X-ray detectors having photoconductors including current resistance layers

An X-ray detector includes a substrate, a plurality of pixel electrodes on the substrate, a photoconductor covering the plurality of pixel electrodes, or a common electrode on the photoconductor. The photoconductor includes at least two photoconductor layers. The photoconductor may also include a current resistance layers disposed between the at least two photoconductor layers. The current resistance layer is configured to reduce current flow between the at least two photoconductor layers.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims priority from Korean Patent Application No. 10-2014-0137854, filed on Oct. 13, 2014, in the Korean Intellectual Property Office (KIPO), the entire contents of which are incorporated herein by reference.

BACKGROUND

Some example embodiments may generally relate to X-ray detectors having photoconductors including current resistance layers.

2. Description of Related Art

An X-ray detector that includes a thin film transistor may have drawn attention for use as a medical diagnosis device. An X-ray detector may output an X-ray image or an X-ray transparent image taken by using X-rays as a digital signal. X-ray detectors may be divided into direct-type X-ray detectors and indirect-type X-ray detectors.

In direct-type X-ray detectors, X-rays may be directly converted into charges by photoconductors, and in indirect-type X-ray detectors, after converting X-rays into visible light by using scintillators, the converted visible light may be converted into charges by using optical transducers, such as photodiodes.

Direct-type X-ray detectors may include photoconductors that generate electron-hole pairs by X-ray irradiation and pixel electrodes that receive charges from the photoconductor.

Materials used to form the photoconductor may include, for example, HgI2. Since HgI2with a small thickness may easily absorb X-rays due to its large atomic number and ionization energy by X-rays may be very small, HgI2may be used as a photoconductor material. However, HgI2may have a high electrical conductivity and, thus, a current leakage that is generated during an X-ray measuring process may occur in the photoconductor. Also, since an amount of current that flows through the photoconductor may be large when a bias voltage is applied thereto before X-ray detection, the amount of current that is generated during X-ray detection may be relatively small and, thus, the X-ray detection efficiency may be low.

SUMMARY

Some example embodiments may provide X-ray detectors having increased detection efficiency due to current resistance layers in the photoconductors.

In some example embodiments, an X-ray detector may comprise: a substrate; a plurality of pixel electrodes on the substrate; a photoconductor covering the plurality of pixel electrodes; and/or a common electrode on the photoconductor. The photoconductor may comprise: at least two photoconductor layers; and/or a current resistance layer, between the at least two photoconductor layers, configured to reduce current flow between the at least two photoconductor layers.

In some example embodiments, the at least two photoconductor layers may comprise: a first photoconductor layer configured to cover the plurality of pixel electrodes; and/or a second photoconductor layer on the current resistance layer.

In some example embodiments, the current resistance layer may comprise material having smaller electrical conductivity than the at least two photoconductor layers.

In some example embodiments, the current resistance layer may comprise alumina, silicon oxide, silicon nitride, parlyene, or conductive polymer.

In some example embodiments, the first photoconductor layer may comprise amorphous selenium (a-Se), HgI2, PbI2, CdTe, CdZnTe, or PbO. The second photoconductor layer may comprise amorphous selenium (a-Se), HgI2, PbI2, CdTe, CdZnTe, or PbO.

In some example embodiments, the first and second photoconductor layers may comprise different materials from each other.

In some example embodiments, the current resistance layer may be further configured to prevent the first photoconductor layer from contacting the second photoconductor layer.

In some example embodiments, a number of the at least two photoconductor layers may be 3 to 15. The 3 to 15 photoconductor layers may be stacked with 2 to 14 current resistance layers respectively formed between adjacent photoconductor layers of the 3 to 15 photoconductor layers.

In some example embodiments, the current resistance layer may comprise material having smaller electrical conductivity than each of the 3 to 15 photoconductor layers.

In some example embodiments, the current resistance layers may comprise alumina, silicon oxide, silicon nitride, parlyene, or conductive polymer.

In some example embodiments, at least one of the 2 to 14 current resistance layers may comprise material different from the other current resistance layers.

In some example embodiments, each of the photoconductor layers may comprise amorphous selenium (a-Se), HgI2, PbI2, CdTe, CdZnTe, or PbO.

In some example embodiments, each of the current resistance layers may be configured to prevent the photoconductor layers on opposite sides of the respective current resistance layer from contacting each other.

In some example embodiments, the X-ray detector may further comprise: a protection layer on the common electrode configured to cover side surfaces of the photoconductor layer and a side surface of the common electrode.

In some example embodiments, the X-ray detector may further comprise: a plurality of chips under the substrate, the plurality of chips including first contacts electrically connected to the plurality of pixel electrodes; and/or a printed circuit board (PCB) electrically connected to second contacts on a bottom surface of the plurality of chips. The plurality of chips may be on the PCB.

In some example embodiments, an X-ray detector may comprise: a plurality of photoconductor layers; and/or a current resistance layer, between the plurality of photoconductor layers, configured to reduce current flow between the plurality of photoconductor layers.

In some example embodiments, the current resistance layer may comprise material having smaller electrical conductivity than each of the plurality of photoconductor layers.

In some example embodiments, the current resistance layer may comprise alumina, silicon oxide, silicon nitride, parlyene, or conductive polymer.

In some example embodiments, the plurality of photoconductor layers may comprise amorphous selenium (a-Se), HgI2, PbI2, CdTe, CdZnTe, or PbO.

In some example embodiments, a number of the photoconductor layers may be 2 to 15.

DETAILED DESCRIPTION

Example embodiments will now be described more fully with reference to the accompanying drawings. Embodiments, however, may be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these example embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope to those skilled in the art. In the drawings, the thicknesses of layers and regions may be exaggerated for clarity.

It will be understood that when an element is referred to as being “on,” “connected to,” “electrically connected to,” or “coupled to” to another component, it may be directly on, connected to, electrically connected to, or coupled to the other component or intervening components may be present. In contrast, when a component is referred to as being “directly on,” “directly connected to,” “directly electrically connected to,” or “directly coupled to” another component, there are no intervening components present. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.

Reference will now be made to example embodiments, which are illustrated in the accompanying drawings, wherein like reference numerals may refer to like components throughout.

FIG. 1is a schematic cross-sectional view of an X-ray detector100having a photoconductor that includes a current resistance layer according to some example embodiments.

Referring toFIG. 1, the X-ray detector100includes a plurality of chips, a substrate130, a plurality of pixel electrodes150, a photoconductor170, a common electrode180, and a protection layer190that are sequentially formed on a printed circuit board (PCB)110in the stated order.

The chips are disposed in an array on the PCB110. InFIG. 1, for convenience of explanation, a single chip120is depicted. A plurality of first contacts112are formed in the PCB110.

The chip120may be an application-specific integrated circuit (ASIC). A plurality of second contacts122are formed in a lower part of the chip120and a plurality of third contacts124are formed in a upper part of the chip120. A plurality of first bumps114is formed between the second contacts122of the chip120and the first contacts112of the PCB110to electrically connect the second contacts122and the first contacts112.

The chip120may be formed of mono-crystal silicon. In this case, the chip120formed of mono-crystal silicon is characterized by high operation speed and low noise. Also, the chip120formed of mono-crystal silicon may increase a primarily processing speed of an electrical signal from the photoconductor170and may transmit the processed electrical signal to the PCB110.

Due to limitations of masks used in semiconductor processes, the chip120may be formed to a maximum size of approximately 2 centimeters (cm)×2 cm. A single chip120may include approximately a few tens to a few hundreds of thousands pixel regions.

The PCB110realizes an image signal from the inputted electrical signal by quantifying an X-ray transmittance of an object to be measured. The chip120provides necessary information to the PCB110by rapidly processing the electrical signal transmitted from the pixel electrodes150and, as a result, a signal processing time in the PCB110may be reduced.

A resin116, for example, an epoxy resin, may be deposited between the PCB110and the chip120to fix them to each other.

The substrate130is formed under the pixel electrodes150. Through holes131are formed in the substrate130, and first vias132may be formed in the through holes131by filling a conductive metal in the through holes131. The first vias132may be formed to be connected to the pixel electrodes150. The first vias132may be formed of copper or aluminum.

The substrate130may be a non-conductive substrate. However, example embodiments are not limited thereto. The substrate130may be a conductive substrate, for example, a silicon substrate. If the substrate130is a conductive substrate, the first vias132are formed to be insulated from the substrate130. For example, as depicted inFIG. 2, a silicon oxide layer133that is formed by oxidizing a silicon substrate is formed on surfaces of the through holes131and the substrate130. In the through holes131, the first vias132are formed in the silicon oxide layer133.

A plurality of pixel pads134is formed on a bottom surface of the substrate130. The pixel pads134are electrically connected to the first vias132. A plurality of second bumps126is formed between the third contacts124of the chip120and the plurality of pixel pads134. A gap between the substrate130and the chip120may be filled with an insulating layer (not shown).

The pixel electrodes150are formed on the substrate130. The pixel electrodes150are electrically connected to the first vias132.

The photoconductor170that covers the pixel electrodes150is formed on the substrate130. The photoconductor170includes a first photoconductor layer171that covers the pixel electrodes150, and a current resistance layer172and a second photoconductor layer173that are sequentially formed on the first photoconductor layer171. The current resistance layer172prevents the first photoconductor layer171from contacting the second photoconductor layer173.

The first and second photoconductor layers171and173may include amorphous selenium (a-Se), HgI2, PbI2, CdTe, CdZnTe, or PbO. The first and second photoconductor layers171and173may not be necessarily formed of the same material. For example, the first and second photoconductor layers171and173may be formed of materials different from each other.

The first and second photoconductor layers171and173respectively may be formed to a thicknesses of approximately a few tens of microns (μm) (e.g., about 10, 11, 12, 13, 14, . . . , 37, 38, 39, or 40 μm.

The current resistance layer172may be formed of a material having smaller electrical conductivity than the first and second photoconductor layers171and173. The current resistance layer172may be formed of an inorganic material, such as alumina, silicon oxide, or silicon nitride, parylene (e.g., poly(p-xylylene) polymer), or conductive polymer. The thickness of the current resistance layer172may vary according to the dielectric constant of the current resistance layer172. For example, if the current resistance layer172is formed of an inorganic material or parylene, the current resistance layer172may be formed to have a thickness in a range from about a few nanometers (nm) (e.g., about 1, 2, 3, or 4 nm) to about 20 nm. If the current resistance layer172is formed of a conductive polymer, the current resistance layer172may be formed to have a thickness in a range from about a few μm to about a few tens of μm (e.g., about 1, 2, 3, 4, . . . , 37, 38, 39, or 40 μm).

The common electrode180is formed to cover the photoconductor170. The common electrode180may be formed of a thin metal electrode material formed of aluminum, copper, ruthenium, palladium, etc.

The protection layer190covers an upper surface of the common electrode180. Although not shown inFIG. 1, the protection layer190may further cover side surfaces of the photoconductor170and the common electrode180. The protection layer190may be formed of parylene.

An operation of the X-ray detector100according to some example embodiments will be described with reference toFIG. 1.

An electric field is formed in the photoconductor170according to direct current applied to the common electrode180. The photoconductor170generates charges in response to the intensity of X-rays incident from an upper surface of the photoconductor170. The photoconductor170includes a plurality of pixel regions. The pixel electrodes150may be formed to correspond to the plurality of the pixel regions. The charges generated from the photoconductor170are collected to the corresponding pixel electrode150. That is, an electrical signal of the pixel region is transmitted to the corresponding third contact124of the chip120through the first via132. The chip120may rapidly process the electrical signal inputted from the pixel electrode150and may transmit processed information to the PCB110. The PCB110generates an image signal from the inputted electrical signal by quantifying an X-ray transmittance of an object to be measured.

The current resistance layer172controls a current that excessively flow (referred to as “dark current”) in the photoconductor170when a bias voltage is applied thereto and, thus, allows the photoconductor170to correctly measure the electrical signal that is generated when an X-ray is detected. That is, in the X-ray detector100according to some example embodiments, a ratio of a measured current to a dark current is increased and, accordingly, the signal-to-noise ratio (SNR) is improved.

FIG. 3is a schematic cross-sectional view of an X-ray detector200having a photoconductor170that includes a current resistance layer172according to some example embodiments. Like reference numerals are used to indicate elements that are substantially identical to the elements of the X-ray detector100ofFIG. 1and, thus, the detailed descriptions thereof will not be repeated.

Referring toFIG. 3, the X-ray detector200has a structure not including the substrate130of the X-ray detector100. A planarizing film230that covers chips120is formed on a PCB110. The planarizing film230may be formed of a polymer, for example, SU-8 photoresist (e.g., Sukhoi-8, epoxy-based negative photoresist) or polyimide. The planarizing film230may be referred to as a substrate.

Via holes231that expose third contacts124of the chip120are formed in the planarizing film230. The via holes231are filled with via metal232. The via metal232may be formed of aluminum, copper, etc.

An electrical signal is transmitted to the chip120from a pixel electrode150through the via metal232.

The other structures and operations of the X-ray detector200ofFIG. 3may be understood from the previous descriptions.

FIG. 4is a schematic cross-sectional view of an X-ray detector300having a photoconductor that includes a current resistance layer according to some example embodiments. Like reference numerals are used to indicate elements that are substantially identical to the elements of the X-ray detector100ofFIG. 1and, thus, the detailed descriptions thereof will not be repeated.

A photoconductor370covering pixel electrodes150is formed on a substrate130. The photoconductor370includes a first photoconductor layer371that covers the pixel electrodes150, and a first current resistance layer372, a second photoconductor layer373, a second current resistance layer374, and a third photoconductor layer375that are sequentially formed on the first photoconductor layer371. The first current resistance layer372prevents the first photoconductor layer371from contacting the second photoconductor layer373, and the second current resistance layer374prevents the second photoconductor layer373from contacting the third photoconductor layer375.

The first photoconductor layer371, the second photoconductor layer373, and the third photoconductor layer375may include amorphous selenium (a-Se), HgI2, PbI2, CdTe, CdZnTe, or PbO. The first photoconductor layer371, the second photoconductor layer373, and the third photoconductor layer375may not be necessarily formed of the same material. For example, the first photoconductor layer371, the second photoconductor layer373, and the third photoconductor layer375may be formed of different materials from each other.

The first photoconductor layer371, the second photoconductor layer373, and the third photoconductor layer375may have a thickness in a range from about a few μm to about a few tens of μm (e.g., about 1, 2, 3, 4, . . . , 37, 38, 39, or 40 μm).

The first and second current resistance layers372and374may be formed of a material having an electrical conductivity smaller than that of the first through third photoconductor layers371,373, and375. The first and second current resistance layers372and374may be formed of an inorganic material, such as alumina, silicon oxide, or silicon nitride, parylene, or conductive polymer. The first and second current resistance layers372and374may be formed of different materials from each other.

The thicknesses of the first and second current resistance layers372and374may vary according to a dielectric constant of the first and second current resistance layers372and374. For example, if the first and second current resistance layers372and374are formed of an inorganic material or parylene, the first and second current resistance layers372and374may have a thickness in a range from about a few nm (e.g., about 1, 2, 3, or 4 nm) to about 20 nm. If the first and second current resistance layers372and374are formed of a conductive polymer, the first and second current resistance layers372and374may have a thickness in a range from about a few μm to about a few tens of μm (e.g., about 1, 2, 3, 4, . . . , 37, 38, 39, or 40 μm).

The common electrode180is formed to cover the photoconductor370. The common electrode180may be formed of indium-tin-oxide (ITO) or a very thin metal electrode material formed of aluminum, copper, ruthenium, palladium, etc.

The protection layer190covers an upper surface of the common electrode180. Although not shown inFIG. 4, the protection layer190may further cover side surfaces of the photoconductor370and the common electrode180. The protection layer190may be formed of parylene.

The first through third photoconductor layers371,373, and375of the photoconductor370may be sequentially formed by an evaporation deposition method. The evaporation deposition method may include a sputtering method, evaporation method, atomic layer deposition method, or chemical vapor deposition method.

According to the X-ray detector300described above, photoconductor layers may be uniformly formed and, accordingly, the X-ray detection characteristic of the X-ray detector300may be improved.

In the example embodiments described above, the photoconductor370includes three photoconductor layers and two current resistance layers. However, the photoconductor370according to example embodiments is not limited thereto, and for example, the photoconductor may include 4 to 15 photoconductor layers and 3 to 14 current resistance layers respectively disposed between the adjacent ones of the 4 to 15 photoconductor layers, and at least one of the current resistance layers may be formed of a different material from the other current resistance layers.

According to some example embodiments, an X-ray detector includes a photoconductor that includes a current resistance layer that reduce a dark current generated in the photoconductor and, accordingly, an SNR of the X-ray detector is increased.

Also, a plurality of photoconductor layers and a plurality of current resistance layers between the plural photoconductor layers may be uniformly formed and, thus, an X-ray detection characteristic of the X-ray detector may be increased.