JP3649799B2 - Display device - Google Patents

Description

[0001]
[Technical field to which the invention belongs]
The invention disclosed in the present specification relates to a display device that projects an image. In particular, the present invention relates to a rear projection type image display device using an active matrix liquid crystal display device.
[0002]
[Prior art]
A liquid crystal electro-optical device (generally called a liquid crystal panel) is used in a wide range of fields such as a computer, a calculator, and a watch as an image display device that is lighter and more compact than a CRT. The liquid crystal panel changes the optical properties (interference, scattering, diffraction, optical rotation, absorption, etc.) of the liquid crystal material due to changes in the alignment state and phase transition of the liquid crystal molecules in response to the application of an external field (electric field, heat, etc.) of the liquid crystal material. This is the principle of operation.
[0003]
In a general liquid crystal panel configuration and driving method, at least one of them has a light-transmitting property and a liquid crystal material is sandwiched between two substrates having a distance of 1 to several tens of μm. An image is displayed by applying an electric field to the liquid crystal material by electrodes formed on both or either side to control the alignment state of liquid crystal molecules for each pixel in the substrate surface and controlling the amount of light transmitted through the liquid crystal panel. Is.
At this time, depending on which of the above optical properties is used, for example, a polarizing plate is provided on the outside of the liquid crystal panel, so that a configuration corresponding to the operation mode is adopted.
[0004]
Currently, the TN (twisted nematic) type or STN (super twisted nematic) type is widely used in liquid crystal panels. These are optical properties such as optical rotation of liquid crystal materials and interference of birefringent light, respectively. The property is utilized, and it is necessary to provide a polarizing plate in any case.
[0005]
Further, when displaying an image on the liquid crystal panel, various methods have been proposed in order to control the operation of many pixels simultaneously. Among them, active matrix driving is widely used as a method capable of high image quality and high density display.
[0006]
The purpose of this is to provide non-linear active elements (diodes, transistors, etc.) in each pixel so that each pixel is in an electrically independent relationship, eliminating interference of extra signals and realizing high image quality. To do. According to this method, each pixel can be viewed as a capacitor to which an electrical switch is connected.
[0007]
Accordingly, the charge can be injected / extracted to / from the pixel by turning on / off the switch as necessary. Further, when the switch is turned OFF, the charge is held in the pixel, so that it is possible to impart memory characteristics.
[0008]
A method for manufacturing a substrate for a liquid crystal panel using an active matrix circuit will be described below. The liquid crystal panel to be described is a monolithic active matrix circuit in which peripheral drive circuits are also formed in the substrate. This production process will be described with reference to FIG. This step is for the low temperature polysilicon process.
[0009]
The left side of FIG. 4 shows the TFT manufacturing process of the drive circuit, and the right side shows the TFT manufacturing process of the active matrix circuit.
[0010]
First, a silicon oxide film having a thickness of 1000 to 3000 mm was formed as a base oxide film 402 on a glass substrate 401 as a first insulating substrate. As a method for forming this silicon oxide film, a sputtering method or a plasma CVD method in an oxygen atmosphere may be used.
[0011]
Thereafter, an amorphous silicon film was formed to 300 to 1500 mm, preferably 500 to 1000 mm, by plasma CVD or LPCVD. Then, thermal annealing was performed at a temperature of 500 ° C. or higher, preferably 500 to 600 ° C., to crystallize the silicon film or improve the crystallinity. After crystallization by thermal annealing, light (laser or the like) annealing may be performed to further increase crystallization. Further, at the time of crystallization by thermal annealing, as described in JP-A-6-244103 and JP-A-6-244104, an element (catalytic element) that promotes crystallization of silicon such as nickel may be added.
[0012]
Next, the silicon film is etched to form TFT active layers 403 (for p-channel TFTs) and 404 (for N-channel TFTs) for the driver circuit on the island and an active layer 405 for TFTs (pixel TFTs) for the matrix circuit. did. Further, a silicon oxide gate insulating film 406 having a thickness of 500 to 2000 mm was formed by sputtering in an oxygen atmosphere. As a method for forming the gate insulating film, a plasma CVD method may be used. In the case of forming a silicon oxide film by the plasma CVD method, it was preferable to use dinitrogen monoxide (N ₂ O) or oxygen (O ₂ ) and monosilane (SiH 4) as a source gas.
[0013]
Thereafter, aluminum having a thickness of 2000 to 6000 mm was formed on the entire surface of the substrate by sputtering. Here, in order to prevent hillocks and whiskers from being generated by a subsequent thermal process, aluminum containing silicon, scandium, palladium, or the like may be used. Then, this is etched to form gate electrodes 407, 408, and 409 (FIG. 4A).
[0014]
Thereafter, phosphorus is implanted into all island-like active layers by ion doping in a self-aligning manner using the gate electrode as a mask and phosphine (PH ₃ ) as a doping gas. The dose is 1 × 10 ^{12 to} 5 × 10 ¹³ atoms / cm ² .
As a result, weak N-type regions 410, 411, 412 are formed. (Fig. 4 (B))
[0015]
Next, a photoresist mask 413 that covers the active layer of the P-channel TFT and a photoresist mask 414 that covers a portion 3 μm away from the end of the gate electrode 409 in parallel to the gate electrode of the active layer 405 of the pixel TFT. It is formed.
[0016]
Then, phosphorus is implanted again using phosphine as a doping gas by ion doping. The dose is 1 × 10 ^{14 to} 5 × 10 ¹⁵ atoms / cm ² . As a result, strong N-type regions (source and drain) 415 and 416 are formed. Of the weak N-type region 412 of the active layer 405 of the pixel TFT, the region 417 covered by the mask 414 remains weak N-type because phosphorus is not implanted in this doping. (Fig. 4 (C))
[0017]
Next, the active layers 404 and 405 of the N channel type TFT are covered with a photoresist mask 418, and boron is implanted into the island regions 403 by ion doping using diborane (B ₂ H ₆ ) as a doping gas. The dose is 5 × 10 ¹⁴ to 8 × 10 ¹⁵ atoms / cm ² .
[0018]
In this doping, since the dose amount of boron exceeds the dose amount of phosphorus in FIG. 4C, the weak N-type region 410 formed previously is inverted to the strong P-type region 419.
[0019]
By the above doping, strong N-type regions (source / drain) 415 and 416, strong P-type regions (source / drain) 419, and weak N-type regions (low-concentration impurity regions) 417 are formed. In this embodiment, the width x of the low-concentration impurity region 417 is about 3 μm. (Fig. 4 (D))
[0020]
Thereafter, thermal annealing was performed at 450 to 850 ° C. for 0.5 to 3 hours to recover the damage due to doping, activate the doping impurities, and recover the crystallinity of silicon. Thereafter, a silicon oxide film having a thickness of 3000 to 6000 mm was formed as an interlayer insulator 420 on the entire surface by plasma CVD. This may be a silicon nitride film or a multilayer film of a silicon oxide film and a silicon nitride film. Then, the interlayer insulating film 420 was etched by wet etching or dry etching to form contact holes in the source / drain.
[0021]
Then, an aluminum film having a thickness of 2000 to 6000 mm or a multilayer film of titanium and aluminum is formed by sputtering. This was etched to form electrodes / wirings 421, 422, 423 of the peripheral circuit and electrodes / wirings 424, 425 of the pixel TFT. Further, a silicon nitride film 426 having a thickness of 1000 to 3000 mm was formed as a passivation film by plasma CVD, and this was etched to form an interlayer film. Further, a transparent electrode 427 made of ITO is formed thereon as a display electrode to a thickness of 1200 mm. (Fig. 4 (E))
[0022]
Further, a silicon nitride film 428 having a thickness of 1000 to 3000 mm is formed as a passivation film by the plasma CVD method to obtain the structure shown in FIG.
The substrate thus obtained is indicated at 502 in FIG.
[0023]
Next, in FIG. 5, a black matrix is formed on the opposing substrate 501 (not shown). The black matrix used here is made of Cr, has a thickness of 1200 mm, and is patterned into a desired shape by a known photolithography method.
[0024]
Here, in this embodiment, a case where color display is performed by incorporating a color filter into a liquid crystal panel will be described.
First, a color filter is formed on a black matrix (not shown) (not shown). A color filter is formed by repeating coating, patterning, and curing (firing) a material in which pigments showing R, G, and B colors are dispersed in a solvent such as ethylene glycol and monoethyl ether acetate to form a micro color filter. . In this embodiment, the film thickness of each color is 1.7 μm.
[0025]
Further, an overcoat agent (planarizing film) (not shown) made of an acrylic resin is formed thereon. The overcoat agent is formed on the entire surface with a thickness of 1 μm.
[0026]
Next, a transparent electrode 503 made of ITO is formed on the entire surface of a color filter (not shown). A transparent electrode 503 is also formed on the substrate 502 on which the matrix circuit is formed. Further, an alignment film 505 made of polyimide is formed on the transparent electrodes 503 and 504.
[0027]
Next, the alignment film 505 is rubbed by a normal method. At this time, the rubbing is performed so that the upper and lower substrates form an angle of 90 °.
[0028]
Next, spacers 506 made of silicon oxide having a diameter of 3.8 μm are dispersed on the substrate coated with the alignment film (not shown).
[0029]
Next, a sealant 507 is printed on the substrate 502 side on which the matrix circuit is formed, and the substrates 601 and 602 are overlapped and fixed. At this time, the sealing material is printed near the outer periphery of the substrate so that the pixel region and the peripheral drive circuit region are inside. Thus, a cell of the liquid crystal panel is formed.
[0030]
Next, a liquid crystal material 508 is injected into the cell by a vacuum injection method. The liquid crystal material used is nematic liquid crystal ZLI-4792 (trade name) manufactured by Merck & Co. In this way, the liquid crystal panel shown in FIG. 6 is formed.
[0031]
There is known a display device of a type that projects an image on a screen using a liquid crystal display panel as described above. Such projection display devices are increasingly used in daily life as their versatility increases. For example, it is used for various purposes such as various events and conferences by taking advantage of the feature that a clear image can be displayed on a large screen.
[0032]
However, the projection display device cannot avoid being relatively large due to its structure, and there is a problem that it takes a lot of trouble to carry the device. In addition, there is a problem that a large space is required for the installation place of the projection display device.
[0033]
For this reason, it is an urgent need to reduce the size of the display device main body as the projection display device spreads socially.
[0034]
An outline of a general projection display apparatus is shown in FIG. The projection display device as shown in FIG. 1 is generally called rear projection, and has a configuration in which an image is viewed from the side opposite to the surface side projected on the screen. On the other hand, a configuration in which an image is viewed from the side projected on the screen is called a projection type projection. In both cases, the basic configuration is the same except that the image is inverted.
[0035]
First, rear projection will be described with reference to FIG.
[0036]
First, light emitted from the light source 101 that emits white light is corrected to light aligned in parallel by a lens (not shown). As the white light source, a halogen lamp, a xenon lamp, a metal halide lamp, or the like is used.
Next, the light is reflected directly above by the reflecting mirror 102 and enters the optical system apparatus indicated by 103.
[0037]
At this time, it is desirable to insert a selective transmission filter for cutting ultraviolet light and far infrared light between the light source 101 and the reflecting mirror 102. The ultraviolet light cut is for protecting the eyes, and the far infrared light cut is for preventing heat from being trapped in the display device.
[0038]
The optical system apparatus 103 is configured to have a liquid crystal panel and a projection lens inside. The light that has entered the optical system device 103 enters the liquid crystal panel having the structure described above, and is optically modulated by using the change in the electro-optical characteristics of the liquid crystal.
[0039]
If the image is displayed in color, a color filter or dichroic mirror corresponding to each of RGB may be incorporated in the optical system device 103 to perform optical modulation corresponding to each of RGB. However, since white light is once split into the three primary colors RGB, optical modulation is performed by three liquid crystal panels corresponding to RGB, and light including the respective image information is synthesized later, a complicated optical system is required.
[0040]
Next, when appropriate optical modulation is performed in the liquid crystal panel, a predetermined display image is formed. The image thus obtained is focused by the projection lens.
[0041]
The output light that has passed through the optical system device 103 through the above process is gradually enlarged while being reflected by the reflection mirror 104. At this time, the light is reflected by the reflection mirror 104 toward the screen 105 installed in the display device main body 106, and an image enlarged and projected from the inside is displayed on the screen 105.
[0042]
The number of reflecting mirrors at this time is not limited to one, and the number of reflection mirrors may be arbitrarily changed depending on the size of the image projected on the screen 105 and the focal length of the projection lens.
[0043]
The reason why the reflection mirror is used for the rear projection as described in FIG. 1 is greatly influenced by the design problem of the projection lens.
[0044]
For example, in the case of projection type projection, the irradiation light focused by the projection lens travels a certain distance X and reaches the screen. This certain distance X is the optical path length necessary for the image to be enlarged and projected until it fits the screen area.
[0045]
The simplest means for shortening the distance X may be adjusted so that the projection lens can be enlarged and projected to a predetermined size by changing various parameters of the projection lens.
In this case, however, the thickness of the projection lens increases and the design of various parameters becomes complicated, resulting in an increase in the manufacturing cost of the projection lens. In addition, since the image is forcibly enlarged with a wide-angle lens, there arises a problem that distortion occurs as the edge of the display image is approached.
[0046]
Therefore, it is necessary to provide a certain distance X between the screen and the projection lens in order to reduce the manufacturing cost of the projection lens. In other words, it can be said that the cost of the projection lens can be reduced correspondingly if a certain distance X is made longer. Of course, a clear image cannot be obtained unless the balance with the light emission intensity of the light source is taken into consideration.
[0047]
The above is an example of the projection type projection, but the situation is different when the rear projection has a structure as shown in FIG.
That is, since the size of the display device main body 106 is limited, it is difficult to ensure an appropriate optical path length.
[0048]
In order to solve this problem, a structure has been adopted in which an appropriate optical path length is secured in a narrow space using a reflecting mirror. By doing so, it has become possible to obtain a predetermined display image using a projection lens having a small thickness.
[0049]
However, when a plurality of reflecting mirrors are installed in the apparatus main body 106, a dead space (empty space) 100 indicated by hatching is formed on the back side of the reflecting mirror indicated by 104 in FIG. This dead space 100 is a part that should be deleted in order to reduce the size and cost of the display device.
[0050]
However, it can be said that the current situation is to reduce the size of the display device at the expense of the manufacturing cost of the lens, or by cutting the shape of the display device body to eliminate the apparent dead space.
[Problems to be solved by the invention]
[0051]
An object of the invention disclosed in this specification is to provide a technique for realizing a reduction in size and cost of a projection-type image display device by using a dead space in a rear projection.
[Means for Solving the Problems]
[0052]
The configuration of the invention disclosed in this specification is as follows.
An optical modulation element that optically modulates incident light emitted from a light source;
A projection lens for collecting the output light of the optical modulation element;
Means for transmitting at least half of the light collected by the projection lens incident from one surface and reflecting at least half of the light collected by the projection lens incident from the other surface;
At least one mirror for reflecting the light transmitted by the means;
A screen for projecting the light reflected by the means or mirror;
A projection-type image display device comprising:
A first path through which the output light of the optical modulation element is transmitted;
A second path reflected by at least one mirror;
A third path reflected by the means;
Through
It is projected on the screen.
[0053]
That is, the configuration is such that a dead space indicated by 100 is utilized by replacing the reflecting mirror indicated by 104 in FIG. 1 with a half mirror or means having the same function as that of the half mirror.
[0054]
【Example】
[Example 1]
[0055]
In the present embodiment, the structure of an image display apparatus that effectively uses a dead space in a rear projection using a semi-transparent mirror (hereinafter referred to as a half mirror) will be described. In the structural diagram (FIG. 2) of the image display device used in this embodiment, the size of the device main body and the components inside the device are all drawn with the same dimensions as those of the image display device having the conventional structure shown in FIG. .
[0056]
First, the light emitted from the light source 201 that emits white light in FIG. 2 is corrected to light that is aligned in parallel by a lens (not shown). As the white light source, a halogen lamp, a xenon lamp, a metal halide lamp, or the like is used.
Next, the light is reflected by the reflecting mirror 202 and enters the optical system apparatus indicated by 203.
[0057]
At this time, it is desirable to insert a selective transmission filter for cutting ultraviolet light and far infrared light between the light source 201 and the reflection mirror 202. The ultraviolet light cut is for protecting the eyes, and the far infrared light cut is for preventing heat from being trapped in the display device.
[0058]
The optical system apparatus 203 has a configuration having a liquid crystal panel and a projection lens inside. The light that has entered the optical system device 203 enters the liquid crystal panel, and is optically modulated by utilizing the change in electro-optical characteristics of the liquid crystal.
[0059]
This liquid crystal panel is an active matrix liquid crystal electro-optical device having a structure in which pixel TFTs arranged in a matrix on a substrate having translucency and peripheral circuits for driving the TFTs are integrated.
[0060]
If the image is displayed in color, a color filter or dichroic mirror corresponding to each of RGB may be incorporated in the optical system device 203 to perform optical modulation corresponding to each of RGB. In this case, the white light is once split into the three primary colors RGB to perform optical modulation, and then a method of combining the light including the respective image information or a method of incorporating a color filter corresponding to RGB in the liquid crystal panel is employed. In any case, a complicated optical system is required.
[0061]
Next, when appropriate optical modulation is performed in the liquid crystal panel, a predetermined display image is formed. The image thus obtained is focused by the projection lens. In the case of color display, light that is spectrally divided into RGB and optically modulated is combined by this projection lens.
[0062]
The output light that has passed through the optical system device 203 through the above process becomes light including predetermined image information and enters the half mirror 204.
[0063]
The light transmitted through the half mirror 204 is reflected by the reflection mirror 205 in the traveling direction, and returns to the half mirror 204 again. Then, approximately half of the returned light is reflected by the half mirror 204 toward the screen 206.
[0064]
In this way, the light that has gained the optical path length by using the reflection is gradually enlarged in the course of progress, and is enlarged and projected on the screen 206 to a predetermined size.
[0065]
As in this embodiment, by effectively using a space that has been a conventional dead space using a half mirror, a longer optical path length can be ensured even in a narrower space than in the past. In the present embodiment, a total of two mirrors are used, but an optical system may be configured by an arbitrary number of mirrors.
[0066]
As described above, if a longer optical path length than the conventional one can be secured, not only the cost of the projection lens can be reduced, but also the projection lens itself can be reduced in size. That is, the price of the image display device itself can be suppressed.
[0067]
Further, since the optical system device 202 is installed in a space that was originally a dead space, the degree of freedom of arrangement of the optical system is widened, and the display device main body can be easily downsized.
[Example 2]
[0068]
In the present embodiment, the structure of an image display apparatus that effectively uses a dead space in a rear projection by utilizing total reflection, which is a physical phenomenon, will be described.
[0069]
Total reflection means that when light travels from an optically dense medium 1 (having a high refractive index) to a sparse medium 2 (having a low refractive index), all incident light is reflected at an incident angle greater than the critical angle I _0. It is a phenomenon. (Figure 3)
For example, when light travels from water to air, the critical angle is about 49 °, and all light incident at an angle higher than that is reflected.
[0070]
That is, by adjusting the optical system in the image display device to an appropriate arrangement, a general translucent substrate can be used like a reflection mirror. The present embodiment is an example of the structure of an image display device using such a principle.
[0071]
The rear projection structure shown in this embodiment is the same as that described in FIG. The difference from the first embodiment is that a translucent substrate is used instead of the half mirror 204 in FIG.
[0072]
That is, light that has been appropriately optically modulated in the optical system apparatus is incident on the translucent substrate as light containing predetermined image information.
At this time, incident light enters the light-transmitting substrate having a large refractive index from the air having a small refractive index, and thus is transmitted without being reflected.
[0073]
Next, the light transmitted through the translucent substrate is reflected by at least one reflection mirror and returns to the translucent substrate again.
[0074]
Here, when the light reflected by the reflection mirror returns to the translucent substrate, it is important that the incident angle is not less than the critical angle. If the refractive index of the translucent substrate is known, the critical angle when light travels from the inside of the translucent substrate into the air can be easily obtained.
[0075]
Thus, if the light reflected by the reflection mirror is arranged so as to be totally reflected when returning to the light transmissive substrate, the light transmissive substrate can be used like a reflection mirror. At this time, if necessary, the surface refractive index may be changed by forming a dielectric multilayer film or the like on the translucent substrate.
[0076]
In this way, the light that has gained the optical path length by using the reflection is gradually enlarged in the course of progress, and is enlarged and projected to a predetermined size on the screen.
[0077]
As in this embodiment, if a function equivalent to that of a reflection mirror is given to a translucent substrate by using total reflection, which is a physical phenomenon, it is possible to effectively use a space that was previously a dead space. Become. That is, a longer optical path length can be ensured even in the same space as the conventional one.
[0078]
Further, in this embodiment, the arrangement of the optical system can be adjusted to provide a structure with less space that becomes a dead space as compared with the prior art.
[0079]
Therefore, not only can the projection lens be reduced in size and cost, but also a display device that is smaller than the conventional one can be configured.
[0080]
【The invention's effect】
The present invention provides a technique for effectively using the back side of a reflection mirror, which tends to be a dead space, as an installation place of an electro-optical device. Thereby, since the optical path length until the light containing image information reaches a screen can be earned, the cost concerning the design of a projection lens is reduced.
[0081]
In addition, since the degree of freedom of the optical system is expanded, the manufacturing cost of the image display device itself can be reduced.
[Brief description of the drawings]
FIG. 1 is a diagram showing an image display device having a conventional structure.
FIG. 2 is a diagram showing an image display device having a structure using the present invention.
FIG. 3 is a diagram illustrating total reflection.
4A and 4B illustrate a manufacturing process of a thin film transistor.
FIG. 5 shows a structure of a liquid crystal cell.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 101 Light source 102 Reflection mirror 103 Electro-optical apparatus 104 Reflection mirror 105 Screen 106 Display apparatus main body 204 Half mirror 401 Glass substrate 402 Silicon oxide film 403, 404, 405 Active layer 406 Gate insulating film 407, 408, 409 Gate electrode 410, 411, 412 Weak N-type region 413, 414 Photoresist mask 415, 416 Strong N-type region 417 Weak N-type region 418 Photoresist mask 419 Strong P-type region 420 Interlayer insulators 421, 422, 423 Peripheral circuit electrodes / wiring 424 425 Pixel electrode / wiring 426 Silicon nitride film 427 Transparent electrode 428 Silicon nitride film 501 Opposing substrate 502 Substrate 503 and 504 on which matrix circuit is formed Transparent electrode 505 Alignment film 506 Spacer 507 Sealant 508 Liquid crystal

Claims (5)

An optical modulation element that optically modulates incident light emitted from a light source;
A projection lens for collecting the output light of the optical modulation element;
Means for transmitting at least half of the light collected by the projection lens incident from one surface and reflecting at least half of the light collected by the projection lens incident from the other surface;
At least one mirror for reflecting the light transmitted by the means;
A screen for projecting the light reflected by the means or mirror;
A projection-type image display device comprising:
A first path through which the output light of the optical modulation element is transmitted;
A second path reflected by at least one mirror;
A third path reflected by the means;
Through
A display device projected onto the screen. 2. The display device according to claim 1, wherein the means having a function of transmitting or reflecting incident light is a semi-transparent mirror. In claim 1, the means having a function of transmitting or reflecting incident light is a translucent substrate,
The display device according to claim 1, wherein the reflection of light by the translucent substrate utilizes total reflection. The display device according to claim 1, wherein a liquid crystal electro-optical device is used as the optical modulation element. In Claim 1, the optical modulation element is a liquid crystal electro-optical device,
The liquid crystal electro-optical device is integrated using the same translucent substrate.

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