KR19990005306A - ESDI protection circuit for driving board of thin film type optical path controller - Google Patents

Abstract

The present invention provides a thin film type optical path control device having a driving substrate in which M × N (M, N is an integer) PMOS transistors are formed in a matrix form for receiving an image signal from an external device through an input pad to adjust a tilting angle of an actuator. And a first transient voltage protection unit for bypassing a current applied to the transistor from the input pad when the transient voltage is higher than a preset voltage level of the input pad. By providing an ESD protection circuit for a driving substrate of the thin-film optical path control apparatus, characterized in that it comprises a second transient voltage protection for bypassing the current applied from the input pad to the transistor when a low transient voltage is applied. Positive static electricity applied during or during the manufacturing process And it is possible to prevent the destruction of the transistor embedded in the driving substrate due to the negative static electricity has the effect of improving the reliability of the thin film type optical path control device.

Description

ESDI protection circuit for driving board of thin film type optical path controller

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to thin-film optical path controllers, and in particular, an ESD protection circuit of a thin-film optical path controller to prevent damage to a driving substrate of the thin-film optical path controller due to electrostatic discharge (ESD). It is about.

In general, a spatial light modulator, which is an apparatus for projecting optical energy onto a screen, may be variously applied to optical communication, image processing, and information display apparatus. Such devices are classified into a direct view type image display device and a projection type image display device according to a method of projecting a light beam incident from a light source onto a screen. The direct view image display device includes a CRT (Cathod Ray Tube), and the projection image display device includes a liquid crystal display (hereinafter referred to as an LCD), a DMD (deformable mirror device), or an AMA (Actuated). Mirror Arrays).

The above-described CRT apparatus is an excellent display apparatus which is guaranteed an average brightness of 100 ft-L (white display) or more, a contrast ratio of 30: 1 or more, a lifetime of 10,000 hours or more. However, since the CRT has a large weight and volume and maintains high mechanical strength, it is difficult to make the screen completely flat, which causes distortion of the peripheral part. In addition, since CRTs excite phosphors with an electron beam to emit light, there is a problem that a high voltage is required to produce an image.

Therefore, LCDs have been developed to solve the above-mentioned problems of CRT. The advantages of such LCDs are explained in comparison with CRTs. LCDs operate at low voltages, consume less power, and provide images without distortion.

However, despite the above-mentioned advantages, the LCD has a low light efficiency of 1 to 2% due to the polarization of the light beam, and there is a problem that the response speed of the liquid crystal material therein is slow.

Accordingly, in order to solve the problems of the LCD as described above, a device such as a DMD or an AMA has been developed. 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.

An operation process of the thin film type optical path control device will be described with reference to FIGS. 1 and 2 as follows.

1 is a plan view of a general thin film type optical path control device, Figure 2 is a cross-sectional view taken along the line AA 'of FIG.

Referring to FIG. 1, one side of the actuator 200 has a concave portion having a rectangular shape at the center thereof, and the concave portion is formed in a stepped shape toward both edges. The other side of the actuator 200 has a rectangular protrusion which narrows in a stepped manner toward the center portion corresponding to the concave portion. Therefore, the concave portion of the actuator 200 is fitted with the protrusion of the neighboring actuator, and the protrusion of the actuator 200 is fitted with the concave portion of the neighboring actuator.

As illustrated in FIG. 2, each of the M × N pixels of the thin film type optical path control device having the planar structure includes a driving substrate 100 having a drain 114 formed on one side of each pixel, and an actuator formed thereon. (Actuator: 200).

In the thin film type optical path control device having such a structure, when an image signal is applied to the driving substrate 100 from the outside, the applied image signal is composed of a drain 114, a source (Source, 112), and a gate (116). It is provided to the power distribution unit 255 formed in the distribution hole 250 via the metal layer 130 connected to the transistor and the drain 114 of the transistor.

In this case, the distributor 255 is connected to the lower electrode 220 made of a conductive metal, and a predetermined image signal applied to the driving substrate 100 is transmitted to the lower electrode 220.

Meanwhile, the bias current signal is applied to the upper electrode 240 from the common electrode.

Accordingly, a bias current signal is applied to the upper electrode 240, and an image current signal is applied to the lower electrode 220, so that an electric field is generated between the upper electrode 240 and the lower electrode 220. The deformation layer 230 causes deformation by the electric field.

On the other hand, as the deformation layer 230 is deformed, each of the mirrors mounted on the upper portion of the actuator 200 is inclined in proportion to the magnitude of the electric field, so that the light incident from the light source is applied to the lower electrode 220. It is possible to reflect at a predetermined angle corresponding to the image signal.

On the other hand, the transistor formed on the driving substrate of the above-described thin film type optical path control device may be damaged by an overcurrent due to an overvoltage that is instantaneously applied by electrostatic discharge applied during a manufacturing process or during use. Therefore, in order to prevent the damage of the driving substrate by the static electricity in the prior art, the conventional ESD protection circuit as shown in Figure 3 was used, the operation process is as follows.

First, when a voltage greater than the power supply voltage V _DD is applied to a pad connected to each transistor of the driving substrate, the diode D is turned on to discharge a current applied to the input terminal to the power supply voltage terminal. At this time, the diode D operates in a state in which the resistance value is 0, that is, a short circuit state due to the forward characteristic of the diode D.

However, in the conventional method, when the positive ESD occurs, the driving board can be protected from the stress caused by static electricity, but the driving board cannot be protected when the negative ESD occurs. .

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems, and an object of the present invention is to discharge thin film type optical paths by discharging an overcurrent caused by ESD to a power voltage terminal or a ground voltage terminal when positive and negative ESD are generated. The present invention provides an ESD protection circuit for a driving substrate of a thin film type optical path control device capable of protecting the driving substrate of a device from stress caused by static electricity.

In order to achieve the above, the present invention, M × N (M, N is an integer) PMOS transistor (not shown) for applying the image signal from the outside through the input pad to adjust the tilting angle of the actuator in the form of a matrix In the thin film type optical path control device having a built-in drive substrate, the first transient voltage protection unit for bypassing the current applied to the transistor from the input pad when a transient voltage higher than a predetermined voltage level is applied to the input pad And a second transient voltage protection unit for bypassing a current applied to the transistor from the input pad when a transient voltage lower than a preset voltage level is applied to the input pad. It provides an ESD protection circuit for the driving substrate of.

1 is a plan view showing one unit pixel among M × N pixels of a general thin film type optical path control apparatus;

FIG. 2 is a cross-sectional view of a unit pixel of the general thin film type light control device shown in FIG. 1 taken along line A-A ';

3 is a circuit diagram showing an ESD protection circuit for a driving substrate of the thin film type optical path control apparatus according to the prior art;

4 is a circuit diagram showing an ESD protection circuit for a driving substrate of the thin film type optical path control apparatus according to the present invention.

* Explanation of symbols for main parts of the drawings

100: driving substrate 110: substrate

112: source 114: drain

116: gate 120: oxide film

125: oxide film 130: metal layer

140: protective layer 150: etch stop layer

200: actuator 210: support layer

220: lower electrode 230: strained layer

240: upper electrode 245: stripe

250: power distribution hall 255: power distribution

P1: first transient voltage protection unit

P2: second transient voltage protection unit

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.

Hereinafter, an ESD protection device for a driving substrate of a thin film type optical path control device according to the present invention will be described in detail with reference to the accompanying drawings.

4 is a diagram illustrating an ESD protection device for a driving substrate of a thin film type optical path control device according to a preferred embodiment of the present invention, wherein the first transient voltage protection unit P1 and the second transient voltage protection unit P2 are PMOS transistors. As a structure of the thin film optical path control device shown in FIG. 2 and the PMOS shown by reference numerals 110 to 125, the structure thereof is the same.

As shown in FIG. 4, the ESD protection device for a driving substrate of the thin film type optical path adjusting device according to the present invention includes a first transient voltage protection unit P1 and a second transient between an input pad and a PMOS transistor embedded in the driving substrate. The voltage protection part P2 is configured, the power supply voltage Vcc is provided to the first transient voltage protection part P1, and the ground voltage Vss is provided to the second transient voltage protection part P2.

Meanwhile, the above-described first transient voltage protection unit P1 and the second transient voltage protection unit P2 are composed of PMOS transistors according to a preferred embodiment of the present invention, and are formed of p-channels on the n-type substrate 110. A drain 114 and a source 112 are formed, and an oxide layer 120 is formed between the drain 114 and the source 112, and a gate 116 is formed by depositing a metal on the oxide layer 120. . At this time, the drain 114, the source 112, and the gate 116 are insulated by the oxide layer 120, and no channel is formed between the drain 114 and the source 112.

On the other hand, the power supply voltage Vcc and the ground voltage Vss provided to the PMOS transistor are a reference for detecting a transient voltage outside the voltage level range of the image signal used in the thin film type optical path control device. At this time, since the thin film type optical path adjusting device uses the voltage level range of the image signal between approximately 0 to 12V, the power supply voltage Vcc is supplied within approximately 13 to 17V, and the ground voltage Vss is approximately -1 to-. It would be desirable to supply in the 5V range.

Hereinafter, the operation process of the ESD protection device for the driving substrate of the thin film type optical path control device according to the present invention having the above-described structure will be described for each of the normal state, the positive static electricity generation state, and the negative static electricity generation state as follows.

First, when a predetermined image signal is applied to the input pad in the normal state, the image signal is smaller than the power supply voltage Vcc supplied to the first transient voltage protection unit P1. Therefore, the first transient voltage protection unit P1 In the turn-off state, no channel is formed between the drain 114 and the source 112 of the first transient voltage protection part P1. That is, the first transient voltage protection part P1 is in an open state and no current flows.

In addition, since the image signal applied to the input pad is greater than the ground voltage Vss supplied to the second transient voltage protection part P2, the second transient voltage protection part P2 is turned off, thereby preventing the second transient voltage. A channel is not formed between the drain 114 of the portion P2 and the source 112. That is, the second transient voltage protection part P2 is in an open state and no current flows.

Therefore, when the normal image signal is applied to the input pad, the first transient voltage protection part P1 and the second transient voltage protection part P2 are in an open state, and the image signal normal to the input pad is provided to the PMOS transistor of the driving substrate. .

On the other hand, when positive static electricity is generated and applied to the input pad, since the static electricity applied to the input pad is supplied to the first transient voltage protection part P1, the static electricity is much larger than the power supply voltage Vcc, and thus, the first transient voltage protection part. Between the drain 114 and the source 112 of P1, electrons are accumulated in the oxide layer 120 and from an n-type substrate to form a channel. That is, the first transient voltage protection part P1 is turned on and short-circuited so that all of the overcurrent flowing from the input pad to the driving substrate is discharged to the power supply voltage Vcc terminal, whereby the PMOS transistor embedded in the driving substrate is positively charged. It is prevented from being destroyed by the resulting overcurrent.

In addition, when the positive static electricity is generated and applied to the input pad, the static electricity applied to the input pad is much smaller than the ground voltage Vss supplied to the second transient voltage protection part P2, and thus, the second transient voltage protection part. Between the drain 114 and the source 112 of P2, electrons are accumulated in the oxide layer 120 and from an n-type substrate to form a channel. That is, the second transient voltage protection unit P2 is turned on and short-circuited so that the negative overcurrent flowing from the input pad to the driving substrate is discharged to the power supply voltage Vss terminal, whereby the PMOS transistor embedded in the driving substrate becomes negative electrostatic. To prevent destruction by overcurrent.

As described above, although the present invention has been described with reference to the drawings, those skilled in the art may variously modify and change the present invention without departing from the spirit and scope of the invention as set forth in the claims below. I can understand that you can.

As described above, by using the ESD protection circuit of the thin film type optical path control apparatus according to the present invention, it is possible to prevent the destruction of the transistor embedded in the driving substrate due to the positive and negative static voltages applied during the manufacturing process or during use. There is an effect that can improve the reliability of the adjusting device.

Claims (4)

In a thin film type optical path control device having a driving substrate in which M × N (M, N is an integer) PMOS transistors are formed in a matrix form to receive an image signal from an external device through an input pad and adjust a tilting angle of an actuator. A first transient voltage protection unit for bypassing a positive overcurrent applied to the transistor from the input pad when a transient voltage higher than a predetermined power supply voltage is applied to the input pad, and a transient lower than a ground voltage preset to the input pad And a second transient voltage protection unit for bypassing a negative overcurrent applied to the transistor from the input pad when a voltage is applied. 2. The ESD protection circuit according to claim 1, wherein the first transient voltage protection part and the first transient voltage protection part are made of diode-connected incremental PMOS transistors. 2. The ESD protection circuit for driving substrates of a thin film type optical path adjusting device according to claim 1, wherein the power supply voltage is set in a range of 13 to 17V. 2. The ESD protection circuit for driving substrates of a thin film type optical path adjusting device according to claim 1, wherein the ground voltage is set in a range of -1 to -5V.