. A charge corresponding to the voltage is accumulated in the liquid crystal capacitor, and the pixels in this area enter a writing (display) state. In addition,
The voltage across the active circuit A1 becomes lower as charge is accumulated in the liquid crystal capacitor, and when this voltage becomes lower than a threshold value, the active circuit A1 is cut off.

Active circuits A1 and A2 are also connected to the signal line 2.
When a data signal with a negative voltage (-Vc) higher than the threshold value of , the active circuits A1 and A2
A voltage with a polarity opposite to that when the positive voltage (+Vc) data signal is applied is applied to both ends of the data signal. In this case as well, the voltage -Vc of the data signal is applied to the active circuit A1,
Since the current is higher than the threshold value of A2, current flows from the pixel electrode 3 to the signal line 2 through the active circuit (active circuit connected to the lower end of the pixel electrode 3 in the figure) consisting of a diode in the opposite direction. .

Furthermore, at this time, since a scanning signal with a positive voltage is applied to the counter electrode 1, charges of opposite polarity are accumulated in the liquid crystal capacitor, and the pixels in this portion perform writing (display) of opposite polarity. ) state. At this time as well, the voltage across the active circuit A2 decreases as charge is accumulated in the liquid crystal capacitor, and when this voltage becomes lower than the threshold value, the active circuit A2 is cut off. become a state.

Even after the active circuits A1 and A2 are cut off, charge is accumulated in the liquid crystal capacitor, so that the liquid crystal between the pixel electrode 3 and the counter electrode 1 is voltage is continuously applied,
This maintains the display state of the pixel.

On the other hand, in a back-to-back liquid crystal display device, as shown in FIG. 7, the signal line 2 and the pixel electrode 3 are connected to an active circuit B in which two thin film diodes are connected in series in opposite directions. The configuration is connected with .

The display operation of this back-to-back liquid crystal display device is basically the same as that of the diode ring structure. However, in this back-to-back liquid crystal display device, the active circuit B is
Since the configuration is such that thin film diodes are connected in series in opposite directions, the threshold voltage of active circuit B is
This is the voltage at which the diode in the opposite direction to the direction of current among the two thin film diodes loses its diode function and a reverse current begins to flow through this diode.

[0017]

However, in the conventional active matrix liquid crystal display device, when the active circuit A1, A2 or B is cut off, the voltage of the liquid crystal capacitor, that is, the voltage across the pixel electrode 3 is The voltage between the selected pixel and the electrode 1 drops significantly, and as a result, it is no longer possible to apply a sufficient electric field to the liquid crystal continuously during the non-selection period until the selected pixel is selected next. There was a problem that "flickering" etc. occurred.

This is because the thin film diode constituting the active circuit A1, A2 or B has a capacitance. That is, a thin film diode has a semiconductor layer with a P-I-N (or N-I-P) junction structure or a semiconductor layer with a P-N (or N-P) junction structure interposed between a pair of opposing electrodes. However, in a thin film diode with a P-I-N junction structure, the I-type semiconductor film between the P-type semiconductor film and the N-type semiconductor film of the semiconductor layer corresponds to the insulating layer of the capacitor. In a thin film diode with a P-N junction structure, when a reverse voltage is applied to it, the P-N
A depletion layer is formed at the junction, and this depletion layer acts as an insulating film for the capacitor, so thin film diodes with any junction structure have capacitance.

[0019] In this way, the active circuits A1 and A2
Alternatively, if the thin film diode constituting B has a capacitance, the voltage of the liquid crystal capacitor that has accumulated the charge of the data signal when selected, that is, when the above active circuit is in a conductive state, is applied to the active circuit A1, A2 or B, which is cut off. state (non-selected state), the voltage is divided between the liquid crystal capacitor and the active circuit according to the ratio of the capacitance of the liquid crystal capacitor to the capacitance of the active circuit (total capacitance of each thin film diode constituting the active circuit). As a result, the liquid crystal capacitor voltage decreases significantly, and as a result, it becomes impossible to apply a sufficient electric field to the liquid crystal between the pixel electrode 3 and the counter electrode 1, and "flickering" or the like occurs in the display.

An object of the present invention is to maintain a sufficient electric field in the liquid crystal between the pixel electrode and the counter electrode even in the non-selected state when the active circuit is cut off, even though the active circuit is configured with thin film diodes. An object of the present invention is to provide an active matrix liquid crystal display device that can display good images without "flickering" or the like by applying .

[0021]

[Means for Solving the Problems] The present invention has a plurality of striped counter electrodes formed in parallel to each other on one side of a pair of transparent substrates facing each other with a liquid crystal layer in between, and the opposite electrodes are formed on the other substrate. A large number of signal lines perpendicular to the length direction of the electrodes are wired in parallel to each other, and a large number of pixel electrodes are arranged and formed along each of the signal lines to face each of the opposing electrodes, In an active matrix liquid crystal display device in which each signal line and each pixel electrode along this signal line are respectively connected via an active circuit made of a thin film diode, the active circuit is brought into conduction with each of the pixel electrodes. A capacitance compensation capacitor for accumulating charge of a signal applied to the pixel electrode is connected in parallel, and the capacitance compensation capacitor is formed of two thin film diodes connected in series in opposite directions. That is.

[0022]

[Operation] That is, in the active matrix liquid crystal display device of the present invention, by connecting a capacitance compensation capacitor to each pixel electrode in parallel, the capacitance of the liquid crystal capacitor formed by the pixel electrode, the counter electrode, and the liquid crystal therebetween can be reduced to the above level. This is supplemented by a capacitive compensation capacitor, which, like the liquid crystal capacitor described above, stores the charge of the signal applied to the pixel electrode at the time of selection.

Further, this capacitance compensation capacitor is made by connecting two thin film diodes in series in opposite directions, and the thin film diode has a P type semiconductor film and an N type semiconductor film connected directly or Since the capacitance compensating capacitor made of thin film diodes has a semiconductor layer stacked with an I-type semiconductor film in between, it has a lower capacitance than a normal capacitor in which a pair of electrodes are opposed to each other with an insulating film in between. The capacity per unit area is large.

Also in this liquid crystal display device, when the active circuit is in the cutoff state (non-selected state), the voltage of the liquid crystal capacitor is equal to the capacitance of the liquid crystal capacitor and the capacitance of the active circuit (which constitutes the active circuit The voltage is divided between the liquid crystal capacitor and the active circuit according to the ratio (total capacitance of multiple thin film diodes), but a capacitance compensation capacitor consisting of a thin film diode with a large capacitance per unit area is connected in parallel to the liquid crystal capacitor. Therefore, the actual capacitance of the liquid crystal capacitor is the total capacitance of the liquid crystal capacitor itself and the capacitance of the capacitance compensation capacitor, and therefore, the actual capacitance of the liquid crystal capacitor is sufficiently larger than the capacitance of the active circuit. By reducing the voltage divided into the active circuit, it is possible to maintain sufficient voltage in the liquid crystal capacitor.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. 1 to 5 regarding an active matrix liquid crystal display device having a diode ring structure. 1 is an equivalent circuit diagram of a liquid crystal display device, FIG. 2 is a plan view of one pixel display section of the liquid crystal display device, FIG. 3 is an enlarged sectional view taken along line III-III in FIG. 2, and FIGS. 4 and 5 are diagrams. 2 IV-IV line and V-
It is an enlarged sectional view along the V line.

The liquid crystal display device of this embodiment has a striped counter electrode 1 on one substrate (not shown) of a pair of transparent substrates (glass substrates, etc.) facing each other with a liquid crystal layer in between.
A large number of signal lines 12 are formed in parallel to each other on the other substrate 10, and a large number of signal lines 12 are arranged in parallel to each other and are perpendicular to the length direction of the counter electrode 11. In addition, each of the above-mentioned counter electrodes 11
A large number of pixel electrodes 13 facing each other are formed in an array,
Each of the signal lines 12 and both ends of each pixel electrode 13 along the signal line 12 are connected via active circuits A1 and A2 made of thin film diodes, and a capacitance compensation capacitor C is connected to each of the pixel electrodes 13.
s connected.

Each of the active circuits A1 and A2 includes a plurality of (two in this embodiment) thin film diodes D1.
a, D1b and D2a, D2b are connected in series, and the direction of the thin film diodes D1a, D1b of one active circuit A1 connected to one end of the pixel electrode 13, and the other end of the pixel electrode 3. the other active circuit A connected to
The directions of the two thin film diodes D2a and D2b are opposite to each other.

The structure of the first active circuit A1 connected to one end of the pixel electrode 13 will be explained. As shown in FIGS. 2 and 4, the first active circuit A1 is It consists of two thin film diodes D1a and D1b formed side by side.

Both thin film diodes D1a and D1b have a P-I-N junction structure, and both diodes D1a and D1b have a P-I-N junction structure.
1a and D1b each have a lower conductive film 22 and a P-type semiconductor film 2 on a base electrode 20 formed on a substrate 10.
3p, an I-type semiconductor film 23i, an N-type semiconductor film 23n, and an upper conductive film 24 are formed in this order to form a semiconductor layer 21, and an upper electrode 25 is formed on this semiconductor layer 21. There is. Note that the upper electrode 25 is the same as the base electrode 20.
and an insulating film (silicon nitride film, etc.) covering the semiconductor layer 21
26 , and is connected to the upper conductive film 24 of the semiconductor layer 21 through a contact hole provided in the insulating film 26 .

Note that each semiconductor film 23 of the semiconductor layer 21
p, 23i, and 23n are made of amorphous silicon or polysilicon, and the lower conductive film 22 and the upper conductive film 24 are made of a metal such as chromium that has good contact with the semiconductor film.

Then, the diode D on the signal line 12 side
1a and the diode D1b on the pixel electrode 13 side, the upper electrode 25 of the pixel electrode side diode D1b is connected to the insulating film 2.
They are connected in series by being connected to the base electrode 20 of the signal line side diode D1a through a contact hole provided at 6, thereby forming a first active circuit A1.

One end of this first active circuit A1, that is, the upper electrode of the signal line side diode D1a is connected to the signal line 1.
2, and the other end, that is, the pixel electrode side diode D1b
The base electrode 20 of is connected to the pixel electrode 13. Note that the base electrodes 20 of both diodes D1a and D1b are
It is formed of the same transparent conductive film as the pixel electrode 13, the base electrode 20 of the signal line side diode D1a is an independent island-shaped electrode, and the base electrode 20 of the pixel electrode side diode D1b is a part of the pixel electrode 13. It is also used.

The signal line 12 is made of a metal film such as chromium on a lower film 12a made of the same transparent conductive film as the pixel electrode 13, or a metal film made by laminating a low resistance film such as aluminum on a chromium film or the like. The upper electrode 25 of both diodes D1a and D1b is formed of the same metal film as the upper layer 12b of the signal line 12.

The second active circuit A2 connected to the other end of the pixel electrode 13 is composed of two thin film diodes formed side by side on the substrate 10, as shown in FIGS. 2 and 5. It is composed of D2a and D2b.

These thin film diodes D2a and D2b are also P-
It has an I-N junction structure, and is constructed by forming a semiconductor layer 21 on a base electrode 20 formed on a substrate 10, and forming an upper electrode 25 on this semiconductor layer 21. The electrode 25 includes the base electrode 20 and the semiconductor layer 21
The semiconductor layer 21 is connected to the upper conductive film 24 of the semiconductor layer 21 through a contact hole provided in the insulating film 26 . Note that the semiconductor layer 21 of the diodes D2a and D2b is the same as that of the diode D1 constituting the first active circuit A1 shown in FIG.
Since it has the same laminated structure as the semiconductor layer 21 of a and D1b, the explanation thereof will be omitted by giving the same reference numeral in the figure.

Then, the diode D on the signal line 12 side
2a and the diode D2b on the pixel electrode 13 side are connected in series by connecting the upper electrode 25 of the signal line side diode D2a to the base electrode 20 of the pixel electrode side diode D2b through a contact hole provided in the insulating film 26. and constitutes the second active circuit A2.

One end of the second active circuit A2, that is, the base electrode 20 of the signal line side diode D2a, is connected to the signal line 12, and the other end, that is, the upper electrode 25 of the pixel electrode side diode D2b is connected to the pixel electrode 13. Therefore, the diodes D2a and D2b of the second active circuit A2 are in the opposite direction to the diodes D1a and D1b of the first active circuit A1.

Note that the base electrodes 20 of both diodes D1a and D1b of this second active circuit A2 are also connected to the pixel electrode 1.
The base electrode 20 of the pixel electrode side diode D2b is an independent island-shaped electrode, and the base electrode 20 of the signal line side diode D2a is formed of the same transparent conductive film as in No. 3.
is connected to the lower layer film 12a of the signal line 12.

On the other hand, the capacitance compensation capacitor Cs is
As shown in FIG. 2, it is formed corresponding to the side edge of the pixel electrode 13 on the side opposite to the signal line connection side, and as shown in FIG. It is constructed by connecting D11 and D12 in series in opposite directions.

The two thin film diodes D11 and D12 constituting the capacitance compensation capacitor Cs are the same as the thin film diodes D1a and D1 constituting the active circuits A1 and A1.
Both diodes D11 and D12 have the same P-I-N junction structure as D2a and D2b, and each of these diodes D11 and D12 has a lower conductive film 32 and a P-type semiconductor on a base electrode 30 formed on a substrate 10. Film 33p and I-type semiconductor film 33i
A semiconductor layer 31 is formed by laminating an N-type semiconductor film 33n and an upper conductive film 34 in this order, and an upper electrode 35 is formed on this semiconductor layer 31. Note that the upper electrode 35 is formed on an insulating film (such as a silicon nitride film) 36 that covers the base electrode 30 and the semiconductor layer 31.
This insulating film 36 is connected to the upper conductive film 34 of the semiconductor layer 31 through a contact hole provided therein.

The upper electrodes 35 of both diodes D11 and D12 are shared by both diodes D11 and D12, and both diodes D11 and D12 have polarities opposite to each other via the upper electrodes 35. state (P-type semiconductor films 33p, 33p of both diodes D11, D12
They are connected in series in a state in which they face each other, forming a capacitance compensation capacitor Cs.

One end of this capacitance compensation capacitor Cs, that is, the base electrode 30 of one diode D11, is connected to the pixel electrode 13, and the other end, that is, the base electrode 30 of one diode D11, is connected to the pixel electrode 13.
The 12 base electrodes 30 are connected to capacitor lines 30a that are wired in parallel to the signal lines 12 between the columns of the pixel electrodes 13. Both ends of this capacitor line 30a are
It is led out to the side edge of the substrate 10 and connected to a ground line (not shown).

However, both ends of this capacitor line 30a may be connected to both ends of the counter electrode 11 on the opposing substrate, and since the potential of the counter electrode 11 is approximately 0 when not selected, the counter electrode 11 can be connected to both ends of the counter electrode 11. It can be used as a ground line for the capacitance compensation capacitor Cs.

Note that the base electrodes 30 of both diodes D11 and D12 and the capacitor line 30a are formed of the same transparent conductive film as the pixel electrode 13, and the base electrode 30 of one diode D11 is a part of the pixel electrode 13. The base electrode 30 of the other diode D12 is also used as a part of the capacitor line 30a.

Further, both diodes D11 and D12 are thin film diodes D constituting active circuits A1 and A1.
It has the same laminated structure as 1a, D1b, D2a, and D2b,
Each film 32, 33p, 33i, 33n of the semiconductor layer 31
, 34 and the material of the upper electrode 35 are also active circuit A1.
, A1. In this way, the thin film diodes D11 and D1 constituting the capacitance compensation capacitor Cs
2 has the same laminated structure as the thin film diodes D1a, D1b, D2a, and D2b constituting the active circuits A1 and A2, it is possible to simultaneously manufacture the capacitance compensation capacitor Cs using the manufacturing process of the active circuits A1 and A2. can.

The capacitance compensation capacitor Cs stores the charge of the image data signal applied to the pixel electrode 13 when either of the active circuits A1, A2 becomes conductive. As shown in the equivalent circuit shown in FIG. 1, is connected in parallel to a liquid crystal capacitor CLC that is composed of a pixel electrode 13, a counter electrode 11, and a liquid crystal therebetween.

The liquid crystal display device of this embodiment has a liquid crystal capacitor CLC formed by the pixel electrode 13, the counter electrode 11, and the liquid crystal therebetween by connecting the capacitance compensation capacitor Cs in parallel to each pixel electrode 13. The capacitance of the pixel electrode 13 is supplemented by a capacitance compensating capacitor Cs, which, like the liquid crystal capacitor CLC described above, accumulates the charge of the image data signal applied to the pixel electrode 13 at the time of selection.

This capacitance compensation capacitor Cs is composed of two thin film diodes D11 and D12 connected in series in opposite directions.
A semiconductor layer 31 is interposed between a pair of electrodes (base electrode and upper electrode) 30 and 35, in which a P-type semiconductor film 33p and an N-type semiconductor film 33n are laminated with an I-type semiconductor film 33i in between. Therefore, these thin film diodes D11, D1
The capacitance compensation capacitor Cs consisting of 2 has a larger capacitance per unit area than a normal capacitor having a pair of electrodes facing each other with an insulating film in between.

That is, the thin film diodes D11, D
If we look at 12 as a capacitor, this thin film diode D
11, P type semiconductor film 33p of semiconductor layer 31 of D12 and N
The I-type semiconductor film 33n corresponds to both electrodes of the capacitor, and the I-type semiconductor film 33i therebetween corresponds to the insulating layer of the capacitor.

On the other hand, the capacitance of a capacitor is proportional to the dielectric constant of the insulating layer between the two electrodes and the area of the capacitor, and inversely proportional to the thickness of the insulating layer, but the thickness of the insulating film of a normal capacitor is To eliminate defects such as holes etc. 400~
It is normal to be quite thick at 600 nm,
In addition, the dielectric constant of this insulating film is approximately 7 in the case of a silicon nitride film.
On the other hand, the thin film diodes D11 and D12
is an I-type semiconductor film 33i corresponding to an insulating layer of a capacitor.
The thickness of the I-type semiconductor 3 is as thin as about 100 nm.
The dielectric constant of 3b is as large as about 11 when it is made of amorphous silicon, so this thin film diode D
The capacitance per unit area of D11 and D12 is much larger than that of a normal capacitor.

Also in this liquid crystal display device, when the active circuits A1 and A2 are in the cutoff state (non-selected state), the voltage of the liquid crystal capacitor CLC is equal to the capacitance of the liquid crystal capacitor CLC and the active circuits A1 and A2. The liquid crystal capacitor CLC and the active circuit A1 are adjusted according to the ratio of the capacitance of A2 (the two thin film diodes D1a, D1b and the total capacitance of D1a, D1b constituting the active circuits A1, A2).
, A2, but the liquid crystal capacitor CLC includes a thin film diode D11, which has a large capacitance per unit area.
Since the capacitance compensation capacitor Cs consisting of D12 is connected in parallel, the substantial capacitance of the liquid crystal capacitor CLC is the total capacitance of the liquid crystal capacitor CLC itself and the capacitance of the capacitance compensation capacitor Cs.
The actual capacitance of the liquid crystal capacitor CLC is the active circuit A1, A
2, the active circuits A1 and A2
By reducing the voltage divided into liquid crystal capacitor CL
C can hold sufficient voltage.

Note that the actual capacitance of the liquid crystal capacitor CLC (
The total capacitance of the liquid crystal capacitor CLC itself and the capacitance of the capacitance compensation capacitor Cs is the active circuit A1, A2.
If the capacitance of the active circuits A1 and A2 is 1/10 or less of the actual capacitance of the liquid crystal capacitor CLC, the voltage divided into the active circuits A1 and A2 can be almost ignored. Therefore, the capacitive compensation capacitor C
The area of the thin film diodes D11 and D12 constituting s is determined by the capacitance of the liquid crystal capacitor CLC itself and the active circuit A1,
Depending on the ratio to the capacitance of A2, the size may be selected so that the actual capacitance of the liquid crystal capacitor CLC is 10 times or more the capacitance of the active circuits A1 and A2.

Therefore, according to this liquid crystal display device, the voltage of the image data signal applied between the pixel electrode 13 and the counter electrode 11 at the time of selection is applied to the non-selection state in which the active circuits A1 and A2 are cut off. Therefore, a sufficient electric field can be applied to the liquid crystal between the pixel electrode 13 and the counter electrode 11 even during the non-selection period, and a good image without "flickering" etc. can be displayed. can do.

In the above embodiment, the semiconductor layer 31 of the thin film diodes D11, D12 constituting the capacitive compensation capacitor Cs is formed for each diode D11, D12.
It may be continuous over D12. Further, both of the diodes D11 and D12 may be connected in series through the base electrode, using the base electrode as a common electrode. In that case, the base electrode is formed independently from the signal line 12 and the pixel electrode 13. and connect the upper electrode to each diode D
11 and D12, one diode D11
The upper electrode of the diode D12 may be connected to the pixel electrode 13, and the upper electrode of the other diode D12 may be connected to the signal line 12.

Furthermore, in the above embodiment, the active circuit A1
, A2 constitute thin film diodes D1a, D1b, D
1a, D1b and thin film diodes D11, D12 constituting the capacitance compensation capacitor Cs, respectively, are connected to P-I-N.
However, each of these thin film diodes has an N-
It may be an I-P junction structure, or an I-P junction structure may be used.
It is also possible to use a P-N junction structure or an N-P junction structure in which a P-type semiconductor film and an N-type semiconductor film are directly laminated without using a type semiconductor film.

In this case, in a thin film diode with a P-N (or N-P) junction structure, when a reverse voltage is applied to it, a depletion layer is formed at the P-N junction, and this depletion layer acts as a capacitor. However, since the thickness of both the P-type semiconductor film and the N-type semiconductor film is as thin as about 100 nm, the spread of the thickness of the depletion layer is small.
A thin film diode with an N-junction structure also has a large capacity. Therefore, even if the thin film diode constituting the capacitance compensation capacitor Cs has a PN junction structure, the capacitance compensation capacitor Cs can have a large capacitance.

Further, although the liquid crystal display device of the above embodiment has a diode ring structure, the present invention connects the signal line and the pixel electrode to one active active device in which two thin film diodes are connected in series in opposite directions. Of course, the present invention can also be applied to active matrix liquid crystal display devices having a back-to-back structure connected by circuits.

In the case of this back-to-back structure, the P-type and N-type thin film diodes constituting the active circuit
The threshold voltage of the capacitive compensation capacitor is made sufficiently higher than the threshold voltage of the active circuit by changing the amount of impurity doping between the type semiconductor film and the P-type and N-type semiconductor films of the thin film diode constituting the capacitive compensation capacitor. Just do it.

[0059]

[Effects of the Invention] In the active matrix liquid crystal display device of the present invention, each pixel electrode is connected in parallel with a capacitance compensation capacitor that stores the charge of a signal applied to the pixel electrode when the active circuit becomes conductive. Moreover, since this capacitance compensation capacitor is formed by connecting two thin film diodes with large capacitance per unit area in series in opposite directions, even though the active circuit is composed of thin film diodes, Even in the non-selected state where the active circuit is cut off, a sufficient electric field can be applied to the liquid crystal between the pixel electrode and the counter electrode, and a good image without "flickering" etc. can be displayed.

[Brief explanation of the drawing]

FIG. 1 is an equivalent circuit diagram of a liquid crystal display device showing one embodiment of the present invention.

FIG. 2 is a plan view of one pixel display section of the liquid crystal display device.

FIG. 3 is an enlarged sectional view taken along line III-III in FIG. 2;

FIG. 4 is an enlarged sectional view taken along line IV-IV in FIG. 2;

FIG. 5 is an enlarged sectional view taken along line V-V in FIG. 2;

FIG. 6 is a circuit diagram of a conventional liquid crystal display device having a die ring structure.

FIG. 7 is a circuit diagram of a conventional back-to-back liquid crystal display device.

[Explanation of symbols]

11... Counter electrode, 12... Signal line, 13... Pixel electrode,
A1, A2...active circuit, D1a, D1b, D2a,
D2b... Thin film diode, Cs... Capacity compensation capacitor, D11, D12... Thin film diode.

Claims (1)

[Claims] 1. A plurality of striped counter electrodes are formed parallel to each other on one of a pair of transparent substrates facing each other with a liquid crystal layer in between, and the other substrate has stripe-shaped counter electrodes formed parallel to each other in the length direction of the counter electrodes. A large number of orthogonal signal lines are wired parallel to each other, and along each signal line,
An active matrix liquid crystal display device in which a large number of pixel electrodes facing each of the counter electrodes are formed in an array, and each of the signal lines and each pixel electrode along the signal line are connected via an active circuit made of a thin film diode. A capacitance compensation capacitor that stores charge of a signal applied to the pixel electrode when the active circuit becomes conductive is connected in parallel to each of the pixel electrodes, and the capacitance compensation capacitor is configured to An active matrix liquid crystal display device characterized in that it is formed of two thin film diodes connected in series in opposite directions.