KR19990085599A - 2-layer thin film type optical path control device - Google Patents

Abstract

The present invention relates to a thin film type optical path control apparatus capable of reducing the thickness of the second sacrificial layer 165 by installing a mirror post 170b on a tip 130a extending at the end of the free end. Is a positive integer) and includes an active matrix 100 having a drain pad 105 formed therein and electrically connected to a drain electrode (not shown) of the transistor, and having a fixed end on the active matrix 100. A pair of cantilever-shaped actuators 160 formed of a 161 and a free end 162 are formed, and the pair of actuators 160 are a membrane 130, a lower electrode 135, and a strained layer 140, respectively. And the upper electrode 145 is sequentially stacked, and the drain pad 105 and the lower electrode 135 are electrically connected to each other through the fixed end 161, and the pair of actuators 160 At the ends of the free ends of the membrane 130 Is connected by an extension, the tip 130a is formed in the center of the extension of the membrane 130, a mirror post 170b is formed on the tip 130a, on the mirror post 170b The mirror 175 is supported.

Therefore, according to the present invention, the mirror post is formed on the tip extending the free end of the free end so that the maximum value of the angle of tilt of the mirror does not change even if the height of the mirror post is lowered, thereby making the second sacrificial layer for mirror formation. Can reduce the thickness.

Description

2-layer thin film type optical path control device

The present invention relates to a thin film type optical path control device, and more particularly to a thin film type optical path control device that can reduce the thickness of the second sacrificial layer by installing a mirror post on the tip extending to the end of the free end.

In general, an optical path control device capable of forming an image by adjusting a light flux is a direct view type image display device such as a CRT (Cathod Ray Tube) or a projection type image display device according to a method of projecting a light beam incident from a light source on a screen. Liquid crystal displays (hereinafter referred to as "LCD"), DMD (Deformable Mirror Device), AMA (Actuated Mirror Array) and the like.

Although CRT devices have excellent image quality, as the screen size increases, the weight and volume of the device increase, and the manufacturing cost thereof increases. In contrast, a liquid crystal display (LCD) can be formed into a flat panel, but the incident light flux Due to the polarization of the light having a low light efficiency of 1 to 2%, there was a problem that the response speed of the liquid crystal material therein is slow.

Accordingly, devices such as DMD or AMA have been developed to solve the problems of LCD as described above. Currently, AMA can achieve a light efficiency of 10% or more, while DMD has a light efficiency of about 5%. In addition, the AMA is not only affected by the polarity of the incident luminous flux but also does not affect the polarity of the luminous flux.

Typically, the respective actuators formed inside the AMA cause deformation depending on the electric field generated by the applied image signal and bias voltage. When this actuator causes deformation, each of the mirrors mounted on top of the actuator is inclined in proportion to the magnitude of the electric field.

Thus, these inclined mirrors can reflect light incident from the light source at a predetermined angle. Piezoelectric ceramics such as PZT (Pb (Zr, Ti) O ₃ ), or PLZT ((Pb, La) (Zr, Ti) O ₃ ) are used as a constituent material of the actuator for driving the respective mirrors. As the constituent material of this actuator, electrodistorted ceramics such as PMN (Pb (Mg, Nb) O ₃ ) can be used.

The AMA is classified into a bulk type and a thin film type. Currently, AMA is the main trend of the thin-film optical path control device.

1 and 2 show a conventional thin film type optical path control device.

As shown in FIG. 2, which is a cross-sectional view taken along line AA ′ of FIG. 1, the conventional thin film type optical path adjusting device drives the active matrix 5 and the actuator 65 and the actuator 65 formed thereon. It is composed of a mirror 75 for adjusting the light path according to the degree.

The active matrix 5 is composed of a semiconductor such as silicon (Si), and includes M × N MOS transistors therein. One side of the active matrix 5 is formed with a drain pad 10 electrically connected to a drain electrode (not shown) of the MOS transistor.

The actuator 65 has a cantilever shape in which one side is supported at a portion where the drain pad 10 is formed, and is composed of a membrane 30, a lower electrode 35, a strained layer 40, and an upper electrode 45. The drain pad 10 and the lower electrode 35 are electrically connected by the via contact 55.

The mirror 75 and the mirror post 70b are made of aluminum with good reflection efficiency, and are supported at the 70a position as shown in FIG. 1 at the end of the free end 62 of the actuator 65.

In the conventional thin film type optical path adjusting device, an image signal voltage is applied from the drain pad 10 of the active matrix 5 to the lower electrode 35, which is a signal electrode, and a bias voltage is applied to the upper electrode 45, which is a common electrode. In this case, an electric field is generated between the upper electrode 45 and the lower electrode 35. By this electric field, the strained layer 40 between the upper electrode 45 and the lower electrode 35 contracts in a direction perpendicular to the electric field. On the other hand, as the shrinkage of the deformable layer 40 is disturbed by the membrane 30, the shrinkage force is concentrated in the upper direction of the actuator 65 in which the membrane 30 is not formed, and the actuator 65 is bent at a predetermined angle. All. At the same time, the mirror 75 mounted on the free end 62 of the actuator 65 is inclined by the bending angle of the actuator 65 to adjust and reflect the light path of the light incident from the light source to form a unit pixel. Countless pixels of light reflected by the mirror 75 are projected onto the screen through the slit to form an image. At this time, since the upper electrode of the free end 65 and one edge of the mirror 75 abut, the maximum value of the inclination angle at which the mirror 75 can be tilted becomes θ as shown in FIG. 6A.

On the other hand, efforts and researches have recently been conducted to reduce the material and time required for the manufacturing process of the optical path control device. In the conventional actuator, the length of the free end of the actuator is short, so that the mirror post may not be long enough. Since it cannot be tilted more than this, the driving range of the mirror is reduced, and thus, the length of the post has to be extended, so that the thickness of the second sacrificial layer has to be thick enough to manufacture the mirror and the mirror post meeting these conditions. Therefore, the material cost constituting the second sacrificial layer and the time taken to etch the second sacrificial layer are long, and the problem of reducing the length of the mirror posts in order to save time and these materials has emerged.

The present invention is to solve the material and time-saving problems that arise in the manufacturing process of the optical path control device as described above, by reducing the length of the mirror post by forming a mirror post on the tip extending the membrane portion of the free end mirror It is an object of the present invention to provide an optical path control apparatus capable of reducing the thickness of the second sacrificial layer for forming a mirror by keeping the maximum value of the inclination angle unchanged.

In order to achieve the above object, the present invention includes an active matrix having M × N (M, N is a positive integer) transistors and a drain pad electrically connected to the drain electrode of the transistor. A pair of cantilever-shaped actuators including a fixed end and a free end are formed, and the pair of actuators are formed by sequentially stacking a membrane, a lower electrode, a strained layer, and an upper electrode, and through the fixed end, the drain pad. And the lower electrode are electrically connected to each other, the pair of actuators are connected to each other by an extension part of the membrane at an end of the free end, and a tip extends in the center of the extension part of the membrane, and a mirror post is placed on the tip. Is formed, and the mirror is supported on the mirror post It provides a thin film type optical path control device.

The above objects and various advantages of the present invention will become more apparent from the preferred embodiments of the invention described below with reference to the accompanying drawings by those skilled in the art.

1 is a plan view of a conventional thin film type optical path control device,

2 is a cross-sectional view taken along line AA ′ of the conventional thin film type optical path adjusting device shown in FIG. 1;

3 is a plan view of a thin film type optical path control apparatus according to the present invention,

4 is a cross-sectional view taken along the line B-B 'of the thin film type optical path control device shown in FIG.

5a to 5i is a manufacturing process diagram of the thin film type optical path control apparatus according to the present invention,

6A is a conceptual diagram conceptually illustrating a prior art;

6b conceptually illustrates the effect according to the invention;

<Explanation of symbols for the main parts of the drawings>

101; Substrate 100; Active matrix

105; Drain pad 110; Protective layer

115; Etch stop layer 120; Sacrificial layer

125; Air gap 130; Membrane

130a; Tip 130b; Indentation

135; Lower electrode 140; Strained layer

145; Upper electrode 150; Via Hole

155; Via contact 160; Actuator

161; Fixed end 162; Free end

165; Second sacrificial layer 170a; Mirror post position

170b; Mirror post 175; mirror

Hereinafter, a thin film type optical path adjusting apparatus according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

Figure 3 is a view showing a plan view of a thin film type optical path control apparatus according to the present invention, Figure 4 is a cross-sectional view taken along the line B-B 'thin film type optical control device shown in Figure 3, Figure 5 is a present invention It is a manufacturing process chart of a thin film type optical path control apparatus.

3 and 4, the thin film type optical path adjusting apparatus according to the present invention includes an active matrix 100, an actuator 160, and a mirror 175 formed on the active matrix 100.

The active matrix 100 includes an M × N MOS transistor embedded therein and includes a drain pad 105 electrically connected to the drain electrode of the MOS transistor. The upper portion of the active matrix 100 includes a protective layer 110 and an etch stop layer 115.

A cantilever-shaped actuator 160 including a fixed end 161 and a free end 162 is formed on the active matrix 100.

The actuator 160 is formed by sequentially stacking the membrane 130, the lower electrode 135, the strained layer 140, and the upper electrode 145, and through the fixed end 161, the drain pad 105. And the lower electrode 135 are electrically connected. Therefore, an electric field is generated between the lower electrode 135 to which the signal voltage is applied and the upper electrode 145 to which the bias voltage is applied, and thus a mechanical stress is generated in the strained layer 140 formed of piezoelectric material or electrostrictive material. 162 is bent in the opposite direction that the membrane 130 is formed, that is, upward.

In the free end 162 of the actuator 160 according to the present invention, the membrane 130 is exposed to a portion connecting the two ends of the free end 162 split from the fixed end, in particular the exposed A tip 130a protruding toward the opposite side from the fixed end is formed at the central portion of the membrane 130. The mirror post installation position 170a is formed on the tip 130a. In addition, an indentation portion 130b having a shape corresponding to the tip 130a is installed at the fixed end 161 of the actuator to form an AMA.

A mirror post 170b is formed at the mirror post installation position 170a on the tip 130a at the end of the free end 162 formed as described above, and a mirror having the same size as the unit pixel area on the mirror post 170b. 175 is integrally formed. The mirror 175 is connected to the mirror post 170b at its center position. The reflection angle of the mirror 175 is determined by the driving angle of the actuator 160 which is changed according to the degree of bending of the free end 162.

That is, FIGS. 6A and 6B show relations between the lengths of the free ends 62 and 162 and the heights of the mirror posts 70 b and 170 b when the maximum reflection angle θ of the mirrors 75 and 175 is to be kept constant according to the prior art and the present invention. Is a comparison of 6A and 6B, it is assumed that portions of the free ends 62 and 162 in which the strained layers are formed are bent in an arc shape. The end of the free end 162 of FIG. 6B is a straight tip 130a. The mirrors 75 and 175 have the same length, and the mirror posts 70b and 170b support the center of each mirror 75 and 175. When the maximum value of the reflection angle is the same as θ, the free end 162 of the present invention is longer by the length of the tip 130a than the free end 62 of the prior art.

The portion where the strained layer is formed in the free end 162 is bent upward, and the tip 130a forming the free end end is connected to the end of the bent portion and moves upward while maintaining the straight shape. The mirror 175 and the mirror post 170b installed on the 130a are inclined until the maximum value of the inclination angle becomes θ so that one edge of the mirror 175 contacts the upper electrode 145. In FIG. 6B, the mirror post 170b may be shorter than the mirror post 70b used in FIG. 6A.

Hereinafter, the manufacturing method of the thin film type optical path control device according to the present invention will be described in detail.

Referring to FIG. 5A, M × N transistors are formed on a substrate 101 in a matrix form, and a drain pad 105 that can be electrically connected to a drain electrode of the transistor is formed thereon, and the silicate glass PSG is formed thereon. The protective layer 110 and the etch stop layer 115 of the material is formed.

The protective layer 110 is formed to have a thickness of about 1.0 to 2.0 μm using a chemical vapor deposition (CVD) method. The protective layer 110 prevents damage to the active matrix 100 in which the transistor is embedded during subsequent processing.

An etch stop layer 115 made of nitride is formed on the passivation layer 110. The etch stop layer 115 is formed to have a thickness of about 1000 to 2000 kPa using a low pressure chemical vapor deposition (LPCVD) method. The etch stop layer 115 prevents the active matrix 100 and the protective layer 110 from being damaged by a subsequent etching process.

Referring to FIG. 5B, the sacrificial layer 120 is formed on the etch stop layer 115. The first sacrificial layer 120 is formed of a silicate glass (PSG) to have a thickness of about 0.5 to 4.0㎛ by the atmospheric pressure chemical vapor deposition (APCVD) method. In this case, since the sacrificial layer 120 covers the upper portion of the active matrix 100 in which the transistor is embedded, the flatness of the surface thereof is very poor. Therefore, the surface of the sacrificial layer 120 is planarized by using a spin on glass (SOG) method or a chemical mechanical polishing (CMP) method. In the subsequent process, a portion of the sacrificial layer 120 where the drain pad 105 is formed is etched to expose a portion of the etch stop layer 115 to form a portion where the fixed end of the actuator is to be formed.

Referring to FIG. 5C, the membrane 130 is formed over the exposed etch stop layer 115 and over the sacrificial layer 120. The membrane 130 is formed to have a thickness of about 0.1 μm to about 1.0 μm using a low pressure chemical vapor deposition (LPCVD) method. The lower electrode 135 is formed on the membrane 130. The lower electrode 135 is formed to have a thickness of about 500 to 2000 mW using a sputtering method of a metal such as platinum or platinum-tantalum. The lower electrode 135 is electrically connected to the drain pad 105 electrically connected to the transistor to apply a signal voltage.

Referring to FIG. 5D, a strained layer 140 is formed on the lower electrode 135. The strained layer 140 is formed to have a thickness of about 0.1 to 1.0 μm using a sol-gel method, a sputtering method, or a chemical vapor deposition (CVD) method for piezoelectric materials such as PZT or PZLT. do. In addition, the strained layer 140 is phase shifted using a rapid heat treatment (RTA) method.

An upper electrode 145 is formed on the strained layer 140. The upper electrode 145 is formed to have a thickness of about 500 to 2000 micrometers by sputtering of aluminum, platinum, or silver. The upper electrode 145 is applied with a bias voltage as a common electrode.

Meanwhile, the membrane 130, the lower electrode 135, the strained layer 140, and the upper electrode 145 formed through the above-described process are patterned to have a predetermined planar shape. After forming the multilayer thin film, patterning is performed collectively. Alternatively, another method may be formed after each layer is formed and patterned immediately.

Referring to FIG. 5E, the strained layer 140, the lower electrode 135, the membrane 130, and the etch stop layer 115 may be formed to form the via hole 150 in a direction perpendicular to the fixed end 161 of the actuator 160. ), And the protective layer 110 is sequentially etched. Subsequently, the via contact 155 may be formed by sputtering a metal such as tungsten, platinum, aluminum, or titanium into the via hole 150 to electrically connect the drain pad 105 and the lower electrode 135. Form. Accordingly, the image signal is applied to the lower electrode 135 through the drain pad 105 and the via contact 155 from the transistor embedded in the active matrix 100.

Referring to FIG. 5F, the sacrificial layer 120 is etched with hydrofluoric acid (HF) vapor to form an air gap 125. That is, the free end 162 except for the fixed end 161 of the actuator 160 is separated from the etch stop layer 115 of the active matrix 100.

Referring to FIG. 5G, the second sacrificial layer 165 is formed on the entire surface of the result of the previous process. The second sacrificial layer 165 is formed by spin coating a photoresist made of a polymer having good fluidity, and is applied to have a predetermined thickness while completely filling the first air gap 125.

Subsequently, a mirror post 170b for supporting the mirror 175 at the position of the end of the free end 162 of the actuator 160 may be formed on the tip 130a of the membrane 130. Patterning is done so.

Alternatively, the first and second sacrificial layers 120 and 165 may be formed of polysilicon and simultaneously controlled.

Referring to FIG. 5H, a mirror 175 and a mirror post 170b are formed on the exposed membrane 130 and the second sacrificial layer in front. The mirror 175 and the mirror post 170b are formed by depositing aluminum (Al) or silver (Ag) having good reflectivity using a sputtering process to a thickness of about 0.5 to 3.0 μm in the case of the mirror 175.

Referring to FIG. 5I, the mirror 175 is patterned to be separated in units of pixels, and then the second sacrificial layer 165 is removed using an oxygen plasma (O ₂ plasma) process to form a mirror separately on the actuator. The manufacturing process of the 2-layer thin film type optical path control apparatus is completed.

Referring to the operation of the present invention prepared as described as follows.

A bias voltage is applied to the upper electrode 145 of the actuator 160 through a TCP pad (not shown) and a pad of an AMA panel. At the same time, the image signal transmitted through the pads of the TCP pad and the AMA panel is applied to the lower electrode 135 through the transistors and the drain pad 105 via contacts 155 embedded in the active matrix 100.

Accordingly, an electric field is generated between the upper electrode 145 and the lower electrode 135 of the actuator 160, and the strained layer 140 between the upper electrode 145 and the lower electrode 135 is deformed by the electric field. Causes

The strained layer 140 contracts in a direction perpendicular to the electric field, and the membrane 130 does not relatively deform, so that the free end 162 is formed on the fixed end 161 to form the membrane 130. The bow is bent in an opposite direction, that is, upward, by a predetermined angle.

At this time, since the end of the free end 162 is the tip 130a, the maximum value of the reflection angle of the mirror 175 supported on the tip 130a is sufficiently large even when the mirror post 170b having a short length is used. Can be maintained.

The mirror 175 driven as described above reflects the light beam incident from the light source and controls the light path of the incident light to project on the screen to form an image.

Therefore, in the thin film type optical path control apparatus according to the present invention, the mirror post is formed on the tip extending the membrane portion of the free end of the actuator so that the maximum value of the tilt angle of the mirror does not change even if the length of the mirror post is reduced. It is possible to provide an optical path control apparatus that can reduce the thickness of the second sacrificial layer for formation.

In the above description, it should be understood that those skilled in the art can make modifications and changes to the present invention without changing the gist of the present invention as it merely illustrates a preferred embodiment of the present invention.

As described above, the thin film type optical path adjusting device according to the present invention allows the mirror post to be formed on the tip extending the membrane portion of the free end so that the maximum value of the tilt angle of the mirror does not change even if the length of the mirror post is reduced. It is to provide an optical path control apparatus that can reduce the thickness of the second sacrificial layer for forming. In addition, when the thickness of the second sacrificial layer is thin, it is possible to obtain an effect of saving the time required to etch the material and the second sacrificial layer formed to form the second sacrificial layer.

Claims (4)

An active matrix including M × N (M and N are positive integers) transistors and a drain pad electrically connected to a drain electrode of the transistor is provided. A pair of cantilevers includes a fixed end and a free end on the active matrix. An actuator having a shape is formed, and the pair of actuators are formed by sequentially stacking a membrane, a lower electrode, a strained layer, and an upper electrode, and the drain pad and the lower electrode are electrically connected through the fixed end. The pair of actuators are connected to each other by an extension of the membrane at the end of the free end, a tip extends in the center of the extension of the membrane, a mirror post is formed on the tip, and a mirror on the mirror post. The thin film type optical path control device, characterized in that supported. The apparatus of claim 1, wherein the tip is formed by extending a membrane layer. The apparatus of claim 1, wherein the tip has a rectangular shape. The thin film type optical path control device according to claim 1, wherein an indentation portion having a shape corresponding to the tip is provided at the fixed end side.