Image sensor using light-sensitive transparent oxide semiconductor material

An image sensor according to example embodiments may include a plurality of light-sensitive transparent oxide semiconductor layers as light-sensing layers. The light-sensing layers may be stacked in one unit pixel region.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 U.S.C. §119 to Korean Patent Application No. 10-2009-0132825, filed on Dec. 29, 2009 with the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.

BACKGROUND

Example embodiments relate to an image sensor using a light-sensitive transparent oxide semiconductor material, e.g., an image sensor using a light-sensitive transparent oxide semiconductor transistor as a light-sensing layer.

2. Description of the Related Art

Complimentary metal oxide semiconductor (CMOS) image sensors, which are solid state image pickup devices using a CMOS, and charge-coupled device (CCD) image sensors are similar to each other in that both of the image sensors use a photodiode, but are different from each other with respect to a manufacturing method and a method of reading a signal. In general, a CMOS image sensor includes a photodiode and a transistor at each unit pixel, and thus may capture an image by sequentially detecting electrical signals generated by each unit pixel in a switching mode. The CMOS image sensor has advantages in that because the CMOS image sensor may be mass produced by using a general semiconductor manufacturing device, the CMOS image sensor has lower manufacturing costs than the CCD image sensor, and because the size of the CMOS image sensor is smaller than the CCD image sensor, the CMOS image sensor has lower power consumption than the CCD image sensor. Also, the CMOS image sensor has other advantages in that the CMOS image sensor may be manufactured along with a plurality of signal processing devices in one chip. Although the CMOS image sensor at an initial stage has a disadvantage in that, because amplifiers are respectively allocated to pixels, noise is generated in the CMOS image sensor due to a difference between characteristics of the amplifiers, a signal to noise ratio (SNR) has been greatly increased due to various technical improvements.

In recent years, research has been conducted into a micro process for manufacturing the CMOS image sensor. If the size of a chip is reduced by using the micro process and the CMOS image sensor is able to maintain the same number of pixels, more image sensors may be produced from one wafer. As a result, the unit cost of the CMOS image sensor may be reduced, production of the CMOS image sensors may be increased, the size of a camera module including the CMOS image sensor may be reduced, and a camera phone including the camera module may be easily made compact and thin. A technology of forming a unit pixel having a size of about 1.4 μm has been established so far, and about 12.25 million pixels may be formed from a 1/2.5 inch chip.

SUMMARY

Example embodiments include an image sensor that may reduce the size of a unit pixel by using a light-sensitive transparent oxide semiconductor material as a light-sensing layer. Additional aspects will be set forth in the description which follows and may be apparent from the description or may be learned by practice of the various non-limiting embodiments.

An image sensor according to example embodiments may include at least one light-sensitive oxide semiconductor layer as a light-sensing layer. The at least one light-sensitive oxide semiconductor layer may include a plurality of light-sensing layers stacked on different levels. In a non-limiting embodiment, the at least one light-sensitive oxide semiconductor layer may include a plurality of light-sensing layers stacked in one unit pixel region.

The image sensor may further include a first filter layer and a second filter layer, wherein the at least one light-sensitive oxide semiconductor layer includes a first light-sensing layer, a second light-sensing layer, and a third light-sensing layer, and the first light-sensing layer, first filter layer, second light-sensing layer, second filter layer, and third light-sensing layer may be sequentially stacked from a side of the image sensor on which light is incident. The image sensor may further include transparent insulating layers disposed between the first light-sensing layer and the second light-sensing layer and between the second light-sensing layer and the third light-sensing layer.

The at least one light-sensitive oxide semiconductor layer constituting the light-sensing layer may be included in a light-sensitive transparent oxide semiconductor transistor having electrical characteristics that vary according to an amount of incident light. The light-sensitive transparent oxide semiconductor transistor may be used in the image sensor according to example embodiments.

The light-sensitive transparent oxide semiconductor transistor may include a substrate; a gate electrode on the substrate; a gate insulating layer on the gate electrode; the at least one light-sensitive oxide semiconductor layer on the gate insulating layer; and a drain electrode and a source electrode on the at least one light-sensitive oxide semiconductor layer.

The at least one light-sensitive oxide semiconductor layer may have light-transmitting properties. For instance, the at least one light-sensitive oxide semiconductor layer may be transparent. In a non-limiting embodiment, the at least one light-sensitive oxide semiconductor layer may be formed of indium zinc oxide (InZnO) or gallium indium zinc oxide (GaInZnO). Each of the gate electrode, the drain electrode, and the source electrode may be formed of indium tin oxide (ITO) or indium zinc oxide (IZO).

Each of the drain electrode and the source electrode may have a straight bar shape, and the drain electrode and the source electrode may be arranged in parallel on opposite sides of the light-sensitive oxide semiconductor layer. Alternatively, the drain electrode may be formed along a periphery of the at least one light-sensitive oxide semiconductor layer so as to surround the source electrode. In another non-limiting embodiment, the drain electrode may be formed along three sides of the at least one light-sensitive oxide semiconductor layer so as to partially enclose the source electrode.

The light-sensitive transparent oxide semiconductor transistor may also include a substrate; the at least one light-sensitive oxide semiconductor layer on the substrate; a gate insulating layer on the at least one light-sensitive oxide semiconductor layer; a gate electrode on the gate insulating layer; and a drain electrode and a source electrode on the at least one light-sensitive oxide semiconductor layer. The gate insulating layer may be partially disposed on the at least one light-sensitive oxide semiconductor layer.

The drain electrode may be formed along a periphery of the at least one light-sensitive oxide semiconductor layer, and the gate electrode may be formed along an inner perimeter of the drain electrode so as to surround the source electrode. Alternatively, the drain electrode may be formed along three sides of the at least one light-sensitive oxide semiconductor layer, and the gate electrode may be formed along an inner boundary of the drain electrode so as to partially enclose the source electrode.

The image sensor may further include a gate signal line connected to gate electrodes of a plurality of the light-sensitive transparent oxide semiconductor transistors, a power line connected to drain electrodes of the plurality of light-sensitive transparent oxide semiconductor transistors, and output lines connected to source electrodes of the plurality of light-sensitive transparent oxide semiconductor transistors.

The image sensor may further include a lens device on the first light-sensing layer. The lens device may focus blue light on the first light-sensing layer, focus green light on the second light-sensing layer, and focus red light on the third light-sensing layer by using chromatic aberration.

The first filter layer may block light having blue wavelengths and transmit light having wavelengths other than the blue wavelengths, and the second filter layer may block light having green wavelengths and transmit light having wavelengths other than the green wavelengths or transmit light having red wavelengths and block light having wavelengths other than the red wavelengths. Each of the first and second filter layers may include a light absorption layer having a light absorption coefficient that varies according to wavelength.

The light absorption layer may include any one of amorphous silicon, crystalline silicon, Ge, GaAs, and GaxInyS2P. The light absorption layer of the first filter layer may be thinner than the light absorption layer of the second filter layer. The first filter layer may be a blue complementary color filter that blocks light having blue wavelengths and transmits light having green and red wavelengths, and the second filter layer may be a green complementary color filter that blocks light having green wavelengths and transmits light having blue and red wavelengths or is a red filter that transmits only light having red wavelengths. The first filter layer may be formed of any one of TiOx, SiOx, Fe2O3, cobalt (Co)-doped ZnOx, and Co-doped Al2O3, and the second filter layer may be formed of any one of TiOx, SiOx, Fe2O3, Co-doped ZnOx, and Co-doped Al2O3.

The image sensor may further include a plurality of image sensor cells arranged in a two-dimensional (2-D) manner, wherein each of the plurality of image sensor cells includes a substrate; the light-sensing layer on the substrate; and a filter layer on the light-sensing layer. The plurality of image sensor cells may be disposed in one unit pixel and may include different color filters as filter layers.

The light-sensing layer may be included in a light-sensitive transparent oxide semiconductor transistor having electrical characteristics that vary according to an amount of incident light. The light-sensitive transparent oxide semiconductor transistor may include a gate electrode on the substrate; a gate insulating layer on the gate electrode; the light-sensing layer on the gate insulating layer; and a drain electrode and a source electrode on the light-sensing layer.

DETAILED DESCRIPTION

Reference will now be made in further detail to various non-limiting embodiments, examples of which are illustrated in the accompanying drawings. In the drawings, like reference numerals denote like elements, and the sizes of elements may have been exaggerated for clarity.

FIG. 1is a cross-sectional view of an image sensor100using a light-sensitive transparent oxide semiconductor material as a light sensor (e.g., light-sensing layer) according to example embodiments. Referring toFIG. 1, the image sensor100may be constructed in such a manner that a plurality of, for example, first through third, light-sensing layers110,120, and130are stacked on different layers over a substrate101in one pixel cell. Although the first through third light-sensing layers110,120, and130are illustrated inFIG. 1, it should be understood that two or four or more light sensors may be stacked according to a color detection method that is to be used.

In further detail, referring toFIG. 1, the image sensor100may include a first transparent insulating layer115, the first light-sensing layer110, a second transparent insulating layer115, a first filter layer140, a third transparent insulating layer115, the second light-sensing layer120, a fourth transparent insulating layer115, a second filter layer150, a fifth transparent insulating layer115, and the third light-sensing layer130sequentially disposed from a side of the image sensor100on which light is incident. Stated more clearly, the third light-sensing layer130, the fifth transparent insulating layer115, the second filter layer150, the fourth transparent insulating layer115, the second light-sensing layer120, the third transparent insulating layer115, the first filter layer140, the second transparent insulating layer115, the first light-sensing layer110, and the first transparent insulating layer115may be sequentially stacked on the substrate101. A lens device160may be further disposed on the first transparent insulating layer115by using an adhesive layer165. For instance, the image sensor100may be constructed in such a way that the first through fifth transparent insulating layers115are disposed in an alternating manner between the three light-sensing layers110,120, and130, and the first and second filter layers140and150are respectively disposed between the second and third transparent insulating layers115and between the fourth and fifth transparent insulating layers115. Each of the first through fifth transparent insulating layers115may be formed of a transparent insulating material (e.g., SiO2).

Light incident on the image sensor100constructed as described above may be detected by the first through third light-sensing layers110,120, and130with respect to color components of the light. For example, the first light-sensing layer110may detect all of red, green, and blue light. Part of the light incident on the image sensor100travels toward the second light-sensing layer120. For example, the first filter layer140may block only light having blue wavelengths and transmit light having wavelengths other than the blue wavelengths. Accordingly, the second light-sensing layer120may detect mostly red and green light. Part of the light passing through the second light-sensing layer120travels toward the third light-sensing layer130. The second filter layer150may block only light having green wavelengths and transmit light having wavelengths other than the green wavelengths. Alternatively, the second filter layer150may transmit only light having red wavelengths and block light having wavelengths other than the red wavelengths. Accordingly, the third light-sensing layer130may detect mostly red light. Accordingly, intensities of red, green, and blue light may be exactly calculated by considering intensities of the light detected by the first through third light-sensing layers110,120, and130and a light loss factor after the light travels through the first through third light-sensing layers110,120, and130.

Improved color separation may be achieved by using chromatic aberration of the lens device160. In general, the index of refraction increases as a wavelength decreases. A refractive power, which is a measurement of how much light is refracted with respect to a wavelength thereof, may vary according to a refractive index of a material of the lens device160and a curvature of a lens surface. Accordingly, if the lens device160is formed of an appropriate material and the lens surface has an appropriate curvature, blue light may be focused on the first light-sensing layer110, green light may be focused on the second light-sensing layer120, and red light may be focused on the third light-sensing layer130, so that specific colors may be respectively detected by the first through third light-sensing layers110,120, and130.

Because the image sensor100includes the first through third light-sensing layers110,120, and130stacked over each other, the image sensor100may reduce the size of one pixel beyond existing size limitations. For example, a conventional CMOS image sensor includes a plurality of light sensors arranged on one layer wherein four photodiodes arranged in a square shape form one pixel. Two photodiode cells form a green cell in one diagonal direction, and the two other diagonal photodiode cells form a red cell and a blue cell in the other diagonal direction. Accordingly, even though the size of each of the photodiodes may be reduced and the size of a driving circuit for driving the photodiodes may be reduced, there is a limitation in reducing the size of a pixel due to limitations in size according to the current integration technology. On the other hand, because the image sensor100ofFIG. 1allows one cell to include the first through third light-sensing layers110,120, and130, which are stacked to form one pixel, the size of a pixel may be less than that of the conventional CMOS image sensor.

To stack the first through third light-sensing layers110,120, and130, light sensors in the light-sensing layers110,120, and130may have light-transmitting properties. Examples of materials for the light sensors having light-transmitting properties may include a light-sensitive transparent oxide semiconductor material. For example, a light-sensitive transparent oxide semiconductor transistor that uses a light-sensitive transparent oxide semiconductor as a channel material may be characterized in that a threshold voltage or the like varies according to a wavelength of light or the amount of light.

FIG. 2is a cross-sectional view illustrating a light-sensitive transparent oxide semiconductor transistor10that may be used in the image sensor100according to example embodiments. Referring toFIG. 2, the light-sensitive transparent oxide semiconductor transistor10may include a transparent substrate11, a gate electrode12partially formed on the transparent substrate11, a gate insulating layer13formed to cover the transparent substrate11and the gate electrode12, an oxide semiconductor layer14covering the gate insulating layer13, and a drain electrode15and a source electrode16formed on opposite sides of the oxide semiconductor layer14. Each of the gate electrode12, the drain electrode15, and the source electrode16may be formed of a transparent conductive material, e.g., indium tin oxide (ITO) or indium zinc oxide (IZO). The gate insulating layer13may be formed of a transparent insulating material, e.g., SiO2. The oxide semiconductor layer14may function as a channel region and may be formed of a light-sensitive transparent oxide, e.g., indium zinc oxide (InZnO) or gallium indium zinc oxide (GaInZnO).

FIG. 3is a graph illustrating operational characteristics of the light-sensitive transparent oxide semiconductor transistor10ofFIG. 2. Referring toFIG. 3, as the amount of incident light increases, a threshold voltage decreases and an output current increases by Δ1at the same gate voltage Vpd. Accordingly, transparent light sensors disposed in the first through third light-sensing layers110,120, and130of the image sensor100ofFIG. 1may be realized having the operational characteristics illustrated inFIG. 3by using the light-sensitive transparent oxide semiconductor transistor10.

FIG. 4is a conceptual view of the image sensor100ofFIG. 1using the light-sensitive transparent oxide semiconductor transistor10ofFIG. 2for each of the first through third light-sensing layers110,120, and130.FIG. 5is a circuit diagram ofFIG. 4. Referring toFIGS. 4 and 5, a power line for applying a driving voltage Vpdto the light-sensitive transparent oxide semiconductor transistor10and a gate signal line for selecting an output may be commonly connected to the first through third light-sensing layers110,120, and130. For example, the power line may be connected to a drain electrode of the light-sensitive transparent oxide semiconductor transistor10, and the gate signal line may be connected to a gate electrode of the light-sensitive transparent oxide semiconductor transistor10. To obtain an output indicating light intensity from the light-sensitive transparent oxide semiconductor transistor10, three output lines OUT may be respectively connected to the first through third light-sensing layers110,120, and130. For example, each of the output lines OUT may be connected to a source electrode of the light sensitive transparent oxide semiconductor transistor10.

In the configuration ofFIGS. 4-5, if a voltage is applied to the gate signal line under the control of a driving circuit (not shown), current begins to flow through the output lines OUT connected to the first through third light-sensing layers110,120, and130. The amount of current flowing through each of the output lines OUT varies according to respective intensities of light incident on the first through third light-sensing layers110,120, and130. As described above, an output from the first light-sensing layer110may indicate intensities of red, green, and blue light. An output from the second light-sensing layer120may indicate intensities of mostly red and green light. An output from the third light-sensing layer130may indicate an intensity of mostly red light. Accordingly, by using the outputs from the first through third light-sensing layers110,120, and130, the intensities of the red, green, and blue light included in the incident light may be exactly calculated as will be described later in detail.

FIG. 6illustrates a plurality of image sensor cells100S of the image sensor100ofFIG. 1. As described above, the image sensor100may be constructed in such a way that one image sensor cell100S including the first through third light-sensing layers110,120, and130, which are stacked, forms one pixel. Referring toFIG. 6, the plurality of image sensor cells100S, each forming one pixel, may be arranged adjacently. Although two image sensor cells100S are illustrated inFIG. 6for convenience of explanation, it should be understood that more image sensor cells100S may be arranged in a two-dimensional (2-D) manner. Each of the plurality of image sensor cells100S may have the structure illustrated in the cross-sectional view ofFIG. 1.

Referring toFIG. 6, a gate signal line102, a power line103, and an output line104may be disposed around each of the image sensor cells100S, and a plurality of contacts111,112,113,121,122,123,131,132, and133for electrical connection between the gate signal line102, the power line103, and the output line104and the light-sensitive transparent oxide semiconductor transistors10in the first through third light-sensing layers110,120, and130may be formed on edges of the image sensor cells100S.

For example, the gate signal line102may be connected to the first through third gate contacts111,121, and131. Although it is shown that the first through third gate contacts111,121, and131are formed on the same layer inFIG. 6, the first through third gate contacts111,121, and131may be respectively formed on the first through third light-sensing layers110,120, and130. The first through third gate contacts111,121, and131and the gate signal line102may be electrically connected to each other through via holes (not shown). Likewise, the power line103is electrically connected to the first through third power contacts112,122, and132. The first through third power contacts112,122, and132may be respectively formed on the first through third light-sensing layers110,120, and130, and may be electrically connected to the power line103through via holes (not shown).

Although one output line104is illustrated for one image sensor cell100S inFIG. 6, three output lines104actually exist to correspond to the first through third light-sensing layers110,120, and130. Stated more clearly, three output lines104may be respectively formed on the first through third light-sensing layers110,120, and130. The first through third output contacts113,123, and133electrically connected to the output lines104may be respectively formed on the first through third light-sensing layers110,120, and130. Accordingly, the first through third output contacts113,123, and133may be electrically connected to the output lines104respectively formed on the first through third light-sensing layers110,120, and130.

To enable the first through third light-sensing layers110,120, and130to detect light having different wavelengths, the first and second filter layers140and150may be used to block light having specific wavelengths as described above. For example, the first filter layer140may block only light having blue wavelengths and transmit light having wavelengths other than the blue wavelengths. The second filter layer150may block only light having green wavelengths and transmit light having wavelengths other than the green wavelengths. Alternatively, the second filter layer150may transmit only light having red wavelengths and block light having wavelengths other than the red wavelengths. The first and second filter layers140and150may be realized by using a light absorption adjustment layer or by using a complementary color filter layer.

FIG. 7is a cross-sectional view of the image sensor100ofFIG. 1, illustrating a non-limiting embodiment where a first light absorption adjustment layer140ais disposed as the first filter layer140between the first light-sensing layer110and the second light-sensing layer120and a second light absorption adjustment layer150ais disposed as the second filter layer150between the second light-sensing layer120and the third light-sensing layer130. Each of the first and second light absorption adjustment layers140aand150amay use a light absorption material that has a light absorption coefficient that varies according to wavelength. For example, amorphous silicon (a-Si) may have a light absorption coefficient that is about 1000 times greater for blue wavelengths than the same for red wavelengths. Accordingly, if amorphous silicon having an appropriate thickness is selected, only light having a specific wavelength may be selectively blocked. Instead of amorphous silicon, a light absorption material, e.g., crystalline silicon, Ge, GaAs, GaxInyS2P, may be used for the first and second light absorption adjustment layers140aand150a.

Referring toFIG. 7, a thickness of the first light absorption adjustment layer140amay be different from a thickness of the second light absorption adjustment layer150a. In order to block only light having blue wavelengths, the first light absorption adjustment layer140amay be relatively thin. On the other hand, in order to block light having blue and green wavelengths and transmit only light having red wavelengths, the second light absorption adjustment layer150amay be relatively thick. For example, if each of the first and second light absorption adjustment layers140aand150ais formed of amorphous silicon, a thickness d1between an uppermost surface and the first light-sensing layer110may be about 0.2 μm, a thickness d2between the uppermost surface and the second light-sensing layer120may be about 0.6 μm, and a thickness d3between the uppermost surface and the third light-sensing layer130may be about 2 μm. The first through third light-sensing layers110,120, and130may each have the same thickness, and the first through fifth transparent insulating layers115may each have the same thickness. In this case, wavelengths of light that are to be incident on each of the first through third light-sensing layers110,120, and130may be selected by adjusting the thicknesses of the first light absorption adjustment layer140aand the second light absorption adjustment layer150a.

FIG. 8is a cross-sectional view of the image sensor100ofFIG. 1, illustrating a non-limiting embodiment where a first complementary color filter layer140bis disposed as the first filter layer140between the first light-sensing layer110and the second light-sensing layer120and a second complementary color filter layer150bis disposed as the second filter layer150between the second light-sensing layer120and the third light-sensing layer130. A complementary color filter is a filter that blocks light having specific wavelengths and transmits light having wavelengths other than the specific wavelengths. For example, a blue complementary color filter may block light having blue wavelengths and transmit light having wavelengths other than the blue wavelengths. Because there is little connection between thicknesses and transmission/blocking characteristics of a complementary color filter, a thickness d4between the first light-sensing layer110and the second light-sensing layer120and a thickness between the second light-sensing layer120and the third light-sensing layer130may be the same. For example, the thickness d4may be about 0.2 μm.

The first complementary color filter layer140bmay be a blue complementary color filter that blocks only light having blue wavelengths and transmits light having green and red wavelengths. The second complementary color filter layer150bmay be a green complementary color filter that blocks only light having green wavelengths and transmits light having blue and red wavelengths. Alternatively, a red filter for transmitting only light having red wavelengths may be used as the second filter layer150as described above. A complementary color filter may be an organic filter or an inorganic filter. The inorganic filter may be formed of TiOx, SiOx, Fe2O3, cobalt (Co)-doped ZnOx, or Co-doped Al2O3.

FIGS. 9 and 10are graphs illustrating light transmittances of complementary color filter layers for the image sensor ofFIG. 8.FIG. 9is a graph illustrating a light transmittance of Fe2O3. Referring toFIG. 9, Fe2O3may be used as a blue complementary color filter for blocking light having blue wavelengths. Fe2O3may be used as the first filter layer140(e.g., first complementary color filter layer140b).FIG. 10is a graph illustrating a light transmittance of Co-doped Al2O3. Referring toFIG. 10, Co-doped Al2O3may be used as a filter transmitting mostly light having red wavelengths. Co-doped Al2O3may be used as the second filter layer150(e.g., second complementary color filter layer150b).

FIGS. 11A through 11Cillustrate photoelectron generation rates at the first through third light-sensing layers110,120, and130according to wavelengths of light incident on the image sensor100ofFIG. 1. InFIGS. 11A through 11C, the vertical axis represents a photoelectron generation rate per scm3. For example, the value “20” in the vertical axis means 1020/scm3. InFIGS. 11A through 110C, the horizontal axis represents locations of the first through third light-sensing layers110,120, and130.

Referring toFIG. 11A, photoelectron generation rates for light having blue wavelengths at the first through third light-sensing layers110,120, and130are respectively B1, B2, and B3. Referring toFIG. 11B, photoelectron generation rates for light having green wavelengths at the first through third light-sensing layers110,120, and130are respectively G1, G2, and G3. Referring toFIG. 11C, photoelectron generation rates for light having red wavelengths at the first through third light-sensing layers110,120, and130are respectively R1, R2, and R3. The photoelectron generation rates B1, B2, B3, G1, G2, G3, R1, R2, and R3may vary according to characteristics of the light-sensitive transparent oxide semiconductor transistors used in the first through third light-sensing layers110,120, and130, and characteristics of the first and second filter layers140and150. Accordingly, after the image sensor100is manufactured, the photoelectron generation rates B1, B2, B3, G1, G2, G3, R1, R2, and R3of the image sensor100may be previously obtained through experiments.

If the photoelectron generation rates B1, B2, B3, G1, G2, G3, R1, R2, and R3may be previously obtained through experiments, the intensity of light having a specific wavelength incident on the image sensor100may be obtained based on the photoelectron generation rates B1, B2, B3, G1, G2, G3, R1, R2, and R3. For example, if output currents from the first through third light-sensing layers110,120, and130are respectively I1, I2, and I3, and intensities of light having blue, green, and red wavelengths among the light incident on the image sensor100are respectively CB, CG, and CR, Equation 1 may be obtained.
I1=CBB1+CGG1+CRR1
I2=CBB2+CGG2+CRR2
I3=CBB3+CGG3+CRR3[Equation 1]

From Equation 1, the intensities CB, CG, and CRof the light having the blue, green, and red wavelengths may be obtained. For example, the intensity CGof the light having the green wavelengths may be obtained by Equation 2.

Similarly, the intensity CBof the light having the blue wavelengths and the intensity CRof the light having the red wavelengths may be obtained. Accordingly, colors of light incident on the image sensor100constructed as described above may be exactly recognized through performing the method described above.

FIGS. 12A through 12Fare plan views and cross-sectional views illustrating various non-limiting light-sensitive transparent oxide semiconductor transistors that may be used in the image sensor100ofFIG. 1. Although each of the various light-sensitive transparent oxide semiconductor transistors ofFIGS. 12A through 12Fmay be disposed on the third light-sensing layer130disposed on the substrate101, each of the various light-sensitive transport oxide semiconductor transistors may also be disposed on the first and second light-sensing layers110and120respectively disposed between the first transparent insulating layer115and the second transparent insulating layer115and between the third transparent insulating layer115and the fourth transparent insulating layer115.

FIGS. 12A through 12Cillustrate bottom gate-type light-sensitive transparent oxide semiconductor transistors. Referring to the lower illustration ofFIG. 12A, a gate electrode134, a gate insulating layer135, and a light-sensitive transparent oxide semiconductor layer (referred to as an oxide semiconductor layer)136may be sequentially stacked on the substrate101. A drain electrode137and a source electrode138may be formed on opposite sides of the oxide semiconductor layer136. A transparent insulating layer115may completely surround the light-sensitive transparent oxide semiconductor transistor. The drain electrode137may be electrically connected to the power line103, the source electrode138may be connected to the output line104, and the gate electrode134may be connected to the gate signal line102. Referring to the upper illustration ofFIG. 12A, each of the drain electrode137and the source electrode138may have a straight bar shape, and the drain electrode137and the source electrode138may face each other in parallel so as to be disposed on opposite edges of the oxide semiconductor layer136.

The light-sensitive transparent oxide semiconductor transistor ofFIG. 12Bmay be the same as the light-sensitive transparent oxide semiconductor transistor ofFIG. 12Aexcept for the shape of each of the drain electrode137and the source electrode138. Referring to the upper illustration ofFIG. 12B, the drain electrode137may have a square shape and may be formed along an outer circumference of the oxide semiconductor layer136, and the source electrode138may be formed on the oxide semiconductor layer136inside the drain electrode137. Stated more clearly, the drain electrode137may surround the source electrode138with a predetermined interval therebetween. In this case, a gate length may be reduced, and a signal delay may be reduced.

The light-sensitive transparent oxide semiconductor transistor ofFIG. 12Cmay be the same as the light-sensitive transparent oxide semiconductor transistor ofFIG. 12Aexcept for the shape of each of the drain electrode137and the source electrode138. Referring to the upper illustration ofFIG. 12C, the drain electrode137may have ⊂-like shape and may be formed along three sides of the oxide semiconductor layer136, and the source electrode138may be formed on the oxide semiconductor layer136inside the drain electrode137. Stated more clearly, the drain electrode137may surround three side surfaces of the source electrode138with a predetermined interval therebetween. In this case, a gate length may be reduced, and a signal delay may be reduced. Also, the area of light incident on the oxide semiconductor layer136ofFIG. 12Cmay be greater than that ofFIG. 12B.

FIGS. 12D through 12Fillustrate top gate-type light-sensitive transparent oxide semiconductor transistors. Referring to the lower illustration ofFIG. 12D, the light-sensitive transparent oxide semiconductor layer136may be formed on the substrate101, and the gate insulating layer135and the gate electrode134may be partially stacked on the oxide semiconductor layer136. The drain electrode137and the source electrode138may be formed on opposite sides of the oxide semiconductor layer136. The transparent insulating layer115may completely surround the light-sensitive transparent oxide semiconductor transistor. As described above, the drain electrode137may be electrically connected to the power line103, and the source electrode138may be electrically connected to the output line104. The gate electrode134may be connected to the gate signal line102. Referring to the upper illustration ofFIG. 12D, each of the drain electrode137and the source electrode138may have a straight bar shape, and the drain electrode137and the source electrode138may face each other in parallel to be disposed on opposite edges of the oxide semiconductor layer136.

The light-sensitive transparent oxide semiconductor transistor ofFIG. 12Emay be the same as the light-sensitive transparent oxide semiconductor transistor ofFIG. 12Aexcept for the shape of each of the gate electrode134, the drain electrode137, and the source electrode138. Referring to the upper illustration ofFIG. 12E, the drain electrode137may have a square shape and may be formed along an outer circumference of the oxide semiconductor layer136. The gate electrode134may have a square shape and may be formed along an inner circumference of the drain electrode137. The source electrode138may be formed on the oxide semiconductor layer136inside the gate electrode134. Stated more clearly, the drain electrode137may surround the gate electrode134with a predetermined interval therebetween. The gate electrode134may surround the source electrode138with a predetermined interval therebetween. In this case, a gate length may be reduced, and a signal delay may be reduced.

The light-sensitive transparent oxide semiconductor transistor ofFIG. 12Fmay be the same as the light-sensitive transparent oxide semiconductor transistor ofFIG. 12Aexcept for the shape of each of the gate electrode134, the drain electrode137, and the source electrode138. Referring to the upper illustration ofFIG. 12F, the drain electrode137may have a ⊂-like shape and may be formed along three sides of the oxide semiconductor layer136. The gate electrode134may have a ⊂-like shape and may be formed along inner three sides of the drain electrode137. The source electrode138may be formed on the oxide semiconductor layer136inside the gate electrode134. Stated more clearly, the drain electrode137may surround three side surfaces of the gate electrode134with a predetermined interval therebetween. The gate electrode134may surround three side surfaces of the source electrode138with a predetermined interval therebetween.

Although it has been described that the image sensor100may include a plurality of light-sensing layers formed of light-sensitive transparent oxide semiconductor materials stacked in one pixel cell, the image sensor100may include only one light-sensing layer.

FIG. 13is a cross-sectional view of another image sensor100′ using a light-sensitive transparent oxide semiconductor material as a light sensor (e.g., light-sensing layer) according to example embodiments. Referring toFIG. 13, the image sensor100′ may include a light-sensing layer130′, a first insulating layer115, a filter layer150′, and a second insulating layer115sequentially stacked on the substrate101. Accordingly, the image sensor100′ ofFIG. 13may be different from the image sensor100ofFIG. 1in that the image sensor100′ ofFIG. 13includes only the third light-sensing layer130and the second filter layer150ofFIG. 1. For example, the image sensor100′ may be a single color image sensor for detecting only a specific color according to the filter layer150′. Alternatively, the image sensor100′ may be used only to measure the intensity of incident light irrespective of colors. The light-sensing layer130′ may have the same structure as that of each of the first through third light-sensing layers110,120, and130and each of the lines102,103, and104. A plurality of image sensor cells having such a structure as shown inFIG. 13may be arranged in a 2-D manner in a unit pixel to detect a color.

FIG. 14illustrates a plurality of image sensor cells100R,100G, and100B of the image sensor100′ ofFIG. 13which are arranged in a unit pixel100P. Referring toFIG. 14, four image sensor cells100R,100G, and100B may be arranged in one unit pixel100P. For example, two green image sensor cells100G may be arranged in one diagonal direction, and a red image sensor cell100R and a blue image sensor cell100B may be arranged in the other diagonal direction. In this case, the filter layer150′ in the green image sensor cell100G may be a red color filter, and the filter layer150′ in the red image sensor cell100R may be a blue color filter.

An image sensor using a light-sensitive transparent oxide semiconductor material has been particularly shown and described with reference to various non-limiting example embodiments. The image sensor may be applied to a digital camera, a camcorder, a mobile phone, a portable electronic device, although example embodiments are not limited thereto.