[Related Applications]

[0001]

The present Application for Patent claims priority to Japanese Patent Application No. 2013- 053203, entitled "Display Device," filed March 15, 2013, and assigned to the assignee hereof and hereby expressly incorporated by reference herein.

[Technical Field]

[0002]

The present invention relates to display devices equipped with a mechanical shutter.

[Background Art]

[0003]

A display device has been developed (see patent document 1) that is equipped with a reflective plate including an opening that allows light from a light source to pass therethrough at a position that corresponds to each pixel; and a mechanical shutter (hereinafter simply referred to as a shutter) that adopts MEMS (Micro Electro Mechanical Systems) at a position that corresponds to the opening in the reflective plate, for displaying images by controlling light and dark in each pixel through mechanical opening and closing behavior of the shutter.

[0004]

In this display device, the shutter disposed at each pixel is driven by electrostatic force according to a signal obtained by the shutter drive unit. The pixel is bright when the shutter is at a position that allows backlight light to pass through, and is dark when it is at a position to block the light. By controlling the light and dark states at each pixel, it is possible to display not only a still image, but also a moving image.

[Prior Art Documents]

[Patent Documents]

[0005]

[Patent Document 1] Japanese unexamined patent application publication 2008-533510 [Summary of the Invention]

[Problem to be Solved by the Invention]

[0006]

It is necessary to operate the shutter properly according to an image signal in a display device that displays images by being equipped with a shutter mechanism for the pixels, and controlling the brightness of the pixel by the opening and closing behavior of the shutter. However, although no structural defects can be found, the existence of faulty pixels can be found where the shutter does not operate even when given a signal. A faulty pixel whose shutter does not operate causes a panel point-defect. Visual quality in the display device suffers.

[0007]

An object of the present invention is to provide a display device that suppresses a problem where the shutter disposed in the pixel does not work, resulting in a display device that does not have faulty pixels.

[Means for Solving the Problems]

[0008]

Pursuant to an embodiment of the present invention, a display device is provided that is equipped with a pixel that includes a shutter plate formed into a plate; a first spring connected to the shutter plate; a first anchor unit that cantilevers the first spring; a second spring having at least one edge disposed near the first spring so that electrostatic force acts with the first spring; a second anchor unit that holds the second spring; a first wiring that gives a predetermined potential to the first anchor unit; a second wiring that gives a predetermined potential to the second anchor unit; a connecting layer disposed between the first anchor unit and the first wiring, and between the second anchor unit and the second wiring; and a shutter drive unit for driving the shutter plate using electrostatic force.

[0009]

With this display device, it is possible to reduce contact resistance between the anchor unit and the wiring by disposing a connecting layer between the first anchor unit and the first wiring and between the second anchor unit and the second wiring.

[0010]

Also, in a different embodiment of the display device, the first anchor unit and the second anchor unit can be formed by silicon. Also, as a connecting layer, the layer may be formed using a material that is conductive even when oxidized, a material that has non-rectifying contact with the silicon, or a material that forms silicide by reacting with the silicon. By using such conductive materials for the connecting layer, it is possible to reduce contact resistance between the anchor unit and the wiring.

[Effect of the Invention]

[001 1]

Pursuant to the embodiment of the present invention, by ensuring an electrical connection by disposing a connecting layer between the anchor in the shutter mechanism and the wiring connected thereto, it is possible to suppress the problem of the shutter not operating, and to provide a display device without faulty pixels.

[Brief Description of the Drawings]

[0012]

Fig. 1 is a plan view and a sectional view to explain a constitution of a display device pursuant to an embodiment of the present invention;

Fig. 2 is a block diagram to explain the constitution of the display device pursuant to the embodiment of the present invention;

Fig. 3 is a perspective view to explain the constitution of a shutter mechanism used in the display device pursuant to the embodiment of the present invention;

Fig. 4 is a plan view to explain the constitution of the shutter mechanism used in the display device pursuant to the embodiment of the present invention;

Fig. 5 is a sectional view to explain the constitution of the shutter mechanism used in the display device pursuant to the embodiment of the present invention; and

Fig. 6 is a graph showing a distribution of anchors (n type a-Si) and wiring (ITO) contact resistance.

(♦: When there is a connected layer; ·: When there is no connected layer)

[Mode for Carrying Out the Invention]

[0013]

An embodiment of the present invention will now be described below with reference to the drawings. However, the present invention can be implemented with a wide variety of modifications. The embodiment described below is not to be interpreted as limiting.

[0014] Fig. 1 shows a constitution of the display device 100 pursuant to an embodiment of the present invention. Fig. 1(A) is a plan view showing a configuration of the display device 100. A sectional structure that corresponds to a cross-section line A-B shown in that drawing is shown in Fig. 1(B). The display device 100 pursuant to this embodiment of the present invention includes an element substrate 102 formed with a switching element and a pixel with the shutter mechanism; and an opposing substrate 104 disposed to oppose the element substrate 102. A backlight 106 used as a light source in Fig. 1(B) is disposed at a side of the element substrate 102, but in an alternative constitution, it can be disposed at a side of the opposing substrate 104.

[0015]

In Fig. 1(A), a plurality of pixels is arranged in a display unit 108. Pixels are composed of a circuit portion that includes the switching element and storage capacitor and a shutter mechanism that is mechanically operated. At an outside of the display unit 108 are disposed a gate driver 110 that outputs a scanning signal to the display unit 108, a data driver 1 12 that outputs an image signal to the display unit 108, and a terminal unit that inputs signals from an external device. Also, the example shown in Fig. 1(A) shows the gate driver 1 10 disposed at both sides of the display unit 108. However, this is not a limitation.

[0016]

Fig. 2 shows one example of a circuit block diagram in the display device 100. A scanning signal from a display control circuit 116 is given to a gate driver 1 10, and an image signal is given to the data driver 112 on the element substrate 102. A timing for the backlight 106 to emit light is controlled by a light-emission control circuit 118. A system control circuit 120 implements comprehensive control of the display control circuit 1 16 and the light-emission control circuit 1 18.

[0017]

Pixel 122, arranged in a matrix, is disposed in the display unit 108. The pixel 122 includes a switching element 124, a storage capacitor 126 and a shutter mechanism 128. These act together to operate the shutter. The data driver 1 12 given the image signal from the display control circuit 1 16 supplies a data signal to the switching element 124 via data lines (Dl, D2, • · ·, Dm). The gate driver 110 given the scanning signal from the display control circuit 1 16 supplies a gate signal to the switching element 124 via data lines (Gl, G2, · · ·, Gn). The switching element 124 drives the shutter mechanism 128 based on the data signal supplied from the data line (Dl, D2, · · ·, Dm). For example, the switching element 124 gate turns on, and the image signal from the data line Dl is inputted to the pixel 122 selected by the gate line Gl. The shutter mechanism 128 is operated based on the inputted image signal.

[0018]

Fig. 3 is a perspective view showing details of the shutter mechanism 128 in the pixel 122, on the element substrate 102. The pixel 122 is formed on a light-transmissive glass substrate 130, and includes a switching element 124 on the glass substrate 130, a storage capacitor 126, a pixel forming layer 132 that includes the gate line and the data line, and the shutter mechanism 128 disposed on the pixel forming layer 132.

[0019]

The shutter mechanism 128 includes a shutter 134 formed in a plate shape to transmit or to block light from the light source (backlight), and a first shutter drive mechanism 136 and a second shutter drive mechanism that drive the shutter 134. The first shutter drive mechanism 136 is composed of a first spring 140 that supports the shutter 134 in a state suspended above the element substrate 102, a first anchor unit 142 that is electrically connected to this first spring 140, a second spring 144, and a second anchor 148 that is electrically connected to this second spring 144. The example depicted of the shutter mechanism 128 in Fig. 3, shows the first spring 140 and the first anchor unit 142 in the first shutter drive unit 136, and the second spring 144 and the second anchor unit 148 arranged to be symmetrical on the left and right when looking from a center line of the shutter 134. Such a configuration is also the same for the second shutter drive unit 138.

[0020]

The shutter 134 is formed by a non-transparent member. When the shutter opening 135 and the opening in the reflective plate disposed on the element substrate 102 or the opposing substrate 104 are substantially overlapped, light from the light source (backlight) passes therethrough; when the shutter 134 portion substantially overlaps the opening, light from the backlight is blocked. The operating length necessary for transmitting or blocking light can be shortened by disposing the shutter opening 135 on the shutter 134.

[0021]

Fig. 4 is a plan view of the shutter mechanism 128 shown in Fig. 3. The shutter mechanism 128 is disposed so that the first shutter drive unit 136 and the second shutter drive unit 138 oppose the shutter 134. The first anchor unit 142 is electrically connected to the first spring 140. When a bias potential is supplied to the first anchor unit 142, the first spring 140 become substantially the same potential. The second spring is electrically connected to the second anchor unit 148. When a ground potential is supplied to the second anchor unit 148, the second spring 144 becomes grounded. [0022]

A predetermined bias potential is supplied to the first spring 140; when the second spring 144 becomes the ground potential, both components have a potential difference. Electrostatic attraction acts between the first spring 140 and the second spring 144 causing both to become mutually attracted. The first spring 140 and the second spring 144 are compliant. For that reason, they are pulled together by electrostatic attraction, or slide the shutter 134 in one direction by a mechanical restoring force. Both of these actions are implemented at the first shutter drive unit 136 and the second shutter drive unit 138 causing the shutter to slide in one direction or in a direction opposite to that direction to open and close. Therefore, in order to implement shutter 134 operations smoothly, it is necessary to give a predetermined potential to the first anchor unit 142 and the second anchor unit 148. For example, a bias potential is given to the first anchor unit 142 based on a control signal, and a ground potential is supplied to the second anchor unit 148.

[0023]

Fig. 5 shows sectional structures of the shutter 134, the first spring 140, the second spring 144, and the first anchor unit 142. This shows a portion that corresponds to the cross- sectional line A-B. As shown in Fig. 5, the shutter 134, the first spring 140, the second spring 144, and the first anchor unit 142 are structural bodies formed by a mechanical layer 150 formed by an electrically conductive material having mechanical strength. An outside of the mechanical layer 150 is covered by an insulating layer 152 to ensure electrical insulation. Example electrically conductive materials with secure mechanical strengths include the following metals and alloys thereof: aluminum (Al), copper (Cu), nickel (Ni), chrome (Cr), molybdenum (Mo), titanium (Ti), tantalum (Ta), niobium (Nb), or neodymium (Nd) and the like, or a semiconductor material or an alloy thereof, diamond-like carbon, silicon (Si), germanium (Ge), gallium arsenic (GaAs), or cadmium telluride (CdTe) and others. Among these, it is preferred to use a semiconductor material represented by silicon from the view point of fabricating ease, heat tolerance and shape stability. For example, when using silicon, it is preferred to use an amorphous silicon or a polysilicon added with an n-type impurity such as phosphorus (p) and the like, or a p-type impurity such as boron (B) or a similar substance, to increase conductivity.

[0024]

The first anchor unit 142 is electrically connected to the wiring 154 that extends from the pixel forming layer 132 given the bias potential. Wiring 154 is formed by a highly conductive material in order to electrically connect the switching element 124 and the first anchor unit 142, in the pixel. Suitable materials used to form the wiring 154 include metallic materials such as Al or an Al alloy, or Cu and the like, used as a wiring material in integrated circuits, or an oxidized conductive material such as indium tin oxide (ITO), or zinc oxide (ZnO) or others, used in liquid crystal panels.

[0025]

A connecting layer 156 is disposed between the wiring 154 and the first anchor unit 142. The connecting layer 156 touches both the wiring 154 and the first anchor unit 142. Contact resistance between the wiring and the anchor unit, or a high-resistance region is prevented from being generated between wiring and the anchor unit. The potential of the anchor unit formed by the conductive material may properly be controlled to drive the shutter 134. However, if the contact resistance is high between the wiring and anchor unit, the potential of the anchor cannot be controlled. Here, in this embodiment of the present invention, this problem is eliminated by disposing the connecting layer 156 between the first anchor unit 142 and the wiring 154. Furthermore, it is preferred to dispose the same kind of connecting layer also between the second anchor unit and the wiring that is connected thereto.

[0026]

It is preferred to use a conductive material for the connecting layer 156 even if it oxidizes. As a conductive material even when oxidized, it is possible to use a metal element, an alloy or a compound of metal elements, such as molybdenum (Mo), tungsten (w), tantalum (Ta), or titanium (Ti) and the like. Also, it is acceptable to use a nitride of the metal elements. Furthermore, it is also acceptable to use ITO or IZO, or others. Even if these materials oxidize, they maintain conductivity, so by using them as the connecting layer between the anchor unit and the wiring, contact resistance can be reduced.

[0027]

Furthermore, it is preferred to form the connecting layer 156 using a material that is a non- rectifying contact (ohmic contact) with silicon. For example, if the electron affinity with an n- type silicon is x, it is preferable to select a material whose work function signal 0m of the material that forms the connecting layer 156 is smaller than the electron affinity x (0m - x). For example, it is possible to use tungsten (w) and titanium (Ti). To lower the Schottky barrier that is generated when the metal and semiconductor touch, it is acceptable to apply a degenerated semiconductor material added with impure elements at a high concentration as the connecting layer.

[0028]

Also, it is preferable to form the connecting layer 156 with a material that forms silicide by reacting with the silicon. As a metal element that forms silicide by reacting with the silicon, it is acceptable to use tungsten (w), tantalum (Ta), cobalt (Co), or nickel (Ni), or to adopt a transition metal element that can form silicide the same way. Silicide is a low-resistant material. Because it is thermally stable, it can be used as a material for connecting between the anchor unit and the wiring.

[0029]

Here, to explain with reference to Fig. 5, if the first anchor unit 142 is formed by an n-type silicon semiconductor, rectifying contact (Schottky contact) can occur depending on the type of metal material used to form the wiring 154. Therefore, depending on the direction that the bias potential is charged, contact resistance can increase, so it is preferable to dispose the connecting layer 156 formed with the material described above. For example, it is possible for non-rectifying contact if the connecting layer 156 is formed using tungsten (w) or titanium (Ti). It is also acceptable to form the connecting layer 156 using silicide.

[0030]

If the first anchor unit 142 is formed by an n-type amorphous silicon semiconductor, it is possible to attain ohmic contact using aluminum (Al), molybdenum (Mo) or titanium (Ti) and the like for the wiring 154 because the defect density is comparatively high. However, when a metal oxide such as indium tin oxide is used for the wiring 154, a layer of silicon oxide is formed between the silicon and the metal oxide, so contact resistance will increase. In such a case, it is possible to reduce the contact resistance between the first anchor unit 142 and the wiring 154 by forming the connecting layer 156 with a metal element, an alloy of these metal elements or a compound of the metal elements, such as molybdenum (Mo), tungsten (w), tantalum (Ta), or titanium (Ti) and the like, as the material having conductivity even when oxidized.

[0031]

If the first anchor unit 142 is formed by the silicon semiconductor, it is acceptable to form silicide therebetween the wiring 154. In such a case, as shown in Fig. 5, it is acceptable intentionally to dispose of the connecting layer 156 that is silicide, and to form using a metal material attained by forming silicide on the wiring 154 itself or an uppermost layer of the wiring.

[0032]

In this way, the thickness of the connecting layer 156 disposed to reduce resistance between the first anchor unit 142 and the wiring 154 should be 100 nm or less, preferably from 30 nm to 60 nm and more preferably from 35 nm to approximately 40 nm. In other words, as long as there is no problem in a resistance value of the connecting layer 156 itself, there is no problem in forming this to be thick. If the connecting layer 156 thickness is 30 nm or less, the characteristics of each type of material will not be attained and resistance is expected to increase. For that reason, the thickness of the connecting layer 156 is preferred to be 30 nm or more.

[0033]

Also, the description focused on the constitution of the first anchor unit 142 in Fig. 5.

However, the same constitution can be applied for the second anchor unit.

[0034]

Fig. 6 shows a distribution of resistance values when an n-type amorphous silicon is used as the material to form the anchors, and when indium tin oxide (ITO) is used to form the wiring. An example of the standard deviation of the resistance values shown in the graph in Fig. 6 when molybdenum tungsten (MoW) is used (plotted with ♦). Also, results when the connecting layer is not used is shown, as a comparative example (plotted with ·). When the connecting layer is used, the resistance value is approximately 1 ΜΩ, with little variation, but when no connecting layer is used, the resistance value increases from 1 GH to 1 ΤΩ or higher. It is clear that there are large variations.

[0035]

The result shown in Fig. 6 is that when there is no connecting layer used in the connection between the anchor unit and the wiring, the contact resistance increases, suggesting that the electrical connection is not very good. If the anchor unit and the wiring are not electrically connected, it is not possible to control the potential of the anchor unit. Also, it is not possible to operate the shutter, so bad pixels that do not operate will appear in the display unit. Conversely, if a connecting layer is disposed, the contact resistance is reduced, and there is little variation in that contact resistance, so no faulty pixels are generated, and uniform operating voltage can be maintained.

[0036]

In this way, pursuant to the embodiment of the present invention, by disposing a connecting layer between the anchor that composes the shutter mechanism and the wiring connected thereto, it is possible to suppress the problem of the shutter not operating, and to supply a display device without faulty pixels.

[0037]

Also, the shutter mechanism 128 depicted in Figs. 3 - 5 is only one example of a shutter mechanism that can be adopted for the display device 100. If the shutter can be driven by a switching element, it can be adopted for other embodiments.

[Explanation of Letters or Numerals]

[0038]

100 Display device

102 Element substrate

104 Opposing substrate

106 Backlight

108 Display unit

110 Gate driver

112 Data driver

114 Terminal unit

116 Display control circuit

118 Light-emission control circuit

120 System control circuit

122 Pixel

124 Switching element

126 Storage Capacitor

128 Shutter mechanism

130 Glass substrate

132 Pixel forming layer

134 Shutter

135 Shutter opening

136 First shutter drive unit

138 Second shutter drive unit

140 First spring

142 First anchor unit

144 Second spring

148 Second anchor unit

150 Mechanical layer

152 Insulating layer

154 Wiring

156 Connecting layer