JP2007095878A - Optical sensor, electro-optical device and electronic device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make it possible to detect exactly outdoor daylight by extending the range of the reverse bias from which optical sensitivity is obtained. <P>SOLUTION: There are provided an indicator 14, and an optical sensor having two or more diodes 29 and 30 whose light-receiving layers are composed of polycrystalline silicon used for detecting the illumination of outdoor daylight around the indicator. The optical sensor comprises a light-receiving element constituted by carrying out serial connection of the two or more diodes. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical sensor, an electro-optical device, and an electronic apparatus suitable for a display device that controls display luminance.

  The liquid crystal panel is configured by sealing liquid crystal between two substrates such as a glass substrate and a quartz substrate. Each substrate is provided with an electrode, and an image signal is supplied to the electrode. The optical characteristics of the liquid crystal between the electrodes of each substrate change according to the image signal. That is, by applying a voltage based on the image signal to the liquid crystal between the electrodes of each substrate, the alignment of the liquid crystal molecules is changed. Thereby, the light transmittance in each pixel changes according to the image signal, and the image display according to the image signal is performed.

  In order to display with high brightness in such a liquid crystal panel, a backlight is generally provided on the back of the liquid crystal panel. As such a backlight, an apparatus for improving the uniformity of illumination using a light guide plate has been developed. By illuminating the display area of the liquid crystal panel with the backlight, the display on the display area can be observed with sufficient luminance.

  By the way, the visibility of the display on the liquid crystal panel changes according to the ambient brightness. For example, the brighter the ambient light, the easier it is to see the display when the illumination in the display area is brighter. Conversely, when the ambient light is sufficiently dark, it is not necessary to make the display area brighter than necessary.

Therefore, in order to provide an easy-to-see display regardless of the ambient brightness, a technique for detecting ambient light and controlling the brightness of the backlight based on feedback information has been proposed.
Japanese Patent Laid-Open No. 2005-19636

  By the way, it is conceivable to employ discrete components as an optical sensor for detecting ambient light (external light). However, in this case, it is necessary to mount the optical sensor on the flexible printed circuit board, which increases man-hours and costs.

  Therefore, it is conceivable to form an optical sensor on a substrate constituting a display panel such as a liquid crystal panel. As a light receiving element formed on a liquid crystal panel manufactured by low-temperature polysilicon technology, a PIN diode can be considered. Such a diode OFF characteristic has a so-called jump-up characteristic in which a current flowing when a reverse bias is applied increases. This jumping characteristic has a drawback that the photosensitivity when a reverse bias is applied is lowered.

  On the other hand, Japanese Patent Application Laid-Open No. 2005-19636 discloses a technique for suppressing off-current by employing an LDD structure for a diode.

However, the jumping characteristics vary depending on the accuracy of the N ⁻ region constituting the LDD. However, the N ⁻ region cannot be configured with sufficient accuracy due to variations in mask accuracy and density. For this reason, the off current jump characteristic, that is, the slope of the change in the off current varies, and the minimum value of the off current also varies. As described above, the low-temperature polysilicon technology has a problem that a photosensor with sufficient accuracy cannot be obtained due to the jumping characteristics.

  An object of the present invention is to provide an optical sensor, an electro-optical device, and an electronic apparatus that can detect external light with high accuracy.

  An optical sensor according to the present invention includes a plurality of diodes each having a light receiving layer made of polycrystalline silicon, the plurality of diodes receiving the same light are connected in series, and the plurality of diodes connected in series are the same. This is characterized in that a light receiving element is configured with a bias of (5).

  According to such a configuration, a diode whose light receiving layer is made of polycrystalline silicon has a relatively narrow reverse bias region having photosensitivity. However, by connecting diodes in series, the range of reverse bias having photosensitivity can be expanded. Thereby, even if a high voltage is applied to the diode, the photosensitivity can be obtained, and the amplitude of the sensor output can be increased by the high voltage. In particular, an electro-optical device using polycrystalline polysilicon is often driven at a relatively high voltage, and even in this case, the diode connected in series is driven at a high voltage to ensure the illuminance of light. Detection is possible.

  In addition, the diode is configured by a P-type region, an intrinsic semiconductor, a low-concentration impurity region, and an N-type region provided in the polycrystalline silicon by introducing impurities into the polycrystalline silicon.

  According to such a configuration, the diode is configured by a P-type region, an intrinsic semiconductor or a low-concentration impurity region, and an N-type region provided in polycrystalline silicon, and has sufficient photosensitivity.

  The electro-optical device according to the present invention is for detecting the illuminance of external light around the display unit and the display unit, and includes a plurality of diodes in which a light receiving layer is formed of polycrystalline silicon. And a plurality of diodes receiving the same light connected in series, and an optical sensor constituting a light receiving element by applying the same bias to the plurality of diodes connected in series.

  According to such a configuration, the diode connected in series has a wide range of reverse bias having photosensitivity even if the light receiving layer is formed of polycrystalline silicon. The display unit is often driven with a relatively high voltage, and a relatively high voltage is also applied to the diode. Even in this case, the diodes connected in series have photosensitivity in a wide voltage range of reverse bias, and light illuminance can be reliably detected. In addition, by applying a high voltage to the diode, the amplitude of the sensor output can be increased, and the light detection accuracy can be improved.

  In addition, the diode is configured by a P-type region, an intrinsic semiconductor, a low-concentration impurity region, and an N-type region provided in the polycrystalline silicon by introducing impurities into the polycrystalline silicon.

  According to such a configuration, the diode is configured by a P-type region, an intrinsic semiconductor or a low-concentration impurity region, and an N-type region provided in polycrystalline silicon, and has sufficient photosensitivity.

The diode has an N ⁻ region having a lower concentration than the N-type region between the intrinsic semiconductor or the low-concentration impurity region and the N-type region.

  According to such a configuration, the range of the reverse bias having photosensitivity can be further expanded, and the light detection accuracy can be further improved.

  Further, the photosensors are connected in series by contact holes provided across the boundary between the N-type region and the P-type region of adjacent diodes.

  According to such a configuration, since adjacent diodes are connected by contact holes, it is not necessary to provide wiring, and the device can be miniaturized.

  The photosensor is used by applying a reverse bias to the diode.

  According to such a configuration, the light detection operation is performed in the reverse bias range having photosensitivity. The diodes are connected in series, and the range of reverse bias having photosensitivity is wide. As a result, light can be detected even when a relatively high voltage is applied to the diode, and a sensor output with sufficient amplitude can be output.

  The electro-optical device according to the present invention detects the illuminance of external light around the display unit and the display unit, and includes a plurality of first diodes in which a light receiving layer is formed of polycrystalline silicon. A plurality of first diodes that receive the first light in series, and a first bias is applied to the plurality of first diodes connected in series to form a light receiving element. And a plurality of second diodes each having a light receiving layer made of polycrystalline silicon, the plurality of second diodes receiving second light being connected in series, and the plurality of second diodes connected in series A second optical sensor that constitutes a light receiving element by applying a second bias to the diode, and a light shielding unit that prevents light from entering the second optical sensor are provided.

  According to such a configuration, the first optical sensor detects the illuminance of external light. The second optical sensor detects, for example, dark current. By using the outputs of the first and second optical sensors, it is possible to obtain a sensor output from which dark current components are removed. Thereby, external light can be detected with high accuracy.

  In addition, the display unit is configured by a liquid crystal panel in which liquid crystal is sealed between first and second substrates, and the optical sensor is configured by a thin film diode formed on the first substrate. It is characterized by that.

  According to such a configuration, the optical sensor can detect external light with high accuracy. Thereby, for example, it is possible to control the brightness of the backlight of the liquid crystal panel according to the brightness of the external light.

  Further, an electronic apparatus according to the present invention is characterized by using the electro-optical device.

  According to such a configuration, it is possible to accurately detect external light and control display luminance, thereby improving display visibility and reducing power consumption.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a plan view showing an outline of the electro-optical device according to the first embodiment of the invention. FIG. 2 is an explanatory diagram for explaining an outline of a cross-sectional structure in a state where the liquid crystal panel is housed in a case when the liquid crystal panel is employed as the electro-optical device of FIG. FIG. 3 is an explanatory view schematically showing a planar pattern of a display panel employed in the electro-optical device of FIG. FIG. 4 is an equivalent circuit diagram showing a specific configuration example of the light receiving element 29 and the light receiving element 30 in FIG. FIG. 5 is a graph showing the off characteristics of a PIN diode constructed using low-temperature polysilicon technology, with voltage on the horizontal axis and current on the vertical axis. 6 is a schematic cross-sectional view taken along the line A-A 'of FIG.

<First Embodiment>
In FIG. 1, an electro-optical device 11 is configured by a display panel configured by bonding two substrates. When a liquid crystal panel is employed as the display panel, the electro-optical device 11 includes a display panel 21 and an illumination device 22 as shown in FIG. Note that a self-luminous display panel may be employed as the electro-optical device, and in this case, an illumination device is not necessary.

  As shown in FIG. 2, the display panel 21 is configured by enclosing a liquid crystal 25 between an element substrate 23 and a counter substrate 24 that transmit light. The element substrate 23 and the counter substrate 24 arranged so as to face each other are bonded together by a sealing material (not shown). The display panel 21 includes, for example, a plurality of scanning lines (not shown) extending in the horizontal direction and a plurality of data lines (not shown) extending in the vertical direction. A pixel is formed corresponding to the intersection of the plurality of data lines.

  On the element substrate 23, a pixel electrode (ITO) (not shown) constituting the pixel is disposed. A counter electrode (common electrode (ITO)) (not shown) is also provided on the counter substrate 24 side. On the pixel electrode of the element substrate 23, an alignment film (not shown) which is in contact with the liquid crystal 25 and has been subjected to a rubbing process is provided. On the other hand, the counter substrate 24 is also provided with an alignment film (not shown) that is in contact with the liquid crystal 25 and has been subjected to a rubbing process. Each alignment film is made of a transparent organic film such as a polyimide film. A light shielding film (not shown) is formed on the counter substrate 24 along the data lines and the scanning lines.

  Although not shown in FIG. 2, polarizing plates are provided on the observation surface side of the counter substrate 24 and the surface opposite to the element formation surface of the element substrate 23, respectively. These polarizing plates are set to a polarization axis corresponding to the rubbing direction of the alignment film formed on the element substrate 23 and the counter substrate 24.

  The illumination device 22 that functions as a backlight emits light from below the element substrate 23 of the display panel 21. The illuminating device 22 includes, for example, a plurality of light emitting diodes (hereinafter referred to as LEDs) that constitute a light source and a light guide plate. The light from the LED is guided into the light guide plate, reflected and scattered by the reflective layers on the bottom and side surfaces of the light guide plate, and emitted from the top surface of the light guide plate. Thus, the backlight light is incident on the display panel 21 disposed above the illumination device 22.

  The lighting device 22 and the display panel 21 are housed in the case 26 in a stacked state. The case 26 has an open top surface, and the display panel 21 is fixed in the case 26 so that the display screen 13 of the display panel 21 faces the opening 27.

  The display panel 21 is provided with an effective display area 14 in the center of the display screen 13 defined by the opening 27 of the case 26. In the effective display area 14, pixels are configured corresponding to intersections of a plurality of scanning lines and a plurality of data lines.

  In the display panel 21, an image signal is supplied to the data line, and a scanning signal is supplied to the scanning line. Thus, each pixel is driven based on the image signal, and the light transmittance changes. Light incident on the display panel 21 from the illumination device 22 is modulated in the effective display area 14 of the display panel 21. Thereby, the image can be visually recognized by observing the effective display region 14 from the opening 27 side of the case 26. The counter substrate 24 is formed with a light shielding film 28 (shaded portion in FIG. 1) for shielding the periphery of the counter substrate 24 from light. The shape and size of the effective display area 14 are defined by the light shielding film 28.

  A non-display area 15 is provided around the effective display area 14 in the display screen 13. In the non-display area 15, light receiving element arrangement areas 16 and 17 are provided in which light receiving elements 29 and 30 for detecting illuminance are arranged, respectively. The light receiving element arrangement regions 16 and 17 are provided in the opening region 19 on the counter substrate 24 where the light shielding film 28 is not formed, and light from the upper surface (observation surface) side of the counter substrate 24 is transmitted into the substrate. This is the area that is transmitted through.

  A light receiving element 29 is arranged in the light receiving element arrangement area 16, and a light receiving element 30 is arranged in the light receiving element arrangement area 17. External light is incident on the light receiving elements 29 and 30 from the observation surface side of the counter substrate 24, and the light receiving elements 29 and 30 can detect the illuminance of the external light.

  In the example of FIG. 1, the display panel 21 has a substantially rectangular planar shape. A Y driver 31 is arranged along one long side of the display panel 21. Further, an X driver 32 is disposed along one short side of the display panel 21.

  As shown in FIG. 3, a plurality of scanning lines 33 extend from the Y driver 31 toward the effective display area 14, and a plurality of data lines 34 extend from the X driver 32 toward the effective display area 14. It is installed. Corresponding to the intersection of the scanning line 33 and the data line 34, a switching element 35 is provided. The switching element 35 is ON / OFF controlled by a scanning signal supplied from the Y driver 31 to the scanning line 33. The switching element 35 that is turned on supplies an image signal supplied from the X driver 32 to the data line 34 to the pixel electrode 36.

  FIG. 3 shows an example in which the display panel 21 is a TFT liquid crystal panel, but other active matrix display panels and passive matrix display panels may be used as long as the pixels in the effective display area are driven by a driver. However, it can be configured similarly.

  A terminal portion 37 is provided on one short side of the display panel 21 in which the X driver 32 is disposed in the vicinity. The Y driver 31 and the X driver 32 and the terminal portion 37 are connected by wiring (not shown).

  As shown in FIG. 3, in the light receiving element arrangement region 16, a plurality of light receiving elements 29 are arranged along the long side of the effective display region 14. In the light receiving element arrangement region 17, a plurality of light receiving elements 30 are arranged along the long side of the effective display region 14. As shown in FIG. 3, the light receiving elements 29 and 30 are constituted by light receiving diodes such as PIN diodes.

  A sufficient number of light receiving elements 29 and 30 are arranged in the longitudinal direction of the display panel 21 by using the elongated light receiving element arrangement regions 16 and 17. The number of the light receiving elements 29 and 30 to be arranged is determined by the length in the longitudinal direction of the light receiving element arrangement regions 16 and 17 and the width of each of the light receiving elements 29 and 30.

  In the present embodiment, the cathode of each diode constituting the light receiving element 29 and the anode of each diode constituting the light receiving element 30 are connected in series via the wiring 42. The anodes of the diodes constituting the light receiving element 29 are commonly connected to the wiring 41, and the cathodes of the diodes constituting the light receiving element 30 are commonly connected to the wiring 44.

  FIG. 4 is an equivalent circuit diagram of an optical sensor constituted by such light receiving elements 29 and 30. FIG. 5 shows the characteristics of a light-receiving diode having an appropriate size.

  FIG. 5 shows the characteristics when light is incident by a broken line, and the characteristics when light is not incident by a solid line. Characteristics A to C show the characteristics of one diode, the characteristics when two diodes are connected in series, and the characteristics when three diodes are connected in series, respectively.

  Each characteristic A to C indicates a characteristic in reverse bias, and a forward bias region is not illustrated. When the reverse bias applied voltage is increased, as shown in FIG. 5, any of the characteristics A to C has a jumping characteristic in which the reverse current gradually increases.

  In each of the characteristics A to C, in a region where the reverse bias voltage is relatively small, the current amount at the time of light incidence indicated by the broken line is larger than the current amount at the dark time indicated by the solid line. That is, the diode has photosensitivity in this broken line region.

  However, as is clear from the comparison between the broken line and the solid line in each of the characteristics A to C, when the reverse bias voltage becomes relatively large, the amount of current at the time of light incidence and the amount of current at the time of darkness coincide with each other. Is equivalent to having no photosensitivity.

  Therefore, in order to use the diode as a light receiving element, it is necessary to use the diode in a region where the reverse bias voltage having a difference between the broken line and the solid line is relatively low. However, a circuit using low-temperature polysilicon technology requires a relatively high voltage, for example, a voltage of 5 V or more, because the performance of the transistors constituting the low-temperature polysilicon technology is lower than the performance of the transistors formed on the wafer. However, as shown in FIG. 5, when one diode is used alone, sufficient photosensitivity cannot be obtained at such a high voltage.

  Therefore, in this embodiment, by connecting two or more diodes in series, the voltage at which the current increase due to the jumping characteristic starts is set to a sufficiently high voltage and used in a region where sufficient photosensitivity can be obtained. Is possible. FIG. 3 shows an example in which two diodes are connected in series.

  In FIG. 4, the optical sensor can be represented by an equivalent circuit by parallel circuits of diodes D1 and D2 such as PIN diodes and capacitors C1 constituting the light receiving element 29 and the light receiving element 30, respectively.

  The voltage from the power supply 45 is applied to the capacitor C1 through the switch 46. After + 5V is applied across the capacitor C1, the switch 46 is turned off. Then, the reverse-biased diodes D1 and D2 cause a reverse current to flow due to photogenerated charges generated by the incidence of light. As a result, the terminal voltage of the capacitor C1 decreases. The amount of voltage decrease is output to the output terminal 48 as a sensor output via the amplifier 47.

  As shown in FIG. 5, when two diodes are connected in series, the photosensitivity is surely obtained in the voltage range of −2V to −5V. Therefore, the circuit of FIG. 4 can output a reliable light detection output.

  In this case, since a change of 2 V to 5 V, which is a relatively high voltage range, is obtained as an absolute value, the amplifier 47 as the detection circuit can also be manufactured by the low temperature polysilicon technique.

  Further, as shown by the broken line in FIG. 5, the amount of current flowing with respect to the reverse bias has a flat characteristic, and thus the amount of current flowing through the diodes D1 and D2 per unit time is constant. In this case, the light receiving elements 29 and 30 output sensor outputs in which the relationship between the light intensity and the output changes linearly.

  The light intensity of the external light obtained by the light receiving elements 29 and 30 in this way can be used for brightness control of the lighting device 22, for example. That is, the output of the optical sensor constituted by the light receiving elements 29 and 30 is given to a controller (not shown) that controls the brightness of the illumination device 22. The controller generates a control signal for controlling the brightness of the lighting device 22 based on the sensor output, and outputs the control signal to the lighting device 22.

  For example, when the sensor output indicates that the external light is relatively bright, the controller can increase the brightness of the lighting device 22 according to the brightness of the external light. Further, the controller may turn off the illumination device 22 and use the display panel 21 as a reflection type when the external light is shown to be brighter than a predetermined threshold. The illumination device 22 emits light with brightness based on the control signal.

  FIG. 6 shows an example of a cross-sectional structure of the light receiving elements 29 and 30. FIG. 6 is a cross-sectional structure taken along line A-A ′ of FIG. 3.

  In FIG. 6, a base insulating film 71 is formed on a transparent substrate 23 such as a quartz substrate or a glass substrate. On the base insulating film 71, a semiconductor layer 73 constituting a TFT as a switching element is formed in a region where a pixel including the effective display region 14 is formed. The semiconductor layer 73 is made of polysilicon as a polycrystalline semiconductor. For example, this polysilicon is formed by crystallization by laser annealing of amorphous silicon as an amorphous semiconductor which is a non-single crystal semiconductor. The polysilicon may be formed by a high temperature polysilicon process.

  At both ends of the semiconductor layer 73, impurities are introduced to form a source region 72 and a drain region 73. A gate electrode 76 is formed on the semiconductor layer 73 via an oxide film 75. The gate electrode 76 has a two-layer structure in which the lower layer is molybdenum and the upper layer is aluminum, and is connected to the scanning line 33. An interlayer insulating film 77 is formed on the oxide film 75, and contact holes 78 a and 78 b are formed in the interlayer insulating film 77 on the source region 72 and the drain region 73, respectively. The source region 72 is connected to the data line 34 through the contact hole 78a.

  An interlayer insulating film 79 is formed on the wiring layer on which the data line 34 is formed and on the interlayer insulating film 77. A contact hole 80 is formed in the interlayer insulating film 79, and the drain region 74 is connected to the pixel electrode 36 formed on the interlayer insulating film 79 through the contact holes 78 b and 80.

  Note that a reflective film 81 is formed on the interlayer insulating film 79 in a part of the opening region of each pixel. The pixel electrode 36 is formed on the interlayer insulating film 79 and the reflective film 81.

  On the other hand, PIN type light receiving elements 29 and 30 are formed on the base insulating film 71 in the light receiving element arrangement regions 16 and 17. The light receiving elements 29 and 30 are formed by the same manufacturing process as the TFT in the effective display area 14.

  That is, the light receiving element 29 includes a P-type region 51 into which a P-type impurity is introduced, an N-type region 53 into which an N-type impurity is introduced, and an intrinsic semiconductor or a small amount of the semiconductor layer formed in the same layer as the semiconductor layer 73. An I-type region 52 into which impurities are introduced is included. Similarly, the light receiving element 30 includes a semiconductor layer formed of the same layer as the semiconductor layer 73, a P-type region 54 into which a P-type impurity is introduced, an N-type region 56 into which an N-type impurity is introduced, and an intrinsic semiconductor or a trace amount. And an I-type region 55 into which impurities are introduced. An oxide film 75 is formed on these regions 51 to 56.

  Although not shown in the example of FIG. 6, since the light receiving elements 29 and 30 are formed in the same manufacturing process as the TFT, a gate electrode made of the same material as the gate electrode 76 is formed on the oxide film 75 on the light receiving element 29. A film having the same shape may be formed. Even in this case, incident light can enter the semiconductor layer.

  Contact holes 78 c to 78 f are formed in the interlayer insulating film 77 on the P-type region 51, the N-type region 53, the P-type region 54, and the N-type region 56. On the interlayer insulating film 77, wirings 41, 42, and 44 are formed in the same layer as the data line 34. The regions 51, 53, 54, and 56 are connected to the wirings 41 and 42 through the contact holes 78c to 78f, respectively. , 44. The wirings 41, 42, and 44 have, for example, a three-layer structure in which titanium, aluminum, and titanium are stacked.

  An interlayer insulating film 79 is formed on the wiring layer on the interlayer insulating film 77 and on the interlayer insulating film 77. An alignment film 84 is formed on the pixel electrode 36 and the interlayer insulating film 79 in contact with the liquid crystal 25. The alignment film 84 is rubbed in a predetermined direction.

  On the other hand, the counter substrate 24 is formed with a light shielding film 28 that partitions the effective display region 14 and partitions the opening region 19 (see FIG. 1). An alignment film 85 is formed on the light shielding film 28 and the counter substrate 24. The alignment film 85 is rubbed in a predetermined direction.

  According to such a configuration, light incident from the observation surface side of the counter substrate 24 travels to the element substrate 23 side through the opening region 19. In the light receiving elements 29 and 30, a detection current corresponding to the photogenerated charge flows through depletion layers generated in the regions 51 to 53 and 54 to 56. This detected current is output to the outside through the wirings 41, 42, 44 connected to the regions 51, 53, 54, 56. In this way, the illuminance of external light can be detected.

  The light receiving elements 29 and 30 are connected in series and have sufficient photosensitivity even when a relatively large voltage is used, as shown by the characteristic B in FIG. By applying a high voltage to the light receiving elements 29 and 30, an output having a sufficiently large amplitude can be obtained as a sensor output. Therefore, highly accurate external light detection is possible.

  By using the detection results of these light receiving elements 29 and 30, for example, it is possible to control the brightness of the illumination device 22 according to the brightness of external light. For example, when it is detected that the outside light is bright, the brightness of the lighting device 22 is increased according to the brightness of the outside light. Thereby, the visibility of display can be improved, and power consumption can be reduced.

  As described above, in the present embodiment, the diodes constituting the light receiving element are used connected in series. Thereby, the range of the reverse bias in which the photosensitivity can be obtained can be expanded, and a reverse bias having a sufficiently high voltage can be used. As a result, even a device that uses a relatively high driving voltage, such as a display panel manufactured using low-temperature polysilicon technology, can be used in a voltage range with sufficient photosensitivity. Further, since a sufficiently high voltage is applied as the reverse bias, an output having a sufficiently large amplitude can be obtained as the sensor output.

  FIG. 7 is a schematic cross-sectional view showing a modification of the present embodiment. In each of the above drawings, an example in which two diodes are connected in series has been described. However, the number of diodes connected in series is not particularly limited. FIG. 7 shows an example in which three diodes are connected in series.

  A semiconductor layer is formed on the base insulating film 91. In this semiconductor layer, in three adjacent light receiving element arrangement regions, a P type region 92 and an N type region 94 constituting three PIN type light receiving elements, and an intrinsic semiconductor or an I type doped with a small amount of impurities. A region 93 is provided. An oxide film 95 is formed on these regions 92 to 94.

  A film 97 similar to the gate electrode constituting the TFT may be formed on the oxide film 95. An interlayer insulating film 96 is formed on the oxide film 95.

  A contact hole 98 is opened in the interlayer insulating film 77 on the P-type region 92 and the N-type region 94. Contact holes 98 connected to the P-type region 92 and the N-type region 94 of adjacent light receiving elements are connected to each other by a wiring 99. Thereby, three light receiving elements connected in series are obtained.

  Such three light receiving elements connected in series can further expand the range of the reverse bias having photosensitivity as shown by the characteristic C in FIG.

<Second Embodiment>
8 to 10 relate to a second embodiment of the present invention, and FIG. 8 is an explanatory diagram schematically showing a planar pattern of a display panel employed in the electro-optical device of the second embodiment. FIG. 9 is an equivalent circuit diagram showing a specific configuration example of the light receiving elements 29a and 29b and the light receiving elements 30a and 30b in FIG. FIG. 10 is a schematic cross-sectional view taken along the line AA ′ of FIG.

  When a thin film diode formed by a process of a polysilicon type thin film transistor and a low temperature polysilicon type thin film transistor manufactured by a suitable process of about 600 ° C. or less is adopted as the light receiving element, sufficient accuracy may not be obtained. Therefore, in the present embodiment, the illuminance detection accuracy of external light is improved by detecting the dark current. In addition, by detecting the illuminance of the illuminating device that can control the illuminance with high accuracy instead of the dark current and detecting the external light based on the illuminance of the illuminating device, the illuminance detection accuracy of the external light is improved. Also good.

  In the present embodiment, light receiving elements 29a, 29b and 30a, 30b connected in series are provided in the light receiving element arrangement area 16 and the light receiving element arrangement area 17 in the non-display area 15 (see FIG. 1). In place of the light shielding film 28 of FIG. 1, a light shielding film 28 ′ that shields light up to the light receiving element arrangement region 16 is employed. That is, in the light receiving element arrangement region 16, a light shielding film 28 ′ is formed on the counter substrate 24, and external light is prevented from entering the element substrate 23 side in the formation region of the light shielding film 28 ′. It has become.

  The light receiving elements 29a, 29b, 30a, and 30b are formed on the element substrate 23 by a process of a so-called polysilicon type thin film transistor, a low temperature polysilicon type thin film transistor that is preferably manufactured at a temperature of about 600 ° C. or lower. A light shielding film 28 'is formed above the light receiving elements 29a and 29b. The light shielding film 28' prevents external light from the observation surface side of the counter substrate 24 from entering the light receiving elements 29a and 29b. Moreover, it is provided in the position where the light of the backlight does not hit. Thereby, the light receiving elements 29a and 29b can detect a dark current.

  In addition, it is possible to make the light from the illumination device 22 that passes through the element substrate 23 incident on the light receiving elements 29a and 29b so that the illuminance of the light from the illumination device 22 is detected. Further, external light from the observation surface side of the counter substrate 24 enters the light receiving elements 30 a and 30 b provided in the light receiving element arrangement region 17.

  In the present embodiment, the light receiving elements 29a, 29b, 30a, 30b are formed by so-called low-temperature polysilicon type thin film transistor processes at positions close to each other, and have substantially the same characteristics. For example, the light receiving elements 29a and 29b can detect dark current, and by using the outputs of the light receiving elements 29a and 29b, the outputs of the light receiving elements 30a and 30b can be calibrated to detect external light with high accuracy. is there.

  In addition, known illuminance from the illumination device 22 whose illuminance is controlled with high accuracy is detected by the light receiving elements 29a and 29b, and the illuminance of external light is relatively obtained from the outputs of the light receiving elements 30a and 30b based on the detection results. Thus, it is also possible to improve the detection accuracy of outside light. In addition, the illuminating device 22 is a structure containing LED, for example, and can control illumination intensity with comparatively high precision.

  FIG. 9 is an equivalent circuit diagram of an optical sensor constituted by such light receiving elements 29a, 29b, 30a, 30b.

  The optical sensor is shown by an equivalent circuit formed by a parallel circuit of diodes D11 and D12 such as PIN diodes constituting the light receiving elements 29a and 29b, diodes D13 and D14 such as PIN diodes constituting the light receiving elements 30a and 30b, and a capacitor C11. it can.

  A voltage is applied to the diodes D11 to D14 via the power supplies 45 and 45 ′. The reverse-biased diodes D13 and D14 cause a reverse current to flow due to photogenerated charges generated by the incidence of light. In addition, the diodes D11 and D12 in the reverse bias state are blocked from entering light and flow a reverse current based on a dark current. When light is incident on the diodes D13 and D14, there is a difference between the current flowing in the diodes D13 and D14 and the current flowing in the diodes D11 and D12, and the difference current is supplied to the capacitor C11. Vary the voltage at both ends. According to this circuit, it is possible to cancel a current increase due to temperature or a noise current and obtain a current corresponding to the increase according to the external light.

  The voltage across the capacitor C11 is set to 0 by turning on the switch 46. Next, when the switch 46 is turned off, the voltage across the capacitor C11 rises due to the current flowing through the connection point between the diodes D12 and D13. The voltage across the capacitor C11 after the elapse of a certain time has a voltage value corresponding to the external light. This voltage is output as a sensor output from the output terminal 48 via the amplifier 47.

  In the circuit of FIG. 9, a relatively high voltage (10 V in the example of FIG. 9) is applied to the light-shielded diodes D11 and D12 and the diodes D13 and D14 irradiated with external light. By applying a high voltage, as described above, a change in sensor output with respect to incident light can be increased, and a highly sensitive device can be obtained. Even in this case, the reverse bias range in which the photosensitivity can be obtained can be expanded by connecting the light-shielded diodes D11 and D12 and the diodes D13 and D14 irradiated with external light in series. Thus, it is used in a region where the photosensitivity can be obtained regardless of the change of the bias point, and it is possible to detect external light with high accuracy.

  FIG. 10 shows an example of a cross-sectional structure of the light receiving elements 29a, 29b, 30a, 30b. FIG. 10 is a cross-sectional structure taken along line A-A ′ of FIG. 8. In FIG. 10, the same components as those in FIG.

  In FIG. 10, light receiving elements 29a, 29b, 30a, 30b are employed instead of the light receiving elements 29, 30, and light shielding films 28 ', 82, 58 for shielding the light receiving elements 29a, 29b are employed. Is different from FIG.

  That is, on the base insulating film 71, PIN type light receiving elements 29a and 29b are formed in the light receiving element arrangement region 16, and PIN type light receiving elements 30a and 30b are formed in the light receiving element arrangement region 17. The light receiving elements 29a, 29b, 30a, 30b are formed by the same manufacturing process as the TFT in the effective display area 14.

  That is, the light receiving elements 29a and 30a include a P-type region 51 into which a P-type impurity is introduced, an N-type region 53 into which an N-type impurity is introduced, and an intrinsic semiconductor or a semiconductor layer formed in the same layer as the semiconductor layer 73. It has an I-type region 52 into which a small amount of impurities are introduced. Similarly, in the light receiving elements 29b and 30b, a P-type region 54 into which a P-type impurity is introduced, an N-type region 56 into which an N-type impurity is introduced, and an intrinsic semiconductor are formed in the same semiconductor layer as the semiconductor layer 73. Alternatively, it has an I-type region 55 into which impurities are introduced in a trace amount.

  An oxide film 75 is formed on these regions 51 to 56. In the present embodiment, a light shielding film 58 is formed on the oxide film 75 on the light receiving elements 29a and 29b. The light shielding film 58 is formed in the same process as the TFT gate electrode 76, and has a two-layer structure in which the lower layer is molybdenum and the upper layer is aluminum.

  Contact holes 78 c to 78 f are formed in the interlayer insulating film 77 on the P-type region 51, the N-type region 53, the P-type region 54, and the N-type region 56. On the interlayer insulating film 77, wirings 41, 42a, 95, 96, 42b, and 44 are formed in the same layer as the data line 34. The regions 51, 53, 54, and 56 constituting the light receiving elements 29a and 29b are connected to wirings 41, 42a, 42a, and 95 through contact holes 78c to 78f, respectively. The regions 51, 53, 54, and 56 constituting the light receiving elements 30a and 30b are connected to wirings 96, 42b, 42b, and 44 through contact holes 78c to 78f, respectively. The wirings 41, 42a, 95, 96, 42b, and 44 have, for example, a three-layer structure in which titanium, aluminum, and titanium are stacked. Note that the wirings 95 and 96 are integrally formed and are electrically connected.

  An interlayer insulating film 79 is formed on the wiring layer on the interlayer insulating film 77 and on the interlayer insulating film 77. In the present embodiment, a light shielding film 82 is formed on the interlayer insulating film 79 so as to correspond to the formation regions of the light receiving elements 29a and 29b. The light shielding film 82 is formed in the same process as the reflective layer 81 formed in the effective display area 14, and for example, an aluminum material is used.

  On the other hand, a light shielding film 28 ′ (see FIG. 8) is formed on the counter substrate 24, which partitions the effective display region 14 and partitions the opening region 19 (see FIG. 1). An alignment film 85 is formed on the light shielding film 28 ′ and the counter substrate 24. The alignment film 85 is rubbed in a predetermined direction.

  According to such a configuration, light incident from the observation surface side of the counter substrate 24 travels to the element substrate 23 side through the opening region 19. In the light receiving elements 30a and 30b, a detection current corresponding to the photogenerated charge flows through a depletion layer generated in the regions 51 to 56.

  On the other hand, the light receiving elements 29a and 29b are prevented from entering external light by the light shielding films 28 ', 82 and 58, and can detect a dark current.

  As described above, by using the detection results of the light receiving elements 29a, 29b, 30a, and 30b, for example, the brightness control of the illumination device 22 can be performed according to the brightness of external light. For example, when it is detected that the outside light is bright, the brightness of the lighting device 22 is increased according to the brightness of the outside light. Thereby, the visibility of display can be improved.

  In the present embodiment, the light shielding films 28 ', 82, and 58 are provided. However, if at least one of the light shielding films is provided, the incidence of external light can be prevented. is there. In this embodiment, since the three-layer light shielding film is provided, it is possible to prevent not only the direct external light but also the reflected light inside the panel from entering the light receiving elements 29a and 29b. Excellent performance.

  As described above, also in this embodiment, the same effect as that of the first embodiment can be obtained. Furthermore, in the present embodiment, a light receiving element that prevents external light from entering is employed, and the detection accuracy of external light can be further improved.

<Third Embodiment>
FIG. 11 is a schematic cross-sectional view showing a third embodiment of the present invention. This embodiment is different only in the configuration of the light receiving element, and is similar to the above embodiments in that the light receiving elements are connected in series.

  FIG. 11 shows two light receiving elements connected in series.

A semiconductor layer is formed on the base insulating film 91. In this semiconductor layer, in two adjacent light receiving element arrangement regions, a P type region 92 and an N type region 94 constituting two PIN type light receiving elements, and an intrinsic semiconductor or an I type doped with a small amount of impurities. A region 93 is provided. Further, an N ⁻ region 101 is provided between the I type region 93 and the N type region 94. The N ⁻ region 101 is an N-type region having a lower concentration than the N-type region 94 and has an effect of reducing the jumping characteristics. An oxide film 95 is formed on these regions 92 to 94, 101.

  A film 97 similar to the gate electrode constituting the TFT may be formed on the oxide film 95. An interlayer insulating film 96 is formed on the oxide film 95. A contact hole 98 is opened in the interlayer insulating film 77 on the P-type region 92 and the N-type region 94. Contact holes 98 connected to the P-type region 92 and the N-type region 94 of adjacent light receiving elements are connected to each other by a wiring 99. Thereby, two light receiving elements connected in series are obtained.

According to such a configuration, the range of the reverse bias having photosensitivity can be further expanded by the effect of the series connection and the effect of providing the N ⁻ region.

<Fourth embodiment>
FIG. 12 is a plan view showing a fourth embodiment of the present invention. FIG. 12 corresponds to FIG. 6. In FIG. 12, the same components as those in FIG.

  This embodiment is different from the first embodiment only in that light receiving elements 121 and 122 in which a part of the light receiving elements 29 and 30 are shared are employed.

  As shown in FIG. 12, the light receiving elements 121 and 122 are formed by injecting impurities into one semiconductor layer. A P-type region 51, an I-type region 52, an N-type region 111, a P-type region 112, an I-type region 55, and an N-type region 56 are formed in one semiconductor layer. As shown in FIG. 12, the P-type region 51, the I-type region 52, and the N-type region 111 constitute a light receiving element 121, and the P-type region 112, the I-type region 55, and the N-type region 56 constitute a light receiving element 122. The

  The anodes of the respective diodes constituting the light receiving element 121 are commonly connected to the wiring 41, and the cathodes are commonly connected to the wiring 105 through the contact hole 78g. The anodes of the respective diodes constituting the light receiving element 122 are commonly connected to the wiring 105 through the contact hole 78g, and the cathodes are commonly connected to the wiring 44.

  The light receiving elements 121 and 122 output an output based on the illuminance of incident light. The sum of the outputs of all the light receiving elements 121 and 122 can be taken out between the wirings 41 and 44. The light receiving elements 121 and 122 are connected to the wirings 41, 105, and 44 through contact holes 78c, 78g, and 78f.

  Other configurations, operations, and effects are the same as those in the first embodiment. In the present embodiment, two diodes are connected in series by the contact hole 78g, and the device can be miniaturized.

<Fifth embodiment>
FIG. 13 is a cross-sectional view showing a cross-sectional structure when an EL (electroluminescence) panel is adopted as an electro-optical device according to the fifth embodiment of the invention.

  A low temperature polysilicon layer 173 is formed on the substrate 171. The substrate 171 and the substrate 172 are disposed to face each other with the organic EL layer 174 interposed therebetween. The organic EL layer 174 forms R, G, and B pixels. A light shielding film 175 is formed on the substrate 172.

  In the present embodiment, a light receiving element arrangement region 176 is provided on the substrate 173 so as to face one of the R, G, and B pixels of the organic EL layer 174 or one by one. In the light receiving element arrangement region 176, for example, two light receiving elements connected in series are formed. A light shielding film 177 is formed on the substrate 172 facing the light receiving element arrangement region 176. As a result, the light receiving elements in the light receiving element arrangement region 176 are blocked from incident external light, and can detect the dark current or the light emission intensity of each pixel of the organic EL layer 174. .

  A light receiving element arrangement region 178 is provided at the end of the substrate 171. In the light receiving element arrangement region 178, for example, two light receiving elements connected in series are formed. Each light receiving element in the light receiving element arrangement region 178 can detect external light.

  Each of the light receiving elements in these light receiving element arrangement regions 176 and 178 is configured to be connected in series with each other, as described above, and the range of the reverse bias voltage for obtaining the photosensitivity is sufficiently wide. Thereby, each light receiving element can reliably detect external light even when driven by a sufficiently high applied voltage.

  As described above, the present embodiment can be applied to a self-luminous element having an organic EL layer.

  The present invention is not limited to the above embodiments, and various modifications can be made. For example, in each of the above embodiments, an example of a two-terminal diode has been described. However, the present invention may be applied to a diode structure obtained by short-circuiting the gate and drain of a three-terminal thin film transistor.

  Further, an electronic apparatus using the above electro-optical device is also included in the present invention. FIG. 14 is a perspective view showing an example of an electronic device, and shows the appearance of a mobile phone. As shown in FIG. 14, the above-described electro-optical device, for example, a liquid crystal display device, is used for the display unit 201 of the mobile phone 200 as an electronic device.

  In addition, as an electronic device, for example, a projection display device including a light source, a light valve that modulates light emitted from the light source, and an optical system for projecting light modulated by the light valve It is. In addition, other electronic devices include televisions, viewfinder type / monitor direct view type video tape recorders, car navigation devices, pagers, electronic notebooks, calculators, word processors, workstations, videophones, POS terminals, digital Examples include a still camera and a device equipped with a touch panel. Needless to say, the electro-optical device according to the present invention is applicable to these various electronic devices.

  The electro-optical device of the present invention is not limited to a passive matrix type liquid crystal display panel but an active matrix type liquid crystal panel (for example, a liquid crystal display panel including a TFT (thin film transistor) or a TFD (thin film diode) as a switching element). It is possible to apply to the same. In addition to liquid crystal display panels, electroluminescence devices, organic electroluminescence devices, plasma display devices, electrophoretic display devices, devices using electron emission (such as Field Emission Display and Surface-Conduction Electron-Emitter Display), DLP ( The present invention can be similarly applied to various electro-optical devices such as Digital Light Processing (aka DMD: Digital Micromirror Device).

1 is a plan view showing an outline of an electro-optical device according to a first embodiment of the invention. FIG. 2 is an explanatory diagram for explaining an outline of a cross-sectional structure in a state where a liquid crystal panel is housed in a case when a liquid crystal panel is employed as the electro-optical device in FIG. 1. FIG. 2 is an explanatory diagram schematically showing a planar pattern of a display panel employed in the electro-optical device of FIG. FIG. 4 is an equivalent circuit diagram illustrating a specific configuration example of the light receiving element 29 and the light receiving element 30 in FIG. 3. The graph which shows the OFF characteristic of the PIN diode comprised using the low temperature polysilicon technique by taking a voltage on a horizontal axis and taking a current on a vertical axis. FIG. 4 is a schematic cross-sectional view taken along line A-A ′ of FIG. 3. The typical sectional view showing the modification of a 1st embodiment. FIG. 6 is an explanatory diagram schematically showing a planar pattern of a display panel employed in an electro-optical device according to a second embodiment. FIG. 9 is an equivalent circuit diagram illustrating a specific configuration example of the light receiving elements 29a and 29b and the light receiving elements 30a and 30b in FIG. FIG. 9 is a schematic cross-sectional view taken along line A-A ′ of FIG. 8. The typical sectional view showing the 3rd embodiment of the present invention. The top view which shows the 4th Embodiment of this invention. Sectional drawing which shows sectional structure at the time of employ | adopting EL (electroluminescence) panel as an electro-optical apparatus which concerns on the 5th Embodiment of this invention. The perspective view which shows the example of an electronic device.

Explanation of symbols

    DESCRIPTION OF SYMBOLS 11 ... Electro-optical apparatus, 16, 17 ... Light receiving element arrangement | positioning area | region, 29, 30 ... Light receiving element.

Claims (10)

  A plurality of diodes each having a light receiving layer made of polycrystalline silicon, the plurality of diodes receiving the same light are connected in series, and the plurality of diodes connected in series are given the same bias to receive the light An optical sensor characterized by comprising:   2. The diode according to claim 1, wherein the diode is configured by a P-type region, an intrinsic semiconductor, or a low-concentration impurity region and an N-type region provided in the polycrystalline silicon by introducing impurities into the polycrystalline silicon. Light sensor. A display unit;
It detects the illuminance of external light around the display unit, has a plurality of diodes whose light receiving layer is made of polycrystalline silicon, and connects the plurality of diodes that receive the same light in series, A photosensor constituting a light receiving element by applying the same bias to the plurality of diodes connected in series;
An electro-optical device comprising:   4. The diode according to claim 3, wherein the diode is configured by a P-type region, an intrinsic semiconductor, a low-concentration impurity region, and an N-type region provided in the polycrystalline silicon by introducing impurities into the polycrystalline silicon. Electro-optic device. 5. The electro-optical device according to claim 4, wherein the diode has an N ⁻ region having a lower concentration than the N-type region between the intrinsic semiconductor or the low-concentration impurity region and the N-type region. .   4. The electro-optical device according to claim 3, wherein the photosensors are connected in series by a contact hole provided across a boundary between the N-type region and the P-type region of an adjacent diode.   The electro-optical device according to claim 3, wherein the optical sensor is used by applying a reverse bias to the diode. A display unit;
The illuminance of external light around the display unit is detected, and includes a plurality of first diodes each having a light receiving layer made of polycrystalline silicon, and receives the first light. A first photosensor that constitutes a light receiving element by applying a first bias to the plurality of first diodes connected in series;
A plurality of second diodes each having a light-receiving layer made of polycrystalline silicon, the plurality of second diodes receiving second light being connected in series, and the plurality of second diodes connected in series; A second photosensor that forms a light receiving element by applying a second bias;
Light blocking means for blocking light from entering the second photosensor;
An electro-optical device comprising: The display unit is configured by a liquid crystal panel in which liquid crystal is sealed between the first and second substrates,
The electro-optical device according to claim 3, wherein the optical sensor includes a thin film diode formed on the first substrate.   An electronic apparatus using the electro-optical device according to claim 1.

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